Effect of CeO₂ on microstructures and mechanical properties of welded high-strength steel weld metal

Abstract The effect of CeO₂ on the microstructures and mechanical properties of welded high-strength steel weld metal was investigated by optical microscopy, scanning electron microscopy and mechanical testing. The results demonstrate that the addition of CeO₂ can promote the refinement and spheroidization of inclusions, refine the grains, and form acicular ferrites in the weld metals. When the addition of CeO₂ increased from 0% to 3%, the content of bainites gradually decreased, and the lath structure disappeared. The formation of the acicular ferrite ductile phase inhibited the formation of bainites and other strengthened phases in the weld metals, and the microstructure of acicular ferrites was excessive. When the CeO₂ content was 1%, the tensile strength was 903 MPa, the yield strength was 848 MPa, and the low-temperature impact toughness was 61 J at −40 °C. When the CeO₂ content was 3%, the low-temperature impact toughness of the weld metal gradually increased to a maximum value of 71 J. The weld metal had the highest toughness but the lowest strength. The addition of CeO₂ changed the pattern of crack generation, and the fracture mode changed from quasi-cleavage fractures to ductile fractures with dimples. To achieve a good matching of strength and toughness, the wire No. 2 with 1% CeO₂ had the best comprehensive mechanical properties.