Copper-tin-zinc-molybdenum cast alloy, casting produced therefrom and method for producing such a copper-tin-zinc-molybdenum cast alloy

Abstract

The invention relates to a copper-tin-zinc-molybdenum casting alloy, a casting made therefrom, and a method for producing such a casting alloy.

Description

[0001] The invention relates to a copper-tin-zinc-molybdenum casting alloy, a casting made therefrom, and a method for producing such a copper-tin-zinc-molybdenum casting alloy.

[0002] Copper-tin-zinc casting alloys, sometimes also referred to as red brass, are known in a variety of ways from the prior art and are used, for example, for the manufacture of machine parts or fitting parts.

[0003] To improve manufacturability and machinability, such copper-tin-zinc casting alloys often contain lead, which, as a toxic heavy metal, is increasingly undesirable as an alloying element.

[0004] To replace lead, the addition of sulfur has been discussed, as it can act as a chip breaker and thus facilitate machining. For example, DE 10 2020 106 999 A1 discloses a lead-free copper-tin-zinc continuous casting alloy comprising at least 83.0 wt.% copper, 4.0–8.0 wt.% tin, 0.2–0.8 wt.% sulfur, 1.1–3.0 wt.% nickel, and 1.0–3.5 wt.% zinc, with the sum of tin and zinc not exceeding 10.0 wt.%. DE 10 2020 106 999 A1 addresses the fact that the addition of sulfur to copper-tin continuous casting alloys can improve their castability, since the copper and zinc sulfides formed by the sulfur accumulate in otherwise typically present micropores and thus seal these cavities.

[0005] However, the addition of sulfur creates a further conflict of objectives in zinc-containing alloys, as the zinc sulfide that forms can reduce strength and, due to the higher hardness, increase tool wear during machining.

[0006] The present invention is based on the objective of providing a copper-tin-zinc casting alloy that can be produced and cast well and economically, and is easily machinable after casting and has good tribological properties.

[0007] This problem is solved according to the invention by a casting alloy with the features of claim 1. This is a copper-tin-zinc-molybdenum casting alloy. The casting alloy comprises, in conclusion: 2.0 - 12.0 wt.% tin, 0.5 - 6.5 wt.% zinc, 0.1 - 2.2 wt.%, in particular 0.15 - 2.2 wt.% molybdenum, 0.1 - 1.5 wt.% sulfur, optionally up to 2.0 wt.% nickel, balance copper and unavoidable impurities. wherein, based on weight percent, the ratio of sulfur to molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, and further in particular at least 0.66 (i.e., a ratio of the mass fraction (in wt.%) of sulfur in the alloy to the mass fraction (in wt.%) of molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, and further in particular at least 0.66), and wherein the total fraction of molybdenum and sulfur (i.e., the sum of the mass fraction (in wt.%) of molybdenum in the alloy and the mass fraction (in wt.%) of sulfur in the alloy) is more than 0.15 times the zinc fraction (i.e., the mass fraction (in wt.%) of zinc in the alloy). Therefore, the following condition applies to the mass fractions of molybdenum, sulfur and zinc: Mass fraction of sulfur (wt%) + mass fraction of molybdenum (wt%) > 0.15 x mass fraction of zinc (wt%).

[0008] The proposed casting alloy is environmentally friendly, casts well, and exhibits good machinability and tribological properties in the cast state. It has been shown that the combination of molybdenum and sulfur can at least partially replace the properties of substituted lead while simultaneously overcoming the aforementioned conflict of objectives. Specifically, it was discovered within the scope of the invention that the combination of molybdenum and sulfur in the claimed mass fraction and mass ratio causes molybdenum disulfide (MoS₂) to precipitate during solidification, and that this molybdenum disulfide adheres to or even encapsulates the zinc sulfide that also precipitates. It has been shown that in this way the damaging effects of the zinc sulfide can be suppressed or at least significantly reduced.Furthermore, it was found that the addition of molybdenum increases the sulfur content in the melt and can also partially suppress or at least slow down unwanted evaporation of sulfur (e.g., in the form of ZnS). Finally, it was shown that the precipitated molybdenum disulfide, in addition to its function of coating zinc sulfide, can exhibit its well-known lubricating properties as a dry lubricant, which has a positive effect on the tribological properties.

