JP6086178B1 - Titanium material for hot rolling - Google Patents

Abstract

A base material 1b made of industrial pure titanium or a titanium alloy, and a surface layer portion 1a having a chemical composition different from that of the base material 1b formed on at least one rolling surface of the base material 1b. When the thickness is 2.0 to 20.0 mm, the proportion of the total thickness is 40% or less per side, and the content of the element contained in the surface layer portion 1a is measured at multiple points, the increase from the base material 1b Relationship between average value CAVE of content and increased content C0 from base material 1b at each measurement location: Titanium material 1 for hot rolling in which | CAVE−C0 | / CAVE × 100 is 40% or less. The chemical composition of the surface layer part includes one or more selected from Mo, V and Nb as the increased content from the base material, and the Mo equivalent is 8.0 to 20.0. This titanium material for hot rolling 1 has desired characteristics despite its low cost.

Description

  The present invention relates to a titanium material for hot rolling.

  Titanium materials are excellent in properties such as corrosion resistance, oxidation resistance, fatigue resistance, hydrogen embrittlement resistance, and neutron blocking properties. These properties can be achieved by adding various alloying elements to titanium.

  Pure titanium for industrial use is mainly composed of an α phase having an hcp (dense hexagonal lattice) structure, and it is known that if a large amount of hydrogen is absorbed in the α phase, a hydride is formed and embrittled. For this reason, depending on the use environment, there is a case where an accident occurs in which hydrogen is absorbed and becomes brittle and breaks. In “Titanium processing technology” (Non-Patent Document 1), for example, accidents due to hydrogen absorption in a plant that handles non-oxidizing acids, or in a urea / ammonia environment or a hydrogen gas environment are reported. For this reason, a titanium alloy material excellent in hydrogen embrittlement resistance has been proposed.

  Japanese Unexamined Patent Publication No. 2013-163840 (Patent Document 1) discloses a titanium alloy containing 50% by volume or more of a β phase and containing 500 to 6000 ppm of hydrogen and having a large elongation at break. Even if it contains a large amount of hydrogen, it is brittle. An example is shown that does not.

  The titanium material is usually produced by the method shown below. First, the raw material titanium oxide is chlorinated to titanium tetrachloride by the crawl method, and then reduced with magnesium or sodium to produce a lump-like sponge-like metal titanium (sponge titanium). This sponge titanium is press-molded to form a titanium consumable electrode, and a titanium ingot is manufactured by vacuum arc melting using the titanium consumable electrode as an electrode. At this time, an alloy element is added as necessary to produce a titanium alloy ingot. Thereafter, the titanium alloy ingot is divided, forged and rolled into a titanium slab, and the titanium slab is further subjected to hot rolling, annealing, pickling, cold rolling, and vacuum heat treatment to produce a titanium thin plate.

  In addition, as a method for producing a titanium thin plate, titanium ingot is smashed, hydroground, dehydrogenated, powder crushed, and classified to produce titanium powder, and titanium powder is powder-rolled, sintered, and cold-rolled. The manufacturing method is also known.

  Japanese Patent Laid-Open No. 2011-42828 (Patent Document 2) discloses that a titanium powder is produced directly from sponge titanium instead of a titanium ingot, and a titanium thin plate is produced from the obtained titanium powder. Sintered compacts are manufactured by sintering pre-sintered compacts made of viscous compositions containing agents and solvents into thin sheets, and sintered compacts are manufactured by compacting the sintered compacts. In the method for producing a titanium thin plate for re-sintering, a method is disclosed in which the fracture elongation of the sintered thin plate is 0.4% or more, the density ratio is 80% or more, and the density ratio of the sintered compacted plate is 90% or more. ing.

  Japanese Patent Laid-Open No. 2014-19945 (Patent Document 3) discloses a composite powder obtained by adding an appropriate amount of iron powder, chromium powder or copper powder to titanium alloy powder using titanium alloy scrap or titanium alloy ingot as a raw material. After extruding the carbon steel capsule, the capsule on the surface of the obtained round bar is dissolved and removed, and further solution treatment or solution treatment and aging treatment are performed to produce a titanium alloy with excellent quality by the powder method A method is disclosed.

  In JP 2001-131609 A (Patent Document 4), a sponge capsule is filled with a sponge titanium powder, and then subjected to warm extrusion at an extrusion ratio of 1.5 or more and an extrusion temperature of 700 ° C. or less. A method for producing a titanium molded body in which 20% or more of the total length of the grain boundary of the molded body is in metal contact is performed by performing outer peripheral processing excluding copper.

  When hot-rolling a hot-rolled material, if the hot-rolled material is a so-called difficult-to-process material with high hot deformation resistance due to insufficient hot ductility, such as pure titanium or titanium alloy, these are thin plates. A pack rolling method is known as a technique for rolling the sheet. The pack rolling method is a method in which a core material such as a titanium alloy having poor workability is covered with a cover material such as inexpensive carbon steel having good workability and hot rolling is performed.

  Specifically, for example, a release agent is applied to the surface of the core material, and at least two upper and lower surfaces thereof are covered with a cover material, or the four peripheral surfaces are covered with a spacer material in addition to the upper and lower surfaces, and the surroundings are welded. Assembled and hot rolled. In pack rolling, a core material, which is a material to be rolled, is covered with a cover material and hot rolled. Therefore, the core material surface does not directly contact a cold medium (atmosphere or roll), and the temperature drop of the core material can be suppressed, so that even a core material with poor workability can be manufactured.

Japanese Laid-Open Patent Publication No. 63-207401 (Patent Document 5) discloses a method for assembling a hermetically sealed box, and Japanese Laid-Open Patent Publication No. 09-136102 (Patent Document 6) discloses a degree of vacuum of 10 ⁻³ torr order or more. A method of manufacturing a hermetically sealed box by sealing the cover material is disclosed, and further, Japanese Patent Application Laid-Open No. 11-057810 (Patent Document 7) covers carbon steel (cover material) and is in the order of 10 ⁻² torr. A method for producing a hermetic coated box by sealing by high energy density welding under the following vacuum is disclosed.

  On the other hand, as a method for manufacturing a highly corrosion-resistant material at a low cost, a method is known in which a titanium material is bonded to the surface of a material serving as a base material.

  In Japanese Patent Laid-Open No. 08-141754 (Patent Document 8), steel is used as a base material and titanium or a titanium alloy is used as a joining material, and the joint surface of the base material and the joining material is evacuated and then assembled by welding. A method for manufacturing a titanium clad steel sheet in which an assembly slab for rolling is joined by hot rolling is disclosed.

