TITANIUM CAST PRODUCT FOR HOT ROLLING UNLIKELY TO EXHIBIT SURFACE DEFECTS AND METHOD OF MANUFACTURING THE SAME

Abstract

Provided is a titanium cast product for hot rolling made of a titanium alloy, the titanium cast product including a melted and resolidified layer in a range of more than or equal to 1 mm in depth on a surface serving as a rolling surface, the melted and resolidified layer being obtained by adding one or more elements out of any one of or both of at least one stabilizer element and at least one neutral element to the surface, and melting and resolidifying the surface. An average value of a total concentration of at least one stabilizer element and at least one neutral element in the range of more than or equal to 1 mm in depth is higher than a total concentration of at least one stabilizer element and at least one neutral element in a base metal by, in mass %, more than or equal to 0.1% and less than 2.0%.

Claims

1.-8. (canceled)

9. A titanium cast product made of a titanium alloy, the titanium cast product comprising: a layer in a range of more than or equal to 1 mm in depth on a surface serving as a rolling surface, the layer containing one or more elements out of any one of or both of at least one stabilizer element and at least one neutral element, wherein a total concentration of at least one stabilizer element and at least one neutral element in the range of more than or equal to 1 mm in depth is higher than a total concentration of at least one stabilizer element and at least one neutral element in a base metal by, in mass %, more than or equal to 0.1% and less than 2.0%.

10. The titanium cast product according to claim 9, wherein the at least one stabilizer element and the at least one neutral element each include Al, Sn, and Zr.

11. The titanium cast product according to claim 9, wherein the layer containing one or more elements out of any one of or both of at least one stabilizer element and at least one neutral element further contains, in mass %, less than or equal to 1.5% of one or more stabilizer elements.

12. A method of manufacturing a titanium cast product, the method comprising: melting a surface serving as a rolling surface of the titanium cast product together with a material containing one or more elements out of any one of or both of at least one stabilizer element and at least one neutral element, and then solidifying the surface, wherein a total concentration of at least one stabilizer element and at least one neutral element in the range of more than or equal to 1 mm in depth is made higher than a total concentration of at least one stabilizer element and at least one neutral element in a base metal by, in mass %, more than or equal to 0.1% and less than 2.0%.

13. The method of manufacturing a titanium cast product according to claim 12, wherein the material containing one or more elements out of any one of or both of at least one stabilizer element and at least one neutral element includes one or more of powder, chips, a wire, a thin film, and swarf.

14. The method of manufacturing a titanium cast product according to claim 12, wherein the surface of the titanium cast product is molten by using one or more of electron beam heating, arc heating, laser heating, plasma heating, and induction heating.

15. The method of manufacturing a titanium cast product according to claim 12, wherein the surface of the titanium cast product is molten in a vacuum atmosphere or an inert gas atmosphere.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0037] FIG. 1 shows a schematic view of change in concentrations of a melted and resolidified layer.

DESCRIPTION OF EMBODIMENTS

[0038] Hereinafter, the present invention will be described in detail.

[Thickness of Melted and Resolidified Layer]

[0039] In the present invention, a titanium material made of a titanium alloy has, on a surface serving as a rolling surface, a melted and resolidified layer of more than or equal to 1 mm. As described above, the occurrence of surface defects after hot rolling is caused by concavities and convexities of the surface of the titanium material, which occur due to a structure having coarse crystal grains. Accordingly, the crystal grain size only in an ingot surface layer portion may be made as small as possible. In order to suppress crystal grain growth during hot rolling heating by adding an stabilizer element and/or a neutral element to be mentioned below and to thereby suppress the occurrence of surface defects, it is necessary that the thickness of the melted and resolidified layer containing the stabilizer element and/or the neutral element be more than or equal to 1 mm. In the case where the thickness of the melted and resolidified layer is less than 1 mm, surface defects occur by being influenced by a cast structure of a lower structure, and the surface properties are not improved. Note that the maximum depth is not particularly defined, but if the melting depth is too large, there is a risk that a layer containing an alloying element may remain even after a shot pickling step which is performed after hot rolling, therefore, the melting depth is desirably up to approximately 5 mm. Note that, examples of the titanium materials to be subjected to hot rolling include an ingot, a slab, and a billet.

