JP2018028131A - Titanium plate having excellent impact resistance and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium plate having excellent impact resistance to a flying body that collides with it at high speed, and a method of producing the same.SOLUTION: The present invention provides a titanium plate having excellent impact resistance, characterized in that: the total content of O, N, C is 0.140-0.190 mass%, Fe is 0.020-0.080 mass%, the balance consists of Ti and impurities, the crystal grain size of an α phase is 150 μm or more, the crystal grain size of the α phase is 10% or less of the plate thickness, and the Vickers hardness (HV) is 130-190.SELECTED DRAWING: None

Description

  The present invention relates to a titanium plate excellent in impact resistance and a method for producing the same.

  Materials that are used for protecting important parts and human bodies, such as automobile doors, movable protective walls, helmets, and helmets, are required to be lighter in order to improve mobility and motion performance. For example, a titanium plate is suitably used as a material for such applications because it is relatively light and has excellent impact resistance. By increasing the energy absorption capacity, that is, the impact resistance against an external impact, the thickness of the titanium plate to be used can be reduced, and the weight can be further reduced. In addition, the impact resistance in this specification refers to a characteristic that prevents a flying object from penetrating when a high-speed flying object collides with a titanium plate. The high-speed flying object collision can be exemplified by, for example, a case where a lump of metal or the like collides with a titanium plate at a speed higher than the speed of sound.

  Titanium plates with excellent impact resistance are required to have a hardness that does not allow the impacting projectile to penetrate. Also, the titanium plate must have an appropriate deformability to absorb impact energy from the projectile during impact. It is done. Since high hardness and high deformability are mutually contradictory characteristics, an invention for achieving both of these characteristics has been conventionally made.

In Patent Document 1, the total of O, N, and C is 0.04 to 0.27 mass%, Fe is 0.1 mass% or less, the balance is made of Ti and inevitable impurities, and by processing Titanium excellent in impact resistance characteristics in which the Vickers hardness of the cross section satisfies a predetermined inequality by being cured is described.
Patent Document 2 discloses excellent impact resistance characteristics in which the Vickers hardness is 125 to 220 and the index α is 0.4 to 1.0 in the hexagonal (0002) plane positive diagram on the plate surface. Titanium plates are described. Here, the index α is the fourth strength contour line from the bottom created by dividing the strength into 15 equal parts in the hexagonal (0002) plane positive electrode diagram measured from the plate direction, and is the final rolling direction axis (RD). A value obtained by dividing the smaller one of the distance (A) between the two intersections with the axis) and the distance (B) between the two intersections with the perpendicular axis (TD axis) by the larger one (A / B or B / A).
Further, in Patent Document 3, in mass%, Si: 0.2% or more and less than 0.5%, Fe: 0.10% or more and less than 0.40%, O: 0.01% or more and less than 0.10% The balance is made of titanium and inevitable impurities, and the distribution of the (0002) plane orientation of the α phase is shown in a section from the rolling direction to the plate vertical direction, the maximum value of the distribution is from the plate vertical direction to the rolling direction Describes a heat-resistant titanium alloy material for cold rolling that is excellent in cold-rolling property and cold handling property that is inclined in a range of 10 ° or more and less than 20 °.

Titanium described in Patent Document 1 has a Vickers hardness of 150 Hv or higher and has a high hardness, but no consideration has been given to deformability, which is another factor of impact resistance.
Although titanium described in Patent Document 2 has a Vickers hardness of 120 Hv or higher and has a high hardness, as in Patent Document 1, the deformability, which is another factor of impact resistance, Nothing has been considered.
The titanium alloy described in Patent Document 3 has a distribution of the (0002) plane orientation of the α phase, mainly for the problem that cracks tend to break in the plate width direction during cold rolling and easily break the plate. It is a titanium alloy that solves the problem by inclining in a predetermined direction and aims at characteristics different from impact resistance against high-speed flying objects. Therefore, in Patent Document 3, no consideration is given to increasing the hardness of the titanium alloy, and no consideration is given to imparting an appropriate deformability. Further, the titanium alloy of Patent Document 3 contains Si, and silicide may be formed. Presence of inclusions such as silicide becomes a factor that lowers the deformability against an impact caused by a high-speed flying object, and impairs the impact resistance against the high-speed flying object.

