LD PROCESS STEEL MAKING OPERATION OVERVIEW

Overview of LD Steel Making Process :


The LD process operation consist of the following which is written below

1. Charging :  The common process solid scrap are charged into Converter first then followed by liquid pig iron. Sometime a bottom batch of lime and dolomite are charge in bottom of Converter because of bottom erroded of refractory bricks. And sometimes iron ore charge due to bottom built-up more than bricks that may be slag or metal mix slag. After charging vessel is kept in vertical position for blowing.

2. Blowing :  After charging Converter turn to vertical for oxygen blowing from top. Before starting blowing the blower checked the all parameters to start blow is ok. Then water cooled oxygen lance is lower through the mouth of vessel and fixed in 1 to 2mt height from the metal bath surface. A high purity oxygen I.e 99.9% pure oxygen is used for blowing at pressure of 7 to 11kg/ cm2 on to the surface of the liquid iron.

3. Refining :  As O2 impact the molten bath with heavy pressure, the faster reaction between O2 and Fe, Si, Mn, and C in the melt. Oxygen jets create turbulence and cause expose of iron and impurities with O2.
                       As oxidation reaction of silicon, phosphorus, manganese and carbon are exothermic in nature, high heat Is generate at about 2200℃. To bring the both slag and metal temperature to working condition steel scrap are charged before blowing and iron ore and dolomite are charge during blowing. Sometime granular pig iron also charge as a coolant.

2Fe + O2 = 2FeO
Si + O2 = SiO2
Si + 2FeO = SiO2 + 2Fe
Mn + FeO = MnO + Fe
2Mn + O2 = 2MnO
2C + O2 = 2CO
C + FeO = Fe + CO
2P + CaO + 3FeO = CaO.P2O5 + 5Fe
FeS + CaO = CaS + FeO

Thus the oxide product SiO2, MnO, P2O5 and CaS formed above refining reaction and join in the slag when lime is added. Carbon and phosphorus are removed at the latter part of the blow. During blowing silicon is first react with oxygen and remove from iron and from SiO2. Then Manganese and Sulphur are react but the carbon is react form begins to end. When carbon get Finished the blowing also ended. During end of blow the oxygen lance returns to top end position by pumping on metal surface. By which phosphorus can remove betterly.


4. Tapping :  After Finish of blow the vessel tilt down for sampling and temperature. If the chemistry get ok then tapping start in the opposite direction of charging of metal. The tapping angle taken in between 78° to 100° in most of the vessel. In the bath sample carbon and phosphorus is the main components that have to observe. After finishing tapping vessel kept in vertical position and splash the slag for turn down the slag temperature and it also helps the slag coating over refractory bricks. Then dumped the slag in slag pot and complete the heat cycle.
Here tap to tap time varies from 25 to 35 or 40min max. So this process is adopted in maximum plant whoes final product are long and flat.

Quality of LD Steel Making :


Proper refined LD steel has low oxygen and gas content and is low in S and P.  It's nitrogen content is very lower that other processes and provided the oxygen used has a purity of above 99.5% their resistance to cleavage fracture. Which is essential property desired in heavy stressed, welded parts and steel. L.D steel should better cold working are superior to open hearth grade and effect of strach headening and strain ageing are considerably less. Mainly due to lower nitrogen content bcoz nitrogen makes steel unfavourable for cold process.


Composition of Slag in LD Process :

The iron content of the slag is on the lower side, if carbon steel is made. If phosphorus in the charge is more intermediate slaging Off is carried our at nearly 2/3 way through the blow. A typical composition of slag form a heat of dead soft steel at the time of tapping is foow


Cao = 47 to 52%.                 SiO2 = 10- 16;t05
MgO= 2 to 5% .                Limmthiu = 3= 5%
P2O5 = 1 to 3.o%.                  Fe= 16-22%

Advanced of LD Process. :
1. It is a faster process than any other processes.
2. LD needs no extra fuel for generation of heat

3. LD Process ellimielim nitrogen content in steel
4. Low P and S steel can be produced.

5. High carbon or low carbon can be produced

6. Over oxidation does not accross as surface blown is carried out.
7. Steel making efficiency is higher in case of LD Process.
8. Installation cost is lesser than other furnace in term of output.
9. LD Process is suitable for Indian pig iron.


Disadvantages :

1. Maximum amount of liquid charge is required for operation.
2. Scrap consumption is less than other processes.
3. Only solid charge can not be possible.

4. There is a chance of over oxidation in case of faulty operation.
5. Oxygen plant is required mostly to produce pure oxygen.

Limitations of LD Process development : 

1. Being faster process the control of the refining process is stringent.

2. Metal, slag or gas emulsion passes problem in process balancy.



NB ::  L.D PROCESS IS THE ONLY PROCESS WHERE SULPHUR CAN BE EASILY CONTROL IN THE OXIDIZING CONDITION.

Refining of steel during blow and secondary steel making will be discuss very soon in upcoming posts.

Share this

Related Posts

Previous
Next Post »

Contact Form

Name

Email *

Message *