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복현호(Hyunho Bok),이명규(Myoung-Gyu Lee),최종원(Jong Won Choi),F. Barlat 한국자동차공학회 2012 한국자동차공학회 부문종합 학술대회 Vol.2012 No.5
In order to consider the effect of hot deformation on following phase transformations in steels, the Avrami type austenite recrystallization model was used to calculate the austenite grain refinement. This refined grain was incorporated into the diffusional phase transformation kinetics suggested by Li et al. As a result, the diffusional phase transformations were enhanced and, therefore, martensite transformation was suppressed.
김석봉(Seokbong Kim),안광현(Kwanghyun Ahn),하지웅(Jiwoong Ha),허훈(Hoon Huh),복현호(Hyunho Bok) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
This paper deals with the formability of CQ and DP590 steel sheets in relation to the strain rate. The high speed forming limit tests were performed using the high speed crash testing machine and high speed forming jig. Compared with the static FLC, the high-speed FLC of CQ is higher in a simple tension region and lower in a biaxial stretch forming region. The high-speed FLC for DP590 decreases in relation to the static FLC throughout the entire region. The elongation at fracture appears to be closely related to the simple tension region of the FLC. The decrease of the high-speed FLC in the biaxial stretch forming region is due to the shear fracture in fracture surfaces. Three theoretical (Hill?Swift, Jun and M?K models) approaches and two empirical (Keeler?Brazier and Raghavan models) approaches were discussed to predict the FLC of sheet metals. The theoretical models are found to be very conservative, especially at plane strain region in FLC. Among the various prediction models, the Raghavan model with NADDRG curve gives better prediction at plane strain region.