FIELD OF THE INVENTION
The current invention relates to a process for producing Goss nuclei in hot-band of Fe-3.2Si
CRGO steel containing C as low as 0.03% against conventional use of 0.06% and Al as the only
inhibitor producing element. The invention avoids several critical stages that are usually used in
prior arts of CRGO steels, i.e., reheating of slabs at high temperature to dissolve the elements
that will produce inhibitors, homogenization of slab in terms of the alloys that will produce
inhibitors, presence of critical amount of austenite during hot-rolling which accounts for
inhibitor alloy dissolution, hot-band annealing at high temperature for dissolution and re-
precipitation of inhibitors at later stage during primary annealing. CRGO steels are utilized for
making transformer as they exhibit high magnetic flux density and low core loss.
Background
The first inventor demonstrating that high magnetic flux density and low core loss can be
obtained in steels alloyed with silicon content more than 3.0% was N.P. Goss (US Pat 1 965
559, 1934). These two magnetic characteristics are most appropriate for the usage of CRGO
steels as transformer core material. The occurrence of a particular crystallographic texture of
[110]<001>, that is, [110] planes parallel to the rolling plane and <100> direction parallel to
the rolling direction, known as Goss texture, is attributed for the excellent magnetic properties
in the steei. The research and development works are continued on to further elevate the
magnetic properties of CRGO steels. A considerable amount of R&D work is concentrated on
forming suitable inhibitors to accomplish particle pinning effects. These inhibitors are
anticipated to limit the growth of non-Goss oriented grains during secondary recrystallisation
process. Non-metallic precipitates and elements having drag effect on grain-boundary
movement has been mainly used as inhibitors of grain growth. The non-metallic precipitates are
formed through complex hot band preparation and cold rolled steel sheet annealing processes.
Fine nitride or sulfide precipitates that may operate as grain growth inhibitors are produced by
alloy additions such as Al, B, Mn, Ti, Se, S, N, etc. [US 5 800 633, EP 0 600 181 Al, US 3 162
553, US 2 867 559, US 3 423 253, US 3 895 974, US 4 225 366, US 6 893 510 B2, US
2014/0230966 Al]. Several of these nitrides or sulfides inhibitors impose very high (in the

range of 1300-1400 °C) slab reheating or hot-rolling temperature depending on alloy chemistry
for preparation of inhibitor particles.
Many of the prior arts use steel containing carbon concentration to the level of more than 0.05
wt % [WO2011063934 A1, EP 0 219 611 B1, US 5 266 129]. A possible reason for usage of
carbon wt% of about 0.05 is that a critical volume fraction of austenite phase is required during
hot-rolling of the material. Carbon more than 0.05 %wt facilitates in achieving critical austenite
volume fraction. Presence of Austenite to enhance improves hot-workability during hot-rolling.
Further austenite is also required for dissolution of inhibitor alloy additions such as A1, Mn, Se S,
N etc as the solubility of them in ferrite is low and hence in 'inherent' inhibitor preparation
method certain amount of austenite is always prescribed [EP 1 025 268 B1, US 4 473 416].
Patent WO2014054961 Al refers that Mn and Cu can be alloyed to produce a certain amount of
austenite (about 40 %) during hot-rolling to ensure proper precipitation of AIN particles.
However, the present invention shows that a ferritic steel can be suitably hot-rolled which can
be further processed as CRGO steel.
Patent [EP 2 933 350 Al] refers to presence of certain amount of austenite at the finishing hot-
rolling stage (2-10 % at 1150-1050 °C) to suppress the recrystallization of ferrite at the
subsurface of the strip which causes ferrite recovery. The recovered ferritic microstructure is
claimed to form Goss texture. Our present invention shows that in ferritic hot-rolling range
suitable hot-rolling schedule can lead to evolution of bi-modal ferrite grain size distribution that
will results in stress and strain partitioning which probably facilitates Goss grain nucleation.
Patent EP 0 600 181 Bl refers that excess of Mn (after combination with S/Se) can be used to
obtain a certain amount of austenite (of at-least 7 %) during hot-band annealing. This is
required for controlling grain growth during hot-band annealing. Patent WO2011063934 Al
describes several conditions to be followed for hot-strip annealing with an aim to recrystallize
the hot-rolled microstructure. High cooling rates upto 100 °C/s is recommended prior to coiling

of the hot-rolled strip to avoid any loss of stored lattice energy by recovery. Hot-strip annealing
is done at a high temperature of 1150 °C. Our co-pending invention patent provides a simpler
hot-band annealing treatment with an objective to make the hot-band softer so that it can be
cold rolled.
Acquired inhibitor route is discussed in prior-arts [US 5 186 762, US 5 266 129, US 7 192 492
B2, WO 2011 063934 A1, US 6 361 620 B1, US 4 473 416]. In patent US 5 186 762 it is
proposed to keep certain amount of AIN undissolved during slab reheating so that they can
control grain growth during primary recrystallization. But this seems to be rather complex
process as precipitation of AIN during slab cooling will be not very homogeneous and to dissolve
them to the same extent throughout the slab will be also not very feasible. This non-
homogeneity of undissolved AIN can render inhomogeneity in primary recrystallized grain sizes
which could lead to undesirable microstructure during secondary annealing. In US patent 5 266
129, a rather high temperature (1150 to 1280 °C) was used for slab reheating and also Sn was
used as an alloying element. In US patent 4 473 416, a rather high temperature (upto 1250 °C)
was used for slab reheating and also Sb/Cu was used as an alloying element. In US patent
6,361,620 B1, a rather high temperature (1150 to 1320 °C) was used for slab reheating and
also Cu was used as an alloying element. In Patent WO2011063934 Al Cu was used as an
alloying element in addition to Al and Mn, and other alloying elements were also proposed, e.g.,
Ti, V, B, W, Zr, Nb, Sn, Sb, As. Patent US 7,192,492 B2 teaches us that to dissolve alloying
elements Mn, A1, Cu, Sn, Cr, Mo,Ni, B re-heating temperature of slab has to be 1210 °C. Our
invention shows that with proper nitriding treatment we can produce suitable inhibitors for
making CRGO steels, without using higher slab reheating temperature or other alloying
elements except Al only.

