EP3024956B1 - Grain-refined copper casting alloy with iron and boron - Google Patents

Description

The invention relates to a copper-zinc casting alloy. In particular, the invention relates to a copper-zinc-silicon alloy in which boron and iron and optionally nickel are added.

It is known that molded parts made of copper alloys are produced as castings. Examples of such molded parts are fittings, elbows, T-pieces for media-carrying piping systems, components for pumps and valves as well as structural parts in mechanical and plant engineering and in vehicle construction. Among other things, silicon-containing brasses are used as material for this purpose.

In order to ensure the mechanical stability of the molded part, a material is required, which already has a homogeneous structure in the cast state. Inhomogeneities in the structure must be taken into account by costly safety margins or they can lead to failure of the component. With wrought materials, the homogeneity of the structure is achieved by forming. In order to achieve a homogeneous structure without forming steps, the material must already have a fine-grained structure in the cast state. After casting, the molding is in many cases by machining, grinding or polishing, such as sealing surfaces, reworked. For this purpose, the material must be free from voids and hard particles. Furthermore, a coarse dendritic microstructure has a negative effect on the corrosion resistance of the material.

In the production of castings, the material is usually melted and poured twice: the first time the alloy is melted, the alloy composition is roughly adjusted. The alloy is poured into ingots. For the production of the castings, the ingots are melted down and the alloy is cast into moldings. A change in the alloy composition during this second reflow and pouring operation is undesirable but unavoidable due to the burning of some elements, such as Zn, Zr or P. For the quality of the product, the casting condition after the second casting is crucial.

It is known that in copper alloys by the addition of certain elements, a fine-grained cast structure can be adjusted. In EP 1 777 305 A1 It is proposed to add 0.0005 to 0.04% zircon for grain refining to a copper-zinc-silicon alloy. A disadvantage of zirconium, however, is its burning during melting and casting. In the production of castings, it is therefore difficult to ensure the desired zirconium content in the finished component.

In EP 1 817 438 B1 It is proposed to add 0.05 to 2 wt .-% manganese to a copper-zinc-silicon alloy to improve the microstructure. It is also proposed to add to the alloy additionally 0.01 to 0.05 wt .-% zirconium as grain refining agent. This is consistent with studies showing that the addition of manganese without zirconium does not cause grain refining.

Using boron as a grain refining agent for copper alloys is known. So will in DE 10 2005 024 037 A1 proposed to add 0.00001 to 0.5% boron to a copper-zinc-silicon alloy. Boron-fines of small amounts of boron are detected by alloys containing approximately 76% copper, 21% zinc and 3% silicon.

The publication 'Grain refining of copper alloys' by F. Romankiewicz et al., Metal, Vol. 48, No. 11/94, pp. 865-871 it can be seen that the grain refining of borosilicate brass is pointless. This finding is based on investigations carried out on the material CuZn16Si4 with boron additions of 0 to 0.06 wt .-%.

The publication CN 103114220 A discloses a Cu-Zn-Si alloy containing 0.11-0.2% Fe and 0.001-0.01% B, Ag and / or Ti.

In the US 2009/0263272 A1 describe copper-zinc-bismuth alloys containing silicon and boron. Further, the alloys may contain small amounts of iron as an unavoidable impurity.

The expert receives from the prior art only unsatisfactory evidence, as in copper-zinc-silicon alloy, a fine-grained cast structure can be adjusted. Zircon is very difficult to use due to its burnup. Boron causes grain refining for zinc contents of about 21% by weight, but not for zinc contents of about 16% by weight. It would therefore be desirable to have a grain refining agent that exerts its effect largely independently of the zinc content. In particular, it should bring about grain refining for copper contents greater than 80% by weight.

The invention has for its object to provide improved copper-zinc casting alloys. In particular, a grain refining of the cast structure should be able to be achieved largely independently of the zinc or copper content. In the absence of alternatives, grain refining agents for copper contents greater than 80% by weight are particularly desirable.

The invention relates to the copper-zinc casting alloy according to claim 1. The others refer back Claims relate to advantageous embodiments and further developments of the invention.

The invention is based on the consideration that by the simultaneous addition of boron and iron to a silicon-containing copper-zinc alloy, a grain refining of the cast structure occurs when boron content and iron content are in a certain ratio. Iron can be partially replaced by nickel. The ratio of boron content and the sum of iron and nickel content is at least 0.025 and at most 0.12. The respective element contents are defined as parts by weight of the total alloy. Are boron content and the sum of iron and nickel content in the relation to each other, iron borides or nickel borides or iron-nickel Mischboride can form. These borides lead to the formation of a fine grain in the cast structure of the material.

