JP2002003968A - Titanium sheet excellent in processability and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium sheet having no surface color a and excellent in seizure resistance and press processability, and to provide its production method. SOLUTION: In this titanium sheet, the arithmetic average roughness of the surface in the direction parallel to the rolling direction is 0.25 to 2.5 μm, the Vickers hardness by the load of 0.098N is higher than the Vickers hardness by the load of 4.9N in the surface by >=20, and also, the Vickers hardness by the load of 4.9N is <=180, and the titanium sheet is produced by holding the titanium sheet stock after cold rolling at 550 to 750 deg.C for >=5 min in an atmosphere in which oxygen fractional ratio is 2×10-7 to 2×10-5 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for members for heat exchangers, consumer goods such as camera bodies and kitchen equipment, members for transportation equipment such as motorcycles and automobiles, and exterior materials for home appliances and the like. The present invention relates to a titanium plate excellent in formability and a method for producing the same.

[0002]

2. Description of the Related Art Titanium generally has good press formability, and various types of soft pure titanium plates (titanium plates) defined by one or two of JIS H4600 require press forming. Used for applications. For example, titanium is used for heat exchangers, etc., utilizing the excellent corrosion resistance of titanium, and recently, taking advantage of its light weight properties, mufflers for motorcycles and automobiles, camera bodies, home appliances, ,Personal computer,
It is also used for exterior materials such as side plates of electronic devices such as mobile phones.

[0003] The titanium plate used for the above applications is generally made from sponge-like titanium metal and titanium scrap as raw materials by vacuum arc melting or electron beam melting to form an ingot, and the ingot is subjected to lumping and hot rolling. After that, it is further manufactured by cold rolling and annealing.

[0004] When this titanium plate is used for each purpose, it is subjected to processing such as press forming. However, since titanium is a chemically active metal, it is necessary to use a tool (die) during press forming. Seizure is likely to occur due to contact. For this reason, it is necessary to grind after press molding, which is one of the causes of an increase in product cost. As a technique for preventing seizure during press forming of a titanium plate and improving formability, for example, Japanese Patent Application Laid-Open No. 6-248404 discloses a technique in which 0.01 to 20% of oxygen is added in a cooling process after final annealing. A method is disclosed in which an oxide film having a thickness of 250 angstroms (25 nm) or more is formed on the surface of a titanium plate by cooling in an atmosphere containing an inert gas. This method aims to improve the press formability by utilizing the lubricating effect of the oxide film on the surface of the titanium plate, but the oxide film on the surface of the titanium plate causes interference of light and the surface is colored. I do. It is known that an oxide film having a thickness of 10 nm or more exhibits a blue color, which is not preferable particularly when design is important. In Japanese Patent Application Laid-Open No. 10-60620, a titanium thin plate having a titanium nitride layer of 0.1 to 1 μm on the surface and excellent in press formability is disclosed in JP-A-10-204609.
In the publication, a titanium thin plate for forming process also having a nitrogen-enriched layer of 0.5 to 5 μm is proposed, and it can be manufactured by annealing titanium under specific conditions in a nitriding atmosphere at the time of final annealing. I have. However, even with such a nitride layer, light interference occurs, so that the appearance of the product is in a colored state.

[0005]

The present invention has been made under such a background, and has good seizure resistance.
It is an object of the present invention to provide a titanium plate which is excellent in press formability and has no surface coloring, and a method for producing the same.

[0006]

In order to solve the above problems, the present inventor paid attention to controlling the roughness of the titanium plate surface and controlling the hardness (hardness).

It is important to control the surface roughness of the titanium plate in order to improve the formability. This is because if the surface roughness is increased to some extent, an effect of drawing in and holding the lubricant between the titanium plate and the tool (die) during press forming occurs, and seizure during press forming can be prevented. Normally, cold rolling of titanium material is performed by a roll polished to a surface roughness of about # 120. However, if a roll polished and finished as described above is used, the surface of the titanium plate after rolling is smooth. Too much, and the above-described lubricant pull-in effect does not occur. To increase the surface roughness of the rolled titanium plate,
Although it is necessary to increase the surface roughness of the rolling roll itself, a method such as a method of applying a shot blast treatment to the surface of the roll to roughen the surface or a method of roughening the surface by electric discharge machining can be employed. . Cold rolled titanium plate,
A method of rolling by a skin pass rolling mill provided with a skin pass roll having a roughened surface can also be adopted. Properly managing the hardness of the titanium plate surface is effective in preventing the occurrence of seizure during press forming, as described below.