[0009] The present invention relates to a casting alloy of the claimed composition in the molten state. Furthermore, the present invention relates to a casting alloy of the claimed composition in the cast state. In particular, the present invention also relates to a casting alloy of the claimed composition in the formed state.

[0010] The casting alloy is specifically lead-free, i.e. . that lead is not actively added as an alloying element and any residual lead due to impurities is at most 0.10 wt.%, in particular at most 0.09 wt.%, in particular at most 0.08 wt.%, in particular at most 0.07 wt.%, in particular at most 0.06 wt.% and preferably at most 0.05 wt.%.

[0011] Preferably, the ratio of sulfur to molybdenum in the alloy is at most 2.5, more preferably at most 1.5, further preferably at most 1.0, and further preferably at most 0.8.

[0012] In particular, the ratio of sulfur to molybdenum in the alloy is between 0.6 and 2.5, preferably between 0.65 and 2.0, more preferably between 0.65 and 1.5, and even more preferably between 0.65 and 1.0. A ratio of sulfur to molybdenum in the alloy between 0.66 and 0.8 is particularly preferred.

[0013] Preferably, the alloy contains 0.3–1.7 wt.%, in particular 0.7–1.4 wt.%, and further, in particular 1.1–1.3 wt.%, molybdenum. In this respect, the alloy can contain at least 0.3 wt.%, in particular at least 0.7 wt.%, and further, in particular at least 1.1 wt.%, and preferably at most 1.7 wt.%, in particular at most 1.4 wt.%, and further, in particular at most 1.1 wt.%, molybdenum.

[0014] Preferably, the alloy contains 0.2–1.5 wt.%, in particular 0.5–1.2 wt.%, further in particular 0.7–1.1 wt.%, and further in particular 0.7–0.8 wt.%, sulfur. In this respect, the alloy can contain at least 0.2 wt.%, in particular at least 0.7 wt.%, further in particular at least 1.1 wt.%, and preferably at most 1.7 wt.%, in particular at most 1.4 wt.%, and further in particular at most 1.1 wt.%, sulfur.

[0015] Preferably, the casting alloy contains 2.5–11.5 wt.%, in particular 3.0–9.0 wt.%, further in particular 3.0–8.5 wt.%, further in particular 3.0–6.5 wt.%, further in particular 3.0–4.0 wt.%, tin. The casting alloy may also contain 8.5–11.5 wt.% tin. In particular, the casting alloy contains at least 2.5 wt.%, preferably at least 3.0 wt.%, further in particular at least 3.5 wt.%, further in particular at least 5.0 wt.%, and at most 11.5 wt.%, preferably at most 8.5 wt.%, further in particular at most 6.5 wt.%, tin.

[0016] With regard to the zinc content, it is advantageous if the casting alloy contains 1.0–6.0 wt.%, in particular 1.5–5.5 wt.%, further in particular 1.5–3.5 wt.%, and further in particular 3.0–3.5 wt.%, zinc. In particular, the casting alloy preferably contains at least 1.0 wt.%, preferably at least 1.5 wt.%, and at most 6.0 wt.%, preferably at most 5.5 wt.%, and further in particular at most 3.5 wt.%, zinc.

[0017] Preferably, the total proportion of tin and zinc (i.e., the tin content (in wt.%) and the zinc content (in wt.%) in total) shall not exceed 14 wt.%.

[0018] Furthermore, it is advantageous if the proportion of unavoidable impurities is less than 0.4 wt.% each, in particular less than 0.1 wt.%, and in total not more than 0.8 wt.%, in particular not more than 0.5 wt.%. The impurities may optionally include: up to 0.02 wt.% aluminum, up to 0.3 wt.% manganese, up to 0.05 wt.% selenium, up to 0.001 wt.% magnesium, up to 0.1 wt.% lead, up to 0.02 wt.% arsenic, up to 0.4 wt.% antimony, up to 0.04 wt.% bismuth.

[0019] One particularly preferred casting alloy consists of: 5.0 - 8.5 wt.%, in particular 5.4 - 8.0 wt.%, tin 1.0 - 5.5 wt.%, in particular 2.0 - 5.0 wt.%, zinc 0.7 - 2.2 wt.%, molybdenum 0.5 - 1.5 wt.%, sulfur, balance copper and unavoidable impurities, in particular up to a maximum of 0.8 wt.%, wherein, based on weight percent, the ratio of sulfur to molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, further in particular at least 0.66, and preferably at most 2.0, further preferably at most 1.5, further preferably at most 1.0, further preferably at most 0.8, and wherein the total proportion of molybdenum and sulfur is more than 0.15 times the proportion of zinc.

