EP3263726A1 - Fe basis material and method for its production - Google Patents

Abstract

The invention relates to an Fe-based material which consists of an iron-based matrix and hard material particles embedded in this matrix, the Fe-based material consisting of (in% by mass) ‰ ¤ 1.0% C, 2.0-25.0 % Cr, 0.5 - 7% Mo, a connection element added to bind the hard material particles to the matrix, which belongs to the transition elements of the 4th - 6th subgroup of the periodic table, in contents of 0.5 - 5.0%, ‰ each ¤ 12% Co, ‰ ¤ 18% Ni, as well as 20 - 40% TiC hard material particles and the remainder of iron and unavoidable impurities, with Ti atoms in the hard material particles being substituted by atoms of the one connection element present in the matrix. Such an Fe base material can be produced according to the invention by adding a powder mixture, which consists of a powder consisting of 0.8% C, 0.5-25% Cr, 0.5-7% Mo, to bind the hard material particles Connection element added to the matrix of the Fe base material, which belongs to the transition elements of the 4th - 6th subgroup of the periodic table, in contents of 0.5 - 5.0%, ‰ ¤ 12% Co, ‰ ¤ 18% Ni and the remainder consists of iron and unavoidable impurities, and a hard material powder is mixed, which consists of TiC hard material particles, the proportion of TiC hard material particles in the powder mixture is 20-40% by mass, is compacted to a solid Fe-base material block, which is then heat-treated The heat treatment comprises a solution heat treatment for a period of 1 to 4 hours at a temperature of 800-1100 ° C.

Description

The invention relates to an Fe base material which consists of a steel matrix and of hard particles embedded in the steel matrix.

Moreover, the invention relates to a method for producing such an Fe base material.

Whenever statements are made below on contents of alloys and the like, they always refer to the mass, unless expressly stated otherwise.

The Fe base material according to the invention is a so-called "hard composite material" in which the hard particles embedded in the steel matrix should ensure the required hardness and the steel matrix, on the one hand, a secure hold of the hard material particles and, on the other hand, the required toughness of the Fe base material.

The term "Fe base material" includes iron-based materials, including, in addition to the steels with carbon contents of up to 1% by mass, in particular also in the technical sense, carbon-free materials.

A successfully used in practice under the brand "Ferro-Titanit", powder metallurgy in the form of a metal matrix composite ("MMC") produced material contains up to 50% by volume (corresponding to up to about 35% by mass) of titanium carbide (TiC ) with a hardness of 2800 - 3500 HV0.05. The Titanium carbide is incorporated in this material into a matrix of steel, the properties of which are adapted to the respective intended use. Ferro-titanitic materials are available, as detailed in the Ferro-Titanit® datasheet collection 08/2003, in which the steel matrix consists of a martensitic, highly resistant steel, a highly corrosion-resistant steel, a hardenable, high tenacity nickel martensitic steel or made of a non-magnetizable, highly corrosion and temper resistant steel. The contents of the respective materials on the particulate TiC hard material grains are typically in the range of 30-35 mass% in practice.

Hard composites are preferably used in areas where technical surfaces must be protected against grossly abrasive wear.

The structure of hard composites usually consists of a metallic matrix with embedded and finely dispersed hard materials and has in comparison to molten metallurgically urgeformten hard alloys the advantage that material structure against thermodynamic boundary conditions by mixing and compacting any hard metal matrix combinations can be produced. The metal matrix is preferably Fe (white cast iron, tool steels), Ni (NiBSi, NiCrBSi) or Co (Stellite) hard alloys. In the case of hard materials, metallic hard materials or metal-covalently bonded hard materials, such as tungsten carbides of the WC or WC-W ₂ C type, are usually used because of the metallurgical compatibility and the material properties.

The hard composites are usually produced by sintering or build-up welding with the methods presented below, which are known per se to those skilled in the art.

During sintering, if desired, solid materials can be produced under pressure and temperature in a known manner or by hard bonding materials on functional surfaces can be applied to functional surfaces by "diffusion welding" (see http://www.ise.rub.de/forschung/projekte/sintercladding. html.de).

In the case of build-up welding, use is made of a powder, strip or rod-shaped welding filler which is applied to a substrate by suitable fusion welding methods (plasma powder build-up welding, oxy-acetylene welding, metal inert gas welding). The applied by means of build-up welding functional layer protects the substrate against external stress due to wear and / or corrosion. Partly tough Ni base hard alloys with 50% by volume WC or tungsten carbide ("WSC") have been able to establish themselves as welding consumables.

In addition to the high fracture toughness for Ni base hard alloys available for hard alloys, these materials can be processed together with the additions of hard material at lower temperatures, so that undesirable hard metal-metal matrix interactions, such as the formation of brittle phases, can be avoided. However, the disadvantage is the cost of these Ni-base / WSC welding consumables.

