KR20150030265A - Titanium alloy material - Google Patents

Abstract

In the surface mapping analysis using the EPMA surface analyzer, the average value of the intensity of the background signal is N, and the value of N + 3N ^1/2 is the intensity of the background signal of Fe or S characteristic X-ray And the area ratio at which a signal of a characteristic X-ray of Fe or S exceeding the maximum strength is obtained is 0.1% or less.

Description

Titanium alloy material {TITANIUM ALLOY MATERIAL}

The present invention relates to a titanium alloy material, and more particularly to a titanium alloy material containing a platinum group element.

Titanium is utilized in a wide range of fields, such as materials for chemical industrial equipment, thermal power, nuclear power generation equipment, and seawater desalination equipment materials, because the characteristics of lightness and strength are utilized, and they are actively used in the field of aircraft and the like and have excellent corrosion resistance. .

However, the environment in which titanium can exhibit high corrosion resistance is limited to an oxidizing acid (nitric acid) environment or a neutral chloride environment such as seawater. (Hereinafter referred to as " corrosion resistance " in this section, " corrosion resistance " in the non-oxidizing acid solution such as hydrochloric acid) under the environment of high temperature chloride of titanium is not sufficient.

Ti-0.15Pd alloy (Gr.7 and Gr.11 of ASTM standard) (hereinafter, "Gr." (Grade) is all according to ASTM standard) as the titanium alloy having improved corrosion resistance. This titanium alloy utilizes the phenomenon that Pd in the alloy lowers the hydrogen overvoltage and maintains the natural potential in the passive region. That is, in this alloy, Pd eluted from the alloy by corrosion is deposited again on the surface of the alloy and deposited, whereby the hydrogen overvoltage is lowered and the natural potential is maintained in the passive region, thereby exhibiting excellent corrosion resistance.

However, Gr.7, which has excellent corrosion resistance, contains Pd which is a platinum group element and is very expensive, and its use field is limited.

In order to solve this problem, a titanium alloy (Gr.17) having excellent interlaminar corrosion resistance, while reducing the content of Pd to 0.01 to 0.12 mass% as compared with Gr.7, as disclosed in Patent Document 1, Have been proposed and put into practical use. Such diffusion of titanium alloys containing platinum group elements has also made it possible to use titanium alloys even in severe environments such as high temperature chloride environments.

However, a corrosion resistant type of titanium alloy containing a platinum group element may be different from that of the formula and so-called gap corrosion (accompanied by whitening by TiO ₂ production and reduction in thickness). The present inventors investigated such corrosion in detail.

1 is a photograph showing an appearance of a Gr.17 titanium alloy material in which corrosion occurs. As shown in Fig. 1, there are many occasions where the surface roughness is large (hereinafter, referred to as " surface roughness ") where the surface roughness is large, and the black deposit adheres to the vicinity of the corrosion site, It was found that the alloy was discolored to black. Then, the present inventors confirmed that a hydride (TiH or TiH ₂ ) exists in the corrosion site. Therefore, this corrosion is closely related to hydrogen.

Fig. 2 is a photograph showing the cross-sectional structure of a Gr.17 titanium alloy material in which corrosion occurs. A plurality of concave portions are formed on the surface of the corrosion portion of the titanium alloy material (a portion where the concave portion is formed in FIG. 2 is indicated by an arrow). From Fig. 2, it can be seen that point-like and needle-like substances are formed from the vicinity of the surface to the inside. The present inventors have confirmed that these substances are hydrides. It is considered that the hydride is generated starting from the hydrogen which has entered from the surface of the material.

Fig. 3 is a photograph showing the cross-sectional structure of the Gr. 17 titanium alloy material in which no corrosion occurred. The surface roughening of the titanium alloy material has not progressed. In such a titanium alloy material, the hydride is not present in a quantity as large as at least the titanium alloy material shown in Fig.

The following Patent Document 2 discloses a material improved in intergranular corrosion resistance by allowing a precipitate (Ti ₂ Ni) contained in a titanium alloy containing a platinum group to follow the rolling direction.

Patent Document 3 discloses a material in which a hydride layer is formed only in the vicinity of the surface in advance in order to prevent embrittlement due to hydrogen absorption and does not cause absorption of hydrogen or hydrogen embrittlement in a use environment of the material in a material environment.

Japanese Patent No. 3916088 Japanese Patent Laid-Open Publication No. 2012-12636 Japanese Patent Application Laid-Open No. 2005-36314

The spatial resolution of EPMA 4.2.4.3 Statistical fluctuation (p.112) The spatial resolution of the EPMA is shown in Fig. 4 (a)

Various countermeasures have been proposed for the problem of corrosion accompanied by surface roughening of the titanium alloy material. However, according to the conventional countermeasures, this type of corrosion can not be sufficiently suppressed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a titanium alloy material containing a platinum group element and capable of sufficiently suppressing corrosion accompanying surface roughening.

