KR20130109368A - Titanium steel and manufacturing method of the same - Google Patents

Abstract

PURPOSE: A titanium steel and a manufacturing method thereof are provided to be used as a plate type heat exchanger by optimizing a process variable at a manufacturing process and by controlling a chemical component of a titanium steel. CONSTITUTION: A titanium steel comprises oxygen (O) which is in excess of 0 and less than 0.05, iron (Fe) which is in excess of 0 and less than 0.40, carbon (C) which is in excess of 0 and less than 0.10, nitrogen (N) which is in excess of 0 and less than 0.10, hydrogen (H) which is in excess of 0 and less than 0.005, and a rest titanium (Ti) and impurities by a weight%. A sum of a content of the oxygen (O) and the iron (Fe) is in excess of 0 and less than 0.085 by a weight%. A sum of a content of the oxygen (O), the iron (Fe), the nitrogen (N), the carbon (C), and the hydrogen (H) is in excess of 0 and less than 0.12 by a weight%. A uniform elongation of the titanium steel is more than 37%. An Erichsen value of the titanium steel is more than 12.0 mm.

Description

Title: TITANIUM STEEL AND METHOD FOR MANUFACTURING THE SAME

TECHNICAL FIELD The present invention relates to a titanium steel and a method of manufacturing the same, and more particularly, to a titanium steel having excellent processability and a manufacturing method thereof.

In general, industrial facilities such as nuclear power plants and marine facilities such as vessels and chemical plants cool the facilities using heat exchangers, and desalination plants perform heat exchanges in condensers that condense heated steam. Particularly, in the case of marine facilities using seawater, materials having high corrosion resistance to brine are used. As a material suitable for such use, titanium can be mentioned. Titanium is known to have almost semi-permanent corrosion resistance to seawater, including salinity. Therefore, the titanium sheet is processed in various forms to be applied to the marine industrial equipment, thereby improving the cooling efficiency. In particular, by increasing the physical surface area, the titanium plate is processed into various complex shapes in order to widen the contact with the cooling water.

The titanium used in the heat exchanger is mainly processed in the form of a tube or a plate. Titanium plate materials processed into a tubular shape are subjected to a relatively simple roll forming process, and therefore, there is a demand for a feature that mechanical scratches do not occur on the surface rather than press formability during processing. The titanium plate used in the plate shape is made of plate-shaped, low-profile, low-profile plates arranged in multiple layers, and hot water discharged from the equipment and seawater used as cooling water are alternately passed between the plates to enable heat exchange with a wider area . In recent years, as a method of increasing the heat exchange efficiency, it is necessary to complicate a shape to be molded or to deepen a forming depth, and therefore, it is advantageous to have excellent workability in a material basically. Generally, in the case of a tubular heat exchanger, it is applied to seawater desalination facilities by means of condensing water vapor. Plate heat exchangers are widely applied to ship engines or nuclear power plants where the volume is small, the heat exchange ability is excellent, have.

Of these, the production of the plate heat exchanger will be briefly described. First, the plate material of titanium is placed between molds designed to have a certain shape by a press, and a press processing step of applying pressure to the upper and lower molds to form irregularities on the surface is performed. At this time, the surface irregularities are formed by the deformation of the material, and generally involves high deformation processing of 3.0 mm or more in height. In addition, the unevenness is processed into complicated shape considering the flow of refrigerant, and the depth and shape are gradually complicated. Since the strength of the material must be increased along with the reduction of the thickness of the material, a technique for controlling the workability and strength of the material is required .

Conventional techniques (Japanese Patent Application Laid-Open No. 2010-255085) and the like have proposed a technique for controlling the roughness of the titanium surface, which prevents microfailure during processing. This is because, rather than controlling the physical properties of the titanium itself, Technology. Japanese Patent Application Laid-Open No. 2001-303223 discloses a titanium plate having excellent moldability. It is said that excellent drawability can be obtained by controlling the contents of iron and impurities such as chromium and nickel in chemical components. Drawability is a form of machining in the form of cylindrical cup machining, which is a form of machining deformation that does not act much in the process of manufacturing a plate-type heat exchanger.

