Papers by Keyword: Bearing Steel

Abstract: The effects of temperature on the friction and wear properties of GCr15 were studied by using a RETC multifunctional friction and wear testing machine. The microstructure characterization of the worn surface of the experimental steel was studied by means of metallographic microscope (OM), white light interferometer, secondary electron image (SEI) and back scattered electron image (BEI).The results show that the wear resistance of GCr15 bearing steel at room temperature is better than that at 100°C, 150°C and 200°C. At room temperature, the main wear forms of GCr15 are adhesion wear and fatigue wear. However, at 100°C, 150°C, 200°C, the friction coefficient and oxidation degree in the wear zone first increase and then decrease with the increase of temperature, and the wear form is mainly oxidized wear, accompanied by abrasive wear.

Abstract: Polytetrafluoroethylene (PTFE) lubricant is commonly applied for dry contact due to its low friction properties. However, low strength properties can lead to short service-life due to high wear rate, especially under high contact load. The method to add PTFE into a solid contact during operation as a transfer layer has been one of the major attempts in this field. This study aims to investigate the influence of operating parameters, i.e., revolution cycle, sliding speed and applied load, on coverage area of transfer PTFE on the bearing steel (AISI 52100) disc. The experiments were performed on the modified pin-on-disc apparatus using a unidirectional ground disc. The areas with disc grinding direction parallel (parallel morphology) and perpendicular (perpendicular morphology) to the pin sliding direction were both examined. The ascending of transfer coverage area with an increasing revolution cycle within the first 1000 cycle was observed on the area with a sliding direction perpendicular to the disc grinding direction while the descending of transfer coverage area was found on the parallel case. The further increase in the revolution cycle led to only a small change in the transfer coverage area. With more revolution cycles, the pin wear rate increased as a decrease in transfer coverage area formed on the counter-face. Research suggested that the amount of transfer coverage area decreased with increasing sliding speed. However, it could be increased by increasing the applied load.

Abstract: One important method to improve the material properties is refinement of the prior austenite grain size. Repeated quenching is used as a grain refinement method. In the present work, samples of SUJ2 steel were furnace quenched once and thrice in order to investigate the effect of repeated quenching on rolling contact fatigue (RCF) strength. After the RCF tests, maicrostructure observations, Vickers hardness and retained austenite measurements, RCF life evaluation using the Weibull distribution were carried out. It was found that the dispersion of the life population was reduced by repeatedly quenching.

Abstract: This paper presents the influences of quenching technologies (classical, with cooling in magnetic field, cryogenic, with cooling in the ultrasonic field) on the dimensional stability in time and the contact fatigue behaviour of some elements of ball bearings made from 100Cr6 (RUL 1) steel. From the analysis of the experimental data obtained it has resulted that the use of ultrasound for martensitic quenching of these steels ensures changes to the properties favorable to elements of ball bearings and may represent an effective way of increasing the quality of bearings; the technology is relatively simple, it does not require substantial constructive changes in the quenching machines and no further investment of large values.

Abstract: Accelerated carbide spheroidisation enables significant shortening of time necessary for formation of steel microstructure consisting of ferritic matrix and globular carbides. Conventional way to obtain such structure is long duration soft annealing after semiproduct hot forming. Research of accelerated carbide spheroidisation showed that it is possible to spheroidise lamellar pearlite in minutes. Accelerated carbide spheroidisation produces very similar microstructure like conventional soft annealing in morphological point of view, but carbide particles and grain size of the matrix is significantly smaller. Finer microstructure results in higher hardness in comparison with conventionally annealed steel. Finer microstructure also ensures more homogeneous and finer structure after final heat treatment, after hardening. This fact indicates, that properties of final product differ according to previous structure after soft annealing. Finer carbides in structure enhance hardness and facilitates carbide dissolution during austenitisation. This effect enables quenching temperature lowering. Steel 100CrMnSi6-4 microstructure and properties are compared in view of various kind of spheroidisation and quenching temperature.

