JP2020501027A - Powder metallurgically produced steel material comprising hard material particles, a method for producing parts from such steel material, and parts produced from steel material - Google Patents

Abstract

The present invention provides a steel material with a long service life, which has a minimum density, good wear resistance, while at the same time maximizing the resistance to extreme temperature changes and also having an optimized corrosion resistance. Such materials according to the invention are particularly suitable for the production of parts which are subjected to high mechanical, corrosive, thermal and abrasive loads in practical use. For this purpose, the steel material according to the invention is produced by powder metallurgy and is constituted as follows (% by weight). C: 1.5 to 5.0%, Si: 0.3 to 2.0%, Mn: 0.3 to 2.0%, P: 0 to <0.035%, S: 0 to <0. 35%, N: 0 to <0.1%, Cr: 3.0 to 15.0%, Mo: 0.5 to 2.0%, V: 6.0 to 18.0%, each depending on the case One or more elements from the group "Nb, Ni, Co, W", where the content of Ni, Co and W is up to 1.0% each, and the content of Nb is up to 2.0%. Certain remaining iron and unavoidable impurities, wherein individually added hard material particles with a content of 2.5-30% by weight, are embedded in the steel matrix. From the steel alloy powder alloyed in this way, a solid semi-finished product is formed by a sintering or additive process, subjected to a heat treatment and then finished to form the respective parts. [Selection diagram] None

Description

  The present invention relates to a steel material produced by powder metallurgy and comprising hard material particles. Such steel materials are also referred to in technical terms as metal matrix composites.

  Similarly, the invention relates to a method for producing such a steel material.

  Finally, the invention also relates to a part manufactured from a steel material of the type according to the invention.

  In particular, the object of the invention is a steel material which is suitable for the production of parts which undergo very high surface loads in practical use and at the same time move at high speed. One example of such a part is a rolling guide roller used in a line rolling machine (rolling mill). On these rollers, lines that are rolled and move at high transport speeds are made while hot at temperatures above 1000 ° C. Due to the high temperature, a scale layer forms on the line. In addition to the high temperature loads and high dynamic loads to which the rollers are exposed due to their high rotational speeds associated with the high transport speeds of the lines, the rolling guide rollers are therefore also capable of handling high abrasive loads while their surfaces are in contact with the lines. Exposed.

  Rolling guide rollers and other parts are manufactured to be able to withstand such load combinations, with abrasion resistance, especially abrasion resistance, corrosion resistance, thermal shock stress resistance, and equivalent stresses in practical use. There is a high demand for the weight of steel.

  Various attempts to satisfy this requirement profile are known. That is, U.S. Pat. No. 5,077,077 describes wear and corrosion resistant powder metallurgy tool steel for the manufacture of components used to process reinforced plastics and other abrasive and corrosive materials. In addition to iron, steel has a Mn content of 0.2-2.0% (by weight), a P content of up to 0.1%, an S content of up to 0.1%, and a Si content of up to 0.1%. 2.0% max, Cr content 11.5-14.5%, Mo content 3.0% max, V content 8.0-15.0%, N content 0.03- It should be 0.46%, C content 1.47-3.77%. The contents of C, Cr, Mo, V and N, on the one hand, are related by two equations so that no ferrite is formed in the structure of the steel part. On the other hand, the formation of excessive amounts of retained austenite during the heat treatment that the part undergoes during its manufacture should be prevented. Similarly, an optimized combination of the wear, abrasion and corrosion resistance of a metal results from the composition determined by the formula. In the course of the production of tool steel, the alloying elements of the steel form M7C3 and MC carbides by precipitation, which can constitute a fraction of 16-35% of the volume of the steel. The maximum hardness of the precipitation hardened steel after hot working, annealing and hardening is 58 HRC.

  Another group of powder metallurgical steel materials for the production of components of the type in question is described, for example, in US Pat. In a preferred embodiment, these steels comprise 0.1-1 wt% Mn, up to 2 wt% Si, 4.5-5.5 wt% Cr, 0.8-1.7 wt%. Mo, up to 0.14% by weight S, 8-10.5% by weight V, 2.2-2.6% by weight C, the balance being iron and unavoidable impurities, with a steel matrix , 13.3-17.3% by volume of vanadium carbide. The hardness of the steel is up to 63 HRC.

