EP3228724A1 - Method for setting the thermal conductivity of a steel, tool steel, in particular hot-work steel, and steel object - Google Patents

Abstract

The present invention relates to a tool steel, in particular a hot work tool, having the following composition: 0.26 to 0.55 wt .-% C; <2% by weight Cr; 0 to 10% by weight of Mo; 0 to 15 wt% W; wherein the content of W and Mo in the sum of 1.8 to 15 wt .-% is; carbide-forming elements Ti, Zr, Hf, Nb, Ta with a content of 0 to 3 wt .-%, individually or in total; 0 to 4% by weight V; 0 to 6% by weight of Co; 0 to 1.6% by weight of Si; 0 to 2% by weight of Mn; 0 to 2.99% by weight of Ni; 0 to 1% by weight of S; Remainder: iron and unavoidable impurities. The hot-work steel has a much higher thermal conductivity compared to known tool steels.

Description

The present invention relates to a method for adjusting the thermal conductivity of a steel, to a tool steel, in particular hot-work tool steel, and to a use of a tool steel. Moreover, the present invention relates to a steel article.

Hot-work tool steels are alloyed tool steels, which in addition to iron as alloying elements contain in particular carbon, chromium, tungsten, silicon, nickel, molybdenum, manganese, vanadium and cobalt with different proportions.

Hot work tool steels may be used to make hot work steel objects, such as tools, which are suitable for machining materials, in particular die casting, extrusion or die forging. Examples of such tools are extrusion dies, forging tools, die casting dies, press dies, or the like, which must have special mechanical strength properties at high working temperatures. Another field of application for hot working steels are tools for the injection molding of plastics.

An essential functionality of tool steels, in particular of hot-work steels, and of steel articles manufactured therefrom, is a sufficient dissipation of previously introduced when used in industrial processes or to ensure heat generated in the process itself.

Hot work tools, which are made of a hot-work steel, must have a high thermal conductivity and a high heat wear resistance in addition to a high mechanical stability at higher working temperatures. Other important properties of hot-work steels are not only a sufficient hardness and strength but also a high hot hardness and high wear resistance at high working temperatures.

A high thermal conductivity of the used for the production of tools hot-work steel is for some applications of particular importance, as this can cause a significant cycle time reduction. Since the operation of hot forming devices for hot working of workpieces is relatively expensive, a significant cost saving can be achieved by reducing the cycle times. A high thermal conductivity of hot-work steel is also advantageous in high-pressure casting, since the casting molds used there have a much longer life due to a greatly increased thermal fatigue strength.

The tool steels commonly used to make tools typically have a thermal conductivity on the order of about 18 to 24 W / mK at room temperature. In general, the thermal conductivities of the hot working steels known from the prior art are about 16 to 37 W / mK.

• 0,30 bis 0,55 Gew.-% C;
• weniger als 0,90 Gew.-% Si;
• bis 1,0 Gew.-% Mn;
• 2,0 bis 4,0 Gew.-% Cr;
• 3,5 bis 7 Gew.-% Mo;
• 0,3 bis 1,5 Gew.-% eines oder mehrerer der Elemente Vanadium, Titan und Niob.

From the EP 0 632 139 A1 For example, a hot-working steel is known which has a comparatively high thermal conductivity of more than 35 W / mK at temperatures up to about 1100 ° C. The one from this Document known hot-work tool steel contains in addition to iron and unavoidable impurities:

• 0.30 to 0.55 wt% C;
• less than 0.90% by weight of Si;
• to 1.0% by weight of Mn;
• 2.0 to 4.0% by weight Cr;
• 3.5 to 7 wt% Mo;
• 0.3 to 1.5 wt .-% of one or more of the elements vanadium, titanium and niobium.

Conventional hot working tool steels typically have a chromium content of more than 2% by weight. Chromium is a comparatively inexpensive carbide former and also provides the hot work tool steel with good oxidation resistance. Further, chromium forms very thin secondary carbides, so that the mechanical strength to toughness ratio is very good in the conventional hot working tool steels.

From the German patent DE 1014577 B1 For example, a method of making hot work tools using a hardening steel alloy is known. More particularly, this patent relates to a process for the manufacture of thermoset hot working tools, especially dies for hot forging, having high crack and fracture strength and high yield strength under static compressive stresses in the heat. In addition, the hot-forming steels described in this document are characterized by a simple, relatively inexpensive chemical composition (0.15-0.30% C, 3.25-3.50% Mo, no chromium) and easy to heat-treat. The most important thing here is the optimal process for the production received from hot press matrices including the associated annealing treatments (curing). Special properties depending on the chemical composition are not explained.

The CH 481222 refers to a chromium-molybdenum-vanadium-alloyed hot work tool steel with good cold insensitivity for making tools such as dies and dies. It should be noted that the tuning of the alloying elements - especially chromium (1.00 to 3.50% Cr), molybdenum (0.50 to 2.00% Mo) and vanadium (0.10 to 0.30% V) - Has a decisive influence on the desired properties, such as a low heat resistance (55 kp / mm ² ), good flow properties, good thermal conductivity and so on.

The Japanese publication JP 4147706 deals with improving the wear resistance of spikes for the production of seamless steel tubes by the geometry of the mandrel and by the chemical composition of the alloy (0.1 to 0.4% C, 0.2 to 2.0% Mn, 0 to 0 , 95% Cr, 0.5 to 5.0% Mo, 0.5 to 5.0% W). Special measures to increase the thermal conductivity of the steel are not the subject of this document.

The Japanese publication JP 2004183008 describes a low-cost ferritic-pearlitic steel alloy of tools (0.25 to 0.45% C, 0.5 to 2.0% Mn, 0 to 0.5% Cr) for the casting of plastics. The focus is on the optimum ratio of processability and thermal thermal conductivity.

The Indian JP 2003253383 described steel includes a precured tool steel for plastic casting with ferritic-pearlitic basic structure (0.1 to 0.3% C, 0.5 to 2.0% Mn, 0.2 to 2.5% Cr, 0 to 0.15% Mo, 0.01 to 0.25% V), in which the excellent workability and weldability are in the foreground.

In order to increase the Ac1 transformation temperature in a tool steel characterized by a high surface temperature during rolling as well as to set excellent processability and low yield stress, in the JP 9049067 a specification of the chemical composition (0.05 to 0.55% C, 0.10 to 2.50% Mn, 0 to 3.00% Cr, 0 to 1.50% Mo, 0 to 0.50% V) and in particular the increase of the silicon content (0.50 to 2.50% Si) proposed.

The publication CH 165893 relates to an iron alloy which is particularly suitable for hot working tools (dies, dies or the like) and has a low-chromium (up to chromium-free) and tungsten cobalt nickel-containing (preferably with additions of molybdenum and vanadium) chemical composition. The reduced chromium content or the complete abandonment of chromium as an alloying element is held responsible for significant property improvements and the combination of positive alloy properties. It was found that even slight reductions in the chromium content have a significantly greater influence on the desired properties (for example, a high hot tensile strength, toughness and insensitivity to temperature fluctuations and thus a good thermal conductivity) than the addition of large amounts of W, Co and Ni.

From the European patent EP 0787813 B1 is a heat resistant ferritic steel with a low Cr and Mn content and with excellent strength at high temperatures Temperatures known. The purpose of the invention disclosed in the aforementioned document was to provide a heat-resistant, low chromium ferritic steel having improved creep rupture strength under the conditions of long time periods at high temperatures as well as improved toughness, machinability and weldability even with thick products having. The description of alloying influences on carbide formation (coarsening), precipitation and solid solution strengthening highlights the need to stabilize the structure of the ferritic steel. The reduction of the Cr content to less than 3.5% is attributed to the suppressed lowering of the creep rupture strength due to the coarsening of Cr carbides at temperatures above 550 ° C, and to the improvement of toughness, workability and thermal conductivity. However, at least 0.8% Cr is considered a prerequisite for maintaining the oxidation and corrosion toughness of the steel at high temperatures.

From the DE 19508947 A1 is a wear-resistant, temper-resistant and heat-resistant alloy known. In particular, this alloy is intended for use in hot work tools in hot forming and hot forming and is characterized by very high molybdenum contents (10 to 35%) and tungsten contents (20 to 50%). Furthermore, the invention described in the above-mentioned document relates to a simple and cost-effective method for the production in which the alloy is first produced from the melt or by powder metallurgy. The content of Mo and W in such large amounts is substantiated by the increase in tempering resistance and hot strength by solid-solution hardening and by the formation of carbides (or intermetallic phases). In addition, molybdenum increases the Thermal conductivity and reduces the thermal expansion of the alloy. Finally, in this document, the suitability of the alloy for the production of surface layers on bases of other composition explained (laser, electron, plasma jet, surfacing).

The German patent DE 4321433 C1 relates to a steel for hot work tools, such as those used for the primary forming, forming and machining of materials (especially in die casting, extrusion, drop forging or as a shear blade) at temperatures up to 1100 ° C. It is characteristic that the steel in the temperature range of 400 to 600 ° C has a thermal conductivity of over 35 W / mK (although this generally decreases with increasing alloy content) and at the same time has a high wear resistance (tensile strength over 700 N / mm ² ). The very good thermal conductivity is attributed on the one hand to the increased molybdenum content (3.5 to 7.0% Mo) and, on the other hand, to a maximum chromium content of 4.0%.

The JP 61030654 relates to the use of a steel with high hot crack and hot break strength and high thermal conductivity as a material for the production of shells for rolls in continuous aluminum casting plants. Here, too, the opposing tendencies in influencing the hot cracking or hot breaking strength and the thermal conductivity through the alloy composition are discussed. Silicon contents above 0.3% and chromium contents above 4.5% are considered to be particularly disadvantageous in terms of thermal conductivity. Possible procedures for setting a hardened martensitic microstructure of the roll shells produced from the steel alloy according to the invention are listed.

The EP 1300482 B1 relates to a hot working steel, in particular for tools for forming at elevated temperatures, with the simultaneous occurrence of the properties: increased hardness, strength and toughness and good thermal conductivity, improved wear resistance at elevated temperatures and service life extension under impact loads. It is shown that by certain concentrations within narrow limits of carbon (0.451 to 0.598% C) as well as special carbide and monocarbide forming elements (4.21 to 4.98% Cr, 2.81 to 3.29% Mo, 0.41 to 0.69% V) promoted a desired Mischkristallhärtbarkeit thermal annealing and a carbide curing or a hardness increasing excretion of coarser carbides at the expense of matrix hardness can be largely suppressed. An improvement of the thermal conductivity by a reduction of the carbide content could be based on an interface kinetics and / or on the properties of the carbides.

