EP2467507B1 - Brass alloy - Google Patents

Description

The invention relates to a brass alloy for use in the manufacture of semi-finished products intended for machining, consisting of copper, zinc and additional alloy components.

Corresponding brass alloys are often produced as semi-finished products in strip or wire form and subsequently processed into finished products. The further processing takes place frequently by application of cutting operations.

When machining brass, it has proven advantageous in the past to add lead to the alloy in an amount of up to four percent by weight. The lead has a positive effect as a chipbreaker, extends tool life and reduces the tensile forces. Important material parameters such as strength and corrosion resistance are not adversely affected by an addition of lead.

Despite the positive properties of lead, efforts are being made, inter alia, to replace brass as a cutting element, supported by the directives of EU Directive 2000/53 / EC on end-of-life vehicles and Directive 2002/96 / EC on waste electrical and electronic equipment ,

In the production of brass alloys is often sought to achieve both a good machinability and good ductility. A simultaneous optimal fulfillment of both requirements proves to be difficult, since usually all measures that support the desired property positive, lead to a reduction of the second property. A compromise is typically chosen so as to impart high strength while maintaining sufficient deformability.

The investigations carried out so far with alternative alloy variants which have no or only low levels of lead have not always led to materials which fulfill the stated requirements. Often these are either significantly more expensive than leaded brass alloys, lead to excessive tool wear or also contain environmentally hazardous alloying elements.

So is out of the WO 2006/136065 A1 a brass alloy of the aforementioned type has become known, which contains in a variant except copper and zinc components of iron, nickel and tin and less than 0.1 weight percent lead, but additionally has a proportion of 0.49 weight percent bismuth. Besides that is from the JP 7 310133 A a brass alloy has become known which has no content of lead, but except copper, zinc, iron and tin a Contains 2.3 wt% bismuth. Finally, from the CN 101 250 641 A Brass alloys containing not or less than 0.05% by weight of lead and in addition to copper and zinc fractions of less than one percent by weight of iron, nickel, tin, manganese and / or silicon, but between 0.7 and 0.91 Percent by weight bismuth.

From the document Spiekermann "Alloys - a special patent law problem?", Messages of the German Patent Attorneys, Heymann, Cologne, DE, ISSN: 0026-6884, Vol. 34, 1 January 1993 (1993-01-01), pages 178-190 "is a patent law paper for the disclosure of compositions of alloys known.

Object of the present invention is to define a lead-free brass alloy of the aforementioned type such that it achieves good machinability, sufficient mechanical properties and the lowest possible wear on the cutting tools used and that at the same time the lowest possible content of expensive and / or having environmentally harmful alloying elements.

The invention is further based on the object to achieve specific properties by the targeted combination of non-polluting alloying elements and on the manufacturing process.

• gute Zerspanbarkeit,
• hohe Festigkeit aber noch gute Duktilität,
• gute Warm- und Kaltumformbarkeit,
• ausreichende Korrosionsbeständigkeit.

In particular, these are the properties:

• good machinability,
• high strength but still good ductility,
• good hot and cold workability,
• adequate corrosion resistance.

Furthermore, an economically sensible mass production should be possible as semi-finished goods.

1. a) Die Gefügestruktur wird durch Änderung des Kupfer/Zink-Verhältnisses derart beeinflusst, dass ein alpha/beta-Kristallgemisch vorliegt, in dem der Anteil an beta-Phase etwa 30 bis 70 % beträgt. Da die beta-Phase unter normalen Zerpspanungsbedingungen ein sprödes Verhalten zeigt, führt ihr erhöhter Anteil zu einem günstigeren Zerspanungsverhalten.
2. b) Weitere Legierungselemente dienen zur Stabilisierung der alpha und der beta-Phase, insbesondere während des Fertigungsprozesses des Halbzeuges.
3. c) Darüber hinaus werden das Zerspanungsverhalten sowie die mechanischen Eigenschaften durch die gezielte Zugabe weiterer Ausscheidungen bildender Elemente positiv beeinflusst. Zum einen wird durch Ausscheidungen ein kurz brechender Span begünstigt. Zum anderen wird eine Kornfeinung bewirkt, wodurch eine verbesserte Duktilität bei hohen Festigkeiten erzielt wird.
4. d) Ein vierter Vorteil kann erreicht werden durch die Beeinflussung der Anordnung bzw. Orientierung der beiden Phasen alpha und beta und/oder der Ausscheidungen, um so gezielt die Verarbeitungseigenschaften einzustellen (z.B. durch eine Kombination aus Umformung oder Wärmebehandlung).

