EP3323902A1 - Steel material containing hard particles prepared by powder metallurgy, method for producing a component from such a steel material and component produced from the steel material - Google Patents

Abstract

The invention provides a steel material which has a minimized density, a good wear resistance and a concomitantly high service life with a maximized resistance to extreme temperature changes and likewise optimized corrosion resistance. Such a material according to the invention is particularly suitable for the production of components which are exposed to high mechanical, corrosive, thermal and abrasive loads in practical use. For this purpose, the steel material according to the invention is powder metallurgically produced and composed as follows (in% by weight): C: 1.5-5.0%, Si: 0.3-2.0%, Mn: 0.3-2.0 %, P: 0 - <0.035%, S: 0 - <0.35%, N: 0 - <0.1%, Cr: 3.0 - 15.0%, Mo: 0.5 - 2.0 %, V: 6.0-18.0%, in each case optionally one or more elements from the group "Nb, Ni, Co, W", wherein the content of Ni, Co and W in each case at most 1.0% and the Content of Nb is at most 2.0%, balance iron and unavoidable impurities, embedded in the steel matrix hard material particles in amounts of 2.5 to 30 wt .-%. From such an alloyed steel alloy powder, a solid semi-finished product is formed by a sintering process or an additive process, which undergoes a heat treatment and is then finished to the respective component.

Description

The invention relates to a steel material which is produced by powder metallurgy and contains hard material particles. Such steel materials are also referred to in technical language as metal matrix composite materials.

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

Finally, the invention also relates to components which are made of a steel material of the type according to the invention.

Specifically, the invention is directed to a steel material which is suitable for the production of components which are subjected to the highest surface loads in practical use and at the same time are moved quickly. An example of such components are roller guide rollers which are used in machines (rolling stands) for wire rolling. On these rollers, the wire to be rolled and moved at a high conveying speed is conducted while hot at temperatures of more than 1000 ° C. Due to its high temperature, a scale layer forms on the wire. In addition to the high temperature and the high dynamic loads, which they are exposed because of their associated with the high conveying speed of the wire high rotational speeds, the roller guide rollers are therefore exposed to their coming into contact with the wire surfaces also high abrasive loads.

In order to be able to withstand this load collective, high demands are placed on the wear resistance, in particular the resistance to abrasive wear, the corrosion resistance, the resistance to thermal shock stress and the weight of steels from which roll guide rollers and other components subjected to comparable stress in practical use posed.

Various attempts are known to meet this requirement profile. So is in the EP 0 773 305 B1 describes a wear and corrosion resistant, powder metallurgical tool steel intended for the manufacture of components used to process reinforced plastics and other abrasive and corrosive materials. In addition to iron (in% by weight), the steel has an Mn content of 0.2-2.0%, a P content of max. 0.1%, an S content of max. 0.1%, a Si content of max. 2.0%, a Cr content of 11.5-14.5%, a Mo content of max. 3.0%, a V content of 8.0-15.0%, an N content of 0.03-0.46%, and a C content of 1.47-3.77% should. The contents of C, Cr, Mo, V and N are linked together via two formulas in such a way that on the one hand the formation of ferrite in the structure of the component made of steel is avoided and on the other hand the formation of excessive amounts of residual austenite during the Prevent heat treatment, which passes through the component during its production. Likewise, an optimized combination of metal wear, abrasion and corrosion resistance is to be obtained through the composition determined by the formulas.

Another group of powder-metallurgically produced steel materials for the production of components of the type in question is, for example, in US 4,249,945 A described. In a preferred embodiment, these steels have a steel matrix consisting of 0.1-1% by weight of Mn, up to 2% by weight of Si, 4.5-5.5% by weight of Cr, 0.8-1 , 7 wt .-% Mo, up to 0.14 wt .-% S, 8 - 10.5 wt .-% V, 2.2 - 2.6 wt .-% C, balance iron and unavoidable impurities exists , and contain 13.3 - 17.3 vol .-% vanadium carbides. The steel achieves a hardness of up to 63 HRC.

Against the background of the prior art explained above, the object was to provide a steel material which offers a further optimized combination of properties for the production of components which are exposed in practice to high mechanical, corrosive, thermal and abrasive loads.

Likewise, a method for the production of components made of such a steel should be mentioned.

Finally, components should be specified for whose production the steel according to the invention is particularly suitable.

With respect to the steel, the invention has achieved this object by the procured according to claim 1 steel.

The solution according to the invention of the object set out above with regard to the method consists in that during the production of components from a steel according to the invention at least the working steps mentioned in claim 12 are run through.

Finally, steel according to the invention is particularly suitable for the production of components which, in practical use, perform movements with high acceleration or speed and in particular are exposed to high surface and temperature stresses.

