Effect of initial grain size on the mechanical behaviour of austenite during deformation under hot-working conditions

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 799; p. 139553
• Main Authors: Puchi-Cabrera, Eli Saúl, Guérin, Jean-Dominique, La Barbera-Sosa, José Gregorio, Dubar, Mirentxu, Dubar, Laurent
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 02.01.2021; Elsevier BV; Elsevier
• Subjects: Austenite; Austenitic grain size; Compression tests; Constitutive description; Deformation; Dynamic recrystallization kinetics; Engineering Sciences; Grain boundaries; Grain growth; Grain growth kinetics; Grain size; Hot working; Kinetics; Mechanical properties; Mechanics; Parameters; Recrystallization; Strain analysis; Strain rate; Yield strength; Yield stress; Grain growth kinetics; Dynamic recrystallization kinetics; Yield stress; Austenitic grain size; Constitutive description; "Dynamic recrystallization kinetics"; "Yield stress"; "Constitutive description"; "Grain growth kinetics"; "Austenitic grain size"
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2020.139553

The present investigation has been conducted to study the effect of the austenitic grain size (AGS) on the flow stress behaviour of austenite, deformed in a wide range of temperatures and strain rates, employing samples of a commercial ER7 steel grade. To accomplish this objective, a novel general methodology for the analysis of the austenitic grain growth kinetics under combined arbitrary isothermal and non-isothermal austenitizing treatments has been developed. In this way, it has been possible to characterize the AGS effect when this parameter varies between approximately 135 to 260 μm. For this purpose, axisymmetric compression tests have been conducted in the temperature range of 850 °C–1250 °C, at strain rates in the range of 0.005–10 s−1. The experimental results show that the constant associated with the strength of grain boundaries in the Hall-Petch relationship, is approximately 57 MPa μm1/2. Accordingly, the athermal stress values are in the range of 3–5 MPa. Also, the exponent which characterizes the effect of the AGS on the time required to achieve 50% DRX, was found to be approximately 0.1, which also reflects a rather weak effect of this parameter on the evolution of the volume fraction recrystallized dynamically. The relevance of analyzing the DRX kinetics of the alloy based on the recrystallization time rather than on the applied strain is also discussed. The prediction of the change in the volume fraction recrystallized dynamically during deformation under variable strain rate conditions is analyzed and the verification of the conditions which promote DRX is highlighted. A set of sequential equations encompassing both a physically-based constitutive description, as well as a simple parametric relationship for the computation of the flow stress of the alloy, are proposed. •The effect of the initial grain size on the mechanical behavior of austenite has been characterized.•A novel general methodology for the analysis of the austenitic grain growth kinetics is proposed.•The global effect of the austenitic grain size on the mechanical strength of austenite is rather weak.•The relevance of analyzing the DRX kinetics on the basis of time rather than strain is discussed.•A sequential set of equations for the physically-based constitutive description of the ER7 steel grade is provided.