JP2005336551A - Fe-containing titanium material having excellent corrosion resistance and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium material excellent in corrosion resistance containing Fe and a method for producing the same.
Titanium containing 0.1 to 2.5 mass% of Fe has a needle-like or lath-like microstructure, and the Fe concentration is an average concentration in a concentration distribution analyzed by an electron beam microanalyzer (EPMA). In contrast, the corrosion resistance of the Fe-containing titanium material can be increased by setting the area of the portion concentrated 1.5 times or more to 5% or more. The corrosion resistance of the Fe-containing titanium material can be improved by heating in the temperature range from 600 ° C. to (β transformation point−20 ° C.) after cooling from the temperature above the β transformation point that becomes the β phase single phase or during cooling. it can.
[Selection] Figure 3

Description

  The present invention relates to a titanium material containing Fe (iron) and excellent in corrosion resistance and a method for producing the same.

  It is known that the amount of corrosion increases as the Fe concentration in titanium increases. As an example of this, in “Influence of trace impurities on the corrosion resistance of pure titanium (author Takamura et al.)” Of Non-Patent Document 1, in pure titanium-based materials having Fe concentration of less than 0.01% by mass to 0.49% by mass, nitric acid It has been reported that in an oxidizing corrosive environment such as the above, corrosion does not affect the corrosion resistance regardless of the Fe concentration and does not affect the corrosion resistance, but in a non-oxidizing corrosive environment such as hydrochloric acid or sulfuric acid, the amount of corrosion increases as the Fe concentration increases. Yes.

  On the other hand, Fe is always contained in titanium like O (oxygen), and in the JIS standard of industrial pure titanium, the Fe concentration is 0.20 mass% or less for JIS type 1 and 0.25 mass% or less for JIS type 2. JIS type 3 is 0.30% by mass or less, and JIS type 4 is 0.50% by mass or less. In addition to increasing the Fe concentration in titanium by using inexpensive raw materials (off-grade sponge titanium, scrap, etc.), Ferro-Cr and Ferro- actively containing Fe and Fe as an inexpensive alloying additive Mo etc. may be added to titanium.

  As a method for improving the corrosion resistance, in the invention of “Industrial Pure Titanium and its Production Method” described in Patent Document 1, hot rolling is applied to industrial pure titanium having an Fe concentration of 0.1 to 0.19 mass%. Next, annealing is performed at a temperature of about 550 to 750 ° C., and the crystal grain size is set to 30 μm or less. On the other hand, in the invention of “Ti member excellent in corrosion resistance” described in Patent Document 2, the average crystal grain size is 20 to 100 μm. Here, in the embodiment of the invention described in Patent Document 2, heat treatment at about 700 to 800 ° C. is performed.

  The inventions described in Patent Document 1 and Patent Document 2 regulate the amount of crystal grain boundaries that easily elute in a corrosive environment and the segregation of trace elements to the crystal grain boundaries by regulating the crystal grain size. It suppresses the elution of crystal grain boundaries and is a general equiaxed structure. The heat treatment temperature range of the inventions described in both patent documents is lower than 882 ° C., which is the β transformation point, and it is understood that the structure is equiaxed. This equiaxed structure is composed of equiaxed α-phase crystal grains, and β-stabilizing elements such as Fe exceeding the solid solubility limit in the α-phase are concentrated at the grain boundaries of the α-phase crystal grains. Incidentally, from the binary phase diagram of Ti and Fe (see Non-Patent Document 2), only about 0.05 mass% of Fe is dissolved in the α phase at the maximum.

Japanese Patent No. 3303534 Japanese Patent Laid-Open No. 05-070913 Anticorrosion technology Vol. 19, no. 5/6, p14 Issued by ASM, PHASE DIAGRAMS OF BINARY TITANIUM ALLOYS

  In the above prior art, when the concentration of Fe, which is a β-stabilizing element, is high and exceeds 0.05 mass%, the temperature of the α phase is less than the β transformation point, which is a general annealing or heat treatment temperature, as described above. Fe and Cr are concentrated at the grain boundaries of the axial crystals. The grain boundaries are easily corroded, and since the inventions described in Patent Document 1 and Patent Document 2 have an equiaxed structure, the crystal grain boundaries are three-dimensionally continuous and the grain boundaries are eluted one after another. For this reason, the corrosion rate is increased as compared with the case where the Fe concentration is low. In addition, the grain boundaries enriched with Fe during annealing suppress the growth of α-phase grains. As a result, the grains become finer and the total volume (total area in the cross section) of the grain boundaries that are susceptible to corrosion becomes a metal structure. End up.