Examples of such components are rolling guides for rolling mills for wire production, but also other tools and other components, of which not only high stability under mechanical stress and wear resistance, but also an optimized behavior under the action of high dynamic forces is required. But also piston pin and push rods for internal combustion engines are named.

Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail.

• jeweils optional ein Element oder mehrere Elemente aus der Gruppe "Nb, Ni, Co, W", wobei der Gehalt an Ni, Co und W jeweils höchstens 1,0 % und der Gehalt an Nb höchstens 2,0 % beträgt,
• Rest Eisen und unvermeidbare Verunreinigungen,
• wobei in der Stahlmatrix Hartstoffpartikel in Gehalten von 2,5 - 30 Gew.-% eingebettet sind.

The steel material according to the invention is produced by powder metallurgy and has the following composition (in% by weight): C: 1.5 - 5.0%, Si: 0.3 - 2.0%, Mn: 0.3 - 2.0%, P: 0 - <0.035%, S: 0 - <0.35%, N: 0 - <0.1%, Cr: 3.0 - 15.0%, Not a word: 0.5 - 2.0%, V: 6.0 - 18.0%,

• each optionally one or more elements from the group "Nb, Ni, Co, W", wherein the content of Ni, Co and W is at most 1.0% and the content of Nb is 2.0% or less,
• Residual iron and unavoidable impurities,
• wherein embedded in the steel matrix hard material particles in amounts of 2.5 to 30 wt .-%.

To maximize the mechanical properties of a steel material according to the invention in the composite according to the invention steel matrix 2.5 to 30 wt .-% separately added hard material particles are present. The hard material particles in question may in particular be titanium carbide particles TiC.

The steel according to the invention is thus composed such that it has a minimized density in addition to a good wear resistance and a concomitantly high life has a maximized resistance to extreme temperature changes and also optimized corrosion resistance.

If statements are made in this text regarding the alloy contents of steels and steel materials, these are in each case based on the weight, unless expressly stated otherwise.

In a steel material according to the invention, the alloy spans are chosen so that a wider and for the use of hard material particles in the jargon also called metal matrix composites ("MMCs"), meaningful area for vanadium alloyed, high-strength and wear-resistant materials is available. The two most important alloying elements in this alloy system are carbon and vanadium.

Carbon is responsible for martensitic hardening as well as for the formation of hard vanadium carbide, which in combination with high hardness and high strength results in optimized wear resistance. C is therefore present in the steel according to the invention in contents of 1.5-5.0% by weight. The carbon has two main tasks: On the one hand C is needed for the martensitic hardening of the metal matrix. On the other hand, the presence of sufficient amounts of C leads to the formation of hard carbides with the existing alloying elements, in particular with V, Cr and, if present, Nb. If there is too little C in the alloy of the steel matrix, the formation of martensite does not take place; if C is too high, retained austenite is stabilized. Both effects can reduce hardness and wear resistance. The ratio of carbon to the carbide-forming elements is therefore always important.

On the one hand, silicon is used for the deoxidation during the melting of the starting materials, which are part of the steel alloy powder alloyed according to the invention for the production of components according to the invention. In addition, the presence of silicon increases the carbon activity and thus leads to a lowering of the melting temperature. Without the targeted addition of at least 0.3 wt .-% Si, in particular At least 0.7 wt .-% Si, higher C contents would be necessary. The lowered melting point in turn facilitates the atomization process. Silicon also reduces the viscosity of the molten metal, which also contributes to the simplification of the powder atomization process. At the same time, silicon increases the through-hardenability of the steel material, since the conversion lugs in the ZTU diagram are shifted to longer times. The strength of the austenite to hardening temperature is increased by the dissolved amount of Si, which explains the higher stability of the austenite and longer cooling periods can be made possible. These effects are achieved at Si contents of up to 2.0% by weight, in particular up to 1.5% by weight. Too high a content of Si would lead to a stabilization of the ferrite, which would reduce the amount of martensite present in the structure of the steel after hardening and thus 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 to optimize the Verdüsbarkeit of the steel in the production of steel powder and its hardness. Thus, by the presence of sufficient contents of Mn, similar to the presence of Si, the melting point of the steel is lowered and the viscosity of the molten metal lowered, so that the targeted addition of Mn also contributes to the simplification of the atomization process. At the same time, manganese also increases the through-hardenability of the steel material. Likewise, the dissolved portion of Mn contributes to the stabilization of austenite. In addition, Mn binds sulfur by forming MnS, reducing the risk of hot cracking and improving machinability. These effects are at Mn contents of at least 0.3 wt .-%, in particular at least 0.7 wt .-%, and Mn contents of up to 2.0 wt .-%, in particular up to 1.5 wt. -%, reliably achieved. Excessive levels of manganese could on the one hand stabilize the austenitic phase to the extent that the soft annealing time would be significantly increased. On the other hand, the austenitic phase could also be stabilized to such an extent by excessively high Mn contents that residual austenite remains in the microstructure after hardening. This microstructure would be significantly softer than martensite, reducing hardness and wear resistance. Mn contents of a steel material according to the invention of about 1.2% by weight prove to be particularly practical.

