Key Takeaways & Executive Findings
- •• EST integrated into cold rolling-quenching-tempering significantly refines grain size (average reduction 10.1%) and reduces dislocation density (average reduction 20.9%). • EST promotes carbide dissolution and more uniform distribution along grain boundaries, contributing to enhanced mechanical properties. • The rolling-quenching-tempering-EST sequence yields excellent overall performance: hardness +1.4%, tensile strength +17.7%, and elongation at break +24.3%. • The rolling-EST-quenching-tempering sequence achieves the best tensile performance, with tensile strength +30.0% and elongation at break +30.7%.
Abstract
Electroshocking treatment (EST), an efficient and rapid material treatment method, promotes microstructure evolution and improves mechanical properties. This study incorporates EST into the conventional cold rolling-quenching-tempering process of M50 steel and investigates the influence and mechanism of applying EST at different stages of the process on the microstructure and mechanical properties. Scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD) were used to characterize the effect of EST on microstructure. The results show that EST can refine the grains of M50 (average reduction of 10.1% in grain size), homogenize the grain size distribution, reduce the dislocation density (20.9% in average), promote the dissolution of carbides in the matrix and distribute them more uniformly along the grain boundaries, resulting in the improvement of mechanical properties. The mechanical properties of the specimen with the process flow of rolling-quenching-tempering-electroshocking showed excellent performance, with an increase in hardness of 1.4%, tensile strength of 17.7%, and elongation at break of 24.3% as compared to the specimen without EST. The tensile properties of the specimen with the process flow of rolling-electroshocking-quenching-tempering showed the best performance, with an increase in tensile strength of 30.0% and elongation at break of 30.7% as compared to the specimen without EST.
1. Introduction
As a typical high-speed bearing steel, M50 is widely used in the aviation industry as the material for engine bearings [1−3]. M50 steel contains Mo, Cr, V, and other alloying elements that contribute to the formation of coarse alloy carbides. During plastic forming (such as cold rolling), the mismatch of strain between the hard carbides and the soft ferrite tends to deteriorate the mechanical properties [4−7]. Meanwhile, in order to ensure the hardness and dimensional stability of M50 at high temperatures, the heat treatment process of quenching and high-temperature tempering is generally used, thus reducing the plasticity [8−13]. Conventional manufacturing processes limit the performance of M50 steel under actual service conditions.
In recent years, electroshocking treatment (EST), as a new material treatment method, has been widely used to promote microstructure evolution and improve the properties of metals due to its high efficiency and rapidity [14−17]. ZHAO et al [18] found that EST promoted the defect reconfiguring in Ti-7Al alloy and improved its plasticity; ZHAO et al [19] obtained the fine lath-martensite with high-density dislocation in 22MnB5 steel by EST, resulting in high strength, plasticity, and work hardening; XIANG et al [20] applied EST to X80 steel and significantly reduced its dislocation density and residual stresses and improved its plasticity.
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WEI Wen-ting, LI Lai-yu, LIU Guo-cheng, LIU Yan-xiong, HUA Lin (2025). Effects of applying electroshocking treatment at different stages of cold rolling-quenching-tempering process on microstructure and properties of M50 steel. Journal of Central South University. https://doi.org/10.1007/s11771-025-6018-z
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Frequently Asked Questions
What is electroshocking treatment (EST)?
Electroshocking treatment (EST) is an efficient and rapid material treatment method that uses electric current pulses to promote microstructure evolution and improve mechanical properties in metals. In this study, EST is incorporated into the conventional cold rolling-quenching-tempering process of M50 bearing steel.
How does EST affect the microstructure of M50 steel?
EST refines the grain size of M50 (average reduction of 10.1%), homogenizes the grain size distribution, reduces dislocation density (by 20.9% on average), and promotes the dissolution of carbides in the matrix, distributing them more uniformly along grain boundaries.
At which process stage does EST provide the best tensile performance?
Applying EST after cold rolling but before quenching and tempering (rolling-EST-quenching-tempering) gives the best tensile properties, with increases of 30.0% in tensile strength and 30.7% in elongation at break compared to the specimen without EST.
What are the quantitative improvements in mechanical properties when EST is applied after tempering?
With the rolling-quenching-tempering-EST process sequence, the specimen shows an increase in hardness of 1.4%, tensile strength of 17.7%, and elongation at break of 24.3% compared to the no-EST specimen.
What are the key mechanisms behind the EST-induced property enhancement in M50 steel?
The key mechanisms include grain refinement, reduction in dislocation density, and enhanced carbide dissolution with uniform distribution along grain boundaries. These microstructural changes collectively improve the mechanical properties of M50 steel.
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