ニッケル含有低温用鋼の引張変形特性に及ぼす焼戻し温度の影響

抄録

Tensile properties of 12% nickel steel plates, which were tempered at various temperatures, were examined at 0 ºC, –90 ºC, and –196 ºC. This research was intended to compare the strain hardening behavior of these steels, which reveals good fracture toughness and inferior fracture toughness, and to clarify the influence of work induced martensitic transformation on strain hardening behavior of nickel bearing cryogenic steel. The strain hardening behavior was divided into two categories. One is that the maximum strain hardening appears just after yielding, then the strain hardening gradually decreases with increasing strain. The other is that the strain hardening increases just after yielding with the increase of strain, then it gradually decreases. In the case of 12% nickel steel, which is tempered at optimum temperature and possesses superior fracture toughness, retained austenite is transformed to martensite in the early stage of plastic deformation, then the gradual increase of strain hardening is derived. It leads to the higher strain hardening in total. On the other hand, in the case of 12% nickel steel, which is tempered at higher temperature and possesses inferior fracture toughness, a part of retained austenite was transformed to martensite in elastic region, then the high strain hardening appears just after yielding, but strain hardening quickly decreases with increasing strain.