JP6787428B2 - Titanium material for hot rolling - Google Patents

Description

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

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

Titanium material is being widely used in the aircraft field due to its excellent specific strength and corrosion resistance, and is also widely used in exhaust systems for automobiles and motorcycles. In particular, instead of the conventional stainless steel material, JIS2 type industrial pure titanium material is used mainly for motorcycles from the viewpoint of reducing the weight of the vehicle. Further, in recent years, a heat-resistant titanium alloy having higher heat resistance has been used in place of the JIS2 type industrial pure titanium material. In addition, a muffler equipped with a catalyst used at a high temperature is also used to remove harmful components of exhaust gas.

The temperature of the exhaust gas exceeds 700 ° C. and may temporarily reach 800 ° C. Therefore, the material used for the exhaust device is required to have strength, oxidation resistance, etc. at a temperature of about 800 ° C., and an index of high temperature heat resistance of creep speed at 600 to 700 ° C. is becoming more important. ing.

On the other hand, in order to improve the high temperature strength of such a heat resistant titanium alloy, it is necessary to add elements such as Al, Cu and Nb that improve the high temperature strength and oxidation resistance, which is higher in cost than pure titanium for industrial use.

In Japanese Patent Application Laid-Open No. 2001-234266 (Patent Document 1), Al: 0.5 to 2.3% (in the present specification, "%" relating to a chemical component means "mass%" unless otherwise specified). A titanium alloy having excellent cold workability and high temperature strength is disclosed.

Japanese Unexamined Patent Publication No. 2001-89921 (Patent Document 2) contains Fe: more than 1% and 5% or less, O (oxygen): 0.05 to 0.75%, and Si: 0.01 · e ^0. A titanium alloy containing ^{5 [Fe] to} 5 · e- ^{0.5 [Fe]} and having excellent oxidation resistance and corrosion resistance ([Fe] indicates the content (% by mass) in the alloy, and e is a constant of the natural logarithm. Is disclosed).

Japanese Patent Laying-Open No. 2005-290548 (Patent Document 3) describes a heat-resistant titanium alloy plate containing Al: 0.30 to 1.50% and Si: 0.10 to 1.0% and having excellent cold workability. The manufacturing method is disclosed.

Japanese Unexamined Patent Publication No. 2009-68026 (Patent Document 4) contains Cu: 0.5 to 1.8%, Si: 0.1 to 0.6%, O: 0.1% or less, and is required. Correspondingly, a titanium alloy containing Nb: 0.1 to 1.0% and having a protective film coated on a surface having a balance of Ti and unavoidable impurities is disclosed.

Further, Japanese Patent Application Laid-Open No. 2013-142183 (Patent Document 5) contains Si: 0.1 to 0.6%, Fe: 0.04 to 0.2%, and O: 0.02 to 0.15%. Disclosed is a titanium alloy containing, having a total content of Fe and O of 0.1 to 0.3%, and having excellent high temperature strength at 700 ° C. and oxidation resistance at 800 ° C. consisting of the balance Ti and unavoidable impurity elements. ing.

Titanium material is usually produced by the method shown below. First, by the Kroll process, titanium oxide, which is a raw material, is chlorinated to obtain titanium tetrachloride, and then reduced with magnesium or sodium to produce massive and sponge-like metallic titanium (sponge titanium). This sponge titanium is press-molded into a titanium consumable electrode, and the titanium consumable electrode is used as an electrode to melt in a vacuum arc to manufacture a titanium ingot. At this time, alloying elements are added as needed to produce a titanium alloy ingot. After that, the titanium alloy ingot is agglomerated, forged, and rolled to obtain a titanium slab, and the titanium slab is hot-rolled, annealed, pickled, cold-rolled, and vacuum-heat-treated to produce a titanium thin plate.

In addition, as a method for producing a titanium thin plate, a titanium ingot is agglomerated, hydrogenated, dehydrogenated, powdered, and classified to produce titanium powder, and the titanium powder is powder-rolled, sintered, and cold-rolled. The method of manufacturing is also known.

Japanese Patent Application Laid-Open No. 2011-42828 (Patent Document 6) describes titanium metal powder, a binder, and plastics in order to produce titanium powder directly from sponge titanium instead of titanium ingot and to produce a titanium thin plate from the obtained titanium powder. A pre-sintered molded body obtained by molding a viscous composition containing an agent and a solvent into a thin plate is sintered to produce a sintered thin plate, and the sintered thin plate is compacted to produce a sintered compact thin plate. In the method for producing a titanium thin plate for re-sintering, a method is disclosed in which the breaking 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.

According to Japanese Patent Application Laid-Open No. 2014-19945 (Patent Document 7), an appropriate amount of iron powder, chromium powder or copper powder is added to titanium alloy powder made from titanium alloy scrap or titanium alloy ingot to form a composite powder. Is extruded into carbon steel capsules, and the capsules on the surface of the obtained round bar are dissolved and removed, and then solution treatment, solution treatment and aging treatment are performed to produce a titanium alloy with excellent quality by the powder method. The method is disclosed.

According to Japanese Patent Application Laid-Open No. 2001-131609 (Patent Document 8), a copper sponge powder is filled in a copper capsule and then warmly extruded at an extrusion ratio of 1.5 or more and an extrusion temperature of 700 ° C. or less to form the outside. Disclosed is a method for producing a titanium molded product in which 20% or more of the total length of the grain boundaries of the molded product is in metal contact with the outer circumference processed except for copper.

