chapter xiv nickellibrary.aimehq.org/library/books/modern uses of nonferrous metals... · rude...

CHAPTER XIV

Nickel

By O. B. ]. FRASER* AND PAUL D. MERICAt

PROBABLY the first metallic objects used by man werenickel alloys. In search for flints suitable for the fashioning of theirrude tools, our paleolithic ancestors, some 25,000 years ago, quitelikely may have come upon some of those heavy, metallic fragments that we now know as meteorites, which consist of an alloy ofnickel and iron containing usually from 5 to 15 pct of nickel.

Whether paleolithic man ever did discover and use meteoriticfragments, his sketchy records do not actually disclose. We doknow, however, that such fragments have been found and used bypeoples, particularly the North American Eskimos, for weapons andimplements in just the same manner as stones, and prior to anyknowledge by those peoples of the reduction of metals from ores.Meteoritic showers were recorded frequently in earliest times andthe meteorites often were found and fashioned into useful objects.The ancient Arabic and other myths of "invincible swords fallenfrom heaven" seem thus to have had a very definite basis in fact,and such weapons, of meteoritic material, have actually been recovered from archeological excavations. It thus seems probable thatmeteoric nickel-iron was found and used long before iron was recovered by smelting iron ores (perhaps about 1200 B.c.) and probably even before there was knowledge and use of bronze and gold.

Although many centuries were to pass before nickel was firstisolated, in 1751, from Swedish ores and recognized as an elemental

* Assistant Manager, Development and Research Division, The International Nickel Company, Inc., New York, N. Y.

t President, The International Nickel Company, Inc.

234

Nickel 235

metal, mankind had early learned to utilize it in forms other thanmeteorites. Certainly before, and probably long before, the Christianera, the Chinese had been smelting and reducing the nickel-coppersulfide ores of Yunnan Province into pei-/ung, or "white copper,"which thereafter was smelted with ores of zinc to form what wenow call nickel silver but in China was called pack/ong. The Chineseused it for household utensils and implements, for weapons, andeven for money. Nickel is essentially a metal of modern times, manyof its present uses being of recent development, yet the story of itsusefulness thus reaches back also to the very dawn of history, when

TABLE I-Principal Forms or Alloys in Which Nickel Is Used in the UnitedStates and Canada

9

67

15

88

Estimated CurrentProportions of Total

Nickel Used, Pct(Year 1947)

916

FormsPure or "malleable" nickel.Nickel plating .Nickel-copper alloys}Nickel silver ...

Structural nickel-alloy steels }Nickel-steel castings .Stainless steel and ferronickel alloysNickel in cast iron .Electrical and heat-resistant alloys .

Edison storage cell lNickel for catalyst and other chemical usesNickel in brass and bronze .Nickel-aluminum alloysMiscellaneous other uses

men accepted "heaven-sent gifts" with gratitude and were not soambitious metallurgically as to attempt ceaselessly to alter and improve them. Interestingly enough, these two ancient forms and usesof nickel have survived to this day in the forms of nickel steel andnickel silver (Fig 1).

The alloys and other forms in which nickel is used today are exceedingly numerous and quite diverse in character (Table 1). They

FIG I-NICKEL SILVERS I N ARCHITECTURAL DlrCORA'I'ION.

Main entrance to Waldorf-Astoria Hotel, New York.

Nickel 237

reflect and well illustrate the sustained inventive activity of engineers in their search for greater material comfort for society, andthe continual effort of metallurgists and chemists to provide newand better materials for the engineers. As recently. as the beginningof this century, one could count but few types of nickel productscurrently in industrial use, whereas today the more specialized needsof industry require a great many compositions, including some 200different alloy types, which at present absorb some 150,000 tons ofnickel annually. By far the major part of this consumption is usedin the form of high-purity electrolytic cathodes, which are shearedto various dimensions to meet the requirements of the melting unitsused in the production of ferrous and nonferrous alloys. Pigs andshot are provided in lesser proportion by remelting electrolyticnickel. In another commercial form, nickel pellets, it is produced inquantity by the g~seous carbonyl method. Cubes and rondellesformed by compressing and reducing oxides of nickel with carbonaceous matter are still other but less important commercialforms. In recent years, a new product, nickel oxide sinter, has comeinto wide use in the making of alloy steels.

One rarely thinks of the constant service given by the variousmetals, and seldom appreciates the extent of man's dependenceupon them for comfort and almost for existence. Even a metal suchas nickel, which stands only ninth in the list of metallic elementsin point of volume of consumption, touches our daily life at practically every stage. From the nickel-plated alarm clock, whichawakens us in the morning, to the electric-light bulb, with nickelalloy lead-in wires, whose extinguishing at night closes our day,each of us meets nickel in the most varied forms all through theday. We eat with it, we ride with it, we talk by it, our radio andtelevision depend upon it, and it buys us our daily newspaper!

What are those attributes of nickel by virtue of which it is ofmetallurgical and engineering service to mankind?

Some metals have certain marked and outstanding chemical orphysical characteristics that determine to a large extent their industrial value and usefulness; copper, with its high electrical conductivity, and aluminum, with its low density, are good examples.

238 Modern Uses of Nonferrous Metals

Other metals are not utilizable in pure form but only in usefulcombination with other metals; antimony and vanadium illustratethis type of metal. Nickel appears to occupy both positions. Theproperties of pu~e nickel accord it definite fields of application,and about 25 pct of the current production of nickel is used in thatform. Nickel, however, is principally useful when alloyed with othermetals. In fact, it is alloyed with most other metals commonlyused. Alloys with iron, with copper, with chromium, and withaluminum, for example, contain nickel in amounts ranging fromas little as 0.5 to as much as 93 pct. More than 3000 nickelcontaining alloys have been listed.

It is impossible to summarize in a few words the contributionsmade by nickel to modern metallurgy. While it is used in commercially pure form largely for its color and corrosion resistance,nickel confers strength, with unimpaired ductility, upon alloy steels,and strength and machinability upon cast iron. Its alloys with ironhave outstanding magnetic properties and to brass-foundry alloys itimparts those somewhat intangible assets spoken of as "good castingproperties." Thus its metallurgical manifestations are numerous andvaried; many of them indeed have been unpredictable and discovered more or less by accident.

One fact concerning the relation of nickel to other metals deserves special mention, particularly from the metallographic stand·point-nickel even in the solid state is very "tolerant" of othermetals and dissolves most of them in generous proportion; andsome of them, particularly iron and copper, in all proportions. Thestudent of metallography recognizes the significance of solid solutions in the field of alloys and without doubt the broad diversityof nickel alloys is due to this capacity of nickel to dissolve othermetals so freely.

PURE NICKEL AND NICKEL PLATING

Nickel plating and nickel long were and still may be practicallysynonymous in the minds of most people, since plated nickel is theform in which pure nickel has been best known to the public. Itwas also the earliest commercial form in which pure nickel was

Nickel 239

used. First developed by Boettger in 1843, the nickel-platingprocess came into use on a commercial scale about 1870, andsince then its use has been expanded greatly. The protection of steeland brass against rusting and corrosion by nickel plating was oneof the principal uses for nickel during the years from 1875 to 1890,before the advent of nickel steel.

The art of nickel plating, in common with that of electroplatinggenerally, was destined to pursue its active industrial course for agreat many years largely without benefit of science; it was practiced according to recipe, just like cooking. Only in recent yearshave science and physical understanding replaced the old plater'ssecrets and his "rule-of-thumb" procedures.

It must be admitted that the nickel plater did have some difficultproblems. Other things than nickel were prone to deposit alongwith it, particularly hydrogen and nickel hydroxide, giving rise todirty and even black deposits, to pits and porosity, and to brittleness, in consequence of which only the thinnest layers of nickel,from 0.00005 to 0.0001 in., could be laid down satisfactorily. Theplater's remedies for such conditions were various secret additionswhich he would make to a refractory bath until finally, having almost everything in it, it became intractable to further "medicine"and was then thrown away, and a fresh start made.

Researches by Watts, Blum, Madsen, and many others clearly indicated the necessity for control of acidity, or more accurately,hydrogen-ion concentration (the so-called pH) control of nickel"plating solutions, in order to prevent the precipitation of nickelhydroxide. They demonstrated likewise how, by the use of oxidiZingagents, the simultaneous deposition of hydrogen with nickel mightbe substantially restrained if not entirely eliminated. More recently,the practice has been developed of adding organic materials to theplating baths to reduce surface tension and thus promot~ the quickrelease of deposited hydrogen from the plated surface. Today,with this better understanding of the physical chemistry of nickelplating, commercial operations are being conducted with thesimplest of plating baths; the aim is to keep them free from impurities rather than to "dose" them up from time to time as in the


empirical past. Under these conditions, it is possible to produce,regularly and dependably, those dense and heavy nickel coatingsthat alone give adequate protection to the underlying metal, be itbrass, aluminum, zinc, or steel, against corrosion and rusting. Anyone who compares the appearance of the nickel plating of the earlybicycle days, with its nickel layer perhaps 0.00005 in. thick, withthat of the plating on the modern automobile, which is generallyfrom 0.0003 to 0.0015 in. thick, will agree that physical chemistryhas rendered substantial service to nickel plating.

Nickel plating for most purposes today is covered with a surfaceflash of chromium in order to secure freedom from tarnishing and"fogging," the heavy layer of nickel assuring protection againstrusting or corrosion of the underlying steel, or other metal. Theautomobile is today the greatest single market for nickel plating,although household appliances of various sorts also require a substantial amount of nickel in this form. The rather large quantity ofnickel so used year after year bears testimony to the value attachedto the "appearance of things." Nickel plating undoubtedly hasserved as a silent salesman of many an article of steel or iron.

Special baths, of which there are several varieties in large-scalecommercial operation, permit the production of "semibright" and"bright" deposits that require little or no buffing before being subjected to final chromium plating.

Of strictly industrial interest are nickel-plated tubing and otheritems of equipment, so coated to provide corrosion resistance, andthe building up of worn surfaces or undersized parts with thickdeposits from special "hard-plating" baths. Another commercialapplication of nickel plating is in the production of electrotypes inthe graphic arts.

"MALLEABLE" NICKEL

Historically, words may be quite revelatory. Never is copperspoken of as "malleable" copper, nor silver or aluminum as "malleable" silver or "malleable" aluminum, although these metals are infact malleable, but nickel in rolled or forged form was formerly

Nickel 241

and often is today referred to as "malleable" nickel. This namearose very simply from the fact that at one time most nickel wasnot malleable.

