Five useful measures to improve the service life of 75t steel ladle lining

The ladle serves to receive molten steel and perform ladle refining. Its service life directly impacts ladle turnover and refractory material consumption, thus affecting the steel mill’s smelting costs. At Taigang Stainless Steel Division, the current service life of a 75t ladle for producing ordinary carbon steel is 135 heats. On average, the ladle is taken offline after 55 and 105 heats to replace the permeable bricks and nozzle seat bricks, and the slag line bricks are replaced at the 105th heat. By analyzing the factors affecting ladle service life and implementing corresponding measures in smelting conditions, ladle baking quality, and ladle maintenance technology, Taigang Stainless Steel Division has increased the ladle service life to 150 heats.

Factors affecting the service life of steel ladles

1)Smelting conditions

The longer the ladle holds steel, the higher the refining temperature, the greater the amount of slag added, the lower the slag basicity, and the stronger the slag oxidizing properties, the faster the ladle lining material will erode.

2)Ladle baking quality

Before being put into use, the steel ladle needs to be baked to ensure that the refractory material is fully sintered, preventing it from peeling off due to rapid heating after the new ladle is filled with molten steel. During the turnover of the steel ladle, slow turnover speed and large temperature drops should be avoided to prevent the refractory material from overheating or cooling, which would affect the life of the steel ladle.

3)Steel ladle lining

The lining material of the ladle comes into direct contact with molten steel. Its material composition, adapted to the smelting conditions, can significantly reduce the erosion of the refractory material by molten steel and slag. Furthermore, improving the performance indicators of the refractory material can reduce the scouring and penetration of molten steel and slag, thus extending its service life. The use of anodizing coatings on the lining can greatly prevent oxidation of the ladle during the baking process, thereby extending the ladle’s service life.

4)Masonry methods and masonry quality

① The construction of the steel ladle must minimize defects such as triangular joints and misalignments to reduce severe corrosion of the refractory material by molten steel or slag, thus affecting the overall lifespan of the ladle.

② Ensure the grout at the back joints of the ladle bricks is firmly compacted to prevent grout movement during ladle turning, which could lead to brick removal, steel seepage, or other accidents.

③ The ladle opening must be firmly secured with a steel plate to prevent brick expansion and subsequent brick falling during use and turning.

④ The external dimensions of the ladle bricks are crucial to the quality of the ladle construction and must be strictly inspected according to quality standards.

Measures to improve the service life of steel ladles

1. Improve smelting conditions

1) Insulating the ladle reduces heat loss from the molten steel, thereby lowering the refining temperature and time, and extending the service life of the refractory materials.

2) Reducing the amount of slag added to the converter decreases the amount of magnesia-carbon bricks dissolved in the slag, thus improving the service life of the refractory materials.

3) Appropriately increasing the amount of lime increases the basicity and viscosity of the slag, reducing slag penetration and melting loss of the refractory materials, thereby improving the service life of the refractory materials.

2. Improve the quality of ladle baking

1) The preheating time for the ladles before they are put into service has been increased from 36 hours to 48 hours. The heating process is strictly carried out according to the preheating curve, and the holding time is guaranteed to meet process requirements. The ladle temperature reaches 900℃ upon entering service.

2) The number of turnover ladles has been reduced from 5 to 4, improving ladle turnover efficiency, reducing ladle processing time, and minimizing the time interval between pouring and refilling molten steel into the ladle. This prevents rapid temperature fluctuations in the ladles.

3. Reinforced lining material

1) Converter slag is characterized by high oxygen content and low alkalinity, resulting in strong penetrating and corrosive properties. Improving the density of the ladle bricks enhances their corrosion resistance.

2) Alternating hot and cold temperatures are a significant factor contributing to the damage to the ladle lining. Improving the thermal shock resistance of the magnesia-carbon bricks in the ladle helps extend its service life.

3) Due to their high carbon content, magnesia-carbon bricks are easily oxidized during ladle baking, and the longer the baking time, the more severe the oxidation. Applying an anti-oxidation coating to the working surface of the magnesia-carbon bricks can greatly prevent oxidation of the ladle during baking, thereby extending its service life.

4. Improve the ladle masonry method

1) Changing the ladle bottom to a cast-in-place method offers several advantages. First, it improves the overall integrity of the bottom, eliminating brick seams. Second, it allows for maintenance during ladle use and upon unloading, eliminating the need for bottom removal and thus enabling indefinite use and reducing refractory material consumption.

2) Areas of the ladle body susceptible to molten steel erosion are weak points and require reinforcement. This can be addressed in two ways: strengthening the material to improve brick density and erosion resistance; and increasing brick thickness to extend lifespan without altering the erosion rate. Alternatively, a combination of these approaches can be considered to synchronize the lifespan of the refractory materials in weaker areas with those in other areas, thereby improving the overall service life of the ladle.

5. Maintenance method

1) Ladle Bottom Lining Repair: Clean the slag from the bottom of the ladle, then pour corundum material for repair. The thickness should be the same as the original bottom lining thickness, but avoid excessive thickness (no more than 50mm) to prevent separation and bulging during use.

2) Ladle Body Excavation Repair: Excavate and repair severely corroded areas to significantly extend the service life of the ladle lining.

3) Ladle Wall Repair Material: Typically, one ladle wall lining is used with multiple slag lines, which can lead to the wall bricks having a thinner residual thickness than the slag line bricks, affecting service life. A suitable ladle wall repair material is used. This material exhibits slight expansion at high temperatures, is less prone to cracking, and has good integrity, significantly extending the service life of the ladle wall. The material’s lifespan is generally over 20 heats. Application method: Mix the material with an appropriate amount of water in a specific ratio, stirring until it reaches an easily spreadable, plastic state. Clean the slag pouring surface of the ladle and other areas with excessive slag thickness. Apply the coating material in small amounts multiple times, from bottom to top, to the original thickness of the ladle wall bricks, generally around 50mm. Let it solidify.

Implementation effect