Rolling of Sintered Chromium

Abstract

The rolling workability of sintered chromium, which is very brittle at room temperature was examined as a function of temperature. The present sintered chromium of 99.9% purity was produced by CIP (cold isostatic press) and HIP (hot isostatic press).
The specimen could be successfully rolled in a limited temperature range from 673 to 1073 K. This formability characteristic is different from the experimental results found in the upset and the tensile tests in which no upper limit of temperature was found for workability and ductility. The deterioration in rolling at temperatures above 1173 K was caused by rapid cooling of the specimen by the rolls. The temperature of the specimen during rolling decreased greatly in the roll-contact region, while the inner part of the workpiece retained its starting temperature. Hence, the large tensile stress in the rolling direction occurred near the roll-contace material because of a large difference in the flow stress between the roll-contact region and the inner part of the workpiece. The tensile stress was responsible for cracking on the surface of the specimen heated at temperatures above 1173 K.
The steel/chromium/steel sandwich plate could be successfully rolled to a large reduction even at temperatures above 1173 K without occurrence of the surface cracks because the steel skins prevented the temperature decrease of the specimen during rolling.