WO2009136552A1 - Brass alloy powder, brass alloy extruded material and method for producing the brass alloy extruded material - Google Patents

Abstract

Disclosed is a brass alloy powder which has a brass composition composed of a mixed phase of an α-phase and a β-phase, and contains 0.5-5.0% by mass of chromium. The chromium contains a component solid-solved in the brass matrix and a component deposited at crystal grain boundaries.

Description

Brass alloy powder, brass alloy extruded material and method for producing the same

The present invention relates to a high-strength brass alloy, and more particularly to a lead-free brass alloy powder and a brass alloy extruded material which are harmful to the environment and the human body.

In recent years, environmental problems have been greatly highlighted, and attention must be paid to this point also in alloy development. 6/4 brass has moderate strength, good mechanical properties, and is nonmagnetic, so it is not only used as a mechanical part, but also widely used in gas piping, water piping, valves, etc. It is done.

In order to improve the workability of a member made of 6/4 brass, a few percent of lead is usually contained in the alloy composition. When this lead-containing brass member is used for water supply piping, there is a risk that lead may dissolve into the water supply water.

In order to solve the above problems, development of lead-free brass materials is in progress. As an example of conventional development, one to which bismuth is added instead of lead, tin is added as disclosed in Japanese Patent Application Laid-Open No. 2000-309835 (Patent Document 1) and International Publication WO 98/10106 (Patent Document 2) There are those in which the γ phase is precipitated by carrying out the reaction and those in which fine particles of silicon are dispersed. Among these developed technologies, not only lead-free but also the strength of brass itself is simultaneously improved to expand the application range.

However, the current situation is that the addition of bismuth is only as strong as the addition of lead. Both bismuth and lead are elements that reduce the strength of brass by being added, and do not contribute to the improvement of the strength of brass members. As disclosed in JP-A-2000-309835 (Patent Document 1) and International Publication WO 98/10106 (Patent Document 2), the method of precipitating the γ phase by the addition of tin is the proof stress value or tension of the brass member. Although the strength and the like are improved, the deformability of the brass member is largely reduced to deteriorate the processability. In addition to that, there arises a problem that the γ phase is a starting point to cause brittle fracture. The method of dispersing the fine particles of silicon contributes to the improvement of the mechanical strength of the brass alloy member, but has a disadvantage that the machinability of the member becomes inferior.

Proceedings of the 46th Annual Conference on Copper and Copper Alloy Technical Conference (2006), pp. Graphite particle dispersed machinability based on powder metallurgy, entitled "Characteristics of complete lead-free machinable brass alloy by powder process" in Kondo et al. (Non-patent document 1) 153-154, Kondo et al. A method of making a brass alloy is disclosed. The merits of the addition of graphite are that it can be made completely lead free and that it is easy to separate because graphite floats on molten brass during recycling. On the other hand, the strength improvement of the brass member by the added graphite can not be expected. Therefore, when adding graphite, a technique for improving the strength of a brass member utilizing powder metallurgy should also be considered.

Generally, when trying to melt a low melting point metal into a high melting point metal at high temperature, the low melting point metal evaporates rapidly during melting because the vapor pressure of the low melting point metal is high, and the desired alloy composition is obtained. So difficult to control.

Brass is an alloy of copper and zinc. If a high melting point metal is added to this brass, there is a possibility that an improvement in strength can be expected. However, the boiling point of zinc is as low as 907 ° C., and it is not easy to add chromium having a melting point of 1907 ° C., vanadium having a melting point of 1902 ° C., and the like. If the temperature of brass in liquid phase is increased, the amount of evaporation of zinc inevitably increases, and the alloy composition rapidly changes in the copper-rich direction.

As a melting method of the high melting point metal, there are an electron beam melting method, a hydrogen plasma arc melting method and the like, but these methods are not suitable for mass production, but are used for small batch processing of rare metals. Moreover, these methods can not prevent evaporation of the low melting point metal.

Although it is conceivable to add a molten high melting point metal to the low melting point metal, it is not industrially possible to dissolve the high melting point metal by heating it to its melting point, and it is difficult to mass-produce it. It is. Therefore, generally, a method utilizing thermite reaction of oxide, a method such as addition of a lower melting point mother alloy, and the like are performed.

Japanese Patent Application Laid-Open No. 10-168533 (Patent Document 3) discloses a method of adding an alloy component to zinc. Although this publication describes that the mother alloy is used for the addition of chromium, it can be seen from the thermal equilibrium phase diagram of Zn-Cr that chromium hardly dissolves in zinc. In other words, it can be understood that Zn ₁₇ Cr or Zn ₁₃ Cr as a compound is dispersed in the zinc matrix. When this master alloy is added to zinc, the change in the chromium compound does not occur only by increasing the proportion of the zinc component. As described above, it is very difficult to dissolve the non-solid solution element and the high melting point metal in the low melting point metal, and it is necessary to develop another method.

The addition of chromium into copper is advanced compared to zinc-containing alloys. As representative ones, there are methods disclosed in Japanese Patent Application Laid-Open No. 11-209835 (Patent Document 4) and Japanese Patent Application Laid-Open No. 2006-124835 (Patent Document 5). The methods disclosed in these publications involve the inclusion of chromium, zirconium, tellurium, sulfur, iron, silicon, titanium or phosphorus in copper. Both are precipitation-type copper alloys, and precipitation of copper / zirconium compounds etc. is performed as a strengthening phase, but unlike zinc-containing alloys, they can be alloyed even at high temperatures, so the preparation of these materials is easy. I have to.

In the development process of lead-less brass, it is known that it is effective to apply powder metallurgy as a method of adding graphite. This is largely because mixing of graphite and brass is made possible by using powder. Even if it is attempted to add graphite by the usual melting method, the graphite floats on the molten brass and can not be dispersed in the brass because of the difference in specific gravity between the two.

