Patent Application
20150165519
The invention relates to metallic shaped parts, to a method for producing the shaped parts, to the use of the shaped parts and also to the use of an alloy for producing shaped parts.
Shaped parts are understood to be single-piece components with a complex geometry. A complex geometry is involved when the component does not have a continuous translation invariance in any direction and consequently cannot be produced by a simple, quasi-continuous shaping process. Examples of such simple shaping processes are the rolling of strips, the pressing of rods or the drawing of pipes. The invention relates in particular to hollow or at least partially hollow shaped parts, for example pipe connectors, bushings, pipe bends or T pieces. Shaped parts of this type made from metallic materials are produced either directly by shape casting and machining or from semifinished product by forming and machining. If high degrees of deformation are to be achieved in this case, the forming process takes place at high temperatures. Examples of this are forging processes, for instance open die forging or drop forging (hot pressing).
Shaped parts made from copper materials are used in many technical fields, for example as housings, connectors, sliding elements or in valves and faucets. On account of their good corrosion resistance, shaped parts made from copper materials are used with preference in piping systems for liquid and gaseous media, as fittings, bends, T pieces, valve bodies or faucets. The use of such shaped parts in drinking water installations plays a special role in this respect. The most important alloy families for shaped parts are red brass and brass.
When producing shaped parts made from brass, use is made of the good forming capacity of said materials. Studs are produced from the alloys by means of continuous casting and are pressed to form large-sized pipes, rods or profiles. These intermediate products are then drawn to form semifinished products with relatively small cross-sectional dimensions by one or more cold forming steps. The grain size of the material is reduced in this process, and the microstructure thereof is compacted and homogenized. Shaped parts are then produced from the semifinished products by means of hot pressing or forging. When in contact with water, brass can tend toward dezincification or stress corrosion cracking, depending on the alloy composition and condition of use.
Red brass has a high corrosion resistance and good castability, and therefore shaped parts made from red brass are produced by casting. The cast parts have very coarse grains, have a rough surface and have only a limited dimensional stability. Furthermore, there is the risk of cavities, segregation and pores in cast parts. Casting defects of this nature can lead to instances of leakage in the components. Red brass parts have considerably poorer formability and machinability than brass parts. The addition of lead provides the microstructure of red brass with somewhat finer grains and improves the machinability of the material. Moreover, lead closes solidification cavities on account of its low melting point, and thereby ensures a dense microstructure. Typical red brass alloys contain 2 to 7% by weight lead.
Already in the past, the regulations for materials used in drinking water installations have been tightened in respect of the elements lead and nickel. In some countries, the lead content is today limited to 0.25% by weight. In the United States of America, this upper limit applies nationwide from 2014. It is to be expected that in future the regulations will be tightened as far as a ban on lead.
EP 2 290 114 A1 proposes configuring water-carrying components as cast parts made from a copper alloy comprising 4 to 6% by weight tin and 4 to 6% by weight zinc. The lead content of the alloy is limited to 0.1% by weight. However, the reduction of the lead content does not improve the disadvantageous properties of the cast parts, but rather worsens them. In particular, it becomes more difficult to ensure the tightness of the components.
EP 1 600 517 B1 discloses a lead-free copper alloy comprising 69 to 79% by weight Cu, 2 to 4% by weight Si, remainder zinc. The Si content largely reduces the susceptibility to stress corrosion cracking. The high zinc content of at least 17% by weight can have a negative effect on the corrosion resistance of this brass material, however.
A copper-tin-zinc alloy with a reduced lead content and comprising approximately 3% by weight tin and approximately 9% by weight zinc is described in DIN CEN/TS 13388. It can be gathered from the corresponding materials data sheet of the Deutsches Kupferinstitut (DKI—German Copper Institute) that this alloy can be hot-formed only to an “adequate” extent, and that it is available only as flat material, i.e. in the form of plates, metal sheets, strips, tabs and round blank sheets. Other semifinished product shapes such as pipes, rods, profiles and forgings made from this material are defined as “non-standardized”. Substantially the same information can be gathered from DIN 17662 for a copper-tin-zinc alloy with a reduced lead content and comprising approximately 6% by weight tin and approximately 6% by weight zinc. In particular, only strips and metal sheets are named as available types of semifinished product.
