Abstract: Two heat treatment experiments of offline-quenching plus offline-tempering (Q+T) and direct-quenching plus offline-tempering (DQ+T) were conducted on steel of 12MnNiVR whose thickness is 40 mm to study the effect of the different heat treatment processes on the microstructural evolution and mechanical properties. The results show that the DQ+T process has a better strength margin indicating the moderate tempering process window even though the Q+T process can also meet the performance requirements. Furthermore, the different heat treatment processes have no impact on the mechanical property after post-weld heat treatment with the performance of strength and impact results.