Casting material made of copper-zinc alloy, method for producing casting product, and casting part

Abstract

The present invention relates to a casting material made of a copper-zinc alloy, having the following composition by weight: Cu: 58.0-66.0%, Si: 0.15-1.2%, P: 0.20-0.38%, Sn: optionally up to 0.5%, Al: optionally up to 0.05%, Fe: optionally up to 0.3%, Ni: optionally up to 0.3%, Pb: optionally up to 0.25%, Bi: optionally up to 0.1%, Te, Se, In: optionally up to 0.1%, each up to 0.1%, B: optionally up to 0.01%, with the balance being Zn and unavoidable impurities, with the proportion of unavoidable impurities being less than 0.2% by weight. The alloy has a structure containing α phase, β phase, and phosphide particles. The proportion of β phase to the total of α phase and β phase is at least 20% by volume and at most 70% by volume. Si is present in both the α phase and the β phase. 21000 μm 2 Within this area, there are 20-300 phosphide particles with equivalent diameters of 0.5-1 μm, 30-120 phosphide particles with equivalent diameters of 1-2 μm, and 20-100 phosphide particles with equivalent diameters of 2-5 μm. The proportion of β phase and the proportions of Si and P are selected so that the alloy satisfies the following condition: 92.7249 - 0.473254 · [Beta] - 80.6378 · [Si] - 142.65 · [P] + 279.309 · [Si] · [P] < 40, where [Beta] is the proportion of β phase in volume percent, [Si] is the proportion of silicon in weight percent, and [P] is the proportion of phosphorus in weight percent.

Description

[Technical Field]

[0001] The present invention relates to a casting material made of a copper-zinc alloy, a method for producing a casting product, and a cast part. [Background technology]

[0002] Copper-zinc casting materials (also called "casting alloys") consisting of alpha and beta phases containing about 1% lead by weight, such as CuZn39Pb1Al-B (CB757S), have excellent castability, very good machinability, and good polishability. Lead-containing copper-zinc casting alloys are used in many applications in the sanitary sector, especially in the drinking water sector, for faucets and plumbing.

[0003] The positive effect of lead in copper-zinc alloys is due to the presence of elemental lead particles in the structure, which act as chip breakers. During cutting, lead exists as a liquid phase due to the strong local deformation of the workpiece and the resulting local temperature rise. Because liquid lead cannot absorb stress, this leads to stress concentration in the weakened load-bearing matrix, which makes chip breaking more likely. In addition, during cutting, lead is incorporated into the tribological layer between the material and the tool, which leads to effective lubrication and therefore reduced friction and wear. Furthermore, lead in copper-zinc alloys is known to produce significant grain refinement. This is favorable for abrasive properties, especially in cast materials. Furthermore, lead is also inexpensive.

[0004] However, lead is harmful to the environment. Even small amounts can accumulate in the human body if ingested, potentially causing health problems. Therefore, the EU, the United States, China, and other countries are constantly lowering the lead content limits in copper alloys and making efforts to use lead-reduced or lead-free machinable copper alloys instead of lead-containing brasses. The upper limit is set at 1000 ppm (0.1%) Pb in EU directives, such as RoHS (Directive 2011 / 65 / EU). To ensure good machinability even at such low lead contents, various alloying elements are proposed as lead replacements.

[0005] It is well known from numerous publications that bismuth (Bi) can be used as a lead substitute to improve machinability. To mitigate the formation of Bi films along grain boundaries and the associated susceptibility to stress cracking and hot tearing, the addition of further elements has been proposed. References in particular to U.S. Pat. Nos. 5,611,149, 5,893, 6,149,150, 6,159,160, 6,169,170, 6,179,180, and 6,179,190 are cited. However, Bi is undesirable because, on the one hand, it is a rare metal that is difficult to obtain, and, on the other hand, it causes high-temperature embrittlement within the material cycle of copper materials.