  In JP-A-11-170076 (Patent Document 9), pure nickel, pure iron, and carbon content are 0.01% by mass or less on the surface of a base steel material containing 0.03% by mass or more of carbon. After the titanium foil material is laminated by interposing an insert material made of any one of the above-mentioned low carbon steels with a thickness of 20 μm or more, a laser beam is irradiated from either side of the lamination direction, A method of manufacturing a titanium-coated steel material by melting and joining at least the vicinity of the edge with a base steel material over the entire circumference is disclosed.

  In JP-A-2015-045040 (Patent Document 10), the surface of a porous titanium raw material (sponge titanium) formed into an ingot shape is melted by using an electron beam under vacuum, and the surface layer portion is made of dense titanium. The titanium ingot is manufactured and hot rolled and cold rolled to form a porous portion in which the porous titanium raw material is formed into an ingot shape, and the entire surface of the porous portion composed of dense titanium. A method for producing a dense titanium material (titanium ingot) having a dense coating portion for coating with very little energy is exemplified.

  Japanese Patent Application Laid-Open No. 62-270277 (Patent Document 11) describes that a surface effect treatment of an engine member for an automobile is performed by thermal spraying.

JP2013-163840A JP 2011-42828 A JP 2014-19945 A JP 2001-131609 A JP-A 63-207401 JP 09-136102 A Japanese Patent Laid-Open No. 11-057810 Japanese Patent Laid-Open No. 08-141754 Japanese Patent Laid-Open No. 11-170076 Japanese Patent Laying-Open No. 2015-045040 JP-A-62-270277

Titanium processing technology, edited by Japan Titanium Association, Nikkan Kogyo Shimbun, p. 214-230, issued in November 1992

  As measures against hydrogen embrittlement, products are generally subjected to surface treatment with hydrogen absorption resistance after processing, or subjected to anticorrosion. However, in any case, it is inevitable that the cost increases due to an increase in the number of processes for product processing or construction, and it is impossible to provide a titanium material excellent in hydrogen embrittlement resistance at a low cost.

  In addition, as in the method disclosed in Patent Document 1, in order to make 50% by volume or more of the entire material a β phase, it is necessary to contain a large amount of an expensive additive element, resulting in an increase in cost.

  Conventionally, when manufacturing a titanium material through hot working, sponge titanium is press-molded to form a titanium consumable electrode, and a titanium ingot is manufactured by vacuum arc melting using the titanium consumable electrode as an electrode. The titanium slab was forged and rolled into a titanium slab, and the titanium slab was manufactured by hot rolling, annealing, pickling, and cold rolling.

  In this case, a process of manufacturing titanium ingot by dissolving titanium has been added. A method of producing titanium powder by powder rolling, sintering, and cold rolling is also known, but in the method of producing titanium powder from a titanium ingot, a step of dissolving titanium is also added.

  In the method for producing a titanium material from titanium powder, even if it does not go through a melting step, expensive titanium powder is used as a raw material, so that the obtained titanium material is very expensive. The same applies to the methods disclosed in Patent Documents 5 to 6.

  In pack rolling, the core material covered with the cover material is slab or ingot to the last, and has undergone a melting step or is made of expensive titanium powder, and the manufacturing cost cannot be reduced.

  In Patent Document 10, a dense titanium material can be manufactured with very little energy, but the surface of the titanium sponge formed into an ingot shape is dissolved, and the dense titanium surface layer portion and the internal components are the same kind of pure titanium. Or it is prescribed | regulated as a titanium alloy, for example, a manufacturing cost cannot be reduced by forming a titanium alloy layer uniformly only over the surface layer part over a wide range.

  On the other hand, many materials that can manufacture inexpensive corrosion-resistant materials and have titanium or a titanium alloy bonded to the surface of the base material select steel as the base material. Therefore, if the titanium layer on the surface is lost, the corrosion resistance is impaired. Even if a titanium material is adopted as a base material, a drastic cost improvement cannot be expected as long as a titanium material manufactured through a normal manufacturing process is used. Then, the present inventors considered providing an alloy layer containing a specific alloy element on the surface layer of a slab made of industrial pure titanium or a titanium alloy to obtain a titanium material that is inexpensive and excellent in specific performance.

  As in Patent Document 11, thermal spraying is a method in which a film is formed by melting metal, ceramics, or the like and spraying it on the surface of a titanium material. When a film is formed by this method, the formation of pores in the film cannot be avoided. Usually, during thermal spraying, thermal spraying is performed while shielding with an inert gas in order to avoid oxidation of the film. These inert gases are entrained in the pores of the coating. Such pores containing the inert gas are not pressed by hot working or the like. Further, in the production of titanium, vacuum heat treatment is generally carried out, but during this treatment, the inert gas in the pores may expand and the film may be peeled off. According to the experience of the present inventors, the abundance ratio (porosity) of pores generated by thermal spraying is several vol. % Or more and 10 vol. % May be exceeded. As described above, a titanium material having a high porosity in the film has a risk of peeling in the manufacturing process, and there is a risk that a defect such as a crack during processing may occur.

  As a method for forming the film, there is a cold spray method. Even when a film is formed on the surface by this method, an inert high-pressure gas is used. In this method, the porosity is 1 vol. However, it is extremely difficult to completely prevent the generation of pores. As in the case of thermal spraying, since the pores contain the inert gas, they do not disappear even by subsequent processing. In addition, when heat treatment is performed in a vacuum, the inert gas in the pores may expand and the film may break.

  In order to suppress surface flaws during hot rolling, there is a melt resolidification process as a process for melting and resolidifying the surface layer of the slab using an electron beam. Usually, the melted and re-solidified surface layer is removed in a pickling step after hot rolling. The present inventors paid attention to this melt resolidification treatment. That is, the present inventors can form a surface layer portion containing a specific alloy element in the slab by melting a specific alloy element when melting the slab surface layer and solidifying it with a slab-derived component. I thought. However, the melt resolidification treatment for the purpose of suppressing surface flaws during hot rolling cannot be used as it is to form a surface layer portion containing a specific alloy element in the slab. This is because the conventional melt resolidification treatment is based on the premise that the formed surface layer is removed by pickling, and no consideration was given to segregation of alloy components in the surface layer portion.

  If segregation of the alloy component exists in the slab surface layer portion containing a specific alloy element, the desired performance cannot be sufficiently exhibited or the desired performance is deteriorated quickly. Therefore, a method of adding a specific alloy element is important.