JP 2005-248303 A proposes a copper alloy with a reduced lead content and comprising 84 to 89% by weight copper, 4 to 6% by weight tin and 5 to 30% by weight zinc, and also a method for processing it. A cold forming step performed by swaging with a degree of deformation of 5 to 30% is essential here. The density of the lattice dislocations is increased as a result and the material is hardened. Good machinability of the material is achieved after homogenization annealing.
It is furthermore known that the microstructure of alloys can be improved by the addition of elements for grain refinement. Thus, JP 2002-275563 A proposes the addition of Fe, Ni, Co or Mn to a lead-free bronze in order to improve the hot rollability. The material is used as a strip in the production of electronic components. JP 2003-013038 A proposes admixing 20 to 1000 ppm carbon to a copper-tin-zinc alloy, in order to achieve good hot formability. The material is used for the production of electronic components. For this purpose, use is made exclusively of flat material, and the semifinished product is formed merely to give a simple geometry. It can be gathered from DE 43 24 008 C2 that a copper alloy comprising 2 to 8% by weight tin, 0.5 to 2.1% by weight silicon, up to 15% by weight zinc and also at least one element selected from the group consisting of titanium, tantalum, niobium, iron, manganese, magnesium or phosphorus is used for producing water pipes. Pipes are pressed from cast studs by means of hot forming and are then cold-drawn to final dimensions. Compared to the production of shaped parts by forging, the hot pressing of pipes is a relatively simple forming process, in which an intermediate product merely with a simple geometry is produced. Furthermore, the addition of silicon to the alloy is undesirable, since it is poorly manageable.
It can be gathered from EP 1 777 307 B1 that it is possible to achieve grain refinement by adding zirconium to a lead-free copper-tin-zinc alloy, such that it also becomes possible to produce shaped parts by means of hot forming. EP 1 777 307 B1 itself refers to the disadvantages of the use of zirconium. According to the teaching of this document, the zirconium content in the case of alloys with compositions like red brass has to be at least 0.017% by weight, but this has an unfavorable effect on the costs of the material. In general, the addition of elements to the alloy for grain refinement is in principle undesirable, since it makes the casting process more complex and is poorly manageable in the scrap cycle.
The invention is based on the object of specifying improved shaped parts in particular for use in water-carrying piping systems, a copper material for use for producing improved shaped parts and also a method for producing shaped parts made from a copper material. In particular, the copper material should have an outstanding corrosion resistance, should be free of the elements lead, antimony, silicon, zirconium or other chemical grain refiners, and should have good hot formability and good machinability. The shaped parts produced from this material should have a homogeneous microstructure, a high dimensional stability and a good surface quality.
The invention is represented in terms of the use of a copper alloy by the features of claim 1, in terms of the shaped parts by the features of claim 4, in terms of the use of the shaped parts by the features of claim 5 and in terms of a method for producing shaped parts by the features of claim 6. The further claims which refer back thereto relate to advantageous embodiments and developments of the invention.
The invention encompasses the use of a copper alloy having the following composition [in % by weight]:
Pb: less than 0.25%,
optionally Ni up to at most 0.6%,
optionally phosphorus, remainder Cu, but at least 84%, and also unavoidable impurities, for producing shaped parts, the production of the shaped parts including at least one hot pressing process.
