EP1273671B1 - Dezincification resistant copper-zinc alloy and method for producing the same - Google Patents

Description

The invention relates to a dezincification-resistant copper-zinc alloy, which is particularly suitable for sanitary applications, e.g. suitable for drinking water fittings, drinking water pipes or pipe binders. The invention further relates to a manufacturing method for such a copper-zinc alloy.

Common copper-zinc alloys, also called brass or brass alloys, can occur in two different metallic phases. In the so-called α-phase, the brass alloy has an fcc (Face-Centered-Cubic) structure, while in the β-phase it has a Bcc (Body-Centered-Cubic) structure. In the phase diagram of a brass alloy, the pure α-phase occurs at a copper content of more than 62% by weight. With a proportion of copper between 54 and 62 wt .-%, the brass alloy is present with portions of both the α and the β phase. In the presence of additional metallic components, the above-mentioned phase boundaries shift.

For sanitary applications, a brass alloy must have high corrosion resistance due to the constant water contact. Brass, and also copper, forms cover layers of copper oxide in aqueous, slightly acidic to alkaline electrolyte solutions, which generally provide some protection against general corrosion. In soft, chloride-containing waters, brass alloys may experience a special form of corrosion called dezincification. The zinc is dissolved out of the brass alloy and a porous copper sponge remains behind. Furthermore, the β-phase is attacked more as the α-phase, since the former is less electropositive to the latter.
To improve the corrosion resistance of a brass alloy, it is therefore known to prevent the formation of a β-phase as much as possible by means of a heat treatment during production. Furthermore, it is also known to add to a brass alloy additional metallic components which protect the α-phase from dezincification. As such metallic components are from the WO 89/08725 Phosphorus, arsenic, antimony, bismuth and silicon known. From the DE 197 22 827 A1 is the addition of arsenic or phosphorus to a brass alloy known.

However, the addition of a single further metallic component can drastically change other characteristics of the brass alloy. So improved according to the WO 89/08725 the additive arsenic, although the corrosion protection for the α-phase, but deteriorates in the presence of α and β phase, the corrosion resistance to sulphate waters. Since the composition of drinking water, ie, the type and concentration of ions dissolved therein, is highly dependent on its geographical origin, lengthy research is needed to assemble a brass alloy that will not corrode even after decades of use and contact with water.

As dezincification and corrosion resistant brass alloy is from the WO 89/08725 a copper-zinc alloy containing up to 0.8% by weight of nickel, between 0.5 and 3% by weight of lead, between 0.3 and 1% by weight of silicon and between 0.07 and 0 , 8 wt .-% iron. Arsenic is considered to be in principle disturbing because it promotes intergranular corrosion, which is why its content should be less than 0.02% by weight.

The object of the invention is to provide a copper-zinc alloy which has a particularly high resistance to dezincification and intercrystalline corrosion, and is particularly suitable for sanitary applications. It is another object of the invention to provide a manufacturing method for such a copper-zinc alloy.

The first-mentioned object is achieved for a copper-zinc alloy according to the invention in that it contains 50 to 80% by weight of copper, 0 to 5% by weight of lead, 0.01 to 0.1% by weight of arsenic, 0, 03 to less than 0.3% by weight of silicon, 0 to 0.3% by weight of iron, 0 to 0.04% by weight of manganese, the balance being zinc and unavoidable impurities, and that the effective copper Equivalent to 60 to 70 wt .-% is.

With the copper equivalent or the effective copper content, one considers the effects of the different alloying elements in brass alloys on the microstructure formation. If, for example, lead or iron are contained in the copper-zinc alloy, then their shares add up in terms of effectiveness to the actual copper content. In this case, the actual copper content is lower than the effective copper equivalent. If the effective copper equivalent is about 60% by weight and additionally contains a lead content of 2% by weight, the actual copper content is (1-0.02) × 60% by weight = 58, 8% by weight.

Extensive studies have shown that a copper-zinc alloy with the said composition both has a high dezincification resistance and also a very low intergranular corrosion, referred to below as IK shows. The invention is based on the recognition that a certain content of arsenic is crucial for the avoidance of intercrystalline corrosion. Furthermore, the invention assumes that iron is not required for the corrosion resistance of the brass alloy, but has a disturbing effect. However, the disturbing influence of iron can be avoided to a limited extent by the addition of silicon.