  Finally, US Pat. No. 6,077,086 discloses a powder metallurgical manufacturing process for steel materials in which a high Mo and / or high W content steel matrix is used and 2 to 12% of the hard material is embedded in the matrix. ing. The hard material can be nitride, carbide or carbonitride. The matrix material contains Mo and W at contents satisfying the condition 18% <W + 2Mo <40%.

  At the same time, the C content of the matrix material is compatible with a high Mo content and a high W content, so that the matrix material itself can produce high hardness by carbide precipitation. The maximum hardness of the material thus produced exceeds 70 HRC.

European Patent No. 0 773 305 (B1) U.S. Pat. No. 4,249,945 (A) U.S. Pat. No. 4,880,461 (A)

  Against the background of the prior art described above, the objective is to provide a steel material that provides a combination of properties that are more optimized for the production of parts that are actually exposed to high mechanical, corrosion, thermal and abrasive loads. Was to provide.

  Similarly, a method of manufacturing such steel parts is provided.

  Finally, parts for which the steel according to the invention is particularly suitable for its manufacture should be specified.

  With regard to steel, the invention has achieved this object by means of the steel obtained according to claim 1.

  A solution according to the invention of the above object for the method consists in performing at least the action steps according to claim 12 during the production of the part from steel according to the invention.

  Finally, the steel according to the invention is particularly suitable for the production of parts that move at high accelerations or velocities in practical use, and are particularly subject to high surface and thermal stresses.

  Examples of such components are the rolling guides of rolling mills for wire manufacturing, which need to have not only high stability and wear resistance under mechanical stress, but also optimized behavior under the action of high power. Tools and other parts. The piston pins and push rods of internal combustion engines can also be mentioned in this context.

  Advantageous embodiments of the invention are defined in the dependent claims and are described in detail below, as are the general concepts of the invention.

The steel material according to the present invention is manufactured by powder metallurgy and has the following composition (% by weight).
C: 1.5-5.0%
Si: 0.3-2.0%,
Mn: 0.3-2.0%,
P: 0 to <0.035%
S: 0 to <0.35%,
N: 0 to <0.1%,
Cr: 3.0 to 15.0%,
Mo: 0.5 to 2.0%,
V: 6.0-18.0%,
In each case one or more elements from the group “Nb, Ni, Co, W”, wherein the content of Ni, Co and W is each up to 1.0% and the content of Nb is up to 2% 0.0%,
Remaining iron and unavoidable impurities,
Here, individually added hard material particles with a content of 2.5 to 30% by weight are embedded in a steel matrix.

  In order to maximize the mechanical properties of the steel material according to the invention, 2.5 to 30% by weight of individually added hard material particles are present in the composite steel matrix according to the invention. The hard material particles can be in particular titanium carbide TiC particles.

  The steel according to the invention is therefore configured with minimal density, good wear resistance and at the same time long life, as well as maximum resistance to extreme temperature changes and optimized corrosion resistance.

  Where steel materials and alloy contents of steel materials are described herein, they are in each case by weight unless otherwise indicated.

  In the steel material according to the invention, the overall length of the alloy is selected such that a larger area is available for the vanadium alloyed high-strength wear-resistant material. Said areas are more useful to use hard material particles, also referred to in technical terms as metal matrix composites ("MMC"). The two most important alloying elements in this alloy system are carbon and vanadium.

  Carbon is responsible for the martensite hardening and for the formation of hard vanadium carbide, and the wear resistance is optimized in combination with high hardness and high strength. Thus, C is present in the steel according to the invention in a content of 1.5-5.0% by weight. Here, carbon has two major roles. That is, on the one hand, C is required for martensite hardening of the metal matrix. On the other hand, the presence of a sufficient amount of C leads to the formation of hard carbides with existing alloying elements, especially V, Cr and, if present, Nb. If the C in the steel matrix alloy is too low, martensite formation does not occur. When C is too large, retained austenite is stabilized. Both effects can reduce hardness and wear resistance. The ratio of carbon to carbide forming element is therefore always important.

