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Formation and Behavior of Metastable Austenite in Advanced High Strength Steels

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Manufacturing Processes and Systems".

Deadline for manuscript submissions: closed (30 April 2020) | Viewed by 14565

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Prof. Dr. Gregory N. Haidemenopoulos

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Department of Mechanical Engineering, University of Thessaly, Athens Avenue, Pedion Areos, 38334 Volos, Greece
Interests: physical metallurgy; computational alloy thermodynamics and kinetics; ICME; alloy and process design; metastable austenite in steels; TRIP effects in steels
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Dear Colleagues

The historical development of advanced high strength steels (AHHS) includes 1^st, 2^nd and 3^rd generation AHHS. The 1^st generation basically includes low-alloy steels with ferritic matrix and multiphase microstructure. Low-alloy TRIP steels, which belong to the 1^st generation, are multiphase steels containing metastable retained austenite, exhibiting the TRIP effect. The 2^nd generation AHHS steels include high-alloy steels containing a high amount of manganese. These steels exhibit a fully-austenitic microstructure and the deformation-induced γ→ε and ε→α’ transformations influence their mechanical behavior. The 3^rd generation AHHS steels include steels with mechanical properties filling the gap between the 1^st and 2^nd generations. Quench & Partitioning (Q&P) and Medium-Mn steels are examples of 3^rd generation AHHS steels.

Regarding the TRIP effect, a common characteristic of these steel groups, is the presence of metastable austenite in their microstructure. The austenite phase can either be homogeneous (2^nd generation) or dispersed (1^st and 3^rd generations) in a multi-phase microstructure. The behavior of the austenitic phase during forming or loading determines the mechanical behavior in terms of strength, ductility and formability of the above steel grades. The behavior of austenite depends, on microstructural details such as size and shape of austenite as well as neighborness with other phases, which are established during processing. The stability of austenite has been recognized as the key issue controlling the mechanical behavior of austenite-containing steels and significant research is currently focused on the control of austenite stability in order to design optimized high-performance steel grades.

This Special Issue, “Formation and Behavior of Metastable Austenite in Advanced High-Strength Steels”, will include research papers and reviews on all aspects of metastable austenite in steels including, but not limited to, advanced processing of austenite-containing steels, austenite formation during heat treatment, microstructure development, solute partitioning and stabilization, effects of chemical composition, size, shape and triaxiality on austenite stability, stacking fault energy (SFE) effects, deformation-induced transformation under monotonic uniaxial or multiaxial loading, as well as cyclic loading, advanced experimental techniques to monitor the deformation-induced austenite transformation, modeling and simulation and finally alloy and process design for enhanced TRIP effects.

Prof. Gregory N. Haidemenopoulos
Guest Editor

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Keywords

Thermodynamics and kinetics of austenite formation
Processing for austenite stabilization
Austenite stability
Stress-assisted and strain-induced transformation kinetics
Mechanical effects of austenite transformation under monotonic or cyclic loading
Microstructural characterization of metastable retained austenite
Hydrogen embrittlement and austenite in steels
Alloy design for austenite-containing steels
Modeling the formation and behavior of austenite in steels
Deformation-induced transformation and constitutive behavior
Low alloy TRIP steels
TWIP steels
High-Mn TRIP steels
Q&P TRIP steels
Medium-Mn TRIP steels
Bainitic steels containing retained austenite
High-Entropy steels with TRIP effect

Published Papers (5 papers)

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Research

13 pages, 8178 KiB

Open AccessArticle

Strong Interactions between Austenite and the Matrix of Medium-Mn Steel during Intercritical Annealing

by Tianpeng Zhou, Cunyu Wang, Chang Wang, Wenquan Cao and Zejun Chen

Materials 2020, 13(15), 3366; https://doi.org/10.3390/ma13153366 - 29 Jul 2020

Cited by 5 | Viewed by 1786

Abstract

The effects of heat treatment on the microstructure evolution was studied in regards to austenite nucleation and grain growth. It was found that the austenite nucleation and matrix recrystallization kinetics of samples annealed at 675 °C for different times were revealed, implying a strong interaction between the ferrite matrix and austenite. The recrystallization of the matrix during annealing provided favorable conditions for austenite nucleation and growth, and the formation of austenite during this process reduced the matrix recrystallization kinetics, thus delaying the recrystallization process of the matrix around the austenite grains. The statistical results for the austenite grain size under different annealing temperatures indicated that the average grain size of the austenite slightly increases with increasing of the annealing temperature, but the austenite with the largest grain size grows faster at the same temperature. This difference is attributed to the strict Kurdjumov Sachs (KS) orientation relationship (OR) between the austenite grains and the matrix, because the growth of austenite with a strict KS OR with the matrix is often inhibited during annealing. In contrast, the austenite maintains a non-strict KS OR with the matrix and can grow preferentially with increasing annealing temperature and time. Full article

(This article belongs to the Special Issue Formation and Behavior of Metastable Austenite in Advanced High Strength Steels)

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12 pages, 3731 KiB

Open AccessArticle

Neutron Diffraction and Diffraction Contrast Imaging for Mapping the TRIP Effect under Load Path Change

by Efthymios Polatidis, Manuel Morgano, Florencia Malamud, Michael Bacak, Tobias Panzner, Helena Van Swygenhoven and Markus Strobl

