EP3320122B1 - Brass alloy - Google Patents

Description

The invention relates to a brass alloy with the features of the preamble of claim 1.

Corresponding brass alloys are often manufactured as semi-finished products in strips, wire form, rods, sheets or plates and then further processed into end products. Further processing is often carried out by using machining processes.

When cutting brass, it has proven advantageous in the past to add up to four percent by weight of lead to the alloy. The lead has a positive effect as a chip breaker, extends tool life and reduces cutting forces. Important material parameters, such as strength and corrosion resistance, are not negatively influenced by the addition of lead.

Despite the positive properties of lead, efforts are being made, among other things supported by the EC Directive 2011/65 / EU (RoHS II) and its predecessor 2002/95 / EC (RoHS I), Directive 2000/53 / EC on end-of-life vehicles and Directive 2002/96 / EG on waste electrical and electronic equipment to replace lead as a cutting element in brass.

However, the investigations carried out to date with alternative alloy variants have not led to materials that meet the requirements. These are either significantly more expensive than leaded brass alloys, lead to excessive tool wear or also contain environmentally harmful alloy elements. A brass alloy with good machinability is used, for example, in WO2011 / 020468 disclosed.

In the manufacture of brass alloys, the aim is to achieve both good machinability and good deformability. A simultaneous optimal fulfillment of both requirements proves to be difficult, since as a rule all measures which positively support a desired property lead to a deterioration of the second property. A compromise is typically chosen in such a way that a high level of strength with sufficient deformation capacity is given at the same time.

The object of the present invention is therefore to create an alternative brass alloy which has good machinability, adequate mechanical properties and causes the lowest possible wear on the cutting tools used.

According to the invention, a brass alloy having the features of claim 1 is proposed to achieve the object. Further preferred embodiments of the invention can be found in the dependent claims, the figures and the associated description.

According to the basic concept of the invention, it is proposed that the brass alloy have an indium content of 0.005 to 1.0 percent by weight and an addition of at least one of the components FE, Sn, Ni or Mn of 0.01 totaling 3.0 percent by weight and no addition of bismuth .

It has been found that the addition of indium improves the chip-breaking properties of the brass alloy can be influenced, so that the workability of the brass alloy can be improved. The indium practically replaces the lead previously used while achieving the same advantages, so that the lead content in the brass alloy can be reduced to zero in extreme cases, and the brass alloy can still be machined very well.

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

The properties that can be achieved by adding indium are in particular:

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

The indium content is preferably 0.005 to 1.0 percent by weight, whereby the advantages to be achieved can already be achieved. In particular, the indium content can be less than 0.25 percent by weight, so that favorable structural properties can already be achieved. In general, the indium content should be chosen to be rather lower, since indium is a comparatively expensive element. In this way, the indium content should be selected as low as possible and the favorable structural properties should nevertheless be achieved, for which an indium content of at least 0.05 and a maximum of 0.25 percent by weight has proven to be useful.

The brass alloy also contains a proportion of zinc of 36.0 to 46 percent by weight and the proportion of copper is between 54 and 64 percent by weight.

Furthermore, the alloy preferably has a mixed crystal with portions of an alpha structure or an alpha / beta structure. In the extreme case, a brass alloy with a 100% alpha structure is also used conceivable if the zinc content is close to or equal to 36 percent by weight. However, a mixed structure of alpha- and beta-structure is preferred, as a result of which in particular good machinability can be achieved. In particular, the copper content can preferably be at most 60 percent by weight, and the zinc content can preferably be between 36 and 40 percent by weight, as a result of which a structure which is particularly favorable in terms of machinability can be achieved.

A mixed structure with particularly good properties can be achieved in that the proportion by weight of the beta structure is 20 to 80 percent by weight, preferably 50 percent by weight.

In addition, at least one additional alloy component with a proportion of at most 3.0 percent by weight can be provided, the sum of the proportions of all additional alloy components preferably being at least 0.2 percent by weight.

The amount of copper is preferably 54 to 64.0 percent by weight, and the amount of zinc is preferably about 42 percent by weight.

