An enhancement in mechanical properties of grade 91 steel on microalloying with boron and nitrogen

ABSTRACT

Effects of microalloying the grade 91 steel with boron along with control on nitrogen content (P91BN) on its microstructure, tensile and creep properties have been investigated and compared with those of the standard grade 91 steel (P91). The P91BN steel possesses finer martensite lath structure and M₂₃C₆ precipitates in comparison with the P91 steel. Tensile strengths of the P91BN steel were comparable with the P91 steel up to 823 K. The P91BN steel has possessed higher tensile strengths than the P91 steel at higher temperatures (above 823 K). Microalloying the steel with boron decreases the creep deformation rate with significant increase in creep rupture life. Finer lath width, higher number density of fine M₂₃C₆ precipitates in pre-creep condition along with sluggish coarsening of M₂₃C₆ precipitates resulting in better stabilisation of martensite structural features in the P91 steel on boron micro-alloying, leads to the significant improvement in high temperature tensile and creep strengths.

KEYWORDS:

• Microalloying of P91 steel with boron
• microstructure
• tensile
• creep

Acknowledgements

The authors wish to thank Dr Arun Kumar Bhaduri, Director, Indira Gandhi Centre for Atomic Research, for his keen interest in the work. The support extended by Dr Syamala Rao Polaki in microstructural investigation is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.