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

Specifically, for example, a release agent is applied to the surface of the core material, and at least the upper and lower two 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 surrounding surfaces are welded. Assemble and hot roll. In pack rolling, the core material to be rolled is covered with a cover material and hot-rolled. Therefore, the surface of the core material does not come into direct contact with a cold medium (atmosphere or roll), and the temperature drop of the core material can be suppressed, so that even a core material having poor workability can be manufactured as a thin plate.

Japanese Patent Application Laid-Open No. 63-207401 (Patent Document 9) discloses a method for assembling a sealed coated box, and Japanese Patent Application Laid-Open No. 09-136102 (Patent Document 10) discloses a vacuum degree of ^10-3 torr or more. to process for producing a sealing covering box to seal the cover material is disclosed, further, Japanese Unexamined 11-057810 (Patent Document 11), ¹⁰ -2 torr order covered carbon steel (cover material) A method of manufacturing a sealed cladding box by sealing by high energy density welding under the following vacuum is disclosed.

On the other hand, as a method for inexpensively producing a material having high corrosion resistance, a method of joining a titanium material to the surface of a material as a base material is known.

Japanese Patent Application Laid-Open No. 08-141754 (Patent Document 12) uses a steel material as a base material and titanium or a titanium alloy as a laminated material, and assembles by welding after vacuum exhausting the joint surface between the base material and the laminated material. A method for manufacturing a titanium clad steel sheet in which an assembly slab for rolling is joined by hot rolling is disclosed.

Japanese Patent Application Laid-Open No. 11-170076 (Patent Document 13) states that 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 laminating and arranging the titanium foil material with an insert material having a thickness of 20 μm or more made of any of the low carbon steels of the above, the titanium foil material is irradiated with a laser beam from either side of the laminating direction. A method for producing a titanium-coated steel material by melt-joining at least the vicinity of the edge portion with the base steel material over the entire circumference is disclosed.

In Japanese Patent Application Laid-Open No. 2015-045040 (Patent Document 14), the surface of a porous titanium raw material (sponge titanium) formed into an ingot shape is melted under vacuum using an electron beam to form a dense titanium surface layer. Titanium ingot was manufactured, and by hot rolling and cold rolling, the porous titanium raw material was formed into an ingot shape, and the entire surface of the porous portion was composed of dense titanium. An example is a method of producing a dense titanium material (titanium ingot) having a densely coated portion for coating with very little energy.

Japanese Patent Application Laid-Open No. 62-270277 (Patent Document 15) describes that surface effect treatment of an automobile engine member is performed by thermal spraying.

Japanese Unexamined Patent Publication No. 2001-234266 Japanese Unexamined Patent Publication No. 2001-89821 Japanese Unexamined Patent Publication No. 2005-290548 JP-A-2009-68026 Japanese Unexamined Patent Publication No. 2013-142183 Japanese Unexamined Patent Publication No. 2011-42828 JP-A-2014-199945 Japanese Unexamined Patent Publication No. 2001-131609 JP-A-63-207401 Japanese Unexamined Patent Publication No. 09-136102 Japanese Unexamined Patent Publication No. 11-057810 Japanese Unexamined Patent Publication No. 08-141754 Japanese Unexamined Patent Publication No. 11-170076 JP-A-2015-045040 Japanese Unexamined Patent Publication No. 62-270277

Since the titanium alloy disclosed in Patent Document 1 contains Al, it adversely affects the molding processability, particularly the overhang formability in which processing occurs in the direction of reducing the wall thickness.

In the titanium alloy disclosed in Patent Document 2, since the total content of Fe and O is large, the strength at room temperature exceeds 800 N / mm ² and the elongation is 20% or less, which is poor in moldability.

In the titanium alloy disclosed in Patent Document 3, since Al is added as described above, there is a possibility that the cold workability, particularly the overhang formability in which the work occurs in the direction of reducing the wall thickness, is adversely affected.

Although the titanium alloy disclosed in Patent Document 4 has sufficient processability and oxidation resistance, it contains a large amount of expensive Nb, which increases the alloy cost.

Further, although the titanium alloy disclosed in Patent Document 5 also has sufficient high-temperature oxidation characteristics, the entire surface of the plate is alloyed, so that the alloy cost increases.

Conventionally, when manufacturing titanium material through hot rolling, titanium sponge is press-molded to form a titanium consumable electrode, and the titanium consumable electrode is used as an electrode to melt a vacuum arc to produce a titanium ingot, and then the titanium ingot is lumped. , Forged and rolled to form titanium slabs, which were manufactured by hot rolling, annealing, pickling and cold rolling.

In this case, a step of melting titanium to produce a titanium ingot was always 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 melting titanium is also added.

In the method for producing a titanium material from titanium powder, since expensive titanium powder is used as a raw material even if it does not go through a melting step, the obtained titanium material becomes very expensive. The same applies to the methods disclosed in Patent Documents 9 to 10.

In pack rolling, the core material covered with the cover material is only a slab or an ingot, which has undergone a melting process or is made from expensive titanium powder, and the manufacturing cost cannot be reduced.

In Patent Document 14, although a dense titanium material can be produced with very little energy, the surface of titanium sponge formed into an ingot is melted and the dense titanium surface layer and internal components are the same type of pure titanium. Alternatively, it is defined as a titanium alloy, and for example, it is not possible to reduce the manufacturing cost by forming the titanium alloy layer uniformly and over a wide range only on the surface layer portion.

On the other hand, steel is selected as the base material for most of the materials in which titanium or a titanium alloy is bonded to the surface of the base material, which can produce an inexpensive corrosion-resistant material. Therefore, if the titanium layer on the surface is lost, the corrosion resistance is impaired. Even if a titanium material is used as the base material, no drastic cost improvement can be expected as long as the titanium material manufactured through a normal manufacturing process is used. Therefore, the present inventors have considered providing an alloy layer containing a specific alloying 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 has excellent specific performance.

