Process for the production of bonded hard alloys

Process for the production of bonded hard alloys, which comprises inserting a thin sheet of a Fe group metal or its alloy as a filler in between the surfaces of at least one kind of hard alloy, and applying a high energy beam to a part or all of the thin sheet to melt and solidify the thin sheet in a slit form, thereby bonding the hard alloys together.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process for the production of bonded hard 
alloys and more particularly, it is concerned with a process for bonding 
one or more kind of hard alloys using a high energy beam. 
2. Description of the Prior Art 
Bonding of a plurality of tool parts of hard alloys such as cemented 
carbides to obtain a tool formed in one body would result in various 
merits such as making it possible to obtain an article with a complicated 
shape or with such a large size as to exceed the limit reached by cemented 
carbides. It would also be possible to combine two or more kinds of hard 
alloys having different properties. However, since the melting point of 
the hard alloy is so high that a high temperature, e.g. 1320.degree. C. or 
higher is required for forming a liquid phase of the alloy, there is no 
way to accomplish this except by effecting diffusion bonding in a furnace 
under pressure. 
Therefore, the most economical bonding method comprises using a silver 
braze or copper braze, but the bonding using such a braze is poor, in 
particular, when wetting of the braze is inferior. Furthermore, even if 
the bonding is completed, a shearing strength only about 10 to 20 
kg/mm.sup.2 is expected. 
When cemented carbides are used as a structural part or as a wear resisting 
tool such as a die, slitter and bit, a higher shearing force, fatigue 
strength and impulsive force are required. 
Thus, it has eagerly been desired to develop a bonding method whereby 
cemented carbides can be bonded easily and completely independently of 
their shapes or sizes. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a process 
for the production of bonded hard alloys. 
It is another object of the present invention to provide an improved method 
of bonding cemented carbides by a high energy beam. 
It is a further object of the present invention to provide a tool of 
cemented carbides bonded together through an interlayer of an iron group 
metal or its alloy. 
These objects can be attained by a process for the production of bonded 
hard alloys, which comprises butting or contacting pieces of one or more 
kinds of hard alloys, inserting a thin sheet of an iron group metal or its 
alloy between the contacted surfaces of the hard alloys, and applying a 
high energy beam to a part or all of the thin sheet to melt and solidify 
it, thereby bonding the hard alloys together.

DETAILED DESCRIPTION OF THE INVENTION 
The inventors have made efforts to develop a method of completely bonding 
hard alloys together, in particular, cemented carbides, and consequently, 
have found that if the interface of a bonded layer has a hardness 
corresponding to at least 60% of that of the hard alloys, the strength of 
the bonded part can be considered sufficient. 
On the contrary, if the hardness of the bonded layer is larger than the 
hard alloy, the toughness is low. Thus, it is most desirable to carry out 
welding in such a manner that the hardness of the bonded layer is as close 
as possible to that of the hard alloy. 
In the present invention, a bonded layer having a hardness lower than that 
of cemented carbides but corresponding to at least 60% of that of cemented 
carbides is obtained by inserting a thin sheet of iron group metal or its 
alloy in between the butted or contacted surfaces of hard alloys, melting 
instantaneously the hard alloys and thin sheet at a high temperature, and 
forming an alloyed layer in which the iron group metal and hard alloy 
components are diffused into each other. 
That is, the present invention provides a process for the production of 
bonded hard alloys, which comprises butting or contacting one or more 
kinds of hard alloys, inserting a thin sheet of iron group metal or its 
alloy as a filler metal in between the surfaces of the hard alloys, and 
applying a high energy beam to a part or all of the filler metal to melt 
and solidify it and thereby bond the hard alloys together. 
The hard alloys used herein consist generally of at least one of carbides, 
nitrides, carbonitrides and carboxynitrides of the Group 4a, 5a and 6a 
elements of the Periodic Table, and solid solutions thereof, bonded by at 
least one iron group metal such as Co, Ni and Fe. In particular, cemented 
carbides such as WC-Co alloys and (Mo, W)C-Co alloys are preferably used. 
As the filler metal, there are generally used iron containing at most 0.5% 
by weight of carbon, steels (SS, SCM), Fe-Ni alloys, Co, Ni and Fe-Ni-Co 
alloys (Kovars), and as the high energy beam, there are generally used an 
electron beam and a laser beam. These filler metals generally have a 
melting point higher than that of the hard alloys. 
In the practice of the present invention, as shown in FIG. 1, iron group 
metal sheet 2 with a thickness of 0.1 to 2 mm is inserted in between 
butted surfaces 1 and 1' of polished hard alloys and high energy beam 3 is 
irradiated on the inserted sheet to melt the hard alloys and sheet and to 
form an alloyed layer. 
FIG. 2 shows the change in hardness when an Fe- Ni alloy and hard alloy are 
contacted and irradiated with an electron beam. The ordinate indicates Hv 
hardness and the abscissa indicates lengths of hard alloy 4, melted and 
solidified part 5 and filler metal part 6. 
