The Ultimate Guide for Austenitic Stainless Steel

Austenitic Stainless Steel

Austenitic stainless steel is one of the top 5 varieties of stainless steel. The other 4 include martensitic, duplex, ferritic, and precipitation-hardened steel.

If you’re curious about the reason why austenitic is the most well-known material, this guide is for you.

Let us also examine it more carefully and compare this specific steel to other types.

This article will surely help you learn about austenitic steel uses, its properties, and its advantages.

Let’s now find out!

Identifying Austenitic Stainless Steel

How Can You Tell Stainless Steel Austenitic
Magnetic Test on Austenitic SS

Austenitic SS is a widely used type of stainless steel. It is extremely oxidation resistance, ductile, and non-magnetic material.

Before you purchase an austenitic type of stainless steel, it is very essential to know how it differs from others.

So, how to know if the stainless steel is austenitic? What to do?

  • First, perform a magnetic test. Austenitic steel is not magnetic, while another type is magnetic, like ferritic. To perform the test, a magnet can be placed against the stainless steel. If the steel is not attracted to the magnet, it is austenitic.
  • Second, identify by its microstructure. The austenitic type has a face-centered cubic structure with an equal atoms number on each lattice side. This creates a body-centered cubic structure, which is visible under a microscope.

Composition

Knowing the material composition allows engineers to select the best grade for a given application. It also helps to identify potential problems before they happen.

Here is the composition of austenitic steel.

Chromium 18-20%
Nickel 8-10.5%
Manganese 2%
Carbon 0.08%
Phosphorus 0.045%
Silicon 1.0%
Sulfur 0.030%

Properties of Austenitic-Type Steel

Properties of Austenitic-Type Steel
Austenitic SS pipes

What made austenitic steel popular in the world are its outstanding properties.

Here are some of its amazing characteristics:

  • Non-Magnetic: Austenitic-type alloy has a non-magnetic property that makes it ideal for applications where magnetism is undesirable.
  • Corrosive Safety: It also has superb corrosion protection properties. Therefore it is often used in environments where other metals may corrode.
  • Non-Heat Treatable: This type is also not heat-treatable. This means it cannot be hardened by conventional methods.
  • Ductility: Austenitic steel has good ductility and can be formed into a variety of shapes.
  • Weldability: If the stainless steel is austenitic type, it can weld easily. Therefore it is used in applications where welding is necessary.

Divided into Two Subgroups: 200 Series & 300 Series

The 200 Series is an economic alternative to the 300 Series. It is made up of chromium-nickel-manganese alloys and is not hardenable to heat treatment. Also, it is magnetic and has a lower oxidation resistance.

On the other hand, the 300 Series is the most common type of stainless steel. It is hardenable by heat treatment. But this time, it is made up of chromium-nickel alloys. Compared to the 200 Series, it is non-magnetic and has a higher oxidation resistance.

Choosing between the 200 Series and 300 Series will depend on your specific application. You can discuss your projects with us so we know how to help.

Austenitic Stainless Steel Grades List

Understanding the stainless steel grades which are considered austenitic will help you choose the right grade for your project.

Let’s explore the following grades and their uses.

304 Stainless Steel

Grade 304 is highly weldable and formable. Its high chromium and nickel content gives it excellent resistance to scaling. Therefore it is ideal for corrosive environments such as:

  • Chemical plants
  • Paper mills
  • Refineries

316 Stainless Steel

It is also known as marine-grade stainless steel due to its increased resistance to chloride corrosion. It is often used in:

  • Food processing
  • Medical equipment
  • Chemical applications

321 Stainless Steel

Grade 321 is a chromium-nickel austenitic steel with titanium added for stabilization. It is often used in applications where long-term exposure to high temperatures is expected, like:

  • Welding filler wire
  • Heat shields
  • Pressure vessels

347 Stainless Steel

This alloy provides good strength in high temperatures. You can use them in applications that require welding.  Suited as well for applications where frequent temperature changes occur, such as:

  • Turbine blades
  • Aircraft structural components
  • Exhaust manifolds

410 Stainless Steel

Grade 410 alloy is heat-treatable and extremely rusting-resistant. It is useful for parts that require high wear resistance and strength. That includes fasteners and valve components.

431 Stainless Steel

Finally, grade 431 austenitic steel is known for its high-chromium properties. It is typically used in applications such as:

  • Valves
  • Fasteners
  • Shafts

Benefits of Using Austenitic Steel

The most significant benefit of using austenitic steel is its exceptional corrosion and oxidation protection. Therefore you can use it in many applications without worrying about being corroded or oxidized.

