Mo-V添加低炭素鋼の時効硬化特性に及ぼす合金元素の影響

概要

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The age-hardening type bainite microalloyed steel that has high strength was examined compared with conventional ferrite perlite type microalloyed steel. The age-hardening characteristics of bainite when Mo, V, Nb and Ti was added individually to carbon steels was investigated, and the order of age-hardening amount was Mo > V > Nb > Ti. The amount of age-hardening was enhanced when V and/or Ti was added together with Mo. The temperature, which showed highest age-hardening, was 898K. The matrix structure of Mo-V co-added SCR415 (JIS standard) was varied in three types, which are martensite, bainite and ferrite perlite structure, by using different heat treatment. The order of the hardness after age-hardened steels were martensite > bainite > ferrite perlite and it is the same order as the steels before the hardening treatment. However only the bainite steel was hardened greatly after aging. The developed steel is highly useful in industrial application since it is comparably soft before heat treatment and can be made harder after aging treatment applied. The developed steel obtains 900 MPa or more of tensile strength and the same amount of proof strength as thermal refining steels. As for rotary bending fatigue limit, this steel showed 1.5 times as high as the conventional microalloyed steels.