This finding is the more surprising as the person skilled in the art, in particular the WO 91/02826 , notes that even small amounts of iron in copper alloys reduce the grain refining effect of boron, and that iron levels 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 adversely affect the polishability of the material. In WO 91/02826 It is therefore proposed to prevent the formation of iron borides by adding to the alloy another element which reacts more quickly with boron than iron.

Optionally, the alloy may contain tin. Tin improves the corrosion resistance of the material. With tin contents greater than 2.0% by weight, unwanted tin blends may occur due to the interaction of all alloy constituents.

Optionally, the alloy may contain phosphorus. In small amounts, phosphorus serves to deoxidize the melt. Furthermore, it can favorably influence the formation of the initial cast structure and the corrosion properties. Phosphorus increases the fluidity of the melt and reduces the susceptibility of the material to stress corrosion cracking.

Lead makes the alloys easier to machine. To comply with the legal requirements 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 .-%. The lead content of the alloy may preferably be at most 0.1% by weight.

Optionally, the alloy may contain small amounts of antimony and / or arsenic. These two elements reduce the tendency of the material for Entzinkung.

In a preferred embodiment of the invention, the ratio of boron content and the sum of iron and nickel content may be at least 0.05 and at most 0.075. Surprisingly, it has been found that, when the alloy composition according to this specification is selected, a fine-grained microstructure already ensues after the first casting. Even after the second casting, the microstructure is always fine-grained. This advantageous selection of the alloy composition thus ensures particularly reliable the formation of a fine-grained cast structure and from the fine grain of the cast blocks can already derive a statement about the quality of the molded parts. This preferred selection of the boron content and the sum of iron and nickel content represents stoichiometrically particularly favorable conditions for the formation of borides.

In a preferred embodiment of the invention, the boron content may be at least 0.005% by weight, more preferably at least 0.01% by weight and at most 0.025% by weight. Boron contents of at least 0.005 wt .-%, preferably at least 0.01 wt .-%, in conjunction with iron and optionally nickel borides can form particularly rapidly. With a boron content greater than 0.025 wt .-% can lead to the formation of undesirable large borides.

Advantageously, the iron content may be at least 0.1% by weight and at most 0.5% by weight. This preferred selection of iron content is stoichiometrically particularly favorable conditions for the formation of borides in suitable frequency and size. In particular, when this preferred iron content is combined with a boron content of not less than 0.01% by weight and not more than 0.025% by weight. -% is already present at the first casting the alloy a fine-grained structure.

In a preferred embodiment of the invention, the nickel content may amount to at most 0.3 wt .-%. With regard to the formation of borides, nickel can at least partially replace the iron. In a particularly preferred embodiment, the sum of iron and nickel content at least 0.1 wt .-% and at most 0.5 wt .-% amount. Furthermore, it may be advantageous to choose the iron content of the alloy greater than the nickel content. The iron content initiates the formation of borides and thus initiates the grain refining effect.

Advantageously, the copper content of the alloy may be more than 80% by weight, preferably at least 81% by weight. Copper contents of more than 80% by weight make the alloy particularly corrosion-resistant and therefore suitable for use in fluid-carrying piping systems, such as drinking water pipes. The silicon content in this copper 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 .-%.

Boron and iron in combination are suitable as grain refining agents in copper-zinc-silicon alloys. The ratio of boron content of the alloy [in% by weight] and iron content of the alloy [in% by weight] is at least 0.025 and at most 0.12. The copper-zinc-silicon alloy may have the following composition [in% by weight]: Cu 70.0 to 97.0%, Si 2.0 to 4.5%, B From 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 still up to 0.15% As or Sb,
Rest Zn as well as unavoidable impurities.

By the addition of boron and iron in the above ratio of the contents, grain refining of the cast structure may occur in a copper-zinc-silicon alloy. The boron content is preferably at least 0.005% by weight and at most 0.025% by weight. The iron content is preferably at least 0.1% by weight and at most 0.5% by weight.

The aspect of using boron and iron to refine copper-zinc-silicon alloys includes all of the above-described preferred embodiments of a silicon-containing copper-zinc casting alloy according to the present invention.

Boron, iron and nickel in combination are suitable as grain refining agents in copper-zinc-silicon alloys. The ratio of boron content of the alloy [in wt .-%] and the sum of iron and nickel content of the alloy [in wt .-%] is at least 0.025 and at most 0.12. The copper-zinc-silicon alloy may have the following composition [in% by weight]: Cu 70.0 to 97.0%, Si 2.0 to 4.5%, B From 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 still up to 0.15% As or Sb,
Rest Zn as well as unavoidable impurities.

