The use of duplex stainless steel filler metals to avoid hot cracking in GTAW welding of austenitic stainless steel AISI 316L

Abstract

Sulfur is an element that is intrinsically and sometimes even deliberately present in stainless steel. It is usually bonded in the form of manganese sulfides, which at low levels can have a significant influence on improving machinability. In this work, solidification cracking in austenitic stainless steels welds was investigated. The solidification mode of stainless steels is of fundamental importance and most austenitic stainless steels are designed to solidify to give primary ferrite and secondary austenite to minimize the occurrence of hot cracks. The primary austenitic solidification mode enables cracks to initiate and propagate more easily. This is further enhanced by sulfur segregation. The primary ferritic mode of solidification, however, inhibits crack initiation and propagation and promotes backfilling. The ability to backfill the cracks also affects the extent of cracking observed in welds. Different filler wires were tested to weld, through GTAW welding process, tubes of type 316L UNS S31603 to forged fittings of type ASTM A182 F316 that presented sulfur and phosphorous contents, respectively, 0.03% and 0.045% wt. Duplex stainless steel filler metals ER 2209 and ER 2594, represented a creative solution to avoid hot cracking observed on those samples welded using austenitic stainless steel filler metals ER 316L and ER 309L. Several complementary techniques of microstructural analysis were used, such as optical emission spectrometry, optical microscopy and scanning electron microscopy with coupled EDS