Effects of Carbon Content Change on Growth of Compound Layer in Surface of Nitrided Steel

Abstract:

When steel is nitrided, a compound layer mainly composed of iron nitrides, ε-Fe_2~3N and the γ’-Fe₄N phase, is formed on the steel surface. It is an extremely important industrial issue to clarify factors governing the formation of the compound layer during nitriding and to establish unified views on the mechanism of compound layer formation. Therefore, in order to clarify the effect of change in carbon concentration on the growth of the ε phase and the γ’ phase in the compound layer on nitrided steel, we evaluated the change over time in the concentration of the alloy elements in the surface layer, and the phases of the compound layer on nitrided steels containing various amount of carbon in the matrix. The results were that the change over time in the carbon concentration in the compound layer was mainly responsible for the change over time in the phases of the compound layer. Furthermore, it was discovered that the change over time in the carbon concentration distribution occurred because both increasing of carbon from the matrix to the compound layer, and decreasing of carbon from the surface of compound layer to the atmosphere. That caused the gradient change of chemical potential of carbon in the through-thickness direction of compound layer, and the phases of the compound layer were changed with the treatment time.

• Periodical: Materials Science Forum (Volume 1016)
• Pages: 1510-1514
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.1016.1510
• Online since: January 2021
• Authors: Takahide Umehara*, Masato Yuya
• Keywords: Carbon, Compound Layer, Microstructure, Nitriding, Nitriding Potential, Thermodynamic Calculation

References

[1] T. Yamada, A. Kono, Netsu Shori 23 (1983) 151-156.

[2] T. Takayama, S. Hinotani, K. Izumi, Y. Kamada and K. Nishida, Sumitomo Met. 48 (1996) 119-127.

[3] A. Kobayashi, S. Maeda, H. Imataka, Y. Gyotoku, M. Yuya, Y. Shimizu and M. Kanayama, JSAE Spring Conv. Proc. (2014) pp.21-26.

[4] S. Takagi, Y. Tonozuka and N. Nakamura: Tetsu-to-Hagane 104 (2018) 594-601.

[5] Y. Hiraoka, A. Ishida and O. Umezawa: Netsu Shori 57 (2017) 64-72.

[6] E. J. Mittemeijer and M. A. J. Somers, Surface Engineering, 12 (1996) 152-162.

[7] H. J. Spies, H. J. Berg and H. Zimdars, Harterei.-Techn. Mitt. 58 (2003) 189-197.

[8] D. Liedtke, et al. Nitriding and Nitrocarburizing on Iron Materials, AGNE Gijutsu Center, Tokyo, 2011 p.41.