EP3272888A1 - Material made from a copper-zinc alloy, method for producing such a material and sliding member made of such a material - Google Patents

Abstract

The invention relates to a material of a copper-zinc alloy having the following composition in wt .-%:

Balance Cu and unavoidable impurities. According to the invention, the material has a microstructure (1) with an alpha-phase matrix in which manganese-containing phosphides are incorporated, wherein the manganese-containing phosphides are formed as phosphide particles (2) with globular shape and wherein at least 90% of these phosphide particles (2) a Have a size of at most 2.0 microns. Furthermore, the invention relates to a method for producing such a material and a sliding element made of such a material.

Description

The invention relates to a material made of a copper-zinc alloy, a method for producing such a material and a sliding element made of such a material.

It is known to use lead-reduced copper-zinc alloys for sliding elements containing manganese-containing silicides. Silicides impart high resistance to abrasive wear as hard phases of a copper-zinc alloy. Furthermore, due to their low tendency to weld, they provide better resistance to adhesive wear. In addition, the alloys usually contain other alloying constituents in considerable quantities, such as Al, Ni and Fe. The structure of such alloys consists either of a combination of α- and β-phase or predominantly of β-phase. Semi-finished products of such alloys are usually produced by processes comprising at least one hot working. For sliding elements, which are produced from strip-shaped semi-finished products, alloys are sought, which are characterized by a high cold workability.

In the patent DE 10 2007 029 991 B4 For improved cold workability, improved copper-zinc alloys are disclosed, as well as methods of making tubes and rods from these alloys. In the copper-zinc alloys, the proportions of silicon, manganese, iron and nickel are adjusted that in the structure of the material both iron-nickel-manganese-containing mixed silicides with stem-like form as well as iron and nickel-enriched mixed silicides are present with globular shape. The structure of the material consists of an α-matrix, in which in addition to the silicides at least 5 vol .-% and up to 50 vol .-% β-phase is incorporated. The globular silicides are considered to cause stabilization of the β-phase. The heterogeneous matrix structure of α- and β-phase, together with the extremely high content of hard phases, in particular the iron-nickel-manganese-containing mixed silicides, ensures a targeted complex wear resistance of the components made from these alloys. The processing of the alloy includes extrusion in a temperature range of 600 to 800 ° C. This hot working is favored by the structure in the cast state up to 50 vol .-% β-phase has. Tubes made from these alloys achieve elongation at break values of up to approximately 13%.

Furthermore, from the document DE 36 26 435 A1 a copper-zinc alloy known for sliding bearings. The alloy contains 66 to 90% by weight of Cu, 1.0 to 8.0% by weight of Mn, 0.3 to 0.7% by weight of Al, 0.3 to 2.0% by weight of P and rest zinc. Manganese phosphides are contained in eutectic form in the structure. The eutectic excretion is controllable by the amount of added aluminum. The ratio of phosphorus to aluminum is important for the processability of this alloy. Silicon is not provided in this alloy. Materials made of this alloy can reach a hardness of up to 207 HB.

The invention has for its object to provide a material which is due to its strength, hardness, ductility and wear properties for plain bearings and has a high formability for economical production. In addition, the material should have a high heat resistance up to over 300 ° C. Furthermore, the invention is based on the object, a production method for such a material and a particular temperature resistance and manufacturing cost improved sliding element specify.

The invention is reproduced in terms of a material by the features of claim 1, with respect to a method by the features of claim 6 and with respect to a sliding member by the features of claim 9. The other dependent claims relate to advantageous embodiments and further developments of the invention.

• 21 bis 27 % Zn,
• 0,2 bis 0,8 % Si,
• 1,1 bis 1,9 % Mn,
• 0,005 bis 0,2 % P,
• wahlweise noch bis maximal 0,2 % Ni,
• Rest Cu und unvermeidbare Verunreinigungen. Erfindungsgemäß weist der Werkstoff ein Gefüge mit einer alpha-Phase-Matrix auf, in die manganhaltige Phosphide eingelagert sind. Die manganhaltigen Phosphide sind als Phosphidpartikel mit globularer Form ausgebildet und mindestens 90 % dieser Phosphidpartikel weisen eine Größe von höchstens 2,0 µm auf.

