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Claims  |
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What is claimed is:
1. A coated cemented carbide cutting tool comprising a substrate consisting
of a matrix of WC and a binder phase of an iron group metal and a
plurality of coated layers provided on a surface of the substrate, in
which (a) an innermost layer, adjacent to the substrate, of the coated
layers consists essentially of titanium nitride having a thickness of 0.1
to 3 .mu.m, (b) on a mirror-polished cross-sectional microstructure of the
said tool, an average crack interval in the coated film on a ridge of a
cutting edge and/or rake face is smaller than an average crack interval in
the coated layer on a flank face, (c) at least 50% of the cracks in the
coated film on the said ridge of the cutting edge and/or rake face have
ends of the cracks in the said innermost titanium nitride layer, in a
layer above the titanium nitride layer or in an interface between these
layers and (d) an average crack length of in the coated film on the said
ridge of the cutting edge and/or rake face is shorter than an average
coated film thickness on the flank face.
2. The coated cemented carbide cutting tool as claimed in claim 1, wherein
the interface between these layers is a interface between the innermost
titanium nitride layer and the layer directly above the titanium nitride
layer.
3. The coated cemented carbide cutting tool as claimed in claim 1, wherein
the said innermost titanium nitride layer is further coated with titanium
carbonitride layer of columnar structure, with an aspect ratio of at least
5, having a thickness of 3 to 30 .mu.m, and is further coated with at
least one alumina layer of 0.5 to 10 .mu.m.
4. The coated cemented carbide cutting tool as claimed in claim 3, wherein
at least 50% of the cracks in the coated film on the said ridge of the
cutting edge and/or rake face have ends of the cracks, at the substrate
side, in the said innermost titanium nitride layer, in the said titanium
carbonitride layer of columnar structure or in an interface between the
said titanium nitride layer and the said titanium carbonitride layer of
columnar structure.
5. The coated cemented carbide cutting tool as claimed in claim 3, wherein
at least 50% of the cracks in the coated film on the said ridge of the
cutting edge and/or rake face exist in only the said titanium carbonitride
layer of columnar structure and are not penetrated to the upper and lower
coated layers thereof.
6. The coated cemented carbide cutting tool as claimed in claim 1, wherein
at least 80% of the cracks in the coated film on the said ridge of the
cutting edge and/or rake face have ends of the cracks, at the substrate
side, in the said innermost titanium nitride layer, in the said titanium
carbonitride layer of columnar structure or in an interface between the
said titanium nitride layer and the said titanium carbonitride layer of
columnar structure.
7. The coated cemented carbide cutting tool as claimed in claim 1, wherein
the said innermost titanium nitride layer is coated with alumina layer of
3 to 20 .mu.m, further coated with titanium carbonitride layer of columnar
structure with an aspect ratio of at least 5, having a thickness of 3 to
30 .mu.m, and further coated with alumina layer of 0.5 to 10 .mu.m.
8. The coated cemented carbide cutting tool as claimed in claim 1, wherein
the average crack intervals in the coated film on the said ridge of the
cutting edge and/or rake face is at most 10 .mu.m.
9. The coated cemented carbide cutting tool as claimed in claim 1, wherein
when a narrower average crack interval in the coated film of the ridge of
the cutting edge or rake face on the said cross-sectional microstructure
is X and an average crack interval in the coated film on the flank face is
Y, a value of Y/X satisfies at least 2.
10. The coated cemented carbide cutting tool as claimed in claim 1, wherein
at least 50% of the ends of cracks, at the surface side, in the coated
film on the said ridge of the cutting and/or rake face are not penetrated
to the surface of the coated film.
11. The coated cemented carbide cutting tool as claimed in claim 1, wherein
the surface of the said cemented carbide substrate has a .beta.-free
layer.
12. The coated cemented carbide cutting tool as claimed in claim 1, wherein
the cracks in the coated film on the said ridge of the cutting edge are
mechanically introduced after coating.
13. The coated cemented carbide cutting tool as claimed in claim 1, wherein
the said titanium carbonitride layer of columnar structure is coated at
800.degree. C. to 1000.degree. C. by a CVD method comprising using an
organo CN compound as a reactant gas.
14. The coated cemented carbide cutting tool as claimed in claim 1, wherein
the total thickness of the coated films is in a range of 3 to 50 .mu.m.
