EP2386660B1 - Casting mould - Google Patents

Description

The invention relates to a cast body, namely a tool for forming or forming a workpiece or a transmission member for transmitting force or torque to a workpiece contacting the original or forming tools, preferably a piston or plunger. The tool or transfer member may be part of a press for forming or forming the workpiece or a forging tool. The invention also relates to the tool or transfer member as such, prior to assembly with other components.

In papermaking, rolls several meters in length and over one meter in diameter are used to make the finished paper web from cellulose sludge by thermal and mechanical treatment. Rollers made of chilled cast iron, in particular shell-cast iron, or forged steel are used. The cast iron bodies are produced by chill casting, usually standing in static chill casting. By the ring molds is achieved that sets in the outer peripheral edge zone, the shell, a carbide, white cast iron. The peripheral edge zone or shell solidifies metastable, white, the carbon is bound there in the form of carbides. At its core, solidification takes place, the melt solidifies in gray, the carbon is present as free graphite in the iron matrix. The required hardness at the outer circumference of the roll body, the surface hardness, is ensured by the material of the shell, the white cast iron. By means of the mold and the alloy elements of the iron base melt, the hardness is set at the surface and in the near-surface depth range. The disadvantage of shell casting is the impact brittleness, its sensitivity to sudden changes in temperature, and uneven wear on the outer circumference of the roll due to the carbides contained in the white iron.

The EP 0 505 343 A1 proposes, in order to overcome the said drawbacks, that the roll body is cast from an iron-base alloy to form a pearlitic or ferritic-pearlitic microstructure which is at least 60% pearlitic. The iron-based alloy contains 3.0 - 3.8% C, 1.5 - 3.0% Si and 0.5 - 0.9% Mn. Maximum levels are given for P and S. As further alloying elements, Cr, Ni, Cu, Mg, Mo, Sn or Al are used. The roll body is surface hardened, called induction and flame hardening, and annealed after the martensitic transformation so that the roll body receives a temper martensite structure in its peripheral edge zone. With the martensitic structure of the peripheral edge zone is accompanied by a considerable risk of cracking.

The EP 2 213 790 A1 describes a roller body for a roller for treating a material, wherein the material of the peripheral edge zone of the roller body compared to the white cast iron has significantly improved strength values.

In the CH 360 701 A discloses a method for surface hardening of cast iron, in which the edge zone of a workpiece is converted into austenite by brief autogenous or induction heating and is then cooled relatively slowly.

With the mentioned alternative, roller bodies made of forged steel, the mentioned material problems can be solved. Surface hardness and hardening depth are adjusted on the roll body by subsequent thermal surface treatment. However, the production takes place from a forging block, the weight of which depends on the size of the roll body. Rolled bodies weigh many tons, for example, large roll bodies have a weight of about 50 tons or more. For such roll body, the weight of the forge block can be up to 200t. A hollow forging is possible in this weight range only with great effort. In addition, high demands are placed on the inner quality of the forged steel with regard to defects, inclusions and the like. The application is therefore very low.

The conditions in tools and force or torque transmitting transmission elements of Ur- or forming devices, in particular for forming metal workpieces are comparable. Such tools and transfer members may be to act about stamps, dies, pistons and rams of presses and blacksmiths.

It is an object of the invention to provide a cast body, namely a master or forming tool or a transfer member for a master or forming device, with improved compared to shell hard casting mechanical properties at a favorable price. The cast body should have the required hardness on the surface and also in the near-surface depth range, but not in the application disadvantageous unevenness in wear and impact brittleness. The risk of cracking associated with a martensite shell should also be avoided.

The invention is based on a cast body which is cast from a single iron-based alloy. The iron-base alloy forms an inner zone of gray cast iron, preferably nodular cast iron, in the cast body, and the inner zone encloses a peripheral edge zone containing the outer circumference of the cast body having a surface hardness greater than 400HV on the outer circumference, as has heretofore been prevalent Shell casting is the case. The cast body can be seen in cross-section of full material, so that the inner zone of gray cast iron forms a central core of the cast body. Instead, the casting may also be a hollow shell, so that the inner zone is an annular zone. The inner zone and the peripheral edge zone are cast in one piece, the use of the two terms is intended to indicate the difference in the microstructure present in the two zones, hereinafter simply microstructure.

