EP3225707B1 - Component for media-conducting gas or water lines comprising a copper alloy - Google Patents

Description

The present invention relates to a component for media-carrying gas or water pipes, in particular a fitting or armature for drinking water pipes, the component at least partially consisting of a lead-free copper alloy.

Metallic materials for use in components for water-bearing, in particular drinking water-bearing trades, such as fittings, armatures, pipes, press connectors, roof gutters or drainage channels, have to meet special requirements. In the case of components in contact with drinking water in particular, the corrosion resistance should be mentioned. Non-ferrous metal alloys with a high copper content, such as bronze, brass or gunmetal, also contain a certain amount of lead because lead improves the machinability of such alloys. In practice, nickel is also present in such alloys to increase the strength and corrosion resistance of the alloys. Due to the toxicity of these metals, however, such materials must have a low tendency for metal ions to migrate into the medium, ie a low release of ions from the alloy components to the medium. To this end, the materials used to protect consumers must comply with very narrow limits, which are regulated by the drinking water regulations. This is from the EP 1 798 298 A1 a largely lead- and nickel-free copper alloy is known which, in addition to copper and unavoidable impurities, contains 2% by weight to 4.5% by weight silicon, 1% to 15% by weight zinc, 0.05% by weight up to 2% by weight manganese and optionally 0.05% by weight to 0.4% by weight aluminum and 0.05% by weight to 2% by weight tin. The ones in the EP 1 798 298 A1 The alloy described shows an improved migration behavior for lead, nickel, copper and zinc ions compared to a conventional gunmetal. After casting, the alloy can be subjected to a heat treatment in order to achieve a high proportion of α mixed crystal and thus a particularly favorable migration behavior of the alloy.

The gunmetal alloy CuSn5Zn5Pb2 with contents of around 5% by weight tin and around 5% by weight zinc is currently widely used for use in drinking water installations. This copper alloy has excellent corrosion resistance and can therefore be used in all water qualities within the drinking water supply. Alloys of this type usually have a single-phase structure and therefore offer high plastic deformability. However, it is precisely this plastic deformability that causes problems during machining. Single-phase copper materials tend to form long chips. This type of chip inhibits the workflow during fully automated turning or drilling and leads to heavy wear on the tool cutting edges. In order to still be able to process the products economically, lead is added to the alloys as a chip-breaking additive. Lead enables economical, fully automated mechanical processing.

Lead is practically insoluble in copper and has a low melting point. As a result, it is the last element to solidify in copper-tin alloys. This constitutional behavior means that, at the end of solidification, lead is present in the structure in the form of evenly distributed, small, drop-shaped particles between the dendrite arms. These fine, drop-shaped particles act as chip breakers without affecting the original properties of the material. This can be seen particularly clearly from the corrosion resistance, since the lead particles are present as incoherent phases and thus cannot interact with the surrounding matrix. The uniform distribution of small, drop-shaped lead particles also ensures that consistently similar mechanical parameters can be expected over a uniform cross-section.

In the patent specification US 8,470,101 B2 describes a lead-free alloy which, in addition to copper and unavoidable impurities, consists of 0.1 wt.% to 0.7 wt.% sulfur, up to 8 wt.% tin and up to 4 wt.% zinc and in which fulfills the task of lead via sulfur phases in the form of sulfide particles. In contrast to the element lead, these sulfides do not have the property of inevitably developing in the form of small, distributed phases at the end of solidification. In the case of an unfavorably chosen composition of the patent specification US 8,470,101 B2 The alloy described here can lead to an unfavorable sulfide formation in the structure. This reduces the strength and there is a lowering of the mechanical parameters. Furthermore have those in the patent US 8,470,101 B2 sulphides described do not have high corrosion resistance. However, precisely for the use of such a sulfur-containing copper alloy in a drinking water installation, a corrosion-resistant matrix is necessary in order to ensure the longevity of the components.

