多合金白鋳鉄の連続冷却変態挙動に及ぼすモリブデン及びタングステンの影響

抄録

  The continuous cooling transformation (CCT) behavior of several multi-component white cast irons, each with molybdenum (Mo) and tungsten (W) contents ranging from 0 to 6 mass% respectively, was investigated at austenitizing temperatures 1273K and 1373K. For the CCT diagrams, pearlite and bainite transformation curves were clearly separated regardless of austenitizing temperature and the contents of Mo and W. When the reciprocal action of Mo and W addition was expressed by a parameter of tungsten equivalence (W_eq (%) ＝ W ＋ 2Mo), the nose temperature of pearlite and bainite transformations did not change regardless of austenitizing temperature even if W_eq value was varied within 2.8 to 18.1%. The nose time of pearlite transformation shifted to the high side with an increase in both austenitizing temperature and Weq value. On the other hand, the nose time of bainite transformation changed little even if the W_eq value and the austenitizing temperature were changed. The M_s temperature was lowered by 50K to 60K when the austenizing temperature was increased by 100K, and this variable rose in proportion to the W_eq value irrespective of austenitizing temperature. The M_f temperature appeared when the W_eq value exceeded 15% at the austenitizing temperature of 1273K. The hardness levels of transformed cast iron specimens depended on the matrix microstructures. The maximum specimen hardness was obtained at conditions where the cooling curve passed through either the pearlite or bainite nose to martensite transformation.