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The single value fluctuation of impact work occurs frequently in high strength steel, especially for medium or super thick plates. With respect to the single value fluctuation of impact work in 700 MPa low alloy thin tempered plate, the present study carried out a comprehensive and comparative analysis through metallographic microstructure, second-phase precipitated particle and inclusion distribution. The results show that the microstructure type, grain boundary ratio of HAGBs/LAGBs, grain size and orientation of the specimens with 37 J and 7 J impact work are basically the same. The two specimens show excellent process-microstructure consistency, which fully indicate that the temperature fields of the two specimens are consistent. Since the temperature field is basically the same, the (Ti, Nb, Mo)C compound precipitated particles in the two specimens maintain a good Baker-Nutting relationship with the matrix, and the interface between the precipitated particles and the matrix maintain a stable coherent/semi-coherent relationship. The main reason for the decrease of impact work of tempered plate is related to the distribution of inclusions. There are more spherical and square large size inclusion particles and microcracks in the specimen with lower impact work. Among them, the large square inclusion particles dominate mostly. And with the increase of the plastic deformation degree of the metal matrix, the large square inclusion has an obvious evolution by separation from the matrix to forming microcracks, and then to fracture.
Yuan et al. (Wed,) studied this question.