Dr. Joachim Boßlet

TUFFTRIDE®-/QPQ®-ProcessTUFFTRIDE®-/QPQ®-Process

Technical Information

Process procedureCompared to other nitrocarburizingmethods, to run this process isvery easy. To begin with, the partsare preheated in air to approximate350 °C. The nitrocarburizing itself ismostly performed at the standardtemperature of 580 °C. The treat-ment time at this temperature isusually 1 to 2 hours.The active elements in the nitrocar-burizing bath are alkali cyanates.During the reaction on the part surface cyanate is transformed tocarbonate, whereas the salt bathcomposition changes slowly.Continuous feed of a polymerregenerator effectuates the recyc -ling of the forming carbonate intoactive cyanate directly within themelt and keeps the salt bath activi-ty in narrow limits (Fig. 1).

2

material can be nitrocarburized insalt melts. The treatment tempera-ture is in the range of 480 °C and630 °C. Monitoring simply con-sists of checking:

● treatment temperature

● treatment time

● chemical composition of saltmelt

Compared to other treatmentmedia the salt melt providesexceptionally high nitrogen offer.The nitrocarburizing process im -mediately starts after immersioninto the melt. Already after someminutes the formation of a com-pound layer can be detected.

Nitrocarburization in salt meltshas firmly established worldwide.Not only the automotive industryemploys TUFFTRIDE®-/respectivelyQPQ® treated parts with great success, but also engineering andtoolmaking, electronic-, oil- andhydraulic-industry as well as avia-tion. The key benefits are highwear resistance, fatigue strengthand in particular the exceptionallyhigh corrosion resistance. Bothprocesses are to be seen as alternative to case hardening orgalvanic processes as well asincreasingly to gas- or plasmanitrocarburizing.

The TUFFTRIDE®-/QPQ®-Process offersprocess specific advantages:

● highest temperature constancy

● fast and constant heat transfer

● very stable chemical composition

● shortest treatment cycles

● simple monitoring

● very flexible in use

Remarkable as well is the relativeinsensibility towards machiningresidues on the parts to be treated.Consequently, extensive and costlypre-cleaning processes are notrequired.

In principle all sorts of ferrousmaterials, such as austeniticsteels, cast iron or sintered

Fig. 1

TUFFTRIDE®-/QPQ®-ProcessTUFFTRIDE®-/QPQ®-Process

Improve e tof part p opert

Improv ment of com rties

li a o s

P t technolo y

Principle of Regenerating

+ REG1

NitrogenCyanate

Iron Nitride

+ Iron

+ Carbonate

3

As the regeneration takes placewithout change of bath volume, nobail out salts occur. The drag-outlosses caused by taking out atreated load are supplemented by replenish salt (TUFFTRIDE®-Process). Unlike gas nitriding orgas nitrocarburizing, neither thereplenish salt for the nitrocarburiz-ing or the oxidation bath (seebelow), nor the regenerator areclassified as toxic or are harmfulto the environment.

The oxidation treatment is per-formed after salt bath nitrocarbur-ization in an especially developedcooling bath at a temperaturerange of 370 - 430 °C. During thetreatment a black iron oxide layer(magnetite) is produced on thesurface of the treated parts, whichenhances substantially the corro-sion resistance. Apart from theoxidative effect, the dimensionalstability of the quenched compo-nent is positively influenced.

In case the corrosion resistancedoesn't play a decisive role, com-ponents and/or tools can, pendingon the risk of cracking or distor-tion, either be cooled directly inwater, by means of air blower,under nitrogen or in vacuum.Nowadays, the oil quench is also,regarded under safety aspects,rather questionable and notrequired any more.

Thereafter, the treated material isfurthermore cooled to room tem-perature as well as cleaned withina well tempered and agitated washing cascade.

Is the surface roughness afternitrocarburization too high, pend-ing on the seize and the shape ofthe parts, various polishing meth-ods can be used.

● Lapping with emery clothgrade 360 or finer;

● Polishing or continuous micro -finishing with special polishingdiscs with the throughfeedmethod, similar to centrelesspolishing, or on an automatedlathe fixed between centrepieces;

● Vibratory finishing; this treat-ment is primarily used for smalland sheet metal components;

● Blasting with glass beads size40 - 70 µm in diameter; to prevent edges being exces-sively rounded, or removal ofthe compound layer beingavoided, the pressure shouldnot exceed 4 bar;

● Automated blasting with metalbeads whose diameter shouldbe less than 1 mm.