In copper alloys, nickel is able to both increase corrosion resistance and improve the distribution of sulfide phases in the structure. However, high nickel contents lead to a high release of metal ions into drinking water and are therefore classified as hygienically questionable. The specified alloy range in the patent US 8,470,101 B2 cannot guarantee over the entire scope described therein that sufficiently high corrosion, strength, processing or hygiene properties are present. But these properties in particular are essential for thin-walled components that carry drinking water.

Against this background, the present invention is based on the object of specifying a lead-free copper alloy for the production of components for media-carrying gas or water pipes which, compared to a conventional gunmetal alloy, e.g. CuSn5Zn5Pb2, a corrosion-resistant matrix, has good strength properties combined with good processing properties, high pressure tightness and improved migration behavior. In addition, the lead-free copper alloy should have good casting behavior, for example in sand or continuous casting.

These and other objects are achieved by a component for media-carrying gas or water lines with the features of claim 1. Preferred embodiments of the component according to the invention are described in the dependent claims.

According to the present invention, it was surprisingly recognized that a lead-free copper alloy, which as alloy components in wt .-% in addition to copper (Cu) and unavoidable impurities still 3.5 wt .-% ≤ tin (Sn) ≤ 4.8 wt .-% , 1.5% by weight ≤ zinc (Zn) ≤ 3.5% by weight, 0.25% by weight ≤ sulfur (S) ≤ 0.65% by weight, 0.04% by weight Phosphorus (P) 0.1 wt%, optionally not more than 0.09 wt% lead; optionally no more than 0.4 wt% nickel; optionally no more than 0.1 wt% antimony; as well as optionally not more than 0.3% by weight iron, zirconium and / or boron alone or in combination of two or more of the elements mentioned, in contact with water of different water qualities one compared to standard brass (CuZn40Pb2) and dezincification-resistant brass (CuZn36Pb2As) Improved surface layer formation shows what has been proven, among other things, by suitable artificial aging tests. Due to this improved formation of the top layer, the lead-free copper alloy shows no dezincification or similar selective corrosion attacks. Therefore, the lead-free copper alloy has improved corrosion resistance over the entire framework specified by the Drinking Water Ordinance (hereinafter referred to as "TWVO"). Accordingly, the present invention preferably represents a component for media-carrying gas or water lines, in particular a fitting or a fitting for drinking water pipes, the component at least partially consisting of the lead-free copper alloy according to the invention, the component having a wall thickness in the range from 0.5 mm to 6.0 mm at least in sections.

It was found that in the alloy used according to the invention two sulfur-containing phases, copper sulfide and zinc sulfide, are formed in the structure as a function of temperature and offset from one another. In order to achieve optimal machining properties with sulfide particles, they should be as round, finely divided and small as possible. This behavior can be observed preferentially with the formation of copper sulfides. Zinc sulfides, on the other hand, tend to have a geometrically unfavorable shape. It was recognized that the point in time of phase formation, the type, number and distribution of the sulfur-containing particles are decisive for the machinability and for the mechanical properties, such as elongation, of the component. The sulfides formed, preferably as copper sulfide, have the advantage, similar to lead particles, of being present as incoherent phases.

The tin content influences the strength, corrosion resistance and phase distribution and, in the claimed range of 3.5% by weight to ≤ 4.8% by weight, achieves an optimally balanced, economic ratio of the properties described above. With a tin content of more than 4.8% by weight, the strength and corrosion resistance in the matrix increase further, but under normal cooling conditions in sand casting, the distribution of the sulfides becomes coarser and the size increases. In the case of tin contents below 3.5% by weight, there is insufficient corrosion inhibition. Also, because of the weak solid solution strengthening, the properties necessary for practice are not achieved. A high tensile strength can be achieved at contents of more than 4.8% wt.% Tin, whereas the elongation values of the material are reduced. Contents of far more than 4.8 wt .-% tin lead to the formation of a structure which has an embrittling and unfavorable effect on the processing.

