EP4713161A1

EP4713161A1 - Cutting tool

Info

Publication number: EP4713161A1
Application number: EP24727663.7A
Authority: EP
Inventors: José Luis Garcia; Andrei Chychko
Original assignee: Sandvik Coromant AB
Current assignee: Sandvik Coromant AB
Priority date: 2023-05-17
Filing date: 2024-05-15
Publication date: 2026-03-25
Also published as: CN121100036A; KR20260012213A; WO2024236022A1

Abstract

The present invention relates to a cutting tool with a cemented carbide substrate comprising WC and 2‐20 wt% Ni‐based metal binder, where the cemented carbide comprises Ni and Cr so that the weight ratio Cr/Ni is between 0.06 and 0.20 and where the cemented carbide comprises eta phase in an amount of 1 to 10 vol% and wherein the average grain size of the eta phase grains is between 0.1 and 10 µm, and where the cemented carbide is free from gamma phase. The cutting tool according to the present invention shows maintained or improved properties compared to cemented carbides having a Co binder.

Description

Cutting Tool

The present invention relates to a cutting tool where the cemented carbide substrate comprises eta phase and a metallic binder comprising Ni and Cr. The invention also relates to a method of making the cutting tool.

Background

Cemented carbides based on tungsten carbide (WC) with a cobalt binder have been known in the art for almost hundred years. Other metals that are known as binder metals in cemented carbides are iron and nickel, however cobalt is by far the most used.

It is an ongoing strive to find alternative binders to cobalt due to its environmental and health impact. However, it is difficult to replace or limit the amount of cobalt without impacting material properties in a negative way. For cutting tools the substrate properties are important for the overall performance of the tool and even small changes in composition can have a detrimental impact on performance.

Nickel provides good wettability to WC which makes it suitable for producing cemented carbides. Nickel also presents better performance in oxidation and corrosion conditions compared to WC-Co cemented carbides. The major drawback of Ni-based cemented carbides is their reduced mechanical strength. One reason is the higher stacking fault energy of Ni compared to Co, which makes work hardening of Ni only moderate as compared to Co.

It has been particularly difficult to find a cemented carbide with an alternative binder that has an acceptable edge line toughness.

It is an object of the invention to provide a cemented carbide with an alternative binder phase which has equal or improved properties compared to a substrate with a Co binder.

It is also an object of the invention to provide a cemented carbide with an alternative binder phase which has equal or improved performance in cutting operations compared to a substrate with a Co binder. Detailed Description of the Invention

The present invention relates to a cutting tool comprising a cemented carbide substrate comprising WC and 2-20 wt% Ni-based metal binder. The cemented carbide comprises Ni and Cr so that the weight ratio Cr/Ni is between 0.06 and 0.20 and the cemented carbide comprises eta phase in an amount of 1 to 10 vol% of the cemented carbide and the average grain size of the eta phase is between 0.1 and 10 pm. The cemented carbide is free from gamma phase.

The cemented carbide according to the present invention is free from gamma phase. Gamma phase (also called cubic phase) is formed during sintering if one or more gamma phase forming elements, e.g. Ti, Ta, Nb, Zr, V, Hf and Mo are present and can be written with the general formula (W,X)(C,N) or (W,X)(C) where X can be one or several of the gamma phase forming elements.

By a cemented carbide free from gamma phase is herein meant that no gamma phase can be seen in the microstructure in a LOM image at 500 times or higher magnification.

A cemented carbide free from gamma phase means that, if added, the content of gamma phase forming elements such as Ti, Ta, Nb, Zr, V, Hf and Mo is to be kept below the solubility of those elements in the binder so that no gamma phase is formed. Gamma phase in the microstructure is less desired due to brittleness.

In one embodiment of the present invention, the total content of the gamma phase forming elements e.g. Ti, Ta, Nb, Zr, V, Hf and Mo are preferably below 1 at% in the binder, more preferably below 0.5 at% of the binder phase in cemented carbide.

In one embodiment of the present invention, the amount of gamma phase forming elements such as Ti, Ta, Nb, Zr, V, Hf and Mo is on a level of impurity, i.e. no raw material comprising gamma phase forming elements such as Ti, Ta, Nb, Zr, V, Hf and Mo is used for manufacturing a cemented carbide according to the present invention.

The cemented carbide according to the present invention comprises eta phase. Eta phase is formed in a cemented carbide if the total carbon content is below a certain value.

The Ni-based metal binder comprises Ni and Cr and the metal binder is present in an amount of 2 to 20 wt% of the sintered body, preferably between 5 to 12 wt% of the sintered body. By Ni-based metal binder is herein meant that the binder comprises more than 70 wt% Ni. The binder will also contain other elements that inevitably will dissolve in the binder during sintering. Such elements are e.g. W and C from the WC.