Further advantageous embodiments can be found in the dependent claims 2-5.

The object of the production method for a copper-zinc alloy, wherein the starting materials are mixed, melted and cast according to the desired composition into a metallic alloy, and wherein the metallic alloy for forming the α-phase at 500-650 Is annealed ° C, is inventively achieved in that the annealed metallic alloy is actively cooled by means of coolants.

Extensive studies have shown that the resistance of the alloy according to the features of claim 1 against intergranular corrosion can be further improved if the annealed alloy is actively cooled by means of coolants. Such an active cooling to accelerate the natural cooling, with no additional aids are used, for example, can be done by means of a cooling fan or it can be cooled rapidly by quenching. Such quenching can be done for example by means of a water bath. When using a cooling fan, the cooling treatment can be designed as a continuous cooling for larger quantities or quantities.

If such a copper-zinc alloy thus produced is further processed by cold working, it has been found that the resistance to intergranular corrosion is reduced. This can advantageously be avoided if the cold-worked alloy is subjected to flash annealing for 10 minutes to 2 hours at a temperature between 250 and 600 ° C.

Figur 1:

Die prozentuale Anfälligkeit für interkristalline Korrosion verschiedener Versuchslegierungen in Abhängigkeit vom Arsengehalt,

Figur 2:

die prozentuale Anfälligkeit für interkristalline Korrosion verschiedener Versuchslegierungen in Abhängigkeit vom jeweiligen Mangangehalt und

Figur 3:

die Abgabe von Blei an Trinkwasser einer Versuchslegierung gegenüber Legierungen des Standes der Technik in Abhängigkeit von der Zeit.

Embodiments of the invention will be explained in more detail with reference to the following experiments, drawings and tables. Showing:

FIG. 1:

The percentage susceptibility to intergranular corrosion of various experimental alloys as a function of the arsenic content,

FIG. 2:

the percentage susceptibility to intergranular corrosion of various experimental alloys depending on the respective manganese content and

FIG. 3:

the delivery of lead to drinking water of a trial alloy compared to alloys of the prior art as a function of time.

A total of 44 copper-zinc alloys of different composition were investigated. Table 1 lists the composition of these 44 experimental alloys in terms of copper, lead, arsenic, iron, silicon, manganese, aluminum and zinc. For the respective metallic component of each alloy, the desired and the actual proportion in wt .-% is reproduced. The trial alloys are each designated with four-digit numbers. This term is used below for the respective alloy.

