FIELD OF THE INVENTION
The current investigation related to a hot-rolling method in fully ferritic region for preparing hot-band to produce CRGO steel. The invention particularly refers to a hot-rolling process to produce Goss nuclei in hot band of Fe-3.2Si electrical steel sheets. CRGO steels are well suited for transformer core application as they have high magnetic flux density and low core loss. The present invention will be applicable to hot-rolling schedule to prepare HB which will be further processed to produce CRGO steel sheets.
BACKGROUND OF THE INVENTION
CRGO steels are mostly used as transformer core material as they exhibit high magnetic flux density and low core loss. These properties of CRGO steels are achieved by [110[<001> crystallographic texture known as Goss texture. The term Goss was coined after N.P. Goss (US Pat 1 965 559, 1934) who was the first inventor of these steels. Since the first patent by N.P. Goss, research and development activities are still in effort to improve the magnetic properties of CRGO steels. Most of these production methods is directed towards producing suitable particle pinning effects that will restrict the growth of all other grains during secondary recrystallization expect for the Goss oriented grains. Suitable precipitates that may exhibit particle pinning effect are obtained through complex cold rolling and annealing processes. Al, B, Mn, Ti, Se, S, N, etc., are added to produce fine nitride or sulfide precipitates that may act as inhibitors for grain growth (US Pat 5 800 633, Eur Pat 0 600 181 A1, US Pat 3 162 553, US Pat 2 867 559, US Pat 3 423 253, US Pat 3 895 974). However, high temperature slab reheating or hot-rolling is required for some of this inhibitors, e.g. MnS. High slab reheating temperature in the range of 1300-1400 oC is required for conventional CRGO production. Current research and development for new product area has set importance on inventing low slab reheating methods for HB preparation for CRGO steels. This approach will be well accepted by the industries. Low

temperature slab reheating approach requires to find out suitable inhibitors and processing steps. Present invention avoids this hindrance by proposing a specific hot-rolling method for HB preparation that will involve low slab reheating temperature as well as low rolling temperatures. The invention describes a novel processing route of HB preparation by a four stage hot rolling. Furthermore, the invention relates preparation of HB directly from the as-cast plate. In-grain stress accumulation and rotation within the deformation bands has been invoked by synergistic recurring deformation and recrystallization effect to form Goss nuclei in the hot band. The above mentioned mechanisms are activated by a controlled hot deformation schedule in four-pass hot-rolling process. This is an effort to simulate four strand industrial hot rolling process in the laboratory.
OBJECTS OF THE INVENTION
The primary object of the invention is to detail a process for producing Goss nuclei in HB of Fe-3.2Si electrical steel Sheets which discards the disadvantages of intrinsic high temperature process method as summarized above. This invention along-with another co-pending patent application describes a complete route to produce CRGO steels via low-temperature slab reheating and low-temperature hot-rolling process.
Another object of the invention is to develop a four stage hot rolling process to introduce Goss nuclei in the hot band of Fe-3.2Si electrical steel starting from the as-cast structure.
Another object of the invention is to hot-roll the steel in fully ferritic region avoiding the presence of austenite phase, a necessary condition in previous patents.
Another object of the invention is to produce Goss nuclei in HB of electrical steel that is present throughout the thickness of the HB.

Yet another objective of the invention is to develop a casting-rolling method for preparing HB of electrical steel.
SUMMARY OF THE INVENTION
The invention describes a HB processing method for Fe-3.2 Si steel that can be further processed to produce CRGO steel. A steel containing 3.0-3.3% Si, and a minimum of 0.03% Al was investigated in this study.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
FIG. 1 Optical micrograph of the casted plate surface, which will be the rolling
plane during the hot-rolling.
FIG. 2 Optical micrograph of the annealed hot-band showing fine deformation
bands, necessary condition for Goss grain nucleation for first rolling experiment.
FIG. 3 SEM-EBSD colour coded grain orientation map showing Goss grain in
Green colour after hot-band annealing for first rolling experiment.
FIG. 4 SEM-EBSD colour coded grain orientation map showing Goss grain in
Green colour after hot-band annealing for second rolling experiment.
FIG. 5 SEM-EBSD colour coded grain orientation map showing Goss grain in
Green colour after hot-band annealing for third rolling experiment.
DETAILED DESCRIPTION OF INVENTION
The present invention provides a method for producing HB of Fe-3.2Si steel. Processing of this HB according to the methodology described in a co-pending patent will produce large Goss grains which is essential for CRGO steels for their application as transformer core material. The embodiment of the invention presents the experimental methods of this invention, which comprises of the following steps:

A Fe-3.2%Si steel ingot with chemical composition (in wt %) consisting of 3.0-3.3 % Si, 0.030-0.035 % C, minimum of 0.03 % Al, 0.03-0.04 % Mn and 0.017 % S was casted in three different sizes. These plates were input material for our four stage hot rolling process.
The plates were soaked at 1070 oC for 30 min and furnace-cooled to 1000 oC for hot-rolling. The plates were subjected to hot-rolling at four passes, wherein the pass-I was estimated to be started at 950 oC. In pass-I, II, III and IV deformations of about 50-60%, 15-25%, 40-50 %, and 20-25% were employed, respectively . Hot-rolled strip of thickness 2 -2.5 mm was annealed at 900-950oC for 5-10 minutes and cooled under forced air for accelerated cooling to room temperature.
Advantages
Following are the advantages of the invention:
i. An easy four pass hot-rolling process is invented to produce hot band
containing few Goss nuclei. ii. The invention may be suitable for the conventional hot-strip rolling mills
with affordable modifications instead of the necessity to built a separate
hot-strip mill for CRGO steels. iii. Hot-rolling was completed in fully ferritic region avoiding necessity of
austenite formation. iv. Casting-rolling method can be used avoiding the slab reheating step.
In the following section we are reporting three rolling experiments as examples without limiting the scope of the invention/claim.
Experiment
Fe-3.2Si steel was produced by air induction melting, containing 3.2 % Si, 0.03 % C, 0.03 % Al and 0.04 % Mn and 0.017% S and balance Fe. The as-cast plates

