The Gas Carburization of Steel by Using Prussian Blue

Abstract

The carburizing of steel by the gases produced by the pyrolysis of the powdered Prussian blue was investigated using ¹⁴C as a tracer.
The carburizing was carried out for 10∼120 min in the temperature range of 500 to 800°C by use of a static apparatus connected to a high vacuum line.
The amount of carburization on the surface layer of steel showed a maximum when the carburizing was carried out at about 700°C. At a lower temperature it increased slightly with the carburizing time, while at a higher temperature it increased initially but decreased considerably with the carburizing time. The depth of carbon penetration was several microns at low temperature (600°C) and proceeded no less than several tens microns at high temperature (800°C). The composition of the gases produced by the pyrolysis of Prussian blue was determined by infrared spectrophotometry. From the result, it was found that the effective gaseous materials for the carburizing were HCN at lower temperatures (400∼600°C) and CO and CH₄ at higher temperatures (600∼800°C). Furthermore, in an atmosphere of NH₃ or H₂, the carburizing was promoted by the enhancement of the formation of CH₄, but it was retarded in O₂ with the formation of CO₂ which was a decarburizing agent.