TW201716231A - Titanium material for use in hot rolling - Google Patents

Abstract

This titanium material 1 for use in hot rolling comprises a base material 1b comprising an industrial pure titanium or titanium alloy, and a surface layer 1a formed on at least one rolled surface of the base material 1b and having a chemical composition different from that of the base material 1b, wherein surface layers 1a have a thickness of 2.0-20.0 mm and make up no more than 40% of the total thickness per side and, when the content of elements included in the surface layer 1a are measured at multiple points, the relation between the average value CAVE of the increased content from the base material 1b and the increased content C0 from the base material 1b at each of the multiple measurement points: |CAVE - C0| / CAVE * 100 is less than or equal to 40%. The chemical composition of the aforementioned surface layer contains, in mass%, B: 0.1-3.0% as the increased content from the base material. This titanium material 1 for hot rolling has prescribed neutron blocking properties despite being inexpensive.

Description

Titanium for hot rolling

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

Titanium has excellent properties such as corrosion resistance, oxidation resistance, fatigue resistance, hydrogen embrittlement resistance, and neutron barrier properties. These characteristics can be achieved by adding various alloying elements to titanium.

In the equipment for handling radioactive waste such as nuclear power generation related equipment, shielded thermal neutrons are used. Regarding the neutron shielding effect, the presence of 19.9% boron 10 ( ¹⁰ B) in the natural B was the highest. As a material for the neutron shielding plate, stainless steel containing B or the like is generally used.

Japanese Patent Publication No. Sho 58-6704 (Patent Document 1) discloses a neutron line barrier material which is a water-rich boehmite (2MgO.3B ₂ O ₂ .13H ₂ O) or a triclinium borosilicate (3CaO. 3B ₂ O ₂ .7H ₂ O), an inorganic borate containing crystallization water such as bauxite (2CaO.3B ₂ O ₂ .5H ₂ O), and inorganics such as hemihydrate gypsum and calcium aluminate cement A cured molded body obtained by kneading an adhesive and water, and contains B: 5% by mass or more. However, since the neutron shielding material disclosed in Patent Document 1 is made of cement, there is a problem in corrosion resistance, manufacturability, and workability.

The use of a B-containing titanium alloy having a superior corrosion resistance than stainless steel as a neutron line barrier material has also been examined. Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei.

Japanese Laid-Open Patent Publication No. Hei 5-142392 (Patent Document 3) discloses a radiation shielding material filled with a boron-containing material (NaB ₄ O ₇ , B ₂ O ₃ , PbO, Fe ₂ ) in a hollow metal casing. The flow of the O ₃ or the like and the metal oxide mixed therein are made into a solidified state. According to Patent Document 3, boron and hydrogen are mainly used to block the neutron beam, and the gamma ray is blocked by the casing and the metal therein.

Titanium is usually produced by the method shown below. First, according to the Kroll method, titanium oxide as a raw material is chlorinated to titanium tetrachloride, and then reduced by magnesium or sodium to produce a massive sponge-like metal titanium (sponge titanium). The titanium sponge was subjected to press forming to form a titanium consumable electrode, and a titanium ingot was produced by vacuum arc melting using a titanium consumable electrode as an electrode. At this time, an alloying element is added as needed to produce a titanium alloy ingot. Then, the titanium alloy ingot is divided, forged, and rolled to form a titanium flat embryo, and the titanium flat blank is further subjected to hot rolling, annealing, pickling, cold rolling, and vacuum heat treatment to produce a titanium thin plate.

Further, as a method for producing a titanium thin plate, a titanium ingot is subjected to blocking, hydrogenation pulverization, dehydrogenation, pulverization, and classification to produce a titanium powder, and a method of manufacturing a titanium powder by powder rolling, sintering, and cold rolling is also known. of.

Japanese Laid-Open Patent Publication No. 2011-42828 (Patent Document 4) discloses a method for producing a titanium thin plate, which is not a titanium ingot but a titanium powder directly from titanium sponge, and in order to produce a titanium thin plate from the obtained titanium powder, A viscous composition containing a titanium metal powder, a binder, a plasticizer, and a solvent is formed into a thin plate-shaped pre-sintered molded body, which is sintered to produce a sintered thin plate, and the sintered thin plate is compacted to produce a sintered compacted sheet, and the sintered compact is pressed. The dense plate is subjected to re-sintering to produce a titanium thin plate having a fracture elongation of 0.4% or more, a density ratio of 80% or more, and a density ratio of the sintered compacted plate of 90% or more.

Japanese Laid-Open Patent Publication No. 2014-19945 (Patent Document 5) discloses a method of obtaining titanium alloy powder using titanium alloy scrap or titanium alloy ingot as a raw material, and iron powder, chromium powder or copper powder in titanium alloy powder. An appropriate amount is added to form a composite powder, and the composite powder is extruded into a carbon steel capsule, and the capsule on the surface of the obtained round bar is dissolved and removed, and further subjected to solution treatment or solution treatment and aging treatment. The powder method produces a titanium alloy excellent in quality.

Japanese Laid-Open Patent Publication No. 2001-131609 (Patent Document 6) discloses a method in which a sponge titanium powder is filled in a copper capsule, and a temperature extrusion process is performed at an extrusion ratio of 1.5 or more and an extrusion temperature of 700 ° C or less. The outer peripheral copper is processed in the outer periphery to produce a titanium molded body in which the entire length of the grain boundary of the molded body is 20% or more in contact with the metal.

The hot-rolled material is subjected to hot rolling, and the hot-rolled material is a so-called difficult-to-machine material having insufficient hot rolling properties and high heat deformation resistance such as pure titanium or titanium alloy. In the case, as a technique of rolling it into a sheet, a lamination method is known. The lap rolling method is a method in which a core material such as a titanium alloy having poor workability is coated with a coating material such as carbon steel which is excellent in workability and inexpensive, and is subjected to hot rolling.

Specifically, for example, a release agent is applied to the surface of the core material, at least the upper and lower surfaces thereof are covered with the covering material, or the peripheral surfaces are covered with a spacer material in addition to the upper and lower surfaces, and the periphery is welded to be assembled and hot rolled. . In the rolling, the core material of the material to be rolled is coated with a covering material and hot rolled. Therefore, the surface of the core material is not directly in contact with the cooled medium (atmosphere or the roller), and the temperature reduction of the core material can be suppressed, and the manufacture of the thin plate can be performed even in the case of a core material having poor workability.

A method of assembling a sealed coated box is disclosed in Japanese Laid-Open Patent Publication No. S63-207401 (Patent Document 7). Japanese Laid-Open Patent Publication No. Hei 09-136102 (Patent Document 8) discloses a method of sealing a coated material at a degree of vacuum of 10 ^-3 torr or more to produce a sealed coated box. Japanese Patent Publication No. Hei 11-057810 (Patent Document 9) discloses a method of coating with carbon steel (coated material) and sealing by high energy density welding under a vacuum of 10 ^-2 torr or less. A sealed box is produced.

On the other hand, as a method of producing a highly corrosion-resistant material at a low cost, a method of joining a titanium material to a surface of a material as a base material is known.

Japanese Laid-Open Patent Publication No. Hei 08-141754 (Patent Document 10) discloses a method for producing a titanium-coated steel sheet using a steel material as a base material and titanium or a titanium alloy as a cladding material to bond the base material and the cladding material. After the surface was evacuated by vacuum evacuation, the assembled flat embryos for rolling were assembled, and the flat blanks were joined by hot rolling to produce a titanium-clad steel sheet.

Japanese Laid-Open Patent Publication No. Hei 11-170076 (Patent Document 11) discloses a method in which a material selected from the group consisting of pure nickel, pure iron, and carbon is 0.01 mass on the surface of a base material steel containing 0.03% by mass or more of carbon. An embedded material having a thickness of 20 μm or more, which is composed of any of the low carbon steels of % or less, is laminated with a titanium foil, and then the laser beam is irradiated from either side of the lamination direction to at least the edge of the titanium foil. A titanium-coated steel material is produced by welding the base material to the entire circumference in the vicinity.

