Method for producing alloyed sintered steel

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

[0001] PROCESS FOR PRODUCING ALLOYED SINTERED STEEL

[0002] 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. Furthermore, the invention relates to the use of a master alloy for alloying sintered steel. Furthermore, the invention relates to a master alloy for alloying sintered steel.

[0003] Background of the invention

[0004] To harden steel and prevent temper embrittlement, refractory metals such as molybdenum or vanadium are increasingly being added as alloying elements. Due to the very high melting point of molybdenum, especially compared to iron, Masteralloy processes have also 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, which 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 vanadiumVanadium-containing master alloys in the powder mixture ensure a good distribution of molybdenum and vanadium in the sintered steel. However, since the molybdenum, and even more so the vanadium, in the master alloy is present as a thermodynamically stable carbide in this process, high sintering temperatures are required for the homogeneous distribution of the Mo and V in the steel matrix.

[0005] A characteristic feature is that all metallic alloying elements are introduced simultaneously via a single master alloy. Other approaches have been described, for example, for Mn-Si master alloys (AN Klein, R. Oberacker, F. Thümmler (e.g., Metal Powder Report June 1984, pp. 335-338 or Modem Dev. In Powder Metall. 16 (1985) pp. 141-152)).

[0006] The addition of the elements Mn, Si, and Mo to sintered steel is also described in EP 0 787 048 B1, 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 B1 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 master alloy powder for producing Fe-Mo-Mn-Si-C sintered steel.

[0007] Brief description of the invention

[0008] 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 homogeneously distributed throughout the finished sintered steel, is technically and energetically complex due to Mo's high melting point (2,623 °C). Sintering powder mixtures with elemental Mo or ferromolybdenum powder requires very high sintering temperatures and thus complex furnace equipment to achieve the uniform distribution of the alloying element in the steel matrix necessary for the required mechanical properties. As mentioned, the previously described master alloy process is also energy-intensive, requiring high sintering temperatures. In this case, high sintering temperatures also lead to noticeable swelling of the sintered steel and a tendency to warp, which is problematic with regard to dimensional stability.Similar problems also occur with sintered steels alloyed with chromium, vanadium or tungsten.

[0009] 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.

[0010] This object is achieved by a process for producing a group 6 element or group 5 element alloyed sintered steel, comprising the steps:

[0011] • 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

[0012] • Production of a green body from this powder mixture and

[0013] • Sintering the green body at a maximum temperature of 1100 to 1250 °C. Group 6 and group 5 elements are understood to be the naturally occurring elements of group 6 and group 5, 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. Within the scope of the invention, the group 6 element molybdenum is preferably provided. Therefore, in addition to the term group 6 element alloyed sintered steel, molybdenum alloyed sintered steel is described below; the same applies to vanadium for the group 5 elements.

[0014] Ferroalloys are master alloys containing 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, ferromolybdenum 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.%.

[0015] Low-refractory metal alloying or low-molybdenum alloying within the meaning of the invention means that the finished sintered steel contains no more than 2 wt.% refractory metal or Mo. Powdered iron has a purity of > 99 wt.%. An iron alloy within the scope of the invention contains at least 90 wt.% iron.

[0016] 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.

[0017] 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 alloying 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.

[0018] A crucial component of the process is the targeted use of the interaction between a high-melting metal - for example Mo - added as an elemental powder (alternatively as a ferroalloy or carbide) and a master alloy powder melting below the isothermal sintering temperature - for example an Fe-Mn-Si-C master alloy - during the sintering process, whereby the resulting master alloy melt serves as a solvent for the Mo and, due to the distribution of the master alloy melt by the 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.

[0019] Within the scope of the invention, it has been found that a master alloy process for alloying iron with group 6 or group 5 elements works well when the master alloy has a melting point of max. 1300 °C. Furthermore, the group 6 or group 5 element must be present as an elemental powder, as a ferroalloy powder, or as a carbide powder. Furthermore, it is advantageous if the master alloy is free of the group 6 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, as a ferroalloy powder, or as molybdenum carbide powder or vanadium carbide powder.