In one embodiment of the present invention, the total amount of Ni, Cr and W in the binder is at least 98 wt %.

Cr is a common addition in cemented carbides but the amount of Cr that can be added is usually limited by the solubility of Cr in the metal binder. If the amount of Cr exceeds the solubility in the binder, a brittle carbide, Cr₇C₃, is precipitated in the microstructure and the mechanical properties of the cemented carbide will deteriorate.

The upper limit for the Cr addition according to the present invention, i.e. formation of the 7C3, can however be higher than for a conventional cemented carbide without eta due to the presence of eta phase in the microstructure. Cr will be part of the eta phase and a higher amount of Cr can thus be added to the cemented carbide without formation of the brittle 7C3 carbides.

Cr can be added up to the limit where Cr₇C₃ is formed, however, for practical reasons it is not suitable to be too close to that limit. Suitably, Cr is added so that the weight ratio Cr/Ni is between 0.06 and 0.20, preferably 0.10 and 0.18.

Adding Cr to the cemented carbide in these amounts is beneficial since it contributes to microstructure refinement and promotes fine grained eta phase. A higher Cr content also leads to solid solution strengthening in the binder which will lead to a higher hardness without decrease in toughness. If the amount of Cr is below the set range, the hardness and other mechanical properties will not be enough.

The cemented carbide according to the present invention have a WC grain size of between 0.1 and 12 pm, preferably between 0.4 to 9 pm measured by e.g. image analysis.

By cemented carbide is herein meant that the cemented carbide comprises at least 50 wt% WC.

The cemented carbide according to the present invention is essentially free from Co. By that is herein meant that no Co powder is added. Co can however be present in smaller amounts due to contamination if the same manufacturing equipment is used as for Co containing cemented carbides and/or if the milling ball media is made of Co containing cemented carbide. By essentially free from Co is herein meant that the cemented carbide comprises less than 1 wt% Co, preferably less than 0.5 wt %. The Co content can be analyzed using conventional chemical analysis.

In one embodiment of the present invention, the cemented carbide comprises Ru so that the weight ratio Ru/(Ru+Ni) is between 0.05 and 0.20. Adding Ru can enhance the binders ability to dissolve elements such as W. The majority of the Ru will be dissolved in the Ni-based binder.

In one embodiment of the present invention, the cemented carbide insert is provided with a wear resistant CVD (Chemical vapor deposition) or PVD (Physical Vapor deposition) coating.

The coating can also be subjected to additional treatments known in the art, such as brushing, blasting etc.

By cutting tool is herein meant tools such as inserts, end mills or drills.

In one embodiment of the present invention, the cutting tool is an insert, preferably a milling insert.

In one embodiment of the present invention, the cemented carbide substrate is used for milling in cast iron, steel, HRSA alloys or Ti-a Hoys.

In one embodiment of the present invention, the cemented carbide is free from gamma phase and comprises WC, 2-20 wt% Ni-based metal binder, where the cemented carbide comprises Cr so that the weight ratio Cr/Ni is between 0.06 and 0.20 and where the cemented carbide comprises eta phase in an amount of between 1 and 10 vol% and where the eta phase grains have an average grain size of between 0.1 and 10 pm. The cemented carbide does not contain any other elements other than W, C, Ni and Cr where balance being unavoidable impurities.

In one embodiment of the present invention, the cemented carbide is free from gamma phase and comprises WC, 8-12 wt% Ni based metal binder where the cemented carbide comprises Cr so that the weight ratio Cr/Ni is between 0.14 and 0.18. The cemented carbide further comprises eta phase in an amount of between 1.5-5 vol% and where the eta phase grains have an average grain size of between 0.5 and 3 pm. The cemented carbide does not contain any other elements other than W, C, Ni and Cr where balance being unavoidable impurities.

In one embodiment of the present invention, the cemented carbide is free from gamma phase and comprises WC, 2-20 wt% Ni-based metal binder, where the cemented carbide comprises Cr so that the weight ratio Cr/Ni is between 0.06 and 0.20, Ru so that the weight ratio Ru/(Ru+Ni) is between 0.05 and 0.2, and where the cemented carbide comprises eta phase in an amount of between 1 and 10 vol% and where the eta phase grains have an average grain size of between 0.1 and 10 pm. The cemented carbide does not contain any other elements other than W, C, Ni and Cr where balance being unavoidable impurities.