Japanese Laid-Open Patent Publication No. 2015-045040 (Patent Document 12) exemplifies a method of producing a surface of a porous titanium raw material (sponge titanium) which is formed into an ingot shape by electron beam melting under vacuum. It becomes a dense titanium ingot of titanium, which is subjected to hot rolling and cold rolling, and produces a dense titanium material (titanium ingot) with very little energy, which comprises: forming a porous titanium raw material into a cast block shape. The porous portion is a dense coating portion made of dense titanium and covering the entire surface of the porous portion.

Japanese Patent Publication No. Sho 62-270277 (Patent Document 13) discloses a surface effect treatment of an engine part for an automobile by spraying.

[Patent Document 1] Japanese Patent Publication No. Sho 58-6704

[Patent Document 2] Japanese Patent Publication No. 1-168833

[Patent Document 3] Japanese Patent Laid-Open No. Hei 5-142392

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2011-42828

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2014-19945

[Patent Document 6] Japanese Laid-Open Patent Publication No. 2001-131609

[Patent Document 7] JP-A-63-207401

[Patent Document 8] Japanese Patent Laid-Open No. 09-136102

[Patent Document 9] Japanese Patent Laid-Open No. Hei 11-057810

[Patent Document 10] Japanese Patent Laid-Open Publication No. 08-141754

[Patent Document 11] Japanese Patent Laid-Open No. Hei 11-170076

[Patent Document 12] Japanese Patent Laid-Open Publication No. 2015-045040

[Patent Document 13] Japanese Laid-Open Patent Publication No. 62-270277

The hot-rolled sheet disclosed in Patent Document 2 has a high B content, which undeniably causes an increase in cost, and the workability is not good, and it is actually difficult to use it as a neutron shielding sheet.

Further, in the radiation shielding material disclosed in Patent Document 3, the boron-containing material is filled in the metal casing material, and processing after filling the boron-containing material is difficult.

Conventionally, when a titanium material is produced by hot working, titanium sponge is press-formed to form a titanium consumable electrode, and a titanium ingot is produced by vacuum arc melting using a titanium consumable electrode as an electrode, and the titanium ingot is further divided into blocks. Forging and rolling to form a titanium flat embryo, the titanium flat blank is subjected to hot rolling, annealing, pickling, and cold rolling to produce a titanium material.

In this case, it must contain smelting titanium to make titanium ingots. The steps. A method of producing powder rolling, sintering, and cold rolling of titanium powder is also known, and a method of producing titanium powder from a titanium ingot still includes a step of melting titanium.

In the method of producing a titanium material from titanium powder, even if the high-priced titanium powder is used as a raw material without passing through the smelting step, the obtained titanium material becomes very expensive. The methods disclosed in Patent Document 7 to Patent Document 8 are also the same.

In the rolling, the core material covered by the covering material is, after all, a flat embryo or an ingot, and it is necessary to pass through a melting step or use a high-priced titanium powder as a raw material, and the manufacturing cost cannot be reduced.

According to Patent Document 12, although a dense titanium material is produced with a very small amount of energy, the dense titanium surface layer portion and the internal composition which are formed by melting the surface of the intumescent sponge titanium are defined as the same type of pure titanium. In the case of a titanium alloy, for example, it is not possible to form the titanium alloy layer uniformly and in a wide range only in the surface layer portion, thereby reducing the manufacturing cost.

On the other hand, a material which can produce inexpensive corrosion-resistant material and which is bonded to titanium or a titanium alloy on the surface of the base material is often selected steel as a base material. Therefore, if the titanium layer on the surface disappears, the corrosion resistance is impaired. Even if the base material is made of titanium, it is impossible to expect a complete cost improvement as long as the titanium material produced by the usual manufacturing steps is used. Then, the present inventors have thought that an alloy layer containing a specific alloying element is provided on the surface layer of a flat embryo made of industrial pure titanium or a titanium alloy, and a titanium material which is inexpensive and has excellent specific properties is obtained.

As in Patent Document 13, the spray is for metal, ceramics, etc. A method of melting and spraying it on the surface of a titanium material to form a film. In the case where the film is formed by this method, pores are inevitably formed in the film. Usually, in the case of spraying, in order to avoid oxidation of the film, it is sprayed while being shielded with an inert gas. These inert gases are drawn into the pores of the membrane. The pores of the inert gas are contained in such a manner that they cannot be crimped by hot working or the like. Further, in the production of titanium, a vacuum heat treatment is generally performed, in which an inert gas in the pores is swollen, which may cause peeling of the film. According to the experience of the present inventors, the existence ratio (void ratio) of the pores generated by the spray is several vol.% or more, and may be more than 10 vol.% depending on the spraying conditions. In this manner, the titanium material having a high void ratio in the film may be peeled off during the production step, and defects such as cracks may occur during processing.

As a method of forming a film, a cold spray method is known. When a film is formed on the surface by this method, an inert high-pressure gas is also used. In this method, although the void ratio may be less than 1 vol.% depending on the conditions, it is extremely difficult to completely prevent the occurrence of pores. Moreover, as in the case of the spray, since the pores contain an inert gas, it cannot be destroyed by subsequent processing. Further, in the case where the heat treatment is performed in a vacuum, the inert gas in the pores may swell, which may cause cracking of the film.

In order to suppress surface defects during hot rolling, a melt re-solidification treatment is known as a process of re-solidifying a surface layer of a flat embryo by using an electron beam. Usually, the surface layer after melting and resolidification is removed by a pickling step after hot rolling. The present inventors have focused on the melting and re-solidification Reason. In other words, the inventors of the present invention considered that a specific alloying element is melted when the surface layer of the flat embryo is melted, and solidified together with the component derived from the flat embryo, whereby the surface layer portion containing the specific alloying element is formed in the flat embryo. However, the purpose is to suppress the melt re-solidification treatment of surface defects during hot rolling, and it cannot be applied to the surface layer portion containing a specific alloying element in the formation of flat embryos. 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 in the surface layer portion is not considered at all.

When the alloy component is segregated in the surface layer portion of the flat embryo containing a specific alloying element, the desired performance cannot be sufficiently exhibited or the deterioration of the desired performance is advanced. Therefore, the method of adding specific alloying elements is important.

An object of the present invention is to reduce the content of an alloying element (the amount of use of a specific alloying element which exhibits a target characteristic) to increase the neutron barrier property, and to suppress the production cost of the titanium material, thereby obtaining a low cost A titanium material for hot rolling having desired characteristics.

The present invention has been developed in order to solve the above problems, and is intended to be the following titanium material for hot rolling.

(1) A titanium material for hot rolling, comprising: a base material composed of industrial pure titanium or a titanium alloy; and a rolled surface formed on at least one of the base materials and having a chemical composition different from that of the base material The surface layer portion; the surface layer portion has a thickness of 2.0 to 20.0 mm, and the ratio of the total thickness is 40% or less per surface, and the chemical composition of the surface layer portion is increased by mass relative to the base material. B: 0.1 to 3.0%, when the content of the element contained in the surface layer portion is measured as a plurality of points, the average value C _AVE of the increased content relative to the base material and the increased content of each measurement site relative to the base material The relationship of C ₀ : |C _AVE -C ₀ |/C _AVE ×100 is 40% or less.

(2) In the titanium material for hot rolling according to (1), the surface layer other than the rolled surface of the base material is formed with another surface layer portion, and the other surface layer portion has the same chemical composition as that of the surface layer portion. Metal structure.

The titanium material for hot rolling of the present invention includes a base material composed of industrial pure titanium or a titanium alloy, and a surface layer portion having a chemical composition different from that of the base material, and a titanium composite material produced by using the same is used. The titanium material composed of the same titanium alloy as a whole has the same neutron barrier properties, but can be manufactured at low cost.

