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Materials Science and Engineering: An Introduction

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253 determine which of the alloys have a 50 HRC hardness at an equivalent distance from the quenched end of 12 mm (1/2 in.). At an equivalent distance of 12 mm (1/2 in.), the following hardnesses are determined from Figure 11.5 for the various alloys. Alloy Hardness (HRC) 4340 55 4140 52 8640 48 5140 42 1040 25 Thus, only alloys 4340 and 4140 will qualify. (b) For moderately agitated water, the cooling rate at the center of a 38 mm diameter specimen is 8 mm (5/16 in.) equivalent distance from the quenched end [Figure 11.8(a)]. At this position, the following hardnesses are determined from Figure 11.5 for the several alloys. Alloy Hardness (HRC) 4340 56 4140 55 8640 54 5140 49 1040 32 It is still necessary to have a hardness of 50 HRC or greater at the center;
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Unformatted text preview: thus, alloys 4340, 4140, and 8640 qualify. 11.D4 A ninety millimeter (three and one-half inch) diameter cylindrical steel specimen is to be quenched in moderately agitated water. We are to decide which of eight different steels will have surface and center hardnesses of at least 55 and 40 HRC, respectively. In moderately agitated water, the equivalent distances from the quenched end for a 90 mm diameter bar for surface and center positions are 3 mm (1/8 in.) and 20 mm (13/16 in.), respectively [Figure 11.8(a)]. The hardnesses at these two positions for the alloys cited are given below. Surface Center...
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