Note: Descriptions are shown in the official language in which they were submitted.
~SZ3~7
This invention relates to a method for forming a carbi-
de layer of a V-a group element of the ~eriodic Table on the
su.face of an iron, ferrous alloy or cemented carbide article,
and more particularly it relates to the formation of the carbide
layer on the surface of the article immersed in a treating molten
bath. The iron ferrous alloy or cemented carbide article with
the carbide layer formed thereof has a greatly improved hardness,
wear resistance and machinability.
There have been reported several kinds of methods for
coating or forming a metallic carbide layer on the surface of
metallic articles~ We have pxeviously developed a method for
forming a carbide layer of a V-a group element on the surface of
metallic article in a treating molten bath consisting of boric
acid or a borate and a metal powder containing a V-a group
element (Canadian Patent N. 935 074). The method can ~orm
~ a uniform carbide layer and is highly productive and cheap.
The carbide of a V-a group element, such as vanadium carbide
(VC), niobium carbide (~b) and tantalum carbide (TaC) has a very
high hardness ranging from Hv 2000 to Hv 3000. Therefore, the
carbide layer formed represents a high value of hardness and a
superior resistance performance against wear and is thus highly
suitable for the surface treatment of moulds such as dies and
punches, tools such as pinchers and screwdrivers, parts for
many kinds of tooling machines, automobile parts to be subjected
to wear.
Further, the carbide of a V-a group element is much
harder and less reactive with iron or steel at a high temperature
than the tungsten carbide forming cemented carbide is. Therefore,
the formation of the carbide layer of a V-a group element on the
surface of a cutting tool made of cemented carbide increases
greatly the durability of the tool.
The method mentioned above, however, takes a relatively
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long time for forming a practically acceptable thick carbide
layer of a V-a group element.
Therefore, it is the pxincipal object of the present
invention to provide an improved method for forming a carbide
layer of a V-a group element on the surface of an iron, ferrous
alloy or cemented carbide article in a treating molten bathO
It is another object of this invention to provide
a method ~or forming quickly a metallic carbide layer with
denseness and uniformity on the surface of the article.
It is still another object of this invention to provide
a method for forming a metallic carbide layer on the surface
of the article by applying an electric current to the article.
It is a still further object of this invention to
provide a method for forming a carbide layer, which is safe and
simple in practice and less expensive.
The above objects are obtained in a method which
ccmprises the steps of:
preparing a treating molten bath composed of molten
boric acid or a borate and a substance containing a V-a group
element of the Periodic Table in a vessel, immersing the article
containing at least 0.05% by weight of carbon into the treating
molten bath, applying an electric current to the treating
molten bath through said article being used as the cathode
for depositing the V-a group element on the surface of the article
and for forming the carbide layer of said V-a group element
with the carbon contained within said article on the surface
of said article and taking said article out of the trca-ting
molten bath.
A description now follows of specific embodiments in
connection with the accompanying drawings, in which:
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Figs. 1 to 4 are photomicrographs showing vanadium car-
bide layers on carbon tool steel, which are formed according to
Example l;
Fig. 5 to 7 are graphs obtained in Example 1 by X-ray
micro analyzer and showing the contents of the components forming
the carbide layers;
Fig. 8 is a graph obtained in Example 1 and showing the
effect of the current density applied to the article treated on
the thickness of khe layer formed;.
" 1~5'~317
Fig. 9 is a photomicro~raph showing a niobium carbide
layer on carbon tool steel, which is forned according to Example
2,
Fig. 10 is a graph obtained in Example 2 by X-ray micro
analyzer and showing the contents of the components forming the
niobium carbide layer;
Fig. 11 to 13 are photomicrographs showing vanadium
carbide layers on carbon tool steels, which are formed according
to Example 3;
10Fig. 14 is a photomicrograph showing a vanadium carbide
layer formed on carbon tool steel according to Example 4,
Fig. 15 and 16 are graphs obtained in Example 6 and
showing the effect of the current density applied to the article
treated on the thickness of the layer form~d;
Fig. 17 is a photomicrograph snowing a van~di~n carblde
layer formed on carbon tool steel according to Example 6,
F_g. 18 is a graph obtained in Example 6 b~ ~-ray micr~,
analyzer and showing the contents of the components formlng the
vanadium carbide layer,
~oFig. 19 is a phot~mierograph showing a vanadlum oarbide
layer formed on carbon tool steel according to Example 7;
Fig. 20 is a photomicrograph showing a niobium carbide
layer formed on carbon tool steel according to Example 9,
Figs. 21 and 22 are photomicrographs showing vanadium
carbide layers fo~med on carbon tool steel according to Example 11
Fig. 23 is an X-ray diffraction chart of the vanadium
carbide layer formed on cemented carbide according to ~xample 12;
Fig. 24 is a photomicrograph showing a vanadium carbide
layer formed on cemented carbide according to Example 14,
30Fig. 25 is a photomicrographic showing a niobium layer
formed or. cemented carbide according to Example~15,
Fig. 26 is a photomicrograph showing a rliobium carbide
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l~Z3~7
layer formed on cemented carbide according to Example 16,
Fig. 27 is an X-ray diffraction chart of the niobium
carbide layer formed on cemented carbide according to Example 16~
Broadly, the present invention ls directed to an improve-
ment of the method for forming a carbide layer of an iron,ferrous
alloy or cemented carbide article in a treating molten bath and
is characterized in that the treating bath is composed of boric
acid or a borate and a V-a group element of the Periodic Table
dissolved therein and in that the article immersed in the treat-
ing molten bath is treated with an electric current for deposit-
ing the V-a group element on the surface of the article. The
element deposited reacts with the carbon contained within the
article and forms the carbide layer of the V-a group element on
thè surface of the article. The method of the present invention
comprises preparing a treating molten bath containing a molten
boric acid or a borate and a V-a group element, immersing an
iron, ferrous alloy or cemented carbide article in the treating
molten bath, applying an electric current to the treating molten
bath with the article being used as the cathode for forming the
carbide layer of the V-a group element on the surface of the
article.
