Metallurgical influence of multi-beam technology on duplex stainless steel welds

Abstract

The main problem of electron beam welding of duplex stainless steels (DSS) is the degradation of the mechanical properties and the corrosion resistance due to an unfavourable ferrite content in the weld metal. This occurs because of the high cooling rate and the effusion of nitrogen from the weld pool, which is characteristic for this welding process. To guarantee the necessary mechanical and technological properties and the corrosion resistance, the DSS are welded with filler material and afterwards undergo a post-weld heat treatment. The present work shows the results of investigations concerning the development of an electron multi-beam technology for welding the thick-walled components of DSS without a filler material and post-weld heat treatment. The electron multi-beam technique allows the formation of many weld pools at the same time, which might achieve slower cooling rates and influence the austenite–ferrite formation of the DSS welds. Based on the results of previous studies, in which the optimum cooling rate and number of weld pools were determined, different electron multi-beam techniques were developed and applied to produce the bead on plates of these steels. The studies were performed on standard duplex stainless steel of type X2CrNiMoN22-5-3 and on lean duplex stainless steel of type X2CrNiN23-4. The resulting austenite formation, mechanical properties and the corrosion resistance of the electron multi-beam welds were investigated and are presented in this work.