Different Types of Stainless Steel
When people use the term “stainless steel,” they often use it as a “catchall” term, but in reality, there are several different types of stainless steel with a variety of uses.
Stainless steel is an alloy that is produced by combining a variety of different base metals to create a new material. Like with other alloys, the final product is considerably stronger than each of the source materials would be on their own.
The History Of Stainless Steel
People have been experimenting with metal alloys for thousands of years. While examples of iron smelting can be found as far back as 1800 B.C., the introduction of crucible steel goes as far back as 300 B.C.
Stainless steel is a very versatile material. Through the years, engineers have experimented with the production of alloys.
By adding and removing certain metals, they were able to produce different types of stainless steel with different characteristics and applications. For example, it is used in everything from the production of kitchen utensils to components for construction projects.
Producing Different Types of Stainless Steel
When producing stainless steel, several different materials can be used to achieve different results. These include:
- Carbon
Stainless steel with high carbon content is much more durable and longer-lasting than other alloys. This type of stainless steel is popular for the production of food-grade utensils and cooking implements. - Chromium
Stainless steel made with chromium is much more resistant to corrosion, stains, and tarnishing. One well-known example of this type of stainless in use is the Gateway Arch in St. Louis. - Nickel
Making stainless steel with nickel improves the formability, weldability, and ductility of the material. This also improves its corrosion-resistant properties. Nickel is what allows for stainless steel to be such a versatile alloy.
The Three Primary Types of Stainless Steel
While there are thousands of different types of stainless steel alloy that can be produced, most alloys will fall into one of the following three categories.
- Austenitic stainless steel
There are two main characteristics of this type of stainless steel. First, there is a lot of chromium included during the production of austenitic stainless steel. Items produced with this material are more corrosion-resistant. Second, these items tend to be non-magnetic, although they can become magnetic with a cold forming process. These are the most common types of stainless steel alloys. - Ferritic Stainless Steel
This type of stainless steel is the second most common type of alloy and is also magnetic. Items produced with this alloy can be hardened through cold forming and also tend to be less expensive than other types due to the lower nickel content. - Martensitic Stainless Steel
This material is the least common type of stainless steel alloy. Martensitic stainless steel is used in applications where high tensile strength is needed or a lot of impact resistance. In many cases, this material is also combined with a protective polymer coating to improve corrosion-resistance
Different Grades of Stainless Steel Alloys
Within the three primary categories mentioned above, there are also different grades of stainless steel.
Within the austenitic steel types, there are two main grades – grade 304 and grade 316. Grade 304 is known for its high tensile strength of roughly 621 MPa (90 ksi). Grade 316 stainless steel also has a tensile strength of 579 MPs (84 ksi), making the two grades reasonably similar in this regard.
They also both have a high maximum operating temperature. Grade 304 has a maximum temperature of 870°C (1598°F) and Grade 316 has a maximum of 800°C (1472°F).
When comparing 304 vs. 316 stainless steel, one major difference is resistance to chlorides such as salt. Grade 316 is more resistant to the elements, making it a more desirable stainless steel for things like maritime applications.
Ferritic stainless steel also has two main grades – grade 430 and grade 434. Grade 430 stainless steel isn’t as strong as either of the austenitic steels but offers better resistance to nitric acid. It is also still strong enough for most heavy-duty applications.
Grade 434 steel has high tensile strength and maximum operating temperature and is tougher than the 430 grade, including better pitting resistance.
Martensitic stainless steel has only one grade, grade 420. This grade offers slightly less resistance to chemicals than the austenitic and ferritic steels, but it still has good resistance to things such as some alkalis, mild acids, water, and food compounds. It also has great tensile strength and impact resistance. This makes it ideal for producing items like cutlery.
Duplex Stainless Steel
Duplex stainless steel is a family of stainless steel that is made of austenitic steel and ferritic steel in nearly equal proportions. This type of stainless steel is both stronger and more resistant to corrosion than your typical types of stainless steel. Duplex stainless steel is also more ductile than ferritic grades, however, it is not quite as ductile as the austenitic grades.