As in Patent Document 15, thermal spraying is a method in which a metal, ceramics, or the like is melted and sprayed onto the surface of a titanium material to form a film. When the film is formed by this method, the formation of pores in the film cannot be avoided. Normally, 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. The pores containing such an inert gas are not crimped by hot working or the like. Further, in the production of titanium, vacuum heat treatment is generally performed, but during this treatment, the inert gas in the pores may expand and the film may peel off. In the experience of the present inventors, the abundance rate (porosity) of pores generated by thermal spraying is several vol. % Or more, and depending on the thermal spraying conditions, 10 vol. May exceed%. As described above, the titanium material having a high porosity in the film has a risk of peeling in the manufacturing process, and there is a risk of defects such as cracks during processing.

As a method for forming a film, there is a cold spray method. When forming a film on the surface by this method, an inert high-pressure gas is also used. In this method, the porosity is set to 1 vol. Depending on the conditions. Although it is possible to make it less than%, it is extremely difficult to completely prevent the formation of pores. Since the pores contain an inert gas as in the case of thermal spraying, they do not disappear by subsequent processing. Further, when the heat treatment is performed in a vacuum, the inert gas in the pores may expand and the film may crack.

There is a melt recoagulation treatment as a treatment for melting and recoagulating the surface layer of the slab using an electron beam in order to suppress surface defects during hot spreading. Usually, the melt-resolidified surface layer is removed by a pickling step after hot spreading. The present inventors have focused on this melt resolidification treatment. That is, the present inventors have stated that when the surface layer of a slab is melted, a specific alloy element is melted and solidified together with a slab-derived component to form a surface layer portion containing the specific alloy element in the slab. I thought about it. However, the melt resolidification treatment for the purpose of suppressing surface defects during hot spreading cannot be used as it is for forming a surface layer portion containing a specific alloying 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 the segregation of the alloy component of the surface layer portion is not considered at all.

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

The present invention reduces the content of alloying elements added to improve oxidation resistance (the amount of specific alloying elements that exhibit target characteristics), and suppresses the manufacturing cost of titanium material. It is an object of the present invention to obtain a titanium material for hot rolling having desired characteristics at low cost.

The present invention has been made to solve the above problems, and the following titanium materials for hot rolling are the gist of the present invention.

(1) Titanium for hot rolling including a base material made of industrial pure titanium or a titanium alloy and a surface layer portion formed on at least one of the rolled surfaces of the base material and having a chemical composition different from that of the base material. The thickness of the surface layer portion of the material is 2.0 to 20.0 mm, the ratio to the total thickness is 40% or less per side, and the chemical composition of the surface layer portion is increased from that of the base material. As the content, in mass%, Si: 0.1 to 0.6%, Nb: 0.1 to 2.0%, Ta: 0.3 to 1.0% and Al: 0.3 to 1.5. One or more selected from%, Sn: 0 to 1.5%, Cu: 0 to 1.5%, Fe: 0 to 0.5%, and the content of the element contained in the surface layer portion is a plurality of points. 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 point when measured: | C _AVE −C ₀ | / C _AVE × 100 is 40% or less Titanium material for hot rolling.

(2) Another surface layer portion is formed on a surface other than the rolled surface of the base metal.
The other surface layer portion has the same chemical composition and metallic structure as the surface layer portion.
The titanium material for hot rolling in (1) above.

Since the titanium material for hot rolling according to the present invention includes 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, it is manufactured using the base material. The titanium composite material has the same oxidation resistance as the titanium material made of the same titanium alloy as a whole, but can be manufactured at low cost.

FIG. 1 is an explanatory diagram showing an example of the configuration of a titanium material for hot rolling according to the present invention. FIG. 2 is an explanatory diagram showing another example of the configuration 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 resolidification. FIG. 6 is an explanatory diagram showing a method of melt resolidification. FIG. 7 is an explanatory diagram showing a method of melt resolidification. FIG. 8 is an explanatory view schematically showing that a titanium rectangular slab and a titanium plate are bonded by welding in a vacuum. FIG. 9 is an explanatory view schematically showing that titanium plates are welded together not only on the surface but also on the side surface of a titanium rectangular slab.

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

1. 1. Titanium material for hot rolling 1-1. Overall Structure As shown in FIG. 1, the titanium material 1 for hot rolling according to the present invention includes a base material 1b and a surface layer portion 1a on the rolled 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 be provided with surface layer portions 1aa and 1ab on both rolling surfaces of the base material 1b. As described above, the oxidation resistance of the titanium material 1 for hot rolling is ensured by the surface layer portion 1a (1aa, 1ab in the example shown in FIG. 2) in contact with the external environment. This titanium material 1 for hot rolling has the same oxidation resistance as a titanium material made entirely of the same titanium alloy, but can be manufactured at low cost.

When the titanium material for hot rolling is a rectangular titanium slab, the dimensions are not particularly limited as long as they can be used for hot rolling as they are. When coil rolling is applied as hot rolling to produce a hot-rolled coil thin medium plate with a plate thickness of about 3 to 8 mm, the rectangular titanium slab 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 will also be thin, and the desired characteristics cannot be sufficiently obtained. On the other hand, if it is too thick, the ratio of the titanium alloy to the entire titanium composite material increases, so that the cost merit becomes small. 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 portion to the total thickness shall be 40% or less per side.

1-2. Base material The base material 1 is made of industrial pure titanium or a titanium alloy. However, by using a titanium alloy, superior mechanical properties (strength, ductility, etc.) can be obtained as compared with the case of using industrial pure titanium.

