TWI608105B - Titanium for hot rolling - Google Patents

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.

Industrial cold-rolled steel sheets (for example, industrial pure titanium cold-rolled sheets) are used in addition to sheet metal heat exchangers, FC separators, and the like, and the use thereof is expanded to a predetermined shape. Therefore, in addition to the formability, the industrial cold-rolled sheet of titanium is required to have a reduced thickness and a high load environment (at a high load) due to an increase in fatigue strength.

On the other hand, similarly to other metal materials, in pure titanium, the ductility and strength (fatigue strength) for controlling the formability have an inverse relationship.

Japanese Laid-Open Patent Publication No. 2008-195994 (Patent Document 1) discloses a method of removing a compound layer existing on a surface of a hardened layer by plasma nitriding treatment and fine particle impact treatment, thereby performing surface modification of a titanium product. And let the fatigue strength increase. The plasma nitriding treatment is pure A titanium product composed of any one of titanium, an α-type titanium alloy, a β-type titanium alloy, or an α+β-type titanium alloy is subjected to plasma nitriding as a treatment target, thereby forming a hardened layer on the surface of the object to be processed; The impact treatment is a treatment target in which one or two or more kinds of fine particles are subjected to plasma nitriding treatment.

Japanese Laid-Open Patent Publication No. 2013-76110 (Patent Document 2) discloses a surface treatment method for a substrate composed of a titanium alloy and titanium, which is provided with a particle impact treatment on the surface of a substrate composed of a titanium alloy and titanium. Step A, the step B of performing the first heat treatment in the temperature zone T1, the step C of performing the second heat treatment in the temperature zone T2, and the step D of performing the third heat treatment in the temperature zone T3 satisfy the relationship of T1>T2>T3, and T1 is set to 900~1000 °C. That is, the surface treatment method is sequentially formed from the surface side in the vicinity of the surface of the titanium material: an amorphous layer, a fine particle layer (α phase, particle diameter: about 300 nm), and a submicron grain layer (α phase) The particle size: about 500 nm), the microparticle layer (β phase, particle diameter: about 3000 nm), thereby increasing the fatigue strength.

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 3) 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 4) 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. The compound powder is added in an appropriate amount to form a composite powder, and the composite powder is extruded into a carbon steel capsule, and the obtained capsule on the surface of the round rod is melted 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 5) 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. To form a shape by processing the outer side of the copper A titanium molded body in contact with a metal in which the entire length of the grain boundary is 20% or more.

In the case where the hot-rolled material is hot-rolled, the hot-rolled material is a so-called hard-to-machine material having insufficient hot rolling properties and high heat deformation resistance, such as pure titanium or titanium alloy, and is rolled as a technique for rolling it into a thin plate. The 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. SHO63-207401 (Patent Document 6). Japanese Laid-Open Patent Publication No. Hei 09-136102 (Patent Document 7) discloses a method of sealing a covering material at a vacuum degree of 10 ^-3 torr or more to produce a sealed coating box. Japanese Laid-Open Patent Publication No. Hei 11-057810 (Patent Document 8) 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 9) 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 10) 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 11) 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. 62-270277 (Patent Document 12) discloses a surface effect treatment of an engine part for an automobile by spraying.

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2008-195994

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2013-76110

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2011-42828

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2014-19945

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2001-131609

[Patent Document 6] JP-A-63-207401

[Patent Document 7] Japanese Patent Laid-Open No. 09-136102

[Patent Document 8] Japanese Patent Laid-Open No. Hei 11-057810

[Patent Document 9] Japanese Patent Laid-Open Publication No. 08-141754

[Patent Document 10] Japanese Patent Laid-Open No. Hei 11-170076

[Patent Document 11] JP-A-2015-045040

[Patent Document 12] Japanese Laid-Open Patent Publication No. 62-270277

According to the method disclosed in Patent Document 1, since the hardened layer is formed by using C and N having high solid solution strengthening ability, the hardened layer is hardened when it is solid-solved, and the fatigue strength is improved, but the sharp ductility is lowered to form the film. Sexual deterioration.

In addition, according to the findings of the present inventors, it has been found that the surface treatment method disclosed in Patent Document 2 does not easily improve the formability.

Further, according to the inventions disclosed in Patent Document 1 and Patent Document 2, it is necessary to perform special surface treatment on the titanium material, so that an increase in manufacturing cost is unavoidable.

