The effect of ageing on crack growth in thermal shock of 316 stainless steel specimens

Initial results of the effect of ageing on crack propagation in creep fatigue for two casts of 316 stainless steel are reported and compared with previous observations in the literature. Specimens from one cast were available in the solution treated condition and after ageing in the laboratory for 26000 hours at 550C. The other cast had been aged in service at 595C for a similar period of time. Some of these specimens were re-solution treated prior to testing. All the specimens contained spark machined slits and were tested either in thermal shock, using a step increase in temperature of 150C, or in uniaxial creep fatigue. The tests consisted of 500 cycles with a tensile hold at 600C of 2 hours (thermal shock) or 1 hour (uniaxial). The solution treated cast and the re-solution treated service aged cast produced similar crack growth rates for similar stress intensity factor ranges. For similar stress intensity factor ranges crack growth rates in the aged condition were lower than those in solution treated material, as found in other studied. (author)