KR20130012643A - Brass alloy of unleaded free cutting with advanced corrosion resistance and superplastic formability and shape memory ability - Google Patents

Abstract

PURPOSE: An unleaded free-cutting brass alloy of which the corrosion-resistance, plastic processability, and shape-memorability are improved is provided to provide a more close and stable bindability, and an extended lifetime because the brass alloy has shape-restorability depending on the temperature change when applying to household materials, many kinds of pipes, and coupling members. CONSTITUTION: An unleaded free-cutting brass alloy comprises 56-58% of Cu, 0.5-1.5% of Sn, 0.2-0.3% of Fe, 0.1-0.2% of Sb, 1.5-2.0% of Ni, 0.04-0.08% of P, 0.8-1.2% of Al, 1.0-1.2% of S, 1.3-1.5% of Bi, 0.1-0.2% of Se, and remnant Zn as basic components. The unleaded free-cutting brass alloy is that Ti is added to the basic components in an identical ratio of Ni, and V, Cr, Mn, and Co are further added to the same in a ratio of 1:1:1:1 within a range of 0.02-0.04 wt%. 0.02-0.04 wt% of Si is further added to the basic components in order to highly improve abrasion-resistance. The unleaded free-cutting brass alloy is that the basic components, to which Ni and V, Cr, Mn, and Co are added, is applied with plastic deformation at a martensitic transformation point, and then, after reheating it to a higher temperature than the temperature at which inverse transformation to a mother phase occurs, is heat-treated so that a face-centered cubic structure of α-phase coexists with a body-centered cubic structure of β-phase at an ambient temperature.

Description

BRASS ALLOY OF UNLEADED FREE CUTTING WITH ADVANCED CORROSION RESISTANCE AND SUPERPLASTIC FORMABILITY AND SHAPE MEMORY ABILITY}

The present invention relates to a lead-free free-cut brass alloy having excellent cutting properties without containing lead, in particular, in addition to excellent cutting properties, excellent corrosion resistance, plastic workability and shape memory properties can be usefully used for living materials, piping equipment, fixing members, and the like. The present invention relates to a lead-free free-cut brass alloy which has been improved.

Brass is a representative nonferrous metal, and is a binary alloy of copper and zinc, and 7: 3 brass and 6: 4 brass, which contain 30-40% of zinc, are widely used.

Such brass has excellent castability, processability and corrosion resistance compared to copper, and is inexpensive compared to bronze, and is beautifully used in automobile parts, shelling materials or various castings because of its beautiful color.

Brass has different physical properties depending on the zinc content. For example, when the zinc content is lower than 34%, the electrical and heat conductivity decreases, and when it is higher, it rises and reaches its maximum value when it reaches 50%. However, when 40% or more of zinc is contained, it should be processed in consideration of chemical properties such that natural cracks occur when residual stresses exist in processed materials such as pipes and rods.

The mechanical property of brass is the maximum elongation when 30% of zinc is contained, the maximum tensile strength up to 40% instead of decreasing the elongation above 35%.

These brasses have high ductility, so they include tin and tombac containing 8-20% of zinc, which are mainly used for gold bars and ornaments. Lead brass, which is called free cutting brass and has high machinability, iron brass, which has high toughness and corrosion resistance by containing iron, and castability and workability. Strong brass, Fe, Ni, Sn, etc. are added to the appropriate amount, called "silver white" or "yang silver", including nickel, wire and plate material used in the manufacture of springs, ornaments, tableware, furniture materials, measuring instruments, medical equipment, etc. Nickel brass and the like.

Among these, free cutting brass (lead brass), which is suitable for manufacturing precision processed products with excellent cutting property, is widely used for bolts, nuts, door handles, plumbing fixtures, faucets, etc. in connection with real life, and thus its utilization is very high.

However, this free cutting brass has been steadily raised the human hazard problem because it is necessary to add lead and cadmium in order to increase the machinability, especially the new brass that can be replaced by the designation as a material that is restricted to use due to the recent environmental regulations Development of the composition was required.

Thus, various types of research have been repeated, for example:

First, heterogeneous particles which are not dissolved in copper base such as graphite powder or BN powder are uniformly dispersed in copper alloy by forcibly adding and stirring in copper (Cu) molten metal. It is difficult, and the processing surface by peeling of dissimilar particles becomes rough and there is a problem in plating property.