The invention is based here on the consideration that the corrosion resistance of metallic materials is determined primarily by the composition thereof. In addition, the production method and the surface properties have a considerable influence on the corrosion resistance of the components. Copper materials having a copper proportion of at least 84% by weight and also alloy proportions of tin (between 2 and 8% by weight), zinc (between 2.5 and 13% by weight) and also optionally up to 0.6% by weight nickel and phosphorus have a very good corrosion resistance in an aqueous environment. Castings made from these materials generally have a coarse, acicular grain structure and can be hot-formed only with difficulty. Owing to suitable conditioning of the material during the melting and casting processes, however, it is possible to set a fine grain structure without additional elements such as, for example, lead in proportions of greater than 0.25% by weight, bismuth, boron or zirconium having to be added to the alloy. According to the invention, a fine-grained microstructure is set in the material by agitating the remaining molten mass which is present during the solidification process. This is preferably done by stirring, particularly preferably by electromagnetic stirring, of the remaining molten mass during the solidification process. The molten alloy mass is solidified in a temperature interval. Initial precipitations firstly form upon cooling of the molten mass when a certain temperature is undershot during the solidification process. Dendritic crystal structures can grow at these nucleation sites upon further cooling. By agitating the remaining molten mass which is present in each case throughout the solidification process and impressing an inner motion on it, the possible formation of a typical cast microstructure with columnar crystals is prevented. Instead, a fine-grained microstructure having small grains which are solidified partly in dendritic form and partly in globular form is formed. The fine-grained microstructure improves the formability of the material. Consequently, materials which have been conditioned in this way can be used for producing shaped parts, it being possible for the production of the shaped parts to be effected in a manner similar to the production of shaped parts made from brass materials. In particular, the production of shaped parts includes a hot pressing step. In contrast to the cast components, the shaped parts produced by means of drop forging (hot pressing) or open die forging are distinguished in particular by a dense, homogeneous microstructure and a smooth surface. At the same time, they have a very good corrosion resistance on account of the material composition.
In a preferred configuration of the invention, the phosphorus content of the copper alloy can be at most 0.04% by weight, and in a particularly preferred configuration at most 0.01% by weight. Phosphorus makes it possible to achieve better castability. With an increasing phosphorus content, however, the hot formability is reduced. The production of the shaped parts by means of a hot pressing process is consequently all the more reliable, the smaller the content of phosphorus in the alloy.
A further aspect of the invention encompasses shaped parts made from a copper alloy having the following composition [in % by weight]:
Pb: less than 0.25%,
optionally Ni up to at most 0.6%, optionally phosphorus, remainder Cu, but at least 84%, and also unavoidable impurities, wherein the shaped parts are produced at least by one hot pressing process.
The invention is based here on the consideration that the microstructure of metallic materials is determined by the composition and by the production method. Shaped parts are produced predominantly by means of casting from copper materials having a copper proportion of at least 84% by weight and also alloy proportions of tin (between 2 and 8% by weight), zinc (between 2.5 and 13% by weight) and also optionally up to 0.6% by weight nickel. Castings made from these materials generally have a coarse, acicular grain structure and a rough surface and have poor machinability. Owing to suitable conditioning of the material during the melting and casting processes, however, it is possible to set a fine grain structure without additional elements such as, for example, lead in proportions of greater than 0.25% by weight, bismuth, boron or zirconium having to be added to the alloy. According to the invention, a fine-grained microstructure is set in the material by agitating the remaining molten mass which is present during the solidification process. This is preferably done by stirring, particularly preferably by electromagnetic stirring, of the remaining molten mass during the solidification process. The fine-grained microstructure improves the formability of the material. The production of shaped parts made from materials conditioned in this way can then be effected in a manner similar to the production of shaped parts made from brass materials. In particular, the production of shaped parts includes a hot pressing step. In contrast to the cast components, the shaped parts produced by means of drop forging (hot pressing) or open die forging are distinguished by a dense, homogeneous microstructure, a better dimensional stability and a smooth surface. Therefore, the shaped parts produced by hot pressing or forging are preferable to cast shaped parts.
