硼钢B1500HS激光焊接接头组织及力学性能研究

发布时间：2018-12-19 13:40

【摘要】：热冲压硼钢具有超高的强度,不仅能增加车身的安全性能,而且能降低车身重量。激光焊接具有焊接质量好、效率高、自动化程度高等优点,目前在汽车工业中得到了广泛应用。因此,研究热冲压硼钢的激光焊接技术对该种钢在汽车工业的应用具有重要的理论意义和工程应用价值。本文以宝钢生产的热冲压硼钢B1500HS为研究对象,采用有限元分析的方法进行焊接工艺参数的初步优选,并用材料性能模拟软件研究不同焊接工艺参数对焊接接头组织和力学性能的影响。之后进行激光对接焊和激光搭接焊试验,研究不同焊接工艺参数对接头组织和力学性能的影响。焊接工艺参数优选的模拟结果表明,热输入相同时,高功率、高焊速焊接相对于低功率、低焊速焊接能够增加热影响区的冷却速度,减少软化区的回火时间。接头组织和力学性能的模拟结果表明,焊缝区、完全淬火区为马氏体组织,软化区有M3C型碳化物析出。焊接速度对焊缝区、完全淬火区的组织和力学性能影响较小。焊缝区和完全淬火区的硬度、强度与母材相当。软化区的硬度和强度随回火温度和回火时间的增加而降低。焊接速度越小,软化区的硬度和强度也越低。硼钢B1500HS激光对接焊试验结果表明,焊缝、完全淬火区都是马氏体组织,不完全淬火区为马氏体加铁素体组织,软化区为回火马氏体加铁素体组织。焊接接头的硬度分布不均匀,在软化区硬度明显降低。拉伸试样都断裂在软化区。焊接接头的抗拉强度随着焊接速度增加而增加,三点弯曲试验试样的最大弯曲角度随着焊接速度的增加而减小。脉冲频率对焊接接头的抗拉强度影响较小,氧化皮会降低焊接接头的抗拉强度。当焊接功率为1000W,焊接速度在10mm/s-15mm/s范围内时,接头抗拉强度和抗弯强度都在1100MPa以上,最大弯曲角度为180°,焊接接头具有良好力学性能。硼钢B1500HS激光搭接焊时,焊缝中出现了小孔型气孔。焊接接头组织和硬度的变化规律与对接焊相似。焊接接头软化区马氏体分解更严重,该区的硬度更低。搭接接头拉伸断裂发生在搭接面处,接头的最大抗剪力随着焊接速度的增加而减小。脉冲频率对激光对接焊接头强度影响很小,对搭接接头的气孔率和接头最大抗剪力有明显影响。硼钢上表面的氧化皮能增加材料对激光的吸收效率,使得焊缝尺寸增加。相同焊接工艺参数下,氧化皮降低了对接接头的强度,但增加了搭接接头的最大抗剪力。
[Abstract]:Hot stamping boron steel has high strength, which can not only increase the safety performance of the body, but also reduce the weight of the body. Laser welding has the advantages of good welding quality, high efficiency and high degree of automation, so it has been widely used in automobile industry. Therefore, the study of laser welding technology of hot stamping boron steel has important theoretical significance and engineering application value for the application of this kind of steel in automobile industry. In this paper, the hot stamping boron steel B1500HS produced by Baosteel is taken as the research object and the method of finite element analysis is used to optimize the welding process parameters. The effects of different welding parameters on the microstructure and mechanical properties of welded joints were studied by means of material performance simulation software. Then laser butt welding and laser lap welding experiments were carried out to study the effect of different welding parameters on the microstructure and mechanical properties of the joints. The simulation results of optimum selection of welding process parameters show that when the heat input is the same, the high power and high welding speed welding can increase the cooling rate of the heat affected zone and reduce the tempering time of the softening zone compared with the low power welding. The simulation results of the microstructure and mechanical properties of the joints show that the weld zone and the complete quenching zone are martensite, and the M 3C carbide precipitates in the softening zone. The welding speed has little effect on the microstructure and mechanical properties of the weld zone and the complete quenching zone. The hardness and strength of weld zone and complete quenching zone are similar to that of base metal. The hardness and strength of softening zone decrease with the increase of tempering temperature and tempering time. The lower the welding speed, the lower the hardness and strength of softening zone. The results of B1500HS laser butt welding of boron steel show that the weld and complete quenching zone are martensite structure, the incomplete quenching zone is martensite plus ferrite structure, and the softening zone is tempered martensite and ferrite structure. The hardness distribution of the welded joints is not uniform, and the hardness decreases obviously in the softening zone. The tensile specimens are fractured in the softening zone. The tensile strength of welded joint increases with the increase of welding speed, and the maximum bending angle of three-point bending test sample decreases with the increase of welding speed. The pulse frequency has little effect on the tensile strength of welded joints, and the oxide coating will decrease the tensile strength of welded joints. When the welding power is 1000W and the welding speed is within the range of 10mm/s-15mm/s, the tensile strength and bending strength of the joint are above 1100MPa and the maximum bending angle is 180 掳. The welded joint has good mechanical properties. In the B1500HS laser lap welding of boron steel, there are small pore holes in the weld. The variation of microstructure and hardness of welded joints is similar to that of butt welding. Martensite decomposition is more serious and hardness is lower in the softening zone of welded joint. The tensile fracture of the lap joint occurs at the lap joint, and the maximum shear strength decreases with the increase of the welding speed. The pulse frequency has little effect on the strength of laser butt welding joint, but has obvious influence on the porosity and the maximum shear resistance of the lap joint. The oxide coating on the upper surface of boron steel can increase the laser absorption efficiency of the material and increase the weld size. Under the same welding parameters, the oxide coating decreases the strength of the butt joint, but increases the maximum shear strength of the lap joint.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG456.7

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