PHASE-DIAGRAM AND SOLIDIFICATION STRUCTURE IN FE-15-PERCENT-CR-C-B ALLOYS

Five kinds of phases were detected in the liquidus phase diagram of the Fe-15%Cr-C-B alloy system. Two types of peritectic reactions {L + M2B-->M3 (C, B) and L + M7 (C, B)3-->M3 (C, B)} and four types of eutectic reactions {L-->gamma + M2B, L-->gamma + M3(C, B), L-->gamma + M23(C, B)6, L-->gamma + M7(C, B)3} were also detected on each liquidus phase boundary. The sum of carbon and boron concentrations in each boro-carbide was almost constant; that is, the sum was about 5.5% in M3 (C, B), about 4.7% in M23 (C, B) 6 and about 7.5% in M7 (C, B) 3; however, the carbon and boron concentrations in each boro-carbide changed compensatory in these constant concentrations. In the M2B liquidus phase region, two types of boride were detected: one was a columnar boride with high boron content, which was identified as a M2B type boride, the other was a plate-like boride with low boron content, which was still unknown in this investigation. The conjugate relations of gamma phase and the compound phase were in good agreement with the solidification structures.