U.S. patent number 3,918,928 [Application Number 05/403,441] was granted by the patent office on 1975-11-11 for shank or back material for high speed steel tools.
This patent grant is currently assigned to Hitachi Metals, Ltd.. Invention is credited to Haruki Hada, Kingo Kiyonaga.
United States Patent |
3,918,928 |
Kiyonaga , et al. |
November 11, 1975 |
Shank or back material for high speed steel tools
Abstract
A shank or back material for high speed steel tools, consisting
of an alloy steel composed of 0.2-0.6% of carbon (C), 3.0-7.0% of
chromium (Cr), 0.1-1.0% of vanadium (V), not more than 0.8% of
silicon (Si), not more than 0.8% of manganese (Mn) and the
remainder of iron (F), or said alloy further containing 0.02-0.3%
of niobium (Nb). By using the alloy of the invention, a defect-free
weld can be obtained, and a strength and toughness degradation can
be avoided.
Inventors: |
Kiyonaga; Kingo (Yonago,
JA), Hada; Haruki (Yasugi, JA) |
Assignee: |
Hitachi Metals, Ltd.
(JA)
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Family
ID: |
27303146 |
Appl.
No.: |
05/403,441 |
Filed: |
October 4, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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164298 |
Jul 20, 1971 |
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Foreign Application Priority Data
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Sep 14, 1970 [JA] |
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45-79950 |
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Current U.S.
Class: |
428/684;
420/104 |
Current CPC
Class: |
B23K
35/308 (20130101); C22C 38/24 (20130101); Y10T
428/12972 (20150115) |
Current International
Class: |
B23K
35/30 (20060101); C22C 38/24 (20060101); B23p
015/18 (); C22c 039/14 () |
Field of
Search: |
;75/126E,126F
;29/196.1,195A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rutledge; L. Dewayne
Assistant Examiner: Steiner; Arthur J.
Attorney, Agent or Firm: Craig & Antonelli
Parent Case Text
This is a division of application Ser. No. 164,298 filed July 20,
1971, now abandoned.
Claims
What we claim is:
1. In a tool including a tool portion of known high speed steel
material and a shank or back portion welded to said tool portion,
the improvement comprising said shank or back portion being of a
steel material consisting of 0.2-0.6% of carbon, 3.0-7.0% of
chromium, 0.1-1.0% of vanadium, 0- 0.3% of niobium, not more than
0.8% of silicon, not more than 0.8% of manganese and the remainder
of iron and inevitable impurities, wherein said steel material of
said shank or back portion prevents decarburization or cementation
in the weld between said shank or back portion and said tool
portion respectively, said shank or back portion maintaining its
toughness when the tool is subjected to heat treatment at high
temperatures, and said steel material of the shank or back portion
having an HRC hardness of more than 40 when subjected to said heat
treatment under the same tempering conditions as for said high
speed steel tool portion, said steel material of the shank or back
portion having good, crack-free weldability with said high speed
steel tool portion.
2. In a tool including a tool portion of a known high speed steel
material and a shank or back portion welded to said tool portion,
the improvement comprising said shank or back portion being of a
steel material consisting of 0.2-0.6% of carbon, 3.0-7.0% of
chromium, 0.1-1.0% of vanadium, 0.02-0.3% of niobium, not more than
0.8% of silicon, not more than 0.8% of manganese and the remainder
of iron and inevitable impurities, wherein said steel material of
said shank or back portion prevents decarburization or cementation
in the weld between said shank or back portion and said tool
portion respectively, said shank or back portion maintaining its
toughness when the tool is subjected to heat treatment at high
temperatures, and said steel material of the shank or back portion
having an HRC hardness of more than 40 when subjected to said heat
treatment under the same tempering conditions as for said high
speed steel tool portion, said steel material of the shank or back
portion having good, crack-free weldability with said high speed
steel tool portions.
3. A tool according to claim 2, wherein said steel material has a
composition consisting of 0.3-0.4% of carbon, 4.0-6.0% of chromium,
0.2-0.5% of vanadium, 0.02-0.3% of niobium, not more than 0.8% of
silicon, not more than 0.8% of manganese and the remainder of iron
and inevitable impurities.
4. A tool according to claim 2, wherein said steel material has a
composition consisting of 0.3-0.4% of carbon, about 5% of chromium,
0.2-0.3% of vanadium, 0.09-0.3% of niobium, not more than 0.2% of
silicon, not more than 0.3% of manganese and the remainder of iron
and inevitable impurities.