The inventors of the present invention have conducted various studies in order to solve such a problem of corrosion, thereby completing the present invention. The present invention relates to the titanium alloy materials of the following (1) to (7).

(1) a titanium alloy containing platinum group elements in the surface mapping analysis performed using the EPMA surface analysis apparatus, when a mean value of the background signal intensity as N, N + 3N ^1/2 of the characteristic of Fe X line of the background Wherein an area ratio at which a signal of a characteristic X-ray of Fe exceeding the maximum intensity is obtained is 0.1% or less, as the maximum intensity of the signal.

(2) a titanium alloy containing a platinum group element, on the surface mapping analysis performed using the EPMA surface analysis apparatus, when a mean value of the background signal intensity as N, N + 3N ^1/2 of the characteristic of S X line of the background Wherein an area ratio at which a signal of the characteristic X-ray of S exceeding the maximum intensity is obtained is 0.1% or less, as the maximum intensity of the signal.

(3) an area ratio at which a signal of a characteristic X-ray of Fe exceeding the maximum intensity is obtained of 0.05% or less and an area ratio at which a characteristic X-ray signal of S exceeding the maximum intensity is obtained is 0.05% Or the titanium alloy material according to (2).

(4) The titanium alloy material according to the above item (1) or (3), wherein the Fe content obtained by point analysis of the presence of Fe on the surface of the titanium alloy material is 0.5 or less in atomic ratio of Fe to Ti.

(5) The titanium alloy material according to any one of (1) to (4), wherein the platinum group element is contained in an amount of 0.01 to 0.25 mass%.

(6) The steel material as described in any one of (1) to (5) above, further containing at least one selected from the group consisting of Ni: 0.05 to 1.0 mass%, Cr: 0.05 to 0.3 mass%, and Mo: 0.05 to 0.5 mass% ). ≪ / RTI >

(7) The titanium alloy material according to any one of (1) to (6), wherein the platinum group element contains 0.01 to 0.25 mass% of Pd.

The titanium alloy material of the present invention can be used for applications requiring excellent corrosion resistance (such as corrosion resistance to the interior of the gap and corrosion resistance), corrosion resistance, processability, and economy. Specifically, the titanium alloy of the present invention can be used in harsh environments such as anodes and decontamination facilities of a salt electrolytic bath.

Fig. 1 is a photograph showing the external appearance of a Gr.17 titanium alloy material in which corrosion occurs.
Fig. 2 is a photograph showing the cross-sectional structure of a Gr.17 titanium alloy material in which corrosion occurs.
Fig. 3 is a photograph showing a cross-sectional structure of a Gr.17 titanium alloy material in which no corrosion has occurred.
4 is a view showing a result of surface mapping analysis by the EPMA surface analyzer of the sample according to the present invention.
5 is a diagram showing the results of surface mapping analysis by the EPMA surface analysis apparatus of a sample not according to the present invention.
Fig. 6 is a schematic view of a specimen used for the corrosion test and a specimen of the gap corrosion test specimen.

The present invention is based on the following findings obtained by the present inventors.

When a titanium alloy is used in a gap structure, there is a case where corrosion accompanied by surface harmony occurs rather than so-called gap corrosion. This corrosion rarely involves expansion. The inventors of the present invention investigated the site where these corrosion occurred. In most cases, it was confirmed that one or both of Fe and S were detected in the corrosion area. The inventors of the present invention investigated the relationship between the surface state of the titanium alloy material and the occurrence of corrosion to control the ratio of Fe and / or S present on the surface to a certain level or less as described below, It is possible to inhibit the occurrence of corrosion accompanied by corrosion.

As described above, when a cross-section of a corrosion-affected site accompanied by surface roughening is observed, hydrides in the form of dots / needles are identified only in the vicinity of the corrosion surface, and therefore it is considered that hydrides are involved in this corrosion. The reason why such corrosion appears as a change in appearance to the naked eye is that after the titanium alloy has been placed in a gap structure under a normal environment for a long time and after a short period of time, Can not be confirmed. Therefore, the present inventors have clarified the relationship between the surface state of the titanium alloy before corrosion and the corrosion by causing these corrosion by the acceleration test.

1) Specification of surface polluting elements

Gr. 11, Gr. 13 and Gr. 17 materials having different degrees of surface contamination were obtained from the market and subjected to surface analysis by EPMA (Electron Probe Micro Analyzer) Were investigated. For each of Gr.11, Gr.13 and Gr.17, the elements present on the surface were as follows.

C, O, Fe, Zn, S, Cl, Na and F (C and below are detected as components other than the matrix component) are added to the surfaces of Gr.11 and Gr. Was detected.

C, O, Fe, Zn, S, Cl, Na, Ca and F (the following C is detected as a component other than the matrix component) is added to the surface of the Gr.13 material. Was detected.

Among these elements, factors for detecting elements other than the matrix component were examined.

