KR20210012639A - Titanium slab and method of manufacturing thereof - Google Patents

Abstract

The present invention provides a titanium slab formed with a thin thickness of an oxygen-enriched layer created on a surface of the slab, and a method for manufacturing the same. According to the present invention, the titanium slab comprises: a titanium base material; and an oxygen-enriched layer provided on a surface of the pure titanium base material. A central portion of the pure titanium base material consists of a cast structure or a forged structure. A surface layer portion within 5 to 10 mm in the thickness direction from the surface of the base material including the oxygen-enriched layer has an average grain size of 10 to 500 μm and is composed of a spherical recrystallized structure. The maximum thickness of the oxygen-enriched layer is 1 mm or less (including 0 mm).

Description

Titanium slab and its manufacturing method {TITANIUM SLAB AND METHOD OF MANUFACTURING THEREOF}

The present invention relates to a titanium slab and a method of manufacturing the same.

Titanium has an HCP (α phase) structure at room temperature, but a BCC (β phase) structure above the in situ transformation temperature. The high-temperature deformation resistance of titanium is several times higher in α-phase, which has a small number of slip surfaces, than β-phase. In addition, since the thermal conductivity is lower than that of Fe or Al, which are commonly used metals, the internal/external temperature variation of the material is deepened during the high-temperature processing process. Due to the high-temperature processing characteristics of titanium, there is a problem that it is difficult to control the crop of the hot-rolled slab due to non-uniform deformation during high-temperature processing, and processing at a high temperature above the β-phase transformation temperature is necessary to solve this problem.

However, the oxygen diffusion rate in the non-dense structure of β-phase (BCC) titanium is more than 100 times that of α-phase (HCP). For this reason, when processing is performed at a high temperature above the β-phase transformation temperature, oxygen is easily diffused and an oxygen-enriched layer in which oxygen is excessively dissolved in the titanium base material is easily formed. Since such an oxygen-enriched layer exhibits high hardness and low ductility properties, it causes surface defects in post-processing such as rolling.

In order to reduce the oxygen-enriched layer, in the prior art, after processing at the β-phase transformation temperature or higher, the oxygen-enriched layer is removed through a separate surface treatment, or low-temperature heating is performed in which the oxygen-enriched layer is heated in the α-phase or in situ transformation temperature range. However, in the case of such a conventional technology, there is a problem that the real rate decreases during surface processing, and the rolling facility load is exceeded due to high deformation resistance during low temperature heating.

Therefore, there is a need for a method of manufacturing a titanium slab having a low oxygen-enriched layer thickness while ensuring hot workability without exceeding the limit of the rolling load of the manufacturing equipment.

Japanese Patent Laid-Open Publication No. Hei 7-102351

An object of the present invention is to provide a titanium slab having a thin thickness of an oxygen-enriched layer formed on the surface of the slab and a method for manufacturing the same.

The subject of the present invention is not limited to the above description. Those of ordinary skill in the art to which the present invention pertains will not have any difficulty in understanding the additional subject of the present invention from the general details of the present specification.

According to an aspect of the present invention, a titanium base material; And an oxygen-enriching layer provided on the surface of the titanium base material, wherein the surface layer portion within 5 to 10 mm in the thickness direction from the surface of the base material including the oxygen-enrichment layer has an average grain size of 10 to 500 μm and has a spherical shape. A titanium slab made of a recrystallized structure and having a maximum thickness of the oxygen-enriched layer of 1 mm or less (including 0 mm) is provided.

The hardness of the oxygen-enriched layer may be 30% or more higher than the average hardness value at a depth of 3 to 5 mm in the thickness direction from the surface of the base material.

The oxygen content of the oxygen-enriched layer may be greater than or equal to 15.5% of an allowable maximum oxygen content according to the alloy composition of the titanium base material.

The oxygen-enriched layer may satisfy the following relationship.

[Relationship 1] (B-A)/A × 100 ≤ 50%

A = ((hardness value of 5mm depth in thickness direction) + (hardness value of 4mm depth in thickness direction) + (hardness value of 3mm depth in thickness direction)) / 3

B = hardness value of 1mm depth in the thickness direction

The thickness of the oxygen-enriched layer may satisfy the following relational formula 2.

