Study On Preparation And Processing Technology Of Duplex Stainless Steel For Tension Compensation Rope

With the development of electrified railway technology,the tension compensating rope made of traditional austenitic stainless steel can no longer meet the performance requirements.Duplex stainless steel has high strength,stress corrosion resistance and fatigue resistance.It is a good material to replace austenitic stainless steel for preparing new high-performance tension compensating rope.However,at present,the problems of harmful phase precipitation and incongruous deformation of duplex stainless steel greatly limit its application and development in steel rope manufacturing.Therefore,in this paper,a special duplex stainless steel for tension compensating rope was designed and fabricated,and the hot working process,solid solution treatment process and effect of cold deformation on Microstructure and propertiesof of this steel were studied.Orthogonal experiment was designed for different contents of main alloy elements,and the composition of steel was designed by software simulation.The results show that the optimal distribution ratio is Cr:23 wt%,Ni:7 wt%,Mo:2 wt%,Cu:0.6 wt%.The peak stress and rheological stress constitutive model of Cr23Ni7Mo2Cu0.6 duplex stainless steel were established by hot compression experiment,which can accurately predict the change of hot deformation stress of this steel.The hot working diagram under different stress variables shows that the best hot working process window of the steel is 1050℃～1150℃/0.01s^-1～1s^-1.The experiment of solid solution process was carried out with temperature,time and cooling mode as variables,and the effects of these three variables on the microstructure and properties were studied by means of metallographic observation,SEM observation,XRD analysis and polarization curve analysis.When the holding time was the same for 2h,With the increase of solution temperature,hardness and strength first decreased and then increased,reaching the minimum value of 94.4HRB and 547MPa at 1020℃and 1050℃respectively.The elongation first increased and then decreased,reaching a maximum of41.5%at 990℃.Cr23Ni7Mo2Cu0.6 duplex stainless steel has the best corrosion resistance after solid solution at 960℃for 2h.At this time,the self-corrosion potential and pitting corrosion potentialin in 3.5%Na Cl solution increases to-0.619V and 0.222V respectively.In addition,higher solution temperature is beneficial to improve the structure uniformity.Prolonging the solution time can significantly improve the homogeneity of the structure,reduce the hardness and strength,and have no significant effect on the elongation.The cooling mode should be water-cooled or oil-cooled,the precipitation ofσphase in air cooling and furnace cooling will reduce the plasticity and corrosion resistance.Combined with the performance requirements of the materials in the subsequent deformation process,the best solution treatment process of Cr23Ni7Mo2Cu0.6 duplex stainless steel for tension compensation rope was determined to be 1020℃heat preservation for 2 hours and then water cooling.The recovery and recrystallization of ferrite and austenite occurred respectively when the cold deformed samples were annealed at 1020℃,the time of hardness reduction to stability at 45%and 60%deformation was 2～4min,and that at 15%and 30%deformation was 8～10min.The effect of cold deformation on stress corrosion sensitivity was investigated by slow strain rate tensile test.The results show that austenite preferentially dissolves in 5%Fe Cl₃ solution,and the strip shape enables it to play a guiding role in corrosion invasion,so can prevent the formation and propagation of transverse cracks,and increasing the degree of cold deformation can reduce the stress corrosion sensitivity.