[0006] Furthermore, Patent Document 6 discloses a copper-zinc alloy containing 0.1 to 1.5 wt.% Si, 0.03 to 0.4 wt.% Al, 0.01 to 0.36 wt.% P, 0.05 to 0.5 wt.% Sn, and 0.001 to 0.05 wt.% rare earths. This alloy exhibits good machinability by forming an α-phase, a β-phase, and occasionally a γ-phase. The Al content generates undesirable Al phosphides. The γ-phase and Al phosphides improve chip formation but shorten tool life. Furthermore, the rare earths are thought to lead to embrittlement of the structure. These alloys are used for cast and hot-pressed parts.

[0007] The substitution of phosphorus for lead, which forms brittle phosphides in the alloy, is further described in U.S. Patent No. 5,623,999 for a cast alloy containing 58.5-65.0 wt.% Cu, 0.40-1.40 wt.% Si, 0.003-0.19 wt.% P, 0.002-0.25 wt.% Pb, balance zinc, and other optional elements, where the addition of 0.003-0.19 wt.% P to form phosphides and 0.4-1.4 wt.% Si to strengthen the α and β phases results in a cast material with good machinability in this case. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent No. 10-0555854 [Patent Document 2] Korean Patent Publication No. 10-2006-096877 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-290475 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-122427 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-083443 [Patent Document 6] European Patent No. 2194150 [Patent Document 7] European Patent Application Publication No. 3992321 Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to provide a copper-zinc alloy casting material that has excellent machinability, good mechanical properties, a small grain size and therefore good grindability, a low tendency to shrinkage cavities, and is as free as possible from alloying elements of environmental concern. Furthermore, the object of the present invention is to provide a method for producing the casting product, and a cast part. [Means for solving the problem]

[0010] The invention is described with respect to a casting material made of a copper-zinc alloy by the features of claim 1 and with respect to a manufacturing method by the features of claim 7. The other related claims are advantageous embodiments and developments of the invention.

[0011] The present invention relates to a casting material made of a copper-zinc alloy having the following composition in weight percent: Cu: 58.0-66.0%, Si: 0.15 to 1.2% P: 0.20~0.38%, Sn: optional up to 0.5% Al: optional up to 0.05% Fe: optional up to 0.3% Ni: optional up to 0.3% Pb: optionally up to 0.25%, preferably up to 0.10% Bi: optional, maximum 0.1% Te, Se, In: optional, up to 0.1% each, B: Arbitrary up to 0.01% The balance includes Zn and inevitable impurities, The alloy relates to a casting material in which the proportion of unavoidable impurities is less than 0.2% by weight. The alloy has a structure including an α phase, a β phase, and phosphide grains. The phosphide grains preferably include or are phosphides containing copper and / or zinc. The proportion of the β phase to the total of the α phase and the β phase is at least 20% by volume, preferably at least 40% by volume, and at most 70% by volume, preferably at most 60% by volume. Silicon is present in both the α phase and the β phase. 21000 μm 2 In this area, there are 20 to 300 phosphide particles with an equivalent diameter of 0.5 to 1 μm, 30 to 120 phosphide particles with an equivalent diameter of 1 to 2 μm, and 20 to 100 phosphide particles with an equivalent diameter of 2 to 5 μm. The volume fraction of the β phase and the proportions of Si and P are determined so that the alloy satisfies the following conditions: 92.7249-0.473254·[Beta]-80.6378·[Si]-142.65·[P]+279.309·[Si]·[P]<40 where [Beta] represents the proportion of the β phase in volume percent, [Si] represents the proportion of silicon in weight percent, and [P] represents the proportion of phosphorus in weight percent.

[0012] The present invention is based on the idea of reducing the proportion of Pb in copper-zinc alloys as much as possible without impairing the machinability of the material. For this purpose, Si and P are added to the alloy appropriately, and the volume fraction of the β phase is adjusted so as to obtain favorable cutting properties on the one hand and refine the cast structure of the original base matrix consisting of the β phase on the other hand. Furthermore, process controls during casting are selected to obtain the desired properties.

