球状黒鉛鋳鉄のガス窒化特性に関する一考察

抄録

  Nitriding of spheroidal graphite cast irons containing 2.04−2.98%Si was carried out at various temperatures from 500 to 620°C and at various lengths of heating time from 10 to 40hr in a tubular furnace using 100% gaseous ammonia. Spheroidal graphite cast irons were sufficiently hardened by gas-nitriding, resulting in a surface hardness between H_v (100g) 700 and 800, and the depth of hardened layer between 0.2 and 0.4mm. Expansion of the test pieces were observed in proportion to the increase in temperature and heating time, and reached 0.12mm, at maximum. It was considered that the precipitated silicon nitride (Si₃N₄) contributes to the hardening of the nitrided spheroidal graphite cast iron.