U.S. patent application number 17/044950 was filed with the patent office on 2021-01-28 for silicon based alloy, method for the production thereof and use of such alloy.
The applicant listed for this patent is ELKEM ASA. Invention is credited to Amelie DIEUDONNE, Ole Svein KLEVAN.
Application Number | 20210025040 17/044950 |
Document ID | / |
Family ID | 1000005165579 |
Filed Date | 2021-01-28 |
United States Patent
Application |
20210025040 |
Kind Code |
A1 |
DIEUDONNE; Amelie ; et
al. |
January 28, 2021 |
SILICON BASED ALLOY, METHOD FOR THE PRODUCTION THEREOF AND USE OF
SUCH ALLOY
Abstract
A silicon based alloy is disclosed having between 45 and 95% by
weight of Si; max 0.05% by weight of C; 0.01-10% by weight of Al;
0.01-0.3% by weight of Ca; max 0.10% by weight of Ti; 0.5-25% by
weight of Mn; 0.005-0.07% by weight of P; 0.001-0.005% by weight of
S; the balance being Fe and incidental impurities in the ordinary
amount, a method for the production of the alloy and the use
thereof.
Inventors: |
DIEUDONNE; Amelie; (Ste
Colombe, FR) ; KLEVAN; Ole Svein; (Stjordal,
NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ELKEM ASA |
OSLO |
|
NO |
|
|
Family ID: |
1000005165579 |
Appl. No.: |
17/044950 |
Filed: |
April 2, 2019 |
PCT Filed: |
April 2, 2019 |
PCT NO: |
PCT/NO2019/050067 |
371 Date: |
October 2, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 38/06 20130101;
C22C 38/04 20130101; C22C 38/14 20130101; C22C 38/02 20130101; C22C
38/002 20130101 |
International
Class: |
C22C 38/02 20060101
C22C038/02; C22C 38/06 20060101 C22C038/06; C22C 38/00 20060101
C22C038/00; C22C 38/14 20060101 C22C038/14; C22C 38/04 20060101
C22C038/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 3, 2018 |
NO |
20180441 |
Claims
1. A silicon based alloy comprising between 45 and 95% by weight of
Si; max 0.05% by weight of C; 0.01-10% by weight of Al; 0.01-0.3%
by weight of Ca; max 0.10% by weight of Ti; 0.5-25% by weight of
Mn; 0.005-0.07% by weight of P; 0.001-0.005% by weight of S; the
balance being Fe and incidental impurities in the ordinary
amount.
2. Silicon based alloy according to claim 1, wherein the silicon
based alloy comprises between 50 and 80% by weight of Si.
3. Silicon based alloy according to claim 2, wherein the silicon
based alloy comprises between 64 and 78% by weight of Si.
4. Silicon based alloy according to any one of the preceding
claims, wherein the silicon based alloy comprises max 0.03% by
weight of C.
5. Silicon based alloy according to any one of the preceding
claims, wherein the silicon based alloy comprises between 0.01-0.1%
by weight of Ca.
6. Silicon based alloy according to any one of the preceding
claims, wherein the silicon based alloy comprises max 0.06% by
weight of Ti.
7. Silicon based alloy according to any one of the preceding
claims, wherein the silicon based alloy comprises between 1-20% by
weight of Mn.
8. A method for producing a silicon based alloy according to any of
the claims 1-7, wherein said method comprises providing a liquid
base ferrosilicon alloy and adding a Mn source comprising carbon as
an alloying element or as an impurity element into said liquid
ferrosilicon thereby obtaining a melt, and refining said obtained
melt, the refining comprising removing formed silicon carbide
particles before and/or during casting of said melt.
9. Method according to claim 8, wherein the added Mn source is in
the form of high carbon ferromanganese alloy, medium carbon
ferromanganese alloy, low carbon ferromanganese alloy, Mn metal, or
a mixture thereof.
10. Method according to any of claim 8 or 9, wherein the liquid
base ferrosilicon alloy comprises: Si: 45-95 wt %; C: up to 0.5 wt
%; Al: up to 2 wt %; Ca: up to 1.5 wt %; Ti: 0.01-0.1 wt %; Mn: up
to 0.5 wt %; P: up to 0.02 wt %; S: up to 0.005 wt %; the balance
being Fe and incidental impurities in the ordinary amount.
