What types of stainless steel microstructures are there?

Ferritic stainless steel

These steels generally contain a certain amount of carbon, but usually less than 0.10% chromium. The microstructure of these steels is similar to both carbon and low-alloy steels. They are typically not heat treatable for hardening due to their lack of toughness. High-chromium steels with added molybdenum can be used in highly aggressive conditions, such as seawater. Ferritic steels are magnetic, making them prone to corrosion and cracking. Currently, immersion in ferritic stainless steel passivation solutions can prevent or extend the anti-corrosion and rust prevention time of ferritic stainless steel.

2. Austenitic stainless steel

Austenitic stainless steel is common. Their microstructure comes from the added nickel, manganese, and nitrogen. This same structure allows for higher temperature resistance compared to ordinary steel. This structure also features the weldability and ease of forming of these steels. Due to the presence of nickel, chromium, molybdenum, and nitrogen in austenitic stainless steel, they can achieve enhanced corrosion resistance more effectively. Their useful properties can be hardened by working, while retaining a useful level of ductility and toughness. High-nickel austenitic steel increases resistance to stress corrosion cracking. They are nominally non-magnetic but usually exhibit some magnetic response, depending on the composition and the steel's work hardening. After being immersed in stainless steel passivation liquid, the salt spray test performance of austenitic stainless steel can be improved over 20 times.

Martensitic Stainless Steel

Martensitic stainless steel is similar to ferritic stainless steel, but it contains a higher carbon content, up to 1%. This makes it resemble carbon steel and low-alloy steel. It is suitable for applications requiring high strength and some corrosion resistance. Martensitic stainless steel also has magnetic properties, as well as generally lower weldability and formability.

4. Precipitation-hardened stainless steel

Martensitic stainless steel boasts exceptional strength. With appropriate "aging" heat treatment, it forms extremely fine particles within the matrix, resulting in steel with superior strength. These steels can be processed into complex shapes, but require precise tolerances prior to aging treatment.