Experimental Study And Numerical Simulation Of Dynamic Recrystallization Behavior For Offshore Steel Bearing Mo?Sn

As the key material of offshore engineering equipment,offshore steel is widely used in offshore oil platforms,oil and gas pipelines and ships.In the harsh marine environment,marine equipment will be eroded and damaged by wind,wave,current,submarine earthquake,microtherm and other natural forces.With the gradual exploitation of deep-sea and polar petroleum resources,it is particularly important to develop offshore steel with high strength,high toughness,favorable weldability and corrosion resistance.In order to improve the comprehensive mechanical properties of offshore steel,in this paper,the effects of microalloying elements Mo,Sn on dynamic recrystallization(hereinafter as DRX)behavior during hot deformation were studied by means of experiment and numerical simulation.And processing maps were constructed to provide theoretical basis for formulating reasonable hot working technology.The main research contents and results obtained in this paper are as follows:(1)Based on the existing standards and related literature,three kinds of experimental steels were designed and smelted.The hot deformation behavior of the experimental steels was systematically investigated within the temperature range of850–1150°C and strain rate range of 0.01–10 s^–1,via hot compression testing.And flow stress curves of experimental steels were obtained.The results show that flow stress decreases with the increase of deformation temperature and the decrease of strain rate,on the contrary,the flow stress increases.In addition,under the same deformation conditions,the flow stress of the experimental steels were increased by Mo and Sn,and the DRX softening behavior was inhibited in varying degrees.(2)The flow stress hyperbolic constitutive model(prediction accuracy>99.2%)and DRX kinetics model(prediction accuracy>97%)of the experimental steels were developed respectively by fitting the experimental data.The effects of deformation temperature,strain rate and microalloying elements on the volume fraction of DRX were analyzed.Based on the dynamic material model and Murty instability criterion,processing maps of the experimental steels under different strains were established respectively.It was found that the processing instability region was enlarged by Mo and Sn in different degrees.The accuracy of processing maps was verified by microstructure analysis,and the optimal hot working process parameters of experimental steels were obtained.(3)The material data and DRX kinetics model of experimental steels were imported into DEFORM finite element numerical simulation software for isothermal hot compression numerical simulation.The simulation results match well with the experimental results in macro and micro aspects,which verified the accuracy of the DRX kinetic model.On this basis,combined with the rolling process parameters determined by processing maps,the rolling numerical simulation model were constructed.The accuracy of rolling model and DRX kinetics model was verified by actual rolling experiments.The dynamic recrystallization microstructure evolution of experimental steel under different rolling temperature,rolling speed and reduction was analyzed by simulation rolling,and the reasonable rolling process parameters of experimental steel were obtained by rolling simulation.