1. Field of the Invention
The invention relates to fused cast blocks based on refractory oxides and having a steel member embedded therein, the blocks being useful, in particular, for the construction of high-productivity steel-making furnaces, especially for the parts of these furnaces which are not in prolonged contact with the liquid metal bath.
2. The Prior Art
For some years, the power of arc furnaces relative to their capacity, or their specific power expressed as the nominal KVA power of their transformer per ton of liquid steel, has been on the increase, and frequently exceeds 500 KVA/ton (in the case of a UHP furnace). The used power even sometimes reaching 750 KW/ton during the fusion period. This trend results in the need for new methods of lining the walls of the furnaces.
The zones of the arc furnace linings which are exposed to the most severe conditions, that is to say the slag line, the tap hole and, particularly, the parts of the wall which are located opposite the three electrodes, currently most commonly consist of fused cast refractory blocks of magnesia/chromium oxide.
These fused cast refractory blocks are in the form of blocks which have been sawn into ingots, the shrinkage cavity of which, on solidification, has been dispersed in a macroporosity, consisting of pores of diameter from 1 to 10 mm, the total porosity due to these being from 16 to 20%, together with a very slight microporosity, and this, together with the very high crystalline cohesion of the blocks, makes the latter superior to other refractory materials such as fired basic refractory materials, or even materials made of rebonded fused grains.
The use of these blocks for constructing the zones of arc furnace linings which are exposed to the most severe conditions, in combination with less high-grade refractory materials for constructing the zones exposed to less severe conditions, generally makes it possible to balance the wear profile of the linings for a wide range of furnace power and capacity, and to optimize the productivity and cost of the refractory materials.
When the operating conditions become too severe, and in particular when the specific power used during the fusion period exceeds 500 KW/ton and when the heat flux reaching the lining cannot be reliably controlled, the use of such refractory blocks no longer makes it possible to achieve reasonable lengths of service life. In effect, the fused cast refractory blocks become destroyed too rapidly, especially at the "hot" points of the lining. This destruction can result from high temperature chemical attack by fumes and slag spray, or from flaking of the working faces as a result of rapid variations of temperature, these two phenomena taking place at varying speeds and to varying extents depending on the method of operation of the furnaces.
One solution to the above problems has consisted in constructing furnace linings free from refractory blocks and consisting of water-cooled metallic members.
These linings also have disadvantages;
they are expensive to install and their life is also short if the specific power used for fusion reaches 750 KW/ton,
they are large consumers of pure water, which is not always easily available, and which can cause severe explosions in the event of a leak,
they considerably increase, by 10 to 20 KWh/ton, the energy consumption relative to that encountered with the above-mentioned linings, which is not desirable in view of the current needs to save energy, and
above all, they do not completely solve the problem because the explosion hazard becomes excessive if they are used too close from the metal bath.
The present invention provides composite refractory blocks for lining steelmaking furnaces, which blocks constitute an advantageous compromise between the prior art solutions reviewed above.