Phase evolution and mechanical properties of coarse-grained heat affected zone of a Cu-free high strength low alloy hull structure steel

Weldability of a Cu-free high strength low alloy (HSLA) hull structure steel is studied. Strengthening contributions of this steel are analyzed and phase continuous cooling transformation in simulated coarse-grained heat affected zone (CGHAZ) is investigated. Indeed, strengthening contributions of simulated CGHAZs under heat input 50 and 20 kJ/cm, respectively, are estimated. It shows this Cu-free HSLA hull structure steel is dominated at grain refinement strengthening and supplemented by precipitation strengthening and phase transformation strengthening, while the simulated CGHAZ under heat input 50 or 20 kJ/cm is dominated at phase transformation strengthening and supplemented by solid solution strengthening and grain refinement strengthening. The drawn simulated heat affected zone continuous cooling transformation (SH-CCT) diagram shows this Cu-free HSLA hull structure steel can obtain main lath-like microstructures in a wide cooling rate range with low phase start temperature. Mechanical property tests of simulated CGHAZ samples indicate high strengths and good low temperature impact toughness. All results exhibit this Cu-free HSLA hull structure steel has satisfactory weldability, which suggests its wide potential applications.