Influence of Ca treatment on particle–microstructure relationship in heat-affected zone of shipbuilding steel with Zr–Ti deoxidation after high-heat-input welding

The effects of Ca treatment on the particle, microstructure, and toughness of heat-affected zone (HAZ) of shipbuilding steel with Zr–Ti deoxidation after high-heat-input welding were investigated. The simulated welding at a high-heat-input welding of 200 kJ/cm was carried out using Gleeble-3800 welding simulation. Then, particle characteristics were characterized using an Aztec-Feature automatic particle analysis system. Additionally, an in-situ observation experiment was performed to study the relationships between particle and microstructure by high-temperature confocal laser scanning microscopy (HT-CLSM). The results indicated that the average HAZ toughness at −40 °C was increased from 183 to 290 J by adding 0.0026 wt.% Ca. Meanwhile, the formation of acicular ferrite ratio was increased from 49.34% to 60.28% due to the addition of Ca. The scanning electron microscopy results clearly showed that CaO–Al2O3–TiOx–ZrO2–MnS particles could act as effective nucleation sites for the formation of acicular ferrite, which has been verified by the observation of the particle–microstructure relationship under HT-CLSM. Furthermore, particle characterization results show that the cumulative frequency of particles with the size of 1–3 μm was 33.2% in HAZ of Zr–Ti shipbuilding steel but 66.2% in HAZ of Zr–Ti–Ca shipbuilding steel.