By reason of its close association with copper and iron in nickelbearing ores, nickel proved to be a difficult metal to recover in pureform for many years after Cronstedt, in 1751, isolated it fromSwedish ores and recognized it as a new element. During the earlyyears of the nineteenth century, it was recovered from Norwegianores and later from Saxon ores. For a long time, the nickel so produced was brittle, and useful only for remelting and alloying withcopper and zinc. Many years were to pass before an American,Joseph Wharton, was able, in 1865, to produce the first commercially pure malleable nickel, and before Fleitman later discoveredthe still commonly used method for obtaining malleability in nickelby the addition of magnesium.

The magnesium method for transforming brittle into ductilenickel worked perfectly, but the theory of its action, curiouslyenough, was quite wrong. Not unnaturally, it was thought thatbrittle nickel contained nickel oxide as the embrittling agent andthat the latter was simply reduced by the magnesium. Long afterward it was found that nickel sulfide (NiaS2 ) is the usual embrittling constituent in nonductile nickel and that magnesium reduces it to nickel, forming simultaneously magnesium sulfide(MgS), in which form sulfur is not detrimental to nickel. Incidentally, 'one of the regular products of today is a highly oxidized(but sulfur-free) nickel anode bar which, in absolute defiance ofthe old oxide theory of nickel brittleness, is produced by the usualprocesses of hot-forging and rolling.

Uses for Malleable Nickel

One of the earliest uses for malleable nickel and one that wasrepresented in Joseph Wharton's exhibit of nickel objects at thePhiladelphia Exposition of 1876, was the humble kitchen utensilpans, pots, and boilers--and it has ever since been an importantand useful application of the metal, particularly in the larger


kitchens of hotels, restaurants, and hospitals. It was from theirnational stock of such pots and pans that the Germans are said tohave secured the necessary nickel for their military requirementsduring World War I.

As compared with metals such as copper, lead, and aluminum,the proportion of nickel used in the pure, malleable form is relatively small, which might be anticipated from consideration of itscost. Its present industrial uses depend upon certain rather specialcharacteristics, chiefly resistance to corrosion and oxidation.

In chemical manufacturing, nickel is used extensively togetherwith nickel-clad steel for a great many kinds of corrosion-resistantequipment. For example, it is accepted as the standard material incaustic-soda plants for equipment parts exposed to the action ofmolten caustic soda, or hot concentrated solutions thereof. Corrosion rates under these conditions are very low and the small amountsof nickel dissolved by caustic do not affect its color or usefulness.

An application of a quite different sort is the spark-plug pointof manganese-nickel alloy used in gasoline motors. This alloy, containing from 1.5 to 5 pct of manganese, has high heat-dissipatingcapacity and will resist both oxidation and corrosion at the hightemperatures of spark-plug operation. The satisfactory performanceof every automobile depends upon the performance of a fewounces of this alloy.

Nickel is likewise an important factor in the construction ofthe modern radio tube or valve. For many of the parts of theseamazing bits of miniature construction, particularly the plates,grids, screens, and cathodes, a metal is required that must meet arather formidable list of requirements. It must not rust or corrode,it must be readily fabricable, and must remain fairly rigid at thetemperatures of "out-gassing." Its vapor pressure at high temperatures must be low and it must be readily freed of absorbed gas. Purenickel meets these requirements admirably and therefore cooperatestoday in most of the operations of radio communication throughoutthe world. It can be said to have made the modern broadcast receiver possible. It is essential also to the ultramodern televisionreceiver.

Nickel 243

NICKEL COINAGE

Token money may be regarded properly as one of man's greatest inventions and was in fact a fairly ancient one, preceding the Christian era by many centuries. It was in the form of token money that nickel made one of its earliest appearances. In the British Museum, there are Bactrian coins bearing the name of King Euthydemus (B.C. 235), which are composed of nickel-copper alloy containing about 20 pct of nickel (Fig 2).

FIG 2-BACTRIAN NICKEL-COPPER COIN BEARING EFFIGY OF APOLLO (CIRCA 235 B.C.).

It was not until some 2000 years later that the idea again oc- curred to civilized man to use this white alloy in substitution for the more expensive silver coins and thus expand the financial re- sources of the sovereign. The step was a modest contribution toward the practice of inflation.

Today, two principal silver-free white metals are used for the world's token money, and one of them, the 25 pct nickel alloy, is close to the old Bactrian coins in composition. It is the alloy used for the U. S. "nickel" as well as for many subsidiary coins of other nations. It is white and corrosion resistant; it maintains its color well and is readily fabricable into coin blanks and coins.

The other principal white coinage metal is pure nickel. Intro- duced in 1881 by the Swiss Federal Government with the idea- now recognized as unnecessary--of maintaining the real value of its coins on a parity with their face value, nickel has been adopted at one time or another by some 43 governments, including those of Argentina, Canada, China, France, India, Italy, Japan, and Germany.


Pure nickel shares with the 25-75 nickel-copper coinage alloy theadvantage of white color and permanently good appearance andhas the further quite substantial advantage of being less readilycounterfeited. It is not readily fabricated except in modern andwell-developed melting, rolling, and press equipment, and, beingmagnetic, it may be distinguished readily from materials used forcounterfeiting purposes.

NICKEL-CLAD STEEL

Often the corrosion-resisting character of the metal surface ofan article is of primary concern in choosing the material for thatarticle, and what is "behind" or "inside" that surface may be ofonly secondary importance. It matters little what is inside an automobile door handle provided its exterior nickel and chromiumplated surface remains bright and attractive in appearance.

This is true for many applications of nickel that depend upon itscorrosion resistance. If the interior surface of a tankcar is resistantto corrosion by caustic soda or other chemical being transported,the remainder of the tank may be steel, since this is normally thecheapest material for such structural purposes.

The practice has been developed of using nickel-clad steel plateand sheet to meet requirements of this sort; products in which thepure nickel layer, ranging in thickness from 0.025 to 0.125 in., hasbeen rolled on to a steel backing plate, either on one or both sides.These products are less costly than solid nickel and for many applications give equally good service. Nickel-clad plate is used largelyfor the construction of tanks and tankcars and for container equipment of various sorts used in handling and in transporting causticsoda and other liquid chemicals.

NICKEL-COPPER ALLOYS

Many of the good things of this world originate by accidentand when the early Chinese and Bactrians first picked packtongout of the metallurgical grab-bag they chose better than they knew.This series of alloys has become widely used and from it have been

Nickel 245

developed, in the course of time, several alloys of considerableindustrial importance.

Nickel and copper dissolve in each other in all proportions andform thus a continuous series of solid-solution alloys, all verymalleable and ductile and readily fabricable into the usual commercial forms, and all exhibiting substantial resistance to corrosion.The characteristic color of copper disappears at about 15 to 20 pctof nickel and all of the nickel-copper alloys containing more thansuch amounts of nickel are white in color.

The high-copper compositions, together with the copper-nickelzinc alloys commonly known as nickel silvers, belong primarily tothe copper chapter, but some discussion of the important modernapplication of the copper-nickel alloys in condenser tubes is introduced here before consideration of the 68 pct nickel alloy produced and sold under the registered trademark Monel.

Condenser Tubes

Most of the nickel-copper alloys exhibit excellent resistance tocorrosion by sea water. This characteristic, in association with theease and economy of their fabrication, has led within recent yearsto adoption of the 20 to 30 pct nickel-copper alloys for condensertubes for marine power installations, both in merchant marineservice and in many of the principal navies. More recently, a 10 petnickel alloy, containing also a small amount of iron, has come intoextensive use. These alloys are substantially free from the troublesome pitting and perforation often encountered with other tubematerials, and experience has shown that cupronickel-tubed condensers may be maintained in service over long periods duringwhich frequent replacement of other materials (principally Admiralty metal) would be required.

These alloys have found additional application for marine service,where their corrosion resistance together with their antifoulingcharacteristics stand them in good stead. Their resistance to foulingdepends upon the maintenance of a slight but definite rate of corrosion and the resulting production, at the metal surface, of copper


ions that discourage marine growths. In these alloys, the rate ofcorrosion appears to be about the minimum that will prevent foul·ing, therefore they fulfill the interesting and apparently useful requirement that they should corrode continuously but at a very slowrate.

Monel

The packtong of the Chinese and the coinage alloy of the Bactrians were undoubtedly "natural" alloys; viz., they were produceddirectly from nickel-copper ores without separation of the nickeland copper. We must acknowledge the very considerable metallurgical skill for those days which the ancient practitioners musthave possessed in order to accomplish this simple reduction.

In 1905, The International Nickel Co. introduced another"natural" nickel-copper alloy, in which, curiously enough, the proportions of the earlier packtollg were practically reversed. This alloycontained about 68 pct of nickel and was called "Monel Metal,"*in honor of the then President of that company, Mr. AmbroseMonell.

The introduction of Monel was based upon a plain fact and abright "hunch." The fact was that at that time a substantially purenickel-copper matte of fairly uniform composition was being produced regularly from the ore of the Creighton mine. The mattecontained about twice as much nickel as copper. The "hunch" wasthat there was going to be a demand for strong, nonrusting materials. It seemed that a useful alloy could be made directly from thismatte and reasonably cheaply, since the cost of separating the nickelfrom the copper would be avoided.

The choice of composition was a happy one and although manyrefinements were subsequently worked out with respect to additionsof carbon, manganese, silicon, and other elements, the originalnickel-copper ratio in Monel has been maintained to this day. Theproduct was, in a few words, a rustless alloy, "strong as steel." In·deed, it can fairly be said to have been the first of its type, although

* Later shortened to Monel, a registered trademark of The InternationalNickel Co., Inc.

Nickel 247

today the soundness of Monel's original hunch is amply proved bythe existence of a number of such strong, rustless alloys, includingparticularly the austenitic stainless steels.

The fields of commercial application of this alloy since 1905,and particularly within the past 20 years, have become exceedinglybroad and diverse; in the chemical field for equipment to handlecorrosive materials of all sorts; in the power engineering field forpump rods, turbine blading, valves, and valve trim; in steel plantsfor the construction of pickling equipment; in laundry machines,and other service equipment; in paper-mill and oil-refinery equipment and in many kinds of services against sea water.

In a quite different direction, Monel has been used extensivelyin the food-handling equipment of modern hotel and restaurantkitchens, in cafeterias, in hospitals, and more recently in the formof fabricated sinks, water heaters, storage tanks, and boilers. Themarkets for this alloy have certainly fulfilled, in diversity at least,the hopes of its original sponsors. Monel-clad steel plate and stripare lower-cost materials that supplement solid Monel as nickel-cladsteel does solid nickel.