An alternative to W-containing hard materials is the hard material TiC, which has a higher hardness compared to W-containing hard materials but a lower fracture toughness. Also hard composites with the hard material TiC could be produced by sintering and thermal spraying on substrates.

In comparison with the extremely hard carbide grades with a hard material volume content of up to 96% by volume, tougher grades are used in the field of mining and the treatment of building materials, in particular of materials resulting from road treatment.

The structure of these grades, also referred to as mining grades, has a lower hard material volume content of 75 to 85 vol .-% with a larger WC carbide size of a few micrometers. Due to a higher co-binder content in the steel matrix in combination with a lower specific carbide surface, a higher wetting surface of the hard materials through the co-binder is present, which promotes the bending strength.

In terms of quantity, Ni base base composites with WSC additions are most commonly processed by build-up welding. There is no practical alternative available for the hard material tungsten carbide. This is due to the fact that tungsten carbide as a metal-ceramic material has a good combination of high hardness and high fracture toughness for ceramic materials. There are no commercially available metal-ceramic materials are known which have this combination of properties.

Although it is already possible to resort to many oxide ceramics or covalent hard materials. However, their processing to hard composite materials is not guaranteed by the associated bonding structure of the respective hard materials. Oxide ceramics, for example, have a chemically inert effect and do not undergo metallurgical reactions with the metal matrix, so that when they are processed into hard composite materials, they are only frictionally bonded into the metal matrix. In comparison, covalently bound hard materials in contact with molten metals behave metastable to unstable and lead to the formation of more stable phases.

However, tungsten, which is essential for hard materials of the type described here, is available on the market only at high cost and to a limited extent.

In order to secure the future demand for wear-resistant hard materials, therefore, independence from certain raw material sources The aim is to expand the hard materials that can be used in applications typical for hard-material composites.

Against this background, the object of the invention was to provide an Fe base material that can be produced cost-effectively with secure raw material availability and thereby has optimized service properties.

Also, a method for producing such an Fe base material should be given.

With respect to the material, the invention has achieved this object by an Fe base material having at least the features specified in claim 1.

The inventive, the above object solving method for producing an Fe base material according to the invention comprises at least the steps specified in claim 7.

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

• wobei der Fe-Basiswerkstoff aus (in Masse-%)
  bis zu 1,0 % C,
  2,0 - 25,0 % Cr,
  0,5 - 7 % Mo,
  mindestens einem zum Anbinden der Hartstoffpartikel an die Matrix des Fe-Basiswerkstoffs zugegebenen Anbindungselement, welches den Übergangselementen der 4. bis 6. Nebengruppe des Periodensystems der Elemente angehört, in Gehalten von 0,5 - 5,0 %,
  optional bis zu 12 % Co,
  optional bis zu 18 % Ni,
  sowie 20 - 40 % TiC-Hartstoffpartikel
  und
  als Rest aus Eisen und herstellungsbedingt unvermeidbaren Verunreinigungen besteht, und
• wobei in den Hartstoffpartikeln Ti-Atome durch Atome des jeweiligen mindestens einen in der Matrix vorhandenen Anbindungselements substituiert sind.

An Fe base material according to the invention consists of an iron-based matrix and of hard material particles embedded in this matrix,

• wherein the Fe base material consists of (in% by mass)
  up to 1.0% C,
  2.0 - 25.0% Cr,
  0.5 - 7% Mo,
  at least one bonding element added for bonding the hard material particles to the matrix of the Fe base material, which bonding element Transition elements of the 4th to 6th subgroups of the Periodic Table of the Elements, in contents of 0.5 - 5.0%,
  optional up to 12% Co,
  optional up to 18% Ni,
  as well as 20 - 40% TiC hard material particles
  and
  as the remainder of iron and production-related unavoidable impurities, and
• wherein Ti atoms in the hard material particles are substituted by atoms of the respective at least one connecting element present in the matrix.

The invention is based on the recognition that the properties of hard composite materials of the type in question can be purposefully improved by influencing the hard material morphology and the hard material properties. For this purpose, the interdiffusion processes between the metal matrix and the hard material, which begin during the production of the hard composite materials, are used to adjust the hard material properties.

The material according to the invention is therefore also a metal-matrix composite ("MMC") in which, according to the invention, optimum bonding of the respectively provided TiC hard materials to the matrix of the material is ensured by adding at least one connecting element.

According to the invention, the composition of the material forming the matrix of the Fe base material according to the invention is selected such that in the course of the production of the Fe base material it leads to a "alloying" of the hard material provided by the invention in the metallic binder matrix or Metal matrix dissolved alloying elements comes.

