About Stainless Steels
Stainless steel is a family of iron-based alloys containing a minimum of approximately 11% chromium — the element responsible for its resistance to rust and its heat-resistant properties. Depending on grade, stainless steels may also include carbon, nitrogen, nickel, molybdenum, titanium, niobium, copper, silicon, sulfur, aluminium and selenium in varying proportions. Individual grades are usually identified by a three-digit number, such as 304 or 316.
Corrosion resistance comes from chromium forming a thin, self-healing passive oxide film on the metal’s surface. This film continuously regenerates in the presence of oxygen, protecting the base metal from attack. Because of this resistance to corrosion and staining, combined with low maintenance and a clean, familiar finish, stainless steel is used across countless industries — supplied as sheet, plate, bar, wire, or tube — wherever both strength and durability are required.
What Strengthens Corrosion Resistance
- Increasing chromium content above 11%
- Adding 8% or more nickel
- Adding molybdenum, which also improves resistance to pitting corrosion
- Adding nitrogen, which improves pitting resistance and mechanical strength
Stainless Steel Series at a Glance
| Series | Common Grades | Characteristics |
|---|---|---|
| 200 Series (Austenitic Cr-Ni-Mn) | 201, 202 | Cold-work hardenable, general-purpose, more economical alternative to 300 series grades |
| 300 Series (Austenitic Cr-Ni) | 304 / 304L | The classic 18/8 grade and the most widely used stainless steel; 304L carries lower carbon for better weldability |
| 316 / 316L | Known as marine grade — molybdenum addition resists chloride corrosion and pitting; used in food, surgical and nuclear reprocessing applications | |
| 321 | Titanium-stabilised version of 304 with lower risk of weld decay at elevated temperatures | |
| 400 Series (Ferritic / Martensitic) | 409 | Most economical grade; widely used for automotive exhaust systems |
| 410 / 420 | Hardenable martensitic grades with good wear resistance; used in cutlery and tooling | |
| 430 | Decorative ferritic grade with good formability, e.g. automotive trim | |
| 440A / 440B / 440C | High-carbon martensitic grades hardenable to roughly 58 HRC; used in cutting tools and blades | |
| 600 Series (Precipitation Hardening) | 630 (17-4 PH) | Combines high strength with corrosion resistance through an age-hardening heat treatment |
| 900 Series (Austenitic Cr-Mo) | 904 | Higher chromium and molybdenum content than 316 for superior corrosion resistance |
Spreadon supplies austenitic, ferritic, martensitic, duplex and precipitation-hardening stainless steel grades to Aerospace, Defence, Power and Industrial customers, with full traceability and mill certification on every order.