[0020] According to the inventors' studies, the distribution of the group 6 element or group 5 element occurs in such a way that the master alloy melts first and is distributed throughout 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 needs to be reached. In addition, the dimensions of the body hardly change during sintering, so that the dimensional accuracy 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, in which case the master alloy is chromium-free or tungsten-free, niobium-free or tantalum-free and has a melting point of max. 1300 °C. If the chromium orthe tungsten, niobium and / or tantalum is added as elemental powder or as corresponding ferroalloy powder.

[0021] 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 prealloy, 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 refractory metal mixed in powder form in the iron-based matrix, and the refractory metal is dissolved in the melt.

[0022] During sintering of the green body, the master alloy can melt and form an intermediate liquid phase. In contrast to known master alloy approaches (as described, for example, in Raquel de Oro Calderon et al.; Powder Metallurgy Progress, Vol. 18 (2018), No. 2, pp. 121-127 http: / / dx.doi.org / 10.1515 / pmp-2018-0014), the element to be alloyed is not incorporated into the master alloy itself, but rather is added as a powder, either directly (preferred) or as a ferroalloy powder or as a carbide.

[0023] This process now makes it possible to easily alloy high-melting elements, as well as those that form high-melting carbides and are difficult to alloy due to their melting or decomposition temperatures. Specific melting and decomposition points for individual Group 6 and Group 5 elements are listed below:

[0024] Cr: congruent melting at 1857°C

[0025] Cr23C6: peritectic decomposition at 1576°C

[0026] Cr7C3: congruent melting at 1766°C

[0027] Cr3C2: peritectic decomposition at 1811°C

[0028] Mo: congruent melting at 2617°C

[0029] Mo2C: congruent melting at 2605°C

[0030] V: congruent melting at 1890°C

[0031] VC: congruent melting at 2656°C

[0032] Nb: congruent melting at 2468°C

[0033] NbC: congruent melting at 3600°C

[0034] Ta: congruent melting at 2996°C

[0035] TaC: congruent melting at 3985°C

[0036] W: congruent melting at 3410°C

[0037] W2C: congruent melting at 2785°C

[0038] WC: peritectic decomposition at 2785°C

[0039] Data sources:

[0040] • Elements: Handbook of Chemistry and Physics, 67th Ed., CRC Press, Boca Raton FL (1987)

[0041] • Carbides: ASM Handbook Vol.3 “Alloy Phase Diagrams”, ASM, Materials Park OH (1992)

[0042] • 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.

[0043] The Masteralloy master alloy is intended to promote the distribution of the Group 6 or Group 5 element in the iron phase. Alloys with an ideal distribution of the Masteralloy melt in the green body have proven to be ideal. Masteralloy master alloys that have proven suitable are those made from

[0044] • 10 to 60 wt.% iron,

[0045] • 0 to 20 wt.% silicon,

[0046] • 0 to 6.7 wt.% carbon,

[0047] • 10 to 60 wt.% manganese,

[0048] • max 30 wt%, preferably max 20 wt% of other elements.

[0049] Other elements include Cu, Ni, Co, Sn and Al in small amounts.

[0050] The master alloy preferably contains < 0.1 wt.%, particularly preferably < 0.01 wt.% of chromium, molybdenum, tungsten, vanadium, niobium and tantalum.

[0051] 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.%.

[0052] 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.

[0053] 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 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 resulting mixture is mixed again, preferably for 10 to 30 minutes. The pressing aid is then added, and the resulting mixture is mixed again, preferably for 10 to 30 minutes. This procedure ensures the optimal distribution of all components in the finished sintered steel.

[0054] The green compact is typically produced by pressing the powder mixture into the desired shape using axial die pressing. This can be achieved in molds by applying a pressure of preferably 500-800 MPa. The sintering process is preferably started at an initial temperature of 600 °C to completely remove the pressing aid.

[0055] Furthermore, 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.

[0056] If a pressing aid is used, the pressing aid should be removed from the green compact prior to sintering by heating it – preferably to a set temperature of 600 °C as mentioned above. This step is preferably carried out in a protective gas atmosphere. For example, heating to remove the pressing aid can be carried out under a nitrogen atmosphere.

[0057] The sintering process is advantageously carried out in an atmosphere consisting of nitrogen and hydrogen, with a dew point below -20°C.

