200 Section 3 Ferrous Metallurgy During a temperature cycle of steel, all three factors—carbon composition, the upper hold temperature, and the cooling rate—strongly influence the microstructure and may even produce different crystal structures than experienced previously. We use phase diagrams to map and predict the crystal structures that are developed with different compositions and temperatures for moderate cooling rates. Isothermal transformation (IT) diagrams map the time-temperature-transformation history of a steel part at different cooling rates, showing which microstructures—and thus properties—are developed for a given composition, hold temperature, and cooling rate. For each application, a designer specified the properties needed. An engineer selected a process cycle to achieve the microstructure producing those properties. Another engineer or production scheduler chose equipment to provide that process cycle. Finally, technicians and operators are expected to process metal through the correct cycle while keeping the process conditions within the production tolerances. Technicians and operators also make sure that all the other conditions, such as heating rate, hold time, and furnace atmosphere, do not degrade the microstructure and properties. An understanding of the cause-and-effect relationships that flow from composition and process to microstructure and properties allows technicians and operators to know which steps can be easily accomplished and which steps require careful attention. With this understanding, an operator can recognize undesired process changes and make needed adjustments to maintain maximum performance. To develop this understanding, in this chapter we first explore the solutions of water and antifreeze found in our automobiles and trucks, observing how different water-antifreeze compositions can turn to ice at various low temperatures, damaging the engine. When we apply the same concepts to steel, we see how thermal processing and composition control the microstructures, and hence the properties. Heat-treating steel surfaces Heat-treating steel for strength, toughness & ductility Recycled steel Chapter 7 Chapter 9 Chapter 8 Chapter 10 Chapter 14 Cast shapes Forgings Extrusions Cold- rolling Cold- forming Cutting & grinding Joining Controlling corrosion Additive manufac- turing Microscopic transformations in steel Cast iron- composition, manufacture & products Powder metallurgy (P/M) Iron ore Scrap Reduction to metal Refined liquid steel Ingot, slabs, blooms Semi- finished goods: plate, sheet, strip, bars Chapter 11 Chapter 13 Chapter 12 Heat-treating large sections of steel Specialty alloys: stainless steel Tool steel HSLA steels, HPS steel Goodheart-Willcox Publisher Figure 10-1. The chapters in Section 3 describe the production of steel products from the mine to the customer’s final application. Here, you can see how this chapter’s content fits into the larger process. The technicians and operators who operate the machinery at each step are central to the production of parts and materials with consistent performance and properties. Copyright Goodheart-Willcox Co., Inc.