Carbide alloy

Abstract

Providing cemented carbide with excellent chipping resistance. [Solution] A cemented carbide containing hard phase WC particles and a binder phase Co, but without Ti, wherein the circular equivalent average particle size D of the WC particles is 1 μm or more and 3 μm or less, and 20% or more of the number of WC particles having a particle size greater than or equal to the average particle size have stepped irregularities on their surface.

Description

Technical Field

[0001] The present invention relates to cemented carbide.

Background Art

[0002] Patent Document 1 discloses a cemented carbide having WC particles with an average particle size of 1 to 2 μm. As disclosed in Patent Document 1, coarse WC particles have a triangular or square shape. Patent Document 2 discloses a cemented carbide in which fine carbonitrides containing titanium as a metal component are dispersed on the surface of WC particles to form fine irregularities on the surface of the WC particles.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present inventor has confirmed that there is room for improvement in chipping resistance for a cutting tool using a cemented carbide having WC particles with an average particle size of 1 μm or more as a hard phase. The present invention aims to provide a cemented carbide excellent in chipping resistance and wear resistance.

Means for Solving the Problems

[0005] The cemented carbide according to one embodiment of the present invention is a cemented carbide containing WC particles as a hard phase and Co as a binder phase, not containing Ti, wherein the equivalent circle average particle size D of the WC particles is 1 μm or more and 3 μm or less, and 20% or more of the number of the WC particles having an equivalent circle particle size of the average particle size D or more have stepped irregularities on the surface.

[0006] The cemented carbide according to one embodiment of the present invention is further Preferably, the mixture contains 5.0-12.0% by mass of Co, 0.3-1.0% by mass of Cr, and 1.0-5.0% by mass of Ta, with the remainder consisting of WC and unavoidable impurities. [Effects of the Invention]

[0007] When the cemented carbide according to this embodiment is applied to a cutting tool, a cutting tool with excellent chipping resistance and wear resistance can be obtained. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram illustrating the stepped surface irregularities on the surface of WC particles. [Figure 2] This is a tissue observation image of Example 1 (SEM observation magnified 10,000 times). [Figure 3] This is a tissue observation image of Comparative Example 1 (SEM observation magnified 10,000 times). [Figure 4] This is a tissue observation image of Comparative Example 2 (SEM observation magnified 10,000 times). [Figure 5] This is a tissue observation image of Comparative Example 3 (SEM observation magnified 10,000 times). [Figure 6] This is a tissue observation image of Comparative Example 4 (SEM observation magnified 10,000 times). [Figure 7] This is a tissue observation image of Comparative Example 5 (SEM observation magnified 10,000 times). [Modes for carrying out the invention]

[0009] The inventors diligently researched the microstructure of cemented carbide alloys with excellent chipping resistance. As a result, they discovered that cemented carbide alloys with a high proportion of WC particles having stepped irregularities on their surface exhibit superior chipping resistance. Although the mechanism by which chipping resistance is improved is not clear, it is presumed that the stepped irregularities on the surface of the WC particles increase the adhesion force with the Co bonding phase, thereby suppressing the loss of WC particles during machining.

[0010] Normally, many fine WC particles have uneven surfaces, but WC particles that have grown larger through grain growth have triangular or square shapes with straight sides. Patent document 2 discloses a cemented carbide in which uneven surfaces are formed on the surface of coarse WC particles, but many fine particles of titanium-containing carbonitrides are present on the surface of the WC particles, which may reduce the adhesion between the WC particles and the bonding phase Co. Since the cemented carbide according to this embodiment does not contain Ti, a certain proportion or more of WC particles within a predetermined particle size range have stepped irregularities on their surface without containing titanium-based carbonitrides.

[0011] In this embodiment, the cemented carbide has an average particle size D of WC particles of 1 μm or more and 3 μm or less. When the average particle size of WC particles is within this range, applying this cemented carbide to the tool base of a cutting tool makes it possible to obtain a cutting tool with an excellent balance of wear resistance and toughness in cutting processes of mild steel and the like.

