Influence of Chemical Composition on Concentration Undercooling of Structural Steels

The article studies the undercooling of steel melt around the solid particles, which is one of the main factors determining the rates of nucleation and growth of crystallization centers. Particularly, the effect of chemical composition on this factor for two grades structural cast steels 20KhGSL and 40Kh3G3S3L mainly containing Cr, Mn, Si was in the focus. The established analytical dependence allowed to determine the development of maximum concentration undercooling over the moving crystallization front depending on the liquidus temperature, the content of elements in the melt, their distribution and diffusion coefficients, the crystallization rate and the temperature gradient in the melt ahead the crystallization front. The correlation of maximum concentration undercooling and width of the columnar dendrite zone was obtained. The effect of chemical composition on steels undercooling and crystallization process was revealed. The efficiency of the elements influence changes for steels 20KhGSL and 40Kh3G3S3L from 20.1 to 25.9% for C, from 31.2 to 25.9% for Si, from 3.8 to 18.0% for Mn, from 34.0 to 10.8% for Cr, from 6.6 to 5.6% for S, from 1.0 to 0.4% for P, from 3.3 to 6.2% for N, respectively. The results obtained give deep insight in obtaining high quality steels.