JP2005105387A - Titanium sheet excellent in surface property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium sheet having excellent appearance reduced in macro patterns, and useful for building materials or the like. <P>SOLUTION: The titanium sheet having excellent appearance is composed of a titanium sheet having an Fe content of 0.030 to 0.25 mass%. In the crystal grain size distribution in the case that at optional five places photographed at a magnification of 400 times at the surface of the titanium sheet, the average crystal grain size is measured at a 1 mm pitch over the length of 10 mm orthogonal to the rolling direction, the existence ratio of the part having coarse crystal grain sizes where the average crystal grain size is ≥1.25 times to the minimum average crystal grain size is ≤20%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a titanium plate having excellent surface properties, and more particularly to a titanium plate having a beautiful appearance with few streaky spots (referred to herein as “macro patterns”) caused by a difference in glossiness.

  Titanium plate is a building material because the passive film formed on the surface is very stable and has excellent corrosion resistance and aesthetics, and is lighter and has higher specific strength than stainless steel plate. There is a tendency for the demand to increase for use in various applications and casing materials.

  By the way, for example, a titanium plate for building materials may cause streaky spots (macro pattern) having high gloss locally in an annealing process after rolling, a subsequent pickling process, and the like, which may cause appearance deterioration. Are known. Therefore, in order to improve such macro patterns, various methods such as optimization of annealing conditions (controlling the grain size of recrystallized grains, etc.) and optimization of pickling conditions (adjustment of pickling amount, homogenization, etc.) are adopted. It is devised so that the glossiness of the entire surface of the plate material is as uniform as possible (Patent Document 1, etc.).

However, even if annealing conditions, pickling conditions, and the like are made as uniform and appropriate as possible, it is not easy to completely eliminate the macro pattern, and the resulting macro pattern often impairs the quality of the product plate.
Japanese Patent Laid-Open No. 9-291326

  The present invention has been made paying attention to the above-described circumstances, and an object of the present invention is to provide a titanium plate having a beautiful appearance with few macro patterns and useful as a building material.

  The titanium plate according to the present invention capable of solving the above problems is composed of a titanium plate having an Fe content of 0.030 to 0.25% by mass, and the surface of the titanium plate was photographed at a magnification of 400 times. Of the crystal grain size distribution when the average grain size is measured at a pitch of 1 mm over a length of 10 mm perpendicular to the rolling direction at any five locations, the average grain size is 1. It is characterized in that the proportion of the portion having a coarse crystal grain size that is 25 times or more is 20% or less.

  The titanium plate according to the present invention has few macro patterns and excellent surface properties, and is particularly useful for building materials.

  According to the present invention, the JIS standard defines a lower limit value of the Fe content particularly in a low Fe content titanium plate belonging to a pure titanium plate, and further controls the annealing conditions after rolling appropriately to control the Fe diluted region. By preventing the generation of coarse crystals that cause macro patterns, it is possible to provide a titanium plate having a beautiful appearance without macro patterns.

  Under the prior art as described above, the present inventors have clarified the cause of the occurrence of a macro pattern on the surface of a titanium plate, and reduced or eliminated the cause, so that the macro pattern is not substantially observed. We have been researching from various angles. As a result, it was found that the amount of Fe contained in a trace amount in titanium has a remarkable effect on the macro pattern.

  It is considered that a very small amount of Fe contained in titanium is generally discharged during the solidification of the molten titanium and concentrated between columnar crystals to partially form an Fe concentrated region. However, the present inventors have confirmed that the following has become clear. That is, in titanium (pure titanium) with an extremely low Fe content, concentration of Fe occurs between columnar crystals in the initial stage of solidification, but basically, Fe is taken into the solid phase within the solid solution limit. In a macro manner, a partially Fe-diluted region is formed. And due to the slight difference in Fe concentration, there is a difference in recrystallization and grain growth behavior during annealing after processing titanium into a plate shape, and from the base part in the Fe dilute region stretched in a streak shape in the rolling direction Coarse crystal grains are formed and appear as a macro pattern.