Many alloys have grown up in steel plants or brass mills, themethods of their production and fabrication having been developedas slight modifications of conventional ones. Monel had that sort ofdevelopment. Readily susceptible to fabrication and forming by theusual general methods, it has displayed also a very definite individuality in this respect and has been to its sponsors an interesting,albeit at times irritating, illustration of the precision. with whichour modern methods of working metals must be adapted to theidiosyncrasies of the metals themselves. Consequently, much thoughtand effort have had to be expended in adjusting the usual operations of forging, rolling, welding and joining, machining andforming generally, to the particular properties of this alloy.

Moreover, it may be pointed out as an illustration of the complexity of the modern requirements for engineering materials thatwhat might appear to be as simple a metallurgical product as Monelis in reality produced in some eight modifications, differing incertain slight but important particulars. One of these, for example,


will be free machining; one, of higher strength; one, of maximumsoftness and ductility, and so on. The high-strength modification,which contains small amounts of aluminum and titanium, unlike theoriginal alloy is nonmagnetic. The trend of modern engineeringtoward specialization of function is reflected faithfully in the production of special alloys to permit it.

ALLOYS OF NICKEL WITH IRON

From the physical standpoint, the nickel-iron alloy series is oneof the most interesting known and poses, even today, puzzlingmetallographic questions, which have not yet been adequatelyanswered. At high temperatures, above 900°C, the two metals formsolid solutions in all proportions but practically all of the alloysundergo one or more transformations upon cooling. In consequence,some peculiar and valuable properties are developed within theseries, of which industry has made full use.

The alloys containing up to about 9 pct of nickel have excellentmechanical properties and may be hardened and strengthened byheat treatment. They comprise the group of constructional nickelsteels. The alloys containing more than 20 pct of nickel are notheat-treatable and are not remarkable in point of strength or hardness, but they are endowed with other useful properties, someunique, and are known generally as the iron-nickel alloys. Betweenthese two groups (between about 9 pct and 20 pct of nickel) lies arange of compositions, normally very hard and brittle and not toany extent in current commercial use.

Nickel-alloy Steels

Nickel steel was one of the earliest alloy steels developed, andnickel remains today, after some 66 years, one of the principal alloying elements used in the production of high-strength steels. Produced first by Marbeau in France about 1885 and independently byHall in England about the same time, it remained for James Riley,in a classic paper before the Iron and Steel Institute in 1889, togive adequate description of this new structural material and tosecure recognition of its industrially useful properties. Subsequently

Nickel 249

the names of many famous physicists and metallurgists have becomeconnected with nickel steel: Hopkinson, LeChatelier, Osmond,Guillaume, Guillet, and others made vital contributions to ourknowledge of it.

What are the characteristics that render nickel steels useful? Undersimilar conditions of manufacture and heat treatment, the nickelsteels are much stronger and tougher than plain carbon steels. Thisis brought out in Fig 3.

As an indication of the tensile properties that may be securedfrom a properly heat-treated nickel-alloy steel (a nickel-chromiummolybdenum steel), the following figures may be quoted: yieldpoint, 255,000 psi; tensile strength, 300,000 psi; elongation, 10 pct;reduction of area, 27 pct. These represent about the maximumstrength properties obtainable in any material in other than wire'iections.

Upon this simple superiority of nickel-alloy steels over carbonsteels is based, to a considerable extent, their present widespreaduse.* Generally speaking, heat-treated nickel-alloy steels are usedwithin a range of tensile strength values from 100,000 to 250,000psi, whereas the useful range in plain carbon steel will not exceed60,000 to 125,000 psi. With the higher range of strength of thealloy steels are also associated higher values of ductility and toughness, as indicated in Fig 4.

The structural or metallographic reason for these superior properties is now fairly well understood, but this understanding wasattained, as so often happens, only long after the discovery andcontinued industrial use of the alloy steels. It is a simple reason andillustrates nicely how critically the important useful properties ofmetallic alloys may depend upon rather simple physical changes.When carbon steel is slowly cooled from temperatures above 900°C(1652 0 F), it normally undergoes a structural transformation at

*There are many combinations of nickel with other alloying elements thatassure similar and in many cases even superior physical properties to those ofthe simple nickel steels. For the sake of simplicity this and some othergeneral statements should be understood as applying not only to straightnickel steels but also to nickel-alloy steels generally.

250 Modem Uses of Nonferrous Metals

700° to 900 0e (1292° to 1652°F). If the steel is cooled quicklyby quenching, this transformation may be suppressed (partially)and then a transformation of somewhat different character takesplace at about 1000e (212 OF) in the portions untransformed at the

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Properties of the steels in as-rolled or forged condition will depend onfinishing temperatures but in general tensile strength and yield point will notbe greatly different, although the proportional limit, elongation, and reductionof area may be appreciably lower than the chart values. (These are averagevalues and are not to be used as minimum specification limits.)

Nickel 251

higher temperature, in consequence of which a very fine-grainedand consequently hard and strong (martensitic) structure is produced. The steel is hardened by quenching. Unfortunately, thefirst transformation takes place very rapidly in plain carbon steeland is therefore, particularly in heavy sections, difficult to suppressentirely. Carbon steel when quenched is only partially hardenedand is deficient in strength properties. The presence of nickelrenders this first transformation in steel much more sluggish, so

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that usually it may be completely suppressed in normal quenchingoperations. The second or hardening transformation then takesplace at the lower temperature, just as in the carbon steel; but inasmuch as none of the nickel steel has undergone the first transformation, all of it undergoes the second one, producing throughout themass of the article treated that fine martensitic structure with whichare associated the higher physical properties of completely hardenedsteel. In small sections (less than about y:! in. in diameter) goodphysical properties can be secured even in plain carbon steels, butin larger sections only alloy steels display the maximum strengthand hardness of which steel is capable.

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The capacity of nickel-alloy steels, in comparison with carbonsteel, for "deep-hardening," as it is called,* is well indicated inFig 5, from which it is evident why nickel is almost an indispensableconstituent of heavy-section forgings or castings that must be heattreated to meet high physical-property specifications.

There are many other characteristics, in addition to this fundamental one of "full" or "complete hardening," in which nickelalloy steels generally exhibit superiority over the carbon steels.Among these may be mentioned particularly their disposition to remain fine-grained during the heating period required before quenching for hardening, even though the temperature is unduly high forthis purpose. The nickel steels are thus more "foolproof" inhardening operations and their resulting properties are less subjectto variation in consequence of faults of manipulation.

While nickel-alloy steels are used generally in the heat-treated(quenched and tempered) condition, they are used also in the un

325

Diameter of section, in.

FIG 5--EFFECT OF SIZE OF SECTION UPON HARDNESS OF QUENCHED AND

TEMPERED CARBON AND NICKEL ALLOY STEELS.

* See also Chapter VI, pp. 97-98, and Chapter XIII, pp. 221-222 for

other features of the "Hardenability" concept.-EDiTOR.

Nickel 253

treated or normalized state for many applications in which considerations of size or intricacy of section preclude liquid quenching.In such cases, because of the solid solution of nickel in iron (ferrite), the steels are strengthened and toughened and their fatigueresistance is improved.

For applications in which enhanced strength is the primary requirement, the so-called "forging" grades of nickel-alloy steels areused, ranging in carbon content from 0.20 to 0.50 pct. Often simplenickel steels are used containing 1 to 3.5 pct of nickel. More generally, however, nickel is used in conjunction with other alloyingelements, including particularly chromium, molybdenum, manganese, and vanadium. Of the many possible combinations of theseelements, a large number and wide variety are actually in commonuse throughout the world today. Two very well-known nickelchromium steels are the lower alloy type known as the AISI 3100series, containing about 1.25 pct of nickel and 0.60 pet of chromium, and the higher alloy type, AISI 3300 series, containing 3.5pet of nickel and 1.10 pct of chromium. Nickel-molybdenum andnickel-chromium-molybdenum combinations are likewise presentday favorites among users of alloy steel.

Although many of these "standard" compositions of nickel-alloysteels do duplicate and overlap each other to some extent in properties and fields of application, still their number and the diversityof their special characteristics also reflect to a much greater extentthe complexity and degree of specialization of the modern requirements for engineering materials. Each steel has its individual nichein the scheme of things. A 3312 steel used for heavy-duty automotive gears will not do for the springs, for which an 8660 steel maybe selected. The American Iron and Steel Institute publishes fullydetailed charts describing the characteristics of the standard alloysteel compositions. Generally speaking, the so-called "merit-index"of steels (related to the product of strength and ductility) increaseswith increasing alloy content.

Carburizing Steels

Many uses for steel require great hardness and resistance to friction or abrasion, in addition to high strength. For such applications,


low-carbon steels are often chosen, tIie surfaces of which are subsequently carburized and thus given a high degree of surface hardness. Nickel-alloy steels are again widely used for carburizing purposes (the compositions in standard use are listed by the AISI).They all range in carbon content from 0.10 to 0.25 pct.

The complete operation of casehardening is a rather delicate oneto carry through properly, since after surface carburization thearticle must be heat-treated in such a way as to develop full hardness in the high-carbon content surface layer and adequate strengthand toughness in the low-carbon content core. Nickel steels, because of their resistance to grain coarsening during heating forquenching, are eminently suited for this difficult trick. Substantialproportions of the nickel steels used in the automotive industryare of the carburizing variety. These are used principally for gearsbut also for roller bearings and for spline shafts and countershafts.As an illustration of the service rendered by steels of this sort maybe mentioned rear-axle and transmission gears for 10-ton trucks,which are required to stand up under heavy static and dynamicstresses (and excessive abuse) for many hundreds of thousands ofmiles without failure.

Industrial Use of Nickel-alloy Steels

The individual demands of industry for steels of high strengthand great wear resistance are so widespread and so diverse in character that only an indication can be given here of the general directions in which such materials are required and used.

By the use of high-strength steel, structures can generally belightened in weight, and since the commercial value of weight reduction is greatest, on the whole, in the field of transportation, itis the transportation industries that, broadly speaking, consumethe major portion of the nickel-alloy and other alloy steels. It isestimated that the American automotive industry alone consumes60 pct of the alloy-steel barstock used in this country. These steelsare used for gears, shafts, roller bearings, bolts, and nuts, and forvarious forgings in cars, trucks, buses, and tractors.