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 is necessary to include a step of melting titanium to produce a titanium ingot. 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 6 to Patent Document 7 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 11, 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 the base metal Titanium is also used, and as long as the titanium material produced by the usual manufacturing steps is used, a complete cost improvement cannot be expected. 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 12, the spraying is a method in which a metal, a ceramic, or the like is melted and sprayed on the surface of the 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. In addition, in the vacuum In the case of heat treatment, the inert gas in the pores may swell, which may cause cracking of the membrane.

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 melt resolidification treatment. 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) added to improve the fatigue resistance, and to suppress the production cost of the titanium material, thereby obtaining a low cost A titanium material for hot rolling of a desired property.

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. The content of one or more selected from the group consisting of Fe, Cr, Ni, Al, and Zr is 0.08 to 1.0%. When the content of the element contained in the surface layer portion is measured as a plurality of points, the average value of the added content relative to the base material is measured. The relationship between C _AVE and the increased content C ₀ of each measurement site relative to the base material: |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 fatigue resistance, 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 layer (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.

Fig. 10 is an explanatory view showing a plane bending fatigue test material.

Fig. 11 (a) to (d) are photographs of an example of a case produced by a melt resolidification method.

The titanium material for hot rolling of the present invention is a material for heat processing (casting of flat embryo, medium embryo, small embryo, etc.), and after heat processing, as necessary Cold processing, heat treatment, and the like are performed to form a titanium composite. 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). The base material 1b is made of pure titanium or a titanium alloy for industrial use, 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 fatigue resistance of the hot-rolled titanium material 1 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 characteristics 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 Thick, because the proportion of titanium alloy in the total proportion of titanium composites 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, JIS grades 1 to 4 of industrial pure titanium among pure titanium specified by JIS 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 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, 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

The surface layer portion 1a is composed of a titanium alloy having a chemical composition different from that of the base material as described above.

(chemical composition)

In order to improve the fatigue resistance of at least one of the surface layers (at least the surface layer in contact with the external environment) of the titanium composite material produced by the titanium material for hot rolling of the present invention, the surface layer portion of the titanium material for hot rolling may contain the following various alloys. element.

One or more selected from the group consisting of Fe, Cr, Ni, Al, and Zr: 0.08 to 1.0%

The starting point of the fatigue fracture is on the surface of the sheet material, and the crystal grain size of the α phase is preferably 15 μm or less in order to maintain moldability and obtain high fatigue resistance. The crystal grain size of the α phase is more preferably 10 μm or less, and particularly preferably 5 μm or less.

In order to obtain high fatigue resistance by setting the crystal grain size of the α phase to 15 μm or less, the total content of Fe, Cr, Ni, Al, and Zr is set to 0.08% or more. On the other hand, when the total content of these elements exceeds 1.0%, the ductility such as elongation and formability can be greatly reduced. Therefore, the total content of one or more selected from the group consisting of Fe, Cr, Ni, Al, and Zr is set to 0.08 to 1.0%.

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, Sn, Mo, V, Mn, Nb, Si, Cu, Co, Pd, Ru, Ta, Y, La, and Ce, etc., plus C, N, O, and H of general impurity elements, the total amount of which is 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 is subjected to cold addition as necessary after hot working. Work, heat treatment, etc., and processed into a titanium composite. 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 fatigue resistance cannot be obtained. Although the thickness of the surface layer changes depending on the thickness of the material used for the production or the subsequent processing ratio, the effect can be sufficiently exhibited as long as 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. Further, the ratio of the surface layer thickness to the total thickness of the titanium composite material (surface occupation ratio) is preferably 1% or more on each side.

On the other hand, when the surface layer is thick, there is no problem in fatigue resistance, but the formability is lowered. In addition, since the proportion of the titanium alloy to the entire titanium composite material increases, the cost advantage is reduced. Therefore, the thickness of the surface layer is preferably 100 μm or less, and more preferably 50 μm or less. Further, the ratio of the surface layer thickness to the total thickness of the titanium composite material (surface occupation ratio) is preferably 20% or less, more preferably 10% or less on each side.

(void ratio)

The void ratio of the surface layer is preferably 0.1% or less. When the void ratio exceeds 0.1%, 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. Observed The void ratio was measured at any 10 to 20 portions of the cross section, and the average was taken as the entire 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 .