One of the main differences in the composition is that duplex stainless steel is made with a higher chromium content and a lower nickel content. This not only makes the material stronger, but it also provides cost benefits. For these reasons, duplex stainless steel is often used in applications like pipes and risers in offshore oil rigs.
Grades of Duplex Stainless Steel
Just as with the other types of stainless steel, duplex stainless steel is also broken down into different grades or groups. The three primary groups are based on the pitting and the corrosion resistance of the material.
- Standard Duplex Steel
Standard duplex steel has a PREN range of 28-38. This is the most typical type of duplex steel used today. It is also sometimes called Grade EN 1.4462 or 2205. - Super Duplex Steel
With a PREN range of 38-45, super duplex steel was created for use in the oil & gas industry and the chemical industry. This grade of steel is stronger and far more corrosive resistant but is more difficult and more costly to process than standard duplex steel. This is typically grade EN 1.4410. - Duplex 2507 Stainless Steel
Duplex 2507 stainless steel is another form of super duplex steel. This material is made with 25% chromium, 4% molybdenum, and 7% nickel. This type of stainless steel is known for its resistance to chloride stress corrosion cracking, high thermal conductivity, and a low coefficient of thermal expansion. - Zeron 100 Stainless Steel
Zeron stainless steel is a super duplex stainless steel that was developed by Rolled Alloys. It contains 25% chromium, 7% nickel, 3.6% molybdenum, along with copper and tungsten additions. - Lean Duplex Grades
Lean duplex steel has a PREN range of 22-27 and was created for use in less demanding applications such as general building and construction. While the corrosion resistance is going to be similar to standard austenitic steel, it has better strength and mechanical properties.
Applications of Duplex Stainless Steel
Duplex stainless steels are very commonly used in more demanding applications due to their corrosion resistance properties, high mechanical properties, and how strong the material is. This makes the material very popular in a wide variety of industries.
You can find duplex stainless steel used in the oil and gas industry, chemical engineering industry, water and energy industries, architecture industry, and in the construction of things like bridges, seawalls, tunnels, and piers.
18/10 Stainless Steel and Other Types of Stainless Steel
When discussing stainless steel alloys, you’ll typically hear numbers such as 18/10, 18/8, and 18/0 used. These numbers identify the percentage of chromium and nickel that are present in a particular alloy.
For example, 18/8 stainless steel is 18% chromium and 8% nickel; 18/0 stainless steel is 18% chromium and contains roughly .75% nickel, and so on. The chromium-nickel mixture is important to know when deciding on the right alloy for your needs.
For example, if you’re a professional cook, you may have specific requirements for the strength, durability, or heat resistance of various tools and appliances in your kitchen. Understanding the composition of the alloys used in the production of equipment will help choose stronger, longer-lasting products for each application.
The Melting Points for Different Grades of Stainless Steel
One of the more important considerations when choosing the right type of stainless steel for your component or application is the melting point of the specific grade.
One of the reasons stainless steel is chosen over other types of materials, for example, plastic polymers, is its ability to stand up to high-temperatures and still retain its strength and durability.
When comparing the melting points of steel alloys, the number is usually given in a range due to the variations used in the metals used in the production. That number also relates to the metals’ resistance to stress, corrosion, cracking, and other attributes.
As a general rule, metals that have been heat-treated have the following melting points:
- Grade 304: 1400-1450°C (2552-2642°F)
- Grade 316: 1375-1400°C (2507-2552°F)
- Grade 430: 1425-1510°C (2597-2750°F)
- Grade 434: 1426-1510°C (2600-2750°F)
- Grade 410: 1480-1530°C (2696-2786°F)
- Grade 420: 1450-1510°C (2642-2750°F)
It is also important to remember that the maximum use temperatures recommended are usually lower than the maximum number listed in the above chart.
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