The experimental alloys listed in Table 1 were prepared as follows:
1. Cast the molten alloy at a temperature of 1050 to 1100 ° C in a steel mold of the dimensions 110 mm x 40 mm
2. Milling the sample to a thickness of 14 mm
3. Rolling the sample to 5 mm, with intermediate annealing for 1 hour at temperatures of about 700 ° C.
4. α-anneal for 2 hours at a temperature of 550 degrees Celsius Table 1: <b> Nominal and actual compositions of the experimental alloys in% by weight </ b> Leg.-Nr. Cu pb ace Fe Si Mn al Zn 2088 Should 62.4 2.6 0.04 - - - rest is 62.6 2.66 0.046 0.01 <0.005 <0.005 rest 2089 Should 62.4 2.6 0.07 - - - rest is 62.65 2.66 0.073 0.01 <0.005 <0.005 rest 2090 Should 62.4 2.6 0.14 - - - rest is 62.53 2.65 0.14 0.01 <0.005 <0.005 rest 2094 Should 62.4 2.6 0.07 0.14 0.08 - rest is 62.59 2.66 0.074 0.14 0.058 <0.005 rest 2102 Should 64 2.66 0.06 0.10 0.2 - rest is 64.01 2.59 0.062 0.10 0.20 <0.005 rest 2106 Should 63.7 2.6 0.06 0.2 0.2 - rest is 63.8 2.64 0,068 0.17 0.18 <0.005 rest 2131 Should 62.4 2.6 0.08 - - - rest is 62.23 2.66 0.096 0.02 <0.005 <0.005 rest 2132 Should 62.4 2.6 0.09 - - - rest is 62.66 0.067 0.01 <0.005 <0.005 rest 2133 Should 64.38 2.6 0.06 - 0.2 - rest is 64.72 0.066 0.01 0.19 <0.005 rest 2134 Should 68.0 2.6 0.06 0.10 0.60 - rest is 67.84 0.064 0.11 0.61 <0.005 rest 2135 Should 82.2 2.6 0.06 - 2.0 - rest is 81.55 0.064 0.01 1.97 <0.005 rest 2136 Should 81.89 2.6 0.06 0.10 2.0 - rest is 81.41 0.062 0.093 1.97 <0.005 rest 2156 Should 65.0 2.0 0.2 0.5 rest 2157 Should 65.0 2.0 0.06 0.2 0.5 rest 2158 Should 65.0 2.0 0.06 - 0.5 rest 2159 Should 62.5 2.0 0.06 0.1 - - - rest is 62.59 0.067 0.082 0,004 <0.002 <0.002 rest 2160 Should 62.5 2.0 0.06 0.1 0.01 - - rest is 62.46 0.064 0.097 0.009 <0.002 <0.002 rest 2161 62.5 2.0 0.06 0.1 0.03 - - rest Should, is 63.2 0,065 0.079 0.024 <0.002 <0.002 rest 2162 Should 63.08 2.0 0.06 0.1 0.06 - - rest is 63.26 0.054 0,089 0.053 <0.002 <0.002 rest 2163 Should 63.9 2.0 0.06 0.1 0.1 - - rest is 64.24 0,065 0.092 0.097 <0.002 <0.002 rest 2164 Should 65.88 2.0 0.06 0.1 0.2 - - rest is 65.86 0.064 0.10 0.18 <0.002 <0.002 rest 2165 Should 67.88 2.0 0.06 0.1 0.3 - - rest is 67.96 0,060 0.098 0.28 <0.002 <0.002 rest 2166 Should 71.88 2.0 0.06 0.1 0.5 - - rest is 71.98 0,060 0,089 0.47 <0.002 <0.002 rest 2167 Should 75.87 2.0 0.06 0.1 0.7 - - rest is 75.93 0,060 0.088 0.67 <0.002 <0.002 rest 2168 Should 66.51 2.0 0.06 - 0.2 0.01 - rest is 66.73 0,065 0,010 0.19 0006 <0.002 rest 2169 Should 66.54 2.0 0.06 - 0.2 0.03 - rest is 66.70 0.062 0.009 0.19 0,017 <0.002 rest 2170 Should 66.16 2.0 0.06 - 0.2 0.06 - rest is 66.25 0.064 0.009 0.19 0.037 <0.002 rest 2171 Should 65.88 2.0 0.06 - 0.2 0.1 - rest is 66,00 0.062 0.009 12:19 0055 <0.002 rest 2172 Should 65.67 2.0 0.06 0.1 0.2 0.03 - rest is 66.08 0,060 0.085 0.19 0,003 <0.002 rest 2173 Should 65.46 2.0 0.06 0.1 0.2 0.06 - rest is 65.69 0,065 0,069 0.19 0,003 <0.002 rest 2174 Should 66.81 2.0 0.06 0.1 0.2 - 0.3 rest is 66.72 0.062 0,080 0.18 0,003 0.30 rest 2175 Should 61.3 2.0 0.08 0.1 - - - rest is 61.85 1.77 0.084 0.073 <0.002 <0.002 <0.002 rest 2176 Should 61.3 2.0 0.08 0.08 - - - rest is 61.85 1.62 0.087 0.057 <0.002 <0.002 <0.002 rest 2177 Should 61.3 2.0 0.08 0.05 - - - rest is 61.68 1.67 0.084 0, 049 <0.002 <0.002 <0.002 rest 2178 Should 61.2 2.0 0.08 0.08 - 0.03 - rest is 61.51 1.83 0,090 0,065 <0.002 0.005 <0.002 rest 2179 Should 61.2 2.0 0.08 0.08 - 0.06 - rest is 61,40 1.71 0.088 0,069 <0.002 0,025 <0.002 rest 2180 Should 61.3 2.0 0.05 0.03 - - - rest is 61.42 1.98 0.058 0,021 <0.002 <0.002 <0.002 rest 2181 Should 61.3 2.0 0.05 0.06 - - - rest is 61.52 1,85 0.047 0,050 <0.002 <0.002 <0.002 rest 2182 Should 62.8 2.0 0.05 0.2 0.2 - 0.3 rest is 62.87 1.73 0.056 0.13 12:19 <0.002 0.31 rest 2183 Should 62.75 2.0 0.05 0.2 0.2 0.03 0.3 rest is 62.72 1.84 0.059 0.13 0.19 0.027 0.32 rest 2184 Should 62.7 2.0 0.05 0.2 0.2 0.06 0.3 rest is 62.70 1.70 0.058 0.11 0.19 0,051 0.32 rest 2185 Should 62.6 2.0 0.05 0.2 0.2 0.1 0.3 rest is 62.35 2.01 0.053 0.13 0.19 0.032 0.32 rest 2186 Should 61.3 2.0 0.05 0.06 0.01 - - rest is 61.35 2.0 0.059 0048 0,010 <0.003 <0.002 rest 2187 Should 61.2 2.0 0.05 0.1 0.01 - - rest is 61.32 1.99 0.059 0.072 0.009 <0.003 <0.002 rest

