JPH032346A - Sintered hard alloy - Google Patents

Abstract

PURPOSE:To obtain a sintered hard alloy excellent in wear resistance in a severe environment by incorporating specific small amounts of hard nitrides of metals, such as Nb, Mo, Ta, and W, to a sintered hard alloy prepared by sintering WC grains as hard phase by using iron group metals as binding phase. CONSTITUTION:One or >=2 kinds among hard metal nitrides, such as NbN, Mo2N, TaN, and WN, are added by 0.1-2.0wt.% to WC as a hard phase, and then, pulverized powders of iron group metals, such as Fe, Co, and Ni, are mixed as binding phase-forming materials at the time of sintering by 6-20wt.% to 80-94wt.% of the above hard phase, and the resulting mixture is mixed sufficiently and subjected to vacuum sintering at a temp., e.g. as high as 1350-1400 deg.C. By this method, the sintered hard alloy in which the average grain size of carbonitride of hard nitride and WC in the sintered alloy is regulated to <=1mum and which is excellent in wear resistance under the environment liable to cause oxidation, corrosion, etc., at high temp., such as hot rolling roll for wire rod, guide roller, and pinch roll, can be obtained.

Description

[Detailed description of the invention]

Field of Application on tSS] The present invention relates to improvement of cemented carbide. Specifically, the present invention relates to expanding the range of applications of cemented carbide with improved wear resistance. [Prior Art] Cemented carbide comprising a WC hard phase and a binder phase of CO has been put to practical use in a variety of applications due to its excellent wear resistance and impact resistance. In particular, the WC-Ta(Nb)C-Co system has a good grain suppression effect and is widely used. In addition, alloys to which a small amount of TiN is added are widely used as P-based layered hard alloys, and the addition of nitrogen makes the B-1 type solid solution phase finer and improves toughness. Conventionally, elements such as TaC and NbC were not added for wear-resistant applications, and the composition was WC-
Co-based binary systems or alloys in which a portion of CO is replaced with Ni, Cr, etc. have been used. However, in wear-resistant alloys, improvements have mainly been made in the binder phase from the viewpoint of oxidation resistance and corrosion resistance, and improvements in hard phases such as nitrides have not been made much. [Problems to be solved by the invention] As mentioned above, conventional cemented carbides for wear resistance are made by bonding coarse grained WC of 4 to 8 microns with Co, Ni, and Cr, and other carbonitrides and nitrides. There were almost no series in which substances were added. However, in recent years, the conditions used for wear and impact resistance have become higher efficiency, so the load has increased, and wear-resistant alloys that originally have a large total bond amount have insufficient wear resistance. Problems have also been pointed out, such as surface roughness due to shedding of WC particles, etc., occurrence of thermal cracks due to repeated heating and cooling, and shortened lifespan. Moreover, a high amount of binder phase is essential for wear-resistant applications, and alloying the binder phase brings out the characteristics of the alloy such as corrosion resistance, oxidation resistance, and heat resistance in the binder phase. That is, solid solution strengthened alloys are the main ones, Cr/Ni, Co/Ni/
There were various compositional characteristics in the bonded phase, such as Cr. [Means for Solving Problem E] However, the present inventors focused on the change in the binder phase when nitride is added, which is practiced in P-based cemented carbide, and found that the alloying of the binder phase itself is greater, In particular, the solid solution in the binder phase increases and solid solution strengthening is achieved.At the same time, when this series alloy was confirmed in a simple system, it was found that some of the nitrides themselves were dissolved in solid solution, but most of them were dispersed. I found out. Therefore, as a result of examining various nitrides to see if the same effect could be applied to solid solution strengthened alloys of W C-Co/Ni/Cr system + additives, we found that due to the effect of Ni, the amount of solid solution is higher than in the case of CO. It was found that solid solution strengthening of the added element itself can be measured. [Function] As described above, the present invention uses niobium nitride, molybdenum nitride,
0.1 to 2.0% of one or more of tantalum nitride and tungsten nitride, the remainder being 80 to 94% of a hard phase made of tungsten carbide, and 6 to 20% of a binder phase made of an iron group metal.
In cemented carbide consisting of % (or more weight percent),
The present invention is a cemented carbide characterized in that the average grain size of the nitride and/or double carbonitride in the sintered body is 1 micron or less. Another feature of the alloy of the present invention is that light elements have a high rate of solid solution strengthening in the binder phase, and heavy elements have a high rate of dispersion strengthening. Vanadium, chromium, etc. are also known as grain suppressants, and even if nitrides are used, most of them decompose during sintering and dissolve into the binder phase, making it possible to achieve solid solution strengthening, but a large amount of addition is required to achieve dispersion strengthening. It is excluded from the scope of the present invention because it requires a large amount of water and its strength deteriorates. Similarly, some of niobium nitride, molybdenum nitride, tantalum nitride, and tungsten nitride decompose and dissolve into the binder phase, but their solid solubility limit is small. However, although nitrides in group 4a of the periodic table have a great effect on solid solution of other elements, they hardly dissolve in solid solution themselves, resulting in lower strength compared to group 5a and 6a carbonitrides. , was excluded from the alloys of the present invention because it has a negative overall effect on wear-resistant applications. The composition of the cemented carbide according to the present invention is limited in scope for the following reasons. l) If the amount of nitride added is less than 0.1%, the dispersion amount will be insufficient and the effect will be small, and if it exceeds 2%, each particle will become coarse due to agglomeration of the particles, significantly reducing the toughness. It was set at 0.1 to 2% to reduce JI. 2) If the amount of iron group metal added is less than 6%, sufficient toughness will not be achieved.
If it exceeds 20%, the wear resistance will deteriorate.
It was set at 6 to 20%. 3) The grain size of the nitride phase was set to be 1 micron or less, since if the grain size in the sintered body exceeds 1 micron, it is a brittle phase compared to the WC phase and the strength deteriorates. Hereinafter, the present invention will be specifically explained based on examples.

