Stainless steel is an iron-chromium alloy containing a minimum of 10.5% chromium by weight. The chromium reacts with atmospheric oxygen to form a stable, self-repairing passive oxide layer — the chemical foundation of its corrosion resistance. Nickel, molybdenum, manganese, and nitrogen are added in controlled proportions to produce the major grade families: austenitic (304, 316), ferritic (430), martensitic (410), and duplex (2205). Every downstream property — corrosion resistance, surface finish, mechanical strength — is determined by decisions made at each stage of manufacturing.
Stainless steel production begins with a precisely calculated charge mix: steel scrap, ferrochrome, ferronickel, and other ferroalloys are proportioned to hit the target chemical composition for the grade being produced. High-nickel austenitic grades require nickel-bearing inputs; high-chromium grades demand more ferrochrome. Raw material quality is the first — and most consequential — control point in the manufacturing chain.
The charge is melted in an electric arc furnace at temperatures above 1,600°C. Oxygen is injected during melting to begin decarburization and remove impurities. EAF melting suits scrap-heavy charges and allows tight initial chemistry control before the melt moves to the refining stage.
After primary melting, the liquid steel is transferred to an Argon Oxygen Decarburization (AOD) converter. Argon and oxygen are injected simultaneously through tuyères at the base of the vessel. The argon dilutes the carbon monoxide partial pressure, allowing carbon to be removed to very low levels — often below 0.03% — without losing chromium through oxidation. AOD is the step that makes low-carbon grades such as 304L and 316L possible and defines the chemical precision of the final product.
The refined melt is cast into slabs, blooms, or billets through continuous casting machines. Controlled cooling rates and electromagnetic stirring during solidification minimize segregation and establish a uniform grain structure. Slab dimensions are selected based on the intended product form — coil, plate, bar, or tube.
Slabs are reheated to 1,150–1,260°C and passed through rolling mills to reduce thickness and develop the grain structure. For flat products, this produces strip coil, sheet, or plate. The resulting scaled surface (No. 1 finish) requires further processing before most fabrication applications.
Cold rolling refines thickness further and improves surface quality. Because cold work strain-hardens stainless alloys, annealing is required at intermediate and final stages to restore ductility and relieve residual stress. After annealing, the surface oxide scale is removed by pickling — treatment with a nitric-hydrofluoric acid solution — which dissolves the oxide layer and restores the passive layer. This sequence establishes standard mill finishes: 2B (cold-rolled, annealed, pickled, skin-passed) is the most common delivery condition for flat austenitic products.
Final surface finish designations range from the matte No. 1 and 2B through brushed No. 4, mirror-polished No. 8, and electropolished. Electropolishing removes a controlled layer of surface metal by electrolytic action, enhancing passive layer uniformity and achieving roughness values as low as Ra 0.05 μm — a requirement in pharmaceutical, food processing, and semiconductor environments.
Stainless steel is produced by melting a charge of steel scrap and ferroalloys in an electric arc furnace, refining the melt in an AOD converter to remove carbon while retaining chromium, continuously casting into slabs, and then hot- and cold-rolling to final dimensions. Annealing and pickling restore ductility and the passive layer. The finished coil, sheet, or bar is then cut, formed, welded, and surface-treated for specific applications.
Stainless steel contains a minimum of 10.5% chromium by mass, which forms the protective passive oxide layer. Common grades add 8–12% nickel (304, 316) for austenitic structure and deeper corrosion resistance, and 2–3% molybdenum (316) for resistance to chloride pitting. Carbon is typically kept below 0.08% — or 0.03% for 'L' grades — to prevent sensitization during welding.
Walmay will help match the right stainless product form and specification for your application, confirm quantities and packing needs, and provide requested documents based on order requirements.
