The composition of eta carbide phase in 2 1/4 Cr-1 Mo Steel
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alloy steels, such as 2 1/4 Cr-1 Mo, are p r o jected for use in the steam generator of the demonstration Liquid-Metal Fast Breeder Reactor (LMFBR). Long-term service, up to 30 years, at high t e m p e r a ture will have significant effect on the alloy m i c r o structure, and hence, its mechanical properties. For design purposes, the mechanical properties of such a steel are important, and, since it is impractical to run tests for significant fractions of the life time of such vessels, extrapolation procedures a r e highly desirable. For such extrapolation procedures, one important quantity is the composition and location of the carbide precipitates which normally exist in these steels. A quantity of 2 1/4 Cr-1 Mo steel, which had been heated 26,500 h at 566~ in sodium with some consequent decarburization, recently became available. During the course of a c u r s o r y examination of the composition of the precipitate and matrix, r e s u l t s were obtained which were in seeming contrast to some of the a c cepted literature. Specifically, we noted that the p r e cipitate phases did not seem to be tending to "'MoC" (a face-centered cubic structure called eta phase, with 96 metal atoms per unit cell, a0 ~ ll.08A) as one might deduce from the precipitation scheme described by Baker and Nutting, 1 but rather seem established by the carbon content between "M~C" and Mz3C6. (Baker and Nutting probably did not intend to imply the endpoint of all carbide phases was " 1 ~ C " ) . Furthermore, from a chemical analysis of the supernate remaining after an electrolytic extraction the m e t a l - t o - c a r b o n ratio, (M:C), of the "M6C" phase was calculated to be about four rather than six. Thus, a more extensive investigation of the phases seemed advisable. The role of carbides in low alloy ferritic steels has been reviewed extensively by Woodhead and Quarrell, 2 and a further review s e e m s unwarranted here. The carbon content of these phases has been inadequately studied, however, an oversight which appears to be a strategic e r r o r if the mechanical properties a r e to be understood at long aging times. Numerous authors have shown that the mechanical properties of an alloy depend in an important way on the composition of the matrix. (See, for example, r e f e r e n c e s cited by WoodJAMES M. LEITNAKER,RONALDL. KLUEH,and WILLIAMR. LAINGare respectively, Research Staff Members, Metals and Ceramics Division, and Group Leader, AnalyticalChemistry Division,Oak Ridge National Laboratory,Oak Ridge, Tenn. 37830. Manuscript submitted January 29, t975. METALLURGICALTRANSACTIONSA
head and Quarrel. 2) Any deviation from the composition M6C will have an important effect on the amount of solute elements and, hence, our knowledge of their effect in solution on properties of interest. For the above reasons, a more extensive investigation of the phases present in 2 1/4 Cr-1 Mo steel seemed advisable. The present investigation involved anodic extraction of the phases and examination by X - r a y diffraction. Where a substantial
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