Study On Prepare Of Heat Resistant Layer Of 316L Stainless Steel And Its Corrosion Behavior In Molten Salt

Solar thermal power generation as a new way, has a very broad prospects for development because of the advantages of non-polluting and sustainable development. Molten salt is the key to regenerative heat transfer medium and has a very influence on the entire solar thermal power generation system. Since the molten salt is highly corrosive, loop piping, salt storage device and other metal materials will be faced with serious corrosion in molten salt. So it is a very important study issue to improve the corrosion resistance of metal materials in molten salt.316L stainless steel is a kind of metal material that has strong corrosion resistance and low cost. It can be candidate structural material in the solar thermal power generation system. In this paper, 316 L stainless steel is analyzed about the corrosion behavior in the(Na, K)2CO3-(Na, K)Cl salt system. And 316 L stainless steel is also analyzed about the corrosion behavior in the(Na, K)2CO3-(Na, K)Cl salt system after plating nickel and chromizing. Combined with analysis method of SEM, XRD and EDS, the main work is investigated the chromizing process of 316 L stainless steel, the corrosion result of 316 L stainless steel and chromizing 316 L stainless steel. The main result and conclusion of corrosion resistance and corrosion mechanism of two types corrosion sample in molten salt could be described as follows.In the process of chromizing for 316 L stainless steel, the factors of chromizing temperature, Cr powder particle size and Cr powder density have a significant impact on chromizing process. Within a certain range, the higher chromizing temperature, the smaller Cr powder particle size and higher Cr powder density are more conducive to chromize for 316 L stainless steel. Finally, the best chromizing environment of chromizing for 316 L stainless steel is: the vacuum degree of 1×10-1 Pa, Cr powder particle size of 50 μm, Cr powder density of 40%, chromizing temperature of 1100℃, holding time of 180 min. After 50 h corrosion in the three ratios of molten salt, the corrosion resistance of 316 L stainless steel substrate is relatively poor. It is mainly intergranular corrosion and the main corrosion product is Fe Cr2O4. As the percentage of chloride increasing,the extent of corrosion of 316 L stainless steel increases. The main corrosion product of 316 L stainless steel after chromizing is Cr2O3. When the percentage of chloride below 20%, the chromizing 316 L stainless steel has excellent corrosion resistance because of the continuous Cr-rich oxide layer, which is far better than the corrosion resistance of 316 L stainless steel substrate. When the percentage of chloride more than 30%, the continuous Cr-rich oxide layer faulting cause corrosion resistance can not meet the requirement. The corrosion resistance difference between 316 L stainless steel substrate and chromizing 316 L stainless steel mainly due to the latter containing large amounts of Cr and Ni elements. Cr and Ni elements are helpful to improve corrosion resistance of 316 L stainless steel.