[0040] The melted and resolidified layer is formed by melting a surface of a titanium cast product, and then quenching and resolidifying the surface. Viewing a cross-section in a direction perpendicular to a scanning direction of a molten bead, the shape of the melted and resolidified layer tends to be the deepest at the center of the molten bead in remelting of the titanium cast product surface layer. When the molten beads are overlapped, a portion midway between adjacent molten beads is the shallowest, and the deepest part and the shallowest part are periodically repeated. In this case, if the difference between the deepest part and the shallowest part is large, this difference causes a difference in deformation resistances in hot rolling, which may cause defects. Accordingly, the difference is desirably less than 2 mm. Note that the depth of the melted and resolidified layer according to the present invention is set to more than or equal to 1 mm, and the depth indicates the depth of the shallowest part as viewed in a cross-section in a direction perpendicular to a scanning direction of a molten bead.

[0041] Here, a titanium alloy is usually molded into a sheet material by hot rolling and/or cold rolling, and is also produced as products in the forms of a wire material, a bar material, and the like. Here, as the titanium alloy, an titanium alloy, an + titanium alloy, or a titanium alloy may be used. Thus, in the present invention, the composition of the titanium alloy is not particularly limited.

[Content of Stabilizer Element or Neutral Element]

[0042] In the present invention, the melted and resolidified layer of the titanium material contains one or more elements out of stabilizer elements or neutral elements, the content of the one or more elements being higher than the content in the base metal portion by more than or equal to a certain content. In the present invention, as will be described later, in order to concentrate one or more elements out of stabilizer elements or neutral elements, a technique is used that the ingot surface layer portion is molten together with a material made of one or more elements out of those elements. When melting and resolidification treatment is performed without adding those elements, since the composition of the molten portion is kept uniform, the crystal grains can be made fine to some extent on their own in accordance with the alloy composition. On the other hand, when the surface layer is molten together with a material containing the stabilizer element(s) and/or the neutral element(s), since the melting time is short and ununiformity of components remains, the structure is rendered ununiform. However, since the melting is only performed to the extent that the molten layer can be removed by a pickling step to be performed thereafter, no influence is exerted on the final product. The ununiformity remains, hence, the stabilizer element(s) and/or the neutral element(s) is/are concentrated at the part at which the ununiformity remains, and a finer structure is formed. Further, when the structure is made fine by the melting and resolidification treatment, a colony in which crystal grains having crystal orientations identical to each other are gathered may be formed. The number of such colonies may be more than the number of single crystal grains, therefore, when colonies occur, there are cases where the colonies may trigger hot rolling defects. However, owing to the ununiformity, the finer structures are formed at some parts as described above, and this can suppress the occurrence of colonies and the growth of colonies during hot rolling heating to be performed after that and can perform hot rolling on the fine crystal grains as they are, therefore, the surface defects during hot rolling can be further suppressed. Moreover, when the stabilizer element(s) and/or the neutral element(s) is/are added, the transformation temperature hardly changes, or the transformation temperature increases, therefore, when the hot rolling heating temperature is immediately below the transformation temperature, a situation in which only the surface layer portion experiences transformation can be suppressed. Only by adding the stabilizer element(s) or neutral element(s) in a manner that the average concentration of the stabilizer element(s) or neutral element(s) in the melted and resolidified layer is higher by more than or equal to 0.1% in total compared to the base metal portion, the above effects can be exhibited, therefore, the lower limit is set to 0.1%. On the other hand, when the average concentration in the molten portion is higher by more than or equal to 2.0% than the concentration in the base metal portion, there are risks that a difference of hot workability may occur between the surface layer portion containing the alloying element and the interior, and that the quality of the material of the product may be deteriorated since the addition amount is large even when the elements are concentrated in the surface layer portion and a large amount of alloying element contained in the surface layer portion is diffused into the interior during heat treatment such as hot rolling heating, therefore, the upper limit is set to 2.0%. Two or more of the stabilizer element(s) and/or the neutral element(s) may be added in combination, and the concentration of the stabilizer element(s) and the neutral element(s) in that case is the total concentration of the concentrations of the respective elements.