As the base material 1, among the pure titanium specified in JIS, JIS 1 to 4 types of industrial pure titanium can be used. That is, it contains 0.1% or less of C, 0.015% or less of H, 0.4% or less of O, 0.07% or less of N, and 0.5% or less of Fe, and the balance is Ti. It is pure titanium for industrial use. If these JIS1 to 4 types of pure industrial titanium are used, a titanium material having sufficient workability, no cracking, etc., and integrated with the titanium alloy on the surface 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 the α-type titanium alloy, for example, 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- 6Al-2.75Sn-4Zr-0.4Mo-0.45Si and the like are exemplified.

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, and Ti-4.5Al-2Fe-2V-3Mo.

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 produced by a known production method such as a dissolution method or a powder metallurgy method, and is not particularly limited. For example, the base metal can be manufactured by cutting and rectifying the ingot into a slab or billet shape by breaking down. When manufactured by breakdown, since the surface is relatively flat due to breakdown, it is easy to disperse the elements containing the alloying elements relatively uniformly, and it is easy to make the element distribution of the alloy phase uniform.

On the other hand, an ingot directly produced at the time of casting can also be used as a base material. In this case, since the cutting and adjusting step can be omitted, the manufacturing can be performed at a lower cost. Further, if the ingot is used after the ingot is manufactured and the surface is cut and refined, the same effect can be expected when the ingot is manufactured through breakdown.

1-3. Surface layer (chemical composition)
Oxidation of titanium takes an oxidation form called inward diffusion, which occurs when oxygen diffuses in the oxide film and binds to titanium on the surface. Therefore, if the diffusion of oxygen is suppressed, the oxidation is suppressed. In titanium alloys, alloying elements such as Si and Nb are added to improve the oxidation resistance at high temperatures of 600 to 800 ° C. When Si is added, silicon oxide is formed on the surface layer when exposed to a high temperature atmosphere to serve as a barrier, so that the diffusion of oxygen into titanium is suppressed and the oxidation resistance is improved. Further, Nb is dissolved in the oxide film of titanium, and titanium is tetravalent, whereas it is pentavalent, so that the pore concentration of oxygen in the oxide film is lowered and oxygen is diffused in the oxide film. Is suppressed.

In order to enhance the oxidation resistance of at least one surface layer (at least the surface layer in contact with the external environment) of the titanium composite material produced from the titanium material for hot rolling of the present invention, the surface layer portion 1a of the titanium material for hot rolling is provided. Contains various alloying elements listed below.

Si: 0.1-0.6%
Si has an action of improving oxidation resistance at a high temperature of 600 to 800 ° C. When the Si content is less than 0.1%, the margin for improving the oxidation resistance is small. On the other hand, when the Si content exceeds 0.6%, the influence on the oxidation resistance is saturated and the workability at not only room temperature but also high temperature is remarkably lowered. Therefore, when Si is contained, the content is set to 0.1 to 0.6%. The Si content is preferably 0.15% or more, and more preferably 0.20% or more. Further, it is preferably 0.55% or less, and more preferably 0.50% or less.

Nb: 0.1 to 2.0%
Nb also has the effect of improving the oxidation resistance at high temperatures. In order to improve the oxidation resistance, the Nb content is 0.1% or more. On the other hand, even if the Nb content exceeds 2.0%, the effect is saturated and Nb is an expensive additive element, which leads to an increase in alloy cost. Therefore, when Nb is contained, the content is set to 0.1 to 2.0%. The Nb content is preferably 0.3% or more, and more preferably 0.5% or more. Further, it is preferably 1.5% or less, and more preferably 1.0% or less.

Ta: 0.3-1.0%
Ta also has the effect of improving the oxidation resistance at high temperatures. In order to improve the oxidation resistance, the Ta content is set to 0.3% or more. On the other hand, even if the Ta content exceeds 1.0%, Ta is an expensive additive element, which not only leads to an increase in alloy cost, but also may cause β phase formation depending on the heat treatment temperature. .. Therefore, when Ta is contained, the content is set to 0.3 to 1.0%. The Ta content is preferably 0.4% or more, more preferably 0.5% or more. Further, it is preferably 0.9% or less, and more preferably 0.8% or less.

Al: 0.3-1.5%
Al is also an element that improves oxidation resistance at high temperatures. On the other hand, when Al is contained in a large amount, the ductility at room temperature is significantly reduced. When the Al content is 0.3% or more, the oxidation resistance property is sufficiently exhibited. Further, when the Al content is 1.5% or less, cold processing can be sufficiently guaranteed. Therefore, when Al is contained, the content is set to 0.3 to 1.5%. The Al content is preferably 0.4% or more, and more preferably 0.5% or more. Further, it is preferably 1.2% or less.

If Si, Nb, Ta and Al are contained alone, the oxidation resistance is improved, but if they are contained in combination, the high temperature oxidation resistance can be further improved.

In addition to the above elements, one or more selected from Sn, Cu and Fe may be contained.

Sn: 0 to 1.5%
Sn is an α-phase stabilizing element and, like Cu, is an element that enhances high-temperature strength. However, when the Sn content exceeds 1.5%, twinning deformation is suppressed and workability at room temperature is lowered. Therefore, when Sn is contained, the content is set to 1.5% or less. The Sn content is preferably 1.3% or less, more preferably 1.2% or less. When the above effect is desired, the Sn content is preferably 0.2% or more, and more preferably 0.5% or more.

