Increasing the Corrosion Resistance in the UNS S32750 Super Duplex Steel Welded Joints through Hybrid GTAW-Laser Welding and Nitrogen

Abstract

The development of techniques to improve the welding of super duplex steels is necessary in order to ensure that the phase balance and properties of the material are not affected during this process. Hybrid arc-laser welding is a perfect combination of the advantages of both processes, producing deeper weld beads with more balanced phases than the pulsed laser process. Here, the objective was to improve the corrosion resistance of UNS S32750 weld beads by increasing the volumetric austenite percentage in the fusion zone (FZ) with a hybrid process of GTAW (gas tungsten arc welding) and pulsed laser Nd-YAG (neodymium-doped yttrium aluminum garnet). Welds were performed in bead on plate conditions with fixed laser parameters and a varying heat input introduced through the GTAW process. Additionally, welds within a nitrogen atmosphere were performed. After base metal characterization, an analysis of the FZ and heat affected zone were performed with optical microscopy, scanning electron microscopy and critical pitting tests (CPT). The synergy between the thermal input provided by the hybrid process and austenite-promoting characteristic of nitrogen led to a balanced volumetric austenite/ferrite fraction. Consequently, the results obtained in CPT tests were better than conventional welding processes, such as laser or GTAW solely.

Correction of Phase Balance on Nd:YAG Pulsed Laser Welded UNS S32750 Using Cobalt Electroplating Technique

“…This is because the cooling rate has increased in this area without enough time for more austenite formation. The HAZ's corrosion resistance is significantly impacted by the ferrite preponderance, which also increases the risk of pitting corrosion [29,34].…”

“…This is because the cooling rate has increased in this area without enough time for more austenite formation. The HAZ's corrosion resistance is significantly impacted by the ferrite preponderance, which also increases the risk of pitting corrosion[29,34].Table3presents the average volume fraction of ferrite and austenite in the fusion zone for each sample. The addition of cobalt, using the electroplating technique, was effective to balance the microstructure once austenite and ferrite were present in almost equal volume fraction in the Co35 sample.…”

Effects of the Volume Fraction of the Secondary Phase after Solution Annealing on Electrochemical Properties of Super Duplex Stainless Steel UNS S32750

“…Extensive research on the manufacturing of SDSS for welding and heat treatment has also been conducted. Videira studied increasing the corrosion resistance of SDSS through hybrid GTAW-Laser welding and nitrogen [13]. Nilson and Shin studied the heat treatment effect on the volume fraction of phased and electrochemical properties [4,5,14,15].…”

Effects of Base Metal Preheating on the Microstructure, Mechanical Properties, and Corrosion Resistance of UNS S32750 SDSS Pulsed Nd:YAG Laser Welding

“…The PREN values of ferrite are lower than those of austenite, as it contains less nitrogen, which results in lower corrosion resistance [13]. As corrosion resistance is a significant advantage of using stainless steel, it is crucial to maintain the right phase balance when welding SDSS.…”