  In view of the above-described problems of the prior art, an object of the present invention is to provide a titanium material excellent in corrosion resistance and a manufacturing method thereof in titanium having a high Fe concentration.

  In order to meet such a purpose, the present inventors have intensively studied, and as a result, the following titanium material and the heat treatment method for improving the corrosion resistance have been achieved.

The titanium material of the present invention and the heat treatment method for improving the corrosion resistance have the following characteristics.
(1) Concentration distribution containing 0.1 to 2.5% by mass of Fe, remaining Ti and inevitable impurities, having a needle-like or lath-like microstructure, and analyzed by an electron beam microanalyzer (EPMA) A Fe-containing titanium material having excellent corrosion resistance, wherein the area of the portion where the Fe concentration is concentrated 1.5 times or more of the average concentration is 5% or more.
(2) A part of the Fe amount is substituted with one or more of β-stabilizing elements of Cr, Ni, Co, V, Mo, Nb, and Cu, and Fe and the β-stabilizing elements are combined in total. The corrosion resistance according to (1) above, wherein the corrosion resistance is 0.1 to 2.5% by mass and the Fe concentration in the microstructure is represented by the total concentration of Fe and the β-stabilizing element. Excellent Fe-containing titanium material.
(3) Further, in terms of mass%, Al: 0.01 to 6.5%, O: 0.15 to 0.4%, C: 0.01 to 0.1%, N: 0.01 to 0.00. The Fe-containing titanium material having excellent corrosion resistance as described in (1) or (2) above, which contains 1% or more of 1% α-stabilizing element.
(4) After cooling the titanium material having the component composition according to any one of the above (1) to (3) from a temperature above the β transformation point at which the β phase becomes a single phase, 600 ° C to (β transformation) It has a needle-like or lath-like microstructure, characterized by heating in a temperature range of −20 ° C.), and the Fe concentration in the concentration distribution analyzed by an electron beam microanalyzer (EPMA) The manufacturing method of the Fe containing titanium material excellent in corrosion resistance whose area of the part concentrated 1.5 times or more is 5% or more.
(5) In the course of cooling when the titanium material having the component composition according to any one of the above (1) to (3) is heated to a temperature exceeding the β transformation point to be a β phase single phase, 600 ° C. It has a needle-like or lath-like microstructure characterized by heat treatment in a temperature range of ˜ (β transformation point−20 ° C.) and the Fe concentration in the concentration distribution analyzed by an electron beam microanalyzer (EPMA) A method for producing an Fe-containing titanium material excellent in corrosion resistance, wherein the area of the portion concentrated 1.5 times or more of the average concentration is 5% or more.

  Here, FIGS. 1A and 1B show a needle-like or lath-like microstructure (hereinafter referred to as a structure a) cooled from a temperature exceeding the β transformation point at which a β-phase single phase is obtained. On the other hand, FIG. 2 shows a typical equiaxed structure (hereinafter referred to as a structure b), which is a completely different structure from (a) and (b) in FIG. The temperature exceeding the β transformation point is a temperature range in which titanium has a single β phase.

  The concentration distribution analyzed by an electron beam microanalyzer (hereinafter referred to as EPMA) refers to polishing by embedding a titanium material in a resin, and in a partial region of the embedded polished surface, Fe, Cr, Ni, Co, V Surface analysis of the total concentration of β-stabilizing elements of Mo, Nb, and Cu. From the “average concentration” and “concentration distribution such as histogram” of the in-plane Fe and β stabilizing elements obtained from this concentration analysis, the total concentration of Fe and β stabilizing elements is the average concentration. The area ratio which is 1.5 times or more is obtained.

  Here, the cooling method after the heat treatment is not particularly limited, such as water cooling, air cooling, cooling with an inert gas flow, and furnace cooling.

