JP2001040462A - Production of titanium or titanium alloy fine diameter wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a fine diameter wire made of titanium or a titanium alloy having a beautiful surface, excellent in secondary cold workability, and in which the time required for mirror polishing of about 1 μm by R max is short as possible in surface polishing for the wire rod executed after heat treatment, i.e., excellent in polishability. SOLUTION: Cold rolling is executed at a reduction of cross-section of >=40% by using a continuous rolling mill in which plural stands provided with rolls integrated by 4 pieces composing circular calibers are successively provided in the pass line direction so as to change the groove bottom directions of the circular calibers of the adjacent stands to each other by about 45 deg., and after that, heat treatment of executing holding under heating to the temp. range of the β transformation point to (the β transformation point-150 deg.C) for 20 to 240 sec in a nonoxidizing atmosphere is applied. The heat treatment is executed preferably by using a continuous furnace capable of wire passing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a titanium or titanium alloy thin wire having excellent cold workability and excellent polishing properties.

[0002]

2. Description of the Related Art In general, a thin wire made of titanium or a titanium alloy having an outer diameter of about 6 mm or less (hereinafter also referred to as a titanium-based wire) is provided by a plurality of stands having a pair of hole-shaped rolls in a pass line direction. After being rolled into a wire having a wire diameter of about 9 to 6 mm by a hot rolling mill arranged in tandem, the surface of the wire is scratched by die peeling or the like, and then reduced to a predetermined finished wire diameter with a hole die. After the cold drawing, the product quality is adjusted by heat treatment (finish annealing) to manufacture.

However, when the diameter of the finished wire is small, disconnection or the like is likely to occur due to a decrease in cold workability due to the reduction in diameter.
In cold drawing, heat treatment (intermediate annealing) is performed every time the cross-sectional reduction rate exceeds about 30 to 40% to restore cold workability. Therefore, when the finish wire diameter is small, a plurality of intermediate annealings are required, and there is a problem that efficiency is reduced and manufacturing cost is increased.

[0004] Further, the titanium-based material has a feature that it is very easy to seize, and seizure between titanium and a hole die occurs frequently even when wire is drawn by a lubricant used in rolling of stainless steel or the like, which is easy to seize. Therefore, for titanium-based materials,
A method is used in which a wire is heated to form an oxide film of titanium on the surface, and this oxide film is drawn as a lubricating film. However, in this method, there is a problem that the titanium oxide derived from the oxide film and peeled off during processing is pushed into the surface and remains as a concave flaw on the surface after processing to deteriorate the surface properties. Also, a part of the oxide film remains on the surface of the drawn wire,
There is also a problem that surface treatment such as pickling is required.

[0005]

The drawbacks of the hole die drawing method can be solved by using an apparatus for producing a small-diameter wire disclosed in Japanese Patent Application Laid-Open No. Hei 6-501 previously proposed by the present applicant.

In this apparatus, a plurality of stands each having four integral hole-type rolls each having a circular hole shape are provided in tandem in the pass line direction. Since the cross-sectional reduction rate that can be processed without intermediate annealing can be increased as compared with the wire, the number of times of intermediate annealing can be reduced or omitted. In addition, processing can be performed without applying an oxide film on the surface, and a product having a good surface of the processed wire can be obtained.

Further, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 9-22550.
No. 1 discloses a method for producing a titanium or titanium alloy fine wire having excellent cold workability and surface properties by combining a rolling method and a heat treatment by the apparatus disclosed in Japanese Patent Application Laid-Open No. 6-501. In this method, a pre-strain is imparted to the crystal grain structure by rolling using the above-described apparatus, and thereafter, a heat treatment is performed in which the material is heated for a short time at a temperature just above the transformation temperature (β transformation) of the material. As a result, the heat-treated wire has uniform and fine crystal grains, and has improved cold workability.