JP 2000-309835 A International Publication WO 98/10106 Unexamined-Japanese-Patent No. 10-168533 JP-A-11-209835 Unexamined-Japanese-Patent No. 2006-124835

The inventors of the present invention have been working on the development of graphite-added brass as a part of the development of leadless brass alloys. However, the graphite particle dispersion type lead-free machinable brass alloy has the same strength as that of lead-containing machinable brass alloy, and the strength is not improved dramatically.

An object of the present invention is to provide a brass alloy powder which contributes to the improvement of the strength of a brass alloy member.

Another object of the present invention is to provide a brass alloy extruded material having excellent mechanical strength.

Still another object of the present invention is to provide a brass alloy member having excellent mechanical strength.

Still another object of the present invention is to provide a method for producing a brass alloy extruded material having excellent mechanical strength.

The brass alloy powder according to the present invention has a brass composition consisting of a mixed phase of α phase and β phase, and contains 0.5 to 5.0% by mass of chromium. The chromium contains a component dissolved in the matrix of brass and a component precipitated in grain boundaries.

By extruding the assembly of the above-mentioned brass alloy powder, a brass alloy extruded material excellent in mechanical strength can be obtained. In order to obtain a desired mechanical strength, the content of chromium needs to be 0.5% by mass or more. In order to further increase the mechanical strength of the finally obtained brass alloy extruded material, the chromium content in the brass alloy powder may be increased, but the limit is 5.0 mass% from the viewpoint of production at the present time is there. The more preferable content of chromium is 1.0 to 2.4% by mass.

The chromium component forcibly dissolved in the matrix of brass suppresses the dislocation motion in the crystal and contributes to the improvement of the proof stress value. On the other hand, the chromium component precipitated at the grain boundaries suppresses grain boundary sliding to cause extreme work hardening and contributes to the improvement of tensile strength. The component dissolved in the matrix of brass includes a component dispersed and dispersed in the matrix and a component dispersed as a precipitate in the matrix.

The brass alloy powder may contain at least one element selected from the group consisting of nickel, manganese, zirconium, vanadium, titanium, silicon, aluminum and tin.

Preferably, the above-mentioned brass alloy powder is a rapidly solidified powder, more preferably a rapidly solidified powder by a water atomizing method.

The extruded brass alloy according to the present invention has a brass composition consisting of a mixed phase of α phase and β phase, contains 0.5 to 5.0% by mass of chromium, and the above chromium is in the matrix phase of brass. It is obtained by extruding an assembly of a brass alloy powder containing a component to be solid-solved and a component to be precipitated at grain boundaries.

In one embodiment, the 0.2% proof stress value of the brass alloy extruded material is 300 MPa or more. Moreover, tensile strength is 500 MPa or more.

In order to improve the machinability of the brass alloy extruded material, in one embodiment, the brass alloy extruded material is added after 0.2 to 2.0% by weight of graphite particles are added to and mixed with the brass alloy powder. Obtained by extruding this mixed powder aggregate. The particle size of the graphite particles to be added is preferably in the range of 1 μm to 100 μm.

A brass alloy member according to the present invention has a brass composition consisting of a mixed phase of α phase and β phase, contains 0.5 to 5.0% by mass of chromium, and further, nickel, manganese, zirconium, vanadium, titanium , At least one element selected from the group consisting of silicon, aluminum and tin. Chromium contains a component dissolved in the matrix of brass and a component precipitated in grain boundaries.

In one embodiment, the brass alloy member further includes graphite particles to improve the machinability of the brass alloy member.

The method for producing a brass alloy extruded material according to the present invention has a brass composition comprising a mixed phase of α phase and β phase, and rapidly solidifies a brass alloy powder containing 0.5 to 5.0% by mass of chromium. And extruding the assembly of the rapidly solidified brass alloy powder described above.

Preferably, the rapid solidification method is a water atomization method. The heating temperature at the time of extrusion processing is preferably 650 ° C. or less.

The manufacturing method in one embodiment includes the step of adding and mixing 0.2 to 2.0% by weight of graphite particles with respect to the brass alloy powder prior to extrusion processing.

The effects and the like provided by the configuration of the present invention, including the items described above, will be described in detail in the following items.

It is a SEM (scanning electron microscope) photograph which shows the powder produced by the water atomization method, (a) is 6/4 brass alloy powder of Cr-free addition, (b) is 6/4 of 0.5 mass% Cr addition. A brass alloy powder, (c) shows a 6/4 brass alloy powder with 1.0 mass% Cr added. It is a figure which shows the X-ray-diffraction result of the produced water atomization powder. It is a figure which shows the stress-strain curve of an extruded material. It is a figure which shows the structure | tissue photograph by the optical microscope of the extruded material, (a) is an extruded material of the brass alloy green compact billet added with 1 mass% Cr, (b) is a brass alloy green compact containing 0.5 mass% Cr. An extruded material of the body billet, (c) shows an extruded material of a brass alloy compacted billet without addition of Cr, and (d) shows an extruded material of a billet alloy-free billet made of Cr. It is a photograph which shows the SEM image of the extruded material of the brass alloy green compact billet of 1.0 mass% Cr addition. It is a figure which shows the relationship between the density | concentration of the chromium component solid-solved in the parent phase of brass, and a proof stress value. It is a figure which shows the relationship between the graphite particle addition amount and machinability.

