Raw Materials: The primary raw materials used are iron ore, chromium, silicon, nickel, carbon, manganese, and sometimes molybdenum.
Electric Arc Furnace (EAF): The raw materials are melted together in an Electric Arc Furnace (EAF). The EAF uses high-power electric arcs to heat and melt the metals at temperatures around 1,500 to 1,600°C (2,732 to 2,912°F).
Refining: After melting, the molten steel is refined to remove impurities. This involves processes like oxidation, where unwanted elements like sulfur and carbon are reduced.
Alloying: Chromium is added to the molten steel, usually between 10.5% and 30%, depending on the type of stainless steel. Other elements like nickel, molybdenum, and nitrogen might be added to improve corrosion resistance, strength, and other properties.
2. Forming
Continuous Casting: The molten stainless steel is cast into semi-finished forms like slabs, billets, or blooms. This is done by pouring the molten steel into a mold, which rapidly cools it.
Hot Rolling: The semi-finished forms are then heated and passed through large rolling mills to reduce their thickness and shape them into flat sheets, plates, or other shapes. This process is called hot rolling because it occurs at temperatures above the recrystallization temperature of steel.
3. Annealing and Pickling
Annealing: The hot-rolled stainless steel is then annealed, a process of heating the steel to high temperatures and slowly cooling it. Annealing relieves internal stresses, improves ductility, and refines the grain structure.
Pickling: After annealing, the steel's surface is usually coated with scale (a layer of oxides). To remove this scale, the steel is pickled in a solution, typically of nitric and hydrofluoric acid. This restores the steel’s corrosion-resistant surface.
4. Descaling
Mechanical Descaling: In some cases, mechanical processes like grinding or brushing might be used to remove the scale instead of chemical pickling.
Electropolishing: An alternative to pickling, electropolishing involves using an electrochemical process to smooth and enhance the stainless steel's surface finish.
5. Cold Rolling
Cold Reduction: After descaling, the stainless steel is cold rolled. This involves passing the steel through rollers at room temperature to achieve the final thickness, improve surface finish, and enhance mechanical properties.
Further Annealing and Pickling: Cold-rolled stainless steel might undergo another round of annealing and pickling to refine its structure and surface finish.
6. Finishing
Cutting: The stainless steel is cut into desired shapes and sizes using processes like shearing, slitting, or sawing.
Surface Finishing: The surface of the stainless steel can be further treated to meet specific aesthetic or functional requirements. Finishes can range from brushed, polished, satin, or mirror finishes.
Coating: Depending on the application, the stainless steel might be coated with additional materials to enhance its properties. For instance, a passivation process can be used to further improve corrosion resistance.
7. Inspection and Quality Control
Testing: The finished stainless steel undergoes rigorous testing to ensure it meets the required specifications. Tests might include chemical analysis, tensile strength tests, corrosion resistance tests, and surface finish inspections.
Certification: Once the stainless steel meets all standards, it is certified and ready for use in various applications.
8. Packaging and Shipping
Packaging: The final products are carefully packaged to protect them from damage during transportation.
Shipping: The stainless steel is then shipped to manufacturers and other end-users for further processing or direct use.
