10Ni-18Co-12Mo-1Ti系マルエージ鋼の冷間加工による強化

抄録

It has been reported that the maximum tensile strength of maraging steel attainable by applying thermomechanical treatment consisting of hot rolling+aging was about 360 kgf/mm². The purpose of this study was to increase further this tensile strength by changing the alloy composition based on 10Ni-18Co-12Mo-1Ti maraging steel and by applying the thermomechanical treatment consisting of the hot rolling+cold rolling+aging. Cold rolling was effective for increasing the strength of 10Ni-18Co-12Mo-1Ti maraging steel by improving toughness and preventing the unstable fracture in low stress levels. However, strengthening and toughening by cold rolling were strongly dependent upon the hot rolling conditions, because the microstructures were greatly changed. This increase in strength was most pronounced for the specimen having the microstructure with the fine grain and the reduced amount of coarse precipitates formed in the austenite. The tensile strength of 397 kgf/mm² was achieved in the 10Ni-18Co-12Mo-2Ti, 10Ni-20Co-12Mo-1Ti, and 10Ni-18Co-14Mo-1Ti maraging steels which were properly hot rolled and then cold rolled for 80% reduction. When the cold reduction exceeded 80%, the specimen became susceptible to unstable fracture in a low stress level and the tensile strength exhibited a wide scatter, but the highest tensile strength of 438 kgf/mm² was achieved by some of 95% cold rolled specimens in this study.