Enhancing strength and ductility in the nugget zone of friction stir welded 7Mn steel via tailoring austenitic stability  

作　　者：Y.Q.Wang F.Y.Li J.X.Su R.H.Duan Z.A.Luo G.M.Xie 

机构地区：[1]State Key Laboratory of Rolling and Automation,Northeastern University,Shenyang 110819,China [2]School of Materials Science and Engineering,Jiangsu University of Science and Technology,Zhenjiang 212003,China

出　　处：《Journal of Materials Science & Technology》2024年第18期174-185,共12页材料科学技术（英文版）

基　　金：supported by the National Nature Science Foundation of China(Nos.52274378,51774085);the Liaoning Province Excellent Youth Foundation(No.2020-YQ-03);the Open Research Fund from the National Key Research and Development Program(No.2018YFA0707304).

摘　　要：The martensite often appears in the nugget zone(NZ)of friction stir welding(FSW)7 wt.%Mn steel due to low austenite stability,deteriorating ductility and toughness.In this work,a 7 wt.%Mn steel was sub-jected to FSW,and preheating was used to tailor the austenitic stability to greatly improve the strength-ductility combination of the NZ.The austenitic deformation behavior and strain hardening mechanism in the NZ were systematically investigated.The microstructure of the as-welded NZ was composed of ultrafine blocky ferrite,austenite,and small amounts of martensite,whereas the as-preheated NZ con-tained ultrafine blocky ferrite and austenite,and the concentration of Mn in austenite was increased from 8.4 wt.%to 10.7 wt.%.This enhanced the austenitic stability,resulting in a significant increase in the volume fraction of austenite in the as-preheated NZ from 37.3%to 66.4%.The product of strength and elongation(PSE)in the as-preheated NZ increased dramatically from 42.6 GPa%to 67.1 GPa%,depending on a persistent high strain hardening rate(SHR).Multiple strain-hardening mechanisms were revealed.The austenite with enhanced stability can provoke sustained transformation-induced plasticity(TRIP)and twinning-induced plasticity(TWIP)effects,and massive dislocation multiplication occurs during tension,resulting in strong strain hardening.

关 键 词：Friction stir welding Medium Mn steel PREHEATING Transformation-induced plasticity Twinning-induced plasticity 

分 类 号：TE973.3[石油与天然气工程—石油机械设备]