The heat treatment characteristics of multi-component white cast irons containing cobalt content varying from 0mass% to 10mass% were investigated, and abrasive wear resistance was also studied by Suga-type wear test.
  The test specimens measuring 55^W × 55^H × 6^Tmm in size were cut from an ingot measuring 55^W × 55^H × 200^Lmm, after which annealing (1123K-18ks FC) was performed. Hardening (1323K-36ks FAC) and tempering (673K～873K-10.8ks AC) were then carried out on the annealed specimens. It was found that the amount of retained austenite (V_γ) in the specimens in the as-cast and as-annealed states decreases with increasing cobalt content, and no austenite could be observed in specimen with 10mass% Co. In the as-hardened state, the V_γ of specimens without cobalt was about 11%. The V_γ decreased to 6% with the addition of 2mass% Co. However, the V_γ value was more or less the same when the cobalt content was increased over 2mass%. The V_γ decreased with increasing tempering temperature regardless of the cobalt content and disappeared at tempering temperatures over 800K.
  The macro-hardness of specimens in the as-cast and as-annealed states decreased gradually with increasing cobalt content. In the hardened state however, the hardness kept to a slight decrease even when the cobalt content was changed, up to 10mass%.
  Secondary hardening occurred conspicuously in the tempered specimens regardless of the cobalt content, and the maximum tempered hardness increased with increasing cobalt content.
  Wear resistance was clearly related to the hardness and increased proportionally with hardness.