Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia

P. P. Poletskov, Dr. Eng., Prof., Dept. of Metal Forming named after M. I. Boyarshinov
N. V. Koptseva, Dr. Eng., Prof., Dept. of Foundry Processes and Materials Science
A. S. Kuznetsova, Cand. Eng., Associate Prof., Engineering Center, e-mail: allakuznetsova.mgtu@mail.ru
A. E. Gulin, Cand. Eng., Associate Prof., Engineering Center

The paper presents the results of a study on high-strength cold-resistant steels for heavy-duty vehicles based on C-Si-Mn system with three different alloying options having various contents of nickel, copper, molybdenum, as well as microalloying additives such as niobium, vanadium, titanium, and boron. In these steels, target mechanical properties values (YS ≥ 950 MPa, UTS ≥ 1200 MPa, δ5 ≥ 10%, HBW ≥ 350, KCV−70 ≥ 30 J/cm²) are achieved by quenching due to formation of mixed bainite-martensitic structure. It has been established that in C-Si-Mn steel alloyed with Ni+Mo+Cu up to 0.35 %, an increase in low temperature toughness is ensured by reducing carbon content down to 0.18 %. Simultaneous improvement in strength characteristics is achieved through increasing manganese content up to 1.29 %. When introducing Ni+Mo+Cu up to 2.0 % into the steel, the best combination of strength properties and low-temperature toughness is provided at carbon content up to 0.22 % and manganese content up to 0.75 %. Additionally, microaddition of titanium up to 0.030 % contributes slightly to the dispersion of bainite-martensitic structure. The optimal set of mechanical properties is reached in steel with similar element composition (Ni+Mo+Cu) up to 2.0 % within the range of 0.22 % C–0.75 % Mn through additional microalloying with Nb+V up to 0.075 %. Microadditions of niobium and vanadium had a decisive influence on low-temperature toughness by enhancing the dispersion of low-temperature transformation products of austenite. An increase in alloying elements content (Ni+Mo+Cu) above 2.0 % does not provide significant growth in strength properties compared to first option alloys.

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