were soaked at 1070 oC for 30 min and furnace cooled to 1000 oC. The plates were subjected to hot-rolling at four passes, wherein the pass-I was estimated to be started at 950 oC.
First rolling experiment
The casting plate has a dimension of 60 mm (width) * 150 mm (length) * 13 mm (thickness). The plate was subjected to four pass rolling. Pass -I: comprised of hot rolling to 55 % deformation. In pass -II the material was hot-rolled to 15 % reduction in thickness. Due to low initial thickness of the plate, before Pass-III the strip was reheated at 900 oC for 2 min for compensating heating loss. In Pass -III the strip was hot-rolled to 40% reduction in thickness. In Pass -IV the strip was hot-rolled to 25% reduction in thickness to finish rolling thickness of 2.2 mm. The hot-rolled strip was subsequently annealed at 900 oC for 5 minutes and forced cooled in air to room temperature.
The optical microstructure of the as-cast plat showing equiaxed grains is shown
in FIG. 1. FIG. 2 reports the optical micrograph of the annealed hot-band
showing fine deformation bands, necessary condition for Goss grain nucleation.
The strips were characterized by scanning electron micro scope (SEM) attached
with electron back scatter diffraction (EBSD) technique to spot the presence of
Goss nuclei. SEM-EBSD colour coded grain orientation map showing Goss
grain in green colour are reported in FIG. 3. Goss nuclei can be observed in
annealed hot-rolled strip . These Goss nuclei are present all throughout the
thickness of the hot band.
Second rolling experiment
The casting had a dimension of 150 mm (width) * 165 mm (length) * 19 mm (thickness). In the Pass-I, Pass-II, Pass-III and Pass-IV, the casting was hot-rolled to 60 %, 25 %, 55 % and 20 % reduction in thickness, respectively, to

finish rolling thickness of 2.2 mm. The hot-rolled strip was subsequently annealed at 900 oC for 5 minutes and forced cooled in air to room temperature.
SEM-EBSD colour coded grain orientation map showing Goss grain in green colour are reported in FIG. 4 for the annealed hot-band. Goss nuclei can be observed in the annealed hot-band. Further it can be observed that the Goss nuclei are present inside the deformation bands. These Goss nuclei are present all throughout the thickness of the hot band.
Third rolling experiment
The casting had a dimension of 150 mm (width) * 250 mm (length) * 19 mm (thickness). In the Pass-I, Pass-II, Pass-III and Pass-IV, the casting was hot-rolled to 60 %, 25 %, 55 % and 20 % reduction in thickness, respectively, to finish rolling thickness of 2.2 mm. The hot-rolled strip was subsequently annealed at 900 oC for 5 minutes and forced cooled in air to room temperature.
SEM-EBSD colour coded grain orientation map showing Goss grain in green colour are reported in FIG. 5 for the annealed hot-band. Goss nuclei can be observed in the annealed hot-band. Further it can be observed that the Goss nuclei are present inside the deformation bands. These Goss nuclei are present all throughout the thickness of the hot band.

WE CLAIM
1. A hot-rolling method in fully ferritic region for preparing hot-band to
produce CRGO steel which comprises
i. preparing steel containing 3.0-3.3 % Si, 0.030-0.035 % C, minimum of 0.03 % Al, 0.03-0.04 % Mn and 0.017 % S and balance Fe and casting into plates of different sizes,
ii. preparing hot-rolling soaking the plates at 1000-1100 oC for a period of 20-40 min followed by furnace cooling to a temperature ranging between 1000-1100 oC,
iii. hot-rolling at four passes, wherein the pass-I to be started at temperature ranging between 900 to 1000oC,
iv. In pass-I the plates were hot-rolled to 50-60 % reduction in thickness,
v. In pass-II the plates are hot-rolled to 15-25 % reduction in thickness,
vi. In pass-III the plates are hot-rolled to 40-50 % reduction in thickness,
vii. In pass-IV the plates are hot-rolled to 20-25 % reduction in thickness, to finish rolling thickness of 2-2.5 mm.
2. A process as claimed in claim1 wherein the hot-rolled strip is annealed thereof at temperature 900-950 oC for period of 5-10 minutes and forced cooled in air to room temperature.
3. A process as claimed in claims 1-2 wherein the evolution of bi-modal grain size distribution results in stress and strain partitioning which facilitates Goss grain nucleation.
4. A process as claimed in claims 1-3 wherein used Si and Al are pure metals.

5. A process as claimed in claims 1-4 wherein wherein, hot-rolling of CRGO plates will take place in ferritic region.
6. A hot-rolling method in fully ferritic region for preparing hot-band to produce CRGO steel as substantially herein describes with reference to Examples and Figures accompanying this specification.