Principles of Billet Soft-reduction and Consequences for Continuous Casting

Abstract

The production of continuously cast products that show very low center segregation and are thus more homogeneous is an important objective, particularly for high-speed continuous casting of billets, in meeting quality requirements that are becoming increasingly stringent. In addition to the well-known methods of reducing macro-segregation in continuous casting, inline thickness reduction of the partially solidified strand, already used successfully in slab and bloom casting, offers an alternative for producing material with low segregation level. In the present report, which considers the feasibility and effectiveness of a mechanical soft-reduction for the continuous casting of billets, the influence of the soft-reduction position from the metallurgical point of view, the reduction parameter and the roll diameter in combination with the structural design of the soft-reduction unit was assessed comparatively. One strand of the billet caster S4 was modified for this purpose and soft-reduction trials were carried out on high carbon steel grade D72C for wire rod application and spring steel grade 54SiCr6 at casting speeds between 2.80 and 3.60m/min. The conclusions drawn from the test results with respect to required solid fraction in the liquid core, effective reduction rate and necessary roll diameter formed the basis for designing the soft-reduction unit of billet caster S0 and for predicting favourable process parameters. First results of billet soft-reduction trials on the caster S0 are presented.