Slide gates and upper/lower nozzles serve as key functional refractory materials in continuous casting production, directly contacting high-temperature molten steel. Their performance is centered on three core requirements: high-temperature resistance, erosion resistance, and structural stability. Based on an aluminum-carbon matrix, the material system achieves precise adaptation to different steel grades and casting conditions through scientific proportioning of core components and targeted addition of functional ingredients. Below is a professional analysis from two aspects: material classification and the functions of core components.

I. Classification of Core Materials and Application Scenarios

According to their composition and performance levels, these refractory materials are divided into four mainstream types, specifically matched to different operating requirements:

1. Aluminum-carbon (Al₂O₃-C): As a basic general-purpose material, it mainly consists of 70%-80% aluminum oxide (Al₂O₃), 10%-20% graphite (C), and special binders. This material combines good high-temperature resistance and erosion resistance with outstanding cost-effectiveness, making it suitable for conventional casting of carbon steel and low-alloy steel. It is a universal choice for slide gate plates, upper nozzles, and lower nozzles.
2. Aluminum-zirconium-carbon (Al₂O₃-ZrO₂-C): An enhanced material, it adds 10%-20% zirconium oxide (ZrO₂) to the aluminum-carbon base. The introduction of zirconium oxide significantly improves the material's resistance to molten steel and molten slag erosion, while optimizing high-temperature stability. It is applicable to casting conditions with strong corrosiveness, such as medium-high alloy steel, stainless steel, and special steel, and can meet higher service life requirements.
3. Magnesium-zirconium-carbon (MgO-ZrO₂-C): A special-purpose material, its core composition is a composite system of magnesium oxide (MgO), zirconium oxide (ZrO₂), and graphite. It exhibits extreme erosion resistance, especially against the strong corrosive effects of high-calcium and high-sulfur molten steel in high-carbon steel and special alloys. Despite its long service life, it has a relatively high cost, and is mainly used in special steel production scenarios with a large number of consecutive casts and harsh operating conditions.
4. Corundum-based: A dedicated material for upper nozzles, it uses fused corundum or sintered corundum as the main raw material, with an aluminum oxide content of ≥91%, high density, and excellent high-temperature resistance. It is divided into permeable and impermeable types by function: the permeable type features a porous structure, which can prevent nozzle clogging through argon purging, making it the preferred type for tundish upper nozzles; the impermeable type is mainly used in ordinary scenarios to undertake the connection function between the ladle/tundish and the slide gate plate.

II. Functions and Roles of Core Components

The performance of refractory materials is determined by the synergistic effect of various core components, with each component assuming clear functional responsibilities:

1. Aluminum oxide (Al₂O₃): As the core framework component of the material, it usually accounts for no less than 70%. With a melting point exceeding 2000℃, it can maintain structural stability in the molten steel environment of 1500-1700℃, providing the material with basic high-temperature resistance and mechanical strength. The aluminum oxide content directly affects the hardness and wear resistance of the material; the higher the content, the more excellent the basic mechanical properties and high-temperature stability.
2. Zirconium oxide (ZrO₂): An erosion-resistant reinforcing component that exhibits excellent chemical stability. In molten steel environments containing corrosive elements such as sulfur and calcium, it can form a stable protective structure, reducing the chemical erosion and penetration of the material by molten slag. It is a key functional component for improving the service life of the material, mainly used in mid-to-high-end enhanced material systems.
3. Graphite (C): A multi-functional auxiliary component with both lubricating and thermal shock resistance effects. Its layered crystal structure can reduce the friction coefficient of the slide gate plate, ensuring the smoothness of opening and closing actions and reducing wear on the sliding surface. Meanwhile, the low thermal expansion coefficient of graphite can alleviate thermal stress caused by alternating high and normal temperatures, reducing the risk of material cracking and improving thermal shock resistance.
4. Binders: Structural integration components, commonly using materials such as phenolic resin. Their core role is to bond dispersed raw materials such as aluminum oxide, zirconium oxide, and graphite into shape. In the high-temperature casting environment, binders are converted into a carbon-bonded structure, enhancing the bonding strength between various components, ensuring that the material does not undergo chipping or cracking during use, and simultaneously affecting the room-temperature strength and high-temperature stability of the material.

III. Core Logic of Material Design

The design essence of such refractory materials lies in the optimized combination of components based on operating requirements: aluminum oxide serves as the basic framework to ensure core performance; the addition of zirconium oxide for erosion resistance enhancement is determined according to the corrosiveness level of molten steel; graphite is used to optimize sliding performance and thermal shock resistance; and binders are employed to achieve structural integrity. The core difference between different materials lies in the adjustment of component proportions and the selection of functional ingredients, ultimately achieving precise matching of operating condition intensity, material performance, and cost control. Specifically, aluminum-carbon is selected for conventional operating conditions, aluminum-zirconium-carbon for medium-corrosion conditions, magnesium-zirconium-carbon for extreme-corrosion conditions, and corundum-based materials for dedicated upper nozzle applications.