Cutting insert and manufacture of same

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to coated cemented carbide cutting inserts, which are particularly useful for turning steel or stainless steel, especially for operations where the toughness properties of the insert are highly demanded. Cemented carbide inserts have a surface region with an elemental composition different from the bulk composition that simultaneously produces excellent toughness properties and good plastic deformation resistance.

【0002】

[Conventional technology]

Today's high-performance cutting tools need to have high wear resistance, high toughness properties, and good composition deformation resistance. Improving the toughness behavior of the cutting insert can be achieved by increasing the WC grain size and / or increasing the overall bound phase content, but such changes simultaneously result in a significant loss of composition deformation resistance. Occurs.

【0003】

A method of improving toughness behavior by introducing the thickness of the surface region, which is essentially gamma-free and enriched with the bound phase, with a thickness of about 20-40 μm in the insert by so-called gradient sintering technology, for example. It is known in US Pat. Nos. 4,277,283, 4,497,874, 4,548,786, 4,640,931, 5,484,468, 5,549,980, 5,649,279, 5,729,823, etc. The feature of these patents is that there is no gamma phase in the surface region and the bound phase is enriched.

【0004】

[Problems to be Solved by the Invention]

By keeping the ratio of Ta to Ti within a certain range and keeping the bonded phase with high W alloyed, the composition of the optimized gamma phase, that is, the gamma consisting essentially of TaC and TiC in addition to WC. The phases reveal that the toughness properties of grade-sintered cutting inserts can be significantly improved without loss of compositional deformation resistance.

【0005】

[Means for solving problems]

According to the present invention, the average bound phase content (by volume) of thickness 5-50 μm, preferably 10-30 μm, essentially free of gamma phase and in the range 1.2-2.0 times the bulk bound phase content. Provided is a coated cemented carbide insert containing a bonded phase-enriched surface region having. The gamma phase essentially consists of TaC and TiC and WC dissolved in the gamma phase during some sintering. The ratio Ta / Ti is 1.0 to 4.0, preferably 2.0 to 3.0.

【0006】

BEST MODE FOR CARRYING OUT THE INVENTION

The bond phase is high and W is alloyed. The W content in the bound phase is CW ratio = M_S/ ((Mass% of Co) × 0.0161) Can be expressed as M here_SIs the measured saturation magnetization of the cemented carbide body at kA / m, and the mass% of Co is the mass ratio of Co in the cemented carbide. The CW ratio takes a value of 1 or less, and the smaller the CW ratio, the higher the W content in the bound phase. It has been clarified by the present invention that the cutting performance is improved when the CW ratio is in the range of 0.75 to 0.95, preferably 0.80 to 0.85.

【0007】

The present invention is a cemented carbide having a composition consisting of a bonded phase consisting of 5 to 12, preferably 9 to 11% by mass of Co, 3 to 11, preferably 7 to 10% by mass of TaC + TiC, and the balance of WC. Applicable to alloys. Nb content should not exceed 0.1% by weight. The mass ratio Ta / Ti should be 1.0 to 4.0, preferably 2.0 to 3.0. The WC has an average grain size of 1.0 to 4.0 μm, preferably 1.5 to 3.0 μm. A small amount of cemented carbide body, less than 1% by volume η phase (M)₆C) may be included.

【0008】

The insert according to the invention is more basically a TiCN layer of 3-12 μm columnar structure deposited according to any of US Pat. Nos. 5,766,782, 5,654,035, 5,674,564, 5,702,808, followed by 1-8 μm Thickness of Al₂O₃It has a coating containing layers, preferably κ-Al.₂O₃It has a layer and preferably the outermost thin layer of TiN, which TiN layer is preferably removed at the cutting edge by brushing or blasting.

【0009】

According to the present invention, by applying coatings having various thicknesses on the cemented carbide body, the characteristics of the coating insert can be optimized to meet specific cutting conditions. In one embodiment, the cemented carbide inserts made according to the present invention are 6 μm TiCN, 5 μm Al.₂O₃And a coating of 1 μm TiN. This coated insert is particularly suitable for working with steel. In another embodiment, the cemented carbide inserts made according to the present invention are 4 μm TiCN, 2 μm Al.₂O₃And a coating of 1 μm TiN. This coating is particularly suitable for cutting work on stainless steel.

【0010】

The present invention is a bonding phase that is essentially free of the gamma phase. It also relates to the method of manufacturing the insert. Bonding phase consisting of 5-12, preferably 9-11 mass% Co, 3-11, preferably 7-10 mass% TaC + TiC, 1.0-4.0, preferably 1.5-3.0 μm average grains Prepare a powder mixture containing the rest of the WC with a size. Nb content should not exceed 0.1% by weight. The mass ratio Ta / Ti should be 1.0 to 4.0, preferably 2.0 to 3.0. A well controlled amount of nitrogen needs to be added by the carbonitride powder and / or during the sintering process through a sintering gas atmosphere. The amount of nitrogen added determines the dissolution rate of the cubic phase during the sintering process and thus the overall 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, especially the amount of cubic phase, and the mass of Ti and Ta elements is 0.6 to 2.0. Change between%. The exact conditions also depend to some extent on the design of the sintering equipment used. It is a skilled technician to determine if the required cemented carbide surface area has been obtained and to change the nitrogen addition and sintering conditions according to the present invention to obtain the desired results.

