Effect of Al content on nanoprecipitates, austenite grain growth and toughness in coarse-grained heat-affected zones of Al–Ti–Ca deoxidized shipbuilding steels

• Higher Al content (0.016wt%) in Al–Ti–Ca deoxidized shipbuilding steels significantly improves CGHAZ impact toughness (134 J vs. 54 J at −40°C) by refining prior austenite grains and enhancing microstructural homogeneity. • The presence of Type III (Nb-rich) precipitates in lower-Al steel reduces the pinning effect during high-heat input welding, leading to abnormal PAG growth up to 1 mm and deteriorated toughness. • Low lattice mismatch among Cu2S, TiN, and γ-Al2O3 promotes the formation of complex γ-Al2O3–TiN–Cu2S particles, which reduces the number density of independently precipitated (Ti,Nb)(C,N) particles and weakens grain boundary pinning. • Optimizing Al content is crucial for controlling nanoprecipitate evolution and ensuring reliable performance of shipbuilding steels under high-heat input welding conditions.