WO2025015363A1 - Method for producing alloyed sintered steel - Google Patents

Abstract

The invention relates to a method for producing a sintered steel alloyed with a Group 6 element and/or a Group 5 element, having the steps of: • providing a powder mixture, comprising o 1 to 6 wt.% of a pulverulent master alloy prealloy, said master alloy prealloy having a melting point of maximally 1300 °C, o 0.1 to 2 wt.% of a pulverulent Group 6 and/or Group 5 element as an elementary powder or as a ferroalloy powder or as a carbide powder, o 0.1 to 1.0 wt.% of carbon, o up to 1.0 wt.% of a compacting auxiliary agent, and o a remainder of: pulverulent iron or a pulverulent iron alloy, • producing a green body from said powder mixture, and • sintering the green body at a maximum temperature of 1100 to 1250 °C.

Description

PROCESS FOR THE PRODUCTION OF ALLOYED SINTERED STEEL

The present invention relates to a method for producing a group 5 or group 6 element alloyed sintered steel, in particular a molybdenum alloyed sintered steel. In addition, the invention relates to the use of a master alloy master alloy for alloying sintered steel. Furthermore, the invention relates to a master alloy master alloy for alloying sintered steel.

Background of the invention

To harden steel and prevent temper embrittlement, refractory metals such as molybdenum or vanadium are increasingly being added to steel as alloying elements. Due to the very high melting point of molybdenum in particular compared to iron, Masteralloy processes have now been described for the production of alloyed sintered steels. In these processes, a master alloy (a "master alloy") with a significant content of the metal to be alloyed (e.g. molybdenum or vanadium) is produced, whereby the master alloy is then mixed in powder form with metallic iron powder, pressed and sintered (see e.g. Zapf, G., Dalal, K.: Modem developments in powder metallurgy, 1977, p. 129; Schlieper, G., Thümmler, F.: Powder Metallurgy International, vol. 11, 1979, p. 172; Banerjee, S., et al.: Progress in Powder Metallurgy, vol. 13, 1980, p. 143). A uniform distribution of the molybdenum- or vanadium-containing master alloy in the powder mixture ensures a good distribution of the molybdenum and vanadium in the sintered steel. However, since in this process the molybdenum and even more the vanadium in the master alloy are present as thermodynamically quite stable carbide, high sintering temperatures are required for the homogeneous distribution of the Mo or V in the steel matrix.

It is characteristic that all metallic alloying elements are introduced simultaneously via the one master alloy. Other approaches are described, for example, for Mn-Si master alloys (A. N. Klein, R. Oberacker, F. Thümmler (e.g. Metal Powder Report June 1984, p.335-338 or Modem Dev. In Powder Metall. 16 (1985) p.141-152)).

The addition of the elements Mn, Si, Mo to sintered steel is also described in EP 0 787 048 Bl, whereby the alloying elements mentioned are added in powder form using different processes and alloying techniques that have long been known in powder metallurgy. However, EP 0 787 048 Bl does not address interactions between these additives during sintering. Z. Zhang, K. Frisk, A. Salwen & R. Sandstrom (2004) Mechanical properties of Fe-Mo-Mn- Si-C sintered steels, Powder Metallurgy, 47:3, 239-246, (DOI: 10.1179/003258904225015572) describes Fe-Mn-Si Masteralloy powder to produce Fe-Mo-Mn-Si-C sintered steel.

Brief description of the invention

Molybdenum-alloyed sintered steels are known from the state of the art, but the production of molybdenum (Mo)-alloyed sintered steel, in which the Mo is distributed homogeneously in the finished sintered steel, is technically and energetically complex due to the high melting point of Mo (2,623 °C). Sintering powder mixtures with elemental Mo or ferromolybdenum powder requires very high sintering temperatures and thus complex furnace units in order to achieve the uniform distribution of the alloying element in the steel matrix required for the required mechanical properties. As mentioned, the master alloy process described above is also energetically complex with high required sintering temperatures. In this case, high sintering temperatures also lead to the sintered steel swelling noticeably or tending to warp, which is problematic in terms of dimensional stability. Similar problems also occur with sintered steels alloyed with chromium, vanadium or tungsten.