[0013] A small β grain size is advantageous for good polishability. Therefore, the β phase must be refined in the as-cast state. Surprisingly, it has been shown that increasing the P content results in significant grain refining of the original base matrix of the β phase. To achieve sufficient grain refinement of the as-cast structure, the addition of at least 0.20 wt.% P is necessary. This is similar to the effect of 1–3 wt.% Pb on the grain refinement of α-β brass. During primary crystallization of the β phase, P accumulates in the residual melt, causing subdivision and thus grain refinement of the β phase. During solidification, a eutectic consisting of phosphides and the β phase is formed. In addition to grain refinement of the base matrix of the β phase, grain refinement of the α phase is also observed.

[0014] When the P content is at least 0.20 wt.%, phosphide particles are present in both the α and β phases in the cast material. Preferably, the alloy contains at least 0.22 wt.% P. At P contents above 0.38 wt.%, coarse phosphides occur in the cast state due to the solidification of individual phosphides into long networks. These coarse phosphides wet the grain boundaries and reduce ductility. When used as mechanical components, such as drinking water valves or connections, the material requires high strength with a corresponding high hardness.

[0015] However, if the cooling rate during casting of the alloy is too slow, for example, in a stationary mold, coarse, undesirable phosphides can form even with a P content of less than 0.38 wt%. The required high cooling rate is achieved, for example, by Tammann casting of small blocks measuring 25 x 55 x 160 mm into a steel mold. Thus, with a P content of 0.20 to 0.38 wt%, the phosphide particles already have a spherical, fine morphology and are dispersed throughout the structure as cast. These act as separation sites during cutting and promote chip breakage. To properly control the phosphide particles, the cooling rate during solidification must be at least 20°C per minute (°C / min), preferably at least 30°C per minute, at most 60°C per minute, and preferably at most 50°C per minute, in the temperature range from 550°C to 350°C. Therefore, the phosphide distribution and β-phase grain size are determined not only by the alloy's chemical composition but also by the casting conditions. The as-cast phosphide signature is therefore like a fingerprint that a particular process control leaves on the product. The as-cast phosphide distribution can be characterized as follows: 2Within this area, there are 20-300 phosphide particles with an equivalent diameter of 0.5-1 μm, 30-120 phosphide particles with an equivalent diameter of 1-2 μm, and 20-100 phosphide particles with an equivalent diameter of 2-5 μm. The equivalent diameter of a phosphide particle is understood to be the diameter of a circle with the same area as the phosphide particle. The majority of phosphide particles with an equivalent diameter of at least 0.5 μm have an equivalent diameter of at most 2 μm. This alloy is suitable for continuous casting, as well as for mold casting, for example, in the form of sand casting or coquille casting, provided that careful attention is paid to the cooling conditions.

[0016] A brittle structural component that acts as a separation site during cutting and thereby supports chip breaking is beneficial to the machinability of the material. The β phase is brittle and promotes machinability. An increase in the β phase proportion can be achieved by increasing the Zn content and / or by adding silicon, since silicon stabilizes the β phase. Furthermore, it has been found that reducing the ductility of the α phase is beneficial to good machinability. This is achieved by adding and embedding silicon in the α phase, as well as by finely dispersing phosphides in the α phase. Therefore, the Si proportion in the alloy must be at least 0.15 wt.%. The aforementioned phosphide particles are the particles that act as separation sites during cutting and promote chip breaking. A P proportion of at least 0.20 wt.% not only improves machinability but also contributes to grain refinement in particular. Furthermore, a low Pb proportion is also beneficial to machinability.

[0017] Therefore, the machinability of the material is determined by the combination of the parameters of the β phase, Si, and P, and the optional small amount of Pb present. In the proposed copper-zinc alloy casting material, the proportion of β phase relative to the total of α and β phases is at least 20% by volume, preferably at least 35% by volume, and particularly preferably at least 40% by volume. A high proportion of β phase has a negative effect on ductility. Therefore, the proportion of β phase is at most 70% by volume, preferably at most 60% by volume. The Si content of the alloy is 0.15-1.2% by weight, and the P content is 0.20-0.38% by weight. Furthermore, up to 0.25% by weight of Pb, preferably up to 0.10% by weight, can be added. In this case, the proportion of β phase and the proportions of Si and P are determined so that the alloy satisfies the following conditions: 92.7249-0.473254·[Beta]-80.6378·[Si]-142.65·[P]+279.309·[Si]·[P]<40 where [Beta] is the percentage of β phase in volume percent, [Si] is the percentage of silicon in weight percent, and [P] is the percentage of phosphorus in weight percent. This relationship quantitatively describes the influence of each parameter, β phase, Si, and P, on the cutting properties of the alloy, as well as the interaction of these parameters. Thus, for example, a low percentage of β phase can be compensated for by a higher percentage of silicon and / or phosphorus in the alloy's composition specification, and vice versa.

