Journal of Northeastern University Natural Science ›› 2020, Vol. 41 ›› Issue (4): 505-510.DOI: 10.12068/j.issn.1005-3026.2020.04.009

• Materials & Metallurgy • Previous Articles     Next Articles

Nitrogen Control Process of COST-FB2 Rotor Steel for Ultra-supercritical Thermal Power Station

PENG Lei-zhen, JIANG Zhou-hua, GENG Xin, LI Xiao-kai   

  1. School of Metallurgy, Northeastern University, Shenyang 110819, China.
  • Received:2019-05-20 Revised:2019-05-20 Online:2020-04-15 Published:2020-04-17
  • Contact: JIANG Zhou-hua
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Abstract: The gas phase nitriding process of COST-FB2 steel was studied by conducting the gas phase nitriding experiment and thermodynamic calculation under different nitrogen partial pressure and nitriding time in a 30kg vacuum induction furnace. The optical emission spectrometer ARL 4460, gas analyzer of TC-500 and infrared analyzer HIR-944B were used to analyze the content in the middle part of ingot sample. The results showed that the calculated data is in a good agreement with the experimental one when the nitriding pressure is ≤20kPa. Since gas phase nitriding is a first-order reaction, the nitrogen content in the tested steel can reach the equilibrium value with the nitriding time of 15min. When the partial pressure of nitrogen is 1.5~6kPa,the mass fraction of nitrogen in COST-FB2 steel can be controlled between 0.015%~0.03%. In order to avoid the formation of porosity defects inside the ingot during casting, pressure casting should be preferred to use with a pressure of at least 20kPa. Moreover, the mass fraction of nitrogen in steel should be controlled between 0.015%~0.02% and the nitrogen partial pressure should be 1.5~3kPa during smelting so that the formation of large particle BN in the tested steel can be avoided.

Key words: COST-FB2, nitrogen alloying, partial pressure of N2, Factsage method, boron nitride(BN)

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