The object of the present invention is therefore to provide a method for producing a low refractory metal alloyed sintered steel, in which the required sintering temperature is lower than in the above-mentioned methods and the dimensional stability is improved.

This object is achieved by a method for producing a group 6 element or group 5 element alloyed sintered steel, comprising the steps:

• Providing a powder mixture comprising o 1 to 6 wt.% of a powdered master alloy, wherein the master alloy has a melting point of max. 1300 °C, o 0.1 to 2 wt.% of powdered group 6 and/or group 5 element as elemental powder or as ferroalloy powder or as carbide powder, o 0.1 to 1.0 wt.% carbon, o up to 1.0 wt.% of a pressing aid, o remainder: powdered iron or powdered iron alloy

• Production of a green body from this powder mixture and

• Sintering of the green body at a maximum temperature of 1100 to 1250 °C. The naturally occurring elements of group 6 and group 5 are understood to be group 6 and group 5 elements respectively. The group 6 elements within the meaning of the invention are therefore the metals chromium, molybdenum and tungsten, the group 5 elements are vanadium, niobium and tantalum. The group 6 element molybdenum is preferably provided within the scope of the invention. Therefore, in addition to the term group 6 element alloyed sintered steel, molybdenum alloyed sintered steel is described below in particular; the same applies to vanadium for the group 5 elements.

Ferroalloys are master alloys that contain elements that are soluble in molten iron and improve the properties of iron and steel (see Fichte R., “Ferroalloys” in Ullmann’s Encyclopedia of Industrial Chemistry, 2012, Vol. 14, 153-155 (https ;//doi . org/ 10, 1002/ 14356007, a 10 05 ) are master alloys). According to the definition of Fichte, which also applies to ferroalloys of the invention, ferro molybdenum has a molybdenum content of 62 to 70 wt.%, ferrochrome a chromium content of 45 to 95 wt.%, ferroniobium a niobium content of 55 to 70 wt.%, ferrotungsten a tungsten content of 70 to 85 wt.% and ferrovanadium a vanadium content of 35 to 80 wt.%.

Low refractory metal alloy or low molybdenum alloy in the sense of the invention means that the finished sintered steel does not contain more than 2 wt.% of refractory metal or Mo. Powdered iron has a purity of > 99 wt.%. An iron alloy in the context of the invention contains at least 90 wt.% iron.

For the purposes of the invention, steel, with reference to EN 10020:2000-07, is understood to mean a material whose mass fraction of iron is greater than that of any other element, whose carbon content is not more than 2 wt.% and which may contain other elements.

In contrast to the prior art, the present invention describes the alloying technology of powder with a master alloy, which is designed in such a way that it melts during heating to sintering temperature, dissolves high-melting pure alloy additives and, as an intermediate liquid phase, alloys the base powder in a molten state via the open porosity with the elements of the master alloy as well as the high-melting additional element.

A crucial component of the process is the targeted use of the interaction between a high-melting metal added as an elemental powder (alternatively as a ferroalloy or carbide) - for example Mo - and a master alloy powder melting below the isothermal sintering temperature - for example a Fe-Mn-Si-C master alloy - during the sintering process, whereby the resulting master alloy melt is used as It serves as a solvent for the Mo and, due to the distribution of the master alloy melt by capillary forces in the pore network of the powder compact, subsequently represents the transport medium for the Mo, which is not very easy to homogenize.

Within the scope of the invention, it has been found that a master alloy process for alloying iron with group 6 elements or group 5 elements works well when the master alloy has a melting point of max. 1300 °C. Furthermore, the group 6 element or group 5 element must be present as an elemental powder or as a ferroalloy powder or as a carbide powder. Furthermore, it is advantageous if the master alloy is free of the group 6 element or group 5 element to be alloyed. In the case of molybdenum and/or vanadium, the master alloy should therefore be molybdenum or vanadium free and molybdenum or vanadium should be added as an elemental powder or as a ferroalloy powder or as molybdenum carbide powder or vanadium carbide powder.

