SE527888C2 - Coated cemented carbide cutter especially intended for turning stainless steel - Google Patents

Description

W U 20 25 30 35 40 527 888 2 chip clamping, can be partially or completely avoided by choosing the right m'crogeometry on the active edge surfaces of the insert, but in many cases this possibility is not sufficient. US. No. 5,786, Ü69 describes a coated turning insert suitable for turning in forged stainless steel components. The insert has a cemented carbide substrate containing 2-10% by weight of cubic carbides of elements belonging to groups IVb, Vb and / or VIb of the periodic table (Y-phase), 5 -11% by weight of cobalt binder phase and the remainder tungsten carbide (WC). The substrate has a binder phase with a high tungsten content and the sintered microstructure exhibits a 15-35 μm deep Co-enriched surface zone free of y-phase. The coating consists of an inner layer of Ti (C, N, O) with columnar grains and an outer layer of fine-grained K-Al2O3. However, with regard to the cemented carbide substrate, the resistance to plastic deformation does not benefit from the combination of a nominally high binder phase content and a thick y-phase depleted surface zone followed by a zone characterized by a high concentration peak of 7-phase. This will result in rapid wear and short life when machining austenitic and duplex stainless steels at high cutting speeds. Increased surface roughness of coatings by mechanical finishing to, for example, reduce the friction between tool and workpiece is shown in EP-A-127416, EP-A-298729, EP-A-693574 and EP-A-683244.

With regard to known technology, there is a need for a insert for machining steel at high speeds in general and stainless steels in particular. This refers in particular to a insert that exhibits increased resistance to abrasive and adhesive wear, plastic deformation, chip hammering and chip pinch damage.

It is an object of the present invention to provide an insert capable of simultaneously resisting all the above-mentioned wear modes.

It is a further object of the present invention to avoid or mitigate problems associated with prior art tool products and to produce high performance tools for high cutting speeds.

It is a further object of the present invention to provide a tool with excellent cutting performance in demanding stainless steel turning operations.

It has surprisingly been found that a cemented carbide insert with a substrate containing comparatively low levels of cobalt and cubic carbides, a thin 1-phase depleted and binder phase-enriched surface zone, in combination with a coating comprising a mechanical finish. 888 3 traded layers of α-Al2O3 meet these requirements. The insert exhibits excellent resistance to plastic deformation, high edge toughness and adhesive wear, especially also a sufficient resistance to __ __ when turning austenitic and duplex stainless steels at high cutting speeds.

Fig. 1 is a scanning electron image (SEM) of the substrate and coating of the present invention wherein: of a cross-section of the surface 7-phase depleted and binder phase-enriched surface zone within the substrate TiN layer, columnar Ti (C, N) layer, Ti (C, N ) -layer,. d-Al2O3 layer. TiCxNy layer.

PIUOUJÃUN More particularly, the invention relates to a WC + Co-based cemented carbide substrate with cubic carbide additives having a 7-phase depleted and binder phase-enriched surface zone, a specific range for WC grain size, a specific composition range for WC + Co, a specific Ti / (Ti + Ta + Nb) ratio and a coating on the cemented carbide substrate comprising an innermost layer system consisting of a thin layer of equiaxial TiCxNyOz followed by a layer of columnar TiCxNyOz and a thin layer of equiaxial TiCxNyOz. This innermost layer system shall contain at least two layers of TiCxNyOz with (x + y + z§l) followed by a layer of column TiCxNyOz, a thin layer of equilateral TiCxNyOz, an Al2O3 layer and an outermost layer of TiCxNy (x + y §L) precipitated. The outermost non-oxide layer is missing in the surfaces of the cutting edge which are in direct contact with material from the workpiece around the cutting edge but also in whole or in part on the chip side.

