Grain-refined copper casting alloy

Abstract

A method for producing a casting from a copper alloy comprising the following steps: a. Melting a copper alloy with the following composition [in wt.%]: Cu 70.0 to 97.0%, Si 2.0 to 4.5%, B 0.002 to 0.03%, Fe 0.01 to 1.0%, optionally up to 2.0% Sn, optionally up to 0.4% Ni, optionally up to 0.2% P, optionally up to 0.25% Pb, optionally up to 0.15% As or Sb, Rest Zn and unavoidable impurities, where the ratio of boron content to the sum of iron and nickel content is at least 0.025 and at most 0.12 b. Casting an ingot, c. Melting the ingot, d. Casting the casting, whereby iron borides and / or iron-nickel mixed borides are formed in the alloy of the casting.

Description

[0001] The invention relates to a method for producing a casting from a copper casting alloy. Furthermore, the invention relates to the use of boron and iron, and optionally nickel, as grain refiners in copper-zinc-silicon alloys in casting alloys.

[0002] It is well known that molded parts made of copper alloys are manufactured as castings. Examples of such molded parts include fittings, bends, tees for media-carrying piping systems, components for pumps and valves, as well as structural parts in mechanical and plant engineering and automotive construction. Silicon-containing brasses are used as a material for these applications, among others.

[0003] To ensure the mechanical stability of the molded part, a material is required that already has a homogeneous microstructure in the as-cast state. Inhomogeneities in the microstructure must be accounted for through costly safety allowances, or they can lead to component failure. In wrought materials, the homogeneity of the microstructure is achieved through forming. To achieve a homogeneous microstructure without forming steps, the material must already have a fine-grained microstructure in the as-cast state. After casting, the molded part is often reworked by machining, grinding, or polishing, for example of sealing surfaces. For this purpose, the material must be free of blowholes and hard particles. Furthermore, a coarse dendritic microstructure has a negative impact on the corrosion resistance of the material.

[0004] In the production of castings, the material is typically melted and poured twice: During the first melting, the alloy composition is roughly adjusted. The alloy is then cast into ingots. To produce the castings, the ingots are melted and the alloy is cast into molded parts. A change in the alloy composition during this second melting and pouring process is undesirable but unavoidable due to the burn-off of certain elements, such as Zn, Zr, or P. The as-cast condition after the second pour is crucial for the quality of the product.

[0005] It is known that a fine-grained cast microstructure can be achieved in copper alloys by adding certain elements. EP 1 777 305 A1 proposes adding 0.0005 to 0.04% zirconium to a copper-zinc-silicon alloy for grain refinement. However, a disadvantage of zirconium is its burn-off during melting and casting. Consequently, it is difficult to ensure the desired zirconium content in the finished component when manufacturing cast parts.

[0006] EP 1 817 438 B1 proposes adding 0.05 to 2 wt.% manganese to a copper-zinc-silicon alloy to improve the microstructure. Furthermore, it is proposed to add 0.01 to 0.05 wt.% zirconium to the alloy as a grain refiner. This is consistent with studies showing that the addition of manganese without zirconium does not result in grain refinement.

[0007] The use of boron as a grain refiner for copper alloys is well known. For example, DE 10 2005 024 037 A1 proposes adding 0.00001 to 0.5% boron to a copper-zinc-silicon alloy. The grain-refining effect of small amounts of boron has been demonstrated using alloys with approximately 76% copper, 21% zinc, and 3% silicon.

[0008] The publication "Grain Refining of Copper Alloys" by F. Romankiewicz et al., Metall, Volume 48, No. 11 / 94, pages 865 to 871, concludes that grain refining of silicon brass with boron addition is futile. This conclusion is based on studies conducted on the material CuZn16Si4 with boron additions of 0 to 0.06 wt.%.

[0009] The document DE 10 2005 024 037 A1 discloses a Cu-Zn-Si wrought alloy comprising in wt.% 70 to 80% copper, 1 to 5% silicon, 0.0001 to 0.5% boron, up to 0.2% phosphorus and / or up to 0.2% arsenic and the remainder zinc together with unavoidable impurities, as well as the use and production of such an alloy.

[0010] JP H04-180 531 A describes an alloy consisting of 0.05 to 3.0 wt.% Si, 0.1 to 5.0 wt.% one or more of the elements Ni, Fe, Co, Cr, and Ti, and the remainder Cu, with unavoidable impurities limited to a maximum of 20 ppm and the size of the precipitates formed limited to a maximum of 2 µm. A total of 0.001 to 5.0 wt.% of one or more of the following elements: Zn, Sn, Mg, Mn, Al, B, P, As, and Sb can be added to the above-mentioned composition. The grain size of the resulting material is preferably about 30 µm.