The invention includes a material of a copper-zinc alloy having the following composition in% by weight:

• 21 to 27% Zn,
• 0.2 to 0.8% Si,
• 1.1 to 1.9% Mn,
• 0.005 to 0.2% P,
• optionally up to a maximum of 0.2% Ni,
• Balance Cu and unavoidable impurities. According to the invention, the material has a structure with an alpha-phase matrix in which manganese-containing phosphides are incorporated. The manganese-containing phosphides are formed as phosphide particles with globular shape and at least 90% of these phosphide particles have a size of at most 2.0 microns.

The invention is based on the idea to choose the composition of a copper-zinc alloy so that a wrought material with high cold workability and good wear properties is formed. The material may preferably be a band material. As a semi-finished such a strip material for the production of rolled plain bearing bushings or half shells is suitable. The material according to the invention is based on a copper-zinc alloy with a comparatively low zinc content for bearing materials. The zinc content should not fall below 21 wt .-%, otherwise the strength of the material is not sufficient. The zinc content should not exceed 27% by weight otherwise the cold workability is limited. The material has a structure with an alpha-phase matrix, which is favorable for high cold workability. Preferably, the zinc content is at least 22.6 wt .-%. From this zinc content, the material has very favorable properties in terms of strength and hardness. Preferably, the zinc content is at most 25.2 wt .-%. Up to this upper limit of the zinc content, the cold workability of the material is excellent.

The copper-zinc alloy of the material according to the invention also contains 0.2 to 0.8 wt .-% Si, 1.1 to 1.9 wt .-% Mn and 0.005 to 0.2 wt .-% P. Bei aus The prior art alloys of similar composition describe the formation of manganese silicides. Surprisingly, in the material according to the invention manganese-containing phosphides are present in a significant amount and with a characteristic distribution, while the expected manganese silicides in the alloy can not be detected, although the silicon content is comparatively high relative to the phosphorus content. It is to be assumed that in the material according to the invention manganese silicides, which are formed as precipitates upon solidification and cooling of the melt, are redissolved in a subsequently performed heat treatment.

In the manganese-containing phosphide particles of the material according to the invention, the mass ratio of manganese to phosphorus is between 2.7 and 3.3. The quantitative composition of the particles is determined by means of energy-dispersive X-ray spectroscopy (EDXS). Furthermore, in the material according to the invention particles can be detected which contain phosphorus, manganese and oxygen. The mass-related manganese content is significantly reduced in these particles compared to the manganese-containing phosphides. It is approximately at the same level as the oxygen content of these particles.

The manganese-containing phosphides are phosphide particles of globular form educated. In the context of this invention, globular form does not only mean the exact sphere, but also all forms which can be described approximately as ellipsoids of revolution. At least 90% of the phosphide particles have a size of at most 2.0 μm. The maximum size of the phosphide particles is 4 μm. In the case of particles with a spherical shape, the diameter of the particle is defined as a measure of the size of the particle. For particles of not exactly spherical shape, "size" is understood to mean the volume-equivalent diameter, that is to say the diameter of a sphere which is the same volume as the particle. The average size of all phosphide particles, which can be seen by light microscopy in the etched microstructure at 1000x magnification, is between 0.8 and 1.5 μm. The smallest light microscopic visible particles have a size of 0.5 microns. This means that phosphide particles smaller than 0.5 μm are not used in a light microscopic determination of the average size of the phosphide particles. The averaging therefore only begins with particles having a size of at least 0.5 μm. From the globular form, it can be concluded that the phosphide particles are not fragments of originally larger particles. The phosphide particles are compact and no cracks occur within the particles. The density of the incorporated in the matrix phosphide particles is inhomogeneous. There are first areas where the matrix is nearly free of phosphide particles, while second areas are rich in phosphide particles.

