A study on tensile and fatigue properties of aged NAS 254N stainless steel at elevated temperatures

The effects of aging on tensile properties and fatigue crack growth behaviors of NAS 254N stainless steel was studied. Yield strength and ultimate tensile strength of the aged specimens were almost the same as the as-received(as-rec.). The fracture strain, however, was decreased significantly by the aging, and the fracture surface of the aged at Room Temperature(RT) test was intergranular. As test temperature increased, yield strength, ultimate tensile strength and elongation decreased. And a type of serration was observed at 550∼650 .deg. C. As strain rate decreased, yield strength and ultimate tensile strength decreased, but elongation increased. It was observed that tensile strength and strain had a sudden change at one point. And this critical temperature Tcr was 550 .deg. C. The effect of aging time on the tensile strength and strain was also investigated. Tensile strength and strain decreased significantly beyond 100hrs. Fatigue crack growth rate at RT was enhanced by the aging at high stress intensity factor range. This is due to the occurrence of the intergranular fracture in the aged specimen. At 650 .deg. C, the fatigue crack growth behavior was almost the same without intergranular fracture