JP2013001973A - Titanium alloy welded pipe having excellent hydrogen absorption resistance and pipe-formability and hoop product for welled pipe, and methods for manufacturing them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium alloy welded pipe which has excellent hydrogen absorption resistance and pipe-formability in roll forming and which is used for a welded pipe product and for a hoop product serving as a material of the welded pipe product, the welded pipe product being used for a condenser and a multitubular heat exchanger or the like of a chemical plant or the like needing corrosion resistance and hydrogen-intrusion resistance, under an environment having a risk of the occurrence of embrittlement caused by hydrogen absorption, to provide a hoop product for the welded pipe, and to provide methods for manufacturing the titanium alloy welded pipe and the hoop product for the welded pipe.SOLUTION: The titanium alloy welded pipe or the titanium alloy hoop product having excellent hydrogen absorption resistance and cold workability is characterized by containing, by mass, 0.6-1.8% of Cu, ≤0.03% of Fe, and ≤0.16% of O, with the balance comprising Ti and ≤0.3%, in total, of impurities, and including 0.5-3.5% by volume fraction of a precipitated phase with TiCu having particle diameters of 10-1,000 nm as the maximum phase. Further, the method for manufacturing the titanium alloy welded pipe or the titanium alloy hoop product is characterized by performing a final annealing in the temperature range of 480°C to 730[%Cu]-160°C.

Description

  INDUSTRIAL APPLICABILITY The present invention is used for multi-tube heat exchanger applications such as condensers and chemical plants that require corrosion resistance and hydrogen penetration resistance in an environment where embrittlement may occur due to hydrogen absorption. Titanium alloy welded pipe excellent in hydrogen absorption resistance and roll forming processability when forming into a welded pipe, and hoop product for welded pipe used in welded pipe products and hoop products used as the materials, and methods for producing the same About.

  Since titanium and titanium alloy welded pipes have excellent corrosion resistance, they are used in multi-tube heat exchangers such as condensers, chemical plants, and seawater desalination plants. At this time, when high strength is not particularly required and cold workability is most important, pure titanium is mainly used. Among them, for example, two materials (TTH340W) described in JIS H4631 (2001) “Titanium tube for heat exchanger” or Grade 2 described in ASTM B338 “Titanium tubes for heat exchanger” are often used.

  On the other hand, in the environment where these titanium and titanium alloy tubes are used, when exposed to a severe corrosive environment, the titanium and titanium alloy tubes may absorb a large amount of hydrogen and titanium hydride may be formed inside. Titanium hydride is remarkably brittle compared to the base material, so that when titanium is produced in large quantities, the titanium and titanium alloy pipes become brittle. Such a phenomenon may occur when a tube for a heat exchanger that is exposed to high-temperature steam, a tube that is exposed to a non-oxidizing acid solution environment, or a steel material that comes into contact is subjected to electrocorrosion protection. Therefore, when titanium and titanium alloy pipes are used in these particularly severe corrosive environments, hydrogen is easily absorbed and hydrides are easily generated, and hydrogen embrittlement cracks are liable to occur. There was a problem that the tube could not be used.

  In order to solve this problem, various alloys have been proposed that are superior in manufacturing methods for preventing hydrogen intrusion and hydrogen absorption resistance.

  Patent Document 1 discloses a method of preventing the embrittlement by enhancing the effect of preventing hydrogen absorption by coating a titanium nitride layer on the titanium surface. Although it is a method that can improve the hydrogen absorption resistance at a relatively low cost, the surface titanium nitride film is in contact with foreign matter, especially in the tube forming process by continuous roll forming where it strongly contacts the tube forming roll, or heat exchange as a tube product. When used in a container or the like, if it is peeled off by sand erosion or the like, the effect is impaired.

  Patent Document 2 discloses a method for improving the hydrogen embrittlement resistance by utilizing the effect that hydrogen absorption does not progress by providing a titanium hydride-containing layer on the surface in advance. However, it is difficult to control hydride formation, and there is a high possibility of reaching the amount of hydride where bulk embrittlement occurs. In addition, if such a low ductility hydride layer is present on the hoop surface, defects such as surface cracks occur during roll forming during pipe making, and the product yield tends to be low. Poor sex.

