Research On The Shrinkage Criterion Of Die Cast Steel Ingot With Modified Feeding Pressure

Large forgings are an important part of the heavy equipment system,and the development of its quality control technology can effectively promote the overall level of progress in the equipment manufacturing industry.Quality control needs to start from the billet of large forgings,die-cast ingots;the quality of ingot products directly affects the quality of the final forgings.During the solidification process,shrinkage can occur in the area inside the ingot that is not effectively replenished by the molten metal in the final stage of solidification.The shrinkage defect will affect the performance of the product,and may also develop into more serious defects during the forging process,even triggering forging fracture.If the area and degree of shrinkage defects within the ingot can be determined by numerical simulation of the casting process,the forging process can be designed based on the shrinkage model to avoid the aggravation of casting defects during the forging process,as well as to achieve the precise removal of serious defect areas and effectively improve the material utilization rate of die cast ingots.Based on the Pro CAST software,numerical simulations of the ingot casting process were performed,and the shrinkage defects in the ingots were calculated qualitatively and quantitatively with the Niyama criterion and the dimensionless Niyama criterion,respectively.In order to ensure the accuracy of the simulation,the temperature-time curves and the geometry of the riser were compared between the measured and simulated results,and the results showed that the errors in the temperature field and geometry of the riser were within the acceptable range and the simulation results were reliable.A scanner,metallurgical microscope and scanning electron microscope were integrated to perform macro and microscopic inspection of the ingots.Using MATLAB software as a platform,image processing of the inspection results was performed to obtain a quantitative description of the shrinkage defects: the shrinkage defects of die-cast ingots were mainly distributed in the range of 690-1350 mm from the spout in the axial direction and 30 mnm symmetrically from the axis in the radial direction,and they were distributed in a funnel shape at the upper and lower ends.Comparing the shrinkage distribution areas obtained from simulation calculation and actual inspection,focusing on the difference between them in axial distribution,it is concluded that the dimensionless Niyama criterion is more accurate in the radial direction of the ingot,while there is a large error in the axial direction.Combining the derivation process of dimensionless Niyama and fluid pressure theory,a new method for calculating the feeding pressure is proposed and verified.The results demonstrate that the shrinkage area predicted by the optimized criterion is closer to the actual test results under the same calculation conditions.