JPS601385B2 - Tungsten carbide-based cemented carbide for hot processing equipment parts - Google Patents

Description

Detailed Description of the Invention The present invention provides excellent toughness and wear resistance of tungsten carbide (hereinafter referred to as WC)-based cemented carbide, as well as excellent high-temperature strength, oxidation resistance, high-temperature hardness, It has thermal shock resistance and thermal fatigue resistance, and is particularly suitable for use as hot processing equipment components such as hot rolling rolls, hot rolling guide rollers, and hot forging dies, which require these properties. This relates to WC-based cemented carbide.

In recent years, WC-Co-based, WC-Co-Ni-based, and WC-Co-Ni-Cr-based cemented carbide alloys have been used in place of tool steel and cast iron to manufacture parts for hot working equipment of this type. However, while WC-Co cemented carbide has excellent grade and wear resistance, it has insufficient high temperature strength, high temperature hardness, thermal shock resistance, oxidation resistance, and thermal fatigue resistance. For this purpose, for example, in a hot rolling roll of steel wire, the roll surface is heated to a high temperature under pressure by a running steel wire of about 1000 to 1100 qo, while the roll surface is also water-cooled. Under repeated heating and cooling conditions, thermal cracks and rough skin will occur, and WC
-Co-Ni and WC-Co-Ni-Cr cemented carbide have better properties than WC-Co cemented carbide, but under severe conditions of low speed and high load, it is thought that thermal cracking may occur. Therefore, when these conventional WC-based cemented carbide alloys are used in the production of hot processing equipment members, they do not exhibit sufficiently satisfactory performance.

Therefore, from the above-mentioned viewpoints, the present inventors sought to obtain an alloy suitable for use in manufacturing hot processing equipment members.
In particular, we focused on WC-based cemented carbide containing WC as a dispersed phase-forming component, which has excellent wettability with the binder phase, high interfacial strength with the binder phase, and superior high-temperature hardness than other carbides. It is necessary to impart high-temperature strength and oxidation resistance, as well as high-temperature hardness, to the binder phase of cemented carbide.As a result of research, we have found that WC-based cemented carbide is expressed in weight% (hereinafter simply % means weight%). ), C: 0.1-2%, AI: 0.1
~3%, Ni: 5-30%, Co: 2.5-15%, B
and one or two of Zr: 0.01 to 0.2
%, further contains Mo: 0.1 to 1% as necessary, and the remainder is composed of WC and unavoidable impurities, and the content of oxygen as an unavoidable impurity is 0.05 %.
% or less, the average grain size of the WC grains is 2 to 8 mm, and the binder phase has a structure in which fine y' (N and AI) phases are uniformly precipitated. W.C.
The base cemented carbide maintains the excellent warpability and wear resistance of ordinary WC base cemented carbide, and has extremely high temperature strength, oxidation resistance, and high temperature hardness, as well as ``thermal shock resistance''. The present invention was made based on these findings, and the present invention was made based on these findings.

The alloy of the present invention can be manufactured by a normal powder metallurgy method, but in particular, regarding the raw material powder, the Cr component is chromium nitride (hereinafter referred to as Cr2N) powder, and the base component is aluminum nitride (hereinafter referred to as AIN) powder. It is best to blend it in the form of
Denitrification occurs during vacuum coupling, and only Cr and AI components become N.
It diffuses into the i-Co alloy binder phase very easily, and the sintered body hardly contains nitrogen, and furthermore, the oxygen content in the sintered body can be reduced to 0.05% or less.

That is, if Ni-AI alloy powder is used as the raw material powder, fine AI203 particles will be present in the binder phase in the sintered body.
However, as the amount of Ni-N alloy powder increases, the amount of AI203 increases, resulting in an increase in pores in the sintered body and precipitation in the binder phase. As the phase becomes coarser, the toughness and strength of the sintered body decrease.
The oxygen content in this case is usually 0.08 to 0.15%.