It was found that, given constant cooling conditions, the proportion of copper sulfide decreases and the proportion of zinc sulfide increases with increasing zinc content. With a zinc content of 1.5% by weight to 3.5% by weight, particularly preferably with a zinc content in the range of 1.8% by weight to 3.0% by weight, it can be ensured that in Walls of up to 6 mm a homogeneous distribution of smaller sulfides is favored. From this point of view, a zinc content of 2.0 wt% to 2.8 wt% is particularly preferred. The salary of max. 3.5% by weight of zinc also ensures that partial corrosion phenomena are avoided and a high level of corrosion resistance can be achieved. The sulfur content of 0.25% by weight to 0.65% by weight also determines the volume fraction of the sulfides. From 0.25% by weight sulfur, an amount of sulfide particles is generated which ensures that the alloy is sufficiently machinable. A sulfur content above 0.65% by weight sulfur can lead to the formation of undesirable, coarse sulfide particles. In addition, due to the high proportion of sulfide particles, the load-transferring cross-section, ie the cross-section of the component that absorbs external stresses, can be reduced so much that the mechanical parameters, such as elongation at break and the like, deteriorate. Further improved properties were achieved with an alloy whose sulfur content is in the range from 0.3% by weight to 0.6% by weight, in particular in the range from 0.35% by weight to 0.55% by weight . Due to the alloy composition used according to the invention, the metal sulfides are present in the lead-free copper alloy as an incoherent, finely divided, disperse phase in the form of finely divided particles with such a sulfur content. This offers the advantage that any corrosion that may occur occurs only to a small extent locally on these particles and not along coherent, larger, individual phases of the alloy structure, as is the case, for example, with standard brass. Due to the small size of the particles, there is no significant corrosion attack.

According to the invention, the proportion of phosphorus (P) in the lead-free copper alloy is 0.04% by weight to 0.1% by weight. Below 0.04% by weight of phosphorus, there is insufficient deoxidation of the melt, which has a negative effect on the phase formation of the alloy. In contrast, the lead-free copper alloy with a phosphorus content of more than 0.1% by weight tends to have adverse effects on the mechanical properties, such as reduced elongation at break. From these points of view, the proportion by weight of phosphorus in the lead-free copper alloy is preferably in the range from 0.04% by weight to 0.08% by weight, particularly preferably in the range from 0.04% by weight to 0.06% by weight. -%.

As used herein, the term "lead-free copper alloy" means a copper alloy that includes lead as an unavoidable impurity in an amount of not more than 0.09% by weight, more preferably not more than 0.05% by weight. The lead content in the alloy is a maximum of 0.09% by weight and particularly preferably a maximum of less than or equal to 0.05% by weight. When the lead migration is tested in accordance with the DIN EN 15664-1 standard, the alloy shows no signs of increased lead release in the first few weeks. Instead, you can From the eighth week of the test, no more significant lead migration into the drinking water can be determined or is within the range of the measurement accuracy of the method. The low lead content in the alloy used according to the invention thus leads to a significant reduction in metal ion migration in drinking water, the low lead content having no negative effects on chip breaking and thus on the machinability of the alloy used according to the invention.

The nickel content in the alloy used according to the invention is a maximum of 0.4% by weight, preferably the nickel content is a maximum of 0.3% by weight. The addition of nickel increases the corrosion resistance of the alloy without contradicting the hygienic safety. Similar to lead, the values of nickel migration in a test according to DIN EN 15664-1 are far below the legally required limit value.

Furthermore, it was found that an antimony content of a maximum of 0.1% by weight is not critical with regard to the properties of drinking water migration. The alloy can also have an iron content of a maximum of 0.3% by weight.

In preferred embodiments, the lead-free copper alloy can also contain proportions of the elements iron (Fe), zirconium (Zr) and / or boron (B) alone or in a combination of at least two of the elements mentioned as grain refiners. It is preferred that iron in a weight fraction of up to 0.3 wt .-%, zirconium in a weight fraction of up to 0.01 wt .-% and / or boron in a weight fraction of up to 0.01 wt. -% are contained in the lead-free copper alloy. The grain refiners avoid hot cracking and influence the mechanical properties, e.g. Tensile strength, material hardness and the like are positive.

The copper content of the lead-free copper alloy is preferably at least 90% by weight, preferably more than 91% by weight.