5. A tool according to claim 1, wherein said steel material has a
composition consisting of 0.3-0.4% of carbon, 3-7% of chromium,
0.2-0.3% of vanadium, not more than 0.2% of silicon, not more than
0.3% of manganese and the remainder of iron and inevitable
impurities.
Description
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
This invention relates to shank or back materials for high speed
steel tools of the type in which a blade element consisting of high
speed steel and a shank or back are welded together by various
welding methods.
2. DESCRIPTION OF THE PRIOR ART
In the production of cutting tools or the like utilizing high speed
steel, it has been practiced, with a view to saving the quantity of
expensive high speed steel, to weld a shank or back of a low grade
steel to a cutting blade element which is made of high speed steel.
For instance, the cutting blade portion of high speed steel and the
shank or back of low grade steel are welded by the friction welding
or butt welding in case of an end mill cutter, and by the electron
beam welding in case of a metal band saw.
The shank or back material is required, as an essential condition,
to be inexpensive, but in addition, it is required to satisfy such
conditions (1) that decarburization or cementation does not occur
at the welded portions of both materials during annealing which
results from the activity difference of carbon contained in both
materials, (2) that it will have a sufficient toughness when
subjected to a heat treatment at elevated temperatures together
with the high speed steel, (3) that it will have an HRC hardness of
40 or higher when subjected to a heat treatment under the same
tempering condition as that for the high speed steel, and (4) that
it has good weldability and gives a crack-free weld.
Speaking about the decarburization or cementation of the weld, when
the cutting blade element of high speed steel and the shank or back
of low grade steel are welded together and annealed at a
temperature sufficiently high enough to cause a sufficient
diffusion of carbon, the carbon diffuses from the shank or back
material into the blade material at the welded portion due to the
activity difference of carbon in both materials, even when the
welding is carried out in a protective atmosphere and under such a
condition as will not induce decarburization or cementation
externally, no matter what welding method is employed. Namely,
regardless of the amount of carbon contained in the shank or back
material, the carbon diffuses from the shank or back material into
the high speed steel material of the blade element, whereby the
shank or back material tends to be decarburized and the high speed
steel material tends to be cemented at the portions on both sides
of the weld. Thus, the structural strength of the product tool is
degraded. In the actual tools, it has been acknowledged that
breakage of the tool occurs from the cemented portion of the high
speed steel material adjacent to the weld, and in this view, it
becomes necessary to add to the shank or back material such
alloying elements which will restrain the diffusion of carbon at
the welded portion, namely chromium, vanadium, etc., which are
effective for lowering the activity of carbon.
The methods of heat-treating the welded tools are classified into
two types, i.e. a method wherein the shank or back material and the
high speed steel are concurrently subjected to quenching and
tempering after they are welded together, and a method wherein the
high speed steel only is subjected to quenching and tempering after
the welding. Where the high speed steel blade and the shank or back
are concurrently subjected to quenching and tempering, as in the
case of metal band saw, the grain size of the crystals tends to
become large, with the result that the tool has a degraded strength
and insufficient toughness, and breakage of the shank or back
frequently occurs during use of the tool. For avoiding such
trouble, it is necessary to add a grain size refining element to
the shank or back material.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a shank or back
material for high speed steel tools of the type having a high speed
steel blade element and a shank or back welded together, which will
not cause decarburization or cementation to occur at the welded
portion in the production of such tools.
Another object of the invention is to provide a shank or back
material for high speed steel tools of the type having a high speed
steel blade element and a shank or back welded together, which will
have a sufficient toughness and hardness even after the entire tool
is subjected to quenching and tempering subsequent to the welding
in the production of such tools.
Still another object of the invention is to provide a shank or back
material for high speed steel tools of the type having a high speed
steel blade element and a shank or back welded together, which
completely prevents the carburization and cementation of the welded
portion, will have sufficient toughness and hardness even after the
entire tool is subjected to quenching and tempering subsequent to
the welding, has good weldability and gives a crack-free weld, in
the production of such tools.
The shank or back material according to the present invention
consists of an alloy composed of 0.2- 0.5 % of carbon (C), 3.0-7.0
% of chromium (Cr), 0.1-1.0 % of vanadium (V), not more than 0.8 %
of silicon (Si), not more than 0.8 % of manganese (Mn) and the
remainder of iron (Fe) and impurities, or said alloy further
containing 0.02-0.3 % of niobium (Nb).
