Bending Fatigue Research On 40Cr Cylindrical Gears Under Nitrogen/Water Spray Quenching Process

Heat treatment is one of the important processes of metal materials forging, which could improve the mechanical properties of materials by changing the internal microstructure or surface chemical composition of metallic materials. Nitrogen/water atomized spray quenching is a novel heat treatment quenching processes. It has gained a wild concern and study for all the advantage of it’s fast cooling rate, uniformity after quenching, and free from environment pollution.This paper focus on 40Cr cylindrical gears for the study, exploring the quenching effect in the field of gears surface quenching of nitrogen/water atomized spray quenching. From the study of surface hardness of the gear after quenching and bending fatigue performance, this paper carries put a study from the optimization of quenching process parameters to the fatigue properties of the gear, after theoretical calculations, equipment improvement and optimization, quench test, fatigue test and test data processing, conclusions are as follows:1.Nitrogen/water atomized spar quenching of 40Cr cylindrical specimenImproving nitrogen pressure and water flow helps to the enhancement of the hardness of specimen, both the surface and the core. The effect caused from the increase of water flow to improve the hardness of the specimen is higher than that from the increase of the nitrogen pressure;Water flow is the major factor of the cooling rate of nitrogen/water atomized spray quenching, with the increase of water flow, the cooling capacity of the medium improved.2.Nitrogen/water atomization spray quenching of40Crcylindrical gear:It has been found from the measurement of the surface hardness of gear that there is only slight difference between the hardness of the specimen when the amount of water is small and when the amount of water is large, and the test piece does not produce quenching cracks. At the same time, when the water amount is small, the quenching data dispersion rate is higher;Nitrogen/water atomizing spray quenching process can gain higher surface hardness than oil quenching, and the degree of dispersion of the surface hardness obtained is smaller, with uniform quenching.3.Bending fatigue test on gear:Water flow has an influence on the bending fatigue on gear, within a certain range, with the decrease of water flow, the bending fatigue strength increases, while when the water flow drops to a certain value, the influence of water flow on the bending fatigue strength decreases;On the condition that when the stress ratio is 0.05, the bending fatigue strength of gear can be obtained when R=0.99 using the normal distribution function processing bending fatigue test results. Compared with other hardening process, nitrogen/water atomized spray quenching process has its advantage that the quenching uniformity and that it could to regulate the bending fatigue strength by controlling the quenching process parameters.