Intermediate treatment, however,may partly reduce the gained cor-rosion resistance. For this reason,in many cases a second oxidativetreatment is carried out. This com-plete sequence is shown in Fig. 2for the QPQ®-Process. QPQ® com-prises TUFFTRIDE® treatment withoxidative cooling, mechanical pro -cessing and oxidative post treat -ment, using the same salt melt forboth oxidative steps.

Fig. 2

Process sequence QPQ®

usual580 °C

Tem

pera

ture

Preh

eatn

g n

ar

Ntr

ocar

burz

ng

Ox

dato

n+

coo

ng

Posh

ng

Post

ox

dato

n

370 -420 °C

370 -420 °C

350 -400 °C

Time

4

cooling the pores are almost filledwith magnetite, which anchorsoptimal the protecting oxide layer.Same time, the residual compres-sive stress in the boundary areaincreases In addition to the treat-ment parameters (temperature,duration, bath composition), thelevels of carbon and alloying elements in the materials to betreated influence the thickness ofthe obtainable layer. Although thelayer growth is lower, the contentof alloy is higher, the hardnesshowever increases to an equalextent. Fig. 3 shows the deter-mined correlation at a tempera-

sess by far most nitrogen offerthe compound layers are almostmonophase existing of ε-iron car-bon nitride. Depending on thematerial used, the compound layerwill have a Vickers hardness ofabout 800 to 1500 HV measuredin the cross section

The compound layer divides in acompact part and a porous partwhich is situated directly at thesurface. The latter is also calledpore zone. It is used as lubricantreservoir and supports the gooddry-running operation properties ofthe treated parts. During oxidizing

During the TUFFTRIDE®-process anitrocarburized layer is formed con-sisting of the outer compound layer(ε-iron nitride) and the diffusionlayer thereunder. The formation,microstructure and properties ofthe compound layer are significantreliant on the base material. Theformation, structure and proper-ties of the compound layer are verymuch depending on the used basicmaterial. Apart from iron somealloying elements, such as Cr, Mo,Al, V, Ti or W, are able to react withnitrogen. The so-called specianitrides are formed within the com-pound layer as well as within thediffusion layer.

Compound layer

While diffusing atomic nitrogen thecompound layer is formed. Withrising nitrogen absorption the solu-bility limit of the boundary layer isexceeded and forms iron nitrides,in case of alloyed steel, addition -ally special nitrides and builds aclosed compound layer. Depend -ing on the nitrogen content it con-tains either ε-iron nitrides, γ'-ironnitride or a mixture of both.Compared to the classical nitridingthe nitrocarburization enriches asmall quantity of carbon in thecompound layer and strictly speak-ing iron carbon nitrides areformed. Because TUFFTRIDE® pos-

Composition and thickness of the nitride layerComposition and thickness of the nitride layer

rt

Improvement of comp nent p ope ties

Applica ions

Pl nt te o ogy

Fig. 3

Compound layer thickness afterTUFFTRIDE® treatment

Treatment time in h0.5

25 Mild steelT 580°C

QT steel

Hot work steel12 % Cr-steelcast iron

20

15

10

5

01 2 3

Com

poun

d ay

er th

ckne

ss n

µm

5

visible darker etched area. Fig. 5shows the nitriding hardnessdepth according to DIN 50190-3on various materials against treat-ment time.

tified metallographically from thecore structure, due to the impro -ved etchability. The actual nitrogenpenetration depth is pending onthe content of alloying elementsconsiderably higher than the

ture of 580 °C. With the usualtreatment time of 60 to 120 minutes a compound layer of 10 - 20 µm is obtained on mostqualities of material.

The metallographic analysisdefines clearly the compound layerfrom the total layer as a slightlyetched zone, followed by the diffusion layer (see Fig. 4).

Diffusion layer

The area below the compoundlayer is called diffusion layer. Dueto the concentration decline fromthe edge to the core, the nitrogencontent is not sufficient to formiron nitride. Obtainable depth andhardness of diffusion layer aredependant on the material.

In case of unalloyed steels, thecrystalline structure of the diffu-sion layer is influenced by the rateof cooling after nitrocarburizing.After cooling in water, the diffusednitrogen remains in solution. Ifcooling is done slowly, or if a sub-sequent tempering is carried out,some of the nitrogen could precip-itate into iron nitride needles. Inthe first mentioned case a higherhardness is achieved, in the sec-ond one the ductility is increased.