The composition of the cemented carbide substrate should be 5.0-9.0% by weight of Co, preferably 5.0- <7.0% by weight of Co, and 3.0-8.0% by weight of cubic carbides, preferably 4.0-7 .0% by weight of cubic carbides of the metals Ti, Ta and Nb and possibly other carbides of the elements from group IVb, Vb or VIb of the Periodic Table and the remainder tungsten carbide (WC). The average grain size for WC is 1.5-3.5 μm, preferably 2.0-3.0 μm. The addition of elements forming cubic carbides should be such that the Ti / (Ti + Ta + Nb) ratio is 0.05-0.3, preferably 0.1-0.25. The depth of zone Z should be 5-30 μm, preferably 5-25 μm. Said cubic carbides may contain some amount of N and O and the amount of N should be 0.01-0.2% by weight. The hard and durable refractory coating (Fig. 1) deposited on the cemented carbide substrate according to the present invention comprises: - a first (innermost) layer (A) of TiCXNyO 2 with X + Y + ZS1f preferably y> x and z <0.2, more preferably y> 0.8 and z = 0, with equal-axis grains of size 0.1 μm, preferably 0.1-1.2 μm. a second layer (s) or Ticxuyoz with x + y + z _ <_ 1, preferably with z = 0, x> 0.3 and y> 0.3, preferably x> 0.5, with a thickness of 1.0 -5.0 μm, preferably 2.0-4.5 μm with columnar grains. a third layer (c) possibly TicxNyoz with x + y + z51, preferably y> x and z <0.2, more preferably y> 0, 8 and z = 0, with equal-axis grains with a size of 0.1 μm, preferably 0 , 2-0.8 pm. the total thickness of the layers A + B + C is 1.5-6.5 μm, preferably 2.0-5.5 μm. Preferably, each of the layers A and C should be thinner than the layer B. - a d-Al 2 O 3 layer with a total thickness of 1.5-5.0 μm, preferably 1, 5-4.0 μm. an outermost layer system (E) consisting of TiCxNy (x + y§l), either as a homogeneous layer or in the form of a TiN + TiC sequence.

The total thickness is <2.0 μm but> 0.1 μm, preferably 0.5-1.5 μm. the total thickness of the layers A + B + C + D + E is 3.0-11.0 μm, preferably 4.5-9.5 μm.

The outermost layer of the coating is missing in the surface corresponding to the chip contact on the chip side. The surface considered is preferably the cutting edge and the surface corresponding to the primary phase on the chip side when a primary phase is present in the geometry. In addition, the outermost layer is also completely or partially missing on the chip side.

Coated inserts according to the present invention comprising preferably a cemented carbide substrate are manufactured in such a way that a zone near the surface depleted of cubic carbide and enriched in binder phase is achieved after an addition of a low amount of nitrogen and sintering in vacuum before coating. The composition of the cemented carbide substrate comprises 5.0-9.0% by weight of Co, 3.0-8.0% by weight of cubic carbides and the remainder is tungsten carbide (WC). The average grain size for WC is in the range 1.5-3.5 μm. The addition of elements forming cubic carbides should be such that the Ti / (Ti + Ta + Nb) ratio is 0.05-0.3, preferably 0.1-0.25. The depth of zone Z should be 5-30 μm, preferably 5-25 μm. Said cubic carbides may contain any amount of N and O and the amount of N should be 0.01-0.2% by weight. These microstructural constituents can be termed, for example, carbonitride from + s11a mainly ~ -...__ 4 __ 'I11. * A Q w Am or oxycarbonitride. The hard metal body by mixing powder, grinding, spray drying, any pressing method followed by sintering according to conventional methods and pretreatment such as egg radiating and pre-coating cleaning.

The body is then coated with - a first (innermost) layer of TiCxNyO total thickness <1.5 μm but> 0.1 μm preferably 0.1-1.2 μm using known chemical vapor deposition, CVD, methods. a second layer of TiCxNyOz (B) with x + y + z§l, preferably with z = 0, x> 0.3 and y> 0.3, more preferably x> 0.5, with a thickness of 1.0 -5.0 μm, preferably 2.0-4.5 μm with columnar grains preferably using moderate temperature CVD, MTCVD, technology (using acetonitrile as carbon and nitrogen source to form the layer in the temperature range 700-900 ° C). The exact conditions depend to some extent on the design of the equipment used. a third layer of TiCxNyOZ (C) with x + y + zíl, preferably y> x and z <0.2, more preferably y> 0, 8 and z = 0, with equal-axis grains with size <0.5 μm and a total thickness <1.5 μm but> 0.1 μm using known CVD methods. This layer (C) is omitted in a second embodiment. the total thickness of the layers A + B + C is 1.5-6.5 μm, preferably 2.0-5.5 μm. Preferably, each of the layers A and C should be thinner than the layer B. - an α-Al 2 O 3 layer (D) with a total thickness of 1.5-5.0 μm, preferably 1.5-4.0 μm. - preferably an outermost layer system (E) consisting of TiCxNy (x + y§l), either as a homogeneous layer or in the form of a TiN + TiC sequence. The total thickness is <2.0 μm. the total thickness of the layers A + B + C + D + E is 3.0-11.0 μm.

