JP2016156054A - Titanium plate and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a titanate plate excellent in strength and moldability.SOLUTION: The titanium plate has, by mass%, an iron content of 0.01 to 0.1%, an oxygen content of 0.02 to 0.15%, a carbon content of 0.015% or less, a nitrogen content of 0.015% or less, a hydrogen content of 0.015% or less and the balance titanium with inevitable impurities. In the titanium plate, the arithmetic average roughness (Ra) in the L direction is 0.2 to 0.8 μm; the arithmetic average roughness in the T direction is not less than 1.1 times to not more than 2 times that in the L direction; deformation twins are present in a range of 0.05 t to 0.2 t from a surface layer when a plate thickness is t; the Vickers hardness at a measurement load of 0.25 N in the surface is 170 or more; the Vickers hardness at a measurement load of 9.8 N in the surface is 90 to 180; and the Vickers hardness at a measurement load of 0.25 N is not less than 1.5 times the Vickers hardness at a measurement load of 9.8 N.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a titanium plate having excellent formability and widely used in fields where higher strength is required.

  Pure titanium and titanium alloys are lighter and stronger than ferrous metal materials such as iron and its alloys, so they are widely used in sports and leisure equipment, medical equipment, various plant components, aerospace equipment, etc. It has been. In addition, since it has excellent corrosion resistance, it is used, for example, as a plate material for a plate heat exchanger, a muffler member for a motorcycle, and the like.

  When manufacturing such a product, various processes accompanied by plastic deformation such as bending, drawing, and pressing are performed. Therefore, in order to provide such various uses, the titanium plate is required to have excellent formability during processing such as drawing.

  However, recently, in order to reduce the required amount of titanium material, thinning is required, and higher strength is required from the present situation. In other words, it is necessary to develop a titanium plate that simultaneously satisfies the material properties that have a trade-off relationship between formability and strength.

  Regarding pure titanium, JIS type 1, JIS type 2, JIS type 3, JIS type 4 and the like are defined according to the content of iron (Fe) and oxygen (O) other than titanium. As for the material characteristics of this pure titanium, it is known that JIS type 1 having a low content of Fe or the like has the lowest strength and excellent moldability, and the strength becomes higher as it becomes JIS type 2 or JIS type 3. However, on the other hand, the moldability decreases as JIS type 2 and JIS type 3, and it is not easy to perform drawing processing using these.

  Conventionally, as a method for increasing the strength of a titanium material, solid solution strengthening by adding Fe, O, etc., and crystal grain refinement strengthening have been performed. However, as described above, this deteriorates ductility as the strength increases, and the moldability deteriorates accordingly.

  In Patent Documents 1, 2, 3 and 4, since the Fe content exceeds 0.1% or the Ni content which is a β-phase stabilizing element similar to Fe is large, the α-phase crystal grains may be small. There is a possibility that sufficient formability cannot be obtained.

  In Patent Document 5, Fe: 1.0 mass% or less is used, but in the examples, the α phase particle size does not reach 20 μm, and the crystal grain size is small, so that sufficient formability cannot be obtained.

  Further, in Patent Documents 6 and 7, the crystal grain size may be less than 30 μm in the description in the examples, and if the crystal grain size is smaller than 30 μm, the moldability may be lowered. In addition, when the oxygen content is less than 0.05% by mass, sufficient strength cannot be obtained.

  In patent document 8, finishing cold work is performed 3.4 to 5.8% after annealing, and the anisotropy of r value is reduced. However, since there is much cold work amount, there exists a possibility that a moldability may fall.

  Patent Document 9 describes that a high-strength titanium alloy sheet is manufactured by maintaining the stretchability at a high level by setting the area ratio of the β phase to 3 to 20%. However, the area ratio of the β phase is 3 If it exceeds 50%, voids are likely to occur during plastic deformation, and this may lead to a decrease in formability.

  On the other hand, in Patent Document 10, a titanium plate excellent in formability and lubricity in which the nitrogen concentration and surface roughness of the surface layer are controlled is proposed, but because a very hard titanium compound is formed on the surface, In press molding or the like to which a large strain is applied, there is a risk of becoming a starting point of cracking.

  In Patent Document 11, the oxide film is formed to have a thickness of 3 to 15 nm, only the extreme surface layer is cured, the surface hardness is controlled, and excellent moldability is exhibited by press molding or the like. Moreover, the cleaning property is enhanced by setting the surface roughness (arithmetic mean roughness (Ra)) to 0.25 μm or less.

