SE1250996A1 - Järn- och volframinnehållande pellets - Google Patents
Järn- och volframinnehållande pelletsInfo
- Publication number
- SE1250996A1 SE1250996A1 SE1250996A SE1250996A SE1250996A1 SE 1250996 A1 SE1250996 A1 SE 1250996A1 SE 1250996 A SE1250996 A SE 1250996A SE 1250996 A SE1250996 A SE 1250996A SE 1250996 A1 SE1250996 A1 SE 1250996A1
- Authority
- SE
- Sweden
- Prior art keywords
- pellets
- tungsten
- iron
- powder
- weight
- Prior art date
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B5/00—General methods of reducing to metals
- C22B5/02—Dry methods smelting of sulfides or formation of mattes
- C22B5/12—Dry methods smelting of sulfides or formation of mattes by gases
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/001—Starting from powder comprising reducible metal compounds
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B34/00—Obtaining refractory metals
- C22B34/30—Obtaining chromium, molybdenum or tungsten
- C22B34/36—Obtaining tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/02—Making ferrous alloys by powder metallurgy
- C22C33/0235—Starting from compounds, e.g. oxides
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C35/00—Master alloys for iron or steel
- C22C35/005—Master alloys for iron or steel based on iron, e.g. ferro-alloys
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Manufacture And Refinement Of Metals (AREA)
Description
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2-90
b) adding to the mixture:
mo lybdenum containing powder
a liquid, preferably water,
optionally one or more of:
binder,
slag former,
desulfiarizer;
c) pelletizing to provide a plurality of green pellets
By this process it is possible to produce iron and tungsten containing green pellets and
reduced green pellets described below.
When preparing the mixture and during pelletizing the total amount of added water is
around 5-25 % by weight the mixture, more preferably 10-20 % by weight.
The green pellets are preferably dried to reduce the moisture content to less than 10 %
by weight, preferably less than 5 % by weight, more preferably less than 3 % by weight.
The moisture content is defined as water present in the pellets apart from Water of
crystallization. By reducing the water content the pellets may be heated at higher
temperatures, e.g. above 200 °C, Without cracking from quick vaporisation of the water
present in the pellets.
The pellets may be dried in ambient air without heating, preferably for at least 12 hours.
When drying the pellets there is a temperature increase even when no external heat is
used. This is believed to be from reactions when the iron oxidises. The strength of the
pellets also increases. This makes it possible to provide sufficiently strong pellets that
can be handled in rotary ovens Without disintegrating, and without the need of adding
binders, i.e. the iron powder replaces the need of a binder. Dust problems are also
minimised.
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The pellets may also be actively dried in as heater at a temperature up to 200 °C,
preferably around 80-150°C. This shortens the required time of drying. The heater may
be a rotary dryer; in particular a first section of rotary kiln that downstream includes a
reduction zone.
However, in some applications it may be advantageous to have a moisture content of the
green pellets around 3-15 % by weight, preferably around 5-10 %. For example if the
green pellets are added directly to a steel melt a “Wet” green pellet may dissolve
quicker.
Preferably reducing the dried pellets at a temperature in the range of 1050-1400 °C,
preferably 1100-1300 °C, more preferably 1150-1250 °C, during at least 0.5 hours.
Depending on the reduction time, the amount of carbon and the temperature the
reducible oxygen in the pellets can be partially or essentially fully reduced. Preferably
the reduction in step e) is performed during 0.5 - 10 hours, preferably 0.5-4 hours, more
preferably 0.5 - 3 hours, most preferably 0.5-2 hours. Preferably, the heat treating step
d) and the reduction step e) are performed at 0.8-1.2 bar, more preferably at atmospheric
pressure.
Optionally pre-reducing the green pellets derived from step c) at a temperature in the
range of 400-800 °C during 0.5-2 hours, preferably less than 1 hour. The optional step is
preferably employed when the green pellet includes mo lybdenum trioxide. By having
pre-reducing at lower temperatures, vapour losses of Mo can be minimised by pre-
reducing most of the MoOg to MoOg at a lower temperature. The atmospheres
surrounding the pellets is preferably reducing during the optional pre-reduction as well
as during the reduction. The optional pre-reduction step can be performed in the same
fumace as the reduction step, or altematively it would be possible to transfer the pre-
reduced green pellets to another fiarnace for the reduction step.