The coating is mechanically post-treated to expose a- with x + y + z§l, Al2O3 layers along the cutting edge with a brushing, blasting, grinding operation or combinations thereof so that the surfaces on the chip side with chip and workpiece contact have been treated .

According to the preferred method, blasting with Al2O3 grains is used with conditions and cutting placement so that the blasting is done mainly on the chip side. The removal of the outermost layer (E) on the cutting edge will expose the α-Al 2 O 3 layer especially on the tension side of the cutting edge and in whole or in part on the tension side.

Examples The following inserts and examples are selected to exemplify the advantages of the invention.

The presented inserts have been tested under identical conditions in each example.

Insert A. Carbide rotary insert according to the invention with 6.0 wt% Co, 1.0 wt% Ti, 0.4 wt% Nb, 3.3 wt% Ta (Ti / (Ti + Ta + Nb) = 0.21), 0.05 wt% N and residual WC and with an average grain size of 2.8 μm and with a binder phase-enriched and cubic carbide depleted surface zone with a depth of 15 μm were coated with 0.5 μm TiN (innermost layer), 3.7 μm columnar Ti (C, N), and 0.4 μm equilateral Ti (C, N), 2.2 μm α-Al 2 O 3 layer and an outer 0.8 μm layer of sequential TiN-TiC.

The coating was blasted with Al 2 O 3 grains on the chip side, especially along the cutting edge.

Inserts B. Carbide rotary inserts according to the invention with 6.0 wt% Co, 1.0 wt% Ti, 0.4 wt% Nb, 3.3 wt% Ta (Ti / (Ti + Ta + Nb) = 0.21), 0.05 wt% N and residual WC and with an average grain size of 2.3 μm and with a binder phase-enriched and cubic carbide depleted surface zone with a depth of 15 μm were coated with 0.5 μm TiN (innermost layer), 3.7 μm column Ti (C, N) and 0.4 μm equiaxed TiN, 2.2 μm α-Al 2 O 3 layer and an outer sequential layer of 0.8 μm TiN - TiC.

The coating was blasted with Al2O3 grains on the chip side, especially along the cutting edge.

Inserts C. Commercial cemented carbide rotary inserts with a substrate composition of 6.2 wt% Co, 2.3 wt% Ti, 2.0 wt% Nb, 0.1 wt% Ta (Ti / (Ti + Ta + Nb) = 0 , 52), 0.14 wt% N and residual WC. The average WC grain size is 2.7 μm and the substrate also has a binder phase-enriched and y-phase depleted zone down to a depth of 26 μm from the surface. The coating consists of a 0.1 μm TiN inner layer, 4.0 μm column Ti (C, N), 0.3 μm uniaxial TiN, 1.9 μm K-Al 2 O 3 and an outer layer of 0.3 μm TiN.

Inserts D. Commercial cemented carbide rotary inserts with a substrate composition of 6.0 wt% Co, 2.1 wt% Ti, 0.4 wt% Nb, 3.3 wt% Ta (Ti / (Ti + Ta + Nb) = 0 , 36), 0.09 wt% N and residual WC. The average WC grain size is 2.4 μm and the substrate also has a binder-phased and y-phase depleted zone down to a depth of 13 μm from the surface. The coating consists of a 0.5 μm TiN inner layer, 3.0 μm co-luminous Ti (C, N), 0.3 μm uniaxial TiN, 1.7 μm K-Al 2 O 3 and an outer layer of 0.3 μm TiN.

Inserts E. Commercial cemented carbide rotary inserts with a steel composition of 7.5 wt% Co, 2.72 wt% Ta, 0.44 wt% Nb, 1:33 wt% Ti (Ti / (Ti + Ta + Nb) = 0 , 37), 0.09 wt% N and residual WC and with an average grain size of 2,0 μm and with a binder phase-enriched and Cubic carbide depleted surface zone down to a depth of 26 μm coated with 0.5 μm TiN (inner layer ), 7.5 μm column Ti (C, N), 1.2 μm a + K-Al 2 O 3 and an outer layer of 1.0 μm TiN.

