Effect of a new two-step austenitizing-Q&P process on the microstructure and mechanical properties of microalloyed 51CrMnV spring steel

• Published in: Journal of alloys and compounds Vol. 1004; p. 175864
• Main Authors: Ma, Yihao, Dong, Minmin, Qi, Peng, Zheng, Shaojie, Feng, Simon Yisheng, Zhang, Yunshan, Xu, Rongfu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05-11-2024
• Subjects: Mechanical properties; Microalloyed spring steel; Proeutectoid ferrite; Quenching and partitioning; Retained austenite; Mechanical properties; Proeutectoid ferrite; Retained austenite; Quenching and partitioning; Microalloyed spring steel
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2024.175864

The evolution of microstructure and mechanical properties were investigated by the two-step austenitizing-Q&P heat treatment for a specific microalloyed 51CrMnV spring steel. The results indicate that the microstructure of the steel treated by two-step austenitizing-Q&P process mainly consists of martensite, retained austenite, proeutectoid ferrite and carbides, with the proeutectoid ferrite predominantly distributed along the prior austenite grain boundaries. As the holding time of the second austenitizing step increased, both the tensile strength and elongation after fracture of the steel exhibited an increasing trend. Under the specific process conditions of austenitizing at 870°C for 30 minutes, followed by a second austenitizing step at 790°C for 2400 s, oil quenching at 120°C, and partitioning at 350°C for 1200 s, the tested steel achieves the best mechanical properties, with a tensile strength of 1845 MPa and an elongation after fracture of 11.4 %. With increasing holding time during the second step of austenitization, the amount and size of proeutectoid ferrite increase. Additionally, variant analysis of the martensite reveals an enhanced dominance of the CP group, resulting in an increase in large-angle grain boundaries. As a result, the spring steel demonstrates improved resistance to crack initiation and propagation, thereby enhancing its strength and plasticity.
•Using a novel two-step austenitizing-Q&P heat treatment process.•Through a two-step austenitization process, some proeutectoid ferrite precipitates in the 51CrMnV matrix.•Analyzed the effect of proeutectoid ferrite on the selectivity of martensite variants.•Integrated mechanical properties of 51CrMnV spring steel with two-step austenitizing-Q&P process are superior.