Investigation of Steel Billets Produced by a Rotary Type Continuous Caster

A rotary type continuous caster with a rotary wheel and an endless belt has been developed in order to establish a direct rolling system for steel billets. The rotary caster allows a long mold, and hence, high speed casting is possible even by a more compactly designed machine as compared with conventional continuous casting machines. However, preliminary examination and discussion on the deformation behavior and the crack formation in the straightening zone and the trapping of non-metallic inclusion in the billet were needed because of the compacted machine and the high casting speed. The casting machine was stopped during test runs and the billet was allowed to cool to the room temperature. The billet was examined as to deformation behavior, crack formation and inclusion trapping. The results were summarized as follows: (1) The total strain of billet in the straightening zone was about 3.2%, which was far higher as compared with the conventional casters. (2) The billet was straightened by continuous bending in accordance with the design concept of the machine. (3) The minimum and the mean values of local strain rate in the straightening zone was 0.40 and 0.18%/sec, respectively. (4) Surface cracks were not observed. (5) Internal cracks were observed at a short distance from the surface of the billet immediately after the straightening zone. But, they were so small that they disappeared by the successive rolling, causing no trouble with the final products. (6) The segregation of C and Si did not occur. But the Mn, P and S contents in the vertical section of billet were higher at the center than near the surface. In contrast to anticipation, inclusions were not trapped under the solidified shell with curvature. From these results, it was judged that production run could be started. The machine has been in satisfactory operation since then.