The coating was post-treated along the edge line resulting in the removal of the outermost coating mainly along the release surface.

Inserts F. Commercial cemented carbide rotary inserts with a substrate composition of 7.9 wt% Co, 0.7 wt% Ta, 0.6 wt% Nb, 0.2 wt% Ti, (Ti / (Ti + Ta + Nb) = 0, 13) and erected WC and with an average grain size of 1.5 μm and without binder phase-enriched and on cubic carbide depleted surface zone coated with 0.2 μm TiN (inner layer), 2.0 μm column Ti (C, N), 0, 7 μm TiN, 1.2 μm α-Al 2 O 3 and an outer layer of 0.2 μm HfN.

Example 1 Inserts from A, B and E were tested in a turning operation.

Operation: External longitudinal turning and leveling of bar Working material: Austenitic stainless steel, AISI304L Cutting speed: 290 m / min Feed rate: 0.2 mm / revolution Cutting depth: 2 mm Cutting type: CNMG120408-MM Result: Service life Cutting A: (invention) 17 min Cutting B: (invention) 17 min Insert E: (prior art) 8 min Comment: Lifetime criterion was maximum phase wear 0.3 mm of the edge line. Wear develops irregularly due to local plastic deformation. This example shows improvement in plastic deformation resistance for the inserts according to the invention. N H 20 25 30 35 40 527 888 Example 2 Cuts from B and D were tested in a turning operation.

Operation: Combined longitudinal turning and planing of small bar Working material: Austenitic stainless steel, AISI304L Cutting speed: 250 m / min Feed rate: 0.4 mm / revolution Cutting depth: 2 mm Cutting type: CNMG 120408-MM Result: Service life Cutting B: (invention) 6 min Insert D: (prior art) 4 min Comment: Lifetime criterion was maximum phase wear 0.3 mm of the edge line. Wear develops irregularly due to local plastic deformation. This example shows the improvement in plastic deformation resistance of the insert according to the invention.

Example 3 Inserts from A, B and E were tested in a turning operation.

Operation: Longitudinal turning and planing against the shoulder Working material: Austenitic stainless steel, AISI304L Cutting speed: 250 m / min Feed rate: 0.4 mm / revolution Cutting depth: 2 mm Cutting styles: CNMG 120408-MM Result: Edge damage Cutting A: (invention) 0, 8 mm / min Insert B: (invention) 0.6 mm / min Insert E: (prior art) 1.2 mm / min Comment: The test is set to cause damage to the edge outside the direct contact surface between tool and workpiece, normally designated chip hammering and chip clamping. Resistance to such damage is directly related to edge toughness. The inserts according to the invention show improvements in these respects.

W 20 25 30 35 40 527 888 vnß An Example 4 Cuts from A and C were tested in a turning operation.

Operation: Planing to the center Working material: Austenitic stainless steel, AISI304L Cutting speed: 180 m / min Feed rate: 0.30 -> 0.15 mm / revolution Cutting depth: 1 mm Cutting type: CNMG 120408-M Result: Service life Cutting A: (invention) 5 min Insert C: (prior art) 3 min Comment: This is an operation that requires edge toughness and the test shows clear improvement for the insert according to the invention compared to inserts according to prior art. However, it is difficult to identify a simple critical wear in this example, but it can be described as a combination of wear due to chipping, flaking of the coating on the chip side and adhesive wear.

Example 5 Inserts from B and E were tested in a turning operation.

Operation: Shaft profiling Working material: Austenitic stainless steel, AISI316L Cutting speed: 200 m / min Feed rate: 0.25 mm / rev Cutting depth: 3 mm Cutting type: TNMG 160408-MM Result: Service life Cutting B: (invention) 15 pcs Cutting E: (prior art) 9 pcs Comment: This test shows improvement of edge toughness and resistance to adhesive wear for the insert according to the invention compared to inserts according to prior art. Edge chipping and beam wear occur earlier for the insert according to known technology.

Example 6 Inserts from B, E and F were tested in a turning operation.

Operation: Planing of a shaft Working material: Austenitic stainless steel, AISI304L Cutting speed: 180 m / min Feed rate: 0.30 -> 15 mm / revolution Cutting depth: 1 mm Cutting type: CNMG 120408-MM Result: Service life Cutting B: (invention) 4 , 5 min Insert E: (prior art) 2.5 min Insert F: (prior art) 1.8 min Comment: This example shows that the insert according to the invention has increased edge toughness. In this example, it is difficult to identify any simple critical wear, but it can be described as a combination of wear due to adhesive wear, chipping and flaking of coating on the chip side.

