CUTTING TOOL

Abstract

A cutting tool insert has an optimal hardness and high toughness for demanding cutting operations in hardened steel and cast iron. The cutting tool includes a substrate of cemented carbide where the cemented carbide has hard constituents of tungsten carbide (WC) and a (Co) binder phase, chromium (Cr) and at least one additional element from the group: Vanadium (V), Niobium (Nb), Molybdenum (Mo) and Iron (Fe). The cemented carbide further has a Co-content of 3.50-4.20 wt % of the cemented carbide, a Cr-content of 0.31-0.38 wt % of the cemented carbide, a WC-content of at least 95.22 wt % of the cemented carbide and wherein the cemented carbide has a coercivity of 26-32 kA/m

Claims

1. A cutting tool insert comprising a substrate of cemented carbide, the cemented carbide comprising hard constituents of tungsten carbide in a metallic binder phase comprising cobalt (Co), wherein the cemented carbide further comprises chromium (Cr) and at least one additional element from the group consisting of: Vanadium (V), Niobium (Nb), Molybdenum (Mo) and Iron (Fe), wherein a content of the Co is 3.50-4.20 wt % of the cemented carbide, a content of the Cr is 0.31-0.38 wt % of the cemented carbide, a content of the WC is at least 95.22 wt % of the cemented carbide, and the cemented carbide has a coercivity of 26-32 kA/m.

2. The cutting tool according to claim 1, wherein the cemented carbide comprises 0.01-0.09 wt % V.

3. The cutting tool according to claim 1, wherein the V+Nb is a maximum 0.12 wt % of the cemented carbide.

4. The cutting tool according to claim 1, wherein a content of V+Nb+Mo+Fe is a maximum 0.2 wt % of the cemented carbide.

5. The cutting tool according to claim 1, wherein the cemented carbide has a hardness of 1960-2020 HV30.

6. The cutting tool according to claim 1, wherein a fracture toughness is 8.6-9.7 MPam.sup.?1/2.

7. The cutting tool according to claim 1, wherein the coercivity is 27-31 kA/m.

8. The cutting tool according to claim 1, wherein the Cr-content of the binder phase is 8-10 wt %.

9. The cutting tool according to claim 1, wherein a coating is deposited on the substrate.

10. The cutting tool according to claim 10, wherein the coating is a PVD or a CVD coating.

11. A method for manufacturing a cemented carbide cutting tool insert according to claim 1, the method comprising: providing a powder composition comprising WC grains having a FSSS mean grain size in an interval of 0.76-0.90 ?m, 3.50-4.20 wt % Co, 0.31-0.38 wt % Cr and raw material powders comprising at least one of the following elements: V, Nb, Mo and Fe; wet milling the powder composition, a polymer forming agent and a milling liquid to form a slurry; spray drying the slurry to form a granulate; forming the granulate into a green body of a desired shape and dimension; and sintering the green body to a sintered body having a smaller volume than the green body.

12. The method according to claim 12, wherein forming of the green body is made by any of the following: pressing, injection molding and extrusion.

13. The method according to claim 12, further comprising coating the sintered body with a wear resistant coating having a thickness above 1.5 ?m.

14. The method according to claim 13, further comprising coating the sintered body by PVD or CVD.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The invention will now be explained more closely by the description of different aspects of the invention and with reference to the appended figures.

[0055] FIG. 1 shows a diagram comparing the tool life of a cutting tool insert according to the disclosure and a comparative cutting tool insert at cutting speeds 160 m/s.

[0056] FIG. 2 shows a block diagram of an example method of manufacturing the cutting tool insert where the steps A-E corresponds to the steps a-e in claim 12.

[0057] FIGS. 3a, 3b and 3c show photographs of the wear of a cutting tool insert according to the disclosure during machining tests after 5, 10 and 15 minutes respectively.

[0058] FIGS. 4a and 4b show photographs of the wear of a comparative cutting tool insert during machining tests after 5 and 10 minutes respectively.

EXAMPLES

[0059] Exemplifying embodiments of the present disclosure will be described more fully hereinafter and with reference to the drawings. The device and method disclosed herein may, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Cutting tool inserts were manufactured and analyzed. Some of the inserts were evaluated in cutting tests.

Manufacturing of Cutting Inserts

Substrates

[0060] Cemented carbide substrates of style SNUN12048 were manufactured for samples A-J. Sample C and sample J were also manufactured in style CNMG. The substrates were produced from raw material powders all containing tungsten carbide (WC), cobalt (Co) powder and chromium carbide (Cr.sub.3C.sub.2) powder according to the composition shown in Table 1. Some samples also contained at least one additional powder element from the group consisting of: Vanadium (V), Niobium (Nb), Molybdenum (Mo) and Iron (Fe). The composition ratio for each sample is shown in Table 1. The carbon concentration used in the samples were estimated from the phase diagram of the system 4 wt % Co, 0.36 wt % Cr, and the remaining part WC, and the knowledge that approx. 0.09 wt % C is lost during sintering.

[0061] The type of WC used for samples A-H had an average grain size of 0.85 ?m as measured with FSSS. For comparative sample J the type of WC had an average grain size of 0.6 ?m as measured with FSSS.

