析出強化型15Cr-26Ni-1.25Mo耐熱鋼の高温強度に及ぼすMo及びVの影響

抄録

Effects of Mo and V contents on high temperature properties, such as creep rupture strength and aging embrittlement, had been investigated in precipitation strengthened type 15Cr-26Ni-1.25Mo alloy. Of test materials, Mo and V content were varied from 1.03 to 2.00 wt%, and from 0.01 to 0.39wt% respectively.
The results obtained are summerized as follows.
1) Both Mo and V did not remarkably affect the tensile properties at 20°C in the above mentioned range of contents.
2) The highest creep rupture strengths were obtained at 650 and 700°C, when the Mo content was 2.00 wt%. The more marked effect of Mo on creep rupture strength was observed, as the exposure time and temperature increased.
3) After aging at 650°C for 6 000 h, the Charpy absorbed energy was decreased with increasing Mo content. In addition, the morphology of the fracture changed from the transgranular fracture to the intergranular one in the alloy with higher Mo content.
4) The aging embrittlement at 650°C seems to be caused by grain boundary precipitates, which mainly consist of χ phase (Mo₅Cr₆Fe₁₈) in the higher Mo added alloys.