Stainless Steel is a common name for metal alloys that consist of 10.5% or more Chromium (Cr) and more than 50% Iron (Fe). It is highly stain resistant. A somewhat dark metal, but looks bright because it reflects light. While the original form of stainless steel, (iron with around 12% Chromium) is still in widespread use, engineers now have a wide choice of different types (grades). In all, there are more than 100 different grades but these are usually sub-classified into distinct metallurgical "families" such as the austenitic, ferritic, martensitic and duplex families.



The proportions of iron to chromium may be varied and other elements such as nickel, molybdenum, manganese and nitrogen may be added to widen the range of capabilities. Each particular grade of stainless steel has its own unique mechanical and physical properties and will usually be produced in accordance with an established national or international specification or standard.

World Austenitic and Ferritic Stainless Steel Production (1985 - 2005)

Source: Inco, BNP Paribas Estimates

There are three major classes of stainless steel:

Austenitic: Chromium-nickel-iron alloys with 16-26% chromium, 6-22% nickel (Ni), and low carbon content, with non-magnetic properties (if annealed - working it at low temperatures, then heated and cooled). Nickel increases corrosion resistance. Hardenable by cold-working (worked at low temperatures) as well as tempering (heated then cooled). Type 304 (S30400) or "18/8" (18% chromium 8% nickel), is the most commonly used grade or composition.

Martensitic: Chromium-iron alloys with 10.5-17% chromium and carefully controlled carbon content, hardenable by quenching (quickly cooled in water or oil) and tempering (heated then cooled). It has magnetic properties. Commonly used in knives. Martensitic grades are strong and hard, but are brittle and difficult to form and weld. Type 420 (S42000) is a typical example.

Ferritic: Chromium-iron alloys with 17-27% chromium and low carbon content, with magnetic properties. Cooking utensils made of this type contain the higher chromium levels. Type 430 is the most commonly used ferritic.

• Equipment for the manufacture of food products and pharmaceuticals
• Plant for the treatment of potable and waste water
• Chemical and petro-chemical plant
• Components for automotive and aero engines
• Fuel and chemical tankers

Read More On The Manufacturing Process of Stainless Steel