The electric current deposits the V-a group element
dissolved in the treating molten bath on the surface of
the article and accelerates the formation of the carbide layer
of the V-a grou~ element on the surface of the articleO ~he
voltage of the electric current is relatively low. It is not
necessary for said voltage to be enough high -for electrolysing
the molten boric acid or borate in the treating molten bath. In
order to accelerate the formation of the carbide layer of a V-a
group element on the surface of the article, a relatively high
voltage (in other words, a relatively large current density of
the cathode3 may be employed. In that case, large current density
deposits a reduced boron on the surface of the article together
b ~ 4
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with a V-a group element and the boron reacts with a part of the
V-a group element. I'hereforç, the carbide layer of the V-a group
element comes to include a small amount oE a boride of a V-a
group element such as vanadium boride (VB2), niobium boride (NbB2)
and tantalum boride (TaB2), and in some cascs,the boride layer of a
V-a group element is formed on the carbide layer of a V~a group
element. Said boride of a V-a group element has been known to
have a much higher hardness than that of the carbide of a V-a
group element. Also said boride has a good wear resistance and
corrosion resistance against chemical reagent and molten metal.
Therefore, the boride layer of a V a group element formed and the
carbide layer containing the boride work as well as the carbide
layer of a V-a group element. However, with a too large current
density, the amount of boron brought Qn the surface is too much
and prevents a V-a group element from reaching onto the surface
of the article. Said boron ~ forms boride such as iron
boride and cobalt boride with metals of the mother material of
the article. Therefore, a too large current density o~ the anode
is not good.
The critical current density of the cathode composed of
the article to be treated depends on the substance including a V-a
group element in the treating molten bath. For example, in the
treating molten bath containing the oxide of a V-a group element,
a relatively large current density, 15 A/cm , can be applied for
forming the carbide layer of a V-a group element on the surface
of the article. In the treating molten bath containing the chlori-
de of a V-a group element, the upper limit of the current density
for forming the carbide layer of a V-a group element is 3 A/cm2.
The practical lower limit of the current density of the
cathode is 0.01 A/cm . ~aowever, when the treating molten bath
includes the oxide of V-a group element, more than 0.1 A/cm2 is
preferable.
The treating molten bath used in the present invention
¢~*
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is composed of a molten bo~ic acid or a borate and a substance
containing a V-a group element. As said substance, the metals of
a V-a group element, alloys containing a V-a g~oup element, the
oxide and chloride of a V-a gxoup element such as V203, V205,
VOCL2, NaV03, Na2VO~, NH~V02, Nb205, Ta205, VC13, VCl~, NbC14,
TaC15, can be used. In order to prepare the treating molten bath,
the powder of said substance is introduced in the molten boric
acid or borate or the powder of said substance and the powder of
said boric acid or borate are mixed together and then the mixture
is heated up to its fusing state. By another method, a block of
said metals or alloys immersed in the bath as the anode and is
anodically dissolved in the molten boric acid or borate for
preparing the treating molten bath.
Borate such as sodium borate (borax) (Na2B~07), potassium
borate,boric acid and the like and the mixture thereof can be used.
The boric acid and borate have a functlon to dissolve a metallic
oxide and to keep the surface of the article to be treated clean,
and also the boric acid and borate are not poisonous and do not
readily vaporize. Therefore, the method of the present invention
can be carried out in the open air.
As the V-a group elements contained in the treating mol-
ten bath, one or more elements of vanadium (V), niobium (Nb) and
tantalum (Ta) can be used, 1% by weight (hereinafter % means iO by
weight) of V-a group element dissolved in the treating molten bath
being sufficient. In practice, however, the V-a group element may
be dissolved into the treating molten bath in a quantity between
1 and 20%. With use of less quantity of V-a group element than 1%,
the speed of formation of the carbide layer would be too slow to
be accepted for the practical purpose. ~oo much addition of V-a
group element in excess of 20% will increase the viscosity of the
treatiny molten bath to such a high value that the dipping of the
article to be treated upon into the bath may become practically
impossible. Even when the immersion is possible with difficulty
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only, the resulting carbide layer will become too uneven to be
accepted.
The remainder of the treating molten bath is molten
boric acid or borate.
When the powders of the metal of a V-a group element
or of the alloy containing a V-a group element such as ferrou's al-
loys are used as the source, of the treatiny molten bath, the trea-
ting molten bath should be ~iven time for dissolving the V-a
group element into the molten boric acid or borate before im-
mersing the article to be treated into the treating molten bath.In case of preparing the treating molten bath by anodically dis-
solving V-a group element, the range of the current density of the
anode (the article) for forming the carbide layer on the surface
of the article may be from 0.01 to 5 A/cm2. When the formation
of the layer is carried out by immersing the article as the
cathode in the treating molten bath including the powder of the
oxide of a V-a group element, the current density of the cathode
may be selected within the range from 0.1 to 15 A/cm2.
When the powder of the chloride of a V-a group element
is used in the treating molten bath, the current density of the
cathode (article to be treated~ may be selected within the range
from O.Ol to 3 A/cm2. When the powder of the oxide or chloride
of a V-group element is used in the treating molten bath ageing
of the treating molten bath is not necessary because said oxide
and chloride can be dissolved quickly into the moIten boric acid
or borate.