The idea is based on the inventions essential to the invention mentioned below in order to achieve the desired material properties:

1. a) The microstructure is influenced by changing the copper / zinc ratio such that an alpha / beta crystal mixture is present in which the proportion of beta phase is about 30 to 70%. Since the beta phase shows a brittle behavior under normal decomposition conditions, its increased proportion leads to a more favorable machining behavior.
2. b) Further alloying elements serve to stabilize the alpha and the beta phase, in particular during the production process of the semifinished product.
3. c) In addition, the chipping behavior and the mechanical properties are positively influenced by the targeted addition of further precipitates of forming elements. On the one hand excretions favor a short breaking chip. On the other hand, a grain refining is effected, whereby an improved ductility at high strengths is achieved.
4. d) A fourth advantage can be achieved by influencing the arrangement or orientation of the two phases alpha and beta and / or the precipitates, so as to adjust the processing properties in a targeted manner (eg by a combination of forming or heat treatment).

For compliance with the requirements of the invention, it proves to be particularly advantageous that the content of lead is at most 0.1 percent by weight, that the proportion of zinc 40.5 to 46 weight percent and the proportion of copper is at most 59 percent by weight and that the alloy mixed crystal having proportions of both an alpha microstructure and a beta microstructure, wherein the weight fraction of the beta microstructure is at least 30% and at most 70%, and that the proportion of each of the additional alloying components is selected from the group consisting of iron, nickel, tin, manganese and silicon is at most 1.0 weight percent and the sum of the proportions of all of these additional alloy components is at least 0.5 weight percent.

A particularly important feature for solving the problem underlying the invention is further that the proportion of elements that are not copper, zinc, iron, nickel, tin, manganese or silicon is less than 0.2 weight percent.

The objects of the invention are achieved by the feature combination of claim no.

It may turn out that certain properties of the alloy are particularly desired depending on the application. For this purpose, it is envisaged to add each of the mentioned alloying elements in a higher concentration in each case, without thereby increasing the total amount of alloying elements (except copper and zinc).

The precipitations contained in the microstructure, which are also found in the soft alpha microstructure, support the chipping behavior positively.

The alpha microstructure of the mixed crystal forms a cubic surface-centered spatial structure. The beta-mixed crystal, however, forms a cubic body-centered structure.

It proves to be particularly advantageous if the proportion of the beta structure is at least 50%. This is particularly supported by the fact that a zinc content of about 42 percent by weight is present.

The elements iron and nickel have a regulative influence on the grain growth of the alpha and beta phase, with nickel additionally promoting the stabilization of the alpha structure. Too high levels lead to embrittlement of the alloy.

The elements tin, silicon, manganese and iron stabilize and increase the proportion of the beta phase.

To improve the corrosion resistance, the addition of phosphorus may be provided. In particular, a maximum proportion of phosphorus in the range of 0.1% by weight is intended.

According to a typical alloy composition, it is provided that the content of copper is 54 to 59.0% by weight.

In addition, it is provided that the proportion of zinc is 40 to 46 weight percent.

A first additional alloying component is defined by the proportion of iron being from 0.1 to 0.5 percent by weight. Iron is used to control the grain size of the alpha and beta phases. Contents less than 0.1% do not have a sufficient effect. Shares greater than 0.5% would lead to very large iron precipitates, which have a negative effect on the mechanical properties of the alloy. In particular, it is contemplated that the proportion of iron is 0.2 to 0.3 weight percent.

A second additional alloying component is defined by the proportion of nickel being from 0.1 to 0.5 percent by weight. Nickel stabilizes the alpha phase.

In particular, it is contemplated that the proportion of nickel is 0.2 to 0.3 weight percent.

An additional optional alloying component is defined by the proportion of silicon being 0.01 to 0.20 percent by weight. Silicon stabilizes the beta phase and together with other elements forms fine precipitates, which have a positive effect on the cutting behavior and are responsible for grain refining. In particular, it is contemplated that the proportion of silicon is 0.03-0.08% by weight.

An additional optional alloying component is defined by the proportion of manganese being 0.01 to 0.20 percent by weight. Manganese stabilizes the beta phase and together with other elements forms fine precipitates, which have a positive effect on the cutting behavior and are responsible for grain refining. In particular, it is contemplated that the proportion of manganese is 0.03 to 0.08 weight percent.

