Coated cemented carbide cutting tool insert

SWEDEN (12) PATENT WRITING (13) C2 (11) 520 253

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(19) SE (51)

International class ⁷

C23C 30/00, 16/30, B23B 27/14

PATENT AND REGISTRATION (45) (41) (22) (24) (62) (86) (86) (83)

Patent issued 2003-06-17

Application widely available 2002-06-20 The patent application was received on 12/12/ 2000

Running day 2000-12-19

Tribal application number

International filing day

Filing date for European patent application

Deposit of microorganism (21) Patent Application Number 0004695 * 3

Application received as:

Swedish patent application completed international patent application with number □ converted European patent application with number (30) Priority information (74) OMBUD (54) NAME (73) PATENTHAVARE Sandvik AB, 811 81 Sandviken SE (72) INVENTOR Gunilla Andersson, Solna SE, Mikael Lindholm SE Sandvik AB

Coated cemented carbide inserts (56) PUBLICATIONS ABOUT:

WO Al 97/15411 (B22F 3/10), EP A2 1,043,415 (C22C 29/08),

EP A2 1,043,416 (C22C 29/08), US A 5,451,469 (428/548) (57) SUMMARY:

According to the present invention there is a coated cutting insert consisting of a cemented carbide substrate and a thin abrasion resistant coating, the substrate comprising WC having a grain size of 0.5-4.0 μιη, preferably 1-2 μιη, 5-15% by weight Co, 1-10 wt% cubic carbides such as TiC, TaC and NbC, with a &lt;70 μτη. thick binder phase enriched surface zone substantially free of gamma phase. Further, the substrate contains 0.5-3 wt.% Mo with the surface zone having one. Moisture content of 0.9-1.1 of that in the interior of the substrate and the WC grains has a duplex structure consisting of a core and a surrounding border containing Mo.

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

520 253

Summary

According to the present invention, there is a coated insert consisting of a cemented carbide substrate and a thin abrasion resistant coating, the substrate comprising WC having a grain size of

0.5-4.0 µm, preferably 1-2 µm, 5-15 wt% Co, 1-10 wt% cubic carbides such as TiC, TaC and NbC, with a &lt;70 µm thick binder phase enriched surface zone substantially free of gamma phase . Further, the substrate contains 0.5-3 wt.% Mo, the surface zone having a Mo content of 0.9-1.1 of that in the interior of the substrate and the WC grains having a duplex structure consisting of a core and a surrounding border containing Mo .

520 253

The present invention relates to a coated cemented carbide insert. The cemented carbide is based on WC, cubic carbides and has a Cobinde phase enriched surface zone. By alloying the cemented carbide with Mo, performance has been particularly improved when used for turning under conditions causing periodic thermal and mechanical stress in stainless steel.

High-performance cutting tools must now have high wear resistance, good toughness properties and good resistance to plastic deformation. Improved resistance to plastic deformation of a cutter can be obtained by reducing the WC grain size or reducing the total binder phase content, but such changes simultaneously result in significant loss of toughness properties.

Methods to improve toughness behavior without loss in plastic deformation by so-called gradient sintering techniques are known. The gradient consists of thick binder phase enriched surface zones (&lt;50 µm) substantially free of cubic carbide in the cemented carbide, for example, through US 4,277,283, US 4,610,931, US 4,830,930, US 5,106,674 and US 5,649,279. Such inserts with binder phase enriched surface zones substantially free of cubic carbide are commonly used today for machining steel and stainless steel. These patents are examples of the importance of the substrate composition within the surface area for cutting performance. The cutting properties such as resistance to plastic deformation and toughness behavior must be balanced for optimum performance during machining to ensure long and stable service life.

Also, there are ways to balance the plastic deformation resistance and toughness properties to some extent by controlling the composition of the surface zone using special sintering techniques or alloying elements, e.g., US 5,484,468, US 5,549,980, US 5,729,823, EP-A-560 212 or EP-A-569 696th

Characteristic of all the above patents is that the surface zones are substantially free of cubic carbide and binder phase enriched, ie they consist of WC and Co. Such surface zones give the insert good egg toughness but make the insert less adequate under conditions causing thermal and mechanical loading of the insert.