According to the inventors' studies, the distribution of group 6 elements or group 5 elements occurs in such a way that the master alloy melts first and is distributed in the powder mixture during melting. The powdered group 6 element or group 5 element dissolves in the melting phase of the master alloy and is distributed together with the master alloy in the green body. In this way, the sintering temperature can be kept low because only the melting temperature of the master alloy has to be reached. In addition, the dimensions of the body hardly change during sintering, so that the dimensional stability is higher compared to other state-of-the-art processes. Similar results are possible when alloying iron with chromium or tungsten or niobium or tantalum, whereby the master alloy is then chromium-free or tungsten-free, niobium-free or tantalum-free and has a melting point of max. 1300 °C and when the chromium or tungsten, niobium and/or tantalum is added as an elemental powder or as a corresponding ferroalloy powder.

Accordingly, in one aspect, it is provided that for the homogenization of the powdered group 6 and/or group 5 element in the matrix of the iron or iron alloy, the powdered group 6 and/or group 5 element is dissolved in the master alloy pre-alloy, which is separately mixed in powder form and melts below the isothermal sintering temperature. During the sintering process, a master alloy, which is separately mixed in powder form and melts below the isothermal sintering temperature, is used to homogenize a high-melting metal mixed in powder form in the iron-based matrix, and the high-melting metal is dissolved in the melt.

During sintering of the green body, the Masteralloy master alloy can melt and form an intermediate liquid phase. In contrast to known master alloy approaches (as described e.g. in Raquel de Oro Calderon et. al; Powder Metallurgy Progress, Vol.18 (2018), No.2, p.121-127 http://dx.doi.org/10.1515/pmp- 2018-0014), the element to be alloyed is not introduced into the master alloy itself, but is added as a powder either directly (preferred) or as a ferroalloy powder or as a carbide.

With this process, it is now possible to easily alloy elements with high melting points, but also those that form high melting carbides and are difficult to alloy due to their melting or decomposition temperatures. Specific melting or decomposition points for individual Group 6 or Group 5 elements are listed below:

Cr: congruent melting at 1857°C

Cr23C6: peritectic decomposition at 1576°C

Cr7C3: congruent melting at 1766°C

Cr3C2: peritectic decomposition at 1811°C

Mo: congruent melting at 2617°C

Mo2C: congruent melting at 2605°C

V: congruent melting at 1890°C

VC: congruent melting at 2656°C

Nb: congruent melting at 2468°C

NbC: congruent melting at 3600°C

Ta: congruent melting at 2996°C

TaC: congruent melting at 3985°C

W: congruent melting at 3410°C

W2C: congruent melting at 2785°C

WC: peritectic decomposition at 2785°C

Data sources:

• Elements: Handbook of Chemistry and Physics, 67th Ed., CRC Press, Boca Raton FL (1987)

• Carbides: ASM Handbook Vol.3 “Alloy Phase Diagrams”, ASM, Materials Park OH (1992)

• NbC, TaC: WGMoffatt: “The Handbook of Binary Phase Diagrams”. Genium Publishing Corp., Schenectady NY (1984) The process according to the invention now also allows these metals or metal carbides to be easily alloyed.

The Masteralloy master alloy is intended to promote the distribution of the group 6 or group 5 element in the iron phase. Alloys in which the distribution of the Masteralloy melt in the green body is ideal have proven to be ideal. Masteralloy master alloys that have proven to be suitable are those that consist of

• 10 to 60 wt. % iron,

• 0 to 20 wt.% silicon,

• 0 to 6.7 wt. % carbon,

• 10 to 60 wt. % manganese,

• max 30 wt. %, preferably a maximum of 20 wt. % of other elements.

Other elements include Cu, Ni, Co, Sn and Al in small amounts.

The master alloy preferably contains < 0.1 wt. %, particularly preferably < 0.01 wt. % of chromium, molybdenum, tungsten, vanadium, niobium and tantalum.

