| 摘要 |
<p>PURPOSE:To improve fatigue characteristic in machine parts by quenching the machine parts composed of a steel having the specific carbon content into the specific temp. of cooling agent after carburizing, and further executing sub-zero treatment to make a martensitic structure only in the surface layer. CONSTITUTION:The machine parts formed by using steel containing 0.1-0.3% C is carburized or carburization-nitrided. Further, in the case of steel containing 0.35-0.75% C, without executing carburization, austenization is executed at 800-900 deg.C. After that, the above parts is quenched into the cooling agent at 60-200 deg.C. By this method, retained austenite is developed only to the surface layer part in the machine parts. Successively, by executing the sub-zero treatment to this, 5% of the retained austenite in the whole constituted metallurgical structure is changed into the martensite only relating to the surface. By this method, the fatigue characteristic in the machine parts is drastically improved due to remarkable compressed residual stress newly developed.</p> |