The alloy layer formed by fusion and diffusion of hard alloys and Fe-Ni 
alloy has an Hv hardness of 800, which corresponds to 70% or more of the 
Hv hardness of the hard alloy whose Hv hardness is 1100 for example. That 
is, it is assumed that the hardness of part 5 is markedly increased 
because W and C elements are diffused into the Fe-Ni alloy while the 
effect of rapid melting and cooling is accomplished by the use of an 
electron beam. When using Co or Ni as the filler metal, in particular, a 
further higher hardness can be obtained due to the fact that these 
elements are precipitated as WC in the alloy layer. 
The most important feature of the present invention is that a filler 
material is inserted between the contacted surfaces of hard alloys and 
melted and bonded by applying a high energy beam. If the filler material 
is not used, for example, if tungsten carbide is melted at a temperature 
of 3000.degree. C. or higher and vaporized as elements W and C, bonding is 
impossible. The use of the filler material results in lowering the melting 
and bonding temperature and preventing W and C from vaporization. 
It is well known to use a filler material in bonding of different metals, 
e.g. in welding of Cu-Al. This serves to prevent formation of an 
intermetallic compound of the different metals. However, the inventors 
have no knowledge of an example wherein a filler material is used for the 
purpose of lowering the melting point and forming an alloy layer with a 
high hardness in welding materials of the same kind. 
In the present invention, the filler material preferably has a thickness of 
0.1 to 2 mm, since if the thickness if less than 0.1 mm, vaporization of 
the hard alloy cannot be prevented, while if more than 2 mm, a sufficient 
hardness cannot be obtained. 
In one embodiment of the present invention, the surfaces of a hard alloy to 
be welded are subjected to polishing, degreasing and demagnetization, and 
an Fe group metal, in particular, an Fe-Ni alloy having a thermal 
expansion coefficient of 8-10.times.10.sup.-6 cm/.degree.C. similar to 
that of the hard alloy, or a Co alloy completely miscible with the hard 
alloy, is sandwiched in between the surfaces thereof. Then, welding is 
carried out by applying a high energy beam to the joint part in such a 
manner that both of the hard alloys are irradiated. Generally, an electron 
beam is used with an accelerating voltage of 60 to 150 KV, beam current of 
10 to 50 mA and welding speed of 0.1 to 1 m/min. Laser beam can also be 
used under the similar conditions that a hard alloy and ferrous filler 
material can simultaneously be melted. 
The following examples are given in order to illustrate the present 
invention in greater detail without limiting the same. 
EXAMPLE 1 
In designing cutter 7 composed of a cemented carbide edge A with a length 
of 3 m, width of 30 mm and thickness of 3 mm on steel B as shown in FIG. 
3, the cemented carbide edge was formed by bonding cemented carbides 8 
formed and sintered in a length of 50 cm as shown in FIG. 4. In FIG. 4, a 
thin sheet of Fe-42 wt% Ni alloy of 0.5 mm in thickness was inserted in 
between surfaces 9 of the cemented carbides to be bonded, and was welded 
by an electron beam, and joint surface 10 of cemented carbide 8 and steel 
B was welded by an electron beam, irradiated at an accelerating voltage of 
150 KV, current of 20 mA and welding speed of 0.5 m/min, thus obtaining a 
long-size edge. 
When a cemented carbide edge of 3 m in length was previously prepared and 
the joint surface of cemented carbide A and steel B shown in FIG. 3 was 
brazed with a silver braze, on the other hand, the cemented carbide edge 
was warped and a part of the cmeneted carbide was cracked. 
The long-size edge of FIG. 4 prepared according to the present invention 
encountered no deformation, nor crack. The bonded cemented carbide layer 
showed an Hv hardness of 900. When the cutter obtained by the process of 
the present invention was subjected to cutting of paper, a uniform cutting 
quality was obtained without wearing of the bonded layer. 
EXAMPLE 2 
The end of a punch with a diameter of 10 mm and a length of 70 mm shown in 
FIG. 5 was cut by 10 mm. Shank part 11 was of WC-20 wt % Co alloy and end 
part 12 was of WC-8 wt % Co alloy. A thin sheet 13 of Co with a thickness 
of 0.3 mm was inserted in between the butted surfaces of shank part 11 and 
end part 12 and subjected to welding by an electron beam (accelerating 
voltage: 150 KV; electric current: 20 mA; welding speed: 0.5 m/min). The 
thus resulting punch was a composite tool composed of an end part of 
cemented carbide having excellent wear resistance, and a shank part of 
cemented carbide having excellent toughness. 
For comparison, punches were respectively made of WC-8 wt % Co alloy, WC-20 
wt % Co alloy and WC-15 wt % Co alloy alone and subjected to comparative 
tests with the composite punch of the present invention. When a silicon 
steel plate with a thickness of 0.5 mm was punched thereby, there were 
obtained results shown in the following Table: 
TABLE 
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Life (hr) Cause of Failure 
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WC - 8% Co alloy 
50 fracture 
WC - 15% Co alloy 
100 wear 
WC - 20% Co alloy 
20 deformation 
Composite Punch of 
200 Normal wear 
Invention 
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The composite punch bonded by the use of an electron beam showed a better 
performance than the punches of the prior art.