1. • CRGO
• CRNGO
• Electrical steel properties
• Reason for the properties
• Manufacturing Process
• CRGO CRNGO and MS
• ES grades
• GOS industry in India and abroad
• Challenges Pratyush Srivastava
Pawandeep Singh Arora
B-tech IIT BHU

2. Electrical steels
 Electrical steel, also called lamination
steel or silicon electrical steel, silicon
steel or transformer steel, is special
steel tailored to produce certain specific
magnetic properties.
 It has specific proportion of silicon that is
responsible for its unique properties.

3. Properties of Electrical steel
 The hysteresis loss is low ie. The magnetic
domains get easily aligned in one or the other
directions and not much of electrical energy is
required for this process.(hysteresis graph on
following slides)
 The magnetic permeability is high ie the
material easily allows formation and
accumulation of magnetic field within.
 Electrical resistance is high to prevent eddy
current losses.(current that flows on the
surface as a result of electro magnetic
induction over the core coil)

4. Raw material for manufacture :
 ferro silicon alloy (15-90% Si) is the
base material.
 The alloy is processed to lower the
silicon content { 3.5% } and remove
constituents like Mn ,S etc.
 Finally the density becomes around
(7600+-50) kg/m3

5. CRGO Vs CRNGO
 CRGO :
 Cold Rolled Grain Oriented steel.
 Rolling done in one direction such that the grains elongate
along one direction.
 CRNGO:
 Cold Rolled Non Grain Oriented steel
 Rolled in random directions such that the grains are
elongated along different direction.
 CRGO needs precise alignment due to its anisotropy( the
properties that are different along different directions are
anisotropic properties) but CRNGO can respond to flux
changes in all directions (ie. Its properties are isotropic)
hence CRNGO is used in motors.

6. CRGO CRNGO grains
Isotropy and anisotropy arise from grain orientations
CRGO CRNGO

7. CRGO /CRNGO manufacturing
• Hot rolling
• Pickling
• Cold rolling
• High temp anealing
• Inspection

8. Why CRGO/ CRNGO over
MS
 In mild steel there is much loss in
electrical energy due to hysteresis and
eddy current hence use of mild steel is The
uneconomical when it comes to usage in hysteresis
loss is
electrical devices. equivalent
to the area
of the
enclosed
loop.
Electrical steel Mild Steel

9. How CRGO reduces losses
 Grain orientation: When cold rolling is done
the grains get elongated in one direction and
get narrowed in the perpendicular direction.
Hence due to the shape it becomes easier for
the domains to change polarity back and forth
along the elongated direction.
 Grain enlargement: when heated at
temperatures around critical temperature
(temp at which the grain boundaries begin to
diffuse ) followed by slow cooling grain
enlargement occurs. This reduces electrical
losses due to hysteresis.

10. Manufacturing
 Ferro silicon steel is heated in a
decarburizing environment(N with H20 and
H2 )
 S N and O must be as low as possible
 More silicon content increases resistivity
but at the same time makes it more brittle.
 Si reduces magnetostriction. (change
shape/size when placed in a
electromagnetic field)

11. Manufacturing
In the final processed material –
 C should be less than .06%
 Mn +Al = .5% (approx.)
 Si =3.2%
Then it is cold rolled to increase grain size :
 2-5 in case of CGOS
 5-20 in case of HGOS
as compared to MS ( .5 mm)

12. Manufacturing
 PAIR = Pre Annealing Intermediate Rolling
 This is done to improve uniformity of
grains. This will ensure easy conformation
of domains when a varying magnetic field
is applied.
 MnS , carbides, oxides, or nitrides used as
the grain growth inhibitors.
 Finally carlite coating is done. It helps
reduce eddy losses.

13. Manufacturing
 Anisotropy correct to 7% in GO and 3%
in Hi-B GO(better grade of CRGO) ie the
direction of elongation should not vary
beyond these angles.
 This elongation is obtained by careful
cold rolling.
 This makes switching cost effective and
improves operational efficiency.

14. Applications
 CRGO (or CGO) is used in transformers where we require
the cost of operation to be less but efficiency more .
 Nickel Iron is an alternative but -> high installation cost.
 Relay steel used in direct current conditions (not good
with AC current)
 CRNGO in motors and generators due to isotropy (Since
in motors the coil is wound on axis and rotates with it so
direction of flux keeps changing and we require similar
properties in all directions), ballasts, small Transformers
generators for steam turbine and water wheels.
 CRGO needs precise alignment and this often increases
the length of appliance.

15. CRGO Production
 No CRGO production in India.
 SAIL made an abortive attempt to
produce CRGO steel at its Bokaro plant
in Jharkhand (1990s) but failed.
 The improvements in GOS have led to
an ever increasing demand of this grade
of steel due to operational cost reduction

16. CRGO Production
 Inspite of being classified as a "steel" is very
rarely impacted by the international price
movement or other factors influencing mild
steels or other categories of steel products.
 No competition from substitutes
 Metglass Amorphous Boron Strip / Mu Metal
/Nickel Iron -- various technical problems and
have already been relegated for use in special
purpose applications (mainly high frequency)
only in developed countries. (suppliers are
mainly developing countries)

17. CRGO Standards

18. CRNGO Standards

19. CRGO Types

20. CRGO Types

21. CRGO Types

22. CRGO Types

23. CRGO Types

24. End Users

25. Challenges :
 Indian testers are widely used but are in-consistent.
SOKEN (Japanese) single sheet tester is best in
category.
 Transformer noise must be low because all the
transformer characteristics depends on core.
 Nomenclature needs to be reviewed in most places.
Many organizations still use obsolete nomenclature.
 For CRGO no definite standards when it comes to
manufacture of transformer cores because there is
always ambiguity in testing and most transformer
manufacturers use secondary/used cores.

26. Grades, Nomenclatures and
Materials
 Different mills have different brand names and
nomenclatures whilst producing GOS and HGOS.
 Most mills have now switched over to the following
method of grading Grain Oriented Steels:
(Thickness) (Brand Name) (Core loss at 1.7T/50Hz)
 For eg. Nippon Steel grade 23ZH100 means
thickness 0.23mm, ZH is the brand name for Hi-B for
Nippon Steel and 100 means 1.00W/kg at
1.7T/50Hz.
 Similarly 23 RGH100 IS Kawasaki Steel
nomenclature for the same material and
23ORSIH100, the Thyssen Krupp Electrical Steel
(TKES) nomenclature for the same material.