The manganese-containing phosphides hinder the recrystallization of the microstructure at elevated temperatures and thus improve the wear resistance of the material.

In the material according to the invention, the manganese content is preferably from 1.3 to 1.6% by weight.

In the material according to the invention, the silicon content is preferably 0.3 to 0.6% by weight.

Preferably, in the material according to the invention, the phosphorus content is 0.03 to 0.08 wt .-%.

Optionally, the copper-zinc alloy can be added up to 0.2 wt .-% nickel. Nickel together with phosphorus forms precipitates that increase the strength of the material.

The copper content of the copper-zinc alloy of the material according to the invention may be between 72 and 76% by weight, depending on the exact composition.

The copper-zinc alloy of the material according to the invention may contain impurities. Impurities are understood to mean elements which are present in the alloy in such a small proportion that they do not significantly affect the properties of the material. Typically, impurities are less than 0.1 wt% per element in the alloy and the sum of all impurities is less than 0.5 wt%, preferably less than 0.25 wt%.

The particular advantage of the material according to the invention is that its alpha-phase matrix allows high degrees of cold work even without intermediate annealing. In the context of this invention, the degree of reduction q is the decrease in the cross-sectional area of the formed material relative to its starting cross-sectional area. For strip-shaped materials, which are formed by rolling from an initial thickness s ₁ to a final thickness s ₂ , the degree of deformation is then calculated as follows: $$\mathrm{q}=\left({\mathrm{s}}_{\mathrm{1}}-{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="imgf0002.png"\; state="\{\{state\}\}">s</figure-callout>}}_{\mathrm{2}}\right)/{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="imgf0002.png"\; state="\{\{state\}\}">s</figure-callout>}}_{\mathrm{1}}$$

The material according to the invention permits cold working degrees of more than 65%, even more than 85%, without intermediate annealing. This allows a cost-effective production of thin strips, which can be used for example as a semi-finished for the production of rolled plain bearing bushes.

Furthermore, the material according to the invention exhibits a significant starting effect. After cold working of more than 60% without intermediate annealing, the strength and hardness of the material can be further increased by annealing at 300 ° C for 1 to 3 hours. As a result, the tensile strength R _m of 740 MPa to at least 780 MPa, the yield strength R _p0.2 of 650 MPa to at least 720 MPa and the hardness of 200 HB 2.5 / 62.5 to at least 230 HB 2.5 / 62, 5 are raised. The elongation at break in this state is about 5%.

In order to increase the elongation at break and thus the ductility of the material in the final state, the material can be subjected to a further heat treatment at temperatures above 300 ° C. By a heat treatment between 380 and 420 ° C, the elongation at break can be increased to 16% to 25%. However, the tensile strength of the material only decreases by 13 to 24% relative to the initial value. The material is therefore very temperature resistant. In particular, its strength and hardness decrease less with increasing temperature than is the case with similar materials known in the art. For example, at temperatures above 440 ° C the hardness is only 20% below the value at 25 ° C. This temperature resistance is particularly important for plain bearings in modern internal combustion engines of great importance.

Another advantage of the material according to the invention is its high wear resistance. This is due to the manganese-containing phosphides, which are embedded as small hard particles with a globular shape in the ductile matrix. On the other hand, the ductile matrix gives the material a high dynamic load capacity.

Plain bearings made of this material have a coefficient of friction of less than 0.1.

