Research on the erosion mechanism of magnesia carbon bricks in slag wire during electric furnace steel making process

  Protecting the furnace lining and reducing the erosion of the furnace lining by slag and electric arc during electric furnace smelting is of great significance, which can increase the furnace life and reduce production costs.

  The working layer of electric furnace refractory materials is mainly composed of magnesia carbon bricks, furnace bottom ramming materials, etc.

Generally speaking, the damage factors of electric furnace refractory materials are: erosion, oxidation, scouring, melting, spalling and hydration, among which oxidation, chemical erosion and scouring are the main damage.

Magnesia carbon bricks are most seriously corroded due to the interaction of slag chemical erosion and arc thermal erosion. They need to be filled in the smelting interval to maintain their thickness and ensure stable production.

The erosion of the ramming material at the bottom of the electric furnace is mainly caused by the addition of scrap steel and the addition of molten iron at the high position of the furnace top, which causes a large mechanical impact and scouring on the refractory materials at the bottom of the furnace.

In addition, the furnace door area is also a weak link in the furnace lining. Due to the influence of thermal expansion during daily use, the refractory materials in this position are prone to arching and brick movement.

In order to improve the furnace life, a domestic electric furnace factory took measures such as optimizing the refractory material, changing the furnace bottom ramming method, improving the furnace lining refractory masonry process, and optimizing the smelting operation process, which significantly improved the furnace life.

Controlling the erosion of magnesia carbon bricks in the slag line of electric furnace smelting is the key to improving furnace life and reducing gunning.

Strengthening the protection of the arc by making foamed slag can greatly reduce the radiation of the arc to the furnace lining, However, the corrosion of magnesia carbon bricks by electric furnace slag is still inevitable.

As for its erosion mechanism, relevant research believes that the highly oxidizing slag in the electric furnace will remove part of the carbon in the magnesia carbon brick, causing the microstructure of the brick working surface to loosen and become brittle, and then peel off and be corroded under the scouring of flue gas, slag and molten steel.

The corrosion of magnesia carbon bricks increases with the increase of FeOx mass fraction in slag. Controlling the FeOx mass fraction of slag to less than 16% can effectively reduce the corrosion of slag on furnace lining.

Through observation and analysis of the use of electric furnace magnesia carbon bricks, it is found that magnesia carbon bricks can be divided into slag layer, magnesia sand layer, decarburization layer and original layer after use. There are a large number of spherical magnesia fusate and calcium magnesium silicate in the slag layer. In the decarburization layer area close to the original layer, there are a large number of iron beads generated by the reduction of iron oxide by graphite.

These observations also indirectly illustrate that slag decarbonization exacerbates the erosion of magnesia carbon bricks.

Slag with basicity less than 2 generates low melting point substances CMS at the erosion interface. The appearance of low melting point substances promotes the dissolution of magnesia particles, thereby accelerating the shedding of magnesia particles. In order to prevent the erosion of magnesia carbon bricks by slag, It was observed under laboratory conditions that the erosion penetration layer is mainly composed of reduced Fe phase, slag phase and magnesia-alumina spinel phase. The formation of magnesia-alumina spinel phase inhibits the penetration of slag into magnesia-carbon bricks. 

Properly increasing the mass fraction of MgO in the slag (greater than 8%) can inhibit the dissolution of refractory materials into the slag, promote the formation of spinel phase, and reduce the erosion rate of slag on the refractory materials of the furnace lining. The above studies did not conduct in-depth discussions on the mechanism of electric furnace slag corrosion of magnesia carbon bricks in actual production, nor on which factor, the oxidizability or alkalinity of electric furnace slag, has a greater impact on the corrosion of magnesia carbon bricks. At the same time, there are few research reports on the impact of thermal changes in refractory materials on the corrosion process.

This paper further studies the corrosion mechanism of magnesia carbon bricks in electric furnace slag line through microscopic analysis of actual production furnace lining and magnesia carbon brick corrosion test using on-site slag, providing technical support for improving the furnace life on site.