EP1647606B1 - High hardness and wear resistant nickel based alloy for use as high temperature tooling - Google Patents

Description

The invention relates to a nickel-based alloy.

Furthermore, the invention relates to a method for producing a nickel-based alloy article.

Finally, the invention comprises a tool consisting of a nickel-based alloy and a starting material for the production of tools.

Tools for cutting or non-cutting metal materials, such as cutting tools or forming tools, are subjected to a variety of stresses in use. These stresses are often mechanical, for example, by contact of the tool with a metallic material, which leads to wear of the tool. In addition, in the case of high operating temperatures, which are often given, also thermally induced loads, so that when using the tool in total, mechanical, thermal and thermomechanical stresses are given.

In the non-cutting as well as the cutting shaping of metallic materials, a trend is to work at the highest possible operating temperatures. As metals become softer with increasing temperature, forming is much easier at higher temperatures. Also in terms of a cutting shaping higher temperatures bring advantages on the workpiece, because a chip removal is facilitated. Therefore, tools are desired which are wear-resistant at the highest possible temperatures, in particular greater than 700 ° C., and have a long service life.

So far, for tools which are exposed on the one hand high abrasive wear and on the other hand used at temperatures of several hundred degrees Celsius or heat when used at such temperatures, eg forming tools or cutting tools, mainly conventional high speed steels used. High-speed steels have a high hardness due to a high proportion of carbides distributed in the steel matrix and are correspondingly wear-resistant. High-speed steels, however, have a natural operational limit approximately at their tempering temperatures (about 530 to 560 ° C). At higher Operating temperatures, especially at temperatures of more than 600 ° C, soften tools made of high-speed steels and deform plastically. In addition, any surface coatings may detach. For tools with operating temperatures of more than 700 ° C, high-speed steels are therefore less suitable.

It is therefore an attempt to develop alternative materials which have a hardness and wear resistance similar to that of high speed steels but can be used at higher temperatures. U.S. 4,727,740 discloses an alloy of 0.55-2.0 C, 10-28 Cr, 1-30 Fe, 0.01-4.5 Ti, 0.01-4.5 Al, 0.1-10 W, 0.1-10 Mo and balance Ni, if appropriate 0.1-3 Si, 0.1- 3 Mn, 1-8 Co at least one from the group 0.005-0.2 N, 0.01-1.5 Nb and Ta and at least one from the group 0.001-0.2 B and Zr.

With nickel-based alloys, suitable materials for components or components with operating temperatures of 700 ° C. or more are generally provided. In comparison with high speed steels, however, nickel base alloys per se have significantly lower hardnesses. It is possible to increase the hardness of nickel-based alloys by alloying measures. In particular, alloy precipitation and suitable heat treatments can achieve precipitation hardening, for example via a so-called γ 'phase (Ni ₃ X, in which X = Al, Ti and / or Nb). However, the hardness achieved thereby lies in a range which is sufficient for some high-temperature applications, for example for gas turbines, but not for applications in which high wear resistance is required.

Other possibilities of increasing the hardness of nickel-based alloys are conceivable, for example via metal carbides precipitated primarily from the melt. In this approach, however, has shown in procedural terms, especially at higher carbide contents that occur in cast blocks to coarse carbides and as a result of uneven solidification segregations or segregations. If such ingots are used for the production of tools, then the tools created can have completely different mechanical properties in regions corresponding to the local structural differences. An inhomogeneous structure and the associated weak points in the tool can lead to premature, unexpected failure of the tool in the sequence.

Based on the aforementioned prior art, it is an object of the invention to provide a high-strength nickel-based alloy with high hardness.
Another object is to provide a method by which a high-strength, high-temperature resistant article of a nickel-based alloy with a homogeneous microstructure can be produced.

Another object of the invention is to provide a tool made of a nickel-based alloy, in particular a cutting tool or a thermally highly stressed tool, which has a high hardness and wear resistance.

Further, it is an object of the invention to provide a starting material for the production of tools, made of a nickel-based alloy, in particular cutting tool or thermally highly stressed tool, which is characterized by a high homogeneity of the structure.

The stated object is achieved by a nickel-based alloy according to claim 1. Advantageous variants of a nickel-based alloy according to the invention are the subject matter of claims 2 to 15.