[Novel brass alloy powder preparation method]
The inventors of the present invention examined a method for producing an unprecedented high strength free-cutting brass member by increasing the strength of brass itself as a base material. As a method of increasing the strength of brass, generally, a method of adding various additives is employed. For example, high-strength brass is obtained by adding iron, aluminum, manganese or the like to a copper-zinc alloy and has a high tensile strength of 460 MPa and good corrosion resistance, and thus is applied to propellers for ships and the like. However, this high strength brass is only guaranteed to have an elongation of about 15%, and it can not be said that the workability is never good.

In order to carry out alloy development with a view to adding graphite, it is necessary to produce a novel brass alloy powder which has never been available, and to extrude the aggregate of the powder to improve the strength. Conventionally, a melting process has been adopted for production of brass, but the present inventors attempted to produce a brass alloy of a new alloy composition by powder metallurgy instead of the melting process.

According to the water atomization method, which is a type of rapid solidification method, since the molten metal is rapidly solidified at a very high speed to produce a powder, not only non-equilibrium phase appears in the powder but also fine crystal grains There is a feature that can be obtained. The inventors of the present invention have newly proposed a powder having a property different from that of a conventional brass powder by adding a small amount of chromium (Cr) as a third element to a brass alloy composed of a mixed phase of α phase and β phase. To obtain a new material by extruding and solidifying the powder assembly by a hot extrusion method.

Many attempts have been made to improve properties by adding various additives to brass, but there has been no precedent of actively adding a transition element to 6/4 brass by water atomization.

The present inventors propose a new method for adding chromium, which is a refractory metal, to 6/4 brass. As described above, in order to melt brass and dissolve chromium therein, the molten metal must be heated to the melting point of chromium, but such heating temperature exceeds the boiling point of zinc. Therefore, practically, it can be said that it is impossible to heat liquid brass to the melting point of chromium in consideration of the high vapor pressure of zinc.

As another method for adding chromium to brass, it is conceivable to use a master alloy containing chromium. However, since the copper-chromium master alloy also has a high melting point, the method of adding brass to the melted copper also evaporates the zinc and can not maintain a predetermined composition.

The present inventors developed a brass alloy production method using a commercially available Cu-10% Cr master alloy. In the mother alloy, chromium is dispersed as grains of about 10 to 50 μm in size and is not necessarily in solid solution in copper. This mother alloy is first melted at about 1200 ° C. At this temperature, the chromium contained in the master alloy does not dissolve, and therefore, it floats in the liquid phase of copper as it is in solid phase. In this state, add copper and adjust the concentration of chromium to be thin. Then, when the chromium concentration reaches about 4%, the solid-liquid phase line in the phase diagram is crossed to be in the one-phase state of the liquid phase. In this way, chromium, which is a high melting point metal, could be made into a mixed liquid phase with copper. In this state, a predetermined amount of zinc was added, and when it was quenched and solidified by a water atomizing method, it was possible to obtain a powder having a non-equilibrium phase in which chromium was forcibly dissolved in brass.

It is also possible to force vanadium into solid solution in brass in the same manner as described above. However, in the binary phase diagram of vanadium and copper, since the solid-liquidus line has a vanadium concentration of about 0.5%, the amount of vanadium added is very small. Therefore, practically, addition of vanadium into brass is not only technically difficult but it is difficult to increase the effect of the addition.

According to the method developed by the present inventors, it is possible to appropriately control the composition of the alloy without evaporating the added zinc as much as possible. In 6/4 brass, it is known that the ratio of the α phase to the β phase changes due to a slight difference in the amount of zinc component. It is also known that the difference between the ratio of the α phase and the β phase affects the mechanical properties of the brass alloy.

Therefore, it is understood that the above-mentioned powder production method developed by the present inventors is an advantageous method for adding a high melting point metal to brass also from the viewpoint of composition control of brass alloy. In addition to this, the addition of relatively low melting point nickel and manganese increases the utility value as a powder which can further improve strength. Further, by adding graphite to the brass alloy powder thus obtained and extruding it, a lead-less machinable brass alloy excellent in strength and machinability can be obtained. As described above, since the application range of the present invention is wide, it can be said that the present inventors have paved the way to the development of various types of leadless brass having various mechanical properties.

The conventional method of grain refinement has been to repeat the plastic working and heat treatment on the member repeatedly, but if powder metallurgy is used as in the present invention, it is already refined as a starting material Since a powder having a crystalline structure is prepared, no special process for micronization is required. In addition, since the material composition is already determined in the powder state, the composition of the final product can be grasped at this stage. In addition to such production advantages, the material according to the invention has several excellent features as described below.

[Effect of addition of third element]
Usually, chromium hardly dissolves in brass. However, by adopting a rapid solidification method such as a water atomization method, chromium dissolved in a liquid phase is forcibly dissolved in a matrix of brass by a certain amount. In addition, with the growth of crystals in the process of solidification, part of chromium condenses at grain boundaries and precipitates as fine crystal grains. Strictly speaking, the component dissolved in the matrix of brass includes a component dispersed and dispersed in the matrix and a component dispersed as a precipitate in the matrix. The chromium component forcibly dissolved in the matrix and the chromium component precipitated at the grain boundaries exhibit different effects on the applied stress. That is, the chromium component forced to form a solid solution in the matrix suppresses the dislocation movement in the crystal and contributes to the improvement of the proof stress value of the brass alloy member. On the other hand, the chromium component precipitated at the grain boundaries suppresses grain boundary sliding to cause extreme work hardening, which greatly contributes to the improvement of tensile strength.

The effects of the addition of manganese are as follows. Manganese, unlike chromium, basically dissolves in brass. Therefore, manganese does not form intergranular precipitates and does not cause extreme work hardening, but acts to improve both the load resistance value and the tensile strength in a well-balanced manner. The reason is believed to be that manganese in solid solution in the matrix phase pinpoints dislocations.