【0011】

The raw materials are mixed with a compression molding agent and optionally W to obtain the desired CW ratio, the mixture is mill mixed and spray dried to obtain a powder material with the desired properties. The powder material is then molded and sintered. Sintering is about 5 x 10³It is carried out in a controlled atmosphere of Pa (50 mbar) at a temperature of 1300 to 1500 ° C and then cooled. After conventional post-sintering treatments, including rounding of the cutting edge, a hard wear resistant coating as described above is deposited by CVD or MT-CVD (medium temperature CVD).

【0012】

[Example]

Example 1 A) Composition of 9.9% by mass Co, 6.0% by mass TaC, 2.5% by mass TiC, less than 0.1% by mass NbC, and 0.3% by mass TiN, and the balance of WC with an average grain size of 2.0 μm. CNMG 120408-PM and SNMG 120412-PR type cemented carbide turning inserts having were prepared according to the present invention. Nitrogen was added to the cemented carbide powder as TiCN. Sintering about 5 x 10³It was performed at 1450 ° C. in an atmosphere consisting of Ar at full pressure of Pa.

【0013】

Observation of the metallographic structure revealed that the inserted insert had a region containing no gamma phase of 15 μm. FIG. 1 shows a graph of Co-enrichment near the surface measured by image analysis technology. Co was enriched to a peak concentration of 1.3 times the bulk content. The saturation magnetization was measured and used to calculate the CW value. An average CW value of 0.81 was obtained.

【0014】

After conventional coating pretreatment such as cutting edge honing, cleaning, etc., MTCVD technology (process temperature 850 ° C, CH as carbon / nitrogen source)₃Using CN), the inserts were coated by the CVD method, including a thin layer of less than 1 μm of the first TiN, followed by a thick layer of TiCN of 6 μm of columnar grains. In the subsequent manufacturing process of the same coating process, κ-Al with a thickness of 5 μm according to U.S. Pat. No. 5,674,564.₂O₃Layers were deposited. κ-Al₂O₃A 1.0 μm TiN layer was deposited above the layer. The coated insert was brushed to smoothly remove the TiN coating from the cutting edge.

【0015】

B) It has a composition of 10.0% by mass Co, 2.9% by mass TaC, 3.4% by mass TiC, 0.5% by mass NbC, and 0.2% by mass TiN, and the balance of WC with an average grain size of 2.1 μm. , CNMG 120408-PM and SNMG 120412-PR type cemented carbide turning inserts were prepared. The insert was sintered in the same manner as in A. Metallographic observations showed that the inserts produced had a gamma phase-free region of 15 μm. The saturation magnetization value was measured and used to calculate the CW value. An average CW value of 0.81 was obtained. The inserts were subjected to the same precoating treatment as A, coated with the same coating treatment, and brushed as with A.

【0016】

C) CNMG 120408-PM and SNMG 120412-PR type cemented carbide having a composition of 10.0% by mass Co, 3.0% by mass TaC, 6.3% by mass ZrC and the balance of WC with an average grain size of 2.5 μm. A hard alloy turning insert was produced. Metallographic observations showed that the inserts produced had a 12 μm gamma phase-free region. The saturation magnetization value was measured and used to calculate the CW value. An average CW value of 0.79 was obtained. The inserts were subjected to the same precoating treatment as A, coated with the same coating treatment, and brushed as with A. Example 2 Inserts A, B and C were evaluated for toughness during longitudinal turning operations in intermittent cutting.

【0017】

Material: Carbon Steel SS1312 Cutting data: Cutting speed 130 m / min Cutting depth 1.5 mm Start with a feed of 0.15 mm and 0.10 mm / min until the blade breaks Increased in Evaluate each of the 8 cutting edges Insert shape: CNMG 120408-PM Result: Average feed on breakage Insert A 0.31 mm / rotation Insert B 0.22 mm / rotation Insert C 0.22 mm / rotation Example 3 Inserts A, B and C were evaluated for plastic deformation resistance during longitudinal turning of alloy steel (AISI 4340).

【0018】

<img file="JP2000334608A_D0001.tif" />The plastic deformation was measured as a dent in the cutting edge at the tip of the insert (nose).

【0019】

Result: Cutting edge depression (μm) Insert A 49 Insert B 63 Insert C 62 Example 4 Tested in the production of rear shafts for trucks. Inserts A and C were evaluated in three types of turning operations that require high toughness due to intermittent cutting. The insert was used until the cutting edge was damaged. SNMG 120412-PR type insert was used.

【0020】

Result Number of machined parts Work 1 2 3 Insert A 172 219 119 Insert B 20 11 50 Examples 2, 3 and 4 show that the insert A according to the invention exhibits significantly better toughness, with some improved compositional deformation resistance, as compared to the inserts B and C according to the prior art.

【0021】

[Effect of the invention]

According to the present invention, the toughness characteristics of a gradient sintered cutting insert can be significantly improved without loss of compositional deformation resistance.

[Simple explanation of drawings]

[Figure 1]

FIG. 1 shows a graph of Co-enrichment near the surface measured by an image analysis technique.