The advantages achieved by the invention are in particular to be seen in the fact that a nickel-based alloy has been created, which is suitable for tools with operating temperatures of more than 700 ° C and at room temperature has a hardness in the range of those conventional high-speed steels. Since the matrix of the nickel-based alloy consists of γ-phase, ie a phase with cubic face-centered lattice, a good temperature resistance is given. The achieved high hardness is due to a dual hardening concept: By a proportion of at least 10% by volume of primary metal carbides, which are metal carbides precipitated from the melt, a basic hardness of the matrix of about 200 HV (Vickers hardness) is increased by about 250 HV. Precipitation hardening or the formation of γ 'phases, for example Ni ₃ Al, can then result in an additional hardness increase of about 200 HV in the sequence.

In order to achieve the highest possible hardness, it is preferred that the proportion of metal carbides is at least 15% by volume, preferably at least 20% by volume.

Although carbides of all kinds can make a contribution to the hardness, metal carbides of the formula M ₆ C, MC, M ₂ C and / or M ₂₃ C _{6 are} preferred because they are characterized by high hardness. It is particularly advantageous if at least 50% by volume of the metal carbides in the form of M ₆ C are present, which form a favorable uniform, globular morphology. The metal carbides are preferably formed as fine as possible in view of a homogeneous structure and then have an average size of 0.5 to 5 .mu.m, in particular 1 to 3 .mu.m.

In a favorable microstructure, a proportion of γ'-phase is at least 10% by volume, in particular from 20 to 65% by volume. This causes on the one hand a high total hardness. On the other hand, an embrittlement of the alloy, which could be due to high carbide contents, effectively counteracted.

The effects of the individual elements in an alloy according to the invention and the interactions between the elements are described below.

Carbon (C):

Carbon is provided in a content range of 0.5 to 1.8 mass%. A minimum content of 0.5% by mass is required to form metal carbides in the proportion of at least 10% by volume and thus to achieve a desired high hardness. Carbon contents of 1.8 mass% or more are not useful because with such high carbon contents, the solidus temperature of the nickel-based alloy is greatly lowered. An optimum range in terms of high hardness and high solidus temperature is given at carbon contents of 0.6 to 1.2 mass%.

Manganese (Mn):

Manganese is used for sulfur setting and solid solution strengthening and may be present in amounts up to 3.0% by weight in an alloy of the invention without adversely affecting the properties of the alloy.

Chrome (Cr):

In an alloy according to the invention chromium is provided with contents of 6.0 to 25.0 mass%. 6.0 mass% chromium is necessary to ensure sufficient carbide formation. Contents of more than 25.0 mass% are disadvantageous, because then forms a high amount of metal carbides of the formula M ₂₃ C ₆ network-like at the dendrite grain boundaries, sub-grain boundaries and grain boundaries of the γ-phase or nickel-based. In the content range of 10 to 18% by weight of chromium, a formation of network-type carbides can be reduced to a favorable level with a high proportion of chromium carbides and / or chromium-containing carbides.

Molybdenum (Mo):

Molybdenum is a strong carbide former and is present in an amount of at least 8.0, preferably at least 10.0, mass% to achieve a high volume fraction of carbides in an alloy of the invention and to contribute to solid solution hardness. Contents of more than 18 mass% molybdenum are not appropriate: Although the carbide content can be further increased, a further increase in hardness is no longer achieved.

Tungsten (W):

Tungsten acts similarly to molybdenum and is a strong carbide former and solid solution promoter, but less effective than molybdenum per unit mass. Therefore, tungsten is used only in combination with molybdenum and can then be present in amounts of up to 10% by mass. It is preferred to use tungsten in contents of 1.0 to 6.0% by mass, because tungsten has a positive effect in these concentrations for the stabilization of carbides of the formula M ₆ C.

In view of the simultaneous presence of molybdenum and tungsten in an alloy according to the invention, it is particularly favorable if a sum (in mass%) of (molybdenum + 0.5 × tungsten) is more than 12.0%. When this condition is satisfied, a content of carbides in the nickel-based alloy can be set to 20% by volume or more, which provides high hardness values of the alloy.

Niobium (Nb):

This element is also a strong carbide former and can be alloyed in levels up to 3.0 mass% to aid in carbide formation. At niobium contents higher than 1.5% by mass, MC type carbides can be particularly stabilized; However, niobium is then partially bound and then only partially available for the formation of γ'-phase (or substitution of Al in the γ'-phase).