Conventional techniques use a method of increasing the grain size by increasing the annealing temperature in order to increase the workability of titanium. However, when the crystal grains are excessively coarsened, there is a problem that the surface is roughened. Moreover, there is a problem that an oxide layer having high strength is formed on the surface due to high temperature annealing and workability is lowered.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a titanium plate having excellent moldability so that it can be processed into a complicated shape by controlling parameters of chemical components, cold rolling and annealing heat treatment.

The titanium steel according to one embodiment of the present invention is characterized in that it contains oxygen (O): more than 0 and less than 0.05, iron (Fe): more than 0 and less than 0.40, carbon (C) More than 0 and less than 0.10, and hydrogen (H): more than 0 and less than 0.005, and the remaining titanium (Ti) and impurities.

The content of oxygen (O) and iron (Fe) may be more than 0 and less than 0.085.

The titanium steel may be in weight percent and the sum of contents of oxygen (O), iron (Fe), nitrogen (N), carbon (C), and hydrogen (H)

The titanium steel may have a uniform elongation of at least 37% and an Ericksen value of at least 12.0 mm.

A method for producing titanium steel according to an embodiment of the present invention is a method for producing a titanium steel according to an embodiment of the present invention, which comprises, by weight, oxygen (O): more than 0 and less than 0.05; iron (Fe): more than 0 and less than 0.40; carbon (C) ): More than 0 and not more than 0.10, and hydrogen (H): not less than 0 and not more than 0.005, the remaining titanium (Ti) and the impurities; and annealing the cold-rolled titanium steel by a vacuum annealing method .

In the step of cold-rolling the titanium steel, the titanium steel may be cold-rolled to have a uniform elongation of not less than 37%.

The step of subjecting the cold-rolled titanium steel to annealing may be carried out at a temperature ranging from a recrystallization temperature to a temperature not higher than 660 ° C.

The titanium steel may be controlled to have an Erichen value of 12.0 mm or more.

In the method for producing titanium steel, the sum of the contents of oxygen (O) and iron (Fe) in weight percent can be controlled in the range of more than 0 and less than 0.085.

The sum of the contents of oxygen (O), iron (Fe), nitrogen (N), carbon (C) and hydrogen (H) in weight percent can be controlled in the range of more than 0 and less than 0.12 have.

According to the present invention, it is possible to manufacture a titanium steel having excellent processability that can be used for a plate heat exchanger by controlling the chemical composition of the titanium steel and optimizing the process parameters in the manufacturing process.

In addition, titanium steel having excellent workability can be manufactured, and it can be applied to a cooling system for marine engines using seawater and a heat exchange facility for cooling nuclear power plants.

1 is a SEM photograph of a titanium steel according to Comparative Example 1 of the present invention.
2 is a SEM photograph of a titanium steel according to Comparative Example 3 of the present invention.
3 is a SEM photograph of a titanium steel according to Example 1 of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified, and that other specific features, regions, integers, steps, operations, elements, components, and / And the like.

Unless otherwise defined, 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 this invention belongs. Commonly used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Since the use environment of the plate heat exchanger is mainly for the heat exchange function, the steam is used at a high temperature or a high pressure. Further, in order to improve the heat exchange ability, a complicated processing condition of forming various irregularities on the surface is provided in order to increase the surface area and improve the contact with the refrigerant. Generally, when the workability of the material is not sufficient, even if a crack occurs or a minute crack occurs during press forming, even if a minute break occurs, since heat exchange conditions are high pressure and high temperature conditions, And there is a problem such as an expense for repairing it. In the case where the titanium plate material is not sufficiently press-formed, a film having a lubricating function is applied to the surface of the material in order to increase the workability of the material, and the material is processed into a desired shape by controlling the inflow amount of the material. It is necessary to attach it before molding and remove it after molding. Therefore, additional costs such as equipment and labor costs arise. As described above, the titanium plate material for a plate heat exchanger requires very precise control and technology in the production process because its processability is very important.

