Steels and Cast Irons Applications and Metallurgy Metallurgy for the Non-metallurgist.

Steels and Cast Irons Steels and Cast Irons Applications and Applications and

MetallurgyMetallurgyMetallurgy for the Non-metallurgist

Learning ObjectivesLearning Objectives• After completing this lesson, students will be able

to:o Describe steelo List some of the properties of steel and explain how they

are different from those of other materialso Tell how steel is producedo Describe cast ironso Tell how cast iron differs from steel

Introduction: Steels and Cast Introduction: Steels and Cast

IronsIrons• Steel as an engineering material• Production of steel and steel shapes• Some mechanical properties/microstructures• Production of cast irons• Microstructures of cast irons

SteelsSteels• 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 Fe3C; heat treatment• Up to 600+KSI• BCC: ductile to brittle transition

ElasticityElasticity• 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

Stress-strain diagram plotted from tensile test results. (Upper curvesshow other possible variations.)

StrengthStrength• 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

Hardness of SteelHardness of Steel

Approximate relationship between hardness and tensile strength forsteel

Impact ResistanceImpact Resistance• Charpy V-notch Impact Test• Ductile to Brittle Fracture Transition

Effect of carbon content on notch toughness

Effect of microstructure on notch toughness

Fatigue ResistanceFatigue Resistance

Effect of shot peening on fatigue behavior

Flow diagram showing the principal processes involved in converting raw steel into mill product forms (excluding coated products)

Cast IronCast Iron• Contain more than 2% carbon• Types of Cast Iron

o White Irono Gray Irono Ductile Irono Malleable Iron

Schematic illustration of the mechanical deforming action that occurs during hot rolling

Types of graphite flakes in gray iron (AFS-ASTM)

Structure of as-cast white iron

Gray cast iron, as-cast. Structure is Type A graphite flakes (dark) in amatrix of pearlite (gray lamellar structure of ferrite and pearlite).

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 untileventually the entire matrix would be ferrite.

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 particlesare MnS

Typical stress-strain curves for three classes of gray iron in tension

Effect of section diameter on tensile strength at center of cast specimen forfive classes of gray iron

Tensile properties of ductile iron vs. hardness

Stress-strain curve for as-cast ductile iron used for crankshafts

Effect of composition and microstructure on Charpy V-notch impact behavior of ductile iron

Fatigue properties of ductile iron (a) ferritic and (b) pearlitic

Rubber wheel abrasion test results

Wear of grinding balls

Relation between gouging wear and carbon content for various typesof steel and cast iron

Melting and CastingMelting and Casting

Sectional view of conventional cupola

Sectional view of a coreless induction furnace. (Arrows in crucibleshow direction of stirring action.)

Design of a bottom-pour ladle used for pouring large steel castings

Typical teapot-type ladle used for pouring small to medium-size castings

SummarySummary• 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