A disadvantage of the tool steels known from the prior art, in particular hot working steels, and the steel articles produced therefrom is that they have only insufficient thermal conductivity for some fields of application. Furthermore, it has not been possible to adjust the thermal conductivity of a steel, in particular a hot-work tool, targeted and thus defined to adapt to the particular application.

This is where the present invention sets and makes it its task to provide a method by means of which a targeted adjustment of the thermal conductivity of a steel, in particular a hot-work tool steel, can be achieved. Moreover, the object of the present invention is to provide a tool steel, in particular a hot-work tool steel, and to provide a steel article having a higher thermal conductivity than the tool steels known from the prior art (in particular hot-work tool steels) or steel articles.

This object is achieved with regard to the method by a method having the features of claim 1 and by a method having the features of claim 2. With regard to the tool steel, the object underlying the present invention by a tool steel (especially hot work tool steel) having the features of claim 4, by a tool steel (in particular hot work tool steel) with the features of claim 5 and by a tool steel (in particular hot work tool steel) with the features of Claim 6 solved. With respect to the steel article, the object underlying the present invention is achieved by a steel article having the features of claim 25. The subclaims relate to advantageous developments of the invention.

According to claim 1, an inventive method for adjusting the thermal conductivity of a steel, in particular a hot-work steel, characterized in that an inner structure of the structure defined steel is generated metallurgically, the carbide components have a defined electron and phonon density and / or their crystal structure by a specifically generated lattice defects have certain mean free path for the phonon and electron flow. An advantage of the solution according to the invention is that the thermal conductivity of a steel can be tailored to the desired size by defining the internal structure of the steel in the manner defined above metallurgically is produced. The method according to the invention is suitable, for example, for tool and hot-work tool steels.

According to claim 2, a method according to the invention for adjusting, in particular for increasing the thermal conductivity of a steel, in particular a hot-work steel, characterized in that an inner structure structure of the steel defined metallurgically generated, which has an increased electron and phonon density in their carbide components and or which has an increased mean free path for the phonon and electron flow due to a low defect content in the crystal structure of the carbides and the surrounding metallic matrix. By this measure, the thermal conductivity of a steel compared to the known from the prior art steels can be set in a defined manner and in particular significantly increased compared to the known hot-work steels.

In a preferred embodiment, the heat conductivity of the steel at room temperature can be set to more than 42 W / mK, preferably to more than 48 W / mK, in particular to more than 55 W / mK.

• 0,26 bis 0,55 Gew.-% C;
• < 2 Gew.-% Cr;
• 0 bis 10 Gew.-% Mo;
• 0 bis 15 Gew.-% W;
• wobei der Gehalt von W und Mo in der Summe 1,8 bis 15 Gew.-% beträgt;
• karbidbildende Elemente Ti, Zr, Hf, Nb, Ta mit einem Gehalt von 0 bis 3 Gew.-% einzeln oder in der Summe;
• 0 bis 4 Gew.- % V;
• 0 bis 6 Gew.-% Co;
• 0 bis 1,6% Gew.-% Si;
• 0 bis 2 Gew.-% Mn;
• 0 bis 2,99 Gew.-% Ni;
• 0 bis 1 Gew.-% S;
• Rest: Eisen und unvermeidbare Verunreinigungen.

According to claim 4, a tool steel according to the invention, in particular hot-work steel, is characterized by the following composition:

• 0.26 to 0.55 wt% C;
• <2% by weight Cr;
• 0 to 10% by weight of Mo;
• 0 to 15 wt% W;
• wherein the content of W and Mo in the sum of 1.8 to 15 wt .-% is;
• carbide-forming elements Ti, Zr, Hf, Nb, Ta with a content of 0 to 3 wt .-%, individually or in total;
• 0 to 4% by weight V;
• 0 to 6% by weight of Co;
• 0 to 1.6% by weight of Si;
• 0 to 2% by weight of Mn;
• 0 to 2.99% by weight of Ni;
• 0 to 1% by weight of S;
• Remainder: iron and unavoidable impurities.

Since it has been shown that carbon can be replaced at least partially by so-called carbon-equivalent constituents nitrogen (N) and boron (B), a tool steel, in particular hot-work steel, with the features of claim 5 or with the features of claim 6, the having the chemical compositions listed below, an equivalent solution to the underlying object of the present invention.

• 0,25 bis 1,00 Gew.-% C und N in der Summe;
• < 2 Gew.-% Cr;
• 0 bis 10 Gew.-% Mo;
• 0 bis 15 Gew.-% W;
• wobei der Gehalt von W und Mo in der Summe 1,8 bis 15 Gew.-% beträgt;
• karbidbildende Elemente Ti, Zr, Hf, Nb, Ta mit einem Gehalt von 0 bis 3 Gew.-% einzeln oder in der Summe;
• 0 bis 4 Gew.- % V;
• 0 bis 6 Gew.-% Co;
• 0 bis 1,6% Gew.-% Si;
• 0 bis 2 Gew.-% Mn;
• 0 bis 2,99 Gew.-% Ni;
• 0 bis 1 Gew.-% S;
• Rest: Eisen und unvermeidbare Verunreinigungen.

According to claim 5, a tool steel according to the invention, in particular hot-work steel, is characterized by the following composition:

• 0.25 to 1.00% by weight of C and N in total;
• <2% by weight Cr;
• 0 to 10% by weight of Mo;
• 0 to 15 wt% W;
• wherein the content of W and Mo in the sum of 1.8 to 15 wt .-% is;
• carbide-forming elements Ti, Zr, Hf, Nb, Ta with a content of 0 to 3 wt .-%, individually or in total;
• 0 to 4% by weight V;
• 0 to 6% by weight of Co;
• 0 to 1.6% by weight of Si;
• 0 to 2% by weight of Mn;
• 0 to 2.99% by weight of Ni;
• 0 to 1% by weight of S;
• Remainder: iron and unavoidable impurities.

• 0,25 bis 1,00 Gew.-% C, N und B in der Summe;
• < 2 Gew.-% Cr;
• 0 bis 10 Gew.-% Mo;
• 0 bis 15 Gew.-% W;
• wobei der Gehalt von W und Mo in der Summe 1,8 bis 15 Gew.-% beträgt;
• karbidbildende Elemente Ti, Zr, Hf, Nb, Ta mit einem Gehalt von 0 bis 3 Gew.-% einzeln oder in der Summe;
• 0 bis 4 Gew.- % V;
• 0 bis 6 Gew.-% Co;
• 0 bis 1,6% Gew.-% Si;
• 0 bis 2 Gew.-% Mn;
• 0 bis 2,99 Gew.-% Ni;
• 0 bis 1 Gew.-% S;
• Rest: Eisen und unvermeidbare Verunreinigungen.

According to claim 6, a further tool steel according to the invention, in particular hot-work steel, is characterized by the following composition:

• 0.25 to 1.00% by weight of C, N and B in the sum;
• <2% by weight Cr;
• 0 to 10% by weight of Mo;
• 0 to 15 wt% W;
• wherein the content of W and Mo in the sum of 1.8 to 15 wt .-% is;
• carbide-forming elements Ti, Zr, Hf, Nb, Ta with a content of 0 to 3 wt .-%, individually or in total;
• 0 to 4% by weight V;
• 0 to 6% by weight of Co;
• 0 to 1.6% by weight of Si;
• 0 to 2% by weight of Mn;
• 0 to 2.99% by weight of Ni;
• 0 to 1% by weight of S;
• Remainder: iron and unavoidable impurities.

The particular advantage of the tool steels according to the invention consists primarily in the drastically increased thermal conductivity in comparison to the tool and hot working steels known from the prior art. It is clear that the tool steel according to the invention in addition to iron as the main component the elements C (or C and N according to claim 5 and C, N and B according to claim 6), Cr, Mo and W in the above-mentioned ranges and unavoidable impurities. The other alloying elements (alloying accompanying elements) are thus optional components of the tool steel, since their content may possibly also be 0% by weight.

An essential aspect of the solution described here is to keep carbon and preferably also chromium in the solid solution state largely out of the steel matrix and to replace the Fe ₃ C carbides by carbides with higher thermal conductivity. Chromium can only be kept out of the matrix by not being present at all. Carbon can be bound in particular with carbide formers, where Mo and W are the most cost-effective elements and have a comparatively high thermal conductivity both as elements and as carbides.

Quantum mechanical simulation models for tool steels and in particular for hot working steels can show that solid state carbon and chromium lead to matrix distortion, resulting in a shortening of the mean free path of phonons. A larger elastic modulus and a higher thermal expansion coefficient are the result. The influence of carbon on electron and phonon scattering has also been investigated using suitable simulation models. Thus, the advantages of a carbon-chromium-depleted matrix could be verified by increasing the thermal conductivity. While the thermal conductivity of the matrix is dominated by electron flow, the conductivity of the carbides is determined by the phonons. In the solid solution state, chromium has a very negative effect on the thermal conductivity achieved by electron flow.

The tool steels according to the invention (in particular hot working steels) according to claims 4, 5 and 6 can have a thermal conductivity at room temperature of more than 42 W / mK, preferably a thermal conductivity of more than 48 W / mK, in particular a thermal conductivity of more than 55 W / mK , Surprisingly, it has been found that thermal conductivities in the order of more than 50, in particular about 55 to 60 W / mK and even beyond can be achieved. The thermal conductivity of the hot work steel according to the invention can thus be almost twice as large as in the known from the prior art hot working steels. Thus, the steel described here is particularly suitable for applications in which a high thermal conductivity is required. In the drastically improved thermal conductivity thus there is the particular advantage of the tool steel according to the invention over the solutions known from the prior art.

In a particularly advantageous embodiment, the thermal conductivity of the tool steel is adjustable by a method according to one of claims 1 to 3. As a result, the thermal conductivity of the tool steel can be specifically adapted and adjusted to the specific application.

Optionally, the tool steel may contain the carbide-forming elements Ti, Zr, Hf, Nb, Ta individually or in a proportion of up to 3% by weight. The elements Ti, Zr, Hf, Nb, Ta are known in metallurgy as strong carbide formers. Strong carbide formers have been found to be beneficial in increasing the thermal conductivity of the tool steel as they have a better ability to remove solid state carbon from the matrix. Carbides with a high Thermal conductivity can further increase the conductivity of the tool steel. It is known from metallurgy that the following elements are carbide formers, the carbon affinity of which is listed below in ascending order: Cr, W, Mo, V, Ti, Nb, Ta, Zr, Hf.

