Chen Zhanglan, Xiong Yunfeng, Li Xiaowen, Li Zongmin
School of Marine Engineering, Jimei University, Xiamen 361021, China.
Materials (Basel). 2022 Mar 14;15(6):2135. doi: 10.3390/ma15062135.
The evolution of the martensite-austenite (MA) constituent in the heat-affected zone (HAZ) of high-strength steel FH690 welds when subjected to electropulsing (EP) treatment was investigated herein, with the aim of eliminating brittle MA to enhance toughness. The features induced by EPT were correlated with the microstructure and fractography through scanning electron microscopy and electron backscatter diffraction analyses, together constituting an impact property evaluation. The Charpy V-notch impact results showed EPT could improve toughness of the HAZ from 34.1 J to 51.8 J (the calibrated value was 46 J). Examinations of EP-treated microstructure showed a preferred Joule heating: at the site of the MA constituent, the cleavage fractography introduced by the MA constituent was substituted with ductile dimples with various sizes. Decreases in grain size of 40% and 47% for the matrix and the retained austenite, respectively, were achieved; while for regions without the MA constituent, microstructural modification was negligible. The temperature rise at sample surface was less than 60 °C. The mechanism behind this favorable Joule heating for the MA constituent was correlated with the electrical properties of the MA constituent in contrast with martensite matrix. The toughness enhancement of the HAZ was thus attributed to the elimination of the coarse MA constituent. The present investigation suggested that electropulsing, characterized as a narrow-duration current, is a promising method for preferred elimination of brittle factors and thus improving the toughness of HAZ of high-strength steel within a limited region with a width less than 2 mm.
本文研究了高强度钢FH690焊缝热影响区（HAZ）中马氏体-奥氏体（MA）组织在经受电脉冲（EP）处理时的演变，目的是消除脆性MA以提高韧性。通过扫描电子显微镜和电子背散射衍射分析，将电脉冲处理诱导的特征与微观结构和断口形貌相关联，共同构成冲击性能评估。夏比V型缺口冲击试验结果表明，电脉冲处理可将热影响区的韧性从34.1 J提高到51.8 J（校准值为46 J）。对经电脉冲处理的微观结构的检查表明存在优先焦耳热：在MA组织部位，由MA组织引入的解理断口形貌被各种尺寸的韧性凹坑所取代。基体和残余奥氏体的晶粒尺寸分别减小了40%和47%；而对于没有MA组织的区域，微观结构改性可忽略不计。样品表面的温度升高小于60℃。这种有利于MA组织的焦耳热背后的机制与MA组织相对于马氏体基体的电学性能相关。因此，热影响区韧性的提高归因于粗大MA组织的消除。本研究表明，以窄持续时间电流为特征的电脉冲是一种很有前途的方法，可在宽度小于2 mm的有限区域内优先消除脆性因素，从而提高高强度钢热影响区的韧性。
