Effects of Inclusions on Delayed Fracture Properties of Three TWinning Induced Plasticity (TWIP) Steels
- PDF / 2,242,017 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 37 Downloads / 219 Views
.
INTRODUCTION
IN automotive industries, highly deformable steel sheets such as TRansformation Induced Plasticity (TRIP) steels and TWinning Induced Plasticity (TWIP) steels have been actively developed for CO2 reduction and increased efficiency.[1–4] In high-Mn TWIP steels composed of austenite, deformation twins formed during deformation prevent the dislocation movement as they play a role in refining grains. The necking is suppressed by a high work hardening rate, which leads to the simultaneous improvement of strength and ductility.[4–9] In spite of the excellent tensile properties, their commercialization has been postponed because they are easily subjected to cracking during forming or to delayed fracture after forming.[10–15] However, the decrease of Mn content is not easy because of the stabilization of SEOKMIN HONG, Research Assistant, and SANG YONG SHIN, Research Professor, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784, Korea. Contact e-mail: [email protected] HYOUNG SEOP KIM and SUNGHAK LEE, Professors, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, and also with the Materials Science and Engineering, Pohang University of Science and Technology, Pohang, 790-784, Korea. SUNG-KYU KIM, Senior Principal Researcher, is with Sheet Products & Process Research Group, Technical Research Laboratories, POSCO, Gwangyang 545-711, Korea. KWANGGEUN CHIN, Senior Vice President, is with TWIP Steel Research Project Team, Technical Research Laboratories, POSCO, Gwangyang, 545-711, Korea. NACK J. KIM, Professor, is with Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, and also with Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang. Manuscript submitted December 30, 2011. Article published online October 17, 2012 776—VOLUME 44A, FEBRUARY 2013
austenite at room temperature and the sufficient formation of twins. Recently, the addition of Al, together with the decreased Mn content, has been conducted to improve formability and to prevent delayed fracture. Al works for decreasing twin formation because it raises the stacking fault energy (SFE).[16–21] Thus, Al-added TWIP steels have excellent formability due to the decreased twin formation and the increased slip activation. Chin et al.[10] reported that the cracking or delayed fracture did not occur during or after the cup forming test of an Al-added TWIP steel, whereas it occurred in a high-Mn TWIP steel. These results were explained by the stress concentration at the cup side in the high-Mn steel and by the occurrence of homogeneous twinning in the Al-added steel.[10,22] Berrahmoune et al.[23] found the delayed fracture after deep drawing of 301LN austenite steels, and explained it by the increased amount of martensite and the localization of residual stresses. However, exact mechanisms behind the delayed fracture are not sufficiently understood in relation to microstructures. This
Data Loading...