The idea is based on the approaches essential to the invention mentioned below in order to achieve the desired material properties: a) The addition of indium has a positive effect on the chip-breaking properties. b) The microstructure is influenced by the proposed copper / zinc ratio in such a way that an alpha / beta crystal mixture is present in which the proportion of beta phase is around 20 to 80%. Since the beta phase shows brittle behavior under normal machining conditions, its increased proportion leads to a more favorable machining behavior, c) Further alloying elements serve to stabilize the alpha and beta phase, especially during the manufacturing process of the semi-finished product. d) In addition, the machining behavior and the mechanical properties are positively influenced by the targeted addition of further elements that form precipitates. On the one hand, a short-breaking chip is promoted by precipitations, and on the other hand, grain refinement is achieved, which results in improved ductility and high strengths. e) A fourth advantage can be achieved by influencing the arrangement or orientation of the two phases alpha and beta and / or the precipitates in order to adjust the processing properties in a targeted manner (e.g. by a combination of forming and heat treatment). The chip-breaking properties are consciously achieved by the alloy additives and in particular by the indium, so that the addition of bismuth is deliberately not provided. However, it cannot be ruled out that small amounts of bismuth get into the alloy due to contaminated scrap, but this should not be understood as a deliberate addition of bismuth. Nevertheless, the solution according to the invention offers the advantage that the chip-breaking properties are now achieved with alloy additives instead of the constituents lead and bismuth which are to be avoided, which are far less harmful in terms of possible health damage.

The precipitates contained in the structure support the machining behavior positively.

The alpha structure of the mixed crystal forms a surface-centered cubic structure. The beta mixed crystal structure, on the other hand, forms a body-centered cubic 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 there is a zinc content of about 42 percent by weight.

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. Excessive proportions lead to the alloy becoming brittle.

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

Phosphorus can be added to improve corrosion resistance. In particular, a maximum proportion of phosphorus in the range of 0.1 percent by weight is intended. According to a typical alloy composition, it is provided that the proportion of copper is 54 to 64.0 percent by weight.

A first additional alloy component is defined in that the proportion of iron is 0.05 to 0.5 percent by weight, preferably 0.2 to 0.3 percent by weight. Iron is used to control the grain size of the alpha and beta phases. Contents less than 0.01% 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.

A second additional alloy component is defined by the fact that the proportion of nickel is 0.05 to 0.5 percent by weight, preferably 0.2 to 0.3 percent by weight, which advantageously stabilizes the alpha phase.

A third additional alloy component is defined in that the proportion of silicon is 0.01 to 0.20 percent by weight, preferably 0.03 to 0.08 percent by weight. Silicon stabilizes the beta phase and, together with other elements, forms fine precipitates, which have a positive effect on the machining behavior and are responsible for grain refinement.

A fourth additional alloy component is defined in that the proportion of manganese is 0.01 to 0.20 percent by weight, preferably 0.03 to 0.08 percent by weight. Manganese stabilizes the beta phase and, together with other elements, forms fine precipitates, which have a positive effect on the machining behavior and are responsible for grain refinement, similar to the proposed additional alloy component silicon.

A fifth additional alloy component is defined in that the proportion of tin is 0.05 to 0.5 percent by weight, preferably 0.2 to 0.3 percent by weight.

A sixth additional alloy component is defined in that the proportion of Cr is 0.01 to 0.2 percent by weight.

Furthermore, calcium and / or magnesium can also be provided in a proportion of 0.05 to 1.0 percent by weight. Phosphorus leads to an improved corrosion resistance of the alloy, in particular P also counteracts dezincification.

It contributes to an optimal composition of the alloy that the proportion of elements that are not copper, zinc, indium, iron, nickel, silicon, manganese, antimony, calcium, cadmium, selenium, magnesium, lead or tin is less than 0, 2 percent by weight.

A preferred embodiment of the alloy preferably has the following percentages by weight with regard to its composition. Copper in the range from 54% to 64%, zinc in the range from 36% to 40.5%, iron in the range from 0.1% to 0.5%, nickel in the range from 0.1% to 0.5%, Silicon in the range from 0.01% to 0.2%, manganese in the range from 0.01% to 0.2%, antimony, calcium, cadmium, magnesium and selenium in the range up to 0.1%, and tin in the range from 0.1% to 0.5% and lead with a proportion of 0.1% or less. The proportion of indium is preferably 0.005 to 0.5%. The lead content of the alloy is, also due to the use of scrap in the production of such alloys, max. 0.1%.

