Increase in Low-Carbon Steel 12GBA Strength and Cold Resistance by a Deformation-Thermal Effect

• Published in: Metal science and heat treatment Vol. 64; no. 5-6; pp. 295 - 300
• Main Authors: Sergeev, S. N., Safarov, I. M., Galeev, R. M., Gladkovskii, S. V.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.09.2022; Springer; Springer Nature B.V
• Subjects: Annealing; Brittleness; Carbon content; Carbon steel; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crack propagation; Deformation effects; Ductile-brittle transition; Engineering Thermodynamics; Forging; Heat and Mass Transfer; Hydraulic presses; Impact strength; Low carbon steel; Low carbon steels; Low temperature resistance; Materials Science; Mechanical properties; Metallic Materials; Steel structures; Steel, Structural; Temperature effects; Tensile tests; Thermal and Thermomechanical Treatment; Thermal resistance; Transition temperature; Ultrafines; ultrafine-grained structure; ductility; low-carbon structural steel; strength properties; impact toughness; cold brittleness
• ISSN: 0026-0673; 1573-8973
• DOI: 10.1007/s11041-022-00804-y

The effect of two regimes of all-round isothermal forging (AIF) in a hydraulic press and subsequent annealing on the structure and mechanical properties of structural low-carbon steel 12GBA is analyzed. Steel structure is studied by the EBSD method and scanning electron microscopy. Steel mechanical properties are determined in tensile tests. Total impact energy in the loading diagrams is plotted in terms of the energy expended on crack generation and propagation. It is shown that AIS forms a relatively equiaxed ultrafine-grained (UFG) structure. Formation of an equiaxed UFG structure with grain/subgrain sizes of 0.4 – 0.5 μm during forging doubles strength properties and retains ductility at a good enough level compared with the initial fine-grained structure. The ductile-brittle transition temperature is lowered. UFG steel has a better impact strength below –40°C compared with the initial condition. Additional annealing at 550°C increases impact strength and shifts the ductile-brittle transition temperature towards lower values.