Development and Commercial Use of Weldable High-Strength Cold-Resistant Steel for Load-Bearing Structures in Transportation Engineering

Ural'skaya Stal' has developed and introduced new grade of steel 12KhGN2MA. The steel is designed for use on the frames of quarry trucks, mining machinery, and other metal structures used at low temperatures. The steel is distinguished by its excellent cold resistance (KCV−70 ≥ 50 J/cm2) and good weldability, and it has satisfactorily high strength and ductility (σ0.2 ≥ 690 N/mm2, δu ≥ 790 N/mm2, and δ5 ≥ 16%) after quenching and tempering. The cold-shortness threshold — corresponding to 50% ductile component in the fracture — is below −40°C for steel 12KhGN2MA (25-mm thick plate). Alloying the steel with elements that help stabilize austenite (chromium, nickel, molybdenum, and magnesium) ensures the formation of a martensite-bainite structure. The technology used to make the steel provides for its refining in electric-arc furnaces, rolling of the steel on a 2800 mill, and subsequent heat treatment of the plates in high-productivity regimes. The weldability of the steel was studied by simulating the effects of the thermal welding cycle on the structure and properties of the metal in the near-weld zone. This metal is given good cold resistance down to −70°C by using cooling rates corresponding to the types and regimes of welding actually used. Ural'skaya Stal' has successfully begun production of plates of the new steel in the 10–45-mm thickness range.