Advances in Formation Mechanism and Susceptibility Evaluation of Liquation Cracking in Welded Cu-Rich Nanoprecipitate-Strengthened Steels: A Review

Liquation cracking is a common type of hot cracking in the heat-affected zone (HAZ) of welded Cu-rich nanoprecipitate-strengthened steels, and its formation is closely related to the remelting of low-melting-point phases at grain boundaries and contraction stresses during cooling. Cu-rich nanoprecipitate-strengthened steels achieve strengthening through the precipitation of Cu-rich nanoprecipitates. However, the welding thermal cycle causes dissolution and coarsening of these nanoprecipitates, while Cu segregates at grain boundaries to form low-melting-point Fe-Cu eutectics, significantly increasing the susceptibility to liquation cracking. This paper systematically reviews the formation mechanisms, evaluation methods, and influencing factors of liquation cracking in Cu-rich nanoprecipitate-strengthened steels, with emphasis on the evolution behavior of Cu-rich nanoprecipitates and its correlation with grain boundary liquid film formation. The common characteristics and material-specific features of liquation cracking are summarized. The susceptibility to liquation cracking depends on the composition, morphology, distribution, and wettability of low-melting-point phases at grain boundaries. The addition of Ni can inhibit Cu penetration into grain boundaries and thus improve cracking resistance. Finally, future research directions are proposed, including multi-physics coupled prediction models, microalloying modulation of grain boundary liquid film behavior, and the development of novel welding materials.