Microstructures and Mechanical Properties of Steels and Alloys Subjected to Large-Strain Cold-to-Warm Deformation

Anastasiia Dolzhenko,Marina Tikhonova,Andrey Belyakov,Rustam Kaibyshev

doi:10.3390/met12030454

Abstract

The effect of large-strain cold-to-warm deformation on the microstructures and mechanical properties of various steels and alloys is critically reviewed. The review is mainly focused on the microstructure evolution, whereas the deformation textures are cursorily considered without detailed examination. The deformation microstructures are considered in a wide strain range, from early straining to severe deformations. Such an approach offers a clearer view of how the deformation mechanisms affect the structural changes leading to the final microstructures evolved in large strains. The general regularities of microstructure evolution are shown for different deformation methods, including conventional rolling/swaging and special techniques, such as equal channel angular pressing or torsion under high pressure. The microstructural changes during deformations under different processing conditions are considered as functions of total strain. Then, some important mutual relationships between the microstructural parameters, e.g., grain size vs. dislocation density, are revealed and discussed. Particular attention is paid to the mechanisms of microstructure evolution that are responsible for the grain refinement. The development of an ultrafine-grained microstructure during large strain deformation is considered in terms of continuous dynamic recrystallization. The regularities of the latter are discussed in comparison with conventional (discontinuous) dynamic recrystallization and grain subdivision (fragmentation) phenomenon. The structure–property relations are quantitatively represented for the structural strengthening, taking into account various mechanisms of dislocation retardation.

Highlights

The deformation microstructures that evolve in steels and alloys by large-strain coldto-warm working are of great importance for materials scientists and mechanical engineers
This gap in the knowledge is associated with practical difficulty in attaining sufficiently large strains to achieve the steady-state deformation behavior when the deformation microstructures are solely controlled by processing conditions
The large strain deformations under conditions of cold-to-warm working are widely used techniques to enhance the mechanical performance of structural steels and alloys

Summary

Introduction

The deformation microstructures that evolve in steels and alloys by large-strain coldto-warm working are of great importance for materials scientists and mechanical engineers.Almost all established thermomechanical treatments and novel metal-forming processing methods involve plastic deformation to rather large strains under various conditions [1–3].Needless to say, the mechanical properties of the final products are highly dependent on the microstructural state, which, in turn, is controlled by preceding plastic working. The regularities of microstructure evolution, including the change in the grain size and the dislocation density during plastic deformation at elevated temperatures, i.e., under hot working conditions, have been fairly clarified in a number of papers [9–13]. The deformation microstructures evolved under conditions of cold-to-warm working have not been quantitatively generalized This gap in the knowledge is associated with practical difficulty in attaining sufficiently large strains to achieve the steady-state deformation behavior when the deformation microstructures are solely controlled by processing conditions. Several special techniques have been developed to realize severe plastic deformation at low-to-moderate temperatures [14–20] Among those techniques, torsion under high pressure and equal channel angular pressing (ECAP) are the most famous ones [21–23]. The most of specific severe plastic deformation techniques are rather cumbersome procedures that are used for research purpose only; some of them, such as ECAP-Conform [28], accumulative roll-bonding [29], and multiple forging [30], can be utilized for sizeable semi-products

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