The following experiments were carried out with regard to an optimization of the composition:

Trial 1:

For each of the experimental alloys listed in Table 1, a dezincification test was performed according to ISO 6509. The degree of dezincification of the respective alloy becomes corroding after a predefined test procedure Liquids determined by measuring a maximum Entzinkungstiefe in microns. The maximum depth of dezincification determined in this way is a measure of the susceptibility of the test alloy to be dezincified. The greater the maximum dezincification depth of the particular experimental alloy, the greater its susceptibility to dezincification.

The maximum dezincification depths determined according to ISO 6509 are reproduced in Table 2 for the experimental alloys.

Trial 2:

The dezincification resistance test according to ISO 6509 uses a very aggressive electrolyte solution for dezincification, which is not suitable for detecting IK due to very fine potential differences between grain boundaries and grain area.

For this reason, all experimental alloys have been subjected to such experimental conditions that are known to cause intercrystalline corrosion. For this purpose, for example, experiments were carried out with ammonium chloride-containing solutions under defined conditions. The degree of intergranular corrosion was related to the degree of intergranular corrosion of a CuZn36 Pb2As alloy whose known intergranular corrosion was set to 100%. The result of these investigations is listed in column 2 of Table 2. Table 2: <b> IK susceptibility of trial alloys and maximum dezincification depth (to ISO 6509) </ b> Leg.-Nr. IK susceptibility compared to CuZn36Pb2As in% Maximum dezincification depth to ISO 6509 in μm 2088 19 13 2089 46 12 2090 100 15 2094 30 6 2102 8th 0 2106 24 12 2131 91 0 2132 25 0 2133 10 0 2134 10 0 2135 65 0 2136 27 0 2156 5 212 2157 7 18 2158 7 0 2159 100 0 2160 100 0 2161 17 0 2162 13 0 2163 10 0 2164 8th 0 2165 23 0 2166 15 0 2167 18 0 2168 18 0 2169 17 0 2170 48 0 2171 100 0 2172 10 0 2173 11 0 2174 10 0 2175 88 50 2176 96 46 2177 100 75 2178 100 45 2179 83 60 2180 42 80 2181 42 95 2182 33 40 2183 58 34 2184 42 38 2185 46 54 2186 21 62 2187 33 108

Trial 3:

It was in Based on NSF Standard 61, 1994 (Drinking Water Systems Components-Health Effects; NSF International Standard 61, Section 9, March 1994 ) examined the lead-release to drinking water. In this case, as an exemplary embodiment of the invention, a brass alloy with proportions by weight of 64.05% copper, 2.7% lead, 0.1% iron, 0.3% aluminum, 0.2% silicon and 0.05% arsenic and the rest zinc with a CuZn36Pb2.7As0.14 alloy and compared with a CuZn39Pb2.7 alloy according to the prior art. All three alloys are in their lead content of 2.7 wt .-% match. The novel alloy is resistant to dezincification and to intergranular corrosion. The CuZn36Pb2.7As0.14 alloy is prior art and known to be low in dezincification, but has less resistance to intergranular corrosion. The CuZn39Pb2.7 alloy is known to be susceptible to dezincification.

