DE102018004702A1 - Moldings made of a corrosion-resistant and machinable copper alloy - Google Patents

Abstract

The present invention relates to a copper alloy, its use and a process for the production of moldings, as well as the moldings produced therefrom.

Description

The present invention relates to a copper alloy, its use and a process for the production of moldings, as well as the moldings produced therefrom.

State of the art

Water is a valuable raw material and indispensable for daily use. Therefore, the drinking water must be microbiologically such that the subsequent consumption does not lead to human disease when it is removed from the supply system. In order to achieve this, high demands are placed on materials that come into direct contact with drinking water. Copper is the noblest utility material and is considered an indispensable material in industry and technology for water-bearing systems. Because copper has bacteriostatic properties and also offers excellent corrosion resistance. Copper also shows positive properties in its shape. Thus, copper casting alloys can be cast well and the high strength and toughness of the material is particularly appreciated in the plastomechanical shaping.

However, it is precisely this plastic deformability that causes problems in machining machining. Here homogeneous copper materials tend to form a long chip. This type of chip inhibits the work flow during fully automated turning or drilling, and leads to heavy wear on the tool cutting edges. Often, the chip formation of copper is the limiting factor in mechanical processing and therefore has a direct influence on the cost-effectiveness of the workpieces.

Gunmetal is one of the cast copper alloys and is characterized by the combination of a good castability with optimum machinability and high strength. Due to its good corrosion resistance, gunmetal is particularly suitable for water-bearing systems such as fittings and sanitary technology. Common gunmetal alloys contain tin to increase strength and corrosion resistance. Zinc is added as an inexpensive substitute for copper. In order to be able to process the produced gunmetal products economically at all, the heavy metal lead is added, which acts as a chipbreaker in the alloy and makes a machining on CNC machines and conventional automatic lathes possible.

If the drinking water stagnates for a long time in commercially available lead-containing fittings, there is the possibility that lead is released by a metal ion migration to the tap water. High lead concentrations are considered harmful to health. As a result, stricter requirements are being imposed on the lead content of materials that come into contact with drinking water worldwide. Within Germany, too, the lead content has been reduced to 10 μg lead / l via the statutory drinking water ordinance since 01.12.2013. The pressure to further reduce lead in drinking water has increased worldwide and will continue to grow. For example, legal requirements from the US require that lead contents in copper alloys must not exceed an average lead content of 0.25%, regardless of the actual lead concentration in drinking water.

The ideal gunmetal would be free of lead and other substances of concern, with consistent or better economy in the production and without affecting the corrosion resistance, high mechanical strength and good processability.

The EP 2290114 A1 describes a lead-free gunmetal alloy with 4 to 6 wt .-% tin, 4 to 6 wt .-% zinc and less than 0.25 wt .-% lead. With this alloy, lead-free components can be produced by casting. The subsequent mechanical processing to produce the functional surfaces of these components remains unconsidered. Without lead, the specified composition shows a homogeneous α-MK microstructure, which tends to form long chips and can not be machined economically. The presupposed casting process also requires a higher material input for the production of the molded part as an alternative transformation process due to the process.

A forming process of a lead-free gunmetal alloy describes the EP 2 872 660 B1 , Described is a process for preconditioning a gunmetal alloy with 2 to 8 wt% tin, 2.5 to 13 wt% zinc and less than 0.25 wt% lead suitable for hot pressing and at the end of the hot pressing process homogeneous structure. The hot forming allows an economical production of moldings with low material usage. Although the process is explained to the shape of the blank, but also disregarded here is the subsequent necessary Zerspanvorgang for working out of functional surfaces of the components. Due to the chemical composition and the subsequent hot forming results in a homogeneous microstructure and also here is the absence of a chip breaker a long chip formation in the machining to be expected, which makes economical processing of the components difficult.

The EP 1 801 250 A1 describes low-migration copper alloy components that have a relatively high level of Si, in addition to lower but significant levels of Mn, Al, and Zr. Similar copper alloys are also in the WO 2007/068470 disclosed.