[0008] When this heat treatment method is used for intermediate annealing, the limit workability in secondary rolling (rolling after intermediate annealing) is improved, so that it is possible to perform rolling to a smaller wire diameter than conventional heat treatment. Become. Further, when used for finish annealing, it is possible to perform a higher degree of processing than a conventional heat-treated material in the subsequent bending or processing into a deformed wire. Hereinafter, cold working performed after intermediate annealing or finish annealing is referred to as secondary cold working. Also,
The wire obtained by the above heat treatment method can be subjected to processing such as rolling while preventing grain boundary cracks, etc., so that the product obtained by the processing has a more beautiful surface compared to the case of processing the conventional heat treated material. Is obtained. Therefore, the above-mentioned wire can be used as a material for welding rods or the like as it is in the heat treatment.

However, for a wire rod which requires a mirror-finished surface (Rmax: 1 μm or less), such as a material such as eyeglasses and decorative articles, it is necessary to polish the surface with a fine abrasive after heat treatment. . Usually, polishing is performed by a method of pressing a rotating brush having abrasive grains on a moving wire.

[0010] The surface roughness after polishing is affected by the polishing time, that is, the moving speed of the wire, and the higher the moving speed, the larger the surface roughness. Therefore, in the polishing of a wire rod that requires a mirror finish as described above, the moving speed is kept low.

The wire rod obtained by the method disclosed in Japanese Patent Application Laid-Open No. 9-225501 has improved cold workability and can be processed while suppressing grain boundary cracking. Can be improved. However, even in the method disclosed in the above-mentioned publication, the improvement of the moving speed is insufficient, and a great improvement in the polishing efficiency is desired.

[0012] From the above, it has been desired to establish a method for producing a titanium or alloy thin wire having a beautiful surface, high cold workability at the time of secondary cold work, and excellent polishing.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to solve the problem of polishing the surface of a wire rod after heat treatment, which has a beautiful surface and excellent secondary cold workability.
It is an object of the present invention to provide a method for producing a thin wire made of titanium or a titanium alloy having excellent so-called polishing properties, in which the time required for mirror polishing of about 1 μm in x is as short as possible.

[0014]

Means for Solving the Problems The present inventor has conducted various experiments in order to solve the above-mentioned problems, and has found the following and completed the present invention.

That is, in order to obtain a titanium or titanium alloy fine wire having a beautiful surface and excellent cold workability and abrasionability, the first cold rolling is performed with a reduction ratio of a cross section of 40% or more. After the primary cold working, it is necessary to perform a heat treatment in a non-oxidizing atmosphere at a temperature lower than the β transformation point and at a temperature range of (β transformation point−150 ° C.) or higher for 20 to 240 seconds. Was found.

The gist of the present invention based on the above knowledge lies in the following method for producing a titanium or titanium alloy thin wire.

(1) A plurality of stands provided with four integral hole type rolls constituting a circular hole type are connected in the pass line direction by changing the groove bottom directions of the circular hole types of adjacent stands by approximately 45 ° with respect to each other. Cold rolling at a cross-sectional reduction rate of 40% or more using a continuous rolling mill consisting of 20% or less in a temperature range of less than the β transformation point and (β transformation point−150 ° C.) or more in a non-oxidizing atmosphere.
A method for producing a thin wire made of titanium or a titanium alloy, comprising performing a heat treatment of heating and holding for up to 240 seconds.

(2) The method for producing a titanium or titanium alloy thin wire according to the above item (1), wherein the heat treatment is performed using a continuous furnace through which the heat treatment can be passed.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The manufacturing method of the present invention will be described in detail with reference to the accompanying drawings.

First, a working method by cold rolling and its conditions will be described.

The continuous rolling mill used in the present invention has a plurality of stands formed by arranging four grooved rolls around a pass line in tandem in the direction of the pass line.

FIG. 1 is a schematic front view of a stand constituting a continuous rolling mill for performing cold rolling according to the present invention. FIG. 1 (a) shows a first stand on the entrance side, and FIG. ) Indicates the second stand. 1 is a stand, 2 is a housing, 3 is a hole, 4a is a hole type roll, 4b is a roll shaft,
Reference numeral 5 denotes a groove, 6 denotes a circular hole, 7 denotes a bevel gear, and 8 denotes an input shaft.

