抄録
Rod-shaped primary carbides, M2C, which were aligned with rolling direction are frequently observed in high-carbon, high-molybdenum high-speed tool steel. It was known that the phase disappeared by silicon addition to the steel. Therefore, the effect of silicon on the carbide transformation and the heat treatment characteristics in AISI M7 was studied under various nitrogen content.
The results obtained are as follows:
(1) The carbide precipitated at the eutectic reaction was M2C and not M6C, and had a plate-like morphology.
(2) Silicon in the matrix accelerated the transformation of M2C to M6C by entering into M2C during heating the ingot above 640-700°C. Considerable primary carbides were retained as M2C even after hot working, when the silicon content in the steel was little.
(3) It was considered that the retained M2C, having the plate-like morphology, became reorientated parallel to the hot working direction, without spheroidization, and therefore was microscopically observed as rod-shaped carbide.
