200 Series Stainless Steels
What is chrome-manganese stainless steel?
Austenitic steels, which includes both the 200 and 300 series stainless steels, are defined by their face-centred cubic structure. That is, the crystal structure has one atom at each corner of the cube and one in the middle of each face.
This is as opposed to ferritic steels, which are characterized by a body-centered cubic structure.
Nickel is the most commonly used element to produce this crystal structure, however, due to a shortage of nickel during and immediately after World War II, efforts were made to reduce use of the metal. This led to the substitution of nitrogen for nickel in the production of some austenitic corrosion-resistant steels, and the creation of 200 series of stainless steels.
While nitrogen alloyed in steel will also form a face-centred cubic structure, it results in harmful chromium nitrides and increases gas porosity. The addition of manganese allows more nitrogen to be safely added, however, nickel cannot be completely removed from the alloy. 200 series stainless steels are, consequently, characterized by their nitrogen and manganese content.
Production and demand for low nickel stainless steels surged in the 1980s as nickel prices soared and, again, efforts were made to reduce use of the metal.
This led to the development of a huge production increase in India. Asia is now a major source for, and consumer of, this family of steels.
While corrosion resistant, the 200 series has a lower ability than 300 series to protect against pitting corrosion, which occurs in environments that have high moisture and chlorine contents, as well as crevice corrosion, which results in stagnant liquid and high acid environments.
This is because, in order to decrease the nickel content, the chromium content must also be reduced, thereby, lowering corrosion resistance.
Series 200 stainless steels have excellent impact resistance and toughness, even in low (even cryogenic) temperatures. They are generally harder and stronger than 300 series steels, primarily due to their higher nitrogen content, which acts as a strengthener. Because they are austenitic, both the 200 and 300 series' of stainless steels are not magnetic.
Although austenitic steels are more expensive than their ferritic counterparts, the 200 series in cheaper to produce than 300 series steels because of their lower nickel content.
Due to its lower corrosion resistance, the range of applications for 200 series stainless steels is narrower than 300 series steels. It is not recommended for use in chemical environments but has found its way into many household items.
Some applications for 200 series stainless steel include in:
- dishwashers and washing machines
- cutlery and cookware
- in-house water tanks
- indoor and non-critical outdoor architecture
- food and beverage equipment
- automobiles (structural)
- automobiles (decorative)
200 Series Stainless Steel. CrMn Grades. ASSDA Technical Bulletin. Edition 1: October 2006.
New 200-Series Steels: An opportunity or a threat to the image of stainless steel? The International Stainless Steel Forum (ISSF). November 2005.
Chemical Composition of 200 Series Stainless Steels
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