In a preferred embodiment of the invention, at least part of the manganese-containing phosphides can be arranged like a pearl cord. In other words, the phosphide particles are arranged along virtual lines like pearls on a string. The lines extend substantially along the forming direction, but they are not perfectly straight. Slight bends and kinks may be present. Also, deviations from the forming direction are present with respect to the alignment of the lines. The lines along which the particles are arranged follow the flow behavior of the matrix structure. The manganese-containing phosphides are arranged along the sliding lines and shear bands of the material. Neighboring phosphide particles are spaced apart with a few exceptions. The bead-like arranged phosphide particles thus form no coherent structure such as a chain or a stalky or needle-like conglomerate. The characteristic arrangement of the manganese-containing phosphides is due to the stretching of the microstructure during forming. In the process, the phosphides interdendritically stored as accumulation during the solidification process are essentially distributed in the shaping direction. In the material according to the invention, the length of the individual bead-cord-like arrangements of phosphide particles is 10 to 60 μm. The length of the bead cord-like arrangement is related to the degree of deformation, which is applied during the forming of the material. The greater the degree of deformation, the greater the length of the bead-string-like arrangements. Since the individual phosphide particles are embedded in the matrix predominantly from adjacent particles, they are completely enclosed by matrix structure and their anchoring in the matrix is particularly firm. Breaking out of the phosphides from the matrix is thereby effectively prevented.

In a particularly preferred embodiment of the invention, the manganese-containing Phosphides may be arranged so that in at least 50% of all bead-like arrangements of manganese-containing phosphides, a section of 20 microns in length is present in which 7 to 30 phosphide particles are arranged with a size of 0.5 to 2.0 microns. The phosphide particles have a size distribution which is influenced, among other things, by the conditions which prevail during the solidification of the melt. The density with which the phosphide particles are arranged along a line correlates with the degree of deformation with which the material was formed. The stronger the deformation, the further the phosphide particles are distributed. By an appropriate process management in the production of the material, the described arrangement of the phosphide particles. In other words, this arrangement of the manganese-containing phosphide particles typical of the material is, as it were, the characteristic "fingerprint" left by the production process in the material. The manganese-containing phosphide particles arranged in this way ensure the particular wear resistance of the material. Consequently, the good suitability of the material for sliding elements is not a property which the alloy has on its own due to its composition, but it is the combination of alloying composition and manufacturing process that results in the inventive material.

Advantageously, the microstructure of the material according to the invention may comprise first regions that are recrystallized and second regions that are not recrystallized. The microstructure is thus incompletely recrystallised after the final annealing. When the melt solidifies, almost phosphide-free dendrites form. In the areas between the dendrites, the phosphides accumulate and are pushed there by the growth of the dendrites to accumulations. As a result of the transformation, the nearly phosphide-free dendrites become areas in the transformed microstructure that are virtually free from phosphides, while from the interdendritic accumulations of the phosphides regions with a high phosphide density in the reshaped microstructure become. After the Transformations is thus a strongly inhomogeneous phosphide distribution. The phosphide-poor regions recrystallize even at a lower temperature than the phosphide-rich regions, because the manganese-containing phosphides inhibit recrystallization in the phosphide-rich regions. The phosphide-poor, recrystallized areas are advantageous for the ductility of the material, the phosphide-rich, non-recrystallized areas are advantageous for its wear resistance. In other words, there are virtually two very different material components next to each other, which complement each other favorably in their properties.

In an advantageous embodiment of the invention, the copper-zinc alloy of the material according to the invention may contain at least 0.03 wt .-% Ni. Nickel, together with phosphorus, forms nickel phosphides embedded in the structure. The nickel phosphides are so small that they are barely visible by light microscopy. They fix the grain boundaries and thus increase the strength of the material. The ratio of the proportions of nickel (in% by weight) and phosphorus (in% by weight) is particularly preferably between 0.8 and 1.2. In such an alloy composition are particularly favorable conditions for the simultaneous formation of manganese-containing phosphides and nickel phosphides before. The former contribute to the wear resistance of the material, the latter increase the strength of the material.

