Thick high-strength low-alloy (HSLA) steel plates with excellent large heat input welding properties are increasingly demanded to build super-large container ships for the globally flourishing marine trade. This article describes the effect of Ca content on the TiN particles, microstructure and impact toughness of the simulated coarse-grained heat-affected zone (CGHAZ) in HSLA steels after large heat input welding at 400 kJ/cm. The quantitative analyses on TiN particles demonstrate that the number densities of the submicron- and nano-scale particles increase with increasing Ca content, but the particle sizes appear to be independent of the Ca content. The prior austenite grains in the CGHAZs of the HSLA steels are comparably coarse, including a small number of extremely large grains, except for 25Ca steel, whose grains are relatively fine and uniform. Moreover, only the impact toughness of the CGHAZ in 25Ca steel is satisfactorily improved with a small test variability, and this could be attributed to the improved precipitation of the submicron-scale TiN particles that effectively refine the grains. Based on the experimental and thermodynamic results, it is strongly recommended to increase the Ca content to > 0.0019 wt pct for the related HSLA steel system in the future steel optimization.

对于全球繁荣的海洋贸易，越来越需要具有出色的大热输入焊接性能的厚高强度低合金（HSLA）钢板来建造超大型集装箱船。本文描述了Ca含量对在400 kJ / cm的大热输入焊接后HSLA钢中模拟粗晶热影响区（CGHAZ）的TiN颗粒，微观结构和冲击韧性的影响。对TiN颗粒的定量分析表明，亚微米级和纳米级颗粒的数量密度随Ca含量的增加而增加，但粒径似乎与Ca含量无关。HSLA钢CGHAZ中的原始奥氏体晶粒相对较粗，除了25Ca钢外，还包括少量极大晶粒。其颗粒相对较细且均匀。此外，只有25Ca钢中的CGHAZ的冲击韧性可以通过较小的测试变异性来令人满意地提高，这可以归因于有效地细化晶粒的亚微米级TiN颗粒析出的改善。根据实验和热力学结果，强烈建议在未来的钢优化中将相关HSLA钢系统的Ca含量增加到> 0.0019 wt pct。