In the press forming of a titanium plate, as the mold is pressed into the material constituting the titanium plate, the material slides on the surface of the mold and is drawn into the concave portion of the mold. In the case of a material having a soft surface, when the material slides on the mold, a film such as an oxide film formed on the material surface is easily broken, and a new surface inside appears on the surface. Titanium is chemically active and easily forms and seizes when the new surface is exposed.Since this seizure rubs the surface of the material that is pushed in, the material is transferred to the product after press molding. Seizure marks (scratches) occur along the direction. In this case, if the surface of the material is hard, a new surface is not formed until distortion due to molding is relatively high, so that seizure with the mold is suppressed. In particular, when the surface roughness is roughened, the true contact area between the material and the tool material at the time of press forming is reduced, and a higher pressure is applied to the tip of the projection on the material surface than in the case where the surface is smooth. As a result, a new surface is more likely to appear. Therefore, when the surface is rough, it is necessary to form a hard layer on the surface so as to reduce the exposure of the new surface.
However, making the entire material hard is effective from the viewpoint of preventing seizure flaws, but such a hard material has a problem that the formability is lower than that of a soft material, and is essentially an issue. Is not a simple solution. The present invention has been made based on such a concept, and its gist lies in the following (1) titanium plate and (2) a method for manufacturing the titanium plate. (1) The arithmetic average roughness of the surface in the direction parallel to the rolling direction is 0.25 μm or more and 2.5 μm or less, and the test load is 0.098 N (10 gf) more than the Vickers hardness at the surface with a test load of 4.9 N (500 gf). 3.) the Vickers hardness is 20 or more higher and the test load is 4.
A titanium plate whose Vickers hardness by 9N is 180 or less. (2) The titanium plate after the cold rolling is performed with an oxygen content of 2 × 10 ^−7.
550 in an atmosphere of not less than 2% by volume and not more than 2 × 10 ^-5 % by volume.
A method for producing a titanium plate which is maintained at a temperature of 750 ° C. or more and 750 ° C. or less for 5 minutes or more.

The above “titanium plate” is defined in JIS H46
Titanium plates specified as one or two of
It refers to a titanium alloy plate with excellent corrosion resistance to which a small amount of Pd or Ni is added.

"Average surface roughness" refers to JIS B06
It refers to the arithmetic average roughness (Ra) specified in 01. Also,
The “oxygen fraction” is obtained by multiplying the oxygen content (volume%) in the atmosphere by the ratio of the atmospheric pressure to the standard pressure (1.013 × 10 ⁵ Pa (1 atm)). . For example, as in the case of Example 1 described below, the oxygen fraction when the inside of the furnace is brought into a reduced pressure state of 0.01 Pa is obtained by setting the content of oxygen in the atmosphere (ie, air) to 20% by volume. 20 × (0.01 / 1.013 × 10 ⁵ ) ≒
It becomes 2 × 10 ⁻⁶ (vol%).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the titanium plate excellent in formability of the present invention and a method for producing the same will be described in detail.
As described above, by increasing the roughness of the surface of the titanium plate to some extent, the amount of lubricant drawn into the titanium plate and the mold during press forming is increased to prevent seizure, and after press forming. Seizure flaws can be reduced.
Since the lubricating effect is enhanced, the formability itself is also improved.

The above effect cannot be obtained if the average roughness of the titanium plate surface is less than 0.25 μm. On the other hand, when the average roughness exceeds 2.5 μm, ductility decreases. Titanium is a material with high notch sensitivity, and if the surface has irregularities exceeding a certain size, it acts as a notch, so strain due to stress concentration concentrates near the notch in the tensile test, and it breaks at that part Because you do. The direction of the roughness measurement is set to the direction parallel to the rolling direction, because in the Erichsen test for evaluating the press formability of the titanium plate, cracks at break occur in the plate width direction which is a direction perpendicular to the rolling direction. It is. That is, by improving the formability in the rolling direction, the formability in press working can be improved. As described above, properly managing the surface hardness is also effective in preventing the occurrence of seizure during press molding. In this case, if the whole material is hard, the formability of the titanium plate itself is reduced, so that only the surface layer is hard, that is, it is necessary that a hard surface layer exists on the surface of the titanium plate. is there.