• 21 bis 27 % Zn,
• 0,2 bis 0,8 % Si,
• 1,1 bis 1,9 % Mn,
• 0,005 bis 0,2 % P,
• wahlweise noch bis maximal 0,2 % Ni,
• Rest Cu und unvermeidbare Verunreinigungen. Das Verfahren umfasst dabei folgende Schritte in der genannten Reihenfolge:
  1. a) Erschmelzen der Legierung,
  2. b) Gießen eines Gussformats,
  3. c) Wärmebehandlung des Gussformats bei einer Temperatur von mindestens 610 °C und höchstens 800 °C mit einer Dauer von 1 bis 6 Stunden,
  4. d) Kaltumformen in einem oder mehreren Schritten mit einem Gesamtumformgrad von mindestens 50 %,
  5. e) Wärmebehandlung bei einer Temperatur von mindestens 280 °C und höchstens 440 °C mit einer Dauer von 1 bis 3 Stunden.

Another aspect of the invention includes a method for producing a material of a copper-zinc alloy having the following composition in% by weight:

• 21 to 27% Zn,
• 0.2 to 0.8% Si,
• 1.1 to 1.9% Mn,
• 0.005 to 0.2% P,
• optionally up to a maximum of 0.2% Ni,
• Balance Cu and unavoidable impurities. The method comprises the following steps in the order named:
  1. a) melting the alloy,
  2. b) casting a casting format,
  3. c) heat treatment of the casting mold at a temperature of at least 610 ° C and at most 800 ° C with a duration of 1 to 6 hours,
  4. d) cold forming in one or more steps with a total degree of deformation of at least 50%,
  5. e) heat treatment at a temperature of at least 280 ° C and at most 440 ° C with a duration of 1 to 3 hours.

In the method according to the invention, an alloy according to the described composition is first melted. In particular, the alloy may also have a limited composition, as specified above in the description of the material according to the invention. The casting format cast in step b) is preferably slab or ribbon. After casting, the surface of the casting format can be milled. For homogenization, a heat treatment of between 610 ° C. and 800 ° C., preferably between 655 ° C. and 695 ° C., is carried out on the casting format. The duration of this heat treatment is between 1 and 6 hours. To get from the casting format to the final dimension of the material, forming steps are carried out. In this case, according to the invention, at least one sequence of cold-forming steps without intermediate annealing is carried out with a total degree of deformation of at least 50%. The Gesamtumformgrad is the accumulated over the sequence of forming steps reduction in cross-section relative to the initial cross-section. It is also possible to achieve a degree of deformation of at least 50% in a single cold forming step. The cold formations may preferably be rolling steps for producing a band-shaped material. In the case of the abovementioned alloy composition, the high degree of cold work leads to the formation of a microstructure in which an alpha-phase matrix is used Inhomogenously distributed, manganese-containing phosphides are incorporated with globular shape and with a maximum size of 4 microns. 90% of the phosphide particles have a size of at most 2.0 μm. This structure gives the material properties which are very advantageous for use as a sliding bearing material. Preferably, the Gesamtumformgrad of carried out without intermediate annealing Kaltumformungen is at least 65%. The material is subjected after the last cold forming a heat treatment at a temperature of at least 280 ° C and at most 440 ° C with a duration of 1 to 3 hours. If the temperature is between 280 ° C and 320 ° C, then the strength and hardness of the material rise above the initial values of the work-hardened material. Preferably, the temperature during the heat treatment is at least 370 ° C and at most 420 ° C. By such a final heat treatment, the strength and hardness of the material are only slightly reduced, at the same time the ductility of the material is increased to a level that is favorable for dynamically loaded plain bearings.

