KR100388759B1 - Coated turning insert - Google Patents

Abstract

A cutting tool insert for turning steel comprises a cemented carbide body and a coating. The body consists of WC, 5-11 wt.% Co and 2-10 wt.% cubic carbides of Ti, Ta and/or Nb and a highly W-alloyed binder phase with a CW-ratio of 0.76-0.92. The coating comprises: (a) a first (innermost) layer of TiCxNyOz with a thickness of 0.1-2 ~mm and with equiaxed grains having a size of less than 0.5 ~mm; (b) a layer of TiCxNyOz with a thickness of 3-15 ~mm with columnar grains having a dia. of less than 5 ~mm; and (c) an outer layer of a smooth, fine-grained (0.5-2 ~mm) kappa-Al2O3 layer having a thickness of 1-9 ~mm. The layer of TiCxNyOz with a thickness of 3-15 ~mm with columnar grains is pref. deposited by a MT-CVD technique, using acetonitrile as the C and N source for forming the layer in a preferred temp. range of 850-900 deg C. The cemented carbide pref. has 6.5-8.0 wt.% Co and a CW ratio of 0.8-0.9. The cemented carbide body has a surface zone 15-35 ~mm thick depleted from cubic carbides. The outermost layer is pref. a thin 0.1-1 ~mm TiN layer, where the outermost TiN layer has been removed along the cutting edge.

Description

Coated turning insert

Stainless and low alloy steels are generally difficult to process with coated or uncoated cemented carbide tools. Smearing from the workpiece material to the cutting edge surface and flaking of the coating often occur. Cutting conditions are particularly challenging during turning of forged low alloy parts under wet conditions (using refrigerant). The hot forged skin (0.05-0.2 mm) is generally decarburized and is softer than the bulk material due to the main ferrite structure. Cold forged skin (<0.05 mm) is cold worked and hardened due to the strain hardening effect. In addition, the ferrite / pearlitic bulk structure of such a material often has a " ferrite-striated &quot; configuration in which the ferrite and pearlite are formed in parallel stripes. This combination of rigid and ductile materials makes the cutting conditions very difficult.

Also, when turning stainless and low alloy steels with coated cemented carbide tools, the cutting edges wear due to chemical wear, scratch wear and so-called adhesion wear. Adhesive wear is predominantly tool wear limit wear. As the workpiece chips are formed, the debris of each layer or the individual particles and the particles of the cemented carbide are continuously pulled from the cutting edge, causing adhesion wear. In addition, wear during wet turning may be accelerated by additional wear mechanisms. The refrigerant and workpiece material can penetrate into the cold cracks of the coating. Due to the infiltration, a chemical reaction occurs between the workpiece material and the refrigerant on the cemented carbide. The Co-binder phase can oxidize along the interface between the coating and the cemented carbide in the region near the crack. After a predetermined time, the coating debris is lost as a fragment.

Swedish Patent Application No. 9501286-0 discloses a coated cutting insert particularly useful for dry milling of gray cast iron. The insert features a coating comprising a TiC _x N _y O _z layer with a straight WC-Co cemented carbide body and columnar grains and an upper layer consisting of finely divided a-Al ₂ O ₃ .

Swedish Patent Application No. 9502640-7 discloses a coated turning insert which is particularly useful for intermittent turning of low alloy steels. The insert comprises a WC-Co cemented carbide body with a high W-alloy Co binder phase, a TiC _x N _y O _z layer with columnar grains and an upper layer consisting of finely divided and aggregated a-Al ₂ O ₃ &Lt; / RTI &gt;

The present invention relates to a method and apparatus for producing hot and cold forged low alloy steel parts such as gear rings and axles for use in the automotive industry, and particularly useful for coating in difficult cutting conditions, such as when turning stainless steel parts such as bars, To a cutting tool (cemented carbide insert).

Figure 1 is a micrograph of a 5000 × magnification of a coating insert according to the invention. Wherein A is a cemented carbide body, B is a layer of TiC _x N _y O _z having coaxial grains, C is a layer of TiC _x N _y O _z having columnar grains, D is a layer of κ-Al ₂ O ₃ layer, and E is a TiN layer (optional).

It is surprising that a cutting tool with excellent properties can be obtained for turning stainless and forged low alloy steel parts by replacing the assembled α-Al ₂ O ₃ layer of the above-mentioned patent application with a κ-Al ₂ O ₃ layer .