The titanium plate material applied to the plate-type heat exchanger is processed into a cylindrical tube or processed into a plate-like plate shape as described above. First, in the case of working in the form of a tube, a roll forming method is used in which a sheet material is loaded between rolls and a cylindrical shape is formed by friction between the sheet material and the sheet material. Therefore, the stretching of the material is relatively low and follows a deformation mode in which the material is formed by uniaxial stretching such as drawing. In this case, the characteristics of the material are greatly affected by the yield strength and tensile strength, and the measurement and evaluation of these indices is possible by tensile test. However, in the case of machining into a plate shape, a plate material is placed between upper and lower dies mounted on a large-sized press, and is processed into a plate shape by a metal already having the concavity and convexity. A blank holder is operated to control the inflow of the sheet material, thereby controlling the inflow amount of each part during the forming process into a desired shape. At this time, the titanium material is deformed in a manner of applying tensile force in two or more directions, which is different from roll forming, which is deformed by a short axis.

As described above, since the shape of the material changes during processing, the index for evaluating the characteristics of the material is different. In the case of the plate material for a plate heat exchanger, the Erichsen value indicating the stretching strain is measured and evaluated desirable. In addition, it is preferable to evaluate the uniform elongation since the material continues to deform until fracture occurs during machining, and fracture begins at a point where local thickness reduction, or necking, occurs. Therefore, in the present invention, the uniform elongation and the Erichen value are evaluated as an index for evaluating the press workability characteristic of the material used in the plate heat exchanger. The uniform elongation of the material indicates the elongation from the start of deformation to the occurrence of local necking, so that the workability is better as the uniform elongation increases. The Erichen value is a method of moving the material by moving a round punch while restraining the material. As the Erichen value increases, the stretchability of the plate heat exchanger is increased.

Therefore, in the present invention, the uniform elongation and the Erichen value measured by a tensile test were measured to evaluate the workability of the material. Usually, the higher the value of the uniform elongation used in the plate heat exchanger is, the higher the desired level is, depending on the type of the heat exchanger and the processing method, but the uniform elongation is preferably 37% or more in order to form the plate shape without occurrence of rupture and local necking Do. In addition, Ericsen values are about 10mm in the case of applications requiring relatively low workability among titanium sheet materials. Recently, the plate shape has been developed as a complicated shape for increasing the surface area, and the depth of curvature of the surface is also increasing. In case of common use, it is preferable to apply Erichen value of at least 12 mm or more.

The present invention has technical features to improve the processability of a titanium plate material for a plate heat exchanger. In order to achieve this, an attempt has been made to control the chemical composition of the material and optimize the process parameters in the manufacturing process to produce a titanium plate having excellent processability.

It can be said that the processability of the titanium plate material is different depending on the chemical composition and the manufacturing method. In the prior art, in order to produce high-porosity titanium with good press formability, the annealing process for obtaining the final material after cold rolling was performed to increase the temperature to make the crystal grains coarse to secure the workability by increasing the elongation. However, as described above, the grain size control technique increases the annealing temperature and facilitates coarsening due to the growth of crystal grains during annealing, but may cause non-uniform deformation due to coexistence of coarse crystal grains and fine crystal grains. In addition, when such a plate is press-molded, there is a problem that irregularities are formed on the surface like an orange surface, resulting in a defect called an orange peel which becomes rough. If the crystal grains are excessively grown, the occurrence of necking is easy and local fracture may occur. In addition, titanium, which is easily reacted with oxygen because of high annealing temperature, is likely to be exposed to the risk of being formed on the surface oxide layer. As described above, the phenomenon that the surface of the plate material becomes rough in the press-molding can be interpreted as a phenomenon in which the deformation behavior between coarse crystal grains differs during the stretching deformation conditions such as plate material formation, and becomes rough due to mutual uniform deformation . Therefore, in order to manufacture a material having a higher cost, it is necessary to change not only the grain size but also the basic characteristics of the material.

The present invention has technical features to improve the processability of a titanium plate material for a plate heat exchanger. In order to accomplish this, the present inventors have tried to produce a titanium plate material having excellent processability by controlling the chemical composition of the material and optimizing process parameters in the manufacturing process. Generally, the material of the plate is affected by the chemical composition, and in the case of titanium steel, it is required to have a high purity because of its high corrosion resistance characteristics. The chemical composition of titanium steel, which is usually used for high corrosion resistance, is composed of 99% or more of purity when no other special elements are added. The elements are composed of nitrogen, carbon and hydrogen based on oxygen and iron And some elements such as chromium and nickel.