C is thought to be attributed to the rolling oil used in the manufacturing process. O is caused by the passive film of titanium, and O is generally observed on the surface of the titanium material.

On the other hand, Fe, Zn and S are elements that are not observed in general titanium alloy materials. In the present specification, these elements are defined as " surface contaminant elements ". However, Fe may be contained in the titanium material for the purpose of improving the strength. In such a titanium alloy material, Fe is contained in the base material irrespective of Fe contamination. Such Fe is usually dissolved in a titanium material and is uniformly distributed. Therefore, when the titanium alloy material is analyzed by an EPMA surface analyzer, the Fe signal is counted as a background. The Fe in the present application is Fe resulting from Fe contamination, and is not dissolved in the titanium material but exists in a state of being concentrated on the surface of the titanium material.

In the surface analysis, Ca, Na and Cl are also detected. However, since the detection amounts of these elements are very small, they are excluded from the pollution elements defined in this specification. It is presumed that these elements are mainly attached to the titanium alloy material from a human body treated with a titanium alloy material in the market.

The surface contamination by Fe is caused by shorting which is caused by stainless steel products or steel products produced on the same production line as the titanium alloy to be used or shot peening which is carried out during descaling of the hot rolled steel sheet, (The Fe contamination due to short flakes is described in detail in " 6) Method of producing titanium alloy material of the present invention " described later). When a titanium alloy material is used for a gap structure, a black oxide, which is assumed to be Fe ₃ O ₄ on the surface, may be generated in the gap structure. As shown in Fig. 1, the portion where such an oxide is produced is corroded to form a surface harmony, and a hydride is formed immediately below. Therefore, it is considered that the Fe generating the oxide is related to the corrosion of the titanium alloy material accompanied by surface roughening.

It is presumed that the surface contamination by Zn is caused by zinc phosphate used as an anti-seizing agent in the process of manufacturing the titanium alloy, and that Zn remains on the surface even after the rolling process. If Zn is present on the surface of the titanium alloy, the dissimilar metals are brought into contact with each other and the hydrogen absorption is promoted, so that hydrides may be generated in the contaminated portion of Zn.

Since S is a component contained in some of the extreme pressure additives used in rolling lubricant oil, surface contamination by S is thought to be caused by such additives. In the gap structure portion, if the surface of the titanium alloy material is contaminated with S and a solution containing chlorine ions is present on the surface, sulfur chloride (S ₂ Cl ₂ ) is generated in the gap. Since sulfur chloride accelerates the corrosion of pure titanium, there is a possibility that the titanium alloy also has a function of promoting corrosion.

Next, various test fabrication materials using the Gr.11 material were manufactured, and the ratio (area ratio) of the areas in which the Fe and S existed among the above-described elements defined as the contamination source on the surface of the test fabrication material was investigated , And the relationship between the distribution and abundance of Fe and S and the corrosion resistance (by visual observation and measurement of corrosion loss) were examined by performing the gap corrosion treatment described in the following examples.

2) About the area ratio of Fe pollution

On the surface of various test fabrics, surface mapping analysis was performed on Fe by using an EPMA surface analyzer with respect to a square area having a side length of 200 mu m. When the average value of the intensity of the background signal by N, N + 3N ^1/2 a, and that the maximum intensity of the characteristic X-rays in the background signal of the Fe, the area ratio obtained by the characteristic X-ray signal of the Fe in excess of the maximum intensity (hereinafter referred to as Quot; Fe area ratio ") was calculated (a detailed calculation method of the area ratio will be described later).

Five arbitrary regions were selected from the surface of the test material and subjected to the surface mapping analysis. The Fe area ratio was 0.002% to 2.4%. It was confirmed that these test materials were partially etched to form a corrosion area having a large surface roughness after the gap corrosion treatment. Among these corrosion areas, the Fe area ratio was more than 0.1% in the case of the test fabrication material in which the corrosion loss was confirmed.

In the test material having an Fe area ratio of 0.1% or less and in which corrosion loss was not confirmed, surface-matched materials were found somewhere. In the test material having an Fe area ratio of 0.01% or less, such a harmonized portion was not confirmed. From the above results, in order to secure the corrosion resistance, in particular, in the case of single contamination of Fe (when S is not contaminated), it is necessary to set the Fe area ratio of the surface of the titanium alloy to 0.1% or less. The Fe area ratio on the surface of the titanium alloy material in the case of single contamination of Fe is preferably 0.01% or less.

3) About area rate of S pollution

On the surface of various test fabrics, surface mapping analysis was performed on S by using an EPMA surface analyzer with respect to a square area having a side length of 200 mu m. When the average value of the intensity of the background signal by N, N + 3N ^1/2 a, and to the S characteristic X-rays in the background signal of the maximum intensity, the area ratio obtained by the characteristic X-ray signals of S in excess of the maximum intensity (hereinafter referred to as Quot; S area ratio ") was calculated.

