Cr-Mo 鋼中の粒界偏析とそれによる脆化

概要

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In P-doped 2.25wt% Cr steels with variations in Mo and C contents, isothermally aged (embrittled) at 773K for times up to∿1000h, the intergranular segregation and embrittlement behavior has been examined by means of Auger electron spectroscopy and instrumented Charpy impact tests. C, Cr, and Mo, together with P, segregated to the grain boundaries, but their segregated concentrations were believed to vary widely in different grain boundary facets. In contrast to the enrichment of the intergranular P concentration, depletion of the grain boundary C concentration was found during the first step of aging. In addition to the retardation effect of Mo on the segregation to grain boundaries of P, it also had an effect of suppressing the decrease in intergranular fracture strength due to P-segregation ("Direct strengthening effect"). The brittle fracture load (L_f) vs. temperature diagrams were divided into the lower temperature region (Region I) where L_f was independent of test temperature and aging time, and the higher temperature region (II) where L_f increased rapidly with test temperature, and also a further brittle region (III) which was specific to the high C steels. The transition temperature from region I to II was very sensitive to aging time in one steel but was not so in the other steel. The reason for this has been discussed.
社団法人日本鉄鋼協会の論文
1979-11-01