Solidification Cracking Studies in Multi Pass Laser Hybrid Welding of Thick Section Austenitic Stainless Steel

Although the austenitic stainless steel grades are commonly considered to be quite easily weldable, there are certain applications which make exception to the above statement. As an example, which has also attributed to this study, it could be mentioned a welded assembly which forms a very rigid structure and has welds with fully austenitic microstructure. It is generally known that hot cracking of austenitic stainless steel during welding is very much coupled to chemical composition and the strains formed during solidification stage of the weld. The level of strains is dependent on e.g. a groove design, used welding parameters and the rigidity of the structure to be welded. The object of this study was to evaluate the hot cracking susceptibility of specially customized ITER-grade heat AISI 316 L(N)-IG austenitic stainless steel when it is being narrow gap multi pass laser hybrid welded under very rigid conditions, similar to occur in very massive components assembly. During the study the self restrained-type test system was developed and further tested with multi pass welding trials. The test welds were carefully visually inspected and evaluated during the welding trials and further evaluated with macroscopic and microscopic examination from the etched weld cross-sections. The test system consists of a very rigid clamping system and specially designed 60 mm thick test piece configuration which was planned to be rigid as itself. The scope of the study did not include strain measurement during testing. However, results of welding tests showed that the developed test set-up can produce critical conditions to promote hot cracking in produced test welds. The test set-up is described and the results of hot cracking tests are reported. The effect of different important factors on the risk of hot cracking susceptibility, such as shape of weld cross-section, chemical composition of the used parent/filler material, dilution and prevailing microstructure of weld metal, is discussed as well