TABLE-US-00001 TABLE 1 C Co Cr V Fe Nb Mo W Sample (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) A Invention 6.01 3.9 0.38 0.05 0.05 0.05 Bal. B invention 5.98 4 0.35 0.02 0.02 Bal. C invention 6.00 4 0.36 0.01 Bal. D invention 6.00 4.2 0.38 0.02 0.08 0.02 Bal. E comparative 6.01 3.5 0.31 Bal. F comparative 5.98 4 0.35 Bal. G comparative 6.01 4 0.35 Bal. H comparative 5.97 4 0.4 Bal. J comparative 5.96 5.0 0.37 Bal.

[0062] The powders for each sample were milled together with a milling liquid and an organic binder being Polyethylene glycol (PEG) in a ball mill. The milling liquid consisted of water and ethanol. The slurry formed was dried in a spray dryer and thereafter pressed to inserts in a pressing operation at about 172 MPa. All powder batches for samples/variants except samples C and J were milled in 1 kg batches and spray dried in a lab-spray. Samples C and J were milled and spray dried in full-scale production. The pressed samples were sintered in vacuum for 30 minutes followed by 30 minutes at an Ar pressure of 30 Bar at a temperature of about 1390? C.

[0063] The coercivity (Hc), degree of magnetic moment (S), hardness (HV30), strength toughness (K.sub.1C), (ds) and shrinkage from pressed to sintered powder were measured on the sintered samples. The result is shown in Table 2.

TABLE-US-00002 TABLE 2 Hc S K.sub.1C Shrinkage Sample [kA/m] [%] HV30 [MPam.sup.?1/2] ds (%) A Invention 29.8 67.37 1978 9.1 15.10 17.62 B invention 28.3 71.59 1966 9.1 15.10 17.49 C invention 30.3 78.73 2002 9.1 15.15 17.94 D invention 30.5 75.16 1970 9.2 15.07 17.44 E comparative 26.6 65.26 1968 8.8 15.20 17.21 F comparative 26.1 71.59 1976 9.1 15.13 17.23 G comparative 27.5 81.17 1972 9.2 15.11 17.26 H comparative 28.4 62.01 1941 9.1 15.13 17.56 J comparative 32.2 90.26 1998 9.8 15.02 20.08

[0064] All sintered samples in Table 2 had a porosity of A00 according to ISO 4499-4:2016 (E), i.e. no pores detected at a magnification of ?100.

Coating of Samples C and J

[0065] Substrates of sample C and sample J were deposited with a 2.6 ?m thick PVD coating, the samples are hereinafter named coated sample C and coated sample J. The PVD coating has an inner layer of 0.3 ?m TiAlN closes to the substrate followed by a 2.3 ?m thick nanolaminate of TiAlN/TiSiN, and a thin outer layer of TiSiN. The layers of the nanolaminate is about 20-40 nm The composition of the TiAlN-layers of the coating is (Ti.sub.0.33Al.sub.0.67)N and the composition of the TiSiN-layers is (Ti.sub.0.90Si.sub.0.10)N.

Cutting Tests

[0066] Longitudinal turning was performed by comparing the performance of coated samples C and J at the same cutting conditions on a workpiece material of toughened steel. The chemical composition and mechanical properties of the workpiece material are presented in Table 1 and Table 2, respectively. [0067] The cutting data used: [0068] cutting speed, v.sub.c: 160 m/min [0069] cutting feed, f: 0.20 mm/revolution [0070] depth of cut, ap: 1 mm [0071] Coolant was used.

[0072] Work piece material: Orvar Supreme from Uddeholm being toughened and with a hardness of 48 HRC.

[0073] The cutting tools used had CNMG120408 insert geometry.

[0074] The tool life of the cutting tools inserts was determined by looking at the flank wear (W) of the inserts after 5, 10 and 15 minutes cutting time, see Table 3 and also FIG. 1. The tests were terminated when the flank wear had passed a maximum value of 0.2 mm or tool breakage.

[0075] 3 edges of each tool were tested and the result can be seen in Table 3 below.

TABLE-US-00003 TABLE 3 Sample Tool life (min) C-1 (Invention) 14 C-2 (Invention) 15 C-3 (Invention) 14 J-3 (Comparative) 4 J-4 (Comparative) 10 J-5 (Comparative) 5

[0076] From FIG. 1 it can be seen that the average tool life at a cutting speed of 160 m/min for three cutting edges according to a cutting tool of the present disclosure are at least twice the average tool life of the three cutting edges of the comparative cutting tool. FIG. 1 also shows that the cutting edge having the shortest tool life of the cutting tool according to the present disclosure sample C, is longer to the longest tool life of the comparative cutting tool, sample J.

[0077] FIGS. 3a-3c shows edge C-2 after 5, 10 and 15 minutes of machining. As can be seen the edge was not exceeding flank wear of 0.2 mm before the control at 15 minutes.

[0078] FIGS. 4a and 4b show the edge J-4 after 5 and 10 minutes of machining, respectively. As can be seen from FIG. 4b the flank face was more than 0.2 mm already at the control after 10 minutes machining.

[0079] As can be seen from the machining test sample C is superior to comparative sample J in turning operations in toughened steel.

[0080] The combination of low cobalt content and a coarser WC grain size provide for a cutting insert having both improved cutting performance as well as improved properties when it comes to shrinkage after sintering.