WL 112

1. Presentations for PowerPoint
Metallurgy
Fundamentals
Ferrous and Nonferrous

2. Production of Steel by
Casting, Forging, Extrusion,
and Powder Metallurgy
Chapter 8

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• List four methods for making steel products, in addition to rolling
sheet and plate.
• Describe one major advantage for each of the following: casting,
forging, extruding, and powder metal production.
• Describe the procedure for investment casting with wax or
Styrofoam™.
• Understand the advantages of recrystallization and grain refinement
for improved performance of forgings and extrusions.
Learning Objectives

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• Explain the advantages of the grain flow developed in forged products.
• Understand why dynamic recrystallization is necessary for producing
extrusions, and the advantages of the resulting equiaxed grain structure
for performance.
• Explain why powder metallurgy is used for making small, complex
shaped parts.
• Understand why there is a great deal of interest in additive manufacturing
(also called 3-D printing) for steel parts.
Learning Objectives

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• Desired shapes cannot always be fabricated from plate or flat sheet.
• Casting requires a mold to pour liquid metal into.
• Mold has desired shape.
• Metal solidifies in mold, making part.
Production of Steel Castings

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• Steel is made by melting scrap in electric furnaces.
• Slag cover used for protection
• Highly alloyed steels add alloys into furnace.
• Small alloy additions for carbon steels are ladle additions.
• Deoxidizers are ladle additions just before casting is done.
• Magnesium and aluminum
Melting and Alloying for Foundry
Castings

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• Ladles transport liquid metal from
furnace to pouring floor.
• Pour temperature is major concern for
good castings.
• Several things must be considered.
• Furnace melt temperature
• Temperature drop while in ladle
• Time from furnace to pouring
Pouring Steel for Foundry Castings
MetalTek International

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• If ladles are moved by forklift, route must be clear.
• Avoid molten metal falling into water.
Pouring Steel for Foundry Castings
(cont.)

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• Molds are made of material with high melting temperature.
• Compacted sand molds are common.
• Moist sand mixed with clay is packed around pattern.
• Patterns produce desired shape in sand.
• Patterns can be removed before casting.
• Rough handling of molds can break sand.
• Trapped sand degrades properties of castings.
Molding and Casting Methods

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• For complex shapes, sand with polymer binder is used.
• After forming, sand is cured.
• Cured sand pieces can be assembled to form a mold.
• Liquid metal is poured in molds.
• After solidification and cooling, sand is knocked off.
• Casting surface finish depends on sand used.
Polymer-Bonded Sand Molds

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• Method has been used since ancient Egypt.
• Wax can be molded or built up into patterns.
• Wax is shape of desired steel part.
Investment Casting (Lost-Wax Casting)
MetalTek International

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• Wax patterns are covered with
ceramic slurry.
• Slurry is dried.
• Wax is melted out, leaving hollow
ceramic shell.
Investment Casting Slurry Coatings
MetalTek International

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• Molds are heated.
• Liquid metal is poured into hollow
cavities.
• Styrofoam™ patterns can be used
instead of wax.
• Called lost-foam casting.
• Styrofoam™ pattern melts/burns away
as molten steel fills cavity.
Wax and Styrofoam™ Patterns/Lost-Foam
Casting
MetalTek International

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• After metal cools, shell is removed.
• Metal parts have exact shape of wax.
• Parts are cut from sprue.
• Sprue is metal left after removing parts.
• Parts are cleaned up for machining or heat treatment.
• Surface is as smooth as original ceramic slurry.
Final Steps for Investment Castings

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• Molds made of steel or oxidation-resistant alloy
• Not disposable like packed sand or ceramic shells
• Graphite inserts assembled inside mold form desired shape.
• Steel mold is not touched by molten steel poured into it.
• After solidifying, mold is opened to remove casting.
Permanent-Mold Casting

