High-Frequency Chromizing

Abstract

IN recent years new processes involving the use of a medium containing 75 per cent chromium with 25 per cent cryolite and high-frequency heating have been developed for the chromizing of ferrous and non-ferrous metals^1–4. Generators operating with frequencies of 3–3.5 Mc/sec have been used, and it has been claimed that coatings which would require the treatment of mild steel for at least 30 min at 1,200 ° C can be produced in 60–80 sec with high-frequency heating. Under these conditions the estimated temperature at the surface of the specimen during inter-diffusion was 1,250° C. Enhanced diffusion-rates under high-frequency heating conditions have been claimed and it has been suggested that there may be some ‘high-frequency effect’ in such processes. Specimen surface temperatures have been measured during recent investigations, and the results shed some light on this problem.