Influence of Y 2 O 3 on microstructure and properties of 800 MPa high-strength steel weld metal

Abstract

This study investigated the effect of Y₂O₃ on the microstructure and properties of 800 MPa high-strength steel weld metal using optical microscopy, scanning electron microscopy, and mechanical testing. The groove faces and contacting surfaces of the base material, hot-rolled Q235 carbon steel, were buttered using high-strength steel metal-powder cored wires. The main welding parameters employed in the experiments included a voltage range of 29–31 V, a current range of 220–240 A, a welding speed of 250–260 mm/min, and shielding gases consisting of 80% Ar and 20% CO₂. The results indicated that the addition of 1% Y₂O₃ effectively refined the grain structure, resulting in a acicular ferrite content of 80%. Furthermore, Y₂O₃ promoted the refinement and spheroidisation of inclusions, leading to an improvement in the toughness of the weld metal. Y₂O₃ also enhanced the lath microstructure and inhibited the formation of martensite and bainite. The mode of crack formation shifted from boundary cracking to the surface shear stress-induced decohesion of inclusions due to the presence of Y₂O₃. The weld metal containing 1% Y₂O₃ exhibited excellent mechanical properties, with a tensile strength of 769 MPa and an impact absorbed energy of 70 J.