LADLE METALLURGY | ARGON STIRRING

Objectives of Ladle Metallurgy


The objective of ladle metallurgy depends on

1. Inert gas stirring
2. Injection metallurgy
3. Heating
4. Degassing
5. Special processes like AOD and VOD.

● There is not necessary to obtained all processes for all types of steel making. More commonly inert gas stirring and heating are required for common grade steel making.

● There are some special types of steel grade in which too much Hydrogen and Nitrogen dose not tolerate by which degassing of liquid steel is required with inert gas stirring and heating of steel. Because degassing is the process in which all the molten gases and inclusion are removed from liquid steel.

Inert gas stirring :

● As we know the steel making have mass transport control reaction and this type of reaction have tremendous influence in the fluid dynamic of the reaction. Therefore in the absence of any stirring there not possible of much rate of reaction, so stirring is necessary. We use Argon inert gas for stirring because it can not  contaminate with liquid steel. Due to the continuous stirring bath, we results such that thermal and materials homogenization, chemical reaction, inclusion flotation this can all operate for better steel refining.

Injection metallurgy :

The injection metallurgy consist of injection of some material or powder for desulphurisation or inclusion morphology change in steel, basically it used may be in solid and powder form. More commonly powder materials are used for injection metallurgy because power have more surface area and rate of reaction is more batter than solid substance.
For example : We used calcium wire in secondary steel making for avoiding of nozzel choking or stopper raising in caster and inclusion free cleanliness steel.

 Heating :

The heating process of ladle metallurgy is noting but a ladle furnace in which we used electrode to heating the liquid bath by arcing. It is necessary because after tapping of steel from primary furnaces, the temperature is much more drops. This temperature drops because of ladle refractory wall direct contamination with open air or stirring operation during mixing of ferro alloys and lime at the time of tapping.

As we know all the above reaction during the material addition are required heat and that heat is consumed from molten bath, the temperature get drop down. So, to overcome these problem ladle heating is necessary otherwise ladle bottom going to be chilled in the time of casting due to low superheat or choke the ladle nozzel, which give more impact on production.

Degassing :

Degassing consist of exposing the molten metal stream to vacuum and removal of dissolved gases in it. When metal steam sudden exposes to vacuum it explodes in to fine droplets and surface area increase. Thus increase in surface area, increases the surface relation process and removal of gases to vacuum.


: Steel Ladle :

● Typically the liquid metal tapped in the ladle which having 300mm to 400mm free board from top of ladle for better homogenization and stirring operation, during refining also avoid the metal spillage from top at the time of ladle handling from one place to another and refining.
Steel ladle - teeming ladle
Steel or teeming ladle

● Then the ladle contains slag zone of 1/3 portion after free board from top side which have lining with magcoke brick to resist the corrosive attack of slag or iron oxide. These slag is mainly contains lime, silica or alumina with some FeO which creat during tapping by addition of lime and aluminum but not oxidise slag from furnace. After then the rest of lining called metal zone up to bottom. Which lining with magcarbon high alumina brick to withstand the hydro dynamic erosion reaction from liquid steel.

● In the bottom of the ladle there are one or two hole for porous plugs and a hole for teeming of ladle metal in to tundish of caster. There is a slide gate arrangement present in bottom of ladle to open or close the teeming nozzle, which inner side of plates are lining with refractory materials. In certain ladle a single hole or two hole present for purging of argon. Mainly bigger capacity ladle have two porous plugs which is more than 200t. These plugs are fitted at the middle portion of the radious of ladle for better homogenization of steel bath. These are mainly made up of high alumina porous bricks.

Argon Stirring :

The Argon stirring from bottom at the pressure of 0.2Nm3/he/ton to 1 Nm3/hr/ton. As the 'Ar' gas is lighter weight than the steel it want to goes up go the ladle. As a result it pull some metal with its pressure of flow and kept metal back after the 'Ar' pass through total liquid medium of steel, which creates a turbulence flow of metal inside the ladle and homogenisation occurs. There is an oxygen plumes eyes create at the top of the liquid bath due to argon stirring by which atmospheric oxygen re-enter to the liquid steel and reoxidation take places. As a result the alumina losses or more alumina consumption and more Al2O3 creation in slag which is not favour for refining as well as it losses heat.

● So soft stirring is carried out after mixing of all lime and ferro alloys for no loss of heat and better homogenization and inclusion free steelmaking. The soft stirring causes the solid inclusion slowly rise up to the slag zone due to lighter weight than the steel bath and contaminated with the liquid at the top of ladle which never revert to the steel bath.

Objective of Argon Stirring :

The objectives of Argon stirring are depends on :
1. Homogenisation : which is carried out after using of all material now it time to only mix up them. At that time we used soft stirring by which oxygen plumes eyes at the top is smaller and loss of heat or chemistry is quite negligible.

2. Arcing : which is carried out for equally distribution of heat to the liquid metal surface by which maintain temperature is equal at any portion of ladle.

3. Deslphurisation : which is carried out for removed of  's' from bath. This  operation carried out for removing of 'S' from bath. This operation carried out in at vigorous stirring. By which ''S" inclusion of liquid steel easily, react with lime and reducing atmosphere.





References :
1. Modern Steel Making :  Dr R.H. Tupkary and V.R. Tupkary.
2. Ironmaking and Steelmaking Theory an d Practice : A. Ghosh and A. Chatterjee
3. Steel Making : A.K.Chakravorty

4. Sr. Professors from IIT's & BPUT. (INDIA)

Author :
Subir Kumar Sahu
Metallurgist.


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