The weight saving over carbon steel made possible by the use of

Nickel 255

nickel-alloy steel in a given part frequently permits a lightening ofadjacent parts as well. A nickel-steel automobile rear-axle shaft,for example, requires smaller-diameter bearings, smaller bearinghousings, and a smaller axle housing. Thus the weight of the entireassembly may be reduced from 30 to 50 pct, depending upon theamount of alloy added. .

In the diesel locomotives that now comprise most of the motivepower of American railroads, wrought nickel-alloy steels are usedfor gears, generators, connecting rods, roof and side sheets; truckframes are of cast nickel-alloy steel. In marine propulsion equipment, such steels are used in turbine-generator rotors and shafts,and in reduction gear assemblies. In air transportation, outstandinguses are in landing-gear parts and in power-transmitting parts ofreciprocating engines.

Apart from the transportation industries, nickel steel has beenused in long-span bridges (for example, the George WashingtonBridge across the Hudson River at New York and the San FranciscoOakland Bridge), in order to reduce dead weight and increasecapacity for carrying pay weight. It is used in equipment for powerproduction and in the shafting and gears of machine tools. Themining industry has long used it in its power units and in excavating machinery and is now using it in the construction of mineskips and mine cages. A rock bit for drilling in the oil industry isillustrated in Fig 6.

J\lthough the greater portion of nickel steel is used in either therolled or the forged condition, industry makes generous use alsoof nickel-steel castings. Cast nickel-alloy steel also responds to heattreatment and substantially higher values of strength and hardnesscan be secured in nickel-alloy steel castings than in those of plainsteel. Railway passenger-car truck frames, rolling-mill rolls, heavycast machinery gears, tractor shoes, and, in the mining and metallurgical industries, crusher jaw castings, impact hammers, grizzlies,chute liners, and power-shovel and dipper-teeth castings are illustrations of the current use of these steels in cast form. Tensilestrength values of 75,000 to 150,000 psi, associated with elongationvalues of 30 to 15 pet, can be obtained in nickel, nickel-chromium-


molybdenum, or other nickel-alloy steel castings, depending upon the size and shape of the casting to be heat-treated.

One of the outstanding characteristics of nickel steels is their resistance to embrittlement at low temperatures, for which reason these steels have many uses.

The steadily mounting severity of the material requirements of the engineering industries of today, and the growing recognition of

FIG 6-OIL-WELL ROCK RIT OF KICKEL-ALLOY STEEL.

(Coarte~y of H. C. Smith Oil Tool Co.)

Nickel 257

the economic value of superior and specialized characteristics inthose materials, are well reflected in the continuously increasing useof alloy steel in America, and this is undoubtedly true also throughout the industrial world, if the appropriate statistics were onlyavailable. Thus in 1951 the domestic production* of alloy steelamounted to 7,000,000 tons as compared with 2,000,000 tons in1924. These figures have been quoted as significant of a trend inthe development of metallic materials and of their use, which ismost important from an engineering standpoint as illustrative ofthe better exploitation of our available materials, and which mustbe gratifying to the mining industry generally as opening up newfields for its various products. Nickel steels naturally share infullest measure in this trend.

Iron-nickel Alloys with Specialized Thermal Behavior

The austenitic iron-nickel alloys containing more than 30 pctof nickel constitute a unique group in which certain compositionsexhibit valuable and very special characteristics not possessed byother metallic materials. Within the range of 30 to 60 pct nickelcontent are several important commercial alloys.

In applications calling for minimum dimensional changes withtemperature, or in other cases for matching the thermal-expansionbehavior of other materials, as in metal-to-glass seals, iron-nickelalloys furnish the answers to many problems.

Development of low-expansion alloys followed the finding, in1896, by the French physicist Guillaume, of an anomaly in thethermal-expansion behavior of iron-nickel alloys as a function ofnickel content. Later another French scientist, Chevenard, foundthat as nickel content was increased beyond 30 pct the coefficientof linear expansion with temperature dropped off very .sharply to aminimum of only about 0.7 X 10-6 per degree Fahrenheit in thetemperature range of 0 to 200°F and then rose again, rapidly atfirst and then more slowly. The minimum value cited is for thealloy containing 36 pct of nickel. Because parts made of it aresubstantially invariable in dimensions over a wide range of tempera-

* Substantially equal to the consumption, for which it is here taken.


tures, this alloy has been named "Invar." It is used for such thingsas length measures-e.g., tapes and wires for geodetic measurements; length standards; parts of instruments requiring constantdistances between fixed points that must be independent oftemperature changes; automotive push rods; hypodermic needles;and textile-machinery parts-all of which are used generally in therange of atmospheric temperatures.

Invar has been used also as struts in light aluminum-alloy automotive-engine pistons, where it serves the purpose of partially

8, iii I I I 17 I

71 I I

on 6.s=:0

~ 5L-+----i--t-1--r-llo.::J

~4L-t--+--t--+-_t/~t/t~1-]?1<:

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100 200 300 400 500 600 700 600 900 1000Temperature,dell F

FIG 7-ExPANSION CURVES FOR SOME IRON-NICKEL ALLOYS.

91~%

neutralizing· the much higher thermal expansion of the aluminumalloy over that of the cast iron of the cylinders that the pistonsmust fit.

The effect of nickel content on thermal-expansion behavior isshown in Figs 7 and 8.

The Curie, or magnetic-change temperatures of the low-expansionalloys are rather high, that of Invar being 530oP. Hence these

Nickel 259

alloys are always nonmagnetic in the temperature range in whichthe low-expansion characteristic is operative.

Thermostatic metal, used in temperature-control instruments, isa bimetallic material in which a low-expansion material is weldedto one of high expansion and the composite bar thus formed isprocessed into strip. This material will bend when heated because

~~ """""---:lI~r ~ .-

V "/V V VLstrV / V V

~~ V / /- 50%Ni I i/..II'I

1/ /r--- 42%Ni _/

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9

10

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~3

]2

o-100 0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Temperature. deg F

FIG 8-VARIATION WITH TEMPERATURE OF THE INSTANTANEOUS COEFFI

CIENT OF EXPANSION OF SOME IRON-NICKEL ALLOYS.

of the great difference in coefficients of expansion of its two components. Invar and the 42 pet nickel alloy, especially the former, areused for the low-expansion material, and iron-nickel alloys towhich chromium is added are the most usual materials for the highexpansion side.

For vacuum-tightness and freedom from stress in glass-to-metaljoints, the expansion characteristics of the metal used should matchthose of the glass as closely as possible. Platinum is such a metal;a much less costly material having about the same expansion rate is


the 46 pet nickel-iron alloy, known as platinite, which at one timewas used for the lead-in wires in eleetric light bulbs and radiotubes. Platinite has been replaced in these uses by Dumet, a duplexwire with a core of 42 pet nickel-iron alloy and a coating of boratedcopper, which forms a very strong bond with the glass.

For soft glasses, the plain 42 pet nickel-iron alloy and a modification with 6 pct of chromium replacing the same amount of iron, areused. For hard glasses, good results are obtained with an alloy containing 17 pct of cobalt and 29 pet of nickel, known as Kovar.

There are many places in which materials having substantiallyconstant elastic moduli with varying temperature are necessary.Alloys of the iron-nickel family again afford the solution. Theoriginal alloy of this type, also developed by Guillaume, contained36 pet of nickel and 12 pct of chromium, and was named Elinvar,from its "invariable elasticity." The modern versions of Elinvarare modified further by additions of such other elements as tungstenand molybdenum to develop special characteristics of secondaryimportance. Representative uses for Elinvar are hair springs intimepieces and other precision instruments, scale springs, bourdontubes, and tuning forks.

Elinvar has a rather low elastic limit, that for the cold-workedmaterial being only about 45,000 psi. A modified compositioncontaining 36 pet of nickel, 8 pet or more of chromium and about4 pet total of the elements manganese, silicon, molybdenum, copper,and vanadium is known as "Iso-Elastic." By suitable processing,its safe working stress in shear can be raised to 60,000 psi. Acomposition of this type known as "Ni-Span C," containing about42 pet of nickel, 5.5 pet of chromium, and 2.2 pet of titanium,possesses age-hardening properties and can be processed to show aproportional limit of about 110,000 psi. The processing involvesthe aging of heavily cold-worked material. An even stronger material in this field of commercial use, but containing only 18 petof nickel, trade-named "Elgiloy," has a proportional limit of about215,000 psi. It is hardly an iron-nickel alloy, however, for it contains only about 23 pet of iron, together with 40 pet of cobalt, 15pet of chromium, and 3.5 pet of molybdenum.

Nickel 261

NICKEL ALLOYS AND MAGNETISM

Out of the iron-nickel system come also magnetic and nonmagnetic alloys of great usefulness to the electrical industry, especiallyin the field of communications. These are not always simple alloysof nickel and iron but often contain also appreciable amounts ofother elements through the agency of which some particular magnetic characteristic may be developed or accentuated.

There is an added requirement of high strength in many applications for nonmagnetic materials, and in some cases high electrical

TABLE ~-Some Nickel Alloyafor Special Uaea in the Field of ElectricalCommunicationa

Alloy Type CommentIron-chromium-nickel:

8% Ni, 18% Cr(AISla type 80~) Used only in annealed condition1~% Ni, 18% Cr(AISI type 805) Used where some cold-working is

required~O% Ni, ~5% Cr(AISI type 310) Not affected magnetically by cold

work70% Ni, 15% Cr, 9% Fe (In

conel)Iron-manganese nickel:

8% Ni, 10% MnNickel-copper:

30% Ni (Cupronickel)60% Ni (Monel. type 8~6)

65% Ni, ~.75% AI, 0.5% Ti ("K"Monel)

a AISI means American Iron and Steel Institute.

resistivity is necessary, as for the retaining bands and end platesof large motors and generators. In a much different field, electronics,there are many applications, as in television tube parts requiringnonmagnetic materials that have strength at high temperatures andthat respond well to "outgassing."

Iron-nickel alloys with a third element, usually chromium ormanganese, provide the answers to many such requirements. Competition in this field is provided by nickel-copper alloys when lower


strengths can be tolerated and by a modified nickel-copper alloy,"K" Monel, which contains small percentages of aluminum andtitanium and can be age-hardened to high mechanical properties.Table 2 contains a list of some of the alloys that have been used.