Depending on purities of the powders, the mixture the pellets may contain further
elements including oxides that are difficult to reduce. The amount of such elements are
mainly deterrnined by the purity of the tungsten containing powder and the optional
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molybdenum containing powder, but may also come from impurities in the iron powder,
the carbon powder, and from reactions with elements in the surrounding atmosphere
during heating, reduction, or cooling.
The total process is endotherrnic and requires heat. To reduce the amount required
external heat, oxygen gas or air can be provided in a pre-heating zone to react with the
formed carbon monoxide to form carbon dioxide gas. If air is used the nitrogen uptake
of the pellets may increase. Using oxygen the nitrogen uptake during the heating and the
reduction step can be minimised.
Preferably cooling the pellets in a non-oxidising atmosphere (e.g. reducing or inert) to a
temperature below 200 °C to avoid re-oxidation of the pellets, more preferably below
150 °C in an inert atmosphere. The atmosphere may e.g. be a 95 vol-% Ng and 5 vol.%
H2 atmosphere. If it is desirable to have very low levels of nitrogen, the pellets may be
cooled in a nitrogen free atrnosphere such as for example an argon gas atrnosphere.
The process may fiirther crushing and/or grinding the pellets, and optionally sieving the
crushed and/or ground pellets.
Suitable fumace types for the pre-reduction step and the reduction step are for example
rotary kilns, rotary heart fumaces, shaft fumaces, grate kilns, travelling grate kilns,
tunnel fumaces or batch fumaces. Other kinds of fumaces used in solid state direct
reduction of metal oxides may also be employed.
In a preferred embodiment a rotary kiln is used to reduce the pellets. In a rotary kiln
furnace the dried green pellets are fed to a rotary kiln rotating on a slightly inclined
horizontal axis, and propagated from an inlet of the kiln towards an outlet of the kiln, as
the kiln is rotated about its axis.
Instead of drying the green pellets before entering the kiln, the kiln may have a drying
zone operating at a temperature in the range of 80-200 °C, preferably 100-150 °C. The
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green pellets are dried in this zone to a moisture content of less than 10 % by weight,
preferably less than 5 % by weight.
The kiln may also include a pre-reduction zone, downstream the drying zone if such is
used, and operating in the range of 400-800 °C, preferably 500-700 °C. A pre-heating
zone may in particular be useful if the green pellet includes MoOg. I.e. to reduce at least
a significant part of MoO; in the green pellets to MoOg. Thereby vaporisation losses of
Mo can be minimised.
The kiln further includes a reduction section, downstream the drying and pre-heating
sections if they are present. The reduction section provides a temperature zone in the
range of 1050-1300 °C in which a significant part of remaining molybdenum oxides are
reduced by the remaining carbon powder to MoO and/or Mo.
Mixture
The mixture provided in step a) comprises (in weight-%):
1-40 iron powder
2-97 tungsten containing powder,
optionally
1-25 carbon powder,
2-90 mo lybdenum containing powder,
Preferably the iron powder is 2-25 % by weight, more preferably 3-15 % by weight.
Preferably the tungsten containing powder is at least 20 % by weight.
Preferably, the tungsten containing powder + mo lybdenum containing powder is more
than 50 % by weight of the mixture, more preferably more than 70 % by weight of the
mixture .
In one embodiment the mixture consists of (in weight-%):
1-40, preferably 3-15 of a iron powder, and
75-99, preferably 85-97 of a tungsten containing powder.
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Preferably, the tungsten containing powder includes tungsten oxides and tungsten
carbides. Preferably, the reducible oxides in the tungsten containing powder and the
iron powder are stoichiometric matched with carbon of the tungsten carbides, so that
after a reduction the carbon content is less than 10 % by Weight preferably less than 5 %
by weight, more preferably less than 1 % by Weight, most preferably less than 0.5 % by
weight, and oxygen is less than 10 % by weight, preferably less than 5 % by weight,
most preferably less than 3 % by weight.
Thereby iron and tungsten containing pellets can be produced that essentially consists of
iron and tungsten and unavoidable impurities.
