30 November 2022

ENGINEERING MATERIALS | Classification of Steel | EFFECT OF ALLOYING ELEMENTS | STAINLESS STEEL | CLASSFICATION OF  STAINLESS STEEL

ENGINEERING MATERIALS

1.) Engineering Material:-

The Engineering metals play an important role in an industry, because the process of all manufacturing starts with the raw materials.

 

2.) Metal Classification:-

Metal The materials, mainly used in actual practice may be broadly divided into the following Two Groups:

1. FERROUS METALS:-

 

The metals, which contain iron as their main constituent, are called Ferrous Metals.  The various ferrous metals used in industry are:-

  1. Pig Iron,
  2. Cast Iron.
  3. Wrought Iron and
  4. Steel

2. NON-FERROUS METALS:-

The metals, which contain a  metal other than iron as their main constituent, are called Non-Ferrous Metals.  The various Non-Ferrous metals used in industry are:-

Aluminum , Copper , Zinc , Brass & Etc.

 

3.) Steel Classification:-

Steel is the generic term for a large family of Iron-Carbon alloys, which are malleable, within some temperature range, immediately after solidification form the molten state.  The principle raw materials used in steel making are Iron ore, Coal, and Limestone

1.) Carbon Steel:-

Is steel that owes its distinctive properties chiefly to the carbon is contains. A steel qualifies as a Carbon Steel while it contains the following materials at the rated percentage.

  Manganese  – 1.65 %    (maximum)

Silicon          – 0.60 %    (maximum)

Copper         – 0.60 %    (maximum)

CLASSIFICATION OF CARBON STEEL :

Carbon Steel can be subdivided roughly into Three groups :

  1. LOW CARBON STEEL :  Carbon   –  0.05 To   0.25  %
  2. MEDIUM CARBON STEEL :  Carbon  –   0.30 To  0.55  %
  3. HIGH CARBON STEEL :  Carbon  –   0.60 To 1.30  %

 

2.) Alloy Steel:-

Is steel that owes its distinctive properties chiefly to same element or elements other that carbon, or jointly to such other elements and carbon.  Alloy steels posses high yield point and high strength.  They are more stronger, tougher and fatigue resistant than carbon steel.

CLASSIFICATION OF ALLOY STEEL:

Alloy  Steel can be subdivided roughly into Three groups:

  1. LOW ALLOYSTEEL   
  2. MEDIUM ALLOY STEEL
  3. HIGH ALLOY STEEL

 

LOW ALLOY STELL :

Alloy steels contain one or more alloying agents to improve mechanical and corrosion – resistant properties over those to carbon steel.  A typical low – alloy grade contains

Carbon  :    0.40 %

Manganese  :    0.70 %

Nickel  :    1.85 %

Chromium          :    0.80 %

Molybdenum  :    0.25 %

 

MEDIUM ALLOY STEEL:

A group of (mostly) proprietary alloys with somewhat better corrosion resistance that stainless steels are called medium alloys.  These alloys have extensive applications in sulfuric acid system.  Because of their increased nickel and molybdenum contents that are more tolerant of chloride-contamination than standard stainless steels.

HIGH ALLOY STEEL:

The groups of materials called high alloys all contain relatively large percentage of nickel

 

EFFECT OF ALLOYING ELEMENTS:

NICKEL:   Increases toughness and improves low-temperature properties and corrosion resistance.

CHROMIUM: Improve hardness, abrasion resistance, corrosion resistance and resistance to oxidation.

SILICON :  Improve hardness, abrasion resistance, corrosion resistance and resistance to oxidation.

MOLYBDENUM :  Provides strength at elevated temperatures.

 

STAINLESS STEEL :

Stainless steels are high-alloy steels and have superior corrosion resistant to the carbon and conventional low-alloy steels because they contain relatively large amount of  Chromium.

Stainless steels are iron base alloy containing Chromium as the main alloying element with a minimum content of 10.5% to make it resistant to staining, rusting, scaling in most of the corrosive environments.

Several other alloying elements like Nickel, Molybdenum, Manganese, Copper, Titanium, etc. are also added in different grades in order to improve its Metallurgical, Physical and Mechanical Properties to suit typical and use requirements.

Most of metals and alloys loose their strength and start scaling when heated to high temperature and become brittle at low temperature. Stainless steel retain its strength to great extent and do not scale at high temperature, and at the same time they maintain their toughness and ductility even at subzero temperature.

 

CLASSFICATION OF  STAINLESS STEEL :

In the broadest sense the Stainless steels can be divided into Three basic groups based on their structures:

  1. AUSTENITIC
  2. FERITIC
  3. MARTENSITIC

The crystal structure of the metal depends upon the configuration of its atoms to form unit cell.

#   In austenitic steel metal atoms are arranged in

        Face Centered Cubic (FCC)

#    In ferritic steel metal atoms are arranged in

        Body Centered Cubic (BCC)

#    In martensitic steel metal atoms are arranged in

        Body Centered Tetragonal (BCT)

 

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