Experimental study on improving the internal quality of 55SiCrA spring steel billet
55SiCrA spring steel is medium and high carbon alloy steel, the solid-liquid two-phase zone is large, and the casting billet is prone to columnar crystal development, central carbon segregation, central porosity and serious shrinkage holes. A large number of practices have proved that the electromagnetic stirring of the crystallizer can enlarge the central equiaxial crystal rate, make the central solidification structure dense, and reduce the central porosity, shrinkage hole and center segregation. The mould electromagnetic stirring makes the liquid steel forced to rotate through the electromagnetic force generated in the mould. In actual production, when the mould electromagnetic agitator is determined, the stirring current and frequency are the two main control parameters.
Aiming at the internal quality problems of 55SiCrA spring steel billet continuous casting in a factory, such as low central equiaxial crystal rate, serious central carbon segregation, central porosity and shrinkage holes, the researchers systematically studied the influence of different electromagnetic stirring process parameters on the magnetic field characteristics in the 150mm×150mm mold. The effects of the current and frequency of electromagnetic stirring (M-MES) on the macroscopic solidification structure and carbon segregation of casting billet were studied by industrial experiments.
The results show that with the increase of electromagnetic stirring (M-MES) current, the central equiaxed crystal rate increases and the central carbon segregation decreases. The effect of stirring frequency on axial crystal rate and carbon segregation in the center of the billet is nonlinear. When the best matched electromagnetic stirring current and frequency are 320A and 3.5Hz respectively, the central equiaxed crystal rate increases from 18.5% to 32.5%, the central carbon segregation index decreases from 1.23 to 1.04, the central shrinkage hole and corner crack are eliminated, and the internal quality of the billet is obviously improved.
