Formation and elimination of abnormal ultra-fine microstructure on surface of GCr15 bearing steel bar

doi:10.13251/j.issn.0254-6051.2025.05.005

Abstract

Abstract: Formation of abnormal ultra-fine microstructure on the surface of GCr15 bearing steel was studied. The evolution of the ultra-fine microstructure during annealing was simulated through high-temperature metallographic tests. The temperature after breaking out of the water to suppress the formation of ultra-fine microstructure on the surface of bearing steel was obtained through simulated water cooling tests, and the elimination method of the ultra-fine microstructure was determined. The results indicate that during the water cooling process, due to the high water flow rate and pressure, the instantaneous surface temperature may be lower than the Ms point of the bearing steel, resulting in the formation of martensite on the surface. After entering the water, it reheats to above 600 ℃, forming the tempered martensite. The cooling intensity is the main cause of the formation of ultra-fine microstructure, and when the cooling intensity is high, the ultra-fine microstructure is easily to completely cover the decarburization layer. Under the heating condition of 800 ℃, the ultra-fine microstructure is completely eliminated, and most of it constitutes the decarburization layer of the bearing steel. The original acicular tempered martensite transforms into resembling spheroidized pearlite and lamellar pearlite. In the simulated water cooling test, when the measured surface temperature of the bearing steel after breaking out of the water is ≥520 ℃, the microstructure of the specimen surface is composed of pearlite. When the measured surface temperature of the bearing steel after breaking out of the water is ≤330 ℃, the martensite layer on the surface completely covers the decarburization layer. And under the same cooling conditions, the appearance of decarburization layer can easily deepen the depth of martensite layer on the surface.

Key words: GCr15 bearing steel, water cooling, ultra-fine microstructure, austenitizing, pearlitic transformation, martensitic transformation

CLC Number:

TG161

Xie Zhaoyuan, Yin Defu, Jiang Ting, Zhou Dayuan, Wang Kaizhong, Ding Lei. Formation and elimination of abnormal ultra-fine microstructure on surface of GCr15 bearing steel bar[J]. Heat Treatment of Metals, 2025, 50(5): 27-32.

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