Special Issue; Products for Industrial Machinery - NTN

NTN TECHNICAL REVIEW No.742006
5. Conclusion
NTN has performed a systematic series of
experiments for carbonitriding with JIS-SUJ2 high
carbon chromium bearing steel in an attempt to clarify
the nitrogen penetration mechanism associated with
this material. Also, assuming that the nitrogen
penetration mechanism is similar to the carbon
penetration mechanism, NTN has established a
method for predicting nitrogen concentration
distribution based on a series of experiments. The
findings are summarized as follows:
1) The nitrogen penetration amount increases
directly with an increases in the partial pressure
of undecomposed NH3.
2) The nitrogen penetration amount increases
directly with decreases in both carbon activity
ac* and H2 partial pressure.
3) NTN has established a method for predicting
the nitrogen concentration distribution of JIS-
SUJ2 material. This method reflects
considerations for the partial pressure of
undecomposed NH3, the carbon activity ac*, H2
partial pressure and the diffusion coefficient
that is dependent on nitrogen concentration.
4) NTN confirmed that, for various carbonitriding
atmospheres, the predicted steel nitrogen
concentration distribution (using NTN’s method
for determining nitrogen concentration
distribution) closely matches actual data
obtained through EPMA analysis.
References
1) N. Tsushima: SAE Technical Paper Series (1986)
860725 (in Japanese)
2) S. Narita and K. Yokose: “Effects of the nitriding potential
caused by surface nitrogen concentration on various
types of carbonitrided case hardening steel,” Japan
Society for Heat Treatment 61st Lecture Series
Preliminary draft (2005) 5 (in Japanese)
3) C. Ohki, M. Kawakita: “Effects of carbon activity from the
carbonitriding process on high-carbon steel,” Japan
Society for Heat Treatment 62nd Lecture Series
Preliminary draft (2006) 5 (in Japanese)
4) C. Ohki, M. Kawakita: “Effects of base gas partial
pressure from the carbonitriding process on high-carbon
steel,” Japan Society for Heat Treatment 62nd Lecture
Series Preliminary draft (2006) 17 (in Japanese)
5) Editorial Committee of the Society of Chemical Engineers
Japan: Chemical Engineering Handbook, Maruzen (1950)
64 (in Japanese)
6) R.Collin, S.Gunnarson, and D.Thulin: "Influence of
Reaction Rate on Gas Carburizing of Steel in a CO-
H2-CO2-H2O-CH4-N2 Atmosphere, "Journal of The Iron
and Steel Institute, (1972), 777
7) F. Neumann and U.Wyss: "Thermodynamische
Grundlagen zum indirekten Messen des C-Pegels, "
H.T.M., vol.49, No.4, (1994) 255 (in German)
-52-