Stainless steel to most people might just be simply as the name suggests, a steel material that does not stain. However, in fact, there are actually more than 200 kinds of stainless steel, all of which are grouped into 5 main categories.
Here we shall explore the five types of stainless steel and their characteristics:
1. Ferritic
Ferritic stainless steels are among the most corrosion resistant materials in the stainless steel family. Their resistance to corrosion, oxidation and stress corrosion cracking are attributed to their high chromium content. With that said, ferritic stainless steels are often used in products that have frequent contact with corrosive materials. These products include automotive parts, kitchen cookware and industrial components.
Ferritic stainless steels are also magnetic. They can be hardened through cold working and softened by annealing. Two of the more common types of ferritic steel are alloys 430 and 434.
2. Austenitic
Austenitic stainless steels are the most common types of stainless steels. Austenitic stainless steels tend to have a high chromium content, giving them higher corrosion resistance and durability, as compared to other steel alloys.
Austenitic stainless steels are widely used in kitchen appliances and storage components, due to their strength, weldability and versatility. Austenitic stainless steels tend to be non-magnetic, but do exhibit some magnetic response depending on the composition and work hardening of the steel. Common types of austenitic stainless steels include alloys 304 and 904L.
3. Martensitic
Martensitic stainless steels are similar to ferritic stainless steels, with the only differences being their percentages of carbon. The carbon percentages in martensitic stainless steel hover around 1%, while carbon percentages in ferritic stainless steel remain below 0.10%.
Unlike ferritic stainless steels, martensitic stainless steels can withstand high enough temperatures to be hardened by heat treatment. Martensitic stainless steels are used in applications where high tensile strength and impact resistance are required, such as kitchen cutlery and multipurpose tools. Martensitic stainless steels are also magnetic with low weldability and formability. Types of martensitic stainless steels include alloy 431 and 420S45.
4. Duplex
Duplex stainless steels comprise of both ferritic and austenitic stainless steels. Duplex stainless steels are stronger than both ferritic and austenitic stainless steels. Due to its enhanced strength and corrosion resistance capabilities, duplex stainless steel is frequently used in the underwater oil industry.
Having fair malleability and weldability, duplex stainless steels can be shaped to form different types of components. Duplex stainless steels are magnetic, but not so much as compared to ferritic and martensitic stainless steels. Two of the common types of duplex stainless steel include S31803 and S32205.
5. Precipitation Hardening
Precipitation Hardening (PH) stainless steels are classified as martensitic or semi-austenitic. They develop their high strength and hardness through a variety of heat treatments, resulting in an exceptional strength-to-weight ratio. In comparison to other types of stainless steel, precipitation hardening stainless steels are easy to work with. They exhibit excellent machining and forming characteristics, and are widely used in aerospace components, flat springs and retaining rings.
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