Materials 2020, 13(6), 1450; https://doi.org/10.3390/ma13061450 - 23 Mar 2020

Cited by 15 | Viewed by 2842

Abstract

The transformation induced plasticity (TRIP) effect is investigated during a load path change using a cruciform sample. The transformation properties are followed by in-situ neutron diffraction derived from the central area of the cruciform sample. Additionally, the spatial distribution of the TRIP effect triggered by stress concentrations is visualized using neutron Bragg edge imaging including, e.g., weak positions of the cruciform geometry. The results demonstrate that neutron diffraction contrast imaging offers the possibility to capture the TRIP effect in objects with complex geometries under complex stress states. Full article

(This article belongs to the Special Issue Formation and Behavior of Metastable Austenite in Advanced High Strength Steels)

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40 pages, 1797 KiB

Open AccessArticle

TRIP Steels: A Multiscale Computational Simulation and Experimental Study of Heat Treatment and Mechanical Behavior

by Ioanna Papadioti, Ilias Bellas, Maria-Ioanna T. Tzini, Peter I. Christodoulou and Nikolaos Aravas

Materials 2020, 13(2), 458; https://doi.org/10.3390/ma13020458 - 18 Jan 2020

Cited by 6 | Viewed by 2871

Abstract

A multiscale investigation of the microstructure and the mechanical behavior of TRIP steels is presented. A multi-phase field model is employed to predict the microstructure of a low-alloy TRIP700 steel during a two-stage heat treatment. The resulting stability of retained austenite is examined [...] Read more.

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temperature. The phase field results are experimentally validated and implemented into a model for the kinetics of retained austenite during strain-induced transformation. The kinetics model is calibrated by using experimental data for the evolution of the martensite volume fraction in uniaxial tension. The transformation kinetics model is used together with homogenization methods for non-linear composites to develop a constitutive model for the mechanical behavior of the TRIP steel. A methodology for the numerical integration of the constitutive equations is developed and the model is implemented in a general-purpose finite element program (ABAQUS). Necking of a bar in uniaxial tension is simulated and “forming limit diagrams” (FLDs) for sheets made of TRIP steels are calculated. The models developed provide an integrated simulation toolkit for the computer-assisted design of TRIP steels and can be used to translate mechanical property requirements into optimised microstructural characteristics and to identify the appropriate processing routes. Full article

(This article belongs to the Special Issue Formation and Behavior of Metastable Austenite in Advanced High Strength Steels)

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18 pages, 6713 KiB

Open AccessArticle

Metastable Austenitic Steel Structure and Mechanical Properties Evolution in the Process of Cold Radial Forging

by Dmitry Panov, Alexey Pertsev, Alexander Smirnov, Vladislav Khotinov and Yuri Simonov

Materials 2019, 12(13), 2058; https://doi.org/10.3390/ma12132058 - 26 Jun 2019

Cited by 20 | Viewed by 3133

Abstract

The article presents the influence of structure formation on the properties of 321 metastable austenitic stainless steel in the process of cold radial forging (CRF). The steel under study after austenitization was subjected to CRF at room temperature with degrees of true strain (e) 0.26, 0.56, 1.00, 1.71 and 2.14. It has been shown that structure formation of the studied steel during CRF consists of three stages: formation of the lamellar structure of austenite, formation of the trapezoidal structure, and formation of the equiaxial grain structure. The kinetics of the strain-induced α′-martensitic transformation is related to the stages of structure evolution. Hardness, ultimate tensile strength and yield strength uniformly increase in all stages of structure formation with a significant decrease of elongation to fracture during the first stage of structure formation while the value of elongation to fracture remains constant in the subsequent stages of deformation. Impact strength of fatigue cracked specimens (KCT) decreases sharply at the first stage of structure formation and smoothly increases at the second and third stages. However, the impact strength of V-notch specimens (KCV) continuously decreases when deformation degree increases in the overall investigated deformation range. Full article

(This article belongs to the Special Issue Formation and Behavior of Metastable Austenite in Advanced High Strength Steels)

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17 pages, 8584 KiB

Open AccessArticle

Microstructure Evolution and Mechanical Stability of Retained Austenite in Thermomechanically Processed Medium-Mn Steel

by Adam Grajcar, Andrzej Kilarski, Aleksandra Kozłowska and Krzysztof Radwański

Materials 2019, 12(3), 501; https://doi.org/10.3390/ma12030501 - 06 Feb 2019

Cited by 15 | Viewed by 3341

Abstract

A microstructure evolution of the thermomechanically processed 3Mn-1.5Al type steel and mechanical stability of retained austenite were investigated during interrupted tensile tests. The microstructural details were revealed using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) techniques. It was found that the strain-induced martensitic transformation began in central regions of the largest blocky-type grains of retained austenite and propagated to outer areas of the grains as the deformation level increased. At rupture, the mechanical stability showed only boundaries of fine blocky grains of γ phase and austenitic layers located between bainitic ferrite laths. The effects of various carbon enrichment, grain size, and location in the microstructure were considered. The martensitic transformation progress was the highest at the initial stage of deformation and gradually decreased as the deformation level increased. Full article

(This article belongs to the Special Issue Formation and Behavior of Metastable Austenite in Advanced High Strength Steels)

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