[0011] Document DE 698 19 104 T2 discloses a process for producing a wrought copper-based alloy. The process comprises casting a copper-based alloy comprising tin in an amount of 0.1 to 1.5 wt.%, phosphorus in an amount of 0.01 to 0.35 wt.%, iron in an amount of 0.01 to 0.8 wt.%, zinc in an amount of 1.0 to 15 wt.%, and the remainder being copper and unavoidable impurities, homogenization, rolling to a final thickness, process annealing followed by slow cooling and stress relief annealing at a final thickness. The microstructure of the copper-based alloy comprises phosphide particles uniformly distributed within the matrix.

[0012] The document US 5 041 176 A describes a copper alloy reinforced by particle dispersion, which essentially consists of copper as the main component, 0.1 to 10 wt% nickel, 0.1 to 10 wt% tin, 0.05 to 5 wt% silicon, 0.01 to 5 wt% iron and 0.0001 to 1 wt% boron.

[0013] WO 2007 / 124915 A2 discloses a multi-component copper alloy consisting of [in wt.%]: Ni 1.0 to 15.0%, Sn 2.0 to 12.0%, Mn 0.1 to 5.0%, Si 0.1 to 3.0%, the remainder Cu, and unavoidable impurities. Optionally, up to 0.5% P, individually or in combination up to 1.5% Ti, Co, Cr, Al, Fe, Zn, Sb, individually or in combination up to 0.5% B, Zr, S, and up to 5% Pb may be added.

[0014] The document US 2007 / 0 039 817 A1 relates to a target material for physical vapor deposition. The target material consists of copper and at least two additional elements selected from Ag, Al, As, Au, B, Be, Ca, Cd, Co, Cr, Fe, Ga, Ge, Hf, Hg, In, Ir, Li, Mg, Mn, Nb, Ni, Pb, Pd, Pt, Sb, Sc, Si, Sn, Ta, Te, Ti, V, W, Zn, and Zr, wherein the total amount of the at least two additional elements is between 100 ppm and 10 atomic %.

[0015] The prior art provides only unsatisfactory guidance for those skilled in the art on how to achieve a fine-grained cast structure in copper-zinc-silicon alloys. Zirconium is very difficult to use due to its erosion. Boron effects grain refinement for zinc contents of approximately 21 wt.%, but not for zinc contents of approximately 16 wt.%. Therefore, a grain refiner that exerts its effect largely independently of the zinc content would be desirable. In particular, it should effect grain refinement for copper contents greater than 80 wt.%.

[0016] The invention is based on the object of providing an improved process for producing a cast part from a copper alloy, as well as an improved use of grain refiners in cast parts made from copper-zinc-silicon alloys. In particular, grain refinement of the cast structure should be achieved largely independently of the zinc or copper content. Due to a lack of alternatives, grain refiners for copper contents greater than 80 wt.% are particularly desirable.

[0017] The invention is defined with respect to a method for producing a cast part from a copper alloy by the features of claim 1, with respect to the use of boron and iron as grain refiners by the features of claim 9, and with respect to the use of boron, iron, and nickel as grain refiners by the features of claim 10. The further dependent claims relate to advantageous embodiments and developments of the invention.

[0018] The invention includes a method for producing a casting from a copper alloy. The method comprises the following steps: a. Melting a copper alloy with the following composition [in wt.%: Cu 70.0 to 97.0%, Si 2.0 to 4.5%, B 0.002 to 0.03%, Fe 0.01 to 1.0%, optionally up to 2.0% Sn, optionally up to 0.4% Ni, optionally up to 0.2% P, optionally up to 0.25% Pb, optionally up to 0.15% As or Sb, The balance is Zn and unavoidable impurities. The ratio of boron content to the sum of iron and nickel content shall be at least 0.025 and at most 0.12. b. Casting an ingot, c. Melting the ingot, d. Pouring the casting, whereby iron borides and / or iron-nickel mixed borides are formed in the alloy of the casting.

[0019] The invention is based on the idea that the simultaneous addition of boron and iron to a silicon-containing copper-zinc alloy results in grain refinement of the cast structure if the boron and iron contents are in a specific ratio to one another. Iron can be partially replaced by nickel. The ratio of boron content to the sum of iron and nickel contents is at least 0.025 and at most 0.12. The respective element contents are defined as weight fractions of the total alloy. If the boron content and the sum of iron and nickel contents are in the aforementioned ratio to one another, iron borides, nickel borides, or iron-nickel mixed borides can form. These borides lead to the formation of a fine grain in the cast structure of the material.

