Simulation Study A .2.25 Cr1mo0.25v Steel Deformation Process Defect Control,

With the rapid development of science and technology, power, chemical, shipbuilding, military and other industrial equipment are all large-scale, the mainly large forging of these equipment require greater and greater ingots. Currently, the ingot for large forging used in nuclear power has reached more than 600 tonnages in our country. large forgings usually works in bad conditions, the load is big, and safety reliability requirement is high,so the quality requirements are extremely stringent. but in the casting and solidification process,central parts of the large ingot inevitably exists, loose and shrinkage cavity defects,with the steel ingot size increasing, loose and shrinkage cavity defects are more serious. The metallurgical defects destroy the continuity of the metal, which make form stress concentration and cracking in the forgings, etc,and reduce the life of forgings or even lead to scrap pieces. Therefore, studying the change rule of loose and compaction, and exploring the condition of loose and compaction, will help improve immanent quality of the forgings.Due to the loose defect inside the large forgings is uncertain, for a comprehensive analysis of the loose defect of internal forging changes in the forging process, the numerical simulation combined with the physical simulation method is used in the dissertation. First, use the finite element software DEFORM to build model to implement numerical simulation,through the stress three dimensions, Rod coefficient and cavity expansion ratio to study the mechanical behavior of each area of internal forging,the second is the physics experiment, the alternative materials is the core of large-scale steel ingot of 240 tons, here the loose is the most serious and representative,in order to be more correspond to reality, using the current cus series of ultrasonic flaw detector to detect instruments, and determine the position of loose defects in the instrument internal. Finally, through previous numerical simulation parameters to carry out the forging experiment, the experimental results demonstrate the correctness of the proposed conclusion.The mainly study contents and conclusions in the dissertation are as follows: (1) under the condition of single step height-diameter ratio is 1.5, for 30% of reduction, the core in three compressive stress state,and in compression class deformation,if there is a loose defect, the defect will be easy to close or forging close. when the pressure reduction reach 40%,the lateral surface is most easy to crack, if defects are in this area, there will be a further expand trend; (2)When in single step stretching swaging,the anvil width ratio W/H is 0.8 and the material width ration B/H is 1, when the double pressure reduction is 30% at stretching swaging, the heart part of the anvil won't appear horizontal pulling stress, which is in the compressive stress state, and in compression class deformation, it will be beneficial to close or forge loose defects. (3)After many numerical simulations, based on the research of step upsetting transitions and long pulled, by simulating physical experiment of Continuous upsetting and pull long , the loose part of blank has been compacted, and with the ratio of forging reduction increasing, grains become more uniform.