| 摘要 |
PURPOSE:To prevent coarsening of crystal grain and not to generate the heat treatment strain etc., by heat treating the steel containing boron regulating the condition of atmosphere gas and treating temperature range and next, carrying out refining treatment. CONSTITUTION:On occasion of carrying out surface hardening treatment of steel for machine structure containing boron, preferably, containing 0.0005-0.05wt% of boron, the treatment is carried out in the atmosphere of endothermic reation type metamorphic gas containing CO or gas containing hydrocarbon or mixed gas of both gases and also, under the condition of nitrogen potential of 0.1-1%. And, heat treatment is carried out at Ac3 transformation temperature of the above-mentioned steel or more and 900 deg.C or less and after that, refining treatment is carried out. Hereby, fine grain of crystal grain number No.6 or more, is obtained in 100%. Further, on occasion demands, the above-mentioned refining treatment is substituted for hardening treatment or hardening and tempering treatment. |