When a thin hard surface layer is present on the surface of the material, it is extremely difficult to accurately evaluate and define the thickness. Therefore, in the titanium plate of the present invention, the hardness of the surface is an appropriate value. The range is defined as shown below. Specifically, when measuring Vickers hardness, test load (hereinafter, referred to as
(Hereinafter simply referred to as load), the Vickers hardness under the load of 0.098 N is 20 or more higher than the Vickers hardness under the load of 4.9 N, and the Vickers hardness under the load of 4.9 N is 180 or less. .

In general, when the load is small, the indentation caused by the diamond indenter of the Vickers tester is small, and the measured value of hardness is mainly affected by the surface layer. On the other hand, when the load is large, the indentation becomes extremely large, so that the influence of the surface layer on the hardness measurement result is small, and reflects the internal hardness of the material. Therefore, in the titanium plate of the present invention,
Vickers hardness was measured at a load of 4.9 N and a load of 0.098 N, respectively, and the difference between the measured values was assumed to be 20 or more. If it is less than 20, the surface is not a hard layer having sufficient hardness, and the raw material and the mold material cause seizure in the initial stage of press molding. Further, the Vickers hardness under a load of 4.9 N is set to 180 or less because if it exceeds 180, the inside of the material is hard, the ductility is low, and cracks are easily generated during press molding. The titanium plate of the present invention is obtained by converting the titanium plate after cold rolling to an oxygen fraction of 2 × 10 ⁻⁷ vol% or more and 2 × 10 ⁻⁵ vol%.
It can be manufactured by holding at 550 ° C. or more and 750 ° C. or less for 5 minutes or more in the following atmosphere. Titanium plates that are press-formed and used for the above-mentioned applications are generally made from sponge-like titanium metal and titanium scrap as raw materials by vacuum arc melting or electron beam melting to form ingots. After being rolled, it is manufactured by performing cold rolling and annealing treatment. In the method for manufacturing a titanium plate of the present invention, the cold rolled titanium plate material is used as a raw material (titanium plate material). The cold rolling conditions and the conditions in each manufacturing process up to the cold rolling conditions may be ordinary conditions. The titanium plate material is subjected to an annealing treatment. If the oxygen content in the atmosphere at that time is less than 2 × 10 ⁻⁷ vol%, a hardened layer is not sufficiently formed on the titanium plate surface after the annealing treatment. The seizure resistance becomes insufficient. On the other hand, the oxygen fraction is 2 × 10 ^-5
If the volume percentage is exceeded, a thick oxide film is formed on the surface of the titanium plate after the annealing treatment, and light interference occurs to color the surface.
Further, if the annealing temperature is lower than 550 ° C., the titanium sheet material is left with distortion due to cold rolling, and thus the material is not given sufficient formability. On the other hand, when the annealing temperature is 75
If the temperature exceeds 0 ° C., the crystal grain size of the material becomes extremely coarse, so that the surface becomes rough after press molding, and the appearance of the product is impaired. The annealing temperature is preferably 6
The temperature is from 00 ° C to 700 ° C. If the holding time during the annealing treatment is less than 5 minutes, the crystal grains do not grow sufficiently,
The formability of the obtained titanium plate becomes insufficient. The upper limit of the holding time is not particularly defined. It is desirable to keep the coil for a short time in consideration of economy, but when annealing the coil, it is necessary to hold the coil for a long time so that the center of the coil is sufficiently heated. The titanium plate of the present invention hardly causes seizure at the time of press molding, and therefore has good moldability, and does not cause coloring on the surface of the titanium plate. This titanium plate can be easily manufactured by the method of the present invention.

[0015]

EXAMPLES (Example 1) The following test was conducted to investigate the influence of surface roughness on moldability and seizure. Table 1
Shows the chemical composition of an industrial pure titanium plate (annealed plate, thickness 0.8 mm) used as a material.