All the elements included in the titanium plate greatly affect the material of titanium and are affected by the oxygen and iron having a relatively high content range. The trace elements nitrogen, carbon, hydrogen and the like which are inevitably contained in the manufacturing process The effect of The oxygen contained in the titanium sheet is due to its strong affinity with oxygen, which is a basic characteristic of titanium, although titanium is produced in vacuum but inevitably contains oxygen. Oxygen reacts with titanium to form a surface oxide layer, which affects the surface properties, but oxygen inside is solved to exhibit the effect of solid solution strengthening. That is, as the oxygen content increases, the strength increases, and the elongation and workability decrease. Therefore, in the case of manufacturing a titanium plate having a high price, as in the present invention, its content needs to be controlled within an appropriate range. Iron in titanium is present as an impurity like oxygen. It is preferable to minimize the content of iron because the affinity with titanium is relatively low to form an intermediate compound or an intermetallic compound in excess, rather than forming an oxide. Generally, since the titanium plate material which is required to have high corrosion resistance is high purity, the content of iron is 0.40% or less so that the iron exists in a state of being solidified in titanium. Accordingly, the iron acts to strengthen the titanium plate, and as the content of iron increases, the strength increases and the workability decreases. Since the titanium plate material for the plate heat exchanger is a plate material having a relatively small content of impurities compared to titanium for other uses, the influence on oxygen and iron materials contained in the plate material is relatively large, and the content of iron on the material of the plate material is the same It is known that the content is higher than the oxygen content. As described above, the content of oxygen and iron is an important element for determining the material of titanium, and it is particularly necessary to precisely control it in applications requiring processability.

(C): more than 0 and less than 0.10; nitrogen (N): more than 0 and less than 0.10; and hydrogen (H) ): Not less than 0 and not more than 0.005, and the remaining titanium (Ti) and impurities. In the present invention, the content of oxygen and iron, which are restricted in order to obtain a highly porous plate, is less than 0.085% by weight in terms of the sum of these elements. On the other hand, in addition to oxygen and iron, a trace amount of impurity elements such as nitrogen, carbon, and hydrogen are also included, and they act as a solid element to affect the quality of the titanium plate material. It contributes mainly to solid solution strengthening and has a grain growth inhibiting effect, so that it is necessary to limit the content of these elements to the minimum condition in order to produce a plate with high uniform elongation and high porosity. In the present invention, the total sum of these impurities is limited to less than 0.12% by weight in weight%, so that a titanium sheet with a high uniform elongation and high porosity can be produced.

As described above, the material of the titanium steel is greatly influenced by the content of the elements and the content thereof. In particular, in the case of a plate material to be applied to a plate-type heat exchanger requiring high porosity, the influence of elements is further exerted. In the present invention, the content of oxygen (O) and iron (Fe) in an element in the titanium plate is controlled to be less than 0.085% by weight in manufacturing a titanium plate to be used for a high price by controlling the content of these elements , The total amount of components of titanium except for titanium is controlled to be less than 0.12% by weight, and the titanium steel subjected to rolling and vacuum annealing is applicable to a high-priced steel having a uniform elongation of not less than 37% and an Ericksen value of not less than 12.0 mm . The titanium plate produced through this process has sufficient processing characteristics to form a desired plate heat exchanger without application of a film for improving processability in a press forming process.

Hereinafter, the reasons for the limitation of the chemical composition of the titanium plate material for a plate heat exchanger according to the present invention will be described. As described above, oxygen and iron are mostly present in a solid solution state, and the material, particularly the workability, of the plate material is greatly influenced by the solid solution strengthening effect. With the increase of these elements, the hardening effect is increased and the workability is degraded relatively. In the present invention, the sum of the content of oxygen and iron contained in the material is limited to less than 0.085% by weight, which is advantageous for obtaining workability as the impurity content of the material is lower. However, since it is not easy to industrially produce, And the upper limit is limited to less than 0.085% in a range that can be used as a reference. When the sum of the content of oxygen and iron was 0.085% by weight or more, the deterioration was remarkable in the material and the uniform elongation tended to be remarkably lowered. In addition, it was difficult to obtain sufficient workability because the Erichen value, which is the workability evaluation index, was low. That is, in order to process a complicated form such as a plate-type heat exchanger into a press, it is necessary to control the content of oxygen and iron contained in the material because the workability of the material must be excellent.

