In previous paper, I have reported the mild carburization by suppressors was not different from that by a mild promoter. Though the annealing treatment of super-carburized layer at high temperature or in vacuum is considered as another mild carburizing method besides the above-mentioned method, various defects in it may be conceived. As it is considered that the best method of mild carburization is to use the adequate mild promoters in each carburizing condition, I tried to establish in this study the suitability of various promoters for the mild carburization. First, the foundamental tendency of surface carbon content of plain carbon steel was studied by changing the carburizing temperature, and time was measured in the case of 35%BaCO3 and 5%Na2CO3, respectivly as promoter. It was found that Na2CO3-CaO system as promoter was excellent for the mild carburization. Finally, the characteristics of various promoters for chrome-steel were clearified from the results of the carburzation by using the eleven sorts of carbrizers in the temperature range of 920∼980° and the time range of 5∼10 hrs.
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