In a preferred embodiment of the inventive method, a band-shaped casting format can be cast in method step b) and after method step c) and before method step d) at least one cold forming, which starts with the casting format and has a degree of deformation of at least 20%, and at least one further Heat treatment done. The heat treatment is carried out at a temperature of at least 610 ° C and at most 800 ° C, preferably between 655 ° C and 695 ° C, with a duration of 1 to 6 hours. Band-shaped casting format is understood in this preferred embodiment of the inventive method, a casting format having a maximum thickness of 20 mm, preferably at most 15 mm. With a casting format of this small thickness, hot forming is not required, but the casting format can be cold formed immediately after homogenizing annealing. The degree of deformation is at least 20%, preferably at least 30%. This first cold forming closes another heat treatment as an intermediate annealing. Depending on the size of the casting format and the size of the final format, after this heat treatment optionally a further cold forming with a degree of deformation of at least 30% and a further heat treatment can be carried out. The last stage of cold working is then carried out as described in process step d) with a degree of deformation of at least 50%, preferably at least 65%.

The advantage of this method is that the casting format is already relatively thin and therefore few forming steps have to be carried out to the final dimension. In particular, no hot forming must be performed. Furthermore, this production route is particularly suitable for the production of relatively small quantities.

As an alternative to a strip-shaped casting format, a slab-shaped or plate-shaped casting format can be cast in method step b). In this alternative, the heat treatment in process step c) is followed by hot working at a temperature of at least 720 ° C. and at most 830 ° C. The degree of deformation during hot forming is at least 60%. It is chosen so that the dimension of the intermediate product after the hot forming is as small as possible, so that the final dimension of the material can be achieved by a sequence of cold forming. Preferably, the process step d) described above, in which a cold working is carried out with a Gesamtumformgrad of at least 50%, preferably at least 65%, this sequence. In this alternative method for producing the inventive material, it is possible to achieve degrees of deformation of at least 85% and reach up to 95% without intermediate annealing. This allows a very economical production of the material according to the invention.

Another aspect of the invention includes a slider of one of the above described, inventive material a. Due to its properties, the material of the invention is very well suited for use as a material for sliding elements. Preferably, the sliding element can be made of a band-shaped material. An example of this are rolled bushes for plain bearings. Another example is half shells for the storage of crankshafts in internal combustion engines. Such half shells can be made of a solid material of the material according to the invention or the material according to the invention is applied as a thin metal layer on a steel backing. In the latter case, the thickness of the metal layer is 0.3 to 0.8 mm. The excellent cold workability of the material according to the invention enables the cost-effective production of such thin strips.

Embodiments of the invention will be explained in more detail with reference to the schematic drawings.

Fig. 1

ein erstes Diagramm zum Entfestigungsverhalten des erfindungsgemäßen Werkstoffs

Fig. 2

ein zweites Diagramm zum Entfestigungsverhalten des erfindungsgemäßen Werkstoffs

Fig. 3

eine Gefügeskizze einer ersten erfindungsgemäßen Werkstoffprobe

Fig. 4

eine Gefügeskizze einer zweiten erfindungsgemäßen Werkstoffprobe

Fig. 5

den Ablauf eines erfinderischen Herstellverfahrens

Fig. 6

den Ablauf eines alternativen erfinderischen Herstellverfahrens.

Show:

Fig. 1

a first diagram for Entfestigungsverhalten of the material according to the invention

Fig. 2

a second diagram for Entfestigungsverhalten of the material according to the invention

Fig. 3

a microstructure of a first material sample according to the invention

Fig. 4

a microstructure of a second material sample according to the invention

Fig. 5

the course of an inventive manufacturing process

Fig. 6

the course of an alternative inventive manufacturing process.

Corresponding parts are provided in all figures with the same reference numerals.