As shown in FIGS. 1 (a) and 1 (b), each stand 1 is provided with a cross-shaped hole 3 formed in the center of a housing 2 having an octagonal shape in a front view. Are provided with four hole-type rolls 4a, 4a, 4a, 4a by inserting the roll shafts 4b, 4b, 4b, 4b into bearing holes formed in the wall surfaces of the holes. On the peripheral surface of the four grooved rolls, a groove forming groove 5 is formed at the center in the roll axis length direction,
A circular die 6 is formed at the center of the housing 2 by the groove, and the wire is rolled through the circular die. One end of the roll shaft 4b of one of the rolls 4a is an input shaft 8 and is connected to a drive mechanism (not shown), and the roll is driven. The other three rolls 4a, 4a, 4a are each driven by a driving force transmitted thereto by bevel gears 7 attached to the side surfaces thereof and meshing with each other.

In the continuous rolling mill, as shown in FIGS. 1 (a) and 1 (b), the first stand and the second stand, that is, the adjacent stands have their circular hole-shaped groove bottoms facing each other by 45 degrees. The material part which is arranged so as to be changed so as not to be reduced by the preceding stand is subjected to the reduction at the groove bottom portion of the roll hole type of the subsequent stand. That is, the hole-shaped rolls are sequentially arranged in the state shown in FIG. 1 (a) for the odd-numbered stands and in the state shown in FIG. 1 (b) for the even-numbered stands. The diameter of the wire is gradually reduced, so that the diameter of the wire is gradually reduced to a predetermined diameter.

FIG. 2 is a schematic front view showing the shape of the circular hole die 6. Reference numeral 9 indicates a gap between groove edges.

As shown in FIG. 2, the circular hole mold 6 of each stand is so formed that the material does not bite into the gap 9 between the groove edges.
The diameter dh between the groove edges is larger than the diameter dm between the groove bottoms. That is, usually, each stand has d
The ratio of h to dm (dh / dm) is set to about 1.02 to 1.06.

Using the continuous rolling mill configured as described above, the wire rod made of titanium or a titanium alloy is cold-rolled to obtain a small diameter wire rod of a predetermined size. The working degree at that time needs to be 40% or more in terms of a cross-sectional reduction rate ((cross-sectional area of the wire-cross-sectional area of the small-diameter wire) / cross-sectional area of the wire × 100%). The crystal grains are refined by rolling, but if the reduction rate of the cross section is less than 40%, the crystal grains are insufficiently refined even if a heat treatment described later is performed, so that the polishing property can be improved. Absent. The upper limit of the cross-sectional reduction rate is not particularly limited. However, when the cross-sectional reduction rate is high, cold workability is insufficient, and fine cracks are easily generated on the surface or inside during rolling. Surface cracks can be removed by shaving the surface and removing flaws, but this increases the cost. Internal cracks are difficult to remove and cause disconnections and surface flaws during secondary cold rolling or cold working for eyeglasses. Therefore, in the rolling of the titanium wire rod, it is desirable that the reduction rate of the cross section is about 80% or less. Further, in the rolling of the titanium alloy wire, it is desirable that the cross-sectional reduction rate is about 85% or less.

Next, the heat treatment method and its conditions will be described.

The material cold-rolled as described above is subjected to a heat treatment to improve the secondary cold-workability for cold-rolling for further reducing the diameter or cold-working for deformed wire. . However, when applying this heat treatment, a commonly used heat treatment method, that is, a method in which the entire coiled wire is charged into a batch or continuous heat treatment furnace and heat treated is applied,
Since the growth rate of crystal grains after recrystallization is high, secondary cold workability cannot be improved. That is, when the entire coil-shaped wire is charged into the heat treatment furnace and heated, the time required to raise the temperature of the entire coil is long, and when the wire is viewed in the longitudinal direction, the soaking time is inevitably long. Part occurs. As a result, in the portion where the soaking time is long, the crystal grains which have once been recrystallized and become fine grains are coarsened, and it is not possible to obtain uniformly fine crystal grains in the longitudinal direction of the wire. Further, in the method of charging the entire coil-shaped wire into the heat treatment furnace, it is difficult to prevent the generation of oxide scale on the surface of the wire, and the surface properties are deteriorated. In order to prevent the generation of oxide scale, it is necessary to perform heat treatment in a non-oxidizing atmosphere. However, in the above method, it is necessary to temporarily evacuate the inside of the furnace and then replace it with an inert gas such as Ar gas in order to obtain a non-oxidizing atmosphere, which requires a lot of time.

