On the importance of mathematical calculations in the study of structure characteristics and the physical and mechanical properties of 30XGSA steel, smelted on a different charge

N. N. Sergeev ; A. N. Sergeev ; S. N. Kutepov ; O. V. Kuzovleva ; A. E. Gvozdev ; D. S. Klement'yev

Čebyševskij sbornik, Tome 22 (2021) no. 2, pp. 449-471

Résumé

The article considers the influence of the quality of the initial charge on the structure and physical and mechanical properties of the structural medium-alloy steel 30KhGSA. It was found that the 30KhGSA steel (smelters No. $3$-$4$) cast in cast-iron molds (ingot weight $2.6$ t) has a significant chemical heterogeneity and liquation in carbon and the main alloying elements (Cr and Mn), and in the melting on the semi-product of the boiling slag layer, the liquation is more pronounced. Starting from the tempering temperature of $500^\circ$C, the structure of both melts (the fluidized slag layer and the ordinary metallized charge) becomes more uniform and the mechanical properties are aligned. Microstructural studies have established that with an increase in the annealing temperature at a single exposure, the chemical inhomogeneity decreases, but not significantly. Starting from $1000~^\circ$C, when the annealing temperature increases, the steel grain diversity and the growth of austenitic grains appear, especially in the melting on the semiproduct of the boiling slag layer. Different grain sizes adversely affect the mechanical properties of steel: grain enlargement reduces the resistance of steel to brittle fracture, worsens the service characteristics of the metal. Elimination of chemical and structural heterogeneity can be achieved by conducting a homogenizing annealing (annealing at $950~^\circ$C for $8$ hours). An increase in the annealing temperature leads to an intensive grain growth, especially in steel smelted on the original charge. It is shown that 30XGSA steel, which is melted on a semi-product of a boiling slag layer, in an improved state with equal hardness and strength characteristics, has increased plastic properties and especially impact strength in comparison with steel on a conventional metallized charge. Apparently, this should also determine the higher operating characteristics of steel obtained with the use of pure primary charge.

Détail

Keywords: surface-active impurities, heat treatment, semi-product of the fluidized slag layer, ordinary metallized charge, homogenizing annealing.