Papers by Keyword: GCr15

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: Turning instead of grinding of the hardened steel is an environmentally cleaner production technology and green fabrication technique. Using the negative rake angle basic shape blades of Mountain of Sweden Sandvik Coromant PCBN7015 cut hardened bearing steel GCr15 and observe fine surface under microscopic condition.. Microscopic observation showed that there was side stream between hard turning two knife marks forming carinata. Side stream level aggravate on the fine surface with the enlargement of Tool Nose radius. The White layer of hard turning fine surface is divided into three areas. White-bright zone is made up of Cryptocrystalline martensite, Dark gray zone is made up of tempered martensite, Grayish zone is made up of the original martensite. This research will enrich theory of hard turning.

Abstract: The spheroidization of the carbide of hot-deformed GCr15 bearing steel was investigated in cyclic annealing process. The results show that most of carbide particles become gradually smaller and more dispersed with the increase of process cycle, however, part of them start to grow for the four cycles, the growth agrees well with Ostwald Ripening Law, and it is not suitable for the further process.

Abstract: In order to explore the influence of the nitrogen concentrations on the impact toughness of the bearing steel GCr15，impact testing has been conducted on the steel samples with variant nitrogen contents (0.1-0.3 wt.%) on the tester JB－30B, and the fracture morphology of the samples after impact was investigated using scanning electron microscopy (SEM) and optical microscopy (OM). The results indicate that the impact toughness of the steel GCr15 with 0.1 wt.% nitrogen exhibits the lowest values with typical quasi-cleavage feature. The steel GCr15 with 0.2 wt.% nitrogen presents the maximum values in impact toughness associated with significant plastic deformation, suggesting ductile nature. The steel with 0.3 wt.% nitrogen presents a quasi-cleavage feature, and micro cracks observed beside the secondary precipitates. The impact toughness values of the steel with 0.3 wt.% nitrogen are higher than that with 0.1 wt.% nitrogen and lower than with 0.2 wt.% nitrogen. The results are valuable for a large-scale bench marked industrial manufacture of the bearing steel GCr15 with the optimized nitrogen concentrations.

Abstract: A novel processing of quick spheroidizing annealing based on DET(divorced eutectoid transformation) mechanism has been presented in this paper. Spheroidized carbide microstructure could be achieved directly by austenite through phase transformation during cooling processing, which is different from the conventional spheroidization annealing where carbide was spheroidized by carbide lamellar gradually resolved and coarsened.The novel processing of spheroidizing annealing presented here will decrease the annealing time from 10-16 hours in conventional processing to around 2-3 hours, which could save about 50% of the energy consumption, comparing to the conventional annealing processing.

Abstract: Surface hardening of GCr15 bearing steel ring was carried out using CW CO2 laser. The laser power used was in the range of 300 to 500 Watts. A rectangular beam shape was used to cover the area to be hardened. A three fold increase in the hardness of the transformed zone was achieved. The depth of hardness attained was around 1mm. The depth and width of the laser treated zone were studied as function of laser power and working speed for specific spot size. The microstructure of the transformed zone is also discussed. Subzero cooling technique was applied to convert the retained austenite to martensite.

Abstract: PCBN cutting tools is in high speed, high temperature and high pressure environment when high speed precision hard cutting hardened steel. Shear extrusion and slip effect in high speed cutting, cutting tools wear mechanisms are different from common cutting, even cutting tools wear mechanisms in high speed is in research stage at present. In this paper, coated PCBN cutting tools wear mechanisms in high speed cutting(v＝200~600m/min) GCr15 (HRC62-64) is studied, it is helpful to obtain cutting tools structure design, cutting parameters and improve cutting tools use efficiency.

Abstract: In this paper, FEM is used to simulate the three stages of catastrophic shear occurrence, expansion and shear band formation when serrated chips are formed under adiabatic shear behavior in high-speed machining of hardened steel GCr15 with PCBN tool. By comparing data of simulation and experiment on chip morphology characters, it is indicated that they are in good accordance. Hereby, the author has analyzed strain and temperature distribution in adiabatic shear band, and dynamic characters of cutting force . The research results show that adiabatic shear band begins from tool tip and extends to workpiece free surface, and it is characterized by large strain and high temperature. In addition, it results from adiabatic shear behavior that cutting force waves regularly in a numerical range.

Abstract: In the cutting process, cutting force is one of the important physical parameters, which affects the generation of cutting heat, tool life and surface precision of workpiece directly. In this paper an orthogonal design of experiment and subsequent data is analyzed using high speed finish hard cutting GCr15 whose hardness is 65HRC. Cutting speed is 200-400m/min, to study the influence of cutting parameters on cutting force, cutting force empirical model has obtained from least square method.

Abstract: Air cooling is a near dry machining method, which cools cutting area and evacuates chips using low temperature cold wind instead of cutting liquid. It can decrease tool wear, increase tool life, reduce machining cost and bring no chemical pollution. In this paper, air cooling test was carried on, in which vortex tube was used for cooling and high hardness bear steel GCr15 was machined by PCBN tool. Experiment results indicated that cold air from vortex tube has a significant effect on cutting force, cutting temperature and chip formation process. This paper’s conclusions will have a great reference value for the practical application of air cooling technology.