12_4

Materials Science and Engineering: An Introduction

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260 12.11 Ferritic and austenitic stainless steels are not heat treatable since "heat treatable" is taken to mean that martensite may be made to form with relative ease upon quenching austenite from an elevated temperature. For ferritic stainless steels, austenite does not form upon heating, and, therefore, the austenite-to-martensite transformation is not possible. For austenitic stainless steels, the austenite phase field extends to such low temperatures that the martensitic transformation does not occur. 12.12 The alloying elements in tool steels (e.g., Cr, V, W, and Mo) combine with the carbon to form very hard and wear-resistant carbide compounds. 12.13 We are asked to compute the volume percent graphite in a 3.5 wt% C cast iron.
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Unformatted text preview: It first becomes necessary to compute mass fractions using the lever rule. From the iron-carbon phase diagram (Figure 12.5), the tie-line in the α and graphite phase field extends from essentially 0 wt% C to 100 wt% C. Thus, for a 3.5 wt% C cast iron W α = C Gr- C o C Gr- C α = 100 - 3.5 100 - 0 = 0.965 W Gr = C o- C α C Gr- C α = 3.5 - 0 100 - 0 = 0.035 Conversion from weight fraction to volume fraction of graphite is possible using Equation (9.6a) as V Gr = W Gr ρ Gr W α ρ α + W Gr ρ Gr = 0.035 2.3 g/cm 3 0.965 7.9 g/cm 3 + 0.035 2.3 g/cm 3 = 0.111 or 11.1 vol%...
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This document was uploaded on 05/04/2010.

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