Investigation of high-temperature carburizing of steel in solid carburizer with high-frequency heating

Abstract

1. An increase in the carburizing temperature of steel using high frequency heating and solid carburizer, increased the productivity by a factor of 3–4 at 1000° C and by 5–8 at 1150° C compared with ordinary heating. 2. Successful high-temperature carburizing in a solid carburizer depended basically on prevention of local carbon pick-up by the steel at its contact points with carburizer particles; this was achieved by precoating the steel with chalk. 3. The results of high-temperature carburizing depend on temperature, duration of treatment and the content of carbonates in the carburizer. The greatest influence is shown by temperature and with its increase, the depth of the case increases rapidly while its saturation with carbon falls off. The optimum content of BaCO3 in the carburizer is 8–10%. 4. Upon holding at high carburizing temperatures, the austenite grain grew violently in the case and less so in the core. After a single quench, the impregnated layer was coarse-grained and had a strong tendency to retain austenite; this resulted into low brittle strength. 5. A double heat treatment was required after high-temperature carburizing to secure high mechanical properties of case and core in the investigated steels. Protection from carbon saturation (stop-off action) could be secured by copper coatings up to 1000° C and by chromium coatings above this temperature.