The present invention also relates to a method of making a cutting tool comprising a cemented carbide substrate according to the above. The method comprises the following steps:

-providing a WC powder; and

- providing powder(s) comprising Cr and Ni forming the binder phase, to from a powder blend

-providing a milling liquid,

-milling, drying, pressing and sintering the powders into a cemented carbide, wherein W and/or W₂C is added to the powder blend in such amounts that the cemented carbide, after sintering, will comprise eta phase in an amount of 1 to 10 vol% of the cemented carbide and wherein the average grain size of the eta phase are between 0.1 and 10 pm.

The amount and distribution of the eta phase is controlled by the carbon content in the cemented carbide. To adjust the carbon content so that the desired eta phase is formed, one or more of W and W₂C is added to the powder blend and thus creating a carbon deficiency.

In one embodiment of the present invention, the one or more of W and W₂C powders is pre-milled prior to the addition to the other raw materials.

The exact amount of W and W₂C depends on the composition of the other raw materials. Usually, some carbon is lost during sintering due to the presence of oxygen. The oxygen will react with carbon and leave as CO or CO2 during sintering thus shifting the carbon balance so that the added amount of one or more of W and W2C have to be adjusted. Exactly how much carbon that is lost during sintering depends on the raw material and production techniques used and it is up to the skilled person in the art to adjust the W and/or W₂C additions so that the desired amount and grain size of eta phase in the sintered material is achieved.

In one embodiment of the present invention, the amount of WC added is between 80 and 98 wt% based on dry powder weight. The grain size (FSSS) of the WC powder is suitably between 0.1 and 12 pm, preferably between 0.4 to 9 pm.

The powder(s) forming the binder phase can be one or more of Ni, NiCr alloy and CrsC2. The powder(s) forming the binder phase are added so that the amount of metallic binder is 2 to 20 wt%, preferably between 5 to 12 wt% based on the dry powder weight.

In one embodiment of the present invention, elements such as Ti, Ta, Nb, Zr, V, Hf and Mo, that are usually considered as gamma phase forming elements, can be added as e.g. carbides/nitrides in small amounts to e.g. inhibit grain growth. However, the amount of those elements has to be low enough to about avoid gamma phase formation.

In one embodiment of the present invention, no raw materials containing gamma phase forming elements such as Ti, Ta, Nb, Zr, V, Hf and Mo is added during manufacturing of the cemented carbide according to the present invention. If present in the sintered cemented carbide the amount of those elements will thus be on a level of impurity.

Any liquid commonly used as a milling liquid in conventional cemented carbide manufacturing can be used. The milling liquid is preferably water, alcohol or an organic solvent, more preferably water or a water and alcohol mixture and most preferably a water and ethanol mixture. The properties of the slurry are dependent on the amount of milling liquid added. Since the drying of the slurry requires energy, the amount of liquid should be minimized in order to keep costs down. However, enough liquid need to be added in order to achieve a pumpable slurry and avoid clogging of the system. Also, other compounds commonly known in the art can be added to the slurry e.g. dispersion agents, pH-adjusters etc. An organic binder is also optionally added to the slurry in order to facilitate the granulation during the following spray drying operation but also to function as a pressing agent for any following pressing and sintering operations. The organic binder can be any binder commonly used in the art. The organic binder can e.g. be paraffin, polyethylene glycol (PEG), long chain fatty acids etc. The amount of organic binder is suitably between 15 and 25 vol% based on the total dry powder volume, the amount of organic binder is not included in the total dry powder volume.

The slurry comprising powders forming hard constituents and powders forming the binder phase, and possibly an organic binder can be mixed by a milling operation, either in a ball mill or attritor mill. Then the slurry is suitably milled in a ball mill or attritor mill to obtain a homogenous slurry blend.

The slurry containing the powdered materials mixed with the organic liquid and possibly the organic binder is atomized through an appropriate nozzle in the drying tower where the small drops are instantaneously dried by a stream of hot gas, for instance in a stream of nitrogen, to form agglomerated granules. For small scale experiments, also other drying methods can be used, e.g. pan drying.

Green bodies are subsequently formed from the dried powders/granules by a pressing operation such as uniaxial pressing, multiaxial pressing etc.

The green bodies formed from the powders/granules made according to the present invention, is subsequently sintered according to any conventional sintering methods e.g. vacuum sintering, Sinter HIP (high isostatic pressure), spark plasma sintering, gas pressure sintering (GPS) etc.

The sintering temperature is typically between 1300 and 1580 °C, preferably between 1350 and 1470°C.

