Quality Controlling Research Of High Standard Bearing Steel SUJ2

With the high-speed development of high-end equipment such as rail transit,tunnel engineering,wind power and automobile,the quality of raw materials used in bearing put forward more and more demanding,especially the metallurgical quality of bearing steel,the uniformity of carbide and the surface decarburization depth and so on.The network of carbon carbide and decarburization depth of hot rolling high-quality bearing steel SUJ2 exists beyond standard in domestic steel company.In this paper,it was researched by the high temperature deformation characteristics,high temperature oxidation and decarburization characteristics,characteristics of mesh carbide in Controlled Rolling and Controlled Cooling Process.It was analyzed the internal and external factors to causing the steel quality unstable,which provide the theoretical basis and experimental basis for improving the quality of the steel.The main contents of this paper are as follows:In order to optimize the hot working technology,the hot deformation behavior of high-standard bearing steel SUJ2 in temperature range of 800¹050°C and strain rate range of 0.01¹0s^-1 were investigated with single-pass compression thermal experiment on Gleeble-3500 thermo-simulation machine.The constitutive equation of high temperature thermal deformation was established.The thermal processing map is established based on DMM dynamic material model and Ziegle-Prasad instability criterion.The influence of process parameters on the thermal performance of SUJ2 steel was analyzed.The results show that: the steel at low temperature and high strain rate,high temperature and high strain rate and high temperature and low strain rate range will be unstable.The steel exhibits a better workability in deformation temperature range from 800⁸30°C or 950¹050°C and strain range from 0.01⁰.1s^-1 or 0.1¹ s^-1.The oxidation and decarburization behaviors of high-standard bearing steel SUJ2 in temperature range of 1000 1220 °C and oxygen flow range of 0.0³.0 L/ min were studied by high temperature heating furnace.The results show that the increasing oxidation weight per unit area increases with the increasing temperature and time,and the depth of decarburization increases first and then decreases with the increasing temperature.The phase composition of the oxide layer is Fe_1-yO,Fe₃O₄,Fe2O3,respectively the ratio of the three phases in the oxide layer is different at different temperatures and different oxygen fluxes.Fe_1-yO and Fe₃O₄ ratio was decreased with the increase of the depth of the decarburization layer.Fe_1-yO to Fe₃O₄ ratio was increases with the decrease of the depth of the decarburization layer.The depth of decarburization is the lowest at 1.5L / min oxygen flow.The microstructure transformation under different cooling rate（0²0°C/s）and the regularity of network carbide precipitation under different cooling rate after rolling（3³0°C/s）,final cooling temperature（750⁵00°C）,slow cooling rate（1⁵°C/s）were investigated with thermal experiment on Gleeble-3500 thermo-simulation machine.The results show that with the increase of the cooling rate,the carbide precipitated at the grain boundary changes from a continuous network to a semi-continuous shape,and finally scattered.The critical cooling transformation rate of inhibiting network carbide precipitation is 8°C/s.In the process of cold control after rolling,the formation of the network carbide can be suppressed,and the hot rolled sorbite microstructure with good performance can be obtained with the cooling rate increases,the cooling temperature decreases and the slow cooling rate increases.The precipitation prediction stage of the mesh carbide and the precipitation node in the cross section during the rolling process are predicted by the laboratory development microstructure performance prediction system of SUJ2 steel.For the bar,the mesh carbide is formed at 1/4 and 1/2 of the cross section.For different specifications of the finished product,the mesh carbide is mainly formed in the finishing and rolling,in the process of cooling the bed or in the cooling bed.