In this case, the alloy of the Fe base material according to the invention is selected such that a sufficient driving force for mass transfer processes occurs at the respective boundary surfaces (steel matrix hard material). In this way, the targeted interdiffusion and the associated changes in the hard material properties achieved.

The invention is based on a composition of the Fe base material, which includes the well-known from the prior art members of FerroTitanit materials, but extends this composition by the sake of simplicity so called "attachment elements". These elements have sufficient solubility in the TiC hard material and diffuse during the production of the material from the metal matrix in the TiC hard material bound in the steel matrix.

According to the invention, such elements which form homologous phases as TiC and thus have a high, partly complete solubility in the kfz lattice of the TiC are used as attachment elements. These elements can be found in the periodic table of elements in the transition elements of the 4th to 6th subgroup. These include Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, with "Zr, Hf, Nb, Ta, V, W" being particularly suitable for the purposes according to the invention. Specially tungsten has been included here as a possible attachment element, since it also has a certain solubility in the kfz lattice of the TiC and as far as the other invention selected connecting elements can substitute Ti atoms.

Associated with the substitution of Ti atoms by the attachment elements is a change in the hard material properties by changing the bonding structures.

Thus, as a result of an increase in the valence electron concentration, the addition of V in the hard material TiC leads to a stronger hybridization between sp orbitals of the carbon and d orbitals of the Ti / V atoms. The consequence of the higher covalent bonding character is the increase in hardness and modulus of the TiC.

The invention thus provides a metal-matrix composite ("MMC") which, with a matrix based on iron and alloyed in accordance with the invention, has optimum conditions for a long and effectively usable service life and also provides optimized performance properties.

Mo and Cr are preferably not among the attachment elements added according to the invention, because with the diffusion of Mo into the TiC hard material particles, a decrease in the Mo content in the metal matrix surrounding the hard material particles and, concomitantly, a decrease in corrosion resistance would be associated.

On the other hand, the selection of the connecting elements according to the invention has succeeded in increasing the corrosion resistance and toughness of the MMC according to the invention. For this purpose, alloying elements have been selected as attachment elements, which have a higher tendency, compared to Mo, to be present in the TiC particles during the production process.

In principle, tungsten is also suitable for the purposes according to the invention, but has a limited solubility in the TiC and is therefore only effective to a limited extent here. In order to avoid negative influences of the presence of W, the presence of W in the MMC material according to the invention is preferably completely omitted in the technical sense. W is then present at most in the impurities attributable amounts in the Fe base material according to the invention.

The content of the bonding elements added according to the invention as alloying elements to the Fe material of the matrix of an MMC according to the invention is, in principle, 0.5 to 5% by mass per added connecting element. Optimum effects are exhibited by the attachment elements if they are present in the matrix in amounts of at least 1% by mass, the minimum content of the particular attachment element also being 1.5% by mass or 2% by mass can. At levels above the upper limit of 5% by mass of the respective attachment element, no increase in the effect could be observed. Optimal effects were obtained at levels of attachment elements of up to 4% by mass, with contents of not more than 3.5% by mass or not more than 3% by mass regularly resulting in good properties of the MMC-Fe base material according to the invention. With regard to the effort associated with the alloying of the connection elements, it may therefore be expedient to correspondingly limit the content of the respectively provided connection element.

It is possible to add two or more of the connecting elements selected according to the invention in combination with one another to the Fe base material according to the invention. In this case, it has proved to be favorable if the sum of the contents of the added elements is 1-5% by mass, in particular at least 2% by mass or at most 4% by mass. In the case of the presence of two joining elements added as alloying element to the Fe-based material of the matrix, the diffusion is promoted or facilitated. In this way, the effects according to the invention of the addition of the attachment elements already set in when only one attachment element is present. However, it has been found to be particularly advantageous if more than one attachment element, in particular two attachment elements, are present in combination.

In this case, Nb and V have been found to be particularly suitable for the purposes of the invention. Extensive investigations have shown that both Nb and V contribute particularly effectively to a significant improvement in the performance of an Fe base material of the type according to the invention. Here, Nb proves to be particularly effective in terms of increasing the wear resistance under the regular operating conditions in practice conditions.

If Nb alone is provided as the attachment element, it has proved to be favorable if the content of Nb, if present, is less than 5% by mass, in particular not more than 4% by mass, with contents of at least 1% by mass or at least 1.5 mass% have been found to be particularly advantageous. These specifications are especially applicable when the frayed material of the matrix is higher, i. having above 10% by mass lying Cr contents or above 4.5% by mass lying Mo contents. Experiments have shown that the limitation of the Nb content to contents of less than 3% by mass, even at such high Mo or Cr contents, prevents the formation of unfavorable sigma phases.