On the other hand, if AIN powder is used as the raw material powder, the oxygen content in the dawn feeder will not increase even if the blended amount is increased, and will always be kept below 0.05%, so the pores will be reduced. No generation or coarsening of the y' phase occurs, and as a result, the strength and balling properties are not impaired. next,
In the WC-based cemented carbide of the present invention, the reason why the component composition range and WC grains are numerically limited as described above will be explained.

(a) Cr The Cr component has the effect of improving the corrosion resistance and oxidation resistance of the alloy, but if the content is less than 0.1%, the desired effect cannot be obtained, whereas if the content exceeds 2%, the desired effect cannot be obtained. If it is, the quality will decrease, so the content should be reduced to 0.
It was set at 1 to 2%.

'b) The AI mountain component dissolves in solid solution in the binder phase and precipitates as the y' phase, which has the effect of improving the high temperature strength and heat resistance of the binder phase, but if its content is less than 0.1%, the On the other hand, if the content exceeds 3%, an intermetallic compound of N will precipitate and cause formation of arms. It was set at 3%.

'c} Nj Ni component has the effect of precipitating the 'c' phase in the binder phase when coexisting with AI and improving the high temperature strength of the alloy, but if its content is less than 5%, the desired high temperature strength cannot be secured. However, if the content exceeds 30%, the hardness decreases, so the content was set at 5 to 30%.

(d) The CoCo component is dissolved in the binder phase and has the effect of strengthening it and improving heat resistance, but if its content is less than 2.5%, the desired effect cannot be obtained,
On the other hand, if the content exceeds 15%, the hardness will decrease like Ni, so the content should be reduced to 2.5 to 1%.
It was set at 5%.

[e} B and Zr These components dissolve in the binder phase and significantly improve oxidation resistance, and also have the effect of improving toughness by increasing the interfacial strength between WC and the binder phase. If the content is less than 0.01%, the desired effect of improving oxidation resistance and grade cannot be obtained, while if the content exceeds 0.2%, it will become vertical. The amount was determined to be 0.01-0.2%.

(8 Mo The Mo component has the effect of solidifying into the binder phase and improving its corrosion resistance and high-temperature hardness, but when its content is 0.
．． If the content is less than 1%, the desired effect cannot be obtained, while if the content exceeds 1%, the strength will decrease, so the content was set at 0.1 to 1%.

■ Oxygen As mentioned above, the alloy of this invention contains fine y-oxygen in the binder phase.
' phase is dispersed and precipitated to dramatically improve high-temperature strength, but when the oxygen content exceeds 0.05%, oxygen preferentially combines with AI to form AI203, resulting in y Not only is the formation of the ′ phase suppressed,
This results in coarsening of the y' phase and the generation of pores, resulting in a significant decrease in the high temperature strength and grade of the alloy.

For this reason, the upper limit of the oxygen content was set at 0.05%. (h) Average grain size of WC grains If the average grain size is less than 2 mm, the desired high-temperature hardness cannot be secured, while if the average grain size exceeds 8 mm, the alloy strength will decrease. Therefore, the average particle size was determined to be 2 to 8 particles.

Next, the cemented carbide of the present invention will be explained using Examples while comparing with Comparative Examples.

Examples of raw material powders include various commercially available WC powders having an average particle size of 2 to 10, Ni powder of 1.5 ounces,
Co powder with 1.2 mu skin, B and public powder with 2 mu skin,
Prepare Cr2N powder of the same 2mm kite, NN powder of the same 1.5 mound, and Mo powder of the same 0.7 mound, and mix these raw powders into the compositions shown in Tables 1 and 2, respectively. The final component composition is substantially the same as the blended composition by mixing under normal conditions, molding into a green compact, and finally condensing in vacuum at a temperature of 1400°C for 1 hour. Inventive cemented carbide alloys 1 to 20 and comparative cemented carbide alloys 1 to 9 were manufactured, respectively.