[Types of Stabilizer Element and Neutral Element]

[0043] In the present invention, as the stabilizer element(s) and the neutral element(s), there may be used Al, Sn, and Zr. Those elements are each dissolved as a solid solution in the phase, and suppress crystal grain growth in the heating temperature range during hot rolling.

[ Stabilizer Element]

[0044] In the present invention, a stabilizer element may be contained together with the stabilizer element(s) and/or the neutral element(s). When the stabilizer element is contained, not only the above-mentioned crystal grain growth, but also further structure-fine-making can be expected, since the phase, which is the second phase in the heating temperature range during hot rolling, is easily generated, so that the crystal grain growth is further suppressed. In addition, by using titanium alloy scrap containing those alloying elements as an addition material, cost reduction can be expected.

[Method of Measuring Thickness of Melted and Resolidified Layer]

[0045] The present invention defines that the melted and resolidified layer in which the content of alloying element(s) of the stabilizer element(s) or the neutral element(s) is/are concentrated has a depth of more than or equal to 1 mm. The method of measuring the thickness of the melted and resolidified layer will be described. An embedded polishing sample of the cross-section of the concentrated layer can be easily determined by scanning electron microscopy (SEM)/electron probe microanalyser (EPMA). FIG. 1 shows a measurement example of change in concentrations of the melted and resolidified layer. Owing to the addition of the stabilizer element(s) and/or the neutral element(s), the melted and resolidified layer has higher concentration of the stabilizer element(s) and/or the neutral element(s) in comparison to the base metal portion, and the thickness of the portion in which the concentration of the stabilizer element(s) and/or the neutral element(s) is higher is set to the thickness of the melted and resolidified layer. Note that, in the case where the melted and resolidified layer is larger than the measurement range of SEM/EPMA, the measurements are performed several times in the thickness direction, and the results are combined to measure the thickness of the melted and resolidified layer.

[Ununiformity in Melted and Resolidified Layer]

[0046] In the present invention, there is ununiformity in the melted and resolidified layer, and this can also be easily confirmed by the above-mentioned SEM/EBSP. As shown in FIG. 1, when melting and resolidification treatment is performed by adding additive elements, the concentration is high in total in the molten-resolidified portion, but at that part, the concentration is not uniform and fluctuates, which is different from the base metal portion, and it can be confirmed that the ununiformity occurs.

[Method of Measuring Element Concentrations in Molten Portion and Base Metal Portion]

[0047] The concentrations in the melted and resolidified layer and the base metal portion are determined by cutting out test pieces for analytical use from a part at which the concentration is increased and a central part of the material and performing ICP emission spectroscopic analysis on the test pieces. Regarding measurement of the concentrations, analysis samples may be collected from within 1 mm of the surface layer of any multiple sites (for example, 10 sites) of the rolling surface of a titanium cast product, ICP emission spectroscopic analysis may be performed on the analysis samples, and the average value thereof may be set as the concentration in the melted and resolidified layer. Further, by way of comparison, analysis samples may be collected from within 20 mm of the surface layer of any multiple sites (for example, 3 sites) of the rolling surface of the titanium cast product before remelting the surface layer of the titanium cast product, the ICP emission spectroscopic analysis may be performed in the same manner, and the average value thereof may be set as the concentration in the base metal portion.

[Addition Method]

[0048] In the present invention, in order to concentrate one or more elements out of stabilizer elements or neutral elements in the surface layer portion of the ingot, a technique is used that the ingot surface layer portion is molten together with a material made of one or more elements out of those elements. In this way, the concentration of those elements in the surface layer portion of the ingot can be increased. Further, a titanium alloy containing those elements may be used. In this way, a stabilizer element may also be contained easily together with those elements. As a material, powder, chips, a wire, a thin film, and swarf can be used individually or in combination.