JP 2001-262257 A JP 2003-147462 A JP 2013-177651 A

  This invention is made | formed in view of the said situation, and makes it a subject to provide the titanium plate excellent in the impact resistance with respect to the flying body which collides especially at high speed, and its manufacturing method.

  The inventors of the present invention have made extensive studies on a titanium plate excellent in impact resistance against a high-speed impact on the titanium plate surface and a manufacturing method thereof. As a result, the Vickers hardness corresponding to the deformation resistance of the titanium plate surface against high-speed impact, and the crystal grain size and chemical composition that are deformed while following high-speed impact and do not cause cracking are suitable. It has been found that high impact resistance not found in the prior art can be obtained by controlling the range. Further, it has been found that even higher impact resistance can be obtained by controlling the crystal orientation distribution (texture) of the titanium α phase. The gist of the present invention is as follows.

[1] The total amount of O, N, and C is 0.140 to 0.260% by mass, Fe is 0.020 to 0.080% by mass, and the balance is made of Ti and impurities.
The average crystal grain size of the α phase is 150 μm or more, and the average crystal grain size of the α phase is 10% or less of the plate thickness,
A titanium plate excellent in impact resistance characterized by having a Vickers hardness (HV) of 130 to 190.
[2] The peak intensity from the (0001) plane viewed from the plate surface direction (ND) in the crystal orientation distribution measured by the electron beam backscatter diffraction method (EBSD method) is 5.00 or less. The titanium plate excellent in impact resistance according to [1].
[3] The titanium plate having excellent impact resistance according to [1] or [2], wherein the plate thickness is 2.0 to 6.0 mm.
[4] The total amount of O, N, and C is 0.140 to 0.260 mass%, Fe is 0.020 to 0.080 mass%, and the balance is heat with respect to titanium composed of Ti and impurities. Rolling between,
Next, heat treatment is performed under the conditions of holding at 650 ° C. to 850 ° C. for 24 hours or more, holding at 700 ° C. to 850 ° C. for 8 hours or more, or holding at 740 ° C. to 850 ° C. for 4 hours or more. The method for producing a titanium plate according to [1] or [3].
[5] The total amount of O, N, and C is 0.140 to 0.260% by mass, Fe is 0.020 to 0.080% by mass, and the balance is heat with respect to titanium composed of Ti and impurities. Rolling between,
Next, after heating to a temperature exceeding the β transformation point and cooling at a cooling rate of 0.5 ° C./second or more, holding at 650 ° C. to 850 ° C. for 24 hours or more, holding at 700 ° C. to 850 ° C. for 8 hours or more, Alternatively, the method for producing a titanium plate according to [2] or [3], wherein the heat treatment is performed under any of the conditions of holding at 740 ° C. to 850 ° C. for 4 hours or more.
[6] The method for producing a titanium plate according to [4] or [5], wherein cold rolling is performed between the hot rolling and the heat treatment.

  ADVANTAGE OF THE INVENTION According to this invention, the titanium plate excellent in impact resistance and its manufacturing method can be provided.

It is the photograph which shows the example of the microstructure of the L cross section of a titanium plate, (a) is a photograph of the conventional material whose average crystal grain diameter of (alpha) phase is about 20-60 micrometers, (b) and (c) 3 is a photograph of the material of the present invention having an α-phase average crystal grain size of 150 μm or more. It is a figure which shows the pole figure of the alpha phase hcp (0001) surface of the titanium plate obtained by the electron beam backscattering diffraction method (EBSD method).

  In order to improve the impact resistance of the titanium plate against the flying object that collides at high speed, the present inventors diligently examined, the Vickers hardness corresponding to the deformation resistance of the titanium plate surface, the average crystal grain size and the chemical composition It has been found that impact resistance can be improved by controlling each of these in a suitable range. It was also found that impact resistance can be further improved by controlling the crystal orientation distribution (texture) of the titanium α phase.