BRIEF DESCRIPTION OF THE DRAWING
FIGS. 1( a) and (b) are a set of microphotographs showing the grain
size increasing tendency of the crystals during quenching;
FIGS. 2(a) and (b) are a set of microphotographs showing the
structures of the blade material and the shank or back material at
portions adjacent to the weld after both materials are welded
together by the electron beam welding and subjected to a constant
temperature annealing;
FIGS. 3(a-c) are a set of microphotograph showing the quenched
structures of both materials at the welded portions; and
FIGS. 4-8 are graphic representations showing the hardness
distribution actually measured of both materials at the portions
adjacent to the weld.
PREFERRED EMBODIMENTS OF THE INVENTION
Examples of the composition of the steel material according to the
invention are shown in Table 1, in which symbol A.sub.1 represents
a high speed steel (equivalent to AlSl M2) used for the blade,
A.sub.2 a steel similar to SAE 1055 which is commonly being used as
a shank or back material, A.sub.3 and A.sub.4 comparative steels
and B, C, D, E, F and G the shank or back materials of the
invention.
Table 1
__________________________________________________________________________
Symbol C Si Mn P S Ni Cr Mo W V Co Cu Nb Remarks
__________________________________________________________________________
A.sub.1 0.88 0.22 0.32 0.022 0.002 0.08 4.08 4.88 6.20 1.84 0.48
0.07 -- Blade material AISI M2 A.sub.2 0.59 0.20 0.35 0.009 0.008
0.09 0.01 0.02 -- 0.01 -- 0.08 -- Conventional steel equivalent to
SAE 1055 A.sub.3 0.54 0.16 0.37 0.009 0.010 0.11 1.16 0.03 -- 0.32
-- 0.10 -- Comparative Steel B 0.40 0.19 0.31 0.008 0.008 0.10 3.01
0.02 -- 0.27 -- 0.09 -- Steel of the invention C 0.35 0.16 0.22
0.009 0.009 0.09 4.98 0.02 -- 0.26 -- 0.09 -- Steel of the
invention D 0.31 0.14 0.30 0.009 0.010 0.07 6.88 0.03 -- 0.28 --
0.08 -- Steel of the invention A.sub.4 0.30 0.16 0.29 0.008 0.010
0.07 9.92 0.02 -- 0.29 -- 0.08 -- Comparative steel E 0.35 0.12
0.26 0.009 0.009 0.09 4.97 0.02 -- 0.27 -- 0.09 0.09 Steel of the
invention F 0.36 0.14 0.28 0.010 0.009 0.09 4.92 0.02 -- 0.28 --
0.09 0.18 Steel of the invention G 0.35 0.14 0.27 0.010 0.009 0.08
4.95 0.02 -- 0.22 -- 0.08 0.30 Steel of the invention
__________________________________________________________________________
A.sub.3, b, c, d and A.sub.4 are materials in which the
concentration of Cr is varied, and E, F and G are materials in
which the concentration of Nb is varied. The concentration of C is
reduced by the addition of Cr because Cr has the effect of
increasing the resistance to temper softening and an HRC hardness
of 45-47 suitable for the shank or back material can be obtained
even when the shank or trunk material is subjected to a heat
treatment concurrently with the high speed steel. FIGS. 1(a) and
(b) are a set of microphotographs of which FIG. 1(a) is the
comparative steel A.sub.3 and FIG. 1(b) is the steel E of the
present invention which were quenched at 1200.degree.C and
1250.degree.C respectively. The steel materials of the invention
has the nature of preventing the grain size from becoming large and
a remarkable difference is noted between them and the comparative
steel A.sub.3 particularly after quenching at temperatures above
1200.degree. C which are used for high speed steels.
Table 2
__________________________________________________________________________
Symbol Quenched at 1200.degree.C., tempered at 560.degree.C.
