Types of Stainless Steel: Ferritic, Martensitic, and Austenitic

Stainless steel is an iron alloy, not pure iron. It must contain a minimum of 10.5% chromium (Cr) and a maximum of 1.2% carbon (C). Chromium is the most important element in stainless steel: it forms an oxide layer (Cr2O3) on the surface of the material, protecting the product from oxygen. The chromium content and degree of passivation determine how stainless the steel is. The oxide layer that forms on the surface is invisibly thin and impermeable to water.

Types of Stainless Steel

• Ferritic stainless steel
• Austenitic stainless steel
• Martensitic stainless steel

Ferritic Stainless Steel

These stainless steels have a low carbon content and contain between 12% and 18% chromium. They offer moderate corrosion resistance and good strength. They cannot be formed as easily as austenitic grades. They are magnetic, and their strength cannot be increased by heat treatment. Typical applications: kitchen utensils, decorative products, automotive chassis components, hot water tanks.

Martensitic Stainless Steel

When stainless steels that have an austenitic structure at high temperatures and a carbon content above 0.1% are quenched, the austenitic structure transforms into a martensitic structure. The martensitic structure has high strength and hardness, but it is relatively brittle. Since excessive hardness leads to brittleness, tempering during production can reduce the hardness slightly and bring the toughness to the required level. These steels have moderate corrosion resistance, are heat treatable and magnetic, and have low weldability. Typical applications: knives and surgical instruments.

Austenitic Stainless Steel

Adding nickel to stainless steel produces an austenitic structure at room temperature. This room-temperature austenitic structure gives the material excellent formability, comparable to that of plastics, while also providing high strength. Its mechanical strength cannot be increased by heat treatment, but it can be increased by cold working. Normally non-magnetic, these steels acquire a slight magnetic response after cold working.

They have good weldability, are hygienic, and offer good impact resistance at low temperatures. Typical applications: machinery and manufacturing, construction materials, architectural products, food processing equipment.