  On the other hand, silicon is used for deoxygenation during the melting of the starting material which is part of the steel alloy powder alloyed according to the invention for the production of the component according to the invention. In addition, the presence of silicon increases carbon activity and therefore lowers the melting temperature. Without the targeted addition of at least 0.3% by weight of Si, especially at least 0.7% by weight, a higher C content would be required. The low melting point facilitates the atomization process. Silicon also reduces the viscosity of the molten metal, which also contributes to simplifying the powder atomization process. At the same time, silicon increases the through-hardenability of the steel material, since the conversion projections in the time-temperature diagram (Umwandlungsnasen, Germany) shift to longer times. The strength of austenite relative to the curing temperature increases with the amount of dissolved Si, which accounts for the higher stability of austenite and allows for a longer cooling period. These effects are obtained with a Si content of up to 2.0% by weight, in particular up to 1.5% by weight. An Si content that is too high will stabilize the ferrite, which will reduce the amount of martensite present in the structure of the steel after hardening, and will therefore also reduce the hardness and wear resistance of the steel material according to the invention.

  Manganese is present in the steel material according to the invention in order to optimize the hardness of the steel and its atomization ability during the production of steel powder. Thus, the presence of a sufficient content of Mn, as well as the presence of Si, lowers the melting point of the steel and lowers the viscosity of the molten metal, so that the targeted addition of Mn also contributes to the simplification of the atomization process. I do. At the same time, manganese also increases the through-hardenability of the steel material. Similarly, the dissolved portion of Mn contributes to stabilization of austenite. In addition, Mn binds to sulfur by forming MnS, reducing the risk of hot cracking and improving machinability. These effects are ensured with a Mn content of at least 0.3% by weight, in particular at least 0.7% by weight, and a Mn content of at most 2.0% by weight, in particular at most 1.5% by weight. On the other hand, an excessive content of manganese stabilizes the austenite phase to the extent that the softening annealing time is significantly increased. On the other hand, the austenite phase may be stabilized by an excessively high Mn content to such an extent that residual austenite remains in the microstructure after curing. This microstructure is much softer than martensite and will reduce hardness and wear resistance. It turns out that a Mn content of about 1.2% by weight of the steel material according to the invention is particularly practical.

  Chromium is used in the steel according to the present invention in combination with Mo and V to control temper resistance, corrosion resistance and hardening. As a result, by changing the Cr content, these three properties can be adapted according to the respective requirements. At a low Cr content of 3.0-8.0% by weight, Cr has a positive effect especially on the tempering resistance and the through-hardening. As the Cr content increases, corrosion resistance increases and the contribution of Cr to carbide formation increases. Therefore, an average Cr content of more than 8.0% by weight and less than 11.0% by weight constitutes a transition region. If the requirement for corrosion resistance is high, the Cr content here is insufficient. However, higher hardness of the steel matrix results from increased Cr carbide formation. With a Cr content of at least 11.0% by weight, in particular at least 12.0% by weight, in the steel material according to the invention, tempering and corrosion resistance are obtained with maximum hardness and strength to withstand the highest requirements. In this case, the advantageous effect of Cr can be used particularly reliably because the Cr content is set to at least 12.5% by weight. A Cr content that is too high will result in the formation of more Cr carbide. However, the formation of Cr carbide binds the C, which suppresses the formation of martensite, so that the desired high hardness of martensite can no longer be obtained. Furthermore, if the Cr content is significantly increased beyond the upper limit specified in the present invention, the ferrite phase will be stabilized and again the required hardness and wear resistance will not be obtained. Therefore, according to the invention, the maximum content of Cr is limited to 15.0% by weight, in particular 14.0% by weight, and a Cr content of up to 13.5% by weight is particularly suitable in practice. There was found.

式中、％Ｖは、鋼マトリックスの合金のそれぞれのＶ含有量である。 The optimal effect of the carbon content of the steel matrix of the steel material according to the invention on the formation of vanadium carbide VC is that the C content% C of the steel matrix is the target content% C _target calculated as follows: Thus, a low Cr content of up to 8% by weight can be ensured.

Where% V is the respective V content of the alloy in the steel matrix.

式中、％Ｖは、やはり鋼マトリックスの合金のそれぞれのＶ含有量を示す。 On the other hand, if Cr is used in the range of 11.0 to 15.0% by weight, the C content% C should be about 30% higher than the target content% C _target determined by the above equation. In this case, the C content of the steel matrix is therefore optimally adjusted to correspond to the target content% C _target calculated as follows.

Where% V also indicates the respective V content of the alloy in the steel matrix.