[0020] This finding is all the more surprising given that the skilled person understands from the prior art, in particular from WO 91 / 02826, that in copper alloys, even small amounts of iron reduce the grain-refining effect of boron, and that iron contents above a limit dependent on the alloy system largely suppress the grain-refining effect of boron in the case of small boron contents or, in the case of larger boron contents, lead to the formation of undesirable hard particles. Such hard particles negatively influence the polishability of the material. WO 91 / 02826 therefore proposes preventing the formation of iron borides by adding another element to the alloy that reacts more rapidly with boron than iron.

[0021] Optionally, the alloy can contain tin. Tin improves the corrosion resistance of the material. At tin contents greater than 2.0 wt.%, undesirable tin segregation may occur due to the interaction of all alloy components.

[0022] The alloy can optionally contain phosphorus. In small amounts, phosphorus serves to deoxidize the melt. Furthermore, it can positively influence the formation of the initial cast microstructure and the corrosion properties. Phosphorus increases the flowability of the melt and reduces the material's susceptibility to stress corrosion cracking.

[0023] Lead makes the alloys easier to machine. To comply with legal regulations for the use of copper alloys in drinking water applications, the lead content of the alloy according to the invention is limited to a maximum of 0.25 wt.%. Preferably, the lead content of the alloy can be a maximum of 0.1 wt.%.

[0024] Optionally, the alloy can contain small amounts of antimony and / or arsenic. These two elements reduce the material's tendency to dezincification.

[0025] In a preferred embodiment of the invention, the ratio of boron content to the sum of iron and nickel content can be at least 0.05 and at most 0.075. Surprisingly, it has been shown that when the alloy composition is selected according to this specification, a fine-grained microstructure is already established after the first casting. Even after the second casting, the microstructure is always fine-grained. This advantageous selection of the alloy composition therefore particularly reliably ensures the formation of a fine-grained casting microstructure, and the fine grain size of the cast ingots already provides an indication of the quality of the molded parts. This preferred selection of the boron content and the sum of the iron and nickel content represents stoichiometrically particularly favorable conditions for the formation of borides.

[0026] In a preferred embodiment of the invention, the boron content can be at least 0.005 wt.%, particularly preferably at least 0.01 wt.%, and at most 0.025 wt.%. At boron contents of at least 0.005 wt.%, preferably at least 0.01 wt.%, borides can form particularly rapidly in combination with iron and optionally nickel. At a boron content greater than 0.025 wt.%, undesirable large borides can form.

[0027] Advantageously, the iron content can be at least 0.1 wt.% and at most 0.5 wt.%. This preferred selection of iron content represents stoichiometrically particularly favorable conditions for the formation of borides in suitable abundance and size. In particular, when this preferred iron content is combined with a boron content of no less than 0.01 wt.% and no more than 0.025 wt.%, a fine-grained microstructure is achieved even during the first casting of the alloy.

[0028] In a preferred embodiment of the invention, the nickel content can be a maximum of 0.3 wt.%. With regard to the formation of borides, nickel can at least partially replace iron. In a particularly preferred embodiment, the sum of iron and nickel content can be at least 0.1 wt.% and a maximum of 0.5 wt.%. Furthermore, it can be advantageous to select a higher iron content of the alloy than the nickel content. The iron content initiates the formation of borides and thus initiates the grain refinement effect.

[0029] Advantageously, the copper content of the alloy can be more than 80 wt%, preferably at least 81 wt%. Copper contents greater than 80 wt% make the alloy particularly corrosion-resistant and thus suitable for use in fluid-carrying pipeline systems, such as drinking water pipes. At this copper content, the silicon content is typically at least 3 wt% and at most 4 wt%. The zinc content is then below 16 wt%, and is preferably at least 8 wt% and at most 15 wt%.

[0030] The invention further encompasses the use of boron and iron in combination as grain refiners in copper-zinc-silicon alloys for castings. According to the invention, the ratio of the boron content of the alloy [in wt.%] to the iron content of the alloy [in wt.%] is at least 0.025 and at most 0.12, and iron borides are formed in the alloy of the casting during the second casting. The copper-zinc-silicon alloy can have the following composition [in wt.%]: Cu 70.0 to 97.0%, Si 2.0 to 4.5%, B 0.002 to 0.03%, Fe 0.01 to 1.0%, optionally up to 2.0% Sn, optionally up to 0.2% P, optionally up to 0.25% Pb, optionally up to 0.15% As or Sb, Rest Zn and unavoidable impurities.