The effects of the addition of nickel are as follows. Nickel also forms a solid solution completely in brass, but promotes the transformation from β phase to α phase in the process of hot extrusion of brass alloy, and forms a fine α phase in the crystal to greatly contribute to the improvement of proof stress . However, since nickel does not contribute to work hardening, the maximum tensile stress is almost the same as that of a powder extruded material to which no nickel is added.

Chromium, manganese and nickel are transition elements that appear in the fourth period of the periodic table, but as described above, their effects when added to brass are different from one another, and they exhibit completely different behavior. The reason is that each transition element strengthens brass by a different mechanism. Therefore, if two or more elements are added, it is considered that the respective effects are exhibited.

Furthermore, from the above-described research results, it has become possible to infer the behavior when other elements are added. Vanadium, a transition element of the fourth period of the periodic table, has an equilibrium diagram similar to chromium. Therefore, if vanadium is added by the same method as the addition of chromium to make atomized powder, the vanadium component which is forced to form a solid solution in the matrix and the vanadium component which precipitates in grain boundaries appear, and the same reinforcement as chromium The mechanism can improve the performance of brass.

In addition to the above elements, titanium, silicon, aluminum, tin, etc., which are generally known as reinforcement elements for brass, are also expected to work effectively for strengthening chromium-added brass as an additional additive element.

[Rapid solidification method]
In addition to the formation of non-equilibrium phase and fine crystal grains by producing a brass alloy powder by a rapid solidification method, a factor for the effects of the present invention to be prominent is a work hardening using grain boundary precipitation of chromium. The cause is The present inventors utilized the water atomization method as an example of the rapid solidification method. The characteristic of water atomized powder of 6/4 brass composition is that it becomes the beta phase of non-equilibrium phase. It will be described more specifically. In the rapid solidification process of the 6/4 brass alloy, the powder solidifies as a β phase because it is a β phase region beyond the solid-liquid line. If it is cooled slowly as it is, the phase transformation should be a mixed phase of α phase and β phase, but this phase transformation hardly occurs because of high quenching degree. When the temperature is raised in the process of hot working of the β phase powder, phase transformation from the β phase to the α phase occurs to become a mixed phase.

One kind of additive element exerts the effect of keeping the β phase stable. Chromium and manganese were found to have the effect of delaying the transformation to the alpha phase. This is an effect of suppressing atomic diffusion in crystal grains, and is considered to be highly effective in maintaining the non-equilibrium phase formed by rapid solidification.

In the present invention, the work-hardening phenomenon is manifested remarkably by the grain boundary precipitates in the solidification process suppressing the grain boundary sliding. Preferably, the size of grain boundary precipitates is controlled to a size (maximum length) of about 100 nm to 500 nm. Further, the dispersion state of the precipitates is also an important factor, and it is desirable that the raw material powder be homogeneous since it is ideal that the precipitates be uniformly dispersed in the structure. If it is an atomizing method as a powder production method, control of the solidification speed and the powder particle size accompanying it is easy.

[Extrusion processing]
The extrusion temperature is a very important factor in improving the strength of the brass alloy extruded material. The extrusion temperature is preferably as low as possible. In order to extrude the powder assembly, the powder needs to be heated. The higher the heating temperature, the faster the atomic diffusion, and the non-equilibrium phase produced by rapid solidification approaches the thermal equilibrium state. Therefore, it is important to extrude the brass alloy powder assembly at the lowest temperature that allows extrusion. The preferred extrusion temperature is 650 ° C. or less. It is difficult to determine the lower limit of the extrusion temperature. This is because the lower limit temperature is determined by the size of the extruded billet, the extrusion ratio, the maximum extrusion load of the apparatus, and the like. If extrusion at 500 ° C. is possible, the temperature is an appropriate condition, but in practice, it seems that 550 ° C. or more is required to carry out the extrusion process.

During extrusion, two factors, the temperature drop due to the heat dissipation of the billet and the temperature rise due to the extrusion pressure, affect the actual extrusion temperature. Therefore, it is not practical to define the extrusion temperature, but it is practical to control the heating temperature of the billet. In the brass extrusion experiment, when the heating control temperature of the billet was 650 ° C., it took 48 seconds to start extrusion. In view of the data obtained in the simulation, the extrusion start temperature at this time is 577 ° C.

The present inventors have found that a material of higher strength can be obtained by controlling the extrusion rate at the time of extruding a chromium-containing brass alloy powder aggregate. As extrusion conditions for obtaining a material of higher strength, extrusion at low temperature is effective, and further improvement in strength can be expected by reducing the extrusion speed. This point will be described later based on the experimental results.

In order to improve the machinability of the brass alloy extruded material, graphite particles may be added to and mixed with the chromium-containing brass alloy powder, and this mixed powder aggregate may be extruded. In order to exhibit the effect of improving the machinability, it is necessary to add 0.2 to 2.0% by weight of graphite particles to the chromium-containing brass alloy powder. The particle size of the additive graphite particles is preferably in the range of 1 μm to 100 μm.

[Amount of addition of element]
The amount of addition of the third element is appropriate for the various elements.

With respect to chromium, an improvement in the proof stress value was observed by the addition of 0.5% by mass. When the addition amount of chromium was further increased to 1% by mass, no difference was found in the proof stress value, but the tensile strength showed a very high value. Therefore, the addition amount of chromium is preferably 0.5% by mass or more, more preferably 1.0% by mass or more.

The upper limit value of the chromium content is 5.0% by mass. Due to limitations at the powder production stage, the upper limit of the chromium concentration in the copper-chromium liquid phase state is 4%. When zinc is added here, the chromium content is 2.4% by mass. It is possible to increase the chromium content by raising the melting temperature of copper-chromium. For example, when the dissolution temperature is raised to 1300 ° C., chromium can be dissolved to a concentration of 8%, and the chromium content when zinc is added is 5.0 mass%. However, at this temperature, the vapor pressure of zinc becomes too high, making composition control difficult. Therefore, the upper limit value of the more preferable chromium content is 2.4 mass%.

