Ferritic stainless steel

Ferritic stainless steel is a special class of stainless steel in which the main alloying element is chromium. The content of this element in the metal can be from 10.5 to 30%. Ferritic grades of stainless steel are magnetic and are mainly classified as 400 series grades. Ferritic steel grades containing a large percentage of carbon are brittle and have relatively low corrosion resistance.

It differs from other types of stainless steel in two important respects: its molecular grain structure and its chemical composition. Ferritic stainless steel is actually defined as a straight class of non-hardened stainless alloys with chromium content in the range of 10.5 to 30% and carbon content less than 0.20%. Ferritic grades of steel are not hardenable by heat treatment and are only slightly hardenable by cold rolling.

The composition of stainless steel plays a significant role in the structure of the metal at the molecular level. It is these structures that give the different types of stainless steel their names. Ferritic steels are so named because they are made up of microstructures known as ferrite.
Ferite is a metallurgical phase of iron in which the metallic alloying elements are in solid solution, but the carbon is virtually insoluble. Ferite is virtually absent from hardened martensitic and austenitic stainless steels, but its presence characterizes stainless steels. It is also worth noting that annealed martensitic stainless steels also contain carbide and ferrite.
Ferritic steels have a three-dimensional cubic grain structure, while austenitic and other types of stainless steel have a face-centered grain structure.
The body-centered cubic grain is responsible for the magnetic nature of ferritic steel. This distinguishes it from almost all other types of stainless steel. This difference lies in the quantum mechanical aspect of the metal's microstructure, i.e., how the electrons are arranged in the core of the metal grain.

There are five important characteristics to remember when considering the properties of ferritic stainless steel. .
1. Ferritic steel is resistant to stress corrosion cracking:
- stress corrosion cracking is a common type of degradation of steel caused by a combination of a corrosive environment and tensile stress. Austenitic stainless steels are particularly vulnerable to stress corrosion cracking when exposed to chlorides. However, the microstructures present in ferritic steels give them a high degree of resistance to cracking, making them a good choice for use in environments and structures where chlorides may be present.
2. The steel has good plasticity and formability:
- The hardness of steel depends on carbon, but carbon also makes the steel less ductile and brittle. Because ferritic steel contains a relatively low percentage of carbon, it usually has above-average ductility. This means that ferritic steels can be shaped significantly without the risk of weakening.
The low carbon content of ferritic steels also gives them exceptional formability, allowing them to be formed into a variety of shapes without having to deal with problems such as cracking or necking.
However, the advantages of the low-carbon composition of ferritic steel come with some trade-offs. For example, ferritic steels cannot be strengthened by heat treatment. In addition, some types of ferritic steel may experience problems when welding, such as unexpected cracking along the heat-affected zone.
3. ferritic stainless steel has a relatively low coefficient of thermal expansion.:
- ferritic steels have a naturally low coefficient of thermal expansion. This can be a real advantage and simply means that ferritic steels experience less expansion when they accept heat.
Because the metal more easily maintains its fixed dimension, this makes some ferritic stainless steels well suited for high temperature applications.
4. It has high thermal conductivity:
- ferritic stainless steels have excellent thermal conductivity properties, meaning that heat can pass through them efficiently. As a result, ferritic steels are widely used in furnace and boiler heat exchangers and other heat transfer applications.
5. It has good oxidation resistance:
- Ferritic stainless steel is quite resistant to oxidation, especially at high temperatures. This resistance is a result of the formation of a protective chromium oxide film on the surface of the steel. It is possible to further improve the oxidation resistance of steel by adding silicon and/or aluminum to the composition during the production of ferritic steel.

A ferroalloy is an iron-containing product that is not classified as a steel but still contains significant amounts of one or more alloying elements.
These elements may include ferromanganese, silicon, vanadium, phosphorus, chromium, ferrophosphorus, manganese, etc. The main role of these alloys is to add the appropriate alloying elements to the molten steel.

Ferritic stainless steels are divided into five different groups. These groups differ in the exact amounts of different metals they contain, as well as their specific performance characteristics.
1. The first group includes ferritic stainless steels, which are among the cheapest types. They have very low levels of chromium, meaning they tend to accumulate a layer of localized surface rust over time.
2. The second group is the most commonly used grades. Due to the higher chromium content, these steels have greater resistance to corrosion. Ferritic steels of the second group are usually used for building elements and interior equipment.
3. Ferritic steels of group III are well known for their ease of forming and welding, which means they are suitable for a wide range of applications.
4. Ferritic stainless steels of group IV contain higher amounts of molybdenum, which further improves their corrosion resistance. This type of steel is typically used for high-humidity applications such as exhaust systems and hot water tanks.
5. Ferritic steels of group V have the highest chromium content, which gives them a degree of corrosion resistance that is unmatched by all but a few other metals.

Ferritic stainless steel has found wide application:
- civil engineering;
- architecture and design;
- food industry;
- manufacture of kitchen utensils, tables, serving tools, sinks, showers, parts of washing machines, drums and trays for dishwashers;
- automotive industry (decorative exhaust systems);
- production of external and internal fittings;
- heat exchanger equipment;
- manufacturing of machine parts and equipment for the wine industry;
Some grades of these steels are approved for use in the manufacture of equipment used in the meat and dairy industries at temperatures of 30 - 140 °C, etc.;
- cutting tools (knives, scissors, etc.);
- turbine and boiler parts;
- fasteners, wear-resistant gaskets;
- thermal and separation screens, filters;
- kitchen utensils;
- manufacturing of containers;
- chemical and petrochemical production;
- paper production;
- processing of household and sewage waste;
- mining (and everything connected with it, including mine development).