steel making

1. SECONDARY STEEL MAKING
AND RH DEGASSER

2. INTRODUCTION
Steel is the world's most important engineering and construction material. It is used in every aspect of
our lives; in cars and construction products, refrigerators and washing machines, cargo ships and
surgical scalpels. It can be recycled over and over again without loss of property.
• Steels are alloy of iron and carbon.
• The amount of carbon in typical steel alloys constitutes up to 2.1% of its weight.
• Because of its high tensile strength and low cost, steel is used in buildings,
infrastructure, tools, ships, trains, cars, machines, electrical appliances, and
weapons.
Today steel is one of the most common material in world, with more than 1.3 billion tonnes being produced annually

3. INTRODUCTION TO SAIL
 Steel Authority of India limited is the largest steel producer in India with a turnover of INR 66,267 crores
in the financial year 2018-19
 SAIL owns and operates five integrated plants at Rourkela, Bhilai, Durgapur, Bokaro and Burnpur. There
are three special steel plants at Salem, Durgapur and Bhadravati
 SAIL’s subsidiary at Chandrapur is a bulk producer of Ferro alloys.
 The company has the distinction of being India’s largest producer of iron-ore
 SAIL manufactures critical items such as rail and wheels/ axles for Indian railways and wide plates to
service several niche marks
 SAIL steel has a strong presence are construction, automobiles, heavy engineering, defense, pipes and
tubes, fabrication, cycle, drum and barrel, containers, wire drawing, agriculture equipment and electrical
equipments.

4. INTRODUCTION TO BHILAI STEEL PLANT
 The Bhilai Steel Plant, major Producer of steel rails as well as
major products of wide steel plates and other steel products.
 It is a subsidiary of SAIL
 The plant also produces other by-products from its plants like
slag, coke etc.
 It was setup with the collaboration of USSR in 1959
 It has its own series of Blast Furnace, LD Converters, Secondary
Metallurgy Ladles, Billet and Bloom Casters, and Research and
Development Lab
 Bhilai specializes in the high strength UTS 90 rails, high tensile
and boiler quality plates, TMT bars, and electrode quality wire
rods
 Bhilai has one in for ISO 14001 certification for its Environment
Management System and its Dalli Mines.

5. HISTORY OF BHILAI STEEL PLANT
 The governments of India and USSR entered into an agreement in New Delhi on 2 March, 1955
for the establishment of integrated iron and steel works at Bhilai with an initial capacity of 1
million tons ingot
 The main consideration of Bhilai was due to availability of iron ore at Dalli, Rajhra about 100 km
from the site, limestone from Nandini about 25 km from the plant and dolomite from Hirri, about
140 km from the site.
 The plant was commissioned with the inauguration of first blast furnace by first president, Dr.
Rajendra Prasad on 4 February, 1959.
 The capacity of plant was extend to 2.5 MT by September 1967 and a further expansion to 4 MT
took place in 1988.

6. INTRODUCTION TO STEEL MELTING SHOP -||
 Steel Melting Shop-II (SMS-II) is designed to produce 1.5 MT of Cast Steel in the form of
Slabs and Blooms.
 The shop was commissioned on 29th of July'1984.
 The revised production capacity is estimated to be about 1.8 MT.
 SMS-II is equipped with secondary steel making units like VAD, Ladle Furnace and RH
Degasser to produce low hydrogen, low sulphur and micro-alloy steels.

7. BASIC FLOW CHART OF HOW STEEL IS PRODUCED IN BSP

8. SMS-II COMPRISES CONVERTER SHOP SECONDARY STEEL MAKING &
CONTINUOUS CASTING SHOP.
SMS-||
CONVERTER SHOP
SECONDARY REFINING UNITS
CONTINUOUS CASTING SHOP

9. CONVERTER SHOP
 The Convertor Shop has 3 convertors of 130 T capacity each.
 The working lining of the Convertor is of 690 mm Magnesia Carbon bricks.
 Tap to tap time of the Convertors is around 60 minutes, with an average heat weight
of nearly 120 Tons.
 There are two hot metal charging cranes of 180 + 50 T capacity and a semi portal
crane of 40 + 40 T capacity.
 The operation cycle of the convertor is as follows:
a) Charging - 5 Min
b) Oxygen blowing - 20 min
c) Sampling & temperature measurement - 8 min
d) Corrections before tapping - 5 min
e) Tapping - 5 min
f) Nitrogen splashing, coating &deslagging - 7 min
TOTAL - 50 min

10. SECONDARY REFINING UNITS
 SMS-II secondary refining units comprise three units:
1) Vacuum Arc Degassing Unit (VAD)
2) Ladle Furnace (LF)
3) RH Degasser (RHD)
The purposes of secondary refining are many: temperature homogenization or adjustment; chemical adjustments
for carbon, sulfur, phosphorus, oxygen and precise alloying; inclusion control; degassing, and others.
Secondary Refining processes are performed at atmospheric pressure or under a vacuum, with or without heating,
solids and/or gas injection, and stirring.

