TWI650427B - Titanium plate - Google Patents

Abstract

A titanium plate whose chemical composition is Cu: 0.70 to 1.50%, Cr: 0 to 0.40%, Mn: 0 to 0.50%, Si: 0.10 to 0.30%, O: 0 to 0.10%, Fe: 0 in mass% ~0.06%, N: 0 to 0.03%, C: 0 to 0.08%, H: 0 to 0.013%, except for the above elements other than Ti: each of 0 to 0.1% and the sum of them is 0.3% or less, and The remainder: Ti; the A値 defined by the formula (1) is 1.15~2.5 mass%; in the metal structure, the area fraction of the α phase is above 95%, and the area fraction of the β phase is below 5%. The area fraction of the compound is 1% or less; the average crystal grain size D (μm) of the α phase is 20 to 70 μm and the formula (2) is satisfied.

Description

Titanium plate

The invention relates to titanium sheets.

Heretofore, the titanium plate has been used for many purposes such as a two-wheel exhaust system such as a heat exchanger, a fusion pipe, a muffler, and a building material. In recent years, in order to reduce the thickness and weight of these products, the demand for high strength of titanium sheets has gradually increased. Further, it is also desired to maintain the formability which can withstand the formation into a complicated shape while being high in strength. In the current state of the art, titanium of one type of JIS H4600 is used, and although the strength is solved by increasing the thickness of the sheet, if the sheet thickness is increased, the lightweight characteristics of titanium cannot be sufficiently exhibited. Among them, in the plate heat exchanger (PHE), a complicated shape press molding is performed, so that sufficient formability is required. Titanium which is excellent in formability even in titanium is used for the demand.

For PHE, we will pursue an increase in heat exchange efficiency, and for this we must be thin. When the thickness is reduced, the moldability is lowered and the pressure resistance is lowered. Therefore, it is necessary to ensure sufficient moldability and strength. Therefore, conventionally, in order to obtain a more excellent strength-formability balance of titanium, the amount of O, the amount of Fe, and the like have been optimized, or the control of the crystal grain size has been studied, or the temper rolling has been used.

For example, Patent Document 1 discloses a titanium plate having an average crystal grain size of 30 μm or more. However, the titanium plate of Patent Document 1 is inferior in strength.

Therefore, Patent Document 2 discloses a titanium alloy sheet having a predetermined O content and containing Fe as a β-stabilizing element and having an α-phase average crystal grain size of 10 μm or less. Patent Document 3 discloses a titanium alloy sheet in which the amount of Fe and O is reduced and Cu is contained, and the Ti ₂ Cu phase is precipitated to suppress the growth of crystal grains by the pinning effect, and the average crystal grain size is 12 μm or less. Patent Document 4 discloses a titanium alloy containing Cu and reducing the O content.

According to the technique disclosed in Patent Documents 2 to 4, when titanium contains a large amount of alloying elements, the crystal grains become fine and easily become high strength, and the moldability is also ensured by reducing the O content or the Fe content. However, the technique disclosed in the aforementioned documents cannot maintain sufficient formability and exhibit high strength to the extent that it can correspond to the demand in recent years.

On the other hand, in contrast to the technique disclosed in the above documents, a technique of containing alloying elements and coarse graining of crystal grains is being studied.

Patent Document 5 discloses a chemical composition comprising Cu and Ni, and the crystal grain size is adjusted to 5 to 50 μm by annealing in a temperature range of 600 to 850 ° C, and is used for a cathode electrode for electrolytic copper foil production. Titanium alloy and its manufacturing method. Patent Document 6 discloses a titanium plate for producing an electrolytic copper foil having a chemical composition containing Cu, Cr, a small amount of Fe, and O, and a method for producing the same. Patent Document 6 describes an example of annealing at 630 to 870 °C. In addition, in the technique described in Patent Document 6, the Fe content is controlled to be low. When a titanium plate is produced by using waste as a raw material by recycling, the Fe content is increased by Fe in the scrap, and it is difficult to manufacture a titanium plate having a low Fe content. Therefore, in order to manufacture the titanium plate described in Patent Document 6 by recycling, it is necessary to use a waste such as a scrap having a low Fe content.

Patent Documents 7 and 8 disclose that high temperature of titanium containing Si and Al is obtained under conditions in which the rolling reduction ratio of the cold rolling is as small as 20% or less and the annealing temperature is 825 ° C or higher and the β transformation point or lower. This is a technique whereby the average crystal grain size is 15 μm or more.

Further, Patent Document 9 discloses that Cu: 0.5 to 1.8%, Si: 0.1 to 0.6%, and oxygen: 0.1% or less, and the balance is composed of Ti and unavoidable impurities, and is excellent in oxidation resistance and formability. The exhaust system parts are made of titanium alloy.

Patent Document 10 describes a heat-resistant titanium alloy sheet which is composed of 0.3 to 1.8% of Cu, 0.18% or less of oxygen, 0.30% or less of Fe, and the remaining part of Ti and less than 0.3% of an impurity element, and is excellent in cold workability. . Further, Patent Document 11 discloses a titanium alloy sheet having high strength and excellent moldability. In the titanium alloy sheet, the maximum crystal grain size of the β phase is 15 μm or less, the α phase area ratio is 80 to 97%, and the average of the α phase. Crystal grain size: 20 μm or less, and the standard deviation of the crystal grain size of the α phase ÷ α phase average crystal grain size × 100 is 30% or less. Further, Patent Document 12 describes a titanium thin plate having a mass ratio of Cu: 0.1 to 1.0%, Ni: 0.01 to 0.20%, Fe: 0.01 to 0.10%, and O: 0.01 to 0.10%, Cr. :0~0.20%, the remainder: Ti and unavoidable impurities, and satisfy the chemical composition of 0.04≦0.3Cu+Ni≦0.44%, and the average crystal grain size of the α phase is 15μm or more, Cu and/or metal of Ni and Ti The amount of the compound is 2.0% by volume or less.

