This study aims to clarify the indentation parameters and corrosion resistance of explosive welded S30400/Q345R clad plates with heat treatment cycles. A series of tests on the mechanical properties of the clad plate in the unseparated state of clad material (CM) and base material (BM) and its free surface corrosion resistance, as well as their evolution with stress relief heat treatment are studied and discussed. The results show that the severely carburised layer (SCL) that occurs on the stainless steel side of the heat treatment was the peak hardness of the entire clad plate, which was significantly reduced after four heat treatments. The worst mechanical performance was observed in three heat treatments. The reduction in free surface corrosion resistance of CM is linearly correlated with the number of heat treatments, but this does not hold true for BM. This study provides valuable references for the assessment of performance loss under heat treatment of clad plates.