Example 7 Inserts from B and E were tested in a turning operation.

Operation: Combined longitudinal turning and planing of a thin rod Working material: Austenitic stainless steel, AISI 304L Cutting speed: 250 m / min Feed rate: 0.4 mm / revolution Cutting depth: 2 mm Cutting type: CNMG 120408-MM Result: Service life Cutting B: (invention) 8 min Cutting E: (prior art) 4 min Comment: The main wear mechanisms are plastic deformation and adhesive wear. This example shows an improvement in resistance regarding both of these mechanisms for the insert according to the invention compared with inserts according to the prior art. 10 20 25 t fi BJ \ J ïv I »än ll Example 8 Cuts from B and E were tested in a turning operation.

Operation: Continuous turning and profiling of forged bar Working material: Austenitic stainless steel, SS2324 Cutting speed: 180 m / min Feed rate: 0.35 mm / revolution Cutting depth: 1 mm Cutting type: TNMG 16o4o8-MM Result: Service life Cutting B: (invention) 53 Cut E: (prior art) 39 pcs Comment: The critical wear criteria are chipping, flaking of the coating and loose edge formation. The insert according to the invention shows improved resistance to these types of wear compared with inserts according to known technology. The profiling operation requires edge toughness, a requirement that the insert according to the invention can withstand in a better way than the insert according to the prior art.

In summary, it can be clearly stated from the results of the examples above that by combining a cemented carbide substrate with the given composition, an α-alumina layer and the special finishing of cutting edge and chip side, it has been possible to create an insert with excellent cutting performance by combining much of what were thought to be contradictory characteristics and which were described initially.

Claims (2)

l0 20 25 30 35 40 527 888 12 Requirements A coated cemented carbide insert specially designed for turning stainless steel characterized by - a cemented carbide substrate having a composition comprising 5.0-9.0% by weight of Co, 3.0-8.0% by weight of cubic carbides of the metals Ti , Ta and Nb and possibly other carbides of the elements from group Ivb, Vb or VIb of the periodic table, addition of elements forming cubic carbide so that the Ti / (Ti + Ta + Nb) ratio is 0.1- 0.25, 0.01-0.2% by weight N and the remainder tungsten carbide, WC, with a grain size of 1.5-3.5 μm in sintered state and with a y-phase depleted and binder phase-enriched surface zone having a depth of 5-30 μm, and 4.5-9.5 μm thick coating consisting of a first, layer system consisting of - a first, innermost layer, A, of TiCxNyOz with x + y + z§l, for- with equal-axis grains innermost retrievably y> x and z <0.2, preferably y> 0.8 and z = 0, with size <0.5 μm and a total thickness <1.5 μm but> 0.1 μm, preferably 0 , ll, 2 pm, - a second layer, B, of TiCxNyOz with x + y + z§l, preferably with z = 0, x> 0.3 and y> 0.3, preferably x> 0.5, with a thickness of 2.0-4.5 μm with columnar grains, - a third layer, C, of TiCxNyOZ with x + y + z§l, y> x and z <0.2, preferably y> 0.8 and z = 0, with uniaxial grains with size <0.5 μm and a total thickness <1.5 μm but> 0.1 pm, 0.2-0.8 μm, the total thickness of the layers A + B + C being 2.0-5.5 μm, an α-Al 2 O 3 layer, D, with a total thickness of 1.5 -4.0 μm directly on top of the innermost layer system and - an outermost layer system, E, consisting of TiCxNy, x + y§l, either as a homogeneous layer or in the form of a TiN + TiC sequence preferably with a total thickness of 0.5-1.5 μm, whereby the outermost layer system has been removed in the surface by mechanical finishing corresponding to chip contact on the chip side. Insert according to Claim 1, characterized in that the cemented carbide substrate has a composition comprising 5.0- <7.0% by weight of Co, 4.0-7.0% by weight of cubic carbides of the metals Ti, Ta and Nb. and Vb or VIb of the Periodic Table, tungsten carbide (WC) with a grain- possibly other carbides of the elements of group IVb, size of 2.0-3.0 μm in sintered state and with a 7-phase depleted and binder phase enriched surface zone with a depth of 5-25 pm.