Depending on the proportion of the above additives, 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 is 41.9% to 42.5%, the proportion of nickel is 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%, antimony, calcium, cadmium, magnesium and selenium in the Range up to 0.1% and the proportion of tin 0.2% to 0.3% and the proportion of Lead and indium each less than 0.1%. In addition, it is particularly intended that the sum of the weight proportions of all further possible constituents is at most 0.2%.

According to a further preferred embodiment, the proportion of copper is 54 to 58%, zinc 41 to 45%, nickel 0.2 to 0.3%, iron 0.2 to 0.3%, silicon 0.03 to 0.06% , Manganese 0.03 to 0.08%, calcium 0.3 to 0.5%, magnesium 0.6 to 0.9%, antimony <0.1%, cadmium <0.1%, selenium <0.1 %, the sum of lead and indium <0.1%, other components <0.2%.

With regard to the above composition, it is basically possible to add only some of the listed elements to the alloy. According to a particularly preferred embodiment, however, it is contemplated to add all of the elements listed above to the alloy in combination with one another in a proportion by weight within the respectively defined intervals.

According to a typical embodiment it is provided that the lead content is in an interval from 0.005% to 0.1%. The indium content should also be between 0.005% and 0.5%. Due to the relationship according to the invention between the alpha mixed crystal and the beta mixed crystal, the desired material properties can be achieved even with reduced lead or indium contents. The alpha mixed crystal leads to a relatively good deformability of the alloy and gives it tough properties. The beta mixed crystal, on the other hand, is relatively difficult to deform and is brittle. These properties are desirable for good machinability. Due to the relation according to the invention of the alpha and beta components thus imparting sufficient toughness to the alloy to aid ductility and sufficient brittleness to aid machinability.

In addition to the pure relationship between the alpha and beta components, it also proves to be useful to influence the grain size of the mixed crystals. It has proven to be positive to support comparatively small and even grain sizes. When iron and silicon are added, iron silicides are formed, which hinder grain growth and thereby have a positive effect on the structure. 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 good machinability. In small amounts, proportions of phosphorus also prove to be positive with regard to the formation of the microstructure.

With regard to the manufacture of the alloy, a preferred production process can be carried out in such a way that hot forming (for example hot rolling or extrusion) is carried out in a temperature range from 600 to 750 ° C. first. This creates a structure that has a beta mixed crystal content of about 50 percent by weight. To support both good machinability and good deformability, it is possible to carry out an intermediate annealing. Here, after a first forming step, an intermediate annealing at a temperature of about 400 to 600 ° C. is carried out. The intermediate annealing leads to recrystallization and thus to a new grain formation. This supports a fine-grain microstructure.

By carrying out the intermediate annealing appropriately, it is possible to achieve a weight fraction of the beta mixed crystal of 30 to 60%. This increases the formability of the semi-finished product.

According to the invention, it is provided in particular to form the brass alloy from copper and zinc, with a lead content of 0.005 to 0.1%, an indium content of 0.005 to 0.5% and at least one further alloy component. This additional alloy component influences the microstructure of the mixed crystal in order to achieve the required material properties depending on the application.

According to a further preferred embodiment, it is provided that the following alloy is produced in terms of weight percentages.

Cu 55 to 56%, Fe 0.2 to 0.3%, Ni 0.1 to 0.2%, Si 0.01 to 0.03%, Mn 0.1 to 0.2%, Sn 0.3 up to 0.5%, In 0.05 to 0.2%, Sb <0.1%, Ca <0.1%, Cd <0.1%, Se <0.1%, Pb <0.1% , Zn remainder. This embodiment leads to a particularly high proportion of beta mixed crystals between 55 and 70% beta proportion, which results in a particularly short-breaking chip.

