Research Of Aluminum On The Hot Deformation Behavior Of Nano-bainite Bearing Steel

Nano-bainite bearing steel is a newly developed high-performance bearing steel.It has attracted the attention of material researchers and bearing industry.Al element has advantages of accelerating bainite transformation,inhibiting carbide precipitation,reducing hydrogen embrittlement sensitivity and so on.It is a beneficial element for nano-bainite bearing steel.However,the hot-workability of nano-bainite bearing steel with Al alloying element is still not clear.In this paper,three GCr15SiMoAl nano-bainite bearing steels with different Al content were chosen as the object of this study.The hot deformation behavior of the three steels was studied and the effect of Al was revealed.Moreover,the influence of Al on the dynamic recrystallization behavior during the hot deformation process was also simulated by finite element method,and the ring rolling process of bearing outer ring was simulated.The following results were obtained:(1)It is found from the hot deformation flow curves that the flow stress of the bearing steel is reduced with increasing the deformation temperature increases or decreasing the strain rate.Under the same deformation condition,the flow stress of the three steels increases with the increase in Al content.And the strain softening process of the bearing steel is promoted with a higher Al content.Analysis on the yield stress reveals that 0.4%Al content is the critical content with decreased yield stress when the content of Al is less than0.4%,and an increased tendency when the content of Al is higher than 0.4%.In addition,the constitutive equation with a accuracy of higher than 99.5%have been established for each steels based on the flow curves.(2)The processing maps have also been established according to the flow curves,which reveals that GCr15SiMoAl-0.43 steel has the largest unstable area and the worst thermal processing performance,and the GCr15SiMoAl-0.97 steel exhibits the best hot workability.The optimal processing parameters for the three steels is respectively GCr15SiMoAl-0.04:1000-1100?(0.1 s-1),GCr15SiMoAl-0.43:1000?(0.01 s-1),GCr15SiMoAl-0.97:1000?(0.01 s-1).Moreover,more Al element content leads the precipitation of AlN,thereby reducing its thermos-plastic and increasing the tendency of forming cracks during the hot deformation process.Therefore,although the hot working property of GCr15SiMoAl-0.97Al steel is the best,the thermos-plasticity is poor,.Therefore an extra attention needs to be paid when formulating the hot processing process.(3)The finite element simulation results of three bearing steels based on the Avrami dynamic recrystallization equation are analyzed.The results show that the equivalent stress becomes larger and the dynamic recrystallization grain size is decreased with the increase in Al element content.Compared with the experiment results,there is a deviation of 10.5%-16.9%for the equivalent stress.The results of point tracking and simulated hot ring rolling have been further analyzed.And it shows that bearing steel with higher Al content has a priority to complete dynamic recrystallization.In addition,with increasing Al content,the overall dimensional error of the ring rolling increases,but the errors are all within 5%.