Reheat cracking in austenitic stainless steels

Several studies concerning reheat cracking of austenitic stainless steels have been conducted in the frame of a collaboration between CEA/SRMA and ENSMP. The present paper summarizes these studies. The first study focused on a Ti-stabilized AISI 321 stainless steel. Heat affected zones (HAZ) were simulated by means of a thermo-mechanical treatment. Relaxation tests on pre-cracked CT specimens were performed in order to reproduce the reheat cracking phenomenon. Comparisons between real and simulated HAZ were made and the whole method was validated. The important role played by the strain accumulated during welding process was shown. Contrarily to the commonly assumed mechanism, aging of HAZ decreased their embrittlement. As the intragranular titanium carbides did not appear to be the major reason for the intergranular embrittlement, the same study was undertaken to investigate the reheat cracking sensitivity of un-stabilized stainless steels AISI 316 and AISI 304. Pre-strain embrittlement was also noticed on these steels. Using the local approach of fracture, an intergranular damage model was developed. It provides quantitative prediction of the reheat cracking risk and can also be used to assess creep damage under multi-axial stress state. (authors)