15. A coated cemented carbide cutting tool comprising a substrate
consisting of a matrix of WC and a binder phase of an iron group metal and
a plurality of coated layers provided on a surface of a substrate, in
which (a) an innermost layer, adjacent to the substrate, of the coated
layers consists essentially of titanium nitride having a thickness of 0.1
to 3 .mu.m, which is further coated with at least one alumina layer of 0.5
to 10 .mu.m, (b) on a mirror-polished cross-sectional microstructure of
the tool, an average crack interval in the coated film on a ridge of a
cutting edge is smaller than an average crack interval in the coated layer
on a flank face, (c) at least 50% of the cracks in the coated film on the
said ridge of the cutting edge have ends of the cracks, at the substrate
side, in the said innermost titanium nitride layer, in a layer above the
titanium nitride layer or in an interface between these layers, (d) an
average crack length in the coated film on the said ridge of the cutting
edge is shorter than an average coated film thickness on the flank face
and (e) at least one of the said alumina layers is removed or polished on
at least a part of the ridge of the cutting edge.
16. The coated cemented carbide cutting tool as claimed in claim 15,
wherein the said innermost titanium nitride layer is coated with at least
one titanium carbonitride layer of columnar structure with an aspect ratio
of at least 5, having a thickness of 3 to 30 .mu.m.
17. The coated cemented carbide cutting tool as claimed in claim 16,
wherein at least 50% of the cracks in the coated film on the said ridge of
the cutting edge have ends of the cracks, at the substrate side, in the
said innermost titanium nitride layer, in the said titanium carbonitride
layer of columnar structure or in an interface between the said titanium
nitride layer and the said titanium carbonitride layer of columnar
structure.
18. The coated cemented carbide cutting tool as claimed in claim 16,
wherein the surface-exposed coated layer A, where the said alumina layer
has been removed, consists of titanium carbonitride layer of columnar
structure with an aspect ratio of at least 5, having a thickness of 3 to
30 .mu.m.
19. The coated cemented carbide cutting tool as claimed in claim 16,
wherein the coated layer A existing under the said alumina-polished part
consists of titanim carbonitride layer of columnar structure with an
aspect ratio of at least 5, having a thickness of 3 to 30 .mu.m.
20. The coated cemented carbide cutting tool as claimed in claim 16,
wherein at least 50% of the cracks in the coated film on the said ridge of
the cutting edge exist on only the said titanium carbonitride layer of
columnar structure and are not penetrated through the upper and lower
coated layers thereof.
21. The coated cemented carbide cutting tool as claimed in claim 16,
wherein the said titanium carbonitride layer of columnar structure is
coated at 800.degree. C. to 1000.degree. C. by a CVD method comprising
using an organo CN compound as a reactant gas.
22. The coated cemented carbide cutting tool as claimed in claim 15,
wherein at least 80% of the cracks in the coated film on the said ridge of
the cutting edge have ends of the cracks, at the substrate side, in the
said innermost titanium nitride layer, in the said titanium carbonitride
layer of columnar structure or in an interface between the said titanium
nitride layer and the said titanium carbonitride layer of columnar
structure.
23. The coated cemented carbide cutting tool as claimed in claim 15,
wherein the average crack inerval in the coated film on the said ridge of
the cutting edge is at most 10 .mu.m.
24. The coated cemented carbide cutting tool as claimed in claim 15,
wherein when an average crack interval in the coated film of the ridge of
the cutting edge on the said cross-sectional microstructure is X and an
average crack interval in the coated film on the flank face is Y, a value
of Y/X satisfies at least 2.
25. The coated cemented carbide cutting tool as claimed in claim 15,
wherein the crack interval in the surface-exposed coated layer A, where
the said alumina layer has been removed, is 0.5 to 5 .mu.m.
26. The coated cemented carbide cutting tool as claimed in claim 15,
wherein the coated layer A provided with cracks whose intervals are in a
range of 0.5 to 5 .mu.m exists under the said alumina polished part.
27. The coated cemented carbide cutting tool as claimed in claim 15,
wherein the surface of the said cemented carbide substrate has a
.beta.-free layer.
28. The coated cemented carbide cutting tool as claimed in claim 15,
wherein the said removed alumina layer essentially consists of
.kappa.-alumina.
29. The coated cemented carbide cutting tool as claimed in claim 15,
wherein the said polished alumina layer essentially consists of
.alpha.-alumina.
30. The coated cemented carbide cutting tool as claimed in claim 15,
wherein the sum of the thickness of the coated layers is in a range of 3
to 50 .mu.m.
31. The coated cemented carbide cutting tool as claimed in claim 15,
wherein the cracks in the coated film on the said ridge of the cutting
edge are mechanically introduced after coating.