[Example 1] Commercially available WC powder (average particle size 6 μm) Mo2N powder (average particle size 1
μm), WN powder (1μrn), NbN powder (1μm), TaN powder (1μm), Co powder (1.3pm), Ni powder (1.2μm), Cr
Powder (2 μm) was 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 obtained alloy was tested for hardness, transverse rupture strength, high temperature creep, and thermal shock resistance, and the results shown in Table 2 were obtained. The high temperature creep test was conducted using JIS specimens (4x8x24+++m
) was subjected to a three-point bending creep test (span distance 20 mm) at 900°C in an inert gas atmosphere with a load stress of 50 kg/g + 2.
The rupture time was investigated. Thermal shock resistance was determined by placing the sample in a furnace with an inert gas atmosphere (900°C) and holding it there for 10 minutes, then quenching it in water at about 20°C, and checking the number of times until thermal cracks occurred. As is clear from Table 2, the performance of the alloy of the present invention at room temperature is equivalent to that of the comparative example, but it exhibits excellent performance at high temperatures. These are caused by the dispersion solid solution strengthening of the binder phase.

[Example 21 Using the alloy of Example 1, the diameter was 160wn and the thickness was 70mm.
We made rolling rolls. Table 2 also shows the results of hot rolling a steel wire using this roll. From Table 2, it can be seen that the conventional cemented carbide roll with Co-Ni-Cr as a binder phase has a capacity of 1200 t at most due to the roughness that occurs on the surface.
2000 t when only about 2000 t of rolling was possible.
Rolls using Co-Ni-Cr as a binder phase are capable of rolling up to 3,000 tons and provide a good surface with little surface roughness. On the other hand, in the roll of the present invention, the opening of cracks is small and the number of dropouts is small. [Example 3] A guide roller with a diameter of 45 mm and a thickness of 25 m was made from the mixed powder obtained in Example I A, and this was used as a guide during hot rolling of steel wire. The guide roller made of cemented carbide with a binder phase had a rough surface and had a lifespan of 480 tons at a point where it had a lifespan of about 2,500 tons.
It was able to withstand use up to 0 tons.

【Effect of the invention】

As mentioned above, the cemented carbide of the present invention is subjected to an excessive load in hot or warm conditions, such as hot rolling rolls of wire rods, guide rollers, pinch rolls, etc. The present invention also provides a cemented carbide that exhibits excellent performance in environments prone to oxidation, corrosion, etc.

Claims (1)

[Claims] 0.1 to 2.0% of one or more of niobium nitride, molybdenum nitride, tantalum nitride, and tungsten nitride remain, 80 to 94% of the hard phase consisting of tungsten carbide, and 6 to 20% of the binder phase consisting of iron group metals ( weight percentage)
A cemented carbide characterized in that the average grain size of the nitride and/or double carbonitride in the final sintered body is 1 micron or less.