[0018] The Cu content of the alloy is 58.0-66.0 wt. %. If the Cu content is less than 58.0 wt. %, the ductility of the alloy is too low. If the Cu content is more than 66.0 wt. %, the zinc content in the alloy is too low, and good machinability cannot be obtained.

[0019] Furthermore, the composition of the alloy can be preferably selected so that the Si / P ratio is at least 0.6, particularly preferably at least 0.9. In a further preferred embodiment, the composition of the alloy can be selected so that the sum of Si and P is at least 0.58% by weight, particularly preferably at least 0.64% by weight. The above two measures, both independently and in combination, contribute to meeting the above ratios and thus to achieving favorable cutting properties.

[0020] The optional elements Sn and Al support the formation of the β phase. If the Sn content is greater than 0.5 wt.%, additional tin-containing phases may form, which may adversely affect the alloy's properties. Preferably, the tin content should be at most 0.3 wt.%, particularly preferably at most 0.2 wt.%. Furthermore, aluminum forms aluminum phosphides together with phosphorus. However, these are undesirable, so the Al content should not exceed 0.05 wt.%.

[0021] Iron leads to a refinement of the grain structure. Furthermore, iron forms hard phosphides and silicides, which adversely affect the tool life and grindability during cutting. Therefore, the iron content is at most 0.3% by weight, preferably at most 0.1% by weight.

[0022] Nickel supports the formation of the α phase. Furthermore, nickel forms phosphides, which do not have a beneficial effect on machinability. Therefore, the nickel proportion is at most 0.3% by weight, preferably at most 0.1% by weight.

[0023] The element Bi is present as an impurity in secondary raw materials, e.g., scrap. It can improve the machinability of the alloy. In amounts up to a maximum of 0.1% by weight, Bi does not adversely affect the alloy. Therefore, a maximum of 0.1% by weight of Bi is permitted in the alloy. Preferably, the Bi content is less than 0.015% by weight.

[0024] The elements Te, Se, and In can have a beneficial effect on the machinability of the alloy. Amounts up to 0.1% by weight each do not have a detrimental effect on the alloy. Therefore, a maximum of 0.1% by weight of Te, Se, and In each is permitted in the alloy.

[0025] Boron in any proportion up to 0.01 wt. % contributes to grain refinement.

[0026] The remainder of the alloy composition consists of zinc and unavoidable impurities. To avoid uncontrollable influence of impurities on the properties of the alloy, the proportion of these impurities is at most 0.2% by weight. Preferably, the proportions of Mn and Mg in particular should each be at most 0.1% by weight, and particularly preferably at most 0.05% by weight, since these elements may form phosphides that can compete with copper- and / or zinc-containing phosphides.

[0027] In a preferred form of the invention, the proportion of Pb in the alloy may be at least 0.02% by weight, with even small proportions of Pb improving cutting properties.

[0028] Advantageously, the weight fraction ratio of P to the sum of Fe and Ni may be greater than 2.0, i.e., P / (Fe+Ni)>2.0, which mainly realizes the formation of copper- and / or zinc-containing phosphides, which are suitable for cutting properties, while suppressing the formation of iron phosphides or nickel phosphides.

[0029] It can be particularly advantageous if the sum of the proportions of Fe and Ni is at most 0.1% by weight, as this limit also suppresses the formation of iron and nickel phosphides compared to the formation of copper- and / or zinc-containing phosphides.

[0030] In a particularly advantageous embodiment of the invention, the proportion of P may be at least 0.26% by weight and at most 0.33% by weight. If the proportion of P is at least 0.26% by weight, a sufficiently large number of phosphide particles are produced, resulting in particularly fine grains and very good machinability.

