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What is Ferritic Stainless Steel? Classification and Applications by Steel Group

What is Ferritic Stainless Steel? Classification and Applications by Steel Group

BlogDate: 13-12-2023 by: Ngoc Cam

Stainless steel has added nickel, chromium and many other alloying elements that other types of steel lack. This difference has resulted in corrosion resistance, high thermal conductivity, ductility and many other superior properties. In this article, MRS Steel will delve deeper into Ferritic stainless steel to examine its strength and applications in construction.

1. What is Ferritic stainless steel?

Ferritic stainless steel, also known as low carbon steel containing about 12-20% chromium, is a straight, non-hardening chromium stainless alloy with a carbon content below 0.2%. After undergoing special heat treatment, mills produce Ferritic stainless steels including: 409, 430, 430 LI, 434, 439, 442, 444, 446,... stainless steel

Ferritic steels are unique in that they contain higher chromium content than other types of stainless steel, which can be up to 27%. However, in some cases the chromium content is only equivalent to Austenitic. Additionally, most Ferritic steels are also nickel-free, similar to Martensitic steel.

2. Characteristics of Ferritic stainless steel 

Resistant to stress corrosion cracking

Stress corrosion cracking (SCC) occurs due to corrosive environments and tensile stresses leading to crack formation. This process significantly reduces the load-bearing capacity of the metal structure. Austenitic stainless steel is highly vulnerable to SCC due to its interaction with chloride-rich environments. However, the structure of Ferritic is resistant to high levels of SCC, making it an excellent choice for applications in harsh environments or those containing high chloride levels.

Ductility and Formability

The carbon content determines the ductility and brittleness of steel, while Ferritic steel only contains below 0.2% carbon, which provides it with moderate ductility and ease of shaping. Its low carbon content also helps prevent cracking and breakage during shaping. However, the low carbon content can lead to issues like cracking during welding and the inability to harden the steel using conventional heat treatment methods.

Low thermal expansion 

Thermal expansion is a physical property representing the change in size of a during heat exchange. A high coefficient of thermal expansion can lead to cracking when there are temperature differences. Ferritic steel has a low coefficient of thermal expansion that helps fix the dimensions of the metal, making it suitable for high-temperature applications.

High thermal conductivity

Compared to other common steel types, Ferritic stainless steel stands out with its excellent thermal conductivity. Therefore, they are also widely used in furnace and boiler heat exchangers as well as other heat transfer components.

High Oxidation Resistance

Ferritic steel is also known for its good oxidation resistance, especially at high temperatures. The chromium oxide film protects steel from rust external rusting factors. In Vietnam, factories also enhance the oxygen resistance of Ferrit steel by adding silicon or aluminum.

3. Ferritic stainless steel classification and equivalent applications

Depending on the composition and application, Ferritic stainless steel is divided into 5 groups including:

Group 1 (Type 409/410 L)

This is the group of Ferrite steels with the lowest chromium content, so the price is also much cheaper among all types of stainless steel. Type 409 is often used as catalytic converter housing or the main application of type 410 L is LCD screen frames, buses,...

Group 2 (Type 430)

Type 430 Ferritic stainless steel has a chromium content ranging from 16-18%, providing better corrosion resistance than Group 1. It is widely used in the production of washing machines, kitchen furniture,... Additionally, with similar properties and strength, 430 Ferrit steel can replace 304 stainless steel in various applications, such as cladding.

Group 3 (Type 430TI, 439, 441)

Group 3 has a chromium content of 17.5 - 18.5%, offering excellent welding and shaping properties, even superior to 304 stainless steel. This group is commonly used in exhaust systems, sink basins,…

Group 4 (Type 434, 436, 444)

Group 4 stands out with its high corrosion resistance thanks to the addition of Molybdenum in the composition. For example:

- Inox 434: 16.0% – 18.0% chromium; 0.9% < Mo < 1.4%

- Inox 436: 16.0% – 18.0% chromium; 0.9% < Mo < 1.4%; 0.3% < Ti < 0.6%

- Inox 444: 17.0% – 20.0% chromium; 1.8% < Mo < 2.5%

They are suitable as materials for applications in high-corrosion environments, water tanks, ovens and outdoor products.

Group 5 (Type 446, 445)

This group has the highest chromium and molybdenum content of all Ferritic stainless steel groups, which corresponds to their excellent corrosion and rust resistance. In practice, Ferritic steel types 446 and 445 are used specifically for heat exchanger components, water heaters, pressure cookers,...

Vietnam has abundant iron ore resources and crude steel output ranks 13th globally. With improvements in production technology and a modern, closed chain system, Vietnam stainless steel is committed to meeting international standards and strict requirements from customers. Importers can contact MRS Steel via Whatsapp: +84 76 911 2358 for advice on the Vietnamese steel market and products.