  If the Vickers hardness of the titanium plate is too low, the deformation resistance against impact becomes small, the deformation site is localized, and the flying object penetrates the titanium plate. Vickers hardness can be increased by adding substitutional elements Al, V, Fe, and Mo to titanium. However, since twin deformation that contributes to deformation is remarkably suppressed, a high-speed flying object It cannot follow the deformation at the time of collision, hardly causes plastic deformation, and the titanium plate is damaged or cracked. On the other hand, Vickers hardness can be increased by interstitial elements O, C, and N, but twin deformation is suppressed similarly to the above substitutional elements.

  On the other hand, by setting the average crystal grain size of the α phase to 150 μm or more and the average crystal grain size to 10% or less of the plate thickness, the addition of interstitial elements O, C, and N results in a certain range of Vickers hardness. Even if it is increased to a high level, it does not suppress twin deformation against high-speed impacts, and the deformation localization due to coarsening of the crystal grain size (such as wrinkles) does not affect the impact resistance. I found out that I can do it.

  Furthermore, the α phase (hcp) of the titanium plate manufactured through hot rolling, cold rolling, and annealing always forms a developed texture due to the deformation direction restriction resulting from the hcp crystal structure. Textures are classified according to the accumulation direction of the c-axis of hcp. Specifically, it is formed by split-TD-Texture, which is represented by an industrial pure titanium plate, in which the c-axis is inclined in a direction inclined by about 35 ° in the rolling width direction, and cross rolling, and the c-axis is in the plate surface direction. Examples include B-Texture accumulated, T-Texture accumulated in the rolling width direction formed by the α phase transformed from the rolled β phase, and the like. In Patent Document 2, B-Texture having no anisotropy in the plate surface is preferable in order to prevent deformation from being localized with respect to the impact on the titanium plate surface. Found that the random one with no developed texture is less likely to localize deformation, and is particularly advantageous in impact resistance against high-speed flying objects. This is because high-velocity impacts have a strong shearing force acting inside the plate thickness, and also the temperature of the titanium plate rises. If a texture is formed in a certain direction, deformation twins are less likely to occur in a specific direction. For this reason, it is considered that the deformation cannot be followed and the deformation is localized.

Hereinafter, the titanium plate excellent in impact resistance of this embodiment will be described.
In the excellent titanium plate of this embodiment, the total amount of O, N, and C is 0.140 to 0.260% by mass, Fe is 0.020 to 0.080% by mass, and the balance is Ti and impurities. The average crystal grain size of the α phase is 150 μm or more, the average crystal grain size of the α phase is 10% or less of the plate thickness, and the Vickers hardness (HV) is 130 to 190. .
Further, the peak intensity from the (0001) plane viewed from the plate surface direction (ND) in the crystal orientation distribution measured by the electron beam backscatter diffraction method (EBSD method) may be 5.00 or less.

[Chemical composition]
When adjusting the Vickers hardness (HV) to the range of 130 to 190, the total amount of O (oxygen), N (nitrogen), and C (carbon) contained in the titanium plate is less than 0.140% by mass. When the crystal grain size is coarsened to 150 μm or more, sufficient hardness cannot be obtained. On the other hand, if the total amount of O, N, and C exceeds 0.260% by mass, even if the average crystal grain size is coarsened, the ductility and toughness are reduced, and cracking is likely to occur. Therefore, the total amount of O, N, and C is preferably in the range of 0.140 to 0.260% by mass, more preferably in the range of 0.140 to 0.0240%, and in the range of 0.140 to 0.0190%. Further preferred.
Moreover, in order not to suppress the coarsening of the average crystal grain size, it is preferable to contain 0.020 to 0.080 mass% of Fe. Furthermore, you may contain 0.020-0.080 mass% of Fe, Cr, Ni in total.
The balance other than the above elements is Ti and impurities.

  In addition, Vickers hardness can be increased by adding substitutional elements Al, V, Fe, and Mo to the titanium plate. However, since twin deformation contributing to deformation is remarkably suppressed, It cannot follow the deformation and breaks or cracks with little plastic deformation. On the other hand, the coarsening of the average crystal grain size is not suppressed by adding a predetermined amount of Fe as described above. Therefore, it is better not to add substitutional elements (Al, V, Mo) other than Fe to the titanium plate of this embodiment.

