The Mechanism of High Strength-Ductility Steel Produced by a Novel Quenching-Partitioning-Tempering Process and the Mechanical Stability of Retained Austenite at Elevated Temperatures |
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Authors: | S Zhou K Zhang Y Wang J F Gu and Y H Rong |
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Affiliation: | (1) School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, P.R. China; |
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Abstract: | The designed steel of Fe-0.25C-1.5Mn-1.2Si-1.5Ni-0.05Nb (wt pct) treated by a novel quenching-partitioning-tempering (Q-P-T)
process demonstrates an excellent product of strength and elongation (PSE) at deformed temperatures from 298 K to 573 K (25 °C
to 300 °C) and shows a maximum value of PSE (over 27,000 MPa pct) at 473 K (200 °C). The results fitted by the exponent decay
law indicate that the retained austenite fraction with strain at a deformed temperature of 473 K (200 °C) decreases slower
than that at 298 K (25 °C); namely, the transformation induced plasticity (TRIP) effect occurs in a larger strain range at
473 K (200 °C) than at 298 K (25 °C), showing better mechanical stability. The work-hardening exponent curves of Q-P-T steel
further indicate that the largest plateau before necking appears at the deformed temperature of 473 K (200 °C), showing the
maximum TRIP effect, which is due to the mechanical stability of considerable retained austenite. The microstructural characterization
reveals that the high strength of Q-P-T steels results from dislocation-type martensite laths and dispersively distributed
fcc NbC or hcp ε-carbides in martensite matrix, while excellent ductility is attributed to the TRIP effect produced by considerable retained
austenite. |
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