Low-cycle fatigue properties of modified 9Cr-1Mo steel forgings for valves bodies in power plants at elevated temperature

Low-cycle fatigue properties of modified 9Cr-1Mo steel at elevated temperature have been studied on thin-walled products of rolled plate and tube sheet etc, but there have been few reports describing heavy forged products using large size ingots. We have tested forged valves of modified 9Cr-1Mo steel from a 25 t ingot and investigated the effects of the strain wave on low-cycle fatigue at 600degC. As a result, we have recognized effects of the strain wave on low-cycle fatigue properties in the low strain region. The cracking form of oxidizing film on the surface of test pieces and the inside oxidation of cracks and the product of mean stress have been related to the lHe of low-cycle fatigue. (author)