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双相不锈钢UNS S32205耐蚀性能及组织研究

发布时间:2018-04-06 21:25

  本文选题:双相不锈钢UNS 切入点:S32205 出处:《西南石油大学》2015年硕士论文


【摘要】:为降低天然气集输管线成本的同时保证其耐蚀性,本文选择了物美价廉的双相不锈钢UNS S32205作为研究对象,研究了其在相关环境中的耐蚀性。通过大量基础性实验完成了对其组织、力学性能和耐蚀性能的研究或评价,在此基础之上,一方面由差示扫描量热法技术研究造成其组织和性能劣化的原因——相变,另一方面,通过模拟实际气田工况环境的腐蚀全浸实验和扫描电化学显微镜技术研究其实际应用的终点——宏观耐蚀性和微观腐蚀行为。主要研究结论如下: 原材料母材两相呈带状组织;焊缝出现范性较差的魏氏体组织;焊缝Ni元素含量高于标准规定的2%以上,根焊位置出现夹杂和裂纹缺陷;HAZ铁素体含量约为29%,低于标准规定的下限30%。 UNS S32205在湿H2S-Cl-环境中能抵抗多种形式的环境开裂EC,但在含Cl-环境中不耐点蚀。三氯化铁点蚀实验显示母材腐蚀速率(288.36~618.26mg.dm-2,d-1),焊缝腐蚀速率(0.00~1.63mg-dm-2·d-1)。由GB/T17899对UNS S32205的应用可知,该标准并不适用UNS S32205点蚀电位的评价。UNS S32205在3.5wt.%NaCl溶液中的极化曲线显示其表面的析氢行为在某一电位区间(-0.5~-1.0V)受到抑制,这可以为其阴极保护提供指导。 DSC实验显示经固溶处理(1050~1080℃温度区间水淬)的原材料中仍然存在a’、χ和M7C3相等二次相,而降温过程中同时受保温温度和降温速率影响的一个二次相的吸热转变,在1095伍1235℃时最剧烈(保温温度1150℃1250℃,降温速率10-50K/min)。因此,所研究UNS S32205的原始热处理工艺(1050~1080℃温度区间水淬)是不当的,该温度区间UNS S32205有极大的二次相析出的可能。 SECM显示在实验条件下,UNS S32205奥氏体和铁素体晶内均发生点蚀,两相中的某一相作为大阴极析氢,而另一相不析氢,析氢相晶内点蚀电流峰值更强。析氢相与不析氢相上耐蚀合金元素富集区均可成为析氢位置。除单独存在的耐蚀合金元素贫化区(或结垢)对应的正向电流峰和富集区对应的负向电流峰,两相内均有成对(或成组)出现的毗邻正向电流峰和负向电流峰。推断阳极溶解位置可能对应两种结构:一是其对应耐蚀合金元素贫化区,二是其对应表面沉积的KC1型结垢,后者可能性更大一些。如果是前者,根据其几微米的间距判断,对应耐蚀合金元素富集区和贫化区是由调幅分解形成。对全部SECM空间图像所呈现电流峰的投影形貌做归纳总结,发现无论是菱形、多边形、锥形、“双子”形抑或是梭形的峰投影,其较小较尖锐的头均指向附近的另一个峰投影。
[Abstract]:In order to reduce the cost of natural gas gathering pipeline and ensure its corrosion resistance, UNS S32205, a duplex stainless steel with good quality and low price, was selected as the research object, and its corrosion resistance in the relevant environment was studied.The research and evaluation of its microstructure, mechanical properties and corrosion resistance have been carried out through a large number of basic experiments. On the one hand, on the one hand, the reason for the deterioration of the microstructure and properties is studied by differential scanning calorimetry (DSC).On the other hand, the macroscopical corrosion resistance and microscopic corrosion behavior of the gas field were studied by simulating the full-immersion corrosion test and scanning electrochemical microscope (SEM).The main findings are as follows:The two-phase microstructure of the raw material is zonal, the microstructure of the welds is poor, and the Ni content of the weld is more than 2% higher than the standard.The content of HAZ ferrite at the root welding position is about 29, which is 30 below the lower limit specified in the standard.UNS S32205 can resist many kinds of environmental cracking in wet H2S-Cl-environment, but it is not resistant to pitting corrosion in Cl-containing environment.The corrosion rate of base metal is 288.36 ~ 618.26 mg 路dm ~ (-2) / d ~ (-1) and the corrosion rate of weld is 0.003 mg ~ (-1) mg ~ (-2) ~ (-1) 路d ~ (-1) ~ (-1).According to the application of GB/T17899 to UNS S32205, this standard is not suitable for evaluating the pitting potential of UNS S32205. The polarization curve of UNS S32205 in 3.5wt.%NaCl solution shows that the hydrogen evolution behavior of UNS S32205 surface is inhibited in a potential range of -0.5 ~ 1.0V, which can provide guidance for cathodic protection.The DSC experiment shows that there is still a second phase, 蠂 and M7C3, in the raw materials quenched at 1050 ~ 1080 鈩,

本文编号:1718981

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