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Chapter 12

Chapter 12. Carbon Steels. Carbon Steels. The cooling curve for pure iron exhibits three crystal structure changes that occur when cooled from the melting point to the ambient temperature.

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Chapter 12

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  1. Chapter 12 Carbon Steels Carbon Steels

  2. The cooling curve for pure iron exhibits three crystal structure changes that occur when cooled from the melting point to the ambient temperature.

  3. Carbon dissolves in the body-centered cubic (BCC) and face-centered cubic (FCC) forms of iron to produce ferrite and austenite, respectively.

  4. The iron-carbon diagram contains peritectic, eutectic, and eutectoid phase transformation reactions and ferrite (α), austenite (γ), cementite (Fe3C), delta ferrite (δ), and pearlite (ferrite and cementite) solid phases.

  5. The eutectoid reaction region is the most important region of the iron-carbon diagram.

  6. Hypoeutectoidsteels contain <0.8% C and exhibit a slow-cooled microstructure consisting of ferrite and pearlite. A hypoeutectoid steel with 0.2% C consists of approximately 76% ferrite and 24% pearlite.

  7. Eutectoid steel contains approximately 0.8% C and exhibits a slow-cooled, 100% pearlite microstructure consisting of ferrite and cementite.

  8. The formation of pearlite from austenite is diffusion controlled and leads to a layered microstructure of ferrite and cementite.

  9. Hypereutectoid steels contain >0.8% C and exhibit a slow-cooled microstructure consisting of cementite and pearlite. A hypereutectoid steel with 1% C consists of approximately 96% pearlite with approximately 4% cementite outlining the grain boundaries.

  10. Critical temperatures are temperatures at which phase transformations begin or are completed in the eutectoid region of the iron-carbon diagram.

  11. Increased carbon content of carbon steels increases the strength and hardness, but decreases the toughness and ductility of the steel.

  12. Carbon steels are strengthened by the addition of carbon and manganese.

  13. Grain size can have either a detrimental or a beneficial effect on properties of carbon steels.

  14. Grain size of a carbon steel can be refined by cycling it through its critical temperatures.

  15. The grain size of coarse-grain steels gradually increases with increasing temperature, whereas fine-grain (fully killed) steels maintain fine-grain size until the grain-coarsening temperature is exceeded.

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