In the case that V is provided as a connection element, it has proved to be favorable, the V content of the Fe base material according to the invention also to at most 5% by mass, in particular at most 4.0% by mass or at most 3.0% by mass In addition, contents of at least 1% by mass or 1.5% by mass have proven to be particularly advantageous here.

In the case of an Fe base material that fulfills the present invention particularly well, the C content is in the range of the impurities, ie it is not present in the technical sense and therefore ineffective, and its (in mass%) is 12.5-14 , 5, in particular at least 13% or at most 14%, its Mo content 4.5-5.5%, its Co content 8.0-10.0%, in particular at least 8.5% or 9.5%, its Ni content is 3.5-4.5% and its TiC content is 27-33%, in particular at least 29% or at most 31%.

To determine the abrasive wear resistance, a pencil-paper wear test was used. In this experiment, a cylindrical sample with a normal force of 37 N and a rotation speed of 47.8 rpm is moved meandering over bonded abrasive. The dimensionless wear resistance W _ab ^-1 can then be calculated with the mass loss m, the material density p, the wear surface A, and the wear path L according to the following formula: $${\mathrm{W}}_{\mathrm{from}}^{-\mathrm{1}}=\frac{\mathrm{\rho }\times \mathrm{A}\times \mathrm{L}}{\mathrm{m}}$$

The alloy produced according to the invention by the addition of at least one of the attachment elements and the concomitant change in the morphology and size of the TiC particles leads to improved wear resistance. Thus, in comparative tests carried out in the above-described manner, in which fine grain (220 mesh) and coarse grain (80 mesh) Al ₂ O ₃ grains were used as abrasives, it could be shown that according to the invention Anchor elements Nb or V alloyed Fe base material compared to a material that lacked the respective attachment element with otherwise the same composition, in the fine abrasives by a factor of 3.5 and the coarse abrasives showed a factor of 2 improved wear resistance.

1. a) Bereitstellen einer Pulvermischung,
   • die aus einem Pulver, das aus (in Masse-%) bis zu 0,8 % C, 0,5 - 25 % Cr, 0,5 - 7 % Mo, mindestens einem zum Anbinden der Hartstoffpartikel an die Matrix des herzustellenden Fe-Basiswerkstoffs zugegebenen Anbindungselement, welches den Übergangselementen der 4. bis 6. Nebengruppe des Periodensystems der Elemente angehört, in Gehalten von 0,5 - 5,0 %, optional bis zu 12 % Co, optional bis zu 18 % Ni und als Rest aus Eisen und herstellungsbedingt unvermeidbaren Verunreinigungen besteht, und
   • einem Hartstoffpulver gemischt ist, das aus TiC-Hartstoffpartikeln besteht,
   • wobei der Anteil der TiC-Hartstoffpartikel an der Pulvermischung 20 - 40 Masse-% beträgt;
2. b) Kompaktieren der Pulvermischung zu einem festen Fe-Basiswerkstoffblock;
3. c) Wärmebehandeln des Fe-Basiswerkstoffblocks, wobei die Wärmebehandlung ein Lösungsglühen über eine Dauer von 1 - 4 h bei einer 800 - 1100 °C betragenden Temperatur umfasst.

The method proposed by the invention for producing an Fe base material according to the invention comprises the following steps:

1. a) providing a powder mixture,
   • from a powder consisting of (in% by mass) up to 0.8% C, 0.5-25% Cr, 0.5-7% Mo, at least one for binding the hard material particles to the matrix of the product to be produced. Base element added to the transition elements of the 4th to 6th subgroup of the Periodic Table of the Elements, in contents of 0.5 to 5.0%, optionally up to 12% Co, optionally up to 18% Ni and the balance iron and production-related unavoidable impurities, and
   • a hard material powder is mixed, which consists of TiC-hard material particles,
   • wherein the proportion of TiC hard material particles in the powder mixture is 20-40 mass%;
2. b) compacting the powder mixture into a solid Fe base material block;
3. c) heat treating the Fe base material block, wherein the heat treatment comprises solution annealing for a period of 1 to 4 hours at a temperature of 800 to 1100 ° C.