A third additional alloying component is defined by the proportion of tin being from 0.1 to 0.5 percent by weight.

In particular, it is contemplated that the proportion of tin is 0.2 to 0.3 weight percent.

Phosphor leads to an improved corrosion resistance of the alloy, in particular P also counteracts dezincification.

It contributes to an optimum composition of the alloy that the proportion of elements other than copper, zinc, iron, nickel, silicon, manganese or tin is less than 0.2 percent by weight.

A preferred embodiment of the alloy preferably has the following percentages by weight with respect to its composition. Copper in the range of 54% to 59.5%, zinc in the range of 36% to 40.5%, iron in the range of 0.1% to 0.5%, nickel in the range of 0.1% to 0.5 %, Silicon in the range of 0.01% to 0.2%, manganese in the range of 0.01% to 0.2% and tin in the range of 0.1% to 0.5% and lead with a maximum of 0.1%. The lead content of the alloy is, also due to the use of scrap in the production of such alloys, max. 0.1%.

According to the proportion of the above additives, the proportions of copper and / or zinc are optionally reduced.

According to a particularly preferred embodiment, the proportion of copper is 57.0% to 57.5%, the proportion of zinc 41.9 to 42.5, the proportion of nickel 0.2% to 0.3%, the proportion of iron 0.2% to 0.3%, the proportion of silicon 0.03% to 0.08%, the proportion of manganese 0.03% to 0.08% and the proportion of tin 0.2% to 0.3 % and lead content less than 0.1%. In addition, it is particularly conceived that the sum of the weight proportions of all other possible components is not more than 0.2%.

As for the above compositions, it is basically possible to add only some of the listed elements to the alloy. According to a very particularly preferred embodiment, however, it is envisaged to add all the above-listed elements with a weight proportion within the respectively defined intervals in combination with one another to the alloy.

According to a typical embodiment it is provided that the lead content is in an interval of 0.01% to 0.1%. Due to the relationship between the alpha-mixed crystal and the beta-mixed crystal according to the invention, the desired material properties can be achieved even with reduced lead contents. The alpha-mixed crystal leads to a relatively good deformability of the alloy and gives this tough properties. The beta-mixed crystal is, however, relatively poorly deformable and brittle. These properties are desirable for good machinability. The relationship of the alpha and beta fractions according to the invention thus gives the alloy sufficient toughness to aid ductility and brittleness to aid machinability.

In addition to the pure relation between the alpha and the beta portions, it also proves to be useful to influence the grain size of the mixed crystals. It has proven to be beneficial to support comparatively small and uniform particle sizes. By adding iron and silicon, iron silicides are formed which impede grain growth and thus have a positive effect on the microstructure. The addition of tin and / or iron promotes the formation of beta-mixed crystals.

It also turns out that the addition of manganese in combination with oxygen or phosphorus favors the precipitation of oxides or phosphides and thereby leads to a finer grain structure. This in turn supports a good machinability. In small amounts, also proportions of phosphorus prove to be positive in terms of the formation of the microstructure.

With regard to the production of the alloy, a preferred production process may be carried out by first performing extrusion molding in a temperature range of 600 to 750 ° C. This produces a microstructure which has a proportion of the beta mixed crystal of about 50 percent by weight.

To support both good machinability and good ductility, it is possible to carry out an intermediate annealing. In this case, an intermediate annealing at a temperature of about 500 to 600 ° C. is carried out after a first forming step. The intermediate annealing leads to a recrystallization and thus to a Kornneubildung. As a result, a fine-grained microstructure is supported.

By suitably carrying out the intermediate annealing, it is possible to realize a weight fraction of the beta mixed crystal of 30 to 45 percent. It is thereby achieved an increased formability of the semifinished product.

According to the invention, it is provided in particular to form the brass alloy of copper and zinc, with a lead content of 0.01 to 0.1 percent and with at least one further alloying component. This further alloying component influences the microstructure of the mixed crystal in order to achieve the respective desired material properties depending on the application.

According to a further preferred embodiment, it is provided to realize the following alloy in terms of weight percent.

Cu 55-56%, Fe 0.2-0.3%, Ni 0.1-0.2%, Si 0.01-0.03%, Mn 0.1-0.2%, Sn 0.3 -0.5%, Zn remainder. This embodiment leads to a particularly high proportion of beta-mixed crystals between 55 and 70% beta-portion, which causes a particularly short-breaking chip.

