两种不锈钢在模拟海洋环境中局部腐蚀行为的研究

发布时间：2018-03-04 01:15

本文选题：海洋环境　切入点：不锈钢　出处：《上海材料研究所》2017年硕士论文　论文类型：学位论文

【摘要】：国家海洋开发战略的实施需要海洋工程装备提供质量保证,而海洋工程的发展需要高性能材料作为支撑。本工作主要采用电化学方法研究了两种不锈钢材料,Z2CND18-12N奥氏体不锈钢和S32760双相不锈钢,在模拟海洋环境中的局部腐蚀行为,包括点腐蚀、缝隙腐蚀及应力腐蚀破裂(Stress Corrosion Cracking,SCC)。根据海洋环境条件,选取的模拟环境有按照ASTM标准制备的人造海水和不同温度和不同浓度的NaCl溶液,其中不同温度条件为3℃、30℃及60℃,NaCl溶液选取的浓度有接近海水浓度的3.5%NaCl溶液及模拟蒸发浓缩情况下的10%NaCl溶液。主要工作内容及结论如下:(1)研究了人造海水和3.5%NaCl溶液中,S32760双相不锈钢和Z2CND18-12N奥氏体不锈钢动电位阳极极化曲线行为,S32760在两种溶液中表现出相似的动电位极化行为,钝化区较宽,点蚀电位较高,在+1000mV(相对于饱和甘汞电极SCE,下同)以上;Z2CND18-12N奥氏体不锈钢在两种溶液中极化行为相近,均表现为较大的亚稳态波动后点蚀击穿。研究了两种材料分别在3℃、30℃及60℃的3.5%和10%NaCl溶液条件下的点蚀行为,S32760双相不锈钢表现出优秀的点蚀抗力,点蚀电位在+1000mV左右,但是在60℃时出现较明显的亚稳态波动;Z2CND18-12N奥氏体不锈钢在低温3℃下表现出与S32760接近的点蚀抗力,低温下耐点蚀性能优良,但是温度升高导致点蚀抗力显著下降,在30℃和60℃测试时,极化曲线上有明显的点蚀击穿,试样上出现明显的点蚀坑,耐点蚀性能不及S32760双相不锈钢。NaCl溶液浓度增大时点蚀电位下降。(2)采用动电位极化、临界点蚀温度(Critical Pitting Temperature,CPT)测试及腐蚀形貌观察方法对比性地研究了材料的点腐蚀行为,结果表明应采用多种方法综合评价较为合理。例如S32760双相不锈钢在60℃下,点蚀电位虽接近+1000mV,但是在扫描电镜下能观察到亚稳态点蚀形貌,此时已有点蚀倾向。CPT测试能较好地反映高耐蚀性材料的耐点蚀性能及其对温度的敏感性。(3)S32760双相不锈钢的缝隙腐蚀抗力明显高于Z2CND18-12N,S32760在3℃、30℃及60℃的3.5%和10%NaCl溶液条件下再钝化电位均高于+800mV。Z2CND18-12N不锈钢的缝隙腐蚀抗力较差,在低温3℃的两种NaCl溶液中及30℃3.5%NaCl溶液中未发生缝隙腐蚀,而在30℃浓度更高的10%NaCl溶液及温度升高到60℃时均对缝隙腐蚀敏感。与点蚀结果对比,Z2CND18-12N缝隙腐蚀抗力低于其点蚀抗力,溶液环境较为苛刻时,在较低电位下易发生缝隙腐蚀。(4)采用慢应变速率试验(SSRT)和电化学测控相结合的方法研究了电位对两种材料在30℃的3.5%NaCl溶液环境中SCC的影响。Z2CND18-12N奥氏体不锈钢在+100mV时发生阳极溶解,在+400m V及+600mV时阳极溶解显著,并伴有SCC裂纹出现,该SCC机理应该是阳极溶解;较正电位容易引发Z2CND18-12N发生点腐蚀及SCC。S32760双相不锈钢在较负电位时发生SCC,测得临界电位在-800mV与-900mV之间,在-900mV电位以及低于-900mV时均会发生SCC;电位为+600mV时,S32760不发生SCC;该材料发生SCC的机理应属于氢致开裂。
[Abstract]:The implementation of the national marine development strategy of ocean engineering equipment to provide quality assurance, and development of marine engineering high performance materials as support. This work mainly adopts the electrochemical method of two kinds of stainless steel, austenitic stainless steel Z2CND18-12N and S32760 dual phase stainless steel, the local corrosion behavior in simulated marine environment, including the point of corrosion. And the stress corrosion cracking of crevice corrosion (Stress Corrosion Cracking, SCC). According to the marine environmental conditions, simulation environment selection according to the ASTM standard preparation of artificial seawater and different temperature and different concentration of NaCl solution, the different temperature is 3 DEG, 30 DEG and 60 DEG C, the concentration of NaCl solution selected 10%NaCl 3.5%NaCl of a solution close to seawater concentration and simulated evaporation conditions. The main contents and conclusions are as follows: (1) study on the artificial seawater and 3.5% NaCl solution, S3 2760 duplex stainless steel and Z2CND18-12N austenitic stainless steel potentiodynamic anodic polarization curve, S32760 in two kinds of solution showed a similar polarization behavior, passivation region is wide, the pitting potential is higher in +1000mV (relative to the saturated calomel electrode SCE, the same below) above; Z2CND18-12N austenitic stainless steel in the vicinity of two kinds of solution of polarization behavior showed the fluctuation of metastable