It is therefore an object of the present invention to provide a cemented carbide insert with improved turning properties when temperature and mechanical load vary without losing resistance to plastic deformation and egg toughness.

520 253

It has now been found that by the addition of Mo to cemented carbide inserts with binder phase enriched surface zones, unforeseen improvements in turning under periodic thermal and mechanical conditions have been obtained.

Fig. 1 shows the distribution of Ti, Ta, Co, C and Mo in the surface zone of a cemented carbide insert according to the invention.

Figure 2 shows the distribution of Ti, Ta, Co, C and (Mo) in the surface zone of a cemented carbide insert according to the prior art.

Fig. 3 shows the microstructure of a cemented carbide insert according to the present invention there

A - W core also

B - W + Mo border.

According to the present invention there is now a cemented carbide having a &lt;70 µm, preferably 10-40 µm, thick binder phase enriched surface zone containing W and Mo but depleted of cubic carbide. The content of Mo in the surface zone is 0.9-1.1 of that in the interior of the cemented carbide.

The present invention can be applied to cemented carbides having a composition of 5-15, preferably 7-11, wt% bonding phase comprising mainly Co (Fe and Ni only at the contaminant level), a total amount of 1-10, preferably 4-7, weight. % cubic carbides such as TiC, TaC, NbC and residual WC. In addition, the cemented carbide contains 0.5-3 wt%, preferably 1-2 wt% Mo. The average WC grain size is 0.5-4.0 µm, preferably 1-2 µm. The tungsten carbide grains have a duplex structure consisting of a core and a surrounding border. The Mo content of the border varies between about 2 and 25% by weight, with the highest amount near the core.

The cobalt binding phase is highly alloyed with W. The content of W in the binding phase can be expressed as

CW ratio = M_s / (wt% Co · 0.0161) where M_s is measured saturation magnetization for the cemented carbide and weight% Co is the weight percent Co in the cemented carbide. The CW value is a function of the W content in the Co-binding phase. A low CW value corresponds to a high W content in the binding phase.

According to the invention, improved cutting performance is obtained if the cemented carbide body has a CW ratio of 0.72-0.94, preferably 0.76-0.90, The cemented carbide body may contain a small amount, &lt;5% by volume, of etaphase (MgC), without any harmful effect.

The cemented carbide inserts are prepared by powder metallurgical methods comprising painting a powder mixture which forms hard constituents and binder phase comprising a small amount of N, drying,

520 253 pressing and sintering under vacuum to obtain the desired binder phase enrichment. Mo is added as M02C.

Carbide inserts according to the invention are preferably coated with a thin durable coating with CVD, MTCVD or PVD technology. Preferably, the coating consists of &lt;1 µm TiN, 1-5 µm MTCVD-TiCN, 1-3 µm k-alumina and &lt;1 µm TiN.

Example 1

A.) CNMG 120408-MM tungsten carbide inserts, a turning machine, with the composition 7.5 wt% Co, 3.8 wt% TaC, 1.9 wt% TiC, 0.4 wt% TiN, 0.4 wt% M0 2 C and residual WC having a mean grain size of 1.7 µm and a CW ratio of 0.86 were prepared by powder metallurgical methods. The powder metallurgical methods include painting a powder mixture which forms hard constituents and binder phase, pressing and sintering. The pressed bodies were sintered at 1450 ° C by standard procedure. The sintered blanks were given a cubic carbide-free zone extending approximately 25 µm into the substrate from the surface, Fig. 1. The tungsten carbide phase of the fabricated cutter had a duplex structure consisting of a core and a surrounding border; Fig. 3. The content of Mo in the bore ranges between about 2 and 25% by weight, with the highest amount near the core. After conventional pre-coating treatment such as edge grinding, cleaning, etc., the inserts are coated in a CVD process which provided 0.4 µm TiN, 2 µm MTCVD-TiCN, 2 µm κ-alumina and 0.8 µm TiN.

