A Novel Approach for Welding SS 304B4 using Standard Austenitic Consumables with Low Cracking Tendency

Abstract

304B4 SS is an austenitic stainless steel used for neutron shielding applications that contains ~1.3 wt.% of boron in the form of Cr B 2 borides distributed in the matrix. Though weldability of this steel is reported to be good because of backfilling of cracks by eutectic liquid formed during solidification, welding using standard E309 electrode during fabrication of components revealed high cracking tendency. This was attributed to base metal dilution in weld metal which alters the microchemistry of a portion of weld metal such that insufficient eutectic liquid is formed to heal the cracks. In order to overcome the cracking issue due to base metal dilution, an additional step of buttering was done using E309 on sides of 304B4 SS plates prior to welding. The concept of buttering was introduced because cracking tendency in the butter layer would be less in spite of significant base metal dilution due to less restraint present while buttering. Thickness of buttering layer is optimized such that at least 2-3 mm of undiluted E309 is deposited at the outermost edge to be joined. Welding is carried out on the buttered edges using E309 and subsequently specimens were suitably extracted for varestraint test from the weld joint. Spot varestraint test carried out at the “butter layer–weld†interface showed very low susceptibility for liquation cracking than direct joint tested at “base metal-weld†interface in earlier study. This is attributed to negligible dilution in the weld metal from the butter layer during actual joining when significant restraint is present.