According to the invention, the peripheral edge zone consists either of fine-grained or very fine-grained perlite with vermicular graphite or preferably spheroidal graphite or of an intermediate-layer structure, preferably ADI with spherical or vermicular graphite. The fine-grained pearlite is also known as sorbitol and the finest-grained as troostite. The invention combines the advantages of castings with those of forged steel and avoids the risk of cracking associated with a martensite shell. The cast body can be made significantly cheaper over its entire dimension in a cast and thus compared to a forged steel body. The gray cast iron inner zone can be worked well, for example by cutting. Thus, near-surface pheripheral holes for the passage of a thermal fluid can be created in the inner zone. The hardness profile of the circumferential edge zone, that is to say the hardness profile applied over the distance to the outer surface, corresponds at least to the hardness profile of conventional tools or transmission elements serving as master or forming and can be controlled by the heat treatment process. However, the mechanical strength is significantly improved compared to shell casting, which is reflected in higher 0.2% yield strength, tensile strength and elongation at break values. Compared to a tempered martensite, the elongation at break is advantageously increased, in particular the risk of cracking is significantly reduced.

In preferred embodiments, in which the free graphite of the circumferential base zone is present at least essentially as spheroidal graphite, the graphite spheres which form the spheroidal graphite in the solidified peripheral edge zone have a maximum size which corresponds to a guide number of at least 5 (0.06-0.12 mm) according to EN ISO 945 corresponds. The precipitation of the graphite in the form of only such small graphite balls is also advantageous for the mechanical strength and is achieved in the casting process by adjusting the cooling rate of the melt. For this purpose, the melt is cooled from the outside, from the outer circumference, wherein the cooling rate is on the one hand so small that sets in the peripheral edge zone to the outer periphery or virtually to the outer periphery of a ductile iron structure, but on the other hand is so large that the Graphite spheres of the peripheral edge zone are smaller than in the conventional nodular cast iron, for example, when poured into a sand mold. It is particularly advantageous if, in the basic structure obtained by the casting in the peripheral edge zone, the nodular graphite has almost only, preferably only, graphite balls having a maximum size which has a guideline value of at least 6 (0.03-0.06 mm), more preferably at least 7 (0.015 mm). 0.03 mm) according to EN ISO 945. In contrast, the graphite spheres of the nodular cast iron structure, which is preferably also present in the inner zone, can be larger. In the illustrated preferred embodiments, the proportion of spheroidal graphite on the free graphite of the solidified peripheral edge zone is at least 80%, preferably at least 90%, and from the graphite spheres of the spheroidal graphite graphite of the peripheral edge zone correspond to at least 90%, preferably at least 95%, the above requirements for the size of graphite nodules. This standard is the currently valid EN ISO 945: 1994. As far as the free Graphite is excreted in vermicular form, for the vermicular graphite particles, the above information on size and percentages also apply. Accordingly, in preferred embodiments, the vermicular graphite particles, if present, have a maximum size, in this case the length, of 0.12 mm, more preferably at most 0.06 mm, and even more preferably at most 0.03 mm. Of the total vermicular graphite particles present, at least 90%, preferably at least 95%, fall into this size range.

As far as the structure of the peripheral edge zone has at all carbides, their proportion is less than 5%, preferably the carbide content makes up at most 3%. Percentages in% are always expressed as mass%, i. understood as% share of the respective total mass. With respect to any carbide content, this means that it is less than 5 mass% of the mass of the peripheral edge zone as a whole, including the carbide portion, preferably at most 3 mass%. By comparison, a white cast iron typically has a carbide content of 15% or more. Also, due to the significantly reduced carbide content and therefore the reduced micro-notch effect, the material of the peripheral edge zone of the cast body according to the invention significantly improved strength values compared to white cast iron.

The casting is a tool for or in a device for prototyping or forming workpieces, in particular metallic workpieces. The cast body may for example form a punch or a die for plastic molding. Particularly advantageously, it can form a transmission element for transmitting force or torque to a tool which acts directly on the material during shaping. Pistons and plungers of or for priming or forming devices are preferred examples. Presses and forging tools, in particular with hydraulic force or torque transmission, are preferred examples of original and forming devices in which a cast body according to the invention can be used.

