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Iron Carbide Phase Diagram

Figure 9.6

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Creating Pearlite

Figure 9.7

Figure 9.8

After W. F. Smith, “The Structure and Properties of Engineering Alloys,” 2nd ed.,McGraw-Hill, 1981, p.8

Hypoeutectoid Plain Carbon Steel

Figure 9.9 Figure 9.10

Pearlite

After W. F. Smith, “The Structure and Properties of Engineering Alloys,” 2nd ed.,McGraw-Hill, 1981, p.10

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Hypereutectoid Plain Carbon Steel

Figure 9.11

After W. F. Smith, “The Structure and Properties of Engineering Alloys,” 2nd ed.,McGraw-Hill, 1981, p.12.

Proeutectoid Cementite (white)

Crystal Structure

Figure 9.17Figure 9.19

After E. R. Parker and V. F. Zackay Strong and Ductile Steels, Sci.Am.,November 1968, p.36; Copyright by Scientific American Inc; all rights reserved

AusteniteFCC

Slightly distorted

MartensiteBCC

Distorted (long in c)BCC- BC Tetragonal

Alpha FerriteBCC <0.2%C

Undistorted

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Microstructure of Fe – C Martensites

Figure 9.13

After A. R. Marder and G. Krauss, as presented in “Hardenebility Concepts with Applications to Steel,” AIME, 1978, p. 238.

Bainite

Figure 9.24

After H. E. McGannon(ed.), “The Making Shaping and Treating of Steel,” 9th ed., United States Steel Corp., 1971

Hot quenched 550-350 Hot quenched 350 - 250

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Crystal Formation Requires Time.

After W. F. Smith, “The Structure and Properties of Engineering Alloys,” McGraw-Hill, 1981, p.14

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Isothermal Transformation (IT)Diagram

Figure 9.22

After W. F. Smith, “The Structure and Properties of Engineering Alloys,” McGraw-Hill, 1981, p.14

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IT Diagrams for Noneutectoid Steels

Figure 9.25

After R. A. Grange, V. E. Lambert, and J. J. Harrington, Trans, ASM, 51:377(1959)

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Continuous Cooling-Transformation Diagram

Figure 9.26

After R. A. Grange and J. M. Kiefer, “Alloying Elements in Steel,” ASM 2nd ed., 1966, p.254.

Continuous Cooling-Transformation Diagram

Figure 9.27

After R. A. Grange and J. M. Kiefer, “Alloying Elements in Steel,” ASM 2nd ed., 1966, p.254.

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Heat Treatments

Annealing

Normalizing

Quenching

Tempering

Austenitizing

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Tempering of Plain Carbon Steel

Tempering Temperature

Below 200 C200 – 700 0C400 – 700 0C

Structure

Epsilon CarbideCementite (rod-like)Cementite (Spheroidite)

Figure 9.31

From “ Suiting the heat Treatment to the job,” United States Steel Corp., 1968, p.34.

Spheroidite – sphere like cementite particlesmost ductile – high energy productionsince keep at 700C for 30 hours or moreresults in softer steel than full anneal

Effects of Tempering

Figure 9.32

After JE. C. Bain, and H. W. Paxton, “Alloying Elements in Steel, “ 2nd ed., American Society for Metals, 1996 p.38.

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Classification

Classification of Alloy Steels

• First two digits: Principle alloying element.

• Last two digits: % of carbon.

Source: “Alooy Steel: Semifinished; Hot-Rolled and Cold-Finished Bars,” American Iron and Steel Institute, 1970.

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Hardenability

Weldability

Machineability

In General Choose between:

1. Load Bearing member – yield strength & toughness

2. Wear application – 60HRC on surface with required thickness

3. Through hardening (C > 0.3%)

4. High-strength, low-alloy – weldability and structural uses

Typical ranges in alloy steels (%) Principal effects

Aluminum <2 Aids nitriding Restricts grain growth

Adds machinabilityReduces weldability and ductility

Increases resistance to corrosion and oxidation Increases hardenabilityIncreases high-temperature strengthCan combine with carbon to form hard, wear-

resistant microconstituents

Sulfur <0.5

Chromium 0.3–4

spheric corrosion resistance

Increases hardenability Promotes an austenitic structureCombines with sulfur to reduce its adverse

effects

Manganese 0.3–2

tant microconstituents

Nickel 0.3–5 Promotes an austenitic structure

Increases hardenabilityCopper 0.2–0.5 Increases toughness

Promotes tenacious oxide film to aid atmo-

Silicon 0.2–2.5 Removes oxygen in steel making Improves toughnessIncreases hardenability

Molybdenum 0.1–0.5 Promotes grain refinement Increases hardenabilityImproves high-temperature strength

Vanadium 0.1–0.3 Promotes grain refinement Increases hardenabilityWill combine with carbon to form wear-resis-

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Mechanical Properties of Low Alloy Steels

4820

Table 9.6

Treatment E (Gpa)

Yield (Mpa)

Ultimate

Elongation

Microstruct

1 Normalized 205 475 793 22.7% Fine Pearlite

2 Annealed 830 C 11C/hr to 650C then air cooled

3 Oil quenched from 845 with 540 C temper

4 Oil quench from 845 with 595 C temper

5 Oil quench from 845 with 650 C temper

5140 Steel

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Aluminum

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Effects of Aging on Strength

Figure 9.43

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Copper

Stainless Steel

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Cast Iron

White Cast iron

Iron Carbide

Pearlite

Figure 9.59

Courtesy of central Foundry

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Gray Cast Iron

GraphiteFlakes

Figure 9.60 Figure 9.61

After “Metals Handbook,” vol. 7, 8th ed., American Society for Metals, 1972, p.82.

Ductile Cast iron

Figure 9.63

After “Metals Handbook,” vol. 7, 8th ed., American Society for Metals, 1972, p.88.

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Malleable Cast Iron

Figure 9.65

After “Metals Handbook,” vol. 7, 8th ed., American Society for Metals, 1972, p.95.

Magnesium Alloys

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Titanium Alloys

Nickel Alloys

Alnico (aluminium, cobalt; used in magnets)Alumel (manganese, aluminium, silicon)Chromel (chromium)Cupronickel (bronze, copper)Ferronickel (iron)German silver (copper, zinc)Hastelloy (molybdenum, chromium, sometimes tungsten)Inconel (chromium, iron)Monel metal (copper, iron, manganese)Nichrome (chromium)Nickel-carbon (carbon)Nicrosil (chromium, silicon, magnesium)Nisil (silicon)Nitinol (titanium, shape memory alloy)

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Shape Memory Effect

Heated(Austenite)

Cooled(Martensite)

Deformed(Martensite)

Heated(Austenite)

NiTi

NiTi

Amorphous Metals

crystalline Amorphous