According to the invention, it is preferred if the sulfides of the lead-free copper alloy are homogeneously distributed in the structure. The number of sulphide particles should be high and their mean size should be small in order to ensure uniform mechanical parameters, good corrosion resistance, improved machinability and high pressure tightness over the entire structure. Copper sulfide is preferred as the material of the sulfide particles, since the occurrence of copper sulfide makes it possible to substitute the volume of lead with a significantly lower content of sulfur.

The component according to the invention has, at least in sections, a wall thickness in the range from 0.5 mm to 6.0 mm, since the thin wall thickness leads to cooling rates suitable for the formation of the copper sulfides. It is also preferred if the entire component according to the invention has a wall thickness within the stated ranges of 0.5 mm to 4.0 mm, since a wall thickness in this range leads to a particularly increased formation of the desired sulfide particles. A wall thickness below 0.5 mm could not have sufficient mechanical strength of the component according to the invention due to the small cross section. From this point of view, it is preferred that the component according to the invention has, at least in sections, a wall thickness in the range from 1.0 mm to 4.0 mm.

It can also be advantageous if the cross-section of the component according to the invention has a wall thickness of less than 6 mm at least 1.6 percent by area of sulfide particles and / or an area index ASP% less than 1000. Such values lead to sulfur sulphides being present as an incoherent, finely divided, disperse phase. This avoids deep trough-shaped and / or hole-shaped attacks, in particular corrosion attacks, on the components according to the invention. As used here, the term "area index ASP%" is the mathematical description for the measure of the shape and position of a bell curve, which is obtained from a plot of the mean values of the area classes (abscissa) in combination with the percentage distribution of the sulfide particles in these area classes (ordinate ) results (cf. Fig. 1 ). The value of the area index ASP% is obtained by measuring the area of the respective particles, for example from an enlarged photograph of a micrograph, the percentage allocation of the particles recognizable in the recording into classes, the multiplication of the percentage values of the allocation by the mean value of the class and the formation of a large mean value from the resulting mean values of the classes, the large mean value being assumed to be the "area index ASP%".

The alloy used according to the invention has the excellent property of forming a top layer very quickly on the inner surface wetted with drinking water. The cover layer has a thickness of preferably at least 2 μm, particularly preferably of at least 3 µm. This top layer increases the corrosion resistance and ensures the longevity of the components made of this material, since further corrosion is prevented. Migration from the material to the drinking water can only take place if corrosion processes take place in the material. Here the top layer functions as a protective layer and limits the further metal release to the drinking water to a minimum. Although the copper content in the alloy described is higher than in conventional gunmetal alloys, such as. B. CuSnZn5Pb2, there is only a reduced copper metal release. The good results of the test in accordance with DIN EN 15664-1 show that, without extensive restrictions in terms of machinability, the composition of the alloy used according to the invention does not impair the quality of the drinking water over the entire area claimed. In comparison to conventional gunmetal alloys, such as, for example, CuSnZn5Pb2, the alloy used according to the invention has at the same time improved migration behavior in combination with excellent corrosion resistance.

In casting tests, it was possible to prove that the components according to the invention for media-carrying gas or water pipes can be produced using conventional casting processes, such as sand, permanent mold or continuous casting processes. The cast part produced by such a casting process can be machined well.

As used herein, the term "component for media-carrying gas or drinking water lines" is to be understood as meaning in particular those components that come into contact with a house installation pipe system, in particular with drinking water, fittings and fittings of such house installation pipe systems being preferred according to the invention. An example of such a fitting is in particular that from EP 2 250 421 A1 to name known connector.

The present invention is to be explained in more detail below with reference to exemplary embodiments and tests carried out therewith, as well as the accompanying drawings. It will be understood that these examples are not to be regarded as limiting the invention in any way. Unless stated otherwise, all percentages and proportions in the present application including the claims are based on weight.