Particularly advantageous in this context is the generation of relatively large and thus long extended carbides, since the entire thermal conductivity of the tool steel follows a law of mixing with negative limit effects. The stronger the affinity of an element for carbon, the greater the tendency to form relatively large primary carbides. However, the large carbides have a certain adverse effect on some mechanical properties of the tool steel, in particular on its toughness, so that a suitable compromise between the desired mechanical and thermal properties must be found for each intended use of the tool steel.

Optionally, the tool steel may contain the alloying element vanadium at a level of up to 4% by weight. As explained above, vanadium accounts for fine carbide networks. As a result, numerous mechanical properties of the tool steel can be improved for some applications. Vanadium is characterized not only by its higher carbon affinity compared to molybdenum, but also has the advantage that its carbides have a higher thermal conductivity. In addition, vanadium is a relatively inexpensive element. A disadvantage of vanadium over molybdenum, however, is that the vanadium remaining in the solid solution state has a comparatively much greater negative effect on the thermal conductivity of the tool steel. For this reason, it is not advantageous to alloy the tool steel with vanadium alone.

Optionally, the tool steel may contain one or more solid solution strengthening elements, in particular Co, Ni, Si and / or Mn. Thus, there is optionally the possibility that the tool steel Mn has a content of up to 2% by weight. In order to improve the high-temperature strength of the tool steel, for example, depending on the concrete application, a content of up to 6 wt% Co may be advantageous. In a further preferred embodiment, the tool steel may have Co with a content of up to 3% by weight, preferably with a content of up to 2% by weight.

In order to increase the toughness of the tool steel at low temperatures, it may optionally be provided that the hot working steel has Si content of up to 1.6% by weight.

In order to improve the machinability of the tool steel, the tool steel may optionally contain sulfur S at a level of up to 1% by weight.

In order to facilitate the basic understanding of the present invention, some essential aspects of the novel metallurgical design strategy for tool steels with high thermal conductivity (hot working steels), which is also the basis of the method according to the invention, will be explained in more detail below.

For a given cross section through a metallographically prepared sample of a tool steel made in Fig. 1 is shown schematically, it is possible in a light or scanning electron microscopic observation of the microstructural structure structure by means of optical image analysis techniques, the area fractions of the carbides A _c and the matrix material Am to be quantified. The large-area carbides are referred to as primary carbides 1 and the small-area carbides as secondary carbides 2. The matrix material shown in the background is shown in FIG Fig. 1 denoted by the reference numeral 3.

Neglecting other microstructure constituents (for example inclusions), the surface area of the entire surface A _{tot of} the tool steel can be determined to a good approximation according to the following equation: $${\mathrm{A}}_{\mathrm{dead}}={\mathrm{A}}_{\mathrm{m}}+{\mathrm{A}}_{\mathrm{c}}$$

By a simple mathematical reformulation one obtains the following equation; $$\left({\mathrm{A}}_{\mathrm{m}}/{\mathrm{A}}_{\mathrm{dead}}\right)+\left({\mathrm{A}}_{\mathrm{c}}/{\mathrm{A}}_{\mathrm{dead}}\right)=\mathrm{1}$$

The summands of this equation are suitable as weighting factors for a mixture control approach.

λ_m ist dabei die Wärmeleitfähigkeit des Matrixmaterials 3 und λ_c ist die Wärmeleitfähigkeit der Karbide 1, 2.Assuming now that the matrix material 3 and the carbides 1, 2 have different properties with regard to their thermal conductivity, the overall integral thermal conductivity λ _{int of} this system can be described by such a mixture control approach as follows: $${\mathrm{\lambda }}_{\mathrm{int}}=\left({\mathrm{A}}_{\mathrm{m}}/{\mathrm{A}}_{\mathrm{dead}}\right)*{\mathrm{\lambda }}_{\mathrm{m}}+\left({\mathrm{A}}_{\mathrm{c}}/{\mathrm{A}}_{\mathrm{dead}}\right)*{\mathrm{\lambda }}_{\mathrm{c}}$$

λ _m is the thermal conductivity of the matrix material 3 and λ _c is the thermal conductivity of the carbides 1, 2.

This formulation undoubtedly represents a simplified system vision, but quite suitable for the phenomenological understanding of the present invention.

For example, a more realistic mathematical modeling of the integral thermal conductivity of the overall system can be accomplished using so-called Effective-Medium Theories (EMT). With such an approach, the microstructural composition of the tool steel is described as a composite system consisting of the carbide properties imaging spherical individual structural elements with isotropic thermal conductivity, which are embedded in a matrix material with different, but also isotropic thermal conductivity: $${\mathrm{\lambda }}_{\mathrm{int}}={\mathrm{\lambda }}_{\mathrm{m}}+{\mathrm{f}}_{\mathrm{c}}*{\mathrm{\lambda }}_{\mathrm{int}}*(\mathrm{3}*\left({\mathrm{\lambda }}_{\mathrm{c}}-{\mathrm{\lambda }}_{\mathrm{m}}\right)/\left(\mathrm{2}*{\mathrm{\lambda }}_{\mathrm{int}}+{\mathrm{\lambda }}_{\mathrm{c}}\right)$$

In this equation, f _{c describes} the volume fraction of carbides1, 2.

However, this equation is not uniquely solvable and therefore only limited for a targeted system design usable. When it comes to maximizing the system thermal conductivity λ _int , it can basically be deduced from the previously formulated mixture rules that such a maximization of the system thermal conductivity λ _{int can} be achieved if the thermal conductivities of the individual system components λ _c and λ _m succeed be maximized.

For the present invention, it is of particular importance that the volume fraction of the carbides f _c ultimately decides which of the two heat conductivities A _c and λ _{m is more} relevant.

The amount of carbides is ultimately defined by the application-specific mechanical resistance requirements and in particular the wear resistance of the tool steel. Thus, especially with regard to the carbide structure for the different main fields of application of the inventively developed tool steels quite different design specifications.

In the field of die-cast aluminum, the wear stress due to contact-bonded wear mechanisms, in particular due to abrasion, is only relatively small. The presence of large-area primary carbides as highly wear-resistant microstructural components is therefore not absolutely necessary. Thus, the volume fraction of carbides f _{c is determined} mainly by the secondary carbides. The amount of f _c is therefore relatively small.

In hot sheet forming, which also includes the conceptual variants of press hardening and mold hardening, the tools are subject to high stress due to contact-bonded wear mechanisms both in adhesive and in abrasive form. Therefore, large area primary carbides are highly desirable because they can increase resistance to these wear mechanisms. The consequence of such a primary carbide-rich microstructure is a high amount of f _c .

Regardless of the carbide structure, the ultimate goal is to maximize the thermal conductivity of all system components. However, the application-specific design specifications for the carbide development result in a weighting of the influence of the thermal conductivities of the system components on the integral thermal conductivity of the overall system.

Even this approach differs drastically from the prior art, in which the thermal conductivity is always regarded as an integral physical material property. If it is a matter of the prior art to detect the influence of individual alloying elements on the thermal conductivity, then, significantly, this is always done by the determination of integral properties. The consideration of the influence of such alloying elements on the microstructural manifestation, ie on the carbide structure and on the matrix and the resulting physical property changes for these microstructural system elements, has hitherto been nonexistent and therefore never a starting point of a metallurgical design concept for a tool steel in the prior art.

Under such integral design considerations, it has been found that a reduction in chromium content and an increase in molybdenum content result in an improvement in integral thermal conductivity. Tool steels developed according to such a metallurgical design approach usually have a thermal conductivity of 30 W / mK, which represents an increase of 25% compared to a thermal conductivity of 24 W / mK. Such an increase is already considered in the art as an effective property improvement.

So far, it has been assumed that a further reduction of the chromium content can not lead to a further significant improvement in the thermal conductivity. Since a further reduction in chromium content in addition to a reduction in the corrosion resistance of the hot-work tool steel, corresponding metallurgical formulations have not been further investigated and implemented with regard to the design of novel tool steels.

For the tool steels according to the invention with a composition according to claim 4, 5 or 6, a completely novel metallurgical concept was applied to achieve a drastically improved thermal conductivity, which is able to design in a precisely defined manner the thermal conductivity of the microstructural system components and thus the integral thermal conductivity drastically improve the tool steel. An important basic idea of the metallurgical concept presented here is that the preferred carbide formers are molybdenum and tungsten and that as a result already small amounts of chromium dissolved in these carbides due to the extension of the mean free path of the phonons by the resulting disturbances in the crystal structure of pure Carbides, the heat transfer properties are adversely affected.

With this novel metallurgical design approach, integral heat conductivities of hot working steels at room temperature of up to 66 W / mK and more can be achieved in an advantageous manner. This exceeds the rate of increase of all concepts known in the art by about ten times. None of the approaches found in the prior art provide a comparable reduction in chromium content for hot work tool steels with the objective of improving thermal conductivity.

For those cases in which a similar low chromium content is provided for the chemical composition described according to the invention, it is explicitly not an effect on the thermal conductivity, but about other functional objectives, such as in the JP 04147706 A the targeted formation of an oxidation layer on the steel surface by reducing the oxidation resistance in this area.

It is known in the art that the higher the purity content of a material, the higher its thermal conductivity. Any contamination - in the case of metallic materials also the addition of any alloying element - inevitably leads to a reduction of the thermal conductivity. For example, pure iron has a thermal conductivity of 80 W / mK, and slightly contaminated iron already has a thermal conductivity of less than 70 W / mK. Even the minimum addition of carbon (0.25% by volume) and other alloying elements, such as manganese (0.08% by volume), leads to a thermal conductivity of just 60 W / mK for steel.

Nevertheless, it is surprisingly possible with the procedure according to the invention to achieve heat conductivities of up to 70 W / mK despite the addition of further alloying elements such as, for example, molybdenum or tungsten. The reason for this unexpected effect is that according to the present invention, it is an objective not to dissolve carbon in the matrix as much as possible, but to bind it in the carbides by strong carbide formers and carbides with a high thermal conductivity to use.

Focusing now on the carbides, it is the phonon conductivity that ultimately dominates the thermal conductivity. If you want to improve this, then it is precisely at this point to intervene creatively. However, some carbides have a fairly high density of conductive electrons, particularly high metal content high melting carbides such as W6C or Mo3C. Recent research has found that even very small additions of chromium to even Such carbides lead to significant disturbances of the crystal lattice structure and thus lead to a drastic extension of the mean free path for the phonon flux. The result is a reduction in thermal conductivity. This leads to the clear conclusion that as far as possible a reduction of the chromium content leads to an improvement in the thermal conductivity of the tool steel.