Even with a very small amount of vanadium, intergranular precipitation occurs. Considering that the upper limit of the concentration of vanadium in the liquid phase of copper-vanadium is 0.5%, vanadium should be added to the vicinity of the upper limit in order to make the most of the effect of vanadium. In that case, the concentration of vanadium is 0.3% by mass by the addition of zinc. In order to make the concentration of vanadium higher than this value, it is necessary to raise the melting temperature. However, at temperatures above 1200 ° C., the vapor pressure of zinc becomes too high, making it difficult to make a powder with an optimal composition. Therefore, the effect of the addition of vanadium can not but be limited, and strengthening in combination with other elements is required.

There are many research examples on the effects obtained by adding manganese to brass, and it has been put to practical use as high manganese brass. In the present invention, the brass alloy can be further strengthened by supplementarily adding manganese in combination with the above chromium addition or chromium and vanadium addition. As the addition amount of manganese, it was confirmed that a sufficient effect can be obtained at 0.5% by mass. According to conventional research examples, it has been recognized that increasing the added amount of manganese significantly reduces the processability of the material, so the preferable upper limit of the added amount of manganese is 7% by mass or less which is a range in which no compound is formed It is. The more preferable addition amount of manganese is 1 to 3% by mass, and when the amount is exceeded, the elongation may be reduced, which may result in the deterioration of the processability of brass.

Since nickel is completely dissolved in copper, it can be alloyed by adding an arbitrary amount in the Cu—Zn—Ni system. Therefore, in the present invention, there is no upper limit in particular about the addition amount of nickel. The addition of nickel has a special effect of increasing only the proof stress value, and a proof stress value exceeding 300 MPa can be realized with an addition amount of 1% by mass.

From the practical point of view of the alloy members, it goes without saying that the proof stress is more important than the tensile strength. The greatest effect of the present invention is the inclusion of a predetermined amount of chromium in 6/4 brass, but the addition of more nickel provides more advantages. Since chromium has a high melting point, it is not easy to add even trace amounts. The use of thermal equilibrium in metallurgy has already been described as a means of overcoming this. Naturally, both elements should be added to simultaneously exhibit the effects of chromium and nickel. There is an easier method as an addition method in this case. That is, in order to add only chromium, the process described above is to be taken, but in order to add also nickel at the same time, it is preferable that the mother alloy initially contains chromium and nickel.

Nickel-chromium alloys are commercially available and their melting point is lowered to 1345 ° C. by alloying. It is possible to melt this alloy and copper using a high frequency furnace. Although the mixing ratio of nickel to chromium is 1: 1, the melt can be made much easier than manufacturing using a copper-chromium master alloy. If it is carried out to add nickel using this method, the preferable upper limit of the amount of added nickel is 2.4% by mass like chromium.

It is possible to increase the amount of nickel added by changing the mixing ratio of nickel and chromium in the mother alloy. Since increasing the chromium content in the mother alloy rapidly increases the melting point, the difficulty of powder production is increased, but even if the ratio of nickel is increased, the melting point does not increase much and does not exceed the melting point of nickel. Therefore, it is possible to make a nickel-rich powder, and it is possible to increase the amount of nickel added. The upper limit of the amount of addition of nickel is not particularly limited, but it is desirable to keep the addition of 5% by mass or less as a range that does not impair the characteristics as brass. If the content of nickel is in this range, it is possible to make an alloy having desired mechanical properties, and it becomes applicable to a wide range of application.

With respect to the other additive elements, the additive effect is exhibited at about several percent, at least 0.1% or more. The appropriate amounts and combinations of various elements differ depending on the mechanical properties to be obtained. From the viewpoint of improving the strength, zirconium exhibits a grain refining effect, so even if it is added at 0.1%, its effect is sufficiently recognized, and it can be said from the hole-pitch's rule of thumb that it is a clear strengthening element.

Titanium, aluminum and the like increase the strength of the matrix by solid solution strengthening, and therefore the addition of a small amount of 1% or less exerts the effect.

Silicon is usually an element used for dispersion strengthening, and addition of about 3% is an appropriate amount. However, due to the balance with other elements, addition may not always lead to strengthening. In particular, in the alloy system of the present invention, if the chromium precipitation site and the silicon dispersion site are at the same location, the strengthening effect can not be obtained. Therefore, the addition amount of silicon is in a relation of being limited by the addition amount of chromium, and it can be said that the total amount of chromium and silicon is 3% or less.

Tin forms a solid solution at about 0.3% to exhibit the effect as a strengthening element, but when the addition amount is increased, a γ phase appears, which causes embrittlement, and a large amount addition is not preferable, 0.1 It can be said that the range of% to 0.5% is preferable.

[Preparation of powder]
From a Cu-40% Zn brass material, a Cr additive-free brass powder, a 0.5 wt% Cr-added brass powder, and a 1.0 wt% Cr-added brass powder were prepared by a water atomizing method. The chemical composition of the powder is shown in Table 1, and a SEM (Scanning Electron Microscope) photograph of the appearance of the powder is shown in FIG. (A) of FIG. 1 shows 6/4 brass alloy powder which does not add Cr, (b) shows 6/4 brass alloy powder which added 0.5 mass% Cr, (c) is 1. The 6/4 brass alloy powder which added 0 mass% Cr is shown.