  Further, unless the impact resistance is impaired, one or more platinum group metal elements such as Pd and Ru may be included in the range of 0.25% by mass or less in order to improve the corrosion resistance. In order to exert the effect of corrosion resistance, 0.01% by mass or more is preferably added. When the platinum group element is 0.25% by mass or less, the impact resistance is not lowered.

[Vickers hardness and average grain size]
The Vickers hardness (HV) is preferably 130 to 190. If the Vickers hardness (HV) is too low, less than 130, the deformation resistance against impact will be small, the deformation part will be localized when a high-speed flying object collides, and the flying object will be titanium without sufficient energy absorption. It penetrates the board. Also, if the Vickers hardness (HV) exceeds 190, the ductility of the titanium plate is reduced, and when receiving an impact, the back side opposite to the impacted surface is likely to crack, and the crack originates. The projectile that collided may penetrate. Therefore, the Vickers hardness (HV) is preferably in the range of 130 to 190.

As described above, the Vickers hardness can be increased by adding interstitial elements O (oxygen), C (carbon), and N (nitrogen). In the same way, twin deformation is suppressed. Therefore, in the titanium plate of this embodiment, the average crystal grain size of the α phase is set to 150 μm or more, and further, the average crystal grain size is set to 10% or less of the plate thickness, so that the interstitial elements O, C, N Can be added to increase the Vickers hardness (HV) to 130 to 190, and to prevent twin deformation against high-speed impact, and further, the deformation due to the coarsening of the average crystal grain size. It is possible to limit the presence (such as wrinkles) to the extent that impact resistance is not affected.
If the average grain size is less than 150 μm, twin deformation is significantly suppressed when the Vickers hardness (HV) is increased to 130-190. Further, if the average crystal grain size exceeds 10% of the plate thickness, a large wrinkle is generated at the time of deformation with respect to an impact, and the deformation may be localized starting from the wrinkle.

  Further, if crystal grains having a crystal grain size exceeding 900 μm are present in the crystal structure, impact resistance may be lowered. Therefore, it is desirable that no crystal grains having a crystal grain size exceeding 900 μm exist in the crystal structure.

  In FIG. 1, the example of the microstructure of the L cross section of a titanium plate is shown. FIG. 1A shows a conventional material having an α-phase average crystal grain size of about 20 to 60 μm. In contrast to this conventional material, the titanium plate of the present embodiment has large average crystal grains of 150 μm or more, as shown in FIG. 1 (b) or 1 (c). The average crystal grain size of the α phase shown in FIG. 1 (b) is 198 μm, and the average grain size of the α phase shown in FIG. 1 (c) is 321 μm.

  The titanium plate of the present embodiment can exhibit excellent impact resistance by making the chemical composition, Vickers hardness, and average crystal grain size of the α phase within a predetermined range, but further, as described below, the texture By controlling, impact resistance can be further increased.

[Crystal orientation distribution of α phase (hcp)]
For impacts caused by collisions of high-speed flying objects, deformation is less likely to be localized in the random direction where the texture is not developed. As the index, the peak intensity from the (0001) plane viewed from the plate surface direction (ND) in the crystal orientation distribution measured by the electron beam backscatter diffraction method (EBSD method) is used. In this embodiment, by setting the peak intensity to 5.00 or less, the localization of deformation is suppressed, and the impact resistance can be improved. The peak intensity is more preferably 3.00 or less which is a further random value. Split-TD-Texture accumulated in a direction inclined about 35 ° in the rolling width direction represented by industrial pure titanium plate, B-Texture accumulated in the plate surface direction formed by cross rolling, and c-axis are rolled. In T-Texture and the like accumulated in the rolling width direction formed by the α phase transformed from the β phase, the peak strength is as high as 7 to 10 or more, so that the impact resistance cannot be further improved.

  FIG. 2 shows a pole figure obtained by an electron beam backscatter diffraction method (EBSD method) of a titanium plate and its peak intensity. The pole figure shown in FIG. 2 is a pole figure of the α phase hcp (0001) plane viewed from the plate direction (ND) in the crystal orientation distribution measured by the electron beam backscatter diffraction method (EBSD method). 2 (a) and 2 (b) are conventional examples in which normal annealing is performed at a temperature below the β transformation point after rolling such as hot rolling, and the peak intensity of the (0001) plane is 5.00. Over 7.00. On the other hand, FIG. 2 (c) to FIG. 2 (e) are examples of the present invention in which the peak intensity on the (0001) plane is 5.00 or less, which is a pole figure as compared with FIG. 2 (a) and FIG. 2 (b). From the figure, it can be seen that a specific direction with a high degree of integration is not observed, and the crystal orientation of the α phase is random. In addition, the titanium plate shown in FIGS. 2C to 2E is a titanium plate that is cooled at a cooling rate equal to or higher than air cooling from a temperature exceeding the β transformation point and held at 600 to 850 ° C. for 1 hour or longer. .

