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Materials Science and Engineering: An Introduction

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244 CHAPTER 11 THERMAL PROCESSING OF METAL ALLOYS PROBLEM SOLUTIONS 11.1 Full annealing--Heat to between 15 and 40∞C above the A 3 line (if the concentration of carbon is less than the eutectoid) or above the A 1 line (if the concentration of carbon is greater than the eutectoid) until the alloy comes to equilibrium; then furnace cool to room temperature. The final microstructure is coarse pearlite. Normalizing--Heat to between 55 and 85∞C above the upper critical temperature until the specimen has fully transformed to austenite, then cool in air. The final microstructure is fine pearlite. Quenching--Heat to a temperature within the austenite phase region and allow the specimen to fully austenitize, then quench to room temperature in oil or water. The final microstructure is martensite. Tempering--Heat a quenched (martensitic) specimen, to a temperature between 450 and 650∞C, for the time necessary to achieve the desired hardness.
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Unformatted text preview: The final microstructure is tempered martensite. 11.2 Three sources of residual stresses in metal components are plastic deformation processes, nonuniform cooling of a piece that was cooled from an elevated temperature, and a phase transformation in which parent and product phases have different densities. Two adverse consequences of these stresses are distortion (or warpage) and fracture. 11.3 This question asks that we cite the temperature range over which it is desirable to austenitize several iron-carbon alloys during a normalizing heat treatment. (a) For 0.20 wt% C, heat to between 890 and 920∞C (1635 and 1690∞F) since the A 3 temperature is 835∞C (1535∞F). (b) For 0.76 wt% C, heat to between 782 and 812∞C (1440 and 1494∞F) since the A 3 temperature is 727∞C (1340∞F). (c) For 0.95 wt% C, heat to between 840 and 870∞C (1545 and 1600∞F) since A cm is 785∞C (1445∞F)....
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