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Vol.50, No.7, 487 ~ 494, 2012
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| Title |
| Effects of Coiling Temperature and Carbides Behavior on Stretch-flangeability for 980MPa Hot-rolled Steels |
| 천은준 Eun Joon Chun , 이주승 Ju Seung Lee , 도형협 Hyeong Hyeop Do , 김성주 Seong Ju Kim , 최윤석 Yoon Suk Choi , 박용호 Yong Ho Park , 강남현 Nam Hyun Kang |
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| Abstract |
| To analyze the factors on stretch-flangeability for 980 MPa-grade hot-rolled steels, two types of steels (Fe-Cr and Fe-Mo) were manufactured by hot-rolling. Manufactured steels at the low coiling temperature, such as 400 and 500℃, had poor stretch-flangeability due to un-uniformly distributed carbides and a large deviation of interphase hardness. However, when the coiling temperature was set at 650℃ with Fe-Cr steel, 998 MPa of ultimate tensile strength, 19% of total elongation and 65% of the hole expanding ratio were achieved by microstructural constituents of polygonal ferrite (PF) and granular ferrite (GF) dispersed with fine carbides (<50 nm). Therefore, the material to attain 980 MPa with superior formability was the Fe- Cr steel that was precipitation-hardened in polygonal ferrite and granular ferrite at the coiling temperature 650℃. |
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| Key Words |
| metals, rolling, precipitation, hardness test, stretch-flangeability |
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