Abstract
This study aims to investigate the microstructures, strength, and impact toughness of low-temperature bainite obtained by isothermal transformation at temperature below Ms (Martensite Starting temperature) for different times and tempering process in 0.53 C wt% bainitic steel. By using the optical microscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), electron back scatter diffraction (EBSD), and mechanical property test, it was found that the microstructures after heat treatment consist of small amounts of martensite, fine bainite, and film retained austenite. After tempered at 250 °C for 2 h, the volume fraction of retained austenite (10.9%) in the sample treated by isothermal transformation at 220 °C for three hours is almost the same as that of the sample without tempering. In addition, the retained austenite fraction decreases with the increase of holding times and is reduced to 6.8% after holding for 15 h. The ultimate tensile strength (1827 MPa), yield strength (1496 MPa), total elongations (16.1%), and impact toughness (up to 58 J/cm2) were obtained by isothermal transformation at 220 °C for three hours and tempered at 250 °C. Whereas, the impact toughness of sample without tempering is 28 J/cm2. After holding for 15 h, the impact toughness raises to 56 J/cm2, while the ductility and strength decreases. These results indicate that the tempering process is helpful to improve the impact toughness of low-temperature bainite.
Highlights
Carbide-free bainite has attracted more attention from researchers for its high strength and good toughness
Based on the concept of carbide-free bainite, low-temperature bainite obtained by isothermal transformation of austenite at low-temperature in the high carbon high silicon steel was investigated firstly by Sandivik and Nevalainen [15]
The low-temperature bainite transformation was carried out at 220 ◦ C, which is below the Ms
Summary
Carbide-free bainite has attracted more attention from researchers for its high strength and good toughness. Previous research has demonstrated that the excellent strength and toughness of carbide-free bainite can be attributed to the fine bainitic ferrite size and the thin films of retained austenite between lath or the subunits of bainitic ferrite [9]. Based on the concept of carbide-free bainite, low-temperature bainite obtained by isothermal transformation of austenite at low-temperature in the high carbon high silicon steel was investigated firstly by Sandivik and Nevalainen [15]. They indicated that the low-temperature bainite in high
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
