stainless steel

Many types of stainless steel have been developed to resist different corrosion environments and working conditions. Stainless steels are chromium containing steel alloys. The minimum chromium content of the standardized stainless steels is 10.5%. The Chromium makes the steel “stainless” and this means improved corrosion resistance.

The better corrosion resistance is due to a chromium oxide film that is formed on the steel surface. This extremely thin layer, under the right conditions, is also self-repairing.

Other alloying elements are added to enhance their structure and properties such as formability, strength and cryogenic toughness. These include metals such as:

  • Nickel 
  • Molybdenum 
  • Titanium 
  • Copper 

The main requirement for stainless steels is that they should be corrosion resistant for a specified application or environment. The selection of a particular “type” and “grade” of stainless steel must initially meet the corrosion resistance requirements. Additional mechanical or physical properties may also need to be considered to achieve the overall service performance requirements.

There are
five types of
stainless steel
as below:

The stainless steels containing chromium and nickel are identified as 300 Series types. Alloys containing chromium, nickel and manganese are identified as 200 Series types. The stainless steels in the austenitic group have different compositions and properties, but many common characteristics. They can be hardened by cold working, but not by heat treatment. In the annealed condition, all are essentially nonmagnetic, although some may become slightly magnetic by cold working. They have excellent corrosion resistance, unusually good formability, and increase in strength as a result of cold work. Type 304 (sometimes referred to as 18-8 stainless) is the most widely used alloy of the austenitic group. It has a nominal composition of 18% chromium and 8% nickel.

The stainless steels are straight-chromium 400 Series types that cannot be hardened by heat treatment, and only moderately hardened by cold working. They are magnetic, have good ductility and resistance to corrosion and oxidation. Type 430 is the general-purpose stainless of the Ferritic group.

Stainless steels have an annealed structure which is typically about equal parts of austenite and ferrite. Although not formally defined, it is generally accepted that the lesser phase will be at least 30% by volume. Duplex stainless steels offer several advantages over the common austenitic stainless steels. The duplex grades are highly resistant to chloride stress corrosion cracking, have excellent pitting and crevice corrosion resistance and exhibit about twice the yield strength as conventional grades. Type 329 and 2205 are typical alloys.

The stainless steels are straight-chromium 400 Series types that are hardenable by heat treatment. They are magnetic. They resist corrosion in mild environments. They have fairly good ductility, and some can be heat treated to tensile strengths exceeding 200,000 psi (1379 MPa). Type 410 is the general-purpose alloy of the Martensitic group.

The stainless steels are chromium-nickel types, some containing other alloying elements, such as copper or aluminum. They can be hardened by solution treating and aging to high strength.


Stainless steels of various kinds are used in thousands of applications.

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Cutlery, sinks, saucepans, washing machine drums, microwave oven liners, razor blades.

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Civil Engineering

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Exhaust systems, car trim/grilles, road tankers, ship containers, ships chemical tankers, refuse vehicles.

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Pressure vessels, process piping.

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Oil and Gas

Platform accommodation, cable trays, subsea pipelines.

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Surgical instruments, surgical implants, MRI scanners.

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Food and Drink

Catering equipment, brewing, distilling, food processing.

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Water and sewage treatment, water tubing, hot water tanks.

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Springs, fasteners (bolts, nuts and washers), wire.

Surface Finish

There are many different types of surface finish on stainless steel. Some of these originate from the mill but many are applied later during processing, for example polished, brushed, blasted, etched and colored finishes.

The importance of surface finish in determining the corrosion resistance of the stainless steel surface cannot be overemphasized. A rough surface finish can effectively lower the corrosion resistance to that of a lower grade of stainless steel.