对于微合金化处理的42CrMoVNb钢, 通过快速循环热处理的方法获得最小2m的超细奥氏体晶粒, 采用缺口拉伸延迟断裂实验研究了超细晶粒试样的延迟断裂行为。结果表明, 随着晶粒细化, 42CrMoVNb钢的强度和缺口拉伸延迟断裂抗力逐渐提高; 但当晶粒细化到2 m时, 强度和延迟断裂抗力均不再提高。在高温回火态, 当晶粒尺寸在20---4 m范围时, 断裂机制主要为穿晶断裂; 但当晶粒进一步细化到2 m时,断裂机制转变为沿晶断裂。在低温回火态, 不同晶粒尺寸的试样均主要为沿晶断裂。从降低应力集中和夹杂元素晶界偏聚等角度对超细晶粒高强度钢的延迟断裂行为进行了探讨。
42CrMoVNb steel with ultrafine prior austenite grain, its size as fine as 2 m, was obtained through rapidly cycle heat treatment. The effect of ultrafine grain size on delayed fracture behavior is studied using sustained load tensile test with notched specimen. It is shown that both strength and delayed fracture resistance of 42CrMoVNb steel increase when its grain size is refined from 20 m to 4 m, but they do not increase when refined to 2 m. When the steel was tempered at high temperature, its fracture characteristic at crack initiation area changes from intergranular to transgranular when its grain size is refined from 20 m to 8---4 m, while the fracture characteristic is intergranular when its grain size is refined to 2 m. Its fracture characteristics are all intergranular fracture for all the grain sizes investigated when tempered at low temperature. The reason for this kind of delayed fracture behavior is discussed mainly from the stress concentration and segregation at grain boundary.
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