[Thickness]
Since the titanium plate of this embodiment absorbs impact energy by deformation when an impact is received on the plate surface, a plate thickness that can be easily deformed is preferably 2.0 to 6.0 mm.

[Production method]
Next, the manufacturing method of the titanium plate of this embodiment is demonstrated.
Titanium composed of the above chemical components is hot-rolled, cold-rolled as necessary, and then annealed at a temperature lower than the β transformation point, whereby the Vickers hardness (HV) is 130 to 190, α A titanium plate having an average crystal grain size of 150 μm or more can be produced.

The annealing is performed until the average crystal grain size of the α phase is coarsened to 150 μm or more. The annealing condition is not particularly limited as long as the average crystal grain size of the α phase is coarsened to 150 μm or more. For example, it is maintained at 650 ° C. to 850 ° C. for 24 hours or more, and 700 ° C. to 850 ° C. for 8 hours or more. It may be performed under any of the conditions of holding or holding at 740 ° C. to 850 ° C. for 4 hours or more.
If the annealing temperature under any of the above conditions is low, the average crystal grain size of the α phase becomes less than 150 μm, which is not preferable. When the annealing temperature exceeds 850 ° C., the average crystal grain size of the α phase becomes excessively coarse and exceeds 1/10 of the plate thickness, or the β phase precipitates during the annealing and partially grows grains. Is suppressed, and grain growth may not occur up to a predetermined crystal grain size. Moreover, if the annealing time under any of the above conditions is insufficient, the average crystal grain size of the α phase becomes less than 150 μm, which is not preferable. Further, if the annealing time is too long, the average crystal grain size of the α phase may be more than 1/10 of the plate thickness. Therefore, it is preferable to adjust the time so that the average crystal grain size is 1/10 or less of the plate thickness.

  Further, the titanium composed of the above chemical components is hot-rolled, cold-rolled as necessary, and then heated to a temperature exceeding the β transformation point (β-region heat treatment) and then cooled at a predetermined cooling rate, Thereafter, by annealing at a temperature lower than the β transformation point, the Vickers hardness (HV) is 130 to 190, the average crystal grain size of the α phase is 150 μm or more, and the electron backscatter diffraction method (EBSD method). A titanium plate having a peak intensity from the (0001) plane viewed from the plate surface direction (ND) in the crystal orientation distribution measured at 5.00 can be produced.

  In order to reduce the peak intensity to 5.00 or less, the metal structure of the titanium plate is once transformed into a β phase single phase by heating to a temperature exceeding the β transformation point (β region heat treatment), and a pre-process such as rolling. The texture of the α phase that was generated in the above is disappeared. Thereafter, recrystallization nuclei are introduced into the structure by cooling at a predetermined cooling rate. Then, the recrystallized nuclei introduced by annealing are grown as crystal grains to grow to a predetermined crystal grain size.

  By heating the titanium plate to a temperature exceeding the β transformation point, the peak intensity from the (0001) plane can be sufficiently reduced without leaving the α phase having the previous texture. If the cooling rate is slow, the number of recrystallized nuclei introduced is reduced, and extremely large crystal grains are mixed. The cooling rate when cooling by heating to a temperature exceeding the β transformation point is preferably 0.5 ° C./s or more for air cooling, and is preferably in the range of about 50 to 100 ° C./s for water cooling. When the cooling rate is less than 0.5 ° C./s, the α-phase crystal grows abnormally, and crystal grains exceeding the crystal grain size of 900 μm are formed, which is not preferable. Moreover, since the average crystal grain size of the α phase may exceed 10% of the plate thickness, it is not preferable. Since so-called furnace cooling that cools the inside of the heating furnace may have a cooling rate of less than 0.5 ° C./s, it is preferably taken out of the heating furnace and air-cooled or water-cooled.