[0031] The addition of boron and iron in the above-mentioned ratios can result in grain refinement of the cast structure in a copper-zinc-silicon alloy. The boron content is preferably at least 0.005 wt.% and at most 0.025 wt.%. The iron content is preferably at least 0.1 wt.% and at most 0.5 wt.%.

[0032] The aspect of the inventive use of boron and iron for grain refinement of copper-zinc-silicon alloys in castings includes all the above-described preferred embodiments of an inventive production method of a casting from a silicon-containing copper-zinc alloy.

[0033] The invention further encompasses the use of boron, iron, and nickel in combination as grain refiners in copper-zinc-silicon alloys for castings. According to the invention, the ratio of the boron content of the alloy [in wt.%] to the sum of the iron and nickel contents of the alloy [in wt.%] is at least 0.025 and at most 0.12, and during the second casting, iron-nickel mixed borides are formed in the alloy of the casting. The copper-zinc-silicon alloy can have the following composition [in wt.%]: Cu 70.0 to 97.0%, Si 2.0 to 4.5%, B 0.002 to 0.03%, Fe 0.01 to 1.0%, Ni 0.01 to 0.4% optionally up to 2.0% Sn, optionally up to 0.2% P, optionally up to 0.25% Pb, optionally up to 0.15% As or Sb, Rest Zn and unavoidable impurities.

[0034] The addition of boron, iron, and nickel in the above-mentioned ratios can result in grain refinement of the cast structure in a copper-zinc-silicon alloy. The boron content is preferably at least 0.005 wt.% and at most 0.025 wt.%. The iron content is preferably at least 0.1 wt.% and at most 0.5 wt.%. The nickel content is preferably at least 0.05 wt.% and at most 0.3 wt.%.

[0035] The aspect of the inventive use of boron, iron and nickel for grain refinement of copper-zinc-silicon alloys in castings includes all the above-described preferred embodiments of an inventive production method of a casting from a silicon-containing copper-zinc alloy.

[0036] The invention is explained in more detail using the embodiments listed in Table 1.

[0037] Table 1 shows the composition of 18 test alloys in wt.%. The penultimate column of the table shows the ratio of boron content to the sum of iron and nickel content. The alloys were melted and cast. The individual casts were remelted and cast a second time. The samples were metallographically characterized. The last column of the table indicates whether the microstructure was coarse-grained or fine-grained after the second casting.

[0038] Samples 1 to 3 contain no boron. The cast microstructure is always coarse-grained. Samples 4 and 11 contain small amounts of boron. Here, too, the microstructure is coarse-grained.

[0039] Samples 5 to 10 contain both boron (0.01 to 0.02 wt.%) and iron (0.1 to 0.3 wt.%). Sample 8 also contains 0.4 wt.% tin. For samples 5 to 10, a fine-grained cast microstructure is always observed after the second casting. The ratio of boron content to iron content for these samples is between 0.03 and 0.11. The addition of tin has no influence on the formation of the fine-grained cast microstructure. Table 1: Test alloys with composition in wt.% sample Cu Si Zn p Fe Ni Mn B Sn B / (Fe+Ni) structure 1 86 3,75 10,2 0,08 0,011 0 0 0 0 0,0000 rough 2 86 3,75 10,2 0,08 0,007 0 0 0 0 0,0000 rough 3 86 3,75 10,2 0,03 0,009 0 0 0 0 0,0000 rough 4 86 3,75 10,0 0,08 0,18 0 0 0,0012 0 0,0067 rough 5 86 3,8 9,9 0,03 0,22 0 0 0,012 0 0,0545 fine 6 86 3,8 10,0 0,03 0,18 0 0 0,019 0 0,1056 fine 7 86 3,8 9,9 0,03 0,30 0 0 0,019 0 0,0633 fine 8 86 | 3,8 9,6 0,03 0,20 0 0 0,012 0,4 0,0600 fine 9 86 3,8 10,0 0,03 0,12 0 0 0,012 0 0,1000 fine 10 86 3,75 9,9 0,03 0,28 0 0 0,01 0 0,0357 fine 11 86 3,75 10,0 0,03 0,03 0,08 0 0,001 0,12 0,0091 rough 12 86 3,8 9,9 0,03 0,11 0,09 0 0,005 0,1 0,0250 fine 13 86 3,8 9,6 0,03 0,19 0,18 0 0,006 0,2 0,0162 rough 14 86 3,8 9,7 0,03 0,20 0,18 0 0,013 0,1 0,0342 fine 15 86 3,8 9,8 0,03 0,11 0,09 0 0,012 0,2 0,0600 fine 16 86 3,8 9,9 0,00 0,11 0,09 0 0,006 0,1 0,0300 fine 17 86 3,8 9,6 0,00 0,2 0,18 0 0,013 0,2 0,0342 fine 18 86 3,75 10,1 0,08 0,007 0 0,078 0 0 0,0000 rough