Therefore, when niobium is added, a concentration of this element of 0.2 to 1.5 mass% is preferred.

Aluminum (AI):

Aluminum is important because this element is essential for the formation of γ'-phase. In this context, it has been found that aluminum contents of at least 2.5 mass% are necessary in order to obtain a material with the desired high hardness. Higher contents than 6.0% by mass of aluminum can lead to an alloy in which the matrix consists of γ'-phase, which is undesirable in the context of the invention. In practice, aluminum contents of 3.0 to 5.0% by mass have proven particularly useful.

Iron (Fe):

In order to introduce niobium in the production of an alloy according to the invention, FeNb alloys are mainly used. Iron thereby becomes part of the alloy and may be present in levels up to 20.0 mass%. Since higher concentrations of iron on the one hand suppress the formation of γ'-phase and on the other hand promote the formation of carbides of the type M ₂₃ C ₆ , iron contents of 1.5 to 5.0 mass% are favorable.

Cobalt (Co):

Cobalt can reduce the solubility of aluminum in concentrations of up to 4.0% by weight of an alloy according to the invention and therefore lead to improved precipitation behavior of the γ 'phase.

Titanium (Ti):

Titanium can be provided at levels of up to 3.0% by mass and, in addition to carbide formation, serves to form a .gamma. 'Phase in these concentration ranges. Greater concentrations than 3.0% by mass preferably cause formation of undesirable η-phase.

Hafnium (Hf):

Hafnium can be used to substitute aluminum in the γ'-phase and in this case be present in amounts up to 1.5 mass%.

Tantalum (Ta):

Tantalum acts as a carbide-forming element and may be present at levels up to 2.0% by weight.

Zircon (Zr):

Zirconium is found to be effective at levels up to 0.5% by weight in order to avoid formation of carbide films at grain boundaries.

Vanadium (V):

Vanadium is a high carbide-forming element and may be provided for purposes of carbide formation at levels up to 3.0% by weight.

Boron (B):

Optionally, boron may be present in amounts of up to 0.1% by weight, especially from 0.001 to 0.02% by weight. Boron can positively contribute to the hardness of an alloy by forming borides. Incidentally, a presence of boron causes a fine-tuning of the γ-grain of the matrix.

Nickel (Ni):

Nickel forms the base of the alloy or is present in the highest concentration and forms the matrix of γ-phase.

An alloy according to the invention further contains manufacturing-related impurities, such as sulfur, phosphorus, nitrogen and / or oxygen in a conventional extent known in the art.

The further object of the invention is achieved by a process for producing a nickel-based alloy article, wherein in a first step a melt containing (in% by mass) 0.5 to 1.8% carbon to 3.0% manganese 6.0 to 25.0% chrome 8.0 to 18.0% molybdenum to 10.0% tungsten to 3.0% niobium 2.5 to 6.0% aluminum to 20.0% iron to 4.0% cobalt to 3.0% titanium to 01.05% hafnium to 2.0% tantalum to 0.5% zircon to 3.0% vanadium,

Residue nickel and impurities, is atomized to a powder, after which in a second step from the powder, a compact article is formed, after which the compact article is subjected to annealing in the temperature range between solution temperature of γ'-phase and solidus temperature of the nickel-based alloy in a third step , whereupon the article is precipitation hardened in a fourth step.

The advantages achieved procedurally are to be seen above all in the fact that an article made of a nickel-base alloy can be provided, which is resistant to high temperatures and high strength and at the same time has a substantially homogeneous structure over a cross section of the solid material. It is important that the melt composed according to the invention is atomized to a powder in a first step, because segregations or demixings are prevented by the associated rapid solidification and preferably eutectic carbides are homogeneously and finely precipitated from the melt. Subsequently, the powder thus produced is formed into a compact article, so that an isotropic solid material is available for further heat treatments. In the planned third step, the carbides are formed by annealing in the temperature range between solution temperature of γ'-phase and solidus temperature. This decomposes the possibly existing Carbidnetzwerk and there are predominantly formed globular carbides, which contribute proportionately to the achieved hardness. In addition, any existing γ 'phase is at least largely dissolved and the material is homogenized. The fact that the solid material used is substantially homogeneous is a prerequisite for obtaining an article with isotropic properties after annealing. Optionally, the article may be subjected to hot working, such as rolling, before and / or after annealing become. It will also be understood by those skilled in the art that the article may be quenched after annealing, such as with water, oil, or by flowing air. The article is subjected to precipitation hardening, in which γ 'phase is precipitated. It is also homogeneously distributed and contributes to hardness similar to that of the globular carbides.