[Relationship 2]

,

,

(Where n _i (n ₁ , n ₂ , …, n ₁₀ ) is the thickness of the oxygen-enriched layer obtained through micro-hardness measurement in the thickness direction for 10 locations at 500 mm intervals in the length direction, respectively, and μ is 10 It is the average value of the thickness of the oxygen-enriched layer in the area.)

The thickness of the titanium slab may be 100 to 300 mm.

According to another aspect of the invention, preparing a titanium ingot; Heating the titanium ingot at a heating temperature equal to or higher than the β-phase transformation temperature and equal to or less than the β-phase transformation temperature +100° C. for 0.3t to 1t minutes (t: ingot thickness, mm); Rolling the heated titanium ingot at the β-phase transformation temperature or higher and the β-phase transformation temperature +100°C or lower; And cooling after the rolling; is provided a method of manufacturing a titanium slab comprising.

Before the rolling, at least one or more of a forging step and at least one rolling step are further performed at a temperature equal to or higher than the β-phase transformation temperature, and at a temperature equal to or higher than the β-phase transformation temperature and lower than the β-phase transformation temperature +100°C. Can be reheated.

The rolling may be performed in one or two or more passes, and the reduction rate per pass may be set such that the strain in the thickness direction of the surface layer is 4% or more greater than the strain in the thickness direction of the center.

The thickness of the titanium ingot may be 700 to 900 mm, and the slab thickness after rolling may be 100 to 300 mm.

The rolling may be performed by a demolition rolling method.

According to the present invention, since the thickness of the oxygen-enriched layer formed on the surface of the titanium slab is thin, it is not necessary to add a separate surface processing process, and it is possible to secure excellent hot workability by reducing the rolling load, so that the error rate can be greatly improved. There is an effect.

The various and beneficial advantages and effects of the present invention are not limited to the above description, and will be more easily understood in the course of describing specific embodiments of the present invention.

1 is a flow chart showing a manufacturing method according to an aspect of the present invention.
2 shows the orthotopic transformation characteristics of pure titanium.
3 is a photograph showing a cross-sectional microstructure of a pure titanium ingot of Grade 1 based on ASTM standards when (a) 860°C rolled, (b) 920°C forged, and (c) 920°C rolled.
FIG. 4 is a photograph showing an enlarged portion of the surface and inside of the cross-sectional microstructure photograph of FIG. 3.
5 is a graph showing changes in microhardness according to thickness when processing is performed on a pure titanium ingot. (a) shows the change in microhardness according to the thickness when forging or rolling is performed at or above the in situ transformation temperature and when rolled under the in situ transformation temperature, and (b) is rolling at 890°C, 940°C and 1050°C. If so, it shows the change in microhardness according to the thickness.
6 shows the experimental results confirming the effect of reducing the oxygen-enriched layer when rolled above the β-phase transformation temperature, (a) is the primary for the slab formed with an oxygen-enriched layer thickness of 1.7 mm after heating at 920°C for 6 hours. It shows the change in microhardness according to the microstructure and thickness after β-rolling (oxygen-enriched layer thickness 0.5mm), and (b) shows the microstructure and thickness after heating at 920℃ for 6 hours for the slab of (a). It shows the change of microhardness according to the microstructure (oxygen enrichment layer thickness 2mm), and (c) shows the change of microhardness according to the microstructure and thickness after the first β-rolling for the slab of (b) (oxygen enrichment Layer thickness is 0.7mm).

The terminology used herein is for reference only to specific embodiments and is not intended to limit the invention. Singular forms as used herein also include plural forms unless the phrases clearly indicate the opposite.

The meaning of "comprising" as used in the specification specifies a specific characteristic, region, integer, step, action, element and/or component, and other specific characteristic, region, integer, step, action, element, component and/or group It does not exclude the existence or addition of

Although not defined differently, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms defined in a commonly used dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal meaning unless defined.

In the specification, "β rolling" or "β forging" means rolling or forging above the β-phase transformation temperature, and "α rolling" means the α-phase temperature range below the β-phase transformation temperature or the in situ transformation temperature. It means to perform rolling in.

Hereinafter, a titanium slab according to an aspect of the present invention will be described in detail. In the present invention, when expressing the content of each element, it is necessary to note that it means weight% unless otherwise specified. In addition, the ratio of crystals or tissues is based on area unless otherwise indicated.