  The present invention reduces the content of alloying elements added to improve hydrogen embrittlement resistance (the amount of specific alloying elements that express target characteristics) and suppresses the production cost of titanium materials Thus, it is an object to obtain a titanium material for hot rolling having desired characteristics at a low cost.

  This invention is made | formed in order to solve the said subject, and makes a summary the following titanium material for hot rolling.

(1) Titanium for hot rolling comprising a base material made of industrial pure titanium or a titanium alloy, and a surface layer portion having a chemical composition different from that of the base material formed on at least one rolling surface of the base material. The surface layer portion has a thickness of 2.0 to 20.0 mm, the ratio of the total thickness to 40% or less per side, and the chemical composition of the surface layer portion is increased from the base material. As a content, one or more selected from Mo, V and Nb is contained, the Mo equivalent calculated by the following formula (1) is 8.0 to 20.0, and the inclusion of the elements contained in the surface layer portion When the amount is measured at multiple points, the relationship between the average value C _AVE of the increased content from the base material and the increased content C ₀ from the base material at each measurement location: | C _AVE −C ₀ | / C _AVE × 100 Is a titanium material for hot rolling, having a content of 40% or less.
Mo equivalent = Mo content (% by mass) + V content (% by mass) /1.5+Nb content (% by mass) /3.6 (1)

(2) Other surface layer portions are formed on a surface other than the rolling surface of the base material,
The other surface layer portion has the same chemical composition and metal structure as the surface layer portion.
(1) Titanium material for hot rolling.

  The titanium material for hot rolling according to the present invention includes a base material made of pure industrial titanium or a titanium alloy and a surface layer portion having a chemical composition different from that of the base material, and is thus manufactured using the base material. Compared with a titanium material made entirely of the same titanium alloy, the titanium composite material has equivalent hydrogen embrittlement resistance, but can be manufactured at low cost.

FIG. 1 is an explanatory view showing an example of the configuration of a titanium material for hot rolling according to the present invention. FIG. 2 is an explanatory view showing another example of the structure of the titanium material for hot rolling according to the present invention. FIG. 3 is an explanatory diagram showing an example of the configuration of the titanium composite material according to the present invention. FIG. 4 is an explanatory diagram showing an example of the configuration of the titanium composite material according to the present invention. FIG. 5 is an explanatory diagram showing a method of melt re-solidification. FIG. 6 is an explanatory diagram showing a method of melt re-solidification. FIG. 7 is an explanatory view showing a method of melt re-solidification. FIG. 8 is an explanatory view schematically showing that a titanium rectangular slab (slab) and a titanium plate are bonded together by welding in a vacuum. FIG. 9 is an explanatory view schematically showing that a titanium plate is bonded to not only the surface of a titanium rectangular cast slab (slab) but also a side surface thereof.

  The titanium material for hot rolling of the present invention is a material (slabs such as slabs, blooms and billets) subjected to hot working, and after hot working, cold working, heat treatment, etc. are performed as necessary. And processed into a titanium composite. Hereinafter, the titanium material for hot rolling according to the present invention will be described with reference to the drawings. In the following description, “%” regarding the content of each element means “mass%”.

1. 1. Titanium material for hot rolling 1-1. Overall Configuration As shown in FIG. 1, a titanium material for hot rolling 1 according to the present invention includes a base material 1b and a surface layer portion 1a on the rolling surface of the base material 1b. The surface layer portion includes a predetermined intermediate layer (not shown). The base material 1b is made of industrial pure titanium or a titanium alloy, and the surface layer portion 1a has a chemical composition different from that of the base material 1b. As shown in FIG. 2, the titanium material 1 for hot rolling according to the present invention may include surface layer portions 1aa and 1ab on both rolling surfaces of the base material 1b. Thus, the hydrogen embrittlement resistance of the titanium material 1 for hot rolling is secured by the surface layer portion 1a (1aa, 1ab in the example shown in FIG. 2) in contact with the external environment. This titanium material for hot rolling 1 has equivalent hydrogen embrittlement resistance as compared with a titanium material made entirely of the same titanium alloy, but can be manufactured at a low cost.

  In addition, the dimension in case the titanium material for hot rolling is a rectangular titanium cast piece will not be specifically limited if it is a dimension which can be used for hot rolling as it is. When coil rolling is applied as hot rolling to produce a hot rolled thin coil sheet having a thickness of about 3 to 8 mm, the rectangular titanium cast has a thickness of about 50 to 300 mm, a length of about 3000 to 10000 m, and a width of 600. It may be about ˜1500 mm.

  If the thickness of the surface layer portion is too thin, the thickness of the surface layer of the final product is also thin, and desired characteristics cannot be obtained sufficiently. On the other hand, if it is too thick, the proportion of the titanium alloy in the entire titanium composite increases, so the cost merit decreases. Therefore, the thickness of the surface layer portion is set to 2.0 to 20.0 mm. The ratio of the thickness of the surface layer part to the total thickness is 40% or less per side.

1-2. Base material Base material 1 consists of industrial pure titanium or a titanium alloy. However, by using a titanium alloy, mechanical properties (strength, ductility, etc.) superior to the case of using industrial pure titanium can be obtained.

  As the base material 1, among the pure titanium prescribed by JIS, JIS 1-4 kinds of industrial pure titanium can be used. That is, it contains 0.1% or less C, 0.015% or less H, 0.4% or less O, 0.07% or less N, 0.5% or less Fe, and the balance is Ti. Pure titanium for industrial use. If these JIS 1-4 types of industrial pure titanium are used, it has sufficient workability, does not generate cracks, etc., and a titanium material integrated with the surface titanium alloy after hot working can be obtained.

  As the base material 1, α-type, α + β-type, and β-type titanium alloys can be used.

  Here, as an alpha type titanium alloy, Ti-0.5Cu, Ti-1.0Cu, Ti-1.0Cu-0.5Nb, Ti-1.0Cu-1.0Sn-0.3Si-0. 25Nb, Ti-0.5Al-0.45Si, Ti-0.9Al-0.35Si, Ti-3Al-2.5V, Ti-5Al-2.5Sn, Ti-6Al-2Sn-4Zr-2Mo, Ti- Examples thereof include 6Al-2.75Sn-4Zr-0.4Mo-0.45Si.