Additionally, it is highly resistant to stress corrosion cracking.  This makes it an ideal material for components that are exposed to high-pressure environments.

Another benefit is its strength-to-weight ratio. Austenitic stainless steel is strong and light. So it can be used in applications where weight is a major factor, such as in aircraft. Plus, because of its strength-to-weight ratio, it became easier to form.

Its extreme durability is another reason why austenitic steel is so popular. It can withstand high temperatures in most environments.

Finally, austenitic-type is highly ductile. Meaning it can be easily formed into desired shapes. This makes it an excellent choice for applications where shape and size are important.

DOWNSIDES

Now let’s talk about the downsides of using austenitic stainless steel.

Due to the several advantages discussed above, using this steel also has downsides that must be kept in mind.

One of the main drawbacks is its relatively high cost. While the increased strength of austenitic steel is beneficial in many applications, its cost is typically much higher than other steels. This is due to the additional alloying elements used to create the austenitic structure, which can add significant costs. For that reason, it became a less-than-ideal choice for cost-conscious applications.

Another downside is its susceptibility to stress corrosion cracking. This is particularly true when the material is used in applications that involve highly corrosive environments. Especially to those encountered in chemical processing plants or off-shore oil rigs.

But good thing! The risk of stress corrosion cracking can be reduced. That is by selecting the right austenitic steel grade for the application. Properly maintaining the components is also one thing that helps.

Finally, austenitic steel is not well suited for welding applications. This is due to its high carbon content, which makes it difficult to weld. Additionally, the austenitic type is not ideal for applications that require high strength and hardness. As it is relatively weak and soft compared to some other steel varieties.

The Difference of Martensitic Over Austenitic

The Difference of Martensitic Over Austenitic

Martensitic and Austenitic are two of the most commonly used stainless steel. They differ in their composition and properties.

Martensitic stainless steel is a steel alloy that contains higher levels of carbon than austenitic steel. This gives it greater strength and hardness, making it well-suited for applications where wear resistance is required. It is generally more magnetic than austenitic. Additionally, it is not as resistant to stress corrosion cracking.

Austenitic SS, on the other hand, contains lower carbon levels. Plus higher levels of chromium and nickel. This gives it greater resistance to rusting and better weldability. It is also non-magnetic and has excellent formability. As result, it became suited for applications where corrosion resistance is a priority.

In summary, martensitic stainless steel is stronger and more wear-resistant than austenitic, but it is more prone to corrosion. Austenitic steel is more corrosion-resistant, non-magnetic, and has superior formability. But sad to say, it is not as strong as martensitic steel.

How to Differ Austenitic-Type from Ferritic Steel

The austenitic and ferritic type has a major difference in their microstructure and applications.

It is important to understand the differences between the two so that you can make the most informed decision when selecting the best option for your application.

AUSTENITIC FERRITIC
 

By Microstructure

Austenitic stainless steel is made up of austenite, which is a nonmagnetic form of iron. Ferritic stainless steel is made up of ferrite. Ferrite is an iron-based compound, which is a magnetic form of stainless steel.
 

 

 By Application

Known for its strength and is used in different applications. It is often used in the food and medical industries. This is because of its ability to resist corrosion from acids and other elements. It is also used in the construction of buildings and bridges. Ferritic stainless steel is often used in applications where cost is a factor. It is widely used in automotive exhaust systems and industrial equipment, as well as in the production of cookware and kitchen utensils.

Duplex Stainless Steel VS Austenitic: Which is Better?

Duplex Stainless Steel VS Austenitic

Duplex and austenitic stainless steels are the top 2 most popular types. Both have corrosion resistance, excellent mechanical properties and have a wide range of applications in many industries. But which one is better?

When it comes to corrosion protection, the two types have their strengths and weaknesses. Duplex has higher protection against chloride pitting. While the austenitic type has better general corrosion protection.

In terms of mechanical properties, the duplex has higher strength and ductility. But austenitic steel is more resistant to fatigue.

However, in terms of cost, an austenitic is usually cheaper than a duplex.

So, which one is better?

The answer depends on the application. If corrosion safety and mechanical properties are your top priorities, then duplex stainless steel is the way to go. But, if cost is a major factor, then austenitic may be the better option.

PH Stainless Steel VS Austenitic

Precipitation-hardened steel (PH) and austenitic are both included in the stainless steel family.

Though both steel types have similar properties, they differ in various aspects.

