The effect of tensile hold time on high-temperature fatigue crack growth and thermal aging on creep rupture behavior in heat-resistant steel

High-temperature materials in service experience mechanical damage due to operating load and metallurgical damage due to operating temperature. When designing or assessing life of high-temperature components, must consider both factors. In this paper, the effect of tensile hold time on high-temperature fatigue crack growth and long-term prior thermal aging heat treatment on creep rupture behavior were investigated by using STS 316L and STS 316, austenitic stainless steels, which are widely used for automotive exhaust and piping of high-temperature component. STS 316L steel was tested for fatigue crack propagation test by applying 0 sec., 5 sec., 10 sec., 50 sec., and 100 sec. tensile hold times in trapezoidal waveform at 600°... and by using the prior aged STS 316, creep rupture tests were conducted under various stress conditions and at various temperatures. In high-temperature fatigue crack growth tests using STS 316L, as tensile hold time increased crack growth rate (da/dN) decreased in relatively short tensile hold time range. In creep rupture tests using STS 316, as aging time increased creep stress exponent (n) decreased and for long-term aged material, cavity type microcracks have been observed at the interface of grain boundary and coarsened carbide.