The powder mixture provided according to the invention can be produced in a conventional manner. The procedures required for this purpose are known and are described, for example, in the brochure " INTRODUCTION TO THE POWDER METALLURGY PROCESSES AND PRODUCTS ", published in the German version by the Powder Metallurgy Association 2010 has been issued and available at the URL www. Pulvermetallurgie.com is available for download, generally described. Likewise, an explanation of the in the production and processing of hard materials containing metal powders can be found in Foller, M .; Meyer, H .; Lammer, A .: Wear and Corrosion of Ferro-Titanite and Competing Materials. In: Tools in the next century: Proceedings of the 5th International Conference on Tooling, September 29th - October 1st, University of Leoben, Austria, 1999, pp. 1-12 ,

For compacting the powder, all the powder metallurgical processes are suitable in which a previously provided metal powder is formed into a compact, coherent block by the application of heat or pressure. The methods suitable for this purpose are known by the generic term "sintering" and are likewise explained in the technical literature already cited above. Especially with these methods, the diffusion processes used according to the invention run particularly reliably as a result of the energy supplied in the form of pressure and / or heat.

The parameters of the sintering can be selected in the compacting step in a manner also known per se so that partial melting of the powder grains occurs. The resulting liquid phase results in practice-oriented process management an optimized binding of the powder grains.

In order to achieve maximum densification, the sintering can be carried out in a likewise known manner under pressure. A variant of this sintering process which is particularly suitable for the purposes according to the invention is the so-called hot isostatic pressing, also known by the name "HIP".

After compacting (step b)), the resulting Fe base material block is subjected, if necessary, still a heat treatment in which it is solution-annealed over a period of 1 - 4 hours at a solution annealing temperature of 800 - 1100 ° C.

By means of the heat treatment steps carried out according to the invention, sigma phases present in the material, which would set Cr and Mo, are dissolved, thus ensuring optimized corrosion resistance of the MMC-Fe base material according to the invention.

In order to avoid excessive scale formation or other reactions of the MMC-Fe base material block produced according to the invention with the ambient atmosphere, the solution annealing can be carried out under vacuum.

After solution heat treatment, the MMC-Fe base material block can also be quenched to obtain a product optimized in mechanical properties. Quenching is preferably carried out in such a way that a purely martensitic structure of the matrix is set up, in which small, technically unavoidable contents of other structural constituents of up to 1% by volume can be present. These other structural constituents may in particular be retained austenite. By creating a purely martensitic structure of the matrix in this sense the required hardness, strength and wear resistance of the MMC material according to the invention safely achieved.

The quenching can be done for example by blowing the block of material with respect to the material according to the invention in particular inert gas. For this purpose, the gas stream can be passed at a pressure of 1 - 4.5 bar in a chamber in which the Fe base material block is located. Particularly suitable for the cooling of gaseous nitrogen.

The cooling can be carried out in the furnace chamber in which the annealing treatment has previously taken place. In order to direct the cooling gas into the furnace chamber, normally openable flaps or the like are provided in heat treatment furnaces used in practice via which, for example by means of fans, the cooling gas, in particular the nitrogen, can be led into the furnace space where it can be circulated and circulated. The cooling gas flow is preferably not directed as a focused nitrogen jet to the refrigerated goods, but passed diffusely into the open chamber. In this way, cooling takes place via the maintained in the furnace chamber and, if necessary, continuously exchanged cooling gas atmosphere.

The cooling gas, in particular the nitrogen, is preferably used at room temperature. It has been found that, with regard to the goal of cooling, namely the formation of a martensitic microstructure, optimized cooling rates result. At lower cooling gas temperatures, the cooling rates would still be increased somewhat. However, experience shows that this has no appreciable influence on the cooling result, so that the expense associated with the additional cooling of the cooling gas can be avoided

Optional solution annealing and optional quenching may be followed by annealing at the end of the heat treatment (optional step c)), where the Fe base material block is heated at 100-550 ° C for a period of 1 - 8 hours is held. In the martensitic matrix, intermetallic phases are formed which further increase the hardness and strength of the matrix.

The invention will be explained in more detail by means of exemplary embodiments.

MMC powders made of a steel matrix forming powder and powdered titanium carbide in an attritor by mechanical alloying have been provided to form a very homogeneous and fine-grained powder. A typical d50 value of the powder was in the range of 10 - 15 μm. That is, the diameter of 50% of the particles is smaller than 10 - 15 μm.

In this case, consisting of the known Fe base material Nikro128 existing steel powder with 1% by mass, 2% by mass, 3% by mass and 4% by mass of powdery Nb or V as connecting elements were mixed.

The mixing was followed by drying and pressing followed by sintering in a vacuum oven in the temperature range of 1200-1500 ° C. over a period of 3 hours at a reduced pressure of about 5 × 10 ^-2 mbar.

The samples were then solution annealed at 850 ° C for two hours, quenched in oil, and then purged for 6 hours at 480 ° C in air.

The compositions of the test pieces obtained are shown in Table 1.

In Table 2, for the samples to which V has been added as the attachment element and the control sample, Nikro 128 is the middle one
Hard particle diameter, the mean hard particle size, the volume fraction of hard particles and the number of particles for each sample specified.

