Preparation And Token Of Fe₃Si Metal Siliconized Layer On 304 Stainless Steel Surface

It was prepared Fe3Si metal siliconized layer with defferent silicon content on the surface of AISI 304 stainless steel by electroless deposition used molten salt. The siliconized samples were characterized by XRD, SEM, EPMA, the paper wased analyzed affect of the process parameters to the thickness of siliconized layer and the porosity, and also the formation mechanism of siliconized layer by molten salt, at the same time, the hardness of the siliconized sample wased tested. In addition, the excellent oxidation resistance of Fe3Si based intermetallics is a predominance for using as the structural layer, so the high temperature oxidation behavior of Fe3Si metal siliconized layer was studied at 800℃,900℃for 120h with the mode of circle oxidation in present work. AISI 304 stainless steel was chosen as a reference. Besides, oxidation rate constant was used to analyze the relative materials' oxidation kinetic process theoretically. Thus we obtained following results:(1)With the increase of the proportion of the silicon infiltration agent in molten salt, it increased the thickness of siliconized layer and silicon content. Improveing siliconized temperature significantly improved the efficiency. Extension of time could improve the density of siliconized layer and refined grain.(2)Siliconized layer consisted of Fe3Si multivariate transitional metal silicide contained Ni, Cr alloy elements and obtained high-silicon phase which could be reached more than 20at.%. The study showed that the the high-silicon phase was still DO3-type ordered Fe3Si. Element of Si was well-distributed in the layer and there was no concentration gradient.That made the hardness of the layer significantly enhance, which could reach more than 660HV.(3)In the high-temperature cyclic oxidation experiment, Fe3Si metal siliconized layer exhibited more excellent oxidation resistance than that of AISI 304 stainless steel. After 120h in high-temperature cyclic oxidation at 800℃and 900℃, the oxidation kinetics of the siliconized layers all showed as quadratic parabolas. As quickly generate a continuous SiO2 protective film, the high temperature resistance at 900°C was better.(4)Experimental results showed that oxide layer made up of the mixed oxide which had multi-layer structure which consisted of the inner layer(SiO2 and Cr2O3), the middle layer(Fe2O3) and the outer layer(SiO2 and Cr2O3). With the continuous oxidation carrying on, Si diffusion bacame the dominance of growth mechanism of oxide film. In addition, at 800℃, the oxide film contained cankerous holes. This special morphology is the result of collapse of the diffusion vacancies in the Cr2O3 due to the effect of internal stress in the scales. Simultaneously, it accompanied by more cracks and a small amount of peelings. And at 900℃, on the surface of oxide film, only a lattle of cracks were found.