1‧‧‧Titanium for hot rolling

1a, 1aa, 1ab‧‧‧ surface layer

1b‧‧‧Material

2‧‧‧Titanium composite

3,4‧‧‧Surface (surface layer)

5‧‧‧ inner layer

Fig. 1 is an explanatory view showing an example of a structure of a titanium material for hot rolling of the present invention.

Fig. 2 is an explanatory view showing another example of the structure of the titanium material for hot rolling of the present invention.

Fig. 3 is an explanatory view showing an example of the structure of the titanium composite material of the present invention.

Fig. 4 is an explanatory view showing an example of the structure of the titanium composite material of the present invention.

Fig. 5 is an explanatory view showing a method of melting and resolidifying.

Fig. 6 is an explanatory view showing a method of melting and resolidifying.

Fig. 7 is an explanatory view showing a method of melting and resolidifying.

Fig. 8 is a schematic view showing the bonding of a titanium rectangular cast piece (flat blank) and a titanium plate by welding in a vacuum.

Fig. 9 is a view schematically showing the bonding of the titanium plate to the surface of the titanium rectangular cast piece (flat blank) and welding the titanium plate on the side surface.

The titanium material for hot rolling of the present invention is a material for heat processing (a cast piece of a flat embryo, a medium embryo, a small embryo, etc.), and after hot working, it is processed into a titanium composite material by performing cold working, heat treatment, or the like as necessary. Hereinafter, the titanium material for hot rolling of the present invention will be described with reference to the drawings. In addition, in the following description, "%" regarding the content of each element means "mass%."

1. Titanium for hot rolling

1-1. Overall composition

As shown in Fig. 1, the titanium material 1 for hot rolling of the present invention comprises a base material 1b and a surface layer portion 1a formed on a rolling surface of the base material 1b. Further, the surface layer portion has a predetermined intermediate layer (not shown). Base metal 1b is used by industry It is composed of 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 of the present invention may have surface layer portions 1aa and 1ab on both rolled surfaces of the base material 1b. In this manner, the sub-barrier property 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. The titanium material 1 for hot rolling has the same neutron barrier properties as the titanium material composed of the same titanium alloy as a whole, but can be produced at low cost.

The size of the case where the titanium material for hot rolling is a rectangular titanium slab is not particularly limited as long as it is available for hot rolling. In the case of hot rolling, a hot rolled coil thin intermediate plate having a thickness of about 3 to 8 mm is produced by roll rolling, and the rectangular titanium cast piece may have a thickness of about 50 to 300 mm, a length of about 3,000 to 10,000 m, and a width. 600~1500mm or so.

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 the desired characteristics cannot be sufficiently obtained. On the other hand, if it is too thick, since the ratio of the titanium alloy to the entire titanium composite material increases, the cost advantage is reduced. Therefore, the thickness of the surface portion is set to 2.0 to 20.0 mm. The ratio of the thickness of the surface portion to the total thickness is 40% or less on each side.

1-2. Base metal

The base material 1 is composed of pure titanium or a titanium alloy for industrial use. Among them, by using a titanium alloy, mechanical properties (strength, ductility, and the like) superior to those in the case of using industrial pure titanium can be obtained.

As the base material 1, it can be used in the pure titanium specified by JIS. JIS grade 1~4 pure titanium for industrial use. 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 rest is industrial pure titanium of Ti. As long as JIS grade 1~4 industrial pure titanium is used, it can be obtained: titanium material which has sufficient workability and does not cause cracking, and can be integrated with the surface titanium alloy after hot working.

As the base material 1, an α type, an α + β type, or a β type titanium alloy can be used.

Here, examples of the α-type titanium alloy include Ti-0.5Cu, Ti-1.0Cu, Ti-1.0Cu-0.5Nb, Ti-1.0Cu-1.0Sn-0.3Si-0.25Nb, and Ti-0.5Al-0.45. Si, 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.

Further, 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. , 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-5Al -2Fe-0.3Si, Ti-5Al-2Fe-3Mo, Ti-4.5Al-2Fe-2V-3Mo, and the like.

Further, examples of the β-type titanium alloy include Ti-11.5Mo-6Zr-4.5Sn, Ti-8V-3Al-6Cr-4Mo-4Zr, Ti-10V-2Fe-3Mo, and 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 can be produced by a known production method such as a melting method or a powder metallurgy method, and is not particularly limited. For example, the base material can be produced by cutting and finishing the ingot by opening the embryo into a flat embryo or a small embryo shape. In the case of manufacturing by the opening of the embryo, since the surface is relatively flat by the opening of the embryo, the material containing the alloying element is easily dispersed uniformly, and the elemental distribution of the alloy phase is easily made 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, the cutting and finishing step can be omitted, and thus it can be manufactured at a lower cost. Further, if the surface of the ingot is subjected to cutting and finishing after the ingot is manufactured, the same effect as that produced by the opening of the ingot can be expected.

1-3. Surface layer

(chemical composition)

In order to provide at least one of the surface layers of the titanium composite material produced by the titanium material for hot rolling of the present invention (at least in contact with the external environment), the surface layer portion of the titanium material for hot rolling may contain the following Various alloying elements.

B: 0.1~3.0%

There is 19.9% of ¹⁰ B in B, and the thermal neutron of ¹⁰ B has a large absorption cross-sectional area, and the shielding effect of the neutron line is large. When the B content is less than 0.1%, a sufficient neutron shielding effect cannot be obtained, and when the B content exceeds 3.0%, cracking and workability at the time of hot rolling may be deteriorated.

Here, the titanium alloy containing B can be produced by adding a boride such as B or TiB _{2 to} titanium. In addition, if ¹⁰ B concentrated boron-containing material ( ¹⁰ B content is about 90% or more) such as H ₃ ¹⁰ BO ₃ or ¹⁰ B ₂ O ¹⁰ B ₄ C is used, the neutron shielding effect is large even if the B content is small. Therefore, it is extremely effective.

When H ₃ ¹⁰ BO ₃ , ¹⁰ B ₂ O, and ¹⁰ B ₄ C are used, H and O in the alloy layer are also concentrated, and H is detached from the material during heat treatment such as vacuum annealing, so The problem is that the O and C can be produced without any problem as long as it is 0.4% by mass or less or less and 0.1% by mass or less or less, based on the upper limit of the content of the pure titanium for industrial use.

The remainder other than the above is titanium and impurities. As an impurity, it can be contained in a range that does not impair the target characteristics, and other impurities, mainly impurity elements mixed from waste, that is, Cr, Ta, Al, V, Cr, Nb, Si, Sn, Mn, Mo, Cu, etc. In addition to the general impurity elements C, N, Fe, O and H, the total amount of 5% or less is acceptable.

2. Titanium composite

The titanium material for hot rolling of the present invention is a material for heat processing (a cast piece of a flat embryo, a medium embryo, a small embryo, etc.), and after hot working, it is processed into a titanium composite material by performing cold working, heat treatment, or the like as necessary. Further, the titanium composite material includes an inner layer of the base material from the titanium material for hot rolling of 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 neutron shielding effect cannot be obtained. On the other hand, when the surface layer is thick, the shielding effect of the neutron beam is improved, but the proportion of the titanium alloy in the entire material increases, so the manufacturing cost increases. In addition, it will have an adverse effect on processability. Therefore, the ratio of the surface layer to the total thickness of the titanium composite material is set to be 5 to 40% on each side.

(void ratio)

The void ratio of the surface layer is preferably less than 3.0%. B precipitates as TiB during melting or heating, and voids are formed at the interface between TiB and the base material during subsequent processing. However, when the titanium material for hot rolling of the present invention is used, TiB is split and finely refined during hot rolling, so that the size of the voids becomes small. However, when the void ratio is 3.0% or more, expansion or peeling of the surface layer may occur during hot rolling.