Magnetic Nickel Alloys

Straight iron-nickel alloys containing between 20 and 30 pct ofnickel are not ustd for magnetic applications. As nickel is increased,the temperature of the magnetic change, or Curie point, rises aboveordinary levels and all compositions containing more than 30 pctof nickel are magnetic at ordinary temperatures. In addition to theirspecial expansion and thermoelastic properties, these alloys ofhigher nickel content provide a series of extremely useful magneticalloys that are highly important to industry. Modifications of magnetic characteristics can be obtained by additions of other elements.An example is aluminum, which confers age-hardening capacityaccompanied by a change from the prevailing high permeabilitiesof the iron-nickel alloys to pronounced magnetic hardness, so thataluminum-containing alloys make excellent permanent magnets.

The magnetic saturation values in these alloys are not quite ashigh as those of pure iron or of the silicon-iron alloys currentlyused in the design of electrical transformers and motors or generators. In certain other respects, however, the magnetic propertiesof some of these alloys are remarkable. It is one of the many distinguished credits to the account of modern industrial research thatthe more subtle aspects of these properties have been worked outand the alloys made available for special problems in electromagnetic engineering design.

For certain purposes, particularly in apparatus used for communication, materials are required that have high magnetic permeabilityin low magnetic fields. Arnold and Elmen, studying the ferronickelalloys in the laboratories of the Western Electric Co., reported in1923 that iron-nickel alloys containing from about 35 to 85 pct ofnickel possessed unusually favorable magnetic properties, the highest initial permeability occurring in the 78.5 pct alloy. ConcurrentlyYensen, at the Westinghouse laboratories, with a different heat treat-

Nickel 263

ment, located another (lower) peak of permeability in the region of50 pct of nickel.

Whereas the maximum magnetic permeability possible with commercial iron or silicon iron is perhaps 10,000, properly heat-treated78.5 pct Permalloy (as Arnold and Elmen named the ferronickelalloys) will develop a permeability of over 100,000. An alloy developed later, Supermalloy, extends the upper limit to 900,000.

200

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Nickel, pct

FIG 9-VARIATION WITH NICKEL CONTENT OF CURIE TEMPERATURE AND

SATURATION MAGNETIZATION OF IRON-NICKEL ALLOYS.

Saturation values at room temperatures and Curie temperaturesfor the iron-nickel alloys are shown in Fig 9.

Alloys of the 80 pet nickel type are used to meet demands forhigh initial and maximum permeabilities, or for extremely lowhysteresis losses. These requirements are met in equipment involving

264 Modern Uses oj Nonjerrous Metals

low magnetizing fields. First applications, dating back to the early'20s, were in telephone loading coils and in the continuous loadingof submarine cables. In the latter case, transmission speeds wereincreased fivefold in a cable between New York and the Azores.For land cables, loading coils, spaced at long intervals, have coresof powdered iron-nickel-base alloys. The most recently developedcomposition for this purpose, containing 81 pct of nickel and 2 pctof molybdenum, not only has improved transmission characteristicsbut also has effected savings in weight and space.

The capacity of the high-permeability material for magnetizationin small fields has made possible the development of such instruments as the Magnesyn compass, the flux-gate compass, and theairborne magnetometer. While originally designed for the detectionof submarines, the airborne magnetometer has had wide applicationin prospecting for oil and minerals in the post-World War IIperiod. Its success is due to its core of a permalloy-type alloy containing 79 pct of nickel and 4 pct of molybdenum. The amount ofmagnetization by the vertical component of the earth's field is measured and recorded. From these data, contour maps can be drawnshowing the variation of the earth's field caused by mineral depositsand subsurface structures. In addition to its successful application inoil prospecting, the airborne magnetometer has disclosed a nwnberof large deposits of iron ore.

Other uses for the permalloy type of material are in shieldingof delicate apparatus from stray magnetic fields, in the cores ofsensitive relays and, especially because of the added value of corrosion resistance, for small motors, selsyns, and similar equipment tobe used in the tropics. With 81 pct of nickel-balance iron, this typeof material has zero magnetostriction, which is responsible for itsuse in transformers mounted on the same chassis, to prevent undesirable coupling.

Alloys of the 50 pct nickel type have permeabilities lower thanthose of the 80 pct group but considerably higher than that of electrical sheet steel. They are used in low-level transformers where highinitial or maximum permeability is required, and in high-qualityaudiotransformers, where there is need for minimum distortion

Nickel 265

and flat frequency response. There are other uses, as in pulse transformers for radar, in current transformers, and in numerous instruments. Its low-loss properties make the 50 pct nickel type alsouseful in portable power tools to minimize heating.

By special fabrication and processing procedures, iron-nickelalloys containing 50 and 65 pct of nickel can be so altered in theirmagnetic behavior as to have a rectangular hysteresis loop. This isof especial importance in mechanical rectifiers, which must hold thecurrent practically at zero for a finite time while the contacts thatrectify the alternating current voltage are being made or broken. Anotable use is in the mechanism of digital computers.

Magnetostriction is a term that refers to the change in dimensions of a ferromagnetic material when it is magnetized; or, conversely, to the change in magnetization of the material with changesin dimensions by an external force. Of commercial materialspossessing this characteristic, the most widely used is commerciallypure nickel (A nickel). The 50 pct nickel-iron alloys can be usedalso, and some use is made of nickel-chromium-iron compositions,such as Ni-Span C, which is used in certain applications that call forconstant modulus of elasticity under varying temperature conditions.As has been noted, the 80 pct nickel alloys have substantially zeromagnetostriction.

The magnetostrictive effect is the important principle in hydrophones for the detection of underwater sounds, in Sonar (underwater radar), and in sonic devices for measuring depth of water.The effect has been used also in a band-pass filter for better radioreception, a phonograph pickup and frequency-control devices.Other uses are in devices for dust precipitation, the nondestructivetesting of metals, the destruction of biological organisms, and thecatalysis of chemical reactions. .

Magnetic characteristics of the alloys discussed in the foregoingparagraphs are shown in Table 3.

Nickel Alloys for Permanent Magnets

Since the days when the original permanent-magnet material,ordinary high-carbon steel, was the only material used for the pur-

TABLE 3-Approximate Magnetic Properties of the Special Alloys

I

Initial Maximum Satura- Electrical Curiel\lalerial Nickel, Pet Perme- Perme- tion Flux Resistivity, Tempera-

ability ability Density, Microhm-em ture.Gausses Deg F

Irons:Iron (99.91'70 Fe). ... '" Nil 200 5.000 21,500 10 1410<I % silicon-iron ......... .... Nil 500 7,000 20,000 60 1270

Very high-permeability alloys;78.5 Permalloy ......... 78.5 9,000 105,000 10,700 16 1075Modified 79 Permalloy. ... 7!) + 4'70 Mo 20,000 90,000 8,000 58 860Mumetal ................................ 77 + 5'70 Cu and 1.5'70 Cr 20,000 100,000 8,000 60 840Supermallo;v .............................. .. 79 + 5'70 Mo 120,000 900,000 8,000 65 715

High-permeability alloys for higher field strengths;50'70 nickel type alloys ....... ...... 45 to 50 5,000 50,000 16,000 45 950Monimax .................... . 47+8'70Mo 3,000 38,000 15,000 798inimax ................... . 48 + 8.25'70 Si 2,000 80,000 11,000 89

Constant-permeabilityallo)"51:a

45-~5 Perminvar . ............ .... .. .... 45 + 25'70 Co 865 1.800 15,500 19 18207-45-25 Perminvar•........... ... .. ... 45 + 7.5'70 Mo and 25'70 Co 550 8,800 10,800 80 1000Conpernik ................. ..... ... 50 1,500 4,500 16,000 45 950

Temperature compensator alloYB:80'70 nickel type.... , ........ .. .... ....... 80 8,500 80 80082,5'70 nickel type ........... . , ........ 82.5 7,000 80 890

Rectangular hysteresis alloys;'50 % nickel-type alloys ... , ........ , .... ... 50 500 217,000 16,000 50 98065 Permalloy ....... , ................. ... 65 2,500 650,000 18,500 25 1150

Magnetostricti ve alloys:A Nickel. ..............•.......... .. ... 99.5 110 600 6,100 8 68045-50'70 nickel.iron alloys (see above)

Insulated-Ft0wder alloy:81+2'70Mo 8902-81 ermalloy ................ .... ... ... 125 130 8,000 10'

a Used at low field strength only. Under these conditions permeability is essentially constant and residual induction, coercive force. and hysteresisloss are negligible.

b Grain orientation by rolling and/or heat treatment in a magnetic field required.

Nickel 267

pose, there have been great developments in this field, outstandingamong which have been a number of nickel-containing alloys. Thehigh-carbon magnet steels and the earlier non-nickeliferous alloysteels depended upon their contents of carbides for the magnetichardness characteristics responsible for their permanent magnetism.The modern permanent-magnet alloys are low-carbon materials thatacquire their magnetic characteristics through the mechanism ofdispersion or precipitation-hardening, known also as age-hardening.The first such alloy, which was patented by Kroll in 1929, was aniron-nickel-beryllium composition. Mishima's nickel-aluminum M.K.magnet steel was announced three years later and since that timequite a family of iron-nickel-aluminum-base alloys, most of whichalso contain cobalt and others include important amounts of copperor titanium, has been developed by the General Electric Co. Thisgroup of alloys has been given the generic designation of Alnico,coined from the names of the three principal alloying elementscontained.

The Alnico alloys are relatively hard and brittle so that theyare produced only by casting, or by powder metallurgy practices,and finished by grinding. The need for malleable permanent-magnetmaterials has been met-with some sacrifice in magnetic properties,however-by a copper-nickel-iron alloy called Cunife, and a coppernickel-cobalt alloy called Cunico.

Compositions and magnetic properties of a number of permanentmagnet materials, both ferrous and nonferrous, are given inTable 4.

The relative positions of the Alnico family, and some others ofthe compositions listed in Table 4, with respect to demagnitizationbehavior are shown in Fig 10. The picture for Cunife is not greatlydifferent from that for Alnico III, but the Cunico curve falls wellbelow both.

A more readily grasped comparison among the materials ofFig 10 is afforded by Fig 11.

IRON-NICKEL ALLOYS AND CORROSION

As early as 1822, Faraday and Stodart had investigated the ironnickel alloys containing 20 to 30 pct of nickel and noted that they

TABLE 4--Representative Magnetic Properties of Some Permanent Magnet Materials

Alloy Composition, Pct(Balance, if any, is Fe)

Coercive IResidualForce, Induc-

He, tion, B,.,Oersteds Gausses

Maximum

EnergyProduct,

BHm • x ,

Millions

300300300

1,0001,0002,0002,0002,0003,0002,5003,0004,0001,0003,2002,4003,0002,800

12,OOOb7,OOOb1,000

20,0003,0001,000

SpecificGravity,Grams

perCuCm

7.87.88.18.48.26.97.16.97.07.37.47.38.28.38.67.46.9

14.613.58.29.03.18.2

N0\00

a Value of the intrinsie coercive force.b Estimated.

