1. Steelmaking Process
Steelmaking is the first step in steel plate production, converting raw materials such as iron ore into molten steel. Steelmaking processes primarily include the following:
Converter Steelmaking
Principle: Oxygen is used to oxidize carbon, silicon, manganese, and other elements in molten iron, removing impurities and adjusting the composition to produce qualified molten steel.
Features: High production efficiency and low cost, making it the most predominant steelmaking method currently.
Electric Furnace Steelmaking
Principle: Scrap steel is used as the primary raw material, which is melted and refined using electrode heating.
Features: High flexibility and the ability to produce specialized steel grades, but energy consumption and costs are relatively high.
External Refining
Purpose: Further remove impurities from molten steel, adjust the composition and temperature, and improve its quality.
Methods: Includes vacuum degassing and ladle refining.
2. Continuous Casting Process
Continuous casting is the process of continuously casting molten steel from steelmaking into billets. The continuous casting process offers advantages such as high production efficiency, high yield rate, and low energy consumption. The continuous casting process primarily includes:
Steel Preparation: Ensuring that the molten steel composition and temperature meet the required standards.
Tundish Casting: Molten steel is poured from a ladle into the tundish and then flows through the nozzle into the mold.
Mold Cooling: Molten steel cools within the mold to form the primary billet shell.
Secondary Cooling: After the billet shell leaves the mold, it passes through the secondary cooling zone for further cooling and solidification.
Drawing and Cutting: The solidified billet is drawn and cut into specified lengths.
3. Rolling Process
Rolling is the process of rolling continuously cast billets through a rolling mill into steel plates of the desired thickness and width. Depending on the rolling temperature and rolling method, rolling processes can be divided into the following:
Hot Rolling Process
Features: Rolling at high temperatures eliminates internal stresses in the billet, improves the microstructure, and enhances the ductility and toughness of the steel plate.
Process: Includes heating, rough rolling, finishing rolling, cooling, and coiling. Cold Rolling Process
Features: Rolling at room temperature further enhances the strength and hardness of the steel plate and improves its surface quality.
Process: Typically includes pickling, cold rolling, annealing, flattening, and shearing. Cold-rolled steel plates are often used in applications requiring high precision and surface quality, such as automotive and home appliance manufacturing.
IV. Heat Treatment Process
Heat treatment is the process of modifying the microstructure of a steel plate through heating, holding, and cooling to achieve the desired properties. Common heat treatment processes include:
Normalizing
Purpose: Refines the grain size and improves toughness and fatigue resistance.
Method: Heat the steel plate above the critical temperature, hold it at this temperature for a period of time, and then cool it in air.
Annealing
Purpose: Eliminate internal stresses and improve workability.
Method: Heat the steel plate to an appropriate temperature, hold it at this temperature for a period of time, and then slowly cool it.
Quenching
Purpose: Increases the hardness and strength of the steel plate.
Method: Heat the steel plate above the critical temperature, hold it at that temperature for a period of time, and then rapidly cool it (e.g., water quenching or oil quenching).
Tempering
Purpose: Eliminate quenching stresses and adjust hardness and toughness.
Method: Heat the quenched steel plate to a temperature below the critical temperature, hold it at that temperature for a period of time, and then cool it.
5. Surface Treatment Processes
Surface treatment is performed to improve the corrosion resistance, wear resistance, or decorative properties of steel plates. Common surface treatment processes include:
Galvanizing
Method: Hot-dip galvanizing, electrogalvanizing.
Purpose: Form a zinc layer on the steel plate surface to improve corrosion resistance.
Coating
Method: Spray coating, roller coating.
Purpose: Form a protective film on the steel plate surface to improve corrosion resistance or decorative properties.
Shot blasting/sand blasting
Purpose: Clean the steel plate surface, increase surface roughness, and improve coating adhesion.
VI. Finishing and Inspection Process
Finishing
Contents: Includes straightening, cutting, grinding, etc., to ensure that the steel plates meet the specified dimensional accuracy and surface quality.
Inspection
Contents: Includes chemical composition analysis, mechanical property testing, and non-destructive testing to ensure that the steel plate quality meets standard requirements.
