Acicular martensite induced superior strength-ductility combination in a 20Cr2Ni2MoV steel

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 848; p. 143400
• Main Authors: Wang, Y.L., Shen, Y.F., Jia, N., Wang, J.J., Zhao, S.-X.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 19.07.2022; Elsevier BV
• Subjects: 20Cr2Ni2MoV steel; Carburization; Carburizing; Chemical precipitation; Dislocation density; Ductility; Grain boundaries; High strength low alloy steels; Martensite; Mechanical properties; Precipitates; Quenching; Re-quenching; Steel; Tensile strength; Ultimate tensile strength; Ultrahigh strength; Re-quenching; Ductility; Ultrahigh strength; 20Cr2Ni2MoV steel; Carburization
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2022.143400

The super combination of ultrahigh strength and good ductility is in high demand for the gear steels. Here we improved the mechanical properties of a micro-alloyed gear steel through the fabrication route composed of carburizing and re-quenching. The results showed that the different re-quenching temperatures significantly affect not only the sizes and morphologies of precipitates and martensite but also the ratio of low-angle grain boundaries to high-angle grain boundaries as well as dislocation densities. The maximum ultimate tensile strength up to 2420 MPa was obtained after re-quenching at 780 °C, while the steel re-quenched at 820 °C exhibited the highest yield strength of 1500 MPa despite of the decreased ultimate tensile strength of 2145 MPa. Especially, a good ductility of 8.5% was maintained in the carburized steel processed after 780 °C re-quenching. The spherically nanosized precipitates together with the high ratio of low-angle grain boundaries were beneficial for the simultaneously improved strength and ductility.