In contrast, cooling has no note-worthy influence on the formationof the diffusion layer at alloyedsteels. Nitrogen has already beenprecipitated as special nitride (i.e.chromium-, aluminium- or vanadi-um-nitride). Therefore, part of thediffusion layer can better be iden-

Fig. 4

Fig. 5

Formation of compound layer

Compound

layer: 15 µm

thereof

pore zone: 5 µm

Etchable

area of

diffusion

layer: 100 µm

Material 41Cr4 H+T TUFFTRIDE® treated

C15

0.5

0.4

0.3

0.2

0.1

00

Treatment time in min.30 60 90 120 150

C45

42CrMo4

16MnCr5

X38CrMo5 1

X20Cr13

Ntr

dng

har

dnes

s de

pth

n m

m

Obtainable nitriding hardness depth in relation to treatment time

6

hand a sufficient thick ε-nitridelayer of minimum 12 µm thicknessand on the other hand the blackiron oxide (magnetite), which isformed during the oxidizing coolingat the outer edge layer and withinthe pores.

The stress combination of corro-sion and wear happens in practicequite often. Almost everywhere,where motional processes withcorrosive strains take place, theuse of nitrocarburization with oxi-dizing cooling unfolds. In case thedemand system asks for softerrunning partners with lower sur-face finish, lapping or polishing isdone to adjust the desired surfacefinish. In this connection it isimportant to remove as little aspossible. This shall ensure thatbesides the sufficient thick com-pound layer as well parts of thepore seem remain preserved, tobe able to obtain an optimal for-mation of the oxide layer as wellas consistent dark coloring of thesurface during the subsequent oxi-dizing finishing treatment (QPQ®-Process). Remarkable is the fact,that the roughness of the polishedsurface hardly changes during sec-ond oxidation.

Surface hardnessand core strength

The surface hardness obtainableby TUFFTRIDE® treatment is mainlyinfluenced by the composition ofthe material. The higher the content of nitride-forming alloyingelements (Cr, Mo, Al, V, Mn, Ti, W)the greater the surface hardness.Fig. 7 gives reference values ofcore hardness and surface hard-ness for different stee s.

Corrosion resistance

With upward trend the nitrocarbur-ization is used for improvement ofcorrosion resistance of par tsmade from unalloyed steels. Aswell as for corrosion resistance itis important to produce preferablymonophase ε-compound layers.Furthermore, there are two morefactors of importance: on the one

The compound layer mostly con-sists of a combination of ron withnitrogen and carbon. Because ofits structure it has no metallicproperties any more. It featureswith except onally good resistanceagainst wear, scuffing and corro-sion and is consistent nearly up toformation temperature Carboncontaining layers with high nitrogenconcentrations, such as gained by the TUFFTRIDE®-/QPQ®-Pro -cesses offer a better wear resist-ance especially corrosion resist-ance as such with lower nitrogencontents respective low-carbon.Fig. 6 shows which area of nitridelayer (compound layer or diffusionlayer) is responsible for the variousproperty improvements.

Improvement of part propertiesImprovementof part properties

of compo ent prope

Applicat ns

Plant t chnol gy

Env onment pects

Summar

Fig. 6

Improvement of component properties

CL  Compound Layer DL  Diffusion Layer

CL

DL

11 µm

105 µm

V = 500:1

7

check parts in a salt mist of 5 %sodium chloride at 35 °C. Evenafter a test period of 500 hoursthere were no corrosion attacksvisible on the functional surface ofthe QPQ® treated piston rods.

As well as after TUFFTRIDE®-treat-ment (incl. oxidizing cooling) aclear increasing of corrosionresistance on components isobserved. Pending on the partgeometry and its surface finish aholding time of up to 200 hoursand more are possible in the saltspray test. In principal the corro-sion resistance increases withdeclining surface roughness.

As test criterion the salt spray test according to DIN EN ISO9227:2006 NSS was chosen to

Fig. 8 shows an overview in corro-sion resistance of various galvaniclayers compared to a QPQ®-layer.