  An alloy has been proposed in which a noble metal element is added to titanium to enhance the corrosion resistance and thereby improve the hydrogen absorption resistance. An alloy to which Pd is added is disclosed in Patent Document 3, and an alloy to which Zr and Hf are added is disclosed in Patent Document 4. In these alloys, the corrosion resistance and hydrogen absorption resistance are greatly improved as compared with pure titanium. However, all of the above-mentioned additive elements are much more expensive than titanium, and there is a problem that the manufacturing cost of the alloy is significantly increased.

  On the other hand, titanium, which is superior in hydrogen absorption resistance, utilizes the fact that adding aluminum, which is cheaper than titanium, to make an alloy and further providing an Al-enriched layer on the outermost surface reduces the inward diffusion of hydrogen. An alloy is disclosed in US Pat. In this alloy, it is said that cold workability equivalent to that of pure titanium can be obtained by keeping the amount of Al added low. However, in Ti, Al easily forms an intermetallic compound with Ti in the presence of O, and accordingly, twin deformation that greatly affects the plastic deformability is suppressed. Further, since the Al-enriched layer on the surface is hard and brittle, surface defects are easily generated in the pipe forming process by roll forming, and it is difficult to stably form a welded pipe.

  Furthermore, a titanium alloy to which Cu is added is disclosed in Patent Document 6 because it is difficult to produce hydride and is optimal as a cathode electrode plate for producing electrolytic copper foil. This is based on a mechanism in which the amount of dissolved hydrogen is increased by adding Cu to Ti. That is, the technique aims to increase the solid solubility limit of hydrogen in the titanium alloy and suppress hydride generation by dissolving as much Cu as possible in titanium. However, in severe hydrogen absorption environments such as heat exchanger applications, the hydrogen concentration exceeds the hydrogen solid solubility limit in a small part of the vicinity of the surface, and there is a possibility that hydride may be generated although it is a little. .

JP-A-3-243759 JP 2005-36314 A JP 2000-248324 A JP 2006-291263 A JP 2003-129152 A Japanese Patent Laid-Open No. 2004-250753 JP 2005-298970 A

  INDUSTRIAL APPLICABILITY The present invention is used for multi-tube heat exchanger applications such as condensers and chemical plants that require corrosion resistance and hydrogen penetration resistance in an environment where embrittlement may occur due to hydrogen absorption. An object of the present invention is to provide a titanium alloy welded pipe excellent in hydrogen absorption resistance and pipe forming property, or a titanium alloy hoop product used as the material thereof, and a method for producing them.

There is a great need for a titanium alloy welded pipe having excellent hydrogen absorption resistance and being less susceptible to hydrogen embrittlement due to hydride and a relatively low production cost, and a hoop material used as the material. The present inventors added a proper amount of Cu, which is a relatively inexpensive element, to Ti to generate a precipitation phase having Ti ₂ Cu as the maximum phase, and to keep the amount of Fe added low, thereby preventing hydrogen absorption. It has been found that the characteristics are improved.

That is, when the present inventors added Cu to Ti and positively generated a precipitation phase having Ti ₂ Cu as the maximum phase, the majority of the added Cu was dissolved in titanium to form a titanium alloy. It has been found that the hydrogen absorption resistance is further improved as compared with the case where the solid solubility limit of hydrogen is increased.

Further, it was found that the precipitation phase having Ti ₂ Cu as the maximum phase has a slight increase in strength due to precipitation strengthening, and does not impair the workability in the roll forming process when manufacturing a welded pipe.

  The present invention has been made against the background of the above circumstances, and an object thereof is to provide a relatively low-cost titanium alloy welded pipe excellent in hydrogen absorption resistance, a hoop material used as the material, and a method for producing the same. It is what.

