Abstract: Ship plate steel with gradient structure was prepared by forming temperature gradient in its thickness direction using microwave quenching and cold rolling processes, and the effect of microwave quenching holding time on microstructure and properties of the steel was studied by means of optical microscope (OM), scanning electron microscope (SEM), hardness test and tensile test. The results show that with the increase of microwave quenching holding time, the microstructure and hardness gradients of the tested steel are deepened, and the tensile strength is also significantly increased. After microwave quenching for 10 min and cold rolling, the hardness difference between the surface and the core of the tested steel is 126.6 HV0.1 as the largest, and compared with that of the traditional quenching process, the tensile strength is increased by 57%, which is 1218 MPa. The tensile fracture morphology of the tested steel is composed of dense and fine dimples with uniform distribution, which is beneficial to improve the resistance to tensile deformation of the material.

Key words: low-alloyed steel, microwave quenching, gradient structure, hardness, strength