Austenitic SS is the largest family of stainless steels, making up about two-thirds of all stainless steel production. They possess an austenitic microstructure, which is a face-centered cubic crystal structure. This microstructure is achieved by alloying steel with sufficient nickel and/or manganese and nitrogen to maintain an austenitic microstructure at all temperatures, ranging from the cryogenic region to the melting point. Thus, austenitic stainless steels are not hardenable by heat treatment since they possess the same microstructure at all temperatures.
There are two subgroups of austenitic stainless steel 200 & 300 series. KOBS INDIA Group produces only 300 series stainless steel pipes tubes which achieve their austenitic structure primarily by a nickel addition.
300 series stainless steels are the larger subgroup. Most common austenitic stainless steels are:
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.
Duplex Stainless Steel is 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.
Duplex Stainless Steel is widely 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.
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 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.
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 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 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.