Post on 12-Nov-2014
description
Muddiest Points Phase Diagrams III: Fe – Fe3C Phase Diagrams
Muddiest Points: • “What is the difference between eutectoid, hypoeutectoid, and hypereutectoid? ”
• “What are ferrite, austenite, and cemenBte?”
• “Reading the phase diagram was very tough.”
• “I don’t know what 1020, 1060, or 10100 steel means.”
• “What does each phase represent? What is gamma?”
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What Are Characteristics of Important Phases on Fe – Fe3C Diagram?
Austenite-‐ (γ) Gamma Iron: FCC iron with Inters//al solid solu/on of C up to 2.14 wt. % C
Ferrite-‐(α) Alpha Iron: BCC Iron with inters//al solid solu/on of C up to 0.022 wt% carbon Carbide (CemenBte)-‐ Iron Carbide: A hard and
bri@le stoichiometric (fixed composi/on) compound, Fe3C. It has an orthorhombic crystal structure. From Wikimedia Commons
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Fe-‐Fe3C Phase Diagram
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Tempe
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Fe-‐Fe3C Phase Diagram Eutectoid ReacBon-‐ Steel
Composi/on-‐ Wt. % C
CEutectoid
Hypereutectoid Comp. Hypoeutectoid Comp.
0.76
γ+ Fe3C
α + Fe3C
727 °C
6.67
Fe3C
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General Proper/es:
• Ferrite: α -‐ BCC Fe 0.022 wt% C max. DucBle.
• Austenite: γ -‐ FCC Fe 2.14% C max. DucBle.
• CemenBte: Fe3C – Stoichiometric. Hard and bri`le ceramic.
SAE-‐AISI Terminology: YY XXX Carbon Steel • First 2 or 3 digits give steel alloy type
• 10xx is plain carbon steel (no alloy elements)
• 41xx is a common alloy steel (Cr 0.5-‐0.95%; Mo 0.12-‐0.30%)
• See h`p://www.keytometals.com/page.aspx?ID=CheckArBcle&site=kts&NM=333 for more informaBon
• Second 2 or 3 digits give %C content x 100 • YY80 has 0.80 wt% C • YY100 has 1.0 wt.% C
Steel Terminology & Phase ProperBes
AISI Carbon Steel ClassificaBon Chart ClassificaBon % Carbon
Low Carbon <0.30% C
Medium Carbon 0.30%-‐0.60%
High Carbon 0.60%-‐1.00%
Ultrahigh Carbon 1.25%-‐ 2.00%
ApplicaBons for Steel Types
Low Carbon Steel: Used for automobile body panels and low-‐strength wires Medium Carbon Steel: Used for axles, gears, rails, and railway wheels High Carbon Steel: Used for springs and high-‐strength wires 41XX Alloy Steels: Used for components in fossil fuel and nuclear power plants
See h@p://www.keytometals.com/Ar/cles/Art62.htm
for more informa/on *= From Clker.com #= Wikimedia Commons, author Rkingsbury-‐ Background removed
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How Does Carbon Content Affect Mechanical Properties?
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Yield an
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% ElongaB
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ComposiBon (wt% C) ComposiBon (wt% C)
Tempe
rature °C
Tempe
rature °C
As wt% C :Yield and Tensile Strength and % ElongaBon
Muddiest Points Phase Diagrams III: Fe – Fe3C Phase Diagrams
Muddiest Points: • “What is the difference between eutectoid, hypoeutectoid, and hypereutectoid? ”
• “What are ferrite, austenite, and cemenBte?”
• “Reading the phase diagram was very tough.”
• “I don’t know what 1020, 1060, or 10100 steel means.”
• “What does each phase represent? What is gamma?”