Therefore, in the present invention, heat treatment is performed by the method and conditions described below.

FIG. 3 is a schematic sectional view showing an example of a continuous furnace used for performing the heat treatment according to the present invention. Reference numeral 21 denotes a continuous furnace, 22 denotes a cooling device, 23 denotes a muffle, 2
4 is a cylinder, 25 is a water tank, 26 is a wire, and 27 is a supply port.

As shown in FIG. 3, the continuous furnace 21 is provided with a cooling device 22 downstream thereof, and is configured so that a line can be connected from the inlet side of the heat treatment furnace to the outlet side of the cooling device. The continuous furnace 21 includes a long cylindrical muffle 23 and appropriate heating means (not shown) such as high-frequency induction heating outside the muffle 23. The cooling device 22 includes a cylinder 24 connected to the muffle of the continuous furnace 21 and a water tank 25 passing through the cylinder.
6 can be cooled indirectly. As shown in part A of FIG. 3, an inert gas such as an Ar gas is supplied into the muffle and the cylinder from the supply port 27, and the atmosphere becomes a non-oxidizing atmosphere. The wire is subjected to a heat treatment by continuously passing the wire through a continuous furnace and a cooling device.

Next, the heat treatment conditions of the present invention will be described.

In the present invention, the temperature is less than the β transformation point, (β transformation point−
(150 ° C.) or more, and heat-treats by heating and holding for 20 to 240 seconds.

Although the material obtained by the cold rolling has a β structure and an α structure, the soaking temperature is (β transformation point −150).
If the temperature is lower than (° C.), not only the β structure but also the α structure are not recrystallized, so that the dislocation formed by the cold rolling does not proceed so that the secondary cold workability cannot be improved. The soaking temperature is (β transformation point-
When the temperature exceeds 150 ° C.), the α structure is recrystallized and dislocations are released to improve the secondary cold workability. However, when the temperature exceeds the β transformation point, the crystal grains which have become fine once become coarse and the polishing property deteriorates. I do. Preferably, the soaking temperature is (β transformation point −100
° C) or more and (β transformation point-20 ° C) or less.

If the soaking time is less than 20 seconds, recrystallization of the α structure is not completed, and the entire cross section of the wire is not softened uniformly.
Secondary cold workability is not sufficiently improved. Soaking time 2
If it exceeds 40 seconds, the crystal grains are partially coarsened as in the case where the holding temperature is high, and the polishing property is deteriorated. Preferably, the soaking time is 30 seconds or more and 200 seconds or less.

In the present invention, heat treatment is performed in a non-oxidizing atmosphere by supplying an inert gas into the muffle. By performing the heat treatment in a non-oxidizing atmosphere, the formation of oxide scale is suppressed, so that a product having a beautiful surface can be obtained even after the heat treatment. In the secondary cold rolling after the heat treatment,
Damage to the roll for rolls due to the oxidized scale formed on the wire and occurrence of scale flaws on the surface of the wire can be prevented.

The β transformation point differs depending on the components contained in titanium or a titanium alloy and the content thereof. For example, the beta transformation point of two kinds of titanium specified in JIS-H4600 is about 910 ° C., % Al-4% V-
The β transformation point of a titanium alloy of Ti is about 990 ° C.

