10_17

Materials Science and Engineering: An Introduction

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243 Spheroidite 88 68 Therefore, none of the microstructures meets both of these criteria. Both fine and coarse pearlites are hard enough, but lack the required ductility. Spheroidite is sufficiently ductile, but does not meet the hardness criterion. 10.D2 This problem asks if it is possible to produce an iron-carbon alloy that has a minimum tensile strength of 690 MPa (100,000 psi) and a minimum ductility of 40%RA. If such an alloy is possible, its composition and microstructure are to be stipulated. From Equation (6.20a), this tensile strength corresponds to a Brinell hardness of HB = TS(MPa) 3.45 = 690 MPa 3.45 = 200 According to Figures 10.22(a) and (b), the following is a tabulation of the composition ranges for fine and coarse pearlites and spheroidite which meet the stipulated criteria. Compositions for Compositions for Microstructure HB 200 %RA 40% Fine pearlite > 0.45 %C < 0.48 %C Coarse pearlite > 0.67 %C < 0.56 %C
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Unformatted text preview: Spheroidite not possible 0-1.0 %C Therefore, only fine pearlite has a composition range overlap for both of the hardness and ductility restrictions; the fine pearlite would necessarily have to have a carbon content between 0.45 and 0.48 wt% C. 10.D3 This problem inquires as to the possibility of producing a iron-carbon alloy having a minimum hardness of 175 HB and a minimum ductility of 52%RA. The composition and microstructure are to be specified; possible microstructures include fine and coarse pearlites and spheroidite. To solve this problem, we must consult Figures 10.22(a) and (b). The following is a tabulation of the composition ranges for fine and coarse pearlites and spheroidite which meet the stipulated criteria. Compositions for Compositions for Microstructure HB ≥ 175 %RA ≥ 52% Fine pearlite &gt; 0.37 %C &lt; 0.34 %C Coarse pearlite &gt; 0.44 %C &lt; 0.40 %C...
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