Improved weldability diagram for pulsed laser welded austenitic stainless steels

Abstract

Pulsed Nd:YAG laser welds were produced on 23 different austenitic stainless steel alloys of known composition. The primary solidification mode (PSM) and solidification cracking susceptibility of individual welds on each alloy were identified and correlated with their compositions. Single phase austenite solidification occurred in alloys with Cr equivalent to Ni equivalent ratios (Creq/Nieq) below approximately 1.59 (Hammar and Svennson equivalency relations). Alloys having a Creq/Nieq value above approximately 1.69 exhibited single phase ferrite PSM, whereas alloys for which Creq/Nieq was between 1.59 and 1.69 displayed either single phase ferrite PSM or a dual PSM with grains of single phase austenite adjacent to grains of single phase ferrite. The results of the present work were combined with those of a previous study to construct an improved weldability diagram for pulsed Nd:YAG laser welding of austenitic stainless steels. Consistent with previous observations, alloys that solidified as primary austenite were more prone to solidification cracking. Alloys that solidified as austenite (Creq/Nieq < 1.59) generally cracked when the combined impurity content (P + S) was greater than approximately 0.02%. However, cracking was not found in alloys that solidified as primary austenite with combined impurity content less than approximately 0.02%. Solidification cracking behaviour of alloys that solidified in a dual mode (1.59 < Creq/Nieq < 1.69) appeared to vary with impurity content. No cracking was observed in any of the alloys that solidified as primary ferrite (Creq/Nieq > 1.59).