In order to solve the above problems, the present invention is based on the following means.
(1) Consisting of 0.6 to 1.8% Cu by mass, 0.03% or less Fe, 0.16% or less O, the balance Ti and a total amount of impurity elements of 0.3% or less, A titanium alloy welded tube excellent in hydrogen absorption resistance, characterized by containing a precipitate having a maximum phase of Ti ₂ Cu having a diameter of 10 to 1000 nm in a volume fraction of 0.5 to 3.5%.
(2) It is composed of 0.6 to 1.8% by mass of Cu, 0.03% or less of Fe, 0.16% or less of O, the balance Ti, and a total amount of impurity elements of 0.3% or less, A titanium alloy hoop product excellent in hydrogen absorption resistance and tube-forming properties, comprising a precipitate having a maximum phase of Ti ₂ Cu having a diameter of 10 to 1000 nm in a volume fraction of 0.5 to 3.5%.
(3) Titanium alloy welded tube excellent in hydrogen absorption resistance as described in (1) above, wherein the final annealing temperature is 480 ° C. or higher and 730 [% Cu] ^{0.126 to} 160 ° C. or lower. Manufacturing method.
Here, [% Cu] is the Cu content chemical analysis value (mass%) of the titanium alloy.
(4) The final annealing temperature is 480 ° C. or higher and 730 [% Cu] ^{0.126 to} 160 ° C. or lower, and the hydrogen absorption resistance and pipe forming properties are excellent as described in (2) above. Manufacturing method of titanium alloy hoop products.
Here, [% Cu] is the Cu content chemical analysis value (mass%) of the titanium alloy.

In order to solve the above-mentioned problems, the present inventors have investigated in detail the influence of component elements on the hydrogen-resistant absorption characteristics of titanium. As a result, a certain amount of Cu is added to titanium, and precipitation with Ti ₂ Cu as the maximum phase is performed. It was found that the hydrogen absorption resistance and the cold workability can be improved by finely depositing the material and adjusting the contents of O and Fe appropriately.

Here, the precipitates and the maximum phase Ti ₂ Cu, Ti, a deposit consisting of Cu and impurity elements, in a volume ratio of Ti ₂ Cu, refers to precipitate the maximum phase. Precipitates with the maximum phase of Ti ₂ Cu can be confirmed by electron diffraction and characteristic X-ray analysis in a transmission electron microscope observation with an X-ray energy dispersive analyzer equipped with a thin film sample. It can be measured. In addition, by electrolysis / chemical treatment, etc., by observing a scanning electron microscope equipped with an electrolytic emission electron gun and an X-ray energy dispersive analyzer with a sample in which a part of the matrix is dissolved and the precipitate is exposed on the surface, You can confirm its existence and measure its size and quantity. According to the X-ray energy dispersive analysis in the transmission electron microscope observation or the scanning electron microscope observation, the atomic% concentration of Cu in the precipitated phase is more than twice that of the impurity element, and the atomic% ratio of Ti and Cu (Ti atom %: The atomic phase of Cu) in the range of 1.8 to 2.0: 1 is a precipitate having the maximum phase of Ti ₂ Cu as referred to in the present invention.

  Hereinafter, the titanium alloy welded pipe of the present invention and the titanium alloy hoop product used as the material of the titanium alloy welded pipe will be described.

  First, the reason for selecting the various contained elements shown in the present invention and the reason for limiting the content range will be described.

  Cu is solid-dissolved in the titanium α phase up to 1.5% by mass. It is known that Cu in a solid solution state has an effect of enhancing the high temperature strength by strengthening the solid solution and strengthening without impairing the occurrence of twin deformation, and the effect is disclosed in Patent Document 7 and the like. In addition, the technique disclosed in Patent Document 6 described above aims to increase the amount of dissolved hydrogen in the titanium alloy and suppress hydride generation by adding Cu to Ti to cause solid solution. It is a thing.

On the other hand, when an appropriate amount of precipitation phase having Ti ₂ Cu as the maximum phase is generated in the α-phase in the Ti—Cu alloy, the increase in strength due to precipitation strengthening is not so large, but the α-phase Has the effect of suppressing grain growth. By these actions, it has been found that the occurrence of wrinkles called orange peel is suppressed in the pipe making process by continuous roll forming, and the pipe making performance is improved. In addition, the present inventors have found that the precipitated phase having Ti ₂ Cu as the maximum phase lowers the hydrogen overvoltage and strengthens the passive film. The precipitation phase with Ti ₂ Cu as the maximum phase acts as a cathode reaction site on the surface of the titanium alloy, and a hydrogen gas generation reaction is likely to occur on the precipitation phase. At this time, hydrogen accompanying hydrogen diffusion into the titanium alloy It was newly found that absorption is suppressed. It has also been found that hydrogen absorption is particularly difficult to occur by controlling the size and amount of the precipitated phase having Ti ₂ Cu as the maximum phase.

