本文選題：海洋 + 薄液��； 參考：《北京科技大學(xué)》2015年博士論文

【摘要】：對海洋資源的開發(fā)利用離不開高強鋼的發(fā)展及應(yīng)用,隨著對海洋資源,尤其是南海等高溫、高濕及高鹽霧的嚴酷環(huán)境海域開發(fā)的不斷深入,海洋工程用高強鋼需求量不斷增大,強度要求不斷升高,其應(yīng)力腐蝕(SCC)問題及風險逐漸增加,制約了海洋工程的發(fā)展。但目前對海洋環(huán)境尤其是海洋薄液環(huán)境下高強鋼的SCC行為研究較少,缺少深入的薄液環(huán)境下SCC敏感性和機理研究,對不同環(huán)境因素與scc敏感性的關(guān)系認識也不充分。 通過建立嚴酷海洋干濕交替環(huán)境下電化學(xué)及SCC的室內(nèi)模擬研究方法,對模擬海洋干濕交替環(huán)境中高強鋼的電化學(xué)腐蝕行為及scc關(guān)鍵影響因素、行為及機理進行研究。結(jié)果表明：模擬海洋干濕交替環(huán)境中,隨實驗周期延長,E690鋼陰極電流密度逐漸增加,陽極電流密度逐漸減小,耐腐蝕性能先減小后略有增大。pH值增大及干濕交替頻率的升高,有利于腐蝕產(chǎn)物的富集和致密化,導(dǎo)致銹層下均勻腐蝕減弱,局部陽極溶解作用加強,SCC敏感性升高；Cl-濃度增大,SCC敏感性先增加,后減少,再增加,NaCl濃度為3.5%時SCC敏感性相對最高。E690高強鋼SCC機理為陽極溶解和氫脆的混合控制機制,裂紋擴展模式為典型的穿晶擴展。 對E690高強鋼在模擬海洋全浸和薄液環(huán)境中的電化學(xué)和SCC機理的對比研究表明：薄液環(huán)境中E690鋼會發(fā)生明顯的SCC,薄液環(huán)境SCC敏感性高于海水環(huán)境的本質(zhì)原因為,薄液環(huán)境更有利于氧的擴散傳質(zhì)、促進了局部氧的去極化過程和腐蝕產(chǎn)物層的致密化,該過程與Cl-在腐蝕產(chǎn)物內(nèi)層的富集過程存在協(xié)同作用,加之應(yīng)力集中作用,促進了銹層下的局部陽極溶解和點蝕底部及裂紋尖端的析氫作用,促進了SCC萌生和擴展。 建立了模擬薄液環(huán)境中力學(xué)-電化學(xué)交互作用的原位測量裝置,對模擬海洋薄液環(huán)境下O2、環(huán)境充氫對E690鋼SCC行為的影響規(guī)律及作用機制進行分析。結(jié)果表明：O2的擴散傳質(zhì)對海洋薄液環(huán)境下的SCC起到關(guān)鍵作用,O2濃度升高,E690鋼的陽極和陰極電流密度逐漸升高,耐腐蝕性能逐漸降低；SCC敏感性先增大,后減小。導(dǎo)致模擬薄液環(huán)境中E690鋼SCC敏感性增大的臨界氧濃度值為21%,當?shù)陀谂R界值時,氧濃度升高,氧擴散速度加快,促進陰極和陽極反應(yīng)過程,加速了局部陽極溶解,當高于臨界值時,裂紋被腐蝕消耗,同時氧還原降低了氫的析出,減小了氫的破壞作用。隨預(yù)充氫電流密度升高,E690鋼的陽極和陰極電流密度逐漸升高,耐腐蝕性能逐漸降低；氫加速了E690鋼的陽極溶解作用,并與陽極溶解協(xié)同作用促進了E690鋼SCC。隨預(yù)充氫電流密度的增加,E690鋼的SCC機理由以陽極溶解為主的混合機制向以氫脆為主的機制轉(zhuǎn)變。 結(jié)合有限元分析方法,通過不同應(yīng)變量下模擬海洋薄液環(huán)境中的電化學(xué)及SCC試驗,研究了應(yīng)變對模擬海洋薄液環(huán)境中E690鋼電化學(xué)和SCC行為的影響,結(jié)果表明：應(yīng)變量增大,E690鋼陽極和陰極電流密度逐漸升高,耐腐蝕性能逐漸減小,塑性應(yīng)變區(qū)此現(xiàn)象尤為明顯。應(yīng)變量增大促進了E690鋼陽極溶解,提升了SCC敏感性。 模擬海洋干濕交替及薄液環(huán)境下,E690鋼腐蝕產(chǎn)物都以Fe304為主,伴有α-FeOOH、β-FeOOH, γ-FeOOH、γ-Fe2O3、α-Fe2O3等,試驗周期延長,有FeOCl、Fe2(OH)2Cl生成。銹層的結(jié)構(gòu)和種類,對SCC敏感性影響明顯,Cr促進了銹層的致密化,降低了均勻腐蝕,C1-富集在腐蝕產(chǎn)物內(nèi)層,促進了銹層下的局部腐蝕,有利于SCC發(fā)生和擴展。 驗證了模擬薄液環(huán)境中外加電位對抑制SCC的可能性,確定了模擬薄液環(huán)境中E690鋼SCC敏感性減小的最佳外加電位為-850mV (vs Ag/AgCl)。OCP電位升高或降低均能增大SCC敏感性,OCP-850mV為陽極溶解和氫脆混合機制,低于-850mV為氫脆機制。犧牲陽極保護方法減緩了E690鋼的腐蝕,降低了SCC敏感性。
[Abstract]:The development and application of marine resources can not be separated from the development and application of high strength steel. With the development of marine resources, especially the high temperature in the South China Sea, high humidity and high salt fog, the demand for high strength steel is increasing, the demand for strength is increasing, and the problem of stress corrosion (SCC) and the risk are increasing gradually. However, there are few studies on the SCC behavior of high strength steel in the marine environment, especially in the marine environment, and lack of the study on the sensitivity and mechanism of SCC in the deep liquid environment, and the understanding of the relationship between the different environmental factors and the sensitivity of the SCC is not fully understood.
