Characterizing and modeling on microstructural evolution during intercritical annealing of high performance medium Mn steel

• Applicant: Professor Dr.-Ing. Ulrich Krupp, since 2/2021
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410335988

• Final Report Year: 2023

Final Report Abstract

The successful implementation of the project delivers the understanding of austenite reverted transformation mechanism and provides knowledge in process – microstructure – property relationship in high-performance medium-Mn steel. Firstly, the fundamentals of the austenite reversion kinetics were investigated by experimental and computational approaches, which explain the fast transformation kinetics and interface migration behaviours. The interface-related phenomena, e.g., interface mobility, interface segregation, and generation of geometry necessary dislocations at interface, has been explicitly investigated and correlated with austenite reverted transformation as well as mechanical properties. Based on the complemented understanding of austenite reversion, the flash-austenite reverted transformation annealing process was proposed and has been proven successful in increasing metastable austenite fraction in hot-rolled medium Mn steel. The obtained knowledge contributes as interface engineering concept and is significant in designing short process for medium Mn steel with balanced mechanical properties. Secondly, the process – microstructure – property relationship was investigated in Cu and Ni alloyed medium Mn steel, in order to balance strength and ductility using the compact processing route. The effect of various annealing parameters, e.g. annealing temperature and annealing time, on austenite characteristics and recrystallization, has been investigated. The compact two-step heat treatment with short intercritical annealing and subsequent tempering was reported beneficial to the balance of austenite reversion and nano-precipitation. Furthermore, contributions of austenite stability and fraction, nano-precipitation, ferrite recrystallization to mechanical enhancement were revealed. With the development of energy technology, electrification and sustainability, the service environment brings new challenges to metallic materials. The lightweight medium-Mn steel with an extraordinary balance of strength and ductility is the promising candidate. The acquired knowledge will enable the design of austenite with targeted fraction, stability, and heterogeneous composition, which fits the demanding requirements of applications. More research works on medium-Mn steels will be stimulated in the future, e.g. carbon-neutral production, and hydrogen embrittlement.

Publications

• In-situ investigation on deformation behavior of Cu-alloyed medium-Mn steels by high energy synchrotron X-ray diffraction. MSE congress (2020), September 22-25, Online.
  Z. Xu, W. Song & W. Bleck
  
• Investigation of microstructural evolution in medium-Mn steels during intercritical annealing. MSE congress (2020), September 22-25, Online.
  X. Shen, W. Song, U. Krupp & W. Bleck
  
• A novel medium-Mn steel with superior mechanical properties and marginal oxidization after press hardening. Acta Materialia, 205, 116567.
  Li, Shuoshuo; Wen, Pengyu; Li, Shilei; Song, Wenwen; Wang, Yandong & Luo, Haiwen
  
• Multiphase-field simulation of austenite reversion in medium-Mn steels. International Journal of Minerals, Metallurgy and Materials, 28(5), 847-853.
  Ma, Yan; Zheng, Rui; Gao, Ziyuan; Krupp, Ulrich; Luo, Hai-wen; Song, Wenwen & Bleck, Wolfgang
  
• Tailoring the Austenite Fraction of a Cu and Ni Containing Medium-Mn Steel via Warm Rolling. Metals, 11(12), 1888.
  Xu, Zigan; Li, Jiyao; Shen, Xiao; Allam, Tarek; Richter, Silvia; Song, Wenwen & Bleck, Wolfgang
  
• Austenite reversion and nano-precipitation during a compact two-step heat treatment of medium-Mn steel containing Cu and Ni. Journal of Materials Research and Technology, 17, 2601-2613.
  Xu, Zigan; Shen, Xiao; Allam, Tarek; Song, Wenwen & Bleck, Wolfgang
  
• Austenite transformation and deformation behavior of a cold-rolled medium-Mn steel under different annealing temperatures. Materials Science and Engineering: A, 829, 142115.
  Xu, Zigan; Shen, Xiao; Allam, Tarek; Song, Wenwen & Bleck, Wolfgang
  
• Nano-precipitation and austenite reversion in a Cu and Ni containing medium-Mn steel. 5th International High Manganese Steel Conference (2022), May 23-26, Linz, Austria.
  Z. Xu, W. Song & W. Bleck
  
• Revealing the austenite reversion mechanism in medium-Mn steel by innovative cyclic partial-transformation annealing. 5th International High Manganese Steel Conference (2022), May 23-26, Linz, Austria.
  X. Shen, Q. Guo, B. Hu, H. Luo, W. Song, U. Krupp & W. Bleck
  
• Yielding behavior of triplex medium Mn steel alternated with cooling strategies altering martensite/ferrite interfacial feature. Journal of Materials Science & Technology, 126, 60-70.
  Hu, Bin; Shen, Xiao; Guo, Qinyi; Wen, Qinghua; Tu, Xin; Ding, Cancan; Ding, Fanglin; Song, Wenwen & Luo, Haiwen
  
• Yielding behaviour of a nanostructured triplex medium Mn steel alternated with cooling strategies. MSE congress (2022), September 27-29, Darmstadt, Germany.
  X. Shen, B. Hu, Q. Guo, H. Luo, W. Song, U. Krupp & W. Bleck
  
• Yielding behaviour of a nanostructured triplex medium Mn steel alternated with cooling strategies. TMS Annual Meeting & Exhibition (2023) March 19-23, San Diego, USA.
  X. Shen, B. Hu, Q. Guo, H. Luo, W. Song, U. Krupp & W. Bleck