11. Method according to any of claims 8 to 10, wherein Al is added
to adjust the Al content within the range 0.01-10 wt %.
12. Use of the silicon based alloy according to any of the claims
1-7 as an additive in the manufacturing of steel.
13. Use according to claim 12, in the manufacturing of non-grain
oriented electrical steel.
Description
TECHNICAL FIELD
[0001] The present invention relates to a silicon based alloy, a
method for the production thereof and the use of such alloy.
BACKGROUND ART
[0002] Ferrosilicon (FeSi) is an alloy of silicon and iron and is
an important additive in the manufacture of steel products. Such
alloys are commonly referred to as ferrosilicon alloys but when the
silicon content is high and/or when the contents of alloying
elements are high, there will be a very small amount of iron in the
alloy, and therefore, the term silicon (Si) alloys are also used to
denote such alloys. Silicon in the form of ferrosilicon is used to
remove oxygen from the steel and as an alloying element to improve
the final quality of the steel. Silicon increases namely strength
and wear resistance, elasticity (spring steels), scale resistance
(heat resistant steels), and lowers electrical conductivity and
magnetostriction (electrical steels). See example of prior art
ferrosilicon qualities produced by Elkem in table 1. Special
ferrosilicon like LA1 (low aluminium), HP/SHP (High Purity/Semi
High Purity) and LC (low carbon) ferrosilicon are used in the
production of special steel qualities, such as electrical steel,
stainless steel, bearing steel, spring steel, and tire cord
steel.
TABLE-US-00001 TABLE 1 Examples of qualities in ferrosilicon alloys
(all in weight %) Qualities Si Al max Ti max C max Standard FeSi
74-78 1.5 0.1 0.1 LC FeSi 74-78 1.0 0.1 0.02 LAl FeSi 74-78 0.1 0.1
0.04 SHP FeSi 74-78 0.1 0.05 0.02 HP FeSi 74-78 0.05 0.02 0.02
[0003] Non-grain oriented electrical steel (NGOES) is essential to
manufacture magnetic cores of electrical machines such as motors,
generators and transformers. NGOES are usually alloyed with silicon
in the range of 0.1-3.7 weight % (wt %) depending on producer and
quality but also higher Si levels can be found. Grades with low
levels (typically <1.5 wt % Si) of Si are referred here as low
grade while the ones with higher levels (>2/2.5 wt %) of silicon
are often called high grade. The demand for high grade NGOES is
increasing worldwide, driven by increasing electrification (like
electromobility) and CO.sub.2 emissions reduction. There is
therefore a need to develop new NGOES grades, which in turn call
for better solutions to be able to produce or develop such
grades.
[0004] NGOES requires having the carbon content as low as possible
(typically C<0.005 wt %). In the production of NGOES, low carbon
alloys should be used in order to minimize carbon pollution in the
steel as much as possible. Additional and costly process steps
would be needed to obtain the required low carbon level if the
carbon level in the steel melt is too high due to pollution from
added alloys. This is why low carbon ferrosilicon/silicon alloys
have been and are still widely used in the making of NGOES, either
in the form of LC, LA1 or HP/SHP FeSi.
[0005] Recently, manganese is being increasingly used as an
alloying element in high grade NGOES. One major source of carbon
pollution in the production of such steel grades in addition to
silicon alloys is the manganese alloys used. To keep the added
carbon low, expensive grades of manganese like low carbon
ferromanganese (LCFeMn) or manganese metal is often used. Current
practice involves using separately addition of low carbon silicon
based alloy, like LC, LA1 or HP/SHP FeSi and low carbon manganese
based alloy, like low carbon ferromanganese (LC FeMn) or manganese
metal, to achieve the desired Si and Mn level in the steel while
keeping carbon in the steel as low as possible. Low carbon silicon
alloys and low carbon ferromanganese alloys are both costly to
produce and requires separate addition of these alloys to the
steel.
