Adwanced Casting Technologies of Round Billet Caster in Sumitomo Metals

摘要

The advanced round billet casting technologies have been developed at Wakayama Steel Works. The round billet casting is efficient in comparison with bloom one, because round billets are directly supplied to seamless pipe mill without blooming (billeting or rolling) process. In the round-shaped billet, transverse surface cracks and centerline cracks tend to appear especially in case of low alloy steel containing Cr or Nb. As-casting billets could not be sent to seamless pipe mill directly because of these defects. Transverse cracks are caused because hot ductility of the low alloy steel remarkably deteriorates. These cracks were reduced by SSC (Surface Structure Control cooling), developed secondary cooling of the round billet caster. SSC prevented film-like ferrite of the round billet surface and improved surface ductility. The centerline cracks are caused by brittle ferrite structure at the billet center. By strong secondary cooling, equiaxed crystal zone ratio increased and centerline cracks could not get large. Applying these technologies, as-casting low alloy round billets could be sent to seamless pipe mill directly, and seamless pipe production was increased.