Patent Application
20060204396
The present invention relates to copper alloys used for connector materials and the like. The present invention provides a producing method of titanium copper alloy having excellent punchability compatible with bendability retaining high strength.
Titanium copper alloy forms supersaturated solid solution by means of solution treatment. Aging at low temperature of the supersaturated solid solution develops a modulated structure which is metastable phase, resulting in remarkable hardening at a point in the course of the developing process (age-hardening). The foregoing modulated structure of titanium copper alloy is caused by the fluctuation of the concentration of solid solution titanium in a matrix formed by spinodal decomposition. Among copper alloys, the titanium copper alloy having a developed modulated structure has the second strength next to beryllium copper, and excellent stress relaxation properties superior to beryllium copper. Thus they are used for connector materials and the like. In recent years, the market demand for titanium copper alloy tends to increase, along with the demand for further high strengthening retaining excellent bendability. In order to respond to the above demands, various researches and developments have been worked on further high strengthening of titanium copper alloy.
For example, in JP6-248375A, disclosed is the method in which at least one selected from Cr, Zr, Ni and Fe is added to titanium copper alloy. In JP 2002-356726A, disclosed is that a method in which at least one selected from Zn, Cr, Zr, Fe, Ni, Sn, In, P and Si is added to titanium copper alloy. All of the foregoing publications are herein fully incorporated by reference.
When titanium copper alloy is punched, the press die more easily wears away than when the other copper alloy is punched. Therefore, since the third element group(s) (Fe, Co, Ni, Si, Cr, V, Nb, Zr, B or P) is added to titanium copper alloy in the conventional method in order to achieve high strength by means of the precipitation of the second phase comprising the third element moiety, punch press work of the strengthened materials causes a more problem of a press mold wear because the precipitates themselves harden the alloy.
Accordingly, the press working of the titanium copper alloy highly strengthened by the above means makes a die easily worn away resulting in the decrease of the dimensional accuracy. Under the circumstances, in the producing process of minute parts such as narrow pitch connectors and the like, it is necessary to exchange a die frequently or to avoid the application of the material for minute parts and the like.
From the above, the object of the present invention is to improve punchability of high strengthened titanium copper alloy by adding the third element, and to provide a titanium copper alloy having excellent punchability by achieving excellent bendability.
The inventors noticed that stress distribution of a material on the shearing process is affected by the crystal orientation of the material, and intensively and extensively researched, and found out that controlling of crystal orientation enables to improve the punchability of the material. Further, regarding that the existence of coarse second phase particles and inhomogeneity of the structure deteriorate bendability, the inventors researched appropriate distribution of the second phase particles, and found out that it is necessary that the second phase particles is distributed not at grain boundaries but at intergranular as fine and homogeneous as possible, so as to contribute to the improvement of the strength without deterioration of bendability.
Further, the inventors has discovered when the composition of titanium copper alloy is a Cu—Ti—X system containing a third elements (X is the third element), the development of the second phase particles at grain boundaries is inhibited resulting in tendency of fine distribution.
The present invention provides (1) to (7) as follows.
(1) A titanium copper alloy consisting of 2.0 to 4.0 mass % of Ti, 0.05 to 0.50 mass % of Fe and the balance of Cu and impurities characterized in that;
it comprises 0.01 mass % or less in total of inevitable impurities; and the ratio of X ray diffraction intensity of the alloy satisfies I(311)/I(111)≧0.5.
(2) A titanium copper alloy consisting of 2.0 to 4.0 mass % of Ti, 0.05 to 0.50 mass % in total of Fe and at least one selected from a group consisting of Co, Ni, Si, Cr, V, Nb, Zr, B and P, and the balance of Cu characterized in that;
it comprises 0.01 mass % or less in total of inevitable impurities; and the ratio of X ray diffraction intensity of the alloy satisfies I(311)/I(111)≧0.5.
(3) A titanium copper alloy consisting of 2.0 to 4.0 mass % of Ti, 0.05 to 0.50 mass % in total of at least one selected from a group consisting of Co, Ni, Si, Cr, V, Nb, Zr, B and P, and the balance of Cu characterized in that;
it comprises 0.01 mass % or less in total of inevitable impurities; and the ratio of X ray diffraction intensity of the alloy satisfies I(311)/I(111)≧0.5.
(4) The titanium copper alloy having excellent punchability according to the item (1), wherein;
the number of Cu—Ti—Fe type composition particles in the second phase particles having an area of 0.01 μm2 or more measured by a cross sectional observation is 50% or more.