A titanium slab according to an aspect of the present invention includes a titanium base material and an oxygen enrichment layer provided on the surface of the titanium base material. In the present invention, the titanium base material includes both a pure titanium base material made of pure titanium containing 99% or more of Ti: 99% or more, and the balance inevitable impurities, and a titanium alloy base material containing a predetermined alloying element in titanium. Can be defined.

Here, slabra can be defined as a semi-finished product before hot rolling in the α phase temperature range during the manufacturing process of a conventional hot-rolled titanium plate or a thick plate, and its thickness is 700 to 900 mm in ingot thickness and 0.3 mm in thickness of the final product (cold-rolled ) ~ 100㎜ (thick plate) may be 100 ~ 300㎜ in the middle level.

The pure titanium base material may be made of pure titanium containing 99% or more of Ti. For example, titanium materials are classified into grades from 1 to 39 based on ASTM standards.If a titanium material that satisfies the standards of grades 1 to 4, it can be considered to satisfy the pure titanium base material condition of the present invention. have.

The pure titanium base material may contain inevitable impurities other than Ti. Inevitable impurities may be unintentionally incorporated in a conventional titanium ingot or slab manufacturing process, and this cannot be completely excluded, and those skilled in the art can easily understand the meaning. In addition, the present invention does not entirely exclude addition of a composition other than the above-mentioned composition.

In addition, the titanium alloy base material refers to a titanium alloy containing Ti as a main component and a small amount of alloying elements such as O, Al, V, Pd, Mo, Ni, etc. As an example, the standard of ASTM standard grade 5 to 39 In the case of a titanium material satisfying, it can be seen that it satisfies the conditions of the titanium alloy base material of the present invention. In addition, the titanium alloy base material may contain inevitable impurities, which is the same as that of the pure titanium base material.

An oxygen-enriched layer may be provided on the surface of the titanium base material. In the present invention, the oxygen-enriched layer may be defined as an area 30% or more higher than the average hardness value at a depth of 3 to 5 mm in the thickness direction from the surface of the base material. When the titanium base material is heated, a region where the hardness gradient according to the thickness suddenly increases occurs near the surface of the base material depending on the heating temperature and time. The oxygen-enriched layer can be distinguished through the result of the hardness measurement. In addition, the thickness of the oxygen-enriched layer of titanium increases by more than a certain thickness and then does not increase any more. Therefore, the average hardness value at a depth of 3 to 5 mm in the thickness direction from the surface of the base material can be seen as the average hardness value of the base material, and an area higher than this by 30% can be determined as an oxygen-enriched layer.

Alternatively, in the present invention, the oxygen-enriched layer may be defined as a region in which the oxygen content is greater than or equal to 15.5% of the maximum allowable oxygen content according to the alloy composition of the titanium base material. Here, the'maximum permissible oxygen content' means the maximum permissible oxygen content per grade specified in the ASTM standard. For example, in the case of grade 1, the maximum oxygen content is 0.18% by weight, and in the case of grade 2, it is 0.25% by weight. On the other hand, in the titanium-oxygen phase diagram, the theoretical maximum oxygen high capacity of pure titanium is 15.5% by weight in the α phase, so this can be set as the upper limit.

The maximum thickness of the oxygen-enriched layer may be 1 mm or less (including 0 mm). An oxygen-enriched layer with a thickness of 1 mm or less is at a level that can be eliminated due to Scale Loss during hot rolling in the α phase temperature range of the post process. Therefore, it is advantageous to improve productivity because a separate surface processing process is not required during slab manufacturing. Meanwhile, the smaller the oxygen-enriched layer is formed, the more preferable it is, so the lower limit of the thickness may not be separately limited.

The maximum thickness of the oxygen-enriched layer can be measured by measuring the hardness from the surface of the base material in the thickness direction. As a preferred embodiment, whether or not the maximum thickness of the oxygen-enriched layer satisfies 1 mm or less can be determined through the following relationship.

[Relationship 1] (B-A)/A × 100 ≤ 50%

A = ((hardness value of 5mm depth in thickness direction) + (hardness value of 4mm depth in thickness direction) + (hardness value of 3mm depth in thickness direction)) / 3

B = hardness value of 1mm depth in the thickness direction

In the above relational formula 1, A substantially means the average hardness of the base metal. Therefore, if the condition of the above relational formula 1 for comparing the hardness value of 1 mm depth in the thickness direction to the average hardness value of the base metal is satisfied, it can be determined that the maximum thickness of the oxygen-enriched layer is 1 mm or less.