In case the treating m~lten bath contains the chloride
of a V-a group element or a V-a group element which have been
dissolved anodically, the sur~ace of the carbide layer formed
is very smooth, and the layer does not contain any undissolved
particles of the treating molted bath.
To form the carbide layer of a V-a group element on the
surface of the article, the ar-ticle is immersed in the treating
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molten bath as the cathode, and a vessel containing the treatingmolten bath may be used as the anode. If the vessel is made of
conductive materials such as steel or carbon and is no-t used
as the anode a metal plate or rod dipped in the treating
molten bath can be used as the anode. In some cases, a metal
block containing a V-a group element can be used as the anode.
Said metal block is anodically dissolved into the treating molten
bath during the formation of the carbide layer.
The iron, ferrous alloy or cemented carbide to be treat-
ed must contain at least 0.05% of carbon, preferably contain 0.1%
of carbon or higher. The carbon in the article becomes a carbide
during the treatment. Namely it is supported that the carbon in
the article diffuses to the surface thereof and reacts with
the metal from the treating molken bath to form the carbide on
the surface of the article. The higher content of the carbon
in the article is more preferable for forming the carbide layer.
The iron, ferrous alloy or cemented tungsten carbide article
containing less than 0.05% of carbon may not be formed with a
uniform and thick carbide layer by the treatment. Also, the
article containing at least 0.05% of carbon only in the surface
portion thereof can be treated to form a carbide layer on the
surface of the article. For example, a pure iron article,
which is case-hardened to increase toe carbon content in the
surface portion thereof, ~an be used as the article of the
present invention.
Instead of iron may be used iron containing carbon and
case-hardened iron, ferrous alloy means carbon steel and alloy
steel, and instead of ~emented tungsten carbide may be used a
s-intered tungsten carbide containing cobalt. Said cemented
3 carbide may include a small amount of titanium carbide, niobium
carbide, tantalum carbide and the like.
In some cases, ~he carbon contained in the treating
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molten bath can be used as the source of the carbon for
forming the carbide layer on the surface of the article.
However, the formation of the carbide layer is not stable
and the use of the carbon
~ ~5'~3~7
in the treating molten bath is not practical.
Before the treatment, it is important to purify the sur-
face of the article for forming a good carbide layer by washing
out the rust and oil from the surface of the article with acidic
aqueous solu-tion.
The treating temperature may be selected within th~
wide rànge from the melting point of boric acid or borate to the
melting point of the article to be treated. Preferably, the treat-
ing temperature may be selected within the range from 800 to
1100C. With lowering of the treating temperature, the viscosity
of the treating molten bath increases gradually and the thickness
of the carbide layer formed decreases. However, at a relatively
high treating temperature, the treating molten bath deteriorates
rapidly. Also the quality of the material forming the article is
worsened by increasing the crystal grain sizes of said material.
The *reating time depends upon the thickness of the car-
bide layer to be formed treating temperature and the current densi-
ty of the anode. Heating shorter than 2 minutes will, however,
provide no practically accepted formation of said layer. With the
increase of the treating time, the thickness of the carbide layer
will be increased correspondingly. In practice, an acceptable
thickness of the layer can be realized within 5 hours or shorter
time. The preferable range of the treating time will be from 2
minutes to 5 hours.
The vessel for ~eeping the treating molten bath of the
present invention can be made of graphite or heat resistant steel.
It is not necessary to carry out the method of the pre-
sent invention in the atmosphere of non-oxidation gas, but the
method can be carried out into effect either under the air atmos-
phere or the inert gas atmosphere.Example 1:
700 grams of borax was introduced into each of two gra-
phite crucibles having a 65mm innerdiameter and heated in an elec-
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1~5;~3~7
tric furnace under the air. One of the crucibles was heated up to930C and the other to 950C. ~hen into each of the crucibles
were introduced 117 grams of ferrovanadium (containing 59% of
vanadium) powder of less than 100 mesh, mixed together and kept
for 1 hour. Thus, two kinds of the treating molten bath were
prepared. By using the treating molten bath kept at 930C, each
of one group of the specimens having a 7mm diarneter and made of
carbon tool steel (JIS SK4) was immersed down to 40mm from the
surface of the treating molten bath and treated with an electric
current for 3 hours using said specimen as the cathode. The cur-
rent density to the cathode applied was within the range from 0 to
2 A/cm2. In the same manner as mentioned above by using the other
treating molten bath kept at 950C, each of the other group of the
specimens having a 7 mm diameter and made of carbon tool steel
was treated for 10 minutes with a current density to the cathod
within the range from 3 to 5 A/cm2. After taking the specimens
out of each of the treating molten bathes, all the specimens treat-
ed were cooled in the air, washed with hot water and examined.
The specimens were cut vertically and the cross sections were
polished and microscopically observed. The photomicrographs shown
in Figs. 1 to 4 were taken from the specimens treated respectively
with a current density of 0.01 A/cm , 0.3 A/cm , 1.0 A/cm and
5.0 A/cm2. From the results by X-ray micro analyzer, the layers
formed with a current density of 0.05 A/cm2 or lower than 0.05 A/
cm2 were vanadium carbide composed of vanadium and carbon . FigO 5
shows the distribution of the contents of vanadium, iron, carbon
and boron contained in the surface portion of the specimen treated
with a current density of 0.01 A/cm . The layers formed with a
current density higher than 0.1 A/cm were recognized to be the
carbide containing boron. Also a boride layer composed of Fe2B
or FeBC and Fe2B was recognized between said carbide layer and the
mother material. Further, it was recognized that the thickness of
the boride layer increases with increase of the current density.