The cast body according to the invention is at least finished insofar as it no longer has to be subjected to thermal treatment and is preferably no longer subjected to it, which specifically serves to adjust the microstructure. Any post-treatment, for example a grinding or polishing, optionally a machining or, for example, a mechanical training and, in principle, thermal treatments that do not change in particular the claimed for the peripheral edge zone structure to such an extent that it no longer corresponds to the claimed invention, are, however, excluded.

A method for producing the cast body comprises at least the following steps: the cast body is cast from a melt of an iron-based alloy, so that the melt is stable as cast iron both in the inner zone of the cast body and in the outer peripheral and reaching to the outer periphery peripheral edge zone and at least in the peripheral edge zone, but preferably also in the inner zone in a nodular cast iron structure or a cast structure with vermicular graphite solidifies. The matrix of the cast iron is pearlitic / ferritic, with the proportion of pearlite being greater than 90% and that of the ferrite being less than 10%. Preferably, the proportion of the perlite of the cast iron matrix is greater than 95% and that of the ferrite is less than 5%. Any amount of carbide in the peripheral edge zone is less than 5%, preferably less than or equal to or less than 3%. The cast body obtained with this cast structure is formed by means of a thermal surface treatment on the outer periphery, i. hardened on the peripheral surface, and in the peripheral edge zone.

According to the invention, the thermal surface treatment is carried out so that the peripheral edge zone forming casting material, cast iron with nodular graphite or nodular graphite, with nodular graphite being preferred, is converted into fine or very fine-grained perlite with vermicular or nodular graphite or into an interstage structure with spheroidal graphite or vermicular graphite. More specifically, the cast iron matrix is converted into said perlite or interstage structure, and the free graphite already precipitated by the casting as a stable phase is retained. Further, the melt is not poured into sand, but against mold to control the cooling rate. Chill casting can be static or instead dynamic, ie centrifugal casting. The cast body is expediently poured upright, that is to say with a main axis in a vertical orientation. Casting against mold permits a more precise setting of the cooling rate, in particular via the choice of the thickness of the mold, the specific or the absolute, measured radially to the main axis of the cast body Heat capacity, the thermal conductivity or the mass of the mold or a suitable combination of such parameters on the part of the mold. In comparison with the conventional shell casting, which is also usually done by chill casting, but with white solidifying peripheral edge zone, the cooling rate can be controlled, for example, by a single or, preferably, a combination of several of the following: lower die thickness, use of a die of a lower heat capacity material , Using a mold of lower thermal conductivity, lower mold mass, in each case in comparison with a mold for casting a cast body of the same geometry and the same material in conventional hard shell casting.

In preferred embodiments, the cooling rate is set by cooling the mold not only so small that the melt solidifies stable in the peripheral edge zone, but on the other hand so large that explained above for the preferred spheroidal graphite nodular graphite is excreted in the peripheral edge zone in graphite spheres a maximum size corresponding to the guideline number 5, preferably a maximum size of the guideline number 6, according to EN ISO 945. Particularly preferred are the graphite balls in the size range between 7 and 8 according to EN ISO 945, ie in the guideline 7/8 before. Such a fine graphite precipitation has a positive effect on the mechanical strength. The fine precipitation of the graphite also increases the regularity of the surrounding cast iron matrix, which in turn is advantageous for the transformation of this basic structure present after casting into fine-grained or ultraprecipitated perlite or into an interstage structure.