At this time, if the particle size of the precipitated phase having Ti ₂ Cu as the maximum phase is ultrafine, less than 10 nm, it is difficult to act as a hydrogen gas generation site accompanying the cathode reaction, and the hydrogen gas generation reaction mainly occurs in the base material. As a result, hydrogen absorption into the base material cannot be suppressed. On the other hand, when the particle size exceeds 1000 nm, the precipitated particles are unlikely to act as uniform cathode reaction sites. In this case, the hydrogen gas reaction also occurs in the base material, and hydrogen is absorbed in the base material. It will deteriorate. Therefore, the particle size of the precipitated phase having Ti ₂ Cu as the maximum phase needs to be 10 to 1000 nm.

In addition, when the volume fraction of the precipitated phase having a maximum phase of Ti ₂ Cu having a particle size of 10 to 1000 nm is less than 0.5%, the hydrogen gas generation reaction does not occur only on the precipitated phase but also on the base material. Hydrogen absorption into the base material is inevitable. On the other hand, if the volume fraction of the precipitated phase having Ti ₂ Cu as the maximum phase exceeds 3.5%, the uneven distribution and coarsening of the precipitated phase tend to occur. At this time, the hydrogen gas generation reaction sites will be unevenly distributed, the hydrogen gas generation reaction will occur unevenly in the system, and the reaction will occur even in the base material, so the hydrogen absorption resistance is descend. Therefore, the precipitation phase having a maximum particle size of Ti ₂ Cu having a particle size of 10 to 1000 nm has a volume fraction of 0.5 to 3 to prevent hydrogen absorption in a corrosive environment where a titanium welded tube is used. It is necessary to deposit 5%. Furthermore, in particular, in applications that require higher hydrogen embrittlement resistance, such as when cathodic protection is used in chemical plants and condenser applications, the precipitated phase having a maximum phase of Ti ₂ Cu with a particle size of 10 to 1000 nm is It is desirable to deposit 0.6 to 2.0% by fraction.

The upper limit of the Cu addition amount is set to 1.8% because if it is added exceeding this, a precipitated phase having a maximum phase of Ti ₂ Cu is generated with a volume fraction exceeding 3.5%. This is because uneven distribution tends to occur, and the coarsening of the precipitated phase particle diameter exceeding 1000 nm occurs, resulting in a decrease in hydrogen absorption resistance. Moreover, the minimum addition amount of Cu that effectively acts as a hydrogen gas generation site in a corrosive environment in which a titanium welded tube is used in which a precipitation phase having Ti ₂ Cu as a maximum phase is uniformly dispersed and precipitated in the alloy is Since it is 0.6%, it is necessary to add Cu 0.6% or more.

Fe is an element that stabilizes the β phase of titanium, and expresses the β phase from room temperature to high temperature. Furthermore, Fe dissolved in the β phase of titanium is likely to absorb hydrogen. If the Fe content is 0.03% or less, the generated β phase is an amount that causes no practical problems in fields where high hydrogen absorption resistance is required, such as heat exchanger applications and cathodic protection environments. However, if it is added in excess of this, the amount of β phase increases, and Cu that tends to concentrate in the β phase tends to concentrate in the β phase. In this way, the precipitation phase having the maximum phase of Ti ₂ Cu concentrates and precipitates in the β phase enriched with Cu, so that the precipitate is likely to be coarsened, and a uniform distribution state and a hydrogen gas generation site cannot be obtained. It will be. At the same time, if more than 0.03% Fe is contained, the fraction of β phase in which Fe is easily dissolved and which is easy to absorb hydrogen increases under severe corrosion conditions such as heat exchanger applications and cathodic protection. This will lead to a decrease in hydrogen absorption resistance. Therefore, the Fe content needs to be 0.03% or less.

  Since O has an action of solid solution in the α phase and strengthening of the solid solution, if added excessively, cold workability at the time of roll forming will be reduced. At this time, in order to maintain the high cold workability corresponding to two types of pure titanium, the O amount needs to be suppressed to 0.16% or less, so the upper limit of the O amount was set to 0.16%.

  In addition, for impurities contained in ordinary titanium materials such as N, C, Ni, Cr, Al, Sn, Si, and H as impurity elements, if the sum of these elements does not exceed 0.3%, hydrogen resistance Does not adversely affect absorbency and cold workability. Therefore, if the total of these impurity elements is 0.3% or less, there is no problem even if it is contained.

  Next, a titanium alloy welded pipe according to the present invention and a method for producing a titanium alloy hoop product as a material of the titanium alloy welded pipe will be described.