Iron and tungsten containing pellets that consist of iron and tungsten and unavoidable
impurities can also be produced from a mixture where tungsten carbides is partially or
fully replaced by a carbon powder, i.e. so that carbon of tungsten carbides and/or carbon
powder stoichiometric matches the reducible oxides in tungsten containing powder and
the iron powder.
Iron and tungsten containing pellets that consists of iron, tungsten and molybdenum and
unavoidable impurities can be produced from the mixture by adding the optional
molybdenum containing powder. Here, carbon from the tungsten carbides and/or carbon
powder is stoichiometric matched with the reducible oxides in molybdenum containing
powder, the tungsten containing powder and the iron powder. Here, the tungsten
containing powder preferably is a tungsten carbide powder comprising at least 70 % by
weight of WC, preferably at least 95 % by weight of WC, or a tungsten oxide powder
comprising at least 70 % by weight of WOg, preferably at least 95 % by weight of WOg,
or a mixture of these powders.
Preferably the carbon and oxygen is balanced so that after reduction, the carbon content
is less than 10 % by weight preferably less than 5 % by weight, more preferably less
than 1 % by weight, most preferably less than 0.5 % by weight, and oxygen is less than
10 % by weight, preferably less than 5 % by weight, most preferably less than 3 % by
weight.
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The relative amounts of mo lybdenum and tungsten can be varied by changing the
relative amounts of the tungsten containing powder and mo lybdenum containing
powder, while considering the carbon and oxygen balance.
In one embodiment the weight ratio of molybdenum and tungsten (Mo/W) are
determined to be within the range 0.25 - 4, preferably 0.5 - 2, more preferably 0.8-1.25.
Tungsten containing powder
The tungsten containing powder is preferably one of:
- a tungsten carbide containing powder,
- a tungsten oxide containing powder,
- a mix of tungsten carbide containing powder and tungsten oxide containing
powder.
Tungsten carbide containing powder
The_tungsten carbide containing powder is a powder that comprises tungsten carbides
contained in a metal matrix. Preferably the tungsten carbide containing powder is
obtained from tungsten cemented carbide scrap. The tungsten carbide containing
powder preferably comprises 1-10 % by weight of carbon, balance tungsten and
incidental impurities. The tungsten carbide containing powder may also include alloy
elements which have formed a matrix (binding material) for the cemented tungsten
carbide material. The proportion of carbide phase is generally between 70-97% of the
total weight of the composite. The carbon is present in the powder particles in the form
of tungsten carbide grains, and typically the grain size averages between 0.10 um and
15 um. Any powder particle may include several tungsten carbide grains, in particular if
the particle sizes are large. Further, the tungsten carbide containing powder may include
powder particles that are void of any tungsten carbide grains; however most of the
powder particles will include one or more grains of tungsten carbide.
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Some tungsten carbide powder can contain cobalt up to 15 %.by Weight; typically
around 1-10 % by weight of Co. For instance, the tool material in circuit board drills
typically comprises fine grained, cemented tungsten carbides existing in a cobalt matrix,
the amount of which represents 6 percent of the total Weight of the tool material, while
coarse grain tungsten carbide materials typically are used for the tool material of mine
drills, where the cobalt content of the cemented carbide material is about 10 Weight-%.
These powders can be used if cobalt can be allowed or is desirable in the pellet to be
produced. If not, these powders can be used after being leached from cobalt. For
instance a commercially available tungsten carbide containing powders from scrap that
comprises 1-10 % by weight Co, usually in amounts of 3-8 % by weight Co, can be
hydrometallurgical leached to reduce the cobalt content to be less than 1 % by weight
Co, preferably less than 0.5 % by weight Co, more preferably less than 0.2 % by weight
Co. The cobalt from the leaching process can be recycled and employed as a
commercial product per se.
Of course a tungsten carbide powder that already is low or void of cobalt can be used.
I.e a powder that contains less than 1 % by weight Co, more preferably less than 0.5 %
by weight Co, even more preferably less than 0.2 % by weight Co.
Preferably the tungsten carbide powder contains at least 90 % by weight of WC, more
preferably at least 95 % by weight.
