JP2007332420A - Method for producing titanium material and stock for hot rolling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a titanium material where, even if a blooming stage is obviated, its surface properties after hot rolling can be satisfactorily maintained, and to provide a stock for hot rolling. <P>SOLUTION: The invention is characterized in that at least the surface layer of a face as the rolling face in an ingot is melted and resolidified, and is thereafter hot-rolled. Further, the depth of the melted-resolidified layer in the surface layer is ≥1 mm from the outermost surface of the ingot. Further, the melting of the surface layer is performed by one selected from induction heating, arc heating, plasma heating, electron beam heating and laser heating or in combination with two or more. Further, the melting part is made into a vacuum or an inert gas atmosphere. Further, the ingot cooled at a cooling rate of air cooling or above after heating from a temperature above a β transformation point to a temperature less than a melting point is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a titanium material manufacturing method and a hot rolling material, and in particular, a titanium material manufacturing method and hot rolling that keeps the surface properties after hot rolling well even if the bundling step is omitted. It is related to the material.

  In general, a titanium material is manufactured by making an ingot obtained from a melting step into a slab or billet shape in a lump step, cleaning the surface, hot rolling, and further annealing and cold working. In addition to the widely used vacuum arc melting (VAR) method, the melting process includes an electron beam melting method and a plasma melting method in which melting is performed at a location different from the mold and poured into the mold. In the former, since the casting mold is limited to a cylindrical mold, a bundling process is essential for the production of the plate material. The latter has a high degree of freedom in the shape of the mold, and a cylindrical mold as well as a square mold can be used. In the case of producing a plate material from a square ingot or in the case of producing a bar or wire from a cylindrical ingot, the bundling process can be omitted from the point of the ingot shape.

  However, coarse grains having a width of several tens of millimeters are formed in the as-cast structure of a large ingot used industrially, as shown in FIG. When this ingot is directly hot-rolled without going through the lump process, irregularities are generated on the surface due to the influence of deformation anisotropy within the grains and between the grains due to the coarse grains. It becomes a surface flaw. In order to remove the surface flaws, it is necessary to increase the amount of surface cutting in the pickling process, which causes a problem of deteriorating cost and yield. In order to solve such a problem, a method of reducing surface flaws by subjecting a hot rolling material to processing or heat treatment has been proposed.

  In Patent Document 1, in the case where a titanium material ingot is directly hot-worked by omitting the lump process, in order to refine the crystal grains in the vicinity of the surface layer, the surface layer is strained and then recrystallized. There has been proposed a method of recrystallizing at a depth of 2 mm or more from the surface by heating above the temperature. Examples of means for imparting strain include forging, roll reduction, and shot blasting.

  In Patent Document 2, a titanium material ingot is heated to Tβ + 50 ° C. or higher, and then cooled to Tβ−50 ° C. or lower and then hot-rolled, so that it is formed during rolling by deformation anisotropy of coarse crystal grains. A method of reducing surface waviness and wrinkles and reducing surface wrinkles has been proposed.

  In Patent Document 3, as a method for reducing surface flaws of a rolled product in a titanium material through a bundling process, the temperature at the end of the bundling process is set to the α range, or further, heating before hot rolling is performed in the α range. By carrying out the above, there has been proposed a method in which 60 μm or more is equiaxed from the surface. As a result, it is possible to avoid partial deepening of the oxygen-rich layer, and it becomes possible to remove the oxygen-rich layer in the descaling process, and there is no portion with non-uniform hardness and ductility. The surface properties are supposed to improve.

Japanese Patent Laid-Open No. 01-156456 Japanese Patent Laid-Open No. 08-060317 Japanese Patent Laid-Open No. 07-102351

  However, in the method described in Patent Document 1, shot blasting is mentioned as a means for imparting strain. However, the depth of strain formed by general shot blasting is about 300 to 500 μm or less, which improves quality. This is insufficient to form a recrystallized layer having a depth of 2 mm or more, which is necessary for the purpose. Therefore, it is substantially necessary to give strain to a deeper position by forging or roll reduction, but large equipment is required to perform forging or roll reduction on a large ingot for hot rolling, The cost is not reduced as compared with a normal lump process.

