Search Results (7)

In this paper, gears made of 18Cr2Ni2MoVNbA steel were taken as the research object, and their cooling curves under different flow rate conditions were determined. By calculating the corresponding heat transfer coefficients, a finite element simulation method was used to study the temperature field distribution law of different flow rate combinations on the gears in the cooling process of pressure quenching. The results show that among the four representative flow combinations, the working condition 1 (A + (A − b − c) + (A − b − c)) has the smallest temperature difference between the inner and outer gears, and can better reduce the temperature difference between the inner and outer parts. Furthermore, in the pressure quenching process of gears, the appropriate extension of the quenching time can keep the quenched gear with a lower average temperature, while promoting the martensitic transformation on the surface of the workpiece. Comparing the simulation results with the experimental data, the reliability of the pressure-quenching temperature field model is verified, which can provide theoretical guidance for the optimization of the pressure quenching process. Full article

The 17CrNi2MoVNb alloy is widely used for manufacturing heavy-duty gears in vehicles’ transmission systems, where grinding is a significant process affecting gears’ working performance and service life. This work comprehensively analyzed the grinding force, surface morphology, and surface roughness when grinding 17CrNi2MoVNb alloy using alumina and CBN grinding wheels. Results showed that the maximum normal grinding force from the CBN wheel was only ~67% of the one from the alumina wheel. Due to the small size and limited cutting depth of CBN grains, the grinding force increased by about 20% when the grinding depth increased from 0.02 to 0.03 mm for CBN grinding wheels. Surface defects, including cavities and material tearing, were mainly found on the ground surface when using an alumina grinding wheel. The surface roughness Ra recorded from the CBN grinding wheel mainly ranged from 0.263 to 0.410 μm, accounting for less than 40% of the one from the alumina grinding wheel. The information from this work could provide benchmark data and references for optimizing grinding tools and parameters when manufacturing gears in the vehicle industry. Full article

Cryogenic treatment as a process that can effectively improve the performance of steel materials is widely used because of its simplicity and speed. This paper investigates the effects of different low temperature treatments on the microstructure and properties of 17Cr2Ni2MoVNb steel. The low temperature treatment range is divided into cryogenic treatment (CT-80), shallow cryogenic treatment (SCT-150) and deep cryogenic treatment (DCT-196), all with a duration of 1 h. The retained austenite content and the change in carbide volume fraction at 0.2 mm in the carburised layer are studied. The microhardness gradient of the carburised layer, as well as the friction coefficient and wear scar morphology at 0.2 mm, was investigated. The results show that the low temperature treatment is effective in reducing the retained austenite content and increasing the volume fraction of carbide. The lowest retained austenite content and highest carbide volume fraction were obtained for DCT-196 specimens at the same holding time. Due to the further transformation of martensite and the diffuse distribution of carbides, the microhardness and frictional wear properties of DCT-196 are optimal. Therefore, low temperature treatment can change the microstructure of the case layer of 17Cr2Ni2MoVNb steel and effectively improve the mechanical properties of materials. Full article

The effects of cryogenic treatment and low temperature tempering on the microstructure, mechanical properties and distortion of the 20Cr2Ni4A and 17Cr2Ni2MoVNb carburized gear steels were investigated. The results showed that the case hardness of the experimental steels was increased after the cryogenic treatment, due to the decrease of the retained austenite content and the precipitation of the tiny carbides. The wear resistance of the two steels after cryogenic treatment was improved, although the wear mechanisms were different for 17Cr2Ni2MoVNb and 20Cr2Ni4A steels. The distortion of the Navy C-ring specimens underwent shrinkage before expansion during the cryogenic process, and the distortion of 17Cr2Ni2MoVNb steel was smaller than that of 20Cr2Ni4A steel. Full article

X6CrNiMoVNb11-2 supermartensitic stainless steel, a special type of stainless steel, is commonly used in the production of gas turbine discs in liquid rocket engines and compressor disks in aero engines. By optimizing the parameters of the heat-treatment process, its mechanical properties are specially adjusted to meet the performance requirement in that particular practical application during the advanced composite casting-rolling forming process. The relationship between the microstructure and mechanical properties after quenching from 1040 °C and tempering at 300–670 °C was studied, where the yield strength, tensile strength, elongation and impact toughness under different cooling conditions are obtained by means of mechanical property tests. A certain amount of high-density nanophase precipitation is found in the martensite phase transformation through the heat treatment involved in the quenching and tempering processes, where M₂₃C₆ carbides are dispersed in lamellar martensite, with the close-packed Ni₃Mo and Ni₃Nb phases of high-density co-lattice nanocrystalline precipitation created during the tempering process. The ideal process parameters are to quench at 1040 °C in an oil-cooling medium and to temper at 650 °C by air-cooling; final hardness is averaged about 313 HV, with an elongation of 17.9%, the cross-area reduction ratio is 52%, and the impact toughness is about 65 J, respectively. Moreover, the tempered hardness equation, considering various tempering temperatures, is precisely fitted. This investigation helps us to better understand the strengthening mechanism and performance controlling scheme of martensite stainless steel during the cast-rolling forming process in future applications. Full article

17Cr2Ni2MoVNb steel is a new type of gear steel in the automotive industry; the rolling contact fatigue behavior is not well documented. In this study, some microscopic analysis methods (optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), and energy dispersive X-ray analysis (EDS)) were used to characterize material microstructure and damage surface. In addition, rolling contact fatigue behavior was evaluated by Weibull curve. The results show that the size of austenite grain increased while the quenching temperature increased. Moreover, the samples with a quenching temperature of 1000 °C exhibited the maximum mean life of 7.33 × 10⁵ cycles. In addition, the failure mode of quenched at 900 °C and 1100 °C were delamination, and pitting was the main failure mode of 1000 °C. Full article

With the rapid development of the automotive industry in China, the common gear steels no longer meet the high speed and heavy load requirements of the automotive industry. 17Cr2Ni2MoVNb steel is a new type of gear steel in the automotive industry, but the mechanical properties of 17Cr2Ni2MoVNb are not well documented. In this study, the tensile properties and rotary bending fatigue behaviors of 17Cr2Ni2MoVNb were investigated, (quenched at 860 °C and tempered at 180, 400, 620 °C); the microstructures and fracture surface were analyzed using an optical microscope, scanning electron microscopy and transmission electron microscopy. The results show that at higher tempering temperatures, the tissue was denser, and the residual austenite transformed into lower bainite or tempered martensite. Dislocation density reduced while tempering temperature increased. Moreover, the samples with a tempering temperature of 180 °C exhibited the highest tensile strength of 1456 MPa, in addition to fatigue limits of 730, 700 and 600 MPa at temperatures of 180, 400, and 620 °C, respectively. Full article