The void ratio allows the material to be photographed by observation with an optical microscope, and the photograph is easily processed by image processing. The arbitrary 10 to 20 parts of the cross section were observed, and the void ratio was measured, and the average was taken as the overall void ratio. The void ratio of the material after hot rolling or cold rolling is the same as the porosity of the titanium material for hot rolling.

(segregation)

When the content of the element contained in the surface layer portion is measured at a plurality of points, the relationship between the average value C _AVE of the increased content of the base material and the increased content C ₀ of the respective measurement sites with respect to the base material: |C _AVE - C ₀ |/C _AVE ×100 is 40% or less. The reason is that when |C _AVE -C ₀ |/C _AVE ×100 exceeds 40%, the desired performance cannot be sufficiently exhibited or the deterioration of the desired performance is advanced. |C _AVE -C ₀ |/C _AVE ×100 is preferably 20% or less.

Specific elements in the surface layer can be measured using EPMA or GDS. Specifically, any 10-20 parts of the surface layer portion can be measured, and the average value of the increased content of each measurement portion relative to the base material is taken as the increase content C _{0 of} each measurement site, and the average value of the increase content C ₀ is taken as The average value of the increased content of the surface layer is C _AVE .

(middle layer)

The surface layer has an intermediate layer near the inner layer. In other words, the titanium material for hot rolling of the present invention has a surface layer portion formed by, for example, a melt re-solidification treatment on the surface of the base material, and the heat treatment step of the surface layer portion after hot rolling and subsequent heat treatment. The diffusion occurs at the interface between the base material and the surface layer portion, and when finally finished into a titanium composite material, an intermediate layer is formed between the inner layer from the base material and the surface layer from the surface layer portion. The intermediate layer strongly bonds the inner layer and the surface layer by metal bonding. 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 alleviated, and cracking during processing can be suppressed. The thickness of the intermediate layer is preferably 0.5 μm or more.

The thickness of the intermediate layer can be measured using EPMA or GDS. More detailed measurements can be made using GDS. In the case of GDS, the surface layer can be removed to some extent by polishing, and then the thickness of the intermediate layer is measured by performing GDS analysis from the surface toward the depth direction. The intermediate layer refers to an increased content relative to the base material (which is the content of the element which is not contained in the base material; in the case where the element is contained in the base material, the content is increased relative to the base material) The amount is set to C _MID , and when the average of the increase in the surface layer portion is C _AVE , it is an area of 0 < C _MID ≦ 0.8 × C _AVE .

(use)

In a device for radiation therapy such as particle therapy or BNCT (boron neutron capture therapy), a polyethylene material having a B content of 3.0 to 4.0% by mass and a plate thickness of 10 to 100 mm is used. In addition, in the nuclear energy related equipment, a stainless steel plate having a B content of 0.5 to 1.5% by mass and a plate thickness of 4.0 to 6.0 mm is used in the nuclear fuel storage rack. By using the titanium composite material in which the B content and the thickness (the thickness of the B concentrated layer) of the surface layer are adjusted, it is possible to exhibit the same or better properties as the above materials.

3. Method for producing titanium material for hot rolling

3-1. Formation of surface layer by melting and resolidifying

In the titanium material for hot rolling of the present invention, a surface layer of a base material is melted, and a specific alloying element is melted and solidified together with a component derived from the base material, whereby a surface layer portion containing a specific alloying element is formed in the base material. 5 to 7 are explanatory views each showing a method of melting and resolidifying.

The method of melting and solidifying the surface of the base material of the titanium material for hot rolling includes laser heating, plasma heating, induction heating, electron beam heating, and the like, and may be carried out by any method. Especially in the case of electron beam heating, since it is carried out in a high vacuum, when it is melted and resolidified, even in the case The layer forms a void or the like, and since it is a vacuum, it can be pressure-bonded by subsequent rolling to make it harmless.

Further, since the energy efficiency is high, it can be melted even if it is subjected to a large-area treatment, and therefore it is particularly suitable for the production of a titanium composite. The degree of vacuum in the case of melting in a vacuum is preferably a higher degree of vacuum of 3 × 10 ^-3 Torr or less. In addition, the number of times of melting and re-solidifying the surface layer of the titanium material for hot rolling is not particularly limited, and the number of times may be increased as needed, as long as the thickness of the alloy layer and the amount of the added element in the surface layer portion of the material are within the above range. Just fine. However, the more the number of times, the longer the processing time increases the cost, and therefore it is preferably 1 to 2 times.

The melt re-solidification method of the surface layer is carried out as shown in Fig. 5 in the case of a rectangular flat embryo. That is, the electron beam is irradiated to the wide surface of the outer surface of the rectangular flat blank 10 at least in the hot rolling step which becomes the rolling surface (the surface in contact with the hot roll), and only the surface layer of the surface is irradiated. Melt. Here, first, one of the two faces 10A, 10B is 10A.

Here, as shown in FIG. 5, in general, the area of the irradiation region 14 of the electron beam of the electron beam irradiation gun 12 with respect to the face 10A of the rectangular cast piece 10 is larger than the entire area of the face 10A to be irradiated. In many cases, in general, electron beam irradiation is generally performed while the electron beam irradiation gun 12 is continuously moved or while the rectangular cast piece 10 is continuously moved. The irradiation area is to adjust the shape and area by adjusting the focus of the electron beam or by using an electromagnetic lens to cause small rays to vibrate at a high frequency (oscillation) to form a beam.

Moreover, as shown by the arrow A in Fig. 5, to let the electrons The following description will be made on the form in which the beam irradiation gun 12 continuously moves. The moving direction of the electron beam irradiation gun is not particularly limited, and is generally continuously moved along the longitudinal direction of the rectangular cast piece 10 (usually the casting direction D) or the width direction (usually the direction perpendicular to the casting direction D) to The width W (the diameter of the circular ray or the beam is the diameter W) of the irradiation region 14 is continuously irradiated. Further, in the strip-shaped region which is not irradiated adjacent thereto, the electron beam irradiation is performed in a strip shape while continuously moving the irradiation gun 12 in the opposite direction (or the same direction). Further, depending on the situation, it is also possible to perform electron beam irradiation on a plurality of regions simultaneously using a plurality of illuminating guns. Fig. 5 shows a case where the rectangular rays are continuously moved along the longitudinal direction of the rectangular cast piece 10 (usually the casting direction D).

The surface (face 10A) of the rectangular titanium slab 10 is irradiated with an electron beam by such a surface heating treatment step to heat the surface thereof, as shown by the center of the left side of FIG. The surface layer of 10A 10 will form a maximum melting at a depth corresponding to the heat input. However, the depth in the direction perpendicular to the irradiation direction of the electron beam is not necessarily a curved shape which is convex downward as shown in FIG. 7, that is, the central portion of the electron beam irradiation is the deepest, and the closer to the strip-shaped end portion, The smaller the thickness.

In the region closer to the inner side of the slab than the molten layer 16, the temperature is increased by the influence of the heat of the electron beam irradiation, and the temperature is higher than the temperature above the β-deformation point of pure titanium (heat-affected layer = HAZ layer). β phase. The region in which the surface layer heat treatment step is changed to the β phase by the heat of the electron beam irradiation also has a downwardly convex curved shape similar to the shape of the molten layer 16.

The material for the hot rolling is alloyed by melting and resolidifying together with the material composed of the alloy element of interest. As the material used at this time, one or more of a powder, a small piece, a wire, a film, a chip, and a mesh can be used. The component and the amount of the material disposed before the melting are set so that the component of the element-concentrated region which is melt-solidified together with the surface of the material becomes a target component.