  That is, the structure that has become coarser than the surrounding base portion due to grain growth during recrystallization increases its glossiness by subsequent pickling, and appears as a streak-like or strip-like macro pattern. The reason why the Fe diluted region is formed to such an extent that it can be recognized as a macro pattern is that the Fe concentration in the bulk state (that is, Fe content) is 0.030% by mass (hereinafter referred to simply as “%” in the case of component content). ) When less than pure titanium is used, and if the Fe content is 0.030% or more, even if there is a difference in Fe concentration, the grain growth during recrystallization is extremely accelerated. Fe diluted regions are not formed.

  However, if the Fe content is too large, not only another macro pattern different from the above mechanism appears due to the formation of the β phase, but also the molding processability when applied as a building material is deteriorated. -2 should be suppressed to 0.25% or less which is the upper limit of the Fe content in pure titanium specified in the above.

  In addition, the portion perceived as a macro pattern on the surface of the titanium plate is coarser than the surrounding crystal structure as described above, but the surface of the target titanium plate was photographed at a magnification of 400 times. In the crystal grain size distribution when the average crystal grain size is measured at a pitch of 1 mm over a length of 10 mm orthogonal to the rolling direction at an arbitrary five locations, the average crystal grain size is 1.25 with respect to the minimum average crystal grain size. If there is a portion with a coarse average crystal grain size that is more than twice as large as 20%, it is perceived as an unfavorable macro pattern for building materials, etc., and is therefore substantially recognized as a macro pattern. In order to enhance the surface appearance to such an extent that it cannot be achieved, it was confirmed that the abundance ratio of the above portion having a coarse average crystal grain size should be suppressed to 20% or less.

  Specific conditions for suppressing the abundance ratio of the portion having a coarse average crystal grain size whose average crystal grain size is 1.25 times or more to the minimum average crystal grain size to 20% or less as described above. Is not particularly limited, but on the premise that the Fe content in the titanium material is adjusted to a range of 0.030 to 0.25% as described above, annealing after hot rolling is performed at 700 ± 20 ° C. for 3 minutes or more. Preferably, the heating is performed for 5 minutes or more, and the heating rate of the titanium plate during heating is preferably 3.9 ° C./second or more.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

Example 1
Pure titanium equivalent to JIS-1 of chemical components shown in Table 1 is melted by a vacuum arc melting (VAR) method to obtain 8.5 tons of pure titanium ingot. This was heated to a β temperature range (980 to 1020 ° C.) and then forged to obtain a slab having a thickness of 150 mm. This slab is heated to 870 ° C., then hot-rolled to a thickness of 4 mm with one heat, subjected to line annealing at 700 ° C. for 5 minutes, then cold-rolled to a thickness of 1.3 mm, and further to 700 ° C. The line was annealed for 3 minutes to obtain a titanium cold-rolled sheet.

  Each obtained titanium cold-rolled sheet is subjected to salt treatment (500 ° C. salt bath) and pickling (pickling solution; 2% hydrofluoric acid + 10% nitric acid aqueous solution), and the surface grain size distribution is measured for each. At the same time, the occurrence of surface macro patterns was examined. The results are also shown in Table 1. The component analysis was performed at the slab stage, and the following method was adopted for the measurement of the crystal grain size distribution.

[Measurement method of crystal grain size distribution]
The surface of each test titanium plate was photographed with a 400 × microscope, and a line segment having a length of 10 mm perpendicular to the rolling direction was drawn at any five locations in the photograph, and the crystal grains cut by the line Measure the number. Then, the length (L) of the line segment when 10 crystal grains are cut is measured on a 400-fold scale (10 mm on the photograph corresponds to 25 μm). The average crystal grain size in the field of view of this photograph is determined, and the average crystal grain size is L / 10 μm. This is calculated | required in each 5 places about a 10 mm line segment, and a total of 50 crystal grain size distribution is measured.

