From the refining point of view, the open hearth bottom is the most important part, and there is no special change in refractory technology. First of all, in the period of shortage of various magnesia bricks after the end of World War II, the attempt to replace the previous magnesium oxide furnace bottom with raw dolomite furnace bottom is of great significance in domestic and foreign companies. Compared with the magnesium oxide knotted furnace bottom, the trial results of various companies are worse in terms of durability (the same is true in theory). However, it may be clear in application. In addition, the test results of Nippon Steel Institute and Muran reported that the refractory consumption index was better than that of magnesia refractory brick, which may be related to the trial use of tar binder.
The furnace bottom is not only necessary to maintain the durability of the means for liquid steel retention and refining reaction, but also can be expected to provide the nuclei produced by CO during decarburization reaction in the case of open hearth furnace bottom, as shown in Figure 1. The above-mentioned raw dolomite (carbonate) furnace bottom, including the impact of CO2 gas, is still unclear.
Compared with that before World War II, the open hearth bottom refractories generally include magnesium oxide (MgO) and dolomite (MgO Cao). The overwhelming magnesium brick is used in the oxygen steelmaking process. However, among the open hearth furnaces with low oxygen consumption in Europe, there were also many factories using traditional dolomite bricks at that time. In this case, there are two types of dolomite refractory brick furnace bottom:
(A) Tar dolomite knotting furnace bottom: adding coal tar to dolomite sand for knotting construction.
(B) Crespi furnace bottom: dry knotting and light burning dolomite powder forming.
In particular, the Crespi furnace bottom may rise rapidly due to the absence of binder. As other methods, the method of repeatedly spraying and sintering refractory materials (such as the mixture of magnesia and light burned dolomite) at the furnace bottom for many times to make the sintering furnace bottom in layers (sintering furnace bottom method) has been implemented, but it has the disadvantage of long operation time.
Operating conditions of open hearth furnace: due to the increased severity of oxygen consumption, the load on the furnace bottom increases. The production obstacles caused by the furnace bottom repair operation (repairing the furnace bottom under hot state) cannot be ignored. From the research on the loss structure of the furnace bed, it is identified that the corrosion of slag and other substances in the furnace, the structural spalling caused by the corrosion of slag, the spalling and floating caused by the cracking caused by the volume change under high temperature, and the further phenomenon that the spalling is promoted by the erosion of molten iron and steel to the cracking place. The disadvantages of knotting the furnace bottom are the insufficient volume density (preferably 2.8g/cm3) and the potential cracking of layers. As one of its countermeasures, the so-called refractory brick furnace bottom was continuously carried out in the United States at first, and Japan also tried. Although it has achieved the desired results, it has not been popularized. We believe that it is caused by refractory brick masonry and mechanized operation.