脉冲TIG堆焊Inconel625工艺及堆焊层组织性能研究

发布时间：2018-07-09 10:41

本文选题：堆焊 + Inconel　；参考：《西南石油大学》2017年博士论文

【摘要】：随着天然气工业的不断发展,高含H2S/CO2酸性气田逐渐步入全面开发阶段,在这类气田开采过程中,若选材或防腐工艺不当,腐蚀介质会造成金属材料的严重腐蚀。Inconel 625合金具有良好的综合性能,其耐腐蚀性能满足API 6A、NACE MR0175/ISO 15156等标准所推荐的用于酸性气田恶劣腐蚀环境的材料要求。然而Inconel 625合金的价格约为普通抗硫钢的10-15倍,材料成本严重地制约了其单独大量使用。因此开展Inconel 625合金的堆焊表面改性研究,具有重要的理论意义和工程应用前景。本文针对热丝脉冲 TIG(Hot-wire pulsed tungsten inert gas,HPTIG)堆焊 Inconel 625合金所涉及的焊缝成形质量控制、微观组织与残余应力调控、微观组织与耐腐蚀性能的关联性以及焊后热处理工艺等关键问题进行了系统地研究,并提出了合理的堆焊工艺和热处理工艺。研究所得的焊件具有较好的力学性能,而且堆焊层具有良好的耐H2S/CO2腐蚀性能。针对HPTIG工艺焊缝成形质量不易控制的问题,采用中心复合试验设计(Central composite design,CCD)法进行堆焊试验,结合响应面法(Response surface method,RSM)建立了工艺参数与焊缝成形质量之间的回归模型,并对模型进行了显著性检验、拟合度检验、残差分析和试验验证。结果表明:所建立的模型能够反映工艺参数与焊缝成形质量之间的关系,能够用于焊缝成形质量的预测。同时揭示了工艺参数对焊缝成形质量的影响规律,主效应对焊缝高度的影响大小依次为:VsδfIpIb,主效应对焊缝宽度和稀释率的影响大小依次为:δVsfIpIb;交互效应对焊缝高度的影响大小依次为:IpδIbδIpI邱;对于稀释率,Ibδ的交互影响较大,而Ipδ的交互影响则较弱。基于所建立的回归模型,以焊缝的高度、宽度和稀释率为优化目标,对工艺参数进行了优化,优化后焊缝的稀释率明显降低。采用优化所得的工艺参数进行多道焊试验,以建立焊件的几何模型;在此基础上以Abaqus软件为平台,结合Fortran和Python编程软件,采用生死单元法模拟焊缝单元的逐步填充,建立了堆焊温度场和应力场的三维耦合有限元模型,并对模型进行了有效性验证。结果表明:所建立的模型是可靠的,能够准确地反映堆焊温度和应力的分布与变化。为了改善堆焊层的微观组织,并降低焊件的残余应力,分析了焊缝间隔时间和堆焊路径对冷却速率、温度梯度和残余应力的影响规律。研究表明:合理地控制间隔时间和优选堆焊路径,能够提高堆焊层微观组织的均匀性,并降低残余应力。根据优化得到的工艺参数和仿真得到的堆焊方案,进行多焊缝单层和两层堆焊。采用扫描电子显微镜(Scanning electron microscope,SEM)、X 射线衍射(X-ray diffraction,XRD)和能谱分析(Energy dispersive spectrometer,EDS)等方法研究了所得堆焊层的微观组织演变和析出相分布规律,结果表明:自熔合界面至堆焊层表面的微观组织演变依次为平面晶、胞状晶、柱状晶和等轴晶;堆焊层主要由γ-Ni固溶体、分布在晶间的Laves相和MC相组成,而且晶体形态对Laves相的分布特征有显著影响。利用电化学阻抗谱(Electrochemical impedance spectroscopy,EIS)、动电位扫描技术和浸泡试验,并结合腐蚀微观形貌,研究了堆焊层的耐点蚀性能和耐晶间腐蚀性能。结果表明:单层Inconel 625堆焊层受母材稀释的影响,其耐腐蚀性能明显低于第二层堆焊层;由于第二层堆焊层的微观组织与成分存在梯度,其不同厚度处的耐点蚀性能和耐晶间腐蚀性能存在差异,大的晶粒尺寸、少的析出相对堆焊层的耐点蚀性能和耐晶间腐蚀有利。为了改善堆焊层的耐腐蚀性能和焊件的力学性能,在考虑母材与堆焊层异种材料的基础上,研究了相同保温时间条件下,热处理温度对堆焊层微观组织、耐腐蚀性能和力学性能的影响规律。结果表明:经750℃热处理后,有部分Laves发生了溶解,并在晶界处析出了 δ相;随着热处理温度的升高,δ相含量增多、尺寸增大。采用电化学测试、浸泡试验和挂片试验,结合腐蚀微观形貌与腐蚀产物,揭示了热处理温度对耐腐蚀性能的影响规律,即随着δ相的增多,堆焊层的耐晶间腐蚀性能和耐H2S/CO2腐蚀性能显著恶化。结合拉伸试验和断口形貌,揭示了热处理温度对堆焊层力学性能的影响规律。发现少量的δ相对堆焊层的屈服强度和抗拉强度有利,然而随着δ相的增多,堆焊层的屈服强度和抗拉强度明显降低。综合热处理对耐腐蚀性能、力学性能的影响,得到了合理的热处理工艺。
[Abstract]:With the continuous development of the natural gas industry, the high H2S/CO2 acid gas field has gradually entered the comprehensive development stage. In the process of exploitation of this kind of gas field, if the material selection or the anticorrosion technology is improper, the corrosive medium will cause serious corrosion of metal material to.Inconel 625 alloy, and its corrosion resistance meets API 6A, NACE MR0175/ISO 151. The material requirements for the harsh corrosive environment of acid gas field recommended by the 56 standards are required. However, the price of Inconel 625 alloy is about 10-15 times as high as that of ordinary sulfur resistant steel. The material cost seriously restricts its use alone. Therefore, it is of great theoretical significance and engineering application prospects to carry out the study of the surface modification of the surfacing surface of Inconel 625 alloy. In this paper, the quality control of weld forming, microstructure and residual stress control, the correlation between microstructure and corrosion resistance, and heat treatment process after welding are systematically studied for the welding of Inconel 625 alloy by hot wire pulse TIG (Hot-wire pulsed tungsten inert gas, HPTIG), and a reasonable pile is put forward. Welding and heat treatment process. The welded parts obtained have good mechanical properties, and the surfacing layer has good H2S/CO2 corrosion resistance. In view of the problem that the weld quality of the HPTIG process is not easy to control, the central composite test design (Central composite design, CCD) is used to carry out the surfacing test, and the response surface method (Response Su) is combined with the response surface method (Response Su). Rface method, RSM) established the regression model between the process parameters and the weld forming quality. The model was tested by the significance test, the fitting degree test, the residual analysis and the test verification. The results show that the model can reflect the relationship between the process parameters and the weld forming quality, and can be used for the prediction of the weld forming quality. The influence of process parameters on weld forming quality is revealed. The main effect of main effect on weld height is Vs [delta] fIpIb. The influence size of main effect on weld width and dilution rate is: Delta VsfIpIb, and the influence of interaction effect on weld height is Ip Delta Ib Delta IpI Qiu, and the interaction effect of Ib Delta on