Stainless steel, types and properties


Stainless steel, types and properties





Stainless steel, types, and properties 


Stainless steel made up of adding chromium and other elements in the iron.
More than 11.5% chromium is added to the iron, a fine film (Chromium oxide) is formed on the surfaces exposed to air, which acts as a fence to further oxidation, corrosion, or retardation. These types of steels cannot be stained easily, that is why these kinds of steels called stainless steel.


Stainless steels can be classified into three metallurgical classes:   
  • Austenitic ·   
  • Ferritic  
  •  Martensite·

Based on their microstructures. Each of the classes has different welding requirements, that will be discussed later.
Stainless steel, types and properties

MATERIALS

Austenitic stainless steel

This steel has a strong structure at room temperature, the highest corrosion resistance compared to all stainless steel, and the greatest strength and scale resistance at high temperatures.

Composition of the Austenitic stainless steel
The composition of the Austenitic stainless steels are as follows:


Carbon
0.03-0.025%

Manganese
2-10%

Silicon
1-2%

Chromium
16-26%

molybdenum and Titanium
In some cases
Nickel
3.2-22%

Sulfur and phosphorus
normal



Applications of the Austenitic stainless steel

Austenitic stainless steel is widely used, Some of the main uses are as follows:

  • Dairy industries, 
  • Transportation industry, 
  • Household items, 
  • Food processing, 
  • Chemical processing, 
  • Aircraft industry, etc

Ferritic stainless steel
With a low amount of carbon to chromium ratio ferritic steels possess a microstructure that is primarily ferritic. These kind of  steels are magnetic and have good ductility and do not work harden to any appreciable degree. Also, this kind of steels have the capacity to resist corrosion more than martensitic steels.

Composition of the Ferritic stainless steel

The composition of the Ferritic stainless steels are as follows:

Carbon
0.08-0.20%

Manganese
1-1.5%
Silicon
1%
Chromium
11-27%

Applications of the Ferritic stainless steel

The uses of the Ferritic stainless steels are as follows:
  • The parts of oil burner 
  • Interior decorative 
  • Screws and fittings
  • Petroleum industries

Martensitic stainless steels

Due to the higher carbon to chromium ratio, Martensitic stainless steels are the only types hardenable by heat treatment. These steels are having good thermal conductivity, hardness, and ductility. This kind of steel is also magnetic in all conditions and can be rectified easily due to magnetic ability.

Composition of the Martensitic stainless steel

The composition of the Martensitic stainless steel is as follows:

Carbon
0.15-1.2%
Manganese
1%
Silicon
1%
Chromium
11.5-18%

Applications of the Martensitic stainless steel

Some typical uses of the Martensitic stainless stees are as follows:
  • The parts of Pumps and valves 
  • Turbine buckets
  • Surgical instruments
  • Rules and tapes, etc

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