Pure titanium forms a dense oxide scale on the surface by heat treatment such as hot working or annealing. After annealing a pure titanium thin plate in the atmosphere, generally, a slightly water-soluble oxide scale is modified to water-soluble Na ₂ TiO ₃ by immersing (salt treatment) in a salt mainly composed of NaOH, Pickle with a mixed solution of nitric acid and hydrofluoric acid (nitric hydrofluoric acid), descal, then wash with water and dry. Various methods have been proposed for this pickling method.

  In Patent Document 12, various pickling conditions such as concentrations of nitric acid and hydrofluoric acid are studied for the purpose of improving the pickling speed.

  In Patent Document 13, in order to prevent the occurrence of spark during descaling in a salt bath, after immersing a titanium material in a molten alkali salt bath, anodic electrolysis and / or alternating electrolysis is performed in an aqueous electrolyte solution. Furthermore, a method of immersing in a nitric hydrofluoric acid pickling solution has been proposed.

  In patent document 14, in order to prevent generation | occurrence | production of the micro recessed part by shot blasting in a stainless hot-rolled steel strip, the method of grinding a hot-rolling scale with a rotating brush and pickling is proposed.

Japanese Patent No. 1696795 Japanese Patent No. 1593477 JP 2004-285457 A JP 2007-162070 A JP 2009-215601 A JP 2011-25269 A JP 2011-26649 A JP 9-216044 A JP 2008-127633 A JP 2004-244671 A JP 2011-020135 A JP 2009-256736 A Japanese Patent Laid-Open No. 11-200078 Japanese Patent Application Laid-Open No. 7-051728

  The titanium plates described in Patent Documents 1 to 9 have attempted to achieve both strength and formability by controlling additive elements and metal structures, but the strength and formability are in a trade-off relationship and increase the strength. There was a problem that sufficient moldability could not be obtained.

  For this reason, the invention which paid attention to surface property like patent documents 10 and 11 for the purpose of improving moldability is also seen. In Patent Document 10, a compound is formed on the surface for the purpose of increasing the surface hardness. This is advantageous for improving seizure resistance and lubricity, but if harsh press molding is performed, a brittle compound may become a starting point of cracking.

  In Patent Document 11, the compound is controlled to be extremely thin, but the surface roughness is small. In this case, a sufficient amount of lubricant cannot be applied, which is disadvantageous for press molding.

  In order to achieve both high strength and high formability, it is necessary to add elements and control the metal structure and surface characteristics. In particular, it is important to control surface hardness and surface roughness, which are factors of surface characteristics that greatly affect moldability. For this reason, the present inventors need to study a manufacturing method for increasing the surface hardness without forming a compound and a manufacturing method for achieving a surface roughness on which the lubricant acts most effectively, without being bound by conventional manufacturing methods. I thought it was.

  This invention makes it a subject to provide the titanium thin plate which was excellent in the intensity | strength and a moldability which increased the intensity | strength without reducing a moldability in view of said situation.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies on a production method for increasing surface hardness without forming a compound and a surface roughness on which a lubricant acts effectively.

  As a result, after the oxide scale generated by atmospheric annealing of the titanium plate is completely modified by salt dipping, the surface roughness is set to a predetermined level by polishing with a brush capable of removing this modified layer with a brush. As a result, it was found that the balance between strength and formability was greatly improved by working and hardening only the surface layer of the titanium plate by deformation twinning, and the present invention was completed. The summary is as follows.

  (1) In mass%, the iron content is 0.01 to 0.1%, the oxygen content is 0.02 to 0.15%, the carbon content is 0.015% or less, and the nitrogen content Is 0.015% or less, the hydrogen content is 0.015% or less, the balance is titanium and inevitable impurities, and the arithmetic average roughness (Ra) in the L direction is 0.2 to 0.8 μm, When the arithmetic average roughness in the T direction is 1.1 to 2 times that in the L direction and the plate thickness is t, deformation twins exist in the surface layer range of 0.05 t to 0.2 t, and The Vickers hardness is 170 or more at a measurement load of 0.25 N, the Vickers hardness at a measurement load of 9.8 N on the surface is 90 to 180, and the Vickers hardness at the measurement load of 0.25 N is the measurement load of 9 A titanium plate characterized by being 1.5 times higher than the Vickers hardness at 8N.