  In addition, the method described in Patent Document 2 has an effect that coarse crystal grains are recrystallized and refined by heating to the β region. However, without passing through the lump process, processing strain is not applied, so there are few recrystallization nuclei, and because the entire ingot is heated, the cooling rate after heating is slow and the crystal grains become coarse. The effect of refining with crystals is limited, and the deformation anisotropy is not sufficiently reduced. Further, even if recrystallization is affected by the crystal orientation of the original coarse grains, it is a factor that does not lead to the elimination of deformation anisotropy. On the other hand, moderate grain refinement may result in an increase in the grain boundary that is the source of surface irregularities, resulting in an increase in the occurrence of surface defects.

  In addition, the method described in Patent Document 3 is based on the premise that the cast structure is broken through the lump process and is made finer and equiaxed. Absent. Even if an equiaxed grain of 60 μm or more is formed from the surface only by heat treatment without the lump process, the crystal orientation is simply affected by the original crystal orientation. Therefore, it is not sufficient to prevent unevenness due to deformation anisotropy due to coarse grains of the structure as cast, and it is clear that problems due to surface flaws arise.

  Then, this invention aims at providing the manufacturing method of a titanium material, and the raw material for hot rolling which can maintain the surface property after hot rolling favorable even if a bundling process is abbreviate | omitted. is there.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have melted and solidified the surface layer of the ingot once when the titanium material is manufactured by performing the hot rolling while omitting the lump process from the ingot. As a result, a solidified structure having a fine and irregular orientation as shown in FIG. 2 can be efficiently formed on the surface layer portion, and as a result, due to the influence of deformation anisotropy of the original coarse solidified structure. It was found that surface wrinkles were reduced, and surface properties equivalent to those obtained through the bulking process could be obtained.

The gist of the present invention is as follows.
(1) A method for producing a titanium material, wherein hot rolling is performed after melting and re-solidifying a surface layer of at least a rolling surface of an ingot.
(2) The method for producing a titanium material according to (1) above, wherein the depth of the melt-resolidified layer of the surface layer is 1 mm or more from the outermost surface of the ingot.
(3) The above (1) or (2), wherein the surface layer is melted by one or a combination of two or more of induction heating, arc heating, plasma heating, electron beam heating, and laser heating. The manufacturing method of the titanium material as described in any one of.
(4) The method for producing a titanium material according to any one of (1) to (3) above, wherein the melted portion is in a vacuum or an inert gas atmosphere.
(5) The titanium material according to any one of (1) to (4) above, wherein an ingot that is heated to a temperature lower than the melting point from the β transformation point and then cooled at a cooling rate equal to or higher than air cooling is used. Manufacturing method.
(6) Titanium characterized in that at least a depth of 1 mm or more from the surface layer corresponding to the rolling surface is a melted and re-solidified structure, and the lower part is a structure as cast or a structure cooled after heating to a β region after casting. Material for hot rolling.

  The present invention makes it possible to produce a titanium material having a surface property equivalent to that in the case of undergoing the bundling step, even if the bundling step conventionally required in the production of the titanium material is omitted. The yield can be improved by reducing the heating time by omitting the process and reducing the pickling amount by improving the surface quality, which has a great effect not only in reducing the manufacturing cost but also in improving the energy efficiency. The effect of is immeasurable.

  The present invention will be described in detail below.

  In the present invention according to claim 1, since only the surface layer portion of the ingot is heated to be rapidly cooled and solidified after melting, the solidified structure having a very fine and irregular orientation as compared with a coarse solid structure as cast. Can be obtained. As a result, a titanium material having excellent surface properties can be obtained by reducing surface wrinkles due to the deformation anisotropy of the original coarse solidified structure. When a square ingot is used, it is effective in improving the surface properties even if the side surface is melted and re-solidified in addition to the rolled surface of the ingot. This is because a portion that was a side surface before rolling appears on the rolled surface due to the metal flow during hot rolling. It should be noted that even if there is an unmelted portion on the surface layer, it does not immediately generate wrinkles, and it is not an essential condition to carry out without gaps. During the surface layer melting treatment, there may be a case where the part other than the part heated for melting is cooled by air cooling or air cooling. Before and after the surface layer melt resolidification, surface care may be performed as necessary. The conditions for heating and rolling before hot rolling may be the same as those in the prior art.