[Method of Melting Surface Layer]

[0049] The present invention is characterized in that the titanium material surface layer portion is heated together with a material made of one or more elements out of stabilizer elements or neutral elements, and is molten and resolidified. As the methods of heating the surface layer portion, there may be used electron beam heating, induction heating, arc heating, plasma heating, and laser heating may individually or in combination. In the case where the above methods are used in combination, for example, the surface layer may be preheated by induction heating, and then may be molten by laser heating. The method to be employed may be selected by taking into account conditions such as cost, the size of the titanium material, and treatment time. In the present invention, the titanium material surface layer portion is preferably heated in a vacuum or an inert gas atmosphere. Since titanium is an extremely active metal, a large amount of oxygen and nitrogen is mixed in the molten-resolidified portion if the treatment is performed in the atmosphere, resulting in change in the quality. Therefore, when the treatment is performed in a container under a vacuum or an inert atmosphere, a satisfactory result can be obtained. Note that inert gases according to the present invention represent argon and helium, and do not include nitrogen which reacts with titanium. The degree of vacuum in the case where the treatment is performed in a vacuum container, the degree of vacuum is desirably approximately higher than or equal to 510.sup.5 Torr.

[0050] The present invention provides a titanium material for hot rolling including a melted and resolidified layer in which one or more elements out of stabilizer elements or neutral elements are concentrated in the above-mentioned range on an surface layer in a range of more than or equal to 1 mm in depth, and the other portion of the material is an as-cast structure or a structure obtained by performing casting, then performing heating to higher than or equal to the transformation temperature, and thereafter performing quenching. Using this material, even when a slabing step is omitted, a titanium material having the same surface quality as the case of undergoing an ordinary slabing step can be obtained.

EXAMPLES

[0051] Hereinafter, the present invention will be described in detail by way of examples. Nos. 1 to 24 shown in Table 1 are each an example in which a sheet material is used, and Nos. 25 to 31 are each an example in which a wire material is used.