  Titanium containing a total of 0.1 to 2.5 mass% of Fe and the β stabilizing element has a needle-like or lath-like microstructure and is analyzed by an electron beam microanalyzer (EPMA). And the corrosion resistance of a titanium material can be improved by making the area of the part which the total density | concentration of the said (beta) stabilization element concentrated 1.5 times or more with respect to average density | concentration into 5% or more. Corrosion resistance of the titanium material can be enhanced by heating at a temperature range of 600 ° C. to (β transformation point−20 ° C.) after cooling from a temperature exceeding the β transformation point at which the β phase becomes a single phase or during cooling.

FIG. 3 shows the total concentration of chemically analyzed Fe and the β-stabilizing element (hereinafter, also simply referred to as Fe, including the β-stabilizing element), Fe concentration distribution by EPMA analysis (Fe concentration area ratio described later) ) And the relationship between the microstructure (structure a, structure b) and the corrosion rate (0.1 mm / year or less, more than 0.1 mm year). The titanium material used here contains 0.1 to 0.25% by mass of Fe, and in addition to those inevitably containing Al, O, N, and C, there is also a material in which one or more of these are added. The microstructure and the concentration distribution of Fe were adjusted by performing various heat treatments after cold working the titanium material. Corrosion rate is the mass before and after immersing a specimen of size 3 mm × 25 mm × 25 mm and surface # 600 polished from the titanium material after the various heat treatments described above and immersing it in 400 ml of boiling 1% hydrochloric acid aqueous solution for 24 hours. Obtained from change. Here, when calculating the amount of corrosion, a density of 4.51 g / cm ³ was used.

  Here, EPMA is carried out with a sample whose surface is mirror-polished using JXA8800R manufactured by JEOL, and the Fe concentration is analyzed with a 1 μm mesh within a range of 200 μm × 200 μm to obtain its concentration distribution. . The “area ratio (%) of the portion where the Fe concentration is concentrated to 1.5 times or more of the average value” on the vertical axis in FIG. 3 is the average value (200 μm × Fe concentration within the range of 200 μm × 200 μm analyzed by EPMA). This is a calculation of the percentage of the area of the portion concentrated 1.5 times or more with respect to the EPMA analysis result in the 200 μm range. Hereinafter, the “area ratio of the portion where the Fe concentration is concentrated to 1.5 times or more of the average value” is referred to as “Fe concentrated area ratio”.

  From FIG. 3, the titanium material having a corrosion rate of 0.1 mm / year or less (◯) has a microstructure “a” and an Fe concentration area ratio of 5% or more on the vertical axis. On the other hand, even when the microstructure is the structure a, the corrosion rate is 0.1 mm / year when the Fe concentration area ratio on the vertical axis is less than 5% (×) or when the microstructure is the structure b (▲). Over.

  In the structure b which is a general equiaxed structure, Fe is concentrated at the grain boundary, and the grain boundary is easily corroded and the volume of the grain boundary is large and is three-dimensionally continuous in the depth direction. Grain boundaries elute and corrosion progresses (the grain boundaries around the entire crystal grains may elute, resulting in a form in which crystal grains are missing). As a result, the corrosion rate is high. Even in a structure a which is a needle-like or lath-like structure cooled from a temperature exceeding the β transformation point at which a β phase becomes a single phase, Fe is supersaturated in a state where Fe concentration is small (Fe concentration area ratio is less than 5%). Since most of the parts are melted, corrosion progresses throughout.

  On the other hand, the needle-like or lath-like portion in which the Fe concentration is 5% or more in the structure a is eluted, but the Fe-concentrated portion is discontinuous in the depth direction. The progress of corrosion along the grain boundary such as the structure b is suppressed. The progress of corrosion is slow in other portions where Fe is not concentrated. As a result, the corrosion rate can be lowered.

  From the above, since the corrosion rate is 0.1 mm / year or less, in the present invention according to claim 1, in titanium containing 0.1 to 2.5 mass% of Fe, the structure a (β phase single phase and A needle-like or lath-like microstructure cooled from a temperature above the β transformation point, and Fe concentration area ratio (Fe concentration is 1.5 times or more of the average concentration in the concentration distribution analyzed by EPMA) The area of the concentrated portion) is 5% or more.

  Here, when Fe is contained in an amount of less than 0.1% by mass, since the Fe concentration is originally low, changes in the microstructure and the Fe concentrated area ratio hardly affect the corrosion rate. It was set as the Fe lower limit of the invention. The upper limit of Fe is set to 2.5% by mass because the corrosion rate may exceed 0.1 mm / year because the area of the Fe-enriched portion increases even in the structure a if the upper limit exceeds 2.5% by mass. These points regarding the Fe concentration are shown in FIG.

