Influence Of Tramp Elements Arsenic, Tin And Antimony Segregation To Grain Boundary On Hot Ductility Of CC Steels

The high temperature mechanical behavior of continuous casting steels containing Arsenic, Tin and Antimony is studied. The mechanical parameters at high temperatures--reduction in area (RA%) and tensile strength(σb) are measured by means of Gleeble-2000 thermal simulating test. Fracture surfaces are analyzed by scanning electron microscopy and optical microscopy. Then the effect of arsenic, tin and antimony and cooling rate on the high temperature mechanical properties is studied. In addition, the influence extent of the three elements on hot ductility is compared. In the meantime, isothermal aging, impact test and Auger electron spectroscopy test are used to study the variations of impact energy Ak with aging time of the As-doped, Sn-doped, Sb-doped steel. And the critical time of non-equilibrium grain boundary segregation of tramp elements arsenic, tin and antimony are obtained. According the results had got, the segregation mechanism of tramp elements As, Sn, Sb during continuous cooling and isothermal aging and its influence on the hot ductility of low carbon steel are discussed.Do thermal simulating test at a strain rate of l0-2/s and a cooling rate of 20℃/s, and then air-cooling quench. There exists a third ductility trough for the four steels at 750℃, although the metallurgical structure is polygon ferrite and perlite exist instead of film-like pre-eutectoid ferrite along austenite grain boundaries. At the same time, in the third ductility region, the existence of As, Sn and Sb deteriorates the hot ductility of As-doped, Sb-doped and Sn-doped steels, deepen and widen the ductility trough. What's more, the reduction in area of the Sb-doped, Sn-doped, As-doped and As-undoped steel is droped off. In other words, from strength to weak, the sequence of the influence extent of the three elements on hot ductility is Sb, Sn and As.Based on the hot tensile test results, there exist a cooling rate at which a minimum reduction in area occurs and the hot ductility is worst. When the cooling rate is lower or higher than 20℃/s, the hot ductility is increased.During isothermal aging, impact energy rapidly decreases and embrittlement rapidly increases with increasing aging time. As time goes on, the minimum impact energy is obtained where the embrittlement attains the largest. Then as the aging time increases further, the impact energy is gradually increased and the embrittlement is gradually improved. The result is that the changing of impact energy with time responses of the kinetics of non-equilibrium segregation. As measure in this experiment the critical time of As, Sn, Sb non-equilibrium segregation is about 120 seconds, 210 seconds and 120 seconds at 750℃separately. In addition, the metallurgical structures are analyzed by optical microscopy and Fracture surfaces are analyzed...