CITATION LIST Patent Literature Patent Literature 1: Japanese Patent No. 4,087,183, Patent Document 2: Japanese Patent Laid-Open Publication No. 2010-031314, Patent Document 3: Japanese Patent Laid-Open Publication No. 2010-202952, Patent Document 4: Japanese Patent No. 4486530 Japanese Patent No. 4091211 Patent Document 6: Japanese Patent No. 4094395 Patent Document 7: Japanese Patent No. 4,147,891 Patent Document 8: Japanese Patent No. 4,147, 893 Patent Document 9: Japanese Patent Laid-Open No. 2009 Japanese Patent Laid-Open Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention The high-strength method is carried out by processing such as alloying, refinement of crystal grains, and temper rolling. On the other hand, the improvement in formability is incompatible with the high strength. Therefore, it is difficult to ensure high strength and sufficient formability. Even if the crystal grains are fine or coarse by containing an alloying element as in the technique disclosed in Patent Documents 2 to 11, it is difficult to claim that the breaking elongation required for the titanium plate in recent years is more than 42%. The excellent moldability and the strength at which the fall strength is 200 MPa or more are increased. Further, although it is unavoidable to contain a certain degree of oxygen in titanium, the fluctuation in the amount of oxygen of about 0.01% by mass causes a large fluctuation in strength and moldability, and the required strength and formability cannot be obtained. It is technically very difficult to manufacture a titanium alloy sheet by strictly managing the amount of oxygen at a trace level of about 0.01% by mass, and it is costly.

In addition, the titanium plates used for the materials of the structures such as automobiles are often welded. Therefore, in order to obtain a product having stable characteristics, it is required to suppress a decrease in strength due to coarsening of crystal grains in the HAZ portion accompanying welding.

Therefore, an object of the present invention is to provide a titanium plate which is excellent in balance between ductility and strength and which can ensure sufficient strength even after welding.

Means for Solving the Problems The gist of the present invention for solving the above problems is as follows. (1) A titanium plate whose chemical composition is Cu: 0.70 to 1.50%, Cr: 0 to 0.40%, Mn: 0 to 0.50%, Si: 0.10 to 0.30%, O: 0 to 0.10%, in terms of mass%, Fe: 0 to 0.06%, N: 0 to 0.03%, C: 0 to 0.08%, H: 0 to 0.013%, elements other than the above and Ti: each of 0 to 0.1%, and the sum of them is 0.3 % or less and the remainder: Ti; The A value defined by the following formula (1) is 1.15 to 2.5% by mass; in the metal structure, the area fraction of the α phase is 95% or more, and the area fraction of the β phase is 5% or less, the area fraction of the intermetallic compound is 1% or less; the average crystal grain size D (μm) of the α phase is 20 to 70 μm and satisfies the following formula (2); A = [Cu] + 0.98 [Cr ]+1.16[Mn]+3.4[Si] (1) Formula D[μm]≧0.8064×e ^45.588[O] (2) Equation, e is the base of the natural logarithm. (2) The titanium plate according to (1), wherein an area fraction of the α phase, the β phase, and the intermetallic compound of the metal structure is 100% in total. (3) The titanium plate according to (1) or (2), wherein the intermetallic compound is a Ti-Si-based intermetallic compound and a Ti-Cu-based intermetallic compound. (4) The titanium plate according to any one of (1) to (3), wherein the plate thickness is 0.3 to 1.5 mm, the 0.2% relief strength is 215 MPa or more, and the width of the parallel portion of the test piece is 6.25 mm, and the test piece The elongation at break of the flat tensile test piece having a distance of 25 mm between the original evaluation points and a test piece thickness of the original plate thickness was 42% or more.

Advantageous Effects of Invention According to the present invention, it is possible to provide a titanium plate which is excellent in balance between ductility and strength and which can ensure sufficient strength even after welding.

In order to carry out the invention, the inventors of the present invention have been able to ensure the formability while increasing the strength, and to ensure sufficient strength after welding, and to optimize the chemical composition, metal structure and crystal grain size of the titanium plate. Thereby, it is possible to exhibit sufficient strength and formability, and it is possible to suppress a decrease in strength due to coarsening of crystal grains in the HAZ portion accompanying welding. As a result, it is possible to increase the strength by alloying by adding a predetermined amount of Cu or Si as an alloying element, and by controlling the metal structure and the crystal grain size, the strength and formability of the HAZ portion can be achieved at a high level. The strength is reduced.

(Target Characteristics of Titanium Sheet of the Present Invention) 0.2% Degradation Strength: 215 MPa or more The base material strength of the titanium sheet of the present invention is set to 215 MPa or more in terms of 0.2% of the drop strength.

Breaking elongation: 42% or more Further, from the viewpoint of formability, the elongation at break of the titanium plate base material at the time of the tensile test is an index of 42% or more. A better elongation at break is 45% or more. The elongation at break is a flat tensile test piece having a thickness of 0.3 to 1.5 mm and a parallel portion width of the test piece of 6.25 mm, a distance between the original evaluation points of the test piece of 25 mm, and a test piece thickness of the original plate thickness. Breaking elongation.

The amount of decrease in the strength of the welded joint (development target value): The heat of fusion at the time of welding at 10 MPa or less causes the strength of the heat affected zone (Heat Affected Zone: HAZ) to decrease, and if the difference between the strength of the base material and the HAZ portion is large, Deformation in use will only focus on the HAZ. Therefore, the strength reduction amount of the base material and the welded joint by Δ0.2% is the development target value: 0.2% of the weld joint of the fusion joint - 0.2% of the strength of the base material, and the target is 10 MPa or less.

(Chemical composition of titanium plate) Hereinafter, the % of the chemical component is "% by mass".

