Dynamic behavior of carbon in steel by using soft X-ray absorption spectroscopy and spectrum simulation

The ferritic steel with supersaturated solid solution carbon remarkable increase in hardness by heat treatment (so-called aging) at low temperature. This has been considered to cause by the formation of the carbon cluster in ferritic steel.¹ In this study, we aimed to understand the low temperature aging behavior of low-carbon steel focusing on carbon atoms, and the chemical state and local structural changes of carbon in low-carbon steel with aging were observed by soft X-ray absorption spectroscopy. Furthermore, we tried to clarify the structure of carbon cluster from the observed absorption spectrum by first principles calculation and spectrum simulation. As a result, we succeeded in clarifying the relationship between microscopic chemical state and macroscopic hardness change. Furthermore, it was found that the chemical state of carbon related to form carbon clusters changes dynamically in the early stage of heat treatment. The results of the spectral analyses suggested that solid solution carbon was interacted with the vacancies in bcc lattice. Therefore, it is suggested that vacancies may play an important role in the formation of carbon clusters.

¹H. Abe, Scand. J. Metall., 13, 226 (1984).