Ensuring combination of strength, ductility and toughness in medium-manganese steel through optimization of nano-scale metastable austenite

Journal Article · Thu Feb 15 04:00:00 EST 2018 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2017.11.058· OSTI ID:22804878

Hu, Jun; Du, Lin-Xiu; Xu, Wei; Zhai, Jian-Han; Dong, Ying ^[1]; Liu, Yu-Jie ^[2]; Misra, R. D.K. ^[3]

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1. The State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819 (China)
2. School of Materials Science and Engineering, Northeastern University, Shenyang 110819 (China)
3. Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials and Biomedical Engineering, University of Texas at El Paso, TX 79968-0521 (United States)

Highlights: • Medium-Mn steel was innovatively designed for medium to heavy steel plates. • Three intercritical annealing processes were adopted to ensure TRIP effect. • Austenite-martensite submicro-laminate structure was obtained after annealing. • The reversed austenite with different stability led to improved ductility. • TRIP effect induced by metastable austenite contributed excellent impact properties. - Abstract: Medium-Mn steel was innovatively designed in terms of alloying elements for medium to heavy steel plates to obtain combination of high strength, good ductility, and excellent low temperature toughness. Martensite was the dominant microstructure in the directly quenched steel plate because of high hardenability obtained by the addition of 5.6 wt% Mn. Three intercritical annealing processes were adopted to ensure transformation-induced-plasticity (TRIP) effect through optimization of the volume fraction, morphology, and C and Mn-enriched reversed austenite. On annealing, the dislocation density of martensite plate was decreased because of recovery and recrystallization, and metastable austenite film nucleated at the interface. Both thermal and mechanical stability of austenite decreased with increase in annealing temperature. The high yield strength of 840 MPa, good elongation after fracture of 24.3%, and excellent toughness at − 60 °C of 130.3 J was obtained at intermediate annealing temperature of 650 °C, and the volume fraction of reversed austenite at room temperature and − 80 °C was 22% and 17%, respectively. The reversed austenite exhibited different stability with increased tensile strain, leading to improved ductility and delayed necking. Moreover, the crack initiation energy and crack propagation energy were increased via dynamic stress partitioning and relaxation together with the transformation of metastable austenite. Thus, significant degree of TRIP effect induced by moderate stability of austenite played an important role in governing mechanical properties.

• OSTI ID: 22804878
• Journal Information: Materials Characterization, Journal Name: Materials Characterization Vol. 136; ISSN 1044-5803; ISSN MACHEX
• Country of Publication: United States
• Language: English

Related Subjects

77 NANOSCIENCE AND NANOTECHNOLOGY
ANNEALING
AUSTENITE
CRACK PROPAGATION
DISLOCATIONS
DUCTILITY
ELONGATION
FILMS
INTERFACES
MANGANESE STEELS
MARTENSITE
MICROSTRUCTURE
NANOSTRUCTURES
PLASTICITY
RECRYSTALLIZATION
RELAXATION
STRAIN HARDENING
STRESSES
TRANSFORMATIONS
YIELD STRENGTH