11. Vacuum Arc Degasser (VAD)
A Vacuum Arc Degasser(“VAD”) is used
 to reduce the concentration of dissolved gases(H2,N2,O2) in the liquid steel.
 To homogenize the liquid steel composition and bath temperature to remove oxide inclusion materials from the
liquid steel and to provide conditions that are favorable for final desulphurization
 The fundamental requirements for the ladle degassing process include:
1. Sufficient freeboard in the ladle to contain the vacuum-induced slag and steel boil.
2. An inert gas percolating through the steel bath for stirring, inclusion separation, and enhancement of vacuum
degassing performance.
3. Sufficient superheat in the steel to avoid skull formation.
4. Means to deliver additives while the ladle is inside the vacuum tank.

12. LADLE FURNACE
Ladle Furnace is a heating unit where liquid
steel tapped in ladle from converter can be
heated using the similar principle that of VAD
unit.
 The lid of Ladle Furnace is water cooled
and is provided with three holes for three
columns of electrodes
 one hole for ferro alloy addition and one
for aluminium / Calcium silicide wire
injection
 A dedicated fume extraction system with
bag filters for dust separation is provided
to suck out the fumes and dust generated
during arcing

13. RH-DEGASSER- (RUHRSTAHL-HERAEUS)
 RH Degasser is basically a degassing unit.
 The principle of creating vacuum is similar to that of VAD unit but
there is basic difference in the working principle of the two
 VAD is a tank degasser while RH Degasser belongs to circulating
degassing system.
 There is a vessel with inlet and outlet snorkels both lined with
refractory.
 The vessel is immersed into the liquid steel.
 The vessel is subjected to low vacuum.
 The metal level rises in both the snorkels due to barometric
pressure.
 Thus the recirculation of molten steel is started and complete
heat thus passes several times through the RH vessel.
 The circulation rate of molten steel is as high as 130 T / minute.
 Operation is performed until we get steel with H2 concentration
less than 1.6 ppm

14. Figure: Schematic Diagram of RH Degasser. Snorkels used for degassing

15. ADVANTAGE OF RH – DEGASSER
 Faster and more effective then VAD process.
 Restricted hydrogen concentration level within 1.6 ppm in
final steel.
 Effective separation and removal of non-metallic inclusions.
 Alloy additions can be made to adjust the specifications more
closely.
 Heat loses are relatively low.
 Reduction of dissolved gases from liquid steel extreme low
levels
 Improved cleanliness of steel.
 Decrease sulphur< 50 ppm.
 Decrease nitrogen < 40 ppm.
 Precise steel refining as per the chemical composition before
casting.

16. Snorkels
 RH snorkels play very important role in RH degasser.
 These are the inlet and outlet snorkel, both of them are completely refractory lined
by magnesia chrome bricks on the inside and these bricks are coated with high
alumina castable on the outside.
 Inlet snorkel is equipped with a number of gas injection pipes distributed around
the circumference.
 Outlet snorkel is simply refractory pipe.
 For preheating of the vessel a movable burner lance is provided
 The burner lance consists of water cooled body with oxygen and COG piping as well
as ignition device.
 Nitrogen is used for lance flooding.
 The greatest wear occurs in the snorkel legs and bottom of the chamber. Refractory
requirement are high strength, good slag resistance and thermal high shock
resistance.

17. Snorkel Life
 Low snorkel life not only has cost implementation but also reduces the
opportunity for heat making through RH degasser.
 Initially RH snorkel gave life of only 66 heats.
 It is now improved to around average 125 heats.
 The lower life results due to higher Temperature demand by casting machine
Components Heats
Snorkel life 100-200
heats Lower vessel 2 – 3
snorkel life Upper vessel > 1000
heats Hot off take > 4000

18.  Dry gunning with or without the use of gunning robots, is a well-
known, modern procedure to increase the life of refractory-lined
vessels quickly, accurately and with low rebound.
 with the new GUNMIX moistening system, it is now possible to
dry gun low cement castables with low rebound, and for small
repairs this is a cost-saving alternative to shotcreting.
 dry gunning the material is discharged from the machine with a
maximum of 5% moisture and then fed to the nozzle by an air
stream
 With wet gunning material is moistened with water in a mixer
and then pumped through a hose by means of an eccentric
screw or a piston pump
 The gunning material is essentially the same as the original
refractory (plus binder material)
 Consumption of gunned refractory is also extremely varied,
ranging from 0.2kg/t steel for new vessels and upto 2kg/t steel
for an old vessel or one in an aggressive environment.
Figure: Showing a worker gunning snorkels.

19.  Degassing time is the total time counted from open
first ejector to close last ejector but actual degassing
time start when vessel reaches up to 10mm bar.
 The degassing time more important factor for
determining the final hydrogen content in the molten
steel.
 Generally 15 minute is sufficient but when tundish
change then degassing time should be 20 minute.
 H2 contents decreases with increases in degassing time
after a time its becomes nearly constant after reaching
0.6 ppm H2
Lift Gas Ar is used as a lift gas. Lift gas pressure should be 8 to 8.5 kg/cm2 for achieving less than 1.6
ppm in 15 minute degassing. The lift gas temperature is about 250m3/hour.

