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Unformatted text preview: 8.1 Which of the alloys in Table 8.1 would you expect to exhibit ductile-to-brittle transition behavior? (State the basis of your selection). SOLUTION As stated in Chapter 8 of the text, page 229, &quot;...bcc alloys show a dramatic variation in fracture mode with temperature. In general, they fail in a brittle mode at relatively low temperatures and in a ductile mode at relatively high temperatures.&quot; This is the behavior associated with a ductile- to-brittle transition. Consequently the alloys in Table 8.1 that would be expected to show a ductile-to-brittle transition are those with a body-centered cubic structure. To determine which of these alloys are bcc, a few fundamental principles can be applied. If the primary constituent (solvent, volume fraction &gt; 50%)) is an element with a bcc structure (such as Nb), the alloys can be assumed to also be bcc. For steels, those containing predominantly ferrite ( !-iron) are bcc. For other alloys, Section 11.1 of the text (pp. 348359) is a useful reference. Consequently the alloys from Table 8.1 that are candidates for ductile-to brittle transition behav- ior include the following, all with a bcc structure. 1. 1040 carbon steel 2. 8630 low alloy steel 4. L2 tool steel 6.(a) Ductile iron 14. Nb-1 Zr Problem 8.1 J. F. Shackelford, Introduction to Materials Science for Engineers , 7 th Edition, Prentice Hall, New Jersey (2009) Problem 8.1 Solution Professor R. Gronsky page 1 of 1 8.2 The relationship between service temperature and alloy selection in engineering design can be illustrated by the following case. ( a ) For the Fe-Mn-0.05C alloys of Figure 8.3b, plot the ductile-to-brittle transition temperature (indicated by the sharp vertical rise in impact energy) against percentage Mn. ( b ) Using the plot from ( a ), estimate the percentage Mn level (to the nearest 0.1%) necessary to produce a ductile-to-brittle transition temperature of precisely 0C. SOLUTION ( a ) The requested plot is obtained by simply gathering the data evident in Figure 8-3b, and dis- playing it as requested ( DBTT vs wt. % Mn). There are only four data points, DBTT (C) wt% Mn 120 0.0 60 0.5 25 1.0 30 2.0 which plot in the following way with the format requested in the problem statement. ( b ) The composition of Mn needed to produce a DBTT of precisely 0C is read directly from the curve above. This composition = 1.4 wt % Mn ....
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This note was uploaded on 01/21/2011 for the course E 45 taught by Professor Gronsky during the Fall '08 term at Berkeley.
- Fall '08