石油钻具用高氮奥氏体不锈钢腐蚀性能的研究

发布时间：2018-04-21 15:19

本文选题：奥氏体不锈钢 + 晶间腐蚀　；参考：《郑州大学》2017年硕士论文

【摘要】：石油工业在拉动经济增长和日常人民生活方面具有很重要的作用,在石油开采过程中,使用的无磁钻铤用奥氏体不锈钢材料因其具有良好的物理性能、力学性能和腐蚀性能而得到了广泛的应用。由于钻铤材料所处环境介质的腐蚀性和材料服役过程中的特殊性,因此研究奥氏体不锈钢的腐蚀行为对于正确评判不锈钢腐蚀敏感性及优化材料生产工艺具有重要的意义。电化学动电位再活化法(EPR)常用来评价奥氏体不锈钢的晶间腐蚀敏感性;尝试采用电化学阻抗技术(EIS)来检测奥氏体不锈钢的腐蚀性能,其测试结果在谱图中表现为阻抗弧的变化,可以提供较多界面电荷转移信息,为材料腐蚀性能的测试提供理论基础。本文采用电化学动电位再活化法、电化学阻抗分析、动电位极化法、Cu-H2SO4-CuSO4法、OM观察、SEM观察等研究了不同固溶处理和敏化处理对奥氏体不锈钢组织及腐蚀行为的影响,确定该不锈钢合适固溶处理工艺和晶间腐蚀的敏感温度;采用草酸浸蚀方法和电化学阻抗技术检测不锈钢晶间腐蚀发生和发展过程,初步建立晶间腐蚀的电化学等效电路,分析了等效电路参数与晶间腐蚀敏感性程度的相关性。研究结果表明:锻态高氮奥氏体不锈钢组织中存在大量的孪晶,组织中存在颗粒状Cr、V的氮化物。当试样在950-1100℃固溶处理30min后,显微组织为完全奥氏体组织,组织晶粒尺寸随固溶温度的升高而变大,晶粒也变得越来越均匀。经过相同敏化处理后,其再活化率R随着固溶处理温度升高而降低,在腐蚀液中试样的容抗弧半径逐渐增大。当固溶温度为1100℃时,阻抗谱的容抗弧半径最大,其耐腐蚀性能也最好。在10%草酸恒电流浸蚀试验中,随着浸蚀时间的增加,试样的腐蚀程度增加,浸蚀90s时试样表现出严重的晶界腐蚀,晶界有腐蚀沟,大部分晶粒被腐蚀沟包围。这说明浸蚀时间不同,晶间腐蚀的发展程度不同,晶间腐蚀的过程和浸蚀时间有一定的依赖关系。高氮奥氏体不锈钢经过相同固溶处理后,在700℃、800℃、900℃敏化温度处理6h;敏化温度为800℃时,试样的显微晶粒尺寸最小,晶粒最为均匀。800℃敏化处理试样EPR的再活化率最大,其腐蚀形貌与其他敏化温度相比较为严重;EIS曲线中,敏化温度800℃处理的试样在腐蚀介质中的容抗弧半径最小,其耐腐蚀性能较差。高氮奥氏体不锈钢在800℃敏化不同时间,随着敏化时间的增长,奥氏体晶粒尺寸逐渐增加,敏化12h时,孪晶消失,基体为全奥氏体组织;随着敏化时间的增加,晶界上析出物开始增加,同时晶粒内部开始析出类珠光体组织层片状的Cr2N,同时试样的再活化率随着敏化时间的延长而增加,试样的晶间腐蚀敏感性增加。通过改变浸泡时间、pH值、NaCl溶液浓度等介质条件,表明随着浸泡时间的增长和NaCl溶液浓度增加,不锈钢的耐点蚀敏感性降低,随着NaCl溶液pH值的增加,不锈钢的耐点蚀敏感性升高。通过研究不同固溶处理和敏化处理参数对高氮奥氏体不锈钢组织和腐蚀性能的影响,该Cr-Mn-N高氮奥氏体不锈钢合适的固溶温度为1100℃,腐蚀敏感温度为800℃,并且在一定范围内随着敏化时间的增加,其耐腐蚀性能降低,材料的力学性能下降,在材料服役过程中应避免在敏化温度范围内长期使用。
[Abstract]:The oil industry plays an important role in stimulating economic growth and daily life. In the process of oil mining, the austenitic stainless steel material used for non magnetic drill collars has been widely used because of its good physical properties, mechanical properties and corrosion properties. It is of great significance to study the corrosion behavior of austenitic stainless steel for evaluating the corrosion sensitivity of stainless steel and optimizing the material production process. Electrochemical potential reactivation (EPR) is used to evaluate the intergranular corrosion sensitivity of austenitic stainless steel. The electrochemical impedance technique (EI) is used. S) to detect the corrosion properties of austenitic stainless steel. The test results show the change of impedance arc in the spectrum, which can provide more interface charge transfer information and provide a theoretical basis for testing the corrosion properties of materials. In this paper, electrochemical potential reactivation, electrochemical impedance analysis, dynamic potential polarization, Cu-H2SO4-CuSO4 method, OM view are used in this paper. The effects of different solid solution treatment and sensitization treatment on the microstructure and corrosion behavior of austenitic stainless steel were investigated by SEM observation, and the appropriate solution treatment process and the sensitive temperature of intergranular corrosion were determined. The process of intercrystalline corrosion and the development process of stainless steel intergranular corrosion were detected by oxalic acid etching and electrochemical impedance technology. The correlation between the equivalent circuit parameters and the degree of intercrystalline corrosion sensitivity is analyzed. The results show that there are a large number of twins in the forged high nitrogen austenitic stainless steel structure, and the granular