邓彩艳,刘 策,刘秀国,龚宝明,王东坡,许全军
AuthorsHTML:邓彩艳，刘 策，刘秀国，龚宝明，王东坡，许全军
AuthorsListE:Deng Caiyan,Liu Ce,Liu Xiuguo,Gong Baoming,Wang Dongpo,Xu Quanjun
AuthorsHTMLE:Deng Caiyan，Liu Ce，Liu Xiuguo，Gong Baoming，Wang Dongpo，Xu Quanjun
Unit:天津大学材料科学与工程学院，天津 300350
Unit_EngLish:School of Materials Science and Engineering，Tianjin University，Tianjin 300350，China
Abstract_Chinese:DP800 双相钢作为一种高强钢，广泛应用于汽车制造业，它的安全性和可靠性满足汽车轻量化对于汽车用 钢的要求．然而 DP800 双相钢焊接时会出现接头的软化问题，针对这一问题，对焊接接头软化区的微观组织和力学 性能进行了研究．采用 Nd：YAG 固体激光器对 DP800 双相钢进行焊接，通过焊接接头硬度测试、拉伸试验、数字 图像相关(DIC)应变测试方法研究软化区的力学性能特点，利用光学显微镜(OM)、扫描电子显微镜(SEM)以及电子 背散射衍射技术(EBSD)分析软化区的微观组织特点．结果表明：焊接接头软化区距离焊缝中心约 2.0～3.6 mm，硬 度范围在 221～243 HV，比母材的硬度值下降了约 10%；相较于焊接接头其他区域，在拉伸过程中软化区应变集中 最为严重，变形量最大，断裂前应变值达到 0.58．焊接接头主要分为焊缝金属区、粗晶热影响区、细晶热影响区、 临界热影响区、亚临界热影响区和母材，其中焊接接头的软化主要发生在亚临界热影响区和临界热影响区，从组织 相变角度分析，亚临界热影响区中马氏体发生了回火，析出碳化物，形成回火马氏体．临界热影响区中铁素体含量 增加 8.1%，引起了接头的软化；从晶体学角度分析，软化区包含的亚临界热影响区和临界热影响区的晶粒尺寸较 大，总晶界长度较少，局部平均取向差(KAM)较低，引起了接头的软化．
Abstract_English:DP800 steel is commonly used in the automobile manufacturing industry as a type of high-strength steel， which meets the automotive lightweight safety and reliability requirements. However，the softening effect of the welded joint typically occurs in the DP800 steel welding process. To solve this problem，the microstructure and me\u0002chanical properties of the softened region of the DP800 steel welded joint were studied. The DP800 steel was welded using the Nd：YAG solid laser. The mechanical properties of the softened zone of the welded joint were tested by the hardness test，tensile test，and digital image correlation(DIC) strain measurement method. Optical microscope (OM)，scanning electron microscope(SEM)，and electron back-scattered diffraction(EBSD) technology were used to study the microstructure characteristics of the softened zone of the welded joint. The results showed that the sof\u0002tened region of the welded joint is 2.0 —3.6 mm away from the weld center. The hardness value ranges from 221 HV to 243 HV，which is around 10% lower than base metal(BM). Compared to the other regions of the welded joint， the softened zone strain localization is the most extreme in the tensile process. The tensile specimen is fractured when the strain reaches 0.58. The DP800 steel welded joint is divided primarily into weld metal(WM)，coarse grain heat\u0002affected zone(CGHAZ)，fine grain heat-affected zone(FGHAZ)，inter-critical heat-affected zone(ICHAZ)，sub\u0002critical heat-affected zone(SCHAZ)，and BM. The softening of the welded joint occurs primarily at SCHAZ andICHAZ. From the perspective of phase transition，the martensite occurs to temper and precipitate carbide and forms the tempered martensite in the SCHAZ，and the ferrite content is increased by 8.1% in the ICHAZ，which cause the softening of the welded joint. From the crystallography perspective，SCHAZ and ICHAZ have a larger grain size， less grain boundary length，and lower KAM value in the softened zone which lead to the softening of the welded joint.
Keyword_Chinese:DP800 钢；激光焊；软化；数字图像相关；电子背散射衍射
Keywords_English:DP800 steel；laser welding；softening；DIC；EBSD

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