In the present invention, when processing a titanium ingot into a slab, rolling is performed at a temperature above the β-phase transformation temperature in the final step. The present inventors have found that when the titanium ingot is rolled above the β-phase transformation temperature, the oxygen-enriched layer formed in the previous manufacturing step is recrystallized and rearranged. The present invention has been completed based on these findings, and since the oxygen-enriched layer is entirely reformed to a uniform thickness through the above phenomenon, the maximum thickness of the oxygen-enriched layer formed on the titanium slab according to the present invention can be reduced.

In particular, the oxygen-enriched layer formed on the titanium slab according to the present invention is rearranged to have a uniform thickness. In the present invention, the uniformity of the thickness of the oxygen-enriched layer can be expressed through the following relational equation 2.

[Relationship 2]

,

,

(Where n _i (n ₁ , n ₂ , …, n ₁₀ ) is the thickness of the oxygen-enriched layer obtained through micro-hardness measurement in the thickness direction for 10 locations at 500 mm intervals in the length direction, respectively, and μ is 10 It is the average value of the thickness of the oxygen-enriched layer in the area.)

The relational expression 2 is a relational expression numerically expressing the uniformity of the thickness of the oxygen-enriched layer in the longitudinal direction. When the thickness of the oxygen-enriched layer satisfies the above relational equation 2, it may be determined that the oxygen-enriched layer is rearranged to a uniform thickness and formed to have a thin thickness.

On the other hand, titanium ingots manufactured through casting typically have coarse grains of several mm in size rather than equiaxed crystal structures, and have a structure in which a needle-like structure exists in the middle, and in the present invention, such a structure is cast Defined as an organization. When forging or rolling processing is applied to the titanium ingot having the above casting structure, it has a different structure depending on the processing method and processing temperature.

Figure 3 shows the cross-sectional fineness of (a) rolling at 860°C, (b) forging at 920°C, and (c) rolling at 920°C with respect to the ASTM standard grade 1 (Grade 1) pure titanium ingot (simultaneous transformation temperature of 890°C). Indicated the organization. Here, the in situ transformation temperature of the pure titanium ingot can be considered to be substantially the same as the β-phase transformation start temperature.

Referring to FIG. 3, first, as shown in FIG. 3 (a), when α-rolling (rolling at a temperature of less than 890°C) on a pure titanium ingot, the surface has a grain size. A spherical recrystallized structure of 1 to 150 μm is formed, and a spherical recrystallized structure with a grain size of 10 to 500 μm is formed in the center of the base material. That is, a spherical recrystallized structure is formed over both the surface and the center.

On the other hand, as can be seen in FIG. 3 (b), when β forging (forging at a temperature of 890°C or higher) is performed on the pure titanium ingot, the crystal grain size from the surface to the center is 300 to several tens of μm. A structure with an irregular shape is formed, and a needle-like structure with a width of 50 to 300 μm is formed in a part.

On the other hand, as can be seen in Fig. 3 (c), when β rolling (rolling at a temperature of 890°C or higher) is performed on the pure titanium ingot, the surface is recrystallized in a spherical shape with a grain size of 10 to 500 μm. Although a structure is formed, the cast structure remains in the center of the base material according to the process performed before that, or the same structure as in β forging is observed. That is, when a separate process is not performed before β-rolling, a casting structure is observed in the center of the base material, and when β forging is selectively performed before β-rolling, a forging structure can be observed in the center.

Therefore, in the present invention, since β-rolling is performed on the heated ingot before final cooling, the surface layer portion of the pure titanium base material within 5 to 10 mm in the thickness direction from the surface of the slab including the oxygen-enriched layer has an average grain size of 10 to 500 μm. It may be made of a spherical (spherical) recrystallized structure. In addition, the center of the titanium slab may be made of a casting structure or a forging structure. The structure of the titanium slab was described as a pure titanium ingot, but the same structure was observed in the titanium alloy ingot.

Hereinafter, a method of manufacturing a titanium slab according to another aspect of the present invention will be described in detail.

