Coated cutting insert

(54) NAME Coated carbide inserts for cast iron milling (56) PUBLICATIONS QUOTED:

SE C2 501 527 (C23C 16/40), SE B 379 559 (C23C 11/08), EP Al 408 535 C23C 16/30), EP Al 440 157 (C23C 16/36), EP Al 594 875 (C23C 30 / 00) (57) SUMMARY:

The present invention relates to a cast iron milling cutter comprising a substrate and a coating. The substrate consists of WC having a grain size of 1-2 µm and 5-8 wt% Co. The coating includes

- a first, innermost layer of TiC_xNYO_z, with z <0.5 and x + y + z = 1, a thickness of 0.1-2 µm and equal-sized grains of size <0.5 µm

- a layer of TiC_xNew with x> 0.3 and y> 0.3 as well as x + y = 1, a thickness of 4-7 µm and columnar grains with a diameter of about <5 µm

- a layer of TiC_xNYO_z with 0.1 <z <0.5 and x + y + z = 1, a thickness of 0.1-2 µm, and axial or needle-shaped grains of size SO.5 µm and

a smooth and fine grained layer of C1-AI2O3 having a thickness of 3-6 µm and a texture in the (012) direction with a texture coefficient TC (012) greater than 1.3.

<img file="SE514181C2_D0001.tif" />

The numbers in brackets indicate international identification code, INID code. Letters in clamps indicate international document code.

514 181

The present invention discloses a coated cutting tool (cemented carbide insert) particularly useful for dry casting in gray cast iron.

Gray cast iron is a material that is usually fairly easy to work with cemented carbide tools and often long tool life can be obtained. However, the castability of cast iron can vary considerably. The life of the tool can be greatly affected by small differences in chemical composition within the material, which may be a consequence of the casting technique used? such as the cooling conditions. Other causes of life-long differences are cast skin and possible sand inclusions or even the stability of the machine used to process the material by some kind of chip separation method. It is a well-known fact that the castability of a cast iron can vary between different manufacturing occasions.

There is always a desire for a reliable and stable tool life in the mass-producing industry and especially in unmanned production.

When cutting machining in gray cast iron with coated cutters, the cutters are mainly worn by a so-called adhesive wear mechanism. This means that fragments or individual grains in the layers, and later also parts of the cemented carbide, are pulled away from the cutting edge of the formed chip from the workpiece. Such a wear mechanism is further enhanced by the formation of cracks at about 50 µm intervals along and perpendicular to the cutting edge commonly referred to as comb cracks. They are the result of thermal fatigue caused by the intermittent cutting operation that is typical of all milling operations. Therefore, commercially available carbide cutters usually contain gamma-phase, which is a solid solution of WC-TiC-TaCNbC, to reduce heat-affected wear mechanism.

As soon as the layer is worn away, the underlying cemented carbide will wear out quickly. This will result in higher cutting forces. The formed cracks will, after some time, cause severe chipping from the cutting edge and the damaged tool will create a poor surface or tearing from the machined part.

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Chip forming operations in which adhesive wear is dominant place high demands on both the layer and the cemented carbide. A cemented carbide that can withstand the formation of comb cracks for as long as possible and a layer that is firmly attached to the cemented carbide is desirable. In addition, it is desired that there be low adhesion forces between the chip and the layer and that the layer has a high internal strength (cohesion), a property which is considered to be of great importance.

Surprisingly, it has been found that a pure WC-Co type cemented carbide body, herein referred to as the substrate, is substantially provided with a first / inner layer having a structure of columnar grains consisting essentially of a TiC_xNYO_z-layer with columnar grains and on top of this a columnar-like, textured, layer of fine-grained CI-AI2O3 gives good performance especially when casting in cast iron. In fact, such a tool has proven to outperform those that characterize today's tool.