In addition, molybdenum and tungsten should be considered as preferred carbide formers. Molybdenum is particularly preferred in this context because it is a much stronger carbide former than tungsten. The effect of depletion of molybdenum in the matrix results in improved electron conductivity in the matrix and thus contributes to a further improvement in the integral thermal conductivity of the overall system.

As mentioned above, too low a chromium content simultaneously leads to a reduction in the corrosion resistance of the tool steel. Although this may be disadvantageous for certain applications, the higher oxidation tendency for the main applications of the tool steel designed according to the invention does not represent a real functional disadvantage since additional corrosion protection effects and measures are part of existing operational processes anyway.

For example, in applications in aluminum die-casting, the liquid aluminum itself provides adequate corrosion protection. In the area of hot sheet forming, it is the surface edge layers of the tools that are nitrided for wear protection. Corrosion-protecting lubricants as well as coolants and release agents also play their part in corrosion protection. additionally For example, very thin protective layers can be applied by electroplating or by vacuum coating.

The use according to the invention of the tool steels described here (in particular hot work steels) as a material for producing steel objects, in particular hot working tools, provides numerous and sometimes extremely remarkable advantages in comparison to the hot working steels known from the prior art, which hitherto have been used as materials for corresponding hot work steel objects ,

The higher thermal conductivity of the tools produced from the tool steels according to the invention (in particular hot-work steels) allows, for example, a reduction in the cycle times during the machining / production of workpieces. Another advantage is a significant reduction of the surface temperature of the tool as well as the reduction of the surface temperature gradient, which has a considerable effect on the longevity of the tool. This is particularly the case when tool damage is primarily due to thermal fatigue, thermal shock or welding. This is the case in particular with regard to tools for aluminum die-casting applications.

It is also surprising that the remaining mechanical and / or thermal properties of the tool steels according to the invention (in particular hot-work steels) could either be improved or at least remain unchanged in comparison with the tool steels known from the prior art. For example, the modulus of elasticity could be reduced; the density of the tool steels according to the invention (in particular hot-work steels) could be increased in comparison to conventional ones Hot working steels increased and the thermal expansion coefficient could be reduced. For some applications, further improvements can be achieved, such as increased mechanical strength at high temperatures or increased wear resistance.

In a preferred embodiment, it is proposed that the tool steel has less than 1.5% by weight Cr, preferably less than 1% by weight Cr. In a particularly preferred embodiment, there is the possibility that the tool steel has less than 0.5% by weight Cr, preferably less than 0.2, in particular less than 0.1% by weight Cr.

As explained above, the presence of chromium in the solid solution state in the matrix of tool steel negatively affects its thermal conductivity. The intensity of this negative effect on thermal conductivity by increasing the chromium content in the tool steel is greatest for the interval of less than 0.4 wt% Cr. An interval graduation in the decrease in the intensity of adverse effect on the thermal conductivity of the tool steel is in the two intervals of more than 0.4 wt .-%, but less than 1 wt .-%, as well as more than 1 wt .-% and less than 2% by weight is preferred. For applications in which the oxidation resistance of the tool steel (hot work tool steel) plays a major role, for example, a balance of the demands made on the tool steel with regard to the thermal conductivity and the oxidation resistance and can be reflected in an optimized Gewichtsprozentanteit of chromium, be made. As a rule, a content of about 0.8% by weight of chromium provides the tool steel with good corrosion protection. It has been found that additives exceeding this content of about 0.8% by weight of chromium an undesirable dissolution of chromium in the carbides can result.

In a preferred embodiment, there is the possibility that the molybdenum content of the tool steel is from 0.5 to 7% by weight, in particular from 1 to 7% by weight. Among the less expensive carbide formers, molybdenum has a comparatively high carbon affinity. In addition, molybdenum carbides have a higher thermal conductivity than iron and chromium carbides. Furthermore, the adverse effect of molybdenum in the solid solution state on the thermal conductivity of the tool steel compared to chromium in the solid solution state is considerably lower. For these reasons, molybdenum is one of those carbide formers that are suitable for a large number of applications. However, for applications requiring high toughness, other carbide formers with smaller secondary carbides, such as vanadium (about 1-15 nm colonies versus up to 200 nm large colonies on molybdenum) are the more preferable choice.

Molybdenum can be replaced by tungsten in many applications. The carbon affinity of tungsten is slightly lower and the thermal conductivity of tungsten carbide is considerably larger.

In a further particularly advantageous embodiment, there is the possibility that the content of Mo, W and V in the sum is 2 to 10% by weight. The content of these three elements in the sum is in particular dependent on the desired number of carbides, that is, on the respective application requirements.

The impurities of the tool steel, in particular hot-work steel, may contain one or more of the elements Cu, P, Bi, Ca, As, Sn or Pb with a content of at most 1% by weight. individually or in total. In particular, Cu is in addition to Co, Ni, Si and Mn another suitable element for solid solution solidification, so that at least a small amount of Cu in the alloy may optionally be advantageous. In addition to S, which may optionally be present with a content of at most 1 wt .-%, also the elements Ca, Bi or As can simplify the workability of the tool steel.

Also of importance is the mechanical stability of the tool steel at high temperatures of the alloying carbides. In this context, for example, both Mo and W carbides are more advantageous than chromium and iron carbides in terms of mechanical stability and strength properties. Depletion of chromium, along with the reduction in carbon content in the matrix, results in improved thermal conductivity, especially when it is due to tungsten and / or molybdenum carbides.

The methods by which the tool steels presented here (in particular hot-work steels) are also produced play an important role in its thermal and mechanical properties. By a specific choice of the manufacturing process, the mechanical and / or thermal properties of the tool steel can thus be selectively varied and thereby adapted to the respective intended use.

The tool steels described in the context of the present invention can be produced, for example, by powder metallurgy (hot isostatic pressing). For example, it is also possible to produce a tool steel according to the invention by vacuum induction melting or by furnace melting. It has surprisingly been found that each selected Manufacturing process may affect the resulting carbide size, which in turn - as stated above - may have effects on the thermal conductivity and mechanical properties of the tool steel.

In addition, the tool steel can also be processed by per se known refining methods, such as VAR (Vacuum Arc Remelting), AOD (Argon Oxygen Decarburization), or so-called ESR (ESR: Electro Slag Remelting) processes.

Likewise, a tool steel according to the invention can be produced, for example, by sand or precision casting. It can be produced by hot pressing or another powder metallurgy process (sintering, cold pressing, isostatic pressing) and all these manufacturing processes with or without the use of thermomechanical processes (forging, rolling, extrusion). Also, less conventional manufacturing methods such as thixo casting, plasma or laser deposition and local sintering can be used. In order to produce objects with a composition which changes within the volume from the tool steel, the sintering of powder mixtures can be advantageously used.

The steel developed in the context of the present invention can also be used as a filler metal filler (for example in powder form for laser welding, as rod or profile for metal inert gas welding (MIG welding), metal active gas welding (MAG welding), tungsten inert gas welding ( TIG welding) or for welding with coated electrodes).

According to claim 24, a use of a tool steel, in particular a hot work tool according to one of claims 4 to 23 proposed as a material for producing a hot-worked steel article, in particular a hot working tool having a thermal conductivity at room temperature of more than 42 W / mK, preferably a thermal conductivity of more than 48 W / mK, in particular a thermal conductivity of more than 55 W / mK.

A steel article according to the invention is characterized by the features of claim 25 and consists at least in part of a tool steel, in particular of a hot-work tool steel, according to one of claims 4 to 23.

In an advantageous embodiment, there is the possibility that the steel article has a substantially constant thermal conductivity over its entire volume. In particular, the steel article in this embodiment can be made entirely of a tool steel, in particular a hot-work tool, according to one of claims 4 to 23.

In a particularly advantageous embodiment it can be provided that the steel article has an at least partially changing thermal conductivity.

According to a particularly advantageous embodiment, the steel article at room temperature at least in sections, a thermal conductivity of more than 42 W / mK, preferably have a thermal conductivity of more than 48 W / mK, in particular a thermal conductivity of more than 55 W / mK. The steel article may at room temperature over its entire volume, a thermal conductivity of more than 42 W / mK, preferably a thermal conductivity of more than 48 W / mK, in particular have a thermal conductivity of more than 55 W / mK.

The steel article may, in advantageous embodiments, be, for example, a forming tool in processes of pressure forming, shear forming, or bend forming metals, preferably in forging processes, drop forging processes, thixo forging processes, extrusion processes, extrusion processes, die bending processes, roll forming processes, or in flat, profile, and cast roll processes ,

The steel article may, in further advantageous embodiments, be a forming tool in processes of draw-forming and tensile-forming of metals, preferably in press-hardening processes, form-hardening processes, deep-drawing processes, stretch-drawing processes and neck-pulling processes.

For example, in further preferred embodiments, the steel article may be a forming tool in processes of forming metallic starting materials, preferably in die casting processes, vacuum die casting processes, thixocasting processes, cast roll processes, sintering processes, and hot isostatic pressing processes.

Furthermore, there is the possibility that the steel article is a shaping tool in processes of primary shaping of polymeric starting materials, preferably in injection molding processes, extrusion processes and extrusion blow molding processes, or a forming tool in processes of primary shaping of ceramic starting materials, preferably in sintering processes.

In a further preferred embodiment, the steel article may be a component for machines and plants for power generation and energy conversion, preferably for internal combustion engines, reactors, heat exchangers and generators.

Furthermore, there is the possibility that the steel object is a component for machines and plants of chemical engineering, preferably for chemical reactors.

Fig. 1

eine schematisch stark vereinfachte Konturdarstellung einer Karbidstruktur im mikrostrukturellen Querschnitt eines typischen Werkzeugstahls;

Fig. 2

die Abriebfestigkeit zweier Proben (F1 und F5) eines Warmarbeitsstahls gemäß der vorliegenden Erfindung im Vergleich zu herkömmlichen Werkzeugstählen;

Fig. 3

die Abhängigkeit der Wärmeleitfähigkeit vom Chromgehalt erfindungsgemäßer Werkzeugstähle (Warmarbeitsstähle), der für den Einsatz in Warmumformprozessen geeignet ist;

Fig. 4

die Abhängigkeit der Wärmeleitfähigkeit vom Chromgehalt für eine weitere Auswahl von Werkzeugstählen gemäß der vorliegenden Erfindung;

Fig. 5

eine Darstellung der über Wärmeleitung in einem beidseitigen Kontakt mit zwei Werkzeugstahlplatten erzielten Wärmeabfuhr in einem vorerwärmten Werkstück.