Nickel 269

exhibited a substantial degree of resistance to rusting and corrosion.Beginning in the early years of the century, use was made of 20 to 25pct nickel steel for boiler tubes and other articles requiring thesecharacteristics, but it was not unti11915, when Strauss, Hatfield, andothers discovered the value of chromium additions to iron-nickelalloys, that the modern "stainless" steels of the austenitic type weredeveloped and made available.

The stainless steels as a class are not resistant to corrosion underall conditions, however. They are vulnerable to attack under reoducing acid conditions, for instance, and hence are not used insuch environments. Some varieties are subject to carbide precipita-

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H. Oersteds

FIG lO-DEMAGNETIZATION CURVES ILLUSTRATING SUCCESSIVE IMPROVE

MENTS MADE DURING THE PAST HALF CENTURY.

270 Modern Uses of Nonferrogs Metals

tion when heated in certain temperature ranges, which leaves them vulnerable to intergranular corrosion. This has been combated suc- cessfully in two ways, one by maintaining extremely low carbon content and the other by adding small amounts of such carbide- stabilizing elements as columbium and titanium.

These steels, containing from 7 to 20 pct of nickel and from 16 to 25 pct of chromium, are metallographically similar to the iron-

FIG 11-RELATIVE SIZES OF EQUIVALENT MAGNETS MADE OF VARIOUS

MATERIALS.

nickel alloys, are substantially nonmagnetic, and are not responsive to heat treatment. They are substantially rustproof and have quite remarkable resistance to corrosion, particularly in media that are oxidizing in character. The name "stainless," which has been very aptly applied to these alloys, reflects correctly a high order of resistance to stain and tarnish, which is perhaps their most striking characteristic and is conferred by the presence of chromium.

The properties of the stainless steels as related to their uses, which are extensive and very diverse, are treated in more detail in the chapter on chromium. They are strong alloys, the more commonly used varieties hardenable only by cold-work, reaching tensile strength

Nickel 271

levels in some compositions as high as 200,000 psi. Age-hardenablevarieties also have been developed.

The largest single application for the stainless steels in the postWorld War II period has been in equipment for food handling andprocessing, including home cooking utensils. Next in order of tonnage taken is the mnsumer appliance field, followed by the chemicaland allied industries, where they are used in quantity in equipmentfor nitric acid manufacture, petroleum refining, pulp and papermills, pharmaceutical manufacture and many other applications.Architectural applications form a fourth and rapidly growing field,and next in importance as to tonnage is transportation equipmentin the air, on land, and to a lesser extent on the water. The modernstreamlined passenger train pictured in Fig 12, and the aircraftjet engine pictured in Fig 13 are examples of uses in transportation.

CAST IRON AND NICKEL

Cast iron at one time, not so very many years ago, was about thelowliest of commercial metallic materials of construction, despiteits low cost, its general availability and ready production into allkinds of intricately shaped castings, and its excellent machinability.Structurally, cast iron is a very complex and interesting material,the properties of which respond flexibly and usefully to changes inits composition-to variations, for example, in its carbon and siliconcontents. It responds also in many useful ways to the addition ofalloying elements, including nickel. Within recent years, there hasbeen a much broader recognition of possibilities in the engineeringuses of cast iron. It is not too much to say that the developmentof nickel and of nickel-chromium, nickel-molybdenum and nickelchromium-molybdenum cast irons have been predominant influences in stimulating this desirable new direction of metallurgicalinterest.

Isolated suggestions of the use and value of nickel in cast ironwere made as early as 1799 but serious attention was not devotedto the subject until about 1920, when the necessity of developingnew uses for nickel resulted in the initiation of researches in thisdirection in the research laboratories of The International Nickel

272 Modern Uses of Nonferrozls Metals

FIG 12-MODERN HIGH-SPEED STREAMLINED TRAIN OF STAINLESS STEEL

CONSTRUCTION (THE SANTA FE SUPERCHIEF).

(Courtesy of Santa Fe Railway.)

FIG 13-GENERAL ELECTRIC COMPANY JET ENGINE IN CONVAIR B-36 INTER-

CONTINENTAL BOMBER.

Stainless steels and Inconel are used in these engines.

(Courtesy of General Electric Co.)

Nickel 273

Co. Necessity (for new markets for nickel) again proved to be themother of invention.

It is an obvious thought that if nickel wiIl improve steel it shouldalso improve its poorer cousin, cast iron, and in a similar manner.This in fact has turned out to be true, but the degree of metallurgicalcooperation between cast iron and nickel is even greater and morediversified in character than that between nickel and steel.

Just as in steel, nickel additions increase the hardness and improvethe wear and abrasion resistance of gray cast iron. Upon these fundamental characteristics depends the use of alloyed gray irons forautomotive-engine cylinders, automotive brake drums, diesel-enginecylinders and liners, cast gears and cams, and steam and pump cylinders. Such castings may contain from 0.5 to as much as 3.0 pct ofnickel. More generally, nickel and chromium combinations for wearresistant gray-iron castings are used; the effects of nickel and ofchromium on iron are in some respects different but of a complementary nature and for many types and grades of castings nickelchromium iron is superior to nickel iron. The compositions actuallyused are widely varied but the ratio of nickel to chromium is normally held between 2 and 3 to 1 and the total alloy content to between 0.5 and 4 pct. Such nickel-chromium alloy gray irons exhibitBrinell hardness values from 200 to 275, as compared with a normalrange of 150 to 200 characteristic of plain iron. The abrasionresistance of the harder alloy irons is found in practice to be severaltimes greater than that of plain iron.

Sometimes these alloy irons are heat-treated in much the samemanner as steel and used in this condition, particularly for largesheet-metal forming dies, like the one illustrated in Fig 14, as wellas for engine-cylinder liners, cams, and many other items requiringsuperior strength and hardness. The fundamental effect of nickel(and of chromium) in retarding the upper transformation in steeland iron is here helpful and often necessary, just as it is in steel.

High-strength cast iron is obtained with the help of nickel andthrough simultaneous lowering of the carbon content. Ordinaryfoundry iron will break under tensile loads exceeding 30,000 to40,000 psi. Nickel iron and sometimes nickel-chromium or nickel-

274 Modern Uses of Nonferrotls Metals

molybdenum irons of lowered carbon content (2.50 to 3.10 pct of carbon) are being produced that exhibit tensile strength values in excess of 50,000 psi, and indeed as high as 75,000 psi. They are used for heavy machinery frames and recently are even replacing steel for automotive-engine cam and crankshafts.

FIG DIE FOR FORMING AUTOMOBILE BODY PARTS, MADE OF CAST IRON

ALLOYED WITH NICKEL. (Courtesy of Baldwin-Lima-Hamilton Corporation.)

Plain gray iron can be hardened and strengthened very simply by lowering its carbon and silicon contents below the normal values of 3.25 to 3.50 pct of carbon and 2.0 to 2.50 pct of silicon. Improve- ment through these means could be carried even further if the iron did not thereby ultimately become white or ungraphitized in structure and consequently brittle, hard, and unmachinable. Although nickel hardens gray iron, it restrains the development of the "white" or "chilled" structure in castings (particularly in thin or sharp sections). It is therefore possible in nickel iron (containing from 0.5 to 3.0 pct of nickel) to utilize better the advantages of low carbon and silicon contents in gray iron and to produce castings of

Nickel 275

more uniform structure and quality and of better machinabilitythroughout various sections, both heavy and light. This effect ofnickel in relieving the normal casting limitations for gray iron is ofpractical value to the foundryman and advantage is taken of it inthe production of many types of gray-iron castings today; especiallythose of varying section-for pumps, gears, machine-tool ways, andother general machinery parts.

A new and outstanding development in cast irons has been theintroduction of fractional percentages of magnesium through theagency of which the graphite, which in ordinary gray iron is in theform of flakes and in malleable iron is nodular, becomes trulyspheroidal. (See Fig 6 of Chapter XI.) The resulting spheroidaliron has strength properties and ductility values approaching thoseof cast carbon steels. Introduction of the magnesium, an extremelyreactive element, is not easy. One way in which it can be introducedis by addition of a nickel-magnesium master alloy.

White or Chilled Iron

When 4 to 4.5 pct of nickel, together with from 1.5 to 2.5 pctof chromium, is added to plain "chillable" or white iron, the structure is rendered "martensitic" and its hardness is mcreased verysubstantially-from about 450 to 600 or 700 Brinell hardness number. The resulting "martensitic" white iron, known as Ni-Hard.*has a quite extraordinary degree of abrasion resistance and is beingwidely used for the wearing parts of crushing and grinding machinery, for grinding balls, and for mill rolls used in the rolling ofsteel and other metals. These martensitic irons often outlast plain"white" iron from 2 to 3 times in crushing and grinding service.They are substituted very often for steel although of course they arenot as ductile and tough as that material.

Corrosion-resistant Nickel Cast Iron

The austenitic structure that characterizes the chromium-nickelstainless steels can be produced in cast irons, and with the parallelresult of greatly increased corrosion resistance. A family of such

• Trademarked by The International Nickel Company, Inc.

T.'BLE 5-Composition Range of Ni-Resist"PER CENT

I I. Type 4,

Ii Type la,

I

Type 2, Type 2a, Type 2b, Type 3, Heat andType 5,

Element Type 1" I High 20 Pct High Heat 30 Pct StainMinovar"

I Strength" Nickelb

I

Strengthb Resistant Nickel Resistant

II I (30-5-5)

Total carbon. 3 .00 max 2.80 max 3.00 max 2.80 max 3.00 max 2.75 max 2.60 max 2.40 maxSilicon ....... 1.00-2.50 1.50-2.75 1.00-2.50 1. 50-2.75 1. 00-2.50 1.00-2.00 5.00-6.00 1.00-2.00Manganese. 1.00-1.50 1.00-1.50 0.80-1. 50 0.80-1.50 0.80-1.50 0.40-0.80 0.40-0.80 0.40-0.80Nickel. ...... 13.50-17.50 13.50-17.50 18.00-22.00 18.00-22.00 18.00-22.00 28.00-32.00 29.00-32.00 34.00-36.00Copper .... 5.50-7.50 5 ..50-7.50 0.50 max 0.50 max 0.50 max 0.50 max 0.50 max 0.50 maxChromium .... 1.75-2.50 1. 75-2.50 1. 75-2.50 1. 75-2.50 3.00-6.00 d 2.50-3.50 4.5-5.5 0.10 max'

a Where the presence of copper offers the advantage of corrosion resistance, types 1 and 1a are recommended.b For handling caustics, food, and so forth, where copper contamination cannot be tolerated, types 2 and 2a are

recommended.C Where minimum thermal expansion is desired.d Where some machining is required, the 3.0 to 4.0 pct chromium level is recommended.• Where higher hardness and greater strength are desired, the chromium may be 2.5 to 3.0 pct at the expense of

increased expansivity.