  In the present invention according to claim 2, since Fe is one of β-stabilizing elements, other β-stabilizing elements Cr, Ni, Co, V, Mo, Nb, Cu acting similarly to Fe and A part of Fe of the present invention described in claim 1 is replaced.

  The effect of the present invention according to claim 3 is the same even when titanium is added with one or more of O, N, C, and Al, which are α stabilizing elements, with respect to Fe, which is a β stabilizing element. Then, in titanium containing 0.1 to 2.5% by mass of Fe (including the β-stabilizing element) and one or more of Al, O, C, and N as α-stabilizing elements, the structure a And a titanium material having an Fe concentration area ratio of 5% or more. Here, in the present invention according to claim 3, Al, O, C, and N are contained in Al: 0.01 to 6.5 mass%, O: 0.15 to 0.4 mass%, and C: 0.00. The content was in the range of 01 to 0.1% by mass and N: 0.01 to 0.1% by mass. Since the concentrations of Al, O, C, and N inevitably contained in titanium are about 0.001, about 0.1, about 0.005, and about 0.005% by mass, the concentration of each element is unavoidable. The concentration having a significant difference beyond the concentration contained in the sample was taken as the lower limit. On the other hand, as the concentration of Al, O, C, and N increases, the workability decreases, so the upper limit is the concentration at which cold rolling of 10% or more is possible (not causing cracking) as an index of cold deformability. did. Preferably, Al: 0.1 to 4 mass%, O: 0.15 to 0.3 mass%, C: 0.01 to 0.1 mass%, N: 0.01 to 0.05 mass% Is within.

  Next, FIGS. 4 and 5 show the influence of the heat treatment method. FIG. 4 shows a heat treatment temperature in the range of 550 to 920 ° C. after air cooling from 1000 ° C. above the β transformation point in five types of titanium materials (symbols C, E, G, I, and J) having different Fe concentrations. The change of the corrosion rate and Fe concentration area ratio when changing by is shown. In addition, since the titanium material of FIG. 4 is once heat-treated at 1000 ° C. above the β transformation point, it exhibits a structure a under all heat treatment conditions. FIG. 5 shows the relationship between the corrosion rate and the Fe concentration (chemically analyzed Fe concentration) contained in the titanium material when various heat treatments are performed.

  Each titanium material was subjected to various heat treatments after cold working. Both the corrosion test and the measurement of the Fe enriched area ratio are the same as described above. The β transformation point was measured by differential thermal analysis (DTA), and was the average value of the temperature at which transformation was completed during heating and the temperature at which transformation was initiated during cooling. For measurement, a titanium test piece 4 mm in diameter x 4 mm in length (about 0.23 g) is heated and cooled at 5 ° C./min from 500 ° C. to 950 ° C. in an argon gas atmosphere, and alumina is used as a standard sample. did.

  From FIG. 4, the Fe-concentrated area ratios (●, ■, ◆, ▲, *) are less than 5% even when heated at 1000 ° C after air cooling at 550 ° C for 8 hours. This is because it is slow. At 600 to 850 ° C. (only symbol G is 600 to 800 ° C.), the diffusion rate of Fe increases and reaches 5% or more. At 920 ° C. above the β transformation point (only symbol G: 850 ° C. and 920 ° C.), all of Fe is transformed into a solid β phase, so the Fe distribution after cooling becomes uniform and the Fe concentrated area ratio decreases to less than 2%. . Corrosion rates (○, □, ◇, △, ×) are as high as over 2 mm / year when the heat treatment temperature after air cooling at 1000 ° C. is 550 ° C., corresponding to the Fe concentration area ratio, 600 to 850 ° C. (only symbol G is 600) It decreases to 0.1 mm / year or less at ˜800 ° C., and increases to more than 2 mm / year at 920 ° C. above the β transformation point (850 ° C. and 920 ° C. only for symbol G). As described above, the upper limit temperature of the heat treatment that has the effect of improving the corrosion resistance is a temperature 20 ° C. lower than the β transformation point by comparing with the β transformation point (891, 870, 839, 872, 889 ° C.) of each titanium material. (Β transformation point −20 ° C.).

