Controlling gradient microstructure to improve crack arrest performance of high-strength low-alloy heavy steel plates for cryogenic service

In order to meet the stringent low-temperature impact performance requirements of 80 mm extra-thick steel plates for high-latitude marine applications, this study optimized the chemical composition by reducing noble metal additions and the carbon equivalent, and developed an innovative thermomechanical control process combined with quenching and tempering (TMCP+Q+T). The steel plate obtained through this process has a gradient microstructure, where the surface layer consists of fine grains with a high fraction of acicular ferrite, while the core is composed of a high proportion of polygonal ferrite. The tensile strength throughout the entire thickness exceeded 520 MPa, and the impact energy at -60°C reached 300 J. This differentiated microstructure design of "surface fine grain strengthening and toughening plus low residual stress toughening in the core" effectively addressed the issue of non-uniform impact performance between the surface and the core of the steel plates, which not only promotes the upgrading of low-temperature equipment steel, but also provides an efficient and feasible technical solution for the low-temperature impact resistance process control of extra-thick steel plate.