[0058] In one aspect, the invention therefore also relates to the use of a Masteralloy master alloy consisting of

[0059] • 10 to 60 wt.% iron,

[0060] • 0 to 20 wt.% silicon,

[0061] • 0 to 6.7 wt.% carbon,

[0062] • 10 to 60 wt.% manganese,

[0063] • max 20 wt.% other elements for alloying sintered steel.

[0064] Detailed description of the invention

[0065] The invention is explained in more detail using examples, figures and the following description of the figures.

[0066] Fig. 1 shows a classic sintering process for high-melting elements

[0067] Fig. 2 shows a known sintering process for refractory elements with Masteralloy.

[0068] Fig. 3 shows a sintering process according to the invention.

[0069] Fig. 1 shows a classic sintering process in which powdered iron or a powdered iron alloy (base powder) is sintered with a Group 6 or Group 5 element (e.g., Mo, Cr, V, or W) and carbon (C). The base powders investigated included ASC 100.29 (Fe), Astaloy 0.85 Mo (Fe_0.85Mo), Astaloy CrA (Fe_1.8Cr), and Astaloy CrM (Fe_3Cr_0.5Mo). Mo, Cr, V, and W were investigated as Group 6 or Group 5 elements, respectively.

[0070] The base powder is mixed with carbon and elemental, powdered Group 6 or Group 5 elements. During the heating phase, the mixture is heated from approximately 20 °C to 1250 to 1300 °C, resulting in carbide formation. If a eutectic reaction occurs with the base powder, intermediate melt formation with secondary pores occurs; after sintering, the Group 6 or Group 5 element is largely homogeneously distributed throughout the iron matrix. However, depending on the alloying element, the eutectic reaction requires temperatures of 1250 to 1370 °C. If the sintering process occurs below this temperature threshold, with pure solid-phase diffusion, the result is a sintered and alloyed powder steel. However, in this case, the Group 6 or Group 5 element is only distributed locally, not throughout the entire body, and the desired effect of these elements on the properties of the sintered steel is not achieved.

[0071] 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 or group 5 element to be sintered (e.g. Mo, Cr, V or W). Carbon (C) is also present. The base powders listed in Fig. 1 were investigated. CrMA (Fe-Si-C-Cr) and CrMnMA (Fe-Si-Cr-Mn) were used as the master alloy, and for comparison, the master alloy powder MnMA (Fe-Si-C-Mn) without the group 6 or group 5 element was used.

[0072] The base powder is mixed with carbon and powdered MA. During the heating phase, the mixture is heated from approximately 20 °C to 1120 to 1180 °C. This melts the master alloy and distributes itself throughout the open pores. After sintering 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 entire body, but not the group 6 element or group 5 element, which remains at least partially present as undissolved carbide. For homogeneous distribution of these latter elements, sintering temperatures of at least 1250 °C are required. 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.

[0073] Fig. 3 shows a master alloy sintering process according to the invention, in which powdered iron or a powdered iron alloy (base powder) is sintered with a master alloy 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 and group 5 element.

[0074] The base powder is mixed with carbon, powdered MA, and powdered group 6 or group 5 elements. During the heating phase, the mixture is heated from approximately 20 °C to 1120 to 1180 °C. The master alloy melts and dissolves the elemental group 6 or group 5 element. This solution is distributed through 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 group 6 or group 5 element is distributed throughout the entire body. In contrast to the example in Fig. 2, a complex master alloy, which requires an alloy with the group 6 or group 5 element, is thus dispensed with.

[0075] The present invention demonstrates that relatively low-melting master alloys promote the homogenization of the high-melting alloying elements of the group 6 elements Mo, Cr and W or the group 5 elements V, Nb and Ta by acting as "solubilizers" and transport media during melting.

[0076] The production of the sintered steel bodies follows the well-known manufacturing process 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 press tools with appropriate geometry, thermal removal of the pressing aid in a furnace unit under a suitable atmosphere, and sintering under an inert or reducing protective gas. With appropriate sintering furnace equipment, 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 a suitably tempered outlet zone of the furnace or in a separate tempering furnace.

[0077] In the specifically described inventive process, a master alloy powder of the described composition is mixed with a pure iron powder or a low-alloy steel powder as the base powder and graphite powder as the carbon carrier. Furthermore, a small amount of the powder of a group 6 and / or group 5 element is added, along with the pressing aid. Advantageously, the mixing process is carried out in stages by first mixing the base powder with the master alloy powder, then the group 6 / group 5 element powder. After another mixing step, the graphite powder is added. After further mixing, the lubricant is added and the mixture is fully mixed.