A method of manufacturing a titanium slab according to another aspect of the present invention comprises the steps of preparing a titanium ingot, wherein the titanium ingot is heated at a heating temperature of not less than β-phase transformation temperature and β-phase transformation temperature +100° C. for 0.3t to 1t minutes (t: Heating during the ingot thickness, mm), rolling the heated titanium ingot at the β-phase transformation temperature or higher and β-phase transformation temperature +100°C or lower, and cooling after the rolling.

First, prepare a titanium ingot. The titanium ingot may be made of pure titanium or a titanium alloy containing 99% or more of Ti: 99% or more, and the balance inevitable impurities, and the thickness may be 700 to 900 mm.

The pure titanium ingot can be applied without limitation to the present invention as long as it is classified as pure titanium in the art. As a preferred example, it may be pure titanium corresponding to grades 1 to 4 based on ASTM standards, but is not limited thereto.

In addition, the titanium alloy ingot may be applied without limitation to the present invention as long as it is a titanium alloy generally used in the art. As a preferred example, it may be a titanium alloy corresponding to grades 5 to 39 based on ASTM standards, but is not necessarily limited thereto.

The prepared titanium ingot is heated for 0.3t to 1t (t: ingot thickness, mm) at a heating temperature of not less than β-phase transformation temperature and not more than β-phase transformation temperature +100°C.

The heating is a preparatory step for rolling in the β-phase region and needs to be heated to a temperature equal to or higher than the β-phase transformation temperature for β rolling. On the other hand, if the heating temperature is too high, the thickness of the oxygen-enriched layer may become too thick or surface defects may occur, so the upper limit of the heating temperature may be limited to β-phase transformation temperature +100°C.

On the other hand, since the thermal conductivity of titanium according to the temperature range is lower than that of general carbon steel, it takes more time than general carbon steel to sufficiently heat up to the center. Depending on the initial thickness of titanium, the minimum time required for heating to the center varies, and considering this, it is preferable to heat at least 0.3t minutes, and if the heating time is less than 0.3t minutes, the temperature to the center may not reach equilibrium. In addition, when considering the maximum aging time that can uniformly induce structure changes such as phase change and recrystallization to the center, it is desirable to limit the heating time to 1t min or less.If the heating time exceeds 1t, the grains become too coarse. Problems can arise.

Thereafter, a titanium slab may be manufactured by rolling the heated titanium ingot at a temperature higher than the β-phase transformation temperature and then cooling, and the thickness of the titanium slab may be 100 to 300 mm.

The β rolling may be performed in one or two or more passes, and the reduction rate per pass may be set such that the strain in the thickness direction of the surface layer of the slab is 4% or more greater than the strain in the thickness direction of the center of the slab. When the strain rate is less than 4%, when the pass schedule is set, the number of passes increases, resulting in a large temperature drop in the trailing pass, which increases the rolling load, so that rolling to the target thickness may be difficult.

On the other hand, the heated titanium ingot may further include one or more of at least one forging step and at least one rolling step at a temperature equal to or higher than the β-phase transformation temperature selectively before rolling. In addition, depending on the temperature of the titanium ingot after performing at least one of the at least one forging process and at least one rolling process, it is reloaded into the heating furnace before the β rolling, and the temperature is higher than the β phase transformation temperature and the β phase transformation temperature is +100°C or less. You can heat it back to temperature.

When the primary processing is performed at the β-phase transformation temperature prior to the β rolling, the deformation applied to the surface layer may induce active surface layer recrystallization in the heating furnace before β rolling, so that the oxygen-enriched layer can be more effectively rearranged.

In addition, β rolling may be performed by a demolition rolling method, but is not limited thereto.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are only for exemplifying the present invention and not for limiting the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and matters reasonably inferred therefrom.

(Example A)

First, in Example A, the effect of reducing the oxygen-enriched layer before and after β rolling was confirmed. To this end, a pure titanium ingot (β phase transformation temperature of 915°C) was prepared that satisfies ASTM standard Grade 2 with Ti: 99% by weight and the maximum impurity content (% by weight) 0.25[O]-0.3[Fe]. . After heating this pure titanium ingot at a temperature of 920° C. for 6 hours, the thickness of the oxygen-enriched layer was confirmed in the same manner as in Example A, and the thickness was 1.7 mm.

