Precipitation behavior of high-Nb containing modified HR3C heat-resistant steels during isothermal aging

ABSTRACT

The effect of Cr content on microstructural stability of the modified high-Nb content HR3C austenitic heat-resistant steel has been investigated during thermal aging at 700°C. It was observed that the σ phase precipitated in the 23.5Cr–18Ni–1.7Nb–0.04C–0.1N (wt.%) steel after aging treatment. However, the σ phase was not observed throughout the aging up to 5000 h as the Cr content was reduced from 23.5 to 21.5 wt-%. Experimental results showed that the yield strength of steel with 23.5 wt-% Cr at room temperature increased from 261 to 492 MPa after aging for 5000 h. The strengthening is closely related to the precipitation of σ phase at early stage of aging (500–2000 h). The influence of alloying elements on the formation of σ phase is discussed.

KEYWORDS:

• HR3C
• austenitic heat-resistant steel
• microstructure stability
• σ phase
• thermal aging
• alloying elements
• Cr content
• yield strength

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Jiaming Bai http://orcid.org/0000-0003-0293-3237

Additional information

Funding

This work has been financially supported by the China Huaneng Group Co. Ltd.: [grant number HNKJ18-H08]; Postdoctoral Science Foundation of Shaanxi Province of China : [grant number 2018BSHQYXMZZ32]; Postdoctoral Research Foundation of China: [grant number 2017M623213].