Ferritic stainless steel is a specific type of steel alloy. They are classified by their body-centered cubic structure, meaning eight atoms are arranged at the corners of the unit cell, connecting to one lattice point in the middle of the structure. As a consequence, ferritic steels have magnetic properties unlike austenitic steels, which show a face-centered cubic structure, rendering them either non-magnetic or remanent. Ferritic stainless steels are best known for their excellent ductility, making them a frequent material for kitchenware and automotive parts.
Generally, ferritic stainless steels are characterized by their high chromium and low carbon content. Many austenitic stainless steel grades can be substituted by ferritic counterparts if they show similar properties. They are less expensive due to their lower levels of chromium and low levels of nickel. While ferritic steels are not as strong or corrosion-resistant as austenitic steels, they are defined by their superior weldability and engineering properties. They cannot be hardened by heat treatment but are suitable for cold-working treatments.
Ferritic steels can be divided into 3 common groups and 2 special ferritic grades:
- Group 1 (Type 409, 410, 420): Stainless steels with a chromium content of 10.5-14% belong to the first group of ferrites. They are not as resistant to corrosion as other ferritic steels which is why they are best suited for low-corrosive environments. Due to their relatively low levels of chromium, stainless steels of this group are the least expensive.
- Group 2 (Type 430): The most used type of ferritic steel shows greater corrosion resistance than types of the first group. Their chromium contents range from 14-18%, making them comparable to austenitic stainless steel grade 304, the most used type of steel. Type 430 often replaces 304 for indoor applications such as household units and kitchenware because it shows magnetic properties.
- Group 3 (Type 430Ti, 439, 441): Ferritic steels of this group show an even higher content of chromium (14-18%). They are defined by their goof weldability, ductility and corrosion resistance. They are best utilized in areas of durability and low levels of maintenance costs and can even be used for outdoor applications. Their properties even surpass those of grade 304 austenitic steel, which is why ferritic steels of this group are used in a wide range of areas, such as valves, exhaust systems, and washing machines.
- Group 4 (Type 434, 436, 444): To increase corrosion resistance, molybdenum can be added to the already high levels of chromium. Ferritic steels of this type can be used in highly demanding environments, such as water tanks, exhaust systems and outdoor applications.
- Group 5 (Type 446, 445): The last group includes ferritic stainless steels with added chromium and molybdenum contents. This results in even higher corrosion resistance and is best suited for areas of high corrosion. Being comparable to titanium metal in terms of wear resistance, these grades are ideal for heat exchangers, water heaters and boilers.