Study On Heat Treatment Process On The Organization And Performance Of 304 Stainless Steel In Pipes

304 stainless, as a type of 18-8 austenitic steel which is widely used in medical appliances, ship-building, food industry and pipes of petroleum chemical plant steel, has good corrosion resistance, heat resistance, plasticity and forming performance. But due to the improper hot and cold processing technology of 304 stainless steel as well as chloride ions that widespread exist in the environment of application, the corrosion resistance of 304 stainless steel decreases apparently, even result in the failure of pipeline made of 304 stainless steel, serious safety accidents and economic losses. Therefore, to research and to improve the corrosion resistance of 304 stainless steel have the vital engineering significance. At present, the ways to improve the corrosion resistance of 304 stainless steel are alloy process and heat treatment etc. There into, improving the corrosion resistance of 304 stainless steel through heat treatment has some characteristics such as simple equipment, low cost and time-consuming etc. The improper use of solution treatment process will bring about some terrible results, such as no alloy elements into matrix or low alloy contests of matrix organization, which thereby reduce the hardness and corrosion resistance. Therefore, through the optimized study of the solid solution treatment process does the optimized process of 304 stainless steel have vital significance to its organization, corrosion resistance, hardness.This paper took 304 stainless steel for pipes as research object on the basis of document study, and comprehensively thought over some factors such as simplicity, easy operation and low cost etc. of 304 stainless steel processing equipment. Solid solution heat treatment was chosen as the technical means to improve the corrosion resistance of 304 stainless steel, and 304 stainless steel was researched by the ways of the sulfuric acid solution corrosion test and electrochemical corrosion test of sodium chloride solution as well as optimized research of solid solution temperature and time. Kinds of detection methods were put into use such as optical microscopy, SEM, EDS, XRD, weight-loss method, analysis of polarization curve and hardness analysis etc. to analyze the influences of solid solution temperature and time to 304 stainless steel's microstructure, corrosion resistance and hardness. Conclusions on 304 stainless steel can be mainly obtained from the paper:(1) 304 stainless steel went through solution treatment of 990°C, 1020°C, 1050°C, 1080°C, 1110°C, 1140°C. The ferrite and alloy carbide in the microstructure of the original structure above the solution temperature can be fully dissolved into the single austenite phase. Under 55 min solution treatment in 990°C can specimen acquire the optimum corrosion resistance and hardness, whose corrosion rate decreased from 0.0263g/d of No B0 to 0.0045g/d and the hardness increased from 69.3HV to 160.4HV. No B6 under 75 min solution treatment in 1020°C can acquire the optimum corrosion resistance and hardness, whose corrosion rate decreased from 0.0263g/d of No B0 to 0.0023g/d and the hardness increased from 63.9HV to 152.5HV. No B8 under 55 min solution treatment in 1050°C can acquire the optimum corrosion resistance and hardness, whose corrosion rate decreased from 0.0263g/d of No B0 to 0.0020g/d and the hardness increased from 63.2HV to 267.5HV. No B11 under 55 min solution treatment in 1080°C can acquire the optimum corrosion resistance and hardness, whose corrosion rate decreased from 0.0263g/d of No B0 to 0.0038g/d and the hardness increased from 110.2HV to 152.9HV. No B14 under 55 min solution treatment in 1110°C can acquire the optimum corrosion resistance and hardness, whose corrosion rate decreased from 0.0263g/d of No B0 to 0.0056g/d and the hardness increased from 90.7HV to 114.2HV. No B16 under 35 min solution treatment in 1140°C can acquire the optimum corrosion resistance and hardness, whose corrosion rate decreased from 0.0263g/d of No B0 to 0.0053g/d and the hardness increased from 101.3HV to 170.7HV.(2) The electrochemical corrosion medium was NaCl whose concentration was 1.5%, 3.5%(the average concentration of chloride ions of seawater is 3.5%), 5.5%. Values of the corrosion potential Ecorr were all negative. The specimen's corrosion current Icorr under 35 min solution treatment in 1140°C was lowest, and the corrosion resistance was best.(3) Through the microstructure, hardness, corrosion rate and analysis research of polarization curve, the optimum heat treatment process of 304 stainless steel was 1140°C · 35 min. Therefore, 304 stainless steel had good organization, hardness and corrosion resistance through the above solution treatment. The study to improve the organization, hardness and corrosion resistance of 304 stainless steel has a certain reference value.