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Figs. 6 and 7 shows each of the distributions of ~alladium, iron,
carbon and boron contained in the layers formed respectively with
a current density of 2 A/cm2 and 5 A/cm2. Fig~ 8 shows the effect
of the current density on the thickness o1E the layer formed. The
thickness of the layers formed increases with increase of the
current density. ~Iowever, the layers formed with a current densi-
ty of 3 A/cm or higher than 3 A/cm consist mainly of FeB and
Fe2B and the thickness of the vanadium carbide layer formed on the
layer composed of Fe~ and Fe2B does not increase. Therefore, it
is not always good to employ a large current density. However, wi-
thin the limits of small current density, the increasing of current
density is p~eferable to form a thicker layer of vanadium carbide or
of the vanadium carbide containing boron. In -the layers formed with
a current density above 0.1 A/cm2, boron was clearly identified.
Although in the layers formed with a current density of Ool A/cm2
or lower than 0.1 A/cm2, boron was not identified, said layers may
possibly include boron.
From this example, it was recognized that the appliea-
tion of an electric current to the specimen treated increased the
thickness of the layers formed on the specimen.
Example 2:
In the same manner as described in Example 1, a treating
molten bath composed of 80% of borate and 20% or ferroniobium (con-
taining 59% of niobium and 3.9% of tantalum) powder of 100 mesh
or finer than 100 mesh was prepared. Each of the specimens made
of earbon tool steel (JIS SK~) was treated respectively at 950C
under each of the conditions. Specimen 2 -1 was treated with a
current density of 0.03 A/cm for 3 hours, Specimens 2-2 and 2-3
were treated respectively with 0.3 A/cm for 3 hours and with
3 A/cm for 10 minutes. As the eomparison, Specimen 2-A was
treated for 3 hours at 950C without applying an elect~ic current.
All the specimens were examined by a microscope, X-ray
~ ~o5Z3~L7
micro analyzer and by X-ray difraction method. The layer formed
on Specimen 2-l is shown in Fig 9. The layer had a thickness of
13 microns and a uniform and smooth surface. Fiy. 10 shows the
distributions of the contents of niobium, carbon and boron
contained in the surface portion of Specimen 2-1, which were
obtained by X-ray micron analyzer. From the results of said
X-ray micron analyzer and X-ray diffraction method, the layer form-
ed was identified to be the niobium carbide containing boron.
Specimen 2-2 was found to have a layer which was similar
with the layer formed on Specimen 2-1.
Specimen 2-3 was found to have a niobium carbide layer
of about 9 microns thick and a layer composed of iron boride
tFe2B) between said niobium carbide and its mother material.
Specimen 2-A was found to have niobiurn carbide layer of
11 microns thick and the layer was recognized to contain a small
amount of tantalum.
Example 3:
1000 grams of borax was introduced into a graphite
crucible and heated up to 900C for melting the borax in an elec-
tric furnace and then a metallic plate, 6 x 40 x 50 mm, made of
ferrovanadium (containing 53.7% of vanadium) was dipped in the
molten borax. With use of the metallic pla-te and the crucible as
an anode and cathode respectively, said metallic plate was anodi-
cally dissolved into the molten borax by applying a direct current
for 2 hours at a current density of 2 A/cm of the anode. Thus
a treating molten bath containing 9.8% of said ferrovanadium.was
prcpared.
Next, Specimens 3-1 to 3-6 having a diameter of 7mm and
made of carbon tool steel (JIS SI~) were respectively imrnersed
into the treating molten bath and were treated at 900C under res-
pective conditions. Specimen 3-1 was treated for 2 hours and with
a current density of 0.03 A/cm . Specimens 3-2 to 3-6 were treated
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respectively for 2 hours and with 0.1 A/cm , for 2 hours with
0.3 A/cm2, for l hour with 0.7 A/cm2, for 10 minutes with 1.0
A/cm , and for 10 minutes with 3.0 A/cm ,
All Specimens 3-1 to 3-6 were examined by a microscope,
X-ray micro analyzer and by X-ray diffraction method. Specimens
3-l to 3-6 were formed with a layer or layers having a respective
thickness of 9 microns, 9 microns, 11 microns, 37 microns, 5 mi-
crons and 47 microns. Only one layer was formed on Specimen 3-l
and Specimens 3-2 to 3-6 were formed each with two layers. Fig.
ll shows a microphotograph of the layer formed on Specimen 3-1
Figs. 12 and 13 shows respectively microphotographs of the layers
formed on Specimens 3-3 and 3-6. From the result of X-ray micro
analyzer and X-ray diffraction method, the layer formed on Speci-
men 3-1 was identified to be vanadium carbide and the two layers
formed on Speclmens 3-2 to 3-6 were identified respectively to
be the vanadiurn carbide containing boron (V(C,B) and to be iron
boride (FeB or Fe2B) composed of boron and iron which is the main
component of the mother material. All the surfaces of the Speci-
men 3-l to 3-6 were very smooth.
From this example, it was recognized that the treating
molten bath prepared by anodic dissolution gives a very smooth
surface of the specimen treated without depositing any small par-
ticles to the surface of the article.
Example 4:
In the same manner as described in Example 3, the molten
borax was prepared and then a metallic plate, 50 x 45 x 6mm, made
of ferrovanadium (containing 53.7% of vanadium~ and a specimen,
40 x 33 x 9mm, made of carbon tool steel (JIS SK5) were dipped in
the molten borax while spaced a distance of 15mm from each other.