In the method for producing a product having a titanium alloy component according to the present invention, the final annealing is performed in a temperature range of 480 ° C. or higher and 730 [% Cu] ^{0.126 to} 160 ° C. or lower. This is a method of manufacturing a titanium alloy welded pipe and a welded pipe hoop material excellent in workability. By performing the final annealing in the temperature range may be one containing 0.5 to 3.5% a precipitation phase to the maximum phase of Ti ₂ Cu particle size 10~1000nm volume fraction.

That is, in the temperature range of 480 ° C. or more and 730 [% Cu] ^{0.126 to} 160 ° C. or less, the precipitation phase having the maximum phase of Ti ₂ Cu is a fine size having a particle size of about 10 to 1000 nm, and 0.5 to 3 It is a temperature range in which it is easy to deposit uniformly with a volume fraction of 0.5%, and by carrying out final annealing in this temperature range, the hydrogen absorption resistance can be enhanced.

Note that 730 [% Cu] ^0.126 ° C. is an equation obtained from a Ti ₂ Cu precipitation curve in a Ti—Cu binary equilibrium diagram. That is, in the titanium alloy within the chemical composition range shown in claim 1 by performing final annealing at 480 ° C. or more and 160 ° C. or less lower than the Ti ₂ Cu precipitation curve, it is shown in claim 1. It has been found that the predetermined state of the Ti ₂ Cu precipitation phase can be obtained industrially. However, it is desirable to avoid as much as possible because the annealing time for producing the effect becomes longer at temperatures lower than 480 ° C.

  The final annealing may be the final annealing after cold rolling in the cold rolled product or the final annealing after hot rolling in the hot rolled product, and indicates the final annealing before product shipment. ing.

<Example 1>
A titanium material having a composition of alloy numbers 1 to 18 shown in Table 1 is melted by a vacuum arc melting method, this is hot forged into a slab, heated to 860 ° C., and hot rolled to a 3 mm thick plate material did.

The hot-rolled plate material was shot blasted and pickled to remove the oxide scale, and then cold-rolled to obtain a thin plate material having a thickness of 0.5 mm. It was subjected to furnace-cooled vacuum annealing as final annealing at 550 ° C. for 6 hours, and then subjected to shape correction. A 25 mm × 50 mm coupon sample cut out from this thin plate material was wet-polished with No. 600 emery paper, and then evaluated for corrosion resistance when immersed in an aqueous solution of 5% H ₂ SO _{4 at} 70 ° C. for 24 hours. Moreover, the test piece for analysis was cut out from the sample after the corrosion test, and the hydrogen concentration was measured by the melting method. The pipe forming property of the welded pipe was evaluated by visually inspecting whether or not a roll flaw occurred up to a pipe forming length of 10000 m in a line continuously formed by roll forming and TIG welding. Further, a specimen for metallographic observation was collected, the longitudinal section was etched with a 2% aqueous hydrofluoric acid solution, and the precipitated phase with Ti ₂ Cu as the maximum phase was observed using a scanning electron microscope (SEM), The volume fraction of the precipitated phase having a diameter of 10 to 1000 nm was examined in the observation cross section. The precipitation phase in which the atomic% concentration of Cu in the precipitated phase is more than twice as high as that of the impurity element and the atomic% ratio of Ti and Cu falls within the range of 1.8 to 2.4: 1 is Ti ₂ Cu maximum. The size and quantity of the precipitates as phases were analyzed using an image analyzer. In the observation visual field, the magnification was appropriately changed depending on the size of the precipitated phase, and 50 to 100 visual fields were observed.

The total of the sphere equivalent volume of the precipitation phase having the maximum phase of Ti ₂ Cu having a sphere equivalent diameter of 10 to 1000 nm obtained here was obtained. Further, the amount of elution of the mother phase by etching is calculated from the weight difference before and after the etching of the sample, which has been measured in advance, and the precipitation phase sphere having the Ti ₂ Cu contained in the sample as the maximum phase. The volume fraction based on the equivalent volume was obtained.

  These evaluation results are also shown in Table 1.

