Analysis of the transformation of the microstructure of axial billets after rolling

Abstract

The task of improving the quality of metal products of large cross-sections pro-duced from continuous cast billets (CBS) is associated with a number of difficulties. These include the presence of internal defects in the macrostructure of the workpiece (axial looseness, porosity, liquation, crystallization cracks, etc.). Processing from the point of view of deformation of cast workpieces is necessary first of all to eliminate cast defects. An increase in working out contributes not only to the welding of existing mi-crodiscontinuities and, in this connection, to an increase in the density of the metal, but also to the extraction, crushing and reduction of the cross-section of the existing non-metallic inclusions. However, the dimensions of the elements of the primary structure, which are presented on the graphs, are also of the greatest importance. The smallest level of liquation is formed in the surface areas during crystallization. At the same time, as a rule, it is necessary to obtain a homogeneous structure in terms of grain size on the cross-section of large-sized metal products. A study of the features of the structure of axle blanks made of steel grade F (AAR M-101-2017 Axles, carbon steel, heat-treated) after longitudinal rolling on a TPA 5-12" pipe rolling unit with pilgrim mills in three crimping modes (1 mode: Ø 470 → Ø 380 → Ø 260 mm; 2nd mode: Ø 470 → Ø 420 → Ø 260 mm; 3rd mode: Ø 470 →Ø 260 mm). Determination of the features of the distri-bution of deformation work and the formation of the final structure after deformation according to the experimental modes of BLZ Ø470 mm per circle Ø260 mm is the pur-pose of the research. Samples for the structure study were taken both from the original BLZ and the finished draft axle along the entire cross-section. The greatest unevenness of the liquation background, which is observed in the axial blank manufactured using mode No. 1, is also manifested during the study of the microstructure of railway of the axes obtained by the indicated modes. It was determined that the uniformity of the grain structure is the highest after using mode No. 3 (Ø 470 →Ø 260 mm).