Cu: 0.70 to 1.50% Cu is advantageous for high strength, and a large amount of solid solution is formed in the α phase in which titanium is formed and has a hcp structure. However, even in the solid solution range, if the amount added is too large, the growth of crystal grains is suppressed, and the elongation is lowered. Therefore, it must contain 0.70% or more and 1.50% or less. The upper limit is preferably 1.45%, 1.40%, 1.35% or 1.30% or less, more preferably 1.20% or less. On the other hand, when any of Cr and Mn is not contained in addition to Cu, the required strength cannot be obtained without adding 0.70% or more. In order to increase the strength, the lower limit may be 0.75%, 0.80%, 0.85% or 0.90%.

Si: 0.10 to 0.30% In order to contribute to strength improvement, 0.10% or more of Si is added. However, when the amount added is too large, the formation of a Ti-Si-based intermetallic compound is promoted, and the growth of crystal grains is suppressed, resulting in a decrease in elongation. In particular, compared with Cu, Cr, Mn, and Ni, even if the added mass is small, the effect of refining the crystal grains and improving the strength is large. Therefore, the amount of addition should be set to 0.30% or less. In addition, the amount of Si added also affects the strength after welding (to suppress the coarsening of the HAZ portion). In order to suppress the decrease in the drop strength in the HAZ portion, the amount of Si is also set to be 0.10 to 0.30%. Further, the lower limit may be set to 0.12%, 0.14% or 0.16% as needed, and the upper limit may be set to 0.28%, 0.26%, 0.24% or 0.22%.

Cr: 0 to 0.40% In order to contribute to the strength improvement, Cr may be added as needed. However, when the amount added is too large, the formation of the β phase is promoted, and the growth of the crystal grains is suppressed, and the elongation is lowered. Therefore, it is required to be 0.40% or less. When it is sufficiently strengthened by adding Cu, Mn, Si, and Ni, it may not be contained. In order to increase the strength, the lower limit of Cr may also be set to 0.05% or 0.10%. However, it is not necessary to contain Cr, and the lower limit is 0%. Further, the upper limit may be set to 0.35%, 0.30%, 0.25% or 0.20% as needed.

Mn: 0 to 0.50% In order to contribute to strength improvement, Mn may be added as needed. However, when the amount added is too large, the formation of the β phase is promoted, and the growth of the crystal grains is suppressed, and the elongation is lowered. Therefore, it is required to be 0.50% or less. When it is sufficiently strengthened by adding Cu, Cr, Si, and Ni, it may not be contained. In order to increase the strength, the lower limit of Mn may also be set to 0.05% or 0.10%. However, it is not necessary to contain Mn, and the lower limit is 0%. Further, the upper limit may be set to 0.40%, 0.30%, 0.25%, 0.15% or 0.10% as needed.

O: 0 to 0.10% Oxygen (O) has a strong binding force with Ti, and is an impurity which cannot be avoided when industrially producing metal Ti. However, if the amount of O is too large, the strength is increased and the formability is deteriorated. Therefore, it must be suppressed to 0.10% or less. O is contained as an impurity, and the lower limit is not required, and the lower limit is 0%. However, the lower limit may also be set to 0.005%, 0.010%, 0.015%, 0.020% or 0.030%. It is also possible to set the upper limit to 0.090%, 0.080%, 0.070% or 0.065%.

Fe: 0 to 0.06% Iron (Fe) is an impurity that cannot be avoided when industrially producing metal Ti. If the amount of Fe is too large, the formation of the β phase is promoted, and the growth of the crystal grains is suppressed. Therefore, the amount of iron should be set to 0.06% or less. If it is below 0.06%, the effect on the 0.2% drop strength is small and negligible. It is preferably 0.05% or less, more preferably 0.04% or less. Further, Fe is an impurity, and the lower limit thereof is 0%. However, the lower limit may be set to 0.01%, 0.015%, 0.02% or 0.03%.

N: 0 to 0.03% Nitrogen (N) also promotes high strength equivalent to oxygen and deteriorates formability. However, since the amount contained in the raw material is less than O, it can be reduced to less than O. Therefore, it is set to 0.03% or less. Further, it is preferably 0.025% or less or 0.02% or less, more preferably 0.015% or less or 0.01% or less. In addition, although there are many cases where 0.0001% or more of N is contained in industrial production, the lower limit is 0%. The lower limit can also be set to 0.0001%, 0.001% or 0.002%. It is also possible to set the upper limit to 0.025% or 0.02%.

C: 0 to 0.08% C promotes high strength like oxygen or nitrogen, but its effect is smaller than oxygen or nitrogen. And if it is less than half of oxygen, if the content is 0.08% or less, the influence on the 0.2% fall strength can be ignored. However, the smaller the content, the more excellent the moldability, so it is preferably 0.05% or less, more preferably 0.03% or less, 0.02% or less, or 0.01%. Moreover, it is not necessary to specify the lower limit of the amount of C, and the lower limit is 0%. If necessary, the lower limit can also be set to 0.001%.

H: 0 to 0.013% H is an element causing embrittlement, and the solid solution at room temperature is limited to about 10 ppm. Therefore, when H of this value or more is contained, there is a fear that hydride is formed and embrittlement is formed. In general, as long as the content is 0.013% or less, there is a problem of embrittlement, but it can be used without any problem in practical use. Moreover, its content is less than that of oxygen, so the influence on the 0.2% drop strength can be ignored. It is preferably 0.010% or less, and more preferably 0.008% or less, 0.006% or less, 0.004% or less, or 0.003% or less. Further, it is not necessary to specify the lower limit of the amount of H, and the lower limit thereof is 0%. If necessary, the lower limit can also be set to 0.0001%.

The elements other than the above and Ti are each 0 to 0.1%, and the sum of them is 0.3% or less, and the remainder: Ti.

