Ferritic stainless steel is a type of stainless steel that contains iron and chromium. The word “ferritic” comes from the Latin word “ferrum,” meaning iron. Ferritic stainless steels are known for their corrosion resistance and high temperature strength. They are often used in automotive and industrial applications. Ferritic stainless steels can be difficult to weld because of their high carbon content.
Definition of ferritic stainless steel
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Ferritic stainless steel is a type of stainless steel that contains iron and chromium. Chromium-containing stainless steel used especially for welding rods and in the automotive industry because of its resistance to corrosion and high-temperature strength.
They are often used in automotive and industrial applications. Ferritic stainless steels can be difficult to weld because of their high carbon content.
Some common grades of ferritic stainless steel include 430 and 434.
430 are widely used in the manufacture of kitchenware, dishwashers, ovens and refrigerators.
434 is often used in automotive applications.
The main difference between ferritic stainless steel and other types of stainless steel is that it has a lower carbon content. This makes it less likely to form intermetallic phases, which can lead to cracking during welding.
Ferritic stainless steels are non-hardenable by heat treatment and cannot be strengthened by cold working. However, they can be strengthened by cold rolling.
Difference between ferritic and other types of stainless steel
The main difference between ferritic stainless steel and other types of stainless steel is that it has a lower carbon content. This makes it less likely to form intermetallic phases, which can lead to cracking during welding.
Ferritic stainless steels are non-hardenable by heat treatment and cannot be strengthened by cold working. However, they can be strengthened by cold rolling.
Applications of ferritic stainless steel
Some common applications for ferritic stainless steel include:
- Automotive exhaust systems
- Petrochemical plants
- Heat exchangers
- Dairy equipment
- Brewery equipment
- Sinks
- Knives
Manufacturing process of ferritic stainless steel
The manufacturing process of ferritic stainless steel begins with the preparation of the raw material. The raw material is then melted in an electric arc furnace.
After the melting process is complete, the molten metal is poured into a ladle and then transferred to a continuous casting machine.
The continuous casting machine cools the metal to create a solid ingot. The ingot is then reheated and hot-rolled to create a flat sheet or plate.
The hot-rolled product is then annealed to relieve stress and improve ductility. Finally, the material is cold rolled to achieve the desired thickness and surface finish.
Comparison of Austenitic and Ferritic Stainless Steel
Austenitic stainless steel is the most common type of stainless steel. It contains high levels of chromium and nickel, which give it excellent corrosion resistance. Austenitic stainless steels are non-magnetic.
Ferritic stainless steels are magnetic and have better weldability than austenitic stainless steels. They are also less expensive. However, they are not as resistant to corrosion and do not have as high of a temperature strength.
What is the Chemical Composition of Ferritic Steel?
The chemical composition of ferritic stainless steel typically includes:
- Iron: 70-85%
- Chromium: 14-18%
- Carbon: 0.08% max
- Manganese: 1% max
- Silicon: 1% max
- Phosphorus: 0.045% max
- Sulfur: 0.03% max
There are many grades of ferritic stainless steel, each with a different chromium and carbon content. The specific composition will determine the properties of the steel.
The Ferritic Grain Structure
Ferritic stainless steels have a body-centered cubic crystal structure. The atoms are arranged in a cubic lattice with the iron atoms at the corners and the chromium atoms in the center of each face.
The microstructure of ferritic stainless steel is generally homogeneous with small, evenly distributed grains. The grain size can be controlled through heat treatment and cold working.
Characteristics of Ferritic Stainless Steel Strip
Steel with Resistance to Stress Corrosion Cracking
Ferritic stainless steels are generally resistant to stress corrosion cracking. However, they can be susceptible to chloride stress corrosion cracking in some environments.
Chloride stress corrosion cracking is a type of corrosion that can occur in austenitic and duplex stainless steels. It is caused by the presence of chlorides in the environment.
Chloride stress corrosion cracking can be prevented by using proper material selection and design, as well as by controlling the environment in which the steel is used.
Magnetic Properties
All ferritic stainless steels are magnetic. The magnetic properties of ferritic stainless steels can be enhanced by cold working.
Cold working is a process that involves the application of mechanical forces to plastically deform the steel. This can be done by rolling, drawing, or pressing.
The amount of cold working that is done will determine the magnitude of the magnetic properties.
Non-Magnetic Properties
Ferritic stainless steels are non-magnetic in the annealed condition. However, they can become magnetic when cold worked.
The magnetic properties of ferritic stainless steels can be enhanced by cold working. Cold working is a process that involves the application of mechanical forces to plastically deform the steel. This can be done by rolling, drawing, or pressing.
The amount of cold working that is done will determine the magnitude of the magnetic properties.
Ductility and Formability
Ferritic stainless steels are generally more ductile and formable than austenitic stainless steels. They can be cold worked to produce a wide variety of shapes and sizes.
However, ferritic stainless steels are not as easily welded as austenitic stainless steels. They are also less resistant to corrosion and have lower temperature strength.
Is 316 stainless steel ferritic?
No, 316 stainless steel is austenitic. Austenitic stainless steels are non-magnetic. Ferritic stainless steels are magnetic and have better weldability than austenitic stainless steels. They are also less expensive. However, they are not as resistant to corrosion and do not have as high of a temperature strength.
Is ferritic stainless steel magnetic?
All ferritic stainless steels are magnetic. The magnetic properties of ferritic stainless steels can be enhanced by cold working.
Can ferritic stainless steel be hardened?
No, ferritic stainless steels cannot be hardened by heat treatment. They can only be hardened by cold working.
Overall
Ferritic stainless steels are magnetic, have a body-centered cubic crystal structure, and are less resistant to corrosion than austenitic stainless steels. They can be cold worked to produce a wide variety of shapes and sizes, but are not as easily welded as austenitic stainless steels.
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