In Table 3, for the samples to which Nb or V has been added as the attachment member and the comparative sample Nikro 128, the chemical compositions of each TiC particle present in the samples are indicated.

In Table 4, for the samples alloyed with Nb or V as attachment elements, as well as the comparative sample Nikro 128, the hardness and the E modulus values determined according to DIN EN ISO 14577-2, May 2003 edition, are indicated. To determine the relevant values, a maximum load of 20 mN at a penetration depth of 60 - 170 nm was determined in the tests.

As a special feature, the Nb-alloyed samples registered a density increase with increasing Nb content due to the higher density of Nb compared to the density of the non-Nb or V-alloyed Nikro128 material. The same has been observed in the V-alloyed samples, since V also has a higher density than the non-Nb or V-alloyed Nikro128 material.

Subsequently, the microstructure was evaluated metallurgically and the property changes associated with the addition of Nb or V were determined by tribological, mechanical and chemical analyzes.

The structure of the alloyed with Nb additions Nikro128 materials is in the FIGS. 1a-1d represented by micrographs ( Fig. 1a : Nikro128 + 1Nb; Fig. 1 b: Nikro128 + 2Nb; Fig. 1 c: Nikro128 + 3Nb, Fig. 1d : Nikro128 + 4Nb).

For comparison, in Fig. 2 reproduced the microstructure of the material Nikro128 without Nb addition in a similarly prepared microsection.

The comparison of the Nb-alloyed starting material Nikro128 with the Nb-alloyed variants makes it clear that the additions of Nb strongly influence the hard-phase morphology.

Thus, on the one hand, with increasing Nb content, the hard phase size of the TiC inclusions increases and, on the other hand, the free matrix path length between the TiC islands is increased by the breaking up of the reticulated hard materials.

In particular, the increase in the free matrix path length leads to a significant increase in the bending strength of the Nb-alloyed hard composite materials compared to the starting material Nikro128.

The samples alloyed with V as attachment element showed corresponding behavior.

It can be seen that both the hardness and the modulus of elasticity of the hard materials can be increased in a targeted manner by alloying in Nb or V, in which case a maximum hardness of approximately 2% by mass V and approximately 2% by mass Nb is achieved becomes. Above these levels, both hardness and modulus drop slightly, with hardness and modulus not falling below the properties of the stoichiometric pure TiC.

The modification of the micromechanical properties, the hard material morphology and the chemical composition of the TiC inclusions additionally have a positive influence on the corrosion and wear properties of the Fe base material.

In the as FIGS. 3a, 3b attached pictures shows the wear resistance of the tested samples ( Fig. 3a : Nikro 128 + xV; Fig. 3b : Nikro128 + xNb), testing for claw wear. The tests were done in the manner already described as pen paper Wear test performed. The abrasive used was Al ₂ O ₃ with two different grain sizes (coarse = 80 mesh, fine = 220 mesh).

The FIGS. 3a, 3b show that, compared to the coarse abrasives, the addition of V only causes a slight increase in the wear resistance compared to the Nikro128 without Nb or V.

This is different with the Nb-alloyed variants. In this case, the wear resistance increases with increasing Nb content due to an increase in hardness, volume content and diameter of the hard material TiC with increasing Nb content.

In general, however, the increase in wear resistance compared to the coarse abrasives is comparably low. This is explained by the fact that the hard materials are of insufficient size compared to the attacking abrasives and are therefore spun out of the coarse abrasives together with the metal matrix.

Another picture arises when considering the wear resistance against the fine abrasive. In this case, the wear resistance increases with increasing V and Nb contents. This behavior is primarily due to the change in hard material morphology (hard material enlargement). Here, the hard materials, due to the alloying of V and Nb, a sufficient hard material size and are no longer herausgespant from the composite material. Thus, the condition becomes

"Hard material diameter ≥ furrow width of the attacking abrasive".

As already mentioned, due to the coarsening of the hard materials and the associated increase in the free matrix path length, the specific internal one decreases Interface length between the added TiC particles and the metal matrix, which offers particular advantages in terms of corrosion protection and mechanical properties.

To evaluate the corrosion behavior, current density potential curves have been created. For this purpose, first corrosion samples have been produced. For this purpose, a wire was welded to the back of the completely heat-treated samples, which is needed for a conductive connection. These samples were then cold-embedded in nonconductive embedding agent (eg Technovit 5071, Heraeus Kulzer GmbH), whereby the exposed part of the wire was isolated. The sample surface was ground to a 1000 mesh grit with SiC abrasive paper to provide a consistent surface condition. The potting agent as well as the gap between sample and potting agent were sealed with varnish to minimize crevice corrosion and effects emanating from the potting agent. Since the current density is required for the creation of SPK, the conductive sample surface was measured using the a4i software from Aquinto.