Cu: 0-1.5%
Cu is an element that enhances high temperature strength. Moreover, since it dissolves in the α phase to a certain extent, it does not form a β phase even when used at a high temperature. However, if the Cu content exceeds 1.5%, a β phase is formed depending on the temperature. Therefore, when Cu is contained, the content is set to 1.5% or less. The Cu content is preferably 1.4% or less, more preferably 1.2% or less. When the above effect is desired, the Cn content is preferably 0.2% or more, and more preferably 0.4% or more.

Fe: 0-0.5%
Fe is a β-phase stabilizing element, but if it is in a small amount, β-phase is less generated and does not significantly affect the oxidation resistance. However, when the Fe content exceeds 0.5%, the amount of β phase produced increases, and the oxidation resistance deteriorates. Therefore, when Fe is contained, the content is set to 0.5% or less. The Fe content is preferably 0.4% or less, more preferably 0.3% or less.

When the total content of Sn, Cu and Fe exceeds 2.5%, the workability at room temperature is lowered, and a β phase is formed depending on the temperature. Therefore, when one or more selected from Sn, Cu and Fe are contained, the total content thereof is preferably 2.5% or less.

The rest other than the above is titanium and impurities. Impurities can be contained within a range that does not impair the target characteristics, and other impurities mainly include Cr, V, Cr, Mn, Mo and the like as impurity elements mixed from scrap, and are general impurity elements. Together with C, N, O and H, a total amount of 5% or less is acceptable.

The surface layer contains elements derived from the slab (base material). Therefore, the content of each element in the surface layer means the content of the element not contained in the slab, and the increased content of the element contained in the slab (increased content from the base material). To do.

2. Titanium composite material The titanium material for hot rolling of the present invention is a material (slabs, blooms, billets, etc.) used for hot rolling, and after hot working, cold working, if necessary, It is processed into a titanium composite material by heat treatment. The titanium composite material includes an inner layer derived from the base material of the titanium material for hot rolling of the present invention and a surface layer derived from the surface layer portion.

(thickness)
If the surface layer in contact with the external environment is too thin, sufficient oxidation resistance cannot be obtained. The thickness of the surface layer varies depending on the thickness of the material used for manufacturing or the subsequent processing rate, but a sufficient effect is exhibited if it is 5 μm or more. Therefore, the thickness of the surface layer is preferably 5 μm or more, and more preferably 10 μm or more.

On the other hand, when the surface layer is thick, there is no problem in oxidation resistance, but the ratio of the titanium alloy to the entire titanium composite material is increased, so that the cost merit is reduced. Therefore, the ratio of the thickness of the surface layer to the total thickness of the titanium composite material (surface layer occupancy) is preferably 40% or less per side, and more preferably 30% or less.

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

(Porosity)
The porosity of the surface layer is preferably 0.1% or less. If the porosity exceeds 0.1%, the surface layer may swell or peel off when hot rolling is performed.

The porosity can be easily measured by taking a picture of the cross section of the material by observing it with an optical microscope and processing the picture. The porosity can be measured by observing any 10 to 20 points on the cross section, and the average thereof can be taken as the total porosity. The porosity of the material subjected to hot rolling or 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 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 point: | C _AVE − C ₀ | / C _AVE × 100 is 40% or less. This is because when C _AVE −C ₀ | / C _AVE × 100 exceeds 40%, the desired performance cannot be sufficiently exhibited or the desired performance deteriorates earlier. | 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, any 10 to 20 points on the surface layer are measured, and the average value of the increased content from the base material at each measurement point is defined as the increased content C ₀ at each measurement point, and the increased content C _0. the average value may be set to increase the content of the average value C _AVE in the surface layer.

(Middle layer)
The surface layer has 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 subjected to subsequent 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 metal-bonds the inner layer and the surface layer to firmly bond them. Further, since a continuous elemental gradient is generated in the intermediate layer, the difference in strength between the inner layer and the surface layer can be softened, and cracking 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. More detailed measurement is possible by using GDS. In the case of GDS, it is possible to measure the thickness of the intermediate layer by removing the surface layer by polishing to some extent and then 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 contained in the base material, its content, and in the case of an element also contained in the base material, the increased content from the base material). ) as the C _MID, when the average of the increase amount in the surface layer and the C _AVE, refers to a region of _{0 <C MID ≦ 0.8 × C} AVE.

3. 3. Manufacturing method of 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 the components derived from the base material. It can be produced by forming a surface layer portion containing the alloying element of. 5 to 7 are explanatory views showing a method of melt resolidification.

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

Further, since it has high energy efficiency, it can be deeply melted even if a large area is treated, so that it is particularly suitable for producing a titanium composite material. The degree of vacuum when melting in vacuum is preferably a higher degree of vacuum of 3 × 10 ^-3 Torr or less. The number of times the surface layer of the titanium material for hot rolling is melted and resolidified 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 of the material and the amount of additive elements added can be increased. 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, so it is desirable that the number of times is once or twice.

The surface layer melt resolidification method is carried out as shown in FIG. 5 in the case of a rectangular slab. That is, among the outer surfaces of the rectangular slab 10, at least the two wide surfaces 10A and 10B that are the rolled surfaces (surfaces in contact with the hot-rolled roll) in the hot rolling process are irradiated with an electron beam, and the surfaces on those surfaces are irradiated. Only the layer is melted. Here, it is assumed that the implementation is first performed on one of the two surfaces 10A and 10B, 10A.

Here, as shown in FIG. 5, the area of the electron beam irradiation region 14 by one electron beam irradiation gun 12 with respect to the surface 10A of the rectangular slab 10 is compared with the total area of the surface 10A to be irradiated. Therefore, in practice, the electron beam irradiation is 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 region 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 to form a beam bundle. can do.