Alloys were used to produce the material according to the invention melted and poured. Table 1 shows the chemical composition of particularly preferred samples in wt .-%. The two samples differ essentially in the zinc content and consequently also in the copper content. Sample 1 has about 23 wt% Zn, sample 2 has about 25 wt% Zn. As a comparative sample, a sample of the alloy CuZn31Si1 is used. This alloy is known as an alloy for sliding elements of the prior art. Table 1: Composition of the samples in% by weight Cu Zn Mn Si P Fe Ni rest Sample 1 75.12 22.92 1.38 0.42 0.05 0.01 0.08 0.02 Sample 2 73.18 24.88 1.36 0.40 0.07 0.01 0.08 0.02

For the production of a strip-shaped material which is suitable for the production of sliding elements, the alloys were cast in the strip casting method into strips with the thickness of 13 mm. After surface milling and homogenizing annealing at 690 ° C./3 hours, three-stage cold rolling was carried out with degrees of deformation of 25% in the first stage, 35% in the second stage and 65% in the third stage to the final dimension of 2 mm thickness. Between the individual forming stages, the alloys were annealed at 690 ° C for 3 hours each. After the last cold forming, heat treatment was performed on each alloy at different temperatures between 300 ° C and 460 ° C to determine the temperature resistance of the materials. Table 2 shows the result of this study. Shown in each case are the yield strength R _p0.2 and the tensile strength R _m in the MPa after a two-hour heat treatment at the temperature indicated in the first column. The values at 25 ° C are the strength values of the material immediately after the last cold forming, ie without final

Heat treatment.

Table 2: Strength values after final heat treatment Sample 1 Sample 2 comparison sample CuZn23Mn1,4Si0,4NiP CuZn25Mn1,4Si0,4NiP CuZn31Si1 T in ° C R _p0.2 in MPa R _m in MPa R _p0.2 in MPa R _m in MPa R _p0.2 in MPa R _m in MPa 25 654 740 654 748 690 800 300 714 779 735 796 730 800 340 666 738 678 747 418 588 380 566 651 569 652 322 523 420 459 571 460 570 290 501 460 385 522 398 530 250 473

In the Figures 1 and 2 the results are shown graphically. In the diagram of FIG. 1 For all three samples the yield strength R _p0,2 and in the diagram of the FIG. 2 the tensile strength R _{m is} plotted against the temperature of the heat treatment carried out in each case. In both diagrams, the tempering effect can be seen: Through a heat treatment at 300 ° C, the yield strength and tensile strength of the materials increase compared to the cold-rolled state. On the other hand, if the annealing temperature exceeds 300 ° C, the yield strength and the tensile strength of the materials decrease. In the case of the comparative material CuZn31Si1, however, this decrease takes place much faster than with the two materials according to the invention. The data points to the comparison material are connected by a dashed line. It can be seen that in both diagrams, the dashed line between 300 ° C and 400 ° C falls much steeper than the solid lines connecting the data points of the samples according to the invention. The material according to the invention is thus significantly more temperature-resistant than the comparative material. This improved temperature resistance is advantageous for the use of the material according to the invention as sliding bearings in modern internal combustion engines.

The elongation at break of the two samples according to the invention in the cold-rolled state and after the heat treatment at 300 ° C is about 4%. Annealing at 340 ° C increases it to about 7%. A further increase in the annealing temperature by 40 ° C leads to a further increase in the elongation at break by 10 percentage points, so that after annealing at 460 ° C, an elongation at break of almost 32% is achieved.

Fig. 3 shows a sketch of the structure 1 of the sample 1 according to the invention after a heat treatment at 420 ° C. Fig. 4 shows a sketch of the structure 1 of the sample 2 according to the invention after a heat treatment at 420 ° C. The sketches were made from light-microscopic photographs of sections of the respective structure. In both figures, the manganese-containing phosphides can be recognized as globular particles 2. The phosphides are distributed inhomogeneously. There are first areas 31 to recognize in the structure, which are low in phosphides. In these areas 31, the microstructure is recrystallized. Likewise, second regions 32 are recognizable in the structure, which are rich in phosphides. In these regions 32, the microstructure is unrecrystallized. The phosphide particles 2 are arranged like a pearl cord, whereupon reference numeral 21 indicates. In particular in Fig. 3 As can be seen, the phosphide particles 2 are arranged along virtual lines that extend substantially in the rolling direction. Also in Fig. 4 Most phosphide particles 2 align along lines that are substantially aligned in the rolling direction. Additionally are in Fig. 4 however, a few phosphide particles 2 visible whose arrangement 21 deviates significantly from the rolling direction. In the FIGS. 3 and 4 corresponds to the rolling direction of the horizontal.

