Fe-15 mass%Cr-C-B合金における鉄基地の相変態

Abstract

In order to clarify the phase transformation of Fe-15 mass%Cr-C-B alloys, we prepared nine kinds of the alloys with different carbon and boron contents. The phase transformation behavior was examined with thermal expansion test, hardness test and SEM observation. The results obtained are as follows.(1) The transformation behavior of the matrix phase depends on carbon and chromium content: that is, in the as-cast condition, the alloy containing more than 2 mass% boron and less than 1 mass% carbon transforms to bainite, while the alloy containing less than 1 mass%B and more than 2 mass%C transforms to pearlite, however, the alloy transforms to martensite in the as-quenched condition.(2) On air cooling, the matrix transforms to pearlite, bainite or martensite with the change in chromium content from less than 6 mass% to more than 8 mass%. The Ms temperature decreases with increasing of carbon content in the matrix.(3) The alloys containing low carbon and high boron possess a very high hardness of about Rockwell C60 even in the as-cast condition. It is possible that the alloys may be used without any heat-treatment, like a Ni-hard cast iron.