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

Abstract

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

[0002] Copper-tin alloys, also known as bronze alloys, are known in a variety of ways from the state of the art and are used, for example, as bearing materials.

[0003] Such bronze alloys often contain lead to improve manufacturability and machinability. However, for health and environmental reasons, lead, as a toxic heavy metal, is increasingly undesirable as an alloying element.

[0004] To replace lead, the addition of sulfur has been discussed. For example, German patent DE 10 2020 106 995 A1 discloses the addition of small amounts of sulfur to a copper-tin bronze to improve machinability and provide lubricating properties. DE 10 2020 106 995 A1 specifically describes a lead-free copper-tin bronze continuous casting alloy comprising at least 84 wt.% copper, 9.0–13.0 wt.% tin, 0.1–0.8 wt.% sulfur, at most 0.5 wt.% zinc, and 0.05–3.0 wt.% nickel. A disadvantage of sulfur mentioned is the formation of zinc sulfide, which, due to its comparatively high hardness, makes machining difficult.

[0005] German patent DE 10 2021 131 763 A1 discloses a copper-tin continuous casting alloy with a further increased sulfur content, wherein the continuous casting alloy comprises at least 86.0 wt.% copper, 3.5–12.0 wt.% tin, 0.9–1.48 wt.% sulfur, at most 4.0 wt.% nickel, and at most 0.09 wt.% zinc. DE 10 2021 131 763 A1 addresses the fact that increasing the sulfur content to the claimed range can improve the tribological properties of the continuous casting alloy.

[0006] The present invention is based on the objective of providing a copper-tin casting alloy with further improved properties. In particular, the copper-tin casting alloy should be easy and economical to produce and cast, and after casting should be easily machinable and exhibit good tribological properties.

[0007] This problem is solved according to the invention by a casting alloy having the features of claim 1. This is a casting alloy consisting of: 3.0 - 16.0 wt.% tin, 0.1 - 1.6 wt.% molybdenum, 0.1 - 1.1 wt.% sulfur, optionally up to 3.0 wt.%, in particular up to 2.5 wt.%, further in particular up to 2.0 wt.%, nickel, optionally up to 0.5 wt.%, in particular up to 0.4 wt.%, phosphorus, optionally up to 1.0 wt.%, in particular up to 0.5 wt.%, zinc; remainder 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 greater than 0.66 (i.e., wherein the 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 greater than 0.66).

[0008] The proposed casting alloy is environmentally friendly, casts well, and exhibits good machinability and tribological properties in the cast state. In particular, 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 disadvantages of sulfur described in the prior art. 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 results in the precipitation of molybdenum disulfide (MoS₂) during solidification. Even in small quantities, MoS₂ can act as a chip breaker, thus improving machinability. Furthermore, it has been found that molybdenum disulfide can also exert its properties as a dry lubricant in the casting alloy, which has a positive effect on the tribological properties.

[0009] Finally, it was discovered that the presence of molybdenum surprisingly makes the alloy robust against potential impurities such as zinc and the zinc sulfide that subsequently forms. Further investigations revealed that the precipitated molybdenum disulfide can bind to any zinc sulfide that may form, or even encapsulate it, thus rendering it harmless.

[0010] 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 and, in particular, the cooled state. In the casting alloy, sulfur and molybdenum are present, in particular at least partially, as MoS₂.

[0011] The casting alloy is in particular lead-free, i.e., that lead is not actively added as an alloying element and that 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.%.

[0012] 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.

[0013] 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.

[0014] It can prove advantageous if the casting alloy contains 0.1–0.3 wt.% molybdenum and 0.1–0.2 wt.% sulfur. According to the invention, it has been found that such a comparatively low molybdenum / sulfur content already contributes to a significant improvement in the machinability of the casting alloy.

[0015] It can also prove advantageous if the casting alloy has a higher molybdenum / sulfur content, which can improve the tribological properties of the alloy. Such casting alloys can be particularly beneficial in bearing technology, for example, as a sliding layer in a plain bearing. Specifically, the casting alloy can contain 0.6–1.6 wt% molybdenum and 0.4–1.1 wt% sulfur.