Chromium is used in the inventive steel in combination with Mo and V to adjust the tempering resistance, corrosion resistance and hardenability. Consequently, by varying the Cr content, these three properties can be adapted according to the respective requirements. At low Cr contents of 3.0-8.0% by weight, Cr has a positive influence on the tempering resistance and the through-hardenability in particular. With increasing Cr contents, the corrosion resistance and the contribution of Cr to carbide formation increase.

Average Cr contents of more than 8.0% by weight to less than 11.0% by weight constitute a transitional area to this extent. For increased requirements on the corrosion resistance, the Cr content is not yet sufficient here. However, a higher hardness of the steel matrix arises as a result of increasing Cr carbide formation. At levels of at least 11.0 wt .-% Cr, in particular at least 12.0 wt .-%, in the steel material according to the invention tempering and corrosion resistance are achieved with maximum hardness and strength, which withstand the highest demands. In this case, the advantageous effects of Cr can be particularly reliable use that the Cr content is set to at least 12.5 wt .-%. Too high Cr contents would cause more Cr carbides to form. However, the formation of Cr carbides would harden C, which would reduce the formation of martensite, so that the desired high hardness of martensite could no longer be achieved. Moreover, if the Cr contents were significantly increased beyond the upper limit prescribed by the invention, the ferritic phase would be stabilized, which would also not achieve the required hardness and wear resistance. Therefore, according to the invention, the maximum content of Cr is limited to 15.0% by weight, in particular at most 14.0% by weight, with Cr contents of up to 13.5% by weight being particularly suitable in practice have exposed.

wobei mit %V der jeweilige V-Gehalt der Legierung der Stahlmatrix bezeichnet ist.An optimized effect of the carbon content of the steel matrix of a steel material according to the invention with respect to the formation of vanadium carbides VC can be ensured at low Cr contents of up to 8% by weight, that the C content% C of the steel matrix Target content% CZiel, calculated as follows: $$\%\mathrm{CZiel}=\mathrm{0}.\mathrm{2}\times \%\mathrm{V}+\mathrm{0}.\mathrm{4}$$

where% V is the respective V content of the alloy of the steel matrix.

wobei auch hier mit %V der jeweilige V-Gehalt der Legierung der Stahlmatrix bezeichnet ist.On the other hand, if Cr is used in the range of 11.0-15.0% by weight, the C content% C should be about 30% higher than the target content% CZiel determined according to the formula given above. In this case, the C content of the steel matrix is thus optimally adjusted to correspond to a target content% CZiel, which is calculated as follows: $$\%\mathrm{CZiel}=\left(\mathrm{0}.\mathrm{2}\times \%\mathrm{V}+\mathrm{0}.\mathrm{4}\right)\times \mathrm{1}.\mathrm{3}$$

again with% V, the respective V content of the alloy of the steel matrix is designated.

Accordingly, in the case of the average Cr contents of> 8.0% by weight to <11.0% by weight, it is advantageous to choose a C content which lies between the C minimum contents which, according to the two preceding formulas, are for the low Cr and high Cr contents can be determined.

The content% CZiel is in each case a target quantity which should be optimally sought for the C content in the production of the alloy powder. It goes without saying that this target content is considered to have been reached if the actual C content% C within the tolerances specified by the alloying technology or standard corresponds to the target content% CZiel of the respective steel material according to the invention. A practical value of the deviation of the actual C content% C from the target content% CZiel, which is still permitted in this respect, amounts to 0.2% by weight. The actual C content% C of the steel matrix should then be% C =% CZiel ± 0.2% by weight.

It is compensated by the C content adjusted in accordance with the above-described proviso that carbon is bound by Cr due to the Cr carbide formation. In this way it can be ensured that sufficient C is always available for the formation of martensite and an optimized hardness and wear resistance is achieved, which are sufficient for most applications.

Accordingly, depending on the respective V content% V at Cr contents of up to 8% by weight for the target content% CZiel, for example, the following values result (data in% by weight): description % V % CZiel V8 8th 2.0 V10 10 2.4 V12 12 2.8 V15 15 3.4 V17 17 3.8

In the case of the steel material V15 with up to 8% by weight Cr and a nominal V content of 15% by weight, a tolerance range of the V content of, for example, +/- 0.5% by weight is permitted, so that its actual V content may vary between 14.5-15.5 wt%. At the same time, a tolerance of +/- 0.2% by weight is allowed for the actual C content by the target value% CZiel. The actual C content of the steel material V15 can thus be 3.2-3.6% by weight.