When any five regions were selected from the surface of the test material and the above surface mapping analysis was performed, the S area ratio was 0.002% to 3.9%. For these test materials, it was confirmed that a corrosion area having a partially large surface roughness was formed after the treatment of gap cracking. The S area ratio of the test material in which the corrosion loss was confirmed, among the test materials having these corrosion areas confirmed, exceeded 0.1%. From the above results, in order to secure the corrosion resistance, it is necessary to set the surface S area ratio of the titanium alloy material to 0.1% or less particularly in the case of S contamination (in the case of not accompanying Fe contamination).

4) About the complex contamination area ratio of Fe and S

In the case of the above-mentioned commercially available material, there are cases where the element is contaminated with both Fe and S elements.

Any five regions were selected from the test materials and subjected to surface mapping analysis by an EPMA surface analyzer with respect to both of Fe and S. The surface area ratio of Fe was 0.001% to 2.4% and the S area ratio Was 0.001% to 3.9%.

For these test assemblies, it was confirmed that, after the treatment of the gap erosion, a partially coarsened surface area was formed. The test piece having the corrosion reduction amount confirmed that the Fe area ratio was larger than 0.05% and the S area ratio was larger than 0.05%. From the above results, in order to secure the corrosion resistance of the titanium alloy material contaminated with both Fe and S elements, the Fe area ratio is 0.05% or less and the S area ratio is 0.05% or less on the surface of the titanium alloy material .

5) About the Fe content

For the test materials contaminated with Fe, not only the Fe area ratio but also the relationship between the content of Fe present in the vicinity of the surface of the test material (by point analysis) and the change in the amount of contained hydrogen with time was examined.

The Fe content in the test material having an Fe area ratio of 0.1% or less, an S area ratio of 0.1% or less and a platinum group element content of 0.01 to 0.25% by mass exceeds 0.5 in atomic ratio of Fe to Ti , And even when the Fe area ratio was the same, the change in the amount of contained hydrogen with time was large, as compared with the case where it did not exceed 0.5.

In addition, as described in the section of "(2) About the area ratio of Fe contamination", there is no test for corrosion loss, but there is a test material in which surface roughening occurs. Since such a test material has a high Fe content, it is considered that Fe accelerates the corrosion due to hydrogen embrittlement by increasing the hydrogen absorption rate.

From the above points, it is preferable that the Fe content obtained by point analysis with respect to the Fe existing portion on the surface of the titanium alloy material is 0.5 or less in atomic ratio of Fe to Ti. On the surface of the titanium alloy material, the content (atomic%) of C varies depending on the residues of the residues. Therefore, the Fe content (atomic%) also fluctuates under the influence of the variation of the content of C in the presence of Fe. In order to avoid such variations, in the present invention, the Fe content is defined as a ratio of the content (atomic%) of Fe to the content (atomic%) of Ti as a component of the base material.

6) Manufacturing method of the titanium alloy material of the present invention

Hereinafter, an example of a method for producing the titanium alloy material of the present invention will be described.

Usually, the manufacturing process of the titanium alloy material is classified into a hot rolling process and a cold rolling process. At the time of hot rolling, scale (oxide) is generated on the surface of the titanium alloy material. For descaling, shot peening is performed on the surface of the hot rolled sheet obtained by hot rolling to remove the scale, cracks are introduced into the scale formed on the surface layer of the hot rolled sheet, and then pickling is performed. At the time of pickling, the cleansing acid penetrates the cracks, so that the remaining portion of the scale is easily removed. However, a part of the shot piece remains on the surface of the titanium alloy material, and can not be completely removed by the subsequent pickling. Particularly, when a shot piece of a large size is used, the descaling property is excellent, but it is difficult to remove the remaining shot pieces to be described later only by the choline treatment and the pickling treatment, so that cleaning with a ferric chloride (FeCl ₃ ) There is a case.

The titanium alloy material subjected to the hot rolling step is subjected to cold rolling and annealing a plurality of times until a desired plate thickness is obtained. Normally, as annealing treatment, light annealing (BA = Bright Annealing) is performed using an argon atmosphere. Since descaling is not performed after the annealing for the bright annealed titanium alloy material, the decontamination of Fe and S accompanying descaling can not be expected.

Through the hot rolling and cold rolling processes, S contamination due to rolling lubricant oil for cold rolling is generated in the titanium alloy material in addition to Fe contamination due to the above-mentioned residual of shot pieces. These pollutants, S and Fe, diffuse into the entire surface of the titanium alloy material by thermal diffusion in the annealing process, and also penetrate into the interior.

Therefore, after the annealing, the surface layer portion of the titanium alloy material is dissolved or mechanically ground by pickling and removed in order to remove these contaminants S and Fe. Further, it is more preferable to carry out a treatment (generally called " Kolene treatment ") with an alkaline molten salt bath (a NaOH-based salt bath containing an oxidizing agent such as NaNO ₃ or KNO ₃ ) before the pickling. The removal of the surface layer portion is preferably performed after all annealing, but if S is performed after the first and the last annealing, S and Fe contamination can be efficiently removed. The removal amount (thickness) at this time is set to 1 탆 or more, preferably 5 탆 or more, with respect to the surface of the titanium alloy material.

