| 摘要 |
PURPOSE:To manufacture a piston ring having good wear resistance and breaking resistance by subjecting the surface of a base metal made of steel to high temp. nitriding, then subjecting it to low temp. nitriding, thereafter removing a porous layer at least on the face to be slid and exposing a diffused layer. CONSTITUTION:The surface of a base metal 11 made of steel is subjected to high temp. nitriding and is thereafter subjected to low temp. nitriding to form a nitrided layer 12. The high temp. nitriding is executed preferably in the temp. range of 560+ or -5 to 600+ or -5 deg.C, by which a diffusion hardened layer is deeply formed in a short time. Furthermore, the low temp. nitriding is executed preferably in the temp. range of 500+ or -5 to 550+ or -5 deg.C and in such a manner that the temp. difference between both nitriding temps. is regulated to >=1 deg.C. In this way, the major part of interstitial nitrogen is fixed on the surface layer to improve its hardness. After that, a brittle and hard porous layer at least on the face 13 to be slid of the nitrided layer 12 is removed to expose a diffused layer. After that, if required, any of a plated layer, a thermally sprayed layer and an ion-plated layer is formed on the diffused layer. In this way, the cracking resistance of the nitrided layer 12 can be improved. |
