Liquation cracking susceptibility of partially melted zone in 304B4 SS multipass weldments

AISI 304B4 stainless steel (SS) containing 1.3 wt% boron is reported to be weldable under moderate restraint forces provided welding parameters are chosen carefully. However, during fabrication of components, extensive cracking issues are being reported. Hence, a study involving assessment of base metal, unmixed zone and partially melted zone (PMZ) of 304B4 steel and its welds made using E309 and boron containing consumables on hot cracking is carried out. In this article, results obtained on cracking susceptibility of PMZ formed in this steel are presented and discussed. In order to evaluate hot ductility behavior of PMZ formed in unmixed zone in a multipass weld, PMZ was first simulated using “Gleeble™” thermo-mechanical simulator. Subsequently, hot ductility tests were conducted on this simulated PMZ. Results of the study showed that liquation cracking susceptibility of PMZ of this steel subjected to repeated thermal cycle is higher than that of 304B4 base material. Microstructural analysis of tested specimens showed that formation of Fe-rich ((Fe,Cr)2B + Cr2B) borides in PMZ lowers ductility recovery temperature by 50 °C which results in an increase in cracking factor by 84% of that of base metal. Reasons for high cracking susceptibility of PMZ formed on fused 304B4 have been deduced.