The production of continuously cast products that display very low centre segregation and thus more homogeneous properties is an important objective, particularly for high-speed continuous casting of billets, in meeting increasingly stringent quality requirements. In addition to the well known methods of reducing macro-segregation in continuous casting, inline deformation of the partially solidified strand, already used successfully in slab and bloom casting, offers an alternative for producing material with low segregation level. The present report considers the feasibility and effectiveness of mechanical soft reduction for the continuous casting of billets. The structural design of the soft reduction unit as a stand or segmental construction was investigated, as well as the influence of varying roll diameters.A strand of the existing billet caster 84 was modified for this purpose and soft reduction tests were conducted on spring steel grade 548iCrS at casting speeds between 3.30 and 3.60 m/min. The conclusions drawn from the test results as regards roll diameter, required reduction rate and necessary reduction force formed the basis for designing the soft reduction unit of the new billet caster 80 that went in operation in March 2004.
Hot tensile tests after applied prior melting down of the specimens were carried out on mainly ledeburitic tool steels and their strength and ductility were determined in the temperature range between liquidus and 900°C. The test parameters and specimen microstructures were adapted to the conditions and structures prevailing in continuous casting and primary hot working of blooms. The metallurgical processes leading to the embrittlement of the material were examined by means of metallographic investigations. The temperature ranges of internal crack susceptibility and low ductility were evaluated.
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