  In addition, as shown in FIG. 5, Fe compared to 750 ° C. (♦) corresponding to general recrystallization annealing after cold working and 1000 ° C. which is a β single phase region (■). When the concentration is in the range of 0.1 to 2.5% by mass, the corrosion rate is reduced to 0.1 mm / year or less by heat treatment at 600, 750, and 800 ° C. after cooling from 1000 ° C. (Δ, ○, □). To do. As described above, since the corrosion rate is originally low when the Fe concentration is less than 0.1% by mass, there is almost no influence of the heat treatment, and when the Fe concentration is 2.5% by mass, the corrosion rate is reduced to 0.1 mm / year or less. If it exceeds this, 3.0% by mass may exceed 0.1 mm / year.

  After cooling from a temperature above the β transformation point, heat treatment is performed at a temperature below the β transformation point (α + β two-phase temperature range), so that it transforms into α + β two-phase, so that Fe in solid solution diffuses and enriches Fe. Phase (β phase during heat treatment) is formed. If the temperature is too low, the diffusion of Fe is slow and the portion enriched with Fe is not formed easily. On the other hand, Fe with low corrosion resistance is enriched immediately below the β transformation point (above “β transformation point−20 ° C.”). In some cases, the amount of the developed phase (β phase during heat treatment) increases and the corrosion rate does not become 0.1 mm / year or less.

  From the above, the titanium material of the present invention according to any one of claims 1 to 3 having high corrosion resistance is cooled from a temperature above the β transformation point, and then a temperature 20 ° C. lower than the 600 ° C. to β transformation point (β It is obtained by heat treatment within the range of transformation point -20 ° C. Therefore, in the present invention according to claim 4, the titanium material is cooled from a temperature exceeding the β transformation point at which the β phase becomes a single phase, and then heat treated in a temperature range of 600 ° C. to (β transformation point−20 ° C.). did.

  Further, even when the heat treatment from 600 ° C. to (β transformation point−20 ° C.) is carried out in the process of cooling from the temperature above the β transformation point, the transformation to the α + β two-phase enriched in Fe occurs in the same manner. Thus, the titanium material of the present invention according to any one of claims 1 to 3 is obtained. During the cooling, heat treatment was performed in a temperature range of 600 ° C. to (β transformation point−20 ° C.).

  Hereinafter, the effects of the present invention will be described with reference to examples.

  Table 1 shows chemical components and β transformation points of titanium materials (A to R) subjected to various heat treatments and corrosion tests. The symbols A to H are different in the Fe concentration range of 0.04 to 2.98% by mass, but the other elements have substantially the same concentration. In addition to Fe, symbol I contains Cr, which is a β-stabilizing element. Symbols I to R are different from each other in the Fe concentration range of 0.15 to 3.93% by mass, and Al, O, N, and C which are α stabilizing elements are added. In the symbol N, Cr which is a β-stabilizing element is further added. Here, the β transformation point is a value measured by differential thermal analysis (DTA).

  Tables 2 and 3 show the various heat treatment conditions applied to the symbols A to I and Table 4 the symbols J to R and their microstructures # 1, Fe enriched area ratio # 2, and corrosion rate # 3. Here, the steps before the heat treatment are all cold rolling. # 1, # 2, and # 3 in the table mean the following comments.

  # 1: The cross section of the sample was embedded and polished, and then etched with an aqueous solution of nitric hydrofluoric acid, and the microstructure was observed with an optical microscope. When the microstructure is a needle-like or lath-like microstructure cooled from a temperature higher than the β transformation temperature to become a β-phase single phase, “tissue a” is obtained. "

  # 2: From the Fe concentration distribution measured by EPMA, the area ratio of the portion where the Fe concentration was concentrated 1.5 times or more of the average value was obtained.

  # 3: A sample (size 2 × 25 × 25 mm) polished after heat treatment and finished to surface # 500 (dimensions 2 × 25 × 25 mm) is immersed in boiling 1% by mass hydrochloric acid (500 ml) for 24 hours, and corrosive from mass change before and after immersion. The speed was determined.

