JP2859891B2 - Cemented carbide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Industrial application field] The present invention relates to improvement of cemented carbide. More specifically, the present invention relates to expanding the application range of cemented carbide with improved wear resistance. [Prior Art] A cemented carbide comprising a WC hard phase and a binder phase of Co has been put to practical use in various applications because of its excellent wear resistance and impact resistance. In particular, the WC-Ta (Nb) C-Co system has a good effect of suppressing grains and is widely used. An alloy containing a small amount of TiN is widely used as a P-type cemented carbide. By adding nitrogen, the B-1 type solid solution phase can be refined, and the toughness is further improved. Conventionally, elements such as TaC and NbC have not been added for wear resistance and the composition is WC-Co based.
Alloys of the original system or a series in which a part of Co is replaced with Ni, Cr, etc. have been used. However, the wear-resistant alloy mainly improves the binder phase from the viewpoint of oxidation resistance and corrosion resistance, and hardly improves the hard phase such as nitride. [Problems to be Solved by the Invention] As described above, the conventional hard metal for wear resistance is obtained by combining coarse-grained WC of 4 to 8 microns with Co, Ni, and Cr. There were few series in which the substance was added. However, in recent years, the conditions used for wear resistance and impact resistance have been increased due to higher efficiency, and the load has been increased. Problems have been pointed out, such as the occurrence of thermal cracks due to repeated heating and cooling of the surface and shortening of the service life due to falling off of particles. In addition, a high binder phase content is essential for wear resistance, and alloying of the binder phase has brought out the characteristics of the alloy such as corrosion resistance, oxidation resistance, and heat resistance in the binder phase. That is, the solid solution strengthened alloy was mainly used, and the composition in the combined phase such as Cr / Ni and Co / Ni / Cr was characteristic. [Means for Solving the Problems] However, the present inventors focused on the change in the binder phase when a nitride, which is used for a P-based cemented carbide, was added, and the alloying of the binder phase itself was larger, In particular, the solid solution in the binder phase increased, and solid solution strengthening was measured.At the same time, when this series of alloys was confirmed in a simple system, the nitride itself was partially dissolved but was largely separated. Was found. Therefore, whether the same effect can be applied to solid solution strengthened alloys of WC-Co / Ni / Cr system and additives, we examined various nitrides and found that the effect of Ni increased the amount of solid solution compared to Co. It was found that the solid solution strengthening of the added element itself can be measured. [Operation] As described above, the present invention provides one or more of niobium nitride, molybdenum nitride, tantalum nitride and tungsten nitride.
0.1 to 2.0% or more of the cemented carbide consisting of 80 to 94% of the hard phase composed of tungsten carbide and 6 to 20% (more than the weight percentage) of the binder phase composed of iron group metal. The cemented carbide is characterized in that the average grain size of the nitride and / or double carbonitride is less than 1 micron. It is also a feature of the alloy of the present invention that a lighter element has a higher solid solution strengthening rate in the binder phase, and a heavy element has a higher dispersion strengthening rate. Vanadium, chromium, etc. are also known as grain suppressants, and even when nitrides are used, most of them decompose during sintering and merge into the binder phase to measure solid solution strengthening, but a large amount of dispersion strengthening is required. Since the amount required and the strength deteriorated due to the adverse effect, it was excluded from the scope of the present invention. Similarly, niobium nitride, molybdenum nitride, tantalum nitride, and tungsten nitride partially decompose and melt into the binder phase, but their solid solubility is small. However, although the nitride of group 4a of the periodic table has a large effect of dissolving other elements in a solid solution, it hardly forms a solid solution itself and causes a decrease in strength as compared with the group 5a and 6a carbonitrides. Since it is negative for wear resistance, it was excluded from the alloy of the present invention. The range of the composition of the cemented carbide according to the present invention is limited for the following reasons. 1) When the amount of added nitride is less than 0.1%, the effect is small because the amount of dispersion is insufficient, and when it exceeds 2%, one particle becomes coarse due to agglomeration of particles and remarkably inhibits toughness.
２2%. 2) If the addition amount of the iron group metal is less than 6%, sufficient toughness cannot be obtained, and if it exceeds 20%, the wear resistance deteriorates.
20%. 3) When the particle size of the nitride phase exceeds 1 micron in the sintered body, it is a brittle phase as compared with the WC phase, and the strength is deteriorated. Hereinafter, the present invention will be specifically described based on examples.

Example 1 Commercially available WC powder (average particle size: 6 μm) Mo ₂ N powder (1 μm)
m), WN powder (1 μm), NbN powder (1 μm), TaN
Powder (1 μm), Co powder (1.3 μm), Ni powder (1 μm)
1.2 μm) and a Cr powder (2 μm) were mixed and molded with the composition shown in Table 1 and vacuum-sintered at a temperature of 1350 ° C. to 1400 ° C. for 1 hour. The resulting alloy was tested for hardness, bending force, high temperature creep and thermal shock resistance, and the results shown in Table 2 were obtained. The high temperature creep test is a three-point bending creep test of a JIS specimen (4x8x24mm) at 900 ° C in an inert gas atmosphere (span distance 2
0 mm) at a load stress of 50 kg / mm ² and the fracture time was examined.
For thermal shock resistance, place the sample in a furnace in an inert gas atmosphere (900 ° C)
, And quenched in water at about 20 ° C., and examined the number of times until a thermal crack was generated. As is clear from Table 2, the alloy of the present invention has the same performance at room temperature as the comparative example, but shows excellent performance at high temperatures. These are due to the dispersion-solid solution strengthening of the binder phase.

Example 2 A roll for rolling having a diameter of 160 mm and a thickness of 70 mm was produced using the alloy of Example 1. The results of hot rolling a steel wire using this roll are also shown in Table 2. From Table 2, the conventional
In the case of cemented carbide rolls with Co-Ni-Cr as the binder phase, rolling of only about 1200 tons was possible at most because of the surface roughness that occurred on the surface, and rolling of 200 to 3000 tons was possible. Co-Ni-Cr
On the other hand, a roll having a binder phase of has a large crack opening and many hard layer drops are observed, whereas the roll of the present invention has a small crack opening and a small drop.

Example 3 From the mixed powder obtained in Example 1 A, the diameter was 45 mm and the thickness was 25.
mm guide roller was used as a guide during hot rolling of steel wire.When using a conventional cemented carbide guide roller with Co-Ni-Cr as a binder phase, the service life was about 2500 tons due to rough surface. It was able to withstand the use of up to 4800 ton in the place where it was.

【The invention's effect】

As described above, the cemented carbide according to the present invention is in a state where an excessive load is applied in a hot or warm state such as a hot rolling roll of a wire such as a roll, a guide roller, and a pinch roll, and an environment such as oxidation and corrosion is easily caused. The purpose of the present invention is to provide a cemented carbide exhibiting excellent performance.

Claims (1)

(57) [Claims] 1. One or two or more of niobium nitride, molybdenum nitride, tantalum nitride and tungsten nitride.
80% to 94% of the hard phase consisting of tungsten carbide
In a cemented carbide comprising 6 to 20% (or more by weight) of a binder phase composed of an iron group metal, the average grain size of the nitride and / or double carbonitride in the final sintered body is 1 micron or less. A hard metal characterized by the following.