Another preferred embodiment is provided in terms of weight percent by the following alloy.

Cu 57-57.5%, Fe0.2-0.3%, Ni 0.2-0.3%, Si 0%, Mn 0%, Sn 0.2-0.3% Zn residue. Target is Here, to achieve a slightly increased alpha content and less hard precipitates.

Moreover, with respect to preferred embodiments, it is also contemplated to realize the following alloy in terms of weight percent.

Cu 56-56.5%, Fe 0.4-0.5%, Ni 0.2-0.3%, Si 0%, Mn 0.1-0.2%, Sn 0.35-0.5 % Zn Rest. Less hard precipitates are formed thereby promoting a formation of the excretion of primary precipitated iron. The increased addition of manganese and tin leads to an increased beta content compared to the previous embodiment.

The brass alloy according to the invention serves to produce so-called semi-finished products which are subjected to at least one further processing step. The semi-finished products are typically produced by a casting process. Typical embodiments of such semi-finished products are wires, profiles and / or rods. The further processing step comprises at least one machining operation. Likewise, the further processing step may comprise a combination of shaping and machining. The shaping can be carried out both at room temperature and at an elevated temperature. At the elevated temperatures, a warm half-temperature can reach up to about 450 ° Celsius and a hot working temperature be distinguished in a range of 600 ° Celsius to 850 ° Celsius.

Claims (12)

1. Brass alloy for use in the production of semifinished product intended for material-removing processing, consisting of copper, zinc and additional alloy components, where the lead content is at most 0.1 per cent by weight, the zinc content is 40.5 to 46 per cent by weight and the copper content is at least 54 and at most 59 per cent by weight, where the alloy contains, as additional alloy components, iron, nickel and tin such that the iron content is 0.1 to 0.5 per cent by weight, that the nickel content is 0.1 to 0.5 per cent by weight, and that the tin content is 0.1 to 0.5 per cent by weight, where the content of each of the additional alloy components is at most 1.0 per cent by weight and the sum total of the contents of all additional alloy components is at least 0.5 per cent by weight, where said alloy comprises a solid solution having components both of an alpha microstructure and of a beta microstructure and the proportion by weight of the beta microstructure is at least 30% and at most 70%, and precipitates are formed in the microstructure, and where the content of substances that are not copper, zinc, iron, nickel, silicon, manganese or tin is less than 0.2 per cent by weight, and where an optional silicon content is 0.01 to 0.20 per cent by weight and where an optional manganese content is 0.01 to 0.20 per cent by weight.
2. Brass alloy according to Claim 1, characterized in that the zinc content is about 42 per cent by weight.
3. Brass alloy according to either of Claims 1 and 2, characterized in that the iron content is 0.2 to 0.3 per cent by weight.
4. Brass alloy according to any of Claims 1 to 3, characterized in that the nickel content is 0.2 to 0.3 per cent by weight.
5. Brass alloy according to any of Claims 1 to 4, characterized in that the silicon content is 0.03 to 0.08 per cent by weight.
6. Brass alloy according to any of Claims 1 to 5, characterized in that the manganese content is 0.03 to 0.08 per cent by weight.
7. Brass alloy according to any of Claims 1 to 6, characterized in that the tin content is 0.2 to 0.3 per cent by weight.
8. Brass alloy according to any of Claims 1 to 7, characterized in that the proportion of the beta microstructure is at least 50 per cent by weight.
9. Brass alloy according to any of Claims 1 to 8, characterized in that the following percentages by weight are achieved: Cu 55-56%, Fe 0.2-0.3%, Ni 0.1-0.2%, Si 0.01-0.03%, Mn 0.1-0.2%, Sn 0.3-0.5%, balance Zn.
10. Brass alloy according to any of Claims 1 to 9, characterized in that the following percentages by weight are achieved: Cu 57-57.5%, Fe 0.2-0.3%, Ni 0.2-0.3%, Si 0%, Mn 0%, Sn 0.2-0.3%, balance Zn.
11. Brass alloy according to any of Claims 1 to 10, characterized in that the following percentages by weight are achieved: Cu 56-56.5%, Fe 0.4-0.5%, Ni 0.2-0.3%, Si 0%, Mn 0.1-0.2%, Sn 0.35-0.5%, balance Zn.
12. Brass alloy according to any of Claims 1 to 11, characterized in that a maximum phosphorus content of about 0.1 per cent by weight is present.