With use of said metallic plate as the anode and the specimen as
the cathode, an electric current was applied to the molten borax
for 4 hours at a cathodic current density of 0.3 A/cm2. By the
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treatment, the specimen was formed with a layer of about 9 microns.
The layer formed is shown in Fig. 14. Also, the layer was identi-
fied to be the vanadium carbide containing boron.
Example 5:
In the same manner as described in Example 4, a metal
plate, 50 x 40 x 6mm, made of ferroniobium (containing 58.9% of
niobium and 3.6% of tantalum) was anodically dissolved into a mol-
ten borax at 900C. Thus, a treating molten bath containing about
8.5% of said ferrovanadium was prepared. Next, a specimen having
a diameter of 7 mm and made of carbon tool steel (JIS SK4) was
dipped into the treating molten bath as the cathode ! With use of
said treating molten bath, said specimen was treated for
3 hours with a current densitv oE 0.03 A/cm . From
microscopic observation, a layer of 14 microns was formed on the
surface of the specimen. Said layer was identified to be the
niobium carbide con~taining a small amount of boron and tantalum
by X-ray micro ana-yzer and by X-ray diffraction method.
Example 6:
90 grams of borax was introduced into a graphite cruci-
ble having a 35 mm innerdiameter and heated up to 950C for mel-
ting the borax in an electric furnace under the air, then 17 grams
of vanadium oxide (V205) powder was gradually introduced into the
molten borax and mixed with the molten borax for preparing a treat-
ing molten bath (which contains 16% of vanadium oxide). In said
treating molten bath, several specimens having a 7mm diameter and
made of carbon tool steel (JIS SI~4) were respectively treated at
950C for a time ranging from 1 to 90 minutes with a current den-
sity ranging from 0 to 15 A/cm2 in the same manner as described
in Example 1. All the specimens treated were taken of the treat-
ing molten bath, cooled in the air, washed with hot water for
dissolviny the treating material adhered to the specimens. The
specimens were cut vertically and the cross sections were polished
- 14 -
~OSZ3~
and examined by a microscope and X-ray micro anàlyzer and by
X~ray diffraction method. The photomicrograph in Fig. 17 is
shown as one of the examples of the layers formed in this example.
From a group of the specimens treated for 10 minutes with a
cuxren-t density ranging from 0 to 15 A/cm I line (a), in Fig.
15, was obtained. Line (a) shows the effect of the current
density applied to a specimen on the thickness of the v~nadium
carbide layer formed on the specimen. In order to show the
difference between the vanadium oxide powder used in this Example
and the ferrovanadium powder used in Example 1, lines (b) and (c)
are shown together with line (a) in Fig. 15. Line (B) was
obtained from the specimens treated in the treating molten bath
containing 20% of ferrovanadium powder instead of vanadium oxide
powder for 30 minutes with a current density rangin~ from 0 to
1 A/cm2. Line (c) was obtained from the specimens treated in
said treating molten bath containing 20% of ferrovanadium for 10
minutes with a current density ranging from 3 to S A/cm2.
Although, the treating molten bath containing said ferrovanadium
powder can form a vanadium carbide layer on the surface of a
specimen without application of an electric current, the treat-
ing molten bath containing the vanadium oxide powder can not
form a vanadium carbide layer on the surface of a specimem with-
out applying an electric current~ Thereforel it is necessary
in the case of the treating molten bath composed of molten borax
and vanadium oxide powder to apply at least 0.1 A/cm2 of electric
current to the specimen to be treated for forming a vanadium
carbide layer on the surface of the specimen (with use of a
current density of 0.1 A/cm , a layer of 1 micron was formed on
the surface of the article treated)O From the difference between
the vanadium oxide powder in this Example and ferrovanadium
powder in Example 1 the conclusion is that the vanadium oxide
must be reduced to metallic vanadium for forming a vanadium carbi-
de layer on the surface of the specimen by an electric curren~.
- 15 -
~Lo5Z3~7
The other difference between the vanadium oxide powder
and ferrovanadium powder is that the treating molten bath con-
taining the vanadium oxide can form a carbide layer with a
relatively large current density at which the treating molten
bath containing the ferrovanadium can not form a carbide layer
on the surface of the specimen treated.
Fig. 18 shows the distributions of the contents of
vanadium, carbon, iron and boron forming the surface portion of
the specimen treated in the treating molten bath containing
vanadium oxide with a current density of 3 A/cm ~ From the
distributions and the result of the X-ray diffraction, the
surface portion of the specimen was identified to be vanadium
carbide containing little boron. Also the layer formed with a
current density of 10 A/cm2 was found to contain a little boron.
The layers formed on the surface treated in the treatin~ molten
bath containing the ferrovanadium with a relatively large current
density were explained in Example l.
From a group of the specimens treated for a time ranging
l to 90 minutes with a current density of 5 A/cm , the graph
shown in Fig. 16 was obtained. The graph shows the effect of
the treating time on the thickness of the carbide layer formed
on the surface of the specimen treated.
V205 was used in this Example. However, ~he following
oxides and compounds containing vanadium can be used as the
oxide of vanadium; VO, V02, V203, Na3V04, NaV03, NH4V03, VOC12,
VOCL~ and the like.
Example_7:
In the same manner as described in Example 6, a trea-
ting molten bath composed of 87% of borax and 13% of vanadium
oxide, V203, was prepared. Next a specimen having a 7mm diameter
and made of caxbon tool steel (JIS SK4) was treated in the treating
molten bath at 900C ~or lO minutes with a current density of
- 16 -
, . .
