Manufacturing process of carbon steel plates

Carbon steel plates are indispensable basic materials in various industrial sectors, widely used for their exceptional strength, versatility, and relatively low cost. Made primarily from plain carbon steel or carbon steel with a carbon content of less than 2.11%, these plates do not have any deliberately added metal elements. Besides carbon, they contain small amounts of sulfur, silicon, phosphorus, manganese, and other elements, contributing to their unique characteristics. Thanks to their excellent comprehensive properties and affordability, carbon steel plates are commonly used in the construction industry for building stable steel structures, providing essential support for high-rise buildings. In the machinery manufacturing sector, carbon steel plates serve as key raw materials for producing mechanical parts, ranging from precision small components to large structural elements. The vital role of carbon steel plates in these industries cannot be overstated.

Iron Smelting: The Beginning of Everything

The journey of carbon steel plate manufacturing begins with the extraction of iron from iron ore. Once mined, the ore contains impurities and must undergo crushing and beneficiation before it can be processed further. The selected iron ore is then fed into a blast furnace along with coke, limestone, and other raw materials. As the reactions inside the furnace take place, molten iron flows out from the bottom of the blast furnace in a liquid state at extremely high temperatures, marking the transformation of ore into iron. This pivotal step lays the foundation for the subsequent steelmaking process.

Steelmaking: Removal of Impurities and Blending of Elements

While the molten iron emerging from the blast furnace is an essential component, it cannot be directly used to manufacture carbon steel plates. It requires further refinement to transform it into steel. One common method used for steelmaking is converter steelmaking, where molten iron is poured into a converter, and oxygen is blown in from the top. The oxygen initiates an oxidation reaction, removing impurities like carbon, silicon, manganese, and phosphorus, effectively purifying the molten iron.

For example, when carbon reacts with oxygen, carbon monoxide gas is formed and discharged, reducing the carbon content in the molten iron. This process releases a large amount of heat, causing the furnace temperature to soar to around 1600°C, which negates the need for additional heating. To further remove impurities such as phosphorus and sulfur, materials like lime are added to form slag, which floats on top of the molten steel and can be easily separated.

Continuous Casting or Rolling: Giving Shape

The refined molten steel, still in its liquid form, has excellent fluidity and is highly susceptible to forming. This molten steel is fed into either a continuous casting machine or a rolling mill. The continuous casting machine, with its crystallizer, acts like a precise mold. It cools the molten steel rapidly, transforming it from liquid to solid, and forms continuous ingots. The ingots are then processed further through continuous rolling, where they pass through multiple rolls to achieve the desired shape and size.

Heat Treatment: Performance Enhancement

Once the carbon steel plates are formed through continuous casting or rolling, they undergo heat treatment to enhance their mechanical properties. Heat treatment involves heating, insulating, and cooling the steel to adjust its internal structure for specific properties such as hardness, toughness, and wear resistance.

- Normalizing: This heat treatment process involves heating the steel plate to 30-50°C above the critical temperature, holding it at that temperature, and then cooling it in air. This process refines the grain structure and enhances the overall strength of the steel.

- Quenching: In quenching, the steel plate is heated to above the critical temperature and then rapidly cooled by immersing it in a cooling medium such as water or oil. This rapid cooling rate creates a martensitic structure, significantly improving hardness and wear resistance. However, the quenching process makes the steel more brittle and increases internal stress, necessitating tempering.

- Tempering: Tempering is the process of heating the quenched steel to below the critical temperature, holding it at that temperature, and then cooling it. There are different tempering temperatures depending on the desired properties:

Low-temperature tempering (150-250°C) reduces internal stress while maintaining high hardness, suitable for cutting tools.

Medium-temperature tempering (350-500°C) enhances elasticity, ideal for parts like springs.

High-temperature tempering (500-650°C) produces a balanced combination of strength, hardness, and toughness, making it suitable for critical parts like shafts and gears.

Surface Treatment: Protection and Beautification

Once the carbon steel plates are heat-treated, they undergo surface treatment to protect against corrosion, improve aesthetic appeal, and enhance durability.

- Spraying: A common surface treatment method involves cleaning the carbon steel plate surface to remove impurities such as oil and dust, followed by electrostatic spraying. This process involves applying a powder coating to the surface, which offers an extra layer of protection and a smooth, uniform finish.

- Galvanizing: Galvanizing, which includes both hot-dip galvanizing and electro-galvanizing, is an effective method of protecting carbon steel from rust. In hot-dip galvanizing, the steel plate is immersed in molten zinc, forming a zinc-iron alloy layer and a pure zinc layer. This double-layer structure acts like a solid armor, providing long-lasting protection against corrosion. Electro-galvanizing uses the principle of electrolysis to deposit a layer of zinc on the steel plate, creating a more uniform and fine finish, which is often used for products with high appearance standards, such as automotive parts and household appliances.

- Chrome Plating: Chrome plating enhances the surface properties of carbon steel plates by providing a layer of chromium that improves hardness, wear resistance, chemical stability, and aesthetics. Chrome plating is especially useful for components that require additional surface protection or decorative qualities.