Production and Properties of Twin Billet by a Continuous Casting Machine with Reduction Mill

The tests to produce two 75 mm square billets from twin-billet, to which a 120 mm square cast billet is rolled by one pass, were carried out by an in-line reduction mill installed in a continuous casting machine. The produced billet is further hot-deformed to square or round bars in order to study the material properties and strength. The results obtained are as follows: 1. No crack was observed even after high reduction since sufficiently high temperature is maintained in the core of the billet during reduction process. The deformation resistance is as small as 5 to 6 kg/mm2. 2. The center porosity and other defects in the central part of the bar which were previously rolled from the twin billet can be completely eliminated, because the central part of the cast billet is deformed into the joint of the twin billet in the process of in-line reduction. 3. The surface of the bars at the joint of the twin billet shows a macro structure with a unique pattern which, however, diminishes by raising the rolling reduction ratio. The mechanical strength of the joint is found to be the same level as the other part for both low and medium carbon steels. But for a high carbon steel, the strength of the joint is lower than the other part.