204 Section 3 Ferrous Metallurgy 10.2.1 Phase Diagram Regions Important to Processing Any liquid iron-carbon alloy with 2.14% to 6.67% carbon will form cast iron upon cooling to room temperature, made of ferrite and large cementite particles. A liquid iron-carbon alloy with 0.022% to 2.14% carbon will solidify to steel, made of ferrite and fine cementite. The division between steel and cast iron composition is indicated by the vertical line at 2.14% carbon in Figure 10-6. Most steel working materials use compositions determined by the designer and specified on the purchase order, so the focus of this chapter is mostly on the effects of temperature changes on a single composition. Most steel alloys contain less than 1.0% carbon. Processing is usually done between 1800°F (980°C) and Delta iron and liquid Delta and austenite Austenite Ferrite plus austenite Ferrite Ferrite and cementite Austenite and cementite Austenite and liquid Liquid iron Cementite and liquid Cementite 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 Delta Percent carbon 0 1 2 3 4 5 6 Temperature, ° F Goodheart-Willcox Publisher Figure 10-5. This iron-cementite phase diagram indicates the phases of iron and cementite present across a wide range of temperatures and compositions. Regions with only one phase, known as phase domains, are: liquid iron with dissolved carbon, delta iron (bcc iron with some carbon), austenite (fcc iron with dissolved carbon), cementite (Fe3C), and ferrite (bcc iron with almost no carbon). Regions of mixtures of two phases are: delta plus liquid, liquid plus austenite, liquid plus cementite, delta plus austenite, austenite plus ferrite, austenite plus cementite, and ferrite plus cementite. Copyright Goodheart-Willcox Co., Inc.