“manufacturing” from refined steel material to shaped product

“Manufacturing”From Refined Steel Material to

Shaped Product

CON 251 Metals Processing

Shaped Products

• The product may be intermediate, as in a rolled steel beam prior to “fabrication”

• The product may be final, as in a steel casting for a bridge saddle or a bollard

Manufactured Steel Products

Two basic categories of manufactured steel products:

•Cast Steel Products made in one basic way in foundries. (Molten metal cast into finished shape)

•Wrought Steel Products made one of several methods in mills. (Shaped through deformation)

Casting

• Casting is generally performed by pouring molten steel into sand molds.

• Casting is used instead of wrought methods when the steel product to be made is of such size and/or complexity that it is uneconomical to produce by other methods.

• Example (big): Bridge saddles, ship anchors, mooring cleats, bollards

Cast Bars & Engine Block

Wrought Steel Products(Formed Through Deformation) • Forging - ( Hammering into shape)

• Extruding - ( Squeezing through a shaped die)

• Hot Rolling - Progressive forming with various rolls. (with or without cold finishing)

Forging

• Forging: Method of forming hot metal by squeezing between heat-resistant dies.

• Open-Die Forging: A large press squeezes (not strikes) steel between two heat-resisting surfaces…can be used to shape very large steel ingots (the ingot may weigh several hundred tons, the forge can squeeze with a force of several thousand tons)

• Closed-Die Forging: A large hammer pounds the steel between two heat-resisting shaped dies until the product is in the desired shape

Forged Steel Parts

Extrusion

• Extruding: Method of converting semi-finished shapes into lengths of uniform cross-section by forcing preheated, plastic steel through a very tough, heat-resistant die (analogy: toothpaste)

• Bars, tubing, pipes, and many unusual cross-sections can be extruded. More complex shapes can be extruded than can be rolled.

• More economical for small quantities than other forming methods.

• A limitation is that cross-section must be uniform. Therefore, Plain round bars could be extruded or rolled, but Ribbed round bars (like rebar) could not be extruded, must be rolled

Aluminum Extrusions

Hot Rolling • Hot Rolling: Used to make semi finished shapes as well as some

finished products.• May be started with reheating of large steel ingots from steel

producer, or may be sequenced directly after the continuous strand casting process.

• Hot steel passes through a system of heat-resistant rolls which gradually, roll by roll, change the ingot or strand into one of three basic intermediate shapes:

• Slabs: Flat, rectangular shapes with width > 2x thickness; Will later become plates, sheets, strips, or products like pipe and tubing (made from plates, sheets, strips)

• Blooms: Rectangular cross-sections, generally larger than 36 sq. in.; Will later become structural shapes, rails, seamless pipe

• Billets: Rectangular cross-sections, less than 36 sq. in. Will later become bars (including rebar), rods, wire

Hot Rolling I & H Beams

Rolled Sheet & Rail

Coiled & Straight Re-bar

Hot & Cold Finishing

• Hot Finishing: (Hot Rolling) This is basically a continuation of hot rolling, where the semi-finished product continues while still hot through more rolls to become the finished structural shape, rail, plate, bar, sheet, etc.

• Cold Finishing: (Cold Rolling) Transition from semi-finished to finished product via room-temperature finishing processes such as rolling, reduction, drawing:

Cold Finishing Processes

• Prior to the cold finishing processes, the semi-finished products from the initial hot-rolling steps must be “cleaned up” by: Descaling: This is removal of the surface oxide scale, usually by a process involving dipping in sulfuric or hydrochloric acid (this process is known as pickling)

• Rinsing: with both hot and cold water• Drying: usually using steam• Oiling: as a temporary sealant and lubricant,

in preparation for cold finishing

Cold Rolling• Cold Rolling: passing the semi finished metal through another series

of rolls to impart desired final shapes and/or mechanical properties and surface finishes

• Cold Reduction: actually another type of cold rolling, but specifically to drastically reduce the thickness of an already-flat hot-rolled product

• (such as sheets or strips) in order to improve strength, finish, flatnessExample: Half-dollar thick, ¾-mile long steel strip + 20 minutes of cold reduction = playing-card thick, 2-mile long strip

• Cold Drawing: making smaller cross-sections (small bars or wire) from hot- rolled bars or rods by pulling the latter through a hard, abrasion-resistant die…cold drawn wire can achieve tensile strength of 500ksi.

Protective Finishes

• Protective Finishes:

• Metallic Coatings

• Vitreous Coatings

• Laminated Coatings

• Painted Coatings

• Needed to protect from corrosion

Metallic Coatings

• Hot dip processes (submerging in molten bath):• Galvanizing – heavy coating with zinc• Aluminizing – coating with aluminum/silicon• Tin, others• Electroplating (electrolytic metal transfer)• Metallizing (spraying molten metal onto surface

to be coated)• Cladding (direct application of thin sheet of

coating metal)

Vitreous Coatings

• Glass-on-steel linings for process piping, tanks

• Porcelain enamel coatings on building panels, plumbing fixtures

Laminated Coatings

• Thin, tough plastic films applied with thermosetting adhesives

Painted Coatings

• Petroleum Based

• Water Based

• Epoxy Based

Two basic types:

Oxidation (Ferrous metals): Iron reacts with oxygen, forming iron oxide (rust)

Galvanic (Dissimilar metals): Creation of an electrolytic cell (water & dissolved minerals are typically the electrolyte)

One metal becomes the positive electrode (anode)… oxidation & loss of materialOne metal becomes the negative electrode (cathode)… reduction & gaining of material

Corrosion

Magnesium, AluminumZinc, IronSteel, Cast IronLead, BrassCopper, BronzeNickel, Stainless steelSilver, Graphite

Example: sacrificial zinc anodes on marine steel hulls Corrosion can be impeded by: coatings, alloying, and other methods

Galvanic series

Sacrificial Anodes