In Table 1, test number 1 is an example of JIS class 2 pure titanium. In test number 1, the corrosion rate is slightly high and the hydrogen absorption is not sufficient. On the other hand, test number 2 is an example of an alloy containing several percent of Al, and an Al concentrated layer is provided on the surface in order to improve hydrogen absorption resistance. In the case of this alloy, the hydrogen absorption resistance is good, but roll scratches occurred immediately after the start of roll forming. This is because the surface Al-concentrated layer was hard and part of the surface layer was cracked during roll forming, and debris adhered to the surface of the roll and transferred to the surface of the welded pipe as roll scratches. I can't say that. In both test numbers 1 and 2, the formation of a precipitated phase with a Ti ₂ Cu maximum phase is not observed.

On the other hand, in the test numbers 5, 6, 8, 10, 11, and 13 to 18, which are examples of the present invention, both the corrosion rate and the hydrogen absorption amount are suppressed to a low level. In addition, the tube forming property is the same as that of JIS class 2 pure titanium and has good workability. All of these contain a precipitated phase having a maximum volume of Ti ₂ Cu of 10 to 1000 nm in a volume fraction of 0.5 to 3.5%, and it is clear that the amount of precipitation is in an appropriate range. .

On the other hand, in test numbers 4, 7, and 9, although the corrosion rate was low, the hydrogen penetration amount was higher than that of the material of the present invention. Among these, in test number 4, the amount of Cu added is less than the lower limit of 0.6% of the present invention, and the amount of precipitation phase having Ti ₂ Cu as the maximum phase is also less than 0.5%. With this material, a precipitated phase that sufficiently functions as a hydrogen gas generation site could not be obtained, so the hydrogen absorption amount was relatively high. In addition, in Test No. 7, since the Cu addition amount was added to exceed the upper limit of 1.8% of the present invention, the precipitated phase having Ti ₂ Cu as the maximum phase had a volume fraction of 3.5%. This is because a large amount of the precipitate is precipitated, causing aggregation and coarsening, and does not function effectively as a hydrogen gas generation reaction site. On the other hand, in Test No. 9, a precipitated phase having a coarse phase of coarse Ti ₂ Cu exceeding 1000 nm in part was generated. This is because the content of Fe, which is a β-stabilizing element, was added in excess of 0.03%, which is the upper limit of the present invention, so the amount of β-phase increased, and Cu concentrated and concentrated there. Precipitation phase was generated, and it did not function effectively as a cathode reaction site in harsh corrosive environments such as chemical plant applications, and because the solid solution Fe promoted hydrogen absorption, hydrogen penetration resistance decreased. Is.

  In Test No. 12, roll flaws occurred although they were minor during pipe making. This is because O was added in excess of 0.16% which is the upper limit of the present invention, so that the strength increased and the contact stress with the tube-forming roll increased.

As described above, the titanium alloy composed of the element content defined in the present invention and the volume fraction of the precipitated phase having the maximum phase of Ti ₂ Cu is equivalent to the hydrogen penetration resistance superior to JIS class 2 pure titanium. However, if the amount of alloying elements specified in the present invention and the volume fraction of the precipitated phase with Ti ₂ Cu as the maximum phase are deviated, the desired hydrogen penetration resistance and cold working You can't get sex.

<Example 2>
Using a hot-rolled sheet having a thickness of 3 mm, which is an intermediate product when producing materials of alloy numbers 8, 11, and 18 in Table 1, after removing the oxide scale by shot blasting and pickling, A thin plate material having a thickness of 1 mm was obtained by rolling. Then, after performing vacuum annealing under the conditions shown in Table 2 as final annealing, shape correction was performed. The thin plate was cut into 25 mm x 50 mm coupon samples, wet-polished with No. 600 emery paper, and then evaluated for corrosion resistance when immersed in an aqueous solution of 5% H ₂ SO _{4 at} 70 ° C for 24 hours. After the test, an analytical test piece was cut out and the hydrogen concentration was measured by a melting method. The pipe forming property of the welded pipe was evaluated by visually inspecting whether or not roll flaws were generated and observing the occurrence of rough surface in a line continuously formed by roll forming and TIG welding. In addition, specimens for metallographic observation were collected, the longitudinal cross section was etched with 2% aqueous hydrofluoric acid, and a scanning electron microscope (SEM) equipped with an electrolytic emission electron gun and an X-ray energy dispersive analyzer was used. Then, the precipitation phase having the maximum phase of Ti ₂ Cu having a diameter of 10 to 1000 nm was observed, and the volume fraction was investigated. The precipitation phase in which the atomic% concentration of Cu in the precipitated phase is more than twice as high as that of the impurity element and the atomic% ratio of Ti and Cu falls within the range of 1.8 to 2.4: 1 is Ti ₂ Cu maximum. The size and quantity of the precipitates as phases were analyzed using an image analyzer. In the observation visual field, the magnification was appropriately changed depending on the size of the precipitated phase, and 50 to 100 visual fields were observed.

