| With characteristics of strong heat resistance and corrosion resistance,316 stainless steel is widely used in petroleum and chemical industry, transportation, construction, national defense security and other fields. As a way of stainless steel processing, welding is one of the main methods to joint 316 stainless steel. After welding, unevenly distributed residual stress will be generated inside of 316 stainless steel. Corrosion will be introduced by the residual stress in electrolyte solution, making a serious threat to the safety of life and property for people. So, it’s of great significance to explore the relationship between welding residual stress and corrosion property of 316 stainless steel.Using argon-arc welding as a method to weld 316 stainless steel has been introduced in this thesis. In this welding process, welding residual stress will be generated on 316 stainless steel, then blind-hole method has been used to test residual stress on stainless steel. Traditional electrochemical measurements and local electrochemical measurements were combined to study respectively the influence of welding residual stress on corrosion of 316 stainless steel, in hope of providing a method on predicting corrosion in welded sample.The main work is as follows:1. Generation and measurement of welding residual stress(1) Using argon-arc welding method to weld 316 stainless steel in order to induce welding residual stress exerted on stainless steel. Then various 316 stainless steel electrodes has been received though wire-electrode cutting.(2) According to blind hole method principle, the residual stress of three different regions on welded 316 stainless steel has been measured and calculated. The reasons why residual stress generated on each region has been analyzed.2. Traditional electrochemical study on welded 316 stainless steelOpen circuit potential-time curves and potentiodynamic polarization curves tests are taken on heat-affected zone and parent material of 316 stainless steel in NaCl solution with different concentrations. This thesis discussed effect of concentration of chloride ions on corrosion-electrochemistry characteristics including open circuit potential, corrosion current and corrosion potential. It also compared corrosion behavior of heat-affected zone and parent material in the same electrolyte concentration.3. Local electrochemical study of corrosion characteristics of welded 316 stainless steel(1) Cyclic voltammetric experiments were performed to test the property of Pt tip. After that, the polarization potential applied on the tip during the measurement of the approach curve and area scan is determined in terms of the potential range corresponding to the diffusion limited current plateau.(2) Based on a proportionality between diffusion limited current and the concentration of Fe2+ ions, the concentration of Fe2+ ions arising from the dissolution of 316 stainless steel specimen in 0.5 M NaCl solution can be calculated by approach curve of the SECM-tip. The result demonstrates that 316 stainless steel has high corrosion resistance.(3) In the sample generation-tip collection mode of SECM measurements, three-dimensional images of probe current were obtained over the sample with different kinds of welding residual stress in NaCl solution. The effect of welding residual stress on local corrosion with different concentrations of NaCl solution and polarization potentials of sample has been investigated respectively.(4) In NaCl solution containing redox mediator Fe(CN)63-, the difference of local corrosion caused by unevenly stress distributing on welded 316 stainless steel has been characterized. This thesis investigated and analyzed the influence of concentration of Cl- ion as well as welding residual stress on corrosion sensitivity of the 316 stainless steel. |
PDF Full Text Request