Tomoki Mori

Effects of tungsten on precipitation behaviour of intermetallic compounds in the HAZ of duplex stainless steel: Study of weldability of high-tungsten duplex stainless steel (2nd Report)

Summary This paper describes an investigation of the effects of tungsten on the precipitation behaviour of intermetallic compounds in the HAZ of duplex stainless steel and the mechanism of these effects to clarify the advantage of having some Mo replaced by W. Fine precipitates of sigma phase are observed in electron micrographs of the simulated HAZ of a 25% Cr-7% Ni-0.3% N sample steel containing 4% Mo, whereas fine precipitates of the chi phase are observed in that containing 3% Mo and 2% W. The addition of tungsten delays sigma phase precipitation in steel aged at 850–950 °C × 600 sec. The sigma phase and austenite phase are identified in steel containing less than 8% W aged at 800–900°C, whereas the sigma, chi, and austenite phases are detected in steel containing more than 12% W. Based on these results and the chemistry data of the respective phases determined with an electron probe microanalyser (EPMA), the phase diagram at 900°C is experimentally derived. The chi phase is precipitated with a smalle...

Effects of tungsten on pitting corrosion resistance and impact toughness in the HAZ of duplex stainless steel ‐ study of weldability of high‐tungsten duplex stainless steel (1st Report)

Summary This paper describes an investigation of the effect of tungsten on the HAZ properties of duplex stainless steel in a programme to develop highly pitting corrosion resistant duplex stainless steel. The steels tested were modified SUS329J4L duplex stainless steel containing added tungsten. The welded joints produced by gas tungsten arc (GTA or TIG) welding and the simulated HAZ were evaluated in terms of the pitting corrosion resistance, impact toughness, and microstructure, including an analysis of precipitates. The results suggest that tungsten added up to 2 mass% is effective for improvement of the pitting corrosion resistance without heavy loss of impact toughness in the HAZ. Tungsten addition exceeding 3 mass%, however, decreases both the HAZ impact toughness and pitting corrosion resistance by accelerating the precipitation of intermetallic compounds during the welding thermal cycles. It is thus demonstrated that the pitting corrosion resistance in the HAZ of duplex stainless steel is improved...