Surface Microstructure And Properties Of FV520B Steel Induced By High Current Pulsed Electron Beam Treatment

High current pulsed electron beam (HCPEB) is a new kind of charged particle beam technology, and has developed rapidly in recent years. HCPEB can generate transient heating (109K/s) and cooling (107-108K/s) of the surface layer (105-10-6m) with a very short time and to which the energy has been delivered. The element distribution, the stress state and microstructure change greatly within the heat affected zone, and unequilibrium formed in the surface layer, which lead to significant surface modification effect unattainable for the conventional methods.The surface modification of FV520B steel was proceeded under the bombardment by high-current pulsed electron beam (HCPEB). The surface microstructure and chemical composition were characterized with optical microscopy, scanning electron microscope and X-ray diffraction (XRD), and the distribution of elements in surface layer, mechanical and corrosion resistance property were tested by electron probe, microhardness and electrochemical corrosion tester.The results show that under the HCPEB irradiation, the crater morphology was formed, and the crater density decreased with the increasing number of HCPEB pulses. With carbides eruptions and remelting occurred in the surface of the specimen, carbide particles significantly reduced, and dense remelted layer formed in the surface of the specimen, and grains in the heat-affected zone were refined. What’s more, column grains appeared in the melted layer. The main reason is that the thermal physical difference between carbide and base material on the incident beam energy region lead to eruption of the melting carbide in the surface of specimen, meanwhile fast cooling rate made grains had no time to grow up. As for the formation of column grains structure, it’s could be explained by the melting of surface under the irradiation of HCPEB, then the melted layer cooled down abruptly, the columnar grains grew fast and the growth of the sides arms was inhibited by the local undercooling at the fine tip of columnar grains and the narrow liquid-solid coexistence region from the large temperature gradient. XRD result showed that there is no phase change in the surface modify layer, however the tensile stress be parallel to the surface of the melted layer caused the (220) diffraction peak moves to the right, and thepreferentialorientationof (200) plane appeared. Meanwhile, electron microprobe analysis show that chemical composition tended to be symmetrical and composition distribution became more uniform with the increasing number of HCPEB pulses. Microhardness value decreased from415HV in the original specimen to330HV in the specimen treated by25pulses. However, the wear resistance increased by60%approximately. The electrochemical corrosion test in3.5%NaCl liquid showed that corrosion resistance was all improved and increased with the increasing number of HCPEB pulses, the corrosion potential increased from-0.213V in the original specimen to0.038V in the specimen treated by25pulses, meanwhile, the corrosion resistance and corrosion rate improved greatly. The main factor of the improvement of corrosion resistance property is the flat, dense-structured, uniform modification layer in the FV520B specimen.