• 0.6 bis 1.2 % Kohlenstoff und/oder
• 10 bis 18 % Chrom und/oder
• mehr als 10.0 % Molybdän und/oder
• 1.0 bis 6.0 % Wolfram und/oder
• 0.2 bis 1.5 % Niob und/oder
• 3.0 bis 5.0 % Aluminium und/oder
• 1.5 bis 5.0 % Eisen und/oder
• bis 0.1 %, vorzugsweise 0.001 bis 0.02 %, Bor vorliegen

und/oder ein Anteil (in Masse-%) an (Molybdän + 0.5 Wolfram) mehr als 12.0 % beträgt.Taking into account the above-described individual and cumulative effects of the elements of an alloy according to the invention, it may be advantageous in view of favorable properties of the article if, in the melt (in% by mass)

• 0.6 to 1.2% carbon and / or
• 10 to 18% chromium and / or
• more than 10.0% molybdenum and / or
• 1.0 to 6.0% tungsten and / or
• 0.2 to 1.5% niobium and / or
• 3.0 to 5.0% aluminum and / or
• 1.5 to 5.0% iron and / or
• to 0.1%, preferably 0.001 to 0.02%, boron

and / or a proportion (in% by mass) of (molybdenum + 0.5 tungsten) is more than 12.0%.

It is preferred to compact the powder by hot isostatic pressing at a temperature of at least 1000 ° C and a pressure of at least 900 bar in order to obtain a substantially dense article so that damage caused by pores in the subsequent heat treatments is minimized.

When annealing to form the carbides is carried out in the temperature range of 1120 ° C to 1280 ° C, complete incorporation of the carbides in moderate times can be achieved. It is particularly preferred if the second and the third step are carried out simultaneously by hot isostatic pressing at a temperature of more than 1120 ° C for more than four hours. It is exploited that the powder or the compacted article in the hot isostatic pressing is already at high temperature and does not need to be heated separately. In other words, the second and third steps can be combined without having to cool and heat the object between these steps.

In order to achieve a favorable through hardening, the precipitation hardening is preferably carried out by aging the article for at least one hour at a temperature of from 700 to 950 ° C. and then cooling it. It is clear to the person skilled in the art that this step can also be carried out several times, with the temperatures being able to be selected variably from the second aging.

The further object of the invention to provide a tool made of a nickel-based alloy, in particular a cutting tool or thermally highly stressed tool, which has a high hardness is achieved by claim 22. An inventive tool is advantageously used at temperatures of more than 700 ° C and at the same time has a high hardness and high wear resistance. Thus, it can be used in particular in applications in which a tool is subjected to a high abrasive load, such as cutting or forming.

The object of the invention to provide a homogeneous starting material for the production of tools, made of a nickel-based alloy, in particular cutting tool or thermally highly stressed tool, is characterized by a starting material for the production of tools, in particular cutting tools and thermally highly stressed forming tools containing 0.5 to 01.08% carbon to 3.0% manganese 6.0 to 25.0% chrome 8.0 to 18.0% molybdenum to 10.0% tungsten to 3.0% niobium 2.5 to 6.0% aluminum to 20.0% iron to 4.0% cobalt to 3.0% titanium to 1.5% hafnium to 2.0% tantalum to 0.5% zircon to 3.0% vanadium,

Residual nickel and production-related impurities, wherein globular metal carbides are present in a proportion of at least 10% by volume.

The advantage of such a starting material for the production of tools is, in particular, that homogeneous starting material is provided, which can be produced with little effort near the final dimensions or, due to moderate hardness, can be machined to the final dimension of the tool. In order to finally give the finished tool the highest hardness, this only needs to be subjected to curing.

In the following, the invention is further illustrated by several examples.

• Figur 1a: Ein Gefügebild einer erfindungsgemäßen Legierung A;
• Figur 1b : Die Abhängigkeit der Härte einer Legierung A von der Auslagerungsdauer;
• Figur 2a: Ein Gefügebild einer erfindungsgemäßen Legierung B;
• Figur 2b: Die Abhängigkeit der Härte einer Legierung B von der Auslagerungsdauer.