In addition to oxygen and iron, titanium is an interstitial element, and nitrogen, carbon, and hydrogen are typical elements that are readily available in the material. These elements are inevitably incorporated in the titanium manufacturing process. However, when the content is increased, the strength is increased by the solid solution strengthening effect, and it is preferable that the content is as low as possible because it interferes with the formation of the aggregate structure, In the case of aiming at high sophistication as in the invention, it is necessary to limit these elements. In the present invention, the sum of the content of nitrogen, carbon, hydrogen, oxygen and iron is limited to less than 0.12% by weight. When the content of these elements is 0.12% or more, each element acts as a solid element in the material, so that it is impossible to obtain sufficient workability due to the problem of grain refinement and strength increase. This means that the contents of nitrogen, carbon and hydrogen, which act on the strengthening effect, should be finely controlled as well as the content of oxygen and iron which are the main elements in controlling the chemical composition of the material.

The titanium plate material having the above-mentioned range of chemical composition was hot-rolled under normal conditions, the surface was cleaned, cold-rolled to obtain a target plate having the final thickness, and then subjected to a recrystallization annealing process by vacuum annealing to evaluate the material. Hot rolling is a process of reheating a sheet from a slab to a medium thickness plate for cold rolling, subjecting it to roughing and finish rolling, and then winding it. In each step, it is important to ensure a sufficient temperature for continuous rolling Do. In the present invention, it was possible to manufacture the product by reflecting the conditions of hot rolling of conventional pure titanium for industrial use. Thereafter, when the oxide layer on the surface is removed and subjected to cold rolling, the final thickness is generally 0.4 to 0.7 mm. In the present invention, it was rolled to a thickness of 0.5 mm. Next, annealing heat treatment is performed to obtain a target material. In this step, the structure deformed by rolling is removed by recrystallization annealing to obtain a final target material. In general, a method of annealing a titanium plate can be divided into a vacuum annealing and a continuous annealing, and a vacuum annealing process is applied in the present invention. Vacuum annealing is advantageous in that it is possible to omit the step of removing the oxide layer on the surface after annealing with the continuous annealing since the annealing atmosphere is an inert gas atmosphere such as vacuum or argon. At this time, the temperature in the vacuum annealing should be designed so that the recrystallization is completed and the target material is obtained. Considering the content of the element of the present invention, the uniform elongation and the Erichen value, the temperature range from the recrystallization temperature to 660 캜 is preferable. If the temperature is lower than the recrystallization temperature, the material remains unstable due to the structure being deformed by rolling. When the material is annealed at a temperature exceeding 660 ° C, the material can be satisfied, but there is a problem that roughness occurs on the surface of the crystal grains after processing . Therefore, in the production of a titanium plate material for a plate heat exchanger having excellent press formability, it is preferable to limit the temperature of the vacuum annealing to a maximum of 660 캜.

The material quality of the titanium sheet obtained through this process was a uniform elongation of more than 37% and an Erichen value of press workability evaluation index of 12 mm or more. The uniform elongation and Ericksen value according to the present invention are superior to the uniform elongation and Erichen values required for conventional plate-type titanium plate materials, and it is possible to produce a titanium plate material having excellent press workability.

Comparative Example  And Example

Hereinafter, the present invention will be described in detail through comparative examples and examples.

Table 1 shows characteristics of the titanium plate materials of Comparative Examples 1-6 and 1-2 according to the range of chemical components and other manufacturing process conditions.

