S T A I N L E S S   S T E E L

What Is It ?
Stainless steels are chromium containing steel alloys. The minimum chromium content of the standardised stainless steels is 11%. Chromium makes the steel 'stainless' this means improved corrosion resistance.

The better corrosion resistance is due to a chromium oxide film that is formed on the steel surface. This extremely thin layer, under the right conditions, is also self-repairing.

Besides chromium, typical alloying elements are molybdenum, nickel and nitrogen. Nickel is mostly alloyed to improve the formability and ductility of stainless steel. Alloying these elements brings out different crystal structures to enable different properties in machining, forming, welding etc.

The four major types of stainless steel are:

• Austenitic

• Ferritic

• Austenitic-Ferritic (Duplex)

• Martensitic

Austenitic is the most widely used type of stainless steel and still represents 80% of the world market. It has a nickel content of at least of 7%, which makes the steel structure fully austenitic and gives it ductility, a large scale of service temperature, non-magnetic properties and good weldability. The range of applications of austenitic stainless steel includes housewares, containers, industrial piping and vessels, architectural facades and constructional structures.

Ferritic stainless steel has properties similar to mild steel but with the better corrosion resistance. The most common of these steels are 12% and 17% chromium containing steels, with 12% used mostly in structural applications and 17% in housewares, boilers, washing machines and indoor architecture.

Austenitic-Ferritic (Duplex) stainless steel has a ferritic and austenitic lattice structure - hence common name: duplex stainless steel. This steel has some nickel content for a partially austenitic lattice structure. The duplex structure delivers both strength and ductility. Duplex steels are mostly used in petrochemical, paper, pulp and shipbuilding industries.

Martensitic stainless steel contains mostly 11 to 13% chromium and is both strong and hard with moderate corrosion resistance. This steel is mostly used in turbine blades and in knives.

Source: CRU and Outokumpu Stainless OY
Classification and Usage Areas
The most important alloying elements in the structure of stainless steels are chromium-nickel-moybdenum and manganese in order of importance. Nickel and chromium specify structure of stainless steel if it is ferritic or austenitic.

Internal StructurePrimary Alloying Elements
AusteniticCr, Ni, Mo
MartensiticCr, C veya Ni
DuplexCr, Ni, Mo

Austenitic :
Austenitic stainless steels are the most commonly used group in industry. This group includes 304, 316 qualities and also high alloy steels such as 310S.

Min.%/7 Ni content is enough to make internal structure austenitic in stainless steels. Nickel improves ductility properties, heat resistance and welding properties to stainless steel.

Housewares, containers, industrial piping and vessels, architectural facades and building structures are some of the austenitic stainless steel industrial applications.

Ferritic :
Ferritic stainless steels include 12-18% Cr and 0.025-0.08% C.430 Quality is the most commonly used ferritic steel in industry. The structure of ferritic stainless steels are similar with steels but their corrosion resistance is extremely high.

The major use areas of ferritic steels are kitchen utensils, washing machines, indoor decorative applications, automobile chassis parts, exhaust components, hot water tanks.

Austenitic-Ferritic (Duplex) :
This kind of stainless steels which are called as duplex in industry, include 18-28% Cr and 4.5 Ni in general. Nickel content is insufficent for making structure fully austenitic that’s why they contain also ferritic structure. This combined structure provides both strength and ductility.

Duplex steels are mainly used in petrochemicals, paper and ship building industry.

Martensitic :
Martensitic stainless steels contain 0.1% carbon and chromium. They have average corrosion resistance. The hardness of martensitic steels can be increased if heat treatment applied.

Turbine blades, knives and surgical operation instruments are the major use areas of martensitic steels.

Stainless steel which can be produced in different chemical, physical and mechanical properties, have high corrosion and heat resistance, mechanical strength, manufacturing ease, aesthetic appearance, hygienic and long lasting properties.

Technical data related to stainless steel can be reached by links below.

Above lists are just for general information, and cannot be accepted as any standart.

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