Fig. 1 is an image in 5000x magnification of a coated insert according to the present invention in which

A - substrate

B - TiC_xNYO_z-layer with even-grained grains

C - TiC_xNew layer with columnar grains

D - TiC_xNYO_z-layer with equal or needle-like grains

E - (012) textured layer of α-Al2C&gt; 3 with column-like grains

According to the present invention, a cutting machining insert is provided with a cemented carbide substrate having WC + Co composition containing 5-8% by weight Co and having a WC grain size of 1-2 microns.

The coating includes

- a first (innermost) layer of TiC_xNYO_z with x + y + z = 1, and z &lt;0.5, with a thickness of 0.1-2 µm, and with equal-sized grains of size &lt;0.5 µm

- a layer of TiC_xNew with x + y = 1, and x&gt; 0.3 and y&gt; 0.3, with a thickness of 4-7 µm, with columnar grains and with a diameter of about &lt;5 µm

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- a layer of TiC_xNYO_z with x + y + z = 1 with 0.1 &lt;z &lt;0.5 with a thickness of 0.1-2 µm and with axial or needle-shaped grains of size &lt;0.5 µm

- an outer layer of a beaten, textured, fine-grained layer of (X-AI2O3 with a thickness of 3-6 gm.

In addition, the layer of α-Al2O₃ a preferred orientation for the crystal growth (012) direction, which is determined by X-ray diffraction (XRD). A texture coefficient, TC, is defined as:

TC (hkT) =

I (hkT) (1 y I₀(HLD) {n^L IN₀{hW&gt;) bad

I (hkl) = measured intensity of the (hkl) reflex

Io (hkl) = standard intensity from ASTM's diffraction data for standard powder n = number of reflexes used in the calculations in which the (hkl) reflections used are: (012), (104), (110), (113), (024) and ( 116)

According to the invention, the TC of the crystal plane group (012) is greater than 1.3

According to the method of the invention, a WC-Co based substrate is coated with

- a first, innermost layer of TiC_xNYO_z with x + y + z = 1, and z &lt;0.5, with a thickness of 0.1-2 µm, and with equal axes of size &lt;0.5 µm using known CVD methods.

- a layer of TiC_xNew, x + y = 1, x&gt; 0.3 and y&gt; 0.3, with a thickness of 4-7 µm, with columnar grains and with a diameter of about &lt;5 µm, coated either with MTCVD technology (using acetonitrile as carbon black). and nitrogen source to form the layer in the temperature range 700-900 ° C) or with CVD technology at high temperature (1000-1100 ° C), the process conditions being selected so that layers grow with columnar grains, i.e., usually high process pressure (0.3-1 bar ). However, the exact conditions depend to a certain extent on the design of the equipment used.

- a layer of TiC_xNYO_z, x + y + z = 1 with 0.l &lt;z &lt;Ö.5 with a thickness of 0.1-2 µm and with axial or needle-shaped grains of size &lt;0.5 µm, using known CVD methods.

an outer layer of a smooth, textured layer of CI-AI 2 O 3 with a thickness of 3-6 µm.

When a TiC_xNYO_zlayers of z&gt; 0 are desired, CO2 and / or CO are added to the reaction gas mixture.

514 181 Η

A) Carbide cutters of types TNEF1204AN-65 and SEKN1204AZ with the composition 6% Co and the remainder WC are coated with a 0.5 µm equilateral TiCN layer followed by a 5 µm thick TiCN layer with columnar grains using MTCVD technology (process temperature 850 ° C). In subsequent process steps during the same coating cycle, a 1 µm thick layer of equal-sized grains of TiC is coated._xNYO_z (about x = 0.6, y = 0.2, and z = 0.2) followed by a 4 µm thick layer of (012)-textured CI-AI2O3 coated according to conditions described in Swedish Patent 501,527. XRD measurements showed a texture coefficient TC (012) of 1.5. After coating, the inserts were smoothed by wet blasting.