  Therefore, when the average Cr content is> 8.0 wt% to <11.0 wt%, the minimum C content that can be determined for the low Cr content and the high Cr content according to the above two equations. It is advantageous to choose a C content that lies between

The content% C _target is a target amount to be optimally determined as the C content in the production of the alloy powder in each case. Needless to say, this target content is such that the actual C content% C is the same as the target content% C _{target of} each steel material according to the present invention within the tolerance specified by the conventional or predetermined alloying technology. Is considered to have been reached. The practical value of the deviation of the actual C content% C from the target content% C _target still acceptable at this point is 0.2% by weight. The following should apply to the actual C content% C of the steel matrix.
% C =% C _target ± 0.2% by weight

  The C content adjusted according to the above conditions supplements the carbon to which Cr has been bound by the formation of Cr carbide. In this way, it is possible to ensure that sufficient C is always available for the formation of martensite and that an optimized hardness and wear resistance that is sufficient for most applications is obtained.

Thus, depending on the respective V content% V at a maximum Cr content of 8% by weight with respect to the target content% C _target , for example, the following values are obtained (data in% by weight):

In the case of steel material V15 having a maximum of 8% by weight of Cr and a nominal V content of 15% by weight, a tolerance of, for example, a V content of ± 0.5% by weight is acceptable, so that its actual V content is reduced. It can be 14.5 to 15.5% by weight. At the same time, a tolerance of ± 0.2% by weight of the actual C content is accepted by the target value% C _target . Therefore, the actual C content of the steel material V15 can be 3.2 to 3.6% by weight.

  Molybdenum, like chromium, when used with a Mo content of at least 0.5% by weight, in particular at least 0.9% by weight, enhances the corrosion, hardening and tempering resistance of parts made from steel according to the invention. Enhance. However, if the Mo content is too high, the high-temperature strength increases considerably, and the formability of the steel deteriorates. Furthermore, a high Mo content will also stabilize the ferrite phase. Therefore, the maximum content of Mo in the steel according to the present invention is limited to 2.0% by weight, especially 1.5% by weight at the maximum. The Mo content of the steel according to the invention, which is particularly suitable for the purposes of the invention, is therefore in the region of 1.2% by weight.

  Vanadium is present in the steel according to the invention in a content of 6.0% to 18.0% by weight to form vanadium-rich carbides or carbonitrides and to optimize wear resistance. In addition, vanadium is increasingly involved in the formation of carbides during tempering at secondary hardness maximums (Sekundaerhaertemaximum, Germany: secondary hardness maximum). These effects increase with the V content, so that by changing the V content, the property profile of the steel material according to the invention can also be adapted to the respective requirements. The greatest positive effect of the presence of V can be obtained when at least 14.5% by weight of V is present in the steel according to the invention. A high V content of at least 16% by weight results in particularly high wear resistance, so that the steel material according to the invention with such a high V content is used as a material for rolling guide rollers which are subjected to maximum loads during use. Particularly suitable for use. On the other hand, by limiting the V content to 17.4% or 17.0% by weight, 16.0% by weight or more preferably up to 15.5% by weight, excess carbon is bound by carbide formation. Can be reliably avoided. With a low V content towards the lower limit of the content range indicated for V according to the invention and a correspondingly low C content, the steel material according to the invention is easier to handle than higher V and C contents. Can be machined. If the V content is limited to a maximum of 12% by weight, in particular to a maximum of 10% by weight, and thus the C content which depends on the V content is also limited as described above, simplified machinability results accordingly. It is.

  Niobium is optionally present in the steel according to the invention in a content of up to 2.0% by weight. Nb has a very similar mode of action to vanadium. It is primarily responsible for the formation of hard, wear resistant monocarbides. Therefore, in each case, at. Based on their content in%, Nb and V can be exchanged in a 1: 1 ratio if found to be advantageous, for example with regard to the effectiveness of these alloying elements.

  Nickel can optionally be present in the steel material according to the invention in a content of up to 1.0% by weight in order to stabilize the austenitic part like Mn and thus improve the hardenability. Thus, the presence of Ni ensures that austenite is actually formed at each hardening temperature and that undesired ferrite is not formed in the structure of the steel. However, an excessively high Ni content increases the cooling time required for martensite formation. At the same time, the Ni content should not be too high, because there is a risk that residual austenite is present in the microstructure after curing. If Ni is added, the Ni content is preferably at least 0.2% by weight, and the optimal effect of the presence of Ni is adjusted by adjusting the Ni content to a maximum of 0.4% by weight.

