Effect of banded carbide structure on the rolling contact fatigue of GCr15 bearing steel

Abstract

In this paper, the influence of banded carbide structure on Rolling Contact Fatigue (RCF) of GCr15 bearing steel was investigated by using MMS-2A double-roller wear tester under dry friction at room temperature. Surface damage was characterized using SEM and OM. The results showed that with the increase of banded carbide grade, wear rate and friction coefficient were obviously increased and contact fatigue performance was deteriorated. For the high grade of banded carbide, the main failure form is fatigue pits and surface cracks. On the contrary, for the low grade of banded carbide, the main failure form is flaking off. Besides, with the increment of banded carbide grade, the thickness of plastic deformation layer increase. The fatigue cracks easy propagated in the plastic deformation layer along the rolling direction. Therefore, by reducing the banded carbide grade can effectively improve the rolling contact fatigue properties of bearing steel. Key words: GCr15 bearing steel; banded carbide; RCF 1.IntroductionBearing balls and rolling-element bearings experience subsurface initiated fatigue failures due to RCF.The bearings used in practical applications are designed to operate at nominal stress levels well below the yield strengths of the materials. However, the presence of imperfections and non-metallic inclusions introduces heterogeneity at the microstructural level [1].With increasing in number of cycles, the ratcheting strain accrues, and therefore it can serve as a meaningful parameter to quantify the evolution of a material damage due to RCF [2,3].Once this damage reaches a critical value, a fatigue crack nucleates in the subsurface of a material. Since this local plastic strain accumulation takes place in the vicinity of carbides, it is important to understand their role towards ratcheting under RCF loading conditions. Generally, the influence factors of RCF failure of bearing steel is non-metallic inclusion, distribution of carbide and purity of steel. Undoubtedly, previous studies have showed the RCF would reduce the life and reliability of many useful components, such as gears, rolling bearings [4][5][6]. Nagao M find the stiffness of an inclusion and its location have a significant effect on the RCF life, stiffer inclusions and inclusions located at the depth of maximum shear stress reversal are more detrimental to the RCF life [7].T.Karsch studied the effects of hydrogen content and microstructure on fatigue behavior of steel GCr15 in the VHCF regime [8],and it is found that increased hydrogen content in bearing steel at 5 ppm (by weight) will significantly promote bearing spalling failure [9,10]. Shigeo shmizu's studies show that the bearing fatigue life is directly related to the instantaneous contact time, with the increase of the instantaneous contact time, the fatigue life is also increased [11]. O.P.Datsyshyn introduced the mechanism of fatigue crack propagation in metallic materials [12]. G.John put forward the using of bearing steel under normal conditions, due

Improvement of centre segregation in continuous casting bloom and the resulting carbide homogeneity in bearing steel GCr15

“…Total oxygen content of GCr15 by produced by integrated bloom continuous casting and rod hot-rolling processes, which can represent the control level of cleanliness and inclusions, has be reduced below 6×10 −6 [9]. Thus, the effect of carbide distribution on fatigue life becomes increasingly important [10,11]. Carbide distribution in hot-rolled rod reveals in the form of network and banded carbides, which are respectively precipitated proeutectoid carbide with band and reticulation form along austenite grain boundary with GCr15 hypereutectoid steel during the cooling process after rolling [12].…”