Study On The Bonding Process Of Inner Void Defects In Heavy Forging At High Temperature

As key parts of large complete sets of equipment, heavy forgings have played important roles in the industry, such as electric power , steel, petro chemistry, shipbuilding, transportation, military, heavy mining machinery, aerospace and so on. Its technology level is one of the most important symbols which represent a country's level of industry. In recent years, the demand for heavy forging is increasing greatly in our country. While the quality of heave forgings is difficult to control, for there always are some inner metallurgy defects, such as cavity, segregation, void, inclusion and so on. Therefore, in addition to producing dimensional satisfactory heavy forgings, the research on upsetting process should pay more attention to modification of inner defects, improvement of material tissue, so that the mechanical performance, inner quality and carrying ability of materials will be improved greatly.The bonding mechanisms of inner void defects in heavy forgings were studied in the article. The bonding condition and factors which affect the bonding of void were revealed base on the hot deformation tests in the alloy steel 30Cr2Ni4MoV, which was the material of low pressure rotor. The main work is as follow:1. Based on the metal diffusion theory, the diffusion and recrystallization bonding mechanisms were investigated, and the bonding model of inner void defects was analyzed based on the vacuum diffusion welding model. Temperature, holding time, deformation and strain rate were revealed as the factors that affect the bonding process. According to the bonding model, the holding time for the inner void bonding under different strain rate and certain temperature, pressure condition was obtained.2. The closing process of forgings with inner void defects was studied based on finite element software MSC.Marc. The required mechanics conditions for void closure were obtained and the impact of void closing on bonding was analyzed qualitatively.3. The physical simulation model with inner void defect for high-temperature diffusion bonding was established. The hot deformation bonding tests were conducted by using the Gleeble-3500 simulator to simulate the bonding process of inner void in heavy forgings.4. By observing the microscopic shape of bonding-surface under the conditions of different temperature, holding time and deformation, the effect of these factors on the bonding process of inner void defects was studied systematically. And the law of void bonding was also obtained.