The obtained cemented carbide alloys 1 to 20 of the present invention and comparative cemented carbide 1 to 9 have tensile strength, normal temperature hardness (Rockwell hardness A scale), and high temperature hardness at 800°C (Vickers hardness). In addition to measuring the hardness) and transverse rupture strength, the increase in acid b content after holding the temperature at 800°C for 1 hour was also measured, and these measurement results are shown in Table 1 and the average grain size and oxygen content of the alloy. It is also shown in Table 2.

In addition, for Comparative Cemented Carbide Alloys 1 to 9, the content of any one of the constituent components and the average grain size of WC grains (indicated with * in Table 1) are within the scope of this invention. It is outside of the .

From the results shown in Tables 1 and 2, cemented carbide alloys 1 to 20 of the present invention all have high strength and high rutting resistance, and also exhibit high hardness at room temperature and high temperature. Comparative cemented carbide 1 to 9 also have excellent oxidation resistance.
It is clear that at least one of these properties is inferior.

Next, from the above-mentioned cemented carbide alloys 3, 14, and 17 of the present invention, as well as conventional spheroidal graphite cast iron (FCD55) and WC-based cemented carbide (WC-15%Co), guide rollers for hot rolling rolls of ordinary steel wire rods were prepared. was manufactured and tested by incorporating it into an actual machine.

This guide loaf is provided to guide the rolled wire and suppress its vibration, and is used under severe conditions where one side is heated by the heating wire and the other side is heated and cooled with water, which involves repeated heating and cooling. It is something that will be done. Further, the usage conditions were a wire temperature: 1050 qC and a wire passing speed: 30 m'sec, and the amount of wire passing through until the end of the service life was measured. As a result, guide rollers made of spheroidal graphite cast iron suffer significant wear on the caliber and reach the end of their service life after 12 ounces of wire passing, and conventional cemented carbide guide rollers reach the end of their caliber after 80 ounces of wire passing. Thermal cracks and peeling phenomena occurred in the parts, and the service life was reached.

On the other hand, those made of cemented carbide of the present invention both have 2
Even after a wire rod of 50 on or more had passed through it, only slight thermal cracks were observed in some parts of the caliber, and it was still sufficient to continue using it. As mentioned above, the WC-based cemented carbide of the present invention has particularly excellent high-temperature strength and oxidation resistance, and also has high high-temperature hardness, as well as excellent thermal shock resistance and thermal fatigue resistance, and has excellent ballability and resistance. It also has excellent abrasion resistance, so when used as a member of hot processing equipment that requires these properties, it exhibits excellent performance over an extremely long period of time.

Claims (1)

[Claims] 1 Cr: 0.1-2%, Al: 0.1-3%, Ni:
5 to 30%, Co: 2.5 to 15%, one or two of B and Zr: 0.01 to 0.2%, and the remainder consists of tungsten carbide and unavoidable impurities (the above % by weight), the content of oxygen as an unavoidable impurity is 0.05% by weight or less, and the average particle size of the tungsten carbide forming the dispersed phase is 2 to 8 μm, and fine γ particles are added to the binder phase. 1. A tungsten carbide-based cemented carbide for hot processing equipment parts, characterized by having a structure in which a '(Ni_3Al) phase is uniformly precipitated. 2 Cr: 0.1-2%, Al: 0.1-3%, Ni:
5 to 30%, Co: 2.5 to 15%, one or two of B and Zr: 0.01 to 0.2%, and further Mo: 0.1 to 1%. , the remainder is tungsten carbide and unavoidable impurities (wt%), the content of oxygen as an unavoidable impurity is 0.05 wt% or less, and the average particle size of tungsten carbide forming the dispersed phase is 2 to 8 μm, with fine γ in the binder phase.
1. A tungsten carbide-based cemented carbide for hot processing equipment parts, characterized by having a structure in which a '(Ni_3Al) phase is uniformly precipitated.