Steel Ladle is an important thermal equipment for steel mills. ladle is mainly composed of cladding, refractory lining and SN mechanism. The metallurgical technology continues to develop, the smelting temperature increases and the continuous casting ratio increases, and the residence time of the molten steel in the ladle is prolonged. The use condition of refractories in ladle lining directly affects the case production and logistics of steelmaking. Therefore, it is considered that Rongsheng refractory material factory pursues the continuous improvement of the life of ladle under the premise of ensuring safe use, reducing the consumption and cost of refractory tons of steel, and improving the thermal turnover rate.
Ladle Lining Refractory Combination Design
The ladle lining refractory can be divided into a working layer and a permanent layer, and different refractory material systems and construction methods are adopted depending on the difference between the bottom and the wall erosion mechanism.
When selecting the permanent layer refractory materials, it is necessary to consider the factors of heat preservation and anti-steel water penetration. The high aluminum castable is used as a permanent layer, high alumina castable has high temperature strength, good thermal stability, strong resistance to molten steel penetration and moderate heat preservation. In order to enhance its thermal insulation performance, a layer of 18mm mullite insulation brick is built between the high aluminum castable and the steel shell, and the temperature of the outer casing during the turnaround of the ladle is between 220 and 400℃. This not only reduces the probability of steel leakage, but also reduces the heat loss of the molten steel during the entire refining and pouring process, which is beneficial to low temperature tapping and energy consumption.
The refractory materials in various parts of the bottom working layer have different damage mechanisms. The bottom of the bag is subjected to molten steel impact and large static pressure, and a refractory material for ladle lining with high softness, low creep and good thermal stability is required, and corundum castable is selected. In order to improve the anti-scour performance, a large precast block is placed in the impact zone, in order to facilitate the repair and reserve a certain expansion joint, the magnesia carbon brick is built around the gas permeable brick and the water block brick.
The wall working layer is subjected to carbon absorption by steel and scouring and slag during refining. The refractory material for ladle in this part should have good erosion resistance, erosion resistance and oxidation resistance, and the thermal expansion rate is required to keep the wall without cracks. Use corundum castable (integral cast ladle) or precast block (brick ladle). The slag line part of the slag line is eroded by the slag and the arc is burned and decarburized. The ladle refractory material is required to have strong anti-oxidation and anti-erosion ability.
Damage Mechanism of Ladle Lining
1.Steel Ladle Permanent Layer Damage
Taking Baosteel ladle as an example, the service life of Baosteel ladle permanent layer is generally 600~800 heats, that is, four overhaul cycles.
During the overhaul, it was found that there were many criss-cross cracks in the permanent layer of the wall, and the cracks widened and deepened with the increase of the number of overhauls. Sometimes the cold steel that poured into the working layer would also penetrate into the cracks of the permanent layer, which would affect the safety of the ladle. Common causes of cracks include: the low strength fiberboard is compressed by the volume to create a condition for the expansion of the permanent layer, the permanent layer castable refractory has a certain shrinkage during use, and the thickness of the permanent layer of the cladding is thin and the thickness is uneven. The ladle cladding is deformed at a high temperature, and the mechanical vibration during the removal of the slag line magnesia carbon bricks also accelerates the development of cracks in the permanent layer.
2.Steel Ladle Working Layer Damage
In the refining process, desulfurization, deoxidation, decarburization, degassing, fine adjustment of alloy composition, removal of non metallic impurities, inclusion denaturation treatment, and molten steel temperature control are required in the ladle. Different refining methods for the ladle working layer are not the same. The main forms of damage are as follows:
1. Slag line: erosion (primary), flaking, erosion, hydration (secondary cause)
2. Wall: erosion (primary), erosion, hydration (secondary cause)
3. Bottom: Scour (main reason), erosion, hydration (secondary cause)
4. Nozzle system: scouring (primary), spalling, erosion (secondary cause)
5.Argon blowing system: peeling (primary), flushing (secondary cause)
1) Erosion
There are two main types of erosion for the lining of the ladle working layer: chemical attack and oxidative attack.
Chemical attack: the acidic substances (such as silica) in iron oxide or slag react with the lining of refractory materials. There are chemical reactions between iron oxide, silica, calcium oxide and magnesium oxide. These reactions make the ladle lining. The change to slag causes damage to the refractory material.
FeO+MgO=FeOMgO
SiO2+2MgO=2MgOSiO2
CaO+SiO2+MgO=CaOMgOSiO2
Oxidation reaction: Oxidation erosion is a special form of refractory lining of ladle, generally refers to the erosion caused by the reaction of carbon in refractory bricks with iron oxide or oxygen in the air. The iron oxide in the slag reacts with the graphite or resin of the hot surface of the brick, and the oxygen erodes the graphite or carbon binder on the surface of the brick lining. In both cases, the internal structure of the refractory brick is loose and the strength is lowered. And eventually the refractory brick lining is washed away by slag or molten steel. This erosion occurs in all parts of the refractory in the ladle, with the most severe slag line.
FeO+C=Fe+CO
O2+2C=2CO
2) Scour
Scouring is the physical wear or scouring of the lining caused by the flow of molten steel or slag through the surface of the refractory. For the ladle used in the eccentric bottom tapping, the molten steel has a great influence on the impact zone of the bottom steel, the nozzle of the nozzle and the permeable brick above the bottom of the package. The ladle treated by LF and CAS, due to the strong agitation of the argon blowing process at the bottom of the ladle, aggravates the scouring effect of the molten steel on the local part of the ladle wall.
3) Peeling off
Peeling is caused by the stress on the refractory lining caused by the rapid chilling of the refractory lining. When the stress exceeds the strength of the refractory material, cracks are generated inside the refractory material. As these cracks expand, intersect and penetrate, the fragments of the refractory material will partially or completely peel off, which is often the case on the nozzle block and the permeable block.
4) Hydration
The ladle work lining adopts the fire mud wet-laying process in the masonry, and the permanent lining is knotted with the refractory castable. The moisture or water vapor reacts with the MgO in the magnesia carbon brick before and during the baking to hydrate. The hydrated refractory is resistant to steel slag and molten steel with poor permeability, reduced physical and chemical properties, and will accelerate the erosion rate of the ladle lining.
MgO+H2O=Mg(OH)2
Through the above analysis of the damage mechanism of the ladle lining, it is not difficult to find that the mechanism of refractory damage in various parts of the ladle working layer is different. Therefore, the whole process of ladle lining needs to be managed, from material selection, masonry construction and baking. Bake, run, and detect, repair, etc. after problems are discovered. When the ladle is used for a certain number of times and needs to be repaired, carefully check the residual thickness of each part of the lining, analyze the damage, and carefully analyze the data in the use of the lining to grasp the damage law of the refractory materials in the lining of the ladle.