~,~
` ~OSZ31 7
3 A/cm2. sy the treatment, a la~er of about 4 microns in thickness
was formed on the surface of the specimen. The surface condition
of the layer was very smooth. The photomicrograph taken from the
cross section of the specimen is shown in Fig. 19. And the layer
was identified to be vanadium carbide (VC) by X-ray diffraction
method.
Example ~3:
In the same manner as described in Example 6, two kinds
of treating molten ba~hs were prepared. One was made of 86 % of
borax and 14 % of ~aVO3 and the other was made of 70 % of borax
and 30 % of NaV04 .H20. Specimen 8-1 having a 7 mm diameter and made
of carbon tool steel (JIS SK4) was trea~ed at 900C in the treating
molten bath containing NaVO3 for 30 minutes with a current density
of 0.1 A/cm2. Specimen 8-2 having the same size and made of the
same steel as Specimen 8-1 was treated at 900C in the treating
molten bath containing NaVO4 .H2O for 10 minutes with a current
density of 1.0 A/cm2. By the treatments, on the surface of
Specimen 8-1 was formed a vanadium carbide (VC) layer of about
5 microns in thickness and on the surface of Specimen 8-2 was
formed a vanadium carbide lay0r of about 4 microns in thickness.
Example 9:
In the manner as described in Example 6, a treating
molten bath made of 93 % of borax and 7 % of Nb2O3 was prepared.
Next, a specimen made of carbon tool steel (JIS SK4) was treated in
the treating molten bath at 900C for 60 minutes with a current
density of 3 A/cm . By the treatment, a niobium carbide layer shown
in Fig. 20 was formed on the surface of the specimen.
Example 1_:
100 grams of borate was introduced into a graphite
crucible and heated up to 900C for melting said borate in an
electric furnace under the air, and -then 16 ~rarr~s of vanadium chlori-
de (VC13) powder was added into the molten borax and mixed together.
~05'~3~7
Thus, a treating molten bath was prepared. Next, Specimens
10-1 to 10-6 having a 7 mm diameter and 40 mm long and made of
carbon tool steel (JIS SK4 containing 1.0 /O of carbon) were res-
pectively treated in the treating molten bath at 900C for a
time ranging from 10 minutes to 60 minutes with a current
density ranging from 0.01 to 3.0 A/cm2. After each of the treatments,
each of the Specimens was taken out from ~he treating molten bath,
cooled in the air and washed out the treating material adhered to
the Specimen with hot water. Specimens 10-1 to 10-6 were cut
vertically and examined by a mieroscope, X-ray micro analyzer and
X-ray diffraction method. On the surface of Specimen 10-1 treated
for60 minutes with 0.01 A/cm was formed a vanadium carbide (VC)
layer of about 9 microns in thickness. Specimen 10-2, which was
treated for 60 minutes with 0.05 A/cm2, was formed with a vanadium
carbide layer of about 9 microns in thickness. The photomicrograph
taken from Specimen 10-1 is shown in Fig. 21. Specimens 10-3 and
10-4 treated respectively for 30 minutes with a current density of
O.1 A/cm2 and 0.S A/cm2 were formed with a layer thereon. The
thickness of the layer of Specimen 10-3 was about 4 microns and the
thickness of the layer on Specimen 10-~ was about ~ microns.
Said two layers were identified to consist of the upper portion
composed of the vanadium carbide containing boron and of the
lower portion composed of iron boride (Fe2B). On the surfaces of
Specinens 10-5 and 10-6 which were treated for 10 minutes with a
current density of 1.0 Ajcm and 3.0 A/cm respectively, a layer
of about 10 microns and a layer of about 16 microns were formed
respectively. And said two layers were identified to consist of
the upper portion composed of the vanadium carbide (VC) containing
boron and the lower portion composed of iron boride (Fe2B). The
photomicrograph taken from Specimen 10-5 is shown in Fig. 22.
Exam~le 11 :
A treating molten bath made of 700 grams of borax and
-18-
~sz~
120 grams of niobium chloridepowder was prepared in a graphite
crucible. Next, specimens havin~ a 8 mm diameter and 40 mm long
and made of tool alloy steel (JIS SKD61 containing 0.45 % of car-
bon)were respectively treated in the treating molten bath at 950C
with use of each of the specimens as the cathode and of the
graphite crucible as the anode. On the surface of the specimen
treated for 60 minutes with a current density of 0.01 A/cm2, a
niobium carbide (NbC) layer of about 4 microns was formed. The
specimen treated for 30 minutes with 0.1 A/cm2 was formed with a
vanadium carbide layer of about 5 microns. From said two vanadium
carbide layers, boron was not detected. On the surface of the
specimen treated for 30 minutes with 0~5 A/cm2, a layer of 7 micrnns
was formed thereon, and which consisted of the upper portion composed
of the niobium carbide containing boron and of the lower portion
composed of iron boride (Fe2B). On the surface of the specimen
treated for 10 minutes with 1.0 A/cm2, a layer of about 9 microns
in thickness was formed thereon. The layer was identified to con-
sist of the upper portion composed of the niobium carbide containing
boron and of the lower portion composed of iron boride (Fe2B).
Example 12 :
90 grams of borax was introduced in-to a graphite
crucible having a 35 mm innerdiameter and heated up to 1000C for
melting the borax in an electric furnace under the air, and then 31
grams of vanadium chloride (VC13) powder was gradually introduced
and mixed into the molten borax. Thus, a treating molten bath was
prepared. ~ext, Specimens 12-1 to 12-5, 40 x 5.5 x 1.0 mm, made
of cemented carbide composed of 9 % of cobalt and 91 % of tungsten
carbide (WC) were treated respectively in the treating molten bath
under each of the conditions shown in Table 1.