  (2) The method for producing a titanium plate according to (1), wherein the titanium material is cold-rolled, the cold-rolled titanium plate is annealed in the atmosphere, and the annealed titanium plate is NaOH in mass%. A method for producing a titanium plate, comprising immersing in a salt bath at 75 to 95%, 520 to 550 ° C. for 15 to 60 seconds, and removing a surface layer of 1 to 3 μm of the titanium plate after the immersion with a grinding brush.

  Here, the L direction is the final rolling direction, and the T direction is a direction orthogonal to the L direction.

  In the present invention, since the element is not added excessively, the formability is not lowered, and the pickling is replaced by brush polishing, so that a decrease in yield can be greatly suppressed. A titanium thin plate that can be increased and is excellent in strength and formability is obtained.

It is a figure which shows the twin of the surface of the titanium plate of this invention. In an Example, it is a figure which shows the shape of the test piece used for the ball head protrusion test. It is a figure which shows the surface layer of the titanium plate which carried out the air annealing and salt process and performed the pickling process. It is a figure which shows the surface layer of the titanium plate which carried out air annealing and salt processing and brush-polished. It is a figure which shows the strength ductility balance of this invention material.

  The titanium plate of the present invention contains 0.01 to 0.1% iron by mass%. In order to make the iron content less than 0.01%, only expensive sponge titanium with a low iron content can be used. Moreover, sufficient strength cannot be imparted to the formed titanium plate. The iron content is preferably 0.015% or more, and more preferably 0.02% or more.

  On the other hand, if the iron content exceeds 0.1%, the crystal grain size becomes too small, and even if the oxygen content in the titanium material is set to a predetermined value, the ductility is lowered and the formability of the titanium plate is lowered. . Moreover, since many β phases that easily absorb hydrogen are generated after hot rolling and heat treatment steps, there is a concern that the corrosion resistance may be lowered. Therefore, the iron content is 0.1% or less. More preferably, it is 0.09% or less.

  The titanium plate of the present invention contains 0.02 to 0.15% oxygen by mass%. In order to make the oxygen content less than 0.02%, high-purity sponge titanium is required, so that not only the use of general raw materials becomes difficult, but also the strength of the titanium material is significantly reduced. The oxygen content is preferably 0.03% or more.

  If the oxygen content exceeds 0.15%, the strength becomes too high and the titanium plate has poor formability. The oxygen content is preferably 0.14% or less.

  In addition, carbon, nitrogen, and hydrogen need to be contained in amounts equal to or less than those of JIS class 2 for the purpose of ensuring good moldability in the molding process. More specifically, the contents of carbon, nitrogen, and hydrogen must each be 0.015% or less by mass.

  Preferably, the carbon content is 0.01% or less, the nitrogen content is 0.01% or less, and the hydrogen content is 0.01% or less.

  From the viewpoint of formability of the titanium plate, there is no lower limit to the content of the carbon, nitrogen, and hydrogen. However, if these contents are extremely reduced, the production cost of the titanium plate is greatly increased. There is a fear. From the viewpoint of suppressing the cost increase, it is preferable that carbon is 0.0005% or more, nitrogen is 0.0005% or more, and hydrogen is 0.0005% or more.

In order to improve the lubricity with the mold by press working, a method of forming a compound layer such as TiC, TiN, oxide film TiO ₂ or the like on the surface in order to harden the surface may be employed. However, since these compound layers are hard and have low deformability, there is a problem that cracking is likely to occur during press working. For this reason, in the titanium plate of the present invention, the surface layer of 0.05 t to 0 .0 is not formed on the surface (except for a passive film that is naturally generated), and the surface layer of the titanium material itself is harder than the center of the plate. The deformation twins are distributed over 2t (t is the plate thickness). A schematic diagram of the titanium plate of the present invention is shown in FIG.

  In the present invention, brush polishing is performed as a method for distributing deformation twins only on the surface layer. Thereby, twins are introduced only into the surface layer, and only the hardness of the surface layer can be increased and the moldability can be improved. If the twin layer is smaller than the surface layer of 0.05 t, the surface layer region that has been work hardened is too small, so strain is introduced into the surface layer during molding, the work hardening of the surface layer proceeds, and the starting point of cracking. Will decline. If the twin layer is larger than the surface layer 0.2t, the difference in hardness between the surface layer and the inside of the plate is small, strain is introduced into the surface layer at the time of molding, work hardening of the surface layer progresses, and it becomes the starting point of cracking, so the moldability is reduced. To do.