Molybdenum, like chromium, increases the corrosion resistance, hardenability and tempering resistance of components made from steel according to the invention when Mo contents of at least 0.5% by weight, in particular at least 0.9% by weight, are present. Excessive contents of Mo, however, worsen the formability of the steel, since the high-temperature strength is significantly increased. In addition, high levels of Mo would also stabilize the ferritic phase. Therefore, the maximum content of Mo in inventive steel to 2.0 wt .-%, in particular max. 1.5% by weight, limited. The Mo content of a steel according to the invention, which is particularly suitable for the purposes of the invention, is accordingly in the range of 1.2 wt .-%.

Vanadium is present in the steel of the present invention at levels of from 6.0% to 18.0% by weight to achieve optimized wear resistance through the formation of vanadium-rich carbides or carbonitrides. In addition, vanadium increasingly participates in the formation of carbides during tempering in the secondary hardness maximum. These effects increase with increasing V contents, so that the property profile of the steel material according to the invention can also be adapted to the respective requirements by varying the V contents. Maximized positive effects of the presence of V can be achieved when at least 14.5 wt% V is present in the steel of the invention. High V contents of at least 16 wt .-% lead to particularly high wear resistance, so that steel materials according to the invention with such high V contents are particularly suitable for use as a material for roller guide rollers, which are exposed to maximum loads in use. On the other hand, by restricting the V content to 17.4% by weight or 17.0% by weight to 16.0% by weight or more preferably at most 15.5% by weight, it can be reliably avoided that too much carbon is set by carbide formation. With low V contents tending towards the lower edge of the content range indicated for V according to the invention and correspondingly reduced C contents, the steel material according to the invention can be processed more easily by cutting than at the higher V and C contents. A simplified machinability results accordingly when the V content to max. 12 wt .-%, in particular max. 10 wt .-%, and thus also limited depending on the V content C content is limited in the manner described above.

Niobium is optionally present at levels of up to 2.0% by weight in the steel of the present invention. Nb has a very similar mode of action as vanadium. It mainly participates in the formation of hard and wear-resistant monocarbides. Therefore, depending on their contents in atomic%, Nb and V in the ratio 1: 1 can be exchanged alternately, if this is useful, for example, in view of the availability of these alloying elements.

Nickel may optionally be present at levels of up to 1.0% by weight in the steel material of the present invention to stabilize the austenite portion similar to Mn and thus improve hardenability. Thus, the presence of Ni ensures that austenite is actually formed at the respective hardening temperature and that no unwanted ferrite is 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, there should not be too high Ni contents, since there is a risk that residual austenite will be present in the microstructure after hardening. If Ni is to be added, therefore, the Ni content is preferably at least 0.2 wt .-%, with adjusted Ni contents of up to 0.4 wt .-% optimized effects of the presence of Ni.

Cobalt may also optionally be present at levels of up to 1.0% by weight in the steel material of the present invention. Similar to nickel, Co has a stabilizing effect on austenite formation and hardening temperature. However, unlike nickel or manganese, Co does not lower the final temperature of the martensite, so its presence is less critical with respect to the formation of retained austenite. In addition, cobalt increases the heat resistance. If these positive effects are to be utilized by the addition of Co, contents of at least 0.3% by weight of Co prove to be particularly expedient, with optimized effects occurring at Co contents of up to 0.5% by weight.

Tungsten, like Co and Ni, can optionally be added to the steel in amounts of up to 1.0% by weight. Above all, tungsten increases the tempering resistance and, above all, participates in carbide formation during tempering in the secondary hardness maximum. The presence of W shifts the tempering temperatures to higher temperatures. In addition, the heat resistance is increased by W, similar to the cobalt. However, excessive W levels would also stabilize the ferritic phase. If the positive effects of W are to be used, contents of at least 0.3% by weight of W are therefore found to be particularly expedient, with optimized effects occurring at W contents of up to 0.5% by weight.

The remainder of the remaining steel consists of iron and unavoidable impurities which enter the steel due to the manufacturing process or the raw materials from which the constituents of the steel alloy powder are recovered, but have no effect on the properties there.

Sulfur may be present in grades up to 0.35% by weight in the steel material to improve machinability. At higher S contents, however, the properties of the composite steel material according to the invention are deteriorated. In order to be able to safely use the favorable effect of the presence of S, at least 0.035% by weight may be present in the steel material according to the invention. If, on the other hand, the machinability is not improved by the targeted addition of S, the S content can accordingly be restricted to less than 0.035% by weight.

