Intergranular reheat cracking in 304H components
Over the past years, failure due to heat affected zone stress relief or reheat cracking in austenitic stainless steels welds, and particularly in stabilized austenitic steels like 321 or 347 have been reported world-wide. More recently similar problems have been discovered on type 316 and 304 stainless steels working in the temperature range 520-550°C. It has been established that these cracks are generally concentrated in sites of high triaxial tension developed in the strain affected zone adjacent to welds as a result of the plastic strains introduced by the welding process, and that they are prevalent in thick sections or near very massive welds. A specific test has been conducted on a component in 304H stainless steel. This component comprises a very massive weld in OKR3U. It was heated at 550°C and kept at this temperature for about 18000h with several stops in order to perform non-destructive controls to follow the cracks evolution. In a first part the experimental device is described, then the different tests campaigns and the results of non-destructive controls are presented. In a second part damage evaluations are explained. Residual stresses due to welding operation being important in the mechanism, it is necessary to evaluate them with refined analyses. Then the creep damage is evaluated using different damage models in order to point out the important parameters.