Formation and Evolution Mechanism of Voids in M50 Bearing Steel During Thermal Deformation
HOU Zhiyuan1,2,3, LIU Weifeng1,3, XU Bin1,3(), SUN Mingyue1,3(), SHI Jing2, REN Shaofei1,3
1 CAS Key Laboratory of Nuclear Materials and Safety, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2 School of Materials Science and Engineering, Ocean University of China, Qingdao 266003, China 3 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
HOU Zhiyuan, LIU Weifeng, XU Bin, SUN Mingyue, SHI Jing, REN Shaofei. Formation and Evolution Mechanism of Voids in M50 Bearing Steel During Thermal Deformation. Acta Metall Sin, 2024, 60(1): 57-68.
M50 bearing steel is widely used in the manufacture of aeroengine spindle bearings. The voids generated by the thermal processing of bearing steel can easily initiate fatigue cracks and lead to fatigue failure of the bearings. Thus, it is essential to understand the steel production conditions, void distribution in the steel, and effect of the subsequent treatment on the healing process of voids to improve the thermal processing and mechanical properties of the steel. In this work, the thermal deformation of the M50 bearing steel was conducted using a thermal simulation machine. The effects of the strain rate (0.001-1 s-1), deformation temperature (1000-1150oC) and strain (10%-50%) on the formation of voids and void healing during the subsequent thermal treatment were systematically studied using OM, SEM, EBSD, and in situ scanning methods. The results show that the formation of voids between the carbide and matrix is attributed to the different hardness values between the matrix and primary M2C and MC carbides. In addition, the carbide fractures can promote the formation of internal voids. The quantitative analysis of the voids indicated that most voids are generated under the following conditions: a high strain rate of 1 s-1, low deformation temperature of 1000oC, and medium deformation of 30%. Applying a heat treatment after deformation can significantly promote the void healing process, and the Cr element is enriched in the healing zone due to its rapid diffusion in γ-Fe.
Fund: National Key Research and Development Program of China(2018YFA0702900);National Natural Science Foundation of China(51774265);National Natural Science Foundation of China(51701225);National Natural Science Foundation of China(52173305);National Science and Technology Major Project of China(2019ZX06004010);Strategic Priority Research Program of the Chinese Academy of Sciences(XDC04000000);Lingchuang Research Project of China National Nuclear Corporation, and Youth Innovation Promotion Association, Chinese Academy of Sciences
Corresponding Authors:
XU Bin, professor, Tel: (024)83970108, E-mail: bxu@imr.ac.cn; SUN Mingyue, professor, Tel: (024)83970108, E-mail: mysun@imr.ac.cn
Fig.1 Hot compression test curve of M50 as-cast sample
Fig.2 OM image of original as-cast microstructures of M50 bearing steel
Fig.3 SEM image (a) and EDS element distribution maps of M50 bearing steel (b-e), Kikuchi patterns of M2C (f) and MC (g), and EDS results of M2C (h) and MC (i)
Fig.4 OM (a) and SEM (b) images of the M50 bearing steel after hot deformation treatment at 1100oC, 0.1 s-1, and 30%
Fig.5 SEM images of voids at different positions inside the M50 bearing steel after hot deformation treatment at 1100oC, 0.1 s-1, and 30% (a), and around different carbides (b, c), Kikuchi lines of MC (d) and M2C (e), and EDS line scan analyses of void (Inset shows the position of the line scan around the void) (f)
Fig.6 SEM images of voids around carbides in M50 bearing steel after hot deformation at strain rates of 0.001 s-1 (a), 0.01 s-1 (b), 0.1 s-1 (c), and 1 s-1 (d) at temperature of 1100oC and strain of 50%, and statistical results of the volume fraction and number density of voids (e)
Fig.7 SEM images of voids around primary carbides in M50 bearing steel after hot deformation at strain rates of 0.1 s-1 (a, c, e, g) and 1 s-1 (b, d, f, h) with temperatures of 1000oC (a, b), 1050oC (c, d), 1100oC (e, f), and 1150oC (g, h) at strain of 50%
Fig.8 Statistical results of the volume fraction (a) and number density (b) of voids at different deformation temperatures with strain of 50%, and strain rates of 0.1 and 1 s-1
Fig.9 SEM images of voids around carbides in M50 bearing steel after hot deformation at strains of 0.1 s-1 (a, c) and 1 s-1 (b, d) for strains of 10% (a, b) and 30% (c, d); and statistical results of volume fraction (e) and number density (f) of voids
Fig.10 SEM images of thermal deformation sample before (a) and after (b) soaking at 850oC for 1 h
Fig.11 SEM image (a), and EDS line scanning analyses from line AD (b) and EG (c) of the voids of the thermal deformation sample soaking at 850oC for 1 h (MZ, M'Z—matrix zones; VZ—void zone; HZ—healed zone; CZ, C'Z—carbide zones)
Fig.12 Trend diagram of element distribution in different regions (a) and statistical results of the average area of voids at different holding time of soaking sample (b)
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