  Surface roughness is also a factor that greatly affects press molding. If the surface roughness is too small, the lubricant cannot be applied sufficiently, and there is a problem that the lubricant is insufficient during molding. If the surface roughness is too large, a large amount of lubricant can be applied, but the lubricant that has entered the back of the recess does not come into contact with the mold during molding and may not be supplied.

  A thin plate of titanium material has a higher deformability in the T direction in a forming process in which the thin plate is deformed without being contracted in width than the simple tension that is contracted in deformation. For example, in an Erichsen test in which tensile deformation is performed in the biaxial direction, it breaks in the direction extending in the L direction at the time of fracture. That is, in the molding process, the L direction is inferior in deformability. Accordingly, if the lubricant is preferentially supplied in the L direction, the deformability is increased as a whole. However, until now, there have been inventions focusing on the surface roughness itself, but no attempt has been made to focus on the anisotropy of the surface roughness.

  The present inventors have intensively studied and found a condition of surface roughness that allows sufficient application of the lubricant and sufficient supply of the lubricant during the molding process. That is brush polishing after the salt treatment, and the surface roughness due thereto is an arithmetic average roughness (Ra) in the L direction of 0.2 to 0.8 μm, and Ra in the T direction is 1. 1 to 2 times.

  When the arithmetic average roughness (Ra) in the L direction is 0.2 μm or less, the lubricant cannot be sufficiently applied. Preferably it is 0.3 micrometer or more. If it exceeds 0.8 μm, the unevenness is too large, and the lubricant that has entered the back of the recess is not supplied during molding, and sufficient moldability cannot be obtained. Preferably it is 0.7 micrometer or less.

  When Ra in the T direction is less than 1.1 times that in the L direction, the lubricant is not supplied in the direction extending in the L direction, and sufficient moldability cannot be obtained. Ra in the T direction is preferably 1.2 times or more in the L direction. If Ra in the T direction exceeds twice that in the L direction, it is difficult to supply the lubricant in the T direction, and sufficient moldability cannot be obtained. Due to the unevenness of 1.1 times to 2 times of the L direction in the T direction, priority is given to the supply of the lubricant in the L direction over the T direction, and the deformability in the L direction is improved, resulting in excellent moldability. Is obtained.

  In the present invention, the surface after brush polishing has a Vickers hardness of 170 or more at a measurement load of 0.25 N, a Vickers hardness of 90 to 180 at a measurement load of 9.8 N, and a Vickers hardness at a measurement load of 0.25 N. Is 1.5 times higher than the Vickers hardness at a measurement load of 9.8 N. In this case, since the surface layer is sufficiently harder than the inside of the plate, the strain is uniformly introduced preferentially into the soft inside due to the improvement in lubricity during molding. In addition, unlike the compound, the surface is a titanium material that can be plastically deformed, so that cracks are less likely to occur. From the above, by increasing the hardness of the surface that can be plastically deformed, the formability is improved by the uniformity of strain due to the improved lubricity that is less likely to crack.

  When the Vickers hardness at a measurement load of 0.25 N is less than 170, strain is also introduced into the surface layer at the time of molding, and the work hardening of the surface layer proceeds and becomes the starting point of cracking, so the moldability is lowered.

  If the Vickers hardness at a measurement load of 9.8 N is less than 90, the strength is insufficient. Preferably it is 100 or more. If it exceeds 180, the strength is too high and the moldability deteriorates. Preferably it is 170 or less, More preferably, it is 160 or less.

  When the Vickers hardness at a measurement load of 0.25N is less than 1.5 times the Vickers hardness at a measurement load of 9.8N, the difference in hardness between the surface layer and the plate is small, and strain is introduced into the surface layer during molding. As a result, the work hardening of the surface layer proceeds and becomes the starting point of cracking, so the moldability is lowered.

  Although it does not specifically limit about the brush used by the brush grinding | polishing which forms the hardness distribution of a surface layer, The grinding | polishing capability which a salt modification layer can remove is required. On the other hand, if the polishing ability is too high, wrinkles are generated on the surface, and polishing with a brush having an excessive polishing ability should be avoided. As described above, polishing may be performed so that deformation twins exist on the surface layer 1 / 5t (t is the plate thickness).

