Elevating carbon diffusion: deciphering the interplay of alloy composition and carburizing treatment in low carbon steels

Abstract

AbstractThe thermodynamics of mass transfer during gaseous carburization and its overall efficiency across various alloyed steels were investigated to discern the influence of alloy content. Quantitative analyses were conducted on the coefficients of mass transfer and carbon diffusivities for EN3, EN35, 20MnCr5, and EN353 steels at a carburization temperature of 930 °C. The study revealed distinct trends in mass transfer dynamics and carbon diffusion rates among the different alloyed steels. For instance, nickel majorly an austenite stabilizer, was found to enhance carbon diffusion in gamma iron, with observed coefficients of mass transfer ranging from 8.85 × 10−6 to 1.87 × 10−5 cm/s. However, EN35 steel exhibited slower mass transfer rates due to weaker atomic interactions, resulting in lower observed coefficients of mass transfer. Conversely, chromium and molybdenum, known carbide-forming elements, facilitated carbon transfer from the gaseous environment to the steel case in 20MnCr5 and EN353 steels, with observed coefficients of mass transfer ranging from 1.39 × 10−5 to 1.55 × 10−5 cm/s. Additionally, the study compared observed carbon diffusivities with those predicted by DICTRA (Diffusion Controlled TRAnsformation) kinetic and thermodynamic datasets, demonstrating excellent consistency. These findings underscore the significance of considering alloy content in achieving consistent carburizing outcomes and suggest potential modifications to existing carburizing methods to improve diffusion depth homogeneity. Overall, the study provides valuable insights into the impact of alloy elements on the carburization process and offers implications for optimizing carburizing practices in alloy steel manufacturing.

Keywords

• Carburizing
• diffusivity
• case hardening
• alloys
• steels
• Dr Ian Phillip Jones, University of Birmingham, United Kingdom of Great Britain and Northern Ireland