Abstract: Simulated post weld heat treatment (PWHT) at 590 ℃ for different holding time (135, 405 min) was conducted on a 55 mm thick 16MnDR steel plate as-normalized and the effect of simulated PWHT on the microstructure and mechanical properties of the plate was studied. The results show that as the holding time of simulated PWHT increases, the strength of the normalized steel plate increases first and then decreases, but the overall change amplitude does not exceed 10 MPa. The impact absorbed energy at 1/4 and 1/2 thickness of the steel plate shows different trends, which decreases monotonically at 1/4 thickness, while increases first and then decreases at 1/2 thickness. After the simulated PWHTs, there are no significant change in the microstructure of the steel plate compared to the normalized state, which remains ferrite+pearlite, but the lamellar cementite gradually transforms into spherical or punctate cementite. The number of precipitated carbides in the steel increases with the increase of holding time, but the growth trend is not obvious, and the precipitation of cementite along grain boundaries is the main reason for the reduction of impact absorbed energy.

Key words: thick gauge 16MnDR steel plate, post weld heat treatment (PWHT), microstructure, mechanical properties