Spray Forming CPM9V High Speed Steel Hot Working Behavior And Finite Element Prediction

High speed steel prepared by spray forming technology not only eliminates the macro segregation and coarse grain, make the materials with excellent mechanical properties, and compared to the traditional powder metallurgy method, production procedures are reduced, production cost reduced.CPM9V high speed steel billet prepared by spray forming is inevitable to produced some holes, in order to increase density, to further improve the size and distribution of carbides, the need for subsequent thermal processing, such as forging or rolling process to optimize the microstructure and properties of the material.Finite element (FEM) numerical simulation method can greatly reduce the amount of experiments and improve work efficiency, thereby reducing the cost of research. It is very important to establish an accurate flow stress constitutive model to improve the accuracy of the finite element numerical simulation according to the experimental results of Gleeble axisymmetric isothermal compression. In this paper, the hot working performance of the spray forming CPM9V high speed steel was studied and the optimum forging process parameters were established by means of Gleeble thermal physical simulation and Deform finite element simulation, combined with the analysis of microstructure. The main research contents are as follows:(1)The flow stress curves of CPM9V high speed steel with different strain rate and temperature were obtained by Gleeble axial symmetry isothermal compression test. Based on the Arrhenius hyperbolic sine model the constitutive model of CPM9V high speed steel was established and a method for modifying the material constants in the constitutive model was proposed. Considering the strain effect on the rheological process, using 6 order polynomial variables will be coupled into the constitutive model, the fitting correlation coefficient of material constant α 、N、Q and lnA were 0.980, 0.997,0.995,0.986.The flow stress predicted values and experimental values of the correlation coefficient was r= 0.9976, the mean absolute relative error was only 3.157%.Showing that establishment of constitutive model can accurately predict the spray forming its formed high speed steel during hot compression process of high temperature rheological behavior.(2)Simulating the isothermal heat compression process by the Deform-3D finite element simulation software. The simulation obtains the thermal compression specimen deformation amount and size, load displacement curve and compared with the actual hot compression experiment measured values. The results showed that the simulated values are in good agreement with the measured values and demonstrated accuracy and feasibility of DEFORM-3D finite element simulation. The equivalent stress and equivalent strain of different typical regions in the section of hot compression specimens were compared with the change of the deformation process. In the dead zone, the large deformation zone and the free deformation zone of P1, P2 and P3 points, equivalent stress value P2>P3>P1, and other effects of P2>P3>P1. Due to the existence of the upper and lower end faces and the friction force, the deformation of the hot compression process is not uniform, so as to show three typical regions. Combined with metallographic analysis shows that large deformation zone is the most easy to preferentially occur dynamic recrystallization region, die area to maintain the deposited state, free deformation zone dynamic recrystallization driving force is lower than that of the large deformation zone.(3) Through Deform-3D simulation gives the stress and strain distribution and contour map of different thermal processing. The effective stress and strain distribution showed a typical "X" shape, that is close to the upper and lower surfaces and both sides of the equivalent stress value is lower, the more close to the middle part of the equivalent stress value and the equivalent effect becomes larger. The higher the temperature, the lower the strain rate, the more uniform the deformation, the larger the range of the middle deformation zone. So, the effect of heat compression experimental parameters on Microstructure and property of material, should mainly to large deformation zone of the organization for reference, so as to exclude due to inhomogeneous deformation of material structure changes to determine the cause interference.(4) According to the DMM theory of the dynamic material model, the hot working diagram of the spray forming CPM9V high speed steel was established from 0.2 to 0.9. Spray forming CPM9V high speed steel under different strain the peak area of the power dissipation efficiency is high temperature and low strain rate area (1120-1180℃、0.01-O.1s-1), and unstable region is high temperature and low temperature under high strain rate area(1120-1150℃、1-10 s-1 和 970-1030℃、1-10 s-1).(5) In view of the microstructure observation of different regions in the heat treatment map, In the peak area A of the dissipation efficiency, the microstructure was fully recrystallization (have fine and uniform grain). In instability zones B and C, except that incomplete recrystallization fibrous grains in the local area, obvious instability characteristics, such as concentrated deformation zone, adiabatic shear band and material peeling phenomenon caused by stress concentration. In other safety areas, also appeared complete recrystallization structures near the peak zone A, but the lower dissipation efficiency values of the other experimental parameters have different degrees of instability characters.