As described above, the range of chemical components in the present invention is characterized by controlling the content of nitrogen, carbon and hydrogen, which are trace elements including oxygen and iron, Since the material is cured, the workability is deteriorated. Therefore, it is preferable to control the content as low as possible. In particular, the content of oxygen and iron greatly influences the material, so it is desirable to control the content of oxygen and iron to be low and to control the content of other elements to be low. In the present invention, in the production of a titanium plate material which is used for high-cost use by controlling the content of these elements, the sum of the content of oxygen (O) and iron (Fe) in the elements in the titanium plate is set to less than 0.085% And the total of the elements excluding the elements is controlled to be less than 0.12% by weight, and the hot rolling, the cold rolling and the vacuum annealing are performed. The material is characterized by having a uniform elongation of not less than 37% and an Ericksen value of not less than 12.0 mm Respectively.

Table 2 shows the tensile properties and workability obtained from the comparative examples and the examples. According to the chemical components and the manufacturing process conditions shown in Table 1, hot rolling and cold rolling were performed to produce a plate having a thickness of 0.5 mm, followed by vacuum annealing The characteristics of the plate produced by the final heat treatment are described. The machinability was evaluated under the stretching deformation condition, which is a deformation method similar to that of the plate heat exchanger, and the Erichen values were measured and compared. In addition, after machining with the same mold, the surface was observed to confirm whether breakage or local necking occurred, and whether roughness occurred on the surface was visually observed.

For reference, the Erichsen test (Erichsen test) It is a test to investigate the deformability of a thin metal plate having a thickness of 0.1 to 2 mm. In the test method, a punch having a diameter of 20 mm is inserted into a metal plate sample, and the extrusion dimension until the gold reaches the sample is calculated to obtain the Ericens value. The larger this value, the larger the deformability of the sample. It is possible to evaluate the press formability in the metal plate and the adhesion in the chromate film of the paint film or zinc plating.

Comparative Example 1 shows a component of a relatively hard material such as titanium, which is generally used for working a tube. The tensile test results showed a high strength and a low uniform elongation as a result of the content of oxygen and iron being out of the range of the present invention. Referring to FIG. 1, the grain size after the heat treatment for annealing did not show sufficient workability to a level of about 10 mu m, and fracture occurred during processing. These material levels usually show a uniform elongation of 30% or more and an Erichen value of 11mm, which is much lower than that required for plate materials, suggesting that the characteristics of the titanium plate for the tube and the plate must be differentiated.

In Comparative Example 2, the sum of the contents of oxygen and iron is 0.105%, which is a comparatively large amount of solid element. The uniform elongation and Ericksen value of Comparative Example 2 were considered to be low characteristics and fracture was observed during processing even though they were produced under the same rolling and annealing conditions as the other comparative examples.

In Comparative Example 3 having a chemical composition similar to that of Comparative Example 2, the annealing heat treatment temperature was increased to 680 占 폚 or higher and the grain size was increased. Referring to FIG. 2, although the size of grains grows as large as about 90 탆 to obtain a relatively soft material, surface roughness is observed by coarse grains during machining due to the formation of irregular crystal grains, A local necking occurred. This means that it is difficult to use it as a plate material for plate because the crystal grain is increased by the high-temperature annealing condition and processing can be carried out by the softening effect of the material, but roughness due to uneven deformation of the crystal grain occurs.

In Comparative Example 4, the sum of the oxygen and iron contents was 0.083%, which satisfied the range of the embodiment of the present invention, 0.085%, while the content of the other elements was 0.123%, which is outside the required level of the present invention. The material annealed under the same conditions as those of the other comparative examples was relatively soft, but the uniform elongation was 31%, which was much lower than that of the present example of 37% and the Ericksen value was 11.6 mm. Which is lower than 12mm. On the other hand, in the press working, local necking was generated and the workability was not excellent.

On the other hand, in Example 1, the sum of the oxygen and iron contents is 0.079%, and the sum of the other elements and the oxygen and iron contents is 0.104%, which satisfies the embodiment of the present invention. In the case of performing hot rolling and cold rolling under ordinary conditions and annealing at an annealing temperature of 658 캜, the yield strength and the tensile strength were comparatively low, and the uniform elongation was particularly 38% or more. Referring to FIG. 3, the size of the crystal grains was about 40 탆, which showed good characteristics such as no breakage or surface roughness during processing. Also, the workability index, Ericksen value, was also shown to be 12.7 mm, which is a very good material property.

