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Stainless steel is known to be a versatile metal and is used in various industries right from kitchen appliances to aerospace. The secret behind its versatility lies in the composition of stainless steel. This article elaborates on the composition of stainless steel and its types according to the composition.
What is the composition of stainless steel?
Stainless steel is an alloy that contains at least 10.5% chromium. Depending on its grade and usage, it may contain various other elements in more or less quantities. Some of the popular alloying elements in the stainless steel include:
- Phosphorus, etc.
According to its composition, stainless steel is divided into the following types:
- Austenitic stainless steel
- Ferritic stainless steel
- Martensitic stainless steel
- Duplex stainless steel
Stainless steel composition: Popular grades
Here are some popular grades of stainless steel and their compositions.
Austenitic stainless steel:
Austenitic stainless steel’s composition includes around 16% chromium and 6% nickel. Series 300 and series 200 are popular grades of austenitic stainless steel. Commonly used austenitic stainless steel grades are:
304 austenitic stainless steel composition: The composition of 304 grade stainless steel includes 18% chromium and 8% nickel, while it also has about 0.8% carbon. It is also known as 18-8 stainless steel due to its composition (18% chromium and 8% nickel). Some of the key features of 304 austenitic stainless steel include corrosion resistance, ease of fabrication, ease of cleaning, aesthetics, etc. Thanks to these characteristics, 304 austenitic stainless steel is commonly used in:
- Tanks for storing a variety of liquids
- Food processing industries (breweries, milk production units, etc.)
- Kitchen appliances
- Chemical industry
- Heat exchangers, etc.
316 austenitic stainless steel composition: The composition of 316 grade stainless steel includes 16-18% chromium, 10-14% nickel, 2 to 3% molybdenum and some percentage of carbon. 316L stainless steel is the low-carbon version of the same grade. The 316 austenitic stainless steel is the second most widely used grade after 304 stainless steel. The composition of 316 stainless steel grade offers one of the key advantages i.e. better corrosion resistance to chlorides such as salt. As a result, 316 austenitic stainless steel turns out to be a material of choice in the coastal regions. Here are some of the common applications of the grade.
- Coastal architecture: steel railings, panels, etc.
- Stainless steel roofing solutions
- Chemical containers
- Food processing industry
- Labs & pharma equipment
- Medical equipment & implants, etc.
904 grade stainless steel:
904 grade stainless steel is low-carbon stainless steel. This grade of stainless steel is resistant to stress corrosion cracking and crevice corrosion. The composition of 904 grade stainless steel offers formability, toughness and weldability.
Ferritic stainless steel composition
The composition of ferritic stainless steel comprises a higher percentage of carbon as compared to austenitic stainless steel. The percentage of chromium ranges from 10.5% to 30%.
430 ferritic stainless steel composition:
430 stainless steel grade is one of the popular grades in the ferritic stainless steel family. The composition comprises a high level of chromium. Since it features good corrosion resistance and formability. The composition of 430 stainless steel grade has mechanical properties, which make it ideal for chemical applications. It is resistant to nitric acid too. Applications of 430 ferritic stainless steel include kitchen appliances, automotive, trims, etc.
434 ferritic stainless steel compositions
434 ferritic stainless steel is known to be non-hardenable. The composition of 434 ferritic stainless steel includes chromium, molybdenum, carbon, etc. The composition makes it an ideal choice for various industries including architecture, automotive, etc. Things such as furnace combustion chambers, dishwashers, gas burners, and so on.
Duplex stainless steel
Duplex stainless steel has a mix of ferrite and austenite types of stainless steel. The composition of duplex stainless steel comprises of very high content of chromium i.e. about 21-25% it also contains around 5% molybdenum. The composition of duplex steel makes it corrosion resistance and tough. As a result, duplex stainless steel is ideal to be used in chemical, oil and gas, marine, shipping industries, etc.
One of the popular grades of duplex stainless steel is 2205. Typically, the composition of 2205 duplex stainless steel is 22% Chromium and 5% Nickel.
Stainless steel composition: Role of alloying element
By now we know that what makes every grade of stainless steel different is alloying elements. Each element has its own advantages. Here is a guide on what features each element adds to stainless steel.
- Chromium: Chromium is an important element as stainless steel is defined by the minimum 10.5% of chromium. A higher percentage of chromium prevents steel corrosion.
- Nickel: Nickel enhances formidability while it also increases strength and corrosion resistance.
- Carbon: Generally, stainless steel has lower carbon content. This is because a higher level of carbon means higher chances of corrosion. On the other hand, carbon content increases the strength of stainless steel.
- Molybdenum: Molybdenum is known for increasing resistance to atmospheric corrosion.
- Nitrogen: Nitrogen offers protection against pitting corrosion.
Concluding remarks: How to select the right steel composition for your project?
Here are some tips to select the right stainless steel composition for your project or manufacturing needs.
- Determining needs: Firstly, understand the requirements of your projects, environmental conditions, etc. In some cases, such chemical industry, oil & gas industry, etc., the requirements are stringent, and one can not compromise on the required grade of stainless steel. However, in other cases, you may have a choice to select the stainless steel composition for your project.
- Check available options: Check stainless steel grades that are locally available. Procuring stainless steel locally can offer multiple advantages such as shorter delivery time.
- Select the best that suits you: Approach multiple vendors, compare grades, prices and delivery timelines and then select the one that suits your requirement the best.