Abstract
The knowledge of the flow behavior of metallic alloys subjected to hot forming operations has particular interest for metallurgists in the practice of industrial forming processes involving high temperatures (e.g., rolling, forging, and/or extrusion operations). Dynamic recrystallisation (DRX) occurs during high temperature forming over a wide range of metals and alloys, and it is known to be a powerful tool that can be used to control the microstructure and mechanical properties. Therefore, it is important to know, particularly in low stacking fault energy materials, the precise time at which DRX is available to act. Under a constant strain rate condition, and for a given temperature, such a time is defined as a critical strain (εc). Unfortunately, this critical value is not always directly measurable on the flow curve; as a result, different methods have been developed to derive it. Focused on carbon and microalloyed steels subjected to laboratory-scale testing, in the present work, the state of art on the critical strain for the initiation of DRX is reviewed and summarized. A review of the different methods and expressions for assessing the critical strain is also included. The collected data are well suited to feeding constitutive models and computational codes.
Highlights
IntroductionRecrystallisation during hot working operations of metals and metallic alloys (temperature in the range of 0.5–0.9Tm, where Tm is the absolute melting temperature [1,2,3]) is commonly called dynamic recrystallisation (DRX) or discontinuous dynamic recrystallisation (dDRX) and has been broadly investigated in the past decades
Recrystallisation during hot working operations of metals and metallic alloys is commonly called dynamic recrystallisation (DRX) or discontinuous dynamic recrystallisation and has been broadly investigated in the past decades
The former will decrease with decreasing strain rate or increasing temperature, as the dislocation density generated at any given level of strain will be lower
Summary
Recrystallisation during hot working operations of metals and metallic alloys (temperature in the range of 0.5–0.9Tm, where Tm is the absolute melting temperature [1,2,3]) is commonly called dynamic recrystallisation (DRX) or discontinuous dynamic recrystallisation (dDRX) and has been broadly investigated in the past decades. The characteristics of the dynamic recrystallisation behavior (i.e., the critical strain value) depend mainly on several parameters and factors, namely, the chemical composition of the alloy, the grain size prior to the deformation, the temperature and strain rate, the deformation mode (torsion, compression, etc.), and the applied thermomechanical cycle. Two of them are closely related to the initiation of DRX: (i) the driving force for dynamic recrystallisation and (ii) the mobility of the sub-boundaries The former will decrease with decreasing strain rate or increasing temperature, as the dislocation density generated at any given level of strain will be lower. This literature review article is an extension of work previously conducted by Varela-Castro et al [31]
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