Preferably at least 90 % by weight, more preferably at least 99 % by weight, of the
particles of the the tungsten carbide containing powder_pass through a test sieve in
accordance to ISO 3310-12000 having nominal aperture sizes of 250 um, more
preferably 125 um, most preferably 90 um. Very fine powder where at least 99 % by
weight, passes through a test sieve of 45 um can suitably be used.
Tungsten oxide containing powder
The tungsten oxide containing powder may be an iron and tungsten oxide containing
powder, more preferably iron tungstate in the form of the mineral Ferberite. Preferably a
feberite that contains over 60 % of WO3, more preferably at least 70 % WOS. The
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Ferberite is crushed and/or milled and/or ground to a powder so that at least 80 % by
weight of the particles, preferably at least 90 %, passes through a test sieve in
accordance to ISO 3310-1:2000 having nominal aperture sizes of 250 um, more
preferably 125 um.
The tungsten oxide containing powder may also be a pure tungsten oxide powder
containing less than 5 % by weight of other elements besides W and O, preferably less
than 1 % by weight of other elements. Eg. a powder that includes at least 95 % by
weight of WOg, preferably at least 99 % by weight.
Preferably at least 80 % by weight of the particles, more preferably at least 90 % by
weight of the particles of the tungsten oxide powder pass through a test sieve in
accordance to ISO 3310-1:2000 having nominal aperture sizes of 250 um, more
preferably 125 um. most preferably 90 um. Very fine powder where at least 99 % by
weight, passes through a test sieve of 45 um can suitably be used.
The tungsten oxide containing powder may also be a mix of iron tungstate and pure
tungsten oxide powder.
Other available grades of tungsten oxide powders may also be used.
Molybdenum containing powder
The mo lybdenum containing powder is preferably a molybdenum oxide powder. The
powder preferably consists of mo lybdenum dioxide and/or mo lybdenum trioxide
powder.
The mo lybdenum oxide powder should contain 50-80 % by weight of Mo, the
remaining elements being oxygen and impurities. Preferably the impurities are less than
10 % by weight, more preferably less than 5 % by weight, most preferably less than 1%
by weight.
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Preferably at least 90 % by weight, more preferably at least 99 % by weight, of the
particles of the molybdenum oxide powder pass through a test sieve in accordance to
ISO 3310-12000 having nominal aperture sizes of 250 um, more preferably 125 um,
most preferably 45 um.
Iron powder
The iron powder is preferably an iron powder containing at least 80 wt% metallic iron,
preferably at least 90 wt% metallic iron, more preferably at least 95 wt% metallic iron,
most reperfably at elast 99 wt% metallic iron. The iron powder can be an iron sponge
powder and/or a water atomised iron powder and/or a gas atomised iron powder and/or
an iron filter dust and/or an iron sludge powder. For instance filter dust X-RFS40 from
Höganäs AB, Sweden is a suitable powder.
Preferably at least 90 % by weight, more preferably at least 99 % by weight, of the
particles of the iron containing powder pass through a test sieve in accordance to ISO
3310-12000 having nominal aperture sizes of 125 um, more preferably 90 um. Very
fine powder where at least 99 % by weight, passes through a test sieve of 45 um can
suitably be used.
Optional carbon powder
The green pellets preferably includes a carbon source. In the preferred embodiment the
carbon source is a tungsten carbide containing powder, where the carbon content
stoichiometric matches the oxide contents in the green pellets. However, a carbon
powder may also be used as the carbon source, either in combination with a tungsten
carbide containing powder or as the sole carbon source.
The carbon powder is preferably chosen from the group of: sub-bituminous coals,
bituminous coals, lignite, anthracite, coke, petroleum coke, and bio-carbons such as
charcoal, or carbon containing powders processed from these resources. The carbon
powder may e.g. be soot, carbon black, activated carbon. The carbon powder can also
be a mixture of different carbon powders.
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Regarding the choice of carbon powder, the reactivity of the carbon is preferably taken
into consideration. Preferably carbon black is used. German brown coal (lignite),
charcoal, bituminous and sub-bituminous coals also have comparably high reactivity.
Preferably at least 90 % by weight, more preferably at least 99 % by weight, of the
particles of the carbon powder pass through a test sieve in accordance to ISO 3310-
132000 having nominal aperture sizes of 125 um, more preferably 45 um, most
preferably 20 um.