dilution ratio is larger. And the interaction of Ip delta is weak. Based on the established regression model, the optimization of the weld seam height, width and dilution rate is optimized and the dilution rate of the weld is reduced obviously. The multi pass welding test is carried out with the optimized process parameters to establish the geometric model of the weld. On this basis, Abaqus The software is used as a platform, combining the Fortran and Python programming software, using the life and death element method to simulate the gradual filling of the weld unit. The three-dimensional coupling finite element model of the temperature field and stress field of the surfacing welding is established, and the validity of the model is verified. The results show that the model is reliable and can accurately reflect the temperature and stress of the welding. In order to improve the microstructure of the surfacing layer and reduce the residual stress of the weld, the influence of the interval time of the weld and the welding path on the cooling rate, the temperature gradient and the residual stress are analyzed. The research shows that the reasonable control of the interval time and the optimum welding path can improve the uniformity of the microstructure of the surfacing layer and reduce the microstructure. Low residual stress. On the basis of the optimized process parameters and the simulated welding scheme, multi weld single layer and two layer surfacing are carried out. Scanning electron microscope (Scanning electron microscope, SEM), X ray diffraction (X-ray diffraction, XRD) and energy spectrum analysis (Energy dispersive spectrometer, EDS) are used to study the surfacing welding. The microstructure evolution and precipitation phase distribution of the layer show that the microstructure evolution of the self fusion interface to the surface of the surfacing layer is the plane crystal, the cell crystal, the columnar crystal and the equiaxed crystal, and the surfacing layer mainly consists of the solid solution of gamma -Ni, which is distributed in the intercrystalline Laves phase and the MC phase, and the crystal morphology has a significant shadow on the distribution of the Laves phase. The corrosion resistance and intergranular corrosion resistance of the surfacing layer were studied by electrochemical impedance spectroscopy (Electrochemical impedance spectroscopy, EIS), dynamic potential scanning and immersion test, and the corrosion micromorphology was combined. The results showed that the corrosion resistance of the monolayer Inconel 625 surfacing layer was significantly lower than second. Layer surfacing layer; due to the gradient of microstructure and composition of the second layer surfacing layer, the corrosion resistance and intergranular corrosion resistance at different thickness are different, the large grain size, less precipitation relative overlay resistance and intergranular corrosion resistance are favorable. In order to improve the corrosion resistance and mechanical properties of the welding parts, the mechanical properties of the surfacing layer are improved. The influence of heat treatment temperature on the microstructure, corrosion resistance and mechanical properties of the surfacing layer under the same holding time was studied on the basis of the dissimilar material of the parent material and the surfacing layer. The results showed that after heat treatment at 750 C, some Laves was dissolved, and the delta phase was precipitated at the grain boundary, with the rise of heat treatment temperature. The effect of heat treatment temperature on corrosion resistance is revealed by electrochemical testing, immersion test and hanging test. The effect of heat treatment temperature on corrosion resistance is revealed. That is, with the increase of the delta phase, the intergranular corrosion resistance and H2S/CO2 corrosion resistance of the surfacing layer are significantly worse. The fracture morphology reveals the influence of the heat treatment temperature on the mechanical properties of the surfacing layer. It is found that the yield strength and tensile strength of a small amount of delta are favorable, but with the increase of the delta phase, the yield strength and tensile strength of the surfacing layer are obviously reduced. The effect of comprehensive heat treatment on corrosion resistance and mechanical properties is reasonable. Heat treatment process.
【学位授予单位】：西南石油大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG444.74

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