A Study On The Unsteady Mathematical Model Of Automobile Catalytic Converter Systems

The dissertation is one of the main part of key project supported by National Natural Sciences Foundation named "Inner crack healing in metal"and project "Self-healing Mechanism and Control Mode of inner Damage in metal". The inner crack healing in metals is studied in order to prolong and saving life of common metal and to improve its quality. The inner cracks in copper and 45 steel are made by plate impacting. In addition, the inner crack in copper, 20 steel, 45 steel, 20MnMo steel and 80 steel are made by another way which compressing drilled hole in column sample. By quasi-original position observation under SEM and ultrasonic scanning, it is found that the inner crack goes minish at elevated temperature. The healing in crack tip is very obvious. There is ferrite in healing area of hypo-eutectoid steel. Many micro-voids in healing area restrain grain boundary from moving. Therefore, the structure in healing area of copper and hypo-eutectoid steel is finer than the matrix. The differences of C, Mn and Mo in steel grade have not distinct effect on crack healing. The experiment on 20 and 20MnMn steel shows that the inner crack can be healed completely and rapidly under hot plastic deforming. The healing process at elevated temperature can be divided into four steps. The experiment on 45 steel shows that intensity goes back at the place where the inner crack is made after healing treatment that temperature is from 1000 to 1100℃and hold time is above 60min. The Molecular dynamics simulation is used to study the microcrack healing in BCC-Fe. The results show that inner crack in BCC-Fe is prone to heal over critical temperature 673K. Vacancies and dislocations appear in crystal during crack healing. They can not disappear though their conformation and position may change. The inner cracks can easily be found in 45 steel rolled bars. Most of the inner cracks are induced by inclusion concentrated among columnar crystal in continuous casting billet. In order to avoid inner crack appearing in bars, both total deformation and pass deformation should be confined, and the temperature of final pass should be up 900℃. The possibility of crack self-healing with minimal influence on microstructure is studied. It is found that crack in 45 steel bar could be healed in a way after holding 2-3 hours at 150-300℃or holding long time at normal temperature.