The unavoidable impurities also include levels of P of up to 0.035 wt .-% and, for example, in total up to 0.2 wt .-% of oxygen.

Nitrogen is also not added to the steel material according to the invention in a targeted manner, but due to the nitrogen affinity of the alloy constituents passes into the steel material during the atomization process. In order to avoid negative effects of N on the properties of the steel material, the content of N should be less than 0.12 wt .-%, in particular be limited to a maximum of 0.1% by weight.

The density of steel material according to the invention is typically in the range of 6.4 to 7.6 g / cm ³ , the density of the pure steel matrix material typically being 7.0 to 7.6 g / cm ³ .

Its minimized density and its resulting low weight makes steel material according to the invention particularly suitable for the production of such components which are repeatedly exposed to rapid acceleration in practical use and in which consequently a lower mass inertia has a particularly favorable effect.

The production of powder metallurgy makes it possible to further optimize the density and wear resistance of steel according to the invention by selective addition of hard phases with low density in the sense of the respective application, if this is desired with regard to the particular desired property. Here it has been shown that the performance characteristics of steel material according to the invention are increased by containing 2.5 to 30 wt .-% hard particles, which are embedded in the finished steel produced in its composite in the manner described above steel matrix.

The hard materials are like the steel matrix forming steel alloy powder in the initial state as a powder before.

Hard materials, also known as "hard phases" in technical language, can be carbides, nitrides, oxides or borides. The group of suitable hard materials accordingly includes 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 of this invention. Titanium carbide has a hardness of 3200 HV and thus increases the hardness and wear resistance of the steel particularly effectively. At the same time, TiC is chemically resistant and has no negative impact on corrosion resistance. Likewise, the low density of TiC has an advantageous effect.

With the steel material alloyed hard material contents of less than 2.5 wt .-%, there is no improvement in the wear resistance. In order to be able to use the effect of the hard materials particularly reliably, it is therefore advantageous to provide at least 5% by weight of alloyed hard material particles in the steel material according to the invention, with contents of at least 7.5% by weight being found to be particularly effective. In order to reliably avoid excessive embrittlement of the material as a consequence of the presence of the hard material particles, the content of alloyed hard material particles can be limited to not more than 25% by weight in the material according to the invention. The contents of hard material particles mentioned here in a steel material according to the invention prove to be particularly useful when the alloyed hard material is titanium carbide TiC.

Steel of the invention, after hardening and tempering, achieves hardness values typically in the range of 58-70 HRC.

After a soft annealing, which is generally carried out for mechanical processing, the typical soft annealing hardness of steel material according to the invention is typically up to 65 HRC due to the presence of the hard material particles provided according to the invention.

1. a) Es wird ein Stahllegierungspulver bereitgestellt, das aus (in Gew.-%) 1,5 - 5,0 % C, 0,3 - 2,0 % Si, 0,3 - 2,0 % Mn, < 0,035 % P, <0,35 % S, < 0,1 % N, 3,0 - 15,0 % Cr, 0,5 - 2,0 % Mo, 6,0 - 18,0 % V, jeweils optional einem Element oder mehreren Elementen aus der Gruppe "Nb, Ni, Co, W", wobei der Gehalt an Ni, Co und W jeweils höchstens 1,0 % und der Gehalt an Nb höchstens 2,0 % beträgt, und als Rest aus Eisen und unvermeidbaren Verunreinigungen besteht.
2. b) Das Stahllegierungspulver wird mit Hartstoffpartikeln mit der Maßgabe vermischt, dass der Gehalt an Hartstoffpartikeln an der erhaltenen Stahllegierungspulver-Hartstoffpartikel-Mischung 2,5 - 30 Gew.-% beträgt.
3. c) Optional wird das Stahllegierungspulver oder die Stahllegierungspulver-Hartstoff-Mischung getrocknet.
4. d) Aus dem Stahllegierungspulver oder der Stahllegierungspulver-Hartstoff-Mischung wird durch ein Sinterverfahren, insbesondere durch Heiß-Isostatisches-Pressen, oder durch ein additives Verfahren ein festes Halbzeug gebildet.
5. e) Das erhaltene Halbzeug wird zu dem Bauteil fertig bearbeitet.

When producing components according to the invention from a steel according to the invention, at least the following working steps are carried out:

1. a) A steel alloy powder is provided which consists of (in wt%) 1.5-5.0% C, 0.3-2.0% Si, 0.3-2.0% Mn, <0.035% P, <0.35% S, <0.1% N, 3.0-15.0% Cr, 0.5-2.0% Mo, 6.0-18.0% V, each optionally one element or more elements of the group "Nb, Ni, Co, W", wherein the contents of Ni, Co and W are at most 1.0% and the content of Nb is 2.0% or less, and the balance of iron and unavoidable Impurities.
2. b) The steel alloy powder is mixed with hard material particles with the proviso that the content of hard material particles in the obtained steel alloy powder-hard material particle mixture is 2.5-30% by weight.
3. c) Optionally, the steel alloy powder or the steel alloy powder-hard material mixture is dried.
4. d) From the steel alloy powder or the steel alloy powder-hard material mixture, a solid semi-finished product is formed by a sintering process, in particular by hot isostatic pressing, or by an additive process.
5. e) The resulting semi-finished product is finished to the component.