The electrochemical corrosion behavior of high strength steel in the simulated ocean dry wet alternate environment and the key influencing factors, behavior and mechanism of SCC are studied by establishing the electrochemical and SCC simulation methods under the dry and wet alternate environment. The results show that in the simulated ocean dry and wet alternate environment, the cathodic electricity of E690 steel is prolonged with the experimental period. The current density gradually increases, the anode current density decreases gradually, the corrosion resistance decreases first and the.PH value increases and the dry and wet alternate frequency increases slightly, which is beneficial to the enrichment and densification of corrosion products, which leads to the weakening of the uniform corrosion under the rust layer, the enhancement of the local anodic dissolution and the increase of the sensitivity of the SCC, the increase of the Cl- concentration and the increase of the sensitivity of the SCC first. Adding, then decreasing and increasing, when the concentration of NaCl is 3.5%, the SCC mechanism of SCC sensitivity relative to the highest.E690 high strength steel is a mixed control mechanism of anodic dissolution and hydrogen embrittlement, and the crack propagation mode is a typical transgranular expansion.
The comparison of the electrochemical and SCC mechanism of E690 high strength steel in simulated marine full immersion and thin liquid environment shows that the E690 steel will have obvious SCC in the thin liquid environment, and the SCC sensitivity of the thin liquid environment is higher than that in the seawater environment. The thin liquid environment is more beneficial to the diffusion of oxygen and promotes the depolarization process and corrosion production of the local oxygen. The densification of the material layer has synergistic effect with the enrichment process of Cl- on the inner layer of corrosion products, and the stress concentration effect promotes the local anodic dissolution under the rust layer and the hydrogen evolution at the bottom of the pitting and crack tip, and promotes the initiation and expansion of the SCC.
An in-situ measurement device was established to simulate the interaction of mechanical and electrochemistry in the simulated thin liquid environment. The influence law and mechanism of the E690 steel SCC behavior under the environment of O2 in the simulated marine environment were analyzed. The results showed that the diffusion mass transfer of O2 played a key role in the SCC in the marine thin liquid environment, the concentration of O2 increased, and the anode of E690 steel was the anode. With the increasing of the current density and the cathode current density, the corrosion resistance gradually decreases, and the sensitivity of SCC increases first and then decreases. The critical oxygen concentration of the SCC sensitivity of E690 steel in the simulated thin liquid environment is 21%. The oxygen concentration increases, the oxygen diffusion speed is accelerated, the reaction process of the cathode and the anode is accelerated, and the local anodic dissolution is accelerated. When the critical value is higher than the critical value, the crack is consumed, and the oxygen reduction reduces the hydrogen precipitation and reduces the hydrogen damage. With the increase of the hydrogen current density, the anode and cathode current density of E690 steel increases and the corrosion resistance gradually decreases, and hydrogen accelerates the anode dissolution of E690 steel, and promotes the synergistic effect with the anodic dissolution. With the increase of pre charge hydrogen current density of E690 steel SCC., the SCC mechanism of E690 steel changed from the mixed mechanism of anodic dissolution to the mechanism of hydrogen embrittlement.
The effect of strain on the electrochemical and SCC behavior of E690 steel in simulated marine environment was studied by the finite element method and the electrochemical and SCC tests were used to simulate the marine thin liquid environment. The results showed that the anode and cathode current density of the E690 steel increased gradually, the corrosion resistance decreased and the plasticity decreased. This strain is particularly evident in the strain zone. The increase of strain rate promotes the anodic dissolution of E690 steel and enhances the sensitivity of SCC.
The corrosion products of E690 steel are mainly Fe304, including alpha -FeOOH, beta -FeOOH, gamma -FeOOH, gamma -FeOOH, gamma -Fe2O3, alpha -Fe2O3 and so on. The test period is prolonged, FeOCl and Fe2 (OH) 2Cl are generated. The structure and types of rust layer have an obvious influence on the sensitivity of the SCC sensitivity, which promotes the densification of the rust layer and reduces the uniform corrosion. The inner layer of corrosion product promotes local corrosion under rust layer, which is favorable for the occurrence and expansion of SCC.
The possibility of inhibiting the SCC by the applied potential of the simulated thin liquid environment is verified. The optimum applied potential of the SCC sensitivity of E690 steel in the simulated thin liquid environment is determined by the increase or decrease of the -850mV (vs Ag/AgCl).OCP potential, which can increase the sensitivity of SCC, OCP-850mV is the mechanism of anodic dissolution and hydrogen embrittlement, and the mechanism of hydrogen embrittlement is lower than -850mV. The polar protection method has slowed down the corrosion of E690 steel and reduced the sensitivity of SCC.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG172

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