The X-ray-diffraction result of the produced powder is shown in FIG. Only the β phase was detected in the Cr-free brass alloy powder and the brass alloy powder to which 0.5% by mass of Cr was added. In the brass alloy powder to which 1.0 mass% of Cr was added, two phases of α phase and β phase were detected. In the case of the 6/4 brass composition, when the liquid phase is crossed the solid-liquid line, it becomes a β phase, and the rapidly solidified powder is generally cooled without α transformation. As a result of investigating in detail the brass alloy powder of 1.0 mass% Cr addition, it was a mixed state of alpha phase powder and beta phase powder. It is considered that a difference in cooling rate occurs in the individual powders in the process of atomization, and an α-transformed powder is formed. In addition, since Cr exists as fine particles, a clear diffraction peak was not detected in X-ray diffraction.

[Extrusion of 1.0 mass% Cr-added brass alloy powder]
A powder of composition 59% Cu-40% Zn-1% Cr prepared by a water atomizing method was pressed at 600 MPa to make a billet for extrusion. The billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were set to four types of 650 ° C., 700 ° C., 750 ° C. and 780 ° C. The billet was processed by an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

A tensile test specimen having a distance between scores of 10 mm and a waist circumference of 3 mm was cut out of the bar and subjected to a tensile test to measure a 0.2% proof stress value and a maximum tensile strength. The results are shown in Table 2.

As apparent from the results in Table 2, the billet was heated to a temperature of 650 ° C. and extruded showed high values in maximum tensile strength and 0.2% proof stress value. These mechanical strengths tended to decrease as the heating temperature was raised. Therefore, as for the heating temperature of the billet before extrusion, 650 degrees C or less is desirable.

[Extrusion of brass alloy powder with 0.5 mass% Cr added]
A powder of composition 59.5% Cu-40% Zn-0.5% Cr prepared by a water atomizing method was pressed at 600 MPa to make a billet for extrusion. The billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were set to four types of 650 ° C., 700 ° C., 750 ° C. and 780 ° C. The billet was processed by an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

A tensile test specimen having a distance between scores of 10 mm and a waist circumference of 3 mm was cut out of the bar and subjected to a tensile test to measure a 0.2% proof stress value and a maximum tensile strength. The results are shown in Table 3.

As apparent from the results in Table 3, the billet heated at a temperature of 650 ° C. and extruded showed high values in maximum tensile strength and 0.2% proof stress value. These mechanical strengths tended to decrease as the heating temperature was raised. Therefore, as for the heating temperature of the billet before extrusion, 650 degrees C or less is desirable.

Further, as understood from comparison with the results in Table 2, regarding the 0.2% proof stress value, the values of 0.5% Cr addition and 1.0% Cr addition showed substantially the same value. Therefore, it was found that the proof stress is maintained even if the amount of chromium added is small. However, the maximum tensile strength decreases as the amount of chromium decreases. While this shows that the proof stress value is determined by the amount of chromium which is forced to form a solid solution, the maximum tensile stress supports the increase of the degree of work hardening due to the precipitation of excess chromium at grain boundaries.

[Extrusion of 1.0% by mass Ni-added brass alloy powder]
A powder of composition 59% Cu-40% Zn-1.0% Ni prepared by a water atomizing method was pressed at 600 MPa to make a billet for extrusion. The billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were set to four types of 650 ° C., 700 ° C., 750 ° C. and 780 ° C. The billet was processed by an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

A tensile test specimen having a distance between scores of 10 mm and a waist circumference of 3 mm was cut out of the bar and subjected to a tensile test to measure a 0.2% proof stress value and a maximum tensile strength. As a result, the one obtained by heating and extruding the billet at 650 ° C. had a 0.2% proof stress value of 311 MPa and a maximum tensile strength of 479 MPa. These mechanical strengths tended to decrease as the heating temperature was raised. Therefore, as for the heating temperature of the billet before extrusion, 650 degrees C or less is desirable.

Extrusion of 0.7 mass% Mn-added brass alloy powder
A powder of composition 59% Cu-40% Zn-0.7 %% Mn prepared by a water atomizing method was pressed at 600 MPa to make a billet for extrusion. The billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were set to four types of 650 ° C., 700 ° C., 750 ° C. and 780 ° C. The billet was processed by an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

A tensile test specimen having a distance between scores of 10 mm and a waist circumference of 3 mm was cut out of the bar and subjected to a tensile test to measure a 0.2% proof stress value and a maximum tensile strength. As a result, the one obtained by heating and extruding the billet at 650 ° C. had a 0.2% proof stress value of 291 MPa and a maximum tensile strength of 503 MPa. These mechanical strengths tended to decrease as the heating temperature was raised. Therefore, as for the heating temperature of the billet before extrusion, 650 degrees C or less is desirable.

[Extrusion of Cr-free brass alloy powder]
A powder of composition 60% Cu-40% Zn prepared by a water atomizing method was compressed at 600 MPa to be a billet for extrusion. The billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were set to four types of 650 ° C., 700 ° C., 750 ° C. and 780 ° C. The billet was processed by an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

A tensile test specimen having a distance between scores of 10 mm and a waist circumference of 3 mm was cut out of the bar and subjected to a tensile test to measure a 0.2% proof stress value and a maximum tensile strength. The results are shown in Table 4.

As apparent from the results in Table 4, the billet heated at a temperature of 650 ° C. and extruded showed high values in maximum tensile strength and 0.2% proof stress. These mechanical strengths tended to decrease as the heating temperature was raised. Therefore, as for the heating temperature of the billet before extrusion, 650 degrees C or less is desirable.

[Extrusion of billet of molten material of brass alloy without addition of Cr]
The ingot billet of composition 60% Cu-40% Zn was heated in an electric furnace for extrusion processing. The temperature conditions of the heating electric furnace were four kinds of 650 ° C., 700 ° C., 750 ° C. and 780 ° C. The billet was processed by an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

A tensile test was carried out by cutting a tensile test specimen having a distance between scores of 10 mm and a waist circumference of 3 mm from the bar. As a result, the one obtained by heating and extruding the billet at 650 ° C. had a 0.2% proof stress value of 226 MPa and a maximum tensile strength of 442 MPa.