With regard to the practical implementation and the embodiments of steps a) to e) of the method according to the invention, the following information applies:

Step a)

Powder production may be accomplished 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 atomization or a combination of these two atomization methods. An atomization of a melt alloyed according to the invention to the alloy powder is conceivable.

Alternatively, however, it is also possible initially to provide the alloying elements of the steel alloy powder individually in powder form in quantities corresponding to the content proportions intended for the respective alloying element and then to mix these quantities of powder into the steel alloying powder composed according to the invention.

If necessary, those are selected from the powder particles for the further processing according to the invention by sieving, which have a mean diameter of less than 500 microns, with powder having mean grain sizes of less than 250 .mu.m, in particular less than 180 microns, have been found to be particularly suitable.

Regardless of the manner in which it is produced, the alloy powder provided according to the invention optimally has a bulk density of 2-6 g / cm 3 (determined in accordance with DIN EN ISO 3923-1) and a tap density of 3-8 g / cm 3 (determined in accordance with DIN EN ISO 3953).

Step b)

The steel alloy powder provided in step a) is mixed with the respectively selected hard material powder. The amount of added hard material particles is determined taking into account the information given above with regard to the optimized selection of the content of hard materials in such a way that the content of the hard material particles in the finished mixture in the range of 2.5 to 30 wt .-%.

Step c)

If necessary, the alloy powder prepared in step a) or step b) may be dried in a conventional manner to remove residues of liquids and other volatiles which could hinder the subsequent forming process.

Step d)

From the hard powder particles containing alloy powder, a blank (semifinished product) is then formed. For this purpose, the alloy powder in a conventional manner by a suitable sintering process, in particular by hot isostatic pressing ("HIPen"), are brought into the respective shape. In general, HIPing will be performed. Typical pressures during HIPing are in the range of 900-1500, in particular 1000 bar, at a temperature of 1050-1250 ° C., in particular 1080-1200 ° C. In the course of hardening, austenite, VC and Cr carbide form in the microstructure of the steel material.

Alternatively, the respective component can also be produced from the inventively prepared and provided alloy powder in an additive process. The term "additive" summarizes all manufacturing processes in which a material is added to produce a component, wherein this addition generally takes place in layers. "Additive manufacturing processes", which are often referred to as "generative processes" in technical jargon, are in contrast to the classical subtractive production processes, such as the machining processes (eg milling, drilling and turning), in which material is removed, in order to achieve this each to be manufactured component to give shape. The additive design principle makes it possible to produce geometrically complex structures that can not be realized or can only be realized with great difficulty using conventional manufacturing processes such as the aforementioned metal-cutting processes or primary molding processes (casting, forging) (see VDI Status Report "Additive Manufacturing Processes", September 2014) from the Association of German Engineers eV, Department of Production Engineering and Manufacturing, www.vdi.de/statusadditiv). details

Definitions of the methods, which are summarized under the generic term "additive methods", can be found, for example, in VDI Guidelines 3404 and 3405.

Step e)

The semi-finished product obtained after step d) still requires a finish in order to give it on the one hand the desired performance and on the other hand the required final shape. Finishing includes, for example, a mechanical, in particular machining of the semifinished product, and a heat treatment, which may consist of hardening and tempering.

• In der voranstehend erläuterten Weise erfindungsgemäß zusammengesetzte Legierungspulver werden beispielsweise durch Heiß-Isostatisches-Pressen oder ein anderes geeignetes Sinterverfahren zu einem Rohteil (Halbzeug) geformt. Hierzu kann das jeweilige Legierungspulver in eine geeignete Form, beispielsweise eine zylindrische Kapsel, gefüllt und dann bei typischen Drücken von 900 - 1500 bar (90 - 150 MPa), insbesondere 1000 bar (100 MPa), bei einer Temperatur von 1050 - 1250°C, insbesondere 1150 °C, über eine ausreichende Dauer gehalten werden, bis ein fester Körper entstanden ist. Typischerweise liegt der Druck beim Heiß-Isostatischen-Pressen im Bereich von 102 - 106,7 MPa und die Erwärmung auf die typischerweise 1150 - 1153 °C betragende Zieltemperatur, die über eine Dauer von typischerweise 200 - 300 min, insbesondere 245 min, gehalten wird, erfolgt ebenso typischerweise mit einer Aufheizrate von 3 K/min - 10 K/min.

