提高高铬铁素体不锈钢耐腐蚀性能的研究

发布时间：2018-05-24 00:30

  本文选题：高铬铁素体不锈钢 + 腐蚀　； 参考：《兰州理工大学》2017年硕士论文

【摘要】：本文研究开发的高铬铁素体不锈钢主要应用在化工领域中的低温热回收系统,该合金要求在硫酸、磷酸及氯离子环境下具有优良的耐腐蚀性能。合金元素铜、钛铌、稀土和热处理工艺都影响材料的耐腐性能,本文主要考察合金元素和热处理工艺对高铬铁素体不锈钢腐蚀性能的影响,希望通过这些研究来拓展其应用。本文以高铬铁素体不锈钢为研究对象,采用真空中频感应冶炼工艺,熔炼了不同设计成分的高铬铁素体不锈钢,考察合金元素Cu、Ti+Nb、稀土和固溶处理对合金在H_2SO4、H_3PO_4、NaCl及FeCl_3溶液中耐蚀性能的影响。用浸泡实验测定合金的全面腐蚀速率;用电化学实验测定合金的极化曲线和阻抗谱,观察合金自腐蚀电流、自腐蚀电位、维钝电流和阻抗的变化;利用扫描电镜与莱卡光学显微镜分析了实验钢的组织、析出相变化及在晶界处的分布等特点;使用扫描电子显微镜观察浸泡腐蚀后合金表面腐蚀形貌,能谱仪分析腐蚀后的合金表面保护膜和组织析出相,观察合金元素的添加对钝化膜形貌和析出相及成分的影响。结果表明:在90%H_2SO_4溶液、40%H_3PO_4溶液和3.5%NaCl溶液中,随着铜含量的增大,试样的腐蚀速度先变小后变大,在合金铜含量为1%时,高铬铁素体不锈钢的耐全面腐蚀性能最优。当合金中铜含量小于1%时,随着铜含量的增加不锈钢表面胞状的钝化膜逐渐变厚变大、蚀坑数减少和面积变小。当合金中铜含量大于1.0%时,合金钝化膜出现缺陷,蚀坑数量变多,面积增大。在FeCl_3溶液中,随着氯离子含量增大不同成分的高铬铁素体不锈钢的平均腐蚀速度均增大,在相同浓度FeCl_3中,随着合金中铜的增加合金耐腐蚀性先增大后减小,在铜含量为1.5%时合金腐蚀速率最小。过量铜的添加使钢中过饱和的铜以富铜相ε-Cu相析出,他们多分布在晶界处又会降低合金的耐腐蚀性。在铜含量为1.0%的基础上,相继添加钛铌和稀土,在三种溶液中,合金钢耐腐蚀性均逐渐增强,对铜含量为1.0%含钛铌和稀土的高铬铁素体不锈钢在950℃、1000℃、1050℃和1100℃固溶处理。结果表明在三种溶液中,固溶温度在1050℃时,合金的耐腐蚀性能最强。实验研究发现向铁素体不锈钢中添加铜,析出物在晶界处的数量明显减少,并且析出相变小,铜的添加会使(Fe,Cr)_(23)C_6等析出相在晶间上的析出受到抑制。当引入钛铌和稀土后,钛铌可以生成很稳定的钛碳化物与铌碳化物从而抑制富铬析出相的生成,稀土的添加可以净化铁素体晶界,提高组织的均匀性,从而使其耐蚀性能显著增强。本文的研究结果对高铬铁素体不锈钢的理论研究和实际应用的发展具有很好的促进作用,为设计开发出耐蚀性能优异的高铬铁素体不锈钢提供了理论参考,为进一步挖掘高铬铁素体不锈钢在化工生产中应用也具有十分重要的现实意义。
[Abstract]:The high chromium ferrite stainless steel developed in this paper is mainly used in the low temperature heat recovery system in the chemical field. The alloy requires excellent corrosion resistance in sulfuric acid phosphoric acid and chloride ion environment. Alloy elements copper, titanium niobium, rare earth and heat treatment process all affect the corrosion resistance of the material. This paper mainly studies the effect of alloy elements and heat treatment process on the corrosion resistance of high chromium ferrite stainless steel, hoping to expand its application through these studies. In this paper, high chromium ferrite stainless steel with different design components was melted by vacuum medium frequency induction smelting process. The effects of the alloying elements Cu-Ti NB, rare earth and solid solution treatment on the corrosion resistance of the alloy in H _ S _ 2SO _ 4 / H _ 3PO _ 4 / FeCl_3 solution were investigated. The total corrosion rate of the alloy was measured by immersion test, the polarization curve and impedance spectrum of the alloy were measured by electrochemical experiment, the changes of corrosion current, corrosion potential, blunt current and impedance of the alloy were observed. The microstructure, precipitation phase change and distribution at grain boundary of the experimental steel were analyzed by scanning electron microscope and Leica optical microscope, and the corrosion morphology of the alloy after immersion corrosion was observed by scanning electron microscope. The surface protective film and precipitated phase of the alloy after corrosion were analyzed by EDS, and the effect of the addition of alloy elements on the morphology, precipitation phase and composition of the passivated film was observed. The results show that the corrosion rate of the sample decreases first and then increases with the increase of copper content in the 90%H_2SO_4 solution 40 H3PO4 and 3.5%NaCl solution. When the copper content of the alloy is 1%, the overall corrosion resistance of the high chromium ferrite stainless steel is the best. When the copper content in the alloy is less than 1, with the increase of copper content, the cellular passivation film on the stainless steel surface becomes thicker and larger, the number of pits decreases and the area becomes smaller. When the copper content in the alloy is greater than 1.0, defects appear in the passivation film, and the number of etch pits increases and the area increases. In FeCl_3 solution, the average corrosion rate of high chromium ferrite stainless steel with different composition increases with the increase of chloride ion content. In the same concentration of FeCl_3, the corrosion resistance of the alloy increases first and then decreases with the increase of copper content in the alloy. The corrosion rate of the alloy is the lowest when the copper content is 1.5. With the addition of excessive copper, the supersaturated copper in the steel precipitates in copper-rich 蔚 -Cu phase, and most of them distribute at grain boundaries and decrease the corrosion resistance of the alloy. On the basis of 1.0% copper content, titanium niobium and rare earth elements were added in succession. The corrosion resistance of alloy steel increased gradually in the three solutions. The high chromium ferrite stainless steel containing 1.0% copper, containing titanium, niobium and rare earth, was treated at 950 鈩，

本文编号：1926989