[0016] A preferred casting alloy contains 3.5–8.5 wt.%, in particular 4.0–8.0 wt.%, tin. Such casting alloys with a comparatively low tin content are particularly suitable for applications where forming is to take place after the alloy has been cast.

[0017] An alternative preferred casting alloy contains 7.0–13.5 wt.%, in particular 8.0–12.0 wt.%, further in particular 8.5–11.5 wt.%, further in particular 9.0–11.0 wt.%, tin. Such casting alloys with a comparatively high tin content are particularly suitable for applications in bearing technology.

[0018] In an advantageous embodiment, the casting alloy may contain 3.5 - 11.5 wt.%, in particular 4.0 - 10.5 wt.%, further in particular 5.5 - 9.5 wt.%, further in particular 6.0 - 8.5 wt.%, tin, 1.1 - 6.4 wt.%, in particular 1.7 - 6.4 wt.%, further in particular 2.2 - 6.4 wt.%, molybdenum and 0.7 - 4.3 wt.%, in particular 1.1 - 4.3 wt.%, further in particular 1.5 - 4.3 wt.% sulfur.

[0019] In an alternative advantageous embodiment, the casting alloy can contain 7.0 - 15.5 wt.%, in particular 8.5 - 14.0 wt.%, further in particular 10.0 - 13.5 wt.%, further in particular 10.5 - 13.5 wt.%, further in particular 12.5 - 13.5 wt.% tin, 0.1 - 0.3 wt.% molybdenum and 0.1 - 0.2 wt.% sulfur.

[0020] Furthermore, it can prove advantageous if the casting alloy contains 0.01–0.5 wt.%, particularly 0.01–0.4 wt.%, of phosphorus. Phosphorus can contribute to the deoxidation of the melt. However, in combination with molybdenum disulfide, excessively high proportions can lead to degeneration of the sulfur phase and the formation of phosphorus-rich intermetallic phases, which, due to their hardness, can impair formability and increase brittleness. Therefore, the phosphorus content should be limited.

[0021] Furthermore, it can prove advantageous if the casting alloy contains 0.4–2.5 wt.%, in particular 0.5–2.0 wt.%, and in particular 1.0–2.0 wt.%, and in particular 1.5–2.0 wt.%, nickel. Nickel in the claimed amounts can contribute to improving the strength of the alloy. In addition, nickel can have a positive effect on the corrosion resistance of the alloy.

[0022] Furthermore, it is advantageous if the proportion of unavoidable impurities is less than 0.4 wt.%, 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 0.04 wt.% silicon, up to 0.1 wt.% aluminum, up to 0.2 wt.% manganese, up to 0.1 wt.% lead, up to 0.3 wt.% arsenic, up to 0.4 wt.% antimony.

[0023] 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.

[0024] The casting consists in particular of 3.0 - 16.0 wt.% tin, 0.1 - 1.6 wt.% molybdenum, 0.1 - 1.1 wt.% sulfur, optionally up to 3.0 wt.%, in particular up to 2.5 wt.%, further in particular up to 2.0 wt.%, nickel, optionally up to 0.5 wt.%, in particular up to 0.4 wt.%, phosphorus, optionally up to 1.0 wt.%, in particular up to 0.5 wt.%, zinc, balance copper and unavoidable impurities, where, based on weight percent, the ratio of sulfur to molybdenum in the alloy is greater than 0.6, especially greater than 0.5, and furthermore especially greater than 0.66.

[0025] 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.

[0026] 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.

[0027] Preferably, the molybdenum-sulfur phases constitute more than 0.8%, preferably more than 1.0%, and more preferably more than 1.3% of the total area considered when viewed in a polished section.

[0028] The 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 area fraction of the molybdenum-sulfur phases relative to the total area. This determination of the area fraction of the molybdenum-sulfur phases can be performed using known measurement software.

[0029] 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 0.8%, preferably more than 1.0%, of the total surface area.

