Effects of Cooling Conditions on Microstructure, Tensile Properties, and Charpy Impact Toughness of Low-Carbon High-Strength Bainitic Steels

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 44; no. 1; pp. 294 - 302
• Main Authors: Sung, Hyo Kyung, Shin, Sang Yong, Hwang, Byoungchul, Lee, Chang Gil, Lee, Sunghak
• Format: Journal Article
• Language: English
• Published: Boston Springer US 2013; Springer; Springer Nature B.V
• Subjects: Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Exact sciences and technology; Fractures; Materials Science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metallic Materials; Metals. Metallurgy; Microstructure; Nanotechnology; Steel; Structural Materials; Surfaces and Interfaces; Tensile strength; Thin Films; Acicular Ferrite; Bainitic Ferrite; Bainitic Steel; Bainitic Microstructure; Granular Bainite; Bainitic steel; Low carbon steel; High strength steel; Rupture; Mechanical properties; Carbon steel; Tensile property; Microstructure; Strength; Fracture toughness
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-012-1372-5

In this study, four low-carbon high-strength bainitic steel specimens were fabricated by varying finish cooling temperatures and cooling rates, and their tensile and Charpy impact properties were investigated. All the bainitic steel specimens consisted of acicular ferrite, granular bainite, bainitic ferrite, and martensite-austenite constituents. The specimens fabricated with higher finish cooling temperature had a lower volume fraction of martensite-austenite constituent than the specimens fabricated with lower finish cooling temperature. The fast-cooled specimens had twice the volume fraction of bainitic ferrite and consequently higher yield and tensile strengths than the slow-cooled specimens. The energy transition temperature tended to increase with increasing effective grain size or with increasing volume fraction of granular bainite. The fast-cooled specimen fabricated with high finish cooling temperature and fast cooling rate showed the lowest energy transition temperature among the four specimens because of the lowest content of coarse granular bainite. These findings indicated that Charpy impact properties as well as strength could be improved by suppressing the formation of granular bainite, despite the presence of some hard microstructural constituents such as bainitic ferrite and martensite-austenite.