鋳鉄の摩耗硬化層について

Abstract

Wear experiments of flaky graphite cast iron against 0.6%C carbon steel, stainless steels (SUS 24, SUS 27) and Ni-Cu alloy (Constantan) were carried out under metal-to-metal, unlubricated conditions. The extremely hardened layers were developed on the sliding surfaces of cast iron at sliding speeds faster than 2 m/sec. The hardened layers were examined by X-ray diffraction and the relation between formation of the hardened layers and wear of cast iron was discussed.The results are summerized as follows:(1) The hardened layers are generated at speeds above the second oxidative wear speed and in mild wear condition, and are not found in severe wear process even at high sliding speeds.(2) The hardened layers are due to rapid solidification of melting regions on real contacting asperities. They may be worked severely during and after solidification and tempered by frictional heating.(3) As the sliding speed is increased at a constant contact pressure, the hardness of the hardened layers decreases and wear varies complicatedly with the minimum wear rate at about 4 m/sec. Softening of the hardened layers with increasing sliding speed may be due to the rise in quenching and tempering temperatures.(4) As the contact pressure is increased at a constant sliding speed, both the wear rate and the hardness of the hardened layers increase exponentially and lineally. The effects of work hardening due to the increase in contact pressure and the shortening of the remaining time of the hardened layers on the sliding surface due to the large wear rate may be stronger than due to the temperature rise with increasing contact pressure.(5) Accordingly, the hardness of the hardened layers is under the influence of the sliding and wear conditions. There is no definite relation between the hardened layers and the wear rate.