高强不锈钢热丝TIG焊工艺及温度场数值模拟

发布时间：2018-08-03 08:31

【摘要】：热丝TIG焊是应用较为广泛的高效焊接方法,S-06强度高、韧性好、耐腐蚀的特点,多应用于航空航天领域。针对某发动机推力室外壁焊接工艺,本课题采用热丝TIG焊技术对推力室外壁环焊缝进行焊接,分析各接头焊缝组织、力学性能和断口形貌,制定并优化焊接工艺,结合温度场分布的特点以及各焊接参数对温度场的影响,共同指导实际构件的焊接。首先进行平板堆焊试验,对比热丝TIG焊与常规冷丝TIG焊各接头的焊缝成形,二者熔深、熔宽均随焊接电流增加而增加,同时热丝TIG焊的熔深更大。进一步通过工艺试验确定热丝电流对焊缝成形的影响,发现随着热丝电流增加,熔深、熔宽均随之增加,并在达到一定程度之后熔深急剧增加。基于响应曲面法设计试验,建立焊接电流、热丝电流和焊接速度与焊缝熔深、熔宽、深宽比之间的关系模型,分析了单因素和多因素交互作用下焊接参数对各响应值的影响规律,发现较小的焊接电流、适中的热丝电流以及焊接速度可以得到较小的熔深,能够尽量减小焊接热源产生的热量在厚度方向上的传递。对优化的工艺进行试验验证,证明了模型的适用性。然后分析热丝TIG焊对接温度场,根据构件尺寸建立实体模型,选择双椭球热源对试板的温度场进行模拟,与实测的热循环曲线吻合,验证了模型的正确性,进一步模拟推力室的温度场,明确焊接参数对焊接温度场的影响规律,热丝电流对焊接温度场基本没有影响,而增大焊接电流及降低焊接速度能够增加焊缝附近各点的温度峰值,通过对实际构件温度场的模拟,得到最大线能量的工艺参数,并对焊接顺序进行了优化,发现对称焊产生的变形低于顺序焊,同时对比了水冷及风冷对焊接温度场的影响,发现风冷具有取代水冷的可行性。最后对模拟得到的工艺参数进行优化,并通过金相观察、能谱分析等方法,系统研究了焊接接头的组织,由于为了改善焊缝的塑性,减少缺陷,焊缝材料与母材的成份差异较大,母材为强度较高,韧性较差的马氏体,热影响区为回火屈氏体,而焊缝组织为塑性、韧性较为优良的奥氏体组织,并在晶界处分布了铁素体,防止了延迟裂纹的产生。通过拉伸试验,发现焊接接头的断裂属于塑性断裂,断口形貌主要为等轴韧窝,接头强度达到1034MPa,强度系数为92.86%,满足使用性能要求,硬度最高值处于热影响区及打底焊缝,最低值出现在填充焊缝。
[Abstract]:Hot wire TIG welding is a widely used high efficiency welding method, which is characterized by high strength, good toughness and corrosion resistance. It is widely used in the field of aeronautics and astronautics. In view of the welding technology of thrust outdoor wall of an engine, the hot wire TIG welding technology is used to weld the circumferential weld of thrust outdoor wall. The weld microstructure, mechanical properties and fracture morphology of each joint are analyzed, and the welding process is established and optimized. Combined with the characteristics of temperature field distribution and the influence of welding parameters on temperature field, the welding of practical components is guided. The weld depth and width of hot wire TIG welding and conventional cold wire TIG welding are increased with the increase of welding current, and the penetration depth of hot wire TIG welding is greater than that of conventional cold wire TIG welding. The weld depth and width of each joint of hot wire TIG welding and conventional cold wire TIG welding are increased with the increase of welding current. Further, the influence of hot wire current on weld formation was determined by the process test. It was found that with the increase of hot wire current, the penetration depth and width increased, and the penetration increased sharply after reaching a certain degree. Based on the design experiment of response surface method, the relationship model between welding current, hot wire current and welding speed and weld penetration depth, width and aspect ratio is established. The influence of welding parameters on each response value under the interaction of single factor and multiple factors is analyzed. It is found that smaller welding current, moderate hot wire current and welding speed can get smaller penetration depth. It can minimize heat transfer from welding heat source in thickness direction. The model is proved to be applicable to the experimental verification of the optimized process. Then the temperature field of hot wire TIG welding butt joint is analyzed, and the solid model is established according to the component size, and the temperature field of the plate is simulated with double ellipsoid heat source, which is in agreement with the measured thermal cycle curve and verifies the correctness of the model. The temperature field of the thrust chamber is further simulated, and the influence of welding parameters on the welding temperature field is determined. The hot wire current has no effect on the welding temperature field. Increasing welding current and decreasing welding speed can increase the peak temperature of each point near the weld seam. By simulating the temperature field of the actual member, the process parameters of the maximum line energy are obtained, and the welding sequence is optimized. It is found that the deformation of symmetrical welding is lower than that of sequential welding, and the effects of water cooling and air cooling on welding temperature field are compared, and it is found that air cooling has the feasibility of replacing water cooling. Finally, the process parameters obtained from the simulation are optimized, and the microstructure of welded joints is systematically studied by means of metallographic observation, energy spectrum analysis, etc., because in order to improve the plasticity of the weld, the defects are reduced. The composition of weld material and base metal is quite different, the base metal is martensite with high strength and poor toughness, the heat-affected zone is tempering flexion, while the microstructure of weld is austenite with good ductility and ductility, and ferrite is distributed at grain boundary. The delay crack is prevented. Through tensile test, it is found that the fracture of welded joint belongs to plastic fracture, the fracture surface is mainly equiaxed dimple, the strength of the joint is 1034 MPA, and the strength coefficient is 92.86, which meets the requirements of performance, and the highest hardness is in the heat affected zone and bottom weld. The lowest value appears in the filler weld.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG444.74

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