If the heat treatment method of the present invention is used for the final finish annealing, the polishing time in the polishing step can be shortened. If the heat treatment method is used for the intermediate annealing, the coarsening of the crystal grains in the intermediate annealing can be suppressed. In the secondary rolling of, further refinement of the crystal grains proceeds, and it becomes possible to produce a titanium and titanium alloy wire rod having further excellent polishing properties.

[0040]

(Example 1) A JIS-H4600 wire having a β transformation point of 910 ° C. was prepared by finishing a wire to a diameter of 6 mm by hot rolling and then adjusting the outer diameter to 5.7 mm by peeling.
And a titanium alloy wire having a β transformation point of 990 ° C. consisting of 6% Al-4% V—remaining Ti and unavoidable impurities (hereinafter referred to as pure titanium wire). , A titanium alloy wire).

As a continuous rolling mill, ten stands provided with four integral rolls each having a maximum outer diameter of 130 mm or less and having a basic structure shown in FIGS. 1A and 1B were used. Further, 10 stands provided with a hole type roll having a maximum outer diameter of 80 mm or less in the above-described basic configuration at the rear thereof were connected at a stand center distance of 80 mm. The hole-shaped shape of the hole-shaped roll incorporated in each stand is as shown in FIG.
04, and the cross-sectional reduction rate per pass in each stand was 5 to 15%.

The continuous furnace has the basic structure shown in FIG.
Stainless steel muffle having an outer diameter of 21.6 mm, a thickness of 2.8 mm, and a length of 4 m, and a central portion of the muffle of 3 m outside the muffle.
Is provided with an induction heating device capable of equalizing the temperature to an arbitrary temperature in a range of 600 to 1100 ° C., and Ar gas is supplied from a supply hole at a rate of 0.5 liter per minute to the inside of the muffle. A non-oxidizing atmosphere was used. Connected to the muffle on the muffle out side, outer diameter 21.6m
A cooling device provided with a stainless steel cylinder having a thickness of 2.8 mm, a thickness of 2.8 mm, and a length of 4 m, and indirectly cooling the wire through the cylinder in a water tank having a capacity of 120 liters was arranged. In addition, cooling water was supplied to the water tank at a rate of 3 liters / minute to suppress a rise in the temperature of the cooling water.

FIG. 4 is a schematic view showing a polishing state by the polishing apparatus used in the embodiment. Reference numeral 41 denotes a wire, 42 denotes a polishing brush, and 43 denotes a nozzle.

As shown in FIG. 4, the polishing apparatus employs a method in which abrasive particles are mixed with water on the surface of a moving wire and the polishing brush 42 is pressed while being sprayed from a nozzle 43. The three sets of polishing stands having a pair of polishing brushes are placed one around each other around the pass line.
Those used were arranged in tandem with phases shifted by 20 °. The outer diameter of the polishing brush was 300 mm, and the rotation speed of the polishing brush was 3 revolutions per second. The abrasive particles used were made of alumina (Al ₂ O ₃ ) having a particle size of 5 μm.

For each of the above-mentioned strands, the number of rolling stands of the above-mentioned continuous rolling mill was changed to change the degree of processing (to reduce the area by 2%).
(0 to 75%) and then rolled, and then heat-treated in the heat treatment furnace at a soaking temperature of (β transformation point −30 ° C.) for a holding time of 100 seconds. After the heat treatment, the cooled wire rod is polished by the polishing apparatus, and the surface roughness is Rmax.
The upper limit of the wire feed speed V of 1 μm or less was determined.
The higher the speed, the shorter the polishing time and the better the polishing ability. Table 1 shows the upper limit of the feed speed.

[0046]

[Table 1]

As is evident from the results shown in Table 1, when the working ratio of any of the wire rods in the continuous rolling mill is 40% or more of the area reduction rate specified in the present invention, the upper limit of the feed rate is high, and the polishing is performed. The properties were good.