Brief description of the drawings

Fig. 1

exemplarische Auftragungen der Flächen der Partikel gegen die prozentuale Verteilung der Partikel in verschiedenen Größenklassen, welche als Basis zur Ermittlung der ASP% dienen ("Glockenkurve");

Fig. 2

eine Übersicht der Prüfwässer im Diagramm nach Turner;

Fig. 3

ein Diagramm, aus dem die Angriffstiefen der Entzinkung beim Standardmessing im durchgeführten Warmauslagerungstest nach 5 Monaten Auslagerungsdauer hervorgehen;

Fig. 4

ein Übersichtsdiagramm, dass die Bildung der Deckschicht bei der verwendeten bleifreien Kupferlegierung im durchgeführten Warmauslagerungstest nach 5 Monaten Auslagerungsdauer zeigt;

Fig. 5

eine fotografische Aufnahme, die ein Beispiel eines Korrosionsangriffs von Standardmessing im Warmauslagerungstest (angelehnt an Turner mit einem Chloridgehalt von 250 mg/l und einer Karbonathärte von 5,5 °dH) zeigt;

Fig. 6

eine fotografische Aufnahme der Legierung 2, die ein Beispiel einer durchgängigen Deckschicht im Warmauslagerungstest (angelehnt an Turner mit einem Chloridgehalt von 250 mg/l und einer Karbonathärte von 5,5 °dH) zeigt;

Fig. 7

ein Diagramm der thermischen Analyse zweier Schmelzen mit unterschiedlichen Zinkgehalten, die unter gleichen Bedingungen vergossen wurden;

Fig. 8

ein Gefügeschliffbild eines Bauteiles aus einer Schmelze, die mit einem Zinkgehalt von ca. 3,9 Gew.-% vergossen wurde;

Fig. 9

ein Gefügeschliffbild eines erfindungsgemäßen Bauteiles aus einer Schmelze, die mit einem Zinkgehalt von ca. 2,4 Gew.-% vergossen wurde;

Fig. 10

ein Gefügeschliffbild eines erfindungsgemäßen Bauteiles aus einer Schmelze, die langsam abgekühlt wurde; und

Fig. 11

ein Gefügeschliffbild eines erfindungsgemäßen Bauteiles aus einer Schmelze, die schnell abgekühlt wurde.

Show in the drawings

Fig. 1

exemplary plots of the areas of the particles against the percentage distribution of the particles in different size classes, which serve as the basis for determining the ASP% ("bell curve");

Fig. 2

an overview of the test waters in the Turner diagram;

Fig. 3

a diagram showing the depth of attack of dezincification on standard brass in the artificial aging test carried out after 5 months of aging;

Fig. 4

an overview diagram that shows the formation of the top layer in the lead-free copper alloy used in the artificial aging test carried out after 5 months of aging;

Fig. 5

a photograph showing an example of a corrosion attack on standard brass in the artificial aging test (based on Turner with a chloride content of 250 mg / l and a carbonate hardness of 5.5 ° dH);

Fig. 6

a photograph of alloy 2 showing an example of a continuous top layer in the artificial aging test (based on Turner with a chloride content of 250 mg / l and a carbonate hardness of 5.5 ° dH);

Fig. 7

a diagram of the thermal analysis of two melts with different zinc contents, which were cast under the same conditions;

Fig. 8

a micrograph of a component from a melt cast with a zinc content of approx. 3.9% by weight;

Fig. 9

a micrograph of a component according to the invention from a melt that was cast with a zinc content of approx. 2.4% by weight;

Fig. 10

a micrograph of a component according to the invention from a melt that was slowly cooled; and

Fig. 11

a micrograph of a component according to the invention from a melt that has been rapidly cooled.

Artificial aging exposure tests for the corrosion resistance of alloys

To assess the corrosion resistance of copper alloys, an artificial aging test was developed that simulates the long-term corrosion behavior of alloys over a five-month test period. The structure and implementation of the test are based on the corrosion test that has been established for decades and the diagram based on it von Turner ("The Influence of Water Composition on the Decincification of Duplex Brass Fittings"; 1965 ) and the further investigations by Ladeburg (" Investigation of dezincification phenomena on fittings made of copper alloys "; 1966 ) at. In these investigations, corrosion curves were recorded for the dezincification of the materials. The surface of the components was assessed after a month's exposure time in various waters and conclusions were drawn about the dezincification resistance of the alloy.