The invention will be explained in more detail below on the basis of exemplary embodiments:

• In the manner explained above, alloy powders composed according to the invention are shaped into a blank (semifinished product), for example by hot isostatic pressing or another suitable sintering method. For this purpose, the respective alloy powder in a suitable form, such as a cylindrical capsule, filled and then at typical pressures of 900 - 1500 bar (90 - 150 MPa), in particular 1000 bar (100 MPa), at a temperature of 1050 - 1250 ° C. , In particular 1150 ° C, are held for a sufficient time until a solid body is formed. Typically, in hot isostatic pressing, the pressure is in the range of 102-106.7 MPa and the heating is typically at the target temperature of 1150-1153 ° C., which is maintained for a duration of typically 200-300 minutes, particularly 245 minutes , is also typically at a heating rate of 3 K / min - 10 K / min.

The production of the semifinished product was followed by the heat treatment. In this case, the respective semi-finished product is heated at a heating rate of typically 5 K / min to a hardening temperature (austenitizing temperature) of 1050 - 1200 ° C, on which it is held until it is completely warmed through. Typically, this will take 30 to 60 minutes. Subsequently, the thus heated semi-finished products are quenched. They are cooled with a suitable quenching medium, for example with water, oil, a polymer bath, moving or static air or, if the cooling is carried out in a vacuum oven, with gaseous nitrogen, within 5-30 min to room temperature. Particularly in the case of large semi-finished products, it may be expedient to carry out the heating to the hardening temperature in several preheating stages, for example 400 ° C., 600 ° C. and 800 ° C. or a preheating temperature in the range from 600 to 800 ° C., in order to ensure uniform heating.

In order to avoid reactions with the ambient atmosphere, curing in a vacuum oven can also be carried out in a manner known per se. However, this is not a prerequisite for the success of the procedure according to the invention.

After hardening, tempering may be carried out in which the semifinished product is held for a period of, for example, 90 minutes at the respective tempering temperature, which is typically 450-550 ° C. The tempering conditions are determined in a manner known per se depending on the respective hardening temperature and the desired level of hardness, i. the desired strength selected. The heating and cooling rates are usually on the order of 10 K / min when starting. In contrast to curing, the heating and cooling rates during tempering are not critical. By tempering the brittle martensite relaxes by diffusion of carbon. This forms together with e.g. V, Cr and Mo the so-called "carbide". This increases the toughness. At the same time, the strength and hardness of the steel material decreases only slightly, since these properties are increased again by the carbide formation.

Since there is usually a narrow temperature range (about 50 ° C coarse between 450 and 650 ° C) in such alloy systems, one speaks of secondary hardness maximum, since temperatures below or above it mean a lower hardness.

Using the general procedure described above in the practical production of steel materials according to the invention and components produced therefrom, cylindrical semifinished products have been produced from four steel materials V10a-V10d according to the invention.

The steel matrix of the steel materials V10a, V10b, V10c and V10d each contained (in wt .-%) 2.5% C, 0.9% Si, 0.9% Mn, 4.5% Cr, 1.2% Mo and 10.0% V, balance iron and unavoidable impurities. In addition, 5% by weight of TiC were added to the steel material V10a, 10% by weight of TiC to the steel material V10b, 15% by weight of TiC to the steel material V10c and 20% by weight of TiC to the steel material V10d.

The austenitizing temperature AT, the hardness HRC ("HRC_v") existing before the subsequent heat treatment step, either when tempering has been performed, the tempering temperature ST and tempering time St, or, if soft annealing has been performed, the soaking temperature WT and the soaking annealing time Wt , the hardness HRC ("HRC_n") after the previous heat treatment step and the density ρ of the samples V1-V8 are given in Table 1.

The heating to the respective austenitizing AT was carried out in a vacuum oven. There, the samples V1 - V8 were kept at the austenitizing temperature ΔT for an austenitizing time Δt. Subsequently, the mixture was cooled to room temperature in the vacuum oven by exposure to gaseous nitrogen applied at a pressure of 3.5 bar.

After curing, Samples 1-8 were subjected to either annealing or annealing treatment. In the tempering treatment, the samples 1, 3, 5, 7 have been kept at the tempering temperature ST over the tempering period St. This tempering treatment was carried out twice to obtain an optimum starting result.