Further features and advantages of the present invention will become apparent from the following description of preferred examples with reference to the accompanying drawings. Show in it

Fig. 1

a schematically highly simplified contour representation of a carbide structure in the microstructural cross-section of a typical tool steel;

Fig. 2

the abrasion resistance of two samples (F1 and F5) of a hot work tool according to the present invention compared to conventional tool steels;

Fig. 3

the dependence of the thermal conductivity on the chromium content of tool steels according to the invention (hot working steels), which is suitable for use in hot forming processes;

Fig. 4

the dependence of the thermal conductivity on the chromium content for a further selection of tool steels according to the present invention;

Fig. 5

a representation of the heat conduction achieved in a two-sided contact with two tool steel plates heat dissipation in a preheated workpiece.

As an introduction, five examples of tool steels (hot working steels) suitable for different applications are explained in more detail

example 1

• 0,32 bis 0,5 Gew.-% C;
• weniger als 1 Gew.-% Cr;
• 0 bis 4 Gew.-% V;
• 0 bis 10 Gew.-%, insbesondere 3 bis 7 Gew.-% Mo;
• 0 bis 15 Gew.-%, insbesondere 2 bis 8 Gew.-% W;
• wobei der Gehalt von Mo und W in der Summe 5 bis 15 Gew.-% beträgt.

It has been found that, for the manufacture of tools (hot work tool steel articles) used for hot stamping steel sheets, the use of a hot work tool steel having the following composition is particularly advantageous:

• From 0.32 to 0.5% by weight of C;
• less than 1% by weight Cr;
• 0 to 4% by weight V;
• 0 to 10 wt .-%, in particular 3 to 7 wt .-% Mo;
• 0 to 15% by weight, in particular 2 to 8% by weight W;
• wherein the content of Mo and W in the sum of 5 to 15 wt .-% is.

In addition, the hot-work steel contains unavoidable impurities and iron as its main component. Optionally, the hot work tool steel may contain strong carbide formers, such as Ti, Zr, Hf, Nb, Ta, at a level of up to 3% by weight singly or in total. In this application, the abrasion resistance of the tool made of hot-work steel plays a particularly important role. The volume of the primary carbides formed should therefore be as large as possible.

Example 2

• 0,3 bis 0,42 Gew.-% C;
• weniger als 2 Gew.-%, insbesondere weniger als 1 Gew.-% Cr;
• 0 bis 6 Gew.-%, insbesondere 2,5 bis 4,5 Gew.-% Mo;
• 0 bis 6 Gew.-%, insbesondere 1 bis 2,5 Gew.-% W;
• wobei der Gehalt von Mo und W in der Summe 3,2 bis 5,5 Gew.-% beträgt;
• 0 bis 1,5 Gew.-%, insbesondere 0 bis 1 Gew.-% V.

Aluminum die casting is a very important market today, in which the properties of the hot working tool used to make the tools play an important role in competitiveness. The mechanical properties at high temperatures of the hot working steel used to produce a die casting tool are of particular importance here. In such a case, the advantage of increased thermal conductivity is particularly important because not only is it possible to reduce the cycle time but also to reduce the surface temperature of the tool and the temperature gradient in the tool. The positive effects on the durability of the tools are considerable. In die casting applications, particularly with regard to die-cast aluminum, the use of a hot-work tool steel as a material for producing a corresponding tool having the following composition is particularly advantageous:

• 0.3 to 0.42% by weight C;
• less than 2% by weight, especially less than 1% by weight Cr;
• 0 to 6 wt .-%, in particular 2.5 to 4.5 wt .-% Mo;
• 0 to 6 wt .-%, in particular 1 to 2.5 wt .-% W;
• wherein the content of Mo and W in the sum of 3.2 to 5.5 wt .-% is;
• 0 to 1.5 wt .-%, in particular 0 to 1 wt .-% V.

In addition, the hot working steel contains iron (as a main component) and inevitable impurities. Optionally, the hot work tool steel may contain strong carbide formers, such as Ti, Zr, Hf, Nb, Ta, at a level of up to 3 weight percent, singly or in total.

For aluminum die casting applications Fe ₃ C should not be present if possible. Cr and V with additions of Mo and W are the preferred elements to replace Fe ₃ C. Preferably, however, Cr is also replaced by Mo and / or W. In order to replace vanadium in some applications, preferably completely or at least partially, W and / or Mo can also be used. Alternatively, however, stronger carbide formers, such as Ti, Zr, Hf, Nb or Ta can also be used. The choice of carbide formers and their proportions, in turn, depends on the particular application and requirements with respect to the thermal and / or mechanical properties of the tool made from the hot work tool steel.

Example 3

• 0,25 bis 0,4 Gew.-% C;
• weniger als 2 Gew.-%, insbesondere weniger als 1 Gew.-% Cr;
• 0 bis 5 Gew.-%, insbesondere 2,5 bis 4,5 Gew.-% Mo;
• 0 bis 5 Gew.-%, insbesondere 0 bis 3 Gew.-% W;
• wobei der Gehalt von Mo und W in der Summe 3 bis 5,2 Gew.-% beträgt;
• 0 bis 1 Gew.-%, insbesondere 0 bis 0,6 Gew.-% V.

In the die casting of alloys with a comparatively high melting point, the use of a hot-work tool to produce a corresponding tool having the following composition is advantageous:

• 0.25 to 0.4% by weight C;
• less than 2% by weight, especially less than 1% by weight Cr;
• 0 to 5 wt .-%, in particular 2.5 to 4.5 wt .-% Mo;
• 0 to 5 wt .-%, in particular 0 to 3 wt .-% W;
• wherein the content of Mo and W in the sum of 3 to 5.2 wt .-% is;
• 0 to 1 wt .-%, in particular 0 to 0.6 wt .-% V.

In addition, the hot-work steel contains unavoidable impurities and iron as its main component. Optionally, the hot work tool steel may include strong carbide formers, such as Ti, Zr, Hf, Nb, Ta, individually or in the amount up to 3% by weight Sum. A greater toughness of the hot work steel is required in this application, so that primary carbides should be suppressed as completely as possible and thus stable carbide formers are more advantageous.

Example 4

• 0,4 bis 0,55 Gew.-% C;
• weniger als 2 Gew.-%, insbesondere weniger als 1 Gew.-% Cr;
• 0 bis 4 Gew.-%, insbesondere 0,5 bis 2 Gew.-% Mo;
• 0 bis 4 Gew.-%, insbesondere 0 bis 1,5 Gew.-% W;
• wobei der Gehalt von Mo und W in der Summe 2 bis 4 Gew.-% beträgt;
• 0 bis 1,5 Gew.-% V.

In the injection molding of plastics as well as in the die casting of alloys with a relatively low melting point, the use of a hot-work tool for producing a corresponding tool having the following composition is particularly advantageous:

• 0.4 to 0.55 wt% C;
• less than 2% by weight, especially less than 1% by weight Cr;
• 0 to 4 wt .-%, in particular 0.5 to 2 wt .-% Mo;
• 0 to 4 wt .-%, in particular 0 to 1.5 wt .-% W;
• wherein the content of Mo and W in the sum is 2 to 4 wt .-%;
• 0 to 1.5% by weight of V.

In addition, the hot-work tool steel contains iron as the main ingredient and inevitable impurities. Optionally, the hot work tool steel may have strong carbide formers, such as Ti, Zr, Hf, Nb, Ta, at a level of up to 3% by weight singly or in total. In these applications, the proportion of vanadium should be kept as low as possible. Preferably, the vanadium content of the hot work tool steel may be less than 1% by weight and more preferably less than 0.5% by weight, and in a most preferred embodiment less than 0.25% by weight.

The requirements with regard to the mechanical properties of the tools are relatively low in injection molding. A mechanical one Strength of about 1500 MPa is usually sufficient. Higher thermal conductivity, however, makes it possible to shorten the cycle times in the production of injection-molded parts, so that the costs for producing the injection-molded parts can be reduced.

Example 5

• 0,4 bis 0,55 Gew.-% C;
• weniger als 1 Gew.-% Cr,
• 0 bis 10 Gew.-%, insbesondere 3 bis 5 Gew.-% Mo;
• 0 bis 7 Gew.-%, insbesondere 2 bis 4 Gew.-% W;
• wobei der Gehalt von Mo und W in der Summe 6 bis 10 Gew.-% beträgt;
• 0 bis 3 Gew.-%, insbesondere 0,7 bis 1,5 Gew.-% V.

In hot forging, it is particularly advantageous to use a hot work tool steel having the following composition for producing a corresponding tool:

• 0.4 to 0.55 wt% C;
• less than 1% by weight Cr,
• 0 to 10 wt .-%, in particular 3 to 5 wt .-% Mo;
• 0 to 7% by weight, in particular 2 to 4% by weight W;
• wherein the content of Mo and W in the sum of 6 to 10 wt .-% is;
• 0 to 3 wt .-%, in particular 0.7 to 1.5 wt .-% V.

In addition, the hot working steel contains iron as the main component and inevitable impurities. Optionally, the hot work tool steel may have strong carbide formers, such as Ti, Zr, Hf, Nb, Ta, at a level of up to 3 percent by weight, singly or in total.

Advantageously, the hot-work steel in this example contain elements for solid solution strengthening, in particular Co, but also Ni, Si, Cu and Mn. In particular, a content of up to 6% by weight of Co has proved to be advantageous in order to improve the high-temperature strength of the tool.

With the aid of the hot working steels described here by way of example, which are suitable for a large number of different applications, one can a thermal conductivity is obtained, which is about twice as large as that of the known hot-working steels.

Table 1 shows some thermoelastic characteristics of five exemplary samples (Sample F1 through Sample F5) of a hot work tool according to the present invention as compared to conventional tool steels. For example, it can be seen that the hot working steels have a higher density than the known tool steels. Furthermore, the results show that the thermal conductivity of the samples of the hot work tool steel according to the invention is drastically increased compared to the conventional tool steels.

Table 2 summarizes the mechanical properties of two hot work steel samples (samples F1 and F5) according to the present invention compared to conventional tool steels.

In Fig. 2 shows the abrasion resistance of two samples (F1 and F5) of a hot work tool compared to conventional tool steels. The abrasion resistance was determined using a pin made of the corresponding steel and a washer made of a USIBOR 1500P sheet. The sample "1.2344" is the reference sample (abrasion resistance: 100%). A 200% abrasion resistance material thus has twice as high abrasion resistance as the reference sample and thus experiences only half the weight loss during the abrasion test procedure. It can be seen that the samples of hot-work steel according to the invention have a very high abrasion resistance compared to most known steels. In the following, further preferred examples of tool steels, in particular hot work steels, according to the present invention and their properties will be explained in more detail.