By the addition of boron, iron and nickel in the above ratio of the contents, grain refining of the cast structure may occur in a copper-zinc-silicon alloy. The boron content is preferably at least 0.005% by weight and at most 0.025% by weight. The iron content is preferably at least 0.1% by weight and at most 0.5% by weight. The nickel content is preferably at least 0.05% by weight and at most 0.3% by weight.

The aspect of using boron, iron and nickel for grain refining of copper-zinc-silicon alloys includes all of the above-described preferred embodiments of a silicon-containing copper-zinc casting alloy according to the present invention.

The invention will be explained in more detail with reference to the embodiments shown in Table 1.

Table 1 shows the composition in% by weight of 18 trial alloys, with samples 1, 2, 3, 4, 11 and 18 not belonging to the invention. The penultimate column of the table gives the ratio of boron content and the sum of iron and nickel content. The alloys were melted and poured off. The individual casts were melted down again and poured off a second time. The samples were characterized metallographically. The last column of the table indicates whether the structure after the second casting was coarse or fine grained.

Samples 1 to 3 contain no boron. The cast structure is always coarse-grained. Sample 4 and sample 11 contain small amounts of boron. Again, the structure is coarse-grained.

Samples 5 to 10 contain both boron (0.01 to 0.02 wt%) and iron (0.1 to 0.3 wt%). Sample 8 additionally contains 0.4% by weight of tin. For samples 5 to 10, a fine-grained cast structure is always observed after the second casting. The quotient of boron content and iron content in these samples is between 0.03 and 0.11. The addition of tin has no influence on the formation of the fine-grained casting structure. Table 1: Experimental alloys with composition in% by weight 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 .0545 fine 6 86 3.8 10.0 0.03 0.18 0 0 0.019 0 .1056 fine 7 86 3.8 9.9 0.03 0.30 0 0 0.019 0 0.0633 fine 8th 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

In Samples 12 to 17, part of the iron is replaced by nickel. The boron content varies from 0.005 to 0.013% by weight. The iron content is between 0.1 and 0.2 wt .-%, the nickel content between 0.08 and 0.18 wt .-%. Further, the tin content varies from 0.1 to 0.2 wt%. With the exception of sample 13, all samples after the second casting show a fine-grained texture. For these samples, the quotient of boron content and the sum of iron and nickel content is between 0.025 and 0.06. For sample 13, this quotient is 0.016. The sample 13 contains in total too much iron and nickel based on the boron content of 0.006 wt .-%. The tin content has no influence on the formation of the fine cast structure.

It should be emphasized that the samples 5, 7, 8 and 15, in contrast to the other samples after the first casting have a fine-grained structure. These samples are characterized in that the quotient of boron content and the sum of iron and nickel content is between 0.05 and 0.065. If one chooses the alloy composition so that said quotient is exactly in this window, then the formation of iron borides or nickel borides or iron-nickel Mischboriden is particularly favored. Iron borides with the stoichiometric formula Fe ₃ B would correspond exactly to this weight ratio of boron and iron.

On the basis of sample 18, the influence of manganese on the cast structure was examined in the form of a random sample. Sample 18 contains no boron but about 0.08 wt% manganese. The manganese-containing sample always shows a coarse-grained cast structure.

Claims (8)

1. Copper/zinc casting alloy with the following composition [in% by weight]: Cu from 70 to 97.0%, Si from 2.0 to 4.5%, B from 0.002 to 0.03%, Fe from 0.01 to 1.0%, optionally further up to 2.0% Sn,
   optionally further up to 0.4% Ni,
   optionally further up to 0.2% P,
   optionally further up to 0.25% Pb,
   optionally further up to 0.15% As or Sb,
   balance Zn and inevitable impurities,
   characterised in that
   the ratio of boron content and the sum of iron and nickel content is at least 0.025 and a maximum of 0.12.
2. Copper/zinc casting alloy according to claim 1, characterised in that
   the ratio of boron content and the sum of iron and nickel content is at least 0.05 and a maximum of 0.075.
3. Copper/zinc casting alloy according to claim 1 or 2, characterised in that
   the boron content is at least 0.005% by weight and a maximum of 0.025% by weight.
4. Copper/zinc casting alloy according to claim 3, characterised in that
   the boron content is at least 0.01% by weight and a maximum of 0.025% by weight.
5. Copper/zinc casting alloy according to any one of claims 1 to 4, characterised in that
   the iron content is at least 0.1% by weight and a maximum of 0.5% by weight.
6. Copper/zinc casting alloy according to any one of claims 1 to 5, characterised in that
   the nickel content is a maximum of 0.3% by weight.
7. Copper/zinc casting alloy according to any one of claims 1 to 6, characterised in that
   the iron content is greater than the nickel content.
8. Copper/zinc casting alloy according to any one of claims 1 to 7, characterised in that
   the copper content is at least 81% by weight.