  The annealing after cooling is performed until the average crystal grain size of the α phase is coarsened to 150 μm or more. The annealing condition is not particularly limited as long as the average crystal grain size of the α phase is coarsened to 150 μm or more. For example, it is maintained at 650 ° C. to 850 ° C. for 24 hours or more, and 700 ° C. to 850 ° C. for 8 hours or more. It may be performed under any of the conditions of holding or holding at 740 ° C. to 850 ° C. for 4 hours or more. If the annealing temperature under any of the above conditions is low, the average crystal grain size of the α phase is less than 150 μm, or the peak intensity from the (0001) plane becomes high, which is not preferable. When the annealing temperature exceeds 850 ° C., the average crystal grain size of the α phase becomes excessively coarse and exceeds 1/10 of the plate thickness, or the β phase precipitates during the annealing and partially grows grains. Is suppressed, and grain growth may not occur up to a predetermined crystal grain size. Moreover, if the annealing time under any of the above conditions is insufficient, the average crystal grain size of the α phase becomes less than 150 μm, which is not preferable. If the annealing time is too long, the average crystal grain size of the α phase may be more than 1/10 of the plate thickness. Therefore, the time may be adjusted so that the average crystal grain size is 1/10 or less of the plate thickness.

  Further, the above heat treatment is suitable in a vacuum atmosphere or an inert gas atmosphere (argon or helium) in order to prevent oxidation of the titanium plate.

  Note that the peak intensity from the (0001) plane can be obtained simply by heating the titanium slab to a temperature above the β transformation point, hot rolling at a temperature above the β transformation point, and then cooling and annealing under conventional conditions. Can not be reduced. When hot rolling is performed at a temperature exceeding the β transformation point, the β phase of titanium composed of bcc is hot rolled. The hot-rolled β phase forms a stronger rolling texture as the rolling reduction increases, but when cooled at a cooling rate equal to or higher than air cooling from the β-phase rolling texture to a temperature below the β transformation point, from hcp It transforms into the α phase. After that, even when crystal grains are grown under the conventional annealing conditions, a texture called so-called T-Texture is formed. In this T-Texture, the c axis of hcp is oriented in the rolling width direction (TD), and the peak intensity of the (0001) plane in the plate direction (ND) measured and analyzed by EBSD is 7.00 or more. It will exceed .00. That is, the α-phase crystal orientation cannot be randomized, and more excellent impact resistance cannot be obtained.

  Titanium ingots having chemical compositions shown in Table 1 were produced by a vacuum arc melting (VAR) method and hot forged. Then, the titanium plate was produced on the manufacturing conditions P1-10 shown below. The plate thickness after hot rolling was 6 mm. Tables 2 and 3 show the details of the manufacturing conditions. Moreover, about some titanium plates, it cold-rolled between hot rolling and annealing, and adjusted to plate thickness 2.0-6.0 mm. In this way, titanium plates of A1 to A46 and B1 to B53 were manufactured.