Thermal and thermal conductivity are the most important thermophysical material parameters for describing the heat transport properties of a material or component. For the exact measurement of the thermal diffusivity, the so-called "laser flash technique" (LFA) has become established as a fast, versatile and accurate absolute method. The relevant test specifications are specified in the relevant standards DIN 30905 and DIN EN 821. For the present measurements, the LFA 457 MicroFlash® from NETZSCH-Gerätebau GmbH, Wittelsbacherstrasse 42, 95100 Selb / Bavaria (Germany) was used.

sehr einfach ermittelt werden.From the measured temperature conductivities a and the specific heat c _p and the sample-specific determined density ρ, the thermal conductivity A can then be calculated on the basis of the calculation equation $$\mathrm{\lambda }=\mathrm{\rho }\cdot {\mathrm{c}}_{\mathrm{p}}\cdot \mathrm{a}$$

be determined very easily.

In Fig. 3 the dependence of the thermal conductivity on the percentage by weight of chromium determined by this method is shown for a selection of tool steels of the chemical composition marked FC or FC + xCr in Table 3. The composition differs above all in the percentage by weight of the alloying element chromium.

These steels additionally have a high resistance to abrasive and adhesive wear due to a comparatively large volume fraction of primary carbides over the possible adjustment of desired thermal conduction properties according to the present invention and are therefore suitable for high mechanical stresses, as typically occur in hot forming processes.

In Fig. 4 is the dependence of the thermal conductivity determined by the method described above on the proportion by weight of chromium for a selection of tool steels of the chemical composition identified in Table 4 with FM or FM + xCr. The compositions differ mainly in the percentage by weight of the alloying element chromium. These tool steels are particularly suitable for use in die-casting processes, since they are characterized by a comparatively small proportion of primary carbides.

Table 5 summarizes the chemical composition of a tool steel F according to the invention for the comparative investigation of the process behavior.

Under process-related conditions, as prevalent among other things also in the hot sheet metal forming, could with a tool steel having the chemical composition marked F in Table 5, compared to a conventional tool steel with the designation 1.2344 according to DIN 17350 EN ISO 4957 accelerated removal the stored heat in the workpiece via the preheating be detected by a pyrometric temperature measurement. The results of pyrometric temperature measurements are in Fig. 5 summarized.

Taking into account the usual in these processes tool temperature of about 200 ° C, it can be achieved over the tool steel according to the invention used here a shortening of the cooling time of about 50%.

In addition to the inventive aspect of the basic setting of the thermal conductivity by the suitable choice of the chemical composition, the present invention also includes the aspect of fine adjustment by a defined heat treatment.

Table 6 shows by way of example the influence of different heat treatment conditions for the alloy variants F with the chemical composition summarized in Table 5 and FC with the chemical composition summarized in Table 3 on the resulting thermal conductivity.

The reason for the varying thermal conductivity depending on the heat treatment is the resulting volume fraction of carbides and their changed distribution and morphology.

It has previously been pointed out that in view of increasing the thermal conductivity in the chemical composition of an alloy according to the invention, the weight fraction of carbon including the carbon equivalent components N and B (carbon equivalent x Ceq = x C + 0.86 x x N + 1.2 x x B where xC is the weight percentage of C, xN is the weight percentage of N and xB is the Weight percentage of B) should be adjusted so that as little carbon in the matrix remains in solution. The same applies to the proportion by weight of molybdenum xMo (% Mo) and tungsten xW (% W); these too should not remain in dissolved form in the matrix if possible, but rather contribute to carbide formation. This applies in a similar way to all other elements; These should also contribute to the carbide formation and therefore not remain dissolved in the matrix, but rather serve to bind carbon and optionally to increase the wear resistance under mechanical stress.

beschrieben werden.The statements made earlier can be - although with some restrictions - converted into a general description approach in the form of an equation for a parameter HC of the tool steel: $$\mathrm{HC}=\mathrm{xCeq}-\mathrm{AC}\cdot \left[\mathrm{xMo}/\left(\mathrm{3}\cdot \mathrm{AMo}\right)+\mathrm{xW}/\left(\mathrm{3}\cdot \mathrm{AW}\right)+\left(\mathrm{xV}-\mathrm{0}.\mathrm{4}\right)/\mathrm{AV}\right]$$

to be discribed.

• xCeq - Gewichtsprozentanteil Kohlenstoffäquivalent (wie oben definiert);
• xMo - Gewichtsprozentanteil Molybdän;
• xW - Gewichtsprozentanteil Wolfram;
• xV - Gewichtsprozentanteil Vanadium;
• AC - Atommasse von Kohlenstoff (12,0107 u);
• AMo - Atommasse von Molybdän (95,94 u);
• AW - Atommasse Wolfram (183,84 u);
• AV - Atommasse von Vanadium (50,9415 u).

In this equation,

• xCeq - weight percent carbon equivalent (as defined above);
• xMo - weight percent molybdenum;
• xW - weight percent tungsten;
• xV - weight percent vanadium;
• AC - atomic mass of carbon (12.0107 u);
• AMo - atomic mass of molybdenum (95.94 u);
• AW - atomic mass tungsten (183.84 u);
• AV - atomic mass of vanadium (50.9415 u).

The amount of HC should advantageously be between 0.03 and 0.165. The amount of HC may also be between 0.05 and 0.158, in particular between 0.09 and 0.15.

The factor 3 appears in the above-mentioned equation in the case where carbides of the M3C or M3Fe3C type are expected in the microstructure of the tool steel according to the invention; M stands for any metallic element. The factor 0.4 appears due to the fact that the desired weight percentage vanadium (V) in the alloy production is usually added in chemical compound in the form of carbides and thus also present up to this proportion as metal carbide MC.

Further fields of application of the tool steels (hot working steels) according to the present invention

With regard to the further use of preferred exemplary embodiments of tool steels according to the invention (in particular hot work steels), those application fields are conceivable in which a high thermal conductivity or a defined set profile of varying thermal conductivities has a positive effect on the application behavior of the tools used and on the properties of the products produced therewith.

With the present invention, a steel having a well-defined thermal conductivity can be obtained. There is even the possibility, by changing the chemical composition, of obtaining a steel object which consists at least partly of one of the tool steels (hot working steels) presented here, with a volume-changing thermal conductivity. It can be any procedure that has a Variation of the chemical composition within the steel article, such as sintering of powder mixtures, local sintering or local melting, or so-called "rapid-tooling" method or "rapid-prototyping" method or a combination of "rapid-tooling" Method and "rapid prototyping" method can be used.

In addition to the above-mentioned applications in the field of hot sheet metal forming (press hardening, tempering) and light metal die casting, there are generally tool and forming metal casting processes, plastic injection molding and massive forming processes, in particular hot massive forming (for example forging, extrusion, extrusion, rolling), the preferred application areas represent for the hot working steels according to the invention.

On the product side, the steels presented here represent ideal conditions for their use in the production of cylinder liners in internal combustion engines, for cutting tools or brake discs.

Table 7 lists, in addition to the alloy variants already listed in Tables 3 and 4, further exemplary embodiments of tool steels according to the invention (hot working steels).

• FA: Aluminiumdruckguss;
• FZ: Umformung von Kupfer- und Kupferlegierungen (einschließlich Messing);
• FW: Druckguss von Kupfer- und Kupferlegierungen; (einschließlich Messing) sowie höherschmelzenden Metalllegierungen;
• FV: Umformung von Kupfer- und Kupferlegierungen (einschließlich Messing);
• FAW: Druckguss von Kupfer- und Kupferlegierungen; (einschließlich Messing) sowie höherschmelzenden Metalllegierungen;
• FA Mod1: Druckguss großvolumiger Bauteile aus Kupfer- und Kupferlegierungen (einschließlich Messing) und Aluminium;
• FA Mod2: Umformung von Aluminium;
• FC Mod1: Warmblechumformung (Presshärten, Formhärten) mit hohem Verschleißwiderstand;
• FC Mod2: Warmblechumformung (Presshärten, Formhärten) mit hohem Verschleißwiderstand.

Tabelle 1 Material Dichte [g/cm³] Spezifische Wärme [J/kg K] Wärmeleitfähigkeit [W/mK] Wärmeleitzahl [mm²/s] Elastizitätsmodul [GPa] Poisson-Zahl Herkömmliche Werkzeugstähle W.Nr.-1.2343 7.750 462 24.621 6.876 221.086 0.28014 W.Nr.-1.2344 7.665 466 24.332 6.811 224.555 0.28123 W.Nr.-1.2365 7.828 471 31.358 8.505 217.124 0.28753 W.Nr.-1.236T 7.806 460 29.786 8.295 220.107 0.28140 Beispiele für Warmarbeitsstähle gemäß der vorliegenden Erfindung Probe F1 7.949 444 56.633 16.0319 197.18 0.2821 Probe F2 7.969 454 58.464 16.1594 Probe F3 7.965 449 55.550 15.5328 Probe F4 7.996 479 61.127 15.9364 Probe F5 7,916 440 64.231 18.4411 195.02 0.2844 Tabelle 2 MATERIAL Härte Streckgrenze Mechanische Festigkeit Bruchdehnung Elastizität Bruchwiderstand K_IC Ermüdungsschwe K_TH [HRc] [MPa] [MPa] [%] [J] [MPa m^-1/2] [MPa m^-1/2] W.Nr.-1.2343 44-46 1170 1410 16 322 56 4.8 W.Nr.-1.2344 44-46 1278 1478 14 364 49 4.7 W.Nr.-1.2365 44-46 1440 1570 12 289 43 W.Nr.-1.2367 44-46 1300 1490 13 215 41 Probe F5 44-46 1340 1510 16 >450 64 5.5 Probe F1 50-52 1560 1680 8 405 41 4.8 Tabelle 3 Chemische Zusammensetzung λ[W/mK] %C %Cr %Mo %W %V %Mn %Si andere FC 0.35 0.03 4 3.3 0.016 0.2 0.03 66 66 FC+0.5Cr 0.34 0.4 4 3.3 0.016 0.2 0.03 48.8 FC+1Cr 0.34 1.01 4 3.3 0.016 0.2 0.03 44.8 FC+1.5Cr 0.34 1.4 4 3.3 0.016 0.2 0.03 42.6 FC+2Cr 0.34 2.04 4 3.3 0.016 0.2 0.03 41.5 FC+3Cr 0.33 2.9 3.9 3.2 0.015 0.2 0.03 37.6 Tabelle 4 Chemische Zusammensetzung λ [W/mK] %C %Cr %Mo %W %V %Mn %Si andere FM 0.33 0.02 4.3 <0.1 <0.01 0.24 0.22 61 FM+0.5Cr 0.33 0.6 4.3 <0.1 <0.01 0.24 0.22 52 FM+1Cr 0.33 0.8 4.3 <0.1 <0.01 0.24 0.22 51 FM+1.5Cr 0.33 1.64 4.3 <0.1 <0.01 0.24 0.22 43 FM+2Cr 0.33 2.07 4.3 <0.1 <0.01 0.24 0.22 43 FM+3Cr 0.32 3 4.2 <0.1 <0.01 0.24 0.22 38 Tabelle 5 Chemische Zusammensetzung λ [W/mK] %C %Cr %Mo %W %V %Mn %Si andere F 0.32 0.02 3.8 3 0.009 0.2 0.04 61 Tabelle 6 Legierungsvariante Austenitisierungstemperatur T[°C] Kühlmedium Härte [HRc] λ [W/mK] F 1040 Luft 41 57 F 1060 Luft 42 58 F 1080 Luft 40 61 F 1250 Luft 42 56 FC 1080 Öl 47 52 FC 1080 Luft 44 66 FC 1060 Öl 45 54 FC 1060 Luft 44 63 Tabelle 7 Chemische Zusammensetzung λ [W/mK] %C %Cr %Mo %W %V %Mn %Si andere FA 0.29 0.02 3.1 2.1 <0.01 0.27 0.1 58 FZ 0.29 0.02 3.3 0.76 0.5 0.32 0.15 Zr:0.11;Co:2.8 Hf:0.14 46 FW 0.27 0.02 2.18 4.1 <0.01 0.25 0.2 56 FV 0.35 0.015 3.3 1.7 0.61 0.27 0.13 51 FAW 0.28 0.02 2.58 3.0 <0.01 0.26 0.16 57 FA Mod1 0.3 0.01 4.0 1.1 <0.01 0.2 0.05 64 FA Mod2 0.37 0.8 4.5 1.5 <0.01 0.24 1.2 58 FC Mod1 0.5 <0.01 6.7 4 <0.01 0.3 0.04 72 F 0.32 0.02 3.8 3 0.009 0.2 0.04 61 FC Mod2 0.5 0.03 9 0.1 <0.01 0.2 0.03 70 Preferred applications of the alloy variants summarized in Table 7 are:

