Study On High Temperature Mechanical Properties And Secondary Cooling System Of Continuous Casting Slab

Continuous casting of steel is an important production technique to link up steelmaking and rolling, and the quality of continuous cast slab has important influence on the final product quality of steel. The statistic show that, more than fifty percent defect of slab related to crack. The cracking of solidified shell due to slab's mechanical properties and their change rules in high temperature. Therefore, research on high temperature mechanical properties of slab has great significance for controlling and improving the quality of slab.Stress strain curve, yield strength, tensile strength, hot ductility, elastic limit, modulus of elasticity and plastic modulus with temperature of steel A, steel B and steel C, which produced by No.2 slab caster in a certain steel plant, have been measured in the temperature range of 600-1300℃by the hot tensile test technique with Gleeble-1500D system. According to the hot ductility curve, the third brittle zone of steel A, steel B and steel C were found. The results of the test show that the third brittle zone of steel A is about between 750℃and 850℃; for steel B, it is about between 800℃and 970℃; and for steel C, it is about between 800℃and 990℃. Moreover, the fracture surface of hot tensile test specimens in the first brittle zone and the third brittle zone were analyzed by using scanning electron microscope. The fracture morphology characteristics and the fracture modes of specimens were obtained.In order to further understand the high temperature mechanical properties of slab, to understand the crack mechanism and the difficult degree of crack's generation of different steels, which have different high temperature mechanical properties, based on the research of high temperature mechanical properties of steel A, steel B and steel C, various mechanical property index among different steels which have different utilization strength were compared.Secondary cooling technology is a critical technique in the continuous casting process. The formation of internal crack, surface crack, bulging, center segregation and so on have close relationship with secondary cooling system. Thus, the secondary cooling technology has important influence on yield of slab caster and quality of slab. In order to ensure the quality of slab, a reasonable secondary cooling system is necessary.After summarizing the structure and technological parameters of No.2 slab caster in a certain steel plant, a two dimension heat transfer mathematical model of continuous casting slab was established by microtomy. And then, the continuous casting process of steel A, steel B and steel C were simulated by using the heat transfer model and the actual secondary cooling system respectively. The change laws of temperature field and solidification of steel A, steel B and steel C in different operating conditions were obtained by simulating. Combined with the results of hot tensile tests, the rationality of secondary cooling system of steel A, steel B and steel C were analyzed respectively. The results show that, secondary cooling systems of steel A, steel B and steel C can satisfy the requests of metallurgical criteria.