Analysis of the strengthening and toughening mechanism of deposited metal of 1000 MPa grade high strength steel

Four kinds of Ni-Cr-Mo wire with different Ni contents were designed, with which the deposited metal of 1000 MPa high strength steel was prepared by TIG welding. Optical microscope , scanning electron microscope, transmission electron microscope, and X-ray diffractometer were used to characterize the microstructure of the deposited metal with varying Ni contents. The mechanical properties of the deposited metal were tested in terms of tensile, impact and hardness to investigate the influencing mechanism of varying Ni contents on the strength and toughness of deposited metal of 1000 MPa high strength steel. The results show that the microstructure of the deposited metal, though with different Ni contents, is composed of lath martensite, lath bainite, combined bainite and retained austenite. Different Ni contents result in different microstructures. With the increase of Ni contents, the width of columnar grains grows, the number of lath martensite, combined bainite and retained austenite also increases, and the number of lath bainite decreases, which have enhanced the strength but weakened the plasticity of the deposited metal. When the Ni content is 5.44 %, the strength- toughness matching is optimal, with the yield strength reaching 1005 MPa, and the impact energy is 95 J at −50 ℃.