(mechanical characteristics)

Titanium composite material can be maintained both excellent formability and high fatigue strength, the fatigue strength ratio ⁽¹⁰⁷ times the fatigue strength / tensile strength) of 0.65 or more. The higher the fatigue strength ratio is, the more excellent the fatigue characteristics are. The titanium material generally has a value of 0.5 to 0.6. Therefore, 0.65 or more indicates that it has more excellent fatigue characteristics than a general titanium material, and 0.70 or more indicates that it is particularly excellent.

In addition, the direction of the titanium composite perpendicular to the rolling direction The elongation at break is 25% or more. In the forming process, the influence of the elongation is large, and the greater the elongation, the more excellent the formability.

(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 .

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. In particular, in the case of electron beam heating, since it is carried out in a high vacuum, when a re-solidification treatment is performed, even if a void or the like is formed in the layer, since it is a vacuum, it can be crimped by subsequent rolling. 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.

Further, as shown by an arrow A in Fig. 5, the following description will be made in such a manner that the electron beam irradiation gun 12 is continuously moved. 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 on the 10th surface will form the maximum with a depth corresponding to the heat input. Melt. 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. another 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 deterioration of characteristics may occur due to peeling of the surface layer portion and occurrence of a portion where the alloy layer is thin. Further, if internal oxidation occurs due to fine cracking, it is necessary to remove it by a pickling step, and the thickness of the alloy layer is further reduced. 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 heated at the time of hot rolling heating and the heat treatment step after cold rolling, and is formed at the interface between the base material and the surface layer portion. Diffusion, when finally finished into a titanium composite, an intermediate layer is formed by a concentration gradient of a specific element between the inner layer from the base material and the surface layer from the surface 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. Moreover, heat treatment during hot rolling and after hot rolling At the time of heat treatment after cold rolling, the alloying elements are diffused and joined from the interface between the base material and the bent base material, and the diffusion direction of the element is not only the depth direction but also diffuses 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.

In the surface layer portion 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. Used to make titanium flat embryo 6 and titanium The welding of the plate 7 is welded 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 adhered by hot rolling coating so that inclusions or the like do not occur therebetween.

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 of the side surface of the titanium flat blank 6 is coarse or there are many defects, the surface near the both ends in the width direction of the hot rolled sheet may be Surface defects can occur. 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 performing high-temperature long-time annealing after hot rolling, the components from the base material can be allowed to enter the inside 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 obtained by opening the ingot After the shape of the flat embryo and the small embryo, it is manufactured by 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. Further, after the ingot is manufactured, if the surface is subjected to cutting and finishing, it is expected to have the same effect as that produced by the opening of the ingot. 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. As long as it is rust-removed, it becomes a two-layer or three-layer structure composed of an inner layer and a surface layer from the base material and the surface layer portion of the titanium material for hot rolling. Create it.

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 a condition in which the base material is not cracked. 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]

The present invention will now be described in more detail by way of examples, but the invention is not limited thereto.

(test material production steps)

Hereinafter, a test material production step will be described as an embodiment of the present invention. As a material for hot rolling, a flat embryo is produced under the conditions of smelting, blasting, and surface treatment shown below. And marked as the symbols S1, S2, S3, S4, S5.

S1: a flat embryo cast by electron beam melting, mechanical cutting on the surface; S2: a flat embryo cast by electron beam melting, the surface is maintained after casting; S3: a rectangle cast by electron beam melting The ingot is opened into a flat embryo shape, and the surface is mechanically cut; S4: the cylindrical ingot cast by the vacuum arc melting method is opened into a flat embryo shape, and the surface is mechanically cut; S5: using a plasma arc melting method Cast flat embryos with mechanical cutting on the surface.

In the present embodiment, the following M1 to M10 titanium alloy and industrial pure titanium were used as examples of the material for hot rolling.

M1: ASTM Grade 7 (Ti-0.15Pd)

M2: ASTM Grade 11 (Ti-0.15Pd)

M3: ASTM Grade 16 (Ti-0.05Pd)

M4: ASTM Grade 26 (Ti-0.1Ru)

M5: ASTM Grade 30 (Ti-0.3Co-0.05Pd)

M6: 0.02% Pd-0.022% Mm-Ti (O: 0.050%, Fe: 0.041%). Here, Mm represents a mixed rare earth element (Mischmetal) before separation and purification, and its composition is 55% Ce, 51% La, 10% Nd, 4% Pr.