32. A coated cemented carbide cutting tool comprising a substrate
consisting of a matrix of WC and a binder phase of an iron group metal and
a plurality of coated layers provided on a surface of the substrate, in
which (a) an innermost layer, adjacent to the substrate, of the coated
layers consists essentially of titanium nitride having a thickness of 0.1
to 3 .mu.m, which is further coated with titanium carbonitride layer of
columnar structure with an aspect ratio of at least 5, having a thickness
of 3 to 30 .mu.m, and further is coated with at least one alumina layer
with a thickness of 0.5 to 10 .mu.m, (b) on a mirror-polished
cross-sectional microstructure of the said tool, at least 50% of ends of
cracks at the surface side in the coated film on a ridge of a cutting edge
and/or rake face are not penetrated to the surface of the coated film, (c)
at least 50% of the cracks in the coated film on the said ridge of the
cutting edge and/or rake face have ends of the cracks, at the substrate
side, in the said innermost titanium nitride layer, in a layer above the
titanium nitride layer or in an interface between these layers and (d) an
average crack length in the coated film on the said ridge of the cutting
edge and/or rake face is shorter than an average coated film thickness on
the flank face, (e) an average crack inerval in the said titanium
carbonitride layer on the said ridge of the cutting edge and/or rake face
is at most 10 .mu.m and (f) an average crack interval in the said alumina
film on the said ridge of the cutting edge and/or rake face is at least
two times as large as an average crack interval in the said titanium
carbonitride layer.
33. The coated cemented carbide cutting tool as claimed in claim 32,
wherein the surface of the said cemented carbide substrate has a
.beta.-free layer.
34. The coated cemented carbide cutting tool as claimed in claim 29,
wherein the said alumina layer is removed or polished on at least a part
of the ridge of the cutting edge. |
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Claims |
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Description |
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TECHNICAL FIELD
This invention relates to a cutting tool, in particular, which is most
suitable as a coated cemented carbide cutting tool used for cutting steels
and cast irons and which is excellent in wear resistance as well as
breakage resistance.
BACKGROUND TECHNIQUE
Hitherto, cemented carbides (WC-Co alloys or WC-Co alloys to which
carbonitrides of Ti, Ta or Nb are added) have been used as a tool material
for cutting metallic materials. However, as cutting speeds have lately
been increased, a tendency of using cemented carbide tools comprising
cemented carbide substrates coated with coated films consisting of
carbides, nitrides, carbonitrides, carboxides, boronitrides or oxides of
Group IVa, Va and VIa elements of the Periodic Table or Al or their solid
solutions by CVD or PVD methods in a thickness of 3 to 15 .mu.m is
enhancing. The thickness of the coated films tends to further increase and
CVD coated cemented carbides with a coating thickness of at least 20 .mu.m
have been proposed. In such CVD coated cemented carbide tools, there
arises a problem that a tensile residual stress occurs in the coated film
during cooling after the coating due to difference in coefficient of
thermal expansion between the coated film and substrate, and the breakage
resistance of the tool is thus lowered.
For a coated cemented carbide tool, on the other hand, it has been proposed
in order to improve its breakage resistance, to introduce cracks into a
coated film to be penetrated therethrough to a substrate by applying
mechanical impact to a surface of a cemented carbide, for example, by
blasting (JP-B-7-6066). In this proposed method, it is confirmed that the
breakage resistance can be improved to some extent, but because of
previously introducing cracks into the coated film to be penetrated
therethrough to the substrate, Griffith' precrack length is increased,
thus resulting in lowering of the breakage resistance, wear fluctuation of
the coated film and deterioration of the wear resistance from the longer
cracks.
As described above, the coated cemented carbide tools of the prior art have
the problems that when the thickness of a coated film is increased to
improve the wear resistance, the breakage resistance of the tool is
decreased and even when cracks are previously introduced into a coated
film with a relatively large thickness, the wear resistance is rather
lowered depending on the cracked state. These problems have not been
solved yet.
Under the situation, the present invention aims at providing a coated
cemented carbide tool whose both properties of a breakage resistance and
wear resistance are improved and service life as a tool is lengthened.
DISCLOSURE OF INVENTION
In order to achieve the above described object, the inventors have made
various studies and consequently, have found that using a cemented carbide
alloy consisting of a matrix of WC and a binder phase of an iron group
metal, a ceramic film having a specified film quality and structure is
coated onto its surface and the lengths and intervals of cracks introduced
into the coated film are precisely controlled by a thermal or mechanical
procedure, whereby to improve both the properties of a breakage resistance
and wear resistance and to lengthen the tool life to a great extent. That
is, the present invention comprises specified inventions or embodiments
summarized below:
(1) A coated cemented carbide cutting tool comprising a substrate
consisting of a matrix of WC and a binder phase of an iron group metal and
a plurality of coated layers provided on a surface of the substrate, in
which (a) an innermost layer, adjacent to the substrate, of the coated
layers consists of titanium nitride having a thickness of 0.1 to 3 .mu.m,
preferably 0.3 to 1 .mu.m, (b) on a mirror-polished cross-sectional
microstructure of the said tool, an average crack interval in the coated
film on a ridge of a cutting edge and/or rake face is smaller than an
average crack interval in the coated layer on a flank face, (c) at least
50%, preferably at least 80% of the cracks in the coated film on the said
ridge of the cutting edge and/or rake face have ends of the cracks in the
said innermost titanium nitride layer, in a layer above the titanium
nitride or in an interface between these layers and (d) an average crack
length in the coated film on the said ridge of the cutting edge is shorter
than an average coated film thickness on the flank face.
