In modern steelmaking processes, the gas-permeable brick is a crucial functional component in ladle refining technology. By injecting inert gases—such as argon—into the molten steel through the gas-permeable brick located at the bottom of the ladle, the system generates the agitation necessary to homogenize the alloy composition and temperature of the melt. These bricks are categorized into split-type and integral-type designs, both of which consist of a core and a seating block. In either configuration, the seating block serves to protect the core, preventing molten steel from eroding any part of the core other than its working face. Common forms of damage to the seating block include erosion caused by the flow of molten steel, spalling or chunking, and transverse or longitudinal cracking. The following section briefly analyzes the factors influencing the service life of gas-permeable bricks and outlines directions for future research and improvement.

Influencing factors

1.Installation Procedure for Porous Plugs

In accordance with standard installation procedures for porous plugs, the steel shell of the ladle must be thoroughly cleaned of all debris and particulate matter before the monolithic porous plug and split-type seating block are installed. The bottom surface must be leveled using bedding materials—such as refractory mortar or sand—to prevent any localized gaps or voids beneath the seating block. Once the ladle receives molten steel, the plug core is subjected to immense hydrostatic pressure, creating a tendency for downward displacement. This is particularly critical for monolithic porous plugs; if the bedding layer beneath the plug core is inadequate—leaving a void—the core may breach the protective layer of the seating block. This can result in longitudinal cracking at the base of the seating block and misalignment of the plug core, posing significant safety risks during operation.

2.Bottom-encasing masonry method

The working layer of a ladle bottom is typically constructed using either brickwork or castable material. For brick-lined bottoms, it is generally recommended to leave a gap of 30–80 mm around the well block, filling this space with corundum-based material or ramming mix to buffer the impact of thermal expansion—occurring during the preheating of the bottom bricks—on the well block. In practice, there have been numerous instances where improper masonry design—specifically failing to leave a gap around the well block or providing insufficient clearance—has resulted in the transverse fracture of the well block.

3.Performance of Ladle Bottom Refractories

Ideally, the well block and the ladle bottom refractory wear at the same rate, allowing the latter to effectively protect the well block; however, if the ladle bottom refractory undergoes severe erosion or spalling—leaving the well block isolated and unprotected—the exposed section is susceptible to transverse fracture caused by the shear forces of the circulating molten steel.

4.Quality and Construction Performance of Seating Block Grouting Material

Leaving a gap around the seating brick is intended to minimize the impact of thermal expansion from the ladle bottom refractory materials; however, if the joint-filling material itself undergoes excessive erosion and develops defects during service, the seating brick is left isolated and unprotected, making it prone to spalling or complete transverse fracture. While the quality of the filling material is crucial, the quality of its installation is equally important. If self-flowing corundum material is used, careful control of the water addition is required to ensure a uniform mixture without water-material separation, followed by compaction with an iron rod; if ramming material is used, it must be rammed to a high density.

5.Ladle preheating practice

If corundum-based material is used for joint filling, the seating block absorbs some of the material’s moisture and gradually releases it during the ladle preheating process. If the preheating procedure fails to follow the sequence of low, medium, and high heat, the rapid release of moisture generates significant stress within the seating block, creating a risk of longitudinal cracking.

6.Argon purging process using porous plugs

During argon blowing through the porous plug, the gas flow causes the molten steel to churn continuously, subjecting the ladle bottom refractories and the plug block to constant scouring and erosion; this leads to a progressive reduction in the plug block’s height, while the high-speed surge of molten steel across the plug’s working face causes the internal bore of the block to gradually widen.

7.Bottom-encasing masonry method

During the oxygen-burning cleaning of the working face of the porous plug core, the temperature generated by the oxygen lance can reach 2,000°C; if the lance blows against the inner wall of the seating brick, it can cause melting damage to the brick. In particular, when the oxygen lance is angled toward the plug core during the process, there is a risk of inadvertently burning the seating brick, leading to abnormal erosion.