M7: 0.03% Pd-0.002% Y-Ti (O: 0.049%, Fe: 0.033%)

M8: 0.5% Cu-Ti (O: 0.048%, Fe: 0.038%)

M9: 1.0% Cu-Ti (O: 0.048%, Fe: 0.033%)

M10: 1.0Cu-0.5% Nb-Ti (O: 0.044%, Fe: 0.040%)

Using this titanium flat embryo, a test piece was produced by dispersing an alloy element material on the surface of the flat embryo, melting and resolidifying to form a surface layer portion as described below. In other words, after dispersing one or more powders of Fe, Cr, Ni, Al, and Zr having a purity of 98% or more from the surface of the flat embryo, the surface of the flat embryo and the powder are melted by electron beam heating, and the flat embryo is melted. The surface layer is formed by a depth of 1 to 28 mm (thickness of the surface layer portion) to form a surface layer region selected from one or more of Fe, Cr, Ni, Al, and Zr. The ratio of the surface layer selected from the solid solution of one or more selected from the group consisting of Fe, Cr, Ni, Al, and Zr to the total thickness of the flat embryo is adjusted by the thickness of the flat embryo and the depth of the resolidification. The standard flat embryo thickness was set to 125 mm. In part, in order to adjust the ratio of the depth of melting and resolidification to the total thickness, the thickness of the flat embryo is 75 mm, 40 mm, or the like. In part, the aforementioned melt resolidification treatment was not performed on the side portion of the slab.

The slab is heated to 700-900 ° C and hot rolled until it becomes 5 mm thick, using bead shot and nitric acid. Hydrofluoric acid is subjected to descaling treatment on the back side of the watch. Because of the alloying component added by the surface layer melting and re-solidification, the rust property during hot rolling heating, the crack formation state caused by beading, and nitric acid. The rate of steaming of hydrofluoric acid will vary, by adjusting the heating temperature of hot rolling, the projection conditions of beading, and nitric acid. The temperature and time of the hydrofluoric acid pickling are allowed to remain in the concentrated region of the added element of a given thickness. Then, cold rolling was performed to obtain a titanium plate having a thickness of 0.5 to 1.0 mm, and annealing was performed in a vacuum or an inert gas atmosphere to prepare a test piece of the present invention.

In addition to the test piece of the example of the present invention, it is used in the table. The titanium flat embryo in which the layer was not formed with the alloy addition element was subjected to the same steps as in the cold rolling, and the mixture was annealed in a vacuum or an inert gas atmosphere to prepare a comparative example.

With respect to each test piece, the α-phase crystal grain size, the elongation, the tensile strength, the fatigue strength, and the formability at each position were evaluated under the conditions shown below.

(α phase crystal grain size)

The thickness of the added element concentration region of the surface layer was measured by EPMA. In the tissue photograph taken by the optical microscope, the average crystal grain size of the α phase is calculated in the thickness of the central portion of the thickness portion and the concentration of the additive element in the surface layer by the cutting method according to JIS G 0551 (2005). .

(tensile strength, elongation)

A tensile test material (half the size of the JIS13-B tensile test material) with a parallel portion of 6.25×32 mm, a punctuation of 25 mm, a head width of 10 mm, and a total length of 80 mm was produced, and 0.5% of the punctuation was determined until the stress measurement was ensured. The tensile speed of min was subjected to a tensile test, and after the stress was ensured, the tensile test was carried out at a tensile speed of 30%/min. Here, the tensile strength and the total elongation in the direction perpendicular to the rolling direction are evaluated.

(fatigue strength)

The fatigue test was carried out under the conditions of a stress ratio R = -1 and a frequency of 25 Hz using the plane bending fatigue test material shown in Fig. 10 and the Tokyo Heng mechanism flat bending tester. Here, the number of times until obtaining repeated until the amplitude of each of the stress fracture stress fatigue curve made, even for evaluation ¹⁰⁷ times repeated bending fatigue limit (fatigue strength) fracture does not occur.

(formability)

a deep extension tester using the Tokyo test mechanism, model SAS-350D, and A 40 mm ball-end punch was subjected to a ball forming stretch forming test on a titanium plate processed into a shape of 90 mm × 90 m × 0.5 mm. The stretch forming test is a high-viscosity oil (#660) made of Japanese working oil (#660), and a plastic sheet is placed thereon to avoid direct contact between the punch and the titanium plate, by comparing the pull of the test piece when it is broken. The forming height was evaluated for evaluation. The tensile forming height in the ball-end stretch forming test is greatly affected by the oxygen concentration, and is 21.0 mm or more in the case of JIS class 1 and 19.0 mm or more in the case of JIS class 2, and is in the case of JIS class 3. When it is 13.0 mm or more, it can be said that the formability is further improved.