  Examples of the α + β type titanium alloy include Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-6Al-7V, Ti-3Al-5V, Ti-5Al-2Sn-2Zr-4Mo-4Cr, and Ti. -6Al-2Sn-4Zr-6Mo, Ti-1Fe-0.35O, Ti-1.5Fe-0.5O, Ti-5Al-1Fe, Ti-5Al-1Fe-0.3Si, Ti-5Al-2Fe, Ti Examples thereof include -5Al-2Fe-0.3Si, Ti-5Al-2Fe-3Mo, Ti-4.5Al-2Fe-2V-3Mo, and the like.

  Further, as the β-type titanium alloy, for example, Ti-11.5Mo-6Zr-4.5Sn, Ti-8V-3Al-6Cr-4Mo-4Zr, Ti-10V-2Fe-3Mo, Ti-13V-11Cr-3Al Ti-15V-3Al-3Cr-3Sn, Ti-6.8Mo-4.5Fe-1.5Al, Ti-20V-4Al-1Sn, Ti-22V-4Al, and the like.

  The base material may be manufactured by a known manufacturing method such as a melting method or a powder metallurgy method, and is not particularly limited. For example, the base material can be manufactured by cutting and refining an ingot into a slab or billet shape by breakdown. When manufactured by breakdown, since the surface is relatively flat by breakdown, it is easy to disperse the element containing the alloy element relatively uniformly, and it is easy to make the element distribution of the alloy phase uniform.

  On the other hand, the ingot directly manufactured at the time of casting can also be used as a base material. In this case, since the cutting and refining process can be omitted, it can be manufactured at lower cost. In addition, if the surface is cut and refined after the ingot is manufactured, the same effect can be expected when it is manufactured through breakdown.

1-3. Surface layer (chemical component)
In order to increase the hydrogen absorption resistance of at least one of the surface layers of the titanium composite material produced from the titanium material for hot rolling of the present invention (at least the surface layer in contact with the external environment), the surface layer portion of the titanium material for hot rolling is Various alloy elements listed below may be included.

Mo equivalent: 8.0 to 20.0
However, Mo equivalent = Mo content (mass%) + V content (mass%) / 1.5 + Nb content (mass%) / 3.6.
The layer for obtaining hydrogen absorption resistance is a titanium alloy layer containing a certain range of β-stabilizing elements. The reason for prescribing the formation of the β phase is that the α phase of titanium forms a hydride even at a hydrogen concentration of only a few tens of ppm, whereas the β phase of the titanium alloy can dissolve about 1000 ppm or more of hydrogen, This is because it has the characteristic that it is difficult to cause embrittlement due to hydrogen.

  When a eutectoid β-stabilizing element such as Fe or Cr is included, titanium and these elements may form a compound, which may lead to embrittlement. However, among the β-stabilizing elements, when Mo, V, and Nb are contained in the range of Mo equivalents: 8.0 to 20.0, the β-phase is stabilized even if Fe and Cr are present at the same time. Since no compound phase is formed, embrittlement does not occur.

  Here, the lower limit of the Mo equivalent is the amount of alloy necessary to obtain a sufficient amount of β phase. The upper limit was determined because a titanium alloy with a large amount of alloy addition is not suitable for use because of its high cost.

  The balance other than the above is titanium and impurities. Impurities can be contained within a range that does not hinder the target characteristics, and other impurities include Ta, Si, Mn, and Cu as impurity elements mainly mixed from scrap, and C, which are general impurity elements, In combination with N, Fe, O and H, a total amount of 5% or less is allowed.

2. Titanium composite material The titanium material for hot rolling of the present invention is a material (slab, slab, bloom, billet, etc.) subjected to hot working, and after hot working, if necessary, cold working, It is processed into titanium composite by heat treatment. The titanium composite material includes an inner layer derived from the base material of the titanium material for hot rolling according to the present invention and a surface layer derived from the surface layer portion.
(thickness)
If the thickness of the surface layer in contact with the external environment is too thin, sufficient hydrogen absorption resistance cannot be obtained. On the other hand, when the surface layer is thick, there is no problem in hydrogen absorption resistance, but the manufacturing cost increases because the ratio of the surface layer to the entire material increases. For this reason, the ratio of the thickness of the surface layer to the total thickness of the titanium composite (surface layer occupancy) is 2 to 20% per side.

  The thickness of the surface layer depends on the thickness of the surface layer portion 1a and the processing rate during the subsequent hot processing.

(Porosity)
The porosity of the surface layer is preferably 0.1% or less. When the porosity exceeds 0.1%, the surface layer may be swollen or peeled off during hot rolling.

  The porosity can be easily measured by taking a photograph of the cross-section of the material with an optical microscope and processing the photograph. Arbitrary 10-20 places of a cross section are observed, the porosity can be measured, and the average can be made into the whole porosity. In addition, the porosity of the material which performed hot rolling or after cold rolling is equivalent to the porosity of the titanium material for hot rolling.

(Segregation)
When the content of elements contained in the surface layer is measured at a plurality of points, the relationship between the average value C _AVE of the increased content from the base material and the increased content C ₀ from the base material at each measurement location: | C _AVE − C ₀ | / C _AVE × 100 is 40% or less. This is because if | C _AVE −C ₀ | / C _AVE × 100 exceeds 40%, the desired performance cannot be sufficiently exhibited, or the degradation of the desired performance is accelerated. | C _AVE −C ₀ | / C _AVE × 100 is preferably 20% or less.

The specific element in the surface layer portion can be measured using EPMA or GDS. Specifically, arbitrary 10 to 20 locations on the surface layer portion are measured, and the average value of the increased content from the base material at each measured location is defined as the increased content C ₀ at each measured location, and the increased content C _{0. May} be the average value C _AVE of the increased content in the surface layer portion.

(Middle layer)
The surface layer includes an intermediate layer in the vicinity of the inner layer. That is, the titanium material for hot rolling of the present invention is provided with a surface layer portion formed by, for example, melt resolidification treatment on the surface of the base material, and the surface layer portion is then subjected to hot rolling heating, and In the heat treatment step after cold rolling, diffusion occurs at the interface between the base material and the surface layer portion, and when the titanium composite material is finally finished, it is between the inner layer derived from the base material and the surface layer derived from the surface layer portion. An intermediate layer is formed. This intermediate layer bonds the inner layer and the surface layer to each other and bonds them firmly. Further, since a continuous element gradient is generated in the intermediate layer, the difference in strength between the inner layer and the surface layer can be reduced, and cracks during processing can be suppressed. The thickness of this intermediate layer is preferably 0.5 μm or more.

