Whether you work in the automotive industry or develop heat transfer products like furnaces, you must have worked with ferritic stainless steel. It has amazing properties, such as high thermal conductivity, incredible ductility, and resistance to oxidation. But what actually is ferritic stainless steel? Why is it so popular? What are its advantages? Let’s find out!
What is Ferritic Stainless Steel?
Typically, ferritic stainless steel is a grade of steel that features 11% to 30% chromium in its structure but little to no nickel. However, not all types of ferritic stainless steel contain such high amounts of chromium, as some variants have a lower content than austenitic stainless steel.
Other than chromium, it also has a carbon content of around 0.20%. There are two major reasons that distinguish ferritic stainless steel from other types of steel, such as:
- Molecular grain structure
- Chemical composition
When it comes to characteristics, it’s magnetic, non-heat treatable, and offers excellent rust and stress corrosion. On top of this, it’s non-hardenable by heat treatment and only slightly hardenable by cold rolling.
Composition of Ferritic Stainless Steel?
Although now you’ve a general idea of the chemical composition of ferritic stainless steel, here’s a table that gives you a detailed glimpse into the elements present in this material:
Elements | Percentage |
Iron | Balance |
Chromium | 10.5-30% |
Manganese | ≤ 1.00% |
Silicon | ≤ 1.00% |
Phosphorus | ≤ 0.040% |
Sulfur | ≤ 0.030% |
Nickel | ≤ 0.50% |
Molybdenum | ≤ 1.00% |
Carbon | ≤ 0.12% |
How Ferritic Stainless Steel is Made?
Compared to other types of stainless steel, ferritic steel requires specialized handling and production. Here’s an overview of the process for the manufacturing of this material:
Raw Materials Preparation
The first step is all about the selection and preparation of raw materials, such as chromium, molybdenum, carbon, phosphorus, and some other elements. These materials then undergo different mechanical processes, including annealing and rolling, to eliminate impurities.
Molten Metal Casting
After preparation, these materials are placed in an electric arc furnace so they turn into molten metal. This molten material is then cast into mold cavities, where it solidifies. However, during this stage, you should ensure that stainless steel is homogeneous and there are no pores or voids.
Solidification and Cooling
It’s an important step in the manufacturing of ferritic stainless steel as the steel crystallizes into a solid structure, and you determine its microstructure to understand its unique properties.
Shaping and Finishing
The metal part now must be shaped and polished to create a variety of products with different surface finishes. Machining, grinding, and polishing are typically employed to achieve this.
Heat Treatment and Cold Rolling
To refine the material properties, it is subjected to heat treatment and cold rolling.
- Heat Treatment: Heat treatment methods, such as tempering and aging, are helpful in relieving stress and improving ductility.
- Cold Rolling: Cold rolling stainless steel helps maintain its magnetic properties and increase overall strength and hardness. If you keep control over the reduction and rolling speed, you can also achieve high formability, so the material doesn’t deform.
Final Quality Control
Manufacturers carefully analyze the products to find signs of folds, cracks, and other irregularities. If there are any issues, they must be addressed before the final product release.
Groups of Ferritic Stainless Steel
There are five different groups of ferritic stainless steel, each having a unique metal content. Let’s discuss them:
Group 1
Group 1 ferritic steel has the least amount of chromium, which makes it prone to rust and corrosion. It is also quite inexpensive and used for applications such as automotive exhaust systems, catalytic converter casings, and LCD monitor frames. The typical grades in this group include 409/410 L.
Group 2
Group 2 (SS430 and other grades) has high chromium content, which also enhances the material’s overall corrosion resistance against nitric acid, sulfuric gases, and many other organic acids. It’s one of the most common groups among all the ferritic stainless steels and is found in the interior of many cooking appliances.
Group 3
Grades like 430Ti, 439, and 441 all fall in Group 3, which has chromium between 17.5% and 18.5%. This content is similar to that of austenitic stainless steel 304 and contributes to the steel’s high weldability and formability. Exchange tubes, exhaust systems, pipes, and sink basins are all applications of Group 3 ferritic stainless steel.
Group 4
Group 4 includes grades 434, 436, and 444, and these steel materials feature a high molybdenum content, enabling them to deter corrosion, especially in high moisture areas. That’s why they are commonly used in hot water tanks, solar water heaters, and even electric kettles.
Group 5
Group 5 has the highest amount of both chromium and molybdenum, which results in excellent protection against corrosion and scaling. Grade SS446 and others are part of this group and are used in offshore or coastal environments.
Advantages and Disadvantages of Ferritic Stainless Steel
Now, let’s look at the advantages and disadvantages of ferritic stainless steel, helping you decide whether you should use it for your applications or not:
Advantages
- Corrosion Resistance: The high chromium content in many groups of ferritic stainless steel makes it highly corrosion and oxidation-resistant. This means if you want to create products for mild and moist environments, you can rely on this material.
- Magnetic Properties: Ferritic steel is also magnetic in nature due to its crystal structure and presence of ferrite (iron and other elements compound). There’s a clear alignment in iron atoms, which creates a magnetic field that is useful in applications such as induction heating.
- Formability: This material also contains a very low quantity of carbon, around 0.03%, which makes the steel more formable and less ductile and eliminates the risk of cracking or other deformation. You can design and shape it in any way to create different products.
Overall, ferritic stainless steel offers a good blend of strength and durability and is also less expensive.
Disadvantages
- Sensitization: It’s often susceptible to sensitization because chromium carbides precipitate along grain boundaries at temperatures between 425-815°C. To avoid sensitization, you must not do heat treatment at this range and also control cooling rates.
- Low Toughness: At low temperatures, ferritic stainless steel becomes less tough, increasing brittleness during welding and other procedures.
Mechanical Properties of Ferritic Stainless Steel
The mechanical properties of two different grades of ferritic steel, including tensile strength and elongation, are given as:
Ferritic Stainless Steel Grades | Yield Stress (MPa) | Tensile Strength (MPa) | Elongation % | Hardness (HV) |
AWM 404GP™ | 310 | 475 | 31 | 157 |
304 | 290 | 600 | 55 | 157 |
Ferritic Stainless Steel vs Austenitic Stainless Steel
Here’s an overview of the differences between ferritic and austenitic stainless steel:
- Ferritic stainless steel primarily contains chromium and iron, but austenitic stainless steel is composed of chromium and nickel.
- Ferritic steel is magnetic in nature due to its structure and ferrite presence, while austenitic stainless steel is non-magnetic.
- The thermal conductivity of ferritic steel is high, which makes it suitable for all heat transfer applications. However, austenitic stainless steel has low thermal conductivity but good toughness.
- Ferritic materials offer good to moderate corrosion resistance. On the other hand, austenitic stainless steel has excellent corrosion resistance in almost all environments.
- When it comes to cost, ferritic stainless steel is less expensive compared to austenitic materials.
Conclusion
Ferritic stainless steel is a good choice if you want something affordable to manufacture products for marine applications. Struggling to get your hands on high-quality ferritic steel and other stainless steel components? Jianglin has your back. We have a variety of certified manufacturers onboard who offer you precise products while ensuring incredible speed and quality. Don’t wait—reach out to our expert team and secure your supply of top-grade materials!