The impurities contained in addition to Cu, Cr, Mn, Si, Fe, N, O, and H may also be contained in an amount of 0.10% or less, respectively, but the total amount of such impurities is, for example, the total amount thereof is set to 0.3. %the following. The above is for the purpose of utilizing the waste material, but it is also high in strength in order to sufficiently contain the alloying element, and the moldability is not excessively deteriorated. The elements which are likely to be mixed are Al, Mo, V, Sn, Co, Zr, Nb, Ta, W, Hf, Pd, Ru, and the like. It is an impurity element with a lower limit of 0%. The upper limit of each impurity element may also be set to 0.08%, 0.06%, 0.04% or 0.03% as needed. The lower limit of the sum is 0%. The upper limit of the sum may also be set to 0.25%, 0.20%, 0.15% or 0.10%.

(A value) The titanium plate of the present invention satisfies the above chemical composition, and the A value defined by the following formula (1) is 1.15 to 2.5% by mass. A=[Cu]+0.98[Cr]+1.16[Mn]+3.4[Si] (1)

A 100 g of Ti ingot containing Cu, Si, Mn, and Cr in the chemical composition range of the present invention was produced by vacuum arc melting, and the like was heated to 1,100 ° C, and then hot rolled and cut to remove the surface. Thereafter, cold rolling was performed in the same direction as the hot rolling, and a sheet having a thickness of 0.5 mm was formed. The sheet was heat-treated under various conditions to adjust the crystal grain size. The relationship between the A value and the 0.2% fall strength is shown in FIG. The relationship between the A value and the elongation is shown in FIG. Further, each of the plotted points in Figs. 1 and 2 is a metal structure other than the A value, and the average crystal grain size D of the α phase is within the scope of the present invention. That is, the area fraction of the α phase is 95% or more, the area fraction of the β phase is 5% or less, the area fraction of the intermetallic compound is 1% or less, and the average crystal grain size D of the α phase (μm). ) is 20 to 70 μm and satisfies the formula (2) described later.

Even if the respective contents of Cu, Si, Mn, and Cr are within the chemical composition range of the present invention, if the A value is too small, the strength is still lowered. In order to make the 0.2% fall strength not lower than 215 MPa, the lower limit of the A value is 1.15 mass%. Moreover, in order to increase the 0.2% drop strength, the lower limit of the A value may be set to 1.20% or 1.25%. On the other hand, if the A value becomes too large, the elongation is lowered and the workability is deteriorated. In order to make the elongation at break not less than 42%, the upper limit of the A value is 2.5% by mass. Moreover, in order to increase the elongation at break, the upper limit of the A value may be set to 2.40%, 2.30%, 2.20%, 2.10% or 2.00%.

(Metal Structure) The titanium plate of the present invention has an area fraction of the α phase of 95% or more, an area fraction of the β phase of 5% or less, and an area fraction of the intermetallic compound of 1% or less.

The relationship between the area fraction of the β phase and the 0.2% fall strength is shown in FIG. Further, each of the plotted points in Fig. 3 is a metal structure other than the area fraction of the β phase, the average crystal grain size D of the α phase, the chemical composition range, and the A value are all within the scope of the present invention. In order to make the 0.2% drop strength not lower than 215 MPa, the upper limit of the area fraction of the β phase is 5%. In order to increase the 0.2% drop strength, the upper limit of the area fraction of the β phase may also be set to 3%, 2%, 1%, 0.5% or 0.1%.

Further, the relationship between the area fraction of the intermetallic compound and the elongation at break is shown in FIG. Further, each of the plotted points in Fig. 4 is a metal structure other than the area fraction of the intermetallic compound, the average crystal grain size D of the α phase, the chemical composition range, and the A value are all within the scope of the present invention. In order to make the elongation at break not less than 42%, the upper limit of the area fraction of the intermetallic compound is 1.0%. In order to increase the elongation at break, the upper limit of the area fraction of the intermetallic compound may also be set to 0.8%, 0.6%, 0.4% or 0.3%. The titanium plate of the present invention has no structures other than the α phase, the β phase, and the intermetallic compound. The lower limit of the area ratio of the α phase may be set to 97%, 98%, 99%, and 99.5%, as needed.

Further, the metal phase other than the β phase and the intermetallic compound is an α phase, and the area fraction of the α phase, the β phase, and the intermetallic compound is preferably 100% in total. The intermetallic compound is a Ti-Cu-based intermetallic compound and a Ti-Si-based intermetallic compound. The Ti-Cu-based intermetallic compound is represented by Ti ₂ Cu, and the Ti-Si-based intermetallic compound is represented by Ti ₃ Si and Ti ₅ Si ₃ .

(Measuring Method of Metal Structure) The area fractions of the α phase, the β phase, and the intermetallic compound were determined by SEM observation and EPMA analysis to obtain an area ratio. In the SEM observation, a backscattered electron image (composed image) was observed, whereby the Ti-Si-based intermetallic compound was observed to be black. On the other hand, the Ti-Cu-based intermetallic compound and the β-phase are white, and therefore it is necessary to separate them. For this reason, in addition to the acceleration voltage of 15 kV for Si, Cu, and Fe, the surface analysis is performed by EPMA in 500 fields of one field (equivalent to 200 μm × 200 μm), and Cr and Mn are also used for Cr and Mn. get on. Further, the area corresponding to a total of 200 μm × 200 μm may be observed in a plurality of fields of view without being limited to one field of view, and the average of these may be calculated. Fe, Cr, and Mn are concentrated in the β phase, but not concentrated in the Ti-Cu intermetallic compound. Therefore, by comparing the backscattered electron image with the element distribution, the white portion can be separated and distinguished. Thereafter, the area ratio in the backscattered electron image is measured, thereby setting the respective area fractions. The measurement sample is mirror-finished using diamond particles on the measurement surface, and C or Au vapor deposition can be performed to ensure conductivity. In Fig. 5, a schematic diagram showing the EPMA analysis in the region of about 100 μm × about 100 μm for the Ti-Cu-Si-Mn component is shown. The rich position of each element is indicated in gray to black. Moreover, the broken line in the figure indicates the grain boundary of the tissue. Fe and Mn are concentrated at the same position and exist in grain boundaries or grains. Although there is a portion where Cu is concentrated at the same position as Fe and Mn, Cu is also present in a different portion from Fe and Mn, and this is a Ti-Cu-based intermetallic compound. Si is almost present in different places from Fe, Mn and Cu. Therefore, the area ratio of the intermetallic compound can be calculated by measuring the area ratio at which no Fe and Mn are concentrated in the concentrated position of Cu (arrow portion). Specifically, a region in which Fe is 0.2% or more is regarded as a β phase, and in a region where Fe is less than 0.2%, a region in which Cu is 5% or more is regarded as a Ti—Cu-based intermetallic compound, and Si is A region of 1% or more is regarded as a Ti-Si-based intermetallic compound. Separation was carried out as described above, and the area ratio of the obtained region was calculated.