(5) The titanium copper alloy having excellent punchability according to the item (2) or (3), wherein;
the number of Cu—Ti—X type composition particles (wherein X is an element selected from Fe, Co, Ni, Si, Cr, V, Nb, Zr, B and P) in the second phase particles having an area of 0.01 μm2 or more measured by a cross sectional observation is 50% or more.
(6) The titanium copper alloy having excellent punchability according to any one selected from the items (1) to (5), wherein;
the average particle size of the second phase having an area of 0.01 μm2 or more measured by a cross sectional observation is 2.0 μm or less.
(7) The titanium copper alloy having excellent punchability according to any one selected from the items (1) to (6), wherein;
the coefficient of variation Cv (standard deviation/mean value) of the density of the second phase particles having an area of 0.01 μm2 or more, observed in each crystal grains by means of a cross sectional observation, is 0.3 or less.
The present invention achieves a titanium copper alloy having excellent punchability while retaining high strength by adjusting the content of the third element group and the crystal orientation and excellent bendability by controlling the distribution of the second phase particles. Therefore, the titanium copper alloy of the present invention is a copper alloy having excellent bendability compatible with excellent punchability while retaining high strength able to be used for connector materials and the like.
(1) Alloy Composition
The present invention defines the amount of Ti as 2 to 4 mass % since sufficient strength is not obtained by Ti of less than 2 mass %, on the contrary Ti of more than 4 mass % easily causes coarse precipitations resulting in deteriorated bendability. The more preferred range of the Ti amount is 2.5 to 3.5 mass %.
One embodiment of the present invention specifies an alloy composition with addition of the third element group. The effect of the elements is that the addition in even a small amount enables to obtain fine crystal structure by solid solution treatment at high temperature at which Ti is satisfactorily solved into matrix without easy generation of coarse crystal grain.
Regarding titanium copper alloys, Fe achieves the highest effect as the third element group. Any one of Co, Ni, Si, Cr, V, Nb, Zr, B and P shows the better effect next to Fe, thus a partial amount of added Fe can be replaced with any one of Co, Ni, Si, Cr, V, Nb, Zr, B and P. Further, these elements can be added alone or in the form of mixture of two or more elements achieving the same effect. Fe and these elements show their effects when they are contained in an amount of 0.01 mass % or more in total. On the contrary, when the amount exceeds 0.5 mass %, the range of solid solution of Ti becomes narrow, the second phase coarse particles tend to precipitate, thus bendability is deteriorated while strength is improved. Here, the term “the second phase particle” refers to a region having a discrete boundary distinct from matrix in the composition, and it includes Cu—Ti—X type particle and Cu—Ti type particle in the titanium copper alloy of the present invention. The preferred content range of the third elements is 0.17 to 0.23 mass % of Fe, 0.15 to 0.25 mass % of Co, Ni, Cr, Si, V or Nb, 0.05 to 0.10 mass % of Zr, B or P.
(2) Crystal Orientation
Generally, the higher ductility, the better bendability, and the lower ductility, the better punchability. Thus, it has been difficult for bendability to be consistent with punchability.
Meanwhile, in the producing process of copper alloy, cold rolling with a high reduction ratio develops a rolling texture along with an increase of I(110) (X ray diffraction intensity of the (110) plane). Then subsequent recrystallization annealing of the rolling texture develops a recrystallization texture along with an increase of I(100). The material obtained immediately after cold rolling lacks ductility. Conversely, the material obtained immediately after recrystallization annealing is soft and readily extendable. Based on the above relationship, many researches in prior art refer to the relationship between I(100) and I(110). Therefore, techniques proposed in the prior arts are such that I(100) is specified as higher than I(110) in order to improve bendability, on the contrary I(110) is specified as higher than I(100) in order to improve punchability.
The present invention regards the relationship between I(311) and I(111) and found the following. No prior arts refer to the relationship between I(311) and I(111).
Generally, in the punch press work shown in
When I(311) develops in comparison with I(111), the angle of the generated crack during the shearing process becomes nearer to 90 degrees in relation to the surface of material as shown in
In the present invention, the relationship represented by the above formula is found out, the satisfaction of which is able to increase punchability without decreasing ductility.
The alloy system of the present invention satisfies I(311)/I(111)≧0.5, preferably I(311)/I(111)≧1.0, more preferably I(311)/I(111)≧1.5.
