Microstructure and Corrosion Properties of Laser Cladding Stellite12 Coating on 304 Steel

In practical applications, 304 stainless steel is prone to pitting and crevice corrosion damage, which will adversely affect the performance of the product. In order to further improve the corrosion resistance and other related properties of 304 stainless steel, surface modification treatment can be carried out on it. At present, the surface modification treatment of laser cladding technology is widely used at home and abroad. The test used a 304 stainless steel plate as the cladding substrate, and the cladding material was Stellite12 alloy powder with an average particle size of 45 μm and a spherical powder morphology. After many experimental studies, the processing parameters were set to a laser power of 1 400 W, a spot diameter of 3 mm, and a scanning speed of 15 mm/s. Field emission scanning electron microscope SEM (FEI, ZEISS) and OXFORD Ultim Extreme energy spectrometer (EDS) were used to observe the microstructure morphology of the coating, the corrosion morphology of the coating and the substrate, and element analysis. An Empyrean X-ray diffractometer was used to determine the phase structure of the coating. An electrochemical workstation with RST5000 three-electrode system was used to conduct electrochemical experiments on the samples. The overall surface of the stellite12 coating was light green, and the overall perfection of the coating showed no obvious defects. The penetrant inspection of the sample did not find defects such as coating surface cracks, and the coating surface roughness Ra=40.1 μm. The upper, middle and lower parts of the coating cross-section showed different microstructure characteristics. The cross-section elements of the coating had abrupt changes in the transition zone, which proved that the coating and the substrate were diluted under strong metallurgical bonding. The dilution rate was calculated to be about 16.9% based on the composition of Fe element in the coating. The coating surface was mainly columnar crystals, small planar crystals, and short dendrites. Compared with the cross-section of the coating, the growth direction of the surface structure of the coating became more disordered. This was because the surface coating had a wide molten pool area and more diversified heat dissipation. The main phase of the coating wasx -Co was mainly contained in the dendrites. The main components of the coating phase were a-Co, CoCaand other compounds. The open circuit potential, Tafel polarization curve, Nyquist plot, and Bode plot of the coating and the substrate in the 3.5wt.% sodium chloride test solution. It can be seen from the figure that the open circuit potential measured by the coating and the substrate remains in a stable state, the self-corrosion potential of the coating was ‒504.5 mV, and the self-corrosion potential of the substrate was ‒579.7 mV. The corrosion potential of the coating was more positive than that of the substrate, and it was more resistant to corrosion than the substrate. At the same time, the annual corrosion rate of the coating was 0.002 mm/a far less than the substrate rate of 0.05 mm/a. A Stellite12 coating was prepared on a 304 stainless steel substrate, and the structure, phase and electrochemical corrosion performance of the coating and the substrate are studied. The interdendritic was a eutectic structure of Co and carbides, and the primary phase ofx and other compounds. The self-corrosion potential of the coating was ‒504.5 mV, and the self-corrosion potential of the substrate was ‒579.7 mV. The corrosion potential of the coating was more positive than that of the substrate. Stellite12 coating can improve the corrosion resistance of 304 stainless steel. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.