The figures show:

• FIG. 1a : A micrograph of an alloy A according to the invention;
• FIG. 1b : The dependence of the hardness of an alloy A on the aging time;
• FIG. 2a : A micrograph of an alloy B according to the invention;
• FIG. 2b : The dependence of the hardness of an alloy B on the aging time.

Powders of alloys A, B, C and D, whose compositions are shown in Table 1, were each prepared by Gasverdüsung a corresponding molten metal and compacting the powder at 1150 ° C and a pressure of 1000 bar hot isostatically to solid material. The articles thus produced were then subjected to annealing at 1250 ° C. for two hours followed by quenching. Subsequently, the alloys were cured at 800 and 900 ° C, respectively. After cooling to room or ambient temperature, the articles were examined from alloys A to D. <u> Table 1: </ u> Chemical Compositions of Inventive Alloys A to D (% by Weight). element Alloy A Alloy B Alloy C Alloy D C [%] 1:04 0.95 0.8 0.7 Mn [%] 2.6 2.7 1.6 --- Cr [%] 13.1 20.0 21.4 21.9 Not a word [%] 13.0 14.7 14.0 12.9 W [%] 3.1 4.5 4.0 2.9 Nb [%] --- --- 0.3 --- Al [%] 3.8 4.1 2.7 3.1 Fe [%] 4.5 3.9 3.0 2.7 Co [%] --- 2.8 2.2 3.3 Ti [%] --- --- --- 2.2 Ni [%] rest rest rest rest

Microstructural investigations showed that in each case a homogeneous microstructure consisting of a nickel matrix (γ-matrix) and globally distributed globular metal carbides of the types M ₆ C, M ₂ C and / or M ₂₃ C _{6 were} present. For example, a microstructure of Alloy A shows primarily globular carbides M ₂ C and M ₆ C having an average diameter of about 1 to 2 μm ( FIG. 1a ). Alloy B also shows globular carbides, but of type M ₆ C and M ₂₃ C ₆ ( FIG. 2a ).

After curing, alloys of the present invention can achieve Vickers hardnesses greater than 750 HV 5, as shown in Table 2. As the FIGS. 2a and 2b For the alloys A and B by way of example, a hardening increase of about 150 HV can be achieved by hardening or precipitating γ'-phase. The highest overall hardness is achieved in alloy D, in which exclusively M ₆ C carbides are present. <u> Table 2: </ u> Structure formation and hardness of alloys A to D according to the invention. Alloy A Alloy B Alloy C Alloy D M ₂ C + - - - structure M ₆ C + + + + M ₂₃ C ₆ - + + - Carbide content [% by volume] about 30 about 25 about 22 about 16 Proportion of γ'-phase [volume%] approx. 50 about 40 about 40 about 40 Maximum hardness [HV 5] > 490 > 650 > 720 > 750 + ... phase is present, -... phase does not exist

Cutting and forming tools made from the alloy according to the invention have proven themselves in practice at operating temperatures of more than 700 ° C.

Claims (23)