[0006] The main polluting element in manganese based alloys is
carbon that can be from 0.04 to 8 wt %. Examples of commercial Mn
alloys are high carbon ferromanganese (HC FeMn) having a carbon
content from 6 to 8 wt % typically, medium carbon ferromanganese
(MC FeMn) with typically 1-2 wt % C and low carbon ferromanganese
(LCFeMn) with about 0.5 wt % C. Also available are electrolytic
manganese having down to max 0.04 wt % C. Other alloys can be
available with different carbon content up to 8%. It is also worth
noting that the lowest carbon content in Mn alloys is found in
electrolytic manganese, whose production process is known to create
environmental issues and are very costly to produce. Table 2 below
shows examples of commercial manganese alloys.
TABLE-US-00002 TABLE 2 Examples of commercial manganese alloys (all
in wt %) Alloy Mn C max P max Si max S max Source HC FeMn Min.
6.5-7.5 0.20 0.3 0.01 Eramet 78 MC FeMn 80-83 1.5 0.20 0.6 0.01
Eramet LC FeMn 80-83 0.5 0.20 0.6 0.01 Eramet Mn metal Min. 0.04
0.005 NA 0.05 Changsha electrolytic 99.7 Xinye Ind. Co. Ltd Mn
metal Min. 0.2 0.07 1.8 0.05 Felman silicothermic 95 trading
[0007] There are several challenges with the current production
method of NGOES containing Mn such as processing time due to
separate additions of silicon alloy and manganese alloy, cost and
quality and that high amount of alloys has to be added.
[0008] Thus, the object of the present invention is to provide a
new cost efficient silicon based alloy having a low carbon content
and containing manganese that can be used as a single alloy
addition to steel qualities such as NGOES that require low carbon
content and a certain manganese content.
[0009] Another object is to provide a method of producing said Si
based alloy.
[0010] A further object is to provide the use of said Si based
alloy.
[0011] These and other advantages with the present invention will
become evident in the following description.
SUMMARY OF INVENTION
[0012] In a first aspect, the present invention relates to a
silicon based alloy comprising between 45 and 95% by weight of
Si;
max 0.05% by weight of C; 0.01-10% by weight of Al; 0.01-0.3% by
weight of Ca; max 0.10% by weight of Ti; 0.5-25% by weight of Mn;
0.005-0.07% by weight of P; 0.001-0.005% by weight of S; the
balance being Fe and incidental impurities in the ordinary
amount.
[0013] In an embodiment, the silicon based alloy comprises between
50 and 80% by weight of Si.
[0014] In another embodiment, the silicon based alloy comprises
between 64 and 78% by weight of Si.
[0015] In an embodiment, the silicon based alloy comprises max
0.03% by weight of C.
[0016] In an embodiment, the silicon based alloy comprises
0.01-0.1% by weight of Ca.
[0017] In an embodiment, the silicon based alloy comprises max
0.06% by weight of Ti.
[0018] In an embodiment, the silicon based alloy comprises 1-20% by
weight of Mn.
[0019] In a second aspect, the present invention relates to a
method for producing a silicon based alloy as defined above,
wherein said method comprises providing a liquid base ferrosilicon
alloy and adding a Mn source comprising carbon as an alloying
element or as an impurity element into said liquid ferrosilicon
thereby obtaining a melt, and refining said obtained melt, the
refining comprising removing formed silicon carbide particles
before and/or during casting of said melt.
[0020] In an embodiment, the added Mn is in the form of high carbon
ferromanganese alloy, medium carbon ferromanganese alloy, low
carbon ferromanganese alloy, Mn metal or a mixture thereof.
[0021] In an embodiment, the liquid base ferrosilicon alloy
comprises:
Si: 45-95 wt %;
C: up to 0.5 wt %;
Al: up to 2 wt %;
Ca: up to 1.5 wt %;
Ti: 0.01-0.1 wt %;
Mn: up to 0.5 wt %;
P: up to 0.02 wt %;
S: up to 0.005 wt %;
[0022] the balance being Fe and incidental impurities in the
ordinary amount.
[0023] In an embodiment, Al is added to adjust the Al content
within the range 0.1-10 wt %.
[0024] In another aspect, the present invention relates to the use
of the silicon based alloy as defined above as an additive in the
manufacturing of steel.