A further aspect of the invention encompasses the use of shaped parts made from a copper alloy having the following composition [in % by weight]:
Pb: less than 0.25%,
optionally Ni up to at most 0.6%, optionally phosphorus, remainder Cu, but at least 84%, and also unavoidable impurities, in water-carrying piping systems, wherein the shaped parts are produced at least by one hot pressing process.
The invention is based here on the consideration that the corrosion resistance of metallic materials is determined primarily by the composition thereof. In addition, the production method and the surface properties have a considerable influence on the corrosion resistance of the components. Copper materials having a copper proportion of at least 84% by weight and also alloy proportions of tin (between 2 and 8% by weight), zinc (between 2.5 and 13% by weight) and also optionally up to 0.6% by weight nickel have a very good corrosion resistance in an aqueous environment. Therefore, shaped parts which are used as faucets, connectors and the like in water-carrying piping systems are produced from these materials. Cast shaped parts made from these materials generally have a coarse, acicular grain structure and a rough surface. Furthermore, they have poor machinability, and therefore the quality of the cast surface is usually retained. In the case of components which are subjected to throughflow, greater flow noises and obstructions to throughflow are the consequence. Owing to suitable conditioning of the material during the melting and casting processes, however, it is possible to set a fine grain structure without additional elements such as, for example, lead in proportions of greater than 0.25% by weight, bismuth, boron or zirconium having to be added to the alloy. According to the invention, a fine-grained microstructure is set in the material by agitating the remaining molten mass which is present during the solidification process. This is preferably done by stirring, particularly preferably by electromagnetic stirring, of the remaining molten mass during the solidification process. The fine-grained microstructure improves the formability of the material. Consequently, materials which have been conditioned in this way can be used for producing shaped parts, it being possible for the production of the shaped parts to be effected in a manner similar to the production of shaped parts made from brass materials. In particular, the production of shaped parts includes a hot pressing step. In contrast to the cast components, the shaped parts produced by means of drop forging (hot pressing) or open die forging are distinguished by a dense, homogeneous microstructure, a better dimensional stability and a smooth surface. At the same time, they have a very good corrosion resistance on account of the material.
A further aspect of the invention relates to a method for producing shaped parts made from a copper alloy having the following composition [in % by weight]:
Pb: less than 0.25%,
optionally Ni up to at most 0.6%, optionally phosphorus, remainder Cu, but at least 84%, and also unavoidable impurities, the method including at least the following steps:
The invention is based here on the consideration that the processability of metallic materials is determined by the composition thereof and the conditions during the production process. Copper materials having a copper proportion of at least 84% by weight and also alloy proportions of tin (between 2 and 8% by weight), zinc (between 2.5 and 13% by weight) and also optionally up to 0.6% by weight nickel are used predominantly for producing shaped parts by means of casting. Castings made from these materials generally have a coarse, acicular grain structure. Owing to suitable conditioning of the material during the melting and casting processes, however, it is possible to set a fine grain structure without additional elements such as, for example, lead in proportions of greater than 0.25% by weight, bismuth, boron or zirconium having to be added to the alloy. According to the invention, a fine-grained microstructure is set in the material by agitating the remaining molten mass which is present during the solidification process. This is preferably done by stirring, particularly preferably by electromagnetic stirring, of the remaining molten mass during the solidification process. The fine-grained microstructure improves the formability of the material. The production of shaped parts made from materials conditioned in this way can then be effected in a manner similar to the production of shaped parts made from brass materials. In particular, the production of shaped parts includes the following steps:
The cold formability of red brass is poorer than the cold formability of brass. It is therefore advantageous to dimension the semifinished products in method step b) in such a way that no cold forming is required between the continuous casting in method step b) and the hot pressing in method step e). It is particularly advantageous to select the cross sections of the cast semifinished products in such a way that the unfinished pressed parts cut to length from the semifinished products have a shape and size which are beneficial for the hot pressing process.