(2) The coated cemented carbide cutting tool as described in the above (1),
wherein the interface between these layers is a interface between the
innermost titanium nitride layer and the layer directly above the titanium
nitride.
(3) The coated cemented carbide cutting tool as described in the above (1)
or (2), wherein the said innermost titanium nitride layer is coated with
titanium carbonitride layer of columnar structure with an aspect ratio of
at least 5, preferably 10 to 50, having a thickness of 3 to 30 .mu.m,
preferably 5 to 15 .mu.m, and further coated with at least one alumina
layer of 0.5 to 10 .mu.m, preferably 1 to 8 .mu.m.
(4) The coated cemented carbide cutting tool as described in the above (3),
wherein at least 50%, preferably 80 to 100% of the cracks in the coated
film on the said ridge of the cutting edge and/or rake face have ends of
the cracks, at the substrate side, in the said innermost titanium nitride
layer, in the said titanium carbonitride layer of columnar structure or in
an interface between the said titanium nitride layer and the said titanium
carbonitride layer of columnar structure. (The existing amount of the ends
of the cracks at the substrate side herein means the total mounts.)
(5) The coated cemented carbide cutting tool as described in the above (1)
or (2), wherein the said innermost titanium nitride layer is coated with
alumina layer of 3 to 20 .mu.m, further coated with titanium carbonitride
layer of columnar structure having a thickness of 3 to 30 .mu.m with an
aspect ratio of at least 5 and further coated with alumina layer of 0.5 to
10 .mu.m.
(6) The coated cemented carbide cutting tool as described in any one of the
above (1) to (5), wherein the average crack interval in the coated film on
the said ridge of the cutting edge and/or rake face is at most 10 .mu.m.
(7) The coated cemented carbide cutting tool as described in any one of the
above (1) to (6), wherein when a narrower average crack interval in the
coated film of the ridge of the cutting edge or rake face on the said
cross-sectional microstructure is X and an average value of the crack
intervals in the coated film on the flank face is Y, a value of Y/X
satisfies at least 2.
(8) The coated cemented carbide cutting tool as described in any one of the
above (1) to (7), wherein at least 50%, preferably 75 to 100% of the ends
of the cracks at the surface side in the coated film on the said ridge of
the cutting edge and/or rake face are not penetrated to the surface of the
coated film.
(9) The coated cemented carbide cutting tool as described in any one of the
above (2) to (8), wherein at least 50%, preferably 70 to 100% of the
cracks in the coated film on the said ridge of the cutting edge and/or
rake face exist in only the said titanium carbonitride film of columnar
structure and are not penetrated to the upper and lower layers thereof.
(10) The coated cemented carbide cutting tool as described in any one of
the above (1) to (9), wherein the surface of the said cemented carbide
substrate has a .beta.-free layer.
(11) The coated cemented carbide cutting tool as described in any one of
the above (1) to (10), wherein the cracks in the coated film on the said
ridge of the cutting edge are mechanically introduced after coating.
(12) The coated cemented carbide cutting tool as described in any one of
the above (3) to (11), wherein the said titanium carbonitride layer of
columnar structure is coated at 800.degree. C. to 1000.degree. C.,
preferably, 850.degree. C. to 950.degree. C. by a CVD method comprising
using an organo CN compound as a reactant gas.
(13) The coated cemented carbide cutting tool as described in any one of
the above (1) to (12), wherein the total thickness of the coated films is
in a range of 3 to 50 .mu.m.
(14) A coated cemented carbide cutting tool comprising a substrate
consisting of a matrix of WC and a binder phase of an iron group metal and
a plurality of coated layers provided on a surface of a substrate, in
which (a) an innermost layer, adjacent to the substrate, of the coated
layers consists of titanium nitride having a thickness of 0.1 to 3 .mu.m,
preferably 0.3 to 1 .mu.m, which is further coated with, as an upper
layer, at least one alumina layer of 0.5 to 10 .mu.m, preferably 1 to 8
.mu.m, (b) on a mirror-polished cross-sectional microstructure of the
tool, an average crack interval in the coated film on a ridge of a cutting
edge is smaller than an average crack interval in the coated layer on a
flank face, (c) at least 50 % of the cracks in the coated film on the said
ridge of the cutting edge have ends of the cracks, at the substrate side,
in the said innermost titanium nitride layer, in a layer above the
titanium nitride layer or in an interface between these layers (interface
between the titanium nitride layer and a layer directly above it and each
interface between the layers in the upper layers), (d) an average crack
length in the coated film on the said ridge of the cutting edge is shorter
than an average coated film thickness on the flank face and (e) the said
alumina layer is removed or polished on at least a part of the ridge of
the cutting edge.
