The Study in Improvement of Hole Expansibility for High-Strength Steel of 980MPa Grade

Abstract:

Recently, due to the requirements of lightweight and safety, the grade of 980MPa high-strength steel has the demand of high hole expansibility and high yield strength. Due to the large difference of hardness between the soft ferrite and hard martensite, the traditional DP980Y dual phase steel has poor hole expansibility. In order to improve the hole expansibility of DP980Y dual phase steel, the best way is to modify the microstructure into a single-phase to eliminate the large difference of hardness. In this paper, the steel of nearly full bainite microstructure with small amount of ferrite and M/A constituents was studied. Compared to the DP980Y dual phase steel, it was found that this modified steel with a single-phase microstructure has the same grade of 980MPa of tensile strength, but can achieve the demand of higher yield strength and hole-expansion ratio. This study shows reducing the amount of ferrite can increase the homogeneity of matrix with the single phase to improve the hole expansibility. In addition, the use of lower bainite transformation temperature and lower carbon content has the higher hole-expansion ratio due to the less amount of M/A constituents.

• Periodical: Materials Science Forum (Volume 941)
• Pages: 492-497
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.941.492
• Online since: December 2018
• Authors: Kuo Cheng Yang*, J.F. Tu, L.J. Chiang, W.J. Cheng, C.Y. Huang
• Keywords: Bainite, High Strength Steel, Hole Expansibility

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