[0016]

[Table 1] This material is cold-rolled to a thickness of 0.5 mm using a rolling roll with a changed surface roughness, and further subjected to shot blasting before and / or after rolling. The titanium plate obtained by changing the surface roughness of the material and then performing an annealing treatment at 650 ° C. for 30 minutes was used as a test material. In the annealing treatment, a test material was charged into a furnace using a vacuum furnace, the furnace was evacuated to 0.01 Pa, and then heated. At this time, the oxygen content in the annealing atmosphere is 2 × 10 ⁻⁶ volume%.
Table 2 shows the conditions used for changing the surface roughness and the surface roughness of the test material. The surface roughness was determined by measuring the average roughness of a portion having a length of 10 mm in a direction parallel to the rolling direction using a contact-type roughness meter.

[0017]

[Table 2] First, to investigate the moldability, 90
A test piece of mm square was collected and subjected to an Erichsen test specified in JIS Z2247. The test was performed on three test pieces. Note that a graphite paste was used as the lubricant. Next, in order to investigate the seizure property, a width of 50 m was used from the above test material so that the rolling direction was the length direction.
A test in which a test piece having a length of 200 mm and a length of 200 mm is sampled, set in a test machine shown in FIG. Was done. Machine oil was used as a lubricant during the test. In FIG. 1, the test piece 1 is a die 2 and a
The right side is a state in which a load is applied to the test piece 1 by the punch 4 to perform a forming process. The test was performed under the conditions of No. 1 to No. 6 shown in Table 2 for 100
The test was performed on the test pieces. That is, the number of repetitions is 10
0 was set. In this test, since many seizure marks were generated, the widths of the seizure marks were totaled, and the value was divided by the width of the test piece (50 mm) to obtain the seizure occurrence rate. The test results are also shown in Table 2. In Table 2, "Erichsen value" is an average value of the Erichsen values of three test pieces. If the average value exceeds 11 mm, the moldability is determined to be good and indicated by a circle in the column of "Evaluation". In the case of 11 mm or less, it was indicated by X mark as poor moldability. The “seizure occurrence rate” is an average value of the seizure occurrence rates of 100 test pieces. When the average value is 15% or less, the seizure resistance is determined to be good. When it exceeds 15%, it was indicated by X as poor seizure resistance. Also,
“Comprehensive evaluation” is indicated by a circle when both the moldability and the seizure resistance are good, and by a cross when at least one of them is poor. As is clear from the results in Table 2, when the average roughness of the surface was 0.20 μm (No. 1), the Erichsen value was low and the occurrence of seizure was high. On the other hand, when the average surface roughness was 0.25 μm or more (Nos. 2 to 4 and No. 6), both the Erichsen value and the seizure occurrence rate were good values. This is because when the surface is moderately rough, the lubricating effect of the lubricant is increased, and the contact state between the tool and the material is reduced.

The conditions (method) for imparting an appropriate roughness to the surface are as follows: the surface of the rolling roll is polished to a surface roughness of # 36 or subjected to a shot blast treatment to make it rough. The material was subjected to a shot blasting process before or after rolling. On the other hand, when the average roughness of the surface exceeded 2.5 μm (No. 5), the Erichsen value decreased. This is due to the fact that unevenness on the surface acts as a notch, and cracks occur early from the notch during the Erichsen test. (Example 2) The following tests were conducted to investigate the effects of annealing conditions on formability, seizure properties, and coloring of the titanium plate surface. Using the industrial pure titanium plate used in Example 1 as a material, a 0.5 m thick roll using a roll roll polished at # 36
m, and then annealed under the conditions shown in Table 3 to obtain a titanium plate as a test material.

[0019]

[Table 3] A vacuum furnace was used for the annealing treatment. After the test materials were charged into the furnace, the furnace was evacuated and evacuated when the furnace reached a predetermined reduced pressure state (indicated by "Initial vacuum degree" in Table 3). Was stopped to change the oxygen content in the annealing atmosphere. From this state, the temperature was raised to a predetermined annealing temperature over a period of 1 hour, and after maintaining at that temperature for a predetermined time, the test material was cooled in the furnace. I took it out.