[0040] In samples 12 to 17, some of the iron has been replaced by nickel. The boron content varies from 0.005 to 0.013 wt.%. The iron content is between 0.1 and 0.2 wt.%, and the nickel content between 0.08 and 0.18 wt.%. Furthermore, the tin content varies from 0.1 to 0.2 wt.%. With the exception of sample 13, all samples show a fine-grained microstructure after the second casting. For these samples, the quotient of boron content and the sum of iron and nickel contents is between 0.025 and 0.06. For sample 13, this quotient is 0.016. Sample 13 contains too much iron and nickel in total, relative to the boron content of 0.006 wt.%. The tin content has no influence on the formation of the fine cast microstructure.

[0041] It is worth noting that, unlike the other samples, samples 5, 7, 8, and 15 already exhibit a fine-grained microstructure after the first casting. These samples are characterized by a ratio of boron content to the sum of iron and nickel content between 0.05 and 0.065. If the alloy composition is selected so that this ratio lies precisely within this range, the formation of iron borides, nickel borides, or mixed iron-nickel borides is particularly favored. Iron borides with the stoichiometric formula Fe3B would correspond precisely to this weight ratio of boron to iron.

[0042] The influence of manganese on the cast microstructure was investigated using a random sample of sample 18. Sample 18 contains no boron, but contains approximately 0.08 wt.% manganese. The manganese-containing sample always exhibits a coarse-grained cast microstructure.

Claims

[1] Method for producing a casting from a copper alloy comprising the following steps: a. Melting a copper alloy with the following composition [in wt.%]: Cu 70.0 to 97.0% Si 2.0 to 4.5% B 0.002 to 0.03% Fe 0.01 to 1.0% optionally up to 2.0% Sn, optionally up to 0.4% Ni, optionally up to 0.2% P, optionally up to 0.25% Pb, optionally up to 0.15% As or Sb each, Residual Zn and unavoidable impurities, where the ratio of boron content to the sum of iron and nickel content is at least 0.025 and at most 0.12 b. Casting a sprue, c. Melting the cast ingot, d. Casting the casting, whereby iron borides and / or iron-nickel mixed borides are formed in the alloy of the casting. [2] Method according to claim 1, characterized by, that in the copper alloy the ratio of boron content to the sum of iron and nickel content is at least 0.05 and at most 0.

075. [3] Method according to claim 1 or 2, characterized by that the boron content of the copper alloy is at least 0.005 wt.% and at most 0.025 wt.%. [4] Method according to claim 3, characterized by that the boron content of the copper alloy is at least 0.01 wt.% and at most 0.025 wt.%. [5] Method according to any one of claims 1 to 4, characterized by that the iron content of the copper alloy is at least 0.1 wt.% and at most 0.5 wt.%. [6] Method according to any one of claims 1 to 5, characterized by that the nickel content of the copper alloy is at most 0.3 wt.%. [7] Method according to any one of claims 1 to 6, characterized by , that the iron content of the copper alloy is greater than the nickel content of the copper alloy. [8] Method according to any one of claims 1 to 7, characterized by that the copper content of the copper alloy is at least 81% by weight. [9] Use of boron and iron in combination as grain refiners in copper-zinc-silicon alloys in castings, characterized by , that the ratio of boron content of the alloy [in wt.%] and iron content of the alloy [in wt.%] is at least 0.025 and at most 0.12, and that iron borides are formed in the alloy of the casting during the second casting. [10] Use of boron, iron and nickel in combination as grain refiners in copper-zinc-silicon alloys in castings, characterized by , that the ratio of boron content of the alloy [in wt.%] to the sum of iron and nickel content of the alloy [in wt.%] is at least 0.025 and at most 0.12, and that iron-nickel mixed borides are formed in the alloy of the casting during the second casting.