Fig. 8

Fig.7

500

C45not treated

QPQ®

17 µmCr

20 µm2 x Cr40 µm

Ni20 µm

400

300

200

100

0

Spr

ay d

urat

ion

[h]

(Salt spray test EN ISO 9227:2006 NSS)

Corrosion behaviour of different layers

Material

Core strength after hardening

and tempering (N/mm2)

Tempering temperature 600 °C

Tempering time

Guideline figures

for surface hardness

90 min 580 °C

TUFFTRIDE® treated

NameMaterialnumber 2 hours 6 hours HV 1 HV 10 HV 30

Ck15 1.1141 600 550 350 300 200

C45W3 1.1730 750 - 850 700 - 800 450 350 250

Ck60 1.1221 750 - 900 700 - 800 450 350 250

20MnCr5 1.7147 800 - 950 800 - 900 600 450 400

53MnSi4 1.5141 850 - 950 800 - 900 450 400 350

90MnV8 1.2842 1000 - 1200 900 - 1100 550 450 400

42CrMo4 1.7225 900 - 1200 900 - 1100 650 500 450

X19NiCrMo4 1.2764 900 - 1100 900 - 1000 600 500 450

55NiCrMoV6 1.2713 1200 - 1400 1150 - 1300 650 550 500

56NiCrMoV7 1.2714 1300 - 1500 1250 - 1400 650 550 500

50NiCr13 1.2721 1200 - 1350 1100 - 1200 600 500 450

X20Cr13 1.2082 1000 - 1200 1000 - 1200 > 900 600 450

X35CrMo17 1.4122 1000 - 1200 1000 - 1200 > 900 700 550

X210Cr12 1.2080 1500 - 1700 1400 - 1600 > 800 600 450

X210CrW12 1.2436 1500 - 1800 1400 - 1650 > 800 600 500

X165CrMoV12 1.2601 1400 - 1900 1400 - 1700 > 800 650 500

45CrMoW58 1.2603 1500 - 1800 1400 - 1700 800 700 600

X32CrMoV33 1.2365 1700 - 1800 1600 - 1750 > 900 850 700

X38CrMoV51 1.2343 1700 - 1900 1500 - 1700 > 900 850 700

X37CrMoW51 1.2606 1700 - 1900 1600 - 1800 > 900 800 700

X30WCrV53 1.2567 1700 - 1900 1600 - 1800 > 900 850 750

X30WCrV93 1.2581 1500 - 1800 1500 - 1700 > 900 850 800

8

Even under these conditions aQPQ® treatment results in consid-erable better corrosion resistance.The first of the samples showed acorrosion attack after 92 hoursand the last, after 159 hours. Theaverage resistance was 114 hours.However, the chrome plated pistonrods failed completely after 21hours.

For the total immersion test accor -ding to DIN 50905-4 a solution of3 % sodium chloride and 0.1 %hydrogen peroxide (H2O2) is used.Prior to being dipped into the solu-tion, the samples are degreased.Fig. 10 shows the results obtainedon samples made from C45 treat-ed by different surface engineeringprocesses after a test lasting 2weeks.

With an average weight loss of 0.4 g/m2 per 24 hours, the QPQ®

treated samples were much betterthan the galvanic or chemicallycoated ones. In case of 12 µmhard chrome and even 45 µm dou-ble chrome plating, the weight losswas 20 times exceeded than thatof the nitrocarburized samples.Only the Triplex layer containing 37 µm copper as well as 45 µmnickel and 1.3 µm chrome is com-parable with the QPQ® treatedsamples.

of a comparison trial with QPQ®

treated, impregnated piston rodsand hard chrome plated ones isdemonstrated in Fig. 9.

One of the hardest corrosion tests according to DIN EN ISO9227:2006 is the AASS test,which test solution additionallycontains acetic acid. The result

Fig. 9

Fig. 10

Spra

y d

ura

ton n h

hard chrome10 15 μm

QPQ®

15 20 μm

Min.

168

144

120

96

72

48

24

0Max. Min.

168

144

120

96

72

48

24

Max.

168

144

120

96

72

48

24

Hard chrome vs. QPQ® in AASS-test

Corrosion behaviour of layers intotal immersion test according to DIN 50905-4

Medium: 3 % NaCl; 0.1 % H2O Material: C45Test duration: 14 days

90 min QPQ® 0.34

7.10

7.20

2.90

12 µm Hard chrome

Double chrome: 20 µm soft chrome 25 µm hard chrome

Nickel: 20 µm Kanigen, age hardened

Triplex: 37.0 µm copper 45.0 µm nickel 0.45 1.3 µm chrome

Layer or treatment Weight lossin g/m2 per 24 h

Improvement of component propertiesImprovement of component properties

lant te hnolog

ects

9

running properties. Fig. 11 showsa gear made of C45N after servicelife of 700,000 km in a com -mercial vehicle. The removal bywear from the upmost mono -phase ε-compound layer was only1 - 2 µm. Even the pore zone isstill clearly visible.