B.) CNMG 120408-MM tungsten carbide inserts having the composition 7.5 wt% Co, 3.8 wt% TaC, 1.9 wt% TiC and 0.4 wt% TiN and the remainder WC having an average grain size of 1.7 µm and a CW ratio of 0.87 was prepared. The inserts were sintered, pretreated and coated to provide the same physical properties as A. The sintered blanks obtained a cubic carbide free zone extending approximately 25 µm into the substrate from the surface. The tungsten carbide phase of the produced insert had no core-borne structure.

C.) CNMG 120408-MM tungsten carbide inserts, a turning machine, having the composition 9.9 wt% Co, 3.0 wt% TaC, 2.5 wt% TiC, 0.3 wt% TiN, 0.4 wt% M0 2 C and residual WC having a mean grain size of 1.7 µm and a CW ratio of 0.78 were prepared by powder metallurgical methods. The powder metallurgical methods include painting a powder mixture which forms hard constituents and binder phase, pressing and sintering. The pressed bodies were sintered at 1450 ° C by standard procedure. The sintered substances obtained a zone free of cubic carbide extending

520 253 approximately 20 μτη into the substrate from the surface. Metallographic examination showed that the hard component of the cutter produced consisted of duplex structures of a core and a surrounding border. After conventional pre-coating treatment such as edge grinding, cleaning, etc., the inserts in a CVD process received a 4 μπι MTCVD-TiCN, 1.5 μπι κ-alumina, 0.5 μπι TiN coating. TiN was subsequently removed on the edge lines by brushing.

D.) CNMG 120408-MM tungsten carbide inserts having the composition 10.0 wt% Co, 6.0 wt% TaC, 2.6 wt% TiC and 0.4 wt% TiN, and the remainder WC having an average grain size of 2.0 nm and a CW ratio of 0.81 was prepared. The inserts were subjected to the same sintering, pre-coating, coating and edge-line brushing as C. The sintered blanks obtained a cubic carbide-free zone extending approximately 20 μπι into the substrate from the surface. The tungsten carbide phase in the produced inserts had no core-borne structure.

Example 2

The inserts from A and B were tested for egg toughness behavior when used for stainless steel turning, AISI316Ti.

Cutting data:

Cutting speed = 110m / min Supply = 0.3mm / rev.

Cutting depth = 2.0 mm

When the maximum wear exceeded 0.3 mm, the sample was stopped. Result: bikes

Cut A 5

Cutting B 3

Example 3

Cuts from A and B were tested for resistance to plastic deformation when used for stainless steel turning, AISI304L.

Cutting data:

Cutting speed = 250 m / min Supply = 0.3 mm / rev.

Cutting depth = 2.0 mm

The plastic deformation was measured as phase wear and the sample was stopped at 0.3 mm wear.

Results:

520 253 cycles

Cutting A 13

Cutting B 15

Example 4

Cuts from A and B were tested in turning with respect to intermittent stainless steel thermal and mechanical loads, SS2343.

Cutting data:

Cutting speed = 190 m / min

Feed rate = 0.3 mm / rev.

Cutting depth = 2.0 mm

When the maximum wear exceeded 0.3 mm, the test was stopped. Results: cycles

Cut A 5

Cutting B 2

Example 5

C and D inserts were tested for resistance to plastic deformation when used for stainless steel turning, AISI304L.

Cutting data:

Cutting speed = 200 m / min Supply = 0.3 mm / rev.

Cutting depth = 2.0 mm

The plastic deformation was measured as phase wear and the sample was stopped at 0.3 mm wear.

Result: bikes

Cut C 13

Cut D 14

Example 6

Cuts from C and D were tested during turning with respect to stainless steel intermittent thermal and mechanical load, SS2343.

Cutting data:

Cutting speed = 190 m / min

Feed = 0.3 mm / rev,

Cutting depth = 2.0 mm

When the maximum wear exceeded 0.3 mm, the sample was stopped

Result: bikes

Cutting C Cutting D

520 253 lo