抄録
Thermalloy 47 specified by the Electro-Alloys Castings, Abex Corp., is one of the high carbon 25 Cr-20 Ni heat resistant alloy oastings, and its chemical composition is as follows : 0.35-0.45%C, 0.75-1.50%Si, 1.25% max. Mn, 24.5-26.5%Cr, 19.5-21.5%Ni and 0.04-0.14%N. As will be observed, this alloy is considered to avoid embrittlement due to sigma formation during high temperature long time service. But even in these composition ranges, if chemical composition is not balanced property, it happens to form sigma phase. Presnt paper described that sigma phase was formed after aging 50 hr at 871°C, in the case of low contents of C, Ni and N, high contents of Si and Cr in the composition ranges of Thermalloy 47. Therefore, it is desirable to aim at C, Ni and N contents high, Si and Cr contents low within the specified composition ranges. It was observed that sigma phase was formed from primary carbide and primary carbide was gradually replaced by sigma phase after long time exposure at 871°C. After aging 2,000 hr at 871°C, yield strength, tensile strength and hardness at room temperature increased, but elongation and reduction of area decreased than those of as cast condition. However, the tensile strength of specimen containing sigma phase decreased than that of as cast condition. The results of impact testing with and without sigma phase showed considerably poor values and the effect of sigma phase formation on the impact toughness was not evident.