(Example 2) The working degree of the continuous rolling mill was 60% in cross-sectional reduction (wire diameter after rolling: 3.6 mm), and the soaking temperature was (β transformation point-200 ° C) to (β transformation). Point +50
(° C.), and the rolling and heat treatment were performed under the same conditions as in Example 1. Next, in the same manner as described above, the upper limit of the feed speed Vw at which the surface roughness of the wire was 1 μm or less in Rmax was determined by polishing. Table 2 shows the upper limit of the feed speed.
In addition, a sample for a tensile test was collected from the wire after the heat treatment, and the elongation and the yield stress were examined, and compared with the as-rolled wire without the heat treatment. Table 3 shows the results.

[0049]

[Table 2]

[0050]

[Table 3]

As is evident from the results shown in Table 2, in the case where the soaking temperature of each wire is in the temperature range of less than the β transformation point defined by the present invention and (β transformation point-150 ° C.) or more, The upper limit of the feed rate was high, and the polishing property was good.

Further, as is apparent from the results shown in Table 3, the soaking temperature of any of the wires was β
In the case where the temperature is lower than the transformation point and equal to or higher than the (β transformation point-150 ° C), the elongation is higher than that of the as-rolled wire,
Yield stress was reduced, and improvement in secondary cold workability was observed.

(Example 3) The soaking temperature is (β transformation point-
Rolling and heat treatment were performed under the same conditions as in Example 2 except that the holding time was in the range of 5 to 300 seconds.
Then, polishing is performed in the same manner as described above to reduce the wire surface roughness to Rma.
The upper limit of the feed speed Vw at which x was 1 μm or less was determined. Table 4 shows the upper limit of the feed speed. In addition, a sample for a tensile test was collected from the wire after the heat treatment, and the elongation and the yield stress were investigated. Table 5 shows the results.

[0054]

[Table 4]

[0055]

[Table 5]

As is clear from the results shown in Table 4, when the soaking time is 20 seconds or more and 240 seconds or less as specified in the present invention, the upper limit of the feed rate is high and the polishing property is good. Met.

Further, as is apparent from the results shown in Table 5, the soaking time of each wire was determined by the present invention.
In the case of 0 to 240 seconds, the elongation was higher and the yield stress was lower than that of the as-rolled wire rod, and improvement in cold workability was recognized.

[0058]

According to the present invention, a wire rod having excellent secondary cold workability and excellent polishing properties can be obtained. As a result, in a thin wire made of titanium or a titanium alloy for spectacles or decorations requiring mirror finishing, the polishing time can be reduced and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic front view of a stand constituting a continuous rolling mill used in the present invention. FIG. 1 (a) shows a first stand on an entrance side, and FIG. 1 (b) shows a second stand. Show.

FIG. 2 is a schematic front view showing a shape of a roll hole type.

FIG. 3 is a schematic cross-sectional view showing one example of a continuous furnace used for performing a heat treatment according to the present invention.

FIG. 4 is a schematic view showing a state of polishing by a polishing apparatus used in Examples.

[Explanation of symbols]

1: Stand, 2: Housing, 3: Hole, 4a: Hole roll, 4b: Roll shaft, 5: Hole forming groove, 6: Circular hole, 7: Bevel gear, 8: Input shaft, 9: Groove edge Gap between parts, 2
1: continuous furnace, 22: cooling device, 23: muffle, 24:
Cylinder, 25: water tank, 26: wire rod, 41, 27: supply port,
42: polishing brush, 43: nozzle.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/00 630 C22F 1/00 630K 686 686A 694 694A

Claims (2)

[Claims] 1. A plurality of stands having four integral hole-type rolls constituting a circular hole form are connected in the pass line direction by changing the groove bottom directions of the circular hole forms of adjacent stands by approximately 45 ° with respect to each other. Cold rolling at a cross-sectional reduction rate of 40% or more using a continuous rolling mill, and then in a non-oxidizing atmosphere at a temperature range of less than β transformation point and (β transformation point -150 ° C.) or more in a temperature range of 20 to 2 ° C.
A method for producing a thin wire made of titanium or a titanium alloy, which comprises performing a heat treatment of heating and holding for 40 seconds. 2. The method according to claim 1, wherein the heat treatment is performed using a continuous furnace through which the heat treatment can be passed.