As described above, the treatment for removing the contamination source is not limited to one treatment, and it may be necessary to perform a plurality of treatments until the surface defined in the present invention is realized.

After the descaling of the hot-rolled steel sheet, a method of using cleaning with a ferric chloride aqueous solution and brushing the surface of the hot-rolled steel sheet is also effective. This is because the aqueous solution of ferric chloride hardly dissolves titanium but the dissolution rate of Fe is faster than that of the mixed solution of fluoric nitric acid so that the short sides of the shot pieces and the titanium base material are dissolved and the shot pieces are effectively used, This is a necessary process when a large size shot piece is used.

It is also effective to reduce the contamination amount of S by adding a step of performing cleaning before annealing and removing lubricating oil or the like.

7) About alloy element

The content of the platinum group element is preferably 0.01 to 0.25 mass%. Thereby, the corrosion resistance of the titanium alloy material can be obtained while suppressing the raw material cost. The platinum group element may be, for example, Pd.

The titanium alloy material of the present invention may further contain one or more kinds selected from the group consisting of 0.05 to 1.0% by mass of Ni, 0.05 to 0.3% by mass of Cr and 0.05 to 0.5% by mass of Mo.

When the titanium alloy material contains Ni, the interstitial corrosion resistance is improved. However, this effect is saturated even when Ni is contained in an amount of more than 1.0% by mass. Further, by adding Ni, workability is lowered. Therefore, when Ni is added, the content is preferably 1.0 mass% or less. In order to reliably obtain the above effect, the content of Ni is preferably 0.05 mass% or more, more preferably 0.1 mass% or more.

When the titanium alloy material contains Cr, the interstitial corrosion resistance is improved. However, this effect is saturated even when Cr is contained in an amount of more than 0.3 mass%. Therefore, when Cr is added, the content is preferably 0.3 mass% or less. In order to reliably obtain the above effect, the Cr content is preferably 0.05 mass% or more.

When the titanium alloy material contains Mo, the interstitial corrosion resistance and sulfuric acid resistance are improved. However, this effect is saturated even when Mo is contained in an amount of more than 0.5% by mass. Further, by adding Mo, workability is lowered. Therefore, when Mo is added, the content is preferably 0.5 mass% or less. In order to reliably obtain the above effect, the content of Mo is preferably 0.05 mass% or more.

Example 1

In order to confirm the effect of the present invention, samples different in contamination amount of Fe and S were produced and subjected to a corrosion resistance test.

1. Preparation of samples used for corrosion resistance test

The base material used for the sample is 3 mm in thickness and has a thickness of 3 mm and is made of ASTM standard Gr.11, Gr.13, Gr.17 material, Gr33 material and laboratory test material [VAR dissolution (Vacuum Arc Remelting) Hot forging and hot rolling in this order], and has the composition shown in Table 1. After performing degreasing and ultrasonic cleaning on these base materials, the following treatments were carried out for the purpose of reproducing contamination during production of actual equipment.

Table 2 shows sample preparation conditions to be provided for the corrosion test and amounts of Fe and S contamination of the sample. In order to easily prepare samples different in degree of Fe and S contamination, the mixing ratio of the iron powder and the extreme pressure additive in the rolling lubricant to be applied to the base material was adjusted so that the contamination amount of Fe and S was different between the samples Examples 4 to 16 and Comparative Examples 1 to 12).

(i) Fe contamination

FEW 13PB iron powder (purity: 2Nup, particle size: 3 to 5 탆) manufactured by Kojundo Chemical Co., Ltd. was mixed with various amounts (mass%) of rolling lubricant oil containing palm oil as main components, The lubricant was applied to a base material having a thickness of 4 mm and rolled so that the base material had a plate thickness of 3 mm to obtain a sample having different amounts of Fe contamination (Fe contamination degree) simulating residual shot of short shot at the time of shot peening.

(ii) S contamination

The rolled lubricating oil was mixed with the DAILUBE GS-440L olefin metal processing oil (pre-sulphurizing agent containing 40% sulfur), which is an extreme pressure additive manufactured by DIC Co., in terms of mass% shown in Table 2, Then, the base material was rolled so as to have a plate thickness of 3 mm to obtain a specimen having different S contamination amount (S contamination degree).

(iii) Complex contamination of Fe and S

By combining the treatments of (i) and (ii), a specimen contaminated with Fe and S was obtained.

(iv) Samples that are not contaminated

In Table 2, the samples described as " (cleaner) " (Examples 1 to 3) did not perform any contamination treatment for either Fe or S. That is, these samples were prepared by applying a rolling lubricant not containing both Fe (iron powder) and S (extreme pressure additive containing sulfur) to a base material having a thickness of 4 mm so that the base material had a thickness of 3 mm Rolled.