The amount of the carbon source (i.e. WC-powder and/or carbon powder) is preferably
deterrnined by analysing the amount of reducible oxides in the tungsten containing
powder, the iron powder, and the optional mo lybdenum containing powder. Preferably
the amounts of the carbon source is chosen to stoichiometric match or slightly exceed
the amount of reducible oxides in the tungsten containing powder, the iron powder, and
the optional molybdenum containing powder. However, the amount of the carbon
source may also be sub-stoichiometric.
The amount of the carbon source can be optimised by measuring the carbon levels and
the oxygen levels in the reduced pellets - increasing or decreasing the amount of carbon
source to achieve desired levels of carbon and oxygen. Oxides which are difficult to
reduce with carbon such as Si, Ca, Al, and Mg may be allowed up to certain levels
depending on in which applications the pellets are to be used in. For instance in many
applications of steel metallurgy these oxides can be handled e.g. by removing them in
the slag of steel melt. If lower amounts of these oxides and elements are desired, purer
grades of the tungsten containing powder, the iron powder, and the optional
molybdenum containing powder can be used, e.g. grades that contains less or no
amounts of these oxides.
Iron and tungsten containing green pellets
The green pellets comprises of the mixture provided in step a). When preparing the
mixture and during pelletisation the total amount of added water is around 5-25 % by
weight of the mixture, more preferably 10-20 % by weight. The green pellets are
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preferably dried to reduce the moisture content to less than 10 % by weight, preferably
less than 5 % by weight, more preferably less than 3 % by Weight.
When producing the green pellets one or more organic or inorganic binders and/or slag
formers and/or desulfiarizers may optionally be added. The binder may e.g. be a carbon
containing binder. Other binders may e. g. be bentonite and/or dextrin. The slag former
may e.g. be limestone, dolomite, and/or olivine. The total amount of optional binder/s
and/or optional slag former/ s and/or desulfurizers should be less than 10 % by weight,
preferably less than 5 Wt%, of the dry matter. Most preferably the green pellets are void
of binders, slag forrners and desulfurizers.
The dried green pellets are surprisingly strong and it may therefore be possible to use
the dried green pellets to directly alloy a steel melt with tungsten and optionally
tungsten and molybdenum, i.e. without prior reduction of the green pellets. The green
pellets can be cost efficient way of alloying with tungsten and optionally tungsten and
molybdenum. The green pellets may also be partially or fiilly reduced in by heating the
green pellets in subsequent steps.
A green pellet comprising 5-15 % by weight iron powder (> 99 Fe) and 85-95% by
weight of a tungsten containing powder (WO3+WC > 95wt%) can have compression
strength around 10-50 N/ cmz directly after pelletizing. After drying the pellets the
compression strength increases to around 50-150 N/cmz. For pellets where the tungsten
containing powder is partially replaced by mo lybdenum oxide powder (e. g. replacing
tungsten oxide) the compression strength is similar directly after the pelletizing, but
after drying the compression strength may reach as high as 600 N/ cmz, depending how
much is substituted.
Iron and tungsten containing pellets
Iron and tungsten containing pellets can be produced by the suggested process that
consists of in weight %:
W 3-97, preferably 30-95,
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Mo+ W 50-97, preferably 70-95,
O S 10, preferably S 5, more preferably S 3,
C S10, preferably S 5, more preferably S 1,
Si S 10, preferably S 5, more preferably S 1,
Co S 10, preferably S 5, more preferably S 1,
Other elements S 5, preferably S 1,
and balance Fe 2-40, preferably 3-25, more preferably 5-20, most preferably 5-15.
These pellets have a geometric density in the range of 2-7 g/cm3, preferably 3-6 g/cm3
and compression strength in the range of 150-600 N/cmz, preferably 200-500 N/ cmz.
According to one example the iron and tungsten containing pellets consists of in Weight
%:
W 60-97, preferably 80-95,
O S 10, preferably S 5, more preferably S 3,
C S10, preferably S 5, more preferably S 1,
Si S 10, preferably S 5, more preferably S 1,
Co S 10, preferably S 5, more preferably S 1,
Other elements S 5, preferably S l,
and balance Fe 2-40, preferably 3-25, more preferably 5-20, most preferably 5-15.