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

Cu 57 to 57.5%, Fe 0.2 to 0.3%, Ni 0.2 to 0.3%, Si 0%, Mn 0%, Sn 0.2 to 0.3%, In 0.05 up to 0.2%, Sb <0.1%, Ca <0.1%, Cd <0.1%, Se <0.1%, Pb <0.1%, Zn rest. Aim of this The proposed composition is to achieve a slightly increased alpha content and less hard excretions.

Furthermore, with regard to preferred embodiments, it is also intended to realize the following alloy with regard to the weight percent.

Cu 56 to 56.5%, Fe 0.4 to 0.5%, Ni 0.2 to 0.3%, Si 0%, Mn 0.1 to 0.2%, Sn 0.35 to 0.5 %, In 0.05 to 0.2%, Sb <0.1%, Ca <0.1%, Cd <0.1%, Se <0.1%, Pb <0.1%, Zn remainder. As a result, less hard precipitates are formed and, instead, the formation of precipitates of primarily precipitated iron is promoted. As a result of the increased addition of manganese and tin, an increased beta component is formed compared to the previous embodiment.

The brass alloy according to the invention is used to manufacture so-called semi-finished products that 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 strips, wires, profiles and / or rods. The further processing step comprises at least one machining process. The further processing step can also 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 temperature of up to about 450 ° C and a hot forming temperature in a range of 600 ° C to 850 ° C can be distinguished.

By adding the alloying elements iron, nickel, magnesium, calcium or chromium, precipitates can be generated in the mixed crystal, which in turn promote chip breaking during subsequent mechanical processing, so that these alloy components also have a similar beneficial effect as that previously used and if possible have avoidant lead. The chip breaking can be favorably influenced, in particular, by a specific ratio of the alloy components iron and tin to one another, since the ratio of these two alloy components to one another particularly favors the formation of the precipitates. Such a favorable ratio of iron to tin would be e.g. 1.0 to 1.2.

Furthermore, the formation of the precipitates or the grain refinement and thus the chip breaking can be favorably influenced if the brass alloy contains chromium in an amount of 0.01 to 0.2 percent by weight and / or calcium and / or magnesium in an amount of 0.05 each up to 1.0 weight percent is added.

In the ideal case, the proportion of bismuth is 0.0 percent, ie the brass alloy is free of bismuth. The properties that favor chip breaking are achieved solely through the indium content and the other alloy components such as iron, tin, nickel, manganese, magnesium, calcium or chromium. This is also worth striving for because bismuth should also be avoided as far as possible due to properties that are disadvantageous to health, or at least should only be used in the smallest possible amount. For this reason, the proportion of bismuth in the brass alloy according to the invention is already limited to a maximum value of 0.1 percent by weight, whereby it is desirable to keep the proportion of bismuth as low as possible. For example, it is possible that a small proportion of bismuth is due to the use of contaminated scrap gets into the brass alloy. This proportion of actually undesirable bismuth is used by the solution according to the invention to form the precipitates and the grain refinement and thus to positively influence the machining behavior, and at least the previously used likewise harmful lead can be dispensed with in the alloy. If the proportion of bismuth cannot be reduced completely to 0.0, for example due to impurities in added scrap, the proportion should not exceed a maximum value of <0.003 percent by weight, if possible. Alternatively, a lead content of a maximum of 0.1 percent by weight can also be provided in this case in order to set the desired chip breaking. In any case, bismuth is not actively added to the brass alloy according to the invention, but instead it is only accepted if it cannot be avoided for technical reasons. However, since it can have positive effects on the material properties of the brass alloy despite its health-damaging properties, very small quantities can also be accepted.

Furthermore, it is possible to produce the structural properties, in particular the formation of the needle-like beta phase, by pressing or drawing, or at least to reinforce the formation of the beta phase or to shape it in a desired direction. Alternatively, the development of a more globular morphology of the beta phase in the mixed crystal can be supported by a combination of the processing steps pressing, annealing and drawing in this order or pressing, drawing, annealing, drawing, whereby the size of the grains and the structural components of the beta phase are determined by the selected Process temperature can be set during annealing, pressing or drawing. The higher the process temperature, the larger the grains and the coarser the structure.