Quenched at 1250.degree.C., tempered at 560.degree. C. Breaking
Maximum deflection Absorbed Hardness Breaking Maximum deflection
Absorbed Hardness load (kg) (mm) energy (kg-m) (HRC) load (kg) (mm)
energy (HRC))
__________________________________________________________________________
A.sub.2 189 1.08 0.131 45.2 182 0.93 0.092 44.9 A.sub.3 196 1.20
0.188 45.6 184 1.04 0.144 45.9 B 190 1.75 0.292 45.5 178 1.68 0.268
45.7 C 190 2.11 0.376 45.5 176 1.86 0.312 45.4 D 206 1.94 0.364
45.0 187 1.90 0.314 45.4 A.sub.4 203 1.93 0.350 45.1 186 1.83 0.303
45.0 E 203 2.33 0.436 46.6 195 2.13 0.402 46.8 F 202 2.84 0.532
46.9 176 2.86 0.468 47.0 G 203 2.66 0.499 46.4 183 2.65 0.451 46.4
__________________________________________________________________________
Table 2 given above shows the toughness of each material obtained
by a transverse breaking test conducted on a test piece having a
thickness of 3 mm, a width of 5 mm and a length of 30 mm. Each test
piece was heat-treated by immersing it in a salt bath held at
1200.degree.C or in a salt bath held at 1250.degree.C, for 60
seconds, then quenched in oil, and tempered twice at 560.degree.C
for 1 hour and cooled in air, and the transverse breaking test was
conducted by using an Amsler universal testing machine by
supporting the test piece at two points (the span being 10 mm).
It will be seen from Table 2 that the steel materials of the
invention, particularly those containing Nb, are greater in
toughness than the conventional and comparative steel materials. It
will also be seen that the toughness increases as the concentration
of Cr increases up to 5 %, but remains substantially the same over
5 %.
FIGS. 2(a) and (b) show microphotographic structures at the welded
portion of a test piece comprising a blade-constituting high speed
steel (AlSl M2) and a shank material (comparative steel A.sub.3)
welded together by the electron beam welding method, shown in FIG.
2(a) and that of a test piece comprising the same high speed steel
and the shank material of the invention (steel C) welded together
by the same method, as seen in FIG. 2(b). Each test piece was
prepared by shaping each material into a plate having thickness of
3 mm, a width of 30 mm and a length of 500 mm, welding the plates
of the respective materials together by electron beam welding,
allowing the welded plate to cool, heating it at 900.degree.C for
30 minutes, maintaining it at 700.degree.C for 5 hours and
subjecting it to a isothermal annealing in air. As shown, a
ferritic decarurized layer is formed in the comparative steel
A.sub.3, FIG. 2(a) but such layer is not formed in the steel C of
the present invention, FIG. 2(b). FIGS. 3(a-c) show micrographic
structures at the boundary of the weld and the high speed steel of
test pieces prepared in the manner described above by using the
comparative steel A.sub.3 in FIG. 3(a), the steel B of the
invention in FIG. 3(b) and the steel C of the invention in FIG.
3(c), which, after the annealing, were respectively immersed in a
salt bath at 1250.degree.C and subjected to quenching in oil. In
these microphotographs, the portions appearing in etched black
color between the grains are intergranular fused layers. It will be
seen that the intergranular fused layers are present in a large
number in the comparative steel A.sub.3 of FIG. 3(a) but decrease
as the concentration of Cr increases, and are extremely decreased
in the steel B of the invention containing 3 % of Cr, FIG. 3(b) and
not present at all in the steel C of the invention containing 5 %
of Cr, FIG. 3(c).
It has been known that the emergence of intergranular fused layers
in high speed steel has a particularly close relation with excess
carbon, and this substantiates the cementation of the high speed
steel.
FIGS. 4-8 show the measured hardness distributions at the welded
portion of the conventional steel, the comparative steel and the
steel of the instant invention after said respective steels are
quenched at 1200.degree.C, maintained at 560.degree.C for 1 hour
and tempered in air, and also quenched at 1250.degree.C and
annealed in the same manner. In the diagrams, a curve a represents
the hardness distribution of each steel which was tempered after
the quenching at 1200.degree.C and a curve b represents the
hardness distribution of the same which was tempered after quenched
at 1250.degree.C. The hatched portion shows the welded portion of
the blade material and the shank material, and the left side of
said hatched portion is the blade material and the right side
thereof the shank material.
FIG. 4 shows the hardness distribution curves when the conventional
steel A.sub.2 is used as the shank material. It will be seen that
the hardness increases at the portion of the high speed steel
adjacent to the weld and decreases at the portion of the shank
material adjacent to the weld. This apparently results from the
cementation of the high speed steel and decarburization of the
shank material during the annealing due to diffusion of carbon from
the shank material into the high speed material. FIGS. 5-7 show the
hardness distribution curves of the steels B, C and D according to
the invention which contains 3 %, 5 % and 7 % of chromium
respectively. The curves in FIG. 5 show less tendency of
cementation and decarburization, and the curves in FIG. 7 show
uniform hardness distributions and no tendency of cementation and
decarburization. FIG. 8 shows the hardness distributions when the
comparative steel A.sub.4 containing 10 % of chromium is used as
the shank material. In this case, the activity of carbon in the
shank material is excessively lower than that of carbon in the high
speed steel, resulting in cementation of the shank material.