(v) Processing after rolling

After the degreasing process, the pressurized strip material obtained by the above processes (i) to (iv) was subjected to an annealing treatment at 750 ° C for 30 minutes in an Ar atmosphere, and thereafter subjected to fluorine nitric acid cleaning Respectively. In Table 2, the sample described as "(choline treatment)" (Example 16) was obtained by carrying out the choline treatment before the fluorine nitric acid cleaning after the Fe contamination treatment. For some of the samples, a choline treatment or a treatment with an aqueous ferric chloride solution (including a brushing treatment) was performed to obtain the surface defined in the present invention. In addition, for some samples (Example 9), fluorine nitric acid was washed twice before annealing and after annealing.

2. Measurement method of surface pollution degree

The surface of the sample before the corrosion treatment was analyzed using an EPMA surface analyzer.

(2-1) EPMA analysis conditions

Apparatus: JXA-8530F manufactured by Nihon Denshi Co., Ltd.

Acceleration voltage: 15kv

Irradiation current: 100nA

Number of measurement points (pixels): 500 × 500

Beam shape: Spot

Measurement pitch: 0.4 탆

Measurement time: 30msec (per one point)

Use Spectroscopic Crystals: LIFH (for Fe Kα radiation), PETH (for S Kα radiation), LIF (for Ti Kα radiation), LIFH (for Zn Kα radiation)

(2-2) Measurement of background intensity of Fe, S and Zn analysis

The high purity Ti of ESCA (Electron Spectroscopy for Chemical Analysis), AES (Auger Electron Spectroscopy) and EPMA standard (UHV STANDARDS) was analyzed under the above analysis conditions and the background count strength of Fe, S and Zn was arranged in a lattice form (Fe), N (S) and N (Zn) of the background count (intensity) of each element were calculated.

According to the Non-Patent Document 1, when a plurality of measured values the mean value of N ₀ to N, the measured value N is N ₀ ± 3N ₀ ratio, as measured away from a range of ^1/2, 0.3%. Therefore, the average value of the background intensities can be substituted into N ₀ of this equation to obtain a threshold value for distinguishing signals whose intensity is increased due to the presence element from the background signal. The threshold values for Fe, S and Zn are set as follows.

Fe threshold strength: N (Fe) + 3N ( Fe) 1/2

S threshold strength: N (S) + 3N ( S) 1/2

Zn threshold strength: N (Zn) + 3N ( Zn) 1/2

In the present embodiment, specific values of the Fe threshold value strength, the S threshold value strength and the Zn threshold value were 25 cnt (count), 15 cnt and 50 cnt, respectively.

When a count of a higher intensity than these threshold values is obtained, there is an element corresponding to the threshold value at the measurement point with a probability of 99.85%, and the signal attributable to the element is measured.

The ratio of the point at which the strength above the threshold value is counted among the 500 × 500 measuring points is defined as the contaminated area ratio. For example, when the intensity over the threshold value is counted at 300 points,

Contaminated area ratio = 300 / (500 x 500) = 0.12%

to be. In Table 2, Table 4, and Table 5, the contamination amount of Fe and S of the sample is represented by the contaminating area ratio (Fe area ratio and S area ratio) of Fe and S, respectively.

4 and 5 show the results of the surface mapping analysis by the EPMA surface analysis apparatus for the sample according to the present invention and the sample not according to the present invention, respectively. Fe, S, and Zn are binarized by whether or not they are higher than the threshold value strength. A point of strength equal to or lower than the threshold value strength is indicated by black, and a point of strength exceeding the threshold value strength is indicated by white.

Fig. 4 shows the results of the analysis of the sample of " Example 3 (cleaning material) " in Table 2. Fig. In this sample, it can be seen that there is hardly any point exceeding the threshold value strength for either Fe, S or Zn.

Fig. 5 shows the results of the analysis of the sample of " Comparative Example 6 " This sample was subjected to contamination treatment for both of Fe and S. From the analysis results of FIG. 5, it can be seen that there exists a point exceeding the threshold value intensity for both Fe and S over the analysis area.

(2-3) Quantitative measurement of contaminants

The quantitative concentration of contaminants can be measured using general analytical means such as EPMA, AES, and the like. In the embodiment, FE-AES (Field Emission-Auger Electron Spectroscopy), in which information on the vicinity of the surface is obtained, is employed as an analysis means for the purpose of measuring surface contamination. The analysis conditions are as follows.

Device: Model 680 manufactured by ULVAK PIE

Primary beam: acceleration voltage 10kV, sample current 10nA

Detection depth: several nm (3 to 5 nm for Ti and Fe)

Based on the measurement results obtained, the ratio of Fe content (atomic%) / Ti content (atomic%) was calculated. The results are shown in Table 5.