[0012] Here, the average particle size D of the WC particles is determined as follows. The surface or cross-section of a cemented carbide is smoothed (mirror finish) so as not to interfere with EBSD and SEM observation, and multiple observation fields (more than 10) measuring 8.93 μm vertically × 12.70 μm horizontally are set up. Then, EBSD observation and SEM observation (at a magnification of 10,000x) are performed in all observation fields to define the outline of the WC particles and determine the diameter of a circle (equivalent circle diameter) that gives an area equal to the area of ​​each WC particle. Then, a graph is created with the diameter of this circle on the vertical axis and the distribution of each WC particle (cumulative number of particles relative to the diameter of the circle relative to the total number of observed WC particles) on the horizontal axis. The average particle size D of the WC particles is defined as the diameter of the circle (median diameter) when the cumulative frequency of the area of ​​the WC particle distribution reaches 50%.

[0013] Furthermore, in this embodiment, it is preferable that 20% or more (more preferably 30% or more) of the WC particles having an average particle size D (cumulative value of 50%) or larger in the distribution of WC particles have stepped irregularities on their surface.

[0014] Here, having stepped irregularities on the surface of WC particles means the following. In all of the aforementioned observation fields, define the outline of each WC particle. Consider each WC particle as a polygon and draw line segments along this outline. That is, the outline of each WC particle is defined by a plurality of line segments. Among these plurality of line segments, there are parallel line segments having an interval of 0.2 μm or more, and a WC particle having at least one location where one line segment exists between these parallel line segments is treated as a WC particle having stepped irregularities. Note that parallel means a state that can be visually recognized as parallel by those skilled in the art in the observation field.

[0015] That is, referring to FIG. 1, define the outline 1 of the WC particle and draw line segments along this outer periphery. Among these line segments, there are parallel line segments such as L1 and L2 having an interval of 0.2 μm or more, and a WC particle having at least one location where L3, which is one line segment, exists between L1 and L2 is called a WC particle having stepped irregularities on the surface.

[0016] For WC particles having a size equal to or larger than the average particle size of WC particles (obtained from all fields) for each observation field, calculate the arithmetic mean value by obtaining the percentage of the number of those having stepped irregularities. If the number of WC particles having these stepped irregularities increases, the defect resistance is enhanced.

[0017] · Preferred composition It is more preferable that the cemented carbide according to the present embodiment contains Co at 5.0 to 12.0 mass% in order to obtain high hardness and high toughness. Furthermore, elements other than W, C, and Co may be contained. For example, Cr and Ta may be contained. Cr suppresses the grain growth of WC and makes it easier to form stepped fine irregularities even on coarse WC particles. Cr is more preferably contained at 0.3 to 1.0 mass% as a metal element. Ta suppresses the grain growth of WC, makes it easier to form stepped fine irregularities even on coarse WC particles, and enhances the heat resistance. Ta is more preferably contained at 1.0 to 5.0 mass% as a metal element.

[0018] In the claims and specification, unavoidable impurities refer to the general term for nonmetallic elements present in solid solution or combination with the metal element, and elements unintentionally included during the manufacturing process. Nonmetallic elements present in solid solution or combination with the metal element are C and N.

[0019] The cemented carbide according to the embodiment of the present invention does not contain Ti. "Ti-free" means that the Ti content is less than 1.0 mass%, and may be below the detection limit. The absence of Ti eliminates the risk of reduced adhesion between the WC particles and the Co bonding phase.

[0020] • Preferred physical properties The cemented carbide according to the embodiment of the present invention preferably has the following physical properties.

[0021] (1) Magnetic saturation value By measuring the magnetic saturation value, it is possible to determine whether carbon is present in an appropriate amount. The magnetic saturation value is 15.0~19.0 (μTm). 3 It is preferable that it be ( / kg).

