マルエージ鋼のα′〓γ繰返し熱処理による強靱化におよぼす合金成分の影響

抄録

The effect of addition of 5Co, 1Ti or 1-2Mo (per cent by weight) to Fe-17Ni-15Co-4Mo-2Ti alloy has been studied in order to produce higher strength maraging steels. Grain refinement through α′_??_γ cyclic heat treatment was applied and the microstructures and mechanical properties were investigated in comparison with the results of conventional solution heat treatment. Initial grain size prior to cyclic treatment was coarse (0.6mm) because of complete solution treatment at high temperature. The addition of each alloying element increased strength level for base alloy from 2550MPa to 2750MPa and lowered fracture toughness irrespective of the kind of alloying elements and the heat treatment. The results of conventional solution treatment showed that there existed little effect of alloying elements on grain size, and the ductility decreased monotonously according to the increase in strength level. In the case of cyclic treatment, the addition of Co promoted grain refinement (7μm) and thus yielded the same ductility as that of the base alloy even at higher strength level, whereas the addition of Ti and Mo suppressed refinement (11-20μm) leading to marked decrease in ductility. The cyclic treatment was thus found to be more useful in obtaining good combination of strength, ductility and toughness than the conventional solution treatment, particularly, in the alloy with high Co.