Vacuum carburizing has attracted attention as the heat treatment strengthening technique that is realized to reduce processing time, cost and carbon dioxide. But currently there is limited knowledge up to 1323 K, the carburizing phenomenon in higher temperature is not clear. This study revealed the cementite generation timing by measuring changs in weight of a specimen during carburizing in real time, under reduced pressure at 1373 K. And it was demonstrated that carburizing phenomenon until generating cementite is essentially same at 1323 K.

Then, we established a simulation model which is capable of predicting the carbon concentration at the edge of the gear test piece, to prevent the generation of cementite at the edge portion carburized at 1373 K.

Finally, by combining the above numerical analysis result and the statistical method called genetic algorithm, the carburizing pulse pattern in the shortest time was derived in a state in which cementite is not precipitated at the edge portion.