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Tailoring the mechanical properties of austempered low‑carbon ferritic-bainitic/martensitic dual‑phase steel

Motallebi Reza, Mirzadeh Hamed

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 1

art. no. e32, 2023

A simple heat treatment of austenitization followed by austempering was proposed to obtain ferritic-bainitic/martensitic dual-phase (DP) microstructure with ~ 18% bainite and ~ 30% martensite in low-carbon steel, which provides a promising way for processing of low-cost high-performance advanced high-strength steels (AHSSs) with improved strength-ductility trade-off, tensile toughness, and fracture behavior. The processed bainite-aided DP steel exhibited high yield stress and high ultimate tensile strength while maintaining high total elongation to failure, which were beyond the expected trends for conventional steels, ferritic-martensitic DP steels, and ferritic-bainitic DP steels. The continuous yielding behavior (with the disappearance of the yield point phenomenon) and more ductile fracture surface appearance were also remarkable. Accordingly, besides grain refinement by cold rolling and intercritical annealing, the present work proposed an alternative way for processing high-performance DP steels.

Superplasticity of high-entropy alloys: a review

Motallebi Reza, Savaedi Zeinab, Mirzadeh Hamed

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 1

art. no. e20, 2022

High-entropy alloys (HEAs) are a new class of engineering materials with unique mechanical and functional properties. Superplastic forming of HEAs might be a viable route for actual applications of these alloys. Accordingly, the superplastic behaviors of HEAs and medium-entropy alloys (MEAs) were summarized in this monograph, along with reviewing the basics of high-entropy alloys and fine-grained superplasticity. Moreover, the HEAs were introduced and the phase formation rules were discussed. Furthermore, the influences of grain refinement (by thermomechanical processing and severe plastic deformation (SPD) methods) and deformation conditions (temperature and strain rate) with special attention to the high strain rate superplasticity were summarized. The significance of thermal stability of the microstructure against grain coarsening was noticed, where the effects of multi-phase microstructure, formation of pinning particles, and favorable effects of the addition of alloying elements were explained. The effects of deformation temperature and strain rate on the thermally activated grain boundary sliding (GBS), precipitation of secondary phases (especially the Cr-rich σ phase), dissolution of phases, deformation-induced (dynamic) grain growth, partial melting, and dynamic recrystallization (DRX) were discussed for different HEAs and MEAs. The final part of this overview article is dedicated to the future prospects and research directions.