With respect to the method for obtaining a specific crystal orientation satisfying I(311)/I(111)≧0.5, when cold rolling is carried out under the condition such that solute atoms are completely dissolved in the form of solid solution, (311) plane develops finally, therefore the solution treatment in an intermediate step should be carried out under the thermal treatment condition such that the second phase particles are completely dissolved in a form of solid solution.
(3) The Composition and Distribution of the Second Phase Particles
The specific embodiment of the present invention defines the composition, average particle size, and dispersion of the density of the second phase.
Generally, the second phase particles include extrinsic inclusions derived from furnace materials and the like, reaction products generated during melting, precipitations generated during solidification, and precipitations formed during heat treatment. In the alloy system relating to the present invention, most of the second phase particles are precipitations formed during heat treatment.
The second phase particles finely and homogeneously dispersed in crystal grains contribute to the improvement of strength as well as bendability. Coarse particles or a locally segregated distribution deteriorate bendability. Concretely, when the average grain particle of the second phase exceeds 2.0 μm, or when the coefficient of variation Cv (standard deviation/average of density of the second phase particles exceeds 0.3, bendability remarkably deteriorates. Here, the term “a particle size” refers to a diameter of the corresponding circle and “a diameter of the corresponding circle” refers to a diameter of a perfect circle having the same area.
According to the above, in order to obtain the fine second phase particles homogeneously dispersed in crystal grains, it is effective that heating is carried out under the condition such that solute atoms are completely dissolved in the form of solid solution and the final solution treatment is conducted at a temperature range slightly above the solid solution curve. The “temperature range” refers to a temperature preferably 20° C., more preferably 10° C. more than the temperature on the solid solution curve.
Generally when a phase is heated to the temperature range, even under the equilibrium condition, owing to the fluctuation of equilibrium in the actual space, many nucleuses of the second phase frequently appear and disappear in everywhere. At the temperature range that these events occur, it is difficult for crystal grains to grow even under recrystallization condition. Therefore, at a temperature range slightly above the solid solution curve, the Cu—Ti—X type second phase particles are dispersed in crystal grains finely, resulting in the fine recrystallization grains.
Further, since the Cu—Ti—X type second phase particles themselves are not easily coarsened in relation to the Cu—Ti type second phase particles, when the number of the Cu—Ti—X type second phase particles is 50% or more of the total number of the second phase particles, the above desirable size and distribution of the second phase particles are achieved and fine recrystallization grains are obtained.
The property such that the Cu—Ti—X type second phase particles are not easily coarsened in relation to the Cu—Ti type second phase particles, is derived from the matter that the second phase particles of the latter develops only by diffusion of Ti while the second phase particles of the former essentially develops by diffusions of both Ti and X. This property is shown at a low temperature, the Cu—Ti—X type second phase particles are not easily coarsened even during aging treatment of final step. From the above, it is preferred that the second phase particles composition is maintained as Cu—Ti—X system during final solution treatment as much as possible.
However, under the circumstances that the second phase particles are precipitated already, final solution treatment under any conditions enhance the development of the second phase which already exist, thus the structure in which only fine particles are dispersed homogeneously are not obtained.
Therefore, in the thermal treatment step before final solution treatment, it is necessary that all solute atoms are solved in matrix. In this point, crystal grains can be coarsened since they does not affect adversely on the final crystal particle size. Fine homogeneous crystal structure can be obtained by cold rolling in the state that solute atoms are completely solved in matrix, and in final solution treatment causing simultaneous recrystallization and precipitation of the second phase particles.
(4) Producing Method
From the above, fundamental steps for producing the alloy of the present invention are; sufficient solution treatment (the first solution treatment), cold rolling (intermediate rolling), solution treatment at a temperature range slightly above the solid solution curve (final(the second) solution treatment), temper rolling (final rolling) and aging in this order.
“The first solution treatment” refers to a solution treatment before intermediate rolling before final rolling. After melting the raw materials adjusted to the specified composition, casting, and hot rolling, a set of cold rolling and annealing is repeated appropriately until the desired thickness, then the first solution treatment is conducted, alternatively the first solution treatment can be carried out immediately after hot rolling.
Also “the second solution treatment” refers to a solution treatment before final rolling, corresponding to the above final solution treatment, hereinbelow referred as “the final solution treatment”.
Hereinafter, steps of the present invention are sequentially described as the embodiment of the invention.
1) Ingot Producing Step
Into an appropriate amount of Cu, 0.01 to 0.50 mass % of at least one selected from a group consisting of Fe, Co, Ni, Si, Cr, V, Nb, Zr, B and P are added as the third element group, after sufficient maintaining, 2 to 4 mass % of Ti is added thereto.