(15) The coated cemented carbide cutting tool as described in the above
(14), wherein the said innermost titanium nitride layer is further coated
with titanium carbonitride layer of columnar structure with an aspect
ratio of at least 5, preferably 10 to 50, having a thickness of 3 to 30
.mu.m, preferably 5 to 15 .mu.m, and further coated with at least one
alumina layer with a thickness of 0.5 to 10 .mu.m, preferably 1 to 8
.mu.m.
(16) The coated cemented carbide cutting tool as described in the above
(15), wherein at least 50%, preferably 80 to 100% of the cracks in the
coated film on the said ridge of the cutting edge have ends of the cracks,
at the substrate side, in the said innermost titanium nitride layer, in
the said titanium carbonitride layer of columnar structure or in an
interface between the said titanium nitride layer and the said titanium
carbonitride layer of columnar structure. (The existing amount of the ends
of the cracks at the substrate side herein means the total mounts.)
(17) The coated cemented carbide cutting tool as described in any one of
the above (14) to (16), wherein the average crack interval in the coated
film on the said ridge of the cutting edge is at most 10 .mu.m.
(18) The coated cemented carbide cutting tool as described in any one of
the above (14) to (17), wherein when an average crack interval in the
coated film of the ridge of the cutting edge on the said cross-sectional
microstructure is X and an average crack interval in the coated film on
the flank face is Y, a value of Y/X satisfies at least 2, preferably at
least 5.
(19) The coated cemented carbide cutting tool as described in any one of
the above (14) to (18), wherein the crack interval in the surface-exposed
coated layer A, at which the said alumina layer has been removed, is 0.5
to 5 .mu.m, preferably 1 to 3 .mu.m.
(20) The coated cemented carbide cutting tool as described in any one of
the above (15) to (18), wherein the surface-exposed coated layer A, at
which the said alumina layer has been removed, consists of titanium
carbonitride of a columnar crystal with an aspect ratio of at least 5,
preferably 10 to 50, having a thickness of 3 to 30 .mu.m, preferably 5 to
15 .mu.m.
(21) The coated cemented carbide cutting tool as described in any one of
the above (14) to (18), wherein the coated layer A provided with cracks
whose intervals in a range of 0.5 to 5 .mu.m, preferably 1 to 3 .mu.m
exists under the said alumina polished part.
(22) The coated cemented carbide cutting tool as described in any one of
the above (15) to (18), wherein the coated layer A existing under the said
alumina-polished part consists of titanim carbonitride layer of columnar
structure, with an aspect ratio of at least 5, preferably 10 to 50, having
a thickness of 3 to 30 .mu.m, preferably 5 to 15 .mu.m.
(23) The coated cemented carbide cutting tool as described in any one of
the above (15) to (20), wherein at least 50%, preferably 70 to 100% of the
cracks in the coated film on the said ridge of the cutting edge exist on
only the said titanium carbonitride layer of columnar structure and are
not penetrated through the upper and lower coated layers thereof.
(24) The coated cemented carbide cutting tool as described in any one of
the above (14) to (23), wherein the surface of the said cemented carbide
substrate has a .beta.-free layer.
(25) The coated cemented carbide cutting tool as described in any one of
the above (14) to (20) and (23) to (24), wherein the said removed alumina
layer essentially consists of .kappa.-alumina.
(26) The coated cemented carbide cutting tool as described in any one of
the above (14) to (18) and (21) to (23), wherein the said polished alumina
layer essentially consists of .alpha.-alumina.
(27) A coated cemented carbide cutting tool comprising a substrate
consisting of a matrix of WC and a binder phase of an iron group metal and
a plurality of coated layers provided on a surface of the substrate, in
which (a) an innermost layer, adjacent to the substrate, of the coated
layers consists of titanium nitride having a thickness of 0.1 to 3 .mu.m,
preferably 0.3 to 1 .mu.m, which is further coated with titanium
carbonitride layer of columnar structure with an aspect ratio of at least
5, preferably 10 to 50, having a thickness of 3 to 30 .mu.m, preferably 5
to 15 .mu.m, and further coated with at least one alumina layer with a
thickness of 0.5 to 10 .mu.m, preferably 1 to 8 .mu.m, (b) on a
mirror-polished cross-sectional microstructure of the tool, at least 50%
of ends of cracks at the surface side in the coated film on a ridge of a
cutting edge and/or rake face are not penetrated to the surface of the
coated film, (c) at least 50% of the cracks in the coated film on the said
ridge of the cutting edge and/or rake face have ends of the cracks, at the
substrate side, in the said innermost titanium nitride layer, in a layer
above the titanium nitride layer or in an interface between these layers
and (d) an average crack length in the coated film on the said ridge of
the cutting edge and/or rake face is shorter than an average coated film
thickness on the flank face, (e) an average crack inerval in the said
titanium carbonitride layer on the said ridge of the cutting edge and/or
rake face is at most 10 .mu.m and (f) an average crack interval in the
said alumina film on the said ridge of the cutting edge and/or rake face
is at least two times as large as an average crack interval in the said
titanium carbonitride layer.