Research on directions for improvement

1.Understand the physical properties of well blocks at different temperatures and improve their intermediate-temperature strength

Finished well blocks typically undergo only low-temperature drying (150–300°C). However, after the ladle is filled with molten steel, the temperature at the top of the well block can reach 1500–1600°C. Heat conduction creates a temperature gradient from the top to the bottom of the block; the temperature at a depth of 100–200 mm from the top typically ranges from 700°C to 1000°C. This specific temperature range represents the point of minimum strength for the well block, making it susceptible to transverse fracture under external lateral shear forces.

Well block castables were molded into standard 40 mm × 40 mm × 160 mm specimens. After heat treatment at temperatures ranging from 110°C to 1550°C, the specimens were tested for linear change after firing (in accordance with GB/T 5988—2007) and for flexural and compressive strength at room temperature (in accordance with GB/T 3001—2007 and GB/T 5072—2008). Regarding strength results, flexural strength showed a gradual decline as the treatment temperature rose from 110°C to 700°C, followed by a gradual increase; however, the strength remained relatively low at temperatures below 1100°C. Compressive strength also remained low below 1100°C, reaching its minimum value within the 700–900°C range. Analysis of linear change revealed negative values below 1100°C, indicating that the specimens underwent shrinkage in this range, while expansion began at temperatures above 1100°C.

2.Study on the Effect of Molding Method on the Properties of Well Blocks

Since seating bricks are cast vertically in molds, the air escape path for the castable at the bottom of the mold is long; consequently, air bubbles often become trapped in the castable at the top of the mold, resulting in high porosity and compromised physical properties in that section. To analyze these properties, samples were taken from the bottom, middle, and top sections of the molded brick and cut into standard 40mm × 40mm × 160mm specimens, designated as Groups A, B, and C, respectively. After drying at 110°C for 24 hours, the specimens were tested for bulk density and apparent porosity using the Archimedes principle in accordance with national standard GB/T 2997—2000, and for flexural and compressive strength at room temperature in accordance with GB/T 3001—2007 and GB/T 5072—2008.

The results showed that from the bottom to the top of the mold, apparent porosity increased, while bulk density, flexural strength, and compressive strength decreased. Based on this pattern, some manufacturers of porous plugs now employ an “upright” molding method—aligning the bottom of the mold with the tail end of the seating brick—to improve the physical properties of the tail section and enhance safety.

3.Study on the Effect of Water Addition on the Properties of Well Blocks

Standard specimens (40 mm × 40 mm × 160 mm) were prepared from the well-block castable using water additions of 4.3%, 4.1%, and 3.9% (wt%), designated as Groups A, B, and C, respectively. The specimens underwent heat treatments at 110°C for 24 h, 1100°C for 3 h, and 1550°C for 3 h. Bulk density and apparent porosity were measured according to the Archimedes principle (GB/T 2997—2000), while flexural and compressive strengths at room temperature were tested in accordance with GB/T 3001—2007 and GB/T 5072—2008. Thermal shock resistance was evaluated using an air-cooling method: specimens were held at 1100°C for 20 min followed by air cooling for 15 min; this cycle was repeated three times before measuring the room-temperature flexural strength.

The three groups of specimens exhibited comparable flexural and compressive strengths after treatment at 1550°C; however, Group A showed the poorest thermal shock stability. These results indicate that the water addition level significantly influences the physical properties of the well-block material across different temperature ranges. Provided that the castable’s installation performance is maintained, reducing the water addition helps improve the physical properties of the well-block.

(1) Strengthening the management of well-block installation on-site and standardizing oxygen lancing operations can extend the service life of the well-blocks.

(2) Improving the flexural strength of the well-blocks in the intermediate temperature range (700–900°C) can enhance their physical properties.

(3) Switching the well-block molding method to direct molding helps improve the physical properties of the well-blocks.

(4) Reducing the water addition during well-block molding helps improve the physical properties of the well-blocks.