[0031] Within the framework of an advantageous embodiment of the invention, the proportion of Si may be at least 0.50% by weight and at most 1.0% by weight. Cast materials made of copper-zinc alloys with a Si proportion within this range are characterized by excellent cutting properties.

[0032] A further aspect of the present invention is a method for producing a cast product, comprising the steps of: a) melting a copper-zinc alloy having a composition similar to that of the former; b) casting the cast product and subsequently cooling the cast product, the cooling rate being at least 20°C per minute and at most 60°C per minute within the temperature range of 550-350°C; Contains:

[0033] This method allows for the production of a cast product from the aforementioned casting material consisting of a copper-zinc alloy. To melt the alloy, a Cu cathode, a Zn block, brass scrap, a Cu-P master alloy, or a Cu-Si master alloy can be used. The melting is preferably carried out in an induction furnace. The melt is then cast into a cast product. The cast product is cooled at a cooling rate of at least 20°C per minute, preferably at least 30°C per minute, and up to 60°C per minute, preferably up to 50°C per minute, within a temperature range of 550°C to 350°C. The defined cooling allows for the production of a cast product with a suitable ratio of the volume fractions of α and β phases in the casting material and a suitable particle dispersion of copper- and / or zinc-containing phosphides. DETAILED DESCRIPTION OF THE INVENTION

[0034] Further technical features and advantages of the method according to the invention are now explicitly given by way of description and examples relating to a casting material made of a copper-zinc alloy according to the invention.

[0035] A further aspect of the present invention relates to a cast part made from the above-described casting material. A cast part is a product in which the material has not been reshaped after casting and cooling. The production of the cast part begins with a cast product that has been melted and cast according to the above-described method. To shape the cast product, the cast product is machined. Furthermore, at least a portion of the surface can be polished. Optionally, the cast part can be fully or partially coated. Thus, the cast part is produced from the above-described casting material or cast product by machining and optional further processing steps. Such a cast part can be, for example, a connector, a T-piece, a part of a valve, a faucet, or a water meter.

[0036] The present invention will now be described in more detail using exemplary embodiments and comparative examples.

[0037] Samples No. 1 through No. 12 were melted in an induction furnace and then poured into coquilles to form small blocks. The cooling rate during solidification was 36°C per minute (°C / min) within the temperature range of 550°C to 350°C. The compositions of the samples are listed in Table 1. Sample No. 5 represents the lead-containing reference alloy CuZn39Pb1Al-B.

[0038] Slices were taken from the cast blocks and the microstructure of the slices was examined using an optical microscope. The volume fractions of α and β phases presented are normalized to the sum of α and β phases. Hardness (HV) was determined. Electrical conductivity was determined by probe using the eddy current method.

[0039] The size of the beta particles was determined according to EN ISO 2624, where line cuts were made across the width of the slice (referred to as the "vertical direction") and the number of beta particles cut along these line cuts was determined. The average line cut length across the width corresponds to the average beta particle size across the width. Similarly, line cuts were made across the thickness of the slice (referred to as the "horizontal direction") and the number of beta particles cut along these line cuts was determined. The average line cut length across the thickness corresponds to the average beta particle size across the thickness.

[0040] Optical microscope images of unetched samples were used to quantitatively determine the size distribution of the phosphide particles. 2 Image sections (equivalent to 1 μm) were selected and evaluated at 1000x magnification using the software ImageJ. This allowed for the recognition of individual particles and the determination of their equivalent diameter and area. Phosphide particles were classified based on their equivalent diameter into categories of 0.5-1 μm, 1-2 μm, 2-5 μm, and, if present, >5 μm.

[0041] The machinability was determined by planing tests. Here, a contoured indexable insert was used, which favors chip breaking. The depth of cut was 125 μm and the planing speed was 35 m / min. During the planing process, the bending moment acting on the tool was measured, from which the mean bending moment value was determined. The corresponding chips were optically evaluated and classified with regard to chip shape. The chip shapes were assigned a chip shape number according to the following list:

[0042] [Table 1]

[0043] Chip shape number 1.0 corresponds to the reference alloy CuZn39Pb1Al-B containing 1 wt% lead (sample No. 5).

