SE519828C2 - Cut off a cemented carbide body with a binder phase enriched surface zone and a coating and method of making it - Google Patents

Abstract

The present invention relates to a cutting tool insert for machining of steel comprising a cemented carbide body and a coating. The cemented carbide body comprises WC, 5-12 wt-% Co and 3-11 wt-% of cubic carbides of metals Ta, Ti and W. The amount of Nb is below 0.1 wt-% and the ratio Ta/Ti is 1,0-4,0. The Co-binder phase is highly alloyed with W with a CW-ratio of 0,75-0,95 and, finally, the cemented carbide body has a binder phase enriched and essentially gamma phase free surface zone of a thickness of 5-50 mu m. <IMAGE>

Description

30 40 «« -. m h- .... 519 828 2 MS is the measured saturation magnetization for the cemented carbide in kA / m and weight% Co is the weight percentage Co in the cemented carbide. The CW ratio assumes a value <1 and the lower the CW ratio, the higher the W content in the binder phase. It has now been found according to the invention that better cutting performance is obtained if the CW ratio is 0.75-0.95, preferably 0.78-0.83.

The present invention can be applied to cemented carbides having a composition of 5-12, and 3-1, WC. The Nb content shall not exceed 0% by weight. The weight ratio Ta / Ti should be 1.0-4.0, WC has an average grain size of 1.0 to 4.0 μm, preferably 1.5 to 3.0 μm. The cemented carbide body may contain small amount, <1% by volume, n-phase (M6C). preferably 9-11, weight percent Co-binder phase, preferably 7-10, weight percent TaC + TiC and residue preferably 2-3.0.

Inserts according to the invention are further provided with a coating consisting of substantially 3-12 μm columnar TiCN layer followed by a 1-8 μm thick Al 2 O 3 layer deposited, for example according to one of the patents US 5,766,782, US 5,654,035, US 5,674,564 , US 5,702,808 preferably with a K-Al 2 O 3 layer.

By using coatings with different thicknesses on the cemented carbide body according to the invention, the properties of the coated insert can be optimized to suit specific cutting conditions. In one embodiment, a cemented carbide insert made according to the invention is provided with a coating consisting of: 6 μm TiCN, 5 μm Al 2 O 3 and 1 μm TiN. This coated insert is specially adapted for operation in steel. according to the invention provided with a coating consisting of: 4 μm In another embodiment, a cemented carbide insert is made of TiCN, 2 μm Al 2 O 3 and 1 μm TiN. This coating is specially adapted for cutting operations in stainless steel.

The invention also relates to a method of manufacturing inserts comprising a cemented carbide substrate consisting of a binder phase of Co, WC and a gamma phase of the elements Ta and Ti with a binder phase-enriched surface zone substantially free of gamma phase and a coating. A powder mixture containing 5-12, preferably 9-1, weight percent of and 3-11, TaC + TiC and residual WC with an average grain size of 1.0-4.0 μm, binder phase consisting of Co, preferably 7-10 , weight pro- preferably 1.5-3.0 μm is prepared. The NB content must not exceed 0.1% by weight. The weight ratio Ta / Ti should be 1.0-4 / 0 / is added either through the powder as carbonitrides or / and preferably below 2.0-3.0. Well-controlled amounts of nitrogen 20 25 30 40 5119 8: 2? šH: u: ïš '"" sintering processes via the sintering gas atmosphere. The amount of added nitrogen will determine the rate of dissolution of the cubic phase during the sintering process and therefore determine the total distribution of the elements in the cemented carbide after solidification. The optimum amount of nitrogen to be added depends on the composition of the cemented carbide and in particular on the amount of cubic phase and varies between 0.6 and 2.0% of the weight of the elements Ti and Ta. The exact conditions depend to some extent on the design of the sintering equipment used. It is within the competence of the person skilled in the art to determine whether the desired surface zone of the cemented carbide has been obtained and to modify the nitrogen addition and the sintering process in accordance with the present description in order to obtain the desired result.

The raw materials are mixed with pressing agent and possibly W so that the desired CW ratio is obtained and the mixture is ground and spray-dried to obtain a powder material with desired properties. Then the powder is pressed and sintered. The sintering is carried out at a temperature of 1300-1500 OC in a controlled atmosphere of about 50 mbar followed by cooling. After conventional post-sintering treatments involving edge rounding, a hard, durable coating is deposited as above with CVD or MT-CVD technology.

Example 1 A.) Cemented carbide cutting inserts of the form CNMG 120408-PM and SNMG1220412-PR with the composition 9.9% by weight of Co, 6.0% by weight of TaC, 2.5% by weight of TiC, an average grain size of 2.0 μm were prepared according to the invention.

The nitrogen was added to the carbide powder as TiCN. Sintering was performed at 1450 ° C in an atmosphere consisting of Ar at a total pressure of about 50 mbar.

Metallographic examination showed that the inserts produced had a gamma-phase-free zone of 15 μm. Fig. 1 shows a curve of the Co-enrichment near the surface measured by image analysis technique. Co is enriched to a peak level of 1.3 times the content of the interior. The saturation magnetization value was measured and used to calculate the CW value. A CW average of 0.81 was achieved.

After conventional pre-coating treatment such as edge rounding, cleaning, etc., the inserts were coated in a CVD process comprising a first coating with a thin layer of 6 μm thick layer of TiCN with columnar grains using 519 828 MTCVD technology (process temperature 850 OC and CH3CN as carbon / nitrogen source). In a subsequent process step during the same coating cycle, a 5 μm thick K-Al 2 O 3 layer was deposited according to patent US 5,674,564. A 1.0 μm TiN layer was precipitated on top of the K-Al 2 O 3 layer.