(Crystal grain size) Average crystal grain size D (μm) of the α phase: 20 to 70 μm In Fig. 6, the average crystal grain size D (μm) of the α phase and the change amount of the 0.2% fall strength of the TIG before and after the TIG fusion are shown. .2% drop strength (= 0.2% relief strength of the base metal - 0.2% fall strength of the welded joint). Further, each of the plotted points in Fig. 6 is a range of chemical components other than the average crystal grain size of the α phase (except oxygen (O)) and A value are within the scope of the present invention. Specifically, a Ti-1.01% Cu-0.19% Si-0.03% Fe component system is used, and the amount of oxygen is changed and melted, and a sheet having a thickness of 0.5 mm is obtained by hot rolling, cold rolling, and annealing. . Further, the crystal grain size was adjusted by variously changing the heat treatment conditions. The tissue has no β phase, and the area fraction of the intermetallic compound is also less than 1%. The obtained sheet was subjected to TIG welding, and a tensile test piece of a welded joint was taken in such a manner that the welded bead was in the central portion of the parallel portion. When TIG is welded, NSSW Ti-28 (corresponding to JIS Z3331 STi0100J) manufactured by Nippon Steel & Sumitomo Metal Co., Ltd. is used. The welding conditions were current: 50 A, voltage: 15 V, and speed: 80 cm/min. The shape of the tensile test piece was a flat tensile test piece having a parallel portion width of 6.25 mm, a distance between the original evaluation points of the test piece of 25 mm, and a test piece thickness of the original plate thickness. However, the shape is corrected when the plate is warped during welding, and the strain caused by the shape correction is removed, and annealing is performed at 550 ° C for 30 minutes. It was confirmed that there was no change in particle size due to the annealing. The strain rate was carried out at 0.5%/min until the strain amount was 1%, and then proceeded to break at 30%/min.

When the average crystal grain size D of the α phase is less than 20 μm, the Δ0.2% fall strength becomes 10 MPa or more. On the other hand, when the average crystal grain size D of the α phase exceeds 70 μm, the particle diameter becomes excessively large, and there is a fear that wrinkles or steps are formed at the time of molding. Therefore, the average crystal grain size D of the α phase is made 20 to 70 μm. The lower limit of the average crystal grain size D of the α phase may be 23 μm, 25 μm or 28 μm as needed, and the upper limit thereof may be 60 μm, 55 μm, 50 μm or 45 μm.

(Relationship between the amount of oxygen and the average crystal grain size D of the α phase) Further, the tensile test was performed on the test piece taken out from the base material, and the relationship between the amount of oxygen and the average crystal grain size D of the α phase and the elongation at break were determined. The rate was investigated and presented as shown in Figure 7. In Fig. 7, ○: the elongation at break is 42% or more, ×: the elongation at break is less than 42%, and the solid line is (2). The breaking elongation is 42% or more in a range not less than the curve recited in Fig. 7, that is, the formula (2). Therefore, it is conditional on (2).

D[μm]≧0.8064×e ^45.588[O] (2) where e is the base of the natural logarithm.

(Effect of the amount of addition of Si on the amount of strength reduction of the base material and the welded portion) The titanium plate of the present invention contains Si: 0.10 to 0.30% as described above, and the amount of Si added also affects the strength of the welded joint (inhibition of the HAZ portion) Coarse). When the titanium plate is welded, a temperature distribution is formed from the molten portion to the base material portion, and the following regions are continuously formed: [1] the molten portion, and heated to a point above the β-metamorphic point or near the β-metamorphic point and needle-like texturization In the region, [2] a region in which the α phase and the β phase are mixed to cause grain growth of the α phase, [3] a region in which the β phase or the α phase is coarsened, and [4] a region in which an intermetallic compound is precipitated. The region [1] is slightly higher in strength than the base material portion due to the randomization or grain shape of the aggregate structure and the absorption of O, N, etc. during welding. In the region [2] or the region [4], the crystal growth of the α phase is suppressed by the β phase or the intermetallic compound, so that the crystal grain size of the same level as that of the base material portion is maintained without a large difference in strength from the base material. . On the other hand, in the region [3], the α phase is coarsened, so the strength is lowered by the Hall-Petch rule. Therefore, in the tensile test of the welded joint of the narrow width of the test piece having a width of about 6.25 mm, cracking occurred in the coarsely granulated region [3] even in the HAZ portion.

Figure 8 is a graph showing the difference between the amount of Si, the 0.2% drop strength of the TIG fusion joint of the region containing the coarse grained portion [3] in the HAZ portion, and the 0.2% fall strength of the base material (= mother A graph of the relationship between the 0.2% relief strength of the material and the 0.2% relief strength of the welded joint. A 100 g ingot containing Cu, Si, Cr, and Mn was produced by vacuum arc melting, and the like was heated to 1,100 ° C, and then hot rolled and cut to remove the surface. Thereafter, cold rolling was performed in the same direction as the hot rolling, and a sheet having a thickness of 0.5 mm was formed. The sheet was heat-treated under various conditions to adjust the average crystal grain size to about 20 to 30 μm. Further, each of the plotted points in Fig. 8 is a chemical component range other than the amount of Si, an A value, and an average crystal grain size D of the α phase are within the scope of the present invention. The area fraction of the intermetallic compound is less than 1%, and the area fraction of the β phase is less than 3%. As a result of performing TIG welding and tensile test in the same manner as in the case of the above-described crystal grain size, when 0.10% or more of Si is used, the decrease in strength after welding can be suppressed to 10 MPa or less. Therefore, it is necessary to contain 0.10% or more of Si. In order to suppress the decrease in strength after welding, the lower limit of the amount of Si may be set to 0.14%, 0.17% or 0.20%.