The thickness of the intermediate layer can be measured using EPMA or GDS. If GDS is used, more detailed measurement is possible. In the case of GDS, after removing the surface layer to some extent by polishing, the thickness of the intermediate layer can be measured by performing GDS analysis in the depth direction from the surface. The intermediate layer is the increased content from the base material (in the case of an element not included in the base material, its content, in the case of an element also included in the base material, the increase in content from the base material) ) _Is C _MID, and the average of the increased content in the surface layer portion is C _AVE , it means a region of 0 <C _MID ≦ 0.8 × C _AVE .

3. 3. Method for producing titanium material for hot rolling 3-1. Formation of surface layer by melt resolidification The titanium material for hot rolling of the present invention is specified as a base material by melting the surface layer of the base material, melting a specific alloy element at that time, and solidifying it together with components derived from the base material. It can manufacture by forming the surface layer part containing these alloy elements. 5-7 is explanatory drawing which shows the method of melt re-solidification all.

  As a method for melting and resolidifying the surface of the base material of the titanium material for hot rolling, there are laser heating, plasma heating, induction heating, electron beam heating, etc., and any method may be used. In particular, especially in the case of electron beam heating, since it is performed in a high vacuum, even if a void or the like is formed in this layer during the melt resolidification treatment, it can be made harmless by pressure bonding in subsequent rolling because it is a vacuum.

Furthermore, since it is high in energy efficiency, it can be melted deeply even if a large area is processed, and is particularly suitable for the production of titanium composite materials. The degree of vacuum in the case of melting in vacuum is desirably a higher degree of vacuum of 3 × 10 ⁻³ Torr or less. In addition, the number of times of melting and resolidifying the surface layer of the titanium material for hot rolling is not particularly limited, and even if the number of times is increased as necessary, the thickness of the alloy layer on the surface layer portion of the material and the amount of additive elements added are not limited. There is no problem if it is within the above range. However, as the number of times increases, the processing time becomes longer and the cost increases.

  In the case of a rectangular slab, the melt resolidification method of the surface layer is performed as shown in FIG. That is, among the outer surfaces of the rectangular slab 10, at least two wide surfaces 10A and 10B that become the rolling surfaces (surfaces in contact with the hot rolling roll) in the hot rolling process are irradiated with an electron beam, and the surfaces on the surfaces are irradiated. Only melt the layer. Here, it is assumed that the surface 10A is one of the two surfaces 10A and 10B.

  Here, as shown in FIG. 5, the area of the electron beam irradiation region 14 by the single electron beam irradiation gun 12 on the surface 10A of the rectangular slab 10 is compared with the total area of the surface 10A to be irradiated. The electron beam irradiation is actually performed while continuously moving the electron beam irradiation gun 12 or continuously moving the rectangular slab 10. It is normal. The shape and area of this irradiation area can be adjusted by adjusting the focus of the electron beam or by using an electromagnetic lens to oscillate a small beam at a high frequency (oscillation oscillation) to form a beam bundle. can do.

  Then, as indicated by an arrow A in FIG. 5, the following explanation will be made on the assumption that the electron beam irradiation gun 12 is continuously moved. Although the moving direction of the electron beam irradiation gun is not particularly limited, it is generally continuous along the length direction (usually the casting direction D) or the width direction (usually the direction perpendicular to the casting direction D) of the rectangular slab 10. Then, the irradiation region 14 is continuously irradiated in a band shape with a width W (in the case of a circular beam or beam bundle, a diameter W). Further, the electron beam irradiation is performed in a belt shape while continuously moving the irradiation gun 12 in the reverse direction (or the same direction) in the adjacent unirradiated belt region. In some cases, a plurality of irradiation guns may be used to simultaneously perform electron beam irradiation on a plurality of regions. In FIG. 5, the case where a rectangular beam is continuously moved along the length direction (usually casting direction D) of the rectangular slab 10 is shown.

  If the surface (surface 10A) of the rectangular titanium cast piece 10 is irradiated with an electron beam by such a surface heat treatment step and heated to melt the surface, the rectangular titanium as shown in the left side of the center of FIG. The surface layer of the surface 10A of the slab 10 is melted at the maximum by a depth corresponding to the heat input. However, the depth from the direction perpendicular to the irradiation direction of the electron beam is not constant as shown in FIG. 7, and the depth becomes the largest at the central part of the electron beam irradiation, and the thickness increases toward the strip-shaped end part. Decreases, resulting in a downwardly convex curved shape.

  The region inside the slab from the molten layer 16 also rises in temperature due to the heat effect of electron beam irradiation, and the portion where the temperature is higher than the β transformation point of pure titanium (heat affected layer = HAZ layer) is the β phase. To metamorphosis. In this way, the region transformed into the β phase by the heat effect of the electron beam irradiation in the surface heat treatment step also has a downwardly curved shape similar to the shape of the molten layer 16.

  The surface layer of the material for hot rolling is alloyed by performing melt resolidification together with the material composed of the target alloy element. As a material used in this case, one or more of powder, chip, wire, thin film, cutting powder, and mesh may be used. The component and amount of the material to be arranged before melting are determined so that the component in the element concentration region after melting and solidifying together with the material surface becomes the target component.

  However, if the material to be added is too large, it causes segregation of alloy components. And when the segregation of an alloy component exists, desired performance cannot fully be exhibited, or deterioration will be accelerated. For this reason, it is important to make the size of the alloy material completely melted while the heated portion on the surface of the titanium base material is in a molten state. In addition, it is important that the alloy material is evenly arranged on the surface of the titanium base material in consideration of the shape and size of the melted part at a specific time. However, when the irradiation position is continuously moved using the electron beam, the molten part is stirred while moving continuously with the molten titanium and the alloy, so that the alloy material is always arranged continuously. There is no need. In addition, it is natural that the use of an alloy material having a melting point extremely higher than that of titanium must be avoided.

  After the melt resolidification treatment, it is preferable to hold at a temperature of 100 ° C. or higher and lower than 500 ° C. for 1 hour or longer. If it is cooled rapidly after melting and resolidification, fine cracks may occur in the surface layer due to strain during solidification. In the subsequent hot rolling process and cold rolling process, the fine cracks may be the starting point, and the surface layer may be peeled off, or a part having a partially thin alloy layer may be generated. Further, if the inside is oxidized due to fine cracks, it is necessary to remove in the pickling process, and the thickness of the alloy layer is further reduced. By maintaining at the above temperature, fine cracks on the surface can be suppressed. At this temperature, atmospheric oxidation hardly occurs even if the temperature is maintained.