The heated pure titanium ingot was subjected to primary rolling at a temperature of 920° C. and then the thickness of the oxygen-enriched layer was measured again, and the thickness of the oxygen-enriched layer was confirmed to be 0.5 mm (see FIG. 6 (a)).

Thereafter, the first rolled rolled material was heated at a temperature of 920°C for 6 hours and then subjected to secondary rolling at the same temperature, and the thickness of the oxygen-enriched layer after heating at 920°C for 6 hours was 2 mm (Fig. 6 (b)), the thickness of the oxygen-enriched layer after secondary rolling was confirmed to be 0.7 mm (see FIG. 6 (c)).

From the results of Example A, it was confirmed that the thickness of the oxygen-enriched layer was reduced when rolling was performed at a temperature above the β-phase transformation temperature.

(Example B)

First, Ti: 99% by weight, a pure titanium ingot that satisfies ASTM standard Grade 1 of 0.18[O]-0.2[Fe] with the maximum content (% by weight) of impurities, and Ti: 99% by weight, the maximum of impurities A pure titanium ingot that satisfies ASTM standard Grade 2 having a content (% by weight) of 0.25[O]-0.3[Fe] was prepared, and rolling or forging was performed according to the conditions of Table 1 below.

Thereafter, the manufactured titanium slab was cut in the longitudinal direction, and the thickness of the oxygen-enriched layer was obtained through micro-hardness measurement in the thickness direction at 10 locations at 500 mm intervals in the longitudinal direction from the cross section. Observation was carried out to measure the average grain size of the oxygen-enriched layer. And the results are shown together in Table 1 below.

division titanium
Ingot
ASTM
standard β-phase transformation temperature
(℃) Processing
Condition Oxygen enrichment layer thickness
(mm) Average grain size of oxygen enriched layer (㎛)
(min~max) Relationship 1 Relationship 2 Maximum load
(Ton) Example 1 Grade 1 890 920℃
minor 2.2 300
(80~400)
Tailing dissatisfaction dissatisfaction - Example 2 Grade 1 890 920℃
Rolling 0.3 80
(30~100) Satisfaction Satisfaction 84 Example 3 Grade 1 890 860℃
Rolling - 100
(50~200) Satisfaction Satisfaction 252 Example 4 Grade 2 915 1050℃
Rolling 1.5 190
(100~250) dissatisfaction Satisfaction 136 Example 5 Grade 2 915 940℃
Rolling 0.8 150
(150~300) Satisfaction Satisfaction 140 Example 6 Grade 2 915 890℃
Rolling 0.2 80
(20~100) Satisfaction Satisfaction 356

Example 1 is a case of forging at a temperature equal to or higher than the β-phase transformation temperature, and it can be seen that not only the thickness of the oxygen-enriched layer was formed thick, but also the oxygen-enriched layer was non-uniformly formed because the relational expression 2 was not satisfied. In addition, a needle-shaped tail-axis structure was observed in the surface layer, rather than a spherical recrystallized structure. On the other hand, in the case of Example 1, since it is a forging operation, the load may vary according to the contact area, and direct comparison with Examples 2 to 6, which is a rolling process, is difficult, so the maximum load is not separately described.

Example 2 is an example that satisfies all the conditions of the present invention, and it can be seen that the oxygen-enriched layer was formed as thin as 0.3 mm (relational expression 1 was satisfied), and a uniform oxygen-enriched layer was formed by satisfying the relational expression 2. In addition, by observing the cross section of the pure titanium slab with an electron microscope, it was confirmed that the center of the base material was made of a cast structure, and that the shape of the recrystallized structure of the surface layer was spherical.

Example 3 is a case in which rolling, that is, α rolling, was performed at a temperature lower than the β-phase transformation temperature, and the oxygen-enriched layer was formed very thin and the exact thickness thereof was not measured, but it was confirmed that the relational expression 1 was satisfied. However, it can be seen that in Example 3, as the rolling at a temperature less than the β-phase transformation temperature, the maximum load during rolling was significantly higher than that of Example 2 in which β-rolling was performed. And it can be seen that the same results appear in the grade 2 titanium slab through Examples 5 and 6.

In the case of Example 4, when rolling was performed at a temperature exceeding the β-phase transformation temperature +100°C, the oxygen-enriched layer was formed thick due to the excessive heating temperature, and the relational expression 1 was not satisfied.