TABLE-US-00001 TABLE 1 Molten-resolidified layer Ingot Content (mass %) of cutting Added stabilizer element No. Material Product Slabing mending Thickness element(s) or neutral element 1 Ti5Al1Fe Sheet Yes Yes material 2 Ti5Al1Fe Sheet No Yes 4.0 5.1 material 3 Ti5Al1Fe Sheet No Yes 0.5 Al 6.0 material 4 Ti5Al1Fe Sheet No Yes 2.6 Al 5.8 material 5 Ti5Al1Fe Sheet No Yes 1.6 Al 6.0 material 6 Ti5Al1Fe Sheet No Yes 2.3 Al 5.8 material 7 Ti5Al1Fe Sheet No No 2.1 Al 5.5 material 8 Ti5Al1Fe Sheet No No 2.2 Sn 5.5 material 9 Ti5Al1Fe Sheet No No 1.9 Zr 5.9 material 10 Ti5Al1Fe Sheet No No 4.1 Al + Zr 5.6 material 11 Ti5Al1Fe Sheet No No 3.5 Al + Sn 5.7 material 12 Ti5Al1Fe Sheet No No 1.9 Al + V 5.9 material 13 Ti5Al1Fe Sheet No No 2.2 Al + Fe 5.5 material 14 Ti5Al1Fe Sheet No No 2.8 Al + Fe + V 5.6 material 15 Ti5Al1Fe Sheet No No 1.7 Al + Fe + Mo 5.6 material 16 Ti0.06Pd Sheet No No 3.5 Al 0.5 material 17 Ti0.5Ni0.05Ru Sheet No No 2.7 Al 0.6 material 18 Ti1Fe0.035O Sheet No No 3.4 Al 0.3 material 19 Ti5Al1Fe0.25Si Sheet No No 4.5 Al 6.0 material 20 Ti3Al2.5V Sheet No No 4.9 Al 4.0 material 21 Ti4.5Al2Fe2Mo3V Sheet No No 3.6 Al 5.9 material 22 Ti1Cu Sheet No No 2.9 Al 0.4 material 23 Ti1Cu0.5Na Sheet No No 3.4 Al 0.4 material 24 Ti1Cu1Sn0.5Si0.2Nb Sheet No No 2.3 Sn 1.5 material 25 Ti3Al2.5V Wire Yes Yes material 26 Ti3Al2.5V Wire No Yes 2.5 2.9 material 27 Ti3Al2.5V Wire No Yes 0.5 Al 4.0 material 28 Ti3Al2.5V Wire No Yes 2.4 Al 3.7 material 29 Ti3Al2.5V Wire No Yes 6.5 Al 3.5 material 30 Ti3Al2.5V Wire No No 2.7 Sn 3.7 material 31 Ti3Al2.5V Wire No No 1.8 Al 3.8 material Deference between Base metal molten-resolidified layer and base material Molten-resolidified layer Content (mass %) of stabilizer element Content (mass %) of stabilizer element Content (mass %) of or neutral element stabilizer element No. stabilizer element or neutral element stabilizer element (mass %) (mass %) 1 2 5.1 0 3 5.1 0.9 4 4.8 1 5 4.7 1.3 6 5.2 0.6 7 4.9 0.6 8 5.3 0.2 9 5.2 0.7 10 5 0.6 11 5 0.7 12 1.8 5.2 1.0 0.7 0.8 13 1.1 5.1 0.9 0.4 0.2 14 2.2 5 1.0 06 1.2 15 2.0 4.7 1.1 0.9 0.9 16 0.003 0.537 17 0.002 0.608 18 0.001 0.299 19 5.1 0.9 20 3.3 0.7 21 4.6 1.3 22 0.002 0.348 23 0.002 0.398 24 1.1 0.4 25 26 2.9 0 27 2.9 1.1 28 2.7 1 29 3.2 0.3 30 3.2 0.5 31 3.2 0.6 Melting and Element resolidification Melting addition No. treatment method method Surface defects Evaluation Notes 1 No Mirror Good Reference Example 2 Yes TIG Mirror, bus defects Fair Comparative present in some Example pares, 3 Yes EB Powder Slightly cores Fair Comparative defects in some Example parts 4 Yes EB Clips Mirror Good Example 5 Yes Laser Foil Mirror Good Example 6 Yes TIG Foil Mirror Good Example 7 Yes EB Powder Mirror Good Example 8 Yes EB Powder Mirror Good Example 9 Yes EB Swarf Mirror Good Example 10 Yes TIG Swarf Mirror Good Example 11 Yes EB Swarf Mirror Good Example 12 Yes EB Swarf Mirror Good Example 13 Yes EB Swarf Mirror Good Example 14 Yes TIG Swarf Mirror Good Example 15 Yes EB Swarf Mirror Good Example 16 Yes EB Powder Mirror Good Example 17 Yes EB Powder Mirror Good Example 18 Yes EB Powder Mirror Good Example 19 Yes EB Powder Mirror Good Example 20 Yes EB Powder Mirror Good Example 21 Yes EB Powder Mirror Good Example 22 Yes EB Powder Mirror Good Example 23 Yes EB Powder Mirror Good Example 24 Yes EB Powder Mirror Good Example 25 No Mirror Good Reference Example 26 Yes TIG Mirror, bus defects Fair Comparative present in some Example pares, 27 No EB Foil Slightly cores Fair Comparative defects in some Example parts 28 Yes EB Foil Mirror Good Example 29 Yes TIG Foil Mirror Good Example 30 Yes Laser Powder Mirror Good Example 31 Yes EB Foil Mirror Good Example indicates data missing or illegible when filed