• FA: die-cast aluminum;
• FZ: forming of copper and copper alloys (including brass);
• FW: die casting of copper and copper alloys; (including brass) and higher melting metal alloys;
• FV: transformation of copper and copper alloys (including brass);
• FAW: die casting of copper and copper alloys; (including brass) and higher melting metal alloys;
• FA Mod1: Die casting of large volume components from copper and copper alloys (including brass) and aluminum;
• FA Mod2: forming of aluminum;
• FC Mod1: hot sheet metal forming (press hardening, form hardening) with high wear resistance;
• FC Mod2: hot sheet metal forming (press hardening, tempering) with high wear resistance.

<u> Table 1 </ u> material Density [g / cm ³ ] Specific heat [J / kg K] Thermal conductivity [W / mK] Thermal conductivity [mm ² / s] Young's modulus [GPa] Poisson's ratio Conventional tool steels W.Nr.-1.2343 7750 462 24621 6876 221086 0.28014 W.Nr.-1.2344 7665 466 24332 6811 224555 0.28123 W.Nr.-1.2365 7828 471 31358 8505 217124 0.28753 W.Nr.-1.236T 7806 460 29786 8295 220107 0.28140 Examples of hot working steels according to the present invention Sample F1 7949 444 56633 16.0319 197.18 0.2821 Sample F2 7969 454 58464 16.1594 Sample F3 7965 449 55550 15.5328 Sample F4 7996 479 61127 15.9364 Sample F5 7,916 440 64231 18.4411 195.02 0.2844 MATERIAL hardness Stretch limit Mechanic solidity elongation elasticity Breaking resistance K _IC Fatigue pig K _TH [HRC] [MPa] [MPa] [%] [J] [MPa m ^-1/2 ] [MPa m ^-1/2 ] W. No. 1.2343 44-46 1170 1410 16 322 56 4.8 W.Nr.-1.2344 44-46 1278 1478 14 364 49 4.7 W.Nr.-1.2365 44-46 1440 1570 12 289 43 W.Nr.-1.2367 44-46 1300 1490 13 215 41 Sample F5 44-46 1340 1510 16 > 450 64 5.5 Sample F1 50-52 1560 1680 8th 405 41 4.8 Chemical composition λ [W / mK] % C % Cr %Not a word % W % V % Mn % Si other FC 12:35 12:03 4 3.3 0016 0.2 12:03 66 66 FC + 0.5Cr 12:34 0.4 4 3.3 0016 0.2 12:03 48.8 FC + 1Cr 12:34 1:01 4 3.3 0016 0.2 12:03 44.8 FC + 1.5Cr 12:34 1.4 4 3.3 0016 0.2 12:03 42.6 FC + 2Cr 12:34 2:04 4 3.3 0016 0.2 12:03 41.5 FC + 3Cr 12:33 2.9 3.9 3.2 0015 0.2 12:03 37.6 Chemical composition λ [W / mK] % C % Cr %Not a word % W % V % Mn % Si other FM 12:33 12:02 4.3 <0.1 <00:01 12:24 12:22 61 FM + 0.5Cr 12:33 0.6 4.3 <0.1 <00:01 12:24 12:22 52 FM + 1Cr 12:33 0.8 4.3 <0.1 <00:01 12:24 12:22 51 FM + 1.5Cr 12:33 1.64 4.3 <0.1 <00:01 12:24 12:22 43 FM + 2Cr 12:33 2:07 4.3 <0.1 <00:01 12:24 12:22 43 FM + 3Cr 12:32 3 4.2 <0.1 <00:01 12:24 12:22 38 Chemical composition λ [W / mK] % C % Cr %Not a word % W % V % Mn % Si other F 12:32 12:02 3.8 3 0009 0.2 12:04 61 alloy variant Austenitizing temperature T [° C] cooling medium Hardness [HRc] λ [W / mK] F 1040 air 41 57 F 1060 air 42 58 F 1080 air 40 61 F 1250 air 42 56 FC 1080 oil 47 52 FC 1080 air 44 66 FC 1060 oil 45 54 FC 1060 air 44 63 Chemical composition λ [W / mK] % C % Cr %Not a word % W % V% Mn % Si others FA 12:29 12:02 3.1 2.1 <00:01 12:27 0.1 58 FZ 12:29 12:02 3.3 0.76 0.5 12:32 12:15 Zr: 0.11, Co: 2.8 Hf: 0.14 46 FW 12:27 12:02 2.18 4.1 <00:01 12:25 0.2 56 FV 12:35 0015 3.3 1.7 0.61 12:27 12:13 51 FAW 12:28 12:02 2:58 3.0 <00:01 12:26 12:16 57 FA Mod1 0.3 12:01 4.0 1.1 <00:01 0.2 12:05 64 FA Mod2 12:37 0.8 4.5 1.5 <00:01 12:24 1.2 58 FC Mod1 0.5 <00:01 6.7 4 <00:01 0.3 12:04 72 F 12:32 12:02 3.8 3 0009 0.2 12:04 61 FC Mod2 0.5 12:03 9 0.1 <00:01 0.2 12:03 70