[0020] Another preferred casting alloy consists of: 3.5 - 6.5 wt.%, in particular 4.0 - 6.0 wt.%, tin 3.5 - 6.5 wt.%, in particular 4.0 - 6.0 wt.%, zinc 1.1 - 1.7 wt.%, molybdenum 0.7 - 1.1 wt.%, sulfur, optionally nickel up to 2.0 wt.%, balance copper and unavoidable impurities, in particular up to a maximum of 0.8 wt.%, wherein, based on weight percent, the ratio of sulfur to molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, further in particular at least 0.66, and preferably at most 1.0, further preferably at most 0.8, and wherein the total proportion of molybdenum and sulfur is more than 0.15 times the proportion of zinc.

[0021] According to another aspect, a copper-tin-zinc-molybdenum casting alloy is proposed, consisting of: 2.0 - 12.0 wt.% tin, 0.5 - 11.0 wt.% zinc, 0.1 - 2.2 wt.%, in particular 0.15 - 2.2 wt.% molybdenum, 0.1 - 1.5 wt.% sulfur, optionally up to 2.0 wt.% nickel, balance copper and unavoidable impurities, wherein, based on weight percent, the ratio of sulfur to molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, and further in particular at least 0.66 (i.e., a ratio of the mass fraction (in wt.%) of sulfur in the alloy to the mass fraction (in wt.%) of molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, and further in particular at least 0.66), and wherein the total fraction of molybdenum and sulfur (i.e., the sum of the mass fraction (in wt.%) of molybdenum in the alloy and the mass fraction (in wt.%) of sulfur in the alloy) is more than 0.15 times the zinc fraction (i.e., the mass fraction (in wt.%) of zinc in the alloy).

[0022] The invention also relates to a casting, in particular a continuous casting, especially in continuous or tube form, made from one of the casting alloys described above. The casting is produced in particular by casting, especially continuous casting, a casting alloy described above to form a casting blank and optionally by machining the casting blank.

[0023] The casting consists in particular of 2.0 - 12.0 wt.% tin, 0.5 - 6.5 wt.% zinc, 0.1 - 2.2 wt.%, in particular 0.15 - 2.2 wt.% molybdenum, 0.1 - 1.5 wt.% sulfur, optionally up to 2.0 wt.% nickel, balance copper and unavoidable impurities. wherein, based on weight percent, the ratio of sulfur to molybdenum in the alloy is between 0.6 and 2.5 (i.e., a ratio of the mass fraction (in wt.%) of sulfur in the alloy to the mass fraction (in wt.%) of molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, and further in particular at least 0.66), and wherein the total fraction of molybdenum and sulfur (i.e., the sum of the mass fraction (in wt.%) of molybdenum in the alloy and the mass fraction (in wt.%) of sulfur in the alloy) is more than 0.15 times the zinc fraction (i.e., the mass fraction (in wt.%) of zinc in the alloy). In this respect, the following condition applies to the mass fractions of molybdenum, sulfur, and zinc: Mass fraction of sulfur (wt%) + mass fraction of molybdenum (wt%) > 0.15 x mass fraction of zinc (wt%).

[0024] In the cast alloy, particularly in the casting, a portion of the sulfur and molybdenum is present as molybdenum-sulfur phases. These molybdenum-sulfur phases have, in particular, the composition MoS₂-x, where 0 ≤ x < 1.1.

[0025] In particular, in the cast alloy, especially the casting, some of the sulfur and molybdenum is present as molybdenum disulfide (MoS₂), especially in the form of, preferably spherical, MoS₂ precipitates. Preferably, the molybdenum sulfide is finely dispersed within the microstructure.

[0026] Preferably, the molybdenum-sulfur phases constitute more than 1.0%, preferably more than 1.5%, of the total area considered when viewed in the polished section (image).

[0027] The surface area fraction of the molybdenum-sulfur phases can be determined, in particular, by preparing at least one metallographic section of the cast alloy, especially the casting, and examining a total area of ​​1.4 mm² at at least five positions on the section using a light microscope (e.g., at 200x to 400x magnification) and determining the surface area fraction of the molybdenum-sulfur phases. This determination of the surface area fraction of the molybdenum-sulfur phases can be performed using known measurement software.