Many wear tests and practicalapplications confirm the advan-tages to other sur face layers.Structure and composition of thecompound layer (proportion N andC) influence the wear resistanceconsiderably. Monophase carbonenriched ε-compound layers, whichexist after TUFFTRIDE® treatment,gain very good results. Layers withlow carbon or having high γ'-pro-portion were in most cases defi-nitely worse.

In the outer zone of compoundlayer occurring porosity is no evi-dence for poor wear properties. Infact, better adhesion of the oil filmcan often lead to more beneficial

Wear resistance andrunning properties

Excellent sliding and running prop-erties, as well as high wear resist-ance, are the well-known advan-tages of TUFFTRIDE®-treated com-ponents. Due to the intermetalliccomposition of the compoundlayer, the friction and the tendencyto weld with a metallic counter-partner are reduced. Compared tocase hardening the nitride layerpossess a much better heat re -sistance. The gained hardnessincrease within the diffusion layerremains the same even at highertemperatures.

Fig. 11

Material: C45N

Section: tooth flank

Loss: approx. 1 - 2 µm

Compound

layer: mainly

ε-iron nitride

Edging: Oberhoffer Source: H.-J. Spies

Gear wheel (commercial vehicle)after 700.000 km operational performance

10

carried out with a disc running at200 rpm against another discbeing fixed. Both parts were treat-ed equally. To avoid adhesivewear, a load of 5 - 30 N wasapplied. Under greater loads thecoefficient of friction increasedwith the load but in the range of 5 - 30 N it remained constant.

The tested samples had a surfaceroughness of around 4 µm. Onlythe surfaces of the QPQ® treatedsamples were reduced to a sur-face roughness of Rm = 1 µm bypolishing. Fig. 14 gives an over -view of the friction coefficient ofdifferent pairings under dry run-ning conditions, and after beinglubricated with oil, type SAE 30.

lished by applying torque to thetooth flank and increasing it untilseizure occurred. Nitrocarburizingby the TUFFTRIDE® process raisedthe scuffing load limit of the mate-rials tested by 2 - 5 times.

Another interesting factor in con-nection with the wear resistanceand running proper ties is the friction coefficient of the outer surface layer. The interfacial reac-tions which occur during slidingare not so much determined bythe absolute hardness of the run-ning partner but by the materialpairing, their microstructural com-position, surface geometry andthe lubricant used.

To determine the coefficient of friction, tests were performed onthe Amsler machine. Trials were

Fig. 12 allows conclusions aboutthe relative wear resistance of sur-face layers after hardening, nitro-carburization and boriding underadhesive stress. Although theborided samples had an approx.1000 Vickers higher surface hard-ness as the TUFFTRIDE® treatedones, the latter had with factor800 higher wear resistance andstill 80-fold higher than the hard-ened samples. This investigationmakes it clear that the hardnessof the surface layer is not the onlyinfluencing factor in respect ofwear properties.

Also scuffing is significantlyreduced compared to other sur-face layers. Fig. 13 shows theresults according to Niemann-Rettig of scuffing load limit testson gears. These data were estab-

Fig. 12

Adhesive wear of different layers

C45 H+T 42CrMo4 H+Tsalt bath

nitrocarburized

42CrMo4 H+Tborided

100

10

1

0.1

0.01

Re

atve

wea

r res

stan

ce

Source: Habig, BAM

Improvement of component propertiesImprovement of component properties

Plant te hnology

Envir l ects

S m ry

11

Under these test conditions, of allvariants the QPQ® nitrocarburizedsamples had the lowest frictioncoefficient.

The TUFFTRIDE® treatment increas-es the rotating bending fatiguestrength as well as the rollingfatigue strength. These are mainlyinfluenced by:

● the level of nitrogen in thecompound and diffusion layer

● the thickness of the diffusionlayer

● the state of solution of thenitrogen on unalloyed steels

Furthermore, the microstructureand the strength of the base mate-rial are to be taken into consider -ation. Whereas with unalloyedsteels the increase in fatiguestrength is determined by the rateof cooling, with alloyed materials,it has no mentionable effect. Anincrease in fatigue strength is pos-sible after 1 - 2 hours TUFFTRIDE®

treatment of 100 % on notchedparts made from unalloyed steels.With alloyed steels a generalimprovement of 30 to 80 % can beobtained.

dition, the hydrodynamic load has tobe taken into account. With theexception of the QPQ® treated sam-ples, there is more solid massbecause of the surface roughnessso that the results presumably liewithin the mixed friction range.

