摘要
目的研究工艺参数对接头微观组织及力学性能的影响规律,观察断口形貌并揭示断裂机理。方法基于生产实际,采用激光焊接技术对304不锈钢进行平板对接试验,利用金相显微镜、扫描电镜和背散射电子衍射等手段观察不同焊接参数下的接头微观组织,利用拉伸试验机及显微硬度仪测试其力学性能;通过疲劳试验机测试不同应力下的疲劳寿命,并绘制相应的S-N曲线;使用扫描电镜观察并分析疲劳断口的形貌特征。结果焊缝中心由等轴状奥氏体和针状铁素体组成,熔合区以柱状晶的形式向焊缝中心生长。激光功率及焊接速度越大,柱状晶的尺寸越小。当激光焊接功率为1390W、焊接速度为13 mm/s、离焦量为-10mm时,304不锈钢激光焊接接头的力学性能最好,此时的抗拉强度为785.9MPa、伸长率为75.6%,拉伸断口呈典型的韧性断裂特征。在高应力水平(350MPa和500MPa)下,疲劳断口由裂纹萌生区、裂纹扩展区和瞬时断裂区组成,焊缝具有优良的抗疲劳性能。结论焊接速度越快、焊接功率越小、离焦量为负,得到的焊接接头硬度越高,由于细晶强化及加工硬化的双重作用,接头达到了最佳力学性能。
The work aims to study the effect of process parameters on the microstructure and mechanical properties of the joint and reveal the fracture mechanism by observing the fracture morphology.The plate butt test was carried out to 304 stainless steel by laser welding technology based on the actual production.The microstructure of the joint under different weld-ing parameters was characterized by metallurgical microscope and scanning electron microscope combined with electron back-scattered diffraction.The mechanical properties were measured by the testing machine and microhardness tester.The fatigue life under different stresses was tested by fatigue test.S-N curves of the three specimens were drawn,and the morphology charac-teristics of the fatigue fracture were observed and analyzed by SEM.The results indicated that the weld center was composed of equiaxed austenite and acicular ferrite, and the fusion zone grew towards the weld center in the form of columnar crystals. The size of columnar crystals decreased with the increase of laser power and welding speed. When the laser welding power was 1 390 W, the welding speed was 13 mm/s, and the defocusing amount was −10 mm, the mechanical properties of 304 stainless steel laser welding joint were the best. The tensile strength reached 785.9 MPa, the elongation was 75.6% and the tensile fracture was typical ductile fracture. The fatigue fracture of the joint which had excellent fatigue resistance was composed of crack ini-tiation zone, crack propagation zone and instantaneous fracture zone under high stress level (350 MPa and 500 MPa). The hard-ness of welding joint is higher under the condition of high welding speed, low welding power and negative defocus. Due to the dual effects of fine grain strengthening and work hardening, the best mechanical properties are achieved.
作者
吕光宙
马泽铭
许爱军
郭文俊
代国宝
郭伟夺
LYU Guang-zhou;MA Ze-ming;XU Ai-jun;GUO Wen-jun;DAI Guo-bao;GUO Wei-duo(CRRC Qingdao Sifang Co.,Ltd.,Shandong Qingdao 266111,China;Beijing Spacecrafts Co.,Ltd.,Beijing 100094,China)
出处
《精密成形工程》
北大核心
2023年第9期74-82,共9页
Journal of Netshape Forming Engineering
基金
国家科技重大专项(2014ZX04001-151)。
关键词
304不锈钢
力学性能
激光焊接
断裂机理
微观组织
304 stainless steel
mechanical properties
laser welding
fracture mechanism
microstructure