[0052] In each of Reference Example, Examples, and Comparative Examples shown in Nos. 1 to 21 of Table 1, a titanium cast product was manufactured by the electron beam remelting method, and was casted using a square-shaped mold. On the other hand, in each of Examples shown in Nos. 22 to 24 of Table 1, a titanium cast product was manufactured by a plasma arc melting method, and was casted using a square-shaped mold. After casting, in the case where cutting mending of a casting surface was performed, the cutting mending of an surface layer of the titanium cast product was performed, and in the case where the cutting mending is not performed, the melting of the surface layer was performed without performing the cutting mending of the surface layer. Next, an ingot having a thickness of 250 mm, a width of 1000 mm, and a length of 4500 mm was hot rolled using a hot rolling plant for a steel material, and was manufactured into a belt-shaped coil having a thickness of 4 mm. Note that an evaluation of surface defects was performed by visually observing a sheet surface layer after being subjected to pickling.

[0053] In each of Reference Example, Examples, and Comparative Examples of Nos. 7 to 24, after an ingot was manufactured, a casting surface of the ingot (cast product) was cut and removed. On the other hand, in each of Examples of Nos. 6 to 31, after an ingot was manufactured, a casting surface was subjected to melting and resolidification treatment.

[0054] In melting method shown in Table 1, EB represents performing melting and resolidification of the surface layer by an electron beam, TIG represents performing melting and resolidification of the surface layer by TIG welding, and laser represents performing melting and resolidification of the surface layer by laser welding. For the melting of the surface layer using the electron beam, an electron beam welding apparatus having a standard output of 30 kW was used. The melting of the surface layer performed by the TIG welding was performed at 200 A without using a filler material. For the melting of the surface layer performed by the laser welding, a CO.sub.2 laser was used.

[0055] Reference Example of No. 1 describes a case where manufacturing was performed by using Ti-5Al-Fe titanium alloy and following a conventional slabing step. Since the slabing step is performed, surface defects of the manufactured sheet material were minor.

[0056] In Comparative Example of No. 2, the ingot was subjected to cutting mending, and then was subjected to surface layer melting treatment using EB without adding an stabilizer element or a neutral element. Therefore, the thickness of the melted and resolidified layer was as deep as more than or equal to 1 mm, and although the surface defects were minor, the surface defects that are not minor occurred in some parts and were deteriorating.

[0057] In Comparative Example of No. 3, the ingot was subjected to the cutting mending, and then the surface of the ingot was subjected to the surface layer melting treatment using EB together with Al powder. Although the content of Al in the molten-resolidified portion was high, which was higher by more than or equal to 0.1% compared to the base metal portion, the thickness was as small as 0.5 mm, and hence, slightly coarse surface defects were observed in some parts.

