焼結クロムのサンドイッチ圧延

抄録

The enhancement in rolling workability of a sintered powder chromium (Cr 1, 99.9 mass%) by CIP and HIP processes was made at elevated temperatures by means of a sandwich rolling, in which the workpiece sandwiched in between two mild steel sheets was rolled. The behavior of ductile-to-brittle transition and recrystallization was also examined in the rolled specimens of 99.99 mass% purity sintered powder (Cr 2) and the above specimen Cr 1, respectively. The results are summarized as follows.
The sandwich rolling was very efficient to prevent the crack generation during rolling of the workpiece at elevated temperatures, especially at the temperatures ranging from 1173 to 1373 K, at which the workability was extremely poor in a conventional rolling.
The ductile-to-brittle transition temperature (DBTT) was lowered by a high rolling reduction given to the specimen. Namely, the DBTT of the specimen rolled to 85% at 973 K and annealed at 1473 K was 510 K which was about 200 K lower than that of the specimens as sintered and/or rolled to 50% after annealing at the same temperature.
Room temperature hardness of the specimen rolled to a given reduction at 973 K, the temperature at which the dynamic strain ageing occurred, was considerably larger than the hardness measured in the specimen rolled to the same amount at 773 K at which the strain ageing did not occur. The recrystallization temperature of the present sintered powder was similar to that of a cast material. The recrystallization during the sandwich rolling at the temperatures beyond the recrystallization temperature occurred evenly on the surface and in the inside of the workpiece, while it occurred only in the inside during the conventional rolling.