Effect of thermal treatment on the evolution of delta ferrite in 11Cr–3Co–2.3W steel

ABSTRACT

Effect of thermal treatment on the evolution of delta ferrite was studied in 11Cr–3Co–2.3W steel. Ferrite-forming alloy elements promoted the formation of delta ferrite during thermo-mechanical processing. The results of JMatPro and chromium equivalent calculations indicated that 11Cr–3Co–2.3W steel partially contained delta ferrite. Cr and W were segregated in/around delta ferrite. Delta ferrite had a bamboo-type morphology and it contained MX-type carbonitrides inside and the Laves phase at the interface between delta ferrite and martensite. On annealing, delta ferrite dissolved especially during the early stage of annealing. After ageing at 600°C for 500 h, some Laves phases were observed in delta ferrite which is regarded as a favourable nucleation site. In the meantime, its precipitation resulted in the reduction of dissolved W and Mo in the matrix.

KEYWORDS:

• Delta ferrite
• precipitation
• Laves phase
• annealing
• dissolution

Acknowledgement

R. D. K. Misra, as an honorary professor, gratefully acknowledges the continued collaboration with Northeastern University for providing guidance to students.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors are grateful for the financial support from National High Technology Research and Development Program of China (2015AA03A501).