  The titanium material for hot rolling provided with a surface layer portion formed by melt re-solidification treatment on the surface of the base material is used at the interface between the base material and the surface layer portion in the subsequent heat treatment process during hot rolling and after cold rolling. When diffusion occurs and finally the titanium composite material is finished, there is a concentration gradient of a specific element between the inner layer derived from the base material and the surface layer derived from the surface layer portion, and an intermediate layer is formed. For this reason, this intermediate | middle layer makes the said inner layer and the said surface layer metal-bond, and joins firmly. Further, since a continuous element gradient is generated in the intermediate layer, the difference in strength between the inner layer and the surface layer can be reduced, and cracks during processing can be suppressed.

  Further, when alloying by melt re-solidification treatment, the shape of the melted portion is curved as described above, so that the shape is also inherited in the final product. And during hot rolling heating, heat treatment after hot rolling, heat treatment after cold rolling, etc., the alloy element diffuses and joins from the interface with the curved base material, so if the element diffusion direction is only in the depth direction In addition, diffusion also occurs in the width direction. Therefore, the gradient of the alloy element in the intermediate portion between the base material and the alloy layer occurs not only in the depth direction but also in the width direction. Therefore, for example, when elements having different solid solution strengthening capabilities are added, the strength difference occurs not only in the direction perpendicular to the depth direction but also in the parallel direction, and the concentration gradient becomes complicated, so that cracks due to the strength difference are unlikely to occur. Become.

  The base metal surface may be melted and re-solidified, and a titanium plate containing a predetermined alloy component may be further attached to the surface layer portion to produce a hot-rolled titanium material.

  FIG. 8 is an explanatory view schematically showing that a titanium rectangular cast piece (slab) 6 and a titanium plate 7 in which a surface layer portion is formed by melting and resolidifying the surface of a base material are bonded together by welding in a vacuum. FIG. 9 is an explanatory view schematically showing that the titanium plates 7 and 8 are bonded together by welding not only on the surface of the titanium rectangular cast slab (slab) 6 but also on the side surfaces. In the following description, the titanium rectangular slab 6 (slab) 6 in which the surface of the base material is formed by melting and re-solidifying the base material surface is referred to as “titanium slab 6”.

  As shown in FIGS. 8 and 9, after the titanium plates 7 and 8 containing the alloying element that expresses the characteristics are bonded to the surface layer of the titanium slab 6, the surface layer 3 of the titanium composite material is bonded by hot rolling cladding. , 4 are alloyed. That is, after the titanium plate 7 containing the alloy element is bonded to the surface corresponding to the rolling surface of the titanium slab 6, the titanium slab 6 and titanium are preferably welded at least in the periphery by the weld 9 in a vacuum vessel. The space between the plates 7 is sealed with a vacuum, and the titanium slab 6 and the titanium plate 7 are bonded together by rolling. In welding the titanium plate 7 to the titanium slab 6, for example, as shown in FIGS. 8 and 7, the entire circumference is welded so that air does not enter between the titanium slab 6 and the titanium plate 7.

  Titanium is an active metal and forms a strong passive film on the surface when left in the atmosphere. It is impossible to remove the oxidized layer on the surface. However, unlike stainless steel, etc., oxygen easily dissolves in titanium. Therefore, when heated in a vacuum and sealed without external oxygen supply, oxygen on the surface diffuses into the solid solution. Therefore, the passive film formed on the surface disappears. Therefore, the titanium slab 6 and the titanium plate 7 on the surface thereof can be completely adhered to each other by the hot-rolled clad method without any inclusions being generated therebetween.

  Furthermore, when the as-cast slab is used as the titanium slab 6, surface defects are generated in the subsequent hot rolling process due to coarse crystal grains generated during solidification. On the other hand, when the titanium plate 7 is bonded to the rolled surface of the titanium slab 6 as in the present invention, the bonded titanium plate 7 has a fine structure, so that surface defects in the hot rolling process can be suppressed.

  When the titanium composite shown in FIG. 1 is manufactured, it is preferable that a titanium plate 7 is bonded to only one surface of the titanium slab 6 in a vacuum as shown in FIG. You may hot-roll without sticking 7.

  As shown in FIG. 9, a titanium plate 7 may be bonded to both sides of the titanium slab 6 instead of just one side. Thereby, generation | occurrence | production of the hot rolling in a hot rolling process can be suppressed as mentioned above. In hot rolling, at least a part of the side surface of the titanium slab 6 usually wraps around the surface side of the hot-rolled sheet by being rolled down by the titanium slab 6. Therefore, if the structure of the surface layer on the side surface of the titanium slab 6 is coarse or a large number of defects are present, surface flaws may occur on the surface near both ends in the width direction of the hot-rolled sheet. For this reason, as shown in FIG. 9, the same standard titanium plate 8 is preferably bonded and welded to the side surface of the titanium slab 6 on the edge side during hot rolling as well as the rolled surface. Thereby, generation | occurrence | production of the surface flaw in the surface near the both ends of the width direction of a hot rolled sheet can be prevented effectively. This welding is preferably performed in a vacuum.

  In addition, although the amount by which the side surface of the titanium slab 6 wraps around during hot rolling varies depending on the manufacturing method, it is usually about 20 to 30 mm, and therefore it is not necessary to attach the titanium plate 8 to the entire side surface of the titanium slab 6. It is only necessary to attach the titanium plate 8 only to a portion corresponding to the amount of wraparound according to the method. By performing high-temperature long-time annealing after hot rolling, the base material-derived component can be contained in the titanium composite material. For example, a heat treatment at 700 to 900 ° C. for 30 hours is exemplified.

Methods for welding the titanium slab 6 and the titanium plates 7 and 8 include electron beam welding and plasma welding. In particular, since electron beam welding can be performed under high vacuum, the space between the titanium slab 6 and the titanium plates 7 and 8 can be made high vacuum, which is desirable. The degree of vacuum when the titanium plates 7 and 8 are welded in a vacuum is desirably a higher degree of vacuum of the order of 3 × 10 ⁻³ Torr or less.

  The titanium slab 6 and the titanium plate 7 are not necessarily welded in a vacuum vessel. For example, a vacuum suction hole is provided in the titanium plate 7 and the titanium plate 7 is overlapped with the titanium slab 6. After matching, the titanium slab 6 and the titanium plate 7 may be welded while evacuating the titanium slab 6 and the titanium plate 7 using a vacuum suction hole, and the vacuum suction hole may be sealed after welding.

