Informal Essay About Stainless Steel - Tianjin Zhongyuanyuanda Steel Co.,Ltd.

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Informal Essay About Stainless Steel

Stainless steel is not a single material but the name for a family of corrosion resistant steels. Like many scientific discoveries the origins of stainless steel lies in a serendipitous accident. In 1913 Sheffield, England, Harry Brearley was investigating the development of new steel alloys for use in gun barrels. He noticed that some of his samples didn't rust and were difficult to etch. These alloys contained around 13% chromium.

The first application of these steels was in cutlery for which Sheffield subsequently became world famous. Simultaneous work in France led to the development of the first austenitic stainless steels.

Grade 1.4301 (304)

This austenitic grade is the most commonly used and is suitable for a broad range of construction applications. It typically contains alloying elements of at least 18% chromium and 8-10% nickel. Marginal differences in composition have no significant effect on the material's excellent all-round corrosion resistance.

Grade 1.4401 (316)

This austenitic grade is recommended for highly corrosive areas such as marine locations or heavily polluted industrial environments. The addition of a small proportion of molybdenum (around 2%) and an increase in the nickel content to 10-13% provide a more robust passive film and hence higher resistance to corrosion.

Grade 1.4462

This is a high strength duplex stainless steel with a minimum chromium content of 22%, a nickel content of 4.5 – 6.5% and a molybdenum content of 2.5 – 3.5%. It offers superior corrosion resistance especially against pitting and crevice corrosion.

Standard Classifications of Stainless Steel

The old AISI three digit stainless steel numbering system (e.g. 304 and 316) is still commonly used. New grades are defined under the SAE and ASTM system that uses a 1-letter + 5-digit UNS number. An example of this is the new term for 304, which is S30400. Other designations include old BS and EN numbers like 304S31 and 58E.

Some grades are not covered by standard numbers and could be proprietary grades or be named using standards for specialist products like welding wire.

Grade Selection of Stainless Steel

The grade selection process for stainless steel is a compromise between the desired properties of the finished product.

When selecting a particular grade of stainless steel, it is essential to consider the primary properties required, such as corrosion resistance and heat resistance. Important consideration must also be given to the secondary properties, like physical and mechanical properties. These properties will determine other factors such as the ease of fabrication of any candidate grades.

If the secondary properties are not adequate, it may not be possible to viably and economically produce the required product.

An example of this is 303 stainless steel. It has excellent machinability due to an addition of Sulphur. However, the Sulphur also gives 303 poor weldability, corrosion resistance and formability.

Selecting the correct grade will ensure the product will have a long trouble-free life combined with cost-effective fabrication and installation.

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