The invention describes an improved and simplified processing route of CRGO steel which
includes casting-rolling method and nitriding to produce AIN precipitate to perform as grain
growth inhibitor for chosen selective grain growth of Goss grains during secondary
recrystallisation annealing step. Furthermore, the invention describes production of hot band
by low temperature hot-rolling process below 1000 °C.
Objects of the Invention
The main object of the present invention is to provide an improved process to develop Fe-3.2Si
CRGO steel containing low carbon of upto about 0.03% and Al as the only inhibitor preparing
element which obviates the drawbacks detailed above.
Another object of the invention is to develop a simplified hot-rolling procedure at low
temperature below 1000 °C.
Another object of the invention is to develop a casting-hot rolling process of hot band
preparation to create Goss nuclei for large size Goss grains to be produced during secondary
annealing of cold rolled sheet.
Another object of the invention is to produce an inhibitor preparation method which will
eliminate high temperature slab reheat of about 1300 °C and hot rolling processes of hot band
preparation.
Another object of the invention is to eliminate complex hot rolling practice of having a critical
austenite volume fraction during hot rolling stage to completely dissolve micro alloys added for
inhibitor preparation in the solution.

Summary of the invention
The invention describes a casting-rolling production method of hot-band preparation for Fe-
3.2Si CRGO steel consisting of low C and Al as the only inhibitor preparation element. Steel
containing 3.0-3.3% Si, 0.03 to 0.055 % C, and a minimum of 0.02-0.03% Al was investigated
in this study.
Brief description of the accompanying drawing
FIG. 1 Optical micrograph of the as thin slab cast showing typical polygonal structure.
FIG. 2 Optical micrograph of the hot-rolled plate showing fine deformation (Expt 2) bands.
FIG. 3 Optical micrograph of the hot-rolled plate showing fine deformation (Expt 3) bands.
FIG. 4 SEM-EBSD colour coded grain orientation map of the hot-rolled annealed plate (Expt 3)
showing Goss grain in Green colour (within 15° deviation).
Detailed Description of Invention
The present invention provides a method for producing Fe-3.2Si CRGO steei consisting of low C
and Al as the only inhibitor preparation element. The hot-rolled strip produced by the casting-
rolling methodology described will produce few Goss grains/nuclei in the hot band. The
embodiment of the invention presents the experimental methods of this invention, which
comprises of the following steps:
The casting was prepared consisting of Fe-3.2%Si steel slabs of 15 or 20 mm thickness with
chemical composition (in wt %) consisting 3.0-3.3 % Si, 0.030-0.043 % C, 0.02- 0.03 % Al and
0.01 % N. An unavoidable impurity of Mn in the range of 0.06 % Mn and 0.017 % S was
present in the castings. These cast slabs were input material for our four stage hot rolling
process.

The slabs were soaked at 1070 °C for 30 min and furnace-cooled to 1000 °C for hot-rolling.
The slabs were subjected to hot-rolling at four passes, wherein the pass-I was estimated to be
started at 950 °C. In pass-I, II, III and IV deformations of about 50-60%, 15-25%, 50-55 %,
and 20-25% were employed, respectively . Hot-rolled slabs of thickness 2 -2.5 mm were
annealed at 900-950°C for 5-10 minutes and cooled under forced air for accelerated cooling to
room temperature.
In the following section we are reporting some of the experiments as an example without
limiting the scope of the invention/claim.
Experiment 1
Steel cast slab of 15 mm thickness with chemical composition (in wt %) consisting of 3.02 % Si,
0.03 % C, 0.03 % A1, and 0.037 % Mn was produced by slab casting. The cast slab was
soaked at 1070 °C for 30 min and furnace-cooled to 1000 °C for hot-rolling. The cast slabs
were subjected to hot-rolling at four passes, wherein the pass-I was estimated to be started at
950 °C. In pass-I, II, III and IV deformations of about 50%, 20%, 50 %, and 20% were
employed, respectively . Hot-rolled strip of thickness 2.4 mm was annealed at 900°C for 5
minutes and cooled under forced air for accelerated cooling to room temperature.
Experiment 2
Steel cast slab of 20 mm thickness with chemical composition (in wt %) consisting of 3.3 % Si,
0.043 % C, 0.018 % A1, and 0.06 % Mn was produced by slab casting. The cast thin slab was
reheated to 1070 °C and soaked for 30 min and furnace-cooled to 1000 °C for hot-rolling. The
cast slabs were subjected to hot-rolling at four passes, wherein the pass-I was estimated to be
started at 950 °C In pass-I, II, III and IV deformations of about 60%, 20%, 55 %, and 20%
were employed, respectively . Hot-rolled strip of thickness 2.3 mm was annealed at 900°C for 5
minutes and cooled under forced air for accelerated cooling to room temperature.

Experiment 3
Steel cast slab of 20 mm thickness with chemical composition (in wt %) consisting of 3.2 % Si,
0.03 % C, 0.028 % A1, and 0.055 % Mn was produced by slab casting. The cast thin slab was
reheated to 1070