[0022] (2) Coercivity Coercivity indicates the average grain size of the hard phase. A coercivity of 130-190 (Oe) is preferable.

[0023] (3)Hardness Hardness is an indicator of resistance to plastic deformation. A hardness of 85.0 to 93.0 (HRA) is preferable.

[0024] (4) Crack resistance Crack resistance serves as an indicator for evaluating toughness. A crack resistance value of 150 to 250 kg / mm ​​is preferable. Crack resistance is calculated by mirror-finishing the surface or cross-section of a cemented carbide, pressing a Vickers indenter into it, and dividing the indentation load by the sum of the lengths of the four cracks that form at the four corners of the indentation.

[0025] The following are examples of conditions that can be used to indent a Vickers indenter. Test machine used: AVK model manufactured by Akashi Seisakusho Co., Ltd. Pushing force: 50kgf (approx. 490N) Push-in holding time: 15 seconds Test machine used: AVK model manufactured by Akashi Seisakusho Co., Ltd. Pushing force: 50kgf (approx. 490N) Push-in holding time: 15 seconds

[0026] ·Manufacturing method The manufacturing method for cemented carbide according to an embodiment of the present invention will now be described. It is preferable to use so-called highly crystalline raw material powder, such as high-temperature carbide WC raw material powder, as the raw material powder for WC. Highly crystalline raw material powder has high powder strength and is less prone to over-grinding. It is preferable to use high-temperature carbide WC raw material powder with an average particle size (Fischer diameter) of 3.0 to 7.0 μm, add WC raw material powder afterwards to suppress over-grinding and mix, hold at 1380°C to 1450°C for 1 hour or more to sinter, and then rapidly cool from the sintering temperature to 1200°C at a cooling temperature of 100°C / min or more. [Examples]

[0027] The manufacturing method of the embodiment will be described. The present invention is not limited to this embodiment. In Example 1, the following WC raw material powders were used: DM300HT (average particle size 3.5 μm) manufactured by Starck, Co powder (average particle size 1.2 μm), Cr3C2 powder (average particle size 1.0 μm), and TaC powder (average particle size 1.5 μm). Here, the average particle size of the powder is the Fischer diameter.

[0028] The raw material powders were blended to achieve the composition shown in Table 1. 2% by mass of paraffin wax and ethyl alcohol (with a water content of less than 10%) relative to the total mass of all raw material powders, along with all other raw material powders except the WC powder, were loaded into an attritor. The mixture was then mixed at 64 rpm for 4.5 hours. After that, the WC powder was added and the mixture was mixed at 20 rpm for 3 hours to prepare a WC mixed slurry.

[0029] Subsequently, the WC mixed slurry was dried and granulated using a spray dryer to obtain granulated powder. A molded body for the base material of a milling insert (SEE42TN-G9Y) was formed using the obtained granulated powder. Then, after heating and holding at a sintering temperature of 1380°C for 1 hour, argon gas was introduced from the sintering temperature and the mixture was cooled to 1200°C at a cooling rate of 120°C / min to produce a sintered body made of a cemented carbide alloy with a medium carbon composition.

[0030] Comparative Example 1 was manufactured in the same manner as Example 1, except that Starck's MAS450 (average particle size 4.5 μm) was used as the WC raw material powder. MAS450 is a powder with inferior crystallinity compared to DM300HT.

[0031] Comparative Example 2 was manufactured using the same DM method as Example 1, except that the sintering temperature was 1400°C and the cooling rate was 1.7°C / min.

[0032] Comparative Example 3 was manufactured in the same manner as Example 1, except that Starck's MAS450 (average particle size 4.5 μm) was used as the WC raw material powder, the sintering temperature was 1400°C, and the cooling rate was 1.7°C / min.