Then, as shown by the arrow A in FIG. 5, the following description will proceed assuming that the electron beam irradiation gun 12 is continuously moved. The moving direction of the electron beam irradiation gun is not particularly limited, but 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. The irradiation region 14 is continuously irradiated in a band shape with a width W (in the case of a circular beam or a beam bundle, a diameter W). Further, the electron beam is irradiated in a band shape while continuously moving the irradiation gun 12 in the opposite direction (or the same direction) to the unirradiated band-shaped area adjacent to the band-shaped area. In some cases, a plurality of irradiation guns may be used to simultaneously irradiate a plurality of regions with an electron beam. FIG. 5 shows a case where the rectangular beam is continuously moved along the length direction (usually the casting direction D) of the rectangular slab 10.

By irradiating the surface (surface 10A) of the rectangular titanium slab 10 with an electron beam by such a surface heat treatment step and heating the surface so as to melt, as shown in the center left side of FIG. 6, rectangular titanium The surface layer of the surface 10A of the slab 10 is maximally melted by a depth corresponding to the amount of 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 is the largest at the central portion of the electron beam irradiation, and the thickness increases toward the end of the band. Is reduced, resulting in a downwardly convex curved shape.

Further, the temperature of the region on the inner side of the slab from the molten layer 16 also rises due to the thermal effect of electron beam irradiation, and the portion (thermal influence layer = HAZ layer) whose temperature is higher than the β transformation point of pure titanium is the β phase. Transform into. In this way, the region transformed into the β phase due to the thermal effect of the electron beam irradiation in the surface layer heat treatment step also has a downwardly convex curved shape similar to the shape of the molten layer 16.

The surface layer of the hot rolling material is alloyed by performing melt resolidification together with the material composed of the target alloying element. As the material used at this time, one or more of powder, chips, wires, thin films, chips, and mesh may be used. The components and amounts of the material to be placed before melting are determined so that the components in the element-concentrated region after melting and solidifying together with the surface of the material are the target components.

However, if the material to be added is too large, it causes segregation of alloy components. If segregation of the alloy component is present, the desired performance cannot be sufficiently exhibited or the deterioration is accelerated. For this reason, it is important to set the size so that the alloy material finishes melting while the heated portion on the surface of the titanium base material is in the molten state. Further, it is important to evenly distribute the alloy material on the surface of the titanium base material in consideration of the shape and width of the molten portion at a specific time. However, when the irradiation position is continuously moved by using an electron beam, the molten portion is agitated while continuously moving together with the molten titanium and the alloy, so that the alloy material is not necessarily arranged continuously. There is no need. In addition, it is natural that the use of alloy materials having a melting point extremely higher than the melting point of titanium should be avoided.

After the melt resolidification treatment, it is preferable to keep the temperature at 100 ° C. or higher and lower than 500 ° C. for 1 hour or longer. If it is cooled rapidly after melt resolidification, fine cracks may occur in the surface layer due to strain during solidification. In the subsequent hot rolling step or cold rolling step, the fine cracks may be the starting point, causing peeling of the surface layer portion, partial thinning of the alloy layer, and other deterioration of the characteristics. Further, when the inside is oxidized due to fine cracks, it is necessary to remove it in a pickling step, further reducing the thickness of the alloy layer. By holding at the above temperature, fine cracks on the surface can be suppressed. Further, at this temperature, even if it is kept in the atmosphere, there is almost no atmospheric oxidation.

The titanium material for hot rolling, which has a surface layer portion formed by melt resolidification treatment on the surface of the base metal, is used at the interface between the base metal and the surface layer portion in the subsequent heat treatment steps during hot rolling and after cold rolling. When diffusion occurs and the titanium composite material is finally 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. Therefore, this intermediate layer metal-bonds the inner layer and the surface layer to firmly bond them. Further, since a continuous elemental gradient is generated in the intermediate layer, the difference in strength between the inner layer and the surface layer can be softened, and cracking during processing can be suppressed.

Further, when alloying by melt resolidification treatment, the shape of the molten portion is curved as described above, so that shape is inherited by the final product. Then, during hot rolling heating, heat treatment after hot rolling, heat treatment after cold rolling, etc., the alloying elements diffuse and join from the interface with the curved base material, so if the diffusion direction of the elements is only in the depth direction However, diffusion also occurs in the width direction. Therefore, the gradient of the alloying element in the intermediate portion between the base metal 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 abilities 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 cracking due to the strength difference is unlikely to occur. Become.

A titanium plate for hot rolling may be produced by melt-resolidifying the surface of the base metal and further attaching a titanium plate containing a predetermined alloy component to the surface layer portion.

FIG. 8 is an explanatory view schematically showing that a titanium rectangular slab 6 and a titanium plate 7 having a surface layer formed by melting and resolidifying the surface of a base material are bonded by welding in a vacuum. FIG. 9 is an explanatory view schematically showing that titanium plates 7 and 8 are bonded to each other not only on the surface but also on the side surface of the titanium rectangular slab (slab) 6. In the following description, the titanium rectangular slab 6 in which the surface of the base metal is melted and resolidified to form the surface layer portion is referred to as “titanium slab 6”.

As shown in FIGS. 8 and 9, the surface layer 3 of the titanium composite material is formed by bonding titanium plates 7 and 8 containing alloying elements that exhibit characteristics to the surface layer of the titanium slab 6 and then joining them by a hot-roll clad method. , 4 are alloyed. That is, the titanium slab 6 and titanium are formed by laminating a titanium plate 7 containing an alloying element on the surface of the titanium slab 6 that corresponds to the rolled surface, and then welding at least the periphery with a welded portion 9 preferably in a vacuum vessel. The titanium slab 6 and the titanium plate 7 are bonded together by sealing the space between the plates 7 with a vacuum and rolling. In the welding of bonding the titanium plate 7 to the titanium slab 6, for example, the entire circumference is welded as shown in FIGS. 8 and 7 so that the atmosphere does not enter between the titanium slab 6 and the titanium plate 7.

