【作者】 张振宁；

【导师】 陈俊梅；

【作者基本信息】 上海交通大学 ， 材料科学与工程， 2020， 硕士

【摘要】 奥氏体不锈钢(ASS)是指以奥氏体为基体相的不锈钢,具有良好的力学性能和耐腐蚀性能。S30403不锈钢是ASS中的一种。在某些特定环境下,S30403不锈钢的抗冲击性能和耐腐蚀性能是影响其寿命的重要因素。因此,本文以不同热处理工艺条件下的S30403不锈钢焊接接头为材料,通过试验研究了热处理对其低温冲击韧性、腐蚀性能的影响,并且依据试验数据,利用相场法对S30403不锈钢焊接接头的点蚀和电偶腐蚀进行了模拟。论文具体工作内容和结果如下:组织分析:通过光学显微镜(OM)、扫描电子显微镜(SEM)以及透射电镜(TEM)分别对S30403奥氏体不锈钢接头的宏观与微观组织进行观察,研究热处理工艺对接头显微组织的影响,结果表明:对于不同热处理工艺的接头,其组织的形貌、尺寸之间有所差异。热处理条件为590℃×1.5h时,其晶界附近会出现大量富铬碳化物。低温冲击韧性研究:通过低温冲击韧性试验研究了热处理工艺对S30403不锈钢焊缝低温冲击韧性的影响。结果表明:不同热处理工艺下的S30403奥氏体不锈钢焊缝的平均冲击值相对于焊态焊缝均有不同程度的下降,且下降程度随热处理温度的升高而增大。腐蚀性能研究:通过电化学腐蚀试验研究了热处理工艺对S30403不锈钢焊缝的电化学腐蚀性能的影响。结果表明:热处理使S30403不锈钢焊缝的腐蚀敏感性增大,且腐蚀敏感性随着热处理温度的提高而增大;热处理使S30403不锈钢焊缝腐蚀后的腐蚀速率减小,且腐蚀速率下降的程度随着热处理温度的提高而增大;热处理使S30403不锈钢焊缝的电偶腐蚀效应减小,且减小程度随着热处理温度的提高而增大。点蚀模拟:利用相场理论和相关试验数据研究了S30403不锈钢焊缝的点蚀。结果表明:在点蚀的活化控制阶段,点蚀深度与时间成正比;在点蚀的扩散控制阶段,点蚀深度与时间的1/2次方成正比;根据模拟结果计算出的阳极极化曲线在活化控制阶段与Tafel曲线拟合良好;相场引导方程中的界面动力学参数与界面移动速率成线性关系;界面动力学参数越大,则腐蚀速率越快,点蚀坑的深度也越大;二维点蚀扩展过程中的点蚀边界上每一个点的扩散距离在相同时刻都相等。电偶腐蚀模拟:利用相场理论、电偶腐蚀理论和相关试验数据研究了S30403不锈钢焊缝的电偶腐蚀。结果表明:相场引导方程与电偶腐蚀引导方程可以通过界面动力学参数相耦合;相场引导方程中的界面动力学参数与电偶腐蚀引导方程中的腐蚀电流密度相关;S30403奥氏体不锈钢中的阴极(奥氏体)在电偶腐蚀过程中会受到作为阳极(铁素体)的阴极保护作用;阳极的腐蚀程度不均匀,且腐蚀程度与电流密度的分布相关。点蚀和电偶腐蚀的模拟结果表明:相场方法对于理解腐蚀的过程很有帮助。更多还原

【Abstract】 Austenitic stainless steel(ASS)is a kind of stainless steel with austenite as matrix phase,which has good mechanical property and corrosion resistance.In some special environments,the impact resistance and corrosion resistance of S30403 stainless steel are important factors that can affect its life.Therefore,S30403 stainless steel welded joints under different heat treatment conditions are used as materials in this paper.The effect of heat treatment on its cryogenic impact toughness and corrosion property are studied through experiments.Based on the experiment data,the pitting corrosion and galvanic corrosion of S30403 stainless steel welded joints are simulated by phase field method.The specific works and results of this paper are as follows:(1)Microstructure analysis: The microstructure of S30403 austenitic stainless steel joints were observed by OM,SEM and TEM respectively.The effect of heat treatment process on the microstructure of the joints was studied.It can be concluded that the microstructure and size of the joints with different heat treatment processes are different.When the heat treatment temperature is very high,chromium rich carbide will appear near the grain boundary.(2)Study on cryogenic impact toughness: The effect of heat treatment process on the cryogenic impact toughness of S30403 stainless steel weld was studied by cryogenic impact toughness test.The results show that the average impact values of S30403 austenitic stainless steel welds under different heat treatment processes decreased in different degrees compared with welded weld,and the decrease degree increased with the increase of heat treatment temperature.(3)Study on Corrosion property: The effect of heat treatment process on the electrochemical corrosion property of S30403 stainless steel weld was studied by electrochemical corrosion test.It can be concluded that heat treatment makes the corrosion sensitivity of S30403 stainless steel weld increase,and the corrosion sensitivity increases with the increase of heat treatment temperature;Heat treatment makes the corrosion rate of S30403 stainless steel weld decrease,and the degree of reduction increases with the increase of heat treatment temperature;Heat treatment makes the galvanic corrosion effect of S30403 stainless steel weld decrease,and the degree of reduction increases with the increase of heat treatment temperature.(4)Pitting simulation: The pitting of S30403 stainless steel weld was studied by phase field theory and relevant test data.It can be verified that :In the activation-control stage of pitting,the depth of pitting is proportional to the time;In the diffusion-control stage,the depth of pitting is proportional to the 1 / 2 power of time;The anodic polarization curve calculated from the simulation results fits well with the Tafel curve in the activation control stage;The interface dynamic parameter is linear with the interface movement rate;The larger the interface dynamic parameter is,the faster the corrosion rate is,and the deeper the pit is;The diffusion distance of every point on the boundary of two-dimensional pitting is equal at the same time.(5)Galvanic corrosion simulation: The galvanic corrosion of S30403 stainless steel weld was studied by using phase field theory,galvanic corrosion theory and relevant test data.It can be verified that :The phase field guiding equation and galvanic corrosion guiding equation can be coupled through the interface dynamic parameter;The interface dynamic parameter in the phase field guiding equation is related to the corrosion current density in the galvanic corrosion guiding equation;The cathode(austenite)in S30403 austenitic stainless steel will be protected by anode(ferrite)during galvanic corrosion;The corrosion of anode is not uniform,it is related to the distribution of current density.The results show that the phase field is a valuable method to understanding corrosion process.更多还原