Effect of microalloying of carbon steel with titanium, aluminum and nitrogen on structural peculiarities and mechanical properties

Abstract

The purpose of this paper is to investigate the effect of microalloying with titanium, nitrogen, and aluminum on the set of mechanical properties of carbon steels with increased manganese and silicon content. This is due to the fact that steels with improved mechanical and operational properties are of great significance in the current situation of technology development. The studies are based on a comparison of the mechanical properties of known steel grades 2 and T, experimental industrial steel grade K and steels microalloyed with complexes – aluminum, titanium and nitrogen; aluminum and nitrogen of steel grade K. Metallographic analysis, determination of mechanical properties, chemical analysis and X-ray microanalysis are used. It is shown that complex microalloying with aluminum, titanium and nitrogen; aluminum and nitrogen of K grade steel contributes to the formation of a more fine-grained structure of pearlite and inclusions, compared to steel grades 2, T and K. In the structure of K steel, which is microalloyed with aluminum, titanium, and nitrogen, after casting, the formation of oxides, nitrides, carbonitrides, and multilayer inclusions located at the grain boundaries and in the grain volume is observed. After a full cycle of deformation and heat treatment, carbides, nitrides, and titanium carbonitrides remain in the steel structure. Whereas in steel, which is additionally microalloyed with aluminum and nitrogen on the basis of K steel, after solidification, a fine-grained structure with an increased volume fraction of pearlite is formed, the formation of inclusions of oxides, monosilicides of manganese and iron; sulfides and complex carbides in comparison with known steel grades K, 2 and T occurs. According to the research results, K2 steel is proposed, which provides a high complex of mechanical properties after accelerated cooling with an average cooling rate of 11.0°C/s from a temperature of 850±10°C and further tempering at a temperature of 550±10 °C for 2 hours due to an increase in dispersivity of the ferrite-pearlite structure, strengthened by dispersed inclusions, in comparison with K1 steel. In steel K2, factors of strength, hardness and impact toughness are 10–15% higher than the same factors for steel K1.