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CON 251 Metals Processing

• ManufacturingFrom Refined Steel Material to
  Shaped Product

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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

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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)

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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

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Cast Bars Engine Block
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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)

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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
  surfacescan 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

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Forged Steel Parts
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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

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Aluminum Extrusions
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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 gt 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

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Hot Rolling I H Beams
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Rolled Sheet Rail
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Coiled Straight Re-bar
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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

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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

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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, flatness
• Example 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 diecold drawn wire can
  achieve tensile strength of 500ksi.

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Protective Finishes

• Protective Finishes
• Metallic Coatings
• Vitreous Coatings
• Laminated Coatings
• Painted Coatings
• Needed to protect from corrosion

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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)

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Vitreous Coatings

• Glass-on-steel linings for process piping, tanks
• Porcelain enamel coatings on building panels,
  plumbing fixtures

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Laminated Coatings

• Thin, tough plastic films applied with
  thermosetting adhesives

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Painted Coatings

• Petroleum Based
• Water Based
• Epoxy Based

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Corrosion
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 material One metal becomes
the negative electrode (cathode) reduction
gaining of material
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Galvanic series
Magnesium, Aluminum Zinc, Iron Steel, Cast
Iron Lead, Brass Copper, Bronze Nickel, Stainless
steel Silver, Graphite Example sacrificial zinc
anodes on marine steel hulls Corrosion can be
impeded by coatings, alloying, and other methods
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Sacrificial Anodes