[0025] In an embodiment, the present invention relates to the use
of the silicon based alloy as defined above as an additive in the
manufacturing of non-grain oriented electrical steel.
DETAILED DESCRIPTION OF THE INVENTION
[0026] According to the present invention it is provided a new
silicon based alloy that is low in carbon and with a manganese
content up to 25% by weight.
[0027] The alloy according to the invention has the following
composition:
Si: 45-95 wt %;
C: max 0.05 wt %;
Al: 0.01-10 wt %;
Ca: 0.01-0.3 wt %;
Ti: max 0.10 wt %;
Mn: 0.5-25 wt %;
P: 0.005-0.07 wt %;
S: 0.001-0.005 wt %;
[0028] the balance being Fe and incidental impurities in the
ordinary amount.
[0029] In the present application, the terms silicon based alloy
and ferrosilicon based alloy are used interchangeably. Si is the
main element in this alloy to be added to the steel melt.
Traditionally, 75 wt % Si or 65 wt % Si are used. Ferrosilicon with
75 wt % Si gives higher temperature increase of the steel melt when
added than 65 wt % Si, which is almost temperature neutral.
Ferrosilicon with lower than 50 wt % Si is rarely used in the steel
industry today, and mean that a high amount of alloy would have to
be added to get to the targeted Si content in the steel and
creating challenges during steelmaking. Higher than 80% is seldom
used today, as the production cost per silicon unit increases when
the silicon content in the Si based alloy increases. Hence, a
preferred Si range is 50-80 wt %. Another preferred Si range is
64-78 wt %.
[0030] Carbon is the main unwanted element in NGOES and should be
as low as possible in this new alloy according to the invention. A
maximum content of carbon in said alloy is 0.05 wt %. A preferred
content should be max 0.03 wt % or even max 0.02 wt %, as in
current low carbon ferrosilicon grades used in making said steel.
It might be difficult to totally remove carbon and therefore
normally 0.003 wt % C can be present in the alloy according to the
invention. More than the carbon content itself, the carbon to
manganese ratio is the one key parameter. With manganese increasing
in the alloy, the carbon content in the new silicon based alloy
according to the invention can be max 0.05 wt %.
[0031] Aluminium is an impurity in the production of silicon based
alloy, typically around 1 wt % out of the furnace in standard
grade. It can be refined down to a maximum of 0.01 wt % although
for NGOES a maximum of 0.03 wt % or even max 0.1 wt % would be good
solutions. However, in NGOES, Al is often added in small or large
quantities. Therefore, adding aluminium up to 5 wt % or even up to
10 wt % in the alloy according to the invention can in some
instances be preferable.
[0032] Calcium is an impurity in the production of silicon based
alloys, and should be kept low to avoid problems during steelmaking
and casting, such as nozzle clogging. In the alloy according to the
invention, the calcium range is 0.01-0.3 wt %. A preferred calcium
range is 0.01-0.1 wt %. A preferred content is max 0.05 wt %. If
the calcium content in the starting material for producing the
alloy according to the invention is higher than the desired calcium
content in said alloy, calcium can easily be removed during the
production by blowing/stirring with oxygen (from air and/or pure
oxygen) thereby forming calcium oxide that can be removed as
slag.
[0033] Titanium is an impurity in the production of silicon based
alloys, typically around 0.08 wt % out of the furnace in 75 wt %
FeSi standard production, but that depends on the raw material mix.
However, in NGOES, a low content of titanium is often beneficial,
to avoid formation of detrimental inclusions. Therefore, a Ti level
of max 0.06 wt % or even max 0.03 wt % in the new alloy according
to the invention is preferable. Traces of Ti might be present in
said alloy, so that a minimum level of Ti can be 0.005% by weight.
It is difficult to refine Ti in the ladle, so good furnace
operation and raw material selection are required to succeed in
getting low titanium content.
[0034] Manganese is typically an impurity in the production of
silicon based alloys. However, the inventors surprisingly found
that alloying a silicon based alloy with manganese in the range of
0.5 to 25% while keeping the carbon content low provides an alloy
with excellent properties particularly for the use in the
production of steel qualities requiring low carbon content such as
NGOES. Other possible Mn ranges are 1-20%, or 1-15% or also
2-10%.