Fig. 2 shows a Turner diagram for the test waters used in the artificial aging test. In the diagram, the carbonate hardness (as a measure of the water hardness) is plotted against the chloride ion content of the test water. The line labeled "Turner classic" represents the corrosion characteristic for dezincification developed by Turner (" The Influence of Water Composition on the Decincification of Duplex Brass Fittings "; 1965 ). According to the current interpretation of the corrosion experts, no dezincification takes place in the area below this line, but above this line there is a very high risk of damage to the component in question due to dezincification. The points shown give an overview of the different test waters that were used in the artificial aging test described.

For the artificial aging tests carried out, the following lead-free copper alloys, among others, were used, the proportions of the components in Table 1 below being given in% by weight: <u> Table 1 (not according to the invention): </u> alloy Cu Sn Zn P S. Pb 1 91.1 4.8 3.0 0.01 0.55 0.01 2 93.4 4.2 1.4 0.02 0.56 0.02

For the production of test specimens, half cylinders with a wall thickness of 5 mm were cast from alloys 1 and 2. The test specimens were then turned on the outside to a roughness Rz of max. 25 µm and machined on the inside by means of drilling with a through-hole with a roughness Rz of max. 40 µm. This special surface treatment should enable the test specimens to be compared with actually manufactured components.

The surface of the test specimen was cleaned with acetone. The test specimens were then placed in a test container in a freely hanging manner. The test containers were then placed in a heating cabinet at 90 ° C. for five months, the test medium being changed at seven-day intervals.

21 different test water with different pH values and carbonate hardnesses (the carbonate hardness (KH) is the proportion of calcium and magnesium ions for which there is an equivalent concentration of hydrogen carbonate ions in the volume unit) were set as test media, and different contents of chloride ions were set and / or sulfate ions set. The contents can be taken from Table 2: <u> Table 2: </u> Water number PH value Carbonate hardness in ° dH Chloride in mg / l Sulphate in mg / l 1 8th 0.5 10 - 2 8th 0.5 100 - 3 8th 0.5 250 - 4th 8th 0.5 1000 - 5 8th 1.5 15th - 6th 8th 1.5 60 - 7th 8th 1.5 140 - 8th 8th 3.0 30th - 9 8th 3.0 100 - 10 8th 5.5 80 - 11 8th 5.5 120 - 12 8th 5.5 250 - 13th 7th 9.0 100 - 14th 7th 9.0 160 - 15th 7th 14.0 140 - 16 7th 18.0 40 - 17th 7th 18.0 100 - 18th 7th 18.0 250 - 19th 8th 0.5 250 250 20th 8th 5.5 250 250 21st 7th 18.0 250 250

At the end of the five-month test period, the test containers are removed from the heating cabinet, cooled to room temperature, the test specimens are removed from the respective test containers, dried, cut open and the cut surface is examined with a light microscope after appropriate processing.

Alloys 1 and 2 showed, over the entire area of the drinking water ordinance tested in the artificial aging, an outstanding formation of a protective, firmly adhering, closed top layer which is necessary for copper alloys, which in the artificial aging test has a thickness of at least 2 µm and thus an improved top layer in relation to a conventional, lead-containing copper alloy based on a CuSnZn alloy (eg CuSn5Zn5Pb). Furthermore, this layer is almost free from disturbances or defects and thus unfolds its complete protection by avoiding a deeper, local corrosion attack (see Fig. 4 and Fig. 6 ).

In the diagram according to Fig. 3 the depths of attack for standard brass (CuZn40Pb2) after a five-month artificial aging test are shown for the respective test waters. Selective corrosion in the form of dezincification, predominantly plug dezincification, is evident in each case. The depths of attack can clearly be seen, some of which extend up to approx. 750 µm and thus illustrate a very poor corrosion resistance.

Fig. 4 however, shows the behavior of the top layer formation of a lead-free copper alloy (alloy 1 and alloy 2) after a five-month artificial aging test for the respective test waters. It turns out that only a protective top layer is formed. No selective corrosion attack whatsoever is visible. The thickness of the firmly adhering protective cover layer formed is at least 4 µm.

