CNIITMASH, Moscow, Russia
E. Yu. Kolpishon, Dr. Eng., Prof., Chief Researcher, e-mail: kolpishon@bk.ru

Peter the Great St. Petersburg Polytechnic University, St. Petersburg, Russia

P. V. Kovalev, Cand. Eng., Associate Prof., Deputy Director for Educational Activities, Institute of Mechanical Engineering, Materials, and Transport, e-mail: kovalev_pv@spbstu.ru

S. V. Ryaboshuk, Senior Lecturer

The article investigates the effect of niobium alloying on the properties of structural steels, including austenitic, ferritic and martensitic grades. Particular attention is paid to the role of niobium carbonitrides in precipitation hardening and grain growth inhibition during heating. It is demonstrated that particles smaller than 300 nm significantly enhance strength, while larger inclusions reduce toughness. The mechanisms of recrystallization suppression by carbonitrides are analyzed, along with the dependence of particle size on niobium concentration, temperature and holding time. Optimal alloying parameters ([Nb] ≤ 0,42 %, [C]+[N] ≤ 0,062 %) ensure a balance between strength and ductility. The research findings can be applied to develop steels with improved mechanical properties and digitalize metallurgical processes. The study shows that existing mathematical methods allow, through proper computational algorithms, to determine appropriate limits for niobium alloying in steels. The objectives of such alloying include carbonitride strengthening, control of niobium carbonitride sizes, regulation of interparticle distances, and austenite grain size restriction. The ratio of average interparticle spacing to azerage particle diameter (s/d) is shown to serve as an important parameter for describing steel properties. The calculations of carbonitride size are based on the assumption of a particle growth feeding zone, whose size is determined by the diffusion path of niobium atoms at temperatures and holding times corresponding to the carbonitride formation and growth process.

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