Second, bismuth (Bi) is added to Pb and the adjacent elements on the periodic table. Bismuth is used as an element that has no solid solubility in the copper base and is not harmful to the human body, but bismuth forms coarse grains and shrinks. It tends to cause pores and severe grain boundary segregation, which causes brittleness of copper alloys, and has a drawback that the grains have to be refined and spheroidized by heat treatment.

Third, bismuth (Bi) is added to bismuth and alloy elements having low melting point process composition. In this method, the crystallized phase is often crystallized at the grain boundary in the form of a thin film, which impairs cutting processability and inhibits the processing surface. There is a concern.

Fourthly, selenium (Se) is a method of adding selenium to form various intermetallic compounds with fine crystallization at grain boundaries, and it is known to improve processability even at a small amount of less than 1%. When used alone, vaporization generates toxic fumes, which limits their use.

Fifth, selenium (Se) is added in the form of bismuth-selenide to prevent the toxicity of selenium and to form bismuth and selenide evenly in the grain boundary and in the mouth to improve processability, but it is known that rod, plate, thin film, etc. It is hard to obtain the effect of improving the machinability and properties compared to the conventional brazed brass (= free-cut brass).

In this regard, there is a domestic development technology, there is a registered patent No. 0389777, in this case it is a trace amount but still using lead, it is difficult to be considered as lead-free brass, and another example there is a registered patent No. 092369, but this has a disadvantage of poor plastic workability .

As another example, there is Patent Publication No. 2004-0062314, and many other patent technologies including Patent Publication No. 2007-0101915, Patent Publication No. 2007-0101916, and Patent Publication No. 2009-0083444 vary depending on the application. It has been disclosed as.

Nevertheless, it is excellent in corrosion resistance, cutting property, plastic processing ability and shape resilience without using lead, so it is suitable for all kinds of living materials, joining members that require close bonding and fixing property, and piping equipment to extend product life. The necessity of lead-free free-cutting brass alloys to increase the safety, and to block the harmfulness has been raised.

The present invention has been created due to the above-mentioned necessity of the prior art, and it is lead-free brass, which does not contain lead, and has excellent machinability, that is, machinability and corrosion resistance is equal to or higher than that of existing brass-containing brass, and in addition, excellent in plastic workability and shape memory. Its main purpose is to provide an advanced lead-free, free-cut brass alloy that enhances the lifespan and safety (inhibiting cracking) of life materials, plumbing fixtures, joints or fastening members.

The present invention as a means for achieving the above object, in a lead-free free-cut brass alloy; The lead-free free-cut brass alloy is in weight percent, Cu: 56-58%, Sn: 0.5-1.5%, Fe: 0.2-0.3%, Sb: 0.1-0.2%, Ni: 1.5-2.0%, P: 0.04-0.08 Lead-free corrosion resistance, plasticity and shape memory, characterized in that the composition is composed of%, Al: 0.8-1.2%, S: 1.0-1.2%, Bi: 1.3-1.5%, Se: 0.1-0.2% and the balance Zn Provides free cutting brass alloys.

In addition, the present invention is a lead-free free-cut brass alloy; The lead-free free-cut brass alloy is in weight percent, Cu: 56-58%, Sn: 0.5-1.5%, Fe: 0.2-0.3%, Sb: 0.1-0.2%, Ni: 1.5-2.0%, P: 0.04-0.08 Based on the composition consisting of%, Al: 0.8-1.2%, S: 1.0-1.2%, Bi: 1.3-1.5%, Se: 0.1-0.2% and the balance Zn; In addition to the basic component, Ti is further added in the same ratio as Ni, and V, Cr, Mn, and Co are further added in a ratio of 1: 1: 1: 1 within a range of 0.02-0.04% by weight. It also provides lead-free free-cut brass alloys with improved corrosion resistance, plasticity and shape memory.

In addition, the addition of 0.02-0.04% by weight of Si to the basic component further improves the wear resistance.