  According to the second aspect of the present invention, the thickness of the melted / resolidified layer is 1 mm or more. This is because, in order to suppress the possibility that an unmelted portion remains due to work variation or the like, it is desirable that the thickness is 1 mm or more.

  According to the third aspect of the present invention, one or two or more of induction heating, arc heating, plasma heating, electron beam heating, and laser heating are used as a melting method.

Induction heating is heated by a coil arranged to go around the ingot. In the high frequency induction heating, the ingot surface layer is heated and melted by the skin effect. The processing time is relatively short, but the equipment cost is high. As for the arc heating, TIG (Tungsten Inert Gas) welding is industrially performed as a welding method, and the method and equipment may be used, and it is an inexpensive method. TIG welding can obtain a molten layer of about 5 mm at a maximum output of 6 kW. Plasma heating can obtain a molten layer of about 10 mm at a maximum output of 15 kW. Electron beam heating can add high-density energy, and a molten layer of about 200 mm can be obtained at a maximum of 100 kW. On the other hand, it is usually necessary to carry out in a vacuum vessel of about 10 ⁻⁵ Torr, which is subject to equipment restrictions. In laser heating, a molten layer of up to about 20 mm can be obtained at a maximum of 15 kW, and processing in the atmosphere is possible.

  When the above methods are used in combination, for example, after preheating by induction heating, the surface layer can be melted by laser heating. Among these, it may be adopted in consideration of conditions such as cost, ingot size, and processing time.

According to the fourth aspect of the present invention, the melting part is set to a vacuum or an inert gas atmosphere. The surface layer may be melted in a vacuum or in an inert gas atmosphere or by spraying an inert gas on the melting portion. As a result, it is possible to prevent oxygen and nitrogen from entering the molten layer and changing the quality. Moreover, the blowing of the inert gas also has an effect of increasing the cooling rate and making the re-solidified structure finer. The inert gas referred to in the present invention refers to argon and helium, and does not include nitrogen that reacts with titanium. The degree of vacuum when performing in a vacuum vessel is preferably about 5 × 10 ⁻⁵ Torr or more.

  The present invention according to claim 5 is a method in which a heat treatment is performed by heating at a cooling rate equal to or higher than air cooling after heating to a temperature lower than the melting point from the β transformation point to further refine the coarse solidified structure as cast solidified, The surface layer is melted and re-solidified. By this method, a solidified structure with smaller deformation anisotropy can be obtained, and the occurrence of surface defects can be reduced.

  The present invention according to claim 6 has a melt-resolidified layer having a depth of 1 mm or more in the surface layer, and the other part is a structure subjected to a heat treatment for cooling after heating to a β region after casting or to a β region after casting. It is a material for hot rolling of titanium material. By using this material, it is possible to obtain a titanium material having a surface quality equivalent to that when the normal block process is performed even when the block process is omitted.

  In the present invention, the term “shard” refers to all methods of processing an ingot into a rolling material shape, and includes forging and pressing in addition to rolling.

  Hereinafter, the present invention will be described more specifically with reference to examples.

  No. in Table 1 In the examples and comparative examples shown in 1 to 13, the titanium ingot was manufactured by an electron beam melting method and cast in a square mold. A plate having a thickness of 4 mm was produced from an ingot having a thickness of 200 mm, a width of 1000 mm, and a length of 4500 mm by hot rolling. After pickling, surface defects were visually evaluated. Surface melting by TIG welding was performed at 200 A without using a filler material. For surface layer melting by an electron beam, an electron beam welding apparatus having a rated output of 30 kW was used. Unless otherwise specified in the following examples, surface layer melting was performed by TIG welding.

  No. In any of Examples 1 to 13 and Comparative Example, the cast surface of the ingot is cut off after the ingot is manufactured, or the surface scale layer is cut off after the ingot is heated and cooled. No. described later. The same applies to 14 to 20.

  No. The comparative example 1 is a case where it is manufactured by a method through a conventional lump process using two types of industrial pure titanium.

  No. The comparative example 2 is a case where hot rolling is performed by using the industrially pure two kinds of titanium material, omitting the lumping process, and the plate subjected to pickling after hot rolling has coarse surface defects. Observed.

