Basic grades and families

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Stainless Steel is an alloy made of iron, chromium and carbon. Occasionally it has other complementing elements, the most common one is nickel.

Chromium is what gives this material its stainless nature. In oxidising atmospheres, for example air, chromium makes a very dense and thin oxide layer which isolates the material from any corrosive action.

The passive layer should always be maintained undamaged, this guaranties stainless steel high corrosion resistance

Stainless Steels are classified depending on their different containing elements and also on the quantity of each of these elements into their composition.

Generally, four basic families are considered: martensitic, ferritic, austenitic and duplex stainless steels.

Information courtesy of ACERINOX

Austenitic

They are iron, chromium, nickel and carbon alloys. Nickel adding modifies their structure.

Their most representative grade is AISI 304, EN 1.4301.

This is the group with bigger benefits in components and equipment manufacturing, as well as service performance. They have excellent forming properties, very easy-welding and great corrosion resistance.

Product data sheets:

Ferritic

The ferritic stainless steels are also alloys made of iron, chromium and carbon with higher chromium content and lower carbon than martensitic ones.

Their typical values are C < 0,10% ; Cr 16 – 18%

The most representative ferritic stainless steel grade is AISI 430, EN1.4016.

Their mechanical characteristics allow medium forming. They are easy-welding and very commonly used in applications where appearance is important.

Their corrosion resistance is higher than the resistance of martensitics. 

Product data sheets:

Duplex

Duplex stainless steels are microstructurally constituted by two phases: ferrite and austenite. As alloying elements, they contain iron, chromium, carbon and nickel, the latter element to lower content than in austenitic stainless steels.

In general, they have higher mechanical properties and corrosion resistance than ferritic and austenitic stainless steel.

Product data sheets:

Martensitic

This stainless steel is an alloy made of iron, chromium and carbon, its typical chemical composition is of C 0.10%; Cr 12-14%.

The main grade of martensitic stainless steel is AISI 420, EN 1.4028.

Martensitic stainless steels suffer structural changes at high temperature therefore they usually get hardening and tempering heat treatments.

After these treatments, these materials get high mechanical properties and enough corrosion resistance.
Their most typical application is cutlery.

Product data sheets: