Corrosion resistance improvement in Gas Tungsten Arc Welded 316L stainless steel joints through controlled preheat treatment

Highlights: → Though the preheat treatment reduced the cooling rate, no sensitization occurred. → The delta ferrite content of welds reduced due to cooling retardment in welds. → Reduction in δ/γ boundaries was accompanied by decrement of passivation current. → Preheat treatment improved pitting resistance characteristics. → Increment of preheat temperature increased breakdown and repassivation potential. -- Abstract: In the present study, an attempt has been made to improve the corrosion characteristics of 316L stainless steel weldments through preheating at 450 oC and 650 oC. The infrared and Tungsten-Rhenium thermocouples were utilized to probe the cooling trend of heat affected zone (HAZ) and weld pool, respectively. X-ray diffraction (XRD) patterns, optical microscopy, electron microscopy, Energy Dispersion Spectroscopy (EDS) and ferritscope were also used to investigate the effect of preheating on microstructural characteristics within the weld and HAZ. Moreover, cyclic potentiodynamic test was carried out to evaluate the corrosion features of welds such as corrosion current, passivation current (IPP), breakdown potential (EB) and repassivation potential (Ere). Results revealed that preheating reduces the cooling rate of weld pool, accompanied by reduction of delta ferrite content of weldments. Moreover, it was observed that increment of preheat temperature improves corrosion behavior of weldments, including a lower passivation current and a more pitting resistance. These outcomes were mainly ascribed to decrease of austenite/delta ferrite interfaces as vulnerable sites to corrosion attacks, through preheat treatment. Observations showed no evidence of sensitization in preheated samples, which guaranteed the feasibility of suggested heat treatment.