B) TNEF1204AN-65 cemented carbide milling cutters are coated with a 1 µm thick layer of equal-sized TiCN granules followed by a µm-thick layer of columnar TiCN with CVD technology at high temperature (1020 ° C, process pressure 400 mbar). In subsequent process steps during the same coating cycle, coating was carried out with a 1 µm thick layer of equilibrium TiC grains._xNYO_z (about x = 0.6, y = 0.2 and z = 0.2) followed by a 4 µm thick layer of (012)-textured α-Αΐ2 &lt;03 coated according to conditions described in Swedish Patent 501,527. XRD measurements showed a texture coefficient TC (012) of 1.6. After coating, the inserts were smoothed by wet blasting.

C) TNEF1204AN-65 cemented carbide cutters with the composition 5.5% Co and 8.5% cubic carbides and the rest WC is coated in the manner described in A). After coating, the notches were smoothed by wet blasting.

D) Milling inserts from the same cemented carbide production as in C) are coated with approximately 5 µm TiCN layer and 4 µm Al 2 O 3 were made according to prior art which resulted in a mixture of coarse α and fine K-Al The inserts were smoothed by wet blasting.

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Example 2

Scores from A) were tested against two types of competitors as follows:

Operation: Floor milling with SANDVIK AUTO cutter, dia: 250 mm 5 Workpiece: Specially designed component.

Material: SS0125 (gray cast iron HB = 205)

Cutting speed: 129 m / min Feed rate: 0.24 mm / tooth Cutting depth: 2.0 mm

Slit type: TNEF1204AN-65

Note: The operation was performed without coolant (dry).

RESULTS:

Sort A (according to the invention) Competitor 1 (prior art)

Competitor 2 (Master of Engineering)

Lifetime, min 40 20 25

Lifetime criterion was chipping on the workpiece output side.

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Exampel_3.

Cuts from A) were tested in another milling operation against two types of competitors as follows:

Operation: Floor milling with SANDVIK 145 cutter, dia: 63 mm

Workpiece: Component for hydraulic motor.

Material: SS0125 (gray cast iron HB = 220)

Cutting speed: 178 m / min

Feed rate: 0.17 mm / tooth Cut up: 2-3 mm Cut type: SEKN1204AZ

Note: The operation was performed without coolant (dry).

RESULTS: Lifespan, hours

Sort A (according to the invention) 24

Competitor 3 (Prior Art) 15

Competitor 4 (Prior Art) 16

Lifetime criterion was surface finesse.

Example 4

Cuts from A), C) and D) were tested against each other in a milling operation.

Operation: Floor milling with SANDVIK AUTO cutter, dia: 250 mm Workpiece: Engine block

Material: SS0125 (GG26Cr) gray cast iron Cutting speed: 120 m / min Feed rate: 0.28 mm / tooth Cutting depth: 4-5 mm Cutting type: TNEF1204AN-65

Note: The operation was performed without coolant (dry).

All of the inserts were tested during 868 passes and compared with respect to egg bursts.

Result: Variation Degree of eggshell rupture

A (according to the invention)

C (improved layer only) D (prior art)

No

Less

Substantial

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The results show the advantage of the coating according to the invention as well as combining this with the WC / Co type cemented carbide substrate to obtain maximum service life.

Example 5

Slits from A), B) and D) were tested against each other in a milling operation.

Operation: Floor milling with SANDVIK AUTO cutter, diameter

250 mm

Workpiece: Specially designed test component Material: SS0125 gray cast iron, HB = 205 Cutting speed: 129 m / min

Feed rate: 0.30 mm / tooth Cut up: 2 mm Cutting type: TNEF1204AN-65

Note: The operation was performed without coolant (dry).

All inserts were tested during 48 passes and compared with respect to ovoid bursts.

Result: Variant Relative width of chipped surface

A (according to the invention) B (according to the invention) D (prior art)

0.3

0.4

1.0

The results are in practice the same for A) and B). The only difference is the coating temperature when coating the TiCN layers. The notches according to known technology show the greatest wear.

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