Metallurgist.in

Handbook for Metallurgists
Menu
  • Home
  • About
  • Glossary
  • Submit Articles
  • Contact Us

Gases and Non-Metallic inclusions of Steel

Metallurgist January 11, 2013

GASES IN STEEL:-
The gaseous elements commonly present in steels are oxygen, hydrogen and nitrogen. In steel ingots or castings, gases may be present in the form of gaseous blow holes, as inclusions of oxides, nitrides or hydrides, or dissolved in the solid solution.
Gases get into the metal from the following principle sources:-

  1. Charge materials.
  2. Furnace atmosphere and the blast given to the surface or into the depth of the metal.
  3. Ferro-alloys and various additions introduced into the metal and slag during melting or teeming.
  4. The atmosphere surrounding molten metal at tapping and teeming.

NON- METALLIC INCLUSIONS IN STEEL:-
Compounds of metals (such as iron, manganese, silicon) with non-metals (such as oxygen, sulphur, nitrogen, etc.) which may be present in steels, are termed as non-metallic inclusions.
According to their size, inclusions are divided into two groups:-

  1. Microinclusions.
  2. Macroinclusions.

According to their composition, they are usually classified as:
Sulphides (FeS, MnS)
Oxides (FeO, MnO)
Phosphides (Fe3P, Fe2P)
Nitrides (NiN, VN)
Carbides (Fe3C, Mn3C)
Complex Inclusions such as silicates, oxysulphides.

The principle sources of non-metallic inclusions in steel are as follows:

  1. Inclusions present in the charge materials; pig iron and scrap.
  2. Inclusions passed to the metal from the lining of the furnace, launders, ladles etc.
  3. Inclusions formed in the steelmaking process; by interaction between metal and slag; on addition of deoxidants or alloying elements; by precipitation from solidifying steel.

EFFECT OF GASES AND INCLUSIONS ON STEEL PROPERTIES:-
The solubility of gases in steel decreases with lowering temperature, especially on the change from liquid to solid state of the metal in moulds, steel that has had a high gas content in molten state will have many blow holes on solidification and possess poor mechanical properties, which can make it unsuitable for application.
Elevated concentrations of oxygen in killed steel can cause the formation of blowholes due to the reaction with carbon: [O] + [C] ó COg. Besides, if oxygen is present in a high concentration in steel, it can form substantial quantities of low melting oxide and oxysulphides inclusions which solidify at grain boundaries, thus lowering the strength of metal at high temperatures (RED SHORTNESS EFFECT).
Nitrogen impairs the plastic properties of steel, increases its brittleness at low temperatures (COLD BRITTELNESS), and makes it liable to ageing.
Hydrogen is responsible for a number of defects in steel (flakes, fish scale fracture, etc.). These defects are associated with evolution of monoatomic hydrogen which has been dissolved in molten metal.

Share
Tweet
Google+
Linkedin
Stumble
Email
Next Article

Related Articles

A brief introduction of Steel Making
      In simple words, steels are deformable alloys of iron …

A brief introduction of Steel Making

Principles of Steel-making
Principal concepts of physical chemistry useful in steel making are; …

Principles of Steel-making

About The Author

Metallurgist

My name is Satyadeo Thakur and most of my friends call me Satya for short. I am a graduate of metallurgical engineering and a self-taught freelance designer specializing in graphic, user interface and web design. I love traveling to distant places and I am fascinated by food.

2 Comments

  1. Sai Kiran

    Can you please explain about morphology of inclusions?

    June 8, 2013
  2. Triloki verma

    Please explain of phosphorus reversion?

    August 20, 2015

Leave a Reply

Cancel reply

Search

Archives

  • June 2020
  • May 2020
  • January 2013

Meta

  • Log in

Metallurgist.in

Handbook for Metallurgists
Copyright © 2021 Metallurgist.in
Theme by MyThemeShop.com

Ad Blocker Detected

Our website is made possible by displaying online advertisements to our visitors. Please consider supporting us by disabling your ad blocker.

Refresh