Corrosion-resistance Of316L Stainless Steel Plasma Sprayed With Ceramic Coatings During Corrosion In Molten Zinc

With the continuous development of world economy, the use of metal has occupied the important proportion. The corrosion problem of metals has been caused more and more attention due to the veried corrosion enviroments in service. In galvanized steel industry, the resistance of sink roll to liquid zinc corrosion has been paid much attention and is one of the most difficult problems in production.In this work, the yttria partially stabilized zirconia (8YSZ) coating, Sr(Yo.o5Ybo.o5Zro.9)02.95(SYYZ) coating and (Sro.3Gdo.7)ZrO3.35(SGZ) coposite coating were deposited on316L stainless steel by air plasma spraying with coatings thicknesses of100μm,300μm and300μm, respectively. The corrosion-resistance of316L stainless steel in molten zinc without or with above mentioned three ceramic coatings was investigated.The results showed that, the thickness of one side of316L stainless steel decreased0.055mm,0.100mm,0.420mm,0.590mm,0.820mm and1.375mm after corrosion for12h,24h,48h,72h,120h and168h in molten zinc, respectively. The thickness of8YSZ coated side of316L stainless steel decreased0.000mm,0.520mm and1.328mm after corrosion for24h,72h and120h in molten zinc, respectively. The thickness of SYYZ coated side of316L stainless steel decreased0.000mm,0.030mm,0.110mm and1.382mm after corrosion for24h,72h,120h and168h in molten zinc, respectively. The thickness of SGZ coated side of316L stainless steel decreased0.000mm,0.000mm,0.010mm and0.385mm after corrosion for24h,72h,120h and168h in molten zinc, respectively. The SGZ coated316L stainless steel has the best corrosion-resistance in molten zinc among the three ceramic coated316L stainless steel, follwed by SYYZ coated one and8YSZ coated one.The SGZ coated316L stainless steel was sealed by SiO2sol, and the microstructures of the smaples before and after sealing were investigated after corrosion in molten zinc for120h and168h, respectively. The results showed, that the SGZ coated316L stainless steel with sealing had better corrosion resistance that that without seatling. The SGZ coating on316L stainless steel disappeared after corrosion in molten zinc for120h, whereas the SGZ coating on316L stainless steel still remained after corrosion in molten zinc for168h. The thickness of the SGZ coated316L stainless steel with SiO2sealing decreased only0.010mm after corrosion in molten zinc for both120h and168h.The corrosion mechnism of ceramic coated316L stainless steel can be explained as follows. The molten zinc goes through the inherent cracks and voids, as well as the horizontal run-through cracks inside the ceramic coatings developed during corrosion. It results in contact of Zn with316L stainless steel and orrurrence of reaction between Zn and Fe. The development of reaction products between Zn and Fe makes the ceramic coating spalled from316L stainless steel substrate surface. The SiO2sealing treatment was condcted on SGZ coating surface, which separated the SGZ coating surface from the molten zinc effectively, resuling in remarkable lifetime increase for the SGZ coated316L stainless steel. The sealing treatment of the ceramic coated316L stainless steel is crucial for molten zinc corrosion.