E690钢及焊接接头在含硫薄液环境中的应力腐蚀行为研究

发布时间：2018-03-26 15:21

本文选题：E690高强钢　切入点：焊接接头　出处：《北京科技大学》2015年博士论文

【摘要】：本文围绕E690钢及焊接接头在含硫海洋薄液环境中的应力腐蚀(SCC)行为和机理,根据真实焊接接头热影响区(HAZ)的组织制备了焊接热模拟组织,并采用恒应变U型弯试样和慢应变速率拉伸(SSRT)实验方法对比研究了E690钢母材以及三种典型HAZ热模拟组织在含硫海洋薄液环境中的SCC行为,对比分析了不同组织的SCC敏感性和开裂机理,并采用SSRT方法研究了硫含量和弹塑性预应变对E690钢在含硫海洋薄液环境中SCC行为的影响。最后通过SSRT实验方法,结合焊接接头不同微区组织的力学和电化学性能分析,研究了E690钢真实焊接接头在模拟SO2污染海洋大气薄液膜中的应力腐蚀行为与机理。结果表明,E690钢在含硫海洋薄液环境中的腐蚀产物由α-FeOOH. γ-FeOOH、β-FeOOH、Fe3O4、FeOCl组成,随着试验周期的延长,锈层中α-FeOOH的相对含量不断增加,同时Cr, Ni合金元素在内锈层发生富集,进而促进了锈层的致密化,导致锈层底部产生氯离子的浓聚,促进点蚀与应力腐蚀裂纹的萌生,因而E690钢在含硫海洋薄液环境中具有较大的应力腐蚀敏感性,应力腐蚀机理为阳极溶解和氢脆的混合机制,开裂模式为穿晶开裂。采用热处理方法制备的焊接热模拟组织可以较好的模拟焊接热影响区的典型组织,母材和焊接热模拟组织在模拟8O2污染海洋大气环境中均具有很高的SCC敏感性,母材、细晶、粗晶、两相组织在这种环境中的SCC敏感性依次增大；母材和粗晶组织的开裂模式为穿过板条贝氏体的穿晶开裂(TG-SCC),细晶和两相组织为沿着M-A岛与基体界面开裂的沿晶开裂模式(IG-SCC)。海洋大气中的S02可通过促进α-FeOOH的生成和Cr、Ni合金元素在内锈层中的富集而促进锈层的致密化,导致Cl-在锈层底部的浓聚和酸化,从而显著促进SCC裂纹的萌生与扩展,因而增加了其应力腐蚀敏感性：SO2对海洋薄液环境中的应力腐蚀具有双重作用：在腐蚀初期可促进SCC裂纹的萌生；后期又通过致密锈层的形成抑制基体的腐蚀和应力腐蚀开裂。应力应变可同时促进E690钢在海洋含硫环境中的阳极过程和阴极析氢反应,因而大大促进了腐蚀和应力腐蚀进程;E690钢在含硫薄液环境中一定弹塑性预变形条件下经过4d后即会产生SCC微裂纹的萌生,且SCC微裂纹沿着原始奥氏体晶界形核；在含硫薄液中不同弹塑性预变形状态下保持4d后,其SCC敏感性随着弹塑性预变形量的增加而升高,特别是在塑性预变形条件下暴露一定时间后,其SCC敏感性大大增加。E690钢焊接接头在含硫薄液环境中具有较高的SCC敏感性,应力腐蚀机制为阳极溶解和氢脆的混合机制。临界热影响区(ICHAZ)由于较低的强度、较负的腐蚀电位和较高的腐蚀电流密度以及M-A岛的存在,而成为焊接接头最薄弱的部位,ICHAZ区中的M-A岛通过应力集中效应、微电偶腐蚀效应以及氢脆效应三者的协同作用对应力腐蚀行为产生不利影响,共同促进SCC裂纹沿M-A岛与铁素体基体的界面开裂。
[Abstract]:This paper focuses on E690 steel and welded joint in the marine environment in the thin liquid sulfur stress corrosion cracking (SCC) behavior and mechanism, according to the joint of the heat affected zone (HAZ) of the real welding organization prepared by thermal simulation and microstructure of welding, using constant strain type U bend test and slow strain rate tensile (SSRT) test method a comparative study of the E690 steel base material and three kinds of typical HAZ thermal simulation SCC behavior in thin liquid sulfur marine environment, a comparative analysis of SCC sensitivity and cracking mechanism of different tissues, studied the effect of sulfur content and the elastoplastic pre strain of E690 steel in marine environment SCC thin liquid sulfur behavior and the the SSRT method. Finally, by the method of SSRT analysis of welding joints with different micro structure mechanical and electrochemical properties of E690 steel were studied real welded joint stress corrosion behavior and mechanism of SO2 in the simulation of marine pollution in the atmosphere of thin film. Show that the corrosion of E690 steel in marine environment in thin liquid sulfur by -FeOOH. gamma alpha -FeOOH, beta -FeOOH, Fe3O4, FeOCl, along with the extension of the test cycle, the relative content of rust layer of alpha -FeOOH increased, while Cr, Ni, the rust layer of alloy elements enriched, and then promote the densification of the rust layer the resulting rust layer at the bottom of the chloride ion concentration, and promote the pitting initiation of stress corrosion cracking of E690 steel, and has greater sensitivity to stress corrosion