Two-phase Deformation And Divorced Eutectoid Transformation Research Of GCr15 Steel

The performance and service life of bearing directly affected by performance of bearing steel.As we know,GCrl5 bearing steel is widely used as the representative of bearing steel.In the production process,the spheroidizing treatment has a great influence on the subsequent processing and service life of GCrl5 steel.Traditional spheroidizing annealing is time-consuming and labor-intensive.The processing time can be greatly shortened with the mechanism of divorced eutectoid transformation.In this paper,the expansion curve of GCr15 steel was measured by the expansion method and the eutectoid transition temperature range was determined.Two-phase deformation in the eutectoid transformation temperature range was simulated by Gleeble3500 thermal simulation testing machine,and process parameters of divorced eutectoid transformation is optimized.At last,the rapid spheroidizing process of GCr15 steel is studied in the box furnace.The main conclusions are as follows:(1)When heating and cooling at a rate of 0.5/s,according to expansion curve of GCr15 steel,eutectoid transformation temperature range is from 737.28? to 673.85?.when austenitized at 820 ? for 5 minutes,eutectoid transformation temperature range arrives 689.42? to 670.82? when austenitized at 850? for 5 minutes.The results show that there are some differences in the eutectoid transformation in different austenitizing conditions.Therefore,the eutectoid transformation temperature ranges of GCr15 is from about 680? to 740? in the cooling stage.(2)It is found that the deformation of GCr15 steel in two phases has some influence on the carbide precipitation.After deformation,lamellar pearlite is precipitated without proper heat preservation,which is harmful to spheroidization of carbides.However,after the plastic deformation,the spheroidal carbide can be obtained in the form of divorced eutectoid transformation with proper heat preservation.Compared with the ordinary transition of the eutectoid transformation,the deformation in two phases takes shorter time.When the spicemen is austenitizing at 790? for 5 minutes,after 40%deformation with deformation rate of 1 s'1 and holding at 720? for 30 minutes,the hardness reached 205.1 HV.(3)In the process for rapid spheroidizing of GCr15 steel in a box furnace,when the spicemen is austenitizing at 790? for 30 minutes in the box furnace,after furnace cooling to 720? and holding for 90 minutes,the hardness reached 198.6 HV(Brinell hardness test was 185 HBW).The spheroidizing effect is satisfactory and the spherical carbide structure is relatively uniform.The rapid spheroidizing treatment takes about 133 minutes.