Investigation of effects of processing on stretch-flangeability of the ultra-high strength, vanadium-bearing dual-phase steels

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:797

Article

Wu, Yingjie¹  Uusitalo, Juha²  DeArdo, Anthony J.^1,2 

[1] Univ Pittsburgh, Swanson Sch Engn, Basic Met Proc Res Inst, Dept Mech Engn & Mat Sci, 636 Benedum Hall,3700 OHara St, Pittsburgh, PA 15261 USA

[2] Univ Oulu, Ctr Adv Steels Res, Dept Mech Engn, Mat Engn Lab, POB 4200, FI-90014 Oulu, Finland

关键词: Dual-phase (DP) steels;    Hole expansion ratio;    Coiling temperatures;    Continuous galvanizing line (CGL);    Hole punching;    Electron backscattered diffraction (EBSD);    Kernel average misorientation (KAM);    Nanoindentation;   

DOI  :  10.1016/j.msea.2020.140094

来源: Elsevier

【 摘 要 】

The purpose of this paper was to gain a better insight into the sheared-edge ductility of high strength dual-phase steels for the purpose of helping improve the hole expansion behavior of such steels. A candidate dual-phase (DP) steel in this study was designed and processed with distinct coiling temperatures after conventional finish rolling, and then further processed with two continuous galvanizing line (CGL) simulations. Two CGL simulations with slightly different thermal paths were conducted on a Gleeble 3800 machine; one was to replicate standard galvanizing (GI), where the intercritically annealed steels were cooled to the zinc pot temperature, and the other one was a supercooling process (SC) where the intercritically annealed steels were first cooled to the M90 temperature of the intercritically formed austenite, then up-quenched to the zinc pot temperature. The findings indicated that the combination of a low coiling temperature and GI anneal can obtain the microstructures characterized by a high-volume-percentage of martensite and fine-grained ferrite with a high tensile strength (UTS) of 1092.8 MPa and a good total elongation (TE) of 20.8%. A large amount of fresh martensite was replaced by tempered martensite caused by the changes in CGL thermal paths from GI to SC anneals, resulting in the considerable increase in sheared-edge ductility properties, although with a loss of UTS. Additionally, the damages caused by hole punching were examined by electron backscattered diffraction (EBSD) - kernel average misorientation (KAM) and nanoindentation technologies. These results showed that the micro-voids or microcracks in the initial punched hole surfaces and plastic internal strains near the initial punched hole sheared edges introduced by hole punching will severely influence stretch-flangeability.

【 授权许可】

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