-19-
~OSZ317
TABLE 1
Specimen 12-1 12-2 12-3 12-4 12-5
_ . _ _ _
curxent density
(~/cm2) 0.03 0.3 1.0 5~0 10
_ _ _
treating time (hour) 5 hr. 5 hr~ 2 hr. 10 min. 1 min.
On the surface of Specimen 12-1, a layer of about 7
microns was formed. The layer was iden-tified to be vanadium
carbide by X-ray diffraction method. Specimens 12-2 and 12-3 were
formed respectively with a layer of about 12 microns and of 5
microns. The two layers were recognized to consist of vanadium
boride (V3B2) (at the upper portion) and vanadium carbide (at the
lower portion). The layer formed on the surface of Specimen 12-5
was identified to be tungsten boride (W2B5). By the result of
X-ray micro analyzer of Specimen 12-2, the layer was fou~d to
contain about 78 % of vanadium and a large amount of boron. Also,
the X-ray diffraction chart of the layer is shown in Fig. 23.
Also the hardness of the layer of Specimen 12-1 was measured to be
about Hv 3000. The hardness of the layer of Specimen 12-~ was
about Hv 3250. By the way, the hardness of the mother material of
Specimens were measured to be about Hv 1525.
Example 13 :
500 grams of borax was introduced into a graphite cruci-
ble having a 65 mm innerdiameter and heated up to 1000C, and then
125 grams of ferrovanadium (containing 92 % of vanadium) powder
was added and mixed into the borate. Thus, a treating molten bath
was prepared. Next two specimens having the same size and made of
the same cemented carbide as the specimens used in Example 12 were
respectively treated in the treating molten bath with use of each
of the specimens as the cathode and of the crucible as the anode.
~he specimen treated for 13 hours with a current density of 0.01
-20-
.~ ~
`- 105'~3~7
A/cm2 was formed with a layer of about 15 microns thereon, and the
specimen treated for 1 hour with 5 A/cm2 was formed with a
layer
-20 a
~OS'~3~L7
o about 7 microns thereon. By X-ray micro analyzer and X-ray
diffraction method, the layer formed under the condition of 0.01
A/cm2 was identified to be vanadium carbide (VC) and the layer
formed under the condition of 5 A/cm2 was identified to consist
of vanadium boride (V3B2) (at the upper portion) and vanadium
carbide (VC) (at the lower portion). The hardness of the layer
formed under the condition of 0.01 A/cm2 was measured to be about
Hv 3014.
Example 14 :
ln the same manner as described in Example 6, a treating
molten bath was made of 500 grams of borax and 100 grams of V205
powder. Specimens 14-1 to 14-7 having the same size and made of
the same cemented carbide were treated respectively in the
treatiny molten bath at 1000C under the conditions shown in Table 2.
TABLE 2
Specimen 14-1 14-2 14-3 14-4 14-5 14-6 14-7
current densitY
(A/cm ) 0.1 0.5 1.0 5.0 10 20 30
_ _ _ _ _ _
treating time 9 hr. 16 hr. 5 hr. 1 hr. 10 min. 3 min. 1 min.
Each of Specimens 14-2 to 14-7 was formed with a layer
thereon. However, Specimen 14-1 was not formed with any layer
thereon. The layers formed on Specimens 14-2 to 14-4 were of
- about 8 microns, 12 microns and 11 microns respectively and were
identified to be vanadium carbide (VC). The layers formed on
Specimens 14-S and 14-6 were of about 6 microns and 4 microns
respectively and were recognized to be a composite layer composed
of vanadium carbide (VC) and vanadium boride (V3B2). However, on
the surface of Specimen 14-7, no vanadium was detected. The layers
of Specimen 14-4 and 14-5 were measured to contain respectively
~ -21-
'
l~)SZ3~7
70 % and 94 %.of vanadium. From the layer of Specimen 14-4, no
boron was detected. But the layer of Spec.imen 14-5 was found
to have a relatively
-21 a-
~05~33L7
large amount of boron. The photomicrograph taken from Specimen
14-5 is shown in Fig. 24. The hardness of each of the layers
formed on Specimen 14-2 and 1~-5 was about Hv 2960 and Hv 3200
respectively.
Fxample 15 :
In the same manner as described in Example 3, the 500
grams of molten borax was prepared, and then a metallic plate,
40 x 35 x 4 mm, made of electroly-tic niobium was anodically
dissolved into the molten borax at 1000C for 2 hours with a
current density of 1 A/cm2. Thus, a treating molten bath
containing about 9.4 % of nio~ium was prepared. Next, Specimens
15-1 to 15-9 having the same size and made of the same cemented
carbide as the Specimens used in Example 12 were treated
respectively in the treating molten bath at 1000C under the
conditions shown in Table 3.
TABLE 3
Specimen 15-1 15-2 15-3 15-4 15-5 15-6 15-7 15-8 15-9
current
density 0.01 0.05 0.1 0.5 1.0 3.0 5.0 10.020
(A/cm2)
.
treating 16hr. 15hr. 15hr. 10hr. 4hr. lhr. lhr. 3min. lmin.
time
By each of the trea-tments, on the surface of Specimen 15-2, a
vanadium carbide ~VC) layer of about 13 microns was formed. The
photomicrograph of the layer is shown in Fig. 25. On each Qf
Specimens 15-4 and 15-5, a composite layer of about 15 microns
and 6 micrcns respectively was formed. From the layer, niobium
carbide (NbC~ and niobium boride (~b3B2) were clearly detected.