  The amount of polishing with the brush is not particularly limited, but the thickness of the oxide scale generated by annealing of the cold-rolled sheet is generally 2 μm or less. Removed.

  In the method for producing a titanium plate of the present invention, after annealing in the air after cold rolling, NaOH is immersed in a salt of 75% or more and 95% or less and 520 ° C or more and 550 ° C or less by mass% for 15s or more and then ground. The surface layer of 1 μm or more and 3 μm or less is removed with a brush.

  What is important at this time is that the surface is completely modified with a salt so that defects such as wrinkles do not occur on the surface and the scale can be completely removed, and brush polishing is appropriately performed. The reason for performing after the salt treatment will be described below.

  When the surface is softened after pickling, the surface is soft and strain is applied deeply into the inside, so that the hardness distribution defined in the present invention cannot be obtained and the moldability deteriorates. Moreover, since the new surface of titanium is exposed, the surface of active titanium may be burned. In the first place, when pickling, the titanium base material also dissolves, so the yield is greatly reduced.

  On the other hand, when brush polishing is performed with the scale generated by annealing attached, it is necessary to use a brush with high polishing ability and a large amount of rolling to remove the scale, and a large load is applied to the titanium surface, so that polishing wrinkles remain. There is a possibility that it becomes a starting point of cracks in press molding. Further, since the scale is hardly water-soluble and cannot be easily removed, it takes time for complete removal. For this reason, it is essential to completely modify the scale into a water-soluble salt-modified layer by dipping in a salt bath so that no scale remains.

  In scale modification with salt performed after cold rolling and annealing, NaOH contained in the salt bath is 75% to 95% by mass.

  When NaOH is less than 75%, it is difficult to completely modify the scale, and it takes a long time for the modification. Since it is difficult to immerse in a continuous line for a long time, the scale may remain by brush polishing. Increasing the brush polishing ability to remove this scale may cause surface flaws. From such a viewpoint, NaOH contained in the salt bath needs to be 75% or more. Preferably it is 80% or more.

When NaOH exceeds 95%, the concentration of NaNO ₃ contained in the salt is lowered, the viscosity of the salt is lowered, the amount of salt taken out is increased, the reduction of the salt is accelerated, and this is not economically favorable. The NaOH contained in the salt bath is more preferably 90% or less.

  The temperature of the salt bath is 520 ° C. or higher and 550 ° C. If it is less than 520 ° C., the scale is not sufficiently modified, and the scale may remain after brush polishing. Above 550 ° C., it reacts excessively with the salt to expose a soft titanium base material on the surface. As a result, excessive strain is introduced not only to the surface layer but also to the inside of the plate, the difference in hardness between the surface layer and the inside of the plate is reduced, strain is also introduced to the surface layer during molding, work hardening of the surface layer proceeds, and cracks start, Sex is reduced. Further, when the exposed base material comes into contact with the roll, a potential difference is generated, and a spark is generated, resulting in a defect. Furthermore, hydrogen is generated by the reaction between titanium and salt, and embrittlement occurs due to the formation of hydride, resulting in a decrease in moldability.

  The salt processing time is 15 seconds or more and 60 seconds or less. If it is less than 15 s, the scale is not sufficiently modified, and the scale may remain after brush polishing. If it exceeds 60 s, the salt and scale react excessively, the soft titanium base material is exposed on the surface, and the formability deteriorates for the above reason.

  Furthermore, as a method for further improving the balance between strength and formability, the annealing temperature and time can be adjusted.

  The annealing temperature is preferably 750 ° C. or higher and 820 ° C. or lower. If the annealing temperature is less than 750 ° C., the crystal grains are difficult to grow and the formability may be lowered. When the temperature exceeds 820 ° C., a β phase is generated and crystal grain growth is suppressed, so that it takes a long time to achieve a crystal grain size of several tens μm or more, at which twin deformation becomes active.

  The annealing time is preferably 60 seconds or more and 600 seconds or less. If the annealing time is less than 60 seconds, the crystal grains may not grow sufficiently. When annealing is performed for an annealing time exceeding 600 s, the oxide scale becomes too thick, and a scale residue may occur even if it is modified with salt.

  EXAMPLES Next, an Example is given and this invention is demonstrated in more detail. The following examples are examples of embodiments of the present invention, and the present invention is not limited thereto.

