Effect of boron and cerium additions on microstructures and mechanical properties in simulated coarse-grained heat-affected zone of Al-killed high-strength steel

The analysis of the microstructures, strength and impact toughness in the coarse-grained heat-affected zone (CGHAZ) was conducted to determine the impact of boron and cerium on welding performance of Al-killed high-strength steel. CGHAZ specimens were taken from four groups of experimental steels (without B and Ce, with 0.0014% B, with 0.003% B and with 0.0015% B and 0.025% Ce) after welding simulation experiments at the heat input of 25 kJ/cm. The results showed that compared to B-free steel, 0.0014% B promoted the lower bainite and martensite formation and increased the proportion of high angle grain boundaries, contributing to improved welding performance. However, 0.003% B coarsened the grains and decreased quantity of high angle grain boundaries, causing a sharp deterioration in toughness. Ce effectively refined the grains and increased the proportion of low-Σ coincidence site lattice boundaries and high angle grain boundaries, increasing the strength and toughness of CGHAZ. In comparison to the steel without B and Ce, B–Ce duplex treatment increased the tensile and yield strength by 17% and 27%, respectively, and the impact absorbed energy increased from 32 to 68 J, giving best welding performance.