Ni-Cr-Mo-V강의 템퍼링에 의한 미세구조 변화와 하한계 피로균열진전 특성

Microstructual Change and Near-threshold Fatigue Crack Growth Behaviors of Ni-Cr-Mo-V Steel by Tempering Treatments

Near-threshold fatigue crack growth characteristics was investigated on the Ni-Cr-Mo-V low alloy steel, which has the different microstructure obtained by tempering at various temperature. The specimens were austenized at $950^{\circ}C$ and then followed by tempering at $200^{\circ}C$, $530^{\circ}C$ and $600^{\circ}C$. Strain rate was obtained from strain gauge attached on the crack tip and crack opening point was observed through load-strain curve. Threshold stress intensity range(${\Delta}K_{th}$) was increased with increasing tempering tempuerature, but the effective threshold stress intensity rage (${\Delta}K_{eff,\;th}$) was not affected with the increasing temperature. Grain size increased with increasing tempering temperature.