(Test piece preparation)
A titanium ingot having an adjusted amount of iron and oxygen was prepared by arc melting, and the ingot was heated to 1150 ° C. and then forged to produce a slab.

  The produced slab was hot rolled at 850 ° C. to a thickness of 4 mm, and then the surface scale was removed by shot blasting and nitric hydrofluoric acid pickling. Furthermore, it cold-rolled and produced the titanium thin plate of thickness 0.5mm.

  The titanium thin plate after cold rolling was annealed in the air at a temperature of 700 to 850 ° C. for 30 to 1000 s.

  The titanium thin plate after annealing was subjected to a salt treatment (immersion) for 10 s to 90 s at a temperature of 480 to 560 ° C. with NaOH of 60 to 95% to modify the scale.

  The salt-modified layer was removed by polishing the titanium thin plate after the salt treatment while spraying hot water at 60 ° C. using a nylon grinding brush. At this time, the surface was polished to prevent wrinkles.

  Moreover, in order to compare with the characteristic of the titanium thin plate obtained by brush polishing, the titanium thin plate after salt modification was immersed in a mixed solution of 10% by mass nitric acid and 3% by mass hydrofluoric acid at 40 ° C., and descaling was performed. I did it.

  Moreover, the iron content of the sample from which the surface scale was removed was measured according to JIS H1614, and the oxygen content was measured according to JIS H1620. Table 1 describes the iron and oxygen content, the salt treatment conditions, and the descaling method.

(Tensile test)
Tensile test pieces with a parallel part of 6.25 x 32 mm, gauge points of 25 mm, a chuck part of 15 mm width, and a total length of 100 mm are prepared, and after 0.2% yield strength measurement, the yield strength is 0.5% / min. Was subjected to a tensile test at a tensile rate of 20% / min. Here, the tensile strength in the rolling width direction (T direction) was evaluated.

(Ball head overhang test)
Using a φ40 spherical head punch in a deep drawing tester, the shape was adjusted to the shape shown in FIG. The stretch forming was performed by applying a high viscosity oil (# 660) manufactured by Nippon Tool Oil Co., Ltd., and the punch raising speed was 8 mm / min. The overhang height of the test piece at this time was comparatively evaluated. The acceptance criterion for the overhang height was 18 mm, which enables severe molding.

(Hardness measurement on the surface)
A 20 mm square test piece was prepared, and the hardness was measured on the surface with measurement loads of 0.25 N and 9.8 N using a micro Vickers hardness tester.

(Surface roughness)
According to JIS B 0601, the arithmetic average roughness Ra (μm) was measured. Table 2 shows the characteristics of the titanium plate manufactured by each manufacturing method. The example numbers in Table 1 and Table 2 correspond to each other.

  FIG. 3 shows the microstructure near the surface of the titanium plate after atmospheric annealing, salt treatment, and pickling, and FIG. 4 shows the microstructure near the surface of the titanium plate after standby annealing, salt treatment, and brush polishing. In FIG. 4, it can be seen that deformation twins were introduced by brush polishing.

  Invention Example No. 2, 4, 6-8, 10, 12, 13, 17-20, 22, 23, 25 are the iron content and oxygen content, salt treatment temperature, salt treatment time as defined in claims 1, 2, and 3. It is a titanium plate that satisfies the NaOH concentration, brush polishing amount, and surface hardness, and has an excellent balance between strength and formability.

  Comparative Example No. No. 1 is Invention Example No. 2, 4 and iron content and oxygen content are the same, but the salt temperature is low, it is not completely modified, and the scale remains even after brush polishing, so the overhang height is 18 mm of the acceptance standard Less than.

  Comparative Example No. 3 is Invention Example No. 2 and 4 have the same iron content and oxygen content, but since they are not brush-polished, the surface hardness is low and strength as high as brush polishing cannot be obtained.

  Comparative Example No. No. 5 is Invention Example No. Although the iron content and oxygen content are the same as 6-8, the salt treatment time is short, it is not completely modified, and the scale remains even after brush polishing, so the overhang height is 18 mm, which is the acceptance standard. Less than.

  Comparative Example No. 9 is Invention Example No. Although iron content and oxygen content are the same as 6-8, since it is not brush-polished, the surface hardness is low and strength as high as brush polishing cannot be obtained.

