Problems and solutions for determination of carbon transfer coefficient β using steel foil carburising method

Abstract

In this paper, the carburising process of steel foil was simulated by numerical method and the carbon transfer coefficient β at the workpiece surface was calculated with the conventional formula for the steel foil carburising test. The results indicated that foil thickness, carburising time and carbon diffusion coefficient in foil apparently affect the calculated carbon transfer coefficient, which always has a smaller value than the preset β value (the true value) and decreases with decreasing carbon diffusion coefficient. This paper suggests that the conventional formula is applicable only when carbon diffusion coefficient in foil is close to infinity; otherwise, the calculated β has obvious error and consequently, gives false information about the influences of other test factors. We propose a new calculation method based on the analytical solution of the diffusion equation during steel foil carburising and a supplementary test, with which the calculated β coefficient is close to the true value, and the carbon diffusion coefficient can be obtained simultaneously.

Keywords:

• Carbon transfer coefficient
• Carbon diffusion coefficient
• Analytical solution
• Numerical solution
• Lumped parameter method

Acknowledgements

The paper is based on a contribution to the Chinese Journal Heat Treatment, 2014, No. 4.