[0030] 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.

[0031] It was discovered according to the invention that a homogeneous melt can be produced by providing, and in particular layering, the alloying elements at room temperature (i.e., the alloying elements are not preheated or added in a molten state). After the melt has been produced, it can be cast and then cooled.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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).

[0038] The invention also relates to the use of one of the copper-tin-molybdenum casting alloys described above for the manufacture of machine parts or gear parts, such as gears, worm gears, bushings or linear guide elements.

[0039] The following table summarizes advantageous compositions of the proposed casting alloy (values ​​in wt.%). Nr. Sn Mo S us P Total impurities change I 10,5-13,0 0,1-0,3 0,1-0,2 < 2,0 < 0,8 With yl 7,5-8,5 0,1-0,3 0,1-0,2 0,01-0,4 < 0,8 With III 9,0-11,0 0,1-0,3 0,1-0,2 < 0,8 With N 13,0-15,0 0,1-0,3 0,1-0,2 < 0,8 With V 9,0-11,0 0,6-1,51 0,4-1,01 < 0,8 With VI 6,0-9,0 0,6-1,56 0,4-1,04 < 2,0 < 0,8 With VII 11,0-13,0 0,1-0,3 0,1-0,2 1,5-2,5 < 0,8 With quick 4,0-8,0 0,6-1,59 0,4-1,06 0,5-2,0 < 0,8 With

Claims

1. Copper-tin-molybdenum casting alloy, consisting of: 3.0 - 16.0 wt.% tin, 0.1 - 1.6 wt.% molybdenum, 0.1 - 1.1 wt.% sulfur, optionally: up to 3.0 wt.%, in particular up to 2.5 wt.%, further in particular up to 2.0 wt.%, nickel, up to 0.5 wt.%, in particular up to 0.4 wt.%, phosphorus, up to 1.0 wt.%, in particular up to 0.5 wt.%, zinc, balance copper and unavoidable impurities, wherein, based on wt. percent, the ratio of sulfur to molybdenum in the alloy is greater than 0.

6.

2. Copper-tin-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-molybdenum casting alloy according to claim 1 or 2, wherein the alloy contains 0.1 - 0.3 wt.% molybdenum and 0.1 - 0.2 wt.% sulfur.

4. Copper-tin-molybdenum casting alloy according to claim 1 or 2, wherein the alloy contains 0.6 - 1.6 wt.% molybdenum and 0.4 - 1.1 wt.% sulfur.

5. Copper-tin-molybdenum casting alloy according to any of the preceding claims, wherein the alloy contains 3.5 - 8.5 wt.%, in particular 4.0 - 8.0 wt.%, tin.

6. Copper-tin-molybdenum casting alloy according to any one of claims 1 to 4, wherein the alloy contains 7.0 - 13.5 wt.%, in particular 8.0 - 12.0 wt.%, further in particular 8.5 - 11.5 wt.%, further in particular 9.0 - 11.0 wt.%, tin.

7. Copper-tin-molybdenum casting alloy according to any of the preceding claims, wherein the alloy contains 0.01 - 0.5 wt.%, in particular 0.01 - 0.4 wt.%, phosphorus.

8. Copper-tin-molybdenum casting alloy according to any of the preceding claims, wherein the alloy contains 0.4 - 2.5 wt.%, in particular 0.5 - 2.0 wt.%, further in particular 1.0 - 2.0 wt.%, further in particular 1.5 - 2.0 wt.%, nickel.

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

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

11. Casting according to the preceding claim, wherein, when viewed in the polished section, the surface area fraction of the molybdenum-sulfur phases is more than 0.8%, preferably more than 1.0%, further preferably more than 1.3%.

12. Casting according to claim 10 or 11, 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.

13. Method for producing a copper-tin-molybdenum-sulfur alloy according to any one of claims 1 to 8, comprising: - layering the alloying elements in a melting furnace, in particular an induction melting furnace, wherein the alloying elements are added at room temperature; - generating a melt from the alloying elements in the melting furnace.

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