(28) The coated cemented carbide cutting tool as described in the above
(27), wherein the surface of the said cemented carbide substrate has a
.beta.-free layer.
(29) The coated cemented carbide cutting tool as described in the above
(27) or (28), wherein the said alumina layer is removed or polished on at
least a part of the ridge of the cutting edge.
(30) The coated cemented carbide cutting tool as described in any one of
the above (14) to (29), wherein the cracks in the coated film on the said
ridge of the cutting edge are mechanically introduced after coating.
(31) The coated cemented carbide cutting tool as described in any one of
the above (15) to (30), wherein the said titanium carbonitride layer of
columnar structure is coated at 800.degree. C. to 1000.degree. C.,
preferably, 850.degree. C. to 950.degree. C. by a CVD method comprising
using an organo CN compound as a reactant gas.
(32) The coated cemented carbide cutting tool as described in any one of
the above (14) to (31), wherein the sum of the thickness of the coated
layers is in a range of 3 to 50 .mu.m.
Between the said innermost titanium nitride layer and the said titanium
carbonitride layer of columnar structure or the alumina layer of the above
described (5) or between the said titanium carbonitride layer of columnar
structure and the said alumina layer, an intermediate layer can be coated
to improve the adhesive strength between these layers. As the intermediate
layer, there can be used layers of titanium boronitride, titanium carbide,
titanium carboxynitride and the like with a thickness of about 0.1 to 5
.mu.m.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an insert of the present invention to
illustrate a edge of a cutting edge, flank face and rake face.
FIG. 2 is a typical plan view of an insert of the present invention.
FIG. 3 is a diagram for showing a positional relationship between ends of
cracks and a subatrate in a coated layer of a cemented carbide according
to the present invention.
FIG. 4 (a) and (b) respectively are typical cross-sectional views of
polished states of alumina layers on mirror-polished cross-sectional
microstructures of inserts according to the present invention.
FIG. 5 is a cross-sectional view of a workpiece of SCM 435 (round rod) used
for a cutting test in Examples.
BEST EMBODIMENT FOR CARRYING OUT PRESENT INVENTION
According to the first feature I of the present invention, in a coated
cemented carbide cutting tool comprising a substrate consisting of a
matrix of WC and a binder phase of an iron group metal, to which a
carbonitride of Ti, Ta, Nb, etc. is optionally added, and a plurality of
coated layers provided on a surface of the substrate, (a) an innermost
layer, adjacent to the substrate, of the coated layers consists of
titanium nitride having a thickness of 0.1 to 3 .mu.m, preferably 0.3 to 1
.mu.m, which is further coated with titanium carbonitride layer of
columnar structure with an aspect ratio of at least 5, preferably 10 to
50, having a thickness of 3 to 30 .mu.m, preferably 5 to 15 .mu.m, and
further coated with at least one alumina layer with a thickness of 0.5 to
10 .mu.m, preferably 1 to 8 .mu.m. (b) On a mirror-polished
cross-sectional microstructure of the said tool, an average crack interval
in the coated film on the ridge of the cutting edge is rendered smaller
than an average crack interval in the coated layer on a flank face. (c) Of
the cracks in the coated film on the ridge of the cutting edge and/or rake
face, those in which the ends of the cracks, at the substrate side, exist
in the said innermost titanium nitride layer, in a layer above the
titanium nitride or in an interface between these layers are in a
proportion of at least 50%, preferably 80 to 100%. In the case of coating
the said titanium carbonitride layer of columnar structure onto the said
innermost titanium nitride layer, the cracks whose ends exist in the said
innermost titanium nitride layer, in the said titanium carbonitride layer
of columnar structure or in an interface between the said titanium nitride
layer and the said titanium carbonitride layer of columnar structure are
in a proportion of at least 50 %, preferably 80 to 100%. (d) It is
important that an average crack length in the coated film on the said
ridge of the cutting edge and/or rake face is shorter than an average
coated film thickness on the flank face.
