Michiharu Ozawa

Development of a rapid solidification process with a double-roller method

Abstract A thin strip caster has been developed which consists of twin cooling rollers, a secondary cooling zone, tension control systems and a continuous-coiling machine. With this caster, fine crystalline strips were continuously produced to a near-net shape whose dimensions were 0.2–1 mm in thickness, 250–500 mm in width and 500 kg in unit coil mass. The characteristics of the thin strip caster are as follows. 1. (1) Many types of metal alloy whose melting points are less than 1800 K are rapidly solidified. 2. (2) Materials with a difficult workability, such as high silicon steel or high alloy stainless steel, are coiled in a net shape or near-net shape. 3. (3) Because of the cooling rate which is of the order of 102 K s−1 in a secondary cooling zone, the coils have such advantages of the rapid solidification process as a fine crystalline structure or decreased precipitation.

Effect of secondary cooling on a rapidly solidified stainless steel strip

Abstract The rapid solidification process, which omits the hot rolling stage, was employed for the production of a thin strip made of materials which typically have poor workability. The process required the solidified strip to be cooled carefully so that embrittlement or recrystallization did not occur: 14Ni-30Cr stainless steel, solidified to a thin strip by a twin roll caster, was subjected to another cooling (secondary cooling) before coiling. The transition of strip temperatures during the cooling was estimated both by measurement and by calculation. From the experimentally observed relationship between the heat treatment and embrittlement, the optimum condition for the secondary cooling was obtained. Experiments showed that the strip became embrittled when it was subjected to 930 K for 5 min. Therefore the cast strip was passed through the secondary cooling zone of water jets. The coiling temperature was kept below 700 K and no embrittlement was observed.