These pellets have a geometric density in the range of 3-7 g/cm3, preferably 4-6 g/cm3
and compression strength in the range of 150-400 N/cmz, preferably 200-300 N/cmz.
These pellets may substitute traditionally manufactured ferrotungsten alloys, When
alloying With tungsten in melting practices. The pellets can be produced at lower costs
than standard grades of ferrotungsten. Furthermore, due to their porous structures the
pellets dissolves quicker than standard grades of ferrotungsten.
According to another example the iron and tungsten containing pellets consists of in
Weight %:
W 20-80, preferably 30-65, more preferably 40-55,
Mo 20-80, preferably 30-65, more preferably 40-55,
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Mo + W > 50, preferably >70,
O S 10, preferably S 5, more preferably S 3,
C S10, preferably S 5, more preferably S 1,
Si S 10, preferably S 5, more preferably S 1,
Co S 10, preferably S 5, more preferably S 1,
Other elements S 5, preferably S 1,
and balance Fe 2-40, preferably 3-25, more preferably 5-20, most preferably 5-15.
Preferably, the Weight ratio of mo lybdenum and tungsten (Mo/W) are determined to be
within the range 0.25 - 4, preferably 0.5 - 2, more preferably 0.8-1.25.
These pellets have a geometric density in the range of 2-6 g/ cm3 , preferably 3-5 g/ cm3
and compression strength in the range of 200-600 N/cmz, preferably 250-500 N/ cmz.
These iron, tungsten and molybdenum containing pellets are suitable for alloying with
tungsten and mo lybdenum in melting practices. The iron, tungsten and mo lybdenum
containing pellets can be produced at comparably lower costs. Furthermore, due to their
porous structures the pellets dissolves quickly in a steel melt.
The amount of other elements is mainly controlled by the purity of the tungsten
containing powder and the optional mo lybdenum containing powder. The purity of the
iron containing powder and optional carbon powder may of course influence the amount
of other elements.
The nitrogen content mainly depends on the nitrogen levels in the atmosphere during
heating, reduction and cooling of the pellets. By controlling the atmosphere in these
steps the nitrogen content can be made lower than 0.5 wt%, preferably lower than 0.1
wt% and most preferably lower than 0.05 wt%.
The average diameter of the pellets are preferably in the range of 3-30 mm, preferably
5-20 mm. Too large pellets may prolong the needed reduction time, while too small
pellets can be difficult to handle.
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The shape of the pellet is typically spherical, spheroidal, or ellipsoidal. When handled,
this form compared to the form a compressed briquettes reduces the risk of shredding.
Furthermore the flow properties are better than that of briquettes.
However, in other applications it may be desirable to have other shapes than spherical,
spheroidal, or ellipsoidal. For instance pellets that are transported on a conveyor belt
may roll of the belt depending on how the conveyor belt is configured.
Pellet agglomerates comprising 2-300 pellets are less likely to roll off a conveyor belt.
The pellets may be agglomerated by means of a binding agent such as glue. Preferably
such agglomerates contain 2-20 pellets, more preferably 5-15 pellets.
It is also possible to form pellets agglomerates by filling plastic bags with pellets, and
preferably hot shrinking the plastic around the pellets and/or vacuum shrinking.
Preferably such agglomerates contain 30-300 pellets, more preferably 50-200 pellets,
most preferably 75-150 pellets.
Another way to avoid the problem is to fill a container, such as a metal canister, with
pellets. Preferably the container have an inner volume in the range of 100- 125000 cm3.
Of course, also the green pellets may be agglomerated or put in containers in the manner
described above.
The pellets may also be crushed to irregular shaped pieces, e. g. a coarse iron and
tungsten containing powder, where 90 % by weight of the powder particles are
contained by a test sieve in accordance to ISO 3310-1:2000 having nominal aperture
sizes of at least 250 um, preferably at least 500 um, more preferably at least 1 mm.
