Electric furnace ladle has harsh operating conditions: high tapping temperature (1640～1690℃), as many as 1,000 steel grades, wide range of slag alkalinity (n(CaO)/n(SiO₂)=0.5～5), refining Long time (120～150min), high heating power, etc. The bottom working layer of the package has long been built with magnesia-aluminum carbon bricks, spinel carbon bricks, magnesia-carbon bricks and other carbon-containing press bricks. However, in accordance with the requirements of ultra-low carbon steel and high-quality steel smelting, the proportion of refining outside the molten steel furnace increases, and the smelting time becomes longer, which leads to an increase in the temperature of the molten steel and a longer residence time in the ladle. This requires refractory materials for ladle Higher and higher.
Corundum-spinel castables are widely used in the working layer below the converter ladle slag line due to its good alkali slag corrosion resistance and excellent high-temperature mechanical properties. The pre-synthesized or in-situ generated magnesia-aluminum spinel is introduced into the corundum castable, mainly to improve the slag resistance and improve the high-temperature mechanical properties. The pre-synthesized magnesium-aluminum spinel has larger grain size, good chemical stability and low solubility, as well as excellent volume stability. It is especially suitable for use in the bottom of high temperature and high pressure ladle. For this reason, Baosteel Electric Furnace Steel Plant decided to try corundum-spinel castables instead of normally used aluminum-magnesium-carbon bricks for the bottom working layer of the ladle of the round billet production line.
Performance comparison of corundum spinel castable and magnesia-aluminum-carbon brick
Compared with magnesia-aluminum carbon bricks, corundum-spinel castables do not contain carbon, have a higher bulk density, and have comparable compressive strength and high temperature flexural strength at room temperature. They expand slightly after firing and exhibit good volume stability. Inferred from the performance indicators, the corundum-spinel castable can meet the smelting process requirements of the electric furnace round billet production line.
Application analysis of corundum spinel castable
2.1 Comparison of corundum-spinel castable and magnesia-aluminum-carbon brick
The main differences between pouring ladle bottom and brick ladle bottom: 1) The turnaround time of pouring ladle bottom is about 24~38h, construction time is 2h, curing time is 16h, baking time is 36h; brick ladle bottom construction time is 4h, baking time 12～24h. 2) The maintenance mode is adjusted. When the brick ladle is repaired, all the bottom working linings, including the aluminum-magnesia-carbon bricks at the bottom of the ladle, need to be replaced; while the pouring ladle is repaired, only the ventilation bricks, nozzles and impact areas need to be replaced.
The corundum-spinel castable is applied to the bottom working layer of the 150t ladle (13# and 8# ladle) of Baosteel’s electric furnace round billet production line, with 5.0%～5.5% of water (w), flow value 180～220mm, stirring The time is 3～5min, the exhaust is vibrated by vibrating rod, and the total construction time is 1～2h.
The service life of the two pouring ladle bottoms during the overhaul was 92 furnaces and 91 furnaces (normally offline). The residual thickness of each area during the overhaul of the pouring ladle and the brick ladle is shown in Table 2. There are only minor cracks in the bottom of the cast ladle when it is used. The most severely damaged area is in the impact area of the bottom of the ladle when it is overhauled, but the residual thickness is >100mm. When the brick bottom is repaired, all the bottom working layers will be replaced. It can be seen that the corundum-spinel castable can meet the working conditions of the electric furnace round billet production line ladle, and has a better service life.
Compared with the brick bottom of the ladle, the use of integral casting at the bottom of the ladle has the following advantages: 1) The number of brick joints in the working layer of the bottom of the ladle is reduced, the probability of cracking of the bottom of the ladle and the penetration of cold steel along the brick joints is reduced, and the safety of the use of the ladle is improved. 2) Strengthen the air tightness and integrity of the bottom working layer of the bag, reduce the probability of “side blowing” of the ventilating brick, reduce the probability of offline due to the abnormal ventilating brick, and improve the safety. 3) In the middle and late stages of use, there will be no abnormal breakage of the brick body due to the gradual enlargement of the brick joints. 4) Mechanical construction is easy to operate and reduces labor intensity. 5) It is not necessary to replace all the working layers of the bottom of the package in the middle repair, and the impact area of the bottom of the package is maintained with the repair material, and the consumption of refractory materials is reduced.
