The influence of low melting point elements on hot-cracking of 310 austenitic stainless steel

This work highlights the influence of the low melting point elements such as sulfur, phosphorus, and silicon together with the delta (d) ferrite content on the susceptibility of austenitic stainless-steel grade 310S welding to hot cracking. Defected weld seams from a vessel component were analyzed in this work. Transverse linear cracks on both the circumferential and longitudinal welding seams, with excess bleeding, were revealed during the examination of the defected welding joints through Dye Penetrant Testing (DPT). The ferrite number (FN), i.e., a description of the ferrite content, was found to be less than 1.0 FN on the weld metal (WM) and 1.5 FN on the parent metal (PM). Hardness testing showed high values (295 HB max.) on the parent material PM while it was found within the range (211 HB max.) at the WM. The chemical composition of the WM, with the use of X-Ray Fluorescence (XRF) spectrometer, revealed 0.09% S, 0.09% P and 2.27% Si which are deemed to be in critical range against the susceptibility of 310S to solidification cracking. The microstructure of the weld material WM displayed extensive cracking at the austenite grain boundaries of the cellular dendrites, in which film-like features were observed on the crack surfaces along the interdentric interfaces. It is suggested that sulfur S and phosphorus P combine with iron to form low-melting compounds, which as a result can form low melting eutectics with impact to segregate at the austenitic grain boundaries during solidification. Hence and in line with the literature, adequate control of S and P to less than 0.002%, and Si away from 1.5-2.5% was found key in minimizing the susceptibility of 310S welding joints to hot cracking.