In a preferred configuration of the invention, the unfinished pressed parts of the alloy can have a microstructure with a mean grain size of less than 1 mm before the hot pressing process. Since there is preferably no method step between the casting of the semifinished products in method step b) and the hot pressing in method step e) which reduces the grain size of the material, the material should be conditioned during the melting and casting processes in such a way that the material already has a microstructure with a mean grain size of less than 1 mm in the cast state. The smaller the grain size, the greater the number of grain boundaries available during the hot pressing process as slip planes. Moreover, the plastic deformation is distributed more effectively over the entirety of the grains. This gives rise to a uniform recrystallization of the microstructure in the forming zones.
Advantageously, the castings can be subjected to a heat treatment between method steps b) and d). As a result, the material is homogenized and the segregation effects and second phases typical of casting can be eliminated. It is thus possible to achieve a microstructure morphology which comes close to the morphology of a wrought microstructure.
In a further advantageous procedure, after method step b), the cast semifinished products can be subjected to a peeling treatment for removing the outer material layer. It is thereby possible to remove undesirable impurities or segregations which may be located in the cast skin. These then no longer impair the subsequent processing steps, and the quality of the end product can be improved further.
In a preferred configuration of the invention, after method step e), the shaped parts can be processed by a cutting process. It is thereby possible to produce the end contour of the shaped part. Furthermore, it is possible to improve the surface quality of the shaped part. As a result of the hot pressing in method step e), the microstructure of the material becomes very fine-grained and the machinability is influenced favorably.
The invention will be explained in more detail on the basis of the following exemplary embodiment and also the figures. In the drawing:
A molten mass having the composition (in % by weight) Sn: 4.5%, Zn: 5.4%, Pb: 0.08%, Ni: 0.4%, P: 0.04%, remainder Cu and unavoidable impurities, which contain inter alia 0.01% by weight Fe, was cast in a precision continuous casting installation to form rods having a diameter of 24 mm. This alloy can be referred to as “lead-free red brass”. At the start of the casting process, no special measures were taken to condition the molten mass. Once a strand length of approximately 200 cm had been cast, conditioning of the molten mass by means of electromagnetic stirring was begun, without interrupting the casting process. This produced a cast body, with reference to which it is possible to directly demonstrate the influence of the stirring on the cast microstructure.
The lead-free red brass cast with electromagnetic stirring was annealed at 350° C., 550° C. and 750° C. At an annealing temperature of 350° C., there is still no significant change in microstructure. At 550° C., the second phases disappear, but the segregation effects can still be identified. Only at 750° C. do these segregations disappear, and the dendritic structure dissolved completely in favor of homogeneous, equiaxial grains. A significant coarsening of the grains did not arise in any of the heat treatments. The grain size always remained smaller than 1 mm.
Tests with a torsion plastometer were able to show that lead-free red brass with a microstructure which was conditioned by electromagnetic stirring during the casting process makes it possible to achieve very high degrees of deformation upon hot forming. At forming temperatures of between 750° C. and 850° C., degrees of deformation of up to φ=0.5 were achieved. In the case of lead-free red brass cast according to the prior art, degrees of deformation of at most φ=0.15 were achieved, and in the case of lead-containing red brass degrees of deformation even of only at most φ=0.03 were achieved.
Shaped parts for water installations were produced by means of drop forging (hot pressing) from the lead-free red brass subjected to electromagnetic stirring. Against all expectation, it was possible to process this lead-free red brass to form hollow bodies by means of drop forging without significant problems.
As alternative measures for conditioning the molten mass by electromagnetic stirring, it is also possible to employ methods such as mechanical stirring, ultrasonic excitation, the injection of gas or similar methods, which bring about grain refinement of the cast microstructure without the addition of further alloying constituents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 013 817.2 | Jul 2012 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/001744 | 6/13/2013 | WO | 00 |