However, if the added material is too large, it will cause segregation of the alloy composition. Further, if segregation of the alloy component is present, the desired performance may not be sufficiently exhibited or the deterioration may be advanced. Therefore, it is important that the alloy material becomes a size at which melting is completed while the heated portion of the surface of the titanium base material is in a molten state. Further, it is important to uniformly arrange the above 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, in the case where the irradiation position is continuously moved by using the electron beam, since the molten portion is continuously moved together with the molten titanium and the alloy to be stirred, it is not necessary to continuously arrange the alloy material. In addition, it is of course necessary to avoid the use of alloy materials having a melting point which is much higher than the melting point of titanium.

After the melt resolidification treatment, it can be maintained at a temperature of 100 ° C or more and less than 500 ° C for 1 hour or more. After melting and re-solidification, if it is cooled rapidly, the strain at the time of solidification may cause fine cracks in the surface layer portion. In the subsequent hot rolling step and cold rolling step, the fine crack is used as a starting point, and peeling of the surface layer portion may occur, and a portion where a part of the alloy layer is formed may be deteriorated. In addition, if internal oxidation occurs due to fine cracking, it must be removed by a pickling step to further reduce the thickness of the alloy layer. less. By holding at the above temperature, it is possible to suppress fine cracks on the surface. Further, as long as the temperature is maintained at this temperature, atmospheric oxidation hardly occurs even if it is held in the atmosphere.

The hot-rolling titanium material having the surface layer portion formed by the melt re-solidification treatment on the surface of the base material is subjected to hot-rolling heating and subsequent heat-treating step in the cold rolling, at the interface between the base material and the surface layer portion. When diffusion is finally performed, when the titanium composite is finally finished, a concentration gradient of a specific element is generated between the inner layer from the base material and the surface layer from the surface layer to form an intermediate layer. Therefore, the intermediate layer strongly bonds the inner layer and the surface layer by metal bonding. 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 relaxed, and cracking during processing can be suppressed.

Further, in the case of alloying by the melt resolidification treatment, since the shape of the molten portion is curved as described above, the shape is continued in the final product. Further, in the hot rolling heating, the heat treatment after the hot rolling, the heat treatment after the cold rolling, or the like, the alloying elements are diffused and joined from the interface between the bent and the base material, and the diffusion direction of the elements is not only the depth direction. Diffusion also occurs in the width direction. Therefore, the gradient of the alloying elements in the intermediate portion between the base material and the alloy layer is not only the depth direction but also the width direction. Therefore, for example, when an element having a different solid solution strengthening ability is added, not only in a direction perpendicular to the depth direction but also in a direction parallel to the depth direction, a difference in strength occurs, so that the concentration gradient is complicated and the strength is poor. Cracks become hard to happen.

a surface layer formed by melting and solidifying the surface of the base material, A titanium plate containing a predetermined alloy component can be further attached to produce a titanium material for hot rolling.

Fig. 8 is an explanatory view showing a titanium rectangular cast piece (flat blank) 6 in which a surface layer portion is melted and solidified to form a surface layer portion, and a titanium plate 7 is bonded by fusion in a vacuum. Fig. 9 is a schematic view showing not only the surface of the titanium rectangular cast piece (flat blank) 6, but also the side faces of the titanium plates 7, 8 welded together. In the following description, a titanium rectangular cast piece (flat embryo) 6 in which the surface of the base material is melted and solidified to form a surface layer portion is referred to as "titanium flat embryo 6".

As shown in Figs. 8 and 9, after the titanium sheets 7, 8 containing the alloying elements having the apparent properties are bonded to the surface layer of the titanium flat blank 6, the surface layer 3 of the titanium composite is bonded by the hot rolling coating method. , 4 alloying. In other words, after the titanium plate 7 containing the alloying element is bonded to the surface of the titanium flat blank 6 as the rolled surface, it is preferable to weld at least the periphery by the welded portion 9 in the vacuum container. The titanium flat blank 6 and the titanium plate 7 are sealed in a vacuum, and the titanium flat blank 6 and the titanium plate 7 are bonded by rolling. The welding for bonding the titanium flat blank 6 and the titanium plate 7 is welded to the entire circumference in order to avoid intrusion of the atmosphere between the titanium flat blank 6 and the titanium plate 7, for example, as shown in Figs.

Titanium is an active metal and, if placed in the atmosphere, forms a strong passive film on the surface. It is impossible to remove the oxidized concentration layer of the surface portion. However, unlike stainless steel or the like, since oxygen is easily dissolved in titanium, if it is sealed in a vacuum and heated without supplying oxygen from the outside, oxygen on the surface diffuses into the inside to cause solid solution, and thus is formed on the surface. The passive membrane will be eliminated. Therefore, the titanium flat blank 6 and the titanium plate 7 on the surface thereof can be completely completely formed by hot rolling coating in such a manner that inclusions or the like do not occur therebetween. adaptation.

Further, as the titanium flat embryo 6 is cast as a flat embryo, the coarse crystal grains generated during solidification cause surface defects in the subsequent hot rolling step. On the other hand, when the titanium plate 7 is bonded to the rolled surface of the titanium flat blank 6 as in the present invention, since the bonded titanium plate 7 has a fine structure, surface defects in the hot rolling step can be suppressed.

In the case of manufacturing the titanium composite material shown in Fig. 1, it is preferable that the titanium plate 7 is bonded to the vacuum only on one side of the titanium flat blank 6 as shown in Fig. 8, and the other side of the titanium flat blank 6 is not The titanium plate 7 is bonded and hot rolled.

As shown in Fig. 9, the titanium plate 7 may be bonded not only to one side of the titanium flat blank 6, but also to both surfaces. Thus, the occurrence of hot rolling defects in the hot rolling step as described above can be suppressed. In the hot rolling, usually, the titanium flat blank 6 is pressed, and at least a part of the side surface of the titanium flat blank 6 is wrapped around the surface side of the hot rolled sheet. Therefore, if the surface layer structure of the side surface of the titanium flat blank 6 is coarse or there are many defects, surface defects may occur on the surface near the both ends in the width direction of the hot rolled sheet. Therefore, as shown in Fig. 9, it is preferable that the side surface of the titanium flat blank 6 on the edge side at the time of hot rolling is welded to the titanium plate 8 of the same specification as the rolled surface. Thus, surface defects on the surface near both ends in the width direction of the hot rolled sheet can be effectively prevented from occurring. The fusion is preferably carried out in a vacuum.

In the hot rolling, the amount of the side of the titanium flat blank 6 is different depending on the manufacturing method, and is usually about 20 to 30 mm, so that it is not necessary to fully fit the titanium plate 8 on the side of the titanium flat blank 6, only in the case of The titanium plate 8 may be attached to a portion corresponding to the amount of wrapping according to the manufacturing method. By making high after hot rolling Annealing for a long time allows the ingredients from the base metal to enter the interior of the titanium composite. For example, heat treatment at 700 to 900 ° C for 30 hours can be exemplified.

A method of welding the titanium flat blank 6 and the titanium plates 7, 8 includes electron beam welding, plasma welding, and the like. In particular, electron beam welding is preferable because it can be carried out under high vacuum, and the titanium flat blank 6 and the titanium plates 7 and 8 can be made to have a high vacuum. The degree of vacuum in the case where the titanium sheets 7, 8 are welded in a vacuum is preferably a higher degree of vacuum of 3 × 10 ^-3 Torr or less.

The welding of the titanium flat blank 6 and the titanium plate 7 does not have to be performed in a vacuum container. For example, a vacuum suction hole may be provided inside the titanium plate 7, and after the titanium plate 7 and the titanium flat embryo 6 are overlapped, they are used. The vacuum suction hole welds the titanium flat blank 6 and the titanium plate 7 by vacuum suction between the titanium flat blank 6 and the titanium plate 7, and closes the vacuum suction hole after welding.

