Effect of second phase morphology on warm stretch-flangeability in high strength TRIP-aided dual-phase steel sheets
- Nagano National College of Technology, Nagano (Japan)
- Shinshu Univ., Nagano (Japan)
The effects of second phase morphology on warm stretch-flangeability in 0.2C-(1.0-2.5)Si-(1.0-2.0)Mn (mass%) high strength transformation-induced plasticity TRIP-aided dual-phase (TDP) steel sheets were investigated. Good warm stretch-flangeability in terms of warm hole-punching and the successive warm hole-expanding was achieved in a TDP steel with an isolated fine and acicular second phase. In the acicular type of TDP steel, volume fraction and carbon concentration (stability) of retained austenite increased considerably over a conventional type of TDP steel with a network second phase along ferrite grain boundary. Warm hole-punching suppressed void formation in a surface layer of punched hole, and developed severe flow band which disturbs crack propagation on expanding. On the successive warm hole-expanding it increased local elongation due to TRIP effect of a large amount of untransformed retained austenite. Optimum forming temperatures for punching and for expanding were between 150-200{degrees}C and between 50-200{degrees}C, respectively. These temperatures were related with retained austenite stability. The acicular type of TDP steel also had the best balance of stretch-formability and stretch-flangeability of conventional high strength steels, such as a bainitic steel and a ferrite-bainite steel which have an excellent stretch-flangeability. Also, it was found that the newest TRIP-aided bainitic steel attained the same good balance as the acicular type of TDP steel.
- OSTI ID:
- 484307
- Report Number(s):
- CONF-961140--
- Country of Publication:
- United States
- Language:
- English
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