On the other hand, Examples 4 to 6 confirmed the thickness and rolling load of the oxygen-enriched layer when rolling was performed at different temperatures for the grade 2 pure titanium slab. As can be seen from the results of Table 1, as the rolling temperature decreases, the thickness of the oxygen-enriched layer is formed thinner, but it can be seen that the rolling load tends to increase.

In addition, when comparing Examples 2 and 3 (Grade 1) and Examples 5 and 6 (Grade 2), it can be seen that the maximum loads of Examples 5 and 6 were greater under similar conditions. This is due to the characteristics of titanium, which increases the deformation resistance as more impurities are added. Grades 3 and 4 have higher deformation resistance than grade 2, and in the case of Ti alloys such as Ti64, the high temperature deformation resistance is several times that of CP-Ti. It leads. Therefore, when β-rolling is carried out under the conditions of the present invention, the rolling load can be effectively reduced while the oxygen-enriched layer is formed thin, and thus an advantageous effect can be obtained that can increase the range of thinner products that can be produced.

Although it has been described with reference to the above embodiments, it will be understood that a person skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention described in the following claims. I will be able to.

Claims (11)

Titanium base material; And
Including; an oxygen-enriched layer provided on the surface of the titanium base material,
The surface layer portion within 5 to 10 mm in the thickness direction from the surface of the parent material including the oxygen-enriched layer has an average grain size of 10 to 500 μm and is made of a spherical recrystallized structure,
Titanium slab with a maximum thickness of the oxygen-enriched layer of 1 mm or less (including 0 mm).
The method of claim 1,
Titanium slab, characterized in that the hardness of the oxygen-enriched layer is 30% or more higher than the average hardness value at a depth of 3 to 5 mm in the thickness direction from the surface of the base material.
The method of claim 1,
The oxygen content of the oxygen-enriched layer is a titanium slab, characterized in that the maximum allowable oxygen content according to the alloy composition of the titanium base material is 15.5% or less.
The method of claim 1,
The oxygen-enriched layer is a titanium slab, characterized in that satisfying the following relational formula 1.
[Relationship 1] (B-A)/A × 100 ≤ 50%
A = ((hardness value of 5mm depth in thickness direction) + (hardness value of 4mm depth in thickness direction) + (hardness value of 3mm depth in thickness direction)) / 3
B = hardness value of 1mm depth in the thickness direction
The method of claim 1,
Titanium slab, characterized in that the thickness of the oxygen-enriched layer satisfies the following relational formula 2.
[Relationship 2]

,

(Where n _i (n ₁ , n ₂ , …, n ₁₀ ) is the thickness of the oxygen-enriched layer obtained through micro-hardness measurement in the thickness direction for 10 locations at 500 mm intervals in the length direction, respectively, and μ is 10 It is the average value of the thickness of the oxygen-enriched layer in the area.)
The method of claim 1,
Titanium slab, characterized in that the thickness of the titanium slab is 100 ~ 300㎜.
Preparing a titanium ingot;
Heating the titanium ingot at a heating temperature equal to or higher than the β-phase transformation temperature and equal to or less than the β-phase transformation temperature +100° C. for 0.3t to 1t (t: ingot thickness, mm);
Rolling the heated titanium ingot at the β-phase transformation temperature or higher and the β-phase transformation temperature +100°C or lower; And
Cooling after the rolling;
Method for producing a titanium slab comprising a.
The method of claim 7,
Before the rolling, at least one or more of a forging step and at least one rolling step are further performed at a temperature equal to or higher than the β-phase transformation temperature, and at a temperature equal to or higher than the β-phase transformation temperature and lower than the β-phase transformation temperature +100°C. Method for producing a titanium slab, characterized in that reheating.
The method of claim 7,
The rolling step consists of one or two or more passes,
The reduction rate per pass is a method of manufacturing a titanium slab, characterized in that the strain in the thickness direction of the surface layer is set to be 4% or more greater than the strain in the thickness direction of the center.
The method of claim 7,
The thickness of the titanium ingot is 700 ~ 900㎜,
The method of manufacturing a titanium slab, characterized in that the slab thickness after the rolling is 100 ~ 300㎜.
The method of claim 7,
The rolling is a method of manufacturing a titanium slab, characterized in that the rolling is carried out by a powder rolling method.

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