According to the invention, it is preferred that the turning tool insert contain 5 to 11, preferably 5 to 8, particularly preferably 6.5 to 8 wt-% Co, and preferably Ti, Ta and / or Co in the IVb, Vb or VIb groups on the periodic table, There is provided a cemented carbide body composed of 2 to 10, preferably 4 to 7.5, particularly preferably 5 to 7 wt-% cubic carbides made of a metal such as Nb and / or Nb and the balance WC. The particle size of WC is about 2 탆. The cobalt binder phase is high alloyed with W. The W content in the binder phase can be expressed as CW-ratio = Ms / (wt-% Co0.0161), where Ms is the saturation magnetization of the cemented carbide measured in kA / m and wt-% Co Is the weight percent of Co in the cemented carbide. The CW-ratio is a function of the W content in the Co-binder phase. The low CW-ratio on the binder corresponds to a high W-content.

It has been found by the present invention that the improved cutting performance is achieved when the cemented carbide has a CW-ratio of 0.76 to 0.92, preferably 0.80 to 0.90. The cemented carbide body does not show any adverse effect even if it contains a small amount of η-phase (M ₆ C) of less than 1 vol-%. In a preferred embodiment, a surface area of about 15 to 35 [mu] m in thickness, which is degraded in cubic carbide and often concentrated on the binder (25% or more in general concentration), can be provided by the prior art as disclosed in U.S. Patent No. 4,610,931 . In this case, the cemented carbide may include a carbonitride nitride or a nitride.

The coating is preferably &lt;

(innermost) layer of TiC _x N _y O _z with coaxial particles having a thickness of from 0.1 to 2 탆 and a size of less than 0.5 탆, wherein x + y + z = 1, preferably z <

- x + y + z = 1, preferably z = 0, x> 0.3, y> 0.3 and a thickness of 3 to 15 μm, preferably 5 to 8 μm, comprising columnar particles and having an average diameter of less than 0.5 μm , preferably a layer of TiC _x N _y O _z is less than 2 ㎛. In another embodiment, the outer portion of this layer comprises oxygen of z < 0.5.

- a layer of Al ₂ O ₃ flat microparticles (particle size 0.5 to 2 μm) consisting essentially of κ-phase. However, the layer may comprise a small amount of the? - or? -Phase of from 1 to 3 vol%, as determined by XRD measurements.

. The Al ₂ O ₃ layer may have a thickness of 1 to 9 μm, preferably 1 to 3 μm, alternatively 4 to 8 μm, and a surface roughness of Rmax ≦ 0.4 μm per 10 μm of length. Preferably, the Al ₂ O ₃ layer is the outermost layer but it may for example be accompanied by other layers such as a thin (about 0.1 to 1 ㎛) of TiN decorative layer (decorativc layer).

According to the method of the present invention, a WC-Co-based cemented carbide body having a high W alloy binder phase having a CW-ratio and a binder phase,

of TiC _x N _y O _z with coaxial particles of a size of 0.1 to 2 탆 and a size of less than 0.5 탆 using a known CVD-method, with the proviso that x + y + z = 1, preferably z < Inner) layer.

x + y + z = 1, preferably z = 0 or alternatively z <0.5, x> 0.3, y> 0.3 and a thickness of 3 to 15 μm, preferably 5 to 8 μm, and preferably MTCVD technology 700 to to form a layer in a temperature range of 900 ℃ using acetonitrile (acetonitrile) as a carbon and nitrogen source), an average diameter of less than 5 ㎛ with preferably TiC _x N _y O _z having a columnar particles of less than 2 ㎛ Layer. The exact conditions are based on the design range of the equipment used.

An outer layer of a flat Al ₂ O ₃ layer consisting essentially of κ-Al ₂ O ₃ deposited under the conditions disclosed in EP 523,021.

. The Al ₂ O ₃ layer has a thickness of 1 to 9 μm, preferably 1 to 3 μm or alternatively 4 to 8 μm and a surface roughness of Rmax ≦ 0.4 μm per 10 μm of length. The flat coated surface may be obtained by light wet wet-blasting the coated side with fine particle (400-150 mesh) alumina powder, or by brushing, for example, based on SiC, as disclosed in Swedish Patent Application No. 9402543-4. By brushing the cutting edge.

