| 摘要 |
PROBLEM TO BE SOLVED: To unnecessitate heating equipment and to attain the reduction of the cost and environmental improvement by annealing martensitic heat resistant steel to reduce its hardness and thereafter executing cold working in a specified temp. range. SOLUTION: Annealing before cold working is executed preferably at 750 to 1,100 deg.C two times. Then, the cold working is executed at a room temp. to 150 deg.C. As the compositional ratio of martensitic heat resistant steel, the one in which the content of C is 0.35 to 0.55 wt.% and the content of Cr is 5 to 12 wt.% is suitable. Moreover, since in the cold working, in a material, heat generation occurs in accompany with the deformation, and its temp. increases, by removing this heat generation with a chiller or the like, its upsetting ratio can be increased. Also, in the case that the cold working is executed by a plurality of stages using different metal molds instead of using a chiller, since cooling is executed at the time of replacing the mold, the critical upsetting ratio becomes higher than that in the case of working by one stage.
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