In addition, the lead-free free-cut brass alloy is heat-treated so that the α phase of the face-centered cubic structure and the β-phase of the body-centered cubic structure coexist at room temperature after reheating above a temperature at which the plastic deformation is applied at the martensite transformation point and then reversely transformed into the mother phase. It also has its features.

According to the present invention, it does not contain lead and is harmless to the human body, and the cutting property and corrosion resistance are equal to or higher than the free cutting brass, and in particular, the material is more closely and stable due to the shape restoring property according to the temperature change when used in living materials, pipes, and coupling members. The effect of providing a binding force and extending the life can be obtained.

Hereinafter, preferred embodiments according to the present invention will be described in detail.

The lead-free free-cut brass alloy with improved corrosion resistance, plastic workability and shape memory according to the present invention is Cu: 56-58%, Sn: 0.5-1.5%, Fe: 0.2-0.3%, Sb: 0.1-0.2% Based on Ni, 1.5-2.0%, P: 0.04-0.08%, Al: 0.8-1.2%, S: 1.0-1.2%, Bi: 1.3-1.5%, Se: 0.1-0.2% and the balance Zn It is made with an ingredient.

In addition, the present invention further adds Ti to the base component in the same ratio as Ni to increase the superplastic formability and shape memory (Shape Memory Ability), and V, Cr, Mn, Co 0.02-0.04 It is made up in the form of adding more evenly in the range of the weight%, ie, 1: 1: 1: 1.

At this time, the basic components are known components contained in many lead-free free-cut brass alloy so far, but in the present invention, the existing components but different composition ratios in order to achieve the object specificity, while changing the composition ratio, cutting, corrosion resistance compared to conventional Maintaining the equivalent or more, in addition to the plastic workability and shape resilience (moulding resistance) features that feature.

In addition, 0.02-0.04% by weight of Si may be further added to the component composition, which is intended to improve wear resistance, but should be limited to the above range because excessively inhibiting machinability.

In general, brass has various kinds of third components added to improve physicochemical or mechanical properties or colors. For example, additive elements for improving corrosion resistance are mainly Sn, Al, Si, Fe, Mn, and Ni. Etc. are used.

Here, Mn will be described as focusing on the shape memory rather than the corrosion resistance as described above, so the rest of the components are related to the corrosion resistance.

These third components are dissolved in the α phase or β phase of the brass to improve the corrosion resistance by controlling the ratio of the α phase or β phase without significantly changing the structure of the brass.

In addition, attention should be paid to the composition of brass, which is a dezincification corrosion phenomenon, which may occur when 15% or more of zinc is added, and Mn and Fe accelerate this phenomenon.

On the other hand, As, Ni, Al, Sb, P, W, etc. reduce this phenomenon, it is very important to control the appropriate ratio between them.

In addition, in the patent technologies disclosed previously, elements such as Fe, Si, and Mn are inevitably added as impurities, but in the present invention, although these components are trace amounts, they participate as essential components necessary for the expression of mechanical properties. There is a difference.

On the other hand, the shape memory implemented in the present invention means shape resilience, it is derived from the shape memory alloy.

In general, shape memory alloy refers to an alloy having a property of remembering a shape at a constant temperature and then returning to its original shape even if the shape is deformed and heated again to a certain temperature even if the shape is deformed. The shape is remembered as an atomic array, and when the temperature rises again, it occurs as a result of rearrangement to the original atomic arrangement.

In the present invention, rather than a concept that is completely contained in the shape memory alloy, it has such a function, for example, a function that can reduce the occurrence of cracks, and extend the life by adding shape memory, that is, shape resilience in the pipe, such as cold and hot cross It is intended to have elasticity in concept.

To this end, in the present invention, Ti is further added to the base component, and the amount of Ti is added in the same ratio as Ni to increase the shape memory, and in addition, the V, Cr, Mn, and Co are the same in order to further increase the shape resilience. The ratio is further added, and in that state, plastic deformation is applied at a number of heat treatment techniques such as solutionization, forced cooling, air cooling, crystallization, and recrystallization, especially martensite, and then transformed into the matrix phase. It is made in the form of heating above the temperature, through which the composition according to the present invention is processed to coexist in the α and the β phase of the body-centered cubic structure at room temperature in addition to the shape memory can be improved along with the plastic workability.

