DE202007000041U1 - Powder mixture for cobalt-bonded sintered hard metal objects - Google Patents

Abstract

Powder mixture as a starting material for cobalt-bonded sintered hard metal objects, wherein the cobalt content in the form of cobalt oxide, in particular as cobalt (II, III) oxide Co ₃ O ₄ , is included.

Description

Introduction:

Under Hard metals are sintered materials made of metallic hard materials based on refractory carbides of the metals from groups 4b to 6b of the periodic table and low-melting binder metals from the iron group, especially cobalt. you will be mainly for the Cutting technology and used for wear control. For the production these hard metals are called powder mixtures, also known as mixture mixtures, used, which is the usual powdery Hard materials and the metal binder, which the hard material during the Sintering process wetted with alloy formation included. First This creates the for the use of suitable tough-hard Microstructure of hard metals.

to Production of sintered carbide rods, for example, a from the basic substances tungsten carbide, vanadium carbide, chromium carbide and cobalt powder mixture by grinding and homogenizing in an attritor (agitator ball mill) or another suitable milling unit produced. This has the Disadvantage that the mixing of the individual components by the different particle sizes and Morphologies especially of cobalt at higher cobalt contents than difficult proves that the cobalt is relatively soft as elemental powder and tends to sticking and agglomerations.

Object of the invention:

• 1. Grindability increase the mixing approach and or
• 2. homogeneous distribution of the Co within the mixture

Solution:

feature combination of claim 1, in particular use of an appropriate amount Cobalt oxide instead of the elemental cobalt, in particular with a Grain size smaller 10 μm.

Since cobalt oxide according to the reaction equation Co ₃ O ₄ + 2C → 3Co + 2CO ₂ reacts, this corresponds to an efficiency of 73.4%. In order to calculate a cemented carbide approach, it is advantageous to calculate the reaction efficiency and the carbon demand. The other encores may be unaffected. This can be achieved that the content of cobalt is not changed.

Embodiment:

A first conventional powder mixture was prepared. These were 1803 g of tungsten carbide (WC) with a grain size of 0.5 microns, 180 g of elemental cobalt (Co) with a mean grain diameter of 5.35 microns, 10 g of chromium carbide (Cr ₃ C ₂ ) and 5 g of vanadium carbide (VC) milled in a laboratory mill for 24 hours. Subsequently, a grain size measurement with a Cilas 1064 was carried out on this first powder mixture. The result was the particle size distribution shown in Table 1. The mean grain diameter was 0.47 μm. Table 1: Grain size distribution conventional powder mixture after grinding Diameter / micron cumulative values of the passage /% 12:04 12:23 12:10 5.12 12:50 53.51 1:00 87.78 2:00 97.14 3:00 98.63 4:00 99.70 5:00 100.00

Subsequently, a second powder mixture according to the invention was prepared. This consisted essentially of the same components. However, the elemental cobalt was cobalt oxide Co ₃ O ₄ er puts. In order to obtain the same cobalt content in the powder mixture, and thus also in the sintered cemented carbide article made therewith, a quantity of cobalt oxide Co ₃ O _{4 was} added by 1.362 times the amount of elemental cobalt.

Before the cobalt oxide was added to the powder mixture, its particle size distribution was determined. The distribution shown in Table 2 resulted. The mean grain diameter was 4.44 μm. Table 2: Grain size distribution of the added cobalt oxide before grinding Diameter / micron cumulative values of the passage /% 12:04 00:00 12:10 12:53 12:50 4:04 1:00 6:54 2:00 16:44 3:00 31.36 4:00 44.84 5:00 55.88 7:00 71.81 10:00 84.25 15:00 93.46 8:00 pm 98.07 30.00 100.00

Thus 1803 g of tungsten carbide (WC) with a grain size of 0.5 μm, 245.158 g of cobalt oxide (Co ₃ O ₄ ), 10 g of chromium carbide (Cr ₃ C ₂ ) and 5 g of vanadium carbide (VC) were used for the second powder mixture according to the invention Milled a laboratory mill for 24 hours. Subsequently, the particle size distribution of the powder mixture was determined according to the method used in the first powder mixture. The result was the particle size distribution shown in Table 3. The mean grain diameter was 0.28 μm. Table 3: Grain size distribution of the powder mixture according to the invention after grinding Diameter / micron cumulative values of the passage /% 12:04 1.18 12:10 12:27 12:50 80.30 1:00 98.41 2:00 100.00 3:00 100.00 4:00 100.00 5:00 100.00

To same Aufmahlzeit resulted for the second invention Powder mixture thus a finer powder mixture. The mean grain diameter was in the second invention Powder mixture 0.28 μm, while he at the conventional first powder mixture 0.47 microns amounted to.

By the addition of cobalt oxide instead of the elemental cobalt could thus sticking and agglomeration of the individual powder components be avoided, thereby improving the grindability. Especially Advantageously, the addition of cobalt oxide with a mean grain size of smaller 10 micrometers, especially less than 5 micrometers exposed.

Also, by the finer Aufmahlung a more homogeneous distribution of the individual components inside half of the powder mixture and thus also in a subsequently produced by sintering from this powder mixture hard metal object possible. This generally leads to homogeneous mechanical properties. Also, a fine-grained structure increases various mechanical properties such as hardness. If hard metal objects which are exposed to a bending load are produced from the powder mixture according to the invention, their bending strength also increases.

Claims (7)

Powder mixture as a starting material for cobalt-bonded sintered hard metal objects, wherein the cobalt content in the form of cobalt oxide, in particular as cobalt (II, III) oxide Co ₃ O ₄ , is included. A powder mixture according to claim 1, wherein the cobalt oxide a mean grain size smaller 10 microns. A powder mixture according to claim 1 or claim 2, wherein the cobalt oxide has a mean grain size less than 5 microns. Powder mixture according to one of the preceding claims, wherein the powder mixture tungsten carbide, vanadium carbide, titanium carbide, tantalum carbide, Contains nickel and / or chromium carbide. Powder mixture according to one of the preceding claims, wherein the powder mixture comprises 85-95% by weight tungsten carbide (WC), 0.1-1.0% by weight vanadium carbide (VC), 0.3-1.0% by weight chromium carbide (Cr ₃ C ₂ ) and / or 5-20 wt% cobalt oxide (Co ₃ O ₄ ). Hard metal object sintered from the powder mixture according to one of the claims 1-5. The cemented carbide article of claim 6, wherein the cemented carbide article a carbide rod with a diameter less than 10 mm is.