Effect of intercritical temperature on the strain hardening of dual-phase bainite/ferrite steel

Abstract

Medium-carbon dual-phase bainite/ferrite steels with different bainite and carbide volume fractions were prepared via intercritical annealing and austempering. Bainite dominated the microstructure at high intercritical temperatures, and carbides and ferrite phase dominated at low temperatures. Carbides existed in two types, undissolved alloy–cementite and vanadium carbide. The ferrite grain size was reduced to 1.22 ± 0.7 µm at 790°C. Modified Crussard–Jaoul (MC–J) model was used to analyse the strain hardening process, and the highest strain hardening rate was obtained at 755°C. The high carbide fraction at 755°C increased the ferrite dislocation density and enhanced the ferrite phase strength. The high dislocation density in ferrite and the small strength difference in bainite and ferrite enhanced the strain hardening rate at 755°C.

KEYWORDS:

• Vanadium carbides
• strain hardening
• cold rolling
• localisation
• Dual-phase
• alloy-cementite
• recrystallization
• mechanical properties

Acknowledgements

This work was supported by the Natural Science Foundation of China (Nos. 51871192, 51831008), the China Postdoctoral Science Foundation (2018M631762) and the Youth Talent Projects of Colleges in Hebei Province (No. BJ2018056).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Natural Science Foundation of China [grant numbers 51871192, 51831008], the China Postdoctoral Science Foundation [grant number 2018M631762] and the Youth Talent Projects of Colleges in Hebei Province [grant number BJ2018056].