激光焊接形成FeMnSi记忆合金焊缝组织的工艺及性能研究

发布时间：2018-03-08 14:37

本文选题：激光焊接　切入点：Fe-Mn-Si　出处：《大连海事大学》2017年硕士论文　论文类型：学位论文

【摘要】：本文选用304不锈钢为连接对象,以激光填粉焊接原位形成Fe-Mn-Si记忆合金焊缝组织为目标,通过填加粉末成分设计、激光工艺参数优化选择,利用CO2激光焊接系统获得具有Fe-Mn-Si记忆合金焊缝组织的304不锈钢焊接接头,并研究其力学性能和焊缝的组织性能。选取激光功率、焊接速度、离焦量三个主要工艺参数,利用单因素试验法,分析了各工艺参数对激光填粉形成Fe-Mn-Si记忆合金焊缝性能的影响规律。结果表明,工艺参数改变,焊缝的热输入量也随之改变,从而影响焊缝熔宽、成分、抗拉强度及硬度。基于单因素试验结果,以抗拉强度为试验指标进行正交试验,通过极差分析和方差分析得出2 mm厚304不锈钢板激光填粉焊接试验的最佳工艺参数为P=2.7 kW、v=160mm/min、z=5mm,其焊接接头的抗拉强度为745.4 MPa,达到了母材抗拉强度(751 MPa)的95%;Fe-Mn-Si记忆合金焊缝成型良好,304不锈钢基材至焊缝中心依次由奥氏体、平面晶、胞状树枝晶、树枝晶、等轴晶组成。为实现激光填粉焊接原位形成Fe-Mn-Si记忆合金焊缝组织的目标,采用混料均匀设计方法,借助DPS数据处理系统得到填加Fe/Mn/Si/Cr/Ni粉末配比和焊缝组织成分之间的回归方程。Fe-Mn-Si记忆合金焊缝区域的平均显微硬度为HV 242.8,较304不锈钢焊缝硬度更高,这是因为Fe-Mn-Si记忆合金焊缝内部有较高硬度的马氏体组织,并且焊缝区域Mn、Si含量较高,有助于硬度的提高;Fe-Mn-Si记忆合金焊接接头的抗拉强度和抗弯曲疲劳性能明显优于304不锈钢焊接接头,6%变形下的应变疲劳强度能达到母材的90%;Fe-Mn-Si记忆合金焊缝的残余应力较低,明显小于304不锈钢焊缝的残余应力。表明Fe-Mn-Si记忆合金焊缝的力学性能更好。Fe-Mn-Si记忆合金焊缝组织具有明显的形状记忆效应,Fe-Mn-Si记忆合金应力诱发γ(?)ε马氏体正逆相变及其变形协调是降低不锈钢焊接接头残余应力并提高焊缝疲劳强度的根本原因。
[Abstract]:In this paper, 304 stainless steel is selected as the connecting object, the microstructure of Fe-Mn-Si memory alloy weld formed in situ by laser powder filling welding is taken as the target, and the laser process parameters are optimized by adding powder composition design. A 304 stainless steel welded joint with Fe-Mn-Si memory alloy weld microstructure was obtained by CO2 laser welding system. The mechanical properties and microstructure of the weld were studied. Three main technological parameters, laser power, welding speed and defocus, were selected. By using single factor test method, the influence of various technological parameters on the weld properties of Fe-Mn-Si memory alloy formed by laser powder filling is analyzed. The results show that the heat input of the weld changes with the change of the process parameters, thus affecting the weld width and composition. Tensile strength and hardness. Based on the results of single factor tests, the orthogonal test was carried out with tensile strength as the test index. By means of range analysis and variance analysis, the optimum technological parameters of laser powder filling welding test for 2 mm thick 304 stainless steel plate were obtained as follows: P0. 7 kW / v + 160 mm / min + 5 mm, and the tensile strength of the welded joint was 74. 4 MPA, reaching the base material tensile strength of 751 MPa.) 95mm Fe-Mn-Si memory alloy welding was obtained. From austenite to the center of weld, the substrates of stainless steel with good joint forming are in turn from austenite to the center of weld. Plane crystal, cellular dendrite, dendritic crystal, equiaxed crystal composition. In order to achieve the goal of laser powder filling welding in situ forming Fe-Mn-Si memory alloy weld microstructure, the mixing uniform design method is adopted. By means of DPS data processing system, the regression equation between Fe/Mn/Si/Cr/Ni powder ratio and weld microstructure was obtained. The average microhardness in weld zone of Fe-Mn-Si memory alloy was HV242.8, which was higher than that of 304 stainless steel. This is due to the higher hardness of martensite in the weld of Fe-Mn-Si memory alloy and the higher content of MNO Si in the weld zone. The tensile strength and bending fatigue resistance of Fe-Mn-Si memory alloy welded joints are obviously better than that of 304 stainless steel welded joints under 6% deformation. The strain fatigue strength of Fe-Mn-Si memory alloy welded joints can reach 90% of the base metal, and the residual stress of Fe-Mn-Si memory alloy welds is lower than that of 304 stainless steel welded joints. The results show that the mechanical properties of Fe-Mn-Si memory alloy weld are better. Fe-Mn-Si memory alloy weld has obvious shape memory effect. 蔚 martensite retrograde transformation and coordination of deformation are the fundamental reasons for reducing residual stress of stainless steel welded joint and increasing weld fatigue strength.
【学位授予单位】：大连海事大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG456.7

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