| M50Nil steel is a new generation of bearing steel developed on the basis of M50 steel by reducing the C element content and increasing the Ni element content.After surface carburizing and nitriding,M50 Nil steel can maintain higher toughness in the core,and has higher surface hardness and wear resistance,so that it has more excellent service performance.However,during the hot working process of M50 Nil steel,the problem of coarse grains is very easy to occur.The precision rolling forming process has the advantages of good forming quality,high production efficiency,high material utilization rate,low production cost,etc.It is widely used in the forming of outer rings of aviation bearings.With the development of the aviation industry,the cross-sectional shape of the outer ring of elastic ball bearings is becoming more and more complex.The traditional rolling blanks are mostly simple circular rings.It is difficult to form bearing forgings with complex cross-sectional shapes,and it is easy to appear due to a large amount of machining.The problem of the streamline outcrop caused a decline in service performance.In response to the above problems,this subject explores the precise hot working window of M50 Nil steel grain growth law and hot deformation behavior research,and uses the finite element simulation method to optimize the M50 Nil steel elastic ball bearing outer ring precision forging process plan,To ensure that the grain size and streamline distribution of the final forging meet the requirements.In this paper,the grain growth law of M50 Nil steel is studied.Through the heating and heat preservation experiment of M50 Nil steel,the influence of heat preservation temperature,heat preservation time and grain size after multi-directional forging on its grain growth rule was analyzed.The results show that the overheating temperature of M50 Nil steel is between 1075℃ and 1100℃,and the initial forging temperature should be controlled below 1075℃.When multi-directional forging billets are used to refine the grains,only when the grains are r efined to less than 10 μm can the refining effect be obtained after reheating.The hot deformation behavior of M50 Nil steel was studied.Through the hot compression experiment of M50 Nil steel,the flow stress curves under different deformation conditions were obtained,the constitutive equation of M50 Nil steel and the hot working diagram under different deformation were constructed,and the hot working interval of M50 Nil steel was obtained: temperature 900 ～950℃,strain rate is 0.01s-1～0.03s-1 or temperature is 1075～1150℃,strain rate is 0.05s-1～0.6s-1.Aiming at the problem of streamline outcrop of M50 Nil steel ball bearing outer ring forgings,this paper proposes a rolling blank with "conformal design",and the finite element simulation is carried out by DEFORM software to analyze the stress and strain of the blank during the rolling process And metal flow characteristics,the results show that: the internal surface slope feature in the conformal design blank exacerbates the upward axial flow and radial flow of the metal at this place,and the flange feature exacerbates the axial flow of the metal outer surface,it should be restricted by closed rolling.By constructing finite element models with different shapes and sizes,the overall height of the rolled billet,the slope of the inner surface and the size of the flange are optimized.At the same time,the finite element model of the billet making process of the rolling billet is constructed to optimize the mold structure design,high-diameter ratio and upsetting ratio of the billet making process. |
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