In the above described feature I of the present invention, the grounds for
specifying (a) to (d) and other inventions will now be illustrated:
(a) The reason for choosing titanium nitride as the innermost layer
consists in that not only the titanium nitride is excellent in adhesive
strength to a cemented carbide material, but also is very excellent as a
film quality capable of preventing cracks in the coated film from
penetration to the substrate. The thickness thereof is specified as above,
since if less than 0.1 .mu.m, the effect thereof cannot be expected, while
if more than 3 .mu.m, the wear resistance is lowered. The titanium
carbonitride film above it is preferably coated from the standpoint of
wear resistance and use of a columnar structure with an aspect ratio of at
least 5 results in easy introduction of cracks and formation of a
tenacious film itself. When the aspect ratio is in a range of 10 to 50, in
particular, excellent properties can be expected. The thickness thereof is
specified as described above, since if less than 3 .mu.m, the effect of
improving the wear resistance becomes smaller, while if more than 30
.mu.m, the breakage resistance is markedly lowered. The alumina layer
above it is necessary from the standpoint of suppressing wear on the rake
face when subjecting steels to high speed cutting. If the thickness is
less than 0.5 .mu.m, the effect thereof is smaller, while if more than 10
.mu.m, the breakage resistance is markedly lowered.
(b) When the average crack interval in the coated film on the ridge of the
cutting edge and/or rake face is smaller than an average crack interval in
the coated layer on a flank face while observing the cross-sectional
microstructure of the tool after mirror-polishing by means of an optical
microscope or scanning electron microscope, the breakage resistance during
intermittent cutting is improved and in addition, breaking, falling-off or
peeling phenomena of the films due to excessive introduction of cracks
into coated film on the flank face, on which the wear resistance is
dependent, can be suppressed. This is preferable. In particular, these
effects remarkably appear when a value of Y/X satisfies at least 2,
wherein a narrower average crack interval in the coated film of the ridge
of the cutting edge or rake face on the cross-sectional microstructure is
X and an average crack interval in the coated film on the flank face is Y.
In this specification, the ridge of the cutting edge means a central part
of the ridge of the cutting edge (range of upto a connection part with a
rake face or flank face), the flank face means a central part of the flank
face and the rake face means a position of approaching by 0 to 100 .mu.m
from the connection part of the ridge of the cutting edge with the rake
face to the rake face side (Cf. FIG. 1 and FIG. 2). The above described
observation of the cross-sectional microstructure by the optical
microscope or scanning electron microscope is carried out to estimate an
introduced state of cracks by photographing a designated site of the
coated film by a length of about 50 to 100 .mu.m and utilizing the same.
When the number of the cracks introduced are smaller in the observed
visual field, the visual field is lengthened. The cracks herein referred
mean cracks introduced in the vertical direction to the coated film
surface by a length of at least 1/2 of the film thickness of each coated
layer (Cf. FIG. 3). This is probably due to the fact that when cracks each
having a crack length of at least 1/2 of the thickness of each layer are
introduced, in particular, the film of each layer is rendered tenacious to
imrpove cutting property. In addition, when the average crack intervals in
the coated layers respectively differ, the smallest average crack interval
is acknowledged as the average crack interval of the present invention.
The cracks referred in the present invention include cracks introduced
during grinding or mirror-polishing, which crack leangths or crack
intervals can be measured by the above described measurement method or a
method mentioned in the following Examples.
(c) When, of the cracks in the coated film on the ridge of the cutting edge
and/or rake face, those in which the ends of the cracks, at the substrate
side, exist in the said innermost titanium nitride layer, in the said
titanium carbonitride layer of columnar structure or in an interface
between the said titanium nitride layer and the said titanium carbonitride
layer of columnar structure are in a proportion of at least 50%, the
proportion of cracks penetrated to the substrate is small so that such a
phenomenon can be suppressed that the cemented carbide substrate tends to
break or fracture from the cracks penetrated through the substrate, as a
stress-concentrated source, during intermittent cutting or the cemented
carbide directly below the coated film is broken to peel off the coated
film and lower the wear resistance. In this case, a proportion of at least
80% is particularly preferred. Because of the above described reason, this
specifying includes also a case where the ends of the cracks, at the
substrate side, exist in the interface between the innermost titanium
nitride layer and substrate, and are not penetrated to the substrate.
(d) When the average crack length in the coated film on the said ridge of
the cutting edge and/or rake face is shorter than the average coated
thickness on the flank face, the cracks penetrated from the surface to the
substrate are decreased and breakage of the cemented carbide substrate due
to oxidation of the cemented carbide substrate at the ends of the cracks
penetrated through the substrate during cutting at high speed and increase
of wearing due to peeling of the film can be suppressed. This is
preferred.
Furthermore, when the said innermost titanium nitride layer is further
coated with alumina layer of 3 to 20 .mu.m, further coated with titanium
carbonitride layer of columnar structure with an aspect ratio of at least
5, having a thickness of 3 to 30 .mu.m, and further coated with alumina
layer of 0.5 to 10 .mu.m, a wear resistance can be satisfied both at high
speeds and low speeds. The reason for limiting the thickness of the inner
alumina layer to 3 to 20 .mu.m consists in that if thinner than 3 .mu.m,
its effect is less, while if thicker than 20 .mu.m, the breakage
resistance is largely deteriorated. The reason for limiting the thickness
of the outer alumina layer to 0.5 to 10 .mu.m consists in that if thinner
than 0.5 .mu.m, its effect is less, while if thicker than 10 .mu.m, the
wear resistance is deteriorated.