In order to compare the weldabilities of the respective shank
materials with each other, with respect to the blade-constituting
high speed steel, the transverse breaking load, the maximum
deflection and the absorbed energy were measured on a test piece
comprising the high speed steel and the respective shank material
welded together by supporting said tests test on both sides of the
weld and applying a concentrated load thereon. the results are
shown in Table 3 given below.
Table 3 ______________________________________ Breaking Maximum
Absorbed HRC hardness load deflec- energy Sample (kg) tion (kg-m)
Shank Blade (mm) material material
______________________________________ Compar- ative 750 0.62 0.13
45.8 65.6 steel A.sub.3 Steel B of the 953 0.71 0.23 45.7 65.5
invention Steel C of the 923 0.60 0.24 45.5 65.6 invention Steel D
of the 870 0.60 0.22 45.3 65.7 invention
______________________________________
From Table 3, it will be seen that the steels of the present
invention also excel the comparative steel in weldability. Each
test piece was prepared by concurrently quenching the blade
material and the shank material and subjecting the same to
tempering.
Now, the reasons for which the concentrations of the respective
elements in the steel materials of the invention are restricted,
will be explained.
Carbon partially forms carbides with chromium, vanadium and
niobium, and partially forms a solid solution with the matrix to
increase the strength of said matrix after quench and tempering. In
the present invention, the carbon concentration is restricted in
the range of 0.2-0.6 % because a concentration lower than 0.2 %
results in an insufficient hardness of the shank or back material,
while a concentration higher than 0.6 % results in an extremely low
toughness of the same. Chromium partially forms a carbide and
partially dissolved in the matrix improving the hardenability of
the matrix. An increasing concentration of chromium tends to lower
the carbon activity, so that the diffusion of carbon from the shank
or back material into the high speed steel is lessened and
accordingly the decarburization of the shank or back material and
cementation of the high speed steel are lessened. This tendency
appears from the chromium concentration of 3 % and the
decarburization and cementation of the weld can be prevented at the
chromium concentration of around 5 %. However, when the
concentration of chromium exceeds 7 %, the self-hardening property
of the weld is enhanced so highly that the hardness of the weld
after the annealing increases, making the subsequent working
difficult. At the same time, an instable retained austenite is
formed at the weld by the quenching and tempering. Furthermore,
because of the excessively low activity of carbon, diffusion of
carbon from the high speed steel into the shank or back material
takes place, with the result that said shank or back material tends
to be carburized and the weldability becomes degraded. The
concentration of chromium is specified to be within the range of
3.0-7.0 % in the present invention for the above reasons. Vanadium
is an element effective for lowering the activity of carbon since
it forms a stable carbide. This carbide is hardly soluble in
austenite and prevents the growth of grains, and vanadium also
increases the resistance to softening of the material. Therefore,
the concentration of vanadium should at least be 0.1 %. However, a
concentration of vanadium exceeding 1 % results in a lowering of
hardness in relation with carbon and niobium. In addition, the
material becomes expensive. Therefore, the vanadium concentration
is restricted within the range of 0.1-1.0 %. Niobium forms fine
special carbides having a high melting point and therefore
effectively prevents the grains from becoming large in size. This
effect of Niobium is noted from a concentration of 0.02 %, and the
grain size becomes smaller and the toughness is remarkably improved
as the concentration increases, but is decreased at concentrations
higher than 0.3 %. Thus, the Niobium concentration is restricted
within the range of 0.02-0.3 %. Silicon and manganese are used as
deoxidizers. The concentrations of these elements are restricted to
be not higher than 0.8 % because concentrations higher than the
value adversely affect the weldability of the material.
As described hereinabove, the shank or back material according to
the instant invention completely eliminate the decarburization and
cementation of the weld between the blade material consisting of
high speed steel and the shank or back material, by virtue of
chromium and vanadium which serve to lower the activity of carbon,
and has improved toughness and weldability by virtue of carbon or
niobium incorporated therein at a suitable concentration.
* * * * *