Despite the many now known copper alloys in the prior art, there is still a challenge to specify copper alloys, on the one hand without the use of problematic from environmental and health points components lead (Pb), on the other hand enable transformation processes without the mechanical characteristics and the Suffer corrosion resistance. The provision of copper alloys has proven to be particularly demanding here, which show good hot workability (ie without significant drop in mechanical characteristics) and are preferably also easy to machine.

Object of the present invention

Due to the above-mentioned disadvantages in the prior art, it is the object of the present invention to provide a copper alloy that overcomes these disadvantages. In particular, it would be desirable to have a copper alloy which comprises as few components as possible, is lead-free or substantially lead-free and, in addition, can dispense with expensive metal components and / or metal components which are difficult to mix. Also, the number of non-metal elements in the copper alloy should be as low as possible.

Brief description of the invention

This object is achieved by the copper alloy according to claim 1, the use thereof according to claim 2, and the method for the production of moldings according to claim 3. Preferred embodiments are given in the subclaims and the following description. Also claimed are the moldings produced using the copper alloy described herein.

Detailed description of the invention

The present invention will initially be described below with regard to the alloy according to the invention. However, it is obvious to the person skilled in the art that the preferred embodiments described in this context can also be transferred to the described use, the described production method and the described molded parts and are also to be regarded as preferred embodiments for these aspects of the invention.

The present invention makes it possible to produce from a gunmetal alloy which has a chip breaker in the structure, hot forming with low material use moldings with high mechanical strength, high dimensional stability and high corrosion resistance, which then also after the hot pressing process even an economical machining can be subjected. The hot-workable gunmetal alloy of the present invention does not require elements such as Al, Si, Pb, Sb, Te, Se, C and Bi for the formation of a chip breaker in the microstructure, and is therefore well reusable.

• Sn: 2 bis 6 %
• Zn: 0 bis 5 %
• S: 0,05 bis 0,6 %
• Pb: weniger als 0,25 %
• Ni: weniger als 0,6 %
• Sb: weniger als 0,2 %,

optional weiter enthaltend Phosphor bis maximal 0,06 Gew.-%, B bis maximal 0,003 Gew.-%, Zr bis maximal 0,03 Gew.-% sowie unvermeidbare Verunreinigungen, wobei die Summe der Verunreinigungen vorzugsweise 0,25 Gew.-% nicht überschreitet, und wobei der Rest Cu ist.The present invention thus provides a copper alloy which, in particular for the production of molded parts from at least one hot-forming process with subsequent machining, has the following composition in% by weight:

• Sn: 2 to 6%
• Zn: 0 to 5%
• S: 0.05 to 0.6%
• Pb: less than 0.25%
• Ni: less than 0.6%
• Sb: less than 0.2%,

optionally further comprising phosphorus up to a maximum of 0.06% by weight, B up to a maximum of 0.003% by weight, Zr up to a maximum of 0.03% by weight and unavoidable impurities, the sum of the impurities preferably being 0.25% by weight does not exceed, and wherein the remainder is Cu.

As already stated above, the alloy according to the invention contains in particular no elements of the group AI, Si, Sb, Te, Se, C and Bi and in preferred embodiments likewise no Pb.

• Sn: 2 bis 4 %, in Ausführungsformen 2 bis weniger als 3,5 %
• Zn: 0 bis 3 %, in Ausführungsformen auch 0 bis weniger als 1,5 %, insbesondere 0,1 bis weniger als 1,5 %
• S: 0,1 bis 0,45 % und in Ausführungsformen 0,1 bis weniger als 0,25 %

Preferred contents of alloy components to be used according to the invention are as follows, these being disclosed and claimed in each case individually as well as in any combination (in each case again in% by weight):

• Sn: 2 to 4%, in embodiments 2 to less than 3.5%
• Zn: 0 to 3%, in embodiments also 0 to less than 1.5%, in particular 0.1 to less than 1.5%
• S: 0.1 to 0.45% and in embodiments 0.1 to less than 0.25%

The copper content in the alloy is preferably 88% by weight or more, more preferably 90% by weight or more.

