In order to ensure the surface quality of the casting, according to the characteristics of large wall thickness, small volume, large weight (1.7t), small heat dissipation surface area and large heat storage of the water-cooled steel brick, in order to prevent the casting from expanding and ensure the dimensional accuracy, the ester cured sodium silicate sand with high strength is selected for molding sand and 2 # and 3 # sand cores. In order to ensure the convenience of sand cleaning for 1 ﹥ strand core, sodium silicate sand with low binder ratio is selected for 1 ﹥ strand core.
In order to prevent the influence of the gas in the core sand on the casting quality, the mold and sand core are dried in the drying kiln. The drying temperature curve is shown in Figure 3. After drying, the mold should be closed and poured in time to prevent the mold from moisture absorption due to long storage time.
When EAF is used for smelting, the charge must be low phosphorus, less rust and dry scrap, and then a certain amount of cast pig iron. The amount of decarburization must be 0.2% ~ 0.4%. In the melting period, when 60% of the burden is melted, appropriate amount of small ore, fluorite and lime are added to make slag [4]. When the temperature of molten steel is 1580 ℃, the ore is added for oxidation. During the oxidation period, the amount of decarburization should be in the range of 0.2% ~ 0.4%, so as to effectively remove the gas and inclusions in the molten steel; The WP must be controlled below 0.025%, the final carbon content (mass fraction) at the end of oxidation is generally below 0.25%, and the net boiling begins. After 10 minutes, ferromanganese is added for pre deoxidation. In order to ensure the deoxidation effect, the amount of calcium carbide used as slag making material in reduction period is 1 ~ 1.5kg/t, which can ensure the deoxidation under white slag. After adjusting the composition and temperature of the molten steel after 30min, the furnace temperature is controlled at (1590 ± 10) The pouring temperature is controlled at 1550 ~ 1560 ℃. Before pouring, it must be calm for 3 ~ 10min to ensure low temperature and fast pouring. After pouring, the riser is covered with covering agent and tamped for about 30 minutes to improve the feeding efficiency of the riser (insulation riser or riser heating agent can also be used).
1) After pouring water-cooled steel brick casting, the box should be loosened in time to reduce the shrinkage resistance.
2) According to the characteristics of wall thickness, large weight and small volume of water-cooled steel brick castings, in order to prevent cracks caused by premature opening of the box, the in mold heat preservation time > 20h is selected according to the calculation.
3) Heat treatment of castings: in order to eliminate the casting stress, improve the cutting performance and comprehensive mechanical properties of castings, heat treatment of castings must be carried out. We adopt the complete annealing method, and the annealing curve is shown in Figure 2. Complete annealing can effectively improve the inhomogeneity of the internal structure of the casting, eliminate the overheated structure and widmanstatten structure, and refine the grain size.