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• Molten metal is poured into rotating mold.
• Metal solidifies while mold rotates.
• Rapid rotation forces liquid metal against inside
of mold.
• Freezing occurs from outside toward center.
• Unlike welded pipe, metal composition is
uniform through entire pipe.
• Avoids galvanic corrosion between base metal
and weld filler metal.
Centrifugal Casting
MetalTek International

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• Molten metal is poured into spinning mold
below floor.
• Finished parts have improved integrity.
• Outer portions have most improved
properties.
• Improved impact strength
• Improved toughness
Vertical-Axis Centrifugal Casting
MetalTek International

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• Major reasons for casting steel parts
• Shapes cannot be made from sheet.
• Machining time and cost to cut from plate are high.
• Yield strength is similar to wrought steel.
• Impact strength and ductility may be reduced.
• Castings have coarser microstructures than wrought steel.
• Surface finish of castings depends on mold material.
Metallurgical Characteristics of Cast
Steel

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• Misrun is a metal casting not fully formed.
• Metal does not properly flow.
• Metal does not fill entire mold.
• Castings are scrapped and remelted.
• Preventing misruns
• Keep metal oxide (dross) off molten metal surface.
• Maintain correct metal temperature in ladle.
Misruns in Castings

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• Metal alloys are denser when solid than
when liquid.
• Solid takes up less volume than liquid.
• Liquid metal must flow in to prevent a void,
or cavity, from forming.
• Mushy zone (liquid-solid) does not flow easily.
• Voids can form near dendrite roots.
• Not a problem with centrifugal casting
Casting Voids
Goodheart-Willcox Publisher

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• Liquid metal contains gas in solution.
• Oxygen and nitrogen
• When metal solidifies, gas comes out of solution.
• Forms bubbles
• Small bubbles form spherical voids (porosity) in castings.
• Porosity can degrade properties.
• Porosity is exposed by machining.
• Causes rejected castings
Casting Porosity

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• Reducing porosity
• Minimize time between melting and pouring.
• Add degassing metals just before pouring.
• Reducing misruns
• Control temperature of liquid metal.
• Transit time from furnace to pouring should be held constant.
Producing Superior Castings

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• Steel supplies needed properties.
• Castings supply needed shapes.
• Large bearing housings
• Valve bodies
• Food processing
• Electronics
• Oil and gas
• Transportation
Typical Cast Steel Applications
Marten_House/Shutterstock.com

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• Forging is shaping metal by plastic
deformation.
• Large hammers or presses force metal
workpiece into die or between two flat faces.
• Can be done hot or cold, but hot is most
common method
• Done between 1900°F and 2200°F (1040°C
and 1200°C)
• Hot steel has ductile fcc microstructure.
• Dynamic recrystallization occurs.
Forging
Olga.Sh/Shutterstock.com

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• Forgings have very high toughness.
• Forgings develop desirable grain flow.
Forged Metal Characteristics

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• Large cast ingots can be forged.
• Most forgings are 1–30 pounds (0.5–14 kg)
when finished.
• Starting material is often strands or bars up
to 30′ long and 4″ to 6″ (100 to 150 mm)
square.
• Billets are cut into multiples.
• Short pieces 4″–20” (100–500 mm) long
• Large enough to make forged part
Preparing Multiples from Billets and
Strands
worldsteel/Robert Kolykhalov

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• Drop forge applies force by dropping large
weight on workpiece.
• Also called hammer forge
• Forge face may be flat or contain a shaped
die.
• Forges are measured by pounds of force
(newtons) they can apply to part.
• Steam or air in a pneumatic cylinder can
increase hammer drop speed and impact
force.
Drop Forge Procedures
Baranov E/Shutterstock.com

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• Hydraulic force is used for very large forges.
• Top side of press forced down onto workpiece by hydraulic action
Hydraulic Press Forging
Milos Zwicer/Shutterstock.com

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• Drop hammer forges can make repeated
hits quickly.
• Air lifts a large weight on a vertical slide.
• Air pressure keeps weight oscillating up
and down near top.
• Operator allows weight to fall when ready.
• Smaller forges have a foot lever control.
• Operator controls amount of force.
Forge Procedures
Kolbakova Olga/Shutterstock.com

