Partial austenitisation and TBF steel composed of ferrite, bainitic ferrite, and austenite

Abstract

A TRIP-aided bainitic-ferritic (TBF) steel with a chemical composition of Fe–0.19C–1.7Mn–1.09Si–0.51Al–0.05Nb (wt-%) was partially austenitised from a hot-rolled martensitic initial microstructure. After the hot rolling, the martensitic specimens were reheated to different intercritical temperatures and then austempered at 350°C. Thus, the effect of the initial microstructure of TBF steel on intercritical austenite formation during partial austenitisation was studied. The microstructures were investigated by scanning electron microscopy and electron backscatter diffraction (EBSD), and the tensile properties were tested. Microstructural observations revealed that a final microstructure of fine ferrite, bainitic ferrite, and retained austenite can be obtained. The steel partial austenitised at 770°C showed a good combination of ultimate tensile strength and total elongation.

KEYWORDS:

• TBF steels
• partial austenitisation
• phase transformations
• microstructural characterisation
• mechanical properties

Acknowledgments

Individual test methods were successfully carried out in cooperation with the following companies: Erdemir T.A.Ş, Zonguldak, Turkey, and Metal Forming Center of Excellence of Atılım University, Turkey. Authors thanks Seda Daldal Akın from Erdemir T.A.Ş, Zonguldak, Turkey for access to FEG-SEM as well as JMatPro Software. They are also grateful to Assoc. Professor Dr. C. Şimşir and Alp Yalçın from Metal Forming Center of Excellence of Atılım University for precision dilatometer testing and EBSD measurements.

Disclosure statement

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

Additional information

Funding

This study was supported by the Scientific and Technological Research Council of Turkey (TÜBİTAK) under research project number 216M447 and by Kocaeli Üniversitesi Research Fund under Project No. FBA-2020-2065.