(An example of the production method) The titanium plate of the present invention can be produced by subjecting a Ti ingot satisfying the above chemical composition and the A value to hot rolling, cold rolling, and annealing conditions after the cold rolling is delayed. . Quenching and tempering may also be performed after the cold rolling delay annealing, as needed. The respective manufacturing conditions will be described in detail below.

(Hot Rolling Condition) The hot rolling is an ingot obtained by a general method using VAR (vacuum arc melting), EBR (electron beam melting) or plasma arc melting. If it is rectangular, it can also be directly subjected to hot rolling. If it is not the case, it is forged or rolled to form a rectangle. The rectangular flat embryo obtained as described above is subjected to hot rolling at a general hot rolling temperature and a rolling reduction ratio of 800 to 1000 ° C and 50% or more.

(Cold rolling condition) Before the cold rolling, the strain relief annealing and general derusting are performed. It is also possible not to perform strain relief annealing (intermediate annealing), and there is no particular limitation on temperature or time. As a rule, strain relief annealing is performed at a temperature lower than the β-deformation point, specifically, at a temperature lower than the β-deformation point by 30 ° C or more. The β-metamorphic point in the alloy system may vary depending on the alloy composition, but it is in the range of 860 to 900 ° C. Therefore, in the present invention, it is preferable to carry out the method at 800 ° C or higher. There is no limitation on the method of derusting, and it may be sand blasting, pickling or mechanical cutting. However, if the rust is not sufficiently removed, damage may occur during cold rolling. In addition, the cold rolling is conventionally performed on the hot rolled sheet at a rolling reduction ratio of 50% or more.

(annealing conditions) Annealing after cold rolling is first performed at a low temperature batch annealing, followed by continuous annealing at a high temperature. The structure of the present invention cannot be obtained by other methods such as annealing only once (high-temperature or low-temperature batch or continuous annealing), and the target characteristics cannot be achieved. Further, even in the case of the secondary annealing, the method of the present invention cannot be obtained by a method other than the continuous annealing at a high temperature after the low-temperature batch annealing, and the target characteristics cannot be achieved.

Here, the purpose of batch-type low-temperature annealing is the solid growth of Cu and the grain growth of the α phase. In the batch type annealing, since the temperature rise rate in the coil material is different, it is necessary to perform annealing for 8 hours or more to suppress unevenness in the coil material. And in order to prevent the bonding of the coils, the annealing must be below 730 °C. Further, in the low temperature region, a Ti-Cu-based intermetallic compound and a Ti-Si-based intermetallic compound are precipitated. Therefore, it is necessary to set the upper limit of the annealing temperature so that the intermetallic compounds do not grow, and the lower limit of the annealing temperature is required, so that the solidification of Cu and the grain growth of the α phase can be performed. Therefore, the annealing temperature is set to 700 to 730 °C.

(High-temperature annealing conditions) In order to reduce the intermetallic compound precipitated in the low-temperature batch annealing, it is maintained at at least a high temperature region for at least 10 seconds in the high-temperature annealing. Keep the temperature at 780~820 °C. If the holding time at this time is long, the hardened layer will be thickened, so the longest time is also set to 2 minutes. Annealing in batch mode does not allow for a short time anneal as described above, but must be a continuous anneal. Although continuous annealing at a high temperature can reduce the area fraction of the Ti-Si-based intermetallic compound, since the Ti-Si-based intermetallic compound precipitates early, the continuous annealing from a high temperature up to 550 ° C is maintained. The cooling rate is set to 5 ° C / s or more.

In the examples, 300 g of Ti ingots containing Cu, Si, Mn, and Cr of Nos. 1 to 97 described in Tables 1 to 3 were produced by vacuum arc melting, and the like was heated to 1,100 ° C, and then hot rolled. And cutting removes the surface. Thereafter, cold rolling was performed in the same direction as the hot rolling, and a sheet having a thickness of 0.5 mm was formed. The thin plates (No. 1 to No. 97) were annealed under various conditions described in Tables 4 to 6 (the first annealing was marked as "annealing 1", and the next annealing was marked as "annealing 2"). Further, for annealing, if the cooling is FC (furnace cooling), batch (vacuum) annealing is performed (labeled as "batch type" in Tables 4 to 6), and in other cases, continuous (Ar gas) annealing is performed. (marked as "continuous" in Tables 4-6). Batch annealing is an analog coil manufacturing process in which two sheets are overlapped for annealing. Only after batch annealing was performed, the presence or absence of joining of the two sheets after annealing was investigated. When two sheets were peeled off without a large deformation, the evaluation was ○, and although it was deformed, the peelable one was evaluated as Δ, and the peelable one was evaluated as ×. In the case of investigation of the presence or absence of the joint, in the case of deformation, it is a bending deformation starting from the joint portion. In addition, if batch annealing is not performed, fill in "-" in the field of "with or without batch bonding". Anneal 2 was not performed in the column where the annealing 2 was "-".

Further, for the jointed person, the TIG welding or the like was not evaluated, and only the tensile test and the measurement of the average crystal grain size were performed. In addition, the surface state of the board after the annealing 2 was confirmed, and the grade corresponding to the current actual mass production material was evaluated as ○, and the grade which could not be shipped as the product was evaluated as × (displayed as "surface state"). In addition, a ball-end protrusion test using a Teflon (registered trademark) sheet having a thickness of 50 μm as a lubricant was performed until the protrusion height reached 15 mm, and the degree of occurrence of wrinkles was observed, so that the surface roughness did not occur. The dermatizer is ○, and the surface roughening is × (displayed as "processed surface").