Example 1

A. A binder having a composition of 7.5 wt-% Co, 1.8 wt-% TiC, 0.5 wt-% TiN, 3.0 wt-% TaC, 0.4 wt-% NbC and balance WC and having a CW- of having a phase CNMG 120408-PM type cemented carbide turning tool insert body MTCVD technique using (temperature 885 to 850 ℃ and as the carbon / nitrogen source CH ₃ CN) to a thickness having a columnar particles involves the TiCN layer 7 ㎛ And coated with a 0.5 탆 coaxial TiCN layer (with a high nitrogen content corresponding to an estimated C / N ratio of 0.05). In a subsequent step in the same coating cycle, a 1.5 탆 thick Al ₂ O ₃ layer was deposited using a H ₂ S dopant at a temperature of 970 캜 and a concentration of 0.4% as disclosed in European Patent Publication No. 523,021. A thin (0.5 탆) decorative layer of TiN was deposited on top of the known CVD-technique. XRD measurements indicated that the Al ₂ O ₃ layer was composed of 100% K-phase. The cemented carbide body has a surface area of about 25 탆 in thickness, which is deteriorated from cubic carbide and has a concentration of about 30% on the binder. The coated insert was brushed with a nylon straw brush containing SiC particles. Light microscopy of the brushed insert revealed a flat Ra = 0.3 μm, leaving only the surface of the Al ₂ O ₃ layer and the thin TiN layer being only brushed along the cutting edge. Coating thickness measurements of the cross-brushed samples showed no reduction in coating along the cutting edge line except for the removed outer TiN layer.

B.) A strong competing cemented alloy grade of CNMG 120408 type from an external tip carbide production machine was chosen for comparison to the turning test. Carbide had a composition of 9.8 wt-% Co, 0.2 wt-% TiC, 2.0 wt-% TaC, the rest WC and a CW-ratio of 0.86. The insert had a coating consisting of a 5 탆 TiCN layer and a 0.5 탆 TiN layer with a 1.5 탆 thick Al ₂ O ₃ layer. The light microscope examination showed that the insert did not become flat along the cutting edge line after the coating step.

A inserts were compared with inserts of B through turning tests of hot forged ring gears (diameter 206 mm, TSCM815H material). Each turn cycle performed on each part consisted of one face cut, one longitudinal cut and one chamfer cut. The feed was 0.35 mm / rev and the cutting speed was about 230 m / min.

First, 150 parts were machined into two inserts A and B and the resulting flank wear was measured and compared. Since the abrasion was considerably undeveloped on insert A, more parts were cut to cut a total of 354 parts. The resulting flank wear is shown in the following table:

Number of parts Flank wear measured (mm)

(According to the invention) insert A 150 0.07

(According to the invention) insert A 354 0.08

(External grade) Insert B 150 0.10

Microscopic examination of the tested insert showed fine flaking on insert B, but no visible flaking occurred on insert A even after processing 354 parts.

It is clear from the obtained flank wear that insert A according to the invention has excellent and longer tool life.

Example 2

D.) Strong competing cemented alloy grades of type CNMG 120408 from another external tip carbide production unit were selected for comparison with turning tests. The chemical composition of the cemented carbide was 7.6 wt-% Co, 2.4 wt-% TiC, 0.5 wt-% TiN, 2.4 wt-% TaC, 0.3 wt-% NbC and the rest WC. The cemented carbide has a surface area of about 20 탆 in thickness which is deteriorated from cubic carbide. The composition of the cemented carbide is similar to that of the present invention but has a high CW-ratio of 0.93 and a different coating consisting of a 5 탆 TiCN layer with a 3.5 탆 TiC layer, a 1.5 탆 Al ₂ O ₃ layer and a 0.5 탆 TiN layer. The light microscope examination showed that the insert did not become flat along the cutting edge line after the coating step.

The inserts A and D were compared through a surface turning test with a feed = 0.25 to 0.35 mm / rev and a cutting speed = 220 m / min for a hot forged ring gear (SCr420H material, outer diameter 180 mm and inner diameter 98 mm) . The inserts worked up to 0.08 mm, the flank wear value, and the number of parts produced was evaluated.

Number of parts Flank wear measured (mm)

(According to the invention) insert A cutting edge 1 203 0.08

(According to the invention) insert A cutting edge 2 226 0.08

(External grade) Insert D 182 0.08

Example 3

C.) A cemented carbide turning tool insert of the same composition as insert A and WNMG 080408-PM type with a CW-ratio of 0.88 was coated according to A. XRD measurements indicated that the Al ₂ O ₃ layer was composed of 100% K-phase. The insert was brushed according to A.

E.) An insert of the type WNMG 080408 with the same CW-ratio, carbide composition and coating as D from the same cemented carbide production unit was selected for comparison via turning tests. The light microscope examination showed that the insert did not become flat along the cutting edge line after the coating step.

The inserts of C and E were compared through a cotton turn test with a feed of a forged axle (50CV4 material, length 487 mm and diameter 27 to 65 mm) = 0.28 to 0.30 mm / rev and a cutting speed = 160 m / min. Three axles were operated on each cutting day and the wear of the cutting edge was examined with a light microscope.