[Production conditions]
P1: Hot rolling (heating temperature: less than β transformation point) ⇒ cold rolling ⇒ annealing (annealing temperature: less than β transformation point)
P2: Hot rolling (heating temperature: less than β transformation point) ⇒ Annealing (annealing temperature: less than β transformation point)
P3: Hot rolling (heating temperature: over β transformation point) ⇒ annealing (annealing temperature: less than β transformation point)
P4: Hot rolling (heating temperature: less than β transformation point) ⇒ β-region heat treatment (heating to a temperature above the β transformation point, then water cooling (cooling rate of 50 ° C / s or more)) ⇒ Annealing (annealing temperature: less than the β transformation point) )
P5: Hot rolling (heating temperature: less than β transformation point) ⇒ β-region heat treatment (heating to a temperature above the β transformation point, then air cooling (cooling rate 0.5 ° C / s or more)) ⇒ annealing (annealing temperature: is β Less than the transformation point)
P6: Hot rolling (heating temperature: less than β transformation point) ⇒ β-region heat treatment (heating to a temperature above the β transformation point, furnace cooling (cooling rate less than 0.5 ° C / s)) ⇒ annealing (annealing temperature: <β transformation point)
P7: Hot rolling (heating temperature: less than β transformation point) ⇒ cold rolling ⇒ β-region heat treatment (heating to a temperature above the β transformation point, then water cooling (cooling rate of 50 ° C / s or more)) ⇒ annealing (annealing temperature: <β transformation point)
P8: Hot rolling (heating temperature: less than β transformation point) ⇒ cold rolling ⇒ β zone heat treatment 2 (heated to a temperature above the β transformation point, then air cooling (cooling rate 0.5 ° C / s or more)) ⇒ annealing ( Annealing temperature: less than β transformation point)
P9: Hot rolling (heating temperature: more than β transformation point) ⇒ β-region heat treatment (heating to a temperature exceeding the β transformation point, then water cooling (cooling rate 50 ° C / s or more)) ⇒ annealing (annealing temperature: less than β transformation point) )
P10: Hot rolling (heating temperature: more than β transformation point) ⇒ β-region heat treatment (heating to a temperature exceeding the β transformation point, then air cooling (cooling rate 0.5 ° C / s or more)) ⇒ annealing (annealing temperature: β transformation) Less than points)

Among the manufacturing conditions, P1 to P3 are conditions that do not include the β-region heat treatment, and are manufacturing conditions for the titanium plates A1 to A46. P4 to P10 are conditions including β-region heat treatment, and are manufacturing conditions for the titanium plates B1 to B53.
In the chemical composition symbols M1 to M12 in Table 1, since the β transformation point is 892 to 932 ° C., the β region heat treatment in the production conditions P4 to P10 is held at 980 ° C. exceeding the β transformation point for 30 minutes, Then, it was cooled to room temperature by water cooling, air cooling, or furnace cooling. In addition to hot rolling and cold rolling, the thickness (plate thickness) of the titanium plate was adjusted by polishing or pickling.
Hereinafter, evaluation methods of the titanium plates A1 to A46 and B1 to B53 will be described.

(1) Vickers hardness (HV)
An average value obtained by measuring five points with a load of 5 kg on the surface of the embedded and polished titanium plate was obtained. The hardness symbol of Vickers hardness in Tables 2 and 3 is HV.

(2) α-phase average crystal grain diameter Hot rolling direction is RD (L direction), and cutting is performed at 1/4, 1/2, and 3/4 of the plate thickness in the L cross section of the titanium plate. The average value was determined.

(3) Determination method of peak intensity from (0001) plane viewed from plate surface direction (ND) of α phase (hcp) The hot rolling direction is set to RD (L direction), and the L cross section of the titanium plate is The crystal orientation was measured by an electron beam backscatter diffraction method (EBSD method). From the measured data, the peak intensity from the (0001) plane viewed from the plate direction (ND) was determined from analysis using a harmonic function using the EBSD data analysis software TSL OIM Analysis ver.7.2. Note that measurement data of EBSD containing 100 or more crystal grains was used.

(4) Impact resistance Spherical lead having a mass of 9.8 g was used as an impact material, and was hit against the surface of the titanium plate at various speeds to determine the limit speed at which the impact material did not penetrate the titanium plate. Hot rolling a titanium plate with chemical components of O: 0.135%, N: 0.003%, C: 0.003%, Fe: 0.051% (chemical composition symbol M2 in Table 1) in mass% And after carrying out cold rolling, sample No. 2 having an average crystal grain size of 27 μm was annealed in vacuum at 650 ° C. for 4 hours. Based on A3 (see Table 2), sample no. The ratio of the critical speed VT of various titanium plates to the critical speed V0 of A3, that is, VT / V0, was squared, and (VT / V0) ² was defined as the “ratio of the critical energy through which the impact object does not penetrate”. The energy ratio is referred to here because the energy of the impact object can be relatively compared by the square of the speed when the impact object has the same mass.

[Effect criteria]
As for titanium plate A1-A43, the ratio of the above-mentioned limit energy set 1.10 or more as the pass. The limit energy ratio of 1.10 or more is the standard No. This means that the impact resistance is higher by 10% or more than A3.
In addition, regarding the titanium plates B1 to B53, the ratio of the limit energy was 1.10 or more as acceptable. In addition, about titanium plate B1-B53, since the crystal orientation of (alpha) phase is randomized to peak intensity 5.00 or less, what satisfy | fills the conditions of this invention among titanium plates B1-B53 is the ratio of a limit energy. Is expected to be 1.20 or more.
The results are shown in Tables 2 and 3.