3-2. Base material of hot-rolling titanium material The base material of the hot-rolling titanium material is usually manufactured by cutting and refining an ingot into a slab or billet shape by breakdown. In recent years, rectangular slabs that can be hot-rolled directly at the time of ingot production are sometimes produced and used for hot-rolling. When manufactured by breakdown, since the surface is relatively flat by breakdown, it is easy to disperse the material containing the alloy element relatively uniformly, and it is easy to make the element distribution of the alloy phase uniform.

  On the other hand, when the ingot directly manufactured in the shape of the hot-rolling material at the time of casting is used as the material, the cutting and refining process can be omitted, so that it can be manufactured at a lower cost. In addition, if the ingot is manufactured and then used after the surface is cut and refined, the same effect can be expected when it is manufactured through breakdown. In the present invention, an alloy layer may be stably formed on the surface layer, and an appropriate material may be selected according to the situation. For this reason, the base material is not particularly limited.

  For example, after assembling the slab and welding the surroundings, it is heated to 700 to 850 ° C. and bonded and rolled at 10 to 30%, and then heated at the β region temperature for 3 to 10 hours to diffuse the base material component to the surface layer portion. It is preferable to perform hot rolling later. This is because by performing hot rolling at a β-region temperature, the deformation resistance becomes low and rolling becomes easy.

4). Manufacturing method of titanium composite It is important to leave the alloy layer formed by the melt resolidification treatment as a final product, and it is necessary to suppress the removal of the surface layer due to scale loss and surface flaws as much as possible. Specifically, this is achieved by optimizing and appropriately adopting the following devices in the hot rolling process in consideration of the characteristics and capabilities of the equipment used for production.

4-1. Heating process When heating the raw material for hot rolling, scale loss can be suppressed by heating at low temperature for a short time, but the titanium material has low heat conduction, and if the inside of the slab is hot rolled at a low temperature, There is also a drawback that cracks are likely to occur, and optimization is performed to minimize the generation of scales according to the performance and characteristics of the heating furnace used.

4-2. Hot rolling process Also in the hot rolling process, if the surface temperature is too high, a large amount of scale is generated during sheet passing, and the scale loss increases. On the other hand, if it is too low, the scale loss is reduced, but surface flaws are likely to occur. Therefore, it is necessary to remove by surface pickling, and it is desirable to perform hot rolling in a temperature range in which surface flaws can be suppressed. . Therefore, it is desirable to perform rolling in the optimum temperature range. In addition, since the surface temperature of the titanium material decreases during rolling, it is desirable to minimize roll cooling during rolling and suppress the decrease in the surface temperature of the titanium material.

4-3. Pickling process Since the hot-rolled plate has an oxide layer on its surface, there is a descaling process for removing the oxide layer in the subsequent process. In titanium, after shot blasting, the oxide layer is generally removed by pickling with a nitric hydrofluoric acid solution. In some cases, the surface may be ground by grinding with a grindstone after pickling. After descaling, a two-layer or three-layer structure including an inner layer and a surface layer derived from the base material and the surface layer portion of the titanium material for hot rolling may be used.

  Since the scale generated in the hot rolling process is thick, usually a shot blasting process is performed as a pretreatment for the pickling process to remove a part of the scale on the surface, and at the same time, cracks are formed on the surface, and in the subsequent pickling process The liquid penetrates into the cracks and removes part of the base material. At this time, it is important to perform weak blasting without causing cracks on the surface of the base material, and it is necessary to select optimum blasting conditions according to the chemical components on the surface of the titanium material. Specifically, for example, by selecting an appropriate projecting material and optimizing the projecting speed (adjustable by the rotation speed of the emperor), a condition that does not cause a crack in the base material is selected. Since optimization of these conditions differs depending on the characteristics of the melt-resolidified layer formed on the surface of the titanium material, the optimum conditions may be determined in advance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.

  The slab, which is a base material for manufacturing the titanium composite 2 having the surface layers 3 and 4 containing a predetermined alloy, is cut by hot forging a Ti-5Al-1Fe alloy manufactured by vacuum arc melting. The produced 28-143 mm-thick slab was used. In addition, the chemical component of the titanium ingot in a present Example is Al: 5%, Fe: 1%, O: 0.15%. Using this titanium slab, an alloy element material of Mo, V, Nb is sprayed on the surface of the slab, melted and re-solidified, and a region (alloy layer) in which the alloy element is solid solution on the entire surface of the slab is 1 to 15 mm deep. Formed.

  The slab is heated to 950 ° C. and hot-rolled to a thickness of 5 mm, then heat-treated at 700 ° C. for 2 hours in an air atmosphere, and then descaled on both the front and back surfaces using shot blasting and nitric hydrofluoric acid. Processed.

  In addition to the present invention, using a titanium slab having no surface layer portion, similarly, hot rolling, heat treatment, and descaling steps were performed to produce a comparative example.

Each titanium plate produced above was exposed at 500 ° C. for 5 hours in a 1% by volume H ₂ + 99% by volume Ar atmosphere as a hydrogen absorption environment.

  The alloy element concentration of the surface layers 3 and 4 of each titanium plate is an average value as a result of performing a line analysis on the range from the surface to the lower end of the alloy concentrated portion using EPMA. The remainder is a component contained in industrial pure titanium except for contamination components such as O and C.

  From each titanium plate, an impact test piece having a plate thickness (4.8 to 5.0 mm) × 10 mm × 55 mm and 2 mmV notch was produced. The longitudinal direction of the test piece was the rolling direction, and the notch direction was the plate thickness penetration direction. Hydrogen brittleness was evaluated by impact value.

When the impact value was evaluated without exposing a titanium plate having a molten layer on the surface layer to a hydrogen environment, it was 20 J / cm ² . From the value, the case of 14 J / cm ² or less, which was reduced by 30% or more, was determined to be unacceptable on the basis of hydrogen embrittlement.

  The results are summarized in Table 1.

なお、表層部には、スラブ（母材）に由来する元素が含まれる。ただし、表の「表層部の組成」には、スラブに含まれない元素については、その含有量を示し、スラブにも含まれる元素については、含有量の増加分がある場合には、その増加含有量を示し、含有量の増加分がない場合には、「−」を示している。

The surface layer portion includes an element derived from a slab (base material). However, the “surface layer composition” in the table indicates the content of elements that are not included in the slab, and for elements that are also included in the slab, if there is an increase in the content, increase the content. The content is shown, and “-” is shown when there is no increase in content.

No. 1 is a case where a surface layer portion (alloy concentrated layer) is not formed, and the impact value after exposure to a hydrogen environment is as low as 13 J / cm ² .