3-2. Base material of titanium for hot rolling

The base material of the titanium material for hot rolling is usually produced by subjecting the ingot to a flat embryo and a small embryo shape by opening the embryo, and then performing cutting and finishing. Further, in recent years, there has been a case where a rectangular flat embryo which can be directly hot rolled is produced at the time of manufacture of an ingot for hot rolling. In the case of manufacturing by opening the embryo, since the surface is made flat by the opening of the embryo, the material containing the alloying element is easily dispersed more uniformly, and the elemental distribution of the alloy phase is easily made uniform.

On the other hand, as a material, when an ingot which is directly formed into a shape of a material for hot rolling at the time of casting is used, since the cutting and finishing step can be omitted, it can be manufactured at a lower cost. In addition, after the ingot is manufactured, if the surface is subjected to cutting and finishing, it can be expected to be opened. The same effect is produced in the case of embryos. In the present invention, as long as a stable alloy layer is formed on the surface layer, an appropriate material can be selected depending on the situation. Therefore, there is no particular limitation on the base material.

For example, it is preferred that after the flat embryo is assembled and welded around, it is heated at 700 to 850 ° C to carry out 10 to 30% bonding rolling, and then heated at a temperature of the β region for 3 to 10 hours to diffuse the base material component to the surface layer. After the ministry, hot rolling is carried out. By performing hot rolling by the temperature of the β region, the deformation resistance is lowered and rolling is easily performed.

4. Method for manufacturing titanium composite material

It is important that the alloy layer formed by the melt resolidification treatment remains as a final product, and it is necessary to suppress the loss of the scale and the removal of the surface layer due to surface defects as much as possible. Specifically, in consideration of the characteristics and capabilities of the equipment used for production, the following methods in the hot rolling step are optimized and suitably employed.

4-1. Heating step

When the material for hot rolling is heated, it is possible to suppress the loss of scale by heating at a low temperature for a short period of time. However, the thermal conductivity of the titanium material is low, and it is easy to cause cracking inside when the inside of the flat embryo is hot-rolled at a low temperature. Therefore, it is possible to minimize the occurrence of scale in accordance with the performance and characteristics of the heating furnace to be used.

4-2. Hot rolling step

Also in the hot rolling step, if the surface temperature is too high, a large amount of scale is generated when the sheet is passed, and the loss of the scale is increased. On the other hand, when the temperature is too low, the scale loss is small, but surface defects are likely to occur, and it is necessary to remove it by pickling in the subsequent step. Therefore, it is preferable to perform hot rolling in a temperature range in which surface defects can be suppressed. Therefore, it is preferable to carry out rolling in an optimum temperature range. Further, since the surface temperature of the titanium material is lowered in the rolling, it is preferable to suppress the cooling of the rolls in the rolling to the minimum and to suppress the decrease in the surface temperature of the titanium material.

4-3. Pickling step

The hot rolled sheet has an oxide layer on the surface, and the subsequent step includes a derusting step of removing the oxide layer. In general, titanium is mainly used after beading, by using nitric acid. The oxidation layer is removed by pickling of the hydrofluoric acid solution. Further, depending on the case, the surface may be ground by grinding with a grindstone after pickling. After the rust removal, the base material and the surface layer portion of the titanium material for hot rolling may have a two-layer or three-layer structure composed of an inner layer and a surface layer.

Since the scale generated in the hot rolling step is thick, usually as a pretreatment of the pickling treatment, a part of the scale of the surface is removed and a crack is formed on the surface by a beading treatment, followed by a pickling step. The pickling solution is allowed to penetrate the crack, and a part containing the base material is also removed. At this time, it is important to perform a weak bead blasting treatment in order to prevent cracks from occurring on the surface of the base material, and it is necessary to select an optimum beading condition in accordance with the chemical composition of the surface of the titanium material. Specifically, for example, the selection of the appropriate projecting material and the projection speed (which can be adjusted by the rotational speed of the impeller) are optimized, thereby selecting the mother. The condition that the material does not cause cracks. The optimization of these conditions differs depending on the characteristics of the molten re-solidified layer formed on the surface of the titanium material, and it is only necessary to determine the optimum conditions in advance.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to the examples.

[Example 1]

Hereinafter, the present invention will be more specifically described with reference to the accompanying drawings and embodiments.

As shown in FIG. 3, in the two-layer structure of the present invention, the strand shield 1 in the titanium composite material is obtained by melting and solidifying one side surface of the base material, followed by hot rolling, thereby forming the surface layer 3 and the inner layer 5 . Further, as shown in FIG. 4, the neutron shielding plate 2 of the three-layer structure of the present invention is formed by melting and solidifying both side surfaces of the base material, followed by hot rolling, thereby forming the surface layers 3, 4 and the inner layer 5. The manufacturing method of the neutron shielding plates 1, 2 will be specifically described.

In Table 1, as the examples (invention examples), the strand shield plates 1, 2 were produced by the following method.

In the surface layer portion, the element derived from the flat embryo (base material) is contained, but the content of the element not included in the flat embryo is shown only in the "composition of the surface layer portion" in the table.

First, a titanium ingot as a material is produced by a rectangular mold by electron beam melting (EB melting) or plasma arc melting (plasma melting), or by a cylindrical mold by VAR melting.

The size of the ingot, the cylindrical ingot is 1200mm in diameter × 2500mm in length, and the rectangular ingot is 100mm in thickness × 1000mm in width × 4500mm in length, and the variety includes: Ti-1Fe-0.35O, Ti-0.5Cu, Ti-1Cu, Ti-1Cu -0.5 Nb, Ti-5Al-1Fe, Ti-3Al-2.5V, Ti-3Al-5V.

Most of the cast ingots are cut after rolling, and melted and solidified. The other ingots are melted and solidified after being cast in the same manner or after cutting the surface of the ingot.

The melt resolidification treatment is performed on at least one of the rolled faces, and can be carried out on the side faces in the longitudinal direction as needed. This treatment was carried out by electron beam welding in a vacuum atmosphere of about 3 × 10 ^-3 Torr, and TiB ₂ powder (100 μm or less), a small Ti-B alloy piece (2 mm square, 1 mm thick), Ti- was added during melting. Any of the B alloy wire (Φ5 mm or less), the Ti-B alloy film (20 μm or less), and the Ti-B alloy mesh (combined Φ1 mm in a lattice shape), and the surface layer portion (melted resolidified layer) becomes Ti- A 0.1~3.2% B alloy is used to produce a titanium flat embryo of a two-layer structure or a three-layer structure. Regarding the surface layer portion (B-concentrated layer), the ratio of the total thickness of the titanium composite material 1 to each surface is adjusted as shown in Table 1, and is adjusted in a three-layer structure so that the B-concentrated layers on both surfaces have the same thickness.

When various materials are added, in order to uniformly add the entire flat embryo, the material containing B is uniformly dispersed in the entire rolled surface of the titanium cast piece to be melt-resolidified. After the melt resolidification treatment, it is kept at 100 ° C or higher and less than 500 ° C for 1 hour or longer.

The titanium flat embryo after melting and resolidification was heated at 800 ° C for 240 minutes using a steelmaking apparatus, and then hot rolled to produce a strip-shaped coil having a thickness of about 4 mm. The strip-shaped coil after hot rolling passes through nitric acid. The continuous pickling line composed of hydrofluoric acid was subjected to derusting treatment, and then visually observed for the occurrence of cracks.

In the method of measuring the depth of the surface layer portion (the B-concentrated layer), a part of the flat embryo (the three portions of the distal end, the center, and the rear end are sampled from the central portion in the width direction) are cut out and ground. Thereafter, SEM/EDS analysis was performed to determine the ratio of the B-concentrated layer to the thickness of the plate and the B concentration of the B-concentrated layer (using the average value in the observed portion).

In addition, in the three portions of the front end, the center, and the rear end in the longitudinal direction, a total of 20 bending test pieces in the L direction were sampled from the center portion in the width direction, and a bending test was performed in accordance with JIS Z 2248 (Metal Material Bending Test Method). The test temperature was set to room temperature, and a bending test was performed at a bending angle of up to 120 degrees by a three-point bending test to evaluate whether or not cracking occurred, and the crack occurrence rate was obtained.

