Study On Chromium Electroplating Process And Properties Of Fastener Surface

In recent years, with the further research of the development and utilization of nuclear power, nuclear energy plays a more important role in the field of energy. In order to solve energy crisis as well as achieve sustainable development, the development of nuclear power industry has become an inevitable choice around the world. However, compared with developed countries, there is still a huge gap in nuclear power equipment manufacturing in our country and some of the key equipments still rely on imports. Main pump design and manufacturing technology have not only become a key constraint in the development of China’s nuclear power industry but also been related to enormous national political and economic interests. Thus, it is extremely urgent to achieve the localization of nuclear main pump. Due to the influence of the working environment, the nuclear main pump fastener surface can easily suffer from wear and corrosion, which shorts its life span and causes hidden trouble to the security and stable operation of nuclear main pump.According to the different process parameters(CrO3 concentration, temperature, current density), hard chromium layers were prepared on the surface of the 1Cr13 steel substrate by direct current(DC) plating process, aiming at improving the surface properties of fasteners. According to ASTM standards and GB standards, the microstructure, thickness, phase constituent, hardness, adhesion strength and the resistance to wear and corrosion of the chromium electroplating layers prepared by various process were investigated using scanning electron microscope(SEM), optical microscope(OM), X-ray diffraction(XRD), Vickers microhardness tester, multi-function material surface performance tester, electrochemical workstation and precision salt spray testing machine, respectively. Finally, the optimal chromium electroplating surface treatment technology was achieved. The evaluation method of chromium electroplating protective coating in nuclear main pump fasteners was established.The results showed that the optimal DC plating process was the process II(250g/L,58℃,30A/dm2). The chromium electroplating layers prepared by process II exhibited homogeneous surface of 19.7μm thick, without the appearance of defects. Moreover, the bonding between chromium electroplating layer and the substrate was good. compared with the membrane-based hardness in 1Cr13 steel system, the curve of membrane-based hardness the most slowly decreased. The critical load was 38.7N, indicating that adhesion strength between the substrate and coating was the highest and the membrane-based cooperative deformation ability was the strongest. The microhardness of the chrome plating was 1174.2HV, which was much higher than that of 1Cr13 steel substrate. The chromium electroplating layer, with average friction coefficient of 0.4092, showed a minimum weight loss and maximum relative wear resistance, indicating the best wear resistance. The chromium electroplating layer prepared by process II exhibited the best electrochemical corrosion resistance in 3.5NaCl solution. The corrosion current density icorr of the chrome plating showed one order of magnitude lower than that of 1Cr13 steel substrate. After salt spray corrosion test for 72 hours, the sign of obvious corrosion could not be found in chromium electroplating layer, achieving 10 protection rate.