| 40CrNiMo is a Cr-Ni-Mo system alloy structural steel,which can change its microstructure and mechanical properties to a large extent through heat treatment.Therefore,the steel has been widely used,such as steam turbine,aircraft landing gear,large generator rotor and jet turbine shaft and other fields.Combined with the production status of a steel rolling plant in China,this paper studies the controlled rolling and controlled cooling process,trying to save the slow cooling process after rolling and the subsequent quenching+high temperature tempering process in the traditional process,in order to improve the production efficiency of 40CrNiMo steel and reduce its production cost.The thermal deformation behavior of 40CrNiMo steel was studied by Gleeble-3500 thermal simulation test machine,and the effect of rolling process on microstructure and mechanical properties of 40CrNiMo steel was simulated,and the effect of supercooled austenite deformation+quenching+tempering on microstructure and mechanical properties of 40CrNiMo steel was investigated.The results of the study show that:When the strain rate is given,the deformation resistance of 40CrNiMo steel decreases with the increase of deformation temperature,and when the deformation temperature is the same,the deformation resistance increases with the increase of the strain rate.Deformation temperature and strain rate have a significant effect on dynamic recrystallization.When the strain rate is 1 s-1,the dynamic recrystallization ratio increases with the increase of the deformation temperature,the dynamic recrystallization occurs between 1050?and 1100?,the dynamic recrystallization grain has a obvious tendency to grow up at 1100?.When the deformation temperature is 850?and the strain rate is 50 s-1,the local temperature is too late to disperse and make the local temperature,partial thermal recrystallization will also occur due to the deformed heat is not enough to spread out and the increase of local temperature.The thermal deformation activation energy of 40CrNiMo steel is in the range of214.01 kJ·mol-1317.05 kJ·mol-1 and the constitutive equation of 40Cr NiMo steel under strain compensation was established.The predicted values of constitutive equations under strain compensation are in good agreement with the measured values.Based on the dynamic atomic theory model,the hot working diagram of40CrNiMo steel was constructed.The thermal processing diagram shows that when the strain is smaller?strain?0.3?,the peak of dissipative efficiency appears in the middle and high temperature high strain rate region,and when the strain is large,the peak of dissipation efficiency appears at the high temperature low strain rate region.In the conditions of low temperature low strain rate,medium temperature low strain rate and high temperature and medium low strain rate,the 40CrNiMo steel is easy to appear the rheological instability.The deformation conditions of safe processing zone,high temperature and high strain rate(928?1000??13.18 s-150 s-1)are in good agreement with the actual production conditions.The dynamic CCT curves of 40CrNiMo steel were plotted,and the microstructure transformation under different cooling conditions was determined.The transformation of bainite at 0.1?/s1?/s and at 2?/s10?/s to martensite.Granular bainite was obtained at 0.1?/s0.2?/s.The experimental results of the simulated controlled rolling and controlled cooling process show that the granular bainite structure is easily obtained under the conditions of 950?,30%deformation and cooling rate 0.1?/s0.5?.After the 40%deformation of the austenite region?700??and quenching,and tempering at450?for more than 1.5 hours,the uniform granular tempering can also be obtained. |
PDF Full Text Request