Retained Austenite Characteristics and Stretch-flangeability of High-strength Low-alloy TRIP Type Bainitic Sheet Steels

Retained austenite characteristics and stretch-flangeability in low alloy TRIP type bainitic sheet steels with different silicon and manganese contents were investigated for automotive applications. As increasing silicon and manganese contents, an initial volume fraction of retained austenite film a...

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Bibliographic Details
Published in:ISIJ International 2002/04/15, Vol.42(4), pp.450-455
Main Authors: Sugimoto, Koh-ichi, Nakano, Kiyotaka, Song, Sung-Moo, Kashima, Takahiro
Format: Article
Language:English
Subjects:
Applied sciences
chemical composition
Cross-disciplinary physics: materials science
rheology
Exact sciences and technology
heat-treatment
high-strength steel
Materials science
Metals. Metallurgy
Other heat and thermomechanical treatments
Physics
retained austenite
strain-induced transformation
stretch-flangeability
Treatment of materials and its effects on microstructure and properties
TRIP
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Summary:Retained austenite characteristics and stretch-flangeability in low alloy TRIP type bainitic sheet steels with different silicon and manganese contents were investigated for automotive applications. As increasing silicon and manganese contents, an initial volume fraction of retained austenite film along bainitic ferrite lath boundary was increased in accompany with a decrease in the carbon concentration. An excellent stretch-flangeability was completed in the steels containing a small amount of stable retained austenites (i.e., volume fraction of 2-4 vol% and carbon concentration of more than 1.0 mass%). This was caused by small surface damage on hole-punching and effective strain-induced transformation plasticity of untransformed retained austenite on hole-expanding. When austempered at temperatures less than MS of the steel after intercritical annealing, further superior stretch-flangeability was achieved due to absence of initial blocky martensite, resulting from developments of long shear section and severe plastic flow and difficult void-initiation on hole-punching.
ISSN:0915-1559
1347-5460
DOI:10.2355/isijinternational.42.450