Etude comparative de la tenue mécanique des joints soudés des réservoirs sous pression de deux aciers inoxydables super austénitique et duplex.

摘要

This thesis focused on the study of low cycle fatigue and crack growth of welded joints of superaustenitic (Alloy28) and Duplex (UNS S32550) stainless steels. The effect of the presence of the welded joint in the structure was also examined.The first part of this work was to study the monotonous and cyclic behavior of the base metal and weld metal of each stainless steel. The behavior laws of each material were identified at room temperature.Low cycle fatigue tests at different levels of deformation were performed on stainless steels and their welded joints. The results indicate that the fatigue life of welded joints is lower than the base metal. The analyses of damage mechanisms show that the short life of welded joints is attributed to the acceleration of the initiation phase.Finally, crack propagation tests in Alloy28 stainless steel show that load ratio has an effect on the crack growth rate due to the closure phenomenon by roughness and plasticity. The crack growth rate in the weld metal is very similar to that of the base metal. This is due to the compensation of various effects such as the roughness, the residual stress and the closure phenomenon. The duplex stainless steel does not present load ratio effect on the crack growth rate. The crack growth rates of the weld metal of the duplex stainless steel are also comparable to those of the base metal.