天然ガスを有効利用した鋼の表面熱処理

Abstract

The gas carburizing atmosphere for surface treatment of steel can be regulated using the carbon potential, which is obtained by measuring the dew point, oxygen concentration or carbon dioxide concentration. The carbon potential which is calculated with carbon dioxide concentration is consistent with the carbon content of carburized steel foil. However, since a zirconium oxide oxygen sensor is easier to handle and its response is better than others, it is generally used for controlling the carbon potential, Methane is the main component of natural gas and it is stable at high temperature, so that the majority of tends to remain in the furnace. Since the retained methane decomposes on the oxygen sensor tip, the oxygen concentration around it decreases. Therefore the measurement of carbon potential with an oxygen sensor has been considered to be difficult when natural gas is used as the enriched gas. In this study, the carbon potential is regulated by taking account of the difference of the carbon potentials which are calculated with carbon dioxide concentration and with oxygen concentration; therefore the carbon potential can be controlled by the oxygen sensor, using natural gas for enriched gas. Target surface hardness and effective case depth are obtained when gas carburizing is carried out using this method, In addition, when the carrier gas is generated with natural gas and air, the carbon oxide concentration is 20.5 volume%, and the hydrogen concentration is 39.0 volume%; therefore the carburizing speed is higher than that when the carrier gas is generated with propane or butane.