凝固直後に高温保持した高クロム鋳鉄の二次炭化物の析出挙動について

抄録

  High chromium cast irons containing 15%Cr and 1.8 to 3.4%C were destabilized at 850° to 1,000°C immediately after solidification and were quenched. The precipitation process of secondary carbides and their effects on Ms temperature and the amount of retained austenite were studied. Secondary carbides first precipitate onto eutectic carbides, decreasing Cr and C concentrations in austenite in the vicinity of eutectic carbides and also the segregation ratio of chromium Is defined as a ratio of Cr concentration at the center of primary austenite dendrite to that in the periphery of the dendrite. Is of 1.8%C iron is still larger than 1 and the following precipitation of secondary carbides occurs from the periphery to the center. While the precipitation conversely proceeds from the center to periphery of dendrites in 3.4%C iron having Is less than 1. The nose of TTT curves for precipitation of carbides in austenite lies at temperatures from 850°C to 900°C in all cast irons. Ms temperature rises and retained austenite decreases with the proceed of precipitation.