(According to the invention) insert C less than 0.07 mm flank wear and no flaking.

(External grade) Insert E Less than 0.07 mm Flank wear and

Flaking and chipping along the cutting edge.

Example 4

F.) A cemented carbide turning tool insert of CNMG 120408-PM type from the same batch as A has a 7 占 퐉 thick TiCN layer with columnar particles according to Swedish Patent Application No. 9502640-7, a 1 占 퐉 coaxial TiCN and a thickness of 4 ㎛ accompanying 012- texture α-Al ₂ O ₃ were coated with TiCN 0.5 shaft. Wet blasting was performed using a water / Al ₂ O ₃ - slurry to smooth the coated surface of the insert.

G.) Cemented carbide turning of the type CNMG 120408-PM type with 6.5 wt-% Co and 8.8 wt-% cubic carbide (3.3 wt-% TiC, 3.4 wt-% TaC and 2.1 wt-% NbC) The tool insert was coated under the process provided in A). The cemented carbide body had a CW-ratio of 1.0 and a surface area of about 23 mu m thick, which was degraded on the cubic and concentrated on the binder. XRD-measurements indicated that the Al ₂ O ₃ layer was composed only in the κ-phase.

The inserts A, F, G and B were compared through turning tests of hot and cold forged ring gears with material SCr420H.

The ring had an outer diameter of 190 mm and an inner diameter of 98 mm. Each turn cycle performed on each part consisted of three face cuts and one longitudinal cut. The feed = 0.25 to 0.40 mm / rev and the cutting speed was about 200 m / min. 170 parts were machined and the wear of the cutting edge was checked.

No visible flaking of the insert A coating was observed

The flank wear (according to the invention) is less than 0.07 mm.

Part of the coating is removed along the insert F cutting edge

(CW-ratio = 0.08) Flank wear is less than 0.08 mm.

Substantial flaking occurred along the insert G cutting edge

(CW-ratio = 1.0) Flank wear is more than 0.10 mm.

Part of the coating is removed along the insert B cutting edge

(Outer) flank wear is less than 0.08 mm.

Although insert F prepared in accordance with Swedish Patent Application No. 9502640-7 is generally excellent when turning low alloy steels, when turning several low temperature and cold forged low alloy steel parts, the insert A You can not always match.

Example 5

H.) From the same arrangement as in Example 1 A, the insert was coated with an Al ₂ O ₃ layer of thickness 5.5 μm according to the procedure provided in Example 1, except that the process time of the Al ₂ O ₃ coating step was extended to 7.5 hours . A thin (0.5 탆) decorative layer of TiN was deposited on top using conventional techniques.

I.) From the same arrangement as H, the insert was coated with a 5 탆 thick Al ₂ O ₃ layer and a 7 탆 coaxial layer of TiCN with a prior art 0.5 탆 TiN top coating. XRD analysis indicated that the Al ₂ O ₃ layer consisted of a mixture of α- and κ-Al ₂ O _{3 with} an approximate composition ratio of 30/70. The inserts of H and A were brushed after coating to remove the TiN layer and to flatten the cutting edges.

The inserts of H, A and H were tested for intermittent longitudinal turning. The workpiece material was a ring-shaped low alloy low carbon steel (SCr420H) having an outer diameter of 190 mm, an inner diameter of 30 mm and a thickness of 22 mm. Each longitudinal passage above the ring thickness consisted of 22 in-cuts of 1 mm each. The number of passages above the ring thickness was recorded for each insert until flaking occurred.

Insertion Thread Cutting Edge

A.) &lt; RTI ID = 0.0 &gt; 240 &

1.5 탆 Al ₂ O ₃

H.) &lt; RTI ID = 0.0 &gt; 180 &

5.5 탆 Al ₂ O ₃

I. &lt; RTI ID = 0.0 &gt; 40 &

5 탆 Al ₂ O ₃

The inserts of H and A were also compared by cutting tests on ball bearing steel (SKF25B, v = 250 m / min, f = 0.3 mm / r, cutting depth = 2 mm). In this test, crater wear was prominent. Was working for 15 minutes body insert formed crater wear was measured in the area of the crater mm ^2.

Insert crater area (mm ² )

A.) 1.5 占 퐉 Al ₂ O ₃ 0.9

H.) 5.5 占 퐉 Al ₂ O ₃ 0.5

From the test results it is clear that insert I has inferior flickering resistance compared to inserts H and A. Insert H exhibits good results for both crater wear resistance and flaking resistance. Insert A exhibits the best flaking resistance and can be used in cutting operations requiring extremely high flaking resistance.

