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Steels and Cast Irons Applications and Metallurgy Metallurgy for the Non-metallurgist
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Learning Objectives After completing this lesson, students will be able to: o Describe steel o List some of the properties of steel and explain how they are different from those of other materials o Tell how steel is produced o Describe cast irons o Tell how cast iron differs from steel
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Introduction: Steels and Cast Irons Steel as an engineering material Production of steel and steel shapes Some mechanical properties/microstructures Production of cast irons Microstructures of cast irons
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Steels Enormous variety, compositions & micros Plain carbon, low alloy, alloy, specialty Range from ELC to 2 % C, plus Si, Mn, Al, S Plastic for forming, elastic for use Modulus: 30 million PSI Properties largely dictated by amount and distribution of Fe 3 C; heat treatment Up to 600+KSI BCC: ductile to brittle transition
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Elasticity Steel is Elastic σ = Eε Elastic Limit—maximum stress steel can withstand without permanent deformation Elastic Modulus is not appreciably affected by carbon content, amount of alloying elements or processing variables
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Stress-strain diagram plotted from tensile test results. (Upper curves show other possible variations.)
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Strength Plasticity—elongation due to load Effect of Composition—effects the shape of the stress-strain curve High carbon steels resist deformation and are more elastic
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Hardness of Steel
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Approximate relationship between hardness and tensile strength for steel
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Impact Resistance Charpy V-notch Impact Test Ductile to Brittle Fracture Transition
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Effect of carbon content on notch toughness
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Effect of microstructure on notch toughness
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Fatigue Resistance
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Effect of shot peening on fatigue behavior
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Flow diagram showing the principal processes involved in converting raw steel into mill product forms (excluding coated products)
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Cast Iron Contain more than 2% carbon Types of Cast Iron o White Iron o Gray Iron o Ductile Iron o Malleable Iron
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Schematic illustration of the mechanical deforming action that occurs during hot rolling
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Types of graphite flakes in gray iron (AFS-ASTM)
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Structure of as-cast white iron
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Gray cast iron, as-cast. Structure is Type A graphite flakes (dark) in a matrix of pearlite (gray lamellar structure of ferrite and pearlite).
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Typical ductile (nodular) iron as-cast. Spheroidal nodules of graphite (dark) surrounded by an envelope (bull’s-eye) of ferrite (white) in a pearlite (gray) matrix. With slower cooling, the ferrite envelope would be larger until eventually the entire matrix would be ferrite.
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Ferritic malleable iron two-stage annealed by holding 4 h at 954 °C (1750 °F), cooling to 704 °C (1300 °F) in 6 h, air cooling. Type III graphite (temper carbon) nodules in a matrix of granular ferrite; small gray particles are MnS
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Typical stress-strain curves for three classes of gray iron in tension
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Effect of section diameter on tensile strength at center of cast specimen for five classes of gray iron
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Tensile properties of ductile iron vs. hardness
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Stress-strain curve for as-cast ductile iron used for crankshafts
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Effect of composition and microstructure on Charpy V-notch impact behavior of ductile iron
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Fatigue properties of ductile iron (a) ferritic and (b) pearlitic
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Rubber wheel abrasion test results
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Wear of grinding balls
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Relation between gouging wear and carbon content for various types of steel and cast iron
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Melting and Casting
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Sectional view of conventional cupola
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Sectional view of a coreless induction furnace. (Arrows in crucible show direction of stirring action.)
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Design of a bottom-pour ladle used for pouring large steel castings
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Typical teapot-type ladle used for pouring small to medium-size castings
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Summary Both steels and irons show wide range of compositions and properties Anisotropy from working or from cast structure Small alloy additions have dramatic effects Heat treatments applicable to both
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