The thus prepared samples were installed as a working electrode in a test stand. The counterelectrode consisted of a platinum plate, while the reference electrode was made of mercuric chloride and was spatially separated but electrically connected via a salt bridge in an external vessel. This separation was made to counteract contamination of the electrode and thus a falsification of the measurement results. Either 0.5 mol H2SO4 (5%) or 0.6 mol NaCl (3%) was used. All electrodes were connected to a potentiostat, which took over the regulation of the voltage and the measurement of the current.

Prior to measurement and after incorporation of the sample into the test stand, the sulfuric acid was purged with nitrogen (2 L / min) for 30 minutes to purge contained oxygen for comparability of results. Subsequently, the sample became cathodic for 60 s -1744 mV cathodized. This serves to remove impurities on the surface and at least a partial dissolution of the natural oxide layer. In the subsequent measurement of the resting potential for 30 min, the passive layer formed with the oxygen in the electrolyte and thus always under comparable conditions new.

Immediately afterwards, the actual measurement of the current density potential curve starts from just below the quiescent potential. Here, a potential change rate of 600 mV / h sample was applied and measured the adjusting between working and counter electrode current with respect to the reference electrode.

The hole corrosion behavior was determined in 0.6 molar NaCl solution. Since in most cases the actual pitting potential Upit, ie the potential indicating the onset of pitting corrosion at the beginning of the steep rise of the potential curve, could not be determined correctly, based on the currently valid standards ASTM G-150-99 and DIN-50905- 2 introduced the breakthrough potential as a benchmark. This value was read at the location of the curve, from which the current density is constant> 100 μA / cm ² .

In Fig. 4 the measured curves determined for the V-containing samples and the sample alloyed neither with V nor Nb are shown for the determination of the breakdown potential (at 100 μA / cm ² ). It can be seen that as the V content increases, the breakdown potential is shifted in the direction of higher potentials and therefore the corrosion resistance (in this case compared with NaCl) increases.

Thus, with the invention, the interdiffusion process between hard materials, such as TiC, and the metal matrix occurring during the alloying of a connecting element, in particular during the alloying of Nb and V, can be used selectively during the compaction of materials containing hard materials. For this purpose, the metal matrix is targeted with sufficient levels Enriched alloying elements that interact chemically during the material compaction with the hard materials and possibly cause the formation of new phases.

The alloying-in of hard materials by alloying elements according to the invention from the metal matrix during the production of the Fe base material according to the invention thus makes it possible to influence the hard material properties in a targeted manner. The result is improved material properties compared to conventionally produced hard composite materials. The invention focuses on the use of TiC hard materials that are available in sufficient quantities and sustainable.

The inventive MMC-Fe base material can be produced in a particularly cost-effective manner if the TiC contained in it is at least partially obtained by recycling Ti-containing Fe base materials. A method of recycling such materials is in the EP 2 678 455 B1 described. Table 1 material Cr Co Ni Not a word Nb V TiC Nikro128 13.5 9 4 5 0 0 30 Nikro128 + 1Nb 13.5 9 4 5 1 0 30 Nikro128 + 2Nb 13.5 9 4 5 2 0 30 Nikro128 + 3Nb 13.5 9 4 5 3 0 30 Nikro128 + 4Nb 13.5 9 4 5 4 0 30 Nikro128 + 1V 13.5 9 4 5 0 1 30 Nikro128 + 2V 13.5 9 4 5 0 2 30 Nikro128 + 3V 13.5 9 4 5 0 3 30 Nikro128 + 4V 13.5 9 4 5 0 4 30 Data in% by mass, remainder iron and inevitable impurities due to production material Hard particle diameter [μm] Hard particle size [μm ² ] Volume fraction [%] particle number Nikro128 2,993 ± 0.211 7.07 ± 1.00 44.54 ± 3.46 910 Nikro128 + 1V 6.152 ± 1.017 30.54 ± 10.16 46.13 ± 3.64 235 Nikro128 + 2V 4.913 ± 0.629 19.27 ± 4.94 41.15 ± 4.36 318 Nikro128 + 3V 5,583 ± 0.720 24.89 ± 6.17 43.40 ± 3.04 262 Nikro128 + 4V 6.408 ± 0.742 32.69 ± 7.71 46.45 ± 3.34 210 sample Ti Not a word Nb / V C Nikro128 48.53 ± 0.31 2,11 ± 0,19 0 48.64 ± 2.56 Nikro128 + 1Nb 49.01 ± 1.41 2.34 ± 0.40 1.36 ± 0.65 47.25 ± 0.86 Nikro128 + 2Nb 47.68 ± 2.38 1.89 ± 0.58 2.09 ± 0.91 48.30 ± 1.10 Nikro128 + 3Nb 46.82 ± 1.20 1.70 ± 0.20 3.26 ± 0.67 48.25 ± 0.77 Nikro128 + 4Nb 46.69 ± 1.00 1.44 ± 0.13 4.16 ± 0.56 47.69 ± 0.73 Nikro128 + 1V 48.42 ± 0.38 2.18 ± 0.32 0.79 ± 0.11 48.07 ± 0.86 Nikro128 + 2V 48.17 ± 019 1.92 ± 0.2 1.3 ± 0.07 48.08 ± 1.1 Nikro128 + 3V 48.36 ± 1.01 1.99 ± 012 2.07 ± 0.29 46.86 ± 0.77 Nikro128 + 4V 47.71 ± 0.11 1.78 ± 0.17 2.32 ± 0.15 47.67 ± 0.73 Data in% by mass material Hardness [GPa] Modulus of elasticity [GPa] Nikro128 33.63 518.61 Nirko128 + 1Nb 35.13 522.39 Nikro128 + 2Nb 37.46 539.96 Nikro128 + 3Nb 34.46 515.84 Nirko128 + 4Nb 34.92 523.91 Nirko128 + 1V 34.92 534.24 Nikro128 + 2V 35.44 514.72 Nikro128 + 3V 35.44 504.19 Nikro128 + 4V 34.79 520.53