Claims (14)

1. Brass alloy made of 54 to 64 wt.% Cu and 36 to 46 wt.% Zn, wherein the alloy has an indium content of from 0.005 to 1.0 wt.%, has the addition of at least one of the components Fe, Sn, Ni or Mn in a total of 0.01 to 3.0 wt.% but not the addition of Bi,

   - optionally has a proportion of Si of 0.01 to 0.2 wt.%,

   - optionally has a proportion of Sb of up to 0.5 wt.%,

   - optionally has a proportion of cadmium of up to 0.5 wt.%,

   - optionally has a proportion of Ca of up to 1.0 wt.%,

   - optionally has a proportion of Mg of up to 1.0 wt.%,

   - optionally has a proportion of Se of up to 0.5 wt.%,

   - optionally has a phosphorus content of at most 0.1 wt.%, and

   - optionally has a proportion of Cr of 0.01 to 0.2 wt.%,
   along with impurities.
2. Brass alloy according to claim 1, characterised in that

   - the alloy has a solid solution having proportions of an alpha structure or an alpha/beta structure having precipitates.
3. Brass alloy according to claim 2, characterised in that

   - the weight proportion of the beta structure is 20 to 80 wt.%.
4. Brass alloy according to any of the preceding claims, characterised in that

   - the total of the proportions of all alloy components provided in addition to Cu and Zn is at least 0.2 wt.%.
5. Brass alloy according to any of the preceding claims, characterised in that the proportion of Zn is 42 wt.%.
6. Brass alloy according to any of the preceding claims, characterised in that the proportion of Fe is 0.05 to 0.5 wt.%.
7. Brass alloy according to any of the preceding claims, characterised in that the proportion of Ni is 0.05 to 0.5 wt.%.
8. Brass alloy according to any of the preceding claims, characterised in that the proportion of Mn is 0.01 to 0.20 wt.%.
9. Brass alloy according to any of the preceding claims, characterised in that the proportion of Sn is 0.05 to 0.5 wt.%.
10. Brass alloy according to any of the preceding claims, characterised in that the proportion of substances which are not Cu, Zn, Fe, In, Ni, Si, Mn, Sb, Ca, Cd, Se, Pb or Sn is less than 0.2 wt.%.
11. Brass alloy according to any of the preceding claims, characterised in that the brass alloy has the following weight percentages: Cu 55 to 56%; Fe 0.2 to 0.3%; In 0.005 to 0.5%; Ni 0.1 to 0.2%; Si 0.01 to 0.03%; Mn 0.1 to 0.2%; Sn 0.3 to 0.5%; Sb < 0.1%; Ca < 0.1%; Cd < 0.1%; Se < 0.1%; Pb < 0.1%; Zn the remainder.
12. Brass alloy according to any of claims 1 to 10, characterised in that the brass alloy has the following weight percentages: Cu 57 to 57.5%; Fe 0.2 to 0.3%; In 0.005 to 0.5%; Ni 0.2 to 0.3%; Sn 0.2 to 0.3%; Sb < 0.1%; Ca < 0.1%; Cd < 0.1%; Se < 0.1%; Pb < 0.1%; Zn the remainder.
13. Brass alloy according to any of claims 1 to 10, characterised in that the following weight percentages are implemented: Cu 56 to 56.5%; Fe 0.4 to 0.5%; In 0.005 to 0.5%; Ni 0.2 to 0.3%; Si 0%; Mn 0.1 to 0.2%; Sn 0.35 to 0.5%; Sb < 0.1%; Ca < 0.1%; Cd < 0.1%; Se < 0.1%; Pb < 0.1%; Zn the remainder.
14. Brass alloy according to any of claims 1 to 10, characterised in that the following weight percentages are implemented: Cu 54 to 58%; Zn 41 to 45%; Ni 0.2 to 0.3%; Fe 0.2 to 0.3%; Si 0.03 to 0.06%; Mn 0.03 to 0, 08%; Ca 0.3 to 0.5%; Mg 0.6 to 0.9%; Sb < 0.1%; Cd < 0.1%; Se < 0.1%; the total of Pb and In < 0.1%; and other components < 0.2%.