Numerical Simulation Research On Controlled Cooling Of Medium-Sized Bearing Steel Bars After Rolling

Bearing steel bar as an important steel production,is widely used in machinery,shipbuilding,metallurgy and other fields.The quality and performance requirements of bar are also increasing.With the increase of diameter,medium-size bars ofΦ50～100mm have great difference in the temperature change and microstructure distribution after cooling.Therefore,it is of great significance for medium-size bearing bars to carry out the research on the temperature field in the cooling process,ensuring microstructure uniformity of bearing steel bar and improving the strength and toughness.In this paper,the simulation software was used to analyse the cooling process of medium size GCr15 bearing steel combined with actual production.The effect of cooling method on cooling rate and microstructure transformation was analyzed The influence of controlled cooling parameters on bearing steel bar temperature change was studied.The feasibility of multi-stage cooling process applied to cooling process was studied.The results show that:(1)Adopting the single air cooling method,the temperature field of the bar is uniform,but the cooling rate is slow,which can not meet the requirements of restraining the reticulated carbide precipitation and refining the microstructure.Adopting the single water cooling method,the surface cooling speed is significantly increased,which can effectively inhibit the carbide precipitation,but the core temperature drop is slow,and the temperature between the inside and outside of the bar is large,resulting in the final microstructure difference.(2)Combining with water cooling and air cooling,small medium size bearing steel bar(Φ 50mm)can effectively improve the cooling rate and ensure uniform structure requirements.For large medium size bars(Φ 70 mm,Φ 90mm),the core cooling speed is too slow to restrain the precipitation of reticulated carbide.So the cooling process needs to be optimized.(3)Different cooling factors have different effects on the temperature index in the cooling process.The start cold temperature,water cooling heat transfer coefficient and water cooling time will be significant impact on the rod cooling process.Reducing the open cold temperature,increasing water cooling heat transfer coefficient and extending cooling time can effectively reduce the end of surface temperature and improve cooling efficiency.The effect of cooling water temperature is not obvious.(4)Using the multi-stage cooling process can effectively improve the ability of control cooling.The cooling rate of the core is greatly increased.The precipitation of reticulated carbides is inhibited.The structure was refined and the uniformity is improved.Combining with the actual production,the multi-stage cooling process for different medium size GCr15 bearing steel bar is proposed.However,the optimization of multi-stage cooling process parameters for GCr15 bearing steel bar remains to be further studied.