[Comparison of maximum tensile strength and 0.2% proof stress value]
The maximum tensile strength and the 0.2% proof stress value of extruded brass alloys extruded by heating various billets to a temperature of 650 ° C. were compared and are shown in Table 5. Also, the stress-strain curve of the extruded material is shown in FIG. The billets compared were a molten billet of a brass alloy with no addition of Cr, a brass alloy green compact billet without a Cr addition, a brass alloy green compact billet with 0.5% Cr addition, a brass alloy with a 1.0% Cr addition There are four types of powder billets.

From FIG. 3 and Table 5, the following can be understood. First, comparing two types of the Cr-free brass alloy billet, the powder billet exhibits higher numerical values in both of the maximum tensile strength and the 0.2% proof stress value than the molten billet. Specifically, by using a green compact billet, the maximum tensile strength is improved by 5.4%, and the 0.2% proof stress value is improved by 20.7%. From this point of view alone, the superiority of powder metallurgy is clear.

Further, comparing a green compact billet to which 1.0% by mass of chromium is added and a molten billet to which Cr is not added, the extruded material of the green compact billet to which 1.0 mass% of Cr is added has the maximum tension The strength is improved by 27.8%, and the 0.2% proof stress value is improved by 40.2%. It is considered that the fact that the 0.2% proof stress value is greatly improved is the solid solution strengthening by the forced-solid solution chromium.

In addition, it is recognized that the maximum tensile strength of the powder billet added with Cr is greatly improved as compared to the powder billet with no addition of Cr. This is because, during the solidification process of the powder production process, chromium which did not form a solid solution is concentrated at grain boundaries to cause segregation of chromium at grain boundaries, resulting in spherical precipitates having a diameter of about 100 nm to 500 nm. It is considered that the cause is mainly existing at grain boundary triple points and grain boundaries. Such fine precipitates act as a large resistance to grain boundary sliding during plastic deformation, and as a result, exhibit a high degree of work hardening.

[Organization observation result]
The structure observation result by an optical microscope of the extruded material extruded at a heating temperature of 650 ° C. for the billet is shown in FIG. (A) of FIG. 4 is an extruded material of a brass alloy green compact billet added with 1 mass% Cr, (b) is an extruded material of a brass alloy green compact billet added with 0.5 mass% Cr, (c) is Cr. An extruded material of the additive-free brass alloy green compact billet, (d) shows an extruded material of the additive-free billet brass alloy infused with Cr.

As apparent from comparison and observation of the photograph of FIG. 4, the powder billet extruded material has finer crystal grains as compared with the molten billet extruded material. In the case of a billet extruded material made of brass alloy melt, the grain size is 3 to 10 μm, whereas the grain size of a brass alloy compacted billet extruded material with no Cr added is as fine as 1 to 6 μm. Further, in the case of using a Cr-added brass alloy green compact billet extruded material, it is recognized that the grain size is progressing to further submicron to 5 μm.

With grain refinement, the resistance value increased according to Hall-Petch's rule of thumb. In the structure of the Cr additive, fine precipitates of 1 μm or less in the form of black dots were observed at grain boundaries. As a result of EDS analysis, it was identified that these precipitates were Cr.

FIG. 5 shows an SEM image of an extruded material of a 1% by mass Cr-added brass alloy green compact billet.

In the above description, the brass alloy powder or brass alloy powder extruded material is mainly described, but the present invention is also applicable to a brass alloy member. That is, the brass alloy member has a brass composition composed of a mixed phase of α phase and β phase, contains 0.5 to 5.0% by mass of chromium, and further, nickel, manganese, zirconium, vanadium, titanium, silicon, It contains at least one element selected from the group consisting of aluminum and tin.

[Increase in yield stress (YS)]
It is recognized that the addition of chromium increases the yield stress of the brass alloy member, and the contribution to the increase of the yield stress is, among the chromium, chromium which is dispersed and dispersed in the matrix of brass in particular. It is an ingredient. Using the result of the structure analysis, the amount of chromium dissolved in the matrix was calculated from the amount of chromium added by quantifying the precipitates.

The difference between the yield stress of the chromium-free brass alloy member and the yield stress of the chromium-added brass alloy member is represented on the vertical axis, and the concentration (%) of the chromium component in solid solution in the matrix is represented on the horizontal axis. Is FIG. The increase in yield stress was 34 MPa when the solid solution amount of chromium was 0.22%, and the increase amount of yield stress was 54 MPa when the solid solution amount of chromium was 0.35%. Thus, it was found that the yield stress increased in proportion to the concentration of chromium in solid solution in the matrix of brass.

[Improvement of machinability by addition of graphite particles]
In the production of a brass alloy extruded material by powder extrusion, it is possible to make it lead-free and suppress an adverse effect on the environment by adding graphite particles. Although the addition of graphite to general brass has been made in the past, there is no precedent to the addition of graphite to a brass alloy whose strength has been improved by the addition of chromium. Therefore, we tried to improve the machinability by adding graphite to brass whose strength was improved by chromium addition.

The average particle size of the graphite particles used was 5 μm. The chromium-containing brass powder produced by the water atomizing method and the graphite particles were mixed by a mechanical stirring method. This mixed powder was made into a powder compact billet in the same manner as the above-mentioned method, and subjected to hot extrusion processing to obtain a bar. The amount of graphite particles to be added was three types of 0.5 wt%, 0.75 wt% and 1.0 wt% with respect to the chromium-containing brass alloy powder.