Further, in the evaluation of the shielding effect of the neutron beam, Am-Be (4.5 MeV) was used as a radiation source, and a test piece of 500 mm × 500 mm × 4 mm thick was fixed at a position of 200 mm from the radiation source. Detector set in the release The position of the source of 300 mm, the peak of the target energy, was measured by measuring the radiation equivalent of Ti-1Fe-0.35O and the test piece in the control test piece, and the neutron line shielding effect was evaluated according to the ratio of the values (Ti-1Fe-0.35) In the O, the sub-line shielding effect is set to 1, and the value of each test piece is described).

The results were compiled together with the test conditions in Table 1.

In Comparative Examples and Examples of Nos. 1 to 9 of Table 1, the VAR ingot of Ti-1Fe-0.35O was subjected to block rolling, and the surface was cut and used. The comparative example of No. 1 is a case where the material containing B is not added at the time of melt resolidification. No crack occurred in the hot rolled sheet, and no crack occurred in the bending test.

In Comparative Examples and Examples of Nos. 2 to 5, TiB ₂ was added as a material containing B in the case of melting and resolidification.

In the comparative example of No. 2, the B concentration in the surface layer portion exceeded 3.0%. Cracks occurred locally in the hot rolled sheet, and the crack occurrence rate in the bending test was also improved.

The comparative example of No. 3 is a case where the thickness ratio of the surface layer portion exceeds 40%. Cracks occurred locally in the hot rolled sheet, and the crack occurrence rate in the bending test was also improved.

The examples (invention example) of Nos. 4 to 9 are cases in which various materials are used as the material containing B in the case of melting and resolidification. In addition, the layer structure, the thickness of the surface layer portion, and the B concentration were changed and evaluated. Since the thickness ratio of the surface layer portion was 5 to 40%, and the B concentration in the surface layer portion was 0.1 to 3.0%, no crack occurred in the hot rolled sheet, and no crack occurred in the bending test. The examples of No. 10 to 15 use Ti-1Fe- In the case of a 0.35O EB smelting ingot, the manufacturing process after casting the ingot is changed. In addition, in the case of melting and re-solidification, various materials were used as the material containing B, and the layer structure, the thickness of the surface layer portion, and the B concentration were respectively changed and evaluated. In the present embodiment, the side surface in the longitudinal direction is also melt-resolidified in the same manner as the rolled surface. Since the thickness ratio of the surface layer portion was 5 to 40%, and the B concentration in the surface layer portion was 0.1 to 3.0%, no crack occurred in the hot rolled sheet, and no crack occurred in the bending test.

The example of No. 16 to 21 is a case where a slurry of Ti-1Fe-0.35O is used to melt the ingot, and the manufacturing history after the ingot is cast is changed. In addition, in the case of re-solidification by melting, various materials were used as the material containing B, and the layer structure, the thickness of the surface layer portion, and the B concentration were respectively changed and evaluated. Since the thickness ratio of the surface layer portion was 5 to 40%, and the B concentration of the thickness of the surface layer portion was 0.1 to 3.0%, no crack occurred in the hot rolled sheet, and no crack occurred even in the bending test.

In the examples of No. 22 to 33, the VAR ingots of various titanium alloys were subjected to block rolling, and the surface was cut and used, and TiB ₂ powder was used as the material containing B in the case of melting and resolidification. Further, as the inner layer 5, various layers of titanium alloy were used, and the layer structure, the thickness of the surface layer portion, and the B concentration were respectively changed and evaluated. Since the thickness ratio of the surface layer portion was 5 to 40%, and the B concentration of the thickness of the surface layer portion was 0.1 to 3.0%, no crack occurred in the hot rolled sheet, and no crack occurred even in the bending test.

In the example of the present invention, the alloy used for the inner layer 5 was subjected to a tensile test using a JIS13B test piece having a thickness of 1.5 mm in advance, and the stress was ensured to be 1000 MPa or less.

Further, in the examples (in the present invention) of Nos. 4 to 33, the neutron shielding effect was 1 or more, and it was confirmed that the neutron shielding effect was obtained.

The stainless steel plate (4 mm thick) having a B content of 0.5% by mass for the nuclear fuel storage rack has a neutron shielding effect of 23.7, and the examples of No. 5, 11, 15, 17, 21, 23 are obtained. The board has a higher neutron line shielding effect.

[Embodiment 2]

The titanium ingot as a material is produced by VAR melting and using a cylindrical mold.

The size of the ingot is 1200mm in diameter × 2500mm in length, and the varieties include: Ti-1Fe-0.35O, Ti-0.5Cu, Ti-1Cu, Ti-1Cu-0.5Nb, Ti-5Al-1Fe, Ti-3Al-2.5V, Ti-3Al-5V.

The cast ingot is subjected to block rolling, and then cut, melted and solidified.

The melt resolidification treatment is performed on at least one of the rolled faces, and is also performed on the side faces in the longitudinal direction as needed. This treatment is carried out by electron beam welding in a vacuum atmosphere of about 3 × 10 ^-3 Torr, and TiB ₂ powder (100 μm or less) is added during melting to make the molten resolidified layer into a Ti-0.1 to 3.7% B alloy. A titanium flat embryo of a two-layer structure or a three-layer structure is obtained. Regarding the surface layer portion (B-concentrated layer), the ratio of the total thickness of the titanium composite material 1 to each surface is adjusted as shown in Table 2, and the surface layer portions of both surfaces are made the same thickness in the three-layer structure.

When various materials are added, in order to uniformly add the entire flat embryo, the material containing B is uniformly dispersed in the entire rolled surface of the titanium cast piece, and the melt resolidification treatment is performed. After the melt resolidification treatment, it is kept at 100 ° C or higher and less than 500 ° C for 1 hour or longer.

The titanium flat embryo after melting and resolidification was heated at 800 ° C for 240 minutes using a steelmaking apparatus, and then hot rolled to produce a strip-shaped coil having a thickness of about 10 mm. The strip-shaped coil after hot rolling passes through nitric acid. A continuous pickling line composed of hydrofluoric acid was subjected to a rust removing treatment, and about 50 μm of scuffing was applied to each side, and then visual observation was made on the occurrence of cracks.

In the method of measuring the depth of the surface layer portion (the B-concentrated layer), a part of the flat embryo (the three portions of the distal end, the center, and the rear end are sampled from the central portion in the width direction) are cut out and ground. Thereafter, SEM/EDS analysis was performed to determine the ratio of the B-concentrated layer to the plate thickness and the B concentration of the B-concentrated layer (using the average value in the observed portion).

In addition, in the three portions of the front end, the center, and the rear end in the longitudinal direction, a total of 20 bending test pieces in the L direction were sampled from the center portion in the width direction, and a bending test was performed in accordance with JIS Z 2248 (Metal Material Bending Test Method). The test temperature was set to room temperature, and a bending test was performed at a bending angle of up to 120 degrees by a three-point bending test to evaluate whether or not cracking occurred, and the crack occurrence rate was obtained.

Further, in the evaluation of the shielding effect of the neutron beam, Am-Be (4.5 MeV) was used as a radiation source, and a test piece of 500 mm × 500 mm × 10 mm thick was fixed at a position of 200 mm from the radiation source. Detector set in the release The position of the source of 300 mm, the peak of the target energy, was measured by measuring the radiation equivalent of Ti-1Fe-0.35O and the test piece in the control test piece, and the neutron line shielding effect was evaluated according to the ratio of the values (Ti-1Fe-0.35) In the O, the sub-line shielding effect is set to 1, and the value of each test piece is described).

The results were compiled together with the test conditions in Table 2.

In the surface layer portion, the element derived from the flat embryo (base material) is included in the "layer composition of the surface layer", and only the content of the element not included in the flat embryo is displayed.

