Study On Plastic Deformation And Damage Mechanism Of 34CrNiMo6 Steel

Axle is one of the key parts of railway transportation.High speed and heavy load are its main operating characteristics.The performance of its products directly determines people's property and life safety,therefore,the performance of axle is extremely high.The plastic damage in the hot forming stage of axle is the most direct source of fatigue crack during the running stage.Therefore,it is of great significance to study the plastic damage mechanism of axle steel in the process of hot forming for improving axle quality.In this paper,the forming mechanism of plastic damage of 34CrNiMo6 steel during hot forming process was studied by physical experiment and numerical simulation.First,the high temperature hot compression test was carried out on Gleeble-3500 thermal simulation testing machine.The true stress-strain curves under different deformation parameters were obtained,and the constitutive equation of 34CrNiMo6 steel was established.The effects of deformation temperature,strain rate and initial grain structure on microstructure were obtained by analyzing the metallographic diagram.Combined with microstructure and flow stress curve analysis,it is concluded that the softening mechanism during compression is dominated by recovery and recrystallization.The thermal processing diagram of the material was drawn,and the optimal thermal processing parameters were obtained by combining with the metallographic structure analysis.Secondly,Based on the macro and micro analysis of axle surface cracks,it is found that the inclusion is the main cause of cracking.Tensile experiments at high temperature were carried out on a thermal simulation testing machine under the optimal thermal processing parameters,and the damage mechanism was plastic damage.Based on flow stress curve and microstructure analysis.Fracture analysis shows that the main cause of damage is the existence of inclusions.Finally,The constitutive model under tensile test were constructed to simulate the deformation and damage of the material containing inclusion.Based on the macroscopic simulation,the body cell model with inclusion was established and the evolution of damage behavior was analyzed.The effects of different deformation parameters on the critical strain values of damage initiation,crack initiation and macroscopic crack formation were studied.