| 304 stainless steel is a typical 18-8 austenitic stainless steel.It has excellent corrosion resistance,heat resistance,plasticity and ductility,and is widely used in various medical equipment processing equipment,shipbuilding,food industry and control valve production.Due to the improper operation of the current hot and cold deformation technology,the widespread presence of chloride ions in the application environment and other factors that seriously affect performance,the corrosion resistance of the 304 stainless steel control valve is reduced,which directly leads to the failure of the control valve,which brings serious safety Accidents and huge economic losses.Therefore,improving the corrosion resistance of 304 stainless steel is a very important technical research topic.At present,the technical approaches and process methods used to improve the corrosion resistance of 304 stainless steel are roughly divided into alloy method and heat treatment method.In these two process methods,heat treatment is used to improve the corrosion resistance of 304 stainless steel,because the process equipment is relatively simple.,Low cost and relatively short process cycle make it more common in China.However,if the solution treatment process is improper,the alloying elements may not be completely dissolved in the matrix,so that the requirement of higher alloy content in the matrix structure cannot be met,and the mechanical properties and corrosion resistance of stainless steel will be reduced.Therefore,through the systematic optimization analysis and research on the solution treatment process,it has very important research significance for the analysis of how to optimize the structure,corrosion resistance and mechanical properties of the 304 stainless steel of the valve body material of the control valve.Based on a large number of literature investigations and studies,this paper selects the solution heat treatment process as a technical means to improve the corrosion resistance of 304 stainless steel.The 304 stainless steel material is subjected to ferric chloride immersion corrosion experiments and sodium chloride solution pitting corrosion experiments.Chemical corrosion test and intergranular corrosion electrochemical corrosion test of potassium thiocyanate and sulfuric acid mixed solution,and use metallographic analysis,XRD,weight loss method,polarization curve analysis,electrochemical impedance spectroscopy analysis and electrochemical potential reactivation method,etc.Means,the effects of solution temperature and holding time on the metallographic structure,corrosion resistance and mechanical properties of 304 stainless steel were studied.The main results obtained in this paper are as follows:(1)After the 304 stainless steel sample undergoes solution heat treatment at 990℃,1020℃,1050℃,1080℃,1110℃,1140℃ and 30min,60min,90min,the ferrite and alloy in the original sample structure The carbides are more fully dissolved,and the formed structure is single-phase austenite.Among them,the sample after solid solution at 1050℃ for 60min has both the best corrosion resistance and good mechanical properties.The corrosion rate drops significantly to 2.4960 g/(m2·h),the hardness drops to 169.82HV,and it yields.The strength dropped to 261.07MPa,the tensile strength dropped to 1234.56MPa,the elongation increased to 54.20%,the yield strength and tensile strength did not change much while the plasticity was improved.(2)Different electrochemical corrosion tests were carried out on the 304 stainless steel samples after solution treatment.In the pitting corrosion test,the corrosion potential Ecor of the samples were all negative.The samples after 1050℃·60min solution treatment The corrosion current density Icorr is the lowest,0.226μA/cm2,and the polarization resistance R2 is the largest,30544Ω,which is 12.5 times that of the original sample.In the intergranular corrosion test,the reactivation rate of the sample after solution treatment at 1050℃ for 60min Rr is the smallest,0.0141,verifying the best corrosion resistance.(3)Through numerical simulation of metal corrosion evolution of samples after solution treatment at 1050℃ for 60 minutes,based on the corrosion mechanism of 304 stainless steel and the cellular automata(CA)theory,the corrosion of stainless steel is obtained from the mesoscopic scale.The evolution of damage.The basic physical and chemical process of stainless steel corrosion in corrosive environment is analyzed,and the corresponding physical model is obtained.The corrosion system is discretized and combined into an ordered cell grid in the cellular automata space to establish a reasonable corrosion model.Considering the influence of different corrosion environments(solution concentration c,dissolution probability p),the corrosion damage morphology and corrosion rate of uniform corrosion and single pit corrosion on the metal surface with time step(Nt)are obtained,which makes up for the experimental research on metal corrosion.It can understand the influence of single factor and multiple factors on corrosion mechanism. |
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