不锈钢凸焊接头组织与超声波检测研究

发布时间：2018-04-02 21:19

本文选题：不锈钢凸焊　切入点：微观组织　出处：《吉林大学》2017年硕士论文

【摘要】：随着工业的发展和工艺的优化,奥氏体不锈钢因其外观光泽度好,耐高温、耐腐蚀性能优良以及加工性能好等特点被广泛应用于各工业制造领域。不锈钢凸焊工艺作为一种比较特殊的电阻点焊工艺方法,具有焊接热量集中、工件变形小等优点,在管材、线材以及一些特殊结构的焊接上被应用。本文就医疗器械行业的一种较特殊的不锈钢凸焊结构焊接接头组织及其质量的无损检测方法进行研究,以解决相关焊接产品的质量控制问题。不锈钢凸焊接头的特殊结构导致凸焊接头质量的检测具有一定困难。目前,国内外工业生产中的不锈钢凸焊质量评价方法主要有两种,即焊接后的破坏性检测和焊接过程中的在线监测,但这两种方法均存在一定不足。超声波检测是一种灵敏度高、检测范围广、原理简单、操作方便、易实现现场检测的无损检测技术。因此,不锈钢凸焊的超声波检测研究对工业生产有重要的价值。本文对316L不锈钢封闭式中空隔条进行双面凸焊,一面直接焊接,另一面利用铜柱对电流与压力的传导作用进行焊接。通过对不锈钢电阻凸焊接头进行金相组织观察分析及力学性能检测,结合超声波扫描检测信号分析,研究不锈钢电阻凸焊接头连接特点及接头质量。不锈钢凸焊接头是一种塑性连接区域相对较大的特殊结构,其超声波检测分析主要有两个难点:一是通过超声波信号分析反映接头内部结构,尤其是塑性连接区域与熔核区域的区分;二是将超声波分析结果与实际微观组织及机械性能结合进行凸焊接头质量评估。本文从解决上述问题出发,对316L不锈钢凸焊接头进行金相观察、拉伸试验、显微硬度测试,并结合扫描电镜分析、能谱分析,研究凸焊接头结构连接状态及力学性能。研究发现,316L不锈钢凸焊接头金相组织中,熔核和母材分界清晰,有一定的热影响区,其热影响区存在晶粒长大现象,熔核区组织为不同状态的铁素体分布在奥氏体基体上,结晶方式为铁素体-奥氏体方式。拉伸试验与显微硬度测试表明两种316L不锈钢凸焊接头强度均超过母材强度。通过分析扫描电镜下断口形貌判断其断裂机制为微孔聚集型韧性断裂。通过能谱分析发现316L不锈钢凸焊接头具有良好的耐腐蚀性,其原因是Cr、Ni、Mn等合金元素的存在。对于未剥离的凸焊接头其断口显示无元素偏聚现象,也无有害相析出,结合力学性能测试,推断其仍满足凸焊工艺质量要求。本文以凸焊试样超声检测数据为基础,分析凸焊接头各个区域的A回波信号,研究超声A回波信号的时域特征及变化规律。时域分析结果能有效表达出凸焊各区域特征,但未能有效区分塑性连接区和熔核区。本文利用加窗滤波处理的FFT变换,研究发现经过变换的超声波回波幅值特征曲线能有效反映凸焊连接结构特点。试验结果与金相分析结果吻合良好,实现了不锈钢凸焊接头塑性连接区域与熔核的识别,满足不锈钢凸焊接头的检测需要。本文以金相组织分析、力学性能分析为基础,结合超声波C成像分析,通过连接状态阀值标定、等效能量计算,研究接头性能与超声波信号之间的联系,研究发现等效能量计算结果与实际力学性能呈负相关关系。同时本文比较了凸焊两面接头的质量差异,通过对比研究发现无铜柱凸焊接头质量要稍优于有铜柱凸焊接头的质量。
[Abstract]:With the development and optimization of process industry, austenitic stainless steel because of the appearance of gloss, high temperature resistance, corrosion resistance and excellent and good processing performance and is widely used in various industrial manufacturing field. The convex welding process of stainless steel as a kind of special resistance spot welding technology, welding with heat concentrated, small deformation of the workpiece etc. the advantages, in pipe, welding wire and some special structure has been used in this study. In this paper, a nondestructive testing method of special stainless steel welding structure of the medical device industry and the microstructure of the welding joint quality, quality control to solve the problem of welding products. The special structure of stainless steel welding joint quality lead to the detection of convex welding joint is very difficult. At present, there are mainly two kinds of stainless steel welding quality evaluation of domestic and foreign industrial production methods, namely after welding destructive inspection Measurement and monitoring of the welding process, but these two methods have some shortcomings. The ultrasonic detection is a kind of high sensitivity, wide detection range, simple principle, convenient operation, easy realization of nondestructive testing technology of field detection. Therefore, ultrasonic testing of stainless steel welding research has important value in industrial production. In this paper, 316L stainless steel closed hollow spacing strip for double-sided welding, welding on the other side by side directly, conduction current and pressure on copper welding. Detect the observation of microstructure analysis and mechanical properties of stainless steel by resistance projection welding head, combined with the analysis of ultrasonic detection signal of stainless steel resistance projection welding head connection characteristics and the joint quality of stainless steel. Welding connection is a plastic connecting area relatively special structure, the ultrasonic detection and analysis there are two main difficulties: one is through Ultrasonic signal analysis reflect the internal structure of joints, especially between plastic connection area and nugget area; two is the ultrasonic analysis results and the actual microstructure and mechanical properties of welding joint quality assessment. This paper from convex to solve the above problems, through metallographic observation, 316L stainless steel welding joint tensile test, microhardness test and scanning electron microscope analysis, energy spectrum analysis, and mechanical properties of welded joint of connecting convex structure. The study found that the microstructure of 316L stainless steel welding joint, nugget and base metal have clear boundaries, the heat affected zone of the grains in the heat affected zone growth phenomenon, organization the nugget zone for different states of ferrite distributed in the austenitic matrix, the crystallization mode for ferrite austenite. The tensile test and microhardness test showed that two kinds of 316L stainless steel welding joint strength are convex More than the strength of the base material. Through the analysis of SEM fractography determine its fracture mechanism is ductile fracture. The porous aggregate through spectrum analysis found that 316L stainless steel welded convex head has good corrosion resistance, the reason is that Cr, Ni, Mn and other alloy elements. For welding joint of the fracture shows without stripping no element segregation, no harmful phases, combining the mechanical performance test, the inference can still meet the requirements. The quality of projection welding process based on welding ultrasonic testing sample data, analysis of A echo signal bump joint of each area, time domain characteristics and variation of ultrasonic echo signals of A time domain analysis results. Can effectively express the regional characteristics of welding, but failed to effectively distinguish between the plastic zone and the nugget zone. The connection with the FFT transform window filter in this paper, the study found that after the ultrasonic echo amplitude transform characteristic curve The line can effectively reflect the welding connection structure features. The experimental results are in good agreement with the results of metallographic analysis, the identification of the connection area and the plastic head of nuclear fusion welding of stainless steel stainless steel welding convex, meet the detection needs. Based on the joint microstructure analysis, mechanical performance analysis as the foundation, combined with the analysis of ultrasonic C imaging, through the connection state threshold calibration, the equivalent energy calculation between joint performance and ultrasonic signal, study found that the equivalent energy calculation results with the actual mechanical performance was negatively correlated. At the same time, this paper compares the differences in the quality of welding joint surface two, through the comparative study found that welding quality was better than that of a convex welding joint quality without pillars convex pillars.

【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG441.7

【相似文献】