  Cobalt can also optionally be present in the steel material according to the invention in a content of up to 1.0% by weight. Like nickel, Co has a stabilizing effect on austenite formation and hardening temperature. However, unlike nickel and manganese, Co does not reduce the final temperature of martensite, and its presence is less important with respect to the formation of retained austenite. In addition, cobalt increases heat resistance. If these positive effects are exploited by the addition of Co, a content of at least 0.3% by weight of Co has proved to be particularly advantageous, the optimum effect being with a Co content of up to 0.5% by weight. Occurs.

  Tungsten, like Co and Ni, can optionally be added to the steel at a content of up to 1.0% by weight. In particular, tungsten enhances tempering resistance and, in particular, participates in carbide formation at the secondary hardness maximum during tempering. The presence of W shifts the tempering temperature to higher temperatures. Further, similarly to cobalt, the heat resistance is increased by W. However, excessive W content will still stabilize the ferrite phase. If the positive effect of W is utilized, therefore, a W content of at least 0.3% by weight has proved to be particularly advantageous, the optimum effect occurring with a W content of up to 0.5% by weight.

  The balance of the steel contains iron and inevitable impurities that enter the steel for the manufacturing process or raw materials, respectively, and the constituents of the steel alloy powder are recovered therefrom, but have no effect on the properties.

  Sulfur can be present at up to 0.35% by weight in steel materials to improve machinability. However, at higher S contents, the properties of the composite steel material according to the invention deteriorate. To safely take advantage of the beneficial effects of the presence of S, at least 0.035% by weight can be present in the steel material according to the invention. On the other hand, if the machinability is not improved by the targeted addition of S, the S content can be limited accordingly to less than 0.035% by weight.

  The unavoidable impurities also include P with a content of up to 0.035% by weight, for example also a total of up to 0.2% by weight of oxygen.

  Nitrogen is also not alloyed as intended with the steel material according to the invention, but migrates into the steel material during the atomization process due to the nitrogen affinity of the alloy components. In order to avoid the negative effects of N on the properties of the steel material, the N content should be limited to less than 0.12% by weight, in particular to a maximum of 0.1% by weight.

Density of steel material according to the present invention is generally in the range of 6.4~7.6g / cm ^3, the density of the pure steel matrix materials are generally 7.0~7.6g / cm ^3.

  Due to its minimized density and consequently low weight, the steel material according to the invention is repeatedly exposed to steep accelerations in practical use, so that lower mass inertia has a particularly advantageous effect. Suitable for the production of

  Powder metallurgy production is based on the targeted addition of a low-density hard phase according to the respective application, if it is desired with respect to the special intended properties, further optimization of the density and wear resistance of the steel according to the invention Enable. Here, since the steel material contains 2.5 to 30% by weight of hard material particles embedded in the finished steel manufactured by the composite like the above-mentioned steel matrix, the performance characteristics of the steel material according to the present invention Was shown to be enhanced.

  The hard material is initially present as a powder, such as a steel alloy powder forming a steel matrix.

Hard materials are also known in technical terms as "hard phases" and can be carbides, nitrides, oxides or borides. Thus, a group of suitable hard materials include Al ₂ O ₃ , B ₄ C, SiC, ZrC, VC, NbC, TiC, WC, W ₂ C, Mo ₂ C, V ₂ C, BN, Si ₃ N ₄ , NbN or TiN.

  Titanium carbide TiC has been found to be particularly suitable for the purposes according to the invention. Titanium carbide has a hardness of 3200 HV and thus particularly effectively increases the hardness and wear resistance of the steel. At the same time, TiC is chemically resistant and does not adversely affect corrosion resistance. Similarly, the low density of TiC has an advantageous effect.

  When the content of the hard material alloyed with the steel material is less than 2.5% by weight, the wear resistance is not improved. In order to make particular use of the effect of the hard material, it is therefore advantageous to provide at least 5% by weight of the alloyed hard material particles in the steel material according to the invention, with a content of at least 7.5% by weight The amounts have been found to be particularly effective. To ensure that excessive embrittlement of the material as a result of the presence of the hard material particles is avoided, the content of alloyed hard material particles can be limited to 25% by weight or less in the material according to the invention. The content of hard material particles described herein in the steel material according to the present invention proves to be particularly advantageous when the alloyed hard material is titanium carbide TiC.

  After hardening and tempering, the steel according to the invention generally has a hardness value in the range from 58 to 70 HRC.

  After soft annealing generally performed for machining, the typical soft annealing hardness of the steel material according to the invention is generally up to 65 HRC, due to the presence of the hard material particles provided by the invention.