Trial 4:

A sample of 27 mm diameter CuZn36Pb2As alloy was quenched once each in a water bath after an α-annealing of 500 and 600 ° C, respectively, and once cooled in the oven. The proportion of IK was measured. It has been shown that active cooling can reduce susceptibility to IK by between 27 and 60%.

Results of Experiments 1 to 3:

In FIG. 1 the susceptibility to intergranular corrosion in% is shown in column 3 of Table 2 for test alloys Nos. 2088, 2089, 2090, 2131 and 2132. These alloys differ in otherwise substantially the same composition in their arsenic content. The respective arsenic content in wt .-% is on the abscissa in FIG. 1 applied. The illustrated experimental alloys have only a negligible or no share of iron, silicon, manganese and aluminum.

It turns out that for a copper-zinc alloy with increasing arsenic content the susceptibility to intergranular corrosion increases. At an arsenic content of 0.14 wt .-%, the IK susceptibility of the comparative alloy according to Table 2 is reached. However, susceptibility to IC decreases significantly for small arsenic levels.

However, for an arsenic-free alloy such as No. 2156, a very high maximum depth of dezincification becomes apparent. If a brass alloy is to be resistant to dezincification, a certain content of arsenic must be present. From this point of view emerges FIG. 1 a necessary for arsenic content between 0.01 and 0.1 wt .-% for a dezincification and resistant to IK brass alloy. Above a proportion of arsenic of 0.1 wt .-% protection against IK is no longer guaranteed. If the arsenic content is reduced below 0.08 wt .-%, the susceptibility to intergranular corrosion is only less than 60%.

The experimental alloys Nos. 2180 and 2181 have a value of 0.05% by weight with respect to their arsenic content which is not critical with respect to the IC. In addition, however, these trial alloys show a small amount of iron of 0.03 wt% and 0.06 wt%, respectively. A comparison with the non-ferrous experimental alloys Nos. 2088 and 2089 shows that the addition of iron obviously lowers the critical upper limit for the arsenic content. Within fault tolerances, susceptibility to intergranular corrosion increases. Likewise, the susceptibility to dezincification increases with the addition of iron. When the trial alloy No. 2159 having an iron content of 0.082% by weight is used, its susceptibility to intergranular corrosion becomes clear. The trial alloy No. 2159 shows a susceptibility to IK of 100% according to Table 2, whereas the trial alloys No. 2088 and No. 2089 show a susceptibility of only 19% and 46%, respectively.

If the arsenic content is increased, the susceptibility to intergranular corrosion by the addition of iron is no longer significantly deteriorated. This can be seen by comparing Experimental alloys Nos. 2175 to 2178, which show an increasing iron content at an arsenic content of 0.08% by weight, with the experimental alloys No. 2089 or No. 2090.

Low iron additions therefore lower the critical upper limit for the arsenic so that intergranular corrosion can ultimately occur due to the influence of iron even with "safe" arsenic contents. Iron is thus a critical element. Iron is therefore undesirable, but can not be avoided for cost reasons, since it flows when using cheap brass scrap as an impurity back into the manufacturing process. The production of an iron-free brass alloy from pure or iron-free starting substances is considerably more expensive.

However, it has surprisingly been found that by adding silicon, the iron can obviously be bound and thus its detrimental impact on the corrosion resistance of a brass alloy can be suppressed. This can be seen in alloys Nos. 2094, 2102 and 2106. These alloys have iron contents at an arsenic content of 0.07 wt% of 0.14 wt .-%, 0.1 wt .-% and 0.2 wt .-% to. At the same time, these experimental alloys contain silicon in a proportion of 0.08% by weight and 0.2% by weight. A look at Table 2 shows that silicon can neutralize the damaging effects of iron. Susceptibility to intergranular corrosion decreases. Likewise, these experimental alloys are generally dezincification.

