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.
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.
When producing stainless steel, several different materials can be used to achieve different results. These include:
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.
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 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.
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.
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.
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.
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:
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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