Experimental investigation on the effect of post-weld heat treatment on intergranular corrosion properties of auto TIG-welded SA213 TP304 grade austenitic stainless steel

The present work investigates the effect of post-weld heat treatment (PWHT) on sensitisation on grade 304 tubes welded by Auto TIG welding using compatible filler ER309. Optimised welding parameters have been used to minimise the welding heat input and to achieve sensitisation resistance along with superior mechanical properties such as tensile, microhardness, and root bend tests. Effect of PWHT with 720 degrees C soaking temperature and variable soaking time and cooling rate on sensitisation behaviour has been examined using (i) elemental (Cr) line mapping using SEM-EDS, (ii) ditch-dual microstructure by oxalic acid etch test and (iii) fissures-cracks on bend surface by modified Straus test. Sensitisation was observed to rise proportionally with prolonged soaking of up to 5 hours with 300 degrees C/hr cooling rate. However, extending the soaking beyond 5 hours (to 10 and 15 hours) followed by cooling within the range of 100-300 degrees C/hr resulted in a wider sensitisation zone, indicating a trend towards desensitisation. Elemental line mapping across the grain boundary indicated increase in cps value at Cr depleted zone from 50cps to 75cps further verified desensitisation after prolonged soaking. The measured values of cps along the grain boundaries were aligned with observations from oxalic acid etch and modified Straus test.