Study On High-temperature Oxidation Resistant Coatings Of Steel

High-temperature oxidation is one of the main causes of steel loss during heattreatment process. It brings many disadvantageous effects for manufacturing, such aslow production efficiency, high energy-consumption and thus high production cost.The steel oxide can even affect normal manipulation in routine manufacture anddepress final product quality. Therefore, it is necessary to avoid or reducehigh-temperature oxidation of steel. Protective coating is one of the most effectivemethods to solve this problem. Compared to the proceeding vacuum furnacetechnique or inert-gases protection technique of heat treatment, coating technique hasmore advantages. It is provided with a simple preparative technics, a better protectiveability and lower unit cost.The heat-treatment temperature of alloy steel usually exceeds 1000℃. However,kindred coating products in market can hardly meet the demand of a satisfactoryquality under such a high temperature at present. Thus, we have to develop a newkind of coating, which has an excellent protective performance under hightemperature condition.Based on previous reports and laboratory tests, we successfully developed a kindof oxide ceramic coating, adopting inert shield protective mechanism. This coatingcan effectively resist oxidation and can scale off inartificially from steel samples. Inchoosing raw materials, we took into account thermodynamics stability, surfacetension, and distensibility. Then, we used chiastic experimentations to optimizedirection of these materials, and finally established the best coating prescriptionthrough high-temperature performance tests.We did oxidation-weightloss experiments to check the oxidation weightloss ofsamples. Then we used metallographic examination to detect its de-carbonizationthickness. Furthermore, we performed energy-dispersive analysis to examine oxygencontent of the sample surfaces. To validate the protective mechanisms, we adoptedTG-DTA experiments to check the intenerate temperature and melting point of thiscoating, and observed its section shape by electron microscope scan experiments.The results show that this coating can significantly reduce the weightloss ofsteel in heat-treatment. Its de-carbonization thickness ranges about 50μm and theoxygen content of base surface has not increased significantly. Besides, the coating has good appearance of inartificially scaling off. The coating begins to soften attemperature of 800℃, which can make steel protected before oxidation becomingintensive. At temperature of 1050℃, the coating massively turns into liquid phase.This can intensify the coating's compactness under high temperatures. These areconsistent with the results of anti-oxidizability tests of this coating. Section shapes ofthe coating that scales off inartificially after protecting basal body indicate that thiscoating has good compactness and no pore penetrates through the section. Theseshow that the coating accords with the protective mechanism of inert shield. Owing toall the characteristics and performance stated above, this coating can be expected tomeet the demand of high-quality heat treatment of steel.