Mechanical Properties and Microstructure in the Softened Zone of the DP800 Steel Joint by Laser Welding

被引：0
|
作者：
Deng C. [1 ]
Liu C. [1 ]
Liu X. [1 ]
Gong B. [1 ]
Wang D. [1 ]
Xu Q. [1 ]
机构：
[1] School of Materials Science and Engineering, Tianjin University, Tianjin
来源：
Tianjin Daxue Xuebao (Ziran Kexue yu Gongcheng Jishu Ban)/Journal of Tianjin University Science and Technology | 2021年 / 54卷 / 03期
基金：
中国国家自然科学基金;
关键词：
DIC; DP800; steel; EBSD; Laser welding; Softening;
D O I：
10.11784/tdxbz202001050
中图分类号：
学科分类号：
摘要：
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 soften-ing effect of the welded joint typically occurs in the DP800 steel welding process. To solve this prob-lem, the microstructure and mechanical 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 prop-erties 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-tened region of the welded joint is 2.0-3.6mm away from the weld center. The hardness value ranges from 221HV to 243HV, which is around 10% lower than base metal(BM). Compared to the other re-gions 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-affected zone(CGHAZ), fine grain heat-affected zone(FGHAZ), inter-critical heat-affected zone(ICHAZ), sub-critical heat-affected zone(SCHAZ), and BM. The softening of the welded joint occurs primarily at SCHAZ and ICHAZ. 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. © 2021, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.
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页码：311 / 317
页数：6
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