An Erichsen test and a seizure test were performed on the test material in the same manner as in Example 1, and the hardness of the test material surface was measured. investigated. In the measurement of hardness on the surface, Vickers hardness was measured under a load of 0.098 N and 4.9 N. The coloring state was examined by visual observation.

The test results are also shown in Table 3. In Table 3, the “Erichsen value” and the “seizure incidence” are each represented by an average value in the same manner as in Example 1, and the “Ericksen value” column “evaluation” and the “seizure incidence” In the column of “Evaluation”, a mark “ま た は” or a mark “X” was given based on the same criteria as in Example 1. In addition, the “overall evaluation” is indicated by a circle (except for No. 11 described later) when all of the moldability, seizure resistance, and coloring state are good, and when at least one of these is bad, Indicated by X mark. As is evident from the results in Table 3, in Nos. 4, 5, 8 to 10, 13 and 14, which satisfy the conditions specified in the present invention, all of the moldability, seizure resistance, and coloring state were excellent. Was.

On the other hand, when the initial vacuum degree during the annealing treatment is lower than 0.1 Pa and the oxygen fraction in the atmosphere exceeds the range specified in the present invention (Nos. 1 to 3), No. 2 And N
In o.3, the moldability and the seizure resistance were good, but the surface was colored. In No. 1, the hardness on the surface was out of the range specified in the present invention, and the moldability was poor. No.6
In this case, since the oxygen content in the atmosphere is low, a hard layer having sufficient hardness is not formed in the annealing treatment. For this reason, the hardness on the surface did not satisfy the condition (hardness difference of 20 or more) specified in the present invention, and the seizure resistance was poor.

In No. 7 having a low annealing temperature and No. 12 having a short holding time during annealing, the hardness inside the material was high due to the remaining strain due to cold rolling, and the formability was poor. Also,
In No. 11 where the annealing temperature exceeds the range specified in the present invention,
All of the moldability, seizure resistance and coloring state were good, but the rough surface after molding was increased due to the large crystal grains of the material. From the above test results, it can be seen that the titanium plate satisfying the conditions defined in the present invention is suppressed from seizure during molding, and has good moldability and surface coloration.

[0024]

The titanium plate of the present invention has good seizure resistance, is excellent in press formability, and has no surface coloring. This titanium plate can be easily manufactured by the method of the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a method of evaluating seizure, and is a cross-sectional view showing a configuration of a main part of a tester.

[Explanation of symbols]

 1: Test piece 2: Die 3: Wrinkle holder 4: Punch 5: Liner

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[Procedure amendment]

[Submission date] June 22, 2000 (2000.6.2)
2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

The "arithmetic mean roughness of the surface" refers to JIS B
0601 means the arithmetic average roughness (Ra). Hereinafter, it is simply referred to as the average roughness of the surface. The “oxygen fraction” is obtained by multiplying the oxygen content (volume%) in the atmosphere by the ratio of the atmospheric pressure to the standard pressure (1.013 × 10 ⁵ Pa (1 atm)). It is. For example, as in the case of Example 1 described below, the oxygen fraction when the inside of the furnace is brought into a reduced pressure state of 0.01 Pa is obtained by setting the content of oxygen in the atmosphere (ie, air) to 20% by volume. 20
× (0.01 / 1.013 × 10 ⁵ ) ≒ 2 × 10 ^-6
(% By volume).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/00 691 C22F 1/00 691B 691C 1/02 1/02

Claims (2)

[Claims] An arithmetic average roughness of a surface in a direction parallel to a rolling direction is 0.25 μm or more and 2.5 μm or less, and a Vickers hardness at a test load of 0.098 N is higher than a Vickers hardness at a surface of a test load of 4.9 N. 2 more
A titanium plate having a height of 0 or more and a Vickers hardness under a test load of 4.9 N of 180 or less. 2. The cold rolled titanium sheet is treated with an oxygen fraction of 2 ×
A method for producing a titanium plate, wherein the titanium plate is kept at 550 ° C. or more and 750 ° C. or less for 5 minutes or more in an atmosphere of 10 ⁻⁷ vol% or more and 2 × 10 ⁻⁵ vol% or less.