Fig. 5 schematically shows the sequence of an inventive manufacturing process in the event that after the melting of the alloy, a band-shaped casting format is poured. In the illustrated procedure, only two cold rolling stages are shown. In addition, another cold rolling stage can be used a degree of deformation of at least 30% be provided. This preferably follows the intermediate annealing after the first cold rolling stage. Before the last cold rolling step with a degree of deformation of at least 50%, an intermediate annealing is then carried out again.

Fig. 6 shows schematically the sequence of an inventive manufacturing method in the event that after melting the alloy by continuous casting a slab or plate-shaped casting format is poured. In the illustrated process sequence, only one cold rolling stage is shown after hot rolling. In addition, a further cold rolling stage can be provided with a degree of deformation of at least 30%. This then follows the hot rolling. Before the last cold rolling stage with a degree of deformation of at least 50% then takes place an intermediate annealing.

LIST OF REFERENCE NUMBERS

1

structure

2

Phosphidpartikel

21

pearl cord-like arrangement

31

first areas, recrystallized

32

second areas, not recrystallized

Claims (9)

Material of a copper-zinc alloy having the following composition in% by weight: Zn: 21 to 27%, Si: 0.2 to 0.8%, Mn: 1.1 to 1.9%, P: 0.005 to 0.2%, optionally Ni: up to a maximum of 0.2%, Balance Cu and unavoidable impurities,
characterized,
in that the material has a structure (1) with an alpha-phase matrix in which manganese-containing phosphides are incorporated, the manganese-containing phosphides being formed as phosphide particles (2) with a globular shape and at least 90% of these phosphide particles (2) having a size of not more than 2.0 microns. Material according to claim 1, characterized in that at least part of the manganese-containing phosphides is arranged like a pearl cord. Material according to claim 2, characterized in that the manganese-containing phosphides are arranged so that in at least 50% of all bead cord-like arrangements (21) of manganese-containing phosphides, a section of 20 microns in length is present in the 7 to 30 phosphide particles (2) with a Size of 0.5 to 2.0 microns are arranged. Material according to one of the preceding claims, characterized in that the structure has first regions (31) which are recrystallized and second regions (32) which are not recrystallized. Material according to one of the preceding claims, characterized in that the copper-zinc alloy contains at least 0.03 wt .-% Ni. Process for producing a material from a copper-zinc alloy having the following composition in% by weight: Zn: 21 to 27%, Si: 0.2 to 0.8%, Mn: 1.1 to 1.9%, P: 0.005 to 0.2%, optionally Ni: up to a maximum of 0.2%, Balance Cu and unavoidable impurities,
the method comprising the following steps in the order named: a) melting the alloy b) casting a casting format c) Heat treatment of the casting mold at a temperature of at least 610 ° C and at most 800 ° C with a duration of 1 to 6 hours d) cold forming with a total degree of deformation of at least 50% e) heat treatment at a temperature of at least 280 ° C and at most 440 ° C with a duration of 1 to 3 hours. Method according to Claim 6, characterized
that in step b) a strip-shaped casting format is poured and that after process step c) and before process step d) at least one cold forming, which begins with the casting format and has a degree of deformation of at least 20%, and at least one further heat treatment, wherein the heat treatment at a temperature of at least 610 ° C and 800 ° C for a period of 1 to 6 hours. A method according to claim 6, characterized in that in step b) a slab-shaped casting is poured and that is followed by the heat treatment in step c) hot working at a temperature of at least 720 ° C and at most 830 ° C. Sliding element made of a material according to one of claims 1 to 5.

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