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고강도 열연강판의 구멍확장 시험 시 균열의 전파거동에 미치는 미세조직의 영향
박세호(Seho Park),변정국(Jungkuk Byun),도형협(Hyeonghyeop Do),정인상(Insang Chung) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
Recently, advanced vehicle concepts and light-weight design of automobiles require improved steel grades with increased strength and formability. Especially, high strength hot-rolled steel sheets applied to chassis such as wheel, lower arm require high hole expansion ratio because of their complicated shapes in cold press processing. Aim of this study is to analyze the effects of microstructures on the crack propagation behavior during hole expansion which is used to estimate stretch-flangeability for steel sheets. For high strength steel sheets which had various microstructures and different components, hole expansion test were carried out and than analyzed the differences of the crack propagation behavior. As the result, it was conclusioned that formation of the 2nd fracture surface, low difference in hardness between the matrix and 2nd phase, excellent uniformity of the microstructures and a small number of the micro-voids led to excellent hole expansion ratio (HER).