In Fig. 5 is a photograph of the microstructure of standard brass (CuZn40Pb2) as the result of an exemplary corrosion attack after the five-month artificial aging test, based on Turner, with a chloride content of 250 mg / l and a carbonate hardness of 5.5 ° dH. An uneven, partially disturbed structure of the top layer and the selective corrosion attack in the form of dezincification can be clearly seen.

In comparison shows Fig. 6 a photographic recording of the microstructure of a result of the five-month artificial aging test, based on Turner, with a chloride content of 250 mg / l and a carbonate hardness of 5.5 ° dH, of a component according to the invention made of alloy 2 (alloy 1 shows a behavior analogous to this ) was carried out. Compared to the in Fig. 4 The microstructure shown shows no selective corrosion attack in the component after an identical heat exposure test, but a uniform, homogeneous structure of a protective, firmly adhering cover layer with a thickness of 4 µm to 23 µm.

Compared to the standard brass, the artificial aging test carried out here shows that the alloy is free of selective corrosion attacks (e.g. dezincification and stress corrosion cracking) and almost all other signs of corrosion based on Turner's approach.

The tests also show that sulfur sulfides, as incoherent, finely divided, disperse phases, have a clear corrosive advantage. This results from the avoidance of deep trough-shaped and / or hole-shaped attacks, which could lead to significantly accelerated corrosion due to a possible drop in the pH value and a concentration of the critical constituents of the medium. In addition, no less noble, non-noble phases with a very large surface area are formed which, as already described above, could be attacked by corrosion and then lead to rapid failure of the component (cf. β-phase in standard brass).

Casting tests to determine the effects on sulphide formation

It could be determined from experiments that the alloy composition has a decisive influence on the distribution, the shape and the point in time of the phase formation and that unfavorable contents have a negative effect on the phase and structure formation.

First, thermal tests were carried out, which were then verified by means of image analysis.

Fig. 7 represents a thermal analysis in a temperature-time diagram, by means of which thermal effects (e.g. release of latent heat) can be detected in metals, which can arise during transitions from solid to liquid or during phase transformations in the solid state. The cooling temperature of the alloy and the first time derivative of the measurement signal are plotted against the time, which is described as the cooling rate. A change in the peak in the cooling rate curve corresponds to a thermal effect in the material. In the case of the lead-free alloy used according to the invention, a sulfide formation should be aimed for shortly before the end of solidification at a low temperature, since this way the sulfides are distributed more homogeneously in the structure, similar to lead. <u> Table 3 </u> alloy Cu Sn Zn S. P Elongation [A] 3 91.0 4.2 3.9 0.45 0.06 25% 4th 92.6 4.1 2.5 0.45 0.06 31%

The cooling rate in Fig. 7 corresponds to the typical solidification process of a copper-tin alloy up to 5% by weight tin in sand casting. A further comparison of the two curves shows that in alloy 3 at approx. 400 s there is an early thermal effect during the ongoing solidification process, which is due to the formation of sulfide. In alloy 4 according to the invention, the sulfide formation takes place with a delay, shortly before the end of solidification. The fact that both samples were cooled under identical conditions underpins the further course of the cooling rate of the samples, which is identical after the phase formation. The varying point in time of the phase formation is therefore due to the different zinc content in the alloys. The early sulfide formation influences the sulfide form and the distribution in the structure. The early sulfide formation in alloy 3 thus leads to a heterogeneous, partial phase distribution, which has a negative impact on the mechanical parameters such as elongation.

In Fig. 8 (Alloy 3) and Fig. 9 (Alloy 4 used according to the invention) are the differences in the structure of components that are made from melts according to alloy 3 and 4 Fig. 7 can be seen with the different zinc contents. According to the present invention, the material composition is adjusted in a way that avoids premature sulfide formation and promotes homogeneous distribution.