  As can be seen from Table 1, the Fe content exceeding 0.030%. In Nos. 1 to 12, a macro pattern which causes a problem in practical use is not recognized, and a titanium plate having a beautiful surface skin is obtained. Moreover, No. whose Fe content is 0.030%. On the 13th titanium plate, a very slight macro pattern was observed, but there is no problem industrially. In addition, those No. In any of the 1 to 13 titanium plates, the abundance ratio of the portion having a coarse crystal grain size having an average crystal grain size of 1.25 times or more with respect to the minimum average crystal grain size is 20% or less.

  On the other hand, No. whose Fe content is less than 0.030%. In each of the 14 to 20 titanium plates, a remarkable streak-like macro pattern was observed. Moreover, according to the average crystal grain size distribution measured by the same method as described above, the abundance ratio of the portion having a coarse crystal grain size whose average crystal grain size is 1.25 times or more with respect to the minimum average crystal grain size is any Is over 20%. Incidentally, no correlation was observed between the components other than Fe and the macro pattern.

  FIG. 1 shows the case where the macro pattern was remarkably recognized. It is an external appearance photograph of 14 titanium plates, and many light gray streak patterns (macro patterns) almost parallel to the direction perpendicular to the rolling direction are recognized in the dark gray base. 2 and 3 are photomicrographs (magnification: 400 times) of the base portion (FIG. 2) and the macro pattern portion (FIG. 3) in FIG. Is formed.

  From these photographs, when the average crystal grain size of the base portion and the macro pattern portion was determined by the intercept method, the base portion was about 8 μm, whereas the macro pattern portion was about 10 μm.

  FIG. 4 shows the result of the SIMS (secondary ion mass spectrometry) study of the Fe concentration distribution from the surface to the inside in the base portion and the macro pattern portion. As is apparent from FIG. The Fe of the macro pattern portion is dilute with respect to the base portion. From this, when the Fe content in the titanium plate is less than 0.030%, the coarsening of the crystal grains occurs in the Fe dilute region, and the difference in the crystal grain size is exposed by pickling, so that it is expressed as a macro pattern. It is thought that it was broken. In other words, even if there is a difference in the average crystal grain size locally with respect to the base portion, if the difference in the average crystal grain size is less than 1.25 times, it is difficult to recognize as a macro pattern, and a beautiful surface It seems to be a titanium plate.

Example 2
In Example 1, no macro pattern was observed. The cold-rolled titanium plate of No. 1 was annealed at 700 ° C. for 3 minutes under various temperature rising conditions in the laboratory, and after performing salt treatment and pickling under the same conditions as in Example 1, generation of macro patterns I checked the situation.

  The results are as shown in Table 2. In 1a and 1b, a remarkable macro pattern was observed because the temperature rising rate during annealing was slow. Moreover, when the particle size distribution on the surface of each titanium plate was examined by the same method as described above, the abundance ratio of coarse particles more than 1.25 times the minimum average crystal particle size exceeded 20%. On the other hand, test No. 1 in which the temperature rising rate during annealing was sufficiently increased. In 1c and 1d, no problematic macro pattern was observed, and the abundance ratio of coarse grains having a grain size of 1.25 times or more with respect to the minimum average crystal grain size was 20% or less.

It is an external appearance photograph (actual size) of a titanium plate having a macro pattern. It is a microscope picture (400 times) of a base part. It is a microscope picture (400 times) of a macro pattern part. It is a graph which compares and compares the Fe ion intensity | strength from the surface in the macro pattern part and base part which were calculated | required by SIMS to the depth direction.

Claims (2)

  It consists of a titanium plate with an Fe content of 0.030 to 0.25% by mass, and the surface of the titanium plate is photographed at a magnification of 400 times at any five locations, over a length of 10 mm perpendicular to the rolling direction. In the crystal grain size distribution when the average crystal grain size is measured at a pitch of 1 mm, the abundance ratio of the portion having a coarse crystal grain size whose average crystal grain size is 1.25 times or more with respect to the minimum average crystal grain size is A titanium plate with less macro pattern and excellent surface properties, characterized by being 20% or less.   The titanium plate according to claim 1, which is used for building materials.