[0028] Preferably, at least a subset of the molybdenum-sulfur phases, when viewed in a metallographic section, exhibit a surface area of ​​more than 30 µm². The surface area can be determined, for example, by light microscopy of a metallographic section of the cast alloy, particularly the casting itself. Molybdenum-sulfur phases of this size have proven to be particularly effective for lubrication. In such a configuration, it can be advantageous if, when viewed in a metallographic section, the surface area of ​​these molybdenum-sulfur phases exceeds 1.0%, preferably 1.5%, of the total surface area.

[0029] In particular, in the cast alloy, especially in the casting, some of the sulfur and zinc is present as zinc sulfide (ZnS).

[0030] Preferably, the cast alloy, and in particular the casting, has a base matrix consisting primarily of copper and zinc, in which ZnS-rich phases, particularly in the form of ZnS precipitates, are present, to which a molybdenum-sulfur phase, preferably a MoS₂-rich phase, particularly in the form of MoS₂ precipitates, is attached. In particular, the zinc sulfide is at least partially enclosed by a molybdenum-sulfur phase, particularly MoS₂, preferably spherically or at least with a rounded outer contour.

[0031] The invention also relates to a method for producing a casting alloy described above. The method comprises the following steps: Providing, in particular layers, of the alloying elements in a melting furnace, in particular an induction melting furnace, wherein the alloying elements are added at room temperature (the furnace itself, however, may have a higher temperature); generating a melt from the alloying elements in the melting furnace to form the alloy, in particular at temperatures between 1100°C and 1300°C.

[0032] It was recognized according to the invention that by providing and in particular layers of the alloy components at room temperature (i.e. . (The alloy components are not preheated or added in a molten state) so that a homogeneous melt can be produced. After the melt has been produced, it can be cast and then cooled.

[0033] The alloying elements can be provided in pure form or as an alloy or compound. In particular, sulfur can be added partially in the form of molybdenum disulfide (MoS₂), which improves the solubility of sulfur and molybdenum in the melt. The molybdenum disulfide is especially dissolved in the melt.

[0034] Furthermore, it has proven advantageous to cover the alloy components with a covering agent, particularly before and during the melting process, to protect the melt from environmental influences, especially oxidation. The covering agent can be, in particular, charcoal.

[0035] Furthermore, it can prove advantageous – as an alternative or in addition to covering the melt with the covering agent – ​​if the melt is produced under a protective gas atmosphere or under negative pressure.

[0036] The invention also relates to a method for producing a casting from a casting alloy as described above. The method comprises the following steps: The process involves generating a melt from the alloy components in a melting furnace, particularly an induction melting furnace, further specifically as described above; casting the melt; cooling (and thus solidifying) the melt, particularly to obtain a casting blank. The casting blank can form the final casting. The casting blank can also be further processed to obtain the final casting. Therefore, the process can optionally include processing the casting blank, in particular forming, heat treatment, and / or machining the casting blank.

[0037] The casting of the molten metal can be carried out in various ways. For example, casting the molten metal can involve one of the following processes: casting into a lost or permanent mold, sand casting, die casting, centrifugal casting, continuous casting, die casting, investment casting, or composite casting by centrifugal injection or injection molding. Continuous casting of the molten metal has proven to be particularly advantageous. Therefore, the casting alloy described above is also, in particular, a continuously cast alloy.

[0038] In particular, the alloy or the cast blank exhibits a dendritic microstructure after casting. This microstructure can be modified for specific applications through subsequent forming and / or heat treatments (e.g., rolling and recrystallization).

[0039] The invention also relates to the use of a cast alloy described above for the manufacture of machine parts or transmission parts, such as gears, worm gears, bushings or linear guide elements, and / or fitting parts.

[0040] The following table summarizes advantageous compositions of the proposed casting alloy (values ​​in wt.%). Nr. Sn Zn With S It’s Verunreiningugen in Summe Rest I 3,8-6,0 4,0-6,0 1,1-1,7 0,7-1,1 < 2,0 < 0,8 Cu FAN 5,4-8,0 1,5-5,0 0,7-2,2 0,5-1,5 < 0,8 Cu III 9,0-11,0 1,0-3,0 0,1-0,9 0,1-0,8 < 0,8 Cu IV 3,0-4,0 1,5-3,0 0,3-1,3 0,2-0,8 < 0,8 Cu

[0041] The Figure 1 This simplified schematic representation shows typical microstructures of a cast alloy. The microstructures were extracted from a micrograph taken under a light microscope.