By means of the thermal surface treatment, the cast body is hardened to a depth of advantageously at least 3 mm, preferably at least 5 mm, by the cast iron matrix being converted into the fine-grained or extremely fine-grained pearlite or the interstitial microstructure up to at least this hardening depth. For the size class of castings, on which the invention is primarily intended, a hardening depth of 7 mm is optimal. Although a hardening depth of more than 10 mm should not be ruled out, large hardening depths produce material stresses in the event of a temperature change, with the risk that the hardened layer, the circumferential edge zone, will flake off. Flame hardening and induction hardening are particularly suitable as methods of thermal surface treatment, with induction hardening preference is given to the fact that flame hardening is limited to the lower part of the hardening depth, generally still below 3 mm. Flame hardening is therefore primarily for castings with small diameters of up to 600 mm into consideration, although the induction hardening is also given preference here. Depending on the desired surface hardness and hardening depth, the peripheral edge zone is briefly heated to the austenitic region, preferably to at least 880 ° C. and particularly preferably to about 950 ° C. The heated material is cooled by a surface cooling, preferably by means of a water quenching, in a short time to below 100 ° C, preferably below 50 ° C, so that the isothermal conversion takes place in the fine or feinststreifigen perlite. If the cast iron of the peripheral edge zone to be converted into an intermediate structure, a higher cooling rate is set, but still not so large that a significant martensitic transformation takes place. Martensite is ideally avoided because of the associated risk of cracking. The cast iron of the peripheral edge zone therefore has, in preferred embodiments, a martensite start temperature M _s which is below the values given above, ie below 100 ° C., preferably below 50 ° C. Particularly preferably, the material of the peripheral edge zone has a martensite start temperature M _s which is below room temperature, ie below 20 ° C.

The surface hardened cast body is advantageously tempered to relieve stress. The tempering temperature is above the temperature that reaches the cast body in later operation at the most, advantageously above 300 ° C, preferably a tempering temperature in the range of 300 to 350 ° C. Even after such tempering, the cast body in the peripheral edge zone has the fine or very fine-grained pearlitic structure with spherical or vermicular graphite or the interstitial structure with spherical or vermicular graphite.

The iron-base alloy has a carbon content of preferably at least 3%, preferably at most 4%. The silicon content is preferably at least 1.7 and preferably at most 2.4%, whereby these are also always% by mass. The degree of saturation Sc of the alloy is preferably in the range of 0.97 to 1.03, preferably it is slightly smaller than 1.0, so that the melt is slightly hypoeutectic. A preferred alloying partner is copper, as a perlitizer, and having a proportion of preferably at least 0.5 and preferably at most 1.3%. A particularly preferred alloying partner is also nickel, which is alloyed in a proportion of preferably more than 0.3%, more preferably more than 0.5%, and preferably at most 1.5%. Nickel increases the toughness and makes the material corrosion-resistant. However, nickel is of particular value for preventing martensite transformation during curing. If the iron-base alloy contains both silicon and nickel, it is advantageous if the silicon content decreases with increasing nickel content and the nickel content decreases with increasing silicon content. Preference is given to a silicon content from the lower half of the range specified for silicon and a nickel content from the middle part of the range specified for nickel. A particularly preferred iron alloy contains as alloying partners both Ni and Cu with preferably at least the minimum proportions indicated for each. Manganese and tin are also preferred alloying agents, manganese preferably from 0.3 to 0.45%, tin preferably from 0.005 to 0.015%. Compared to the other alloying elements mentioned above, however, the meaning of manganese and tin is reversed. Accordingly, a preferred iron-based alloy contains C, Si, Ni and Cu within the preferred limits of the proportions, optionally Mn and Sn, as well as unavoidable residual P and S and the remainder Fe. Any proportions of phosphorus and sulfur are advantageously each well below 0.1%, more preferably still well below 0.05%.

Advantageous features are further disclosed in the subclaims and their combinations.

Figur 1

eine nicht beanspruchte Walze mit einem Walzenkörper;

Figur 2

den Querschnitt A-A der Figur 1;

Figur 3

Details zum Mikrogefüge des Walzenkörpers;

Figur 4

den Walzenkörper während einer thermischen Oberflächenbehandlung;

Figur 5

ein Schliffbild des Grundgefüges des Walzenkörpers;

Figur 6

ein Schliffbild des Gefüges einer mittels der thermischen Oberflächenbehandlung gehärteten Umfangsrandzone des Walzenkörpers;

Figur 7

den Mikrohärteverlauf in der gehärteten Umfangsrandzone;

Figur 8

eine Presse mit einem erfindungsgemäßen Kolben; und

Figur 9

einen erfindungsgemäßen Kolben einer modifizierten Form.

Hereinafter, embodiments of the invention will be explained with reference to figures. The features disclosed in the exemplary embodiments form each individually and in each combination of features the subject-matter of the claims and also the embodiments described above. Show it:

FIG. 1

an unclaimed roller having a roller body;

FIG. 2

the cross section AA of FIG. 1 ;

FIG. 3

Details of the microstructure of the roll body;

FIG. 4

the roll body during a thermal surface treatment;

FIG. 5

a microsection of the basic structure of the roll body;

FIG. 6

a micrograph of the structure of a cured by means of the thermal surface treatment peripheral edge zone of the roller body;

FIG. 7

the microhardness curve in the hardened peripheral edge zone;

FIG. 8

a press with a piston according to the invention; and

FIG. 9

a piston according to the invention of a modified form.