It has unexpectedly been found that the known disadvantages of the prior art can be overcome with the copper alloys disclosed here. In particular, semifinished products / intermediates produced from the copper alloy can very well be subjected to hot forming. Despite the degradation of work hardening which frequently occurs during hot working (typically at temperatures of about 600 to 950 ° C.), the alloy according to the invention makes it possible to produce molded parts (which may then be further processed, eg by machining), which still have excellent mechanical characteristics and also show no degradation of corrosion resistance.

Furthermore, it has been shown that the molded parts thus obtained (ie after hot working) can also be further processed in an economical manner, since in particular the undesirable long-chip formation does not occur. It thus turns out that, despite the processes taking place in a hot forming process, chip-breaking components are still present in the microstructure of the alloy, although the alloy according to the invention dispenses with typical chip-breaking components such as Pb or Si. Thus, the present invention provides a copper alloy that has an excellent balance of desired properties. It is thus possible to produce molded parts from this alloy, in particular by hot forming, if necessary connected to further processing steps as described herein, without having to fear compromises with respect to the further, desired properties of the copper alloy and its suitability for use in hot forming.

The alloy according to the invention can thus be used advantageously for the production of molded parts, these production methods comprising hot working, if necessary combined with further processing methods, for example a subsequent machining.
In view of obtaining the desired properties of the copper alloy described here, the individual alloy constituents in each case alone, but also in their interaction, enable a good and reproducible control of the alloy properties.

Tin acts as a solid solution in the alloy and thus increases the tensile strength, yield strength and hardness, but reduces the elongation at break. Furthermore, tin increases corrosion resistance, with corrosion resistance increasing with increasing tin contents. During the production of blanks for hot forming, it was recognized that tin in the microstructure causes strong segregation, which leads to the formation of zone crystals during solidification. At the beginning of solidification, tin-poor copper crystals are precipitated and the residual melt accumulates with a tin content above the average content of the alloy. Deviating from the stable state diagram copper-tin can be present at levels of more than 7 wt .-% tin in the microstructure at room temperature, an (a + δ) - eutectoid, which under equilibrium conditions only at max. 15.8 wt .-% tin is formed. The possible δ phase crystallizes in the kfz lattice and thus would have to be well deformable per se, but the phase has a brittle behavior due to its voluminous unit cell of 416 atoms. This complicates the later hot forming process. By heat treatment at high temperatures with sufficient time, the (a + δ) - eutectoid can be eliminated, but a heat treatment is associated with high energy expenditure.

Furthermore, there is a risk of grain enlargement of the structure during the treatment. This would lead to a reduction in elongation, making the later hot forming process more difficult. With a content of 2 to 6 wt .-% tin, more preferably 2-4 wt .-% tin high mechanical strength is ensured with high elongation and avoid formation of the (α + δ) - eutectoid in the cast state.

Sulfur is almost insoluble in solid copper and the original properties of the material, such as corrosion resistance, are not affected by the addition of sulfur. Due to the insolubility in the solid copper sulfur leads to a behavior of behavior that influences the course of solidification of copper-tin alloy similar to lead. Unlike lead, however, sulfur does not exist elementarily in the microstructure at the end of solidification, but in the form of an intermetallic metal-sulfur compound that is evenly distributed throughout the structure. It could be recognized that this phase is incoherent and brittle in the microstructure and thus produces a chipbreaking mechanism.

The properties of the sulfides influence the mechanical, plastic behavior of the gunmetal material. The influence is determined by the proportions of sulphide phases in the material. From sulfur contents of more than 0.6% by weight, the stress-transmitting α-Cu matrix is so severely affected by the sulfides that a hot pressing process is severely impeded. The sulfur content of 0.05% by weight to 0.6% by weight, particularly preferably 0.1% by weight to 0.45% by weight, ensures that sufficient sulfide inclusions are present in the microstructure around a chipbreaker To create mechanism and to ensure a hot forming process.

