<p>In the present paper, the steel plate that can meet the requirement of high heat input welding (HHIW) is developed to improve the mechanical properties of the heat-affected zone (HAZ), which can extend the service life of the steel plate to meet the sustainable development requirements. The effect of Ti/N ratio on the inclusions, microstructure, and low-temperature impact toughness of CGHAZ after the HHIW of 400 kJ/cm is elucidated for three groups of Ca-deoxidized steels, namely TN16, TN38, and TN50 with corresponding Ti/N ratios of 1.61, 3.79, and 5.00, respectively. The precipitation behavior of inclusions is calculated using FactSage thermodynamics, and the proportion of TiN precipitates significantly increased with the increase in the Ti/N ratio. It is worth noting that in TN38 steel, the number density of MnS–CaS–Al₂O₃–CaO–Ti₂O₃ inclusions in CGHAZ is the greatest among the three steels, which promote the formation of the Mn-depleted zone (MDZ), and has the greatest potential to induce intragranular acicular ferrites (IAFs) in CGHAZ. Therefore, the CGHAZ microstructure of TN38 steel has the highest value of IAF, and the area fraction of fiber zone in TN38 steel is the largest among the three steels. Consequently, the low-temperature impact toughness of HAZ of TN38 steel is 169 J, which is greatly improved by comparison with 88 J and 105 J of the impact toughness of HAZ of TN16 and TN50 steels.</p> Graphical Abstract <p></p>