Removal of microinhomogeneities in grade 4Kh12N8G8MFB (EI481) creep resistant steel by electroslag remelting

Conclusions

• 1. In grade 4Kh12N8G8MFB steel alloyed with elements exhibiting a strong tendency to carbide formation and with carbon, the basic components segregate in the interaxial space.

  The tendency of an alloying element to segregation is directly related to the thermodynamic interaction parameter for the element with carbon in the iron melt.

• 2. The segregation inhomogeneity is determined by the nature of the macrostructure. In the columnar zone the degree of segregation increases linearly with increase in the thickness of the crystallized layer. The maximum development of segregation is attained in the center of the equiaxed zone.

• 3. The maximum inhomogeneity in ER and OA ingots is the same irrespective of the significant difference in weight and cross section of the ingots investigated, and therefore in the larger ER ingots, because of the greater number of intermediate heatings and the significant reduction, the ER metal is more homogeneous.

• 4. Because of the marked interdendritic segregation, grade 4Kh12N8G8MFB steel exhibits anisotropy. The anisotropic properties of the steel are affected by two factors: the chemical inhomogeneity and the associated different degree of hardening corresponding to the axes and interaxes, and the nonuniform distribution of insoluble inclusions. Below the temperature limit of solubility of the dispersed hardening phases, inhomogeneous decomposition is of fundamental importance. During high-temperature tests the magnitude of the anisotropy is determined by the residual quantity of undissolved inclusions.