Workability in rolling and upsetting of cast chromium

The workability of cast pure chromium was investigated through the study of rolling and isothermal upsetting. The present cast block produced by means of a high energy induction slag melting (HESM) process was 99.99 % mass purity and this material had large crystal grains elongated along the solidification direction. The ductile-brittle transition temperature (DBTT) of small specimens taken from the block was found to be about 500 K in a tension strained at 0.024 s(-1). Considerable workability appeared in upsetting at 400 K, at which the small workpiece could be deformed to 25 % in height reduction without cracking on the piece wall. The upsetting workability increased rapidly with increasing temperature, that is, the piece was deformed up to 80 % at 773 K and more than 90 % at higher temperatures than 873 K. At all temperature, cracks occurred in the as-east specimen deformed by a conventional rolling. In addition, cracks occurred slightly in the specimen even in a sandwich rolling by which sintered chromium was successfully deformed. Cracking in the as-cast specimen was mainly due to the coarse structure with large crystal gains. Once the coarse gram structure in the cast material was changed to a finer one by upsetting and successive annealing treatment, the present chromium could be successfully rolled to a thin sheet at temperatures above 673 K.