[0042] As in Figure 1In schematic representation, the cast alloy has a base matrix 10 consisting primarily of copper and zinc. ZnS-rich phases 12, particularly in the form of ZnS precipitates, are present in the base matrix 10 (in Figure 1 (shown hatched). A MoS₂-rich phase 14 is deposited on the ZnS-rich phases 12, preferably completely enclosing the ZnS phase 12. As mentioned above, this reduces the damaging effects of the ZnS. Furthermore, pure MoS₂-rich phases 14, preferably spherical or nodular, can be present in the base matrix 10. These MoS₂-rich phases 14 can serve as a dry lubricant and thus improve the tribological properties of the casting alloy or a casting produced therefrom.

Claims

1. Copper-tin-zinc-molybdenum casting alloy, consisting of: 2.0 - 12.0 wt.% tin, 0.5 - 6.5 wt.% zinc, 0.1 - 2.2 wt.% molybdenum, 0.1 - 1.5 wt.% sulfur, optionally up to 2.0 wt.% nickel, balance copper and unavoidable impurities, wherein, based on wt.%, the ratio of sulfur to molybdenum in the alloy is greater than 0.6, and wherein the total proportion of molybdenum and sulfur is more than 0.15 times the proportion of zinc.

2. Copper-tin-zinc-molybdenum casting alloy according to claim 1, wherein the ratio of sulfur to molybdenum in the alloy is at most 2.5, in particular at most 2.0, further in particular at most 1.5, further in particular at most 1.0, further in particular at most 0.

8.

3. Copper-tin-zinc-molybdenum casting alloy according to claim 1 or 2, wherein the alloy contains 0.3 - 1.7 wt.%, in particular 0.7 - 1.4 wt.%, further in particular 1.1 - 1.3 wt.%, molybdenum.

4. Copper-tin-zinc-molybdenum casting alloy according to any of the preceding claims, wherein the alloy contains 0.2 - 1.5 wt.%, in particular 0.5 - 1.2 wt.%, further in particular 0.7 - 1.1 wt.%, further in particular 0.7 - 0.8 wt.%, sulfur.

5. Copper-tin-zinc-molybdenum casting alloy according to any of the preceding claims, wherein the alloy contains 2.5 - 11.5 wt.%, in particular 3.0 - 9.0 wt.%, further in particular 4.0 - 9.0 wt.%, further in particular 5.0 - 9.0 wt.%, further in particular 5.5 - 8.0 wt.%, tin.

6. Copper-tin-zinc-molybdenum casting alloy according to any of the preceding claims, wherein the alloy contains 1.0 - 6.0 wt.%, in particular 1.5 - 5.5 wt.%, further in particular 1.5 - 3.5 wt.%, further in particular 3.0 - 3.5 wt.%, zinc.

7. Copper-tin-zinc-molybdenum casting alloy according to any of the preceding claims, wherein the total proportion of tin and zinc is at most 14 wt.%.

8. Casting, in particular continuous casting, especially in continuous or tube form, produced by casting a copper-tin-zinc-molybdenum casting alloy according to one of the preceding claims.

9. Casting according to the preceding claim, wherein a portion of the sulfur is in the form of molybdenum-sulfur phases of the composition MoS₂ 2-x with 0 ≤ x < 1.1, especially as MoS2.

10. Casting according to the preceding claim, wherein, when viewed in polished section, the surface area fraction of the molybdenum-sulfur phases is more than 1.0%, preferably more than 1.5%.

11. Casting according to claim 9 or 10, wherein at least a subset of the molybdenum-sulfur phases has a surface area of ​​at least 30 µm² when viewed in a polished section. 2 exhibit.

12. Casting according to one of claims 9 to 11, wherein part of the sulfur is present as zinc sulfide, wherein a molybdenum-sulfur phase, in particular a MoS2-rich phase, is attached to the zinc sulfide.

13. Method for producing a copper-tin-zinc-molybdenum casting alloy according to any one of claims 1 to 7, comprising: - layering the alloy components in a melting furnace, in particular an induction melting furnace, at room temperature; - generating a melt from the alloy components in the melting furnace.

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