It was also recognized that the cooling conditions of the melt for a component according to the invention have an influence on the sulfide formation. A high cooling rate, as is preferred with a thin wall, creates a fine-meshed dendrite network with fine residual melt areas from which a globular formation of the sulfides is supported. In this respect, rapid cooling is preferred according to the invention. Figures 10 and 11 shows microstructural images of components according to the invention from an identical melt that was cooled under varying conditions. In the case of rapid cooling, the microstructure shows in Fig. 11 a structure that leads to higher mechanical characteristics such as tensile strength, elongation at break and the like.

To confirm this characteristic, the particles were examined and characterized by means of image analysis on ground structures of the test specimens.

It has been shown that in the production of components according to the invention under the stated cooling conditions of a melt, a melt composed according to the invention Alloy, it can be achieved that at least in sections in a microstructure of the cast part at least 1.8 area percent of the total area is formed as sulfide particles.

Among other things, the volume of sulphides and the area can be determined by means of this image analysis.

Various size classes are introduced to determine the sulfide particles more precisely (see Table 4). The particles are then measured and assigned to the classes as a percentage. Now the percentage allocations are multiplied by the mean value of the class. The resulting mean values of the classes are combined into a large mean value. The resulting value represents the area index for sulphide particles ASP%.

The alloys used according to the invention can be characterized with an area index ASP% of less than 1000. <u> Table 4: </u> Class number Lower limit of class [µm ² ] Upper limit of class [µm ² ] Mean value of the class [µm ² ] 1 0 10 5 2 10 30th 20th 3 30th 60 45 4th 60 100 80 5 100 150 125 6th 150 200 175 7th 200 300 250 8th 300 500 400 9 500 800 650 710 800 + Inf 950

In the foregoing, the present invention has been described with reference to examples and comparative examples. However, it will be apparent to those skilled in the art that the invention is not limited to these examples, but the scope of the present invention is determined from the appended claims.

Claims (9)

1. Component for media-carrying gas or water pipes, in particular fitting or valve for drinking water pipes, wherein the component consists at least partially of a lead-free copper alloy, which has the following alloy components in % by weight:

   3.5 % by weight ≤ Sn ≤ 4.8 % by weight;

   1.5 % by weight ≤ Zn ≤ 3.5 % by weight;

   0.25 % by weight ≤ S ≤ 0.65 % by weight;

   0.04 % by weight ≤ P ≤ 0.1 % by weight;

   optionally no more than 0.09 % by weight lead;

   optionally no more than 0.4 % by weight nickel;

   optionally no more than 0.1 % by weight antimony;
   optionally no more than 0.3 % by weight iron, zirconium and/or boron alone or in combination of two or more of said elements;

   unavoidable impurities and

   to the remainder copper,
   wherein the component has a wall thickness at least in sections in the range of 0.5 mm to 6.0 mm.
2. Component according to claim 1, characterised in that the sulphur proportion in the alloy is 0.3 % by weight ≤ S ≤ 0.60 % by weight, in particular 0.35 % by weight ≤ S ≤ 0.55 % by weight.
3. Component according to claim 1 or claim 2, characterised in that the zinc proportion in the alloy is 2.0 % by weight ≤ Zn ≤ 3.0 % by weight.
4. Component according to one of the preceding claims, characterised in that the phosphorus proportion in the alloy is 0.04 % by weight ≤ P ≤ 0.08 % by weight, in particular 0.04 % by weight ≤ P ≤ 0.06 % by weight.
5. Component according to one of the preceding claims, characterised in that the lead content is not more than 0.05 % by weight.
6. Component according to one of the preceding claims, characterised in that copper is contained in the lead-free copper alloy in a quantity of more than 90 % by weight.
7. Component according to one of the preceding claims, characterised in that the component has a wall thickness at least in sections in the range from 1.0 mm to 4.0 mm.
8. Component according to one of claims 1 to 7, characterised in that it has a homogeneous, protective cover layer of at least 2 µm.
9. Component according to one of the preceding claims, characterised in that the material has no increased lead or nickel migration according to DIN EN 15664-2 after 16 weeks and conforms to the provisions of DIN EN 15664-2.

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