1. Precipitation hardened nickel based alloy, wherein primary metal carbides are present with a proportion of at least 10 % by volume, and which contains (in % by mass) 0.5 to 1.8 % of carbon up to 3.0 % of manganese 6.0 to 25.0 % of chromium 8.0 to 18.0 % of molybdenum up to 10.0 % of tungsten up to 3.0 % of niobium 2.5 to 6.0 % of aluminium up to 20.0 % of iron up to 4.0 % of cobalt up to 3.0 % of titanium up to 1.5 % of hafnium up to 2.0 % of tantalum up to 0.5 % of zirconium up to 3.0 % of vanadium, the rest being nickel and production conditioned impurities.
2. Nickel based alloy according to claim 1, which contains (in % by mass) 0.6 to 1.2 % of carbon.
3. Nickel based alloy according to claim 1 or 2, which contains (in % by mass) 10 to 18 % of chromium.
4. Nickel based alloy according to any of claims 1 to 3, which contains (in % by mass) more than 10.0 % of molybdenum.
5. Nickel based alloy according to any of claims 1 to 4, which contains (in % by mass) 1.0 to 6.0 % of tungsten.
6. Nickel based alloy according to any of claims 1 to 5, wherein a sum (in % by mass) of (molybdenum + 0.5 x tungsten) amounts to more than 12.0 %.
7. Nickel based alloy according to any of claims 1 to 6, which contains (in % by mass) 0.2 to 1.5 % of niobium.
8. Nickel based alloy according to any of claims 1 to 7, which contains (in % by mass) 3.0 to 5.0 % of aluminium.
9. Nickel based alloy according to any of claims 1 to 8, which contains (in % by mass) 1.5 to 5.0 % of iron.
10. Nickel based alloy according to any of claims 1 to 9, which contains (in % by mass) up to 0.1 %, preferably 0.001 to 0.02 %, of boron.
11. Nickel based alloy according to any of claims 1 to 10, wherein the proportion of metal carbides amounts to at least 15 % by volume, preferably to at least 20 % by volume.
12. Nickel based alloy according to any of claims 1 to 11, wherein metal carbides of the formula M₆C, MC, M₂C and/or M₂₃C₆ are present.
13. Nickel based alloy according to claim 12, wherein at least 50 % by volume of the metal carbides are present in the form of M₆C.
14. Nickel based alloy according to any of claims 1 to 13, wherein the metal carbides have an average size of 0.5 to 5 µm, particularly of 1 to 3 µm.
15. Nickel based alloy according to any of claims 1 to 14, wherein a fraction of a γ'-phase amounts to at least 10 % by volume, particularly to 20 to 65 % by volume.
16. Process for producing an object from a nickel based alloy, wherein, in a first step, a melt containing (in % by mass) 0.5 to 1.8 % of carbon up to 3.0 % of manganese 6.0 to 25.0 % of chromium 8.0 to 18.0 % of molybdenum up to 10.0 % of tungsten up to 3.0 % of niobium 2.5 to 6.0 % of aluminium up to 20.0 % of iron up to 4.0 % of cobalt up to 3.0 % of titanium up to 1.5 % of hafnium up to 2.0 % of tantalum up to 0.5 % of zirconium up to 3.0 % of vanadium, the rest being nickel and production conditioned impurities, is atomised to a powder, after which, in a second step, a compact object is formed from the powder, after which, in a third step, the compact object is subjected to annealing within a range of temperature between the solution temperature of the γ'-phase and the solidus temperature of the nickel based alloy, and the object is precipitation hardened thereafter in a fourth step.
17. Process according to claim 16, wherein in a melt (in % by mass)
    0.6 to 1.2 % of carbon and/or
    10 to 18 % of chromium and/or
    more than 10 % of molybdenum and/or
    1.0 to 6.0 of tungsten and/or
    0.2 to 1.5 of niobium and/or
    3.0 to 5.0 % of aluminium and/or
    1.5 to 5.0 % of iron and/or
    up to 0.1 %, preferably 0.001 to 0.02 % of boron are present
    and/or a fraction (in % by mass) of (molybdenum + 0.5 x tungsten) amounts to more than 12.0 %.
18. Process according to claim 16 or 17, wherein the powder is compacted by hot-isostatic compaction at a temperature of at least 1000°C and a pressure of at least 900 bar.
19. Process according to any of claims 17 to 19, wherein annealing is carried out in a temperature range of 1120°C to 1280°C.
20. Process according to any of claims 16 to 19, wherein the second and the third step are carried out simultaneously by hot-isostatic compaction at a temperature of more than 1120°C during more than four hours.
21. Process according to any of claims 16 to 19, wherein precipitation hardening is effected by ageing the object during at least one hour at a temperature of 700 to 950°C and subsequent cooling the object.
22. Tool, particularly cutting tool or thermally highly loaded transforming tool, which consists of a nickel based alloy according to any of claims 1 to 15.
23. Starting material for producing tools, particularly cutting tools or thermally highly loaded transforming tools, which contains 0.5 to 1.8 % of carbon up to 3.0 % of manganese 6.0 to 25.0 % of chromium 8.0 to 18.0 % of molybdenum up to 10.0 % of tungsten up to 3.0 % of niobium 2.5 to 6.0 % of aluminium up to 20.0 % of iron up to 4.0 % of cobalt up to 3.0 % of titanium up to 1.5 % of hafnium up to 2.0 % of tantalum up to 0.5 % of zirconium up to 3.0 % of vanadium, the rest being nickel and production conditioned impurities, globular metal carbides being present in a proportion of at least 10 % by volume.

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