Under dry running conditions, nitro-carburized samples have a muchlower coefficient of friction thancase hardened or hard chrome plat-ed ones. Due to the oxidation of thecompound layer, the coefficient offriction increases. In lubricated con-

Fig. 13

Fig. 14

Frct

on c

oeff

cen

t n

µ

30 µmchromeplated

case hardened

90 min 580°C TUFFTRIDE®

SW Ox QPQ®

not lubricatedlubricated,SAE 30

Amsler discsPartner sametreatment

0.4

0.3

0.2

0.1

(salt water) (oxidized)

600

500

400

300

200

100

0

Scu

ffng

oad

m

t n

Nm

18/8 34Cr4H+T

16MnCr5case

hardened

600

500

400

300

200

100

018/8

TUFFTRIDE® treated

34Cr4H+T

16MnCr5case

hardened

Scuffing load limits of gears

Friction coefficient of different layers

12

better service life results afterTUFFTRIDE® treatment. Reasonedby the non-metallic character ofthe compound layer the functionalsurface remains smooth for muchlonger. The affinity of adhesion isminimized and the metallic make-up is virtually avoided. User reportthat, compared to plasma- or gasnitrided resp. nitrocarburizedextrusion dies, significantly betterpress performances are achievedand that tools can even be re-treated several times. Especially,the risk of chipping is considerablyreduced. A further advantage arethe short treatment times. Thetools are much quicker ready foruse. This also results in remark-able savings in tooling costs. As

Beside the conventional applica-tions, improving the wear andfatigue resistance by nitrocarburiz-ing in salt melts, the corrosion pro-tection gains more and more inter-est. Increasingly, the TUFFTRIDE®

treatment in combination withoxidative post treatment respec-tively the QPQ® treatment is usedas substitution for galvanic coatingprocesses such as hard chromeplating, nickel plating, zinc platingetc., or used as substitution of corrosion resistant steels. Sub -sequent, there are given represen-tative applications.

Tools made of hot working steel for extrusion (see Fig. 16), forg ingor die-casting achieve much

Fig. 15

well as injection molds for plasticmaterials are successfully saltbath nitrocarburized.

Valves in combustion engines (seeFig. 17) are parts having to standhigh standards in respect of thermal capacity, wear resistanceand corrosion resistance. Comp -ared to hard chrome plating theTUFFTRIDE® process offers costsavings to manufacturing costs,because inductive hardening andfinal grinding is not necessary.Fur ther more, the necessity tomanufacture the exhaust valvesfrom inductive hardenable steel isnot applicable. It can rather be pro-duced from heat resisting aust -enitic steel.

X

XX

XX

X

Rol

atin

g be

ndin

g fa

tigue

stre

ngth

in N

/mm

2

500

400

300

200

Load cycles104 105 106 107

1000

90 min QPQ®

untreated

hard chrome plated

X

C45N

notched samples

ak = 2 Ø = 10/7 mm

Comparison of rotating bending fatique strength

QPQ® vs. hard chrome

ApplicationsApplications

In this connection we would like topoint out that hard chrome platingreduces the rotating bending fatigue strength of the base mate-rial. A similar situation is noted forzinc plating. Fig. 15 shows theresults of a fatigue strength testconducted on notched samplesmade from material C45N. QPQ®

treatment increased the fatiguestrength by more than 50 %. Hardchrome plating, however, reducedthe fatigue strength by 20 %.

Industrial Application of theTUFFTRIDE®-/QPQ®-process

Fig. 17

Extrusion dies for producing

aluminium profiles

13

The treatment times are, depend-ing on the specification between20 and 90 minutes. Pending onthe plant seize batches varybetween 2500 and 4000 pieces.This way, a productivity of lessthan 1 s per valve is realized. Onthe basis of short treatment timesthere are no big buffer capacitiesnecessary even at changinggeometries, steel grades or speci-fications.