  In the production of the component according to the invention from the steel according to the invention, at least the following working steps are performed.

  a) 1.5-5.0% C (by weight), 0.3-2.0% Si, 0.3-2.0% Mn, <0.035% P, <0 0.35% S, <0.1% N, 3.0-15.0% Cr, 0.5-2.0% Mo, 6.0-18.0% V, each optionally Contains one or more elements from the group "Nb, Ni, Co, W", wherein the content of Ni, Co and W is at most 1.0% each, and the content of Nb is at most 2.0%. Yes, a steel alloy powder is provided, the balance being iron and unavoidable impurities.

  b) The steel alloy powder is mixed with the hard material particles provided that the content of the hard material particles in the resulting steel alloy powder-hard material particle mixture is 2.5 to 30% by weight.

  c) In some cases, the steel alloy powder or a mixture of the steel alloy powder and the hard material is dried.

  d) From the steel alloy powder or a mixture of the steel alloy powder and the hard material, a solid semi-finished product is formed by a sintering process, in particular a hot isostatic pressing, or an additional process.

  e) The resulting semi-finished product is processed into parts.

  For practical implementations and embodiments of steps a) to e) of the method according to the invention, the following information applies.

  Step a)

  Powder production can be carried out in a conventional manner, for example by gas atomization or any other suitable method. For this purpose, the alloy powder can be produced, for example, by gas or water spraying or a combination of these two spraying methods. Spraying of the melt alloyed according to the invention for the alloy powder is conceivable.

  Alternatively, however, first prepare the alloying elements of the steel alloy powder in individually powder form in amounts corresponding to the content proportions specified for the respective alloying elements, and then configure these amounts of powder according to the invention It is also possible to mix in the steel alloyed powder which has been prepared.

  If necessary, those having an average diameter of less than 500 μm are selected from the powder particles by sieving for further processing according to the invention. It turns out that powders with an average particle size of less than 250 μm, especially less than 180 μm, are particularly suitable.

Regardless of their preparation manner, the alloy powder provided by the present invention, the optimum bulk density 2 to 6 g ^/ cm 3 (measured according to DIN EN ISO3923-1) and a tap density 3~8g ^/ cm 3 (DIN EN Measured according to ISO3953).

  Step b)

  The steel alloy powder prepared in step a) is mixed with the respectively selected hard material powder. Determine the amount of mixed hard material particles, taking into account the above information on the optimal selection of hard material content, such that the content of hard material particles in the finished mixture is in the range of 2.5-30% by weight I do.

  Step c)

  If necessary, the alloy powder prepared in step a) or step b) can be dried in a conventional manner to remove residues of liquids and other volatiles which can interfere with the subsequent molding process. .

  Step d)

  A blank (semi-finished product) is then formed from the alloy powder containing the hard material particles. For this purpose, the alloy powder can be brought into a respective form in a manner known per se, by means of a suitable sintering process, in particular hot isostatic pressing ("HIPing"). Generally, HIPing is performed. Typical pressures during HIPing are in the range 900-1500 bar at a temperature of 1050-1250 ° C., in particular 1800-1200 ° C., in particular 1000 bar. During the course of hardening, austenite, VC and Cr carbide form in the microstructure of the steel material.

  Alternatively, each part can be made from an alloy powder prepared and provided according to the invention in an additional process. The term "addition" is a summary of all manufacturing processes in which a material is added to produce a part, and this addition generally occurs in multiple layers. “Additive manufacturing processes” (Germany: Additive manufacturing processes) are often referred to in technical terms as “productive processes” (Germany Verfahren, English: generative processes). In contrast to conventional subtractive manufacturing processes, such as machining processes in which material is removed to impart a (eg, milling, drilling and lathe). The additional design principles may not be achievable using conventional manufacturing processes, such as the machining or primary forming processes (casting, forging), or may be realized only marginally, Enables manufacturing of structures (German Institute of German Engineers (Germany: Association of German Engineers), Production Technology and Manufacturing Method Division (Germany: Fachbereich Produktionstechnik und Fertigungsverfahren, UK: Production Technology and VDI status report "Additive Verfahren (Germany: Additive Manufacturing)", September 2014, www.vdi.de/statusadditiv. Further definitions of the method summarized under the generic term "additional method" can be found, for example, in the VDI Guidelines (VDI-Richtlinien, VDI Guidelines) 3404 and 3405.

