Sohn Seok Su, Song Hyejin, Jo Min Chul, Song Taejin, Kim Hyoung Seop, Lee Sunghak
Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784, Korea.
HIMASS research project team, Technical Research Laboratories, POSCO, Kwangyang, 545-875, Korea.
Sci Rep. 2017 Apr 28;7(1):1255. doi: 10.1038/s41598-017-01514-9.
Needs for steel designs of ultra-high strength and excellent ductility have been an important issue in worldwide automotive industries to achieve energy conservation, improvement of safety, and crashworthiness qualities. Because of various drawbacks in existing 1.5-GPa-grade steels, new development of formable cold-rolled ultra-high-strength steels is essentially needed. Here we show a plausible method to achieve ultra-high strengths of 1.0~1.5 GPa together with excellent ductility above 50% by actively utilizing non-recrystallization region and TRansformation-Induced Plasticity (TRIP) mechanism in a cold-rolled and annealed Fe-Mn-Al-C-based steel. We adopt a duplex microstructure composed of austenite and ultra-fine ferrite in order to overcome low-yield-strength characteristics of austenite. Persistent elongation up to 50% as well as ultra-high yield strength over 1.4 GPa are attributed to well-balanced mechanical stability of non-crystallized austenite with critical strain for TRIP. Our results demonstrate how the non-recrystallized austenite can be a metamorphosis in 1.5-GPa-grade steel sheet design.
对具有超高强度和优异延展性的钢材设计的需求，一直是全球汽车行业中实现节能、提高安全性和碰撞性能的一个重要问题。由于现有1.5 GPa级钢材存在各种缺陷，因此迫切需要开发新型的可成型冷轧超高强度钢材。在此，我们展示了一种可行的方法，通过在冷轧和退火的Fe-Mn-Al-C基钢中积极利用未再结晶区和相变诱发塑性（TRIP）机制，实现1.0~1.5 GPa的超高强度以及超过50%的优异延展性。我们采用由奥氏体和超细铁素体组成的双相组织，以克服奥氏体的低屈服强度特性。高达50%的持久伸长率以及超过1.4 GPa的超高屈服强度，归因于未再结晶奥氏体与TRIP临界应变之间良好平衡的机械稳定性。我们的结果表明，未再结晶奥氏体在1.5 GPa级钢板设计中如何能够成为一种变体。
