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

The effects of aging on tensile properties and fatigue crack growth behavio rs of NAS 254N stainless steel was studied. Yield strength and ultimate ten sile strength of the aged specimens were almost the same as the as-received (as-rec.). The fracture strain, however, was decreased significantly by th e 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 obse rved at 550 similar to 650 degrees C. As strain rate decreased, yield stren gth and ultimate tensile strength decreased, but elongation increased. It w as observed that tensile strength and strain had a sudden change at one poi nt. And this critical temperature T-cr was 550 degrees C. The effect of agi ng time on the tensile strength and strain was also investigated. Tensile s trength and strain decreased significantly beyond 100hrs. Fatigue crack gro wth rate at RT was enhanced by the aging at high stress intensity factor ra nge. This is due to the occurrence of the intergranular fracture in the age d specimen. At 650 degrees C, the fatigue crack growth behavior was almost the same without intergranular fracture.