Abstract
AbstractThe effects of the cooling rate after hot deformation on phase transformation, the microstructure of the designed nonquenched and tempered medium-carbon carbide-free bainitic steel have been investigated during the dynamic continuous cooling process. The results show that with the increase of the cooling rate, the morphology of the carbide-free bainite of the experimental steel evolves from granular bainite to lath bainite. Meanwhile, the hardness increases, and the amount of the retained austenite decreases with the increase of the cooling rate. Besides, the morphology evolution of the retained austenite from block to film is revealed by EBSD. Moreover, 0.5°C/s is considered to be the favorable cooling rate to obtain the best strength–toughness matching. Furthermore, the semi-industrial experimental results proved that the tensile strength, yield strength and Charpy impact energy were 1,298 MPa, 847 MPa and 38 J, respectively.
Highlights
Over the last several decades, nonquenched and tempered steels, obtained by alloy design and thermomechanicallyClearly, the morphology of bainite has an apparent influence on mechanical properties
When the cooling rate increased to 0.1°C/s, the size of polygonal ferrite (PF) was reduced to less than 10 μm, and the microstructure was almost composed of granular bainite (GB), as shown in Figures 5(b) and 6(b)
The microstructure changed from GB to lath bainite (LB), and the volume fraction of LB increased with the increase of the cooling rate from 0.3 to 1°C/s, as shown in Figures 5(c)–(e) and 6(c)–(e)
Summary
Over the last several decades, nonquenched and tempered steels, obtained by alloy design and thermomechanicallyClearly, the morphology of bainite has an apparent influence on mechanical properties. The carbide-free bainite is generally obtained by adding Si or Al to hinder the precipitation of brittle carbides such as cementite to preserve the carbon-rich retained austenite and to achieve better mechanical properties [6], which benefit the future wider applications of the carbide-free bainite steels [7,8,9,10]. The technology widely applied to obtain the carbide-free bainite microstructure is to use the austempering heat treatment method in the bainitic temperature range generally [11,12,13], which is conducive to low production efficiency and high energy consumption. In this study, the chemical composition was designed to promote the bainite transformation kinetics and to retard the carbide precipitation, to obtain the carbide-free bainite under nonquenched and tempered conditions, such as air cooling or controlled cooling after hot deformation. C was added to ensure the high strength by solid solution strengthening
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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.
