オーステンパ球状黒鉛鋳鉄のころがり疲労強度に及ぼす残留オーステナイトの影響

抄録

  The cast iron contaning 3.70 % C, 2.41 % Si, 0.16 % Mn and 0.041 % Mg were austempered at 648 K for 3.6 ks to 259.2 ks, in order to change the amount of retained austenite from 0 % to 32 %. The lnfluence of retained austenite on rolling contact fatigue strength of austemperd spheroidal graphite cast iron were investingated by using a Nishihara-type wear machine under a light oil lubricant. The rolling fatigue limit (F^∗) became larger as their retained austenite increased from 20 % to 30 %, while retained austenite less than 20 % had little influence on F^∗. F^∗ of austempered spheroidal graphite cast iron without retained austenite was still much larger than that of quenched and tempered spheroidal graphite cast iron at the same hardness level. Martensite transformation was accompanied with the propagation of fatigue crack in austempred spheroidal graphite cast iron, which should retard the crack propagation and raise the fatigue life.