Preferably, the content of the group 6 or group 5 element to be alloyed in the Masteralloy master alloy is < 0.1 wt. %, particularly preferably < 0.01 wt. %.

The distribution of the powdered group 6 or group 5 element is ideal if it has a particle diameter dso measured by laser diffraction of < 10 pm.

In an advantageous embodiment, the powder mixture is prepared in several steps: In a first step, the powdered Masteralloy master alloy and the powdered iron or the powdered iron alloy are mixed for preferably 10 to 30 minutes; then the powdered Group 6 or Group 5 element is added and mixed again for the same time. Carbon is then added and the mixture thus obtained is mixed again - preferably for 10 to 30 minutes. The pressing aid is then added and the mixture thus obtained is mixed again - preferably for 10 to 30 minutes. This procedure ensures the optimal distribution of all components in the finished sintered steel.

The green compact is typically manufactured by pressing the powder mixture into the desired shape by axial die pressing. This can be done in molds by applying a pressure of preferably 500-800 MPa. Preferably, the sintering process is started at an initial temperature of 600 °C in order to completely remove the pressing aid.

In addition, it has proven advantageous if the sintering temperature is increased from the initial temperature to the maximum temperature at a rate of 5 to 15 K/min, preferably about 10 K/min.

If a pressing aid is used, the pressing aid should be removed from the green body before sintering by heating it - preferably to a set temperature of 600 °C as mentioned above. This step is preferably carried out under a protective gas atmosphere. For example, heating to remove the pressing aid can be carried out under a nitrogen atmosphere.

The sintering process is preferably carried out under an atmosphere consisting of nitrogen and hydrogen, with a dew point below -20°C.

In one aspect, the invention therefore also relates to the use of a Masteralloy master alloy consisting of

• 10 to 60 wt. % iron,

• 0 to 20 wt.% silicon,

• 0 to 6.7 wt. % carbon,

• 10 to 60 wt. % manganese,

• max 20 wt. % other elements for alloying sintered steel.

Detailed description of the invention

The invention is explained in more detail using examples, figures and the following description of the figures.

Fig. 1 shows a classic sintering process for high-melting elements

Fig. 2 shows a known sintering process for refractory elements with Masteralloy.

Fig. 3 shows a sintering process according to the invention.

Fig. 1 shows a classic sintering process in which powdered iron or a powdered iron alloy (base powder) is sintered with a group 6 element or group 5 element (eg Mo, Cr, V or W) and carbon (C). The base powder For example, ASC 100.29 (Fe), Astaloy 0.85 Mo (Fe_0.85Mo), Astaloy CrA (Fe_1.8Cr) and Astaloy CrM (Fe_3Cr_0.5Mo) were investigated. Mo, Cr, V and W were investigated as group 6 and group 5 elements respectively.

The base powder is mixed with carbon and elemental, powdered group 6 element or group 5 element. In the heating phase, the mixture is heated from around 20 °C to 1250 to 1300 °C, which leads to the formation of carbide. If a eutectic reaction takes place with the base powder, an intermediate melt formation with secondary pores occurs; after sintering, the group 6 element or group 5 element is largely homogeneously distributed in the iron matrix. However, depending on the alloying element, the eutectic reaction requires temperatures of 1250 to 1370 °C. If the sintering process takes place below this temperature threshold, with pure solid phase diffusion, the result is a sintered and alloyed powder steel. In this case, however, the group 6 element or group 5 element is only distributed locally, not over the entire body, and the desired effect of these elements on the properties of the sintered steel is not achieved.

Fig. 2 shows a state-of-the-art master alloy sintering process in which powdered iron or a powdered iron alloy (base powder) is sintered with a master alloy powder. The master alloy powder contains the group 6 element or group 5 element to be sintered (e.g. Mo, Cr, V or W). Carbon (C) is also present. The base powders mentioned in Fig. 1 were investigated as base powders. CrMA (Fe-Si-C-Cr) and CrMnMA (Fe-Si-Cr-Mn) were used as master alloys and, for comparison, the master alloy powder MnMA (Fe-Si-C-Mn) without group 6 element or group 5 element was used.

