Optimal configuration of ladle refractory materials

The ladle is a crucial piece of equipment in the steelmaking process. Modern industry, in particular, places increasingly stringent demands on steel quality, with a growing demand for pure steels such as low-carbon and ultra-low-carbon steel. However, converter steelmaking often cannot meet these requirements. This necessitates off-furnace refining to reduce the carbon content and other impurities in the molten steel. Consequently, the requirements for the ladle are becoming increasingly stringent. Conventional ladle refractory materials either fail to meet these requirements or have a very short lifespan, lacking cost competitiveness. Therefore, the development of high-efficiency, long-lasting ladle refractory materials is an inevitable trend.

The primary factor affecting the service life of a ladle is refractory damage, caused by chemical attack and spalling and cracking due to thermomechanical stress. Furthermore, material and dimensions, masonry structure, expansion joint size, and refining conditions also significantly impact lifespan. Currently, the main obstacles hindering the development of ladle refractory materials in my country are low ladle age and slag adhesion to the ladle wall. Currently, the ladle lining primarily utilizes magnesia-carbon bricks, alumina-magnesia-carbon bricks, magnesia-alumina spinel monolithic castables or precast blocks. The slag line utilizes low-carbon magnesia-carbon bricks or low-carbon alumina-magnesia-carbon bricks, and the ladle bottom utilizes magnesia-carbon bricks or high-alumina castables. The ladle lifespan is generally around 100 furnaces, with a few steel mills achieving 150-180 furnaces. Compared to comparable Japanese steel mills, the average ladle lifespan is around 250 furnaces.

Ladle slag sticking is also a common problem in Chinese steel mills. The primary influencing factors are the ladle slag composition and refractory material. Furthermore, steelmaking process and operational factors can exacerbate slag sticking. The measures that can be taken to prevent slag sticking to the ladle are: 1) Improve the thermal turnover rate of the ladle and reduce the number of ladle turnovers; 2) Strengthen the maintenance of the ladle, clean the slag on the edge of the ladle in time, prevent the ladle slag from not being completely poured out after the ladle slag forms a ring at the edge of the ladle, and promptly repair the obvious melting loss and peeling parts of the ladle wall to prevent the slag and molten steel from infiltrating and aggravating the slag sticking; 3) Drain the slag as soon as possible after the pouring is completed, strengthen the production organization of the crane behind the furnace, reduce the time from pouring to turning the ladle, and avoid the occurrence of slag sticking to the ladle; 4) Improve the slag blocking operation level of the converter tapping, reduce the converter slag from entering the ladle, and prevent the converter slag from entering the ladle. Add lime during post-refining to fully melt the ladle slag; 5) Control the number of ladles in use to reduce ladle waiting time; heat the ladle before steelmaking; use a ladle cover during use; use an insulating layer in the permanent ladle layer; and use low-thermal-conductivity refractory materials for the ladle walls; 6) Regarding refractory materials, improve masonry quality, control brick joint dimensions, reduce thermal stress in the ladle lining, enhance thermal shock resistance, and minimize cracking; 7) Use effective ladle covering agents: Improve the spreadability of the ladle covering agent to enhance its thermal insulation performance, reduce the SiO2 content in the covering agent, reduce its viscosity, and reduce slag sticking to the ladle.

To address these issues, simply focusing on controlling refractory cost per ton of steel in the narrow sense will not solve the problem. Refractory suppliers and steel companies need to work together to explore solutions and achieve the lowest cost from a broader perspective.

Practical applications have shown that reducing refractory consumption per ton of steel has profound implications for the production of clean steel, lowering tapping temperatures, and energy conservation, and is sometimes essential. For example, the production of clean steel is a leading concept in modern steelmaking. This typically refers to high-quality steel with minimal harmful elements (S, P, O, H, and N), minimal non-metallic inclusions, controlled morphology, and precise and uniform distribution of alloying elements. High refractory consumption leads to increased refractory content in the molten steel, typically in the form of melt loss and spalling. Melt loss often increases carbon and oxygen content and produces small non-metallic inclusions, while spalling often produces larger non-metallic inclusions. Small non-metallic inclusions (≤50 ppm) are difficult to remove using existing smelting processes. Therefore, low refractory consumption is essential for clean steel production. Furthermore, low ladle refractory consumption indicates a high ladle heat turnover rate, less cold ladle tapping, and lower average converter tapping temperatures. This translates to reduced consumption of oxygen, alloying agents, and other materials. Typically, a 1°C reduction in tapping temperature reduces the cost per ton of steel by 1 yuan. Furthermore, lower tapping temperatures are also beneficial for ingot quality.

According to the above, the ideal configuration of ladle refractory materials should be: the ladle wall insulation layer is 30 mm thick, the permanent layer integral castable is 80~100 mm thick, and the working layer integral castable is 180~210 mm thick; low carbon magnesia carbon bricks are selected for the slag line, with a thickness of 180~230 mm; the ladle bottom is cast integrally. The appropriate integral lining thickness is selected according to the size of the ladle. Drawing on the management experience of advanced foreign counterparts and referring to the actual use of air-permeable bricks in my country, the repair model shown in Table 1 is formulated. At the same time, the research and development of ladle integral castables and application technologies should be continuously strengthened. The following two points are particularly important: 

(1) Develop effective repair technology to repair the damaged part of the lining locally instead of replacing the entire lining with materials with good durability. This technology can ensure uniform wear of the lining during the service life and produce as little residual refractory as possible. 

(2) Develop continuous pouring repair technology to continuously construct the lining without discarding the original residual lining refractory materials.