At this time, the V, Cr, Mn, Co contributes to widen the coexistence region of the α phase and β.

Then, the reason for limitation of the composition ratio which concerns on this invention is demonstrated.

[Cu: 56-58 wt%]

Cu is an essential component in brass alloy, in view of stress corrosion cracking resistance in the present invention should be added in the above range.

In particular, Cu changes the metal structure by the inclusion of Sn, so care must be taken when determining the component ratio.

[Sn: 0.5-1.5 wt%]

Sn is a component added in brass alloy to improve zinc rust corrosion resistance, corrosion resistance and erosion resistance.

In particular, it contributes to stabilizing β-phase tissue, and in order to obtain stress corrosion cracking resistance, it should be added at least 0.5% by weight or more, and when it exceeds 1.5% by weight, the machinability and mechanical properties (especially elongation force) are drastically reduced. It should be limited to the above range.

[Fe: 0.2-0.3 wt%]

Fe is mainly added to increase the mechanical strength, but when it exceeds 0.3% by weight is inhibited in grain refinement, when it is added below 0.2% by weight, the mechanical strength does not improve and should be added in the above range.

[Sb: 0.1-0.2 wt%]

Sb is a component to improve the zinc zinc resistance of the brass alloy, and is utilized in the form of Bi + Sb and Bi + Se + Sb containing Sn to suppress cracking.

[Ni: 1.5-2.0 wt%]

Ni is added to improve the tensile strength as well as to realize the shape resilience by bonding with Ti, in particular to promote the α phase.

In addition, Ni also improves the yield of Se when it contains Se, it should be limited to the above range in consideration of this relationship.

[P: 0.04-0.08% by weight]

P is a component that lowers the tensile strength as opposed to Ni, but care must be taken when Sb is included.

In addition, P has corrosion inhibitory power by inhibiting ionization of Cu during corrosion.

In the present invention, it should be limited to the above range in consideration of Sb and Ni.

[Al: 0.8-1.2 wt%]

Al is a component added to increase the strength of the α-phase and β-phase tissue without affecting hot workability, corrosion resistance, corrosion resistance, slipperiness and durability.

In addition, the fluidity and flowability at the time of molding is improved, but in the present invention, it is preferable to limit to the above range in view of fluidity and flowability.

[S: 1.0-1.2% by weight]

S forms Cu-S on the base metal and provides the effect of improving machinability.

Such S, together with Se, contributes to improving machinability, but may cause segregation, and therefore S should be added in a limited range.

[Bi: 1.3-1.5 wt%]

Bi is also added to improve machinability. At least 0.5 wt% of Bi should be added to obtain machinability equivalent to that of cast brass.

In addition, in the case of excessive addition, the tensile strength is lowered and corrosion resistance is caused. Therefore, the present invention should be limited to the above range in consideration of the relationship with other components and the above characteristics.

[Se: 0.1-0.2 wt%]

Se must be added at least 0.1% by weight in order to be effective as a component added to improve machinability with Bi in brass alloy.

However, if the content exceeds 0.2% by weight, the tensile strength falls, so it should be limited to the above range. In the brass alloy, ZnSe or CuSe intermetallic compound is formed by combining with zinc or copper.

In addition, since Zn added to remainder is well-known matter, it abbreviate | omits.

In addition, when Al and Mn are added together, Si increases the wear resistance by precipitating the MnSi structure in the brass matrix (α + β).

At this time, a small amount of Cr reduces the surface migration of Mn, Al in the molten metal to induce a fine and even matrix structure.

Hereinafter, examples will be described.

[Example]

In order to confirm the characteristics of the brass alloy according to the present invention, a sample was prepared by dissolving and quenching continuous casting to form a component as shown in Table 1 below.

At this time, the melting process was carried out in the low-frequency induction melting furnace in the atmosphere, the quench continuous casting process was carried out through a horizontal continuous casting machine.

In addition, the cooling conditions were carried out in a three-stage cooling method, the cooling water temperature is 27 ~ 30 ℃, the cooling water amount 2300 ~ 2500l / min, the cooling water pressure 5 ~ 6kg / ㎜, the casting speed is 70 ~ 80mm / min continuous casting conditions Was carried out.