The base powder is mixed with carbon and powdered MA. In the heating phase, the mixture is heated from around 20 °C to 1120 to 1180 °C. The master alloy melts and spreads over the open pores. After the sintering process with solid phase diffusion at 1120 to 1180 °C, a sintered and alloyed powder steel is obtained. The elements Mn and Si are distributed throughout the body, but not the group 6 element or group 5 element, which is still present at least partially as undissolved carbide. For a homogeneous distribution of these latter elements, sintering temperatures of at least 1250 °C are also required here. Only when the master alloy powder MnMA is used are sintering temperatures of 1120-1180 °C sufficient to homogenize the alloying elements; However, in this case the beneficial effect of group 5 or group 6 elements is omitted.

Fig. 3 shows a Masteralloy sintering process according to the invention, in which powdered iron or a powdered iron alloy (base powder) is mixed with a Masteralloy powder and a group 6 element or group 5 element in powder form. The master alloy powder is free of the group 6 element or group 5 element to be sintered (e.g. Mo, Cr, V or W). Carbon (C) is also present. The base powders mentioned in Fig. 1 were also investigated as base powders. MnMA (Fe-Si-C-Mn) was used as the master alloy. Mo, Cr, V and W were investigated as group 6 element or group 5 element.

The base powder is mixed with carbon, powdered MA and powdered group 6 element or group 5 element. In the heating phase, the mixture is heated from around 20 °C to 1120 to 1180 °C. The master alloy melts and dissolves the elemental group 6 element or group 5 element. This solution is distributed over the open pores. After the sintering process with solid phase diffusion at 1120 to 1180 °C, a sintered and alloyed powder steel is present. The group 6 element or group 5 element is distributed over the entire body. In contrast to the example in Fig. 2, a complex master alloy, for which an alloy with the group 6 element or group 5 element must be provided, can be dispensed with.

The present invention demonstrates that relatively low-melting master alloys promote the homogenization of the high-melting alloy elements of the group 6 elements Mo, Cr and W or the group 5 elements V, Nb and Ta by acting as a “solubilizer” and transport medium during melting.

The production of the sintered steel bodies follows the known production route for powder metallurgical molded parts, i.e. mixing the starting powder with the addition of a suitable pressing aid, pressing by uniaxial die pressing in pressing tools with the appropriate geometry, thermal removal of the pressing aid in a furnace unit under a suitable atmosphere and sintering under inert or reducing protective gas. If the sintering furnace is suitably equipped, the sintered material can be quenched and thus hardened by blowing cold inert gas immediately after leaving the high-temperature zone of the furnace; this is followed by tempering in an appropriately tempered outlet zone of the furnace or in a separate tempering furnace.

In the specifically described method according to the invention, a master alloy powder of the described composition is mixed with a pure iron powder or a low-alloy steel powder as a base powder and graphite powder as a carbon carrier; furthermore, a small amount of the powder of a group 6 and/or group 5 element is added, as well as the pressing aid. The mixing process is advantageously carried out in stages by first mixing the base powder with the master alloy powder, then the group 6-/Group 5 element powder, after a further mixing process the graphite powder and after further mixing the lubricant is added and mixed in.

Pressing takes place in a press tool shaped according to the geometry of the component to be produced at a pressure of 500 to 800 MPa, depending on the relative density to be achieved. The green body thus obtained, which typically contains 8-12% porosity, is first thermally dewaxed and then sintered in the furnace unit. During the heating process to the sintering temperature, which is preferably between 1120 and 1180°C, the added master alloy powder melts and forms an intermediate liquid phase that is able to dissolve the added group 6 or group 5 element. Under the effect of capillary forces, the liquid phase with the group 6 or group 5 element contained in it is distributed in the pore network of the body; the alloying elements are thus distributed macroscopically homogeneously in the body. The elements then diffuse into the particles of the base powder, causing the liquid phase to disappear.

