Refractory for converter steelmaking

The main steelmaking in the world are converter steelmaking, arc furnace steelmaking and open hearth furnace steelmaking. In recent years, the converter smelting technology has also obtained great development, especially the development of the converter blowing process technology, that is placed in the bottom of a converter gas brick, brick by gas supply to the blowing nitrogen, carbon dioxide, argon gas or oxygen inside the furnace, to strengthen the bath stirring, improved the smelting reaction, so that shorten the steelmaking time, increase the steel quality and reducing the cost of steelmaking. But reblowing also accelerates the erosion of lining refractories. Refractory material is an important factor affecting the service life of furnace lining. However, operating conditions are more important. Good service conditions are the foundation of high service life of furnace lining. The service life of furnace lining can be increased several times by protecting furnace, and the maintenance of furnace lining is very important.

 

Before the development of magnesia carbon bricks, the converter lining was mainly made of magnesia bricks and magnesia dolomite bricks fired or combined with tar pitch, with the initial 200-300 furnaces (small converters). Since the successful application of magnesia carbon brick in the converter lining, the proportion of magnesia carbon brick in the converter lining is increasing. Now the converter lining is basically built with magnesia carbon brick. Permanent lining with magnesia brick, joint material with magnesia ramming material. The service life of the converter has gradually developed to thousands of furnaces without splashing slag, and through splashing slag, the service life can reach tens of thousands of furnaces, furnace lining has become permanent. In general, small converter out of steel temperature is high, its smelting conditions are relatively harsh, the use of refractory quality is also low, therefore, its service life is correspondingly low.

 

The factors affecting the service life of the converter are as follows :(1) the composition of slag. For every 1% increase of iron oxide in slag, the service life is reduced by 18~20 times. The higher the CONTENT of MgO in slag, the lower the erosion to furnace lining. The higher alkalinity in slag is, the lower the erosion of lining is. (2) The higher the outlet temperature, the lower the service life. Generally above 1600℃, the service life is reduced twice for every 50℃ increase. (3) The longer the smelting time, that is, the longer the blowing time, the faster the furnace lining erosion, and the service life is inversely proportional to the smelting time. (4) Intermittent operation. When the metallurgical furnace is stopped, the temperature drops, and when the furnace is opened for use, the temperature rises rapidly, which leads to strong thermal shock, which often leads to thermal stress, resulting in accelerated erosion and cracking, and even peeling, thus significantly reducing the lining service life. (5) When adding molten iron and charge, the furnace tilts and hits or scour, which all cause the discontinuous damage of furnace lining, only timely repair, otherwise it will greatly reduce the service life.

 

However, it is worth pointing out that refractories used in our converter are basically the same as those in Japan. Magnesium carbon bricks with 18% carbon content are more commonly used, whereas in Europe, magnesium carbon bricks with 10%~15% carbon content are more commonly used. According to the author's research results, if the production load is heavy and the steelmaking pace is fast, the magnesium carbon brick with lower carbon content should be selected as the best, because its corrosion resistance will be better. On the contrary, if the steelmaking rhythm is slow and the interval is long, it is better to choose magnesium carbon bricks with higher carbon content.