Matérials

For a steel to claim stainless status, it must contain a minimum of 12% chromium.

The main families of stainless steel are broken down into families, of which the most important are:

Ferritics

We talk about ferritic steel when the alloy mainly contains chromium and is magnetic. Ferritic steels dissipate heat easily.

Austenitics

An alloy containing mainly chromium and nickel is said to be austenitic. Austenitic steels are not magnetic and do not dissipate heat easily. They resist corrosion very well and are very malleable with a fairly substantial elongation capacity.

Martensites

Alloys that contain a minimum of 0.08% carbon are called martensitic. Martensitic steels have good mechanical strength and are magnetic. Sensitive to quenching, they have good corrosion resistance.

The refractories

These are the steels that are used for temperatures above 300° Celsius. Refractory steels offer good resistance to oxidation and corrosion by gases at high temperature.

Austeno-ferritics also called duplex

Austenitic-ferritic stainless steels, known as “duplex” stainless steels, contain 20 to 30% chromium, 2 to 10% nickel and a nitrogen content of between 0.1 and 0.3% (table 7). They may also contain other elements such as molybdenum (up to around 4.5%), copper (up to 2%) and tungsten. They have an austenitic and ferritic two-phase structure at room temperature. They are more resistant to breaking load, offer more elasticity and better corrosion resistance than austenitic steels.

Austenitic steels subjected to the heat treatment of hyperquenching

This is the quality heat treatment typically applied to austenitic stainless steels. It consists of maintaining a high temperature (from 1,000 to 1,150°C) followed by rapid cooling. Austenitic steels having undergone this treatment have great flexibility and good resistance to intergranular corrosion.