FIG. 1 shows a roller for the treatment of a web material, for example a calender roll, with a cast body 1, namely a roller body, and two flange pins 2 and 3, one of which is mounted on the left and the other on the right front side of the cast body 1. The roller is rotatably mounted in the region of the journal flanges 2 and 3 about an axis of rotation R or provided for pivotal mounting. For the thermal treatment of the web material is in the cast body 1 via one of the pin flanges 2 and 3, a thermal fluid can be supplied, which can be derived via the other or preferably the same pin flange 2 or 3 again. The cast body 1 pass through from one axial end to the other, continuous, near the outer periphery of the cast body 1 located, peripheral tempering 4, which are flowed through during the thermal treatment of the material of the thermal fluid.

FIG. 2 shows the cast body 1 in cross section AA. In the cast body 1, a central cavity is continuously formed axially. The cast body 1 is poured in a chill casting, for example in static chill casting, standing from a melt of an iron-based alloy. The central cavity is formed or incorporated later in this Urformung. As the iron-base alloy, a cast iron alloy is used. The cooling, which experiences the melt primarily on the mold, is controlled so that the melt solidifies over the entire axial length of the cast body 1 from radially inward to radially outward to the outer circumference or almost to the outer circumference stably in a ductile iron structure, ie in the form of a cast iron with nodular graphite. The control of the cooling is done by customized design of the mold. The cooling rate can be adjusted in particular via the radial thickness of the mold, the heat capacity of the mold, the thermal conductivity of the mold material or the total mass of the mold. For adjustment, the mold can only with respect to a single of the mentioned parameters or a combination be designed by two, three or all four of these parameters by appropriate material selection and dimensioning.

The solidification process is controlled so that the melt solidly solidifies not only in an inner zone 5 surrounding the rotation axis R, but also in a peripheral edge zone 6 enclosing the inner zone 5, which forms the outer circumference of the cast body. The cast body 1 thus solidifies over its entire cross-section stable and not white. The carbon is eliminated in the stable solidification in the form of nodular graphite. The cast body 1 immediately obtained by the casting process thus has everywhere a nodular cast iron structure. Due to the cooling rate set deliberately by means of the mold, however, the graphite in the peripheral edge zone 1 separates out more finely than in the inner zone 5. The graphite spherulites SG (sphero-graphite particles) of the peripheral edge zone 6 have a size in the range of the guide numbers of 5 to 8, ie a maximum dimension of at most 0.12 mm. More preferably, the cooling rate is set so that the graphite particles SG of the peripheral edge zone 6 have a size in the range of the guide numbers of 7 (0.022 microns) to 8 according to EN ISO 945, ie a maximum dimension of at most 0.03 mm. The cast iron matrix is also in the peripheral edge zone 6 perlitic with at most a low ferrite content. The pearlite content is at least 90%, more preferably at least 95%, and the ferrite content at most 10%, more preferably at most 5%. If carbide formation can not be prevented, the carbide content is less than 5%, more preferably less than 3%, not only in the inner zone 5 but also in the peripheral edge zone 6 solidified at a higher cooling rate.

FIG. 3 shows a part of the FIG. 2 and further, extracted, a further enlarged view of the microstructure of the casting obtained by the casting. These are the different microstructures of the inner zone 5 and the peripheral edge zone 6 with respect to the fineness of the precipitated graphite particles SG. The microstructure shown next to the cross section of the cast body 1 are primarily of a schematic nature, but qualitatively illustrate that the graphite particles SG are in the peripheral edge zone 6 are smaller than the graphite particles SG in the inner zone 5 and present in the peripheral edge zone 6 correspondingly in finer distribution.

