Effect of Ce on microstructures, carbides and mechanical properties in simulated coarse-grained heat-affected zone of 800-MPa high-strength low-alloy steel

The application of oxide metallurgy technology to induce the formation of acicular ferrite in coarse-grained heat-affected zone (CGHAZ) to improve the welding performance of steel is a research hotspot in recent years. However, the enhancement mechanism of mechanical properties after Ce addition and the behavior of microstructures in CGHAZ of 800-MPa high-strength low-alloy (HSLA) steel are rarely reported. In the present study, the effect of Ce addition on the welding performance of 800-MPa HSLA steel was investigated by analyzing the microstructures, carbides and mechanical properties in the simulated CGHAZ. The results indicated that after the welding thermal cycle, the decrease in toughness in the CGHAZ was mainly caused by the significant decrease in the crack propagation energy. Compared to the Ce-free steel, Ce addition improved the toughness of the base metal and CGHAZ by increasing the crack propagation energy. With the same heat input, the CGHAZ strength of the Ce-containing steel was higher than that of the Ce-free steel. During the welding thermal cycle, the Nb and Ti carbonitrides greatly affected the grain growth in the CGHAZ. Ce addition significantly refined these carbonitrides, providing a stronger pinning pressure to inhibit austenite grain growth in the CGHAZ. Ce addition also refined the austenite grains and increased the proportion of high-angle boundaries in the CGHAZ, increasing the impact absorb energy and decreasing the strength loss of the CGHAZ, essentially improving the welding performance of the HSLA steel. These results are helpful for clarify the mechanism by which Ce improved the welding performance of the 800-MPa HSLA steel.