20.  Free Board: Free board is the space in ladle. Free board is directly affecting circulation rate, if free
board is more than circulation rate is more. When circulation rate is more then hydrogen removal is
more else hydrogen content in liquid steel is less.
 Ladle: when ladle is circulating then there is no effect but when new ladle is used then hydrogen
ppm increases up to 0.2 ~ 0.3 ppm.
 Tundish: Tundish is simple device where liquid steel stays for a while before entering the mould.
Steel is teemed into the mould via Tundish.
 Burner: burner is basically lance used for removal of scale from the vessel. Oxygen
and COG is used in burner. Burner takes a part for removal of hydrogen ppm indirectly.

21. Gases in Steels
 Impurities like C, Si, Mn, S, P etc are eliminated but gases like oxygen, nitrogen and
hydrogen may still remain in solution as deleterious impurities
 On solidification, the excess dissolved gases are liberated which may cause irregularities
 The amount of dissolved gases depends on
 Quality of raw materials used
 Steel making process.
 Composition and temperature.

22. Oxygen in Steel
 Oxygen is supplied for refining iron and hence a certain fraction is
inevitably left over as dissolved oxygen in liquid steel.
 Excess oxygen causes defects like blow holes and non metallic
inclusions.
 Oxygen is lowered by deoxidizers like Mn, Si, and Al etc.
 the oxygen will react with some of the carbon in the steel to produce
carbon monoxide (CO).
 Strong deoxidizer such as aluminium, titanium and silicon, when
added to the molten steel are effective in reducing the oxygen content
so that carbon can no longer react with oxygen when the steel is
vacuum degassed.

23. Nitrogen In Steel
 Nitrogen may have an undesirable effect on the properties of steel
 Nitrogen in steel comes from atmospheric air, raw material charges,
process adopted and purity of oxygen used
 Low nitrogen contents (0.004% maximum) is desired in low carbon
steel
 some nitrogen is removed from molten steel by inert gas flushing or
vacuum degassing
 To get very low nitrogen, vacuum must be very low. Compared to
Hydrogen, nitrogen removal rate is low due to low diffusibility.
 low nitrogen contents are attained mainly by the control of primary
steel making practices.
 Presence of nitrogen shows adverse effect during welding

24. Hydrogen In Steel
 H2 is formed when water vapour comes in contact with
steel & slag
 The amount of H2 dissolved in steel varies with the partial
pressure of H2, composition of steel & its temperature
 Hydrogen is a particularly troublesome gas
 It is the cause of bleeding ingots, embrittlement, low
ductility and the presence of blow holes.
 During complicating heating and cooling cycles steel might
absorb hydrogen.

25. Major defects due to hydrogen
 Hydrogen embrittlement
Hydrogen embrittlement is a metal's loss of ductility and reduction of load bearing capability due to the absorption
of hydrogen
. The result of hydrogen embrittlement is that components crack and fracture at stresses less than the yield
strength of the metal

26.  Hydrogen Blistering
Hydrogen Blistering (HB) refers to the formation of subsurface planar cavities
resulting from excessive internal hydrogen pressure.
Growth of near-surface blisters in low-strength metals usually results in surface
bulges.

27.  Loss of tensile ductility
Hair line cracks are formed all through the section and are revealed only after deep etching
Hydrogen is desorbed very slowly even after cooling the steel for days or even weeks.

28.  Flakes
One of the most harmful effects of hydrogen is the formation of flakes
Preferred locations for flake formation are around inclusions and areas of martensite or segregation.
Flakes are not observed in unalloyed steel, but are easily formed in manganese, chrome and nickel steels
prevention of flakes is crucial for example for heavy plates, rails, and pipeline.

29.  Hydrogen induced Cracks (HIC)
Hydrogen will diffuse in steel collect itself into weak spot that is sufficient to induce cracks resulting
premature failure
 Fish eyes
The occurrence of fish eyes is related to the hydrogen contact of the steel.
Fish eyes are formed in the presence of tensile strains above the yield stress of steel.

30.  Blowholes and pinholes
blowholes are a major cause of surface defects in
the as-rolled product and are due to excessive
amounts of dissolved gas N2, CO and hydrogen
 Longitudinal surface cracks
The incidence of longitudinal surface cracks is
increased if the hydrogen content of the steel
increases.

31. Conclusion
 Hydris system is very consistent and very accurate instrument for the Hydrogen Measurement
in steel.
 H2 ppm decreases with increase in degassing time, but after a certain period of time it becomes
independent of time. So based on techno-economics, the degassing are limited to a certain
threshold value.
 Lift gas or Argon gas is vital aspect in RH Degassing Process, without which practically no
degassing is possible
 If we would kept inlet hydrogen level on lower side by carefully handling different Processes
which involves entrance of Hydrogen, our degassing process would be much efficient
 The chemistry of the heat should be such that the casting operation goes Uninterrupted

32. THANK YOU
By
- Ayush kumar jain
- Yogesh markandey