Since titanium is an active metal, it forms a strong passivation film on its surface when left in the atmosphere. It is impossible to remove the oxidized concentrated layer on the surface portion. However, unlike stainless steel, oxygen easily dissolves in titanium, so if it is sealed in a vacuum and heated without the supply of oxygen from the outside, the oxygen on the surface will diffuse to the inside and dissolve in it. Therefore, the passivation 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-roll clad method without generating inclusions or the like.

Further, if a slab as cast is used as the titanium slab 6, surface defects will occur in the subsequent hot rolling process due to the 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, surface defects in the hot rolling process can be suppressed because the bonded titanium plate 7 has a fine structure.

When producing the titanium composite material shown in FIG. 1, it is preferable to attach the titanium plate 7 to only one side of the titanium slab 6 in a vacuum as shown in FIG. 8, and to attach the titanium plate 7 to the other side of the titanium slab 6. Hot rolling may be performed without attaching 7.

As shown in FIG. 9, the titanium plates 7 may be attached to both sides of the titanium slab 6 instead of only one side. Thereby, as described above, the occurrence of hot flaws in the hot rolling process can be suppressed. In hot rolling, usually, at least a part of the side surface of the titanium slab 6 wraps around to the surface side of the hot-rolled plate by being pressed down by the titanium slab 6. Therefore, if the surface layer structure on the side surface of the titanium slab 6 is coarse or a large number of defects are present, surface defects may occur on the surface near both ends in the width direction of the hot-rolled plate. Therefore, as shown in FIG. 9, it is preferable that the side surface of the titanium slab 6 on the edge side during hot rolling is also welded by laminating titanium plates 8 of the same standard as on the rolled surface. As a result, it is possible to effectively prevent the occurrence of surface defects on the surface near both ends in the width direction of the hot-rolled plate. This welding is preferably performed in vacuum.

The amount of the side surface of the titanium slab 6 wrapping around during hot rolling varies depending on the manufacturing method, but it is usually about 20 to 30 mm, so it is not necessary to attach the titanium plate 8 to the entire side surface of the titanium slab 6 for manufacturing. The titanium plate 8 may be attached only to the portion corresponding to the wraparound amount according to the method. By performing high-temperature long-term annealing after hot rolling, components derived from the base metal can be contained inside the titanium composite material. For example, 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 a high vacuum, a high vacuum can be created between the titanium slab 6 and the titanium plates 7 and 8, which is desirable. When the titanium plates 7 and 8 are welded in a vacuum, the degree of vacuum is preferably a higher degree of vacuum of 3 × 10 ^-3 Torr order or less.

The titanium slab 6 and the titanium plate 7 do not necessarily have to be welded in a vacuum vessel. For example, a vacuum suction hole is provided inside the titanium plate 7, and the titanium plate 7 is overlapped with the titanium slab 6. After the alignment, the titanium slab 6 and the titanium plate 7 may be welded while drawing a vacuum between the titanium slab 6 and the titanium plate 7 using the vacuum suction holes, and the vacuum suction holes may be sealed after the welding.

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

On the other hand, when an ingot directly produced in the shape of a hot spreading material at the time of casting is used as a material, the cutting and adjusting step can be omitted, so that the ingot can be produced at a lower cost. Further, if the ingot is used after the ingot is manufactured and the surface is cut and refined, the same effect can be expected when the ingot is manufactured through breakdown. In the present invention, the alloy layer may be stably formed on the surface layer, and an appropriate material may be selected according to the situation. Therefore, the base material is not particularly limited.

For example, after assembling a slab and welding the surroundings, it was heated to 700 to 850 ° C. to perform joint rolling of 10 to 30%, and then heated at a β region temperature for 3 to 10 hours to diffuse the base metal component to the surface layer portion. It is preferable to perform hot rolling later. This is because hot rolling at a temperature in the β region lowers the deformation resistance and facilitates rolling.

4. Manufacturing method of titanium composite material It is important to leave the alloy layer formed by 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 defects as much as possible. Specifically, it is achieved by optimizing and appropriately adopting the following ingenuity in the hot rolling process in consideration of the characteristics and capacities of the equipment used for production.

4-1. Heating process When heating a material for hot rolling, scale loss can be suppressed low by heating at a low temperature for a short time, but titanium material has low heat conduction and if hot rolling is performed inside the slab at a low temperature, it will be inside. It also has the drawback of being prone to cracking, and is optimized to minimize scale generation according to the performance and characteristics of the heating furnace used.

4-2. Hot rolling process Even in the hot rolling process, if the surface temperature is too high, a large amount of scale is generated during plate passing, and the scale loss becomes large. On the other hand, if it is too low, the scale loss will be small, but surface defects will easily occur. Therefore, it is necessary to remove it by pickling in the subsequent process, and it is desirable to perform hot rolling in a temperature range in which surface defects can be suppressed. .. Therefore, it is desirable to roll in the optimum temperature range. Further, since the surface temperature of the titanium material decreases during rolling, it is desirable to minimize the roll cooling during rolling and suppress the decrease in the surface temperature of the titanium material.

4-3. Pickling step Since the hot-rolled plate has an oxide layer on the surface, there is a descaling step of removing the oxide layer in a subsequent step. For titanium, it is common to remove the oxide layer mainly by pickling with a nitre hydrofluoric acid solution after shot blasting. In some cases, the surface may be ground by grindstone polishing after pickling. After descaling, it may have a two-layer or three-layer structure composed of an inner layer and a surface layer derived from the base material and the surface layer portion of the titanium material for hot rolling.