Nickel 277

highly alloyed irons, known generically as Ni-Resist,* affords avariety of properties to suit many industrial needs. These alloysare moderately priced and fill a very useful commercial positionbetween ordinary gray irons and the more costly nonferrous corrosion-resisting materials, or the stainless steels.

The Ni-Resist irons are used widely in the oil, paper, and chemical industries, for corrosion resistance; and in the foods, plastics,soap, and other industries to minimize product contamination. Inindustry generally they are used for resistance to wear and to reducedeterioration in parts of machinery, power units, and furnaces. Theyhave good resistance to alkalies, many acids, salts, oils, foods, andplastics; resistance to wear; high electrical resistivity; controlledthermal expansivity; good strength and toughness; and are nonmagnetic. For their excellent resistance to galling, they have beenused for valve guides and in ball-and-socket exhaust manifoldjoints in aircraft reciprocating-engine units. The compositions andspecial characteristics of the Ni-Resist alloys are indicated inTable 5.

NICKEL-CHROMIUM AND RELATED ALLOYS

Much of the early development of nickel-chromium and relatedalloys was linked with commercial and domestic needs for materialsof high electrical resistivity. Nearly everyone is familiar with rheostats, simple electrical devices that depend for their usefulness uponthe high electrical resistivity of a wire that concomitantly generatesconsiderable heat within itself. This heating effect that accompaniesthe passage of current, while an unavoidable evil in rheostats, isthe very essence of usefulness in domestic electrical heating unitstoasters, grills, coffee urns, flatirons, space heaters, and other appliances-which are made by the million every year.

From the earliest days, nickel alloys were the standard materialsfor motor controls and other rheostats. Constantan, a copper-nickelalloy containing about 4s pct of nickel, together with an iron-nickelalloy containing about 30 pct of nickel, were the favorite materialsused, and they were in many ways well suited for the purpose; their

* Trademarked by The International Nickel Company, Inc.

278 Modern Uses of Nonferrous lvletalJ

electrical resistivities were high and stable, provided the rheostatswere not allowed to overheat. Indeed, these two materials are stillused, though to a limited extent, for electrical resistor service, wherethe conditions, particularly as to operating temperature, are sufficiently moderate. Constantan and a related alloy, Manganin, areamong electrical resistance alloys distinguished by the fact that theirelectrical resistivity is practically unaffected by moderate temperaturevariations (in the neighborhood of ordinary temperatures). Theyare, therefore, used for those accurate resistors that are requiredin control and measuring electrical instruments and in laboratories.

During the early years of the twentieth century, the idea wasdeveloped of using rheostats to heat bread, warm irons, and performother such services. Unfortunately, the older materials would notstand operation at red-hot temperatures very long. In 1906, Marshpatented, for high-temperature resistor service, the alloys of chromium and nickel that have since become known as Chromel, Nichrome, and other trade names. They contain from 65 to 85 pct ofnickel and from 15 to 20 pct of chromium (often together withsome iron), and in addition to excellent electrical properties (highresistivity and low temperature coefficient thereof) they proved tobe very resistant to destruction by oxidation, even when continuouslyexposed to air at temperatures as high as 1000° to 1l00°e. At thehigh temperatures used today in such heating appliances, the modernchromium-nickel alloys outlast the steel and the alloys used at thebeginning of the century 500 to 1-an excellent illustration incidentally of the type of contribution to engineering practice thathas been made by metallurgical improvements in alloys.

The availability of such a material, together with the awakeninginterest of the power companies in selling more electrical power,stimulated mightily this industry of household electric heating appliances. Today, these nickel-chromium alloys are used exclusivelyin such appliances, from cigar lighter to hot-water heater, andalthough the amount of wire or strip used in each unit is verymodest, the number of units sold annually is so large that a considerable consumption of nickel is involved.

Electrical heating has been substantially extended, as well, into

Nickel 279

the field of industrial heating--for metal annealing and heat-treating furnaces, for enamelware firing, and for heating operations inthe manufacturing industries generally where close control of temperatures is required.

Interesting is the fact that the critical characteristic of these alloys--of being able to resist oxidation at red heat-is not due to anyproperty of the metal itself but is a characteristic of its oxide. Pillingand Bedworth demonstrated that these alloys actually initially oxidize rapidly at these temperatures but that the surface oxide formedis of such a dense and adherent nature that the first very thin layerformed effectually prevents further access of air to the underlyingmetal. Oxidation therefore comes quickly to a stop. These alloys,in a sense, are parasites to their own oxides; they live (economically) by the latter's performance.

Nickel-chromium alloys as well as Constantan are likewise usedsomewhat similarly for high-temperature service in the form ofthermocouple pyrometers. Substantial and stable thermal electromotive force is developed between combinations of these materialswith nickel and iron, and several such combinations have beencalibrated carefully and standardized for pyrometer service.

It was soon discovered that the nickel-chromium and the nickelchromium-iron alloys possess certain additional characteristics valuable in high-temperature service. Although at ordinary temperaturesthey are not much stronger than medium hard steel (their tensilestrength is about 90,000 psi) they retain their strength at hightemperatures to a surprising degree. This is particularly true whenexposures of long duration are considered, as actually occur in normal service. So-called "creep tests" have shown, for example, thatat 980°C cast alloys of this type may be safely loaded up to about1500 psi, whereas a steel casting having about the same strengthat ordinary temperature will not long stand a load of more than100 psi at the higher temperature. At these temperatures, the alloyis 15 times as strong as steel.

Here again metallurgical research has provided industry withvastly improved materials of which it has not been slow to takeadvantage. For a host of applications in the metallurgical, the chemi-


cal, and allied industries where structures, retorts, furnaces, andconveyors are required to operate at temperatures from 550° to1l000C, these alloys have replaced the steel and iron formerly used.Many or most of these structures are made of castings for which avariety of compositions are currently used, containing from 10 to 80pct of nickel, from 15 to 25 pet of chromium, and the remainder

T ADLE 6-Classification, by Chemical Composition Ranges, of Heat-resistingCasting Alloys·

Comment

Composition, Service

Group I Pet Tempera-ture,

Ni Cr Deg C

--1-1 4-1'2---

18-30 650-8751125 max

2 11-" I "-,, 11150 mm

3 33-68 IO-'ll 1125 Illax

For lower alloy contentsFor higher alloy contents; greaterload-carrying capacity

All group 1 alloys have good resistanceto sulfur conditions

High load-carrying capacity; goodresistance to oxidation and furnaceatmosphere; moderate resistance tosulfur conditions

High load-carrying capacity; highresistance to oxidation, carburizingand nitriding conditions; vulnerableto sulfur conditions

• The eompositionHl groupings are those of the Alloy Casting Institute.The ACI distinguishes among compositions by letter symhols; th,. groupnumbers of this tabl,. are the authors' designation.

iron. In most of these applications are required simultaneously the"creep strength" and the oxidation resistance so strikingly exhibitedby these alloys.

The Alloy Casting Institute has standardized on commercial compositions for heat-resisting alloys along the lines indicated in a generalized manner in Table 6. The less highly alloyed members ofgroup 1 are used for parts of heat-treating furnaces, oil-refineryequipment, cement kilns, and other equipment. The more highly

Nickel 281

alloyed group 2 compositions are used for such services as rabblearms and blades in ore-roasting furnaces, dampers, sintering bars,grates, tuyeres, and in salt pots for heat-treating. Group 2 includesthe so-called 25-12 (12 Ni, 25 Cr) alloy, which is about the mostwidely used for furnace parts. Others of this group have fields ofapplication similar to those of the lower alloyed materials of group1, but under more severe operating requirements. Sulfur resistancein these alloys increases with increasing chromium content.

TABLE 7-Classiji.catian, by Chemical Composition Ranges, of CorrosionrC8isting Casting Alloys"

Composition, Pct

Group Comment

Ni Cr

1 1-4, max 11.5-30 Nickel content incidental, from scrap sources;no new nickel added

2 8-12 18-30 '2 to 3 pct of molybdenum in one grade3 9-12 18-21 0.4 to 0.8 pet of molybdenum in one grade;

2 to 3 in another; 1.5 pct max molybdenum +about 0.25 pct selenium (for free machin-ability) in one grade; one grade stabilized withcolumbium

4 12-31 18-27 One grade has added molybdenum and copper

"The compositional groupings are those of the Alloy Casting Institute.The ACI distinguishes among compositions by letter symbols; the groupnumbers of this table are the authors' designations.

Nickel is the preponderant alloying element of group 3, whichincludes the well-known 35-15 (35 Ni, 15 Cr) composition widelyused in heat-treating furnaces, chains, lead and salt pots, furnacerolls, annealing and carburizing boxes, skid rails, glass lehr rolls,enameling racks, radiant-heater tubes, and fixtures for cyclic heating operations. Other alloys of group 3 are used against variousseverities of service; for example, greater resistance to hot-gascorrosion.

Cast alloys of the same general nature as those of Table 6, asmight be expected, are highly resistant to many corrosive environ-


ments. Their uses are legion; in petroleum refineries, pulp and papermills, and many others of the chemical and allied industries. TheAlloy Casting Institute's grouping of alloys for corrosive servicesis shown in Table 7.

One of the oldest uses for nickel-chromium alloy castings wasthe carburizing box used to hold steel articles during the carburizingheat treatment at about 875° to 925°C. Experience has shown thatsuch alloy boxes exhibit a useful life of 5000 hr as compared with100 to 250 hr from steel.

Compositions not included in Table 7 are used for specific andvery severe services; for instance, against hydrochloric acid andstrongly oxidizing acid solutions. The nickel·molybdenum andnickel-molybdenum-chromium alloys known by such trade namesas Hastelloy and Chlorimet, and containing about 60 pct or moreof nickel, are noteworthy. These alloys contain up to about 6 pct ofiron. The Hastelloys are used in both cast and wrought forms. Evenmore complex compositions are used-for instance, that known asIllium-which, in addition to about 60 pct of nickel, contains significant amounts of iron, molybdenum, copper, and tungsten.Illium's principal use is against very highly oxidizing solutions suchas nitric acid.

