Short Term Metallurgy and Hot Cracking During Laser Beam Welding of Austenitic Stainless Steels

Abstract

Industrial application of high alloyed austenitic stainless steel laser welding has grown significantly in the recent time due to the continuous improvement of compact and high power density lasers systems. The application of such processes meanwhile ranges from pipeline or railway car body manufacturing to the production of household wares. The largest advantages of the laser application to welding production are much higher welding speeds, reduction or complete exclusion of welding consumables, easy design of the weld joints, decrease of thermal distortions and thus, costs saving. In contrast to arc welding, laser beam welding might particularly be associated with metallurgical defects, like the formation of hot cracks. Such phenomena are related to an order of magnitude higher temperature gradients and cooling rates in the solidification zone, providing rapid solidification kinetics which may cause significant segregation of alloying elements such as Ni and Cr and respective undercooling of the solute at the solidification front. In specific metastable austenitic stainless steels alloys in vicinity of the so called eutectic rim of the Fe-Cr-Ni constitutional diagram, such effects might entail a change of solidification mode from primary ferrite to austenite, providing an increased risk of solidification cracking. Previous studies has shown that the primary solidification mode change during laser beam welding of Cr-Ni austenitic stainless steels such alloys could be effectively influenced by nitrogen absorption as well as by the laser plasma type and also proved the occurrence of metastable primary ferritic solidification. In the present contribution, such results are compared to recent investigations of laser welding newer austenitic Fe-Cr-Mn-Ni steel grades by identification of respective hot cracking critical welding parameter intervals and strain rates in the Controlled Thermal Weldability (CTW) Test.