In this case, after extrusion, the extrusion rod was manufactured into a specimen by extrusion into a rod having a length of 550 mm having a diameter of 175 mm.

In this case, the content is weight percent, and V, Cr, Mn, and Co were added in the same amounts, respectively 0.03 wt%.

In order to measure the machinability of the brass alloys prepared in the compositions of Examples A, B, and C, a drill torque value during a drilling operation was measured using a tool dynamometer.

In this case, the relative ratio of the existing lead-containing brass alloy, that is, the cutting index (torque: 8.21) of the free cutting brass was set to 100.

In this case, the cutting resistance is a torque (kgf / cm) value when cutting under conditions of a cutting speed of 1100 rpm, depth 10mm with a high speed steel (HSS) drill is shown in Table 2 the results.

division A B C Torque (kgf / cm) 7.88 8.06 8.00 Machinability (%) 96 98.2 97.5

As shown in Table 2, A, B, C according to an embodiment of the present invention was confirmed to have almost the same cutting ability at least 96% or more compared to the machinability of the existing free cutting brass.

In addition, the corrosion resistance test was immersed in an aqueous solution of cupric chloride dihydrochloride (CuCl ₂ · 2H ₂ · O) of 1.0% and maintained for 24 hours at a temperature of 75 ℃ to determine whether the corrosion.

As a result, all of Examples A, B, and C did not generate corrosion.

In addition, a high temperature tensile test was conducted to confirm the plastic workability of the brass alloy according to the present invention.

At this time, the rod-shaped extruded specimen was fabricated into a plate-like tensile specimen having a thickness of 2 mm, a width of 3 mm, and a gauge distance of 5 mm for tensile testing, and then 400 using a mechanical universal tensile tester (Instron 4481) equipped with a heat treatment furnace. The strain was carried out at a strain rate of 1 × 10 ⁻² / s, and the elongation was evaluated by measuring the gauge length of the specimen after fracture.

As a result of the test, Examples A, B, and C exhibited elongations of 322.4%, 336.1%, and 341.2%, respectively, and it was confirmed that the present invention sufficiently achieved the intended purpose.

In addition, the shape memory is also related to the elongation, and since the shape memory was added within the range of proven components, the proof experiment was omitted.

As described above, it was confirmed that the lead-free free-cut brass alloy according to the present invention sufficiently achieved the desired purpose.

Claims (4)

In lead-free free-cut brass alloys;
The lead-free free-cut brass alloy is by weight,
Cu: 56-58%, Sn: 0.5-1.5%, Fe: 0.2-0.3%, Sb: 0.1-0.2%, Ni: 1.5-2.0%, P: 0.04-0.08%, Al: 0.8-1.2%, S Lead-free brass alloy with improved corrosion resistance, plastic workability and shape memory, comprising: 1.0-1.2%, Bi: 1.3-1.5%, Se: 0.1-0.2%, and balance Zn.
In lead-free free-cut brass alloys;
The lead-free free-cut brass alloy is by weight,
Cu: 56-58%, Sn: 0.5-1.5%, Fe: 0.2-0.3%, Sb: 0.1-0.2%, Ni: 1.5-2.0%, P: 0.04-0.08%, Al: 0.8-1.2%, S Based on: 1.0-1.2%, Bi: 1.3-1.5%, Se: 0.1-0.2%, and the balance Zn;
In addition to the basic component, Ti is further added in the same ratio as Ni, and V, Cr, Mn, and Co are further added in a ratio of 1: 1: 1: 1 within a range of 0.02-0.04% by weight. Lead-free free-cut brass alloy with improved corrosion resistance, plasticity and shape memory.
The method of claim 2,
Lead-free free-cut brass alloy with improved corrosion resistance, plasticity and shape memory, characterized in that the addition of 0.02-0.04% by weight of Si to the basic component further improved wear resistance.
The method of claim 2,
The lead-free free-cut brass alloy is heat-treated such that the α phase of the face-centered cubic structure and the β-phase of the body-centered cubic structure coexist at room temperature after reheating to a temperature above which the plastic deformation is applied at the martensite transformation point and then reversely transformed into the mother phase. Lead-free, free-cut brass alloy with improved corrosion resistance, plasticity and shape memory.