[0035] Phosphorous is an impurity in the production of silicon
based alloys. In particular, in silicon based alloys without Mn
additions, P levels are below 0.04%. However, P is normally higher
in Mn alloys, therefore alloying with Mn may lead to a higher P
content in the final product. However, P in the steel originating
from addition of the silicon alloy of the present invention will be
the same or slightly lower than from separate addition of silicon
alloy and manganese alloy.
[0036] Sulphur is usually low in silicon alloys production.
However, S is normally slightly higher in Mn alloys, so alloying
with Mn may lead to higher S in the final product. However, S in
the steel originating from addition of the silicon alloy of the
present invention will be the same or slightly lower than from
separate addition of silicon alloy and manganese alloy.
[0037] A preferred composition of the alloy according to the
invention is:
Si: 64-78 wt %;
C: max 0.03 wt %;
Al: 0.1-10 wt %;
Ca: 0.01-0.05 wt %;
Ti: max 0.06 wt %;
Mn: 1-20 wt %;
P: 0.005-0.05 wt %;
S: 0.001-0.005 wt %;
[0038] the balance being Fe and incidental impurities in the
ordinary amount.
[0039] The alloy according to the present invention is made by
adding a Mn source comprising carbon as an alloying element or as
an impurity element into a liquid Si based alloy. The Mn source can
be in the form of solid or liquid manganese units, in the form of a
manganese alloy or manganese metal or a mixture thereof. The
manganese source can comprise normal impurities/contaminants. The
manganese alloy can for example be a ferromanganese alloy, such as
high carbon ferromanganese, medium carbon ferromanganese, low
carbon ferromanganese or a mixture thereof. A commercial manganese
alloy, for example as given in table 2 above, or a combination of
two or more of such alloys, are suitable for use in the present
invention. Preferably the added Mn is in the form of high carbon
ferromanganese or medium carbon ferromanganese.
[0040] The added carbon from the manganese source will react with
silicon thereby forming solid SiC (silicon carbide) particles that
during refining are removed from the melt to the ladle refractory
or to any slag that has been formed before or during the casting
process, preferably with stirring in the ladle. Slag formers can be
added if needed to have a sufficiently large receptor for the
formed SiC particles. This results in a Si alloy according to the
invention with low carbon content and containing manganese, with
the range of elements as indicated above.
[0041] An example of a composition for the starting material could
be liquid FeSi from furnace, but many others are possible depending
on the final specification to be reached. Remelting any commercial
silicon based alloys like standard ferrosilicon or high purity
ferrosilicon could also be a possible starting material.
[0042] Thus, a possible starting material can comprise:
Si: 45-95 wt %;
C: up to 0.5 wt %;
Al: up to 2 wt %;
Ca: up to 1.5 wt %;
Ti: 0.01-0.1 wt %;
Mn: up to 0.5 wt %;
P: up to 0.02 wt %;
S: up to 0.005 wt %;
[0043] the balance being Fe and incidental impurities in the
ordinary amount.
[0044] If the aluminium content is to be increased in the final
product (up to 10%), addition of solid or liquid aluminium units
can be made in the ladle. Alternatively, aluminium from the furnace
can be increased by selection of raw materials to the furnace. Al
can be added to adjust the Al content within the range 0.01-10 wt
%.
[0045] To produce the alloy according to the invention, additional
steps involving slag refining, skimming and/or stirring according
to generally known techniques can be performed, in particular to
reach the low levels of carbon claimed by the present invention.
Such steps can be performed before or during the casting process or
in combination.
[0046] The following Examples illustrate the present invention
without limiting its scope.
Example 1
[0047] In two separate trials, ferrosilicon was tapped as normal
into a tapping ladle (Ladle 1 and Ladle 2) with bottom stirring
with air. The amount of ferrosilicon that was tapped was about 5900
kg into each of Ladle 1 and Ladle 2. Table 3 shows the starting
material composition in the two ladles used.