Cr, V nitrogen compounds exist in the tissue. The microstructure is the complete austenite group when the sample is treated with 30min at 950-1100 C. After the same sensitization treatment, the reactivation rate R decreases with the increase of the solution treatment temperature and the radius of the resistance arc of the specimen in the corrosion solution. When the solid solution temperature is 1100, the resistance arc radius of the impedance spectrum is the largest, and its corrosion resistance is resistant to corrosion. In the 10% oxalic acid constant current immersion test, the corrosion degree of the sample increases with the increase of the etching time. The specimen shows a serious grain boundary corrosion, the grain boundary has a corrosion ditch, and most of the grain is surrounded by corrosion ditch. This indicates that the etching time is different, the development degree of intergranular corrosion is different, the process of intergranular corrosion and the process of intercrystalline corrosion are explained. The etching time has a certain dependence. After the same solution treatment, the high nitrogen austenitic stainless steel is treated at 700 C, 800 C and 900 C sensitized temperature for 6h. When the sensitization temperature is 800 C, the microcrystalline grain size of the sample is the smallest, and the most homogeneous.800 C sensitized sample EPR has the greatest reactivation rate, and the corrosion morphology and other sensitization temperature phase In the EIS curve, the resistance arc radius of the sample treated at 800 centigrade temperature is the smallest and its corrosion resistance is poor. The austenite grain size of high nitrogen austenitic stainless steel increases with the sensitization time at 800 centigrade, and the twins disappears and the matrix is full austenite when sensitized 12h. With the increase of sensitization time, the precipitates on the grain boundary begin to increase, and the Cr2N of the lamellar pearlite like layer begins to be precipitated inside the grain. At the same time, the reactivation rate of the sample increases with the prolongation of the sensitization time, and the intergranular corrosion sensitivity of the sample increases. By changing the medium conditions such as the soaking time, the pH value and the concentration of NaCl solution, it is shown that the sample has the same medium. The pitting resistance of stainless steel decreased with the increase of soaking time and the increase of NaCl solution concentration. With the increase of pH value of NaCl solution, the resistance to pitting resistance of stainless steel increased. The effect of different solution treatment and sensitization parameters on Microstructure and corrosion properties of high nitrogen austenitic stainless steel was studied, and the Cr-Mn-N high nitrogen austenitic stainless steel was studied. The suitable solution temperature is 1100 C and the corrosion sensitive temperature is 800. And with the increase of the sensitization time in a certain range, the corrosion resistance of the material is reduced and the mechanical properties of the material decrease. The long-term use of the sensitized temperature should be avoided in the service process of the material.

【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE921.2;TG142.71

【参考文献】