[0044] The machinability of the samples was evaluated using the bending moment and chip shape calculated during planing. The highest average bending moment was 37 Nm, and the chips with chip shape numbers of 1.0 and 1.25 were evaluated as being very favorable.

[0045] The test results are shown in Tables 2 and 3. Samples No. 1 to No. 4 are samples according to the present invention. Samples No. 5 to No. 12 are comparative samples and are marked with (*).

[0046] Furthermore, we attempted to parameterize the measured average bending moment as a function of the volume fraction of the β phase and the weight fractions of Si and P. The functional relationship thus calculated can be expressed as follows:

[0047] f=92.7249-0.473254·[Beta]-80.6378·[Si]-142.65·[P]+279.309·[Si]·[P] where f approximately quantifies the measured bending moment in Nm, [Beta] denotes the proportion of β phase in volume %, [Si] denotes the proportion of silicon in weight %, and [P] denotes the proportion of phosphorus in weight %. The values of f calculated according to this formula are given in the last column of Table 3. A comparison of this value of f with the measured bending moment shows a very good agreement between the two quantities (with the exception of samples No. 6 and No. 7, which have very poor machinability). Samples No. 1 to No. 4 according to the invention, all of which had measured bending moments below 37 Nm, are characterized by values of f below 40.

[0048] [Table 2]

[0049] [Table 3]

[0050] Samples No. 1 to No. 4 are samples according to the invention. The volume fraction of the β phase is at least 38% and at most 57%. The β grain size is at most 645 μm in the width direction ("vertical") and at most 781 μm in the thickness direction ("horizontal"). The ratio of the β grain size in the thickness direction to the β grain size in the width direction is at most 1.21. The grains therefore have a topology without a preferred direction and are considered spherical. The hardness is at least 110 HV10. The measured bending moment is at most 36.5 Nm. The chip shape corresponds to chip shape number 1.25 in all samples. The chip shape is therefore very favorable.

[0051] Samples No. 5 to No. 12 are comparative samples. Reference sample No. 5 contains 1.1 wt. % lead and is characterized by a very small grain size, a very low bending moment, and good chip shape. Samples No. 6 and No. 7 contain copper and zinc, as well as traces of silicon and phosphorus. Both samples have a very large β grain size, which results in high bending moments measured during cutting and poor chip shape.

[0052] Samples 8 through 11 each contain approximately 0.55 wt.% silicon. Samples 8 and 10 contain no or very little phosphorus, while Samples 9 and 11 contain 0.126 wt.% and 0.067 wt.% phosphorus, respectively. The zinc percentage in Samples 10 and 11 is approximately 1 wt.% higher than that in Samples 8 and 9. The higher the zinc percentage, the greater the volume fraction of the β phase. A comparison of Samples 8 and 10 with Samples 6 and 7 shows that the addition of approximately 0.55 wt.% silicon significantly reduces the bending moment acting during cutting by hardening the α and β phases. Here, the higher volume fraction of the β phase in Samples 6 and 7 is fully compensated for by the silicon percentage in Samples 8 and 10. Furthermore, the bending moment also decreases with increasing P percentage. Samples No. 8 to No. 11 have a suitable chip shape.

[0053] The β grain size in samples No. 8 to No. 11 is smaller than that in samples No. 6 and No. 7. The β grain size tends to decrease with increasing P content. On the other hand, samples No. 8 to No. 11 have larger β grain sizes than those in samples No. 1 to No. 4. In particular, in samples No. 8 to No. 11, the horizontal β grain size is more than 1.25 times, and in most cases more than 2.5 times, the vertical β grain size, whereas in samples No. 1 to No. 4, the horizontal β grain size is at most 1.25 times the vertical β grain size.