The total of the sphere equivalent volume of the precipitation phase having the maximum phase of Ti ₂ Cu having a sphere equivalent diameter of 10 to 1000 nm obtained here was obtained. Further, the amount of elution of the mother phase by etching is calculated from the weight difference before and after the etching of the sample, which has been measured in advance, and the precipitation phase sphere having the Ti ₂ Cu contained in the sample as the maximum phase. The volume fraction based on the equivalent volume was obtained.

These evaluation results are also shown in Table 2. Further, T (° C.) in Table 2 is the upper limit temperature for annealing shown in claim 2 calculated by T (° C.) = 730 [% Cu] ^0.126 −160 ° C.

Table 2 shows the results of thin plate test materials using the compositions shown in Alloy No. 8, Alloy No. 11 and Alloy No. 18 in Table 1 as raw materials. Test numbers 20, 21, 24, 25, 28, and 29, which are examples of the present invention in which the final annealing was performed in a temperature range of 480 ° C. or higher and 730 [% Cu] ^{0.126 to} 160 ° C., all have high corrosion resistance. The hydrogen absorption amount was very low, and the hydrogen absorption resistance was excellent. On the other hand, about the test numbers 19, 22, 23, 26, 27, and 30 which are comparative examples, the final annealing temperature was outside the range of the present invention, and as a result, the hydrogen absorption amount was high. This is because in Test Nos. 19, 23, and 27 where the annealing temperature is less than 480 ° C., the proportion of fine precipitates having a maximum phase of Ti ₂ Cu of 10 nm or less increased. On the other hand, in the test numbers 22, 26, and 30 where the annealing temperature exceeds 730 [% Cu] ^{0.126 to} 160 ° C., a part of the precipitated phase having Ti ₂ Cu as the maximum phase is re-dissolved, and the amount of the generated precipitated phase is increased. This is because it is slightly lower. From these results, in the use in which hydride precipitation due to hydrogen absorption and the accompanying hydrogen embrittlement are particularly problematic, the method of the present invention in which annealing is performed at 480 ° C. or higher and 730 [% Cu] ^{0.126 to} 160 ° C. or lower is performed. ₂ shows that the titanium alloy welded pipe and the hoop product for welded pipe of the present invention can be obtained by uniformly and finely dispersing the precipitated phase having the maximum phase of Cu.

  The titanium alloy welded pipe and hoop product of the present invention are used in an environment in which hydrogen embrittlement due to hydrogen absorption is a problem in pure titanium, and has roll forming workability equivalent to that of two types of pure titanium.

Claims (4)

It contains 0.6 to 1.8% Cu, 0.03% Fe or less, 0.16% or less O in mass%, the balance is Ti, and the total amount of impurity elements is 0.3% or less. A titanium alloy welded tube excellent in hydrogen absorption resistance, characterized by containing a precipitated phase having a maximum volume of Ti ₂ Cu having a diameter of 10 to 1000 nm in terms of volume fraction. It contains 0.6 to 1.8% Cu, 0.03% Fe or less, 0.16% or less O in mass%, the balance is Ti, and the total amount of impurity elements is 0.3% or less. A titanium alloy hoop product excellent in hydrogen absorption resistance and tube-forming properties, characterized by containing a precipitated phase having a maximum volume of Ti ₂ Cu having a diameter of 10 to 1000 nm in terms of volume fraction. The method for producing a titanium alloy welded tube having excellent hydrogen penetration resistance according to claim 1, wherein the final annealing temperature is performed in a temperature range of 480 ° C or higher and 730 [% Cu] ^0.126 -160 ° C or lower. .
Here, [% Cu] is the Cu content chemical analysis value (mass%) of the titanium alloy. The titanium alloy hoop having excellent hydrogen absorption resistance and pipe forming property according to claim 2, wherein the final annealing temperature is 480 ° C or higher and 730 [% Cu] ^{0.126 to} 160 ° C or lower. Product manufacturing method.
Here, [% Cu] is the Cu content chemical analysis value (mass%) of the titanium alloy.