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• Two types of dies are used in forging.
• Open-face die and closed (shaped) die
• Open-face dies consists of two flat surfaces.
• One on ram and one on base
• Shaped dies have desired shape of part as a hollow in die.
Open-Face and Shaped Dies

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• Sometimes metal must be shaped in stages.
• Two or three sets of shaped dies in a single forge
• Each gets closer to final part shape
Forging in Stages
Aumm graphixphoto/Shutterstock.com

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• When completed, workpiece is allowed to cool.
• Workpiece may be sent for heat treatment.
Forging in Stages (cont.)

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• Drop hammer forges are very loud.
• High-quality ear protection is necessary for employees.
• OSHA Standard 1910.95 specifies limits of sound intensity and
duration for employees.
• Hearing protectors must have suitable noise reduction rating (NRR).
• NRR determined by ANSI/ASA procedure
Noise Protection in a Forging Operation
Safety Note

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• To make a strong, tough metal part, forging is a
good choice.
• Forging metal flow pattern improves strength in
bolts.
• High toughness assures component will not
fracture suddenly.
• If overloaded, parts fail in ductile fashion (slowly).
• Gives workers time to get to safety
Forging Applications:
Steel Scaffolding Bolts
Prabhjit S. Kalsi/Shutterstock.com

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• Ring-shaped parts can be made.
• Multiple is pierced and then rolled to
proper dimensions.
• Heads of rivets are hot forged (hot
headed).
• Hot metal is clamped to maintain
diameter.
• One end is hammered to flatten and
increase its diameter.
Forging Applications:
Ring Rolling/Rivets and Bolts
Scot Forge

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• Forgings can form a lap where metal folds over itself.
• Laps form a small crack (stress riser) during service.
• Sharply reduces strength
• Dye penetrant inspection is used to detect surface flaws.
• Critical forgings may be inspected for internal cracks.
• Requires X-ray or other nondestructive inspection methods
Forging Inspection

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• Forgings have higher toughness and impact strength than cast
parts.
• During forging, grains flow around bends.
• Grain flow pattern remains once at room temperature.
• Grain structure is recrystallized during hot forging.
• Final grain structure at room temperature is refined.
Grain Structure and Flow in Forgings

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• Experience is needed to produce high-quality parts.
• Operator controls number and magnitude of hits.
• Timing of multistage forging is important.
• Temperature control is critical.
• Multiples need consistent temperature.
• Multistage die forging must control temperature at each step.
Operator Contributions to Superior
Forgings

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• Steel can be made into seamless
pipe, rod, or special section shapes
by extrusion.
• Extrusion pushes heated billet
through die.
• Extrusion dies shaped to guide hot
metal into desirable shape
Production of Extrusions
Goodheart-Willcox Publisher

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• For hollow shape, metal flows around
spider supports in die.
• These support center section.
• Metal flows around supports and
back together to metallurgically bond.
• Extruded part has no seams.
Extruding Hollow Shapes
Goodheart-Willcox Publisher

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• Extruded parts have very uniform, equiaxed
grain structure.
• Free of porosity
• Uniform composition
• Applications
• Seamless tubing for heat exchanger
• Hydraulic system tubing that must not crack
during later cold forming
• Fuel and lubricant distribution lines for jet
engines
Applications of Extruded Steel
worldsteel/Shawn Koh

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• Casting, forging, and extrusion operations generate smoke laden
with VOCs.
• As vapors, these compounds can be harmful to humans.
• Workers (who do not wear proper air filters)
• Surrounding neighborhoods
Volatile Organic Compounds (VOCs)
Safety Note

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• Small, reliable parts made from metal powders
• Powders compacted in small presses
• Compacted parts heated just below melting temperature
• Heating process called sintering bonds particles together.
• Produces shapes and compositions difficult to forge, extrude, or
machine
Production of Powder Metal (PM) Parts
Goodheart-Willcox Publisher