Zinc is added to the alloy as an economical substitute for copper. It has been recognized that there is a close correlation between the zinc content and the sulfur content over the timing and type of distribution of sulphide formation. The higher the zinc content, the earlier the sulfide inclusions form during the casting solidification in the microstructure. If the zinc content is above 5% by weight, the sulfide formation is shifted to temperatures in the range of the solidification temperature of the gunmetal alloy. In this temperature range, there are still high molten parts in the cast structure, which are in some places connected to each other.

Due to a high zinc content, it then comes to an early formation of sulfides. These sulfides are inhomogeneous and locally concentrated in the structure before and thus complicate the hot pressing process by a local weakening of the α-MK matrix. If the zinc content is low, the formation is shifted to lower temperatures and the sulfides are present in former residual melt areas separated from each other and homogeneously distributed. The zinc content of 0 to 5 wt%, more preferably 0 to 3 wt% zinc ensures that sulfide formation is avoided at higher temperatures.

Investigations have shown that the copper alloy according to the invention by the specific composition has a particular suitability for use in a production process for moldings, this process comprising at least one hot working. Due to the special composition of the alloy, further processing steps can easily be carried out after the hot forming, for example, a subsequent machining.

A hot forming according to the invention can be, for example, a hot pressing process. According to the invention, however, other hot forming operations are possible, which are known to the person skilled in the art. Before a hot forming, for example, a hot pressing process, the blank is heated to 600 ° C to 950 ° C. From 600 ° C the yield strength is sufficiently low to plastically deform the red brass material via a hot forming process. In the present invention, hot working may be performed at any suitable temperature in the above-mentioned temperature window, for example at 700 to 900 ° C. The particular temperature is selected by the person skilled in the art depending on the type of molded part, the desired rapidity of the forming, etc.

It was recognized that in the specified temperature range, the atomic bonds of the sulfides are weaker, so that dislocation movements are facilitated in these superstructures. The phases lose their brittleness in this temperature range and become deformable and thus do not inhibit the hot forming process. Immediately after the transformation, a dynamic recrystallization of the α-MK matrix takes place, which eliminates the previously existing in the casting state zone mixed crystal with different tin concentration and ensures a homogeneous concentration and thus constant mechanical properties and corrosion properties over the cross section.

However, the sulfides are distributed after the deformation process at room temperature in the microstructure and brittle, so they act as a chip breaker. It could be determined that, even with hot-formed moldings with low sulfur contents from 0.05% by weight, the mold is jerked during machining due to time-varying friction conditions between the chip and the tool. These altered friction conditions are due to the inhomogeneous structure of the structure, which consists of a copper-containing α-MK matrix with embedded sulfides after the hot pressing process. The stick slip produces shear bands in the chip which lead to lamella chips and shearing chips and, in the course of processing, break down in the tool when discharged via a chip breaker. This prevents long chips and enables economical machining.

In order to enable the hot-pressing process provided according to the invention, the mean grain size present in the cast condition should not exceed 2 mm. The necessary measures to ensure such a mean grain size are known in the art. For example, grain refinement is possible through the use of chemical additives such as zirconium and boron to levels of 0.005 to 0.03 wt.% Or other alternative methods of grain refining such as electromagnetic stirring, sonication, vibration, gas injection, or high subcooling Melt during casting.

The copper alloy described above is particularly suitable for use in the production of molded parts, wherein the production comprises at least one hot working. Also possible is the use for the production of molded parts, in which after the at least one hot forming further processing steps take place, for example, a subsequent machining. The corresponding production method is suitable in particular for the production of components, for example media, eg gas or water-carrying lines and thus components to be connected, such as fittings, etc. Specifically focused moldings are components of domestic plumbing systems, including pipes, fittings, end caps, and fittings. The basic process steps for producing such molded parts are known to the person skilled in the art and therefore will not be described in detail here.

