Effect of welding speed on the microstructure and corrosion resistance of laser deep penetration welded joints of nuclear-grade 316H stainless steel

Abstract

A single-pass laser self-melting welding of nuclear-grade 316H stainless steel plate welding experiments, the study of different welding speed under the molten pool morphology and weld corrosion resistance of the changing law. The results show that with the increase of welding speed, the δ ferrite content in the weld gradually decreases, and the corrosion resistance of the weld shows a trend of increasing and then decreasing. When the welding parameters are laser power 9 kW, welding speed 1.6 m/min, and out-of-focus amount −5 mm, the weld corrosion resistance is the best.SEM observation shows that the increase of welding speed promotes the transformation of weld organization from columnar crystals to fine and uniform equiaxial crystals, and the formation of equiaxial crystals significantly improves the corrosion resistance of the weld.EDS analysis shows that the elements of Cr and Mo diffuse at high temperatures, enrich in grain boundaries, and promote ferrite and ferrite. at grain boundaries, promoting ferrite nucleation and growth, and forming coarse ferrite regions at lower welding speeds, while at higher welding speeds, rapid cooling limits element diffusion and ferrite generation, and the microstructure prefers the formation of fine equiaxed crystals.XRD analysis shows that high heat input and high temperature residence time at low welding speeds lead to the precipitation of carbon as metal carbides from the FCC lattice, and at the same time, the accumulation of carbides at grain boundaries further affects the microstructure of the weld. Carbides further affect the microstructure and corrosion resistance of the weld.

Keywords

• Laser penetration welding
• Thick plate
• Microstructure
• Corrosion resistance