The niobium boride was contained in the upper portion of the
layer and the niobium carbide was contained in the lower portion
-22-
3~7
of the layer. On Specimen 15-7, a composite layer of about 25
microns was formed. The layer was found to consist of Nb3B2 at
its upper portion, NbC at its middle and W2B5 at its lower portion.
On Specimens 15-8 and 15-9, composite layers of about 10 microns
and 13 microns were formed. The composite layers were found to
consist of Nb3B2 at its upper portion, NbC at its middle and Co3B
at its lower portion. The thickness of the layers composed of
Nb3s2 and NbC was decreased as the increaseof the current density
applied.
By X-ray micro analyser, the layer formed on Specimen
15-8 was found to consist of about 60 % of niobium. ~Iowever the
layer formed on Specimen 15-9 does not contain niobium. A
large amount of boron was detected from both of said layers.
However, the layer formed with a higher current density was
found to contain a higher content of boron. The hardness of each
of the layers formed on Specimens 15-2 and 15-4 was measured
to be about Hv 2920 and ~Iv 3190.
Example 16 :
In the same manner as described in Example 6, a treating
molten bath composed of 500 grams of borax and 80 gxams of Nb2O5
powder was prepared. Next, Specimens 16-1 to 16-9 having the
same size and made of the same cemented carbide as the Specimens
used in Example 12 were treated respectively in the treating
molten bath at 1000C under the conditions shown in Table 4.
TABLE 4
Specimen 16-1 16-2 16-3 16-4 16-5 ~6-6 16-7 16-8 16-9
current
density 0.01 0.03 0.05 0.1 0~5 loO 3~0 5~0 10
(A/cm2)
treating
time 14hr. 15hr. 10hr. 5hr. 13hr. 5hr. 3min. lhr. 10min.
-23-
Specimen 16-1 was not Eormed with any layer thereon,
however, on the surface of each of Specimens 16-2 to 16-9 a
layer having a thickness ranging from 3 to 15 microns was formed.
The layers formed on Specimens 16-2 and 16-3 were identified to
be NbC and the layers formed on Specimens 16-4 to 16-~ were
recognized to contain NbC and Nb3B2. The layer formed on
Specimen 16-9 was identified to be W2B2. As the example an
X-ray diffraction chart taken from the layer of Specimen 1~-6
is shown in Fig. 27. By X-ray micro analyser, the layers formed
on Specimens 16-4 and 16-7 were measured to contain about 67~ and
57% of niobium respectively. It was difficult to measure the
content of boron in each of the layer. However, a relatively
large amount Q~ boron was included in each of the layers. The
hardness of each layers of Specimens 16-2 and 16-6 was measured
to be about Hv 2980 and Hv 3230 respectively.
Exemple 17:
In the same manner as described in example 10, a
treating molten bath composed of 115 grams of borax and 25 grams
of NbC15 powder was prepared. Next, Specimens 17-1 to 17-7
having the same cemented carbide as the Specimens used in
Example 12 were treated respectively in the treating molten
bath at 1000 C under the conditions shown in Table 5.
_ Table 5
-
Specimen 17-1 17-2 17-3 17-4 17 5 17-6 17-7
Current
density 0.05 0.1 0.5 1.0 5.0 15 20
tA/cm2 )
Treating 14 hr. 10 hr. 8 hr. 5 hr. 1 hr. 10 min. 1 min.
._ _
- 24 -
~5,,~3~7
On the surf~ce of each of Specimens 17-1 to 17-7 was
`formed a layer. The thickness of the layer of each of Specimens
17-1 to 17-6 was about 25,27,30,20, 18 and 8 microns respectively.
Each o said layers were recognized to consist o a NbC portion
and a W2B5 portion. The thickness of said NbC portion was de-
creased as the increase of the current density applied. The
layer of Specimen 17-7 was composed of only W2B. The hardness
of the layer formed on Specimen 17-2 was about Hv 3000.
Example 18:
In the same manner as described in Example 3, the 500
grams of molten borax was prepared, and then a metallic plate,
50 x 40 x 4mm, made of electrolytic tantalum was anodically dis-
solved into the molten borax at 1000C for 1 hour with a current
density of 1 A/cm2. Thus, a treating molten bath containing about
11.2% of tantalum was prepared. Next Specimens lg-l to 18-5
having the same size and made of the same cemented carbide as
the Specimens used in Example 12 were treated respectively in the
treating molten bath at 1000 C under the conditions shown in
Table 6.
Table 6
_
Specimen 18-1 18-2 18-3 18-4 18-5
.
(A/cm2) 0.01 0.0S 0.5 1.0 10
Treating time 16 hr. 14 hr. 12 hr. 1 hr. 5 min.
-
All the Specimens 18-1 to 18-5 were ormed with a
layer thereon. The thickness of the layer of each of
Specimens 18-1 to 18-5 was about 20, 23, 25, 13 and 5 microns
respectively. By the X-ray difraction method, the layers
- 25 -
iLo~'~3~t7
formed on Specimens 18-1 to 18 3 were identified to be tantalum
`carbide (TaC). The layer ormed on the surface of Specimen 18-4
was recognized to be composed of TaC and W2B5. The layer formed
on Specimen 18-5 was identified to be W2BS. Also by X ray micro
analyser, the layers o~ Specimens 18-1 to 1.8-3 were recognized
to contain ~oron within the TaC.
- 26 -
