High temperature deformation behaviour and microstructure evolution in Cu containing High Strength Low Alloy (HSLA) steel

ABSTRACT

The hot deformation behaviour of a Cu containing high strength low alloy (HSLA) steel has been evaluated by carrying out hot compression tests over a temperature range of 900 °C to 1100 °C and constant true strain rates of 0.0003 to 1 s⁻¹. Although single peak flow curve is observed predominantly, a tendency to exhibit multiple peaks at low strain rates (0.0003 and/or 0.001 s⁻¹) at temperature greater than 950 °C. The important parameters pertaining to dynamic recrystallisation (DRX), such as critical, peak, steady state stress and strain were ascertained, and the DRX state diagram depicting the variation of critical parameters governing DRX with Zener-Hollomon parameter Z was established. The volume fraction of recrystallised grains, computed from flow stress, as expected, follows a sigmoidal trend indicating higher kinetics at low strain rates for a given temperature. Reconstruction of prior austenite grain boundaries (PAGB) based on electron back scattered diffraction (EBSD) technique for a few select specimens clearly elucidated the effect of temperature and strain rate on the DRX behaviour of the steel. The DRX state diagram established here clearly demarcates the deformation space i.e. temperature-strain rate-stain space into regimes where the material exhibits full DRX, hardening/softening + DRX and only hardening (no DRX) behaviour. This would be useful for designing suitable forging sequence to achieve the desired microstructure and mechanical properties.

KEYWORDS:

• High strength low alloy steel
• Hot deformation
• Dynamic recrystallisation
• Electron back scattered diffraction
• Prior austenite grain boundary

Acknowledgements

The authors sincerely thank DRDO, India for funding the research work and Director, Defence Metallurgical Research Laboratory for his continuous support and permission to publish this work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Credit authorship contribution statement

A. Venkata Ramana: Methodology, acquisition of data, Visualization, Writing original draft. I. Balasundar: Resources, Conceptualization, review and editing. M.J. Davidson: Supervision. Vajinder Singh: EBSD Software, formal analysis. J.P.Gautam: Data supervision, investigation. K. Gopinath: Review and editing, investigation. R. Balamuralikrishnan: Review and editing, project administration, funding acquisition. T. Raghu: Resources, investigation.