Analysis of reheat embrittlement and softening of coarse-grained zone of Q960E welding joint

In order to accurately obtain the microstructure and properties of the welding heat affected zone under different temperature gradient conditions, two simulated thermal cycle tests were carried out on a low carbon equivalent Q960E and its comparative steel by using the welding thermal simulation method. And the microstructures of CGHAZ after the first thermal simulation, and UA CGHAZ, SCR CGHAZ, ICR CGHAZ and SR CGHAZ after the second thermal simulation were obtained. Microstructures were analyzed, impact toughness test and hardness characterization were carried out in this paper. Results showed that both ICR CGHAZ and SR CGHAZ of Q960E and comparative steel had reheat embrittlement sensitivity. The impact toughness of SR CGHAZ of comparative steel was as low as 9 J at −40 ℃. And the distribution of point-type and strip-type carbides formed at the grain boundary was the main reason for reheating embrittlement. The softening of SR CGHAZ with low carbon equivalent Q960E is the most serious, which is caused by the combined loss of fine-grain strengthening, dislocation strengthening and precipitation strengthening.