J. Mater. Sci. Technol. ›› 2017, Vol. 33 ›› Issue (11): 1300-1307.DOI: 10.1016/j.jmst.2016.06.026

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Effect of Solution Annealing on Microstructure and Mechanical Properties of a Ni-Cr-W-Fe Alloy

Ou Meiqiong1,2, Ma Yingche1,3,*(), Hao Xianchao1, Wan Baifang3, Liang Tian1, Liu Kui1   

  1. 1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
    2 School of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China
    3 Jiangsu Toland Alloy Co., Ltd. Danyang 212352, China
  • Received:2016-05-03 Revised:2016-06-07 Accepted:2016-06-14 Online:2017-11-20 Published:2018-01-25
  • Contact: Ma Yingche
  • About author:

    1 These two authors contributed equally to this paper.

Abstract:

The effect of solution annealing on the microstructure and mechanical properties of a Ni-Cr-W-Fe alloy developed for advanced 700 °C ultra-supercritical power plants was investigated. Test samples in this study were subjected to different solution treatments and the same aging treatment (at 760 °C for 1 h). When solution annealing temperature was elevated from 1020 °C to 1150 °C, the stress-rupture life at 750 °C/320 MPa was increased from 60 h to 300 h, the stress-rupture elongation was enhanced from 12% to 17%, and the elongation of the tensile at 750 °C was improved from 11% to 24%. All tensile and stress-rupture samples displayed an intergranular dimple mixed fracture. Intergranular micro-cracks had a great relationship with the morphology of grain boundary carbides. Most carbides retained the morphology of globular shape and continuous thin plate. After tensile and stress-rupture tests, a few carbides were converted into lamellar. The results showed that intergranular micro-cracks were easier to form at continuous thin plate carbides than at globular shape carbides. Lamellar carbides hardly caused the nucleation of micro-cracks. Besides, grain boundaries sliding and elements diffusion during stress-rupture tests led to the formation of precipitate free zones, which accelerated the extension of micro-cracks and influenced the stress-rupture life.

Key words: Ni-Cr-W-Fe alloy, Solution annealing, Grain boundaries carbides, Precipitate free zones, Mechanical properties