When the average crack interval in the coated film on the said ridge of the
cutting edge and/or rake face is at most 10 .mu.m, furthermore cutting
stress loaded on the ridge of the cutting edge can be prevented from
concentration on specified crack ends, that is, the stress can be
dispersed, thus improving the breakage resistance, suppressing abnormal
abrasion and improving the wear resistance.
When, of the cracks in the coated film on the ridge of the cutting edge
and/or rake face, those in which the ends of the cracks, at the surface
side, are not penetrated to the surface of the coated film exist in a
proportion of at least 50%, a rapid abrasion-increasing phenomenon due to
deterioration of the film quality, breakage of the film and peeling of the
film, which are caused by a high temperature generated during high speed
cutting and then through oxidation of the coated film, can be suppressed.
During the same time, in particular, when at least 50% of the cracks in the
coated film on the said ridge of the cutting edge exists in only the said
titanium carbonitride layer of columnar structure and are not penetrated
to the upper and lower layers thereof, the cracks are hardly propagated in
parallel to the film surface and hardly integrated with each other even
under such a cutting condition that impacts are repeatedly loaded as in
intermittent cutting and a rapid wear-increasing phenomenon due to
adhesion breakage resulting from chipping of the film and due to peeling
of the film can be suppressed, because grain shape of the titanium
carbonitride layer of columnar structure is columnar.
In the coated cemented carbide having the above described feature I
according to the present invention, the total film thickness of the
coatings is preferably in a range of 3 to 50 .mu.m.
When the surface of the said cemented carbide has a .beta.-free layer
(layer having no other precipitates than WC and a binder metal), cracks
are hard to be propagated and the breakage resistance can further be
improved because of improved toughness on the surface area of the cemented
carbide when the cracks are allowed to progress through the substrate by
cutting stress. Furthermore, when there is a higher hardness area directly
below the .beta.-free layer, than hardness inside the alloy, balance of
the breakage resistance and wear resistance is improved. The .beta.-free
layer can be obtained by sintering a cemented carbide composition powder
containing a nitride and/or carbonitride in a denitrization atmosphere,
e.g. in vacuum. Its thickness is preferably 5 to 50 .mu.m.
According to the second feature II of the present invention, in a coated
cemented carbide cutting tool comprising a substrate consisting of a
matrix of WC and a binder phase of an iron group metal, optionally further
containing a carbonitirde of Ti, Ta, Nb, etc., and a plurality of coated
layers provided on a surface of the substrate, (a) an innermost layer,
adjacent to the substrate, of the coated layers consists essentially of
titanium nitride having a thickness of 0.1 to 3 .mu.m, preferably 0.3 to 1
.mu.m, which is further coated with at least one alumina layer having a
thickness of 0.5 to 10 .mu.m, preferably 1 to 5 .mu.m. Preferably,
titanium carbonitride layer of columnar structure with an aspect ratio of
at least 5, preferably 10 to 50, having a thickness of 3 to 30 .mu.m,
preferably 5 to 15 .mu.m is further coated between the said titanium
nitride and the said alumina. (b) On a mirror-polished cross-sectional
microstructure of the said tool, an average crack interval in the coated
film on the ridge of the cutting edge is rendered smaller than an average
crack interval in the coated layer on a flank face. (c) Of the cracks in
the coated film on the ridge of the cutting edge and/or rake face, those
in which the ends of the cracks, at the substrate side, exist in the said
innermost titanium nitride layer, in a layer above the titanium nitride or
in an interface between these layers are in a proportion of at least 50%,
preferably 80 to 100%. In the case of coating the said titanium
carbonitride layer of columnar structure onto the said innermost titanium
nitride layer, the cracks whose ends exist in the said innermost titanium
nitride layer, in the said titanium carbonitride layer of columnar
structure or in an interface between the said titanium nitride layer and
the said titanium carbonitride layer of columnar structure exist in a
proportion of at least 50%, preferably 80 to 100%. (d) An average crack
length in the coated film on the said ridge of the cutting edge is shorter
than an average coated film thickness on the flank face. (e) It is herein
important that at least one layer of the said alumina layers is removed at
least on a part of the ridge of the cutting edge.
In the third feature III of the present invention, the above described (a)
to (d) are similarly accepted and as (e), it is important that the said
alumina layer is polished at least on a part of the ridge of the cutting
edge.
In the above described features II and III, the grounds for specifying (a)
to (e) and other inventions will now be illustrated.
(a) The reason for choosing titanium nitride as the innermost layer
consists in that not only the titanium nitride is excellent in adhesive
strength to a cemented carbide material, but also is very excellent as a
film quality capable of preventing cracks in the coated film from
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