Relationship between treating conditions and surface carbon concentration of low carbon steel vacuum-carburized with propane

摘要

A low carbon steel, S15CK, was carburized at the temperatures of 1113 to 1313K for times up to 20.571ks in a propane atmosphere at 2.67kPa and thereafter diffused below 0.133Pa for times ranging from 0 to 18.9ks at the same temperature where carburizing was done. Carbon profiles were determined by a succession of grindings and emission spectrochemical analyses of the ground surfaces. The uptake amount of carbon by a thin specimen was measured by infrared absorptiometric method after combustion in the current of oxygen. Carbon flux was evaluated from dependence of the amount on carburizing time. A mathematical model is proposed to describe carburizing behaviors. Comparison between the calculated and the experimental profiles revealed that the model was able to represent the carburizing behaviors precisely. Both experimental and calculated results verified that treatments at the same ratio of carburizing time to diffusing time give the same surface concentration of carbon. This fact is very useful to find out the optimum condition in vacuum carburizing.