Internal Crack Healing And Outside Crack Prevention Of Large Forging During Forging Process

Large forgings are basic components of large critical equipment.There are many inevitable internal defects in large ingot,which may lead to crack defects in large forgings.In this paper,the behavior of crack defect during forging process was investigated by physical and numerical simulation,respectively.Healing behavior of internal cracks in ingot during forging process was analyzed by physical simulation study in the second and third chapter.Surface crack defect of large forging was analyzed by numerical simulation in the fourth and fifth chapter.During the experiment of physical simulation,specimens with artificial crack were hot compressed by Gleeble,and the effect of temperature and deformation on internal crack healing was studied.In the study of physical simulation experiments,it is easy to find surface cracks on the samples.The result of surface stress analysis by finite element simulation shows that surface axial stress changing from compression to tensile causes surface cracks.Based on this result,a wasp-waist forging process was designed to prevent this problem.The main study results are as follows:1.The effect of temperature and deformation on internal crack healing was studied by means of the prefabricated cracks in hot compression specimens of Gleeble.The experimental results show that the higher the deformation temperature or the larger deformation degree is,the better the crack heals.2.In order to verify the accuracy and applicability of the Gleeble results in actual forging process,an industrial experiment of internal crack healing was designed and carried out.The result shows that internal cracks can be effectively metallurgical bonded at temperature of 1200? and deformation ratio of 40%.3.Surface stress analysis shows that the surface axial stress will change from compression to tensile during upsetting process.The surface axial stress is one of the factors causing forging's surface cracks.If forgings suffer from repeated upsetting and cogging,minor cracks formed in anvil overlapping part during cogging may rapidly expand to large cracks during following upsetting process.4.The surface axial stress transfer point from compression to tensile is related to billet drum shape parameter d/h.The surface axial stress changes from compression to tensile when d/h approaches 0.17.5.Based on change rule of surface axial stress during upsetting process,the wasp-waist forging process was designed.The transfer of surface axial stress from compression to tensile was effectively prevented by the wasp-waist forging process.Deformation uniformity of billet was improved,and surface cracks of forging were prevented.With the help of Deform3 D software,the quantitative design of wasp-waist forging is realized.