Experimental Investigation on Solidification Structure and Carbides in Continuously Cast Slab of High Manganese Steel Mn13.

Due to the high carbon and manganese content in high manganese steel Mn13, as-cast high manganese steel usually suffers from coarse solidification structure and carbide, which have a great detrimental effect on the high temperature mechanical properties of high manganese steel Mn13, and thus it is difficult to be produced by continuous casting process. In order to elucidate the solidification structure formation and carbide precipitation in the continuously cast slab of high manganese steel Mn13, several experiment methods, such as optical microscope (OM), electron backscatter diffraction (EBSD), field emission electron probe microanalyzer (EPMA), scanning electron microscope (SEM) and infrared C/S analyzer, and thermodynamic software Thermo-Calc were used to investigate the as-cast solidification structure, macro/micro solute segregation, and 2D/3D carbide morphology in the continuously cast slab of high manganese steel Mn13. The results show that the solidification structure of the Mn13 slab is mainly composed of coarse columnar crystals and the proportion of coarse columnar crystals is as high as 65.22 pct. The proportion of high angle grain boundaries (HAGB) in the equiaxed zone is 46.12 pct, but the proportion of HAGB in the columnar zone is only 11.98 pct. Both the C solute and Mn solute are rejected from the solid and enriched at the grain boundary, especially at the HAGB, where the growth direction of adjacent grains is quite different. The significant solute segregation and high grain boundary energy are both beneficial for the eutectic carbide formation and growth at the HAGB. Thus, the eutectic carbide is prone to form at the HAGB than the low angle grain boundaries (LAGB), and the thickness of the eutectic carbide at the HAGB is significantly thicker than that at the LAGB. The morphology of carbide from the slab subsurface to the center changes as follows: slender strip and small block → long strip and needle → long strip and lamellar. The secondary dendrite arm spacing (λ_II, μm) and the average carbide thickness (λ_c,μm), in the continuously cast slab of Mn13 steel, are formulated as functions of local cooling rate, (ν, °C s⁻¹), and determined by λ II = 54.98 × ν - 0.34 , R 2 = 0.9802 λ c = 31.10 × e - 10.59 × v + 2.26 × e - 4.17 × 10 - 2 × v , R 2 = 0.9327 . [ABSTRACT FROM AUTHOR]