What Is Ferritic Stainless Steel?
Ferritic stainless steel is a general term for a type of stainless steel composed mainly of iron and chromium, an alloy that constitutes a ferrite phase at room temperature.
Ferritic stainless steel has excellent corrosion resistance and is more resistant to rust than ordinary steel. This makes it widely used in various fields.
Some grades contain elements such as molybdenum, niobium, and copper, but little or no nickel, which is frequently used in other stainless steels.
Applications of Ferritic Stainless Steel
Ferritic stainless steel has excellent formability, corrosion resistance, and weldability. The characteristics of ferritic stainless steel vary greatly depending on the ratio of the constituent element chromium and the additive elements, and its uses are also diverse.
1. Building and Construction Industry
Used in building components such as exterior walls, roofs, and pillars, it is suitable for buildings that require durability.
2. Food Processing Industry
Used in contact parts of food processing equipment, containers, etc., it is suitable for the food industry, where corrosion resistance is important.
3. Medical Equipment
Used in surgical instruments and medical equipment.
4. Automotive Industry
Used for automobile exhaust pipes, parts, body parts, etc., it is suitable for the automotive industry, which requires durability and heat resistance.
Properties of Ferritic Stainless Steel
Ferritic stainless steel has a variety of properties. In addition, it is less expensive than austenitic stainless steel due to the almost complete absence of nickel addition.
1. Magnetism
Ferritic stainless steel has a variety of characteristics, depending on the type of steel, but one common characteristic is its ferromagnetic properties. This is because the crystal structure of ferritic stainless steel is a body-centered cubic lattice. Martensitic stainless steels with a similar crystal structure are paramagnetic, while austenitic stainless steels with a face-centered cubic lattice are non-magnetic.
2. Strength
Ferritic stainless steel is known for its almost complete lack of hardening by heat treatment and is not suitable for applications requiring high strength because it does not show any strength increase by quenching and tempering.
3. Brittleness
Ferritic stainless steel is known to be brittle depending on the temperature conditions. High-temperature embrittlement occurs in the 400~540°C range, and storage in the 550~800°C temperature range causes embrittlement.
There is also a ductile-to-brittle transition temperature in the low-temperature range, where the impact resistance decreases rapidly. The low-temperature brittleness can be improved by using high-purity ferritic stainless steel with low carbon and nitrogen content.
4. Other Features
Other characteristics of ferrite stainless steel include corrosion resistance, workability, and strength, which are generally inferior to those of austenitic stainless steel, such as Type 304, but superior to those of martensitic stainless steel, such as Type 403.
Types of Ferritic Stainless Steel
Ferritic stainless steel is the type of stainless steel with the number in the 400 series in the name of SUS. The most common type of ferritic stainless steel is SUS430, and other types of ferritic stainless steel are made by adding various elements to SUS430 or changing the ratio of elements.
The physical properties that can be improved from SUS 430 and the types of SUS are as follows.
1. Oxidation Resistance (SUS405)
Oxidation resistance is improved by reducing chromium content from 18% to 13% and adding aluminum.
2. Workability (SUS410L, SUS429)
Chromium content is reduced.
3. Machinability (SUS430F)
Machinability is improved by adding sulfur.
4. Workability, Weldability (SUS430LX, SUS430J1L)
Machinability and weldability are improved by adding titanium and niobium and reducing carbon content.
5. Corrosion Resistance (SUS443J1, SUS434, SUS436J1L, SUS436L, SUS444)
Corrosion resistance is improved by adding molybdenum, titanium, and niobium. It has the same corrosion resistance as austenitic SUS304 and is used not only in outdoor panels and chemical plants but also in corrosive environments such as in seawater.