激光熔凝核工程结构材料不锈钢的抗腐蚀性研究
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摘要
不锈钢是核工程结构中常用的材料。大量用于制作燃料元件包壳，工艺管道，蒸汽发生器，泵，阀等，由于工作条件极端苛刻，尽管不锈钢具有优异的抗腐蚀性，但仍会出现许多腐蚀问题，例如应力腐蚀、晶间腐蚀、隙缝腐蚀和点腐蚀等。
本文利用TJ-HL-T5000型CO_2激光器对1Crl8Ni9Ti奥氏体不锈钢基材和焊接接头进行激光熔凝处理，改善焊接接头抗腐蚀的均匀性，并提高不锈钢抗腐蚀性能。利用JSM-6360V扫描电镜、OXFORD能谱仪、OLYMPUS GX51金相显微镜等仪器对熔凝层进行微观检测，利用CHI660B电化学分析仪对试样进行抗腐蚀性试验，分析其内部组织结构、化学成份与抗腐蚀性能的关系，并对影响腐蚀效果的因素进行了综合研究。试验结果表明：
(1)激光熔凝层比不锈钢基体具有更强的耐蚀性，这和熔凝层的结构有关。1Crl8Ni9Ti奥氏体不锈钢基体组织为单相奥氏体等轴晶，经激光表面熔凝处理后，除组织形态发生了显著变化外，在表面的熔化区获得极细的等轴晶和超微晶。
(2)由于焊接自身的工艺特点，造成焊接接头的组织和性能不均匀，在核工程恶劣工况下，常出现晶间腐蚀和应力腐蚀。激光熔凝焊接接头中的薄弱环节-近焊缝区，可使近焊缝区的粗大组织细化，改善微观结构和成分偏析，从而提高抗蚀能力。采用加速腐蚀试验方法，对焊接试样施加拉应力，发现近焊缝区经激光熔凝后，应力腐蚀倾向减小。阳极极化曲线测试结果也表明，激光熔凝后不锈钢的抗晶间腐蚀能力有所提高。
本研究对不锈钢焊接接头采用激光熔凝改善其抗腐蚀性进行了有益尝试，为激光熔凝技术在更广阔的领域得到应用提供了实验依据。
Stainless steel is one of the common materials for engineering structure. It is used for shell of fuel component, process piping, steam generator, pumps and valves. Although stainless steel has the advantage of superior corrosion resistance, many corrosion problems ccur when it is used under bad condition, such as stress corrosion, intergranular corrosion, crevice corrosion and pitting. The paper deals with the influencing factors of corrosion effect and analyzes the relationship between its microstructure, chemical composition and corrosion resistance by the following means: Firstly, to treat 1Cr18Ni9Ti austenitic stainless steel base material and welding joint by laser melting using TJ-HL-T5000 CO_2 laser to improve its evenness and increase the corrosion resistance; Secondly, to examine the microstructure of melting layer by such instruments as SEM of JSM-6360V, EDX of OXFORD, and OM of OLYMPUS GX51. Thirdly, to test corrosion resistance of the sample by an electrochemistry analytical instrument of CHI660B. Research results show:
(1) The laser melting layers have the better ability of corrosion resistance than the stainless steel substrates relating to their organization. The organization of 1Cr18Ni9Ti austenitic stainless steel substrates is single-phase austenitic cubic crystal. After processed by the laser surface melting the organization of stainless steel substrates change greatly, especially the cubic crystal and super-micro crystalline appear on the surface of the reeking area.
(2) On account of the characteristic of welding technology the organization and property of welding joint is not homogeneous. Under bad condition of nuclear engineering, stress corrosion and intergranular corrosion appear in the welding area. The area close to the welding line is the weaker part of the welding joint, laser melting can improve its microstructure and make it finer. So the ability of corrosion resistance of the area close to the welding line improves. Adopting the method of accelerating corrosion experiments by applying tensile stress on the specimen, the tendency of stress corrosion of the area declines. The anodic polarization curves shows that the ability of intergranular corrosion resistance of the stainless steel is stronger after the process of laser melting.
The research makes a profitable attempt to improve the corrosion resistance of stainless steel welding joint by laser melting and lays foundation for applying laser melting technology in a much wider field.
