Study On Grain Evolution Of 15-5PH Steel During Forging Based On Thermoplastic

15-5PH steel is widely used in the manufacture of aerospace,thermal power,and a major components in the field of petroleum chemical industry,etc.The complex working conditions and harsh service environment require the components to have good macro and micro structure and comprehensive performance.Therefore,the actual forging process can be optimized by studying the possible damage defects and microstructure evolution of 15-5PH steel in the forging process,thus laying a good foundation for the quality and performance of products.In this paper,physical simulation experiment and finite element numerical simulation are intrgrated to conduct basic study on the microstructure evolution,thermal processing performance and damage and cracking in the hot deformation behavior of 15-5PH steel.The main conclusions are as follows:Based on high temperature tensile test,the hot tensile behavior of 15-5PH steel was studied.According to Normalized Cockcroft&Latham（NCL）ductile fracture damage criterion,the critical damage values of materials under different deformation conditions were calculated.The zener-Hollomon parameter（Z parameter）was introduced to establish the high temperature damage evolution model of the steel.The effects of different heating parameters on austenite grain size of15-5PH steel were analyzed based on heating and holding experiments under different heating parameters.The Beck model and Sellars model for grain growth of the steel were established.It is found that the Sellars grain growth model can more accurately predict the grain growth behavior of the steel.The flow stress-strain curves of 15-5PH steel were acquired by single-pass hot compression measurement.The influence of deformation parameters on flow stress was analyzed.The constitutive model is deduced.By establishing the hot working diagram of the steel,the optimum hot deformation parameter of the steel is obtained:The deformation temperature is 800-1000℃,the strain rate should be higher than 0.05s^-1;Deformation temperature of 1000-1200℃,the strain rate should be less than 0.05s^-1.Based on the stress-strain curves and microstructure obtained by experiments,the dynamic recrystallization model of the steel was established.The static recrystallization action and sub-dynamic recrystallization action of 15-5PH steel during hot deformation were studied by two-pass hot compression measurement.The effect of different deformation parameters on static recrystallization behavior was analyzed,and the static recrystallization correlation model and sub-dynamic recrystallization percentage model were established.Deform-2D finite element software was used to simulate the thermal compression process at constant temperature and constant strain rate according to the critical damage value,and the critical value of instantaneous tangential tensile stress at the bursting point of the outer edge of the compression part was determined under different temperatures and strain rates.According to the quantity of the technical requirements for upsetting,the pump head body are calculated billet upsetting does not occur in the process of the outer surface of the surface cracking temperature low for 950℃.Finally,Deform-3D software was used to simulate the actual forging process of pump head,and the grain evolution law of pump head billet forging process was obtained under the condition of thermoplastic temperature field,which provided a basis for preventing the cracking of pump head forging and controlling the grain structure inside the forging.