Essential to the invention in this context is that the above-described specific composition of the copper alloy to be used in the absence of mechanical properties and corrosion resistance even after hot working. In addition, it has been shown that both before and after a hot forming, the resulting moldings can be subjected to other operations without problems. In particular, a machining is possible because the problematic and undesirable Langspanbildung is omitted. Thus, a molded article can be produced in an economical manner (in particular, because the other desirable properties of the copper alloy, such as good hot workability, inertness to the workpieces, especially drinking water, and corrosion resistance, are not compromised). Particularly noteworthy in this context is that the advantages of the present invention described here are achieved, although the use of the components Pb, Si, which are otherwise often considered necessary in the prior art, is dispensed with.

This unexpected advantage of the copper alloy described herein enables its economical use for the manufacture of the moldings described above.

example

From a lead-free gunmetal in the grain-refined state by means of a hot forming with subsequent machining a molded part for drinking water installation was produced. It was found that chip breakers were present in the microstructure of the alloy after the hot pressing process, so that economically viable, fully automated mechanical processing became possible.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2290114 A1 [0007]
• EP 2872660 B1 [0008]
• EP 1801250 A1 [0009]
• WO 2007/068470 [0009]

Claims (10)

Copper alloy suitable for the production of molded parts by a process with at least one hot forming operation, the alloy having the following composition in% by weight: Sn: 2 to 6% Zn: 0 to 5% S: 0.05 to 0.6% Pb: less than 0.25% Ni: less than 0.6% Sb: less than 0.2% and optionally phosphorus up to a maximum of 0.06% by weight, B up to a maximum of 0.03% by weight, Zr up to a maximum of 0.03% by weight, and unavoidable impurities, and wherein Rest Cu is. Use of a copper alloy for the production of molded parts by a process with at least one hot-forming process, wherein the alloy has the following composition in% by weight: Sn: 2 to 6% Zn: 0 to 5% S: 0.05 to 0.6% Pb: less than 0.25% Ni: less than 0.6% Sb: less than 0.2% and optionally phosphorus up to a maximum of 0.06% by weight, B up to a maximum of 0.03% by weight, Zr up to a maximum of 0.03% by weight, and unavoidable impurities, and wherein Rest Cu is. Process for the production of molded parts from a copper alloy, the alloy having the following composition in% by weight: Sn: 2 to 6% Zn: 0 to 5% S: 0.05 to 0.6% Pb: less than 0.25% Ni: less than 0.6% Sb: less than 0.2% and optionally phosphorus up to a maximum of 0.06% by weight, B up to a maximum of 0.03% by weight, Zr up to a maximum of 0.03% by weight, and unavoidable impurities, and wherein Balance is Cu; the method comprising the steps of: at least one hot working process of the copper alloy to produce a molded article Copper alloy after Claim 1 , Use after Claim 2 or method after Claim 3 wherein the sum of the contaminants does not exceed 0.25% by weight. Copper alloy, use or method according to one of the preceding claims, characterized in that the tin content is 2 to 4 wt .-%. Copper alloy, use or method according to any one of the preceding claims, characterized in that the zinc content is 0 to 3 wt .-%. Copper alloy, use or method according to one of the preceding claims, characterized in that the sulfur content is 0.1 to 0.45 wt .-%. A copper alloy, use or method according to any one of the preceding claims, wherein the alloy contains no elements of the group AI, Si, Sb, Te, Se, C and Bi and / or wherein the alloy contains no Pb. The copper alloy, use or method of any one of the preceding claims, wherein the copper alloy is suitable for producing molded parts by a method further comprising machining after the at least one hot working, the method comprising the further step of machining after the at least one hot working; or wherein the use comprises a subsequent to the hot forming machining. Molding made of the copper alloy according to any one of Claims 1 or 4 to 9 Obtained according to use according to one of Claims 2 and 4 to 9 or obtained by the method according to one of Claims 3 to 9 ,