The pellets may further be ground and optionally sieved to provide a fine iron and
tungsten containing powder. Preferably the fine powder having particle size wherein at
least 90 % by weight, more preferably at least 99 % by weight, of the particles pass
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through a test sieve in accordance to ISO 3310-12000 having nominal aperture sizes of
250 um, more preferably 125 um, most preferably 45 um. The fine powder can e.g. be
provided as a core filling of a cored wire for injection alloying or welding application.
The powders may be cold briquetted.
The pellets may further be hot briquetted at a temperature in the range of 250-1000 °C,
preferably 400-800 °C, and more preferably between two counterrotating rollers, most
preferably at a pressing force in the range of 60-200 kN per cm active roller width.
Suitable hot briquetting machines are for instance sold by Maschinenfabrik Köppem
GmbH & Co. A binder may optionally be added in the hot briquetting step. The volume
of a briquette is preferably between 15 and 200 cm3 . Of course, also the green pellets
may be hot briquetted.
Claims (13)
1-25 carbon powder,
2-90 mo lybdenum containing powder - optionally up to 10 of a binder and/or slag former and/or a desulfurizer; and - 5-25 of moisture. 10 15 20 25 30 10. 19 Iron and tungsten containing pellets consisting of in Weight %: W
3-97 Mo+ W 50-97 O S 10 C S10 Si S 10 Co S 10 Other elements S 5 and balance Fe 2-40. Iron and tungsten containing pellets according to claim 7, Wherein the pellets have a geometric density in the range of 2-7 g/cm3, preferably 3-6 g/cm3 and compression strength in the range of 150-600 N/cmz, preferably 200-500 N/cmz. Iron and tungsten pellets according to claim 7 consisting of in Weight %: W 60-97, preferably 80-95, O S 10, preferably S 5, more preferably S 3, C S10, preferably S 5, more preferably S 1, Si S 10, preferably S 5, more preferably S 1, Co S 10, preferably S 5, more preferably S 1, Other elements S 5, preferably S 1, and balance Fe 2-40, preferably 3-25, more preferably 5-20, most preferably 5- 15. Iron and tungsten containing pellets according to claim 9, Wherein the pellets have a geometric density in the range of 3-7 g/cm3, preferably
4-6 g/cm3 and compression strength in the range of 150-400 N/cmz, preferably 200-300 N/cmz 10 15 20 11. 12. 13. 20 Iron and tungsten containing pellets according to claim 7 consisting of in Weight %: W 20-80, preferably 30-65, more preferably 40-55, Mo 20-80, preferably 30-65, more preferably 40-55, Mo + W > 50, preferably >70, O S 10, preferably S 5, more preferably S 3, C S10, preferably S 5, more preferably S 1, Si S 10, preferably S 5, more preferably S 1, Co S 10, preferably S 5, more preferably S 1, Other elements S 5, preferably S 1, and balance Fe 2-40, preferably 3-25, more preferably
5-20, most preferably 5- 15. Iron and tungsten containing pellets according to claim 11, Wherein the pellets have a geometric density in the range of 2-6 g/cm3, preferably 3-5 g/cm3 and compression strength in the range of 200-600 N/cmz, preferably 250-500 N/cmz. An iron and tungsten containing pellet according to any one of claims 7 - 12, Wherein the pellets having an average diameter in the range of 3-30 mm, preferably 5-20 mm.
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
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SE1250996A SE537463C2 (sv) | 2012-09-05 | 2012-09-05 | Järn- och volframinnehållande pellets |
PCT/EP2013/068263 WO2014037385A1 (en) | 2012-09-05 | 2013-09-04 | Iron and tungsten containing pellets and iron, tungsten and molybdenum containing pellets |
TW102131784A TW201430143A (zh) | 2012-09-05 | 2013-09-04 | 含有鐵及鎢之丸粒 |
Applications Claiming Priority (1)
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SE1250996A SE537463C2 (sv) | 2012-09-05 | 2012-09-05 | Järn- och volframinnehållande pellets |
Publications (2)
Publication Number | Publication Date |
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SE1250996A1 true SE1250996A1 (sv) | 2014-03-06 |
SE537463C2 SE537463C2 (sv) | 2015-05-12 |
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SE1250996A SE537463C2 (sv) | 2012-09-05 | 2012-09-05 | Järn- och volframinnehållande pellets |
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SE (1) | SE537463C2 (sv) |
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