  Comparative Example No. 11 is Invention Example No. 10, 12 and 13 have the same iron content and oxygen content, but are not brush-polished, so the surface hardness is low and strength as high as brush polishing cannot be obtained.

  Comparative Example No. 14 is Invention Example No. The iron content and oxygen content are the same as 17-20, but the salt temperature is low, it is not completely reformed, and the scale remains even after brush polishing, so the overhang height is 18 mm of the acceptance standard Less than.

  Comparative Example No. 15 is Invention Example No. The iron content and oxygen content are the same as 17-20, but the salt temperature is low, it is not completely reformed, and the scale remains even after brush polishing, so the overhang height is 18 mm of the acceptance standard Less than.

  Comparative Example No. 16 is Invention Example No. The iron content and oxygen content are the same as 17-20, but the salt treatment time is short, it is not completely modified, and the scale remains even after brush polishing. Less than.

  Comparative Example No. 21 is Invention Example No. 22 and 23 have the same iron content and oxygen content, but the salt treatment time is short, they are not completely modified, and the scale remains even after brush polishing. Less than.

  Comparative Example No. 24, Invention Example No. 25, iron content and oxygen content are the same, but the salt treatment time is short, it is not completely modified, and the scale remains even after brush polishing, so the overhang height satisfies the acceptance standard of 18 mm. Absent.

  Comparative Example No. 26, Invention Example No. 25, the iron content and oxygen content are the same, but the salt treatment time is long and the titanium metal is exposed on the surface, so when brush polishing, strain is introduced to the inside of the plate, and the difference in hardness between the surface layer and the inside of the plate is reduced. The overhang height is less than the acceptance standard of 18 mm.

  Comparative Example No. 27, Invention Example No. 25 has the same iron content and oxygen content.

  Since the surface layer is brush-polished in the state of titanium ingot, strain is introduced to the inside of the plate, the difference in hardness between the surface layer and the inside of the plate is reduced, and the overhang height is less than the acceptance standard of 18 mm.

  Comparative Example No. 28, Invention Example No. 25, the iron content and the oxygen content are the same, but since the Ra in the T direction is less than 1.1 times that in the L direction, the lubricity is inferior and the overhang height is less than the acceptance standard of 18 mm.

  Comparative Example No. No. 29 is Invention Example No. 25, the iron content and the oxygen content are the same, but since Ra is larger than 0.8 μm, it is difficult to supply the lubricant, and the overhang height is less than the acceptance standard of 18 mm.

  Comparative Example No. Since No. 30 has a large oxygen content, the overhang height is less than the acceptance standard of 18 mm.

  Comparative Example No. No. 31 has a large iron content, so the overhang height is less than the acceptance standard of 18 mm.

  Comparative Example No. Since No. 32 is subjected to brush grinding without salt treatment, the scale remains and the overhang height is less than the acceptance standard of 18 mm.

  FIG. 5 shows the balance between the tensile strength and the overhang height of the inventive example and the comparative example. It can be seen that the inventive example is superior in balance to the comparative example.

Claims (2)

In mass%, the iron content is 0.01 to 0.1%, the oxygen content is 0.02 to 0.15%, the carbon content is 0.015% or less, and the nitrogen content is 0.00. 015% or less, the hydrogen content is 0.015% or less, the balance is titanium and inevitable impurities,
The arithmetic average roughness (Ra) in the L direction is 0.2 to 0.8 μm,
The arithmetic average roughness in the T direction is 1.1 to 2 times that in the L direction,
When the plate thickness is t, deformation twins exist in the range of the surface layer 0.05t to 0.2t,
A Vickers hardness of 170 or more at a measurement load of 0.25 N on the surface,
Vickers hardness at a measurement load of 9.8 N on the surface is 90 to 180,
A titanium plate, wherein the Vickers hardness at the measurement load of 0.25N is 1.5 times higher than the Vickers hardness at the measurement load of 9.8N. It is a manufacturing method of the titanium plate according to claim 1,
Cold rolled titanium material,
Annealing the cold-rolled titanium plate in the atmosphere,
Immerse the titanium plate after annealing in a salt bath at a mass% of NaOH of 75 to 95% and 520 to 550 ° C. for 15 to 60 seconds,
A method for producing a titanium plate, comprising removing 1 to 3 μm of the surface layer of the titanium plate after the immersion with a grinding brush.