Abstract: This paper discusses the effects of aging precipitates at grain boundaries on crack growth and on crack propagation of high temperature low cycle fatigue of Ni-Cr austenitic stringed steel in air and in vacuum by using various quantitative measures, such as crack densities, presenting of intergranular cracks, crack propagating rate and electron fractography, and also analyses the interdependent relationship between these effects and grain size. The cycles for the fatigue crack growth, propagating rate and propagating fashions of aged materials at high temperatures and low cycles depend on the joint effects of oxidization degree, the strength of grain boundaries relative to grain and the brittleness of grain boundaries. In air the precipitates at frail boundaries remarkably raise the strength of grain boundaries relative to grain, so grain boundaries with precipitates are stranger and in vacuum the grain boundaries with precipitates are weaker, because the brittleness caused by precipitates at grain boundaries has become the chief influential factor.

Key words: 高温低周疲劳, 裂纹扩展速率, 裂纹萌生, 裂纹密度, 时效