Relaxation cracks in austenitic stainless steels near weld zones

Intergranular cracks may appear in weld zones of austenitic stainless steels when they are reheated to 500-700 Celsius degrees. In this temperature range post-welding residual stresses disappear through viscous-plastic deformation and it may happen that these zones near the weld are so fragile that they can not sustain this slight deformation. The micro-structures of these zones have been thoroughly studied and it appears that a local residual strain hardening is responsible for a high rise in the toughness. A similar microstructure has been simulated through hyper-quenching and laminating, mechanical tests (tension, creep and relaxation) have been performed at 550 and at 600 Celsius degrees, they show that strain hardening drives down ductility in the range of intergranular rupture. It is assumed that during the pre-deformation phase the deformation incompatibilities between grains may generate high local stresses that may promote the growth of intergranular cavities. (A.C.)