The coated insert was brushed to evenly remove the TiN coating from the edge line.

B.) Heavy metal lathe inserts of the form CNMG 120408-PM and SNMG120412-PR with the composition 10.0 wt% Co, 2.9 wt% TaC, 3.4 wt% TiC, 0.5 wt% NbC and 0.2 wt% TiN and balance WC with an average grain size of 2.1 μm was prepared. The inserts were sintered in the same process as A. Metallographic examination showed that the produced inserts had a gamma phase free zone of 15 μm. The saturation magnetization value was measured and used to calculate the CW value. A CW mean of 0.81 was obtained. The inserts were subjected to the same pre-coating treatment as A, coated in the same coating process and also brushed in the same way as A.

C.) Carbide lathe inserts of the form CNMG 120408-PM and SNMG120412-PR with the composition 10.0 wt% Co, 3.0 wt% TaC, 6.3 wt% ZrC and balance WC with an average grain size of 2.5 μm were prepared.

Metallographic examination showed that the inserts produced had a gamma-phase-free zone of 12 μm. Saturation magnetization value A CW mean value The inserts were subjected to the same pre-coating treatment and were used to calculate the CW value. of 0.79 was obtained. as A, was coated in the same coating process and also brushed in the same manner as A.

Example 2 Cuts from A, B and C were tested for toughness in an intermittent longitudinal turning operation. Material: Carbon steel SS13l2.

Cutting data: Cutting speed = 130 m / min Cutting depth = 1.5 mm Measurement = Start with 0.15 mm and gradually increased by 0.10 mm / min to edge breakage. 8 edges of each variant were tested Cutting shape: CNMG120408-PM 20 30 - »«. . a 519 8285 §_g§: j3zï __. f Result: Average feed at break Cutter A 0.31 mm / revolution Cutter B 0.22 mm / revolution Cutter C 0.22 mm / revolution Example 3 Cuts from A, B and C were tested with with respect to resistance to plastic deformation in longitudinal turning of alloy steel (AISI 4340).

Cutting shape: CNMG 120408-PM Cutting data: Cutting speed = 100 m / min Feed rate = 0.7 mm / RPM.

Cutting depth = 2 mm Time in engagement: 0.50 min The plastic deformation was measured as edge depression in the nose of the inserts.

Result: Edge lowering, um Insert A 49 Insert B 63 Insert C 62 Example 4 Test performed at a final consumer who manufactures rear axles for trucks. The inserts from A and C were tested in a three-turn operation with high toughness requirements due to intermittent interventions. The inserts were driven to edge breakage. The cutting mold SNMG120412-PR was used.

Results: Number of machined components Operation 1 2 3 Variant A 172 219 119 Variant C 20 11 50 Examples 2, 3 and 4 show that the inserts A according to the invention show much better toughness in combination with slightly better resistance to plastic deformation in comparison with the inserts. B and C according to known technology.

Claims (10)

20 25 30 35 i! mm Requirements A cutting insert for machining steel comprising a cemented carbide body and a coating characterized in that said body consists of WC, 5-12% by weight of Co and 3-11% by weight of cubic carbides of the metals Ta, Ti and W and that the amount of Zr, Nb and Hf is less than or equal to 0.1% by weight respectively and that the ratio Ta / Ti is 1.0-4.0 and that the Co-binding phase is highly alloyed with W with a CW ratio of O 75-0.95 and that said cemented carbide body has a binder phase-enriched and substantially gamma-phase-free surface zone of a thickness of 5-50 μm. A insert according to claim 1, characterized in that the thickness of the surface zone is within 10-30 μm. A insert according to claim 1 or 2, characterized in that the Co content is preferably within 9-11% by weight. A insert according to claim 1, 2 or 3, characterized in that the content of TiC and TaC is preferably within 7-10% by weight. An insert according to any one of claims 1-4, characterized in that said coating comprises a 3-12 μm columnar TiCN layer followed by a 2-12 μm thick Al 2 O 3 layer. A insert according to the preceding claim, characterized in that said Al2O3 layer is K-Al2O3. An insert according to any one of claims 1 to 6, characterized by an outermost layer of TiN. An insert according to the preceding claim is characterized in that the TiN layer in the edge line is removed by brushing or by blasting. A cutting insert according to any one of claims 1-8, characterized in that the average WC grain size is 1.0-4.0 hm. A method of making an insert comprising a cemented carbide substrate having a binder phase-enriched surface zone and a coating, wherein said WC and a cubic carbon-said binder phase-enriched surface zone are substantially free of substrate consisting of a binder phase of Co, nitride phase, said cubic carbonitride phase and with a substantially constant thickness around the insert characterized by the preparation of a powder mixture containing WC, 5-12, preferably 9-11, weight percent Co and 3-11, preferably 7-10, weight percent cubic carbides of the metals Ta and Ti, wherein N .4-.1 ..-.- =; . . .. is added in an amount of between 0.6-2.0% by weight of the elements of Ta and Ti mixture of said powder with pressing agent and optionally W so that the desired CW ratio is obtained grinding and spray drying of the mixture to a powder material. material with desired properties pressing and sintering of the powder material at a temperature of 1300-1500 ° C in a controlled atmosphere of about 50 mbar followed by cooling conventional treatments after sintering comprising edge rounding and precipitation of a hard, durable coating with CVD or MT CVD technology.