[0054] Sample No. 12, with a phosphorus content of 0.276 wt%, exhibits spherical beta grains with a vertical beta grain size of 605 μm and a horizontal beta grain size of 856 μm. However, sample No. 12 has a beta phase volume fraction of only 22% and a low Si fraction of 0.277 wt%, which increases the bending moment acting during cutting and reduces the cutting conditions. 92.7249-0.473254·[Beta]-80.6378·[Si]-142.65·[P]+279.309·[Si]·[P]<40 The value of f calculated from the Si content, P content, and β-phase volume fraction is 42.0, which is in good agreement with the measured bending moment of 42.5 Nm. Comparison of Sample No. 12 with Sample No. 4, which has a similar composition, indicates that the low Si content must be compensated for by a higher Zn content so that the cast material has a sufficient β-phase volume fraction and therefore favorable machinability. Therefore, it is necessary to select the alloy composition and process control so that the above conditions are met in the interaction of these variables and parameters. It is not sufficient to consider each of the above variables and parameters individually.

[0055] Samples No. 1 to No. 4 are characterized by grains with a topology without a preferred orientation, i.e., spherical grains, and beta grain sizes up to 800 μm, while Samples No. 8 to No. 11 have essentially larger beta grain sizes. Furthermore, in Samples No. 8, No. 10, and No. 11, the beta grain size in the thickness direction ("horizontal") is significantly larger than in the width direction ("vertical"). Therefore, the grain formation in Samples No. 8, No. 10, and No. 11, like Samples No. 6 and No. 7, is described as stalk-like and is rated unfavorable. The favorable topology and size of the grains in Samples No. 1 to No. 4 are due to a phosphorus content of at least 0.24 wt.% in combination with a specially selected cooling rate in the temperature range of 550°C to 350°C during solidification after casting. The favorable topology and size of the grains in Samples No. 1 to No. 4 result in good mold filling during casting and, on the other hand, good polishability of these samples.

Claims

1. A casting material consisting of a copper-zinc alloy having the following composition in weight percent: Cu: 58.0 to 66.0%, Si: 0.15-1.2%, P: 0.20-0.38%, Sn: optionally up to 0.5%; Al: optionally up to 0.05%; Fe: optional up to 0.3%; Ni: optional up to 0.3%; Pb: optionally up to 0.25%; Bi: optional up to 0.1% Te, Se, In: optional, up to 0.1% each; B: optional up to 0.01%; The balance includes Zn and inevitable impurities, the proportion of the inevitable impurities is less than 0.2% by weight, the alloy has a structure including an α phase, a β phase, and phosphide particles, and the proportion of the β phase relative to the total of the α phase and the β phase is at least 20% by volume and at most 70% by volume; Si is present in both the α phase and the β phase, 21000 μm ２ in an area of the particle, there are 20 to 300 phosphide particles having an equivalent diameter of 0.5 to 1 μm, 30 to 120 phosphide particles having an equivalent diameter of 1 to 2 μm, and 20 to 100 phosphide particles having an equivalent diameter of 2 to 5 μm; The proportion of the β phase and the proportions of Si and P are such that the alloy satisfies the following conditions: 92.7249-0.473254・[Beta]-80.6378・[Si]-142.65・[P]+279.309・[Si]・[P]<40 wherein [Beta] represents the proportion of the β phase in volume percent, [Si] represents the proportion of silicon in weight percent, and [P] represents the proportion of phosphorus in weight percent.

2. 2. The casting material made of a copper-zinc alloy according to claim 1, wherein the Pb content is at least 0.02% by weight.

3. 3. The casting material made of a copper-zinc alloy according to claim 1, wherein the weight ratio of P to the total of Fe and Ni is greater than 2.

0.

4. 4. A casting material made of a copper-zinc alloy according to claim 1, wherein the proportion of Fe and Ni is at most 0.1% by weight in total.

5. 5. A casting material made of a copper-zinc alloy according to claim 1, wherein the proportion of P is at least 0.26% by weight and at most 0.33% by weight.

6. 6. A casting material made of a copper-zinc alloy according to claim 1, wherein the proportion of Si is at least 0.50% by weight and at most 1.0% by weight.

7. 1. A method for producing a cast product, comprising: a) melting a copper-zinc alloy having a composition according to any one of claims 1 to 6; b) casting the cast product followed by cooling the cast product, the cooling rate being at least 20°C per minute and at most 60°C per minute within the temperature range of 550-350°C; A method including:

8. A cast part made from the casting material according to any one of claims 1 to 6.

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