Carburizing and quenching is known as a surface modification treatment applied to impart mechanical properties to materials. The authors have developed an ultra-rapid carburizing using induction heating above the eutectic temperature, which enables in-line carburizing as a next-generation heat treatment method, in order to coexist in the future carbon-neutral society. Previous studies have reported on carbon penetrating behavior at a constant 1523 K, for carburizing on an alloyed steel SCM420. However, in order to apply it to various steels, it is necessary to elucidate the carburizing mechanism of this treatment, which is different from gas carburizing and vacuum carburizing. In this study, the temperature range was expanded to 1473 K and 1573 K to investigate the carbon penetration characteristics as a detailed mechanism elucidation. As a result, it was shown that the tendency of carbon penetration characteristics was similar to that of 1523 K. Moreover, the rate of carbon penetration varied exponentially with the carburizing temperature. The activation energy of the ultra-rapid carburizing reaction obtained by the Arrhenius plot was equivalent to that of the methane decomposition reaction, which was the raw material gas. Thereby, it was verified that carburizing reaction was rate-controlled by the decomposition reaction of methane.

Multilayer Si-DLC/DLC films with different layer thicknesses and number of layers were deposited on austenitic stainless steel. The effect of the number of layers and film thickness ratio on the adhesion and wear resistance of the films was investigated. The samples were subjected to nano-indentation, Rockwell indentation, scratch, friction and wear, and delamination tests. Scratch testing showed that adhesion was improved by increasing the number of layers from two to four, but the adhesion was deteriorated in the sample with a thin film on the substrate side and when the film reached eight layers. Delamination testing showed that the delamination distance among samples coated four layers increased in the sample with a thick film on the substrate side compared to the sample with a thin film on the substrate side.