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Improving flangeability of multiphase steel by increasing microstructural homogeneity

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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.

Multiphase steelFlangeabilityMartensite/austenite islandMicrostructural homogeneityMicrostructureCompact strip production process

Xiao-yu Yang、Yong-gang Yang、Xing Fang、Han-long Zhang、Zhen-li Mi

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Beijing Advanced Innovation Center for Materials Genome Engineering,Institute of Engineering Technology,University of Science and Technology Beijing,Beijing 100083,China

Shanghai Baosteel Group Corp.Technology Center,Shanghai 201900,China

National Natural Science Foundation of ChinaNational Natural Science Foundation of ChinaNational Key R&D Program of ChinaFundamental Research Funds for the Central Universities

52274372522011012021YFB3702404FRF-TP-22-013A1

2024

10.1007/s42243-023-01075-4

钢铁研究学报(英文版)
钢铁研究总院

钢铁研究学报(英文版)

CSTPCD
影响因子：0.584
ISSN：1006-706X
年,卷(期)：2024.31(7)