In the comparative examples of Nos. 34 to 36 of Table 2, Ti-1Fe-0.35O was used. The comparative example of No. 34 is a case where the material containing B is not added at the time of melt resolidification. No crack occurred in the hot rolled sheet, and no crack occurred in the bending test.

In the comparative example of No. 35, the B concentration in the surface layer portion exceeded 3.0%. Cracks occurred locally in the hot rolled sheet, and the crack occurrence rate in the bending test was also improved.

The comparative example of No. 36 is a case where the thickness ratio of the surface layer portion exceeds 40%. Cracks occurred locally in the hot rolled sheet, and the crack occurrence rate in the bending test was also improved.

Further, in the examples (invention examples) of Nos. 37 to 50, the neutron shielding effect was 1 or more, and it was confirmed that the neutron shielding effect was obtained.

[Example 3]

According to the same procedure as in Example 2, the titanium flat embryo after melting and resolidification was heated at 800 ° C for 240 minutes using a steelmaking apparatus, and then hot rolled to obtain a tape-shaped coil having a thickness of about 5 mm. The strip-shaped coil after hot rolling passes through nitric acid. The continuous pickling line composed of hydrofluoric acid is subjected to derusting treatment. Further, cold rolling was carried out to obtain a titanium plate having a thickness of 4 mm, and as an annealing treatment, heat treatment was carried out by heating to 600 to 750 ° C in a vacuum or an inert gas atmosphere for 240 minutes. The cold-rolled sheet is a surface inspection step after annealing, and the occurrence of cracks is visually observed.

In the method of measuring the depth of the surface layer portion (the B-concentrated layer), a part of the flat embryo (the three portions of the distal end, the center, and the rear end are sampled from the central portion in the width direction) are cut out and ground. Thereafter, SEM/EDS analysis was performed to determine the ratio of the B-concentrated layer to the thickness of the plate and the B concentration of the B-concentrated layer (using the average value in the observed portion).

In addition, in the three portions of the front end, the center, and the rear end in the longitudinal direction, a total of 20 bending test pieces in the L direction were sampled from the center portion in the width direction, and a bending test was performed in accordance with JIS Z 2248 (Metal Material Bending Test Method). The test temperature was set to room temperature, and a bending test was performed at a bending angle of up to 120 degrees by a three-point bending test to evaluate whether or not cracking occurred, and the crack occurrence rate was obtained.

Further, in the evaluation of the shielding effect of the neutron beam, Am-Be (4.5 MeV) was used as a radiation source, and a test piece of 500 mm × 500 mm × 4 mm thick was fixed at a position of 200 mm from the radiation source. The detector is placed at a position of 300 mm from the radiation source, and the peak value of the object energy is measured by measuring the radiation equivalent of Ti-1Fe-0.35O and the test piece in the control test piece, and the neutron line shielding effect is evaluated according to the ratio of the values. The sub-line shielding effect of Ti-1Fe-0.35O was set to 1, and the value of each test piece was described).

The results were compiled together with the test conditions in Table 3.

In the surface layer portion, the element derived from the flat embryo (base material) is contained, but the content of the element not included in the flat embryo is shown only in the "composition of the surface layer portion" in the table.

In Table 3, the comparative example of No. 51 is a case where the material containing B is not added at the time of melt resolidification. No crack occurred in the hot rolled sheet, and no crack occurred in the bending test.

In the comparative example of No. 52, the B concentration in the surface layer portion exceeded 3.0%. Cracks occurred locally in the hot rolled sheet, and the crack occurrence rate in the bending test was also improved.

The comparative example of No. 53 is a case where the thickness ratio of the surface layer portion exceeds 40%. Cracks occurred locally in the hot rolled sheet, and the crack occurrence rate in the bending test was also improved.

In the examples of Nos. 54 to 67, the inner layer 5 was evaluated by using various titanium alloys to change the layer structure, the thickness of the surface layer portion, and the B concentration, respectively. Since the thickness ratio of the surface layer portion was 5 to 40%, and the B concentration in the surface layer portion was 0.1 to 3.0%, no crack occurred in the hot rolled sheet, and no crack occurred in the bending test.

Further, in the examples (in the present invention) of Nos. 54 to 67, the neutron shielding effect was 1 or more, and it was confirmed that the neutron shielding effect was obtained.

[Example 4]

According to the same procedure as in Example 2, the titanium flat embryo after melting and resolidification was heated at 800 ° C for 240 minutes using a steelmaking apparatus, and then hot rolled to obtain a tape-shaped coil having a thickness of about 10 mm. Hot rolled strip Rolled material, through nitric acid. The continuous pickling line composed of hydrofluoric acid was subjected to a rust removing treatment, and about 50 μm of gas cutting was performed on each side, and then the occurrence of cracks was visually observed.

In the method of measuring the depth of the surface layer portion (the B-concentrated layer), a part of the flat embryo (the three portions of the distal end, the center, and the rear end are sampled from the central portion in the width direction) are cut out and ground. Thereafter, SEM/EDS analysis was performed to determine the ratio of the B-concentrated layer to the thickness of the plate and the B concentration of the B-concentrated layer (using the average value in the observed portion).

In addition, in the three portions of the front end, the center, and the rear end in the longitudinal direction, a total of 20 bending test pieces in the L direction were sampled from the center portion in the width direction, and a bending test was performed in accordance with JIS Z 2248 (Metal Material Bending Test Method). The test temperature was set to room temperature, and a bending test was performed at a bending angle of up to 120 degrees by a three-point bending test to evaluate whether or not cracking occurred, and the crack occurrence rate was obtained.

Further, in the evaluation of the shielding effect of the neutron beam, Am-Be (4.5 MeV) was used as a radiation source, and a test piece of 500 mm × 500 mm × 10 mm thick was fixed at a position of 200 mm from the radiation source. The detector is placed at a position of 300 mm from the radiation source, and the peak value of the object energy is measured by measuring the radiation equivalent of Ti-1Fe-0.35O and the test piece in the control test piece, and the neutron line shielding effect is evaluated according to the ratio of the values. The sub-line shielding effect of Ti-1Fe-0.35O was set to 1, and the value of each test piece was described).

The results were compiled together with the test conditions in Table 4.

In the surface layer portion, the element derived from the flat embryo (base material) is contained, but the content of the element not included in the flat embryo is shown only in the "composition of the surface layer portion" in the table.

In the examples of No. 68 to 70, the inner layer 5 was evaluated by using various titanium alloys to change the layer structure, the thickness of the surface layer portion, and the B concentration, respectively. Since the thickness ratio of the surface layer portion was 5 to 40%, and the B concentration in the surface layer portion was 0.1 to 3.0%, no crack occurred in the hot rolled sheet, and no crack occurred in the bending test.

Further, in the examples (invention example) of No. 68 to 70, the neutron shielding effect was 1 or more, and it was confirmed that the neutron shielding effect was obtained.

1‧‧‧Titanium for hot rolling

1a‧‧‧Surface

1b‧‧‧Material

Claims (2)

A titanium material for hot rolling, comprising: a base material made of industrial pure titanium or a titanium alloy; and a surface layer formed on a rolled surface of at least one of the base materials and having a chemical composition different from the base material The surface layer portion has a thickness of 2.0 to 20.0 mm, and the ratio of the total thickness is 40% or less per surface, and the chemical composition of the surface layer portion is contained in an amount of % by mass relative to the base material. : 0.1 to 3.0%, when the content of the element contained in the surface layer portion is measured as a plurality of points, the average value C _AVE of the increased content with respect to the base material and the increased content C ₀ of the respective measurement sites with respect to the base material Relationship: |C _AVE -C ₀ |/C _AVE ×100 is 40% or less. The titanium material for hot rolling according to the first aspect of the invention, wherein the surface layer other than the rolled surface of the base material is formed with another surface layer portion, and the other surface layer portion is provided in the same manner as the surface layer portion. Chemical composition and metal structure.