Enhancing impact toughness in 904L stainless steel welded joints using ultrasound-assisted laser welding without sacrificing the strength and ductility

Abstract

904L super austenitic stainless steel, a high-alloy steel known for its superior toughness and corrosion resistance, is utilized in petrochemical applications. However, the primary limitation for welded components is the low impact toughness of welds, caused by microstructural inhomogeneity during welding process. This study introduces ultrasound-assisted laser welding as a strategy to address this issue, significantly enhancing the impact toughness of the weld seam while preserving high strength and ductility. The impact mechanical properties of a 904L stainless steel plate after ultrasound-assisted laser welding were examined, with a focus on the post-weld microstructure. Experimental results demonstrate that ultrasonic assistance effectively refined the dendritic size, reduced element segregation along the interdendritic regions, as well as the second phase and the residual tensile stress in the weld seam. Ultrasonic vibration and thermal stress accelerate the movement of dislocations and the migration rate of grain boundaries, resulting in a high density of high angle grain boundary (HAGB). Additionally, a dispersion of fine MnO along the interdendritic region was observed. These improvements led to 61.3 % enhancement in the impact mechanical properties of the laser-welded joint compared to the sample without ultrasonic assistance. Our work highlights the potential of ultrasound-assisted laser welding as an effective approach to address the limitations of conventional welding methods, offering promising opportunities for advancing the welding of high-alloy steels in critical industrial applications.

Keywords

• 904L stainless steel
• Ultrasound-assisted laser welding
• Impact toughness
• Residual stress
• Secondary phase