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• Most steel powders made by decomposing
metal compounds
• PM particles are small.
• About 180 μm (0.007″) diameter
• Iron and carbon powder blended to make steel
parts
• Different metal powders blended to create alloys
• Lubricant may be added to improve forming.
Making Metal Powder and Powder Alloys
MarinaGrigorivna/Shutterstock.com

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• Powdered metal can burn.
• Powdered metals should be stored in flameproof metal containers.
• Only Class D extinguishers work on metal fires.
• Once metal powder is compacted, flammability is not an issue.
High Flammability
Safety Note

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• Typically, mixed powder is compacted in a single die
at room temperature.
• Dies can have any shape in horizontal directions.
• Small cams and gears are frequently made using
PM methods.
Compacting to Shape
Goodheart-Willcox Publisher

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• Mechanical presses are faster than hydraulic presses.
• Hydraulic presses can apply much higher force.
• During compaction, powder particles are pressed together.
• Compacted powder parts are called green compacts.
• Can be handled gently
• Can chip or break if handled roughly
Press for Making PM Compacts

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• Green compacts are heated in process
called sintering.
• Soaking temperature for steel is
between 2150°F (1180°C) and 2500°F
(1370°C).
• Soak time is between one and six
hours.
• Longer for lower sintering temperatures
Sintering
Goodheart-Willcox Publisher

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• During sintering, void space between particles gets smaller.
• Part shrinks in all directions, increasing density.
Density of Sintered Compacts
Goodheart-Willcox Publisher

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• PM parts must be sintered under
controlled atmosphere.
• Assures steel does not oxidize
• Carbon is not added or subtracted
from parts.
Furnace Sintering
Goodheart-Willcox Publisher

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• In continuous furnace, parts sintered as they travel on belt.
• Stationary atmosphere-controlled furnace may be used.
• Requires door seals to control atmosphere
• Low-volume production only
Continuous and Stationary Atmosphere-
Controlled Furnace Sintering

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• Voids in PM part can be filled to improve properties.
• Prevents excess oxidation or corrosion
• Chip of copper placed on steel PM part going into furnace
• Copper melts during sintering.
• Absorbed (infused) into PM part by capillary action
• Capillary action causes liquid to flow into small spaces due to surface
tension.
• Copper-infused steel PM parts are more corrosion-resistant.
Infusing PM Parts with Metals

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• Controlling degree of compaction is
important.
• Proper mixing of powders
• Proper amount of lubricant
• Tensile properties are improved with
greater density of parts.
• Density depends strongly on
sintering time and temperature.
Performance of PM Parts
Goodheart-Willcox Publisher

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• Recent development in powder metallurgy
• Builds parts a layer at a time
• Computer directs a laser beam.
• Laser beam bonds thin layers of metal
powder (partial melting).
• Parts may be sintered afterward.
• Machines are small.
• Part size depends on laser’s working space.
Additive Manufacturing (3-D Printing)
Goodheart-Willcox Publisher

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• Additive manufacturing produces very complex
shapes.
• Avoids difficult assembly operations
• Process is slow.
• Technicians should carefully monitor process.
• Powder must flow smoothly.
• Laser components can come loose and misdirect
laser beam.
Additive Manufacturing Quality
Moreno Soppelsa/Shutterstock.com

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• A difficulty with additive manufacturing is
each part is produced separately.
• Cannot destructively test every part
• Nondestructive tests must be used for
critical parts.
• Rapid improvements continue to occur.
Additive Manufacturing Quality (cont.)
sspopov/Shutterstock.com

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• Excess metal generated by casting, forging, and extrusion is plant
scrap and is recycled directly.
• Spent lubricating fluids may contain heavy metals.
• Disposal into groundwater or surface water is not safe.
• Must be reprocessed, repurposed, or properly discarded.
Recycling Materials
Sustainable Metallurgy