The obtained thin plate was subjected to TIG welding, and a tensile test piece was taken in such a manner that the welded bead was in the central portion of the parallel portion. In the case of TIG welding, NSSW Ti-28 (corresponding to JIS Z3331 STi0100J) manufactured by Nippon Steel & Sumitomo Metal Co., Ltd. was used in consideration of versatility. The welding conditions were current: 50 A, voltage: 15 V, and speed: 80 cm/min. The shape of the tensile test piece was a flat tensile test piece having a parallel portion width of 6.25 mm, a distance between the original evaluation points of the test piece of 25 mm, and a test piece thickness of the original plate thickness. However, the shape is corrected when the plate is warped at the time of welding, and the strain due to the shape correction is removed, and annealing is performed at 550 ° C for 30 minutes (the average crystal grain size is not changed). The strain rate was carried out at 0.5%/min until the strain amount was 1%, and then proceeded to break at 30%/min. In addition, the TIG welding and the tensile test after welding are tested for a part. Moreover, the 0.2% drop strength difference (shown as Δ0.2% drop strength (MPa)) before and after TIG welding was acceptable when it was 10 MPa or less. Tables 7 to 9 show the average crystal grain size D (shown as particle diameter (μm)) of the α phase obtained for each of the sheets of No. 1 to No. 97, and the area fraction of the α phase (shown as α phase). Rate (%)), area fraction of β phase (shown as β phase ratio (%)), area fraction of intermetallic compound (shown as intermetallic compound (%)), 0.2% drop strength (shown as fall strength) (MPa)), elongation at break (displayed as elongation (%)), appearance (displayed as surface state), value of 0.8064 × e ^{45.588 [O]} (right of formula (2): display as "(2) The judgment result of the formula (μm)") and (2) (displayed as "(2) Formula (μm) judgment"): when the value of D-0.8064 × e ^{45.588 [O]} is negative, it is "X", 0 The above is "○"), and the classification of the present invention and the comparative example.

The chemical composition range, the A value, the metal structure, and the average crystal grain size D of the α phase are all in the range of No. 1, 34 to 37, 60 to 62, 80, 86 to 97 (invention of the present invention) within the scope of the present invention. Item: 0.2% relief strength: 215 MPa or more, elongation at break: 42% or more, strength reduction of welded joint: 10 MPa or less.

Other (comparative examples) are as follows. The A value of No. 2 was less than 1.15 mass%, and the 0.2% fall strength was low. Further, since Si is not added, the strength of the welded joint is lowered. No. 3 is not added with Si, so the strength of the welded joint is lowered. The A value of No. 4 was less than 1.15 mass%, and the 0.2% fall strength was low. Further, the decrease in the strength of the welded joint is small because the average crystal grain size D of the α phase of the base material is large. The α-phase of the base material of No. 5 had an average crystal grain size D of more than 70 μm, and wrinkles were formed on the surface during processing. Further, since the particle diameter D is large, even if the A value is 1.15 or more, the 0.2% lodging strength is low. Further, the decrease in the strength of the welded joint is small because the average crystal grain size D of the α phase of the base material is large. The A value of No. 6 was less than 1.15 mass%, and the 0.2% fall strength was low. Further, since Si is not added, the strength of the welded joint is lowered. No. 7 is not added with Si, so the strength of the welded joint is lowered. The A value of No. 8 was less than 1.15 mass%, and the 0.2% fall strength was low. Further, since Si is not added, the strength of the welded joint is lowered. No. 9 is not added with Si, so the strength of the welded joint is lowered. The A value of No. 10 was less than 1.15 mass%, and the 0.2% fall strength was low. Further, since Si is not added, the strength of the welded joint is lowered. No. 11 is not added with Si, so the strength of the welded joint is lowered. The A value of No. 12 was less than 1.15 mass%, and the 0.2% fall strength was low. Further, since Si is not added, the strength of the welded joint is lowered. No. 13 is not added with Si, so the strength of the welded joint is lowered. No. 14 and 15 were too low in annealing, and the average crystal grain size D of the α phase was less than 20 μm, and the elongation at break was small. No. 16, 17 caused the joining of two sheets due to annealing and could not be peeled off. Therefore, the tensile test was not carried out. No. 18 and 19 were too low in annealing, and the average crystal grain size D of the α phase was less than 20 μm, and the elongation at break was small. Since No. 20 and 21 are annealed for a long time in a high temperature region, the elongation at break becomes small. The average crystal grain size D of the α phase of No. 22 to 29 does not satisfy the formula (2), and the elongation at break becomes small, and the strength of the welded joint is also lowered. Further, in Nos. 22 to 25, the annealing averaged too low, and the average crystal grain size D of the α phase was less than 20 μm, and the area fraction of the intermetallic compound also became high. The average crystal grain size D of the α phase of No. 30 to 33 is less than 20 μm, and the elongation at break becomes small. Further, the strength of the welded joint is lowered. Since the annealing of No. 38 and 39 is too low temperature and furnace cooling, the average crystal grain size D of the α phase is less than 20 μm, and the area fraction of the intermetallic compound also becomes high. The annealing of No. 40 and 41 was at a high temperature, so that two sheets were joined and could not be peeled off. Therefore, the tensile test was not carried out. Since the annealing of Nos. 42 and 43 is too low temperature and furnace cooling, the average crystal grain size D of the α phase is less than 20 μm, and the area fraction of the intermetallic compound also becomes high. The average crystal grain size D of the α phase of No. 44 and 45 did not satisfy the formula (2), and the elongation at break became small. Since the annealing of No. 46 to 49 is too low and the furnace is cooled, the average crystal grain size D of the α phase is less than 20 μm, and the area fraction of the intermetallic compound is also high. The α-phase of the base material of No. 50 and 51 had an average crystal grain size D of more than 70 μm, and wrinkles were formed on the surface during processing, and the 0.2% lodging strength was low. Further, since Si is not added, the strength of the welded joint is lowered. The average crystal grain size D of the α phase of Nos. 52 and 53 is less than 20 μm, and the strength of the welded joint is lowered due to the absence of Si. No. 54 to 56 are not added with Si, so the strength of the welded joint is lowered. The average crystal grain size D of the α phase of No. 57 to 59 is less than 20 μm, and the strength of the welded joint is lowered due to the absence of Si. The average crystal grain size D of the α phase of No. 63 does not satisfy the formula (2), and the elongation at break becomes small. The average crystal grain size D of the α phase of No. 64 is less than 20 μm, and the elongation at break becomes small. The average crystal grain size D of the α phase of No. 65 does not satisfy the formula (2), and the elongation at break becomes small. The average crystal grain size D of the α phase of No. 66 and 67 was less than 20 μm, and the elongation at break was small. The annealing of No. 68 was at a high temperature, so that two sheets were joined and could not be peeled off. Therefore, the tensile test was not carried out. The A value of No. 69 is less than 1.15 mass%, and the 0.2% fall strength is low. No. 70 and 71 were not added with Si, so the strength of the welded joint was lowered. The average crystal grain size D of the α phase of No. 72 to 75 is less than 20 μm, and the strength of the welded joint is lowered. The area fraction of the intermetallic compound of No. 76 to 79 exceeds 1%, and the elongation at break becomes small. The average crystal grain size D of the α phase of No. 81 is less than 20 μm, and the elongation at break becomes small. The batch annealing of No. 82 and 83 has a slow cooling rate, so the area fraction of the intermetallic compound exceeds 1%, and the elongation at break becomes small. Also, the appearance is poor. No. 84 burned in batch annealing and had a poor appearance. No. 85 is a high temperature due to continuous annealing, so the area fraction of the β phase exceeds 5%, and the elongation at break becomes small.