In one embodiment of the present invention, the sintering process comprises a sinter HIP step performed at a temperature of between 1350 and 1550°C, and a pressure of at least 40 Bar, preferably between 40 and 80 Bar. Usually, an inert argon atmosphere is used during the high isostatic pressure (HIP) step, without intentional addition of CO or H₂. However, residual amounts of other gases (H₂O, CO, CO₂) can be formed in-situ during the sintering process. In yet another embodiment of the present invention, the cemented carbide insert is provided with a wear resistant CVD or PVD coating.

Drawings

Figure 1 shows the impact on the toughness and hardness (calculated as delta) by different Cr additions as well as the presence and absence of gamma phase.

Example 1

Samples were prepared to see the impact of different Cr additions as well as addition of TiC (to form gamma phase). The raw material powders according to Table 1, where the balance was WC with a grain size (FSSS) of 0.81-0.87 pm, were milled in a ball mill for 10 h together with an organic binder (2 wt% PEG based on total powder weight) and a milling liquid (water/ethanol) to form a slurry which was dried and milled in agate mortar to obtain a powder blend. The powder was pressed into green bodies. The green bodies were sintered in a HIP (hot isostatic pressure) furnace where maximum sintering temperature was 1410°C and sintering time was 1 h at 40 mbar vacuum sintering followed by a 15 min high-pressure sintering step, 50 bar Ar, to reduce porosity of the samples. The average cooling speed was 1.6 °C/min from 1410 to 1100°C and 6.6 °C/min from 1100 to 100°C.

Table 1

The toughness (K1C) and the hardness (HV30) were measured on the sintered bodies after grinding and polishing. The HV30 has been measured according to ISO 6507:2018. The fracture toughness, K1C, has been measured according to ISO 28079. The volume fraction of eta phase and its particle size was determined by image analysis using the software Image J using the "Analyze particles" function with "include holes" and the "0-lnfinity" filter settings. When measuring the eta phase, the Feret size option "exclude on edges" was additionally activated in the "Analyze particles" function. Prior to the measurements, color LOM images were converted into 8-bit black and white images using Automatic threshold setup. The images used for the analysis was LOM images with a magnification of 1000X, between 10 and 12 images were processed and the values in Table 2 are an average value of these. The average grain size for eta is given as the minimum Feret grain size. When studying the LOM images of the samples, all samples disclosed fine dispersed eta phase and the gamma phase was clearly visible in the comparative samples. The results are given in Table 2.

Table 2

The data from Table 2 is also be displayed in Figure 1, where the impact of different additions of Cr (x-axis), as well as the presence/absence of gamma phase are shown.

In Figure 1 the toughness and hardness values have been recalculated into "delta" (y- axis). For cemented carbides having Co as binder, it is possible to obtain a reference line from literature data where the hardness is plotted against the toughness (KIC). "delta" is a calculated value of the distance from that reference line to the experimentally measured values of HV and KIC.

The delta value should be as close to (or above) zero as possible.

Delta is:

Where AHV and AKIC are differences between measured (HV, KIC) and calculated (HVcaic, KICcaic) values and the coefficient I gets the value -1 when AHV and AKIC are negative numbers and +1 when AHV and AKIC are positive values.

AHV = HV - HV_Caic, (2)

AKIC = KIC - KICcaic, (3)

Where a, b and c are constants determined by fitting experimentally measured HV and KIC values to the equation 4: a = 2670000, b = 4590, c = 1240. In Figure 1 it can clearly be seen that the addition of TiC in such amounts so that gamma phase is formed, will lower the delta value compared to a corresponding cemented carbide without gamma phase.

Example 2

Cemented carbide inserts of geometry R390-11T308M-PM were manufactured by using from the raw materials given in Table 3 where the balance was WC with a grain size (FSSS) of 0.81-0.87 pm.

Table 3

The raw material powders were milled in a bead mill, Labstar from Netzsch, at an effect of 1-2 kWh together with an organic binder (2 wt% PEG based on total powder weight) and a milling liquid (water/ethanol) to form a slurry which was dried and milled in agate mortar to obtain a powder blend. The powder was pressed into green bodies.

The green bodies were sintered in a HIP (hot isostatic pressure) furnace where maximum sintering temperature was 1410°C and sintering time was 1 h at 40 mbar vacuum sintering followed by a 15 min high-pressure sintering step, 50 bar Ar, to reduce porosity of the samples. The average cooling speed was 1.6 °C/min from 1410 to 1100°C and 6.6 °C/min from 1100 to 100°C.

The inserts were coated with a PVD coating.

The inserts are herein after called Invention 6 (without Ti addition) and Comparative 9 (with Ti addition).