For highly stressed 4 strokeengines, met in motorbikesrespectively sports car industry,as well as two stroke engines forsmall planes or snowmobiles, thecrank shafts and cam shafts aretreated with the TUFFTRIDE®

process. Despite or just becauseof the clearly visible pore seam inthe compound layer the highdemands are fulfilled without anyproblems. The pore zone facili-tates the running-in wear behaviorand offers good dry-running prop-erties due to the micro lubricationslots effect. As well for big dieselengines for SUVs or commercialvehicles the crank shafts, tappetsor steering wheels are nitrocarbur-ized in big quantities in salt melts.Further applications are gear anddifferential parts.

properties. In the meantime, morethan 250 million valves per yearwith upward trend are treated insalt melts.

The new generation of engines,which can alternatively be run bybiofuel, the TUFFTRIDE® layeroffers superior wear protection

Fig. 16

Intake and exhaust valves for

gasoline engines

14

loyed or low alloyed steel is used.The required testing time in thesalt spray test is mostly 144 hourswithout corrosion point. In somecases there are even 400 hoursrequired, which are also reachedsuccessfully.

Fig. 19 shows gas spring pistonrods, which are utilized in the auto-mobile and aircraft industry, forengineering or in office chairs. Bysubstitution of the chrome layerconsiderable cost reductions wereachieved. The QPQ® treatment isper formed in fully automatedplants. The combination of up to

In the motorcycle industry also various TUFFTRIDE® respectiveQPQ® treated engine and powertransmission parts are in use. Fig. 18 shows parts with better corrosion resistance than gas orplasma nitrocarburized ones.Owing to the short treatment timeand the high flexibility there isgiven an optimal integration intothe production flow with theaccording cost advantage.

The QPQ®-process finds constantgrowing application for pistonrods, hydraulic cylinders or bush-ings. As material mild steel, unal-

Fig. 18 Fig. 19

4 nitrocarburizing furnaces in onetreatment line allows cycle timesof 0.5 - 0.6 s per piston rod.

The examples could be endlesslycontinued. The TUFFTIRDE®-/QPQ®

process is also used for compo-nents in the aircraft, in the off-shore technology, in the plant andmachine construction, in energytechnology, in the food industry,photo and computer industry aswell as in the manufacture of textile machines or hydraulicaggre gates.

Drive and clutch components formotor bikes

Piston rods for gas springs and dampers

ApplicationsApplications

p

S mma y

15

Fig. 20 shows a nitrocarburizationfurnace of the newest generation.It has a pneumatic closeable, iso-lated lid and offers considerableenergy savings at base load oper-ation. Furthermore, this furnace isequipped with external placed,continuous working filtrationdevice for cleaning the salt meltand also with a feed unit for regeneration.

and are consequently advancedunder the aspect of

● reduction of energy consumption

● process security

● operator friendliness

To run the TUFFTRIDE®-/QPQ®

process it is easy compared toother nitrocarburizing processes,be cause there is no complicatedplant technology required. Thetreatment can be done both manu-ally and in fully automated plants.They are arranged in line in a mod-ular concept (please see Fig. 23)

Fig. 20

Features:

● Pneumatic

closable lid

● TENOCLEAN®

filtration device

● Regenerator

dosing device

Plant technologyPlant technology

um

New generation of energy saving furnaces

For hand operated plants alsoelectronic systems are available,which record all relevant parame-ters and assort them to a batchdocumentary. Compared to thegaseous processes an online mon-itoring of the chemical parametersis not required due to the high sta-bility of the melt. Daily analysis areallocated to the treated batchesvia computer.

Sometimes the remaining saltresidues on the components arecriticized but they only arise frominsufficient cleaning equipment.

Fig. 21 shows a microprocessormonitored capsuled plant. Bat -ches with dif ferent treatmentparameters are operated by com-puter controlled guidance with aspecial software to guarantee anoptimal batch flow. Big slidingdoors allow easy access to theindividual plant components. Thefeeding of the refill salt respectiveregenerator salt is done by accord-ing channels from outside.

Fig. 22 shows exemplary the dia-gram for the control of the nitrocar-burizing furnace.

State of the art are meantimethree to four step, heated and agi-tated washing cascades (pleasesee down right of Fig. 23), whichper form not only very good washing results, but allow consid-erable water savings.

