Abstract
Carbon diffusion in austenite plays a critical role in phase transformation in steel. However, it can only be estimated in the fully austenitic range and has then to be extrapolated to the temperature range of the phase transformation. Therefore, published data are limited to temperatures above 750 °C. In this study, new experiments are carried out to determine the carbon diffusion coefficient in austenite at temperatures as low as 500 °C. Carburization experiments are performed in the austenitic range for a Fe-1.5 pct Mn 0.13 pct C and a Fe-31 pct Ni alloy (wt pct). Composition profile measurements, which are done using glow discharge optical emission spectrometry (GDOES), show that the surface composition is not constant with time. A methodology has been developed to assess the diffusion coefficient of carbon in austenite combining the measured carbon profiles and a numerical method to compute the diffusion profile taking into account the time evolution of the boundary condition. This method is first validated on the Fe-C-Mn steel. Carburization experiments are carried out on a Fe-31 pct Ni alloy at 900 °C, 800 °C, 700 °C, 600 °C, and 500 °C. The carbon diffusion coefficient is assessed using the method described above and fitted with the following expression (T in Kelvin): \( D = 1.23\cdot10^{{ - 6}} \cdot e^{{ - \frac{{15,050}} {{T{\left( {\text{K}} \right)}}}}} ({\text{m}}^{{\text{2}}} {\text{/s}}) \). The new expression is compared with previous experimental results measured for comparable nickel content at higher temperatures, and it shows a reasonable agreement. The model proposed by Agren for carbon diffusion has been modified to take into account the thermodynamic contribution of nickel. This model also shows good agreement with the present experimental results, even if it was fitted to experiments performed at higher temperatures.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.