During the soft annealing, the samples 2, 4, 6, 8 have been kept at the annealing temperature WT for a duration Wt. After the end of the annealing period, the oven was switched off and the samples 2, 4, 6, 8 were cooled slowly in the oven switched off to room temperature. Table 1 sample material alloyed TiC content AT At HRC_v ST st WT wt HRC_n ρ [Wt .-%] [° C] [Min] medium [° C] [Min] [° C] [H] medium [g / cm ³ ] 1 V10a 5 64.0 500 90 - - 62.5 7.19 2 V10a 5 - - 900 8th 39.0 3 V10b 10 69.0 500 90 - - 65.0 7.05 4 V10b 10 1800 60 - - 900 8th 44.0 5 V10b 15 69.0 500 90 - - 65.0 6.88 6 V10b 15 - - 900 8th 46.0 7 V10b 20 69.0 500 90 - - 66.0 6.72 8th V10b 20 - - 900 8th 50.0

Claims (15)

A steel material produced by powder metallurgy and having a steel matrix composed as follows (in% by weight): C: 1.5 - 5.0%, Si: 0.3 - 2.0%, Mn: 0.3 - 2.0%, P: 0 - <0.035%, S: 0 - <0.35%, N: 0 - <0.1%, Cr: 3.0 - 15.0%, Not a word: 0.5 - 2.0%, V: 6.0 - 18.0%, each optionally one or more elements from the group "Nb, Ni, Co, W", wherein the content of Ni, Co and W is at most 1.0% and the content of Nb is 2.0% or less,
Residual iron and unavoidable impurities,
wherein embedded in the steel matrix hard material particles in amounts of 2.5 to 30 wt .-%. Steel material according to claim 1, characterized in that at Cr contents of up to 8.0 wt .-%, the C content of the steel matrix with an absolute deviation of at most 0.2 wt .-% of a target size corresponds to CZiel, for the % CZiel = 0.2 x% V + 0.4% by weight, where% V denotes the respective V content of the steel matrix. Steel material according to claim 1, characterized in that at Cr contents of at least 11.0 wt .-%, the C content of the steel matrix with a magnitude deviation of at most 0.2 wt .-% of a target size% CZiel for which the following applies:% C = (0.2 x% V + 0.4% by weight) x 1.3, where% V denotes the respective V content of the steel matrix. Steel material according to claim 1, characterized in that at Cr contents of more than 8 wt .-% and less than 11 wt .-%, the C content of the steel matrix is between the determined according to claim 2 and 3% CZiel contents. Steel material according to one of the preceding claims, characterized h characterized in that its Si content is at least 0.7 wt .-% or at most 1.5 wt .-%. Steel material according to one of the preceding claims, characterized h characterized in that its Mn content is at least 0.7 wt .-% or at most 1.5 wt .-%. Steel material according to one of the preceding claims, characterized h characterized in that its S content is at least 0.035 wt .-%. Steel material according to one of the preceding claims, characterized h characterized in that its Mo content is at least 0.9 wt .-% or at most 1.5 wt .-%. Steel material according to one of the preceding claims, characterized h that s is valid in the presence of an element or several elements from the group "Ni, Co, W" for the contents of the element Ni, Co or W (in wt .-%): Ni: 0.2 - 0.4%, Co: 0.3 - 0.5%, W: 0.3 - 0.5%. Steel material according to one of the preceding claims, characterized h characterized in that the hard material particles are TiC particles. Steel material according to one of the preceding claims, characterized h characterized in that the hard material particles are present in a d50 grain size of at most 50 microns. Method for producing a component which consists of a steel obtained according to one of the preceding claims, comprising the following working steps: a) A steel alloy powder is provided which consists of (in wt%) 1.5-5.0% C, 0.3-2.0% Si, 0.3-2.0% Mn, <0.035% P, <0.35% S, <0.1% N, 3.0-15.0% Cr, 0.5-2.0% Mo, 6.0-18.0% V, each optionally one element or plural elements of the group "Nb, Ni, Co, W", wherein the content of Ni, Co and W is 1.0% or less, and the content of Nb is 2.0% or less, and the remainder is iron and unavoidable Impurities. b) The steel alloy powder is mixed with hard material particles with the proviso that the content of hard material particles in the obtained steel alloy powder-hard material particle mixture is 2.5 to 30 wt .-%. c) Optionally, the steel alloy powder or the steel alloy powder-hard material mixture is dried. d) From the steel alloy powder or the steel alloy powder-hard material mixture, a solid semi-finished product is formed by a sintering process, in particular by hot isostatic pressing, or by an additive process. e) The resulting semi-finished product is finished to the component. A method according to claim 12, characterized in that for the working step a) the alloy components of the steel alloy powder are respectively provided in powder form and mixed into the steel alloy powders. Method according to one of claims 12 or 13, characterized in that the finishing (step e)) comprises a machining of the semifinished product. Component which, in practical use, performs high acceleration or velocity movements made of a steel material obtained according to any one of claims 1 to 11.