3. Evaluation of corrosion resistance

In order to investigate the influence of surface contamination on the corrosion resistance, a test similar to a general corrosion resistance test was performed by mimicking the environment in which a titanium alloy containing a platinum group element is used.

Fig. 6 is a schematic view of a specimen used for a corrosion test and a schematic view of a specimen of a corrosion test. As shown in Figs. 6A and 6B, the specimen 1 provided in the corrosion test has a square planar shape with a thickness of 3 mm and a side of 30 mm, , And a hole having a diameter of 7 mm is formed. 6 (c), two samples 1 produced under the same conditions were placed on one side and the other side of the gap-forming film (gap-forming material) 2, CP The bolts of the Ti bolts and nuts 4 were passed through the test pieces 1 and the test pieces 1 were fastened with the CP Ti bolts and nuts 4 through the PTFE bushes 3 to form the gap corrosion test sample 5.

The surface skin of the sample (1) Quot ;, " Method of making sample to be used for corrosion resistance test ", was maintained. As the gap-forming film 2, NEOFLON (trademark) PCTFE film (thickness: 50 mu m) manufactured by Daikin Industries, Ltd. was used. As the CP Ti bolt and nut (4), a surface heated by a gas burner and sufficiently oxidized was used. The tightening torque of the CP Ti bolt and nut 4 was 40 kgf · cm (1 kgf is about 9.8 N).

In order to carry out an acceleration test that clarifies the influence of the contamination on the corrosion resistance, the sample was subjected to treatment using an autoclave (autoclave treatment). Prior to the autoclave treatment, as the pre-test measurement, the weight of the sample (1) was measured using a precision balance. The weight of the sample (1) was in the range of 11 to 11.5 g. Thereafter, the gap corrosion test sample 5 was treated with an autoclave. Table 3 shows the conditions of the autoclave treatment.

After completion of the treatment, the CP Ti bolt and nut 4 was loosened to decompose the gap corrosion test sample 5, and the sample 1 was subjected to ultrasonic cleaning and washing water three times to replace the sample 1 ) Was thoroughly dried and then weighed with a precision balance. Then, the corrosion loss amount D determined by the following formula was calculated.

Corrosive weight loss D (mg) = Weight after corrosion treatment (mg) - Weight before corrosion treatment (mg)

The weight of the sample 1 was measured for two samples 1 (on the side of the bolt side and the nut side) of the gap corrosion test sample 5 and the corrosion loss D Were the average values of these two samples.

There was a sample 1 showing a slight increase in the amount of corrosion loss measurement, which was not reduced to 0, but was considered to be an increase due to oxidation. Therefore, the corrosion loss amount D was set to zero for the sample 1 .

Further, the hydrogen increase amount (absorption amount) H obtained by the following equation was calculated.

Increase in hydrogen H (ppm)

= Hydrogen content (ppm) of sample (1) (bulk) after corrosion treatment - hydrogen content (ppm) of sample (1)

Table 4 shows the base material, Fe area ratio and S area ratio of the sample (1) provided in the corrosion test, and the results of the corrosion test.

From the test results shown in Table 4, the following 1) to 3) can be found.

Examples 1 to 9, Examples 9 to 11, and Examples 14 to 14, which were prepared in the same manner as in Example 1 (cleaning material) (Hereinafter referred to as " non-complex contaminated sample ") is 0.1% or less, and the Fe contamination on the surface is low. Likewise, the S area ratio of the uncombusted contaminated sample is 0.1% or less, and the S contamination degree on the surface is low.

In addition, for the non-composite contaminated sample, the corrosion loss by corrosion treatment is not confirmed, and it is clear that the non-composite contaminated sample is excellent in corrosion resistance. Further, the hydrogen increase amount H due to the corrosion treatment of the non-composite contaminated sample is 20 ppm or less. (Examples 1 to 3, 6, 7, 11, and 16) in the non-composite contaminated samples had an Fe area ratio of 0.01% or less, surface smoothness of the surface as a gap was not confirmed and corrosion resistance was excellent, The amount of absorption is also extremely small, less than 10 ppm.

2) Even if the Fe area ratio was 0.1% or less, complex contamination with S was confirmed, and in the samples having the Fe area ratio and the S area ratio both exceeding 0.05% (the sample described as "Example 13" in Table 4) Corrosion loss is confirmed. The hydrogen increase amount H of this sample is greater than 15 ppm. In the case of complex contamination of Fe and S, in order to realize a material having higher corrosion resistance, it is preferable that the Fe area ratio and the S area ratio are all 0.05% or less.

3) The sample of Example 16 was subjected to Fe contamination treatment (rolling and rolling with iron powder mixed) as described in " (v) Treatment after Rolling ", and then, before fluorine nitric acid cleaning , And choline treatment. Although the sample of Example 16 shows Fe contamination area ratio at a level close to that of the clean material even though the Fe contamination treatment is performed, the choline treatment is an effective means for obtaining a titanium alloy material having a clean surface Able to know.

