Study On Distortion In Heat Treatment Of Bearing Ring

Heat treatment is a crucial working procedure in bearing ring process,and it is a key process to increase bearing strength,hardness,wear resistance.Meanwhile heat treatment makes distortion and accuracy reduction.The precision reduction of bearing induces serious noise and abnormal voice in bearing rotation,and even causes early failure of the bearing.The distortion control in heat treatment is an important process in bearing industry to research for a long-term.In this paper,combining with the production practice,the principle of heat treatment deformation and various influencing reasons are studied,and many measures to stabilize the deformation of heat treatment are summarized in view of the influencing reasons.The deformation of bearing rings after martensite quenching and tempering on the salt bath quenching production line in RDES-450-950 CN with controllable atmosphere is mainly studied.The main parameters influencing the deformation of heat treatment,such as the heating time,austenitizing temperature and medium stirring rate in quenching process,were selected and verified by the orthogonal test.It was found that the three technological parameters of heating time,heating temperature and medium stirring rate had great influence on the deformation after heat treatment.With higher austenitizing temperature and longer heating time,the diameter variation of bearing ring increases significantly.Therefore,under the condition that the mechanical properties required by the product can be achieved and good quenching structure can be obtained,the austenitizing temperature can be set at the lower limit and the total heating time should be shortened as far as possible.In the quenching process,reducing the stirring rate of quenching medium can reduce the cooling speed of cooling medium.When austenite structure is transformed into martensite structure,it is relatively gentle,and the microstructure stress is correspondingly small.The influence of microstructure stress on the heat treatment process of bearing ring becomes small,which is conducive to reducing the quenching deformation of bearing ring.A reasonable quenching process scheme has been worked out through experiments.After many times of production practice,the process scheme can stabilize the deformation of heat treatment and guarantee the quality of bearing ring.On the basis of determining the reasonable heat treatment process,the martensite quenching and tempering heat treatment test was carried out for bearing rings of different sizes.According to the test results,after the salt bath martensite quenching was carried out on the production line of RDES-450-950 CN controllable atmosphere bottom furnace,the size of bearing rings as a whole expanded outwardly.The larger the outer diameter of bearing rings,the larger the expansion.To summarize the rule that the size of shaft sleeve ring increases after quenching and return of martensite can provide data basis for the car machining allowance in the process before heat treatment,and make the adjustment of size precision in the process after heat treatment more convenient and quick.