Since the scale generated in the hot rolling process is thick, shot blasting is usually 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 is infiltrated into the cracks, and a part of the base metal is also removed. At this time, it is important to perform a weak blasting treatment without causing cracks on the surface of the base material, and it is necessary to select the optimum blasting condition according to the chemical composition of the surface of the titanium material. Specifically, for example, by selecting an appropriate projection material and optimizing the projection speed (which can be adjusted by the rotation speed of the emperor), conditions under which cracks do not occur in the base material are selected. Since the optimization of these conditions differs depending on the characteristics of the molten resolidification layer formed on the surface of the titanium material, the optimum conditions may be determined in advance.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

No. in Table 1 In the examples shown in 1 to 3, the titanium material for hot rolling had a rectangular shape from the breakdown, and then the surface corresponding to the rolled surface was cut and refined to have a thickness of 200 mm, a width of 1000 mm, and a length of 4500 mm. No. 1 is Ti-1.0Cu, No. No. 2 is Ti-1.0Cu-1.0Sn, No. Reference numeral 3 denotes a titanium alloy made of Ti-0.5Cu.

On the other hand, No. 4-8 and No. In the examples shown in 13 to 15, the titanium slab was subjected to electron beam melting, cast in a square mold, and then the surface corresponding to the rolled surface was cut and refined. The surface was used. In addition, No. In the examples shown in 9 to 12, the titanium slab is electron beam melted, cast in a square mold, and then the surface corresponding to the rolled surface is cut and refined to form an ingot having a thickness of 50 mm, a width of 1000 mm, and a length of 4500 mm. The surface was used. No. No. 4 is Ti-0.5Al, No. 5 is Ti-0.9Al, No. No. 6 is Ti-3Al-2.5V, No. No. 7 is Ti-1Fe-0.35O, No. No. 8 is Ti-1.5Fe-0.5O, No. No. 9 is Ti-5Al-1Fe, No. No. 10 is Ti-6Fe-4V, No. No. 11 is Ti-0.5Al, No. Reference numeral 12 denotes a titanium alloy made of Ti-5Al-1Fe. In addition, No. No. 13 is JIS type 1. 14 is JIS2 type, No. Reference numeral 15 denotes pure industrial titanium made of JIS3 type.

After performing melt resolidification treatment on the surface of these titanium materials for hot rolling together with a material consisting of one or more selected from Si, Nb, Al and Ta, the surface temperature of the material is set to 200 ° C. for 1 hour. I kept it above. Then, the slab was heated to 950 ° C., hot-rolled to a thickness of 5 mm, and then descaled on both the front and back surfaces using shot blasting and nitre hydrofluoric acid. No. For 1 to 8, cold rolling was performed to obtain a titanium plate having a thickness of 1 mm, and as an annealing treatment, heat treatment was performed by heating to 600 to 700 ° C. in a vacuum or an atmosphere of an inert gas and holding for 240 minutes. No. For 9 to 11, after the descaling treatment, as an annealing treatment, heat treatment was performed by heating to 600 to 700 ° C. in a vacuum or an atmosphere of an inert gas and holding for 240 minutes.

A 20 mm × 20 mm test piece from these test materials was sanded on the surface and edges with # 400 sandpaper, and then exposed to the atmosphere at temperatures of 700 and 750 ° C. for 200 hours to change the weight before and after the test. Was measured, and the amount of oxidation increase per unit cross-sectional area was determined. The results are summarized in Table 1. The element concentration in the surface layer portion in Table 1 is the result of performing line analysis using EPMA and averaging the range from the surface to the lower end of the alloy layer.

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 contains elements derived from the slab (base material). However, in the "Composition of the surface layer" in the table, the content of elements not contained in the slab is shown, and for the elements contained in the slab, if there is an increase in the content, the content is increased. The content is indicated, and when there is no increase in the content, "-" is indicated.

No. In each of the examples 1 to 15 (example of the present invention), the surface layer contains at least one selected from Si, Nb, Al and Ta, and the thickness thereof is 5 μm or more, which is a sufficient thickness. Further, the oxidative increase after heating at 700 ° C. for 200 hours is 25 g / m ² or less, and the oxidative increase after 200 hours of heating at 750 ° C. is 70 g / m ² or less, showing excellent oxidation resistance.

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

Claims (2)

And the base material made of titanium alloy,
A titanium material for hot rolling, which has a chemical composition different from that of the base material formed on at least one of the rolling surfaces of the base material and has a surface layer portion having no surface cracks.
The surface layer portion has a thickness of 2.0 to 20.0 mm, and the ratio to the total thickness is 40% or less per one side.
The chemical composition of the surface layer is defined as the increased content from the base material (the content of elements not contained in the base material is increased, and the increased content of the elements contained in the base material is increased from the base material). By mass%
Si: and from 0.1 to 0.6%,
Nb: 0.1 to 2.0%,
Ta: 0.3 to 1.0% and Al: 0.3 to 1.5% one or more selected from a,
Sn: 0-1.5%,
Cu: 0-1.5%,
Fe: and a 0 to 0.5 percent,
When the content of the elements contained in the surface layer 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 point: | C _AVE -C ₀ | / C _AVE x 100 is 40% or less,
Titanium material for hot rolling. Other surface layer portions are formed on surfaces other than the rolled surface of the base metal.
The other surface layer portion has the same chemical composition and metallic structure as the surface layer portion.
The titanium material for hot rolling according to claim 1.

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