Finite Element Simulation Of Closing Defects Of Cr8Mo2SiV Steel In Forging Process

With the development of the mold industry,mold-related industries have increasingly higher quality requirement to mold steel.The internal defects and surface cracks of the mold steel seriously affect its quality,so it is increasingly important to reduce or eliminate defects during the forging process.Most of the void defects occur in the center of forgings,and the void shapes are mostly spherical and ellipsoidal.In the paper,Forge software was used to simulate the closing process of internal spherical void defects during forging and to predict cracks in the forging,and numerical simulation results were verified by physical simulation.The main work and results are as follows:(1)A forging model with a Φ2 mm single void located 25 mm to the right of the Z axis of the forging was established,and the equivalent stress-strain distribution around the forging and the void,the void closing process and influencing factors were simulated.The simulation results indicate that the single void on the right side of the Z axis was completely closed when the upsetting reduction rate reached 55%.Among the various parameters affecting cavity closure,forging temperature and height-diameter ratio are the main factors influencing void closure.(2)A forging model with a single void of Φ2 mm located at the non-axis line at the difficult-to-easy deformation junction under the upsetting hammer head was established,adopted a forging process of 1 pass upsetting+4 pass drawing process+1 pass upsetting process in numerical simulation,simulated the stress-strain around the void in each pass,analyzed the closing process of the void and predicted the forging cracks.The simulation results indicate that under the premise of the 55%rolling reduction rate of the first pass and the 25%rolling reduction rate of the 4 passes,the condition for closing the void is that the rolling rate of the second pass reaches 50%.Cracks do not occur in the forgings in each step in line with the aforementioned forging process.(3)A finite element model with a double void at the center of the forging was established,and simulated the closing process of the double void and the equivalent strain distribution around the void under the conditions of disjointness,tangency and intersection.The simulation results indicate that the perforation does not occur in disjoint and tangential voids during reduction,and the double voids are closed separately.The upsetting reduction rate is 50%when the disjoint and intersecting voids are completely closed,and that is 55%when the tangent voids are completely closed.(4)A small sample of Φ8 × 15 mm was used to simulation verification experiments during upsetting to analyze the void closing process and compared the stress-strain of forgings in physical and numerical simulation.The results indicate that both the results of numerical and physical simulation for the critical reduction rate of the void closure are 45%,which are identical.The stress-strain change of forgings in physical simulation is the same as that in numerical simulation.