[Table 1] [Table 2] [table 3] [Table 4] [table 5] [Table 6] [Table 7] [Table 8] [Table 9]

Industrial Applicability The titanium plate of the present invention can be suitably applied to, for example, a two-wheel exhaust system such as a heat exchanger, a fusion pipe, a muffler, and the like.

Figure 1 is a graph showing the relationship between the A value and the 0.2% fall strength. Figure 2 is a graph showing the relationship between the A value and the elongation at break. Fig. 3 is a graph showing the relationship between the area fraction of the β phase and the 0.2% fall strength. 4 is a graph showing the relationship between the area fraction of an intermetallic compound and the elongation. Fig. 5 is a schematic view showing the EPMA analysis of the Ti-Cu-Si-Mn component in a region of about 100 μm × about 100 μm. Fig. 6 is a graph showing the relationship between the average crystal grain size D (μm) of the α phase and the amount of change in the 0.2% drop strength of the TIG fusion joint and the base material. Fig. 7 is a graph showing the relationship between the amount of oxygen and the average crystal grain size D of the α phase and the elongation at break of the base material. Fig. 8 is a graph showing the relationship between the amount of Si and the amount of decrease in the drop strength of the Δ0.2% before and after the TIG welding in the region [3] after coarsening in the HAZ portion.

Claims (8)

A titanium plate whose chemical composition is Cu: 0.70 to 1.50%, Cr: 0 to 0.40%, Mn: 0 to 0.50%, Si: 0.10 to 0.30%, O: 0 to 0.10%, Fe: 0 in mass% ~0.06%, N: 0~0.03%, C: 0~0.08%, H: 0~0.013%, elements other than the above and Ti: each is 0~0.1%, and the sum of them is less than 0.3%, And the remainder: Ti; the A value defined by the following formula (1) is 1.15 to 2.5% by mass; in the metal structure, the area fraction of the α phase is 95% or more, and the area fraction of the β phase is 5% or less. The area fraction of the intermetallic compound is 1% or less; the average crystal grain size D (μm) of the α phase is 20 to 70 μm and satisfies the following formula (2); A = [Cu] + 0.98 [Cr] + 1.16 [ Mn]+3.4[Si] (1) Formula D [μm] ≧ 0.8064 × e ^{45.588 [O]} (2) Formula, where e is the base of the natural logarithm. The titanium plate according to claim 1, wherein the area fraction of the α phase, the β phase, and the intermetallic compound of the metal structure is 100% in total. The titanium plate according to claim 1, wherein the intermetallic compound is a Ti-Si-based intermetallic compound and a Ti-Cu-based intermetallic compound. The titanium plate according to claim 2, wherein the intermetallic compound is a Ti-Si-based intermetallic compound and a Ti-Cu-based intermetallic compound. The titanium plate of claim 1 has a plate thickness of 0.3 to 1.5 mm, a 0.2% relief strength of 215 MPa or more, and a parallel portion width of the test piece of 6.25 mm, a distance between the original evaluation points of the test piece of 25 mm, and a test piece thickness. The elongation at break measured for the flat tensile test piece of the original thickness was 42% or more. The titanium plate of claim 2 has a plate thickness of 0.3 to 1.5 mm, a 0.2% relief strength of 215 MPa or more, and a parallel portion width of the test piece of 6.25 mm, a distance between the original evaluation points of the test piece of 25 mm, and a test piece thickness. The elongation at break measured for the flat tensile test piece of the original thickness was 42% or more. The titanium plate of claim 3 has a plate thickness of 0.3 to 1.5 mm, a 0.2% relief strength of 215 MPa or more, and a parallel portion width of the test piece of 6.25 mm, a distance between the original evaluation points of the test piece of 25 mm, and a test piece thickness. The elongation at break measured for the flat tensile test piece of the original thickness was 42% or more. The titanium plate of claim 4 has a plate thickness of 0.3 to 1.5 mm, a 0.2% drop strength of 215 MPa or more, and a test piece. The flat elongation test piece having a width of 6.25 mm in parallel and a distance between the original evaluation points of the test piece of 25 mm and a test piece thickness of the original plate thickness was measured to have a breaking elongation of 42% or more.