How to improve the life of converter taphole

The tapping hole serves as the sole passage for molten steel to flow from the converter into the ladle. During actual production, the converter's tapping hole handles substantial steel flow and is continuously subjected to high-temperature molten steel erosion and highly oxidizing slag corrosion. This leads to various issues such as severe localized erosion and irregular shapes. The significantly reduced service life and frequent replacement of the tapping hole adversely affect molten steel quality and production stability. At a certain steel mill, an 80-ton converter experienced an average nozzle lifespan of only about 180 furnaces due to factors like poor nozzle material quality, high tapping temperature, and strong oxidizing conditions. Through continuous exploration, practical testing, and technical breakthroughs, the service life of the nozzle lining bricks was significantly extended. This led to a marked reduction in converter smelting cycles, improved converter operating rates, and delivered substantial economic and social benefits.

Mechanism of Ladle Nozzle Damage

The shape of the inner wall of the converter taphole significantly impacts steelmaking production. An excessively small taphole diameter prolongs tapping time, increasing secondary oxidation of molten steel, accelerating temperature drop during tapping, disrupting the converter smelting cycle, and reducing productivity. Conversely, an overly large inner diameter complicates slag containment, impairs alloy absorption efficiency, and heightens the risk of taphole perforation accidents.

During tapping, molten steel and slag flow through the outlet with immense impact force, causing friction and erosion against the inner wall and directly inflicting mechanical damage. At typical tapping temperatures of 1680°C to 1710°C, the outlet material softens or even melts under the influence of high-temperature molten steel, significantly reducing its strength and leading to outlet failure. Oxygen atoms in molten steel and slag can displace carbon atoms from the magnesium-carbon refractory material of the taphole, causing the refractory structure to become porous and weakening its strength. Low MgO content in the slag promotes reactions between SiO₂ in the slag and carbon atoms in the taphole, further accelerating chemical erosion of the taphole.

Measures to increase service life

Improvements were made to the tapping hole dimensions. The inner diameter of the tapping hole lining brick was increased from 130 mm to 140 mm, while the outer diameter was increased from 170 mm to 180 mm. This resulted in an average reduction of 60 seconds in tapping time. The shorter tapping duration significantly mitigated the oxidative erosion and mechanical scouring of the tapping hole inner wall caused by high-temperature molten steel.

Optimize the material composition of the tapping hole. Based on operational requirements, the lining bricks exhibit excellent thermal stability, strong slag resistance, and resistance to molten steel erosion. During lining material selection, enhancing MgO purity and carbon content in raw materials serves as the primary means to improve lining properties. Adding iron-based antioxidants endows the tapping hole with superior oxidation resistance, high-temperature corrosion resistance, erosion resistance, and minimal high-temperature creep, thereby extending the service life of the lining bricks.

Lowering tapping temperature. Measures to reduce tapping temperature include implementing online and offline ladle red-hot tapping, covering ladles and tundishes for insulation, and employing higher-performance insulating agents. Achieving fully protected pouring on continuous casting machines enables low-superheat steel pouring. Through these measures, the average pouring temperature was reduced by 15°C to below 1680°C. This significant temperature reduction mitigates erosion and corrosion of the tapping hole by high-temperature molten steel and slag, effectively extending its service life.

Promoting high-carbon steelmaking technology. By adopting high-carbon steelmaking technology, the oxidizing properties of molten steel and slag at the final stage have been effectively reduced, mitigating oxidative erosion of the tapping hole by molten steel and slag. This creates favorable conditions for extending the service life of the tapping hole.

Implementing dual slag-blocking tapping. After completing the previous furnace's tapping, the tapping hole is sealed with a slag-blocking plug. During the later stages of tapping, slag-blocking balls are added into the furnace from above the furnace opening. This dual slag-blocking method effectively prevents erosion and scouring of the tap hole lining bricks by high-temperature furnace gases and slag during blowing and tapping.

Maintenance of the Tap Hole. Enhanced maintenance measures for the tap hole include: First, utilizing specialized tools for rapid replacement of the tap hole lining bricks. Second, when replacing the lining bricks, fill the surrounding area uniformly with filler material and increase the sintering temperature to prevent the lining from deforming into a gourd shape, which could cause spillage or penetration by molten steel. Third, ensure the replaced tapping hole remains perpendicular to the furnace centerline and maintains an appropriate distance from the furnace opening to guarantee complete steel discharge.

Through improvements in taphole dimensions, material replacement, and optimized maintenance procedures, the plant significantly extended the service life of its tapholes. Post-modification, the average taphole lifespan reached approximately 300 furnaces per unit, later increasing to 350 furnaces per unit. This extended taphole life not only shortened smelting cycles but also improved alloy recovery rates and molten steel quality.