| As the key part of the precision machine tool,bearing can be formed by the advanced cold rolling forming technology.By using this forming technology,uniformity thickness,high dimensional precision and fined grains could be obtained in the microstructure,and the products also owned high mechanical properties.This article is aimed to study the precision bearing of GCr15 steel,which was made in domestic precision forging company,in which,the precision bearing were formed by upsetting and precision forging process,which arised the non-uniformity cooling problem.And more than ten hours could be taken on spheroidizing annealing process was another problem.The forging stock with poor quality controllability and technical economy under the traditional cooling way and spheroidizing annealing process,which is lack of reasonable cooling ways and pretreatment process design of forging stock that match the requirement of microstructure and properties.Thus,it is necessary to seek more efficient cooling controll and prepare-heat treatment to optimize the process.The cooling processes of bearing forging were designed via three different cooling processes,air-cooling,force air-cooling and water-cooling,which were conducted on the bearing forging with the high speed precision forging temperature of 850 ℃.With the increased cooling capicity,the spacing lamellar in the tissues of pearlite got decreased,pearlite contours got decreased and network carbide thickness got decreased too.in which,the water-cooling had significant influence on the microstructure compared to other cooling processes.For the further study of how the different ending tempreture works on bearing forgings,the boiling water cooling processes were carried on,at the temperature range of 80-85℃,and the relationship between cooling conditions and microstructures was established.the reslut showed that,bearing forgings of cooling temperature 550 ℃,410 ℃and 340 ℃,which microstructure of bearing forging were consisted of tempering martensite,lower bainite and a small amount of residual austenite when water-cooling holding time extended to 5-10 s.For the bearing forging with the same water-cooling holding time,the amount of bainite in the surface were lower than that in the core.For the bearing forging with different water-cooling holding time,the amount of bainite decreased with the extension of holding time.Round-fine carbides could be obtained according to the rapid heat treatment process of hierarchic isothermal spheroidizing annealing and divorced eutectoid spheroidizing.Besidese,the influnces of cooling process to spheroidizing structure also could be showed in the carbide particle size of quenching process,the fine carbide particle after quenching could be obtained with fine spheroidizing carbide particle,and the volμme fraction of undissolved carbides exist certain positive correlation with carbide particle size in spheroidizing.On the premise that the mechanical properties are all in accordance with the requirements,the isothermal spheroidizing process which hardness was lower than divorced eutectoid spheroidization,for the matching of controlled cooling bearing forging was more favorable to the subsequent machining and cold rolling process.By using the rapid heat treatment process of divorced eutectoid spheroidizing,total energy consumption was 927080 KJ,taking 5h,energy saving up to 26.42% per ton,and improving the production efficiency has been improved 3.7 times higher than traditional technology.The technique of divorced eutectoid spheroidizing was more economical than the technique of hierarchic isothermal spheroidizing annealing. |
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