pitting breakdown. After the study of two kinds of materials respectively at 3 C, 30 C and 60 C pitting 3.5% and 10%NaCl solution under the condition of S32760 dual phase stainless steel exhibits excellent corrosion resistance and pitting potential of about +1000mV, but at 60 DEG C when metastable fluctuations obviously; Z2CND18-12N austenitic stainless steel at low temperature under 3 DEG C and corrosion resistance of S32760 showed a close, low temperature corrosion resistance is excellent, but the increasing temperature pitting resistance obviously under Drop in 30 degrees and 60 degrees test, there are obvious pitting breakdown on the polarization curves and corrosion pits appeared in the sample, the concentration of.NaCl solution increases when the decrease in pitting potential pitting resistance of duplex stainless steel is less than S32760. (2) by potentiodynamic polarization, critical pitting temperature (Critical Pitting, Temperature, CPT) test the corrosion morphology observation method and the comparative study of corrosion behavior of the materials. The results show that we should adopt various methods of comprehensive evaluation more reasonable. For example, S32760 duplex stainless steel under 60 degrees, although the pitting potential close to +1000mV, but under the scanning electron microscope to observe the metastable pitting morphology, while the pitting tendency of.CPT testing can be better the high corrosion resistance of materials corrosion resistance and sensitivity to temperature. (3) the crevice corrosion resistance of S32760 duplex stainless steel is higher than that of Z2CND18-12N and S32760 at 3 C, 30 C and 60 C 3.5 The crevice corrosion resistance and poor% 10%NaCl solution under the condition of repassivation potential was higher than that of +800mV.Z2CND18-12N stainless steel, corrosion occurred in two NaCl solution at low temperature 3 DEG C and 30 C in 3.5%NaCl solution, 10%NaCl solution and the temperature of 30 DEG C higher concentration increased to 60 DEG are sensitive to crevice corrosion. Contrast the results of Z2CND18-12N and pitting, crevice corrosion resistance than the pitting resistance, harsh environmental solution, prone to crevice corrosion at low potential. (4) using slow strain rate test (SSRT) method and electrochemical measurement on the combination of the two materials in the potential effects of 30 DEG 3.5%NaCl in solution SCC.Z2CND18-12N austenitic stainless steel anode dissolved in +100mV, +400m and V in +600mV and SCC with significant anodic dissolution, cracks, the mechanism of SCC should be relatively easy to anodic dissolution; positive lead Z2CND18-12N point corrosion and SCC.S32760 duplex stainless steel SCC occurs at a negative potential, the measured critical potential between -800mV and -900mV, SCC in -900mV and -900mV were lower than the potential will; the potential of +600mV, S32760 SCC SCC does not occur; mechanism of the material should belong to hydrogen induced cracking.

【学位授予单位】：上海材料研究所
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG178

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