From the above test results, it became clear that the corrosion resistance (resistance to corrosion of the inner wall of the pipe, resistance to corrosion accompanying surface roughening) can be secured by suppressing the contamination amount of Fe and S present on the surface of the titanium alloy material.

Example 2

Next, the effect of the concentration of Fe as a pollutant element was examined. Table 5 shows the production conditions and evaluation results of the samples provided in the test.

The samples of Examples 17, 19, and 21 were obtained by rolling a base material having a thickness of about 4 mm in two passes, and the thickness of the sample was reduced to 3.5 mm in the first pass and 3.0 mm in the second pass Respectively. On the other hand, the samples of Examples 18 and 20 were obtained by rolling a base material having a thickness of about 4 mm so as to have a thickness of 3.0 mm in one pass. The samples of Comparative Examples 13, 14, and 15 were obtained by rolling a base material having a thickness of about 4 mm in a single pass so as to have a thickness of 3.0 mm.

With respect to the obtained sample, the Fe area ratio and the S area ratio were measured in arbitrary five areas, and a part showing the maximum Fe intensity in each area was subjected to quantitative analysis to determine Fe (atomic%) with respect to the Ti content (Atomic%) was calculated. The average values of the five regions are shown in Table 5 with Fe / Ti (atom ratio) representing this sample.

Samples of Examples 17 to 21 and Comparative Examples 13 to 15 were subjected to an autoclave treatment (corrosion treatment) under the conditions shown in Table 3 to analyze the hydrogen content before and after the treatment.

From Table 5, the following 1) to 5) can be found.

1) No corrosion loss was observed for any of the samples (Examples 17 to 21) according to the present invention by the treatment with an autoclave (150 DEG C x 1000 hours).

2) For the samples having an Fe / Ti (atomic ratio) exceeding 0.5, an increase in the hydrogen content was confirmed by the corrosion treatment. In these samples, it is presumed that the amount of hydrogen after corrosion treatment exceeds 100 ppm, and hydrogen absorbs with time.

3) Samples of samples (Examples 18, 20 and 21) having Fe / Ti (atom ratio) of more than 0.5 in Examples 17 to 21 are within the range of the present invention, ), It is preferable that Fe / Ti (atomic ratio) is 0.5 or less.

4) A sample deviating from the scope of the present invention (a sample described in " Comparative Examples 13 " to " Comparative Example 15 " in Table 5) had concave portions on its surface and a large loss of corrosion was confirmed. Even if these samples are Ti alloys containing a platinum group, they can not be said to be intrinsic to the treatment under strict conditions for these samples (the above autoclave treatment). In these samples, the amount of hydrogen increase H due to the treatment is more than 35 ppm, and corrosion of these samples is thought to be related to hydrogen absorption. In these samples, the hydrogen increase amount H exceeds 200 ppm, and this value is a level at which hydrogen embrittlement is likely to occur.

5) In the samples of Comparative Examples 13 to 15, a high Fe area ratio and a high Fe / Ti (atom ratio) all exhibited a large loss of corrosion, a hydrogen content after the corrosion treatment exceeded 200 ppm, .

While the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the appended claims. Of the present invention.

Claims (7)

A titanium alloy material containing a platinum group element,
In surface mapping analysis performed using the EPMA surface analysis apparatus, when a mean value of the background signal intensity by N, and the N + 3N ^1/2, with the characteristic X-rays in the background signal of Fe maximum intensity, that the art than the maximum intensity Wherein an area ratio at which a characteristic X-ray signal of Fe is obtained is 0.1% or less. A titanium alloy material containing a platinum group element,
In surface mapping analysis performed using the EPMA surface analysis apparatus, when a mean value of the background signal intensity by N, and the N + 3N ^1/2, the maximum intensity of the S characteristic X-rays in the background signals, which the art exceeds the maximum intensity Wherein an area ratio at which a characteristic X-ray signal is obtained is 0.1% or less. 3. The method according to claim 1 or 2,
Wherein an area ratio at which a signal of a characteristic X-ray of Fe exceeding the maximum intensity is obtained is 0.05% or less and an area ratio at which a signal of the characteristic X-ray of S exceeding the maximum intensity is obtained is 0.05% or less. The method according to claim 1 or 3,
Wherein the Fe content of the Fe existing portion of the surface of the titanium alloy material obtained by point analysis is not more than 0.5 in atomic ratio of Fe to Ti. 5. The method according to any one of claims 1 to 4,
Wherein the titanium alloy contains 0.01 to 0.25 mass% of the platinum group element. 6. The method according to any one of claims 1 to 5,
0.05 to 1.0% by mass of Ni, 0.05 to 0.3% by mass of Cr, and 0.05 to 0.5% by mass of Mo, based on the total mass of the titanium alloy. 7. The method according to any one of claims 1 to 6,
Wherein the platinum group element contains 0.01 to 0.25 mass% of Pd.

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