TABLE-US-00003 TABLE 3 Starting materials (wt %) Starting material
Al Si P Ca Ti Mn C Ladle 1 0.78 77.26 0.012 0.16 0.058 0.172 0.0533
Ladle 2 1.60 75.25 0.011 0.98 0.057 0.234 0.3794
[0048] After tapping, lumpy FeMn, with 75.7 wt % Mn and 6-8 wt % C;
the balance being Fe and incidental impurities in the ordinary
amount, was added into the liquid ferrosilicon in each ladle in an
amount equal to 246 kg of Mn unit to reach 4.5 Mn in the final
product. As the Mn yield was not known, FeMn was added gradually
over a period between 20-25 minutes until the Mn target of 4.5% was
reached. (Additions can be done in a shorter or longer time). The
bottom stirring was kept during the whole addition process,
ensuring good Mn dissolution and that formed SiC particles were
removed from the Si alloy melt to the slag formed and the ladle
walls. After the refining step, the ladles were taken to the
casting area where final liquid sample was taken before casting
into cast iron moulds.
[0049] Samples of the new alloy produced according to the invention
were taken at the end of the liquid stage, just prior to casting.
Results of the two ladles are shown in table 4.
[0050] All samples were analyzed with XRF (Zetium.RTM. from Malvern
Panalytical) for Al, Si, P, Ca, Ti, Mn, and for C, LECO.RTM. CS-220
(combustion analysis) was used.
TABLE-US-00004 TABLE 4 Analysis (wt %) at the end of liquid stage
Al Si P Ca Ti Mn C Ladle 1 0.27 74.18 0.016 0.02 0.057 4.43 0.018
Ladle 2 0.22 73.47 0.015 0.01 0.058 4.74 0.008
Example 2
[0051] Liquid ferrosilicon was tapped as normal into a tapping
ladle with bottom stirring with air. The amount of ferrosilicon
that was tapped into the ladle was about 6000 kg. The starting
material composition can be seen in table 5.
[0052] During tapping, lumpy FeMn, with 78.4 wt % Mn and 6.85 wt %
C; the balance being Fe and incidental impurities in the ordinary
amount, was added into the liquid ferrosilicon in an amount equal
to 950 kg. Together with FeMn, 100 kg of quartz was added to the
melt to increase the volume of receptors to support the capture of
the formed SiC. The bottom stirring was kept during the whole
addition process, ensuring good Mn dissolution and that formed SiC
particles were removed from the FeSi alloy melt to the ladle walls
and slag formed. After the refining step, the ladle was taken to
the casting area where final liquid sample was taken before casting
into cast iron moulds.
[0053] Samples of the new alloy produced according to the invention
were taken at the end of the liquid stage, just prior to casting,
and on final product after casting. Results are shown in table
5.
[0054] All samples were analyzed with XRF (Zetium.RTM. from Malvern
Panalytical) for Al, Si, P, Ca, Ti, Mn, and for C, LECO.RTM. CS-220
(combustion analysis) was used.
TABLE-US-00005 TABLE 5 Chemical composition (wt %) at different
steps of the experiment Al Si P Ca Ti Mn C Starting material 0.57
75.66 0.008 0.33 0.017 0.21 0.030 Before casting 0.10 68.71 0.021
0.03 0.018 9.04 0.004 Final product 0.09 68.76 0.019 0.03 0.018
8.91 0.005
[0055] By applying such method, the inventors achieved a low carbon
level, which can be explained by the low solubility of carbon in
high silicon alloys. It was however surprising that it was possible
to reach carbon levels as low as in current low carbon ferrosilicon
grades (see table 1).
[0056] The alloy according to the invention is a cost-efficient
alternative to separately adding the required alloying elements Si
and Mn separately as ferrosilicon and manganese alloy or a
manganese metal, by improving process time and quality. Said alloy
could also help NGOES producers to decrease the overall carbon
content in the steel and reach a lower level than by adding
ferrosilicon/Si based alloy and manganese in the form of low carbon
manganese alloy or manganese metal separately. Further, said alloy
could allow electrical steel producers to make new grades with
higher Mn level and at the same keep the carbon content low in the
steel using only one alloy additive.
[0057] Having described different embodiments of the invention it
will be apparent to those skilled in the art that other embodiments
incorporating the concepts may be used. These and other examples of
the invention illustrated above are intended by way of example only
and the actual scope of the invention is to be determined from the
following claims.
* * * * *