Investigation of the Changes of Surface Carbon of Carbon Steel during Heat Treatment

Research Summary

Carbon steel is actively researched in various fields due to its versatility. The understanding of carbon steel is deeper than any other metallic material. As in-situ analysis methods have been developed and refined, new phenomena in carbon steel have been reported.

In this study, we investigated the dynamic changes in surface carbon collapse and phase transformation of carbon steel during heat treatment using a synchrotron radiation and a Cr X-ray source (Chromium: X-ray energy ~ 5.4 keV). The temperature at which carbon steel collapses and forms cementite or ferrite structures was observed to be below the surface temperature of conventional carbon steel, which is 822 ℃ in the bulk. Furthermore, we distinguished three depth ranges from the surface and determined the different carbon distributions at each depth range. we revealed that the phase transition behavior between the surface and bulk differs during rapid heat treatment.

Expected Outcomes

This study, which elucidated the carbon collapse and phase transition on the surface of carbon steel using in-situ spectroscopy, is expected to be applicable to process design for surface treatment of carbon steel in the future steel industry.

Related Figures

• (a) Scanning Electron Microscopy images of carbon steel before and after heat treatment. (b) Contour plot of the C1s state spectrum measured during the heat treatment process of carbon steel. (c) Intensity profile corresponding to Carbide and C-solute in Figure 1-(b).
• Spectrum of the C1s state measured on the surface and subsurface of carbon steel before and after heat treatment, corresponding to the inelastic mean free path of (a) 2.0 nm and (b) 0.9 nm.