Low-temperature bainite in low-carbon steel

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 594; pp. 344 - 351
• Main Authors: Long, X.Y., Zhang, F.C., Kang, J., Lv, B., Shi, X.B.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 31.01.2014; Elsevier
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Elasticity and anelasticity; Elasticity, elastic constants; Exact sciences and technology; Low-carbon steel; Low-temperature bainite; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Mechanical properties of solids; Mechanical property; Metals. Metallurgy; Microstructure; Physics; Treatment of materials and its effects on microstructure and properties; Low-carbon steel; Low-temperature bainite; Microstructure; Mechanical property; Heat treatment; Work hardening; Ultimate strength method; Volume fraction; Low carbon steel; Cooling rate; Mechanical properties; CCT curve; Optimization; Tensile strength; Thin film; Fracture toughness; Dislocation density; Retained austenite; Fine particle; Yield strength; Elongation (mechanics)
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2013.11.089

The microstructures and the mechanical properties of 30MnSiCrAlNiMo low-carbon steel were systematically optimized by a series of heat-treatment processes, and the heat-treatment process of low-temperature bainite in low-carbon steel was explored. Results showed that the microstructure of low-temperature bainite in the low-carbon steel, containing a fine plate of carbide-free bainitic ferrite and a thin film of retained austenite, could be produced by continuous cooling transformation around the Ms temperature from Ms+10°C to Ms−20°C at a cooling rate of 0.5°Cmin−1. A new model was proposed to evaluate the comprehensive mechanical properties of steel, which found that the low-temperature bainite had the best comprehensive mechanical properties compared to any other microstructures for the low-carbon steel. The higher dislocation density and finer bainitic ferrite plate in the low-temperature bainite resulted in the higher yield strength and the higher toughness, but relatively lower ultimate tensile strength owing to the lower work-hardening rate caused by the higher initial dislocation density. There were some very fine particles in the bainitic ferrite of the steel after isothermal treatment at higher temperature. The ultimate tensile strength and the low-temperature impact toughness of the steel decreased with the volume fraction of the retained austenite increasing, while the elongation initially increased with an increase in the volume fraction of the retained austenite (<10%) and then remained constant.