Corrosion-resisting characteristics of the wrought forms of nickelcontaining stainless steels were discussed in the section on ironnickel alloys and corrosion (p. 267). Nickel-base alloys containingIS to 20 pct of chromium, some iron-free and others with up toabout 25 pct of iron, occupy an important area in the commerciallyavailable materials for resistance to heat and corrosion. For somehigh-temperature services, there is a small use of an 80 pct nickeland 20 pct chromium alloy, and a greater use of one containing60 pct of nickel, IS pet of chromium, and about 23 pct of iron.The wrought 80-20 alloy has good hot strength and excellent resist·ance to most forms of high-temperature corrosion. It is used at temperatures up to about HOODC for many parts of furnace equipmentfor copper brazing, powdered-metal sintering, oxide reduction, andin ceramic glazing kilns and vitreous enameling equipment. Modifications of this alloy type are used under the generic name of

Nickel 283

Nimonics* and are the favored materials in Great Britain for thecombustion systems of aircraft jet engines. The 60-15 alloy has goodhigh-temperature strength and heat resistance. It is used for resistance wire, and also for equipment for carburizing and nitridingof steels, quenching and pickling trays and baskets and racks forvitreous enameling. Large use is made in jet-engine construction ofInconel, t and its age-hardenable modifications Incond X and Inconel W. The parent alloy contains approximately 78 pct of nickel,15 pct of chromium and 7 pct of iron. It resists scaling very well upto about l100 0 C and is widely used also for heat-treating equipmentsuch as trays, quenching fixtures, muffles, radiant tubes, conveyorbelts, salt-bath electrodes, and retorts for carburizing and nitriding.Like the Nimonics, it has extensive use in aircraft power plants,for many parts of jet engines and for piston-engine exhaust-collectorsystems, exhaust-gas heat exchangers and cabin heaters. In thechemical industries, it has such high.temperature uses as in equipment for cracking hydrocarbons, handling fused caustic soda, andcarrying out chlorination and fluorination reactions at high temperatures. The age-hardenable modifications have excellent high-temperature strength, which makes them desirable for highly stressedparts of jet engines.

Incone! is highly resistant to many corrosive materials. For thisreason, as well as to guard against contamination of products, ithas many uses; for instance, in equipment for the manufacture ofpharmaceuticals and antibiotics, hot fatty acids, hot concentratedcaU:Stic soda solutions, hot chlorine (up to about 500°C) and hydrogen chloride gas (up to about 550°C).

AGE-HARDENING NICKEL ALLOYS

During the past 30 years, there have been opened up broad fieldsfor alloys, particularly nonferrous alloys, in consequence of the development of the art of "age-hardening." Additions may be madeto practically all metals and alloys which will render them amenableto hardening and strengthening by age-hardening, and the result-

• Trademark of The Mond Nickel Co., Ltd.t Trademark of The International Nickel Co., Inc.


ing physical properties are in many cases quite astonishing. Nickelalloys share in the benefits of application of this art and several ofthe commercially used age-hardening alloys today contain nickel.

Among the best known alloys of this sort are the aluminumtitanium-nickel-copper and the silicon-nickel-copper alloys. Bothaluminu1l1 and silicon in amounts varying from 0.5 to 5.0 pct (depending on the relative amounts of nickel and copper) confer agehardening response on the nickel-copper alloys, in consequence ofwhich the tensile strength of the copper-rich alloys may be increasedfrom about 40,000 or 50,000 psi to about 100,000 psi; and thestrength of Monel from about 85,000 psi in the annealed conditionto over 150,000 psi after age-hardening. Such properties are comparable with those of heat-treated alloy steels and the time has therefore passed when steel must be regarded as our only strong material.A hardenable modification of malleable nickel containing smallamounts of aluminum and titanium is similarly much stronger, inthe heat-treated condition, than nickel; the increase being to theorder of 200,000 psi from the 80,000 psi for annealed nickel.Nickel and nickel-copper are also hardened by beryllium and the2 to 3 pct beryllium-nickel alloys develop exceptional values ofhardness after suitable heat treatment; that is, from 400 to 500Brinell hardness number. (See also p. 67.)

The nickel-chromium-iron alloy Inconel acquires age-hardeningcharacteristics with addition of aluminum and titanium, and sometimes columbium in further addition. The tensile strength of Inconel in the annealed condition is about 100,000 psi; that of the ~ge

hardened modification, trademarked Inconel X, may be as high as184,000 psi.

The expanding family of nickel-containing stainless steels alsohas age-hardenable members, which have opened new fields forthese versatile alloys.

Nickel also serves an an effective age·hardening addition elementin other metals or alloys. Thus in the tin-copper bronzes, additionsof 3 to 1°pct of nickel so affect the solubility of tin as to producevery sensitive response to age-hardening treatments, and a bronzethat as normally cast possesses a tensile strength of perhaps 40,000

Nickel 285

to 50,000 psi may be so altered in this manner as to permit of thedevelopment through heat treatment of tensile strength values ofabout 100,000 psi.

The use of such alloys, especially the aluminum-titanium-hardened Monel and beryllium copper, expanded greatly during thetime of World War II and in later years. Their application to theproblems of industry however is still growing.

CHEMICAL USES FOR NICKEL

Not all nickel is used for steel and alloying purposes. Oneexception, made famous by its association with perhaps the world'sgreatest inventor, is the Edison storage battery. Seeking a storagecell that would be free from some of the inconveniences of the leadaccumulator, Edison in 1901 invented the battery that bears hisname, which utilizes the peroxide (Ni02 Aq) of nickel as the positive electrode with iron as the negative one. Upon discharge, nickeloxide (NiO.Aq) is formed at the positive and iron oxide (FeO.Aq)at the negative end. The electrolyte is potassium hydroxide. Anothertype of storage battery, used widely in Europe and now cominginto prominence in the United States, differs from the Edison batteryin having cadmium as the negative electrode.

The characteristics of these cells are in many respects quite different from those of the lead cell and fit them particularly well forcertain types of service where long life, .freedom from noxiousfumes, and insensibility to abuse compensate for greater initial cost.Particularly in the field of transportation, for electrically drivenmine cars and for industrial trucks, has the Edison cell becomepopular. It has been used extensively for electric-power storage onrailway cars, especially in connection with the recent developmentof air conditioning.

In a quite different direction, use is made of the high surfaceadsorptive capacity of nickel for gases, particularly hydrogen. Whenfinely divided nickel is exposed to gaseous hydrogen, it adsorbsand retains the gas on the nickel surfaces in active, probably atomic,form. Such a surface containing chemically active hydrogen canserve as a powerful catalyst in reactions involving hydrogen. One


such reaction commonly carried out with the aid of nickel is thehydrogenation of unsaturated fatty acid esters or oils. These oils,olein in particular, which are liquid and somewhat unstable chemically, may be "hardened" and rendered chemically more inert byhydrogenation, and this reaction is generally practiced today withthe aid of finely divided powdered nickel made by reducing nickelcarbonate or formate in hydrogen at relatively low temperatures.Used primarily in the soap-manufacturing industry, nickel catalystsaid also in the production of those synthetic edible oils and fats thatare so widely used today and that usually are derived from cottonseed oil.

Nickel catalysts are used in the petroleum industry for promoting the reaction between hydrocarbons and steam to form hydrogenand carbon monoxide as the initial stage in manufacture of hydrogen from natural and refinery gases. Other uses are in the reforming of natural gas, the production of aromatic from aliphatic hydrocarbons, and in many other industrial organic chemical reactions.

Appreciable quantities of nickel oxide are used in the ceramicindustry as a constituent of ground coats in the vitreous enameling of steel, where it serves with its brother element, cobalt (oxide). There is a small use in ceramic colors. More recently a largeuse of nickel oxide has arisen in the electronics industries, whereit is used in the manufacture of nickel ferrite.

In addition to the foregoing rather substantial chemical uses,nickel compounds of diverse nature have been used for many miscellaneous purposes.

METALS DO THEIR BIT

There is perhaps nothing more impressive to those who are engaged in the practice of metallurgy than the steadily and rapidlygrowing complexity and diversity in the demand for metallic materials. Whereas iron, steel, brass, and bronze served industry wellenough in the nineties, today even the hundreds of specialized andcarefully studied out alloys, steels, and irons that are available hardlysatisfy the materials hunger of the engineer. Simplification andstandardization of alloys, constantly sought and actively promoted,

Nickel 287

scarcely can keep pace with the simultaneous diversification of bothdemand and supply of alloy materials.

Throughout this continual turmoil of development, two very useful and fundamental objectives are being realized. First, materialsare being better adjusted in performance and contribution to therequirements of engineering and of industry and, second, we areexacting from them, as we understand and "compound" them better, their utmost in quality and performance. This trend in metallurgical progress appears to be well illustrated in the history of themetal nickel, of which the varied uses and many alloy combinationswell exemplify the process of adaptation of metallurgical materialsto industrial needs that is so actively going on about us.

By itself nickel serves as a material of construction that haspleasing color, is resistant to corrosion or chemical deteriorationand affords, in processing equipment, protection from metallic contamination to foods, pharmaceuticals, and other products. It is of inestimable value in electronics and for special properties, magnetostriction for example, in numerous useful devices. In its alloys withother metals it contributes to a very broad assortment of usefulmaterials. Its alloys with copper are corrosion-resistant, like nickelitself, but some are sufficiently soluble in sea water to combineusefully antifouling characteristics with much greater strength thanpure copper. There are modifications of nickel-copper alloys thathave great strength; great hardness as the result of heat treatment;magnetic or nonmagnetic behavior; enhanced machinability andformability. Alloys with iron, with or without other elements, afforda wide range of useful characteristics-strength; toughness; depthhardening; case-hardening capacity; special thermal expansion, bothhigh and low; a wide range of magnetic characteristics. Nickelalloys provide materials of great strength and resistance to oxidationat' high temperatures, and, at the other extreme, materials of hightoughness and impact resistance at very low temperatures. Addedto all these virtues in structural materials are its great usefulness tochemical industry for its catalytic activity, and in this and otherindustries for special properties of its chemical compounds. Trulyit is a versatile element.

chapter xiv nickellibrary.aimehq.org/library/books/modern uses of nonferrous metals... · rude...

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