  Symbols A and B, which have a low Fe concentration of 0.07% by mass or less, As shown in 1 to 5, the corrosion rate is as low as 0.1 mm / year or less regardless of the heat treatment conditions. On the other hand, symbols B to I having a high Fe concentration of 0.1 to 2.98% by mass are No. 1 in Table 2. 6-13 (symbol C), no. 14, 15 (symbol D), no. 16-23 (symbol E), no. 24 to 28 (symbol F), no. 29-35 (symbol G), no. 36-38 (symbol H), no. As shown in 39 to 45 (symbol I), the microstructure and the Fe enriched area ratio change depending on the heat treatment conditions, and the corrosion rate also changes accordingly.

  A heat treatment of 750 ° C., 1 hour, air cooling, which is a general recrystallization annealing heat treatment, without heat treatment at a temperature exceeding the β transformation point (Comparative Examples No. 6, 14, 16, 24, Table 2 in Table 2) In Comparative Example No. 29, 36, 39) of No. 3, the microstructure exhibits the structure b, and in any case, the corrosion rate is as large as 2 mm / year or more.

  Further, those subjected to heat treatment of 1000 ° C., 20 minutes, air cooling, which is above the β transformation point (Comparative Examples Nos. 7 and 17 in Table 2 and Comparative Example No. 37 in Table 3), and then further β transformation Heat treated at 920 ° C. (symbols C, E, G, I) and 850 ° C. (only symbol G) exceeding the point (Comparative Examples Nos. 13 and 23 in Table 2 and Comparative Example No. 35 in Table 3 respectively) 45, and Comparative Example No. 34) in Table 3 has a microstructure a, but the Fe-concentrated area ratio is as low as 1.7% or less, and the corresponding corrosion rate is 2. It is as large as 4 mm / year or more.

  On the other hand, when the heat treatment at the first stage was performed at 1000 ° C. above the β transformation point and then the heat treatment was performed at a temperature range of 550 ° C. to “β transformation point−20 ° C.” at the second stage, When the heating temperature is 550 ° C. (Comparative Examples Nos. 8 and 18 in Table 2 and Comparative Examples Nos. 30 and 40 in Table 3), the microstructure is the structure a, but the Fe concentration area ratio is less than 5%. It is low and the corrosion rate is 0.9-4.2 mm / year and over 0.1 mm / year.

  On the other hand, when the heating temperature of the second stage is 600 ° C. to (β transformation point −20 ° C.) (Nos. 9 to 12, 15, 19 to 22, 26 to 28 in Table 2 as examples) 3 No. 31-33, 41-44), the microstructure is the structure a and the Fe concentration area ratio is 5% or more, and the corrosion rate is as low as 0.1 mm / year or less accordingly. Yes. However, with the symbol H in which the Fe concentration exceeds 2.5 mass%, the corrosion rate does not decrease to 0.1 mm / year or less even when heated at 750 ° C. after heat treatment exceeding the β transformation point (Table 3). Comparative Example No. 38).

  In addition to the fact that the Fe concentration is different in the range of 0.15 to 3.93% by mass, symbols I to R to which Al, O, N, and C which are α stabilizing elements are added are also shown in Table 4. Thus, the results are the same as those in Tables 2 and 3 described above.

  In Examples (Nos. 48 to 51, 54, 56, 58, 60, 62, 64, and 67 to 69 in Table 4) in which the structure a and the Fe concentration area ratio are 5% or more, all exceed the β transformation point. After the first heat treatment at 1000 ° C., the second heat treatment is performed at 600 ° C. to (β transformation point−20 ° C.), and the corrosion rate is reduced to less than 0.1 mm / year. However, with the symbol R in which the Fe concentration exceeds 2.5 mass%, the corrosion rate does not decrease to 0.1 mm / year or less even when heated at 750 ° C. after the heat treatment exceeding the β transformation point (Table 4). Comparative Example No. 71).

  On the other hand, it is the comparative example (No. 46, 53, 55, 57, 59, 61, 63, 65, 70 which performed only 750 degreeC heating in Table 4) and organization a which are organization b. No. 47, 52, 66 in Table 4 in which the Fe concentration area ratio is less than 5% (the heating temperature of the second stage is as low as 550 ° C. or 920 ° C. and exceeds the β transformation point) The corrosion rate is as high as 2.9 mm / year or more.

  Next, Table 5 shows examples in which titanium materials having symbols C, E, F, I, and K are held at a predetermined temperature during cooling from a temperature exceeding the β transformation point, or when a predetermined temperature range is gradually cooled. Indicates.