  Step e)

  The semifinished product obtained after step d) still needs finishing in order to give it the desired performance characteristics on the one hand and the required final shape on the other hand. Finishing includes, for example, semi-finished product machines, especially material removal machining, and heat treatments that may include hardening and tempering.

  The invention is explained in more detail below on the basis of exemplary embodiments.

  As explained above, the alloy powder constructed according to the present invention is formed into a blank (semi-finished product), for example, by hot isostatic pressing or another suitable sintering process. For this purpose, the respective alloy powder is filled into a suitable mold, for example a cylindrical capsule, and then at a temperature of 1050-1250 ° C., in particular 1150 ° C. and a typical pressure of 900-1500 bar (90-150 MPa), in particular A sufficient time can be maintained at 1000 bar (100 MPa) until a solid is formed. Generally, in a hot isostatic press, the pressure is in the range of 102-106.7 MPa, the heating is generally at a target temperature of 1150-1153 ° C., generally maintained for 200-300 minutes, especially 245 minutes, and generally at a heating rate of 3K. / Min to 10 K / min.

  Heat treatment follows the production of the semi-finished product. In this case, each semi-finished product is generally heated at a heating rate of 5 K / min to a curing temperature (austenitizing temperature) of 1050 to 1200 ° C. and held until it is completely heated. Generally, this takes 30-60 minutes. Subsequently, the semi-finished product thus heated is rapidly cooled. Cool them to a suitable quench medium, such as water, oil, polymer bath, dynamic or static air, or gaseous nitrogen if cooling is done in a vacuum dryer, to room temperature in the range of 5-30 minutes. I do. Especially in the case of large semi-finished products, heating at several preheating stages up to the curing temperature, for example at 400 ° C, 600 ° C and 800 ° C, or a preheating temperature in the range of 600-800 ° C to ensure uniform heating. Sometimes it is convenient.

  Curing in a vacuum dryer can also be carried out in a manner known per se in order to avoid reaction in the ambient atmosphere. However, this is not a prerequisite for the success of the method according to the invention.

  After curing, tempering can be performed, and the semifinished product is kept at the respective tempering temperature, typically 450-550 ° C., for 90 minutes, for example. The tempering conditions are determined in a manner known per se, depending on the respective curing temperature and the desired hardness level, ie the desired strength selected. The heating and cooling rates are usually about 10 K / min for tempering. In contrast to curing, the rate of heating and cooling during tempering is not critical. By tempering, brittle martensite is relaxed by diffusion of carbon. For example, together with V, Cr and Mo, this forms what is known as "tempered carbide". This increases toughness. At the same time, the strength and hardness of the steel material is only slightly reduced as these properties are increased again by carbide formation.

  Usually, there is a narrow temperature range (about 50 ° C. between about 450-650 ° C.) in such alloy systems, so this is called the secondary hardness maximum. This is because lower or higher temperatures cause a decrease in hardness.

  Using the above general procedure for the actual production of the steel material according to the invention and the parts produced therefrom, cylindrical semi-finished products were produced from the four steel materials V10a to V10d according to the invention.

  The steel matrices of the steel materials V10a, V10b, V10c and V10d have 2.5% C, 0.9% Si, 0.9% Mn, 4.5% Cr, 1.2% (by weight), respectively. % Mo and 10.0% V, the balance of iron and unavoidable impurities. Further, 5% by weight of TiC was alloyed with steel material V10a, 10.0% by weight of TiC was alloyed with steel material V10b, 15% by weight of TiC was alloyed with steel material V10c, and 20% by weight of TiC was alloyed with steel material V10d.

  The following is shown in Table 2. Austenitizing temperature AT, hardness HRC (“HRC_v”) present before subsequent heat treatment step, tempering temperature ST and tempering time St if tempering has been performed, or soaking temperature WT if soft annealing has been performed. And the soaking time Wt, the hardness HRC after the previous heat treatment step (“HRC_n”), and the density ρ of the samples V1 to V8.

  Heating to each austenitizing temperature AT was performed by a vacuum dryer. Therefore, the samples V1 to V8 were kept at the austenitizing temperature AT at the austenitizing time At. Subsequently, the sample was cooled to room temperature by exposing it to gaseous nitrogen applied at a pressure of 3.5 bar in a vacuum dryer.

  After curing, samples 1 to 8 were subjected to tempering or annealing treatment. In the tempering process, samples 1, 3, 5, and 7 were kept at the tempering temperature ST for the tempering period St. This tempering treatment was performed twice to obtain an optimal tempering result.