The toughness (K1C), the hardness (HV30) and the vol% and average grain size (minimum feret) of the eta phase were measured on the sintered bodies after grinding and polishing in the same manner as for the samples in Example 1. The total carbon content in the sintered material is measured by using a LECO CS- 844. A pre-weighed sample of approximately 0.2 gram is combusted in a stream of purified oxygen using RF induction to heat the sample. Carbon present in the sample is oxidized to carbon dioxide (CO2) and swept by the oxygen carrier through a heated dust filter, a drying reagent, and then through non-dispersive infrared (NDIR) cells.

The results are given in Table 4.

Table 4

Example 3

For comparison, a cemented carbide insert with the same geometry as the inserts Invention 6 and Comparative 9, comprising 10 wt% Co, 0.39 Cr and balance WC was produced. A WC powder with an average grain size (FSSS) 0.81-0.87 pm was used. The cemented carbide was produced according to standard methods, i.e. milling, spray drying, pressing and sintering. The cemented carbide insert was coated with the same PVD coating as the insert according to the invention. The insert is herein after denoted Comparative 10.

Working Example 1

In this milling test, coated cemented carbide inserts according to the present invention, Invention 6, has been compared to an insert having gamma phase, Comparative 9, and an insert having Co as binder, Comparative 10, all having the same geometry, R390- 11T308M-PM. The test has been performed in a tool steel, Toolox33, under dry conditions with the following cutting parameters:

Vc: 250 (m/min)

Fz: 0.20 (mm) ap: 2.0 (mm) ae: 49.0 (mm) Minutes per cut 0.29

Tool life criterion was chipping on flank side (mm) > 0.50.

The results are shown Table 5, where the tool life is an average of 4 tests.

Table 5

As can be seen in Table 5, the inserts according to the present invention perform equally to the corresponding insert with Co as binder.

As can be seen in Table 5, the inserts according to the present invention perform slightly better than the corresponding insert with Co as binder.

Working example 2

In this milling test, coated cemented carbide inserts according to the present invention, Invention 6, has been compared to an insert having Co as binder, Comparative 10, all having the same geometry, R390-11T308M-PM. The test has been performed in steel, Dievar, under dry conditions with the following cutting parameters:

Vc: 215 (m/min)

Fz: 0.15 (mm) ap: 3.0 (mm) ae: 12.0 (mm)

Minutes per cut 0.04

Tool life criterion was width of chipping along the edge line (mm) > 0.50.

The results are shown Table 6, where the tool life is an average of 8 tests.

Table 6

As can be seen in Table 6, the inserts according to the present invention perform considerably better than the corresponding insert with Co as binder.

Claims

1. A cutting tool comprising a cemented carbide substrate comprising WC and 2-20 wt% Ni-based metal binder, where the cemented carbide comprising:

Ni and Cr so that the weight ratio Cr/Ni is between 0.06 and 0.20, and wherein the cemented carbide comprises eta phase in an amount of 1 to 10 vol% of the cemented carbide and wherein the average grain size of the eta phase is between 0.1 and 10 pm, and wherein the cemented carbide is free from gamma phase.

2. A cutting tool according to claim 1 wherein the weight ratio between Cr/Ni is between 0.10 and 0.18.

3. A cutting tool according any of the proceeding is essentially free of Co.

4. A cutting tool according any of the proceeding claims wherein the cemented carbide comprises eta phase in an amount of between 1 to 7 vol %.

5. A cutting tool according any of the proceeding claims wherein the cemented carbide comprises eta phase in an amount of between 1.5 to 5 vol %.

6. A cutting tool according any of the proceeding claims wherein the cemented carbide comprises eta phase with an average grain size of between 0.5 and 3 pm.

7. A cutting tool according any of the proceeding claims wherein the cemented carbide comprises Ru so that the weight ratio Ru/(Ru+Ni) is between 0.05 and 0.20.

8. A cutting tool according any of the proceeding claims wherein the cutting tool comprises a coating.

9. A method of making a cutting tool comprising a cemented carbide substrate according to any of claims 1-8 comprising the steps of:

-providing a WC powder; and

- providing powder(s) comprising Cr and Ni forming the binder phase to form a powder blend;

-providing a milling liquid,

-milling, drying, pressing and sintering the powders into a cemented carbide, wherein W and/or W2C is added in to the powder blend in such amounts that the cemented carbide will comprise eta phase in an amount of 1 to 10 vol% of the cemented carbide and wherein the average grain size of the eta phase are between 0.1 and 10 pm.

10. A method of making a cutting tool comprising a cemented carbide substrate according to claim 9 wherein the sintering comprises a sinter HIP step performed at a temperature of between 1350 and 1550°C, and a pressure of at least 40 Bar, preferably between 40 and 80 Bar.