Soft reduction control investigation of spot segregation in continuous casting bloom for 42CrMoA crankshaft steel

The crankshaft is subjected to complex rotational centrifugal force, periodic gas inertia force, and reciprocating inertia force during its working process. Consequently, the homogeneity requirement for crankshaft steel is exceptionally high. The distribution characteristics of center segregation and spot segregation of continuous casting bloom 42CrMoA crankshaft steel were analyzed by experiments, and the control mechanism of spot segregation by soft reduction zone and reduction amount was discussed. When the center solid fraction is between 0.61 and 1.00, an 8-mm soft reduction has a negligible impact on the flow of liquid steel at the end of solidification. Although it effectively improves center segregation, the improvement of spot segregation is limited. On the other hand, when the center solid fraction is between 0.31 and 1.00, a reduction of 10–12 mm, along with an expanded reduction zone and increased reduction amount, significantly promotes the flow of liquid steel at the end of solidification, reduces the size of equiaxed grains, mitigates the center negative segregation, and decreases the maximum size of spot segregation from 2954.29 to 1354.07 μm. The number of spot segregations and the solutes enrichment degree of C, Cr, and Mn have also been significantly improved. An appropriate soft reduction zone and reduction amount can markedly ameliorate the semi-macro spot segregation of crankshaft steel blooms, thereby providing high-quality raw materials for subsequent products and enhancing the competitiveness of crankshaft products.