So as to act the third element group effectively, solution residue should be solved, thus molten metal is maintained for sufficient time until the added metals are melted completely. Since Ti is more easily melted into molten Cu than the third element group, Ti may be added after melting of the third element group.
Besides, when oxide-type inclusions occur, the strength and bendability of the material are adversely affected. Therefore, so as to prevent the generation of an oxide, melting and casting are carried out under vacuum or in the atmosphere of inert gas.
2) Step After Ingot Producing Step
After the above ingot producing step, homogeneous annealing is preferably carried out at 900° C. or more for 3 hours or more. At this point, when segregation and crystallized particles generated during casting disappear completely, precipitations of the second phase particles can be dispersed finely and homogeneously at intragranular regions and formation of duplex grain structure is prevented.
Subsequently, hot rolling, repetition of cold rolling and annealing, and solution treatment are carried out. When the temperature of intermediate annealing is lower than the desired temperature, the second phase particles are formed, thus these steps are conducted at a temperature such that the second phase particles are completely solved into matrix. With respect to the temperature at which the second phase particles are completely solved into matrix, a temperature of 800° C. is acceptable for usual titanium copper alloy to which the third element group is not added. However as for a titanium copper alloy to which the third element group is added, the temperature is preferably 900° C. or more. The rising rate and cooling rate of the temperature should be as high as possible such that the second phase particles are not precipitated. Cold rolling at a state such that solute atoms are completely solved in matrix makes (311) plane to be developed finally. Further, in the cold rolling immediately before solution treatment, the higher a reduction ratio the finer and more homogeneous the precipitation of the second phase particles in solution treatment.
3) Final Solution Treatment
When heating is carried out quickly to the temperature range slightly above the solid solution curve and the cooling rate is fast, the generation of the coarse second phase particles is inhibited. Further, the shortened heating time at the solid solution temperature brings fine crystal grains. Since the second phase particles generated at grain boundaries at this point develop in final aging, it is preferred that the second phase particles at this point is as small and few as possible.
4) Final Cold Rolling and Final Aging Treatment
After the above solution treatment, cold rolling and aging treatment are carried out. Regarding cold rolling, a reduction ratio of 25% or less is preferable since the higher a reduction ratio, the more precipitation at grain boundaries occurs in the next aging treatment.
Regarding aging treatment, the lower the temperature is, the less precipitation at grain boundaries occurs. Even in the condition that the same strength is obtained, a combination of low temperature and long period more inhibits precipitation at grain boundaries than a combination of high temperature and short period. In the range of 420 to 450 ° C. which is considered as an appropriate range in prior art, the strength is improved according to the aging process, however precipitation at grain boundaries tends to occur and slight over-aging deteriorates bendability. An appropriate aging condition which varies depending on the added elements, is 380° C.×3 hs at the highest temperature, or 360° C.×24 hs at the low temperature while a long period of heating is accepted.
Hereinbelow, examples of the invention are described in detail. In preparing a copper alloy of the present invention, since Ti which is an active metal is added as the second element, a vacuum melting furnace is used in melting. Further, in order to obviate the unexpected harmful effect by the contamination of inevitable impurities other than elements specified in the present invention, used materials are precisely selected so as to have relatively high purity.
Firstly, in examples 1 to 7 and comparative examples 8 to 12, in order to obtain the composition shown in Table 1, main raw materials Cu, Ti and additional elements (Fe, Co, Ni, Cr, Si, V, Nb, Zr, B or P) are compounded and melted. The molten metal is maintained sufficiently such that the solution residue is solved so that the third element groups act effectively, then Ti is added. The above prepared molten metal is poured into a mold under the atmosphere of Ar to produce approximately 2 kg of ingot.
The above ingot is coated with an antioxidant. After 24 hours of drying at a room temperature and heating at 950° C. for 12 hours, hot rolling was conducted to obtain a plate having a thickness of 10 mm. Subsequently in order to inhibit segregation, further antioxidant is coated on the plate and the plate was heated at 950° C. for 2 hours and cooled with water. The above water-cooling is employed for completion of solid solution as far as possible, and the coating with an antioxidant is employed for protecting grain boundary oxidation and internal oxidation causing generation of inclusions as much as possible, which internal oxidation is caused by the reaction of oxygen entered from the surface with additional elements.
