Title

Dynamic Strain Aging Phenomena and Tensile Response of Medium-Mn TRIP Steel

Abstract

Dynamic strain aging (DSA) and rapid work hardening are typical behaviors observed in medium-Mn transformation-induced plasticity (TRIP) steel. Three alloys with manganese ranging from 10.2 to 13.8 wt pct with calculated room temperature stacking fault energies varying from − 2.1 to 0.7 mJ/m2 were investigated. Significant serrations were observed in the stress-strain behavior for two of the steels and the addition of 4.6 wt pct chromium was effective in significantly reducing the occurrence of DSA. Addition of chromium to the alloy reduced DSA by precipitation of M23(C,N)6 during batch annealing at 873 K (600 °C) for 20 hours. Three distinct DSA mechanisms were identified: one related to manganese ordering in stacking faults associated with γ-martensite and austenite interface, with activation energies for the onset and termination of DSA being 145 and 277 kJ/mol. A second mechanism was associated with carbon diffusion in γ-austenite where Mn-C bonding added to the total binding energy, and activation energies of 88 and 155 kJ/mol were measured for the onset and termination of DSA. A third mechanism was attributed to dislocation pinning and unpinning by nitrogen in α-ferrite with activation energies of 64 and 123 kJ/mol being identified. Tensile behaviors of the three medium manganese steels were studied in both the hot band and batch annealed after cold working conditions. Ultimate tensile strengths ranged from 1310 to 1404 MPa with total elongation of 24.1 to 34.1 pct. X-ray diffraction (XRD) was used to determine the transformation response of the steels using interrupted tensile tests at room temperature. All three of the processed steels showed evidence of two-stage TRIP where γ-austenite first transformed to ε-martensite, and subsequently transformed to α-martensite.

Department(s)

Materials Science and Engineering

Comments

This work was supported by the Peaslee Steel Manufacturing Research Center (PSMRC). Companies directly involved in this work include AK Steel, ArcelorMittal, Nucor Steel, and U. S. Steel. The FEI Helios NanoLab dual beam FIB was obtained with a Major Research Instrumentation grant from the National Science Foundation under contract DMR-0723128.

Keywords and Phrases

Activation energy; Austenite; Binding energy; Carbon; Chemical activation; Chromium; Chromium alloys; Cold working; Dynamics; Hot working; Manganese; Martensite; Martensitic steel; Precipitation (chemical); Stacking faults; Steel; Strain hardening; Tensile strength; Tensile testing; X ray diffraction, Dislocation pinning; Dynamic strain aging; Epsilon martensite; Interrupted tensile test; Stacking fault energies; Stress-strain behaviors; Transformation induced plasticity steel; Ultimate tensile strength, Plasticity

International Standard Serial Number (ISSN)

1073-5623; 1543-1940

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2018 The Minerals, Metals & Materials Society and ASM International, All rights reserved.

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