The above-mentioned transport mechanism via the liquid phase, brought about by the inventive combination of a master alloy melting below the isothermal sintering temperature with the high-melting group 6 or group 5 element, results in a much more uniform distribution of the group 6 or group 5 element in the sintering body than would be possible by mixing elemental powder of the group 6 or group 5 element into an iron-carbon powder mixture. In the latter case, either the group 6 or group 5 element would have to be distributed in the base material by solid phase diffusion, which would be a very slow and lengthy process due to the very low diffusion coefficients of the group 6 or group 5 elements in the austenite, or the sintering temperature would have to be chosen so high that a liquid phase forms intermediately between the group 6 or group 5 element and the carbon-containing austenite, which would require temperatures well beyond 1300°C depending on the C content and the group 6 or group 5 element selected, since a carbide is formed from the group 6 or group 5 element and the added carbon when heated up, and a carbonitride is formed in the case of group 5 elements in a nitrogen-containing sintering atmosphere. Sintering at such high temperatures would be economically and ecologically disadvantageous due to the complex and expensive furnace units required and the high energy consumption. Furthermore, the intermediate liquid phase in this case leads to swelling and thus a decrease in the sintered density, which is unfavorable for the mechanical properties.

The process according to the invention thus makes it possible to sinter high-melting group 6 or group 5 elements with the iron-based matrix metal and thus fully exploit the positive effect of the group 6 or group 5 elements on the properties of the sintered steel.

Examples of implementation:

For this study, material compositions and manufacturing parameters were used which showed that the systems already had usable mechanical properties without the addition of Mo or V. This was used to specifically investigate whether and to what extent the addition of these elements resulted in further improvement.

Example 1:

The following powders are mixed:

- 4 wt. % Masteralloy powder Fe-40%Mn-9%Si-1.5%C, high-pressure water atomized

- 2 wt. % Masteralloy powder Fe-33%Mn-7.5%Si-3.44%C, high-pressure water atomized

- 0.5 wt. % Mo powder <32 pm, elemental

- 0.471 wt.% graphite powder

- Rest: pure iron powder water atomized

The mixture is mixed with 0.6% ethylene bisstearamide as a lubricant and pressed in a press tool with a floating die at 600 MPa pressure to form cuboid-shaped test specimens according to ISO 5754. As a reference, similar test specimens are produced, but without Mo addition.

The pellets of both compositions produced in this way are dewaxed in a furnace with a tubular, gas-tight retort made of heat-resistant steel for 30 min at 600°C under pure nitrogen and then sintered in another furnace with a tubular, gas-tight retort made of a superalloy for 60 min at a temperature of 1180°C and cooled to room temperature in the water-cooled outlet zone of the furnace at approx. 0.4 K/s.

For each composition, a portion of the test specimens is characterized in the sintered state, another portion is heated again to 1100°C in the latter furnace, held for 30 minutes and then cooled in a quenching device with pure nitrogen so that a cooling rate of 3 K/s linearized between 900° and 100°C is obtained. Immediately afterwards, the material is annealed in air at 180°C for 60 minutes. These samples are also characterized.

The following properties are measured: AS (as sintered): sintered state; GQ (gas quenched): gas quenched and tempered

Example 2:

The following powders are mixed:

4 wt. % Masteralloy powder Fe-40%Mn-9%Si-1.5%C, high-pressure water atomized

2 wt. % Masteralloy powder Fe-33%Mn-7.5%Si-3.44%C, high-pressure water atomized

0.5 wt. % V-powder <90 pm, elemental

0.471 wt. % graphite powder Rest: pure iron powder, water atomized

The powder mixture is mixed with lubricant as described in Example 1, pressed, dewaxed and sintered or partially subsequently gas quenched and tempered. The following properties are measured:

AS (as sintered): sintered state; GQ (gas quenched): gas quenched and tempered

Claims

1. A process for producing a group 6 element and/or group 5 element alloyed sintered steel, comprising the steps: • Providing a powder mixture comprising o 1 to 6 wt.% of a powdered master alloy, wherein the master alloy has a melting point of max. 1300 °C, o 0.1 to 2 wt.% of powdered group 6 and/or group 5 element as elemental powder or as ferroalloy powder or as carbide powder, o 0.1 to 1.0 wt.% carbon, o up to 1.0 wt.% of a pressing aid, o remainder: powdered iron or powdered iron alloy • Production of a green body from this powder mixture and • Sintering of the green body at a maximum temperature of 1100 to 1250 °C. 2. Process according to claim 1, characterized in that for the homogenization of the powdered group 6 and/or group 5 element in the matrix of the iron or iron alloy, the powdered group 6 and/or group 5 element is dissolved in the master alloy master alloy which is mixed separately in powder form and melts below the isothermal sintering temperature. 3. Process according to claim 1 or claim 2, characterized in that during the sintering of the green body, the master alloy melts and forms an intermediate liquid phase. 4. Method according to one of claims 1 to 3, characterized in that the master alloy is an alloy consisting of • 10 to 60 wt.% iron, • 0 to 20 wt.% silicon, • 0 to 6.7 wt. % carbon, • 10 to 60 wt. % manganese, • max. 30 wt. %, preferably max. 20 wt. % other elements. 5. Process according to one of claims 1 to 4, characterized in that the group 6 element is selected from the group consisting of molybdenum, chromium and tungsten, preferably the group 6 element is molybdenum and the group 5 element is selected from the group consisting of vanadium, niobium and tantalum, preferably the group 5 element is vanadium. 6. Process according to one of claims 1 to 5, characterized in that the master alloy powder has an average diameter of d50 < 45 pm measured by laser diffraction. 7. Process according to one of claims 1 to 6, characterized in that the powdered group 6 or group 5 element has an average diameter of dso < 45 pm, preferably dso < 10 pm, measured by means of laser diffraction. 8. Method according to one of claims 1 to 7, characterized in that the provision of the powder mixture comprises several steps, wherein in a first step the powdered Masteralloy master alloy and powdered iron are mixed for preferably 10 to 30 minutes, wherein the powdered Group 6 or Group 5 element is then added and the mixture thus obtained is mixed again - preferably for 10 to 30 minutes -, wherein carbon is then added and the mixture thus obtained is mixed again - preferably for 10 to 30 minutes -, wherein the pressing aid is then added and the mixture thus obtained is mixed again - preferably for 10 to 30 minutes. 9. Method according to one of claims 1 to 8, characterized in that the green compact is produced by pressing the powder mixture into the desired shape. 10. Method according to one of claims 1 to 9, characterized in that the sintering is started at an initial temperature of 600 °C. 11. Process according to one of claims 1 to 10, characterized in that the maximum sintering temperature is between 1100 and 1200°C. 12. The method according to claim 10 or claim 11, characterized in that the sintering temperature is increased from the initial temperature to the maximum temperature at a rate of 5 to 15 K/min, preferably about 10 K/min. 13. Method according to one of claims 1 to 12, characterized in that a pressing aid is present, wherein the pressing aid is removed from the green body before sintering, preferably by heating to a maximum of 600 °C. 14. The method according to claim 13, characterized in that the heating to remove the pressing aid is carried out under a nitrogen atmosphere. 15. Process according to one of claims 1 to 14, characterized in that the sintering takes place under an atmosphere consisting of nitrogen and hydrogen. 16. Process according to one of claims 1 to 15, characterized in that the master alloy contains less than 0.01 wt.% of Mo, Wo, V, Nb and Ta. 17. Use of a Masteralloy master alloy consisting of • 10 to 60 wt. % iron, • 0 to 20 wt.% silicon, • 0 to 6.7 wt. % carbon, • 10 to 60 wt. % manganese, • max. 30 wt. %, preferably max. 20 wt. % of other elements for alloying sintered steel with a group 6 and/or group 5 element. 18. Use according to claim 17, characterized in that the group 6 and/or group 5 element is selected from the group consisting of Mo, W, V, Nb and Ta, preferably from the group consisting of Mo, W and V.