[0033] Comparative Example 4 was manufactured in the same manner as Example 1, except that, in order to achieve a hardness (HRA) similar to Example 1, equal amounts of WC50U (average particle size 4.5 μm) from Nippon Shinkinzoku Co., Ltd. and WC25K (average particle size 2.5 μm) from Tegutec Co., Ltd. were blended as WC raw material powders, and the content of Co, Ta, and Cr was reduced as shown in Table 1. All of the WC raw material powders in Comparative Example 4 are powders with the same crystallinity as DM300HT.

[0034] Comparative Example 5 evaluated a commercially available insert having almost the same Co content and almost the same hardness (HRA) as Example 1.

[0035] Next, the sintered bodies of Example 1 and Comparative Examples 1-5, which were prepared by mirror finishing, were subjected to microstructural observation using EPMA (JEOL JXA-8530F). Then, WC particles were observed at a magnification of 10,000x using EBSD (Electron Back Scatter Diffraction) as described above. The results of the microstructural and physical property evaluations are shown in Table 2.

[0036] [Table 1]

[0037] In Table 1, "-" indicates that the value is below the detection limit. The WC column indicates that the sample contains unavoidable impurities.

[0038] [Table 2]

[0039] Figure 12 shows a photograph of the microstructure of Example 1. It can be confirmed that Example 1 has a large number of WC particles with stepped irregularities on the surface. In Example 1, 31% of WC particles with a particle size of average particle size D or larger had stepped irregularities on the surface.

[0040] Figures 3-6 show photographs of the tissue observations of Comparative Examples 1-4. In all cases, less than 10% of the WC particles had stepped irregularities on their surface. Figure 7 shows a photograph of the microstructure of Comparative Example 5. In Comparative Example 5, 18% of WC particles with an average particle size of D or larger had stepped irregularities on their surface, which was less than in Example 1.

[0041] Next, coated inserts were fabricated for the cemented carbide alloys of the examples and comparative examples by CVD, consisting of TiCN with an average film thickness of 5 μm and α-Al2O3 with an average film thickness of approximately 4 μm on top of it. Cutting performance evaluations were performed under the following conditions. The results of the cutting performance evaluations are shown in Table 3.

[0042] (Processing condition 1: Conditions for evaluating chipping properties) • Cutter model number: A45E4125R-6 Insert model number: SEE42TN-G9Y • Number of teeth: 1 ·Cutting method: Plane processing • Workpiece material: S50C (220HB) with φ4 hole • Cutting depth: 1.0 mm axially, 85 mm radially ·Cutting speed: 250m / min • Feed rate per blade: 0.3 mm / blade • Projection: 63mm ·Cutting length: 7.00m

[0043] (Processing conditions 2: Conditions for evaluating wear resistance) • Cutter model number: A45E4125R-6 Insert model number: SEE42TN-G9Y • Number of teeth: 1 ·Cutting method: Plane processing • Workpiece material: SLD(A) • Cutting depth: 1.5 mm axially, 100 mm radially ·Cutting speed: 200m / min • Feed rate per blade: 0.20 mm / blade • Projection: 63mm ·Cutting length: 2.00m

[0044] [Table 3]

[0045] In Table 3, "-" indicates that measurement was not performed.

[0046] Table 3 shows that Example 1 exhibited a smaller maximum flank wear width under all machining conditions than any of the comparative examples, demonstrating superior chipping resistance and wear resistance. [Explanation of symbols]

[0047] 1: Outer shell of WC particle L1~L3: Line segments along the outer edge of WC particles

Claims

1. A cemented carbide containing hard phase WC particles and a binder phase Co, but without Ti, wherein the circular equivalent average particle size D of the WC particles is 1 μm or more and 3 μm or less, and 20% or more of the number of WC particles having a circular equivalent particle size of D or more have stepped irregularities on their surface.

2. The cemented carbide according to claim 1, characterized in that it contains Co: 5.0 to 12.0 mass%, Cr: 0.3 to 1.0 mass%, Ta: 1.0 to 5.0 mass%, with the remainder being WC and unavoidable impurities.

Images