Thermal Simulation On Phase Transformation And Micro-structure Of GCr15SiMn Bearing Steel

Bearing is known as the heart of the industrial,with the rapid development of modern industry,the requirement to bearing steel become more and more strict.This article focuses on bearing steel GCr15 SiMn,its study is based on control technology and controlled cooling process,thermal simulation experiment method is used,phase transformation and microstructure change is systematic researched for bearing steel production procedure.The main contents and results are as follows:(1)Pearlite transformation temperature is between 600℃ and 700℃,during continuous cooling stage of bearing steel GCr15 SiMn.With the increase of the cooling rate,transformation temperature decrease,the content of pearlite become lower in room temperature,while martensite become larger,compared to static state,pearlite transformation CCT curve moves to the left and up direction under the dynamic condition,deformation promotes the content of pearlite increased,and make the microstructure obviously refined,critical cooling rate of pearlite transformation increase from 2℃/s in static to 3℃/s in dynamic deformation,deformation make martensite transformation temperature from 204℃ decrease to 166℃(2)When the cooling rate is 0.3℃/s,carbides precipitate along the grain boundary,gather together and accumulate,connection with each other to form the carbide network,with the increase of cooling rate,the carbide precipitations gradually reduced;Compared with the static,dynamic deformation will promote the precipitation of secondary carbides,critical cooling rate which significantly inhibited carbide network generated increase from 3℃/s in static to 5℃/s,Due to the high cooling rate,martensite structure is also found at room temperature.(3)With the increase of cooling rate,the micro-hardness of the test steel keep increasing.When the cooling rate is less than 2℃/s,compared with the static,the deformation promotes the recrystallization,and refine the grain,so micro-hardness is greater When the cooling rate is increased to 2℃/s and above,the martensite is produced in the static structure,and the micro-hardness increases obviously.When the cooling rate is the same,it is higher than the micro-hardness under the deformation condition.(4)Deformation rate and degree has little influence on the precipitation of carbide network,the lower the finish rolling temperature,the stronger the effect on carbide network broken,while the lower the temperature,the higher requirements for rolling mill,to make the rolling mill broken easily,compared with the deformation rate,deformation degree and the finish rolling temperature,cooling rate has significantly influenced bearing steel GCr15 SiMn microstructure morphology,as the increase of cooling rate after rolling,the content of secondary carbide precipitations obviously decreased,its thickness decreases,which can effectively restrain the network carbon,while under high cooling condition,there exist large amounts of martensite in room microstructure.(5)Combined with the actual production,after finish rolling subsection cooling process is applied,in high temperature stage,fast cooling in order to avoid temperature region which quantities secondary carbide precipitation,to a reasonable final cooling temperature,then slow cooling to room temperature,to make austenite fully transform to pearlite phase,at the same time to inhibit net carbon precipitation and to avoid producing martensite.Cooling rate during the fast cooling stage and final cooling temperature is the key factors of technology,during fast cooling stage when the rate increase to 5℃/s at 610℃,then slow cooling to room temperature at the speed of 1℃/s,which can effectively inhibit the formation of net carbon and obtain ideal pearlite structure.