The cast body 1 is made wear-resistant in its subsequent higher-hardness peripheral edge zone 6 already obtained by the casting in a subsequent hardening process. Before or after curing, the peripheral tempering 4 are incorporated, preferably drilled. The circumferential edge zone 6 is that annular zone of the cast body 1 which, after hardening, has the hardness required for the respective application everywhere, ie extends from the outer circumference to the hardening depth. If the peripheral edge zone 6 of the hardened cast body 1 extends radially inwardly up to or even over the tempering channels 4, these are expediently incorporated before hardening. Otherwise, the tempering 4 can just as well be incorporated after curing.

The hardening process is carried out in such a way that the basic structure of the peripheral edge zone 6 obtained directly from the casting is converted into finely striated or, even more advantageously, finely striated perlite. The graphite spherulites SG are thereby not or at least not changed in a manner relevant to the invention. Alternatively to the transformation into fine or microstrip pearlite, i. In sorbitol or troostite, the hardening process can also be designed so that the cast iron matrix within the peripheral edge zone 6 converts into an interstage structure, preferably in austempered ductile iron (ADI). In both variants, the cast body 1 is heated uniformly in the peripheral edge zone 6 to a temperature in the austenitic region, for example at 950 ° C, and then quenched, wherein the quenching rate for the formation of an interstage structure is set higher than for the transformation into the fine perlite, but still not so big that a martensite transformation can take place. The interstitial structure is similar to bainite, preferably the lower bainite, but is not bainite because it contains no or, for the desired strength, only negligible carbides. It is also true for the interstitial structure that the carbide fraction is advantageously less than 5%, preferably at most 3%. It would be ideal if neither the fine pearlitic structure nor the alternative interstitial structure would contain carbides.

FIG. 4 illustrates a curing process using the example of the preferred induction hardening. For hardening, an induction device 8 and a quenching device 9 are moved axially from one end face of the cast body 1 to the other. The movement is uniform with the speed v and a constant during the hardening process axial Distance x, by which the induction device 8 precedes the quenching device 9. The induction device 8 surrounds the cast body 1 by means of the induction device 8 up to the predetermined hardening depth, ie within the peripheral edge zone 6, uniformly throughout the temperature range and then quenched by means of the quenching device 9. The quenching is preferably carried out with a liquid quenching fluid, for example water, which is injected onto the outer circumference of the cast body 1. Although induction hardening is a preferred method of thermal surface treatment curing, the peripheral edge zone 6 may in principle be heated by any other thermal surface treatment method as long as only the required temperature is adjusted with the required uniformity. As an alternative to induction hardening, in particular flame hardening comes into consideration, but primarily only for lower hardening depths. With increasing depth of cure, induction hardening is the preferred choice. The Einhärttiefe and, accordingly, the thickness of the peripheral edge zone 6 is preferably at least 3mm, more preferably at least 5mm. On the other hand, it is advantageous in terms of thermal cycling, if the Einhärttiefe does not exceed 10mm. The hardening depth can be influenced in particular by a variation of the distance x, in the case of induction hardening also by varying the frequency of the respective induction coil 8. Further adjusting parameters for influencing the hardening depth are the speed v, the choice of the quenching fluid and the throughput of quenching fluid.

The FIGS. 5 and 6 are micrographs of the structure of the peripheral edge zone. 6 FIG. 5 shows the basic structure obtained directly from the casting in the scale 50: 1, and FIG. 6 is a microsection of the structure after hardening, thus showing the hardness structure, also in scale 50: 1. In the basic structure of the FIG. 5 the graphite spheres or graphitic spherolites are denoted by SG, the perlite by P and ferrite islands by α. As can be seen, the basic structure consists essentially of perlite and precipitated nodular graphite and small amounts of ferrite, less than 10% ferrite in the exemplary embodiment. The hardness structure consists of fine-grained and very fine-grained pearlite, ie sorbitol and troostite, as well as the embedded sphero-graphite particles SG, the pearlite areas being designated S for sorbitol and T for troostite according to the fineness of the lamellae.

In FIG. 7 the microhardness curve is shown at a given hardening depth of 3 mm, namely the hardness H in HV0.1 over the distance d from the outer circumference of the cast body 1, that is to say over the depth d.

The hardened cast body 1 is tempered, advantageously to a tempering temperature between 300 and 350 ° C.

