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Stainless steels are divided into three
main groups, namely Martensitic, Ferritic
and Austenitic.

Martensitic
A steel containing 11% to 18% chromium is magnetic
and can be hardened by heat treatment. Suitable for less onerous corrosive conditions. Welding of these steels is not recommended. Carbon content varies from 0.08% to 2.0%.

Ferritic
Contains increased chrome content to a minimum level of 17% which enables it to retain a higher corrosion resistance. Magnetic. The carbon range remains the same as that of the Martensitic.

Austenitic
This group of alloys contains a chrome content ranging from 18% to 25% and a nickel content of 8% to 20%. The addition of elements such as Titanium, Niobium and Molybdenum increases its chemical resistance. Mechanical properties are increased by coldworking. A non-magnetic range of steel, which unlike the Martensitic steels cannot be hardened by heat treatment.

GRADES
316
Contains molybdenum and is highly resistant to corrosion, it has a wide application in the chemical, photographic and marine engineering fields. Available in all forms, fully weldable, it is easily worked and takes a good polish. Not recommended for temperatures exceeding 300°C. Available with a low carbon content. Non-magnetic.

321
An Austenitic steel containing titanium which acts
as a stabiliser against the effects of weld decay. Extensively used in the manufacture of welded plant and equipment in the dairy, brewing and chemical industries. Maximum service temperature is 800°C. Available in all forms.
Non-magnetic

 

304
This specification is a good general purpose
austenitic steel, having good corrosion resistance
and cold forming properties. Popular in the dairy and food industries. A good steel for polishing. Maximum
service temperature is 300°C. Available with low carbon content. Mainly a sheet specification, but can
be obtained in bar and tube form. Non-magnetic.

303
A free machining grade available in hexagon and round bar form. Contains sulphur or selenium, allowing rapid machining. Non-magnetic.

325
Similar to T.303. A free machining variant of T.321.
Fully weldable. Non-magnetic.

416
A Martensitic free machining grade available in bar form. Heat treatment advisable after welding. Magnetic.

431
A ferritic hardened steel. Poor welding qualities, not
fully corrosion resistant, but good machining qualities provide a wide range of general engineering applications. Magnetic.

430
A ferritic, non-hardenable steel with good cold
forming properties. Mainly produced in sheet form. Used extensivelyin the catering industry. Takes a good polish and has good resistance to scaling up to 800°C. Can be welded but there is a tendency for welds to be brittle. Magnetic.

310
A 25% chrome, 20% nickel Stainless. Maximum service temperature of 1100°C and possesses
good welding qualities. Suitable for high temperature application. Available in sheet/plate/pipe and bar form.
Non-magnetic.

NOTE:
The corrosion resistance properties of stainless steel can be attributed to an extremely thin oxide layer om its surface. This oxide or Passive film can only form on clean, uncontaminated metal. When working with stainless steel, contamination can occur as a result of welding, grinding, forming, contact with other metals and even general workshop storage and handling.