[0078] Pressing takes place in a press tool shaped according to the geometry of the component to be manufactured at a pressure of 500 to 800 MPa, depending on the desired relative density. The resulting green body, which typically contains 8-12% porosity, is first thermally dewaxed and then sintered in a furnace. 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 capable of dissolving the added Group 6 or Group 5 element. Under the effect of capillary forces, the liquid phase, containing the Group 6 or Group 5 element, is distributed throughout the pore network of the body; thus, the alloying elements are macroscopically homogeneously distributed throughout the body. The elements then diffuse into the particles of the base powder, causing the liquid phase to disappear.

[0079] The aforementioned 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 sintered body than would be possible by adding elemental powder of the Group 6 or Group 5 element to an iron-carbon powder mixture. In this 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 austenite, or the sintering temperature would have to be selected so high that a uniform diffusion zone would form between the Group 6 or Group 5 element and the base material.A liquid phase forms intermediately between the Group 5 element and the carbon-containing austenite. However, depending on the C content and the selected Group 6 or Group 5 element, this would require temperatures well in excess of 1300°C. This is because, upon heating, a carbide forms from the Group 6 or Group 5 element and the added carbon. In the case of Group 5 elements, a carbonitride forms in a nitrogen-containing sintering atmosphere. Sintering at such high temperatures would be economically and ecologically disadvantageous due to the complex and expensive furnace equipment 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 detrimental to the mechanical properties.

[0080] The process according to the invention thus makes it possible to alloy high-melting group 6 or group 5 elements with the iron-based matrix metal even at moderate sintering temperatures and thus to fully utilize the positive effect of the group 6 or group 5 elements on the properties of the sintered steel.

[0081] Examples of implementation:

[0082] For this study, material compositions and manufacturing parameters were used that demonstrated that the systems already exhibited usable mechanical properties without the addition of Mo or V. This specifically investigated whether and to what extent the addition of these elements would result in further improvements.

[0083] Example 1:

[0084] The following powders are mixed:

[0085] - 4 wt. % Masteralloy powder Fe-40%Mn-9%Si-1.5%C, high-pressure water atomized

[0086] - 2 wt. % Masteralloy powder Fe-33%Mn-7.5%Si-3.44%C, high-pressure water atomized

[0087] - 0.5 wt. % Mo powder <32 pm, elemental

[0088] - 0.471 wt.% graphite powder

[0089] - Rest: Pure iron powder water atomized

[0090] The mixture is mixed with 0.6% ethylenebisstearamide as a lubricant and pressed in a compression mold with a floating die at 600 MPa pressure to form cuboid-shaped specimens according to ISO 5754. Similar specimens, but without Mo additive, are produced as references.

[0091] 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 approximately 0.4 K / s.

[0092] For each composition, a portion of the 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 quencher with pure nitrogen to achieve a cooling rate of 3 K / s, linearized between 900°C and 100°C. Immediately following, the material is annealed in air at 180°C for 60 minutes. These samples are also characterized.

[0093] The following properties are measured: AS (as sintered): sintered state; GQ (gas quenched): gas quenched and tempered

[0094] Example 2:

[0095] The following powders are mixed:

[0096] 4 wt. % Masteralloy powder Fe-40%Mn-9%Si-1.5%C, high-pressure water atomized

[0097] 2 wt. % Masteralloy powder Fe-33%Mn-7.5%Si-3.44%C, high-pressure water atomized

[0098] 0.5 wt. % V-powder <90 pm, elemental

[0099] 0.471 wt. % graphite powder Rest: pure iron powder, water atomized

[0100] The powder mixture is mixed with lubricant as described in Example 1, pressed, dewaxed, and sintered, or partially gas quenched and tempered. The following properties are measured:

[0101] AS (as sintered): sintered state; GQ (gas quenched): gas quenched and tempered

Claims

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. Method 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 pre-alloy which is mixed separately in powder form and melts below the isothermal sintering temperature.

3. A method 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. The method according to any 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 laser diffraction.

8. The method according to any one of claims 1 to 7, characterized in that the provision of the powder mixture comprises a plurality of 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. A 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. A method according to any 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.

Images