Grain growth during reheating of HSLA steels with a narrow segregation separation

Abstract

Reheat treatments for two HSLA steels, a forged Al-Nb-containing steel (Steel-1) and an as-rolled Nb-containing steel (Steel-2), were carried out for one to three hours at temperatures between 1090 and 1250°C which were selected by the precipitates’ dissolution temperatures predicted by Thermo-Calc and DICTRA. Steel-1 contains continuous segregation bands with segregation spacing of 65 ± 10 µm, whereas Steel-2 contains discontinuous segregation bands with spacing of 35 ± 10 µm. Uniform grain size distributions occurred in Steel-1 for all reheat temperatures whereas abnormally large grains were observed in Steel-2 when reheating at 1090°C. A mechanism for grain size development in materials with continuous and discontinuous segregation bands based on austenite nucleation and growth and precipitate pinning in the segregation band is proposed.

KEYWORDS:

• HSLA steels
• grain growth
• segregation spacing
• reheating
• abnormal grain growth
• uniform grain growth
• microalloying precipitates
• thermodynamic calculation

Acknowledgements

The authors would like to thank Tata Steel Europe for the provision of material and the School of Metallurgy and Materials at the University of Birmingham for providing the facilities required for the research.

Disclosure statement

No potential conflict of interest was reported by the authors.