A Study On Cladding Technology And Performance Of Wear-resistant Coating On CWS Nozzle

With the extensive application of coal water slurry(CWS), the requirements of extending the life of CWS nozzle has become increasingly urgent. Using the induction cladding to prepare wear-resisting coating at the inner hole of CWS nozzle has become an effective way to extend the life of nozzle. In this paper, the properties of nickel base alloy coating prepared by different processes were compared. And the vacuum high frequency induction cladding was chosen to prepare Ni60+30%WC alloy coating in the nozzle inner hole of 45 steel and 304 stainless steel. Then the influence of cladding effects on different heating current was contrasted. And the microstructure and morphology, microhardness and corrosion resistance of coating were analyzed. At last, the coating performance by Electrical-discharge machining(EDM) was explored.There are two main ways to form alloy coating on the metal surface, high frequency induction cladding(HFIC) or high frequency induction remelting(HFIR). Through experiment contrast, metallurgical bonding was produced between alloy coating and matrix by both ways. And HFIC coating was superior to HFIR coating in coating density, microhardness and corrosion resistance.By vacuum high frequency induction cladding, the Ni60+30%WC alloy coating was prepared at the CWS nozzle of 45 steel and 304 stainless steel. And the coating was counterbored by EDM shaping machine. The binder using in the experiment was improved. The coating shrinkage during induction cladding was studied. The heating current of induction cladding was explored. Cladding of coating was heated by grading current. When the final current reached to 600 A, the cladding worked best. The difficulty in processing the inlet angle of CWS nozzle was solved by cladding.By observing the microstructure of coating with scanning electron microscope, the results shows, the porosity exsits in infusion cladding coating, while the EDM coating surface will be more compact and less defective. Both the 45 steel and 304 stainless steel form metallurgical bonding between matrix and coating. By microhardness testing of different coating, the following points are found: the coating hardness of CWS nozzle shows a rising trend from bottom to top, and reaches the peak at the top. The coating hardness distribution of 45 steel matrix is more uniform than that of 304 stainless steel matrix. And the hardness of EDM coating is obviously improved. By the reason of EDM, the porosity of coating reduces, its density better and its corrosion resistance better than coating without EDM.