In Comparative Example 5, the chemical composition was similar to that of Example 1, and the range of the present invention was satisfied. However, the press-processability of the soft material was confirmed by increasing the annealing heat treatment temperature. As a result, the material level of Comparative Example 5 was almost similar to that of Example 1, and the uniform elongation was 35.3% and the Ericksen value was 12.3 mm, which was close to the present invention. However, there has been a problem that surface roughness occurs in press forming. This is because the crystal grains were excessively coarsened due to the upward temperature of the annealing heat treatment. That is, the soft annealing effect of the material could be expected by the increase of the annealing heat treatment temperature, but there was a limit in satisfying the workability, and also suggest that the optimum annealing heat treatment temperature range was more than the recrystallization temperature and less than 660 ℃.

In Example 2, the sum of oxygen and iron contents is 0.075%, and the sum of oxygen and iron contents including other elements is 0.081%. This is considered to be a high-purity sheet compared to ordinary titanium. The material of the plate produced through the same manufacturing conditions as in Example 1 exhibited excellent properties of softness, with a uniform elongation of 37.6% and an Erichen value of 13.2 mm as a workability index. It can be predicted that the elements present as impurities, in particular, the lower the content of the solid elements, the better the material and workability, and the higher the utilization cost for the production of such high purity titanium, the higher the utilization.

Finally, in Comparative Example 6, the chemical composition was similar to that of Example 1, which satisfied the range of the present invention, but the softness of the material was obtained by lowering the annealing heat treatment temperature and the press workability was confirmed. As shown in the tensile properties in Table 2, the material exhibits rigid characteristics, low uniform elongation and low Erichen value. Further, fracture occurred during press working. This implies the importance of annealing heat treatment temperature and means that annealing heat treatment temperature should be controlled not only in chemical composition but also in appropriate range in order to satisfy soft material and workability. The appropriate annealing temperature obtained through an annealing heat treatment of the present invention in vacuum was higher than that of recrystallization and a temperature below 660 ° C. was appropriate.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the present invention.

Claims (11)

By weight, oxygen (O): greater than 0 and 0.05 or less, iron (Fe): greater than 0 and 0.40 or less, carbon (C): greater than 0 and 0.10 or less, nitrogen (N): greater than 0 and 0.10 or less and hydrogen (H): 0 Titanium steel exceeding 0.005 or less and including the remaining titanium (Ti) and impurities. The method of claim 1,
Titanium steel, in weight percent, wherein the sum of the contents of oxygen (O) and iron (Fe) is greater than 0 and less than 0.085. The method of claim 1,
A titanium steel having a total content of oxygen (O), iron (Fe), nitrogen (N), carbon (C) and hydrogen (H) The method of claim 1,
Wherein the titanium steel has a uniform elongation of at least 37%. The method of claim 1,
Wherein the titanium steel has an Ericksen value of 12.0 mm or more. (Fe): more than 0 and not more than 0.40, carbon (C): more than 0 and less than 0.10, nitrogen (N): more than 0 and less than 0.10, and hydrogen (H): 0 Cold rolling the titanium steel containing the remaining titanium (Ti) and impurities in an amount of not more than 0.005; And
A method of manufacturing titanium steel comprising the annealing heat treatment of the cold rolled titanium steel by vacuum annealing. The method according to claim 6,
In the step of cold-rolling the titanium steel,
Wherein the titanium steel is cold-rolled such that the uniform elongation is not less than 37%. The method according to claim 6,
The annealing heat treatment of the cold rolled titanium steel,
A method for producing titanium steel, which is carried out at a recrystallization temperature not lower than 660 ° C. The method according to claim 6,
Wherein the titanium steel is controlled to have an Erichen value of 12.0 mm or more. The method according to claim 6,
A method for producing titanium steel, in weight percent, in which the sum of the contents of oxygen (O) and iron (Fe) is controlled in a range of more than 0 and less than 0.085. The method according to claim 6,
Wherein the sum of the contents of oxygen (O), iron (Fe), nitrogen (N), carbon (C) and hydrogen (H) is controlled to be in the range of more than 0 and less than 0.12.

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