  As shown in Tables 2 and 3, it can be seen that the titanium plate in the range of the present invention has a higher ratio of limit energy than the comparative example and is excellent in impact resistance. In addition, the titanium plate of the present invention example shown in Table 3 has a peak intensity from the (0001) plane viewed from the plate surface direction (ND) of 5.00 or less, so that the ratio of critical energy is 1.20 or more, Impact is improved.

Moreover, as shown in Table 2, the titanium plates A1, A2, A33, A34, A37, and A38 had a ratio of the critical energy decreased because the chemical component of titanium was out of the scope of the invention.
Titanium plates A3, A5-A7, A13, A14, A16, A18, A19, A21, A23-25, A31, A33, A35, A39, A41, A43, A45, because the annealing conditions were out of the scope of the present invention, The average crystal grain size was less than 150 μm, and the ratio of critical energy was reduced.
Since the plate thickness of the titanium plates A12 and A30 was too thin with respect to the average crystal grain size, the average crystal grain size of the α phase exceeded 10% of the plate thickness, and the ratio of critical energy decreased.

Moreover, as shown in Table 3, since the chemical components of titanium deviated from the scope of the invention for titanium plates B1 to B3, B40, and B43, the ratio of critical energy decreased.
Since the annealing conditions of the titanium plates B7, B8, and B28 were out of the range of the present invention, the average crystal grain size was less than 150 μm, and the ratio of the critical energy was lowered.
Since the plate thickness of the titanium plates B14 and B34 was too thin with respect to the average crystal grain size, the average crystal grain size of the α phase exceeded 10% of the plate thickness, and the ratio of critical energy decreased.
Titanium plates B17 and 37 had an average crystal grain size because the cooling condition after the β-region heat treatment was furnace cooling, and the plate thickness was too thin for this coarsened crystal grain size. The average crystal grain size exceeded 10% of the plate thickness, and the ratio of critical energy decreased.

Claims (6)

The total amount of O, N, and C is 0.140 to 0.260% by mass, Fe is 0.020 to 0.080% by mass, and the balance is made of Ti and impurities.
The average crystal grain size of the α phase is 150 μm or more, and the average crystal grain size of the α phase is 10% or less of the plate thickness,
A titanium plate excellent in impact resistance characterized by having a Vickers hardness (HV) of 130 to 190.   The peak intensity from the (0001) plane viewed from the plate direction (ND) in the crystal orientation distribution measured by the electron backscatter diffraction method (EBSD method) is 5.00 or less. 1. A titanium plate excellent in impact resistance as described in 1.   The titanium plate excellent in impact resistance according to claim 1 or 2, wherein the plate thickness is 2.0 to 6.0 mm. The total amount of O, N, and C is 0.140 to 0.190% by mass, Fe is 0.020 to 0.080% by mass, and the remainder is hot-rolled with titanium and Ti. Giving,
Next, heat treatment is performed under the conditions of holding at 650 ° C. to 850 ° C. for 24 hours or more, holding at 700 ° C. to 850 ° C. for 8 hours or more, or holding at 740 ° C. to 850 ° C. for 4 hours or more. The manufacturing method of the titanium plate of Claim 1 or Claim 3. The total amount of O, N, and C is 0.140 to 0.190% by mass, Fe is 0.020 to 0.080% by mass, and the remainder is hot-rolled with titanium and Ti. Giving,
Next, after heating to a temperature exceeding the β transformation point and cooling at a cooling rate of 0.5 ° C./second or more, holding at 650 ° C. to 850 ° C. for 24 hours or more, holding at 700 ° C. to 850 ° C. for 8 hours or more, The method for producing a titanium plate according to claim 2 or 3, wherein the heat treatment is performed under any of the conditions of holding at 740 ° C to 850 ° C for 4 hours or more.   The method for producing a titanium plate according to claim 4 or 5, wherein cold rolling is performed between the hot rolling and the heat treatment.