Claims (15)

Fe base material consisting of an iron-based matrix and hard particles embedded in this matrix, - where the Fe base material consists of (in% by mass)
up to 1.0% C,
2.0 - 25.0% Cr,
0.5 - 7% Mo,
at least one connecting element added to the matrix for binding the hard material particles, which belongs to the transition elements of the 4th to 6th subgroups of the Periodic Table of the Elements, in contents of 0.5% to 5.0% in each case,
optional up to 12% Co,
optional up to 18% Ni,
as well as 20 - 40% TiC hard material particles
and
as the remainder of iron and production-related unavoidable impurities
exists, and - Where in the hard material particles Ti atoms are substituted by atoms of the respective at least one existing in the matrix attachment element. Fe-base material according to claim 1, characterized in that the connection element belongs to the group "Zr, Hf, Nb, Ta, V, W". Fe-base material according to claim 2, characterized in that the connecting elements Nb or V are. Fe base material according to claim 3, characterized in that the contents of Nb, if present, are 1 to 4.0% by mass. Fe-base material according to claim 2, characterized in that the contents of V, if present, 1 to 4.0% by mass. Fe-base material according to one of the preceding claims, characterized in that (in% by mass) its C content is in the range of impurities and its Cr content is 12.5-14.5%, its Mo content is 4.5 - 5.5%, its Co content is 8.0-10.0%, its Ni content is 3.5-4.5% and its TiC content is 27-33%. A method for producing an Fe base material formed according to any one of claims 1 to 6, comprising the following steps: a) providing a powder mixture, consisting of a powder consisting of (in% by mass) up to 0.8% C, 0.5-25% Cr, 0.5-7% Mo, at least one for bonding the particles of hard material to the matrix of Fe, Base material added attachment element, which the transition elements of the 4th to 6. Subgroup of the Periodic Table of the Elements belongs, in contents of 0.5 - 5.0%, optionally up to 12% Co, optionally up to 18% Ni and the balance of iron and production-related unavoidable impurities, and mixed with a hard material powder consisting of TiC hard material particles, - wherein the proportion of TiC hard material particles in the powder mixture is 20 - 40 mass%; b) compacting the powder mixture into a solid Fe base material block; c) heat treating the Fe base material block, wherein the heat treatment comprises solution annealing for a period of 1 to 4 hours at a temperature of 800 to 1100 ° C. A method according to claim 7, characterized in that the compacting (step b)) is performed as a sintering process. A method according to claim 8, characterized in that the sintering is carried out under pressure. A method according to claim 8 or 9, characterized in that the sintering is carried out with liquid phase. Method according to one of claims 8 to 10, characterized in that the sintering is carried out as hot isostatic pressing. Method according to one of claims 7 to 11, characterized in that in the course of the heat treatment (step c)) carried out solution annealing is carried out under vacuum. Method according to one of claims 7 to 12, characterized in that the Fe base material block is quenched after the solution annealing carried out in the course of the heat treatment (step c)). A method according to claim 13, characterized in that for quenching nitrogen is blown with a pressure of 1 - 4.5 bar on the Fe base material block. Method according to one of claims 7 - 14, characterized in that the Fe base material block to complete the heat treatment (step c)) is subjected to tempering at 100 - 550 ° C for a period of 1-8 hours.

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