Abstract: The effect of 0.018% niobium additions on austenite grain coarsening behavior of GCr15 bearing steel was studied. Results indicate that the coarsening temperatures of No.1 and the No.2 experimental steel were 950°C and 1100°C. The austenite grain coarsening temperature was increased by 150°C by the addition of 0.018% Nb in bearing steel. The grain growth equations of two experimental steels at different soaking temperatures from 850°C to 1250°C with the soaking time of 30 min are as follows: the equation of No.1 steel is D₁=1.85×10⁵·exp (-6.57×10⁴/RT); the equations of No.2 steel below and above 1100°C is D₂=5.08×10²·exp (-2.49×10⁴/RT) and D₂=1.06×10⁸·exp (-1.31×10⁵/RT), respectively. The grain growth equations of two experimental steels at different soaking time from 15 to 120 min with the soaking temperature of 840°C are as follows: the equation of No.1 steel is D₁=4.83×10^-2·t^0.72 while that of No.2 steel is D₂=1.25·t^0.18.

Abstract: The effect of heat treatment on transformation of residual austenite in bearing steel is studied, by adding the cryogenic treatment into the normal heat treatment process. The results indicate that the residual austenite content is decreased and the hardness is improved obviously, when putting the cryogenic treatment at -70°C or lower directly behind the quenching process. While when the tempering is added between quench and cryogenic treatment, the temperature of cryogenic treatment must be much lower than -70°C to offset the thermal stability of residual austenite, which is given by tempering.

Abstract: Inspection on chips from oil system is an important method for modern aeroengine condition monitoring. Energy spectrum analysis technique is the most widely used and effective method in inspection on metal chips. In this method, size and quantity of chips are observed by scanning electronic microscope and qualitative and quantitative analysis of element contents are finished by energy dispersive spectrometer. Through above experiments, material type of metal chips can be analyzed and material mark can be determined by comparison with the materials list used in the aeroengine. In this article, characteristics and advantages of energy spectrum analysis technology are systematically introduced and typical appearance feature and energy spectrum curve of common l chips are summarized in engineering practice. In addition, problems and prospects of energy spectrum analysis technique are proposed.

Abstract: Ceramic cutting tools have a large potential by high speed processing of difficult-to-cut steels and alloys, however due to its fragility they don’t assure the required reliability level of cutting process. For improving the operational characteristics of the ceramic cutting tool combined treatment can be used namely the preliminary planetary grinding of the insert surface and the following deposition of the vacuum-plasma coatings (TiCr)N, (ZrCrHf)N and other.

Abstract: Cutting tool durability is very important cutting tool property. Especially for cutting ceramic is necessary to define durability dependence on available set of cutting speeds and to determine lifetime of tools made of cutting ceramic. Durability of cutting tools is defined in standard ISO 3685. In standard ISO 3685 is defined T-v_c dependence for different cutting materials and standard included process evaluation of tool durability for cutting materials made of high speed steel, sintered carbide and cutting ceramic. Specification cutting tools durability made of cutting ceramic in machining process of steel 100Cr6 is very important for economics of small and medium-sized enterprises, because cutting tool durability is factor that significantly affects the budget of these enterprises. This problematic is determined for small and medium-sized manufacturers of bearings, because steel 100Cr6 is most commonly used for production of bearing rings 100 mm in diameter. This material is usable for actuator (actuators and reduction gears) too. Description of cutting ceramic durability could mean for bearings manufacturer determination of optimal cutting parameter with maximum possible use of tool lifetime. Standard ISO 3685 contains instructions how to create T-v_c dependence for cutting tools made of cutting ceramic. In this standard are only instructions how to create T-v_c dependence according to Taylor. The article compares T-v_c dependencies for various cutting ceramics (Al₂O₃, Al₂O₃+ZrO₂, Al₂O₃+TiCN) with T-v_c dependence defined in standard ISO 3685, because this standard describes T-v_c dependence for all entered cutting materials together.