218 Section 3 Ferrous Metallurgy 10.5.2 Spheroidizing Pearlite Aging pearlite just below the A1 temperature allows the cementite to form small spheres, producing very high ductility. The pearlite in Figure 10-26 has been aged u ntil it is spheroidized. Spheroidized pearlitic steel is often used for deep-drawing, which requires high formability. Deep-drawing is a process of forming sheet into deep well or cylinder shapes by pulling, or drawing, it into a die cavity. Figure 10-27 shows a sink drain connection for a sink-mounted food waste disposal that has been drawn into a flared tube shape from a flat sheet. Spheroidized pearlite is also used for drawn wire, where the repeated cold work and annealing aids the formation of a fine spheroidized structure. The high ductility of that spheroidized structure makes further wire drawing easier. Many tool-steel bars are supplied to the toolmaker in the spheroidized pearlite condition, so that the toolmaker can machine them easily and then heat-treat them to achieve high strength and hardness, as discussed in Chapter 13. Chapter Wrap-Up Chapter 2 introduced the logic flow of making metal parts, from composition, to process, to microstructure—all coming together to produce the properties of a part. In this chapter, you learned that the definition of steel—iron plus 0.02% to 2.12% carbon—is revealed in the phase diagram, which is the map showing the phases present at each temperature and composition. You learned that steel can form three structures— pearlite, bainite, or martensite—depending on how it is cooled from the austenite phase. Cooling a steel part rapidly produces different microstructures and properties than cooling at a moderate rate. Thus, processing steel for strength requires control of the high and intermediate soak temperatures, plus the cooling rate and hold times. Additional thermal processing produces yet different microstructures, such as tempered martensite and spheroidized pearlite, with yet different properties for the steel. Jay Warner Figure 10-27. This flared tube connects a garbage disposal to a sink drain so that the connection will not leak, yet the disposal can be removed easily if necessary. Cementite 20 μm ASM International Figure 10-26. A sample of pearlite that has been aged slightly below the A1 temperature for hours develops this spheroidized structure. It has very high formability and ductility. The etching solution used to bring out the microstructure in this sample outlined each cementite particle. Copyright Goodheart-Willcox Co., Inc.