Analysis on microstructure and impact absorbed energy of 960 MPa deposited metal

The solid wire of high strength and toughness was successfully developed. The microstructure and impact absorbed energy of deposited metal were analyzed in detail by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and instrumented impact test. Results showed that the microstructure was the mixture of granular bainite and low carbon martensite, while the formation of martensite was probably attributed to composition segregation. The bainite ferrite nucleated on grain boundary and then intragranular growth occurs. The existence of the film-like residual austenite was found between the lath-like bainite ferrites, and its appearance was beneficial to toughness. It was evident that the microstructure of bainite-martenite acquired an excellent toughness. Meanwhile, with the heat input of 13.7 kJ/cm, the crack propagation energy was about 63 J and the total impact absorbed energy was about 75 J.