本文利用TJ-HL-T5000型CO_2激光器对1Crl8Ni9Ti奥氏体不锈钢基材和焊接接头进行激光熔凝处理，改善焊接接头抗腐蚀的均匀性，并提高不锈钢抗腐蚀性能。利用JSM-6360V扫描电镜、OXFORD能谱仪、OLYMPUS GX51金相显微镜等仪器对熔凝层进行微观检测，利用CHI660B电化学分析仪对试样进行抗腐蚀性试验，分析其内部组织结构、化学成份与抗腐蚀性能的关系，并对影响腐蚀效果的因素进行了综合研究。试验结果表明：
(1)激光熔凝层比不锈钢基体具有更强的耐蚀性，这和熔凝层的结构有关。1Crl8Ni9Ti奥氏体不锈钢基体组织为单相奥氏体等轴晶，经激光表面熔凝处理后，除组织形态发生了显著变化外，在表面的熔化区获得极细的等轴晶和超微晶。
(2)由于焊接自身的工艺特点，造成焊接接头的组织和性能不均匀，在核工程恶劣工况下，常出现晶间腐蚀和应力腐蚀。激光熔凝焊接接头中的薄弱环节-近焊缝区，可使近焊缝区的粗大组织细化，改善微观结构和成分偏析，从而提高抗蚀能力。采用加速腐蚀试验方法，对焊接试样施加拉应力，发现近焊缝区经激光熔凝后，应力腐蚀倾向减小。阳极极化曲线测试结果也表明，激光熔凝后不锈钢的抗晶间腐蚀能力有所提高。
本研究对不锈钢焊接接头采用激光熔凝改善其抗腐蚀性进行了有益尝试，为激光熔凝技术在更广阔的领域得到应用提供了实验依据。
Stainless steel is one of the common materials for engineering structure. It is used for shell of fuel component, process piping, steam generator, pumps and valves. Although stainless steel has the advantage of superior corrosion resistance, many corrosion problems ccur when it is used under bad condition, such as stress corrosion, intergranular corrosion, crevice corrosion and pitting. The paper deals with the influencing factors of corrosion effect and analyzes the relationship between its microstructure, chemical composition and corrosion resistance by the following means: Firstly, to treat 1Cr18Ni9Ti austenitic stainless steel base material and welding joint by laser melting using TJ-HL-T5000 CO_2 laser to improve its evenness and increase the corrosion resistance; Secondly, to examine the microstructure of melting layer by such instruments as SEM of JSM-6360V, EDX of OXFORD, and OM of OLYMPUS GX51. Thirdly, to test corrosion resistance of the sample by an electrochemistry analytical instrument of CHI660B. Research results show:
(1) The laser melting layers have the better ability of corrosion resistance than the stainless steel substrates relating to their organization. The organization of 1Cr18Ni9Ti austenitic stainless steel substrates is single-phase austenitic cubic crystal. After processed by the laser surface melting the organization of stainless steel substrates change greatly, especially the cubic crystal and super-micro crystalline appear on the surface of the reeking area.
(2) On account of the characteristic of welding technology the organization and property of welding joint is not homogeneous. Under bad condition of nuclear engineering, stress corrosion and intergranular corrosion appear in the welding area. The area close to the welding line is the weaker part of the welding joint, laser melting can improve its microstructure and make it finer. So the ability of corrosion resistance of the area close to the welding line improves. Adopting the method of accelerating corrosion experiments by applying tensile stress on the specimen, the tendency of stress corrosion of the area declines. The anodic polarization curves shows that the ability of intergranular corrosion resistance of the stainless steel is stronger after the process of laser melting.
The research makes a profitable attempt to improve the corrosion resistance of stainless steel welding joint by laser melting and lays foundation for applying laser melting technology in a much wider field.
引文
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[21] 张友寿，王巍等．不锈钢激光快速熔凝处理与表面合金化[J]．光电子．激光，2002，1
[22] Sun Z, et al. Effect of laser surface remelting on the corrosion behavior of commercially pure titanium sheet[J]. Materials Science and Engineering A, 2003, 345(1-2): 293-300.
[23] Perez del Pino A, et al. Oxidation of titanium through Nd:YAG laserirradiation[J]. Applied Surface Science, 2002, 197-198: 887-890.
[24] Lavisse L, et al. Early stage of the laser-induced oxidation of titanium substrates[J]. Applied Surface Science, 2002, 186(1-4): 150-155.
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[26] Mudali U K, Dayal R K, Gnamamoorthy J B, Kanetkar S M, Ogale S B. Mater Trans JIM, 1991; 33: 845
[27] 蔡伟平．马氏体不锈钢表面激光熔化处理后的组织特征[J]．武汉钢铁学院学报，1994．9
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