A Novel High-Strength Oxidization-Resistant Press Hardening Steel Sheet Requiring No Al–Si Coating
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Press-hardening steels (such as 22MnB5) have been widely used in automobile structure for light-weighting. However, these steels have relatively low elongation (< 8%), and particularly are severely oxidized if an Al–Si coating is not applied during the hot forming process; while the addition of Al–Si coating causes a high cost for paying the intellectual property. In this paper, we present a new medium-Mn TRIP steel, which not only has better mechanical properties but also higher resistance to oxidation than 22MnB5 so that requires no Al–Si coating for protection. A relatively low austenitization temperature was employed, leading to the formation of very fine prior austenite grains (< 1 μm), and the final microstructure composed of martensite as matrix, carbide precipitates and about 11% retained austenite. As a consequence, this newly designed steel possesses more than 1400 MPa yield strength, 1700 MPa ultra-tensile strength, and about 12% total elongation after press hardening. Furthermore, the thickness of oxidation layer is less than 3 μm, which is much smaller than the one for 22MnB5 steel.
KeywordsMedium-Mn TRIP steel Microstructure High strength High temperature oxidation resistance Press hardening
The authors would like to thank the National Natural Science Foundation of China (Nos. U1460203, 51831002, 51861135302) and the Fundamental Research Funds for the Central Universities (Grant No. FRF-TP-18-002C2). This study was financially supported by the Innovation Talent Cultivation Fund of the University of Science and Technology Beijing.
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