Fig. 21

Computer controlled and multi-purpose TUFFTRIDE® plant

Plant technologyPlant technology

Summ

17

Fig. 22

Fig. 23

Control of the TUFFTRIDE® furnace via PC

Effluent free TUFFTRIDE® plant

Fresh Water

Waste WaterTank

Wet ScrubberEvaporator

Exhaust

Cleaning Cascade

TUFFTRIDE® TUFFTRIDE® AB 1

Preheating

10 % 1.0 % 0.1 %

Cold WaterRinse

18

Fig. 24

6000

expr

esse

d in

nan

o po

ints

afte

r nor

mal

izin

g

Det

rmen

t ev

e

15.000 km/a

100 cars

Gasfurnace3.6 m3

Salt bathelectr.heated

Salt bathgas

heated

Evaluation containscontamination through:

➜ Deposition space

➜ Acidification

➜ Nutrient enrichment

➜ Form. of photo oxidants

➜ Effect on ecotoxity

➜ Effects on health

➜ Ozone degradiation

➜ Greenhouse effect

➜ Resource Consumption

5000

4000

3000

2000

1000

0

Source: J. Buchgeister

Environmental aspectsEnvironmental aspects

for Environ ment/Berlin. Fig. 25shows the results of this compari-son. It reflects that the salt bathnitrocarburizing process from eco-logical point of view tends to resultin a better valuation than gas nitro-carburizing.

In the year 2000 an ecologicalassessment of salt nitrocarburiz-ing and gas nitrocarburizing wasestablished. Failing sufficient pro-vided data the originally planedplasma process could not be con-sidered. For the study all for theprocess comprising energy andmass flow had been taken intoaccount and set in relation to thequantity of treated goods. Theevaluation had been effected bygiving "harm points" for the mate-rial and energy input as well as forexhausts, waste water and wast -age. This was done by consultingcriterion of the Federal Office

Against overwhelming prejudices,the authorization of a new plant "inthe green" is not more complicat-ed than for other nitrocarburizingprocesses. Without any problemthe effective environmental as wellas work place regulations will bemet. The relevant plant compo-nents are equipped with an effi-cient exhaust device. Evenalthough in most cases the legiti-mate allowance for air cleaningprocedures is met the exhaust airis lead through a dry filter deviceor if applicable through a wetscrubber device, to respect envi-ronmental aspects (see Fig. 23).

Ecobalance on Nitrocarburizing

SummarySummary

19

the TUFFTRIDE®-/QPQ® is themost widely used nitrocarburizingprocess. The process is very easyto carry out and does not requirecomplicated plant technology.Electronic monitoring and docu-mentation of the processsequence up to automated proce-dure, efficient devices for filteringthe melt as wells as for subse-quent cleaning of the treated partsare state of the art today. Theplant itself is run effluent-free.Environ mental specifications canbe complied without difficulty.

The TUFFTRIDE® process is knownin English-speaking and Asiancountries under that name, inEurope and German-speakingcountries as TUFFTRIDE® and inthe USA as MELONITE®. TUFFTRIDE®,QPQ®, TUFFTRIDE®, MELONITE®

and MELONIZING® are registeredtrade marks of Durferrit GmbH.

Due to the characteristics of theprocess, such as

● excellent reproducibility, on high quality level

● shortest treatment times

● most negligible distortion

● high flexibility

In addition to the significantimprovement of wear protection,fatigue strength and sliding proper-ties, the TUFFTRIDE® treatmentplus oxidative cooling or QPQ®

treatment produces a majorincrease in corrosion resistance.Results of tests and industrialapplications show that the qualityof the treated components is oftensuperior to that of electro galvaniclayers and other nitrocarburizingprocesses. This opens a broadfield of application, in which expen-sive materials can often be substi-tuted.

The data contained in this publication arebased on our current knowledge and expe-rience. In view of the many factors that mayaffect processing and application of ourproduct, these data do not relieve proces-sors from carrying out their own investiga -

tions and tests; neither do these dataimply any guarantee of certain properties,nor the suitability of the product for a specific purpose. Any descriptions, draw -ings, photographs, data, proportions,weights etc. given herein may change

without prior information and do not constitute the agreed contractual quality ofthe product. It is the responsibility of therecipient of our products to ensure that anyproprietary rights and existing laws and legislation are observed.

Durferrit GmbHIndustriestrasse 3D-68169 MannheimTelefon +49 (0) 621 / 3 22 24-0Fax +49 (0) 621 / 3 22 24-809

www.hef-durferrit.com E-Mail: technical-service@hef-durferrit.com