FIG. 7 is a graph showing the relationship between the amount of graphite particles added and the machinability. It was found that when the graphite particles were added to the chromium-containing brass alloy powder and extrusion processing was performed, the machinability was dramatically improved. Evaluation of machinability was performed by measuring the test time of the penetration test by a drill. The test piece was a round bar cut to a length of 5 cm, which was subjected to a penetration test with a drill diameter of 4.5 mm. A load of 1.3 kgf was applied to the drill, and the spindle rotational speed was 900 rpm. Ten tests were conducted, and the time required for penetration was averaged and displayed in the graph of FIG.

In the test piece to which no graphite was added, the drill did not penetrate at all even when cutting for 180 seconds or more. As the cutting progress of the drill appeared to stop, we decided to stop the test there for those that did not penetrate in 180 seconds.

The relationship between the amount of graphite added and the time required for drill penetration was investigated. In the 0.5% chromium-containing brass alloy, the drill penetrated in a time of an average of 28 seconds at a graphite addition amount of 0.5%, though it was 180 seconds or more when no graphite was added. When the amount of graphite added was 0.75% or more, the penetration time was 20 seconds or less, and a drastic improvement in the machinability was observed. Therefore, in the case of a 0.5% chromium-containing brass alloy, it can be said that the addition of 0.75% or more of graphite is a condition suitable for greatly improving the machinability.

In the 1.0% chromium-containing brass alloy, the penetration time was 180 seconds or more even when 0.5% of graphite was added. The drill penetration occurred in an average of 38 seconds as the graphite loading was increased to 0.75%. In addition, when the amount of graphite added was 1.0%, the penetration time was 20 seconds or less. Therefore, in the case of a 1.0% chromium-containing brass alloy, it can be said that the addition of 1.0% or more of graphite is a suitable condition for greatly improving the machinability.

[Strength improvement by low speed extrusion]
The present inventors have found that by controlling the extrusion rate of the chromium-containing brass alloy, a higher strength material can be obtained. As extrusion conditions for obtaining high strength materials, extrusion at low temperature is effective, but by further reducing the extrusion speed, the strength can be further improved. In the case of a 1.0% chromium-containing brass alloy, the proof stress value is 317MPa and the maximum tensile strength is 565MPa when extruded at a normal extrusion speed (ram speed 3 mm / s). When extrusion was carried out by reducing the extrusion speed to one tenth (ram speed 0.3 mm / s), the yield strength was improved to 467 MPa and the maximum tensile strength was improved to 632 MPa.

Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to the illustrated embodiments. Various modifications and variations can be made to the illustrated embodiment within the same or equivalent scope of the present invention.

The present invention can be advantageously utilized in the manufacture of 6/4 brass alloy members having excellent mechanical properties.

Claims (17)

1. It is a brass alloy powder having a brass composition consisting of a mixed phase of α phase and β phase,
   Containing 0.5 to 5.0% by mass of chromium,
   The above-mentioned chromium is a brass alloy powder including a component which is solid-solved in a matrix phase of brass and a component which is precipitated in crystal grain boundaries.
2. The brass alloy powder according to claim 1, wherein the component dissolved in solid solution in the matrix of brass includes a component dispersed in solid solution in the matrix and dispersed therein, and a component dispersed as precipitate in the matrix.
3. The brass alloy powder according to claim 1, wherein the content of the chromium is 1.0 to 2.4% by mass.
4. The brass alloy powder according to claim 1, wherein the powder contains at least one element selected from the group consisting of nickel, manganese, zirconium, vanadium, titanium, silicon, aluminum and tin.
5. The brass alloy powder according to claim 1, wherein the powder is a rapidly solidified powder.
6. The brass alloy powder according to claim 5, wherein the rapidly solidified powder is a powder which is rapidly solidified by a water atomizing method.
7. It has a brass composition consisting of a mixed phase of α phase and β phase, contains 0.5 to 5.0% by mass of chromium, and the above-mentioned component of chromium forms a solid solution in the matrix of brass and precipitates at grain boundaries An extruded material of brass alloy obtained by extruding an assembly of brass alloy powder containing the following components.
8. The brass alloy extruded material according to claim 7, having a 0.2% proof stress value of 300 MPa or more.
9. The brass alloy extruded material according to claim 7, having a tensile strength of 500 MPa or more.
10. The brass alloy extrusion according to claim 7, obtained by extruding the mixed powder aggregate after adding and mixing 0.2 to 2.0 wt% of graphite particles with respect to the brass alloy powder. Material.
11. The brass alloy extruded material according to claim 10, wherein a particle diameter of the additive graphite particles is in a range of 1 μm to 100 μm.
12. It has a brass composition consisting of a mixed phase of α phase and β phase, contains 0.5 to 5.0% by mass of chromium, and further comprises nickel, manganese, zirconium, vanadium, titanium, silicon, aluminum, and tin A brass alloy member containing at least one selected element, a component in which the chromium is solid-solved in a matrix of brass, and a component precipitated in crystal grain boundaries.
13. The brass alloy member according to claim 12, further comprising graphite particles.
14. producing a brass alloy powder having a brass composition consisting of a mixed phase of α phase and β phase and containing 0.5 to 5.0% by mass of chromium by a rapid solidification method;
    And extruding the assembly of the rapidly solidified brass alloy powder.
15. The method for producing a brass alloy extruded material according to claim 14, wherein the rapid solidification method is a water atomization method.
16. The method for producing a brass alloy extruded material according to claim 14, wherein the heating temperature at the time of the extrusion processing is 650 ° C or less.
17. The method for producing a brass alloy extruded material according to claim 14, comprising the step of adding and mixing 0.2 to 2.0% by weight of graphite particles with respect to the brass alloy powder prior to the extrusion processing.
    
    

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