  No. The comparative example 3 was obtained by performing hot rolling after heating the ingot to the β region and holding it for 30 minutes after cooling using an industrial pure titanium type 2 material, omitting the lump process. The surface wrinkle of the hot-rolled pickled plate is coarse, and the wrinkle frequency is no. More than 2. This is presumably because the coarse crystal grains of the ingot were changed to a large number of crystal grains having a medium grain size by the β-region heating, and the grain boundaries that caused the surface irregularities increased.

  No. In Example 4, after using an industrial pure titanium type 2 material to cut and remove the casting surface of the ingot, the surface layer was melted and re-solidified, and the surface was further cut so that the thickness of the melt-resolidified layer was 0.5 mm. The depth is adjusted and then hot rolled. A slightly coarse surface flaw was observed, but no surface melting occurred. Compared to 2, it was improved.

  No. Example 5 uses industrial pure titanium type 2 material and cuts and removes the casting surface of the ingot, then melts and resolidifies the surface layer, and further cuts the surface so that the thickness of the melted and resolidified layer is 1 mm from the surface. The depth is adjusted and then hot rolled. The surface wrinkles were slight and greatly improved, and the level was the same as that of the conventional method of passing through the lump process.

  No. In Example 6 of the present invention, the cast surface of the ingot was cut and removed by using two types of industrial pure titanium, and then a molten resolidified layer was formed from the surface to a depth of 4 mm and hot rolled. The surface wrinkles was slight and was at the same level as the method through the conventional lump process.

  No. In Example 7, after using an industrial pure titanium two-type material to cut and remove the cast surface of the ingot, a molten resolidified layer was formed from the surface to a depth of 20 mm and hot rolled. Surface melting was performed using an electron beam welding apparatus. The surface wrinkles was slight and was at the same level as the method through the conventional lump process.

  No. Example 8 uses two types of industrial pure titanium, heated to the β region, cooled after holding for 30 minutes, cut off the surface scale layer, melted and resolidified the surface layer, and further cut the surface Then, the thickness of the melt-resolidified layer was adjusted to a depth of 1 mm from the surface, and then hot-rolled. Even in this case, there was an effect of surface melting and re-solidification, the surface flaws were slight, and the level was the same as that of the conventional method of passing through the lump process.

  No. A comparative example 9 is a case where a Ti-1% Fe-0.36% O alloy is used and manufactured by a method that undergoes a conventional lump process.

  No. Comparative example 10 is a case where Ti-1% Fe-0.36% O alloy is used and the hot-rolling is performed by omitting the lump process, and the hot rolled pickled plate has a rough surface. A wrinkle was observed.

  No. In Example 11, the Ti-1% Fe-0.36% O alloy was used to cut and remove the cast surface of the ingot, and then the surface layer was melted and re-solidified, and the surface was further cut to form a melt-re-solidified layer. The thickness is adjusted to a depth of 0.5 mm, and then hot rolled. A slightly coarse surface flaw was observed, but no surface melting occurred. Compared to 10, it was improved.

  No. In Example 12, the Ti-1% Fe-0.36% O alloy was used to cut and remove the casting surface of the ingot, and then the surface layer was melted and re-solidified, and the surface was further cut to form the melt-resolidified layer. The thickness is adjusted from the surface to a depth of 1 mm, and then hot rolled. The surface wrinkles was slight and was at the same level as the method through the conventional lump process.

  No. Example 13 uses a Ti-1% Fe-0.36% O alloy, heats to the β region, cools after holding for 30 minutes, cuts and removes the surface scale layer, melts and resolidifies the surface layer, Further, the surface is cut to adjust the thickness of the melt-resolidified layer to a depth of 1 mm from the surface, and then hot rolled. Even in this case, there was an effect of surface melting and re-solidification, the surface flaws were slight, and the level was the same as that of the conventional method of passing through the lump process.

  No. in the table. In the examples and comparative examples shown in 14 to 20, the titanium ingot was manufactured by an electron beam melting method and cast in a cylindrical mold. A wire rod having a diameter of 13 mm was manufactured from an ingot having a diameter of 170 mm × 12 m by hot rolling. After pickling, surface defects were visually evaluated. Surface layer melting was performed by TIG welding, and was performed at 200 A without using a filler metal.

  No. The comparative example of 14 is a case where it manufactured by the method through a conventional lump process using 2 types of industrial pure titanium.

  No. The comparative example of 15 is a case where the hot-rolling is performed by omitting the lumping process using the industrial pure titanium two-type material, and