Aspects PH Steel Austenitic
 Composition A type of martensitic steel that has undergone a precipitation hardening process. It contains a higher amount of carbon and other alloying elements such as chromium, molybdenum, nickel, and copper. On the other hand, austenitic is an iron-carbon alloy that contains nickel, chromium, and other alloying elements.
 Hardness The hardness of PH steel is higher than austenitic types. PH steel has a hardness of around 50-60 HRC. Its higher hardness makes it more resistant to wear and tear. On the other hand, austenitic has a hardness of around 25-30 HRC.
 Heat Treatment Process PH steel is usually heat treated to increase its hardness and strength. The heat treatment process of PH steel involves quenching and tempering the material in order to achieve desired mechanical properties. Austenitic steel is heated to a temperature above the transformation range. Then it rapidly cooled in order to trap the austenite phase in the steel. The rapid cooling process prevents the formation of martensite, which is a harder form of steel.

How to Maintain Austenitic SS?

How to Maintain Austenitic SS
Regular Checking on Austenitic SS

Proper maintenance of austenitic stainless steel is essential for ensuring its longevity and performance.

One of the most important steps in maintenance is to keep it clean. All dirt should be removed using a soft cloth or brush and a non-abrasive cleaner. It is important to avoid using harsh cleaners or abrasive materials on the steel. As these can damage the steel surface and reduce its protection against rust. It is also important to rinse the steel thoroughly after cleaning. This ensures all traces of the cleaners are removed.

Another important step in the maintenance is to avoid exposing it to chlorine or other oxidizing agents. Chlorine and other oxidizing agents can cause pitting on the steel surface –which then can reduce its strength. But if the steel needs to be exposed to chlorine or other oxidizing agents, it should be protected with a protective coating.

It is important to note that austenitic stainless steel does require regular maintenance to keep it in good condition. Also, it’s important to regularly inspect the steel for signs of corrosion damage. So that can address these issues as soon as possible.

You should store the said material in a dry, clean environment, as exposure to moisture can lead to extreme rust. Finally, it’s important to use the appropriate polishing products to avoid damaging the steel surface.

What is Sigma Phase in Austenitic Stainless Steel?

The Sigma phase is an intermetallic compound found in certain austenitic steels.

This compound is formed at temperatures between 600 and 900 degrees Celsius. And it is a result of chromium precipitation and iron carbides. This precipitation process is known as sigma phase precipitation. It can cause a decrease in the ductility and corrosion resistance of the stainless steel.

The formation of this compound is accelerated by the presence of sulfur and phosphorus in the steel. It is important to note that the sigma phase is not always detrimental and can sometimes be beneficial. For instance, it can provide a strengthening effect and improve the weldability of stainless steel.

Sensitization in Austenitic Steels

Sensitization in austenitic stainless steel is an important phenomenon. It can lead to corrosion and premature failure of components in various applications.

Sensitization is the formation of chromium carbides at grain boundaries. Which then results to weakens the alloy and can cause corrosion. Sensitization is caused by heating austenitic steels to temperatures above about 900°C. That can occur during welding, hot forming, and heat treatment.

The chromium in the steel reacts with carbon to form chromium carbides, which depletes the chromium content of the grain boundaries. This reduces the steel corrosion protection –allowing corrosion to occur at the grain boundaries.

How to prevent sensitization?

This can be prevented by controlling the cooling rate after heat treatment. Or by adding certain elements such as niobium or titanium. As this can form stable carbides and prevent sensitization.

In applications where sensitization is a concern, austenitic stainless steel should be carefully specified. This ensures that they are not susceptible to sensitization. Post-weld heat treatments may also be necessary to prevent sensitization. Sensitization can be tested using a variety of methods, such as ASTM A262 or ASTM A923. This measures chromium depletion in the grain boundaries.

Does Austenitic Stainless Steel Rust?

No. Austenitic stainless steel is widely known for its rusting-proof properties in certain environments. This makes it one of the most popular steels in the world.

When exposed to an environment with a high enough concentration of oxygen and moisture, its chromium oxide layer will slowly break down, eventually leading to rust.

But, if used in most indoor environments, it will not rust as the oxygen and moisture concentrations are too low. However, if the steel is exposed to a particularly humid environment, or if it is frequently exposed to salt water, then it is possible for the steel to rust.

In order to prevent rust from forming on austenitic stainless steel, it is important to understand how the metal behaves in different environments.

Conclusion

After reading this guide, you’ve learned a lot about austenitic stainless steel and how it can benefit your applications.

The above information definitely helps you determine where austenitic steel is more suitable to use so you can avoid rust. You are now also aware of the maintenance steps to prolong the material.

Our service team in Tuolian will always be ready to respond to your inquiries. Kindly contact us!

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Whether you need stainless steel materials for your business or fabrication projects, TuoLian is your best supplier. You can find all types, grades, and thicknesses based on your needs. Guaranteed that we provide the best quality at a reasonable cost.
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