in the marine sulfur thin liquid environment, the mechanism of the stress corrosion mechanism for hybrid anodic dissolution and hydrogen embrittlement, the cracking mode is transgranular cracking. By heat treatment the preparation methods of the welding thermal simulation can better welding typical microstructure of heat affected zone and base metal and welding thermal simulation organization has the sensitivity of SCC is high in 8O2 simulation of marine pollution in the atmospheric environment of parent material, fine grain, coarse grain, two-phase The sensitivity of SCC organization in this environment increases; the cracking mode of base material and coarse grain structure for the lath bainite transgranular cracking (TG-SCC), fine grain and phase organization mode of M-A along the island and the interfacial crack intergranular cracking (IG-SCC). In the marine atmosphere can promote S02 generation and Cr alpha -FeOOH, Ni, enrichment of alloy elements in the rust layer and promote the densification of the rust layer, resulting in Cl- accumulation and acidification of the bottom of the rust layer, which improved SCC crack initiation and expansion, thus increasing the stress corrosion sensitivity: has the dual role of stress corrosion of SO2 on the sea the thin liquid in the environment: in the early stages of corrosion can promote SCC crack initiation; later by the rust layer on corrosion inhibition of substrate and stress corrosion cracking. Stress strain can also promote the anodic process of E690 steel in marine environment and Yin sulfur Polar hydrogen evolution reaction, and the corrosion and stress corrosion process greatly promote initiation of E690 steel in sulfur; thin liquid environment in elastoplastic pre deformation condition after 4D SCC will lead to micro cracks, and SCC micro cracks along the original austenite grain boundary nucleation; keep the 4D in different elastic thin liquid sulfur plastic pre deformation condition, the sensitivity of SCC increased with the increasing of elastoplastic pre deformation, especially to spend some time in the pre plastic deformation condition, the sensitivity of SCC greatly increased the welded joints of.E690 steel SCC has a high sensitivity in thin liquid sulfur environment, stress corrosion mechanism is mixed the mechanism of anodic dissolution and hydrogen embrittlement. The critical heat affected zone (ICHAZ) due to the low strength, low corrosion potential and high corrosion current density and the presence of a M-A Island, and become the weakest part of the welding joint in the ICHAZ area of M-A island. The synergistic effect of the three synergies between the micro couple corrosion effect and the hydrogen embrittlement effect has an adverse effect on the stress corrosion behavior, which promotes the SCC crack propagation along the M-A Island interface with ferrite substrate.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG172.9

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