In the table below, a particularly preferred iron-base alloy for casting the cast body 1 is specified in the last column of the table. The second and third columns contain preferred ranges for the respective alloying partner, with the narrower ranges within the respective wider range being particularly preferred for the same alloying element. For the respective alloying partner, in turn, the proportion specified in the last column is most preferred. The iron-based alloy contains in a preferred embodiment at least carbon, silicon, copper and nickel within the respective specified ranges of shares. Copper as a perlite former and nickel to prevent martensite transformation are preferably used in combination. Fe makes up the rest of the respective alloy. alloying element Share in mass% Share in mass% Share in mass% C 3.0 - 4.0 3.4 - 3.8 3.6 Si 1.7-2.4 1.9 - 2.2 2.1 Cu 0.5 - 1.3 0.7 - 1.0 0.90 Ni 0.3 - 1.5 0.7 - 1.0 0.85 Mn ≤ 0.5 ≤ 0.5 12:35 sn ≤ 0.05 ≤ 0.05 12:01 P <0.1 <0.05 ≤ 0.03 S <0.1 <0.05 ≤ 0.01

Alloy elements of the iron-based alloy

The iron base melt of the composition of the last column has a saturation degree Sc of 0.99 to 1.00. Preference is given to iron-base alloys having a degree of saturation Sc in the range from 0.97 to 1.03, from which range of alloys of near-eutectic composition those having a degree of saturation Sc from the lower half of the stated range are preferred.

1. (i) 0.2%-Dehngrenze R_{p, 0.2} > 400 N/mm²;
2. (ii) Zugfestigkeit R_m > 650 N/mm²;
3. (iii) Bruchdehnung A > 3-4%.
4. (iv) Härte > 400 HV

On a sample cast and hardened according to the disclosed method with fine-grained and very fine-grained perlite with spheroidal graphite, on which also the micrographs of the FIGS. 4 and 5 taken and the hardness profile of FIG. 6 The measurements made in the tensile test gave the following properties in terms of strength and hardness:

1. (i) 0.2% proof stress R _{p, 0.2} > 400 N / mm ² ;
2. (ii) tensile strength R _m > 650 N / mm ² ;
3. (iii) Elongation at break A> 3-4%.
4. (iv) hardness> 400 HV

FIG. 8 shows a hydraulic press with a cast body 10 according to the invention, which forms a piston of the press. The cast body 10 is guided in a cylinder 11 of the press along a working axis A back and forth. On a front side of the cast body 10, a forming tool 12, for example a stamp, is arranged. The press has the die 12 axially opposite a die 13. The cylinder 11 forms at the back of the casting 10 a pressure space with an inlet 14 and an outlet 15 for a hydraulic working fluid to the casting 10 for molding workpieces with a working pressure P of more than 100 bar, preferably at least 200 bar, in direction to be able to act on the die 13.

FIG. 9 shows a casting 10 with a modified form. The modified cast body 10 may also be used as a piston of a press, preferably a hydraulic press. While the cast body 10 of the previous embodiment is at least substantially cylindrically shaped, the modified cast body 10 is at least substantially in the shape of a pot with a bottom forming the back of the piston and a side wall. The punch 12, which contacts the workpiece during forming, protrudes from the molded body 10 from the pot. Also marked is the working axis A for the installed in a press state.

The cast bodies 10 each have a microstructure corresponding to the cast body 1 with a gray-solidified inner zone 5 and an outer peripheral edge zone 6, which encloses the inner zone 5 over the circumference and preferably also over the end faces. The pot-shaped cast body 10 has a peripheral edge zone 6 according to the invention, as also preferably on that outer peripheral surface which rotates on the inside and preferably also on the end face located in the pot. A peripheral edge zone 6 according to the invention preferably encloses the respective cast body 10 on all sides. For the zones 5 and 6 of the cast body 10, the statements made on the zones 5 and 6 of the cast body 1 apply.

The cast bodies 1 and 10 are each solidified in a nodular cast iron structure. In alternative embodiments, the embedded free graphite in the inner zone 5 and also in the peripheral edge zone 6 may be excreted substantially in the form of vermicular graphite or else in the form of spheroidal graphite and vermicular graphite. However, the excretion of nodular graphite is given preference over the excretion of vermicular graphite. In embodiments in which the free graphite is present as spheroidal graphite and also as Vermikulargraphit, it is advantageous if the spheroidal graphite makes up the vast majority of the free graphite.