embodiments

1. 1. A method for adjusting the thermal conductivity of a steel, in particular a hot-work steel, characterized in that an inner structure of the structure defined steel is generated metallurgically, the carbide constituents have a defined electron and phonon density and / or their crystal structure determined by selectively generated lattice defects mean has free path for the phonon and electron flow.
2. 2. A method for adjusting, in particular for increasing the thermal conductivity of a steel, in particular a hot-work steel, characterized in that an inner structure of the structure defined steel is metallurgically generated, which has in their carbide components an increased electron and phonon density and / or by a low defect content in the crystal structure of the carbides and the surrounding metallic matrix has an increased mean free path for the phonon and electron flow.
3. 3. The method according to embodiment 1 or 2, characterized in that the thermal conductivity of the steel at room temperature to more than 42 W / mK, preferably to more than 48 W / mK, in particular to more than 55 W / mK is set.
4. 4. Tool steel, in particular hot-work tool steel, characterized by the following composition:
   • 0.26 to 0.55 wt% C;
   • <2% by weight Cr;
   • 0 to 10% by weight of Mo;
   • 0 to 15 wt% W;
   • wherein the content of W and Mo in the sum of 1.8 to 15
   • Wt .-% is;
   • carbide-forming elements Ti, Zr, Hf, Nb, Ta with a content of 0 to 3 wt .-%, individually or in total;
   • 0 to 4% by weight V;
   • 0 to 6% by weight of Co;
   • 0 to 1.6% by weight of Si;
   • 0 to 2% by weight of Mn;
   • 0 to 2.99% by weight of Ni;
   • 0 to 1% by weight of S;
   • Remainder: iron and unavoidable impurities.
5. 5. Tool steel, in particular hot-work tool steel, characterized by the following composition:
   • 0.25 to 1.00% by weight of C and N in total;
   • <2% by weight Cr;
   • 0 to 10% by weight of Mo;
   • 0 to 15 wt% W;
   • wherein the content of W and Mo in the sum of 1.8 to 15 wt .-% is;
   • carbide-forming elements Ti, Zr, Hf, Nb, Ta with a content of 0 to 3 wt .-%, individually or in total;
   • 0 to 4% by weight V;
   • 0 to 6% by weight of Co;
   • 0 to 1.6% by weight of Si;
   • 0 to 2% by weight of Mn;
   • 0 to 2.99% by weight of Ni;
   • 0 to 1% by weight of S;
   • Remainder: iron and unavoidable impurities.
6. 6. Tool steel, in particular hot-work tool steel, characterized by the following composition:
   • 0.25 to 1.00% by weight of C, N and B in the sum;
   • <2% by weight Cr;
   • 0 to 10% by weight of Mo;
   • 0 to 15 wt% W;
   • wherein the content of W and Mo in the sum of 1.8 to 15 wt .-% is;
   • carbide-forming elements Ti, Zr, Hf, Nb, Ta with a content of 0 to 3 wt .-%, individually or in total;
   • 0 to 4% by weight V;
   • 0 to 6% by weight of Co;
   • 0 to 1.6% by weight of Si;
   • 0 to 2% by weight of Mn;
   • 0 to 2.99% by weight of Ni;
   • 0 to 1% by weight of S;
   • Remainder: iron and unavoidable impurities.
7. 7. tool steel, in particular hot-work steel, according to one of embodiments 4 to 6, characterized in that the hot-work steel at room temperature, a thermal conductivity of more than 42 W / mK, preferably a thermal conductivity of more than 48 W / mK, in particular a thermal conductivity of more than 55 W / mK has.
8. 8. tool steel, in particular hot-work steel, according to embodiment 7, characterized in that the thermal conductivity of the tool steel by a method according to one of embodiments 1 to 3 is adjustable.
9. 9. Tool steel, in particular hot-work steel, according to one of embodiments 4 to 8, characterized in that the hot-work steel contains 2 to 15 wt .-% Mo and W in the sum.
10. 10. tool steel, in particular hot-work tool steel, according to one of embodiments 4 to 9, characterized in that the tool steel contains 2.5 to 15 wt .-% Mo and W in the sum.
11. 11. Tool steel, in particular hot-work tool steel, according to one of embodiments 4 to 10, characterized in that the tool steel contains less than 1.5 wt .-% Cr.
12. 12. tool steel, in particular hot-work tool steel, according to one of embodiments 4 to 11, characterized in that the tool steel contains less than 1 wt .-% Cr.
13. 13. Tool steel, in particular hot-work tool steel, according to one of embodiments 4 to 12, characterized in that the tool steel less than 0.5 wt .-% Cr, preferably less than 0.2 wt .-% Cr and in particular less than 0.1 Wt .-% Cr contains.
14. 14. Tool steel, in particular hot-work steel, according to one of embodiments 4 to 13, characterized in that the tool steel 0.5 to 10 wt .-%, in particular 1 to 10 wt% Mo contains.
15. 15. Tool steel, in particular hot-work steel, according to one of embodiments 4 to 14, characterized in that the content of Mo, W and V in the sum of 2 to 10 wt .-% is.
16. 16. Tool steel, in particular hot-work tool steel, according to one of embodiments 4 to 15, characterized in that the tool steel contains a maximum of 3 wt .-% Co.
17. 17. Tool steel, in particular hot-work steel, according to one of embodiments 4 to 16, characterized in that the tool steel contains a maximum of 2 wt .-% Co.
18. 18. Tool steel, in particular hot-work steel, according to one of embodiments 4 to 17, characterized in that the molybdenum content of the tool steel> 1 wt .-%, preferably > 1.5 wt .-%, in particular> = 2 wt .-% is.
19. 19. Tool steel, in particular hot-work steel, according to one of embodiments 4 to 18, characterized in that the vanadium content of the tool steel <= 2 wt .-%, preferably <= 1.2% wt .-% is.
20. 20. Tool steel, in particular hot-work steel, according to one of embodiments 4 to 19, characterized in that the impurities one or more of the elements Cu, P, Bi, Ca, As, Sn or Pb with a content of at most 1 wt .-% individually or included in the sum.
21. 21. Tool steel, in particular hot-work tool steel, according to one of embodiments 4 to 20, characterized in that a parameter HC = xCeq - AC [xMo / (3-AMo) + xW / (3-AW) + (xV-0.4) / AV] is between 0.03 and 0.165, where xCeq is the weight percentage of carbon equivalent, xMo is the weight percent molybdenum, xW is the weight percent tungsten, xV is the weight percent vanadium, AC is the atomic mass of carbon, AMo is the atomic mass of molybdenum, AW is the atomic mass of tungsten and AV is the atomic mass of vanadium.
22. 22. Tool steel, in particular hot-work tool steel, according to embodiment 21, characterized in that HC is between 0.05 and 0.158.
23. 23. Tool steel, in particular hot-work tool steel, according to embodiment 21 or 22, characterized in that HC is between 0.09 and 0.15.
24. 24. Use of a tool steel, in particular Hot work steel, according to one of embodiments 4 to 23, as a material for producing a hot-work tool, in particular a hot working tool, which has a thermal conductivity at room temperature of more than 42 W / mK, preferably a thermal conductivity of more than 48 W / mK, in particular a thermal conductivity of more than 55 W / mK.
25. 25. A steel article, characterized in that the steel article at least partially consists of a tool steel, in particular of a hot-work tool steel, according to one of embodiments 4 to 23.
26. 26. A steel article according to embodiment 25, characterized in that the steel article has over its entire volume substantially constant thermal conductivity.
27. 27. Steel article according to embodiment 25, characterized in that the steel article has an at least partially changing thermal conductivity.
28. 28 steel article according to one of embodiments 25 to 27, characterized in that the steel article at room temperature at least partially a thermal conductivity of more than 42 W / mK, preferably a thermal conductivity of more than 48 W / mK, in particular a thermal conductivity of more than 55 W. / mK.
29. A steel article according to any one of embodiments 25 to 28, characterized in that the steel article is a forming tool in processes of pressure forming, shear forming, or bend forming of metals, preferably in forging forging processes, drop forging processes, thixo forging processes, Extrusion processes, extrusion processes, Gesenkbiegeprozessen, Walzprofilierprozessen or in flat, profile and Gießwalzprozessen is.
30. 30. A steel article according to any one of embodiments 25 to 28, characterized in that the steel article is a forming tool in processes of train forming and tensile forming of metals, preferably in press-hardening processes, mold-hardening processes, thermoforming processes, stretch-drawing processes and collar-drawing processes.
31. 31. A steel article according to any one of embodiments 25 to 28, characterized in that the steel article is a forming tool in processes of primary forming of metallic starting materials, preferably in die casting processes, vacuum die casting processes, thixocasting processes, cast roll processes, sintering processes and hot isostatic pressing processes.
32. 32. A steel article according to any one of embodiments 25 to 28, characterized in that the steel article is a forming tool in processes of molding of polymeric starting materials, preferably in injection molding, extrusion processes and extrusion blow molding processes.
33. 33. A steel article according to any one of embodiments 25 to 28, characterized in that the steel article is a forming tool in processes of forming original ceramic materials, preferably in sintering processes.
34. 34. A steel article according to any one of embodiments 25 to 28, characterized in that the steel article is a component for machines and plants of power generation and energy conversion, preferably for internal combustion engines, reactors, heat exchangers and Generators, is.
35. 35. Steel article according to one of embodiments 25 to 28, characterized in that the steel article is a component for machines and plants of chemical engineering, preferably for chemical reactors.

Claims (15)

Method for adjusting the thermal conductivity, in which the basic setting of the thermal conductivity is determined by the choice of a steel having the composition: 0.26 to 0.55 wt.% C or 0.25 to 1 wt.% C and N and B in the sum; <2% by weight Cr; 0 to 10% by weight of Mo; 0 to 15 wt% W; wherein the content of W and Mo in the sum of 1.8 to 15 wt .-% is; carbide-forming elements Ti, Zr, Hf, Nb, Ta with a content of 0 to 3 wt .-%, individually or in total; 0 to 4% by weight V; 0 to 6% by weight of Co; 0 to 1.6% by weight of Si; 0 to 2% by weight of Mn; 0 to 2.99% by weight of Ni; 0 to 1% by weight of S; Remainder: iron and unavoidable impurities, carried out and the fine adjustment of the thermal conductivity to a value of more than 42 W / mK, preferably more than 48 W / mK, and in particular more than 55 W / mK by a heat treatment. Tool steel, in particular hot-work tool steel, having the composition: 0.26 to 0.55 wt.% C or 0.25 to 1 wt.% C and N and B in the sum; <2% by weight Cr; 0 to 10% by weight of Mo; 0 to 15 wt% W; wherein the content of W and Mo in the sum of 1.8 to 15 wt .-% is; carbide-forming elements Ti, Zr, Hf, Nb, Ta with a content of 0 to 3 wt .-%, individually or in total; 0 to 4% by weight V; 0 to 6% by weight of Co; 0 to 1.6% by weight of Si; 0 to 2% by weight of Mn; 0 to 2.99% by weight of Ni; 0 to 1% by weight of S; Rest: iron and unavoidable impurities, characterized in that the tool steel has a thermal conductivity at room temperature of more than 42 W / mK, preferably more than 48 W / mK, in particular more than 55 W / mK. Tool steel according to claim 2, characterized in that the tool steel contains less than 1 wt .-% Cr, preferably less than 0.5 wt .-% Cr and in particular less than 0.1 wt .-% Cr. Tool steel according to claim 2 or 3, characterized in that the molybdenum content of the tool steel is> 1 wt .-%, preferably> 1.5 wt .-%, in particular> = 2 wt .-% is. Tool steel according to one of claims 2 to 4, characterized in that the impurities one or more of the elements Cu, P, Bi, Ca, As, Sn or Pb having a content of maximum 1 wt .-% individually or in total. Tool steel according to one of claims 1 to 5, characterized in that the tool steel contains 2 to 15 wt .-%, preferably 2.5 to 15 wt .-% Mo and W in the sum. Tool steel according to one of claims 1 to 6, characterized in that the tool steel contains 0.5 to 10 wt .-%, in particular 1 to 10 wt .-% Mo. Tool steel according to one of claims 1 to 7, characterized in that the vanadium content of the tool steel ≤ 2 wt .-%, preferably ≤ 1.2 wt .-% is. Use of a tool steel according to any one of claims 2 to 8 as a material for producing a hot-work tool steel article. Steel article, characterized in that the steel article at least partially consists of a tool steel according to one of claims 2 to 9. Steel article according to claim 10, characterized in that the steel article has a substantially constant thermal conductivity over its entire volume. Steel article according to claim 10, characterized in that the steel article has an at least partially changing thermal conductivity. Steel article according to one of claims 10 to 12, characterized in that the steel article is a shaping A tool in processes of pressure forming, shear forming, or bend forming of metals, preferably in forging processes, die forging processes, thixo forging processes, extrusion processes, extrusion processes, die bending processes, roll forming processes, or in flat, profile, and cast roll processes, or a forming tool in train and tensile forming processes of metals, preferably in press-hardening processes, mold-hardening processes, thermoforming processes, stretch-drawing processes and collar-drawing processes. A steel article according to any one of claims 10 to 12, characterized in that the steel article is a forming tool in processes of forming metallic starting materials, preferably in die casting processes, vacuum die casting processes, thixocasting processes, cast roll processes, sintering processes and hot isostatic pressing processes, or a forming tool in processes of molding polymer starting materials , preferably in injection molding processes, extrusion processes and extrusion blow molding processes or is a shaping tool in processes of primary shaping of ceramic starting materials, preferably in sintering processes. A steel object according to any one of claims 10 to 12, characterized in that the steel object is a component for machines and plants of power generation and energy conversion, preferably for internal combustion engines, reactors, heat exchangers and generators, or a component for machines and plants of chemical engineering, preferably for chemical reactors, is.

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