Improving flangeability of multiphase steel by increasing microstructural homogeneity  

作　　者：Xiao-yu Yang Yong-gang Yang Xing Fang Han-long Zhang Zhen-li Mi 

机构地区：[1]Beijing Advanced Innovation Center for Materials Genome Engineering,Institute of Engineering Technology,University of Science and Technology Beijing,Beijing 100083,China [2]Shanghai Baosteel Group Corp.Technology Center,Shanghai 201900,China

出　　处：《Journal of Iron and Steel Research International》2024年第7期1736-1745,共10页钢铁研究学报（英文版）

基　　金：financial support from the National Natural Science Foundation of China (Grant Nos.52274372 and 52201101);the National Key R&D Program of China (2021YFB3702404);the Fundamental Research Funds for the Central Universities (FRF-TP-22-013A1).

摘　　要：Multiphase microstructure significantly increases the strength,usually at the expense of flangeability because of lacking microstructure homogeneity.To further improve the strength-flangeability of multiphase steel,the microstructural homogeneity was advanced by adjusting the hard martensite/austenite(M/A)islands.The strength-flangeability was measured via uniaxial tensile tests and hole expansion tests.Their microstructures were characterized using a scanning electron microscope equipped with an electron backscatter diffraction detector and a transmission electron microscope.Nanoindentation tests were supplementally used to quantitatively reveal the microstructural homogeneity of the steels.Results show that the adjusted multiphase steel achieves an excellent ultimate tensile strength(~800 MPa)and flangeability(~135%hole expansion ratio).A promising homogeneous multiphase microstructure was obtained by controlling undercooled austenite transformed at about 600℃.This microstructure consists of soft polygonal ferrite,blocky bainitic ferrite,and hard M/A islands.The volume fraction of M/A islands is around 5%,and the average size is less than l pm.Detailed nanoindentation analysis indicated that the participation of M/A islands impressively influenced the microstructural homogeneity.Weakened strain partition and better mechanical compatibility were present in the adjusted multiphase steel since the plasticity initiation started late,which resulted in a positive flangeability.Moreover,avoiding M/A islands distributed in the chain along the rolling direction on the matrix hindered the possibility of voids coalescing into cracks and stabilized the flanging performance.

关 键 词：Multiphase steel Flangeability Martensite/austenite island-Microstructural homogeneity-Microstructure Compact strip production process 

分 类 号：TG142.1[一般工业技术—材料科学与工程]