(metal organization)

Fig. 11 shows an example of a tissue photograph produced by the melt resolidification method. Fig. 11 (a) is a photograph of the structure of the test material No. A1, Fig. 11 (b) is a photograph of the structure of the test material No. A8, and Fig. 11 (c) is a photograph of the photograph of the test material No. A14, Fig. 11 (d) It is a photograph of the tissue of the test material No. A29.

Table 1 shows the results of the case of using the titanium alloy M2 as a material for hot rolling.

In the surface layer, an element derived from a flat embryo (base metal) is included, and the "layer composition" in the table indicates the content of the element not included in the flat embryo; the element contained in the flat embryo shows the content. The amount of increase (increased content).

In Table 1, the test materials No. A6, 8, and 11 are examples in which the melt re-solidification treatment is not performed on the side surface portion of the flat embryo.

The test materials No. A1 to 3 are conventional examples in which the surface layers 3 and 4 are not provided, and the fatigue strength ratios are 0.63, 0.63, and 0.55, respectively, and are generally values for the titanium material.

In the examples of the present invention, both the formability and the fatigue strength were excellent.

On the other hand, as the test material No. A4 of the comparative example, since the segregation was too large, the elongation was poor.

As the test material No. A16 of the comparative example, since the thickness of the surface layer portion was lower than the range of the present invention, the surface layer thickness of the final product was also thin, and the fatigue strength ratio was a general value with respect to the titanium material.

Further, as the test material No. A27 of the comparative example, since the alloying element (Al) content of the surface layer 3, 4 exceeded the range of the present invention, the elongation was not good.

Table 2 shows the results of the case where titanium alloy M1 was used as the material for hot rolling.

In the surface layer, an element derived from a flat embryo (base metal) is included, and the "layer composition" in the table indicates the content of the element not included in the flat embryo; the element contained in the flat embryo shows the content. The amount of increase (increased content).

In Table 2, the test materials No. B4, 7, and 8 are examples in which the melt re-solidification treatment is not performed on the side surface portion of the flat embryo.

The test materials No. B1, 2 are conventional examples in which the surface layers 3 and 4 are not provided, and the fatigue strength ratios are 0.58 and 0.59, respectively, and are generally values for the titanium material.

In the examples of the present invention, both the formability and the fatigue strength are excellent.

On the other hand, as the test material No. B3 of the comparative example, since the segregation was too large, the elongation was not good.

Table 3 shows the results of the case of using titanium alloys M3 to 10 as materials for hot rolling.

In the surface layer, an element derived from a flat embryo (base metal) is included, and the "layer composition" in the table indicates the content of the element not included in the flat embryo; the element contained in the flat embryo shows the content. The amount of increase (increased content).

The test materials No. C1 to 8 have no conventional examples of the surface layers 3 and 4, and the fatigue strength ratio is 0.61 or 0.62, which is a general value for the titanium material.

In the examples of the present invention, both the formability and the fatigue strength are excellent.

Table 4 shows the results of the case of using pure titanium as a material for hot rolling.

In the surface layer, an element derived from a flat embryo (base metal) is included, and the "layer composition" in the table indicates the content of the element not included in the flat embryo; the element contained in the flat embryo shows the content. The amount of increase (increased content).

The test materials No. D1, 5, 6, 16, and 17 have no conventional examples of the surface layers 3 and 4, and the fatigue strength ratio is a general value with respect to the titanium material.

In the examples of the present invention, both the formability and the fatigue strength are excellent.

On the other hand, the test material No. D7 which is a comparative example has a poor elongation, because the Fe content is too much.

As the test material No. D18 of the comparative example, since the Fe content was too large and the segregation was too large, the elongation was poor.

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 is a surface layer of the final product, and 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 relative to the base material. When the content is increased by mass, the content of one or more selected from the group consisting of Fe, Cr, Ni, Al, and Zr is 0.08 to 1.0%, and when the content of the element contained in the surface layer portion is measured as a plurality of points, The relationship between the average value of the increased content of the material C _AVE and the increased content C ₀ of each measurement site relative to the base material: |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.