Claims (15)

1. A cast body, being a tool for forming or original moulding a work piece, or a transfer member (10) for transferring a force or torque onto a tool (12) which contacts the work piece during forming or original moulding, wherein the cast body is not a roller and

   a) is cast from an iron base alloy

   b) which forms an interior zone (5) of the cast body (10) made of grey cast iron (GJS, GJV) and,

   c) around the interior zone (5), a circumferential rim zone (6) which includes the outer circumference of the cast body (1)

   d) and has a surface hardness which is greater than 400 HV,

   e) wherein the circumferential rim zone (6) consists of ribbon grain or superfine ribbon grain pearlite (P) with embedded free graphite, preferably spheroidal graphite (SG) or vermicular graphite (V), or of an intermediate structure (ADI) with spheroidal graphite or vermicular graphite.
2. The cast body according to the preceding claim, characterised in that the embedded free graphite is at least substantially spheroidal graphite (SG) and the graphite pebbles of said spheroidal graphite in the solidified circumferential rim zone (6) exhibit a size which corresponds to an index value of at least 5 and preferably at most 7 in accordance with EN ISO 945.
3. The cast body according to any one of the preceding claims, characterised in that the cast iron in the circumferential rim zone (6) contains at least 95% pearlite and at most 5% ferrite.
4. The cast body according to any one of the preceding claims, characterised in that the material of the circumferential rim zone (6) exhibits at least one of the following stability values:

   (i) 0.2% proof stress R_{p, 0.2} > 400 N/mm²;

   (ii) tensile strength R_m > 600 N/mm², preferably R_m > 650 N/mm²;

   (iii) elongation at rupture A > 1.5%, preferably A > 2%.
5. The cast body according to any one of the preceding claims, characterised in that the cast body (10) is a constituent of a forging tool or press for forming or original moulding the work piece.
6. The cast body according to any one of the preceding claims, characterised in that the cast body (10) is a piston or plunger, preferably for a hydraulic application of force.
7. The cast body according to any one of the preceding claims and at least one of the following features:

   (i) the iron base alloy contains at least 0.3% nickel and preferably at most 1.5% nickel;

   (ii) the iron base alloy contains at least 0.5% copper and preferably at most 1.3% copper.
8. The cast body according to any one of the preceding claims, characterised in that the iron base alloy contains at least 1.7% silicon and preferably at most 2.4% silicon.
9. The cast body according to any one of the preceding claims, characterised in that the iron base alloy contains 3% to 4% carbon.
10. A method for manufacturing a cast body according to any one of the preceding claims, wherein:

    a) the cast body (1; 10) is die-cast from a molten mass of an iron base alloy;

    b) the cooling speed at the die is set to be low enough that the molten mass does not solidify white but rather stably as cast iron (GJS, GJV) with freely embedded graphite, preferably spheroidal graphite (SG) or vermicular graphite (V), even in a circumferential rim zone (6) which includes the outer circumference of the cast body (1; 10);

    c) and the material of the circumferential rim zone (6) is transformed by means of a thermal surface treatment into ribbon grain or superfine ribbon grain pearlite (P) with spheroidal or vermicular graphite (SG, V) or into an intermediate structure (ADI) with spheroidal graphite or vermicular graphite.
11. The method according to the preceding claim, characterised in that the embedded free graphite of the circumferential rim zone (6) is at least substantially spheroidal graphite (SG), and the cooling speed at the die is set to be high enough that the graphite pebbles of said spheroidal graphite (SG) in the solidified circumferential rim zone (6) exhibit a size which corresponds to an index value of at least 5 and preferably at most 7 in accordance with EN ISO 945.
12. The method according to any one of the preceding claims, characterised in that the cast iron in the circumferential rim zone (6) contains at least 90% pearlite and at most 10% ferrite before the surface treatment.
13. The method according to any one of the preceding claims, characterised in that the iron base alloy is composed in such a way that the martensite starting temperature (M_s) of the cast iron is lower than 20 °C.
14. The method according to any one of the preceding claims, characterised in that the surface treatment is performed without martensitic transformation.
15. The method according to any one of the preceding claims, characterised in that after a surface treatment has been performed, the cast body (1; 10) is tempered and cooled again, without martensitic transformation.

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