  In Example 5 of Table 5, air-cooled after being held at 750 ° C. or 800 ° C. which is a temperature range of 600 ° C. to (β transformation point−20 ° C.) during cooling. In each of 72 to 75 and 77 to 82, the microstructure is the structure a and the Fe concentrated area ratio is 5% or more, and the corrosion rate is as small as less than 0.1 mm / year. Moreover, Example No. of Table 5 which annealed between 750 degreeC-800 degreeC which is a temperature range of 600 degreeC-((beta) transformation point -20 degreeC) in 1 hour during cooling. Similarly, Nos. 76 and 83 have the microstructure a and the Fe enriched area ratio of 5% or more, and the corrosion rate is as small as less than 0.1 mm / year. In Table 5, only the examples of symbols C, E, F, I, and K are shown for the effect of holding the cooling process and slow cooling, but the same effect can be obtained with other chemical components.

  The effect of heat treatment in the region of 600 ° C. to (β transformation point−20 ° C.) performed after heating at a temperature exceeding the β transformation point is performed in the cooling process from the temperature range exceeding the β transformation point as shown in Table 5. Even so, it can be seen that this is equivalent to the case where the second heat treatment is performed after cooling to room temperature.

  As mentioned above, although the Example was described about the material cold-rolled, the same effect is acquired also with a rod, a wire, a thick board, etc., and this example does not limit the shape of a titanium material to a cold-rolled sheet. Absent.

It is a figure which shows the needle-like or lath-like microstructure (structure | organism a) cooled from the temperature exceeding the beta transformation point used as beta phase single phase. It is a figure showing a typical equiaxed organization (tissue b). It is a figure which shows the relationship of the chemically analyzed Fe density | concentration, Fe concentration area ratio, a microstructure (structure | tissue a, structure | tissue b), and the corrosion rate (0.1 mm / year or less, more than 0.1 mm year). The figure which shows the change of the corrosion rate and Fe concentration area rate when the heat processing temperature implemented after air-cooling from 1000 degreeC over β transformation point is changed in the range of 550-920 degreeC in four types of titanium materials from which Fe concentration differs. It is. It is a figure which shows the relationship between the Fe density | concentration (chemically analyzed Fe density | concentration) which the titanium material at the time of implementing various heat processing, and a corrosion rate.

Claims (5)

  Fe concentration is 0.1 to 2.5% by mass, the balance is Ti and unavoidable impurities, has a needle-like or lath-like microstructure, and is analyzed by an electron beam microanalyzer (EPMA). An Fe-containing titanium material having excellent corrosion resistance, characterized in that the area of the portion concentrated at least 1.5 times the average concentration is 5% or more.   A part of the Fe amount is substituted with one or more of β-stabilizing elements of Cr, Ni, Co, V, Mo, Nb, and Cu, and Fe and the β-stabilizing elements are 0.1 in total. Fe of excellent corrosion resistance according to claim 1, wherein the Fe concentration in the microstructure is expressed by the total concentration of Fe and the β-stabilizing element. Contains titanium material. Furthermore, in mass%,
Al: 0.01 to 6.5%,
O: 0.15-0.4%
C: 0.01 to 0.1%,
N: 0.01 to 0.1%
The Fe-containing titanium material having excellent corrosion resistance according to claim 1, wherein the α-stabilizing element is contained in one or more kinds.   After cooling the titanium material having the component composition according to any one of claims 1 to 3 from a temperature exceeding the β transformation point at which the β phase single phase is obtained, the temperature is from 600 ° C to (β transformation point-20 ° C). It has a needle-like or lath-like microstructure characterized by heating in a temperature range, and the Fe concentration in the concentration distribution analyzed by an electron beam microanalyzer (EPMA) is 1.5 times or more of the average concentration. A method for producing an Fe-containing titanium material excellent in corrosion resistance, wherein the area of the concentrated portion is 5% or more.   In the course of cooling when the titanium material having the component composition according to any one of claims 1 to 3 is heated to a temperature higher than a β transformation point that becomes a β phase single phase, And having a needle-like or lath-like microstructure characterized by heat treatment in a temperature range of 20 ° C.), the Fe concentration in the concentration distribution analyzed by an electron beam microanalyzer (EPMA) is 1 with respect to the average concentration. A method for producing an Fe-containing titanium material having excellent corrosion resistance, wherein the area of the portion concentrated 5 times or more is 5% or more.