Study On The Influence Of Heat Treatment On The Corrosion Behavior Of 347H Stainless Steel

In order to solve the environmental pollution problems caused by the use of fossil fuels,solar thermal power generation technology can solve the current problems,the core problem of the technology is the choice of materials in the heat storage system.As the energy storage material of solar thermal power generation system,nitrate molten salt has entered the mature stage.However,nitrate molten salt will corrode the pipeline material storing molten salt at high temperature.Stainless steel is a common material for storing nitrate molten salt,it has low cost,corrosion resistance and other properties,widely used in aviation,petrochemical and other occasions.In this paper,the corrosion behavior of molten nitric acid(60%Na NO₃—40%KNO₃)on 347H stainless steel after hot rolled and solution treatment at 565?was studied.Combined with XRD,SEM and EDS,the phase,morphology and element distribution generated in the process of molten salt corrosion for 120h were studied.The corrosion resistance of the best solution heat treatment process in molten salt was obtained by comparison,and the corrosion behavior of 347H stainless steel after different solution heat treatment in molten salt of nitric acid was analyzed.The corrosion behavior of hot-rolled 347H stainless steel after solution heat treatment at room temperature was tested by electrochemical workstation,and the electrochemical corrosion behavior of 347H stainless steel in different corrosive media in different states was discussed.The results showed that:The corrosion kinetics curve of hot-rolled 347H stainless steel in molten nitrate salt obeys the parabolic law.According to the XRD pattern,the corrosion products on the surface of stainless steel are mainly Fe₂O₃,and a small amount of Fe₃O₄ and Na Fe O₂.Due to the dense structure of Fe₃O₄,the corrosion rate of the stainless steel in the late corrosion period slows down.According to the corrosion depth image,the corrosion between the corrosion product and the stainless steel substrate is selective corrosion,preferentially nucleating and growing at the defects formed on the stainless steel surface.The hot-rolled 347H stainless steel was subjected to solution heat treatment to obtain austenitic stainless steels of different grain size grades.Then,the nitrate molten salt corrosion experiment was carried out.It was found that the corrosion kinetic curve obeys the linear law.The quality loss of molten salt corrosion is significantly reduced.It can be found from the corrosion form,after soli d-soluble heat treatment of stainless steel corrosion product shape changes,after 1160?-1h solid-soluble heat treatment of stainless steel grain grade 7,the corrosion in molten salt corrosion rate is lowest.According to the corrosion depth,the thickness of the corrosion layer at this time is0.661?m.By calculation,the corrosion rate of 347H stainless steel under this process is 0.01317mm/a.In the 3.5%NaCl,5%H₂SO₄,5%NaOH corrosion solution,the electrochemical corrosion behavior of hot-rolled 347H stainless steel,solid-solution pickled 347H stainless steel and hot-rolled 347H stainless steel after solution heat treatment was detected.Through research,it is found that in the 3.5%NaCl solution,the solid solution pickling 347H stainless steel has a positive self-corrosion potential of-0.362V,and a smaller self-corrosion current density of 1.129×10^-6A·cm^-2.Therefore,solid solution pickling 347H stainless steel has better corrosion resistance.In the 5%H ₂SO₄ solution,the hot-rolled 347H stainless steel after 1160?-2h solution heat treatment has good corrosion resistance,and the fitting parameters of the 347H stainless steel obtained from the polarization curve are not much different.In 5%NaOH solution,as the solution temperature increases,the corrosion resistance of stainless steel decreases.As the holding time increases,the corrosion resistance of stainless steel first decreases and then increases.It is found by comparison that hot-rolled 347H stainless steel has the smallest self-corrosion current density,so its corrosion resistance is the best.