  No. No. 2, the thickness of the surface layer portion is within the range of the present invention, but the Mo equivalent is low, and the impact value after exposure to a hydrogen environment is also low.

  No. No. 3, Mo equivalent is within the scope of the present invention, but segregation of the surface layer part is outside the scope of the present invention, and the impact value after exposure to a hydrogen environment is low.

No. As for 4-8, the thickness and Mo equivalent of a surface layer part satisfy | fill the range of this invention, and an impact value is as high as 16 J / cm < ² > or more.

  No. 9, 10, and 15 have Mo equivalents outside the scope of the present invention.

  No. 11-14 is the range of this invention, and the impact value after exposure to a hydrogen environment is high.

  A 70 mm thickness of Ti-6Al-4V produced by vacuum arc melting, forging and cutting processes was used for the slab to be the base material. Using this titanium slab, Mo, V, and Nb alloy element materials are sprinkled on the slab surface, melted and re-solidified, and a region (surface layer part) where the alloy element is solid solution on the entire surface of the slab is 3 to 10 mm deep. Formed.

  The slab is heated to 950 ° C. and hot-rolled to a thickness of 5 mm, then heat-treated at 700 ° C. for 2 hours in an air atmosphere, and then descaled on both the front and back surfaces using shot blasting and nitric hydrofluoric acid. Processed.

  In addition to the present invention, using a titanium slab having no surface layer portion, similarly, hot rolling, heat treatment, and descaling steps were performed to produce a comparative example.

As in Example 1, hydrogen embrittlement was evaluated by impact value. When the impact value was evaluated without exposing a titanium plate having a molten layer on the surface layer to a hydrogen environment, it was 20 J / cm ² . From the value, the case of 14 J / cm ² or less, which was reduced by 30% or more, was determined to be unacceptable on the basis of hydrogen embrittlement.

  The above results are summarized in Table 2.

なお、表層部には、スラブ（母材）に由来する元素が含まれる。ただし、表の「表層部の組成」には、スラブに含まれない元素については、その含有量を示し、スラブにも含まれる元素については、含有量の増加分がある場合には、その増加含有量を示し、含有量の増加分がない場合には、「−」を示している。

The surface layer portion includes an element derived from a slab (base material). However, the “surface layer composition” in the table indicates the content of elements that are not included in the slab, and for elements that are also included in the slab, if there is an increase in the content, increase the content. The content is shown, and “-” is shown when there is no increase in content.

No. 1 is a case where a surface layer portion (alloy concentrated layer) is not formed, and the impact value after exposure to a hydrogen environment is as low as 14 J / cm ² .

No. In Nos. 2 to 4, the thickness of the surface layer portion and the Mo equivalent are within the range of the present invention, and the impact value after exposure to a hydrogen environment is 15 J / cm ² or more and is high.

  Two types of 70 mm thick pure titanium produced by vacuum arc melting, forging, and cutting processes were used for the slab to be the base material. Using this titanium slab, an alloy element material of Mo was sprayed on the surface of the slab and melted and re-solidified to form a region (surface layer portion) having a depth of 3 to 10 mm in which the alloy element was dissolved in the entire surface of the slab.

  The slab was heated to 850 ° C. and hot-rolled to a thickness of 4.8 to 5.0 mm, and then annealed at 600 to 650 ° C. for 4 to 10 hours in a vacuum atmosphere. Next, descaling treatment was performed on both the front and back surfaces using shot blasting and nitric hydrofluoric acid.

Each titanium plate produced above was exposed at 500 ° C. for 5 hours in a 1% by volume H ₂ + 99% by volume Ar atmosphere as a hydrogen absorption environment.

  The alloy element concentration of the surface layers 3 and 4 of each titanium plate is an average value as a result of performing a line analysis on the range from the surface to the lower end of the alloy concentrated portion using EPMA. The remainder is a component contained in industrial pure titanium except for contamination components such as O and C.

  From each titanium plate, an impact test piece having a plate thickness (4.8 to 5.0 mm) × 10 mm × 55 mm and 2 mmV notch was produced. The longitudinal direction of the test piece was the rolling direction, and the notch direction was the plate thickness penetration direction. Hydrogen brittleness was evaluated by impact value.

When the impact value was evaluated without exposing the titanium plate having the melt layer formed on the surface layer to a hydrogen environment, it was 2.7 J / cm ² . From the value, the case of 1.9 J / cm ² or less, which was reduced by 30% or more, was determined to be unacceptable on the basis of hydrogen embrittlement.

  The results are summarized in Table 3.

なお、表層部には、スラブ（母材）に由来する元素が含まれる。ただし、表の「表層部の組成」には、スラブに含まれない元素については、その含有量を示し、スラブにも含まれる元素については、含有量の増加分がある場合には、その増加含有量を示し、含有量の増加分がない場合には、「−」を示している。

The surface layer portion includes an element derived from a slab (base material). However, the “surface layer composition” in the table indicates the content of elements that are not included in the slab, and for elements that are also included in the slab, if there is an increase in the content, increase the content. The content is shown, and “-” is shown when there is no increase in content.

No. 1 to 3, the surface layer thickness and Mo equivalent are within the scope of the present invention, and the impact value after exposure to a hydrogen environment is 15 J / cm ² or more, which is high.

1. Titanium materials for hot rolling 1a, 1aa, 1ab. Surface layer part 1b. Base material 2. Titanium composite 3,4. Surface layer (surface layer)
5). Inner layer

Claims (2)

A base material made of pure titanium or titanium alloy for industrial use;
A titanium layer for hot rolling comprising a surface layer portion having a chemical composition different from that of the base material formed on at least one rolling surface of the base material,
The surface layer portion has a thickness of 2.0 to 20.0 mm, and the proportion of the total thickness is 40% or less per side,
The chemical composition of the surface layer part is an increased content from the base material,
One or more selected from Mo, V and Nb are contained, and the Mo equivalent calculated by the following formula (1) is 8.0 to 20.0.
When the content of the element contained in the surface layer is measured at a plurality of points, the relationship between the average value C _AVE of the increased content from the base material and the increased content C ₀ from the base material at each measurement location: | C _AVE −C ₀ | / C _AVE × 100 is 40% or less,
Titanium material for hot rolling.
Mo equivalent = Mo content (% by mass) + V content (% by mass) /1.5+Nb content (% by mass) /3.6 (1) Other surface layer portions are formed on surfaces other than the rolling surface of the base material,
The other surface layer portion has the same chemical composition and metal structure as the surface layer portion.
The titanium material for hot rolling according to claim 1.

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