[0001] This invention relates to a method of producing cube-on-edge oriented silicon steel
in the form of sheets is known for use in various electrical applications including
transformer cores..With cube-on-edge silicon steel the alloy is characterized by secondary
recrystallization in the (110) (001) position, which is termed the cube-on-edge position.
This material in sheet form has the direction of easy magnetization in the direction
of rolling. In applications for this material, and specifically when used in the manufacture
of transformer cores, the material is required to have reduced watt loss, because
the consumption of electrical energy decreases as iron loss decreases. Reduced watt
loss may be promoted by achieving fine secondary grain size during texture annealing.
[0002] It is accordingly an object of the present invention to provide a method whereby
during the texture annealing of cube-on-edge silicon steel the secondary grain growth
is inhibited to provide a relatively fine grained material after texture annealing
with reduced watt loss.
[0003] Broadly, in the practice of the invention a silicon steel which has been conventionally
processed by hot rolling and cold rolling with intermediate anneals is surface coated
with a manganese-bearing material prior to texture annealing and is texture annealed
in the conventional manner with said manganese-bearing material thereon. A manganese-bearing
material particularly suited for use in the invention is Mn
3(N0
2). It has been found that the presence of the manganese-bearing compound during annealing
inhibits secondary grain growth and thus reduces watt loss. This may be further enhanced
if the steel is serrated prior to texture annealing. Although the practice of the
invention finds utility with cube-on-edge oriented silicon steels generally, it is
particularly adapted to steels of this type within the following composition limits
in percent by weight:
[0004] By the practice of coating steel with a manganese-bearing compound and texture annealing
with the compound being present on the steel, said practice is believed to be effective
for the purpose by diffusing manganese into the steel during annealing, which promotes
primary grain coarsening by interaction with the solute sulfur, which sulfur would
tend to inhibit grain growth. Hence a region is provided in which primary grain growth
occurs and restricts the growth of secondary grains through this region. It would
appear that the extent of grain refinement of the secondary grains after texture annealing
depends on the spacing of the regions of primary grain growth on the areas of application
of the manganese-containing material, provided that the width of the treated region
is sufficient to act as a barrier to the secondary grains. This effect may be supplemented
by creating similar barriers by subjecting the steel to serrating or the like.
[0005] The silicon steel composition used in the specific examples, and identified as SX-14,
was of the following nominal composition in percent by weight:
[0006] Epstein packs of final normalized SX-14 composition, identified as Heat No. 154684,
were coated with a water slurry comprising 300cc of water, 46gm. of MgO and 2gm. of
H
3B0
3. This material with the coating thereon was then texture annealed in a hydrogen atmosphere
in the conventional manner. Specifically, the texture annealing consisted of charging
the material into a furnace at a temperature of 760°C (1400°F) heating at a rate of
10°C (50°F) per hour to a temperature of 1177
0C (2150°F), holding at temperature for 12 hours and then cooling to 649
0C (1200°F), at which time the material was removed from the furnace. One of the Epstein
packs, prior to the above slurry coating, was painted with a mixture of 30cc of 50%
Mn (N0
3)
2 and an inert thickner, which was applied in lmm stripes perpendicular to the sheet
rolling direction at intervals of lOmm; this painted coating was then air dried..This
Epstein pack constituted treatment in accordance with the practice of the invention;
whereas, the second pack was used as a control and typified a conventional practice.
Following the texture annealing procedure, as described above, the average lineal
dimension of the secondary grains of the conventional, control pack specimen in the
sheet rolling direction was l3mm. In contrast, the average lineal dimension of the
secondary grain of the specimen treated with Mn(N0
3)
2 in accordance with the practice of the invention was 7mm; these grains it was observed
were often separated by the aforementioned bands of smaller primary grains where normal
grain growth was stimulated by the application of the manganese-bearing compound.
[0007] In a second specific example, a single Epstein strip of final normalized SX-14 composition
from the same heat as in the aforementioned Example 1 was scribed with a metal scribe
to produce serrations in the strip perpendicular to the rolling direction at intervals
of lOmm. After the scribing operation, the strip was slurry coated and texture annealed
under the conditions described above with respect to the first specific example. Following
this texture annealing, the average lineal dimension in the sheet rolling direction
of the secondary grain in the scribed strip was 9.5mm.
1. A method of producing cube-on-edge oriented silicon steel, characterized by reduced
watt loss, including the steps of hot-rolling, cold-rolling with intermediate annealing
and a final texture annealing, characterized in comprising surface coating said steel
with a manganese-bearing material prior to texture annealing and texture annealing
said steel with said coating thereon, whereby secondary grain growth is inhibited
during texture annealing.
2. A method according to claim 1, characterized in that said manganese-bearing material
is Mn(NO3)2.
3. A method according to claims 1 or 2, characterized in that said steel is serrated
prior to texture annealing.