[0058] In Example of No. 4, the ingot was subjected to the cutting mending, after that, the surface of the ingot was subjected to the surface layer melting treatment using EB together with Al chips, the content of Al in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0059] In Example of No. 5, the ingot was subjected to the cutting mending, after that, the surface of the ingot was subjected to the surface layer melting treatment using laser together with Al foil, the content of Al in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness of the Al-concentrated layer was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0060] In Example of No. 6, the ingot was subjected to the cutting mending, after that, the surface of the ingot was subjected to the surface layer melting treatment using TIG together with Al foil, the content of Al in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0061] In Example of No. 7, the ingot was not subjected to cutting, the surface of the ingot was subjected to the surface layer melting treatment using EB together with Al powder, the content of Al in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0062] In Example of No. 8, the ingot was not subjected to cutting, the surface of the ingot was subjected to the surface layer melting treatment using EB together with Sn powder, the content of Sn in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0063] In Example of No. 9, the ingot was not subjected to cutting, the surface of the ingot was subjected to the surface layer melting treatment using EB together with Zr swarf, the content of Zr in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0064] In Example of No. 10, the ingot was not subjected to cutting, the surface of the ingot was subjected to the surface layer melting treatment using TIG together with powder of Al and Zr, the total content of Al and Zr in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0065] In Example of No. 11, the ingot was not subjected to cutting, the surface of the ingot was subjected to the surface layer melting treatment using TIG together with swarf of a titanium alloy containing Al and Sn, the total content of Al and Sn in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0066] In each of Examples of No. 12 to 15, the ingot was not subjected to cutting, the surface of the ingot was subjected to the surface layer melting treatment using TIG together with swarf of a titanium alloy containing Al and a stabilizer element, the content of Al in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the content of the stabilizer element was as low as less than or equal to 1.5%. Further, the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0067] Each of Examples of Nos. 16 to 24 is a result of an ingot made of a titanium alloy. No. 16 is Ti-0.06Pd titanium alloy, No. 17 is Ti-0.5Ni-0.05Ru titanium alloy, No. 18 is Ti-1Fe-0.350 titanium alloy, No. 19 is Ti-5Al-1Fe-0.25Si titanium alloy, No. 20 is Ti-3Al-2.5V titanium alloy, No. 21 is Ti-4.5Al-2Fe-2Mo-3V titanium alloy, No. 22 is Ti-1Cu titanium alloy, No. 23 is Ti-1Cu-0.5Nb titanium alloy, and No. 24 is Ti-1Cu-1Sn-0.3Si-0.2Nb titanium alloy. In each of the above, the ingot was not subjected to cutting, the surface of the ingot was subjected to the surface layer melting treatment using EB together with Al powder, the content of Al in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0068] In each of Reference Example, Comparative Examples, and Examples shown in Nos. 25 to 31 of Table 1, Ti-3Al-2.5V titanium alloy was used, and a titanium ingot was manufactured by the vacuum arc remelting method or the electron beam remelting method. An ingot having a diameter of 170 mm and a length of 12 m was hot rolled, and was manufactured into a wire material having a diameter of 13 mm. Note that an evaluation of surface defects was performed by visually observing a sheet surface layer after being subjected to pickling.

[0069] In each of Reference Example, Comparative Examples, and Examples of Nos. 25 to 29, after an ingot was manufactured, a casting surface of the ingot was cut and removed. On the other hand, in each of Examples of Nos. 30 and 31, after an ingot was manufactured, a casting surface was subjected to melting and resolidification treatment.

[0070] Reference Example of No. 25 describes a case where manufacturing was performed by following a conventional slabing step.

[0071] In Comparative Example of No. 26, the ingot was subjected to cutting mending, and then was subjected to surface layer melting treatment using EB without adding an stabilizer element or a neutral element. Therefore, the thickness of the molten-resolidified portion was as deep as more than or equal to 1 mm, and although the surface defects were minor, they occurred in some parts and were deteriorating.

[0072] In Comparative Example of No. 27, the ingot was subjected to the cutting mending, and then the surface of the ingot was subjected to the surface layer melting treatment using EB together with Al foil. Although the content of Al in the molten-resolidified portion was high, which was higher by more than or equal to 0.1% compared to the base metal portion, the thickness was as small as 0.5 mm, and hence, slightly coarse surface defects were observed in some parts.

[0073] In Example of No. 28, the ingot was subjected to the cutting mending, after that, the surface of the ingot was subjected to the surface layer melting treatment using EB together with Al foil, the content of Al in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0074] In Example of No. 29, the ingot was subjected to the cutting mending, after that, the surface of the ingot was subjected to the surface layer melting treatment using TIG together with Al foil, the content of Al in the melted and resolidified layer was high, which was higher by more than or equal to 0.1%, and the thickness was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0075] In Example of No. 30, the ingot was subjected to the cutting mending, after that, the surface of the ingot was subjected to the surface layer melting treatment using laser together with Sn powder, the content of Sn in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness of the Sn-concentrated layer was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.

[0076] In Example of No. 31, the ingot was subjected to the cutting mending, after that, the surface of the ingot was subjected to the surface layer melting treatment using EB together with Al foil, the content of Al in the melted and resolidified layer was high, which was higher by more than or equal to 0.1% compared to the base metal portion, and the thickness of the Al-concentrated layer was as deep as more than or equal to 1 mm, and hence, the surface defects were minor, which was the same level as the case of undergoing the slabing step.