抄録
The rapid solidification of high speed steel was investigated by using a water-cooled chill block apparatus, which was expected to function as a caterpillar-type caster or a roll caster. The secondary dendrite arm spacing near the surface was 4μm in every cast ingot. The dendrite arm spacing at the center increases with increasing thickness of the ingot. By using relationship between the dendrite arm spacing and the cooling rate, the cooling rates near the surface and at the center of the 40mm-thick cast ingot are estimated to be 103 and 100°C/s, respectively. The size of eutectic carbide decreased with decreasing thickness of the cast ingot. Lamellar eutectic carbides were spheroidized by the heat treatment of the cast ingots at 1150°C for 2h.
Furthermore, plates of high speed steel were made by the twin roll test caster. Casting speed was 5-10m/min. The cast plate was 1-2 mm in thickness and 260mm in width. Fine eutectic carbide was observed in the cast plate due to heat treatment. The plates of carbon tool steel were also made by a twin roll test caster. A spheroidal cementite structure was obtained by the heat treatment of the carbon tool steel plate at 690°C for 1-50h.