  During the soft annealing, Samples 2, 4, 6, and 8 were held at the annealing temperature WT for a time Wt. After the end of the annealing time, the dryer was turned off, and the samples 2, 4, 6, and 8 were gradually cooled to room temperature in the turned-off dryer.

Claims (15)

A steel material produced by powder metallurgy and having a steel matrix (in% by weight) configured as follows:
C: 1.5-5.0%
Si: 0.3-2.0%,
Mn: 0.3-2.0%,
P: 0 to <0.035%
S: 0 to <0.35%,
N: 0 to <0.1%,
Cr: 3.0 to 15.0%,
Mo: 0.5 to 2.0%,
V: 6.0-18.0%,
In each case one or more elements from the group “Nb, Ni, Co, W”, wherein the content of Ni, Co and W is each up to 1.0% and the content of Nb is up to 2% 0.0%,
Remaining iron and unavoidable impurities,
Wherein individually added hard material particles with a content of 2.5 to 30% by weight are embedded in said steel matrix,
Steel material. At a Cr content of up to 8.0% by weight, the C content of the steel matrix with a maximum deviation of at most 0.2% by weight corresponds to the target amount% C _target ,% C _target = 0.2 ×% V + 0. 2. The steel material according to claim 1, wherein the steel material is 4% by weight, wherein% V represents the respective V content of the steel matrix. At a Cr content of at least 11.0% by weight, the C content of the steel matrix with a maximum deviation of at most 0.2% by weight corresponds to the target amount% C _target ,% C = (0.2 ×% V + 0. Steel material according to claim 1, characterized in that it is 4% by weight) x 1.3, wherein% V represents the respective V content of the steel matrix. 4. The steel matrix according to claim 1, wherein at a Cr content of more than 8% by weight and less than 11% by weight, the C content of the steel matrix lies between the% C _target contents determined according to claims 2 and 3. The steel material according to the above.   5. The steel material according to claim 1, wherein the Si content is at least 0.7% by weight or at most 1.5% by weight.   6. The steel material according to claim 1, wherein the Mn content is at least 0.7% by weight or at most 1.5% by weight.   The steel material according to any one of claims 1 to 6, wherein the S content is at least 0.035% by weight.   8. The steel material according to claim 1, wherein the Mo content is at least 0.9% by weight or at most 1.5% by weight. 9. In the presence of one or more elements from the group "Ni, Co, W", the following applies to the content (% by weight) of the respective elements Ni, Co or W. The steel material according to any one of the above.
Ni: 0.2-0.4%,
Co: 0.3-0.5%,
W: 0.3-0.5%.   The steel material according to any one of claims 1 to 9, wherein the hard material particles are TiC particles.   The steel material according to claim 1, wherein the hard material particles are present with a D50 particle size of at most 50 μm. A method for producing a part comprising steel obtained according to any one of claims 1 to 11, comprising the following steps:
a) 1.5-5.0% C (by weight), 0.3-2.0% Si, 0.3-2.0% Mn, <0.035% P, <0 0.35% S, <0.1% N, 3.0-15.0% Cr, 0.5-2.0% Mo, 6.0-18.0% V, each optionally Contains one or more elements from the group "Nb, Ni, Co, W", wherein the content of Ni, Co and W is at most 1.0% each, and the content of Nb is at most 2.0%. Yes, the balance is iron and unavoidable impurities, steel alloy powder is prepared,
b) the steel alloy powder is mixed with the hard material particles provided that the content of the hard material particles in the resulting mixture of the steel alloy powder and the hard material particles is 2.5 to 30% by weight;
c) optionally, drying the steel alloy powder or a mixture of the steel alloy powder and a hard material;
d) from the steel alloy powder or a mixture of the steel alloy powder and the hard material, a solid semi-finished product is formed by a sintering process, in particular a hot isostatic pressing, or an additional process;
e) the resulting semi-finished product is processed into said parts;
A method that includes   13. The method according to claim 12, characterized in that in step a) the alloying components of the steel alloy powder are each supplied in powder form and mixed into the steel alloy powder.   14. The method according to claim 12, wherein finishing (step e)) comprises material removal machining of the semi-finished product.   A part manufactured from a steel material obtained according to any one of claims 1 to 11, which carries out movements involving high accelerations or velocities in practical use.