Example 6

Insertion of a cemented carbide turning tool of the TNMG160408-MM type having a composition of H. 7.5 wt-% Co, 1.8 wt-% TiC, 3.0 wt-% TaC, 0.4 wt-% NbC and balance WC and a CW-ratio of 0.88 A sieve was provided. The cemented carbide has a surface area of about 25 탆 in thickness which is deteriorated from cubic carbide. The insert was coated with the innermost 0.5 탆 coaxial TiCN layer with a high nitrogen content of C / N ratio estimated at 0.05 and with a 7.2 탆 pillar thickness TiCN layer deposited using MT-CVD technology. Al ₂ O layer of 1.2 ㎛ in subsequent steps in the same coating process is performed onto the pure κ- by the process disclosed in European Patent Publication No. 523 021. A thin 0.5 탆 TiN layer was deposited on top of the Al ₂ O ₃ layer during the same cycle. After coating, the coated insert was brushed with SiC containing a nylon straw brush to remove the outer TiN layer on the cutting edge.

I. Competitive cemented carbide turning tool inserts of the type TNMG 160408 from an external cemented carbide production machine were selected for comparison via turning tests. The carbide had a composition of 9.0 wt-% Co, 0.2 wt-% TiC, 1.7 wt-% TaC, 0.2 wt-% NbC balance WC and a CW-ratio of 0.90. The insert had a coating consisting of 1.0 urn TiC, 0.8 urn TiN, 1.0 urn TiC and an outermost 0.8 urn TiN. Optical microscopy showed that there was no subsequent cutting edge treatment of the coating.

Inserts H and I were tested by longitudinal, dry, and turning of shafts made of two-phase stainless steels.

The feed rate was 0.3 mm / rev, the speed was 140 m / min, and the cutting depth was 2 mm. The total cutting time per component was 12 minutes.

Insert I was plastically deformed while insert H had a slight notch wear.

The insert H according to the present invention required one cutting edge to complete one part while four insert edges were required to finish one part using the insert I.

Claims (9)

A cutting tool insert for turning a steel, comprising a cemented carbide body and a coating, The cemented carbide body comprises WC, 2 to 10 wt-% cubic carbide on Ti, Ta and / or Nb and a high W alloy binder having 5 to 11 wt-% Co and a CW-ratio of 0.76 to 0.92 , Said coating comprising a first (innermost) layer of TiC _x N _y O _z having a coaxial particle size of less than 0.5 microns and a thickness of from 3 to 15 microns with columnar particles less than 5 microns in diameter, Characterized in that it comprises an outer layer of a layer of TiC _x N _y O _z and a κ-Al ₂ O ₃ - layer of smooth, fine particles (0.5 to 2 μm) of 1 to 9 μm in thickness sieve. The cutting insert according to claim 1, wherein the thickness of the κ-Al ₂ O ₃ - layer is 1 to 3 μm. The cutting insert according to claim 1, wherein the thickness of the κ-Al ₂ O ₃ - layer is from 4 to 8 μm. The cutting insert according to any one of the preceding claims, wherein the cemented carbide body has a surface area of 15 to 35 탆 in thickness which is deteriorated from cubic carbide. The cutting insert according to any one of claims 1 to 3, wherein the cemented carbide body has a composition of 6.5 to 8.0 wt-% Co and a CW-ratio of 0.80 to 0.90. The cutting insert according to any one of claims 1 to 3, wherein the outermost layer is a thin 0.1 to 1 탆 TiN layer. 7. The cutting insert according to claim 6, wherein the outermost TiN layer is removed along the cutting edge. A method of making a turning insert comprising a cemented carbide body and a coating, A WC-Co based cemented carbide body having a high W-alloy binder phase with a CW-ratio of 0.76 to 0.92 was deposited on a TiC with a coaxial particle size of less than 0.5 mu m and a thickness of 0.1 to 2 mu m using a known CVD method (innermost) layer of _x N _y O _z and a second (innermost) layer of less than 5 탆 diameter deposited by MTCVD techniques using carbon and nitrogen source as the nitrogen source to form a layer at a preferred temperature range of 850-900 캜 Characterized in that the layer is coated with a layer of TiC _x N _y O _z 3 to 15 탆 in thickness with columnar particles and a layer of flat κ-Al ₂ O _{3 with} a thickness of 1 to 9 탆. The method according to claim 8, wherein the cemented carbide body has a binder phase for concentrating the surface area.