Each hot rolled plate was ground mechanically and descaled by pickling, then processed by cold rolling to the thickness of 0.2 mm. After the above process, the plate was inserted into an annealing furnace to conduct rapid heating at rising rate of 50° C./second to the temperature slightly above the solid solution curve (for example, 800° C. for the alloy having 3 mass % of added Ti and 0.2 mass % of added Fe), then maintained for 2 minutes and water-cooled. The water-cooled plate was pickled for descaling and cold rolled to the plate thickness of 0.15 mm, then aged under the atmosphere of inert gas to obtain a sample piece for an example.
As for preparation of sample pieces for comparative examples, the composition were adjusted for comparative examples 8 to 11, the conditions of intermediate solution treatment step which is an important step in the invention were adjusted for comparative examples 12to 14.
In the table, “—” means no elements are added.
Diffraction intensity values of (111) and (311) planes of each sample pieces were measured by X-ray diffractometer (XRD) and I(311)/I(111) was calculated.
The distribution of the second phase particles was evaluated by use of Field Emission Auger Electron Spectroscopy analyzing apparatus (FE-AES) and Image Analysis device connected therewith. The second phase particles having an area of 0.01 μm2 existing in a scanning visual field unit was evaluated. Then based on the total number of the second phase particles (S) and the total number of the Cu—Ti—X type second phase particles (Sx), value “A” ((Sx/S)×100) was obtained. Likewise the above, areas of 5000 optional second phase particles were averaged and a diameter of a corresponding circle thereof is defined as an average particle size “D” of the second phase particles. Further, regarding optional 100 crystal grains in a population of crystal grains, the number of the second phase particles existing in each grain was divided by the area of the respective crystal grain to obtain a value (average density). The coefficient of variation Cv (standard deviation of the average density/mean value) was calculated. I(311)/I(111), “A” value, “D” value, and Cv of sample pieces are shown in Table 2.
Subsequently to the above, a tensile test was conducted for measuring 0.2% offset yield strength, and a W bending test was conducted for measuring MBR/t value which is a ratio of minimum bending radius without cracking (MBR) to a plate thickness (t).
Wear of a press die was evaluated by actual punching using a press for certain times and measuring the ratio of a burr height of the material and the ratio of an area of the fractured surface which varies depending on the wear of a mold. During the mold wear test, the mold was sharpened after an evaluation thus the pressing was conducted in the same condition. The burr height means a height of convex part shown in
The other press conditions were as follows:
Material of die and punch; SKD11, clearance; 10 μm, stroke; 200 rpm.
A set of press tools used in the evaluation is shown in
Apparent from Table 3, each example has a 0.2% offset yield strength of 850 MPa or more, a MBR/t value of 2.0 or less, and a fractured surface ratio of 0.10 or more and a burr height of 40 μm or less after 100,000 times punching without a lubricant. These examples achieve high punchability in addition to high strength and excellent bendability compatibly. In examples 3 to 7, since the amount of added Ti is in the especially preferred range (2.5 to 3.5 mass %), 0.2% offset yield strength is significantly improved to more than 900 MPa.
Regarding the distribution of the second phase particles, except for example 5, “A” value representing a ratio of Cu—Ti—X type particle existence, average particle size “D” and “Cv” representing the homogeneousness of the distribution are in the preferred range, therefore bendability is improved. In examples 1 to 2 and 5 to 7, I(311)/I(111) is in the more preferred range, thus punchability is more improved.
In example 5, regarding the distribution of the second phase particles, the amount of the added third elements is small, thus the ratio of Cu—Ti—X type particle existence is less than 50%, resulting in inferior bendability to other examples.
On the contrary, in comparative example 8, since the amount of added Ti is less than 2.0 mass %, sufficient 0.2% offset yield strength is not obtained. Alternatively, in comparative example 9, since the amount of added Ti is more than 4.0 mass %, bendability deteriorated. In comparative example 10, since the third element group of the invention is not added, strength and bendability are deteriorated. Alternatively, in comparative example 11, since the total amount of the added third element is more than 0.5 mass %, the second phase particles precipitated more than necessary resulting in deterioration of bendability.
Regarding the solution treatment conducted before intermediate cold rolling, a heating temperature is low in comparative example 12, a rising rate is low in comparative example 13, and a cooling rate is low in comparative example 14. Illustratively, the heating temperature is 800° C. in comparative example 12, the rising rate is 5° C./sec in comparative example 13, and the cooling rate is 30° C./sec in comparative example 14. In all of comparative examples 12 to 14, intermediate cold rolling was conducted while Cu—Ti—X type precipitations were remaining, finally I(311)/I(111) values regarding the above comparative examples were less than 0.5, resulting in poor punchability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-72006 | Mar 2005 | JP | national |