Further, from the experimental alloys No. 2160-2167, the influence of silicon on the corrosion resistance of the trial alloys becomes apparent. With otherwise equal amounts of lead, arsenic and iron, the silicon content is increased from test alloy No. 2160 to test alloy No. 2167. Again, while general corrosion resistance remains consistently good, it can be seen that adding silicon in small amounts can prevent the deleterious effects of small amounts of iron. However, from about 0.3% by weight, susceptibility to intercrystalline corrosion increases again. If small amounts of iron are to be tolerated in a brass alloy in order to obtain favorable production costs, these can be rendered harmless by the addition of small amounts of silicon. At tolerable levels of iron up to 0.3% by weight, therefore, silicon should be included between 0.03 and 0.3% by weight.

It is apparent from alloys Nos. 2135 and 2136, which have a silicon content of about 2% by weight, that they again become susceptible to intergranular corrosion.

In FIG. 2 the susceptibility to intergranular corrosion is shown according to the results of Table 2 for trial alloys Nos. 2168 to 2171. These alloys differ in their composition in terms of their manganese content, which increases from the test alloy No. 2168 to the test alloy 2171 of 0.006 wt .-% to 0.055 wt .-%. It turns out that manganese is a very critical element in intercrystalline corrosion, and can not be neutralized by a proportion of silicon. All trial alloys Nos. 2168 to 2171 have a silicon content of about 0.2% by weight.

The permissible tolerances for manganese must therefore remain low. At a level of 0.04 wt%, the susceptibility to intergranular corrosion is less than 50%.

If silicon is contained in a brass alloy, then it has also been found that the scale of these brass rings can easily come off. This leads to the fact that the circulating tinder contaminates production plants. This problem can be solved by adding aluminum. Annealing tests (duration: 2 hours, temperature: 750 degrees Celsius) on the experimental alloy No. 2102, which is resistant to intergranular corrosion, confirmed that its scale layer easily peels off. By adding aluminum in a proportion of about 0.2 wt .-% could be achieved that improves the adhesion of the scale layer.

In FIG. 3 is for a trial alloy containing 64.05% copper, 2.7% lead, 0.1% iron, 0.3% aluminum, 0.2% silicon and 0.05% arsenic and the remainder zinc (* symbol) , a CuZn36Pb2.7As0.14 alloy (O symbol) and a CuZn36Pb2.7 alloy (□ symbol), the lead release to drinking water based on NSF Standard 61, 1994 shown. The lead levy is shown in μg per liter over time.

It is surprisingly found that an alloy resistant to intergranular corrosion, namely the trial alloy, exhibits a lower lead output than the dezincification resistant brass alloy CuZn36Pb2.7As0.14 according to the prior art.

Claims (6)

1. Copper-zinc alloy resistant to dezincification, in particular for use in the sanitary sector, characterized in that it comprises
   50 to 80% by weight Cu,
   0 to 5% by weight Pb,
   0.01 to 0.10% by weight As,
   0.03 to less than 0.3% by weight Si,
   0 to 0.3% by weight Fe,
   0 to 0.04% by weight Mn,
   and optionally 0.15 to 0.3% by weight Al,
   remainder Zn and also inevitable impurities, and in that the effective Cu equivalent is 60 to 70% by weight.
2. Copper-zinc alloy according to Claim 1, characterized in that 0 to 0.02% by weight Mn are present.
3. Copper-zinc alloy according to either of the preceding claims, characterized in that 0.02 to 0.08% by weight As are present.
4. Copper-zinc alloy according to one of the preceding claims, characterized in that up to 0.2% by weight Fe and 0.15 to 0.25% by weight Si are present.
5. Process for producing a copper-zinc alloy according to one of the preceding claims, wherein the starting materials are mixed in the weight ratio indicated, melted and cast to form a metallic alloy, and wherein the metallic alloy is annealed to form the α-phase at 500-650°C, characterized in that the annealed metallic alloy is actively cooled by means of coolants.
6. Process according to Claim 5, characterized in that the metallic alloy is subjected to stress-relief annealing after a further treatment by cold forming at 250 to 600°C for between 10 min and 2 h.

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