The Effect of NbC Precipitates and Nb in Solid-Solution on the Phase Transformation Kinetics in High-Purity Fe-C-Mn-Nb Alloys

Abstract:

The precipitation of NbC in austenite is an important mechanism for improving the strength of steel because NbC-precipitates are known to decrease the ferrite grain size during the subsequent phase transformations upon cooling. The effect of the interaction between niobium (Nb) in solid solution and NbC-precipitates on the austenite-to-ferrite phase-transformation kinetics is not entirely clear. We study a high-purity Fe-C-Mn-Nb alloy cooled at different rates. Different annealing times at 850°C were applied to create different number densities and sizes of the NbC-precipitates in order to study the effect of NbC precipitation on the transformation kinetics. The alloy that is used in this study has an atomic ratio of Nb:C=1.3:1. The fraction of ferrite is measured as a function of temperature during cooling by means of dilatometry. The ferrite grain size is measured by means of optical microscopy. The results are interpreted with thermodynamic and kinetic models.

• Periodical: Solid State Phenomena (Volumes 172-174)
• Pages: 499-504
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.172-174.499
• Online since: June 2011
• Authors: Emine Gözde Dere, Hemant Sharma, S. Erik Offerman, Jilt Sietsma
• Keywords: High-Purity Alloy, Niobium Carbide, Phase Transformation Kinetics, Precipitation, Solid Solution

References

[1] Y. Takahama, J. Sietsma: ISIJ International, 2008. 48(4): pp.512-517.

[2] M. Suehiro, Z. K. Liu, J. Ǻgren: Acta Mater., 1996. 44: p.4241.

[3] R.G. Thiessen, I.M. Richardson and J. Sietsma: Mater Sci Eng A 427 2006, p.223.

[4] Y.H. Choi, H.C. Shin, C.S. Choi, and Y.K. Lee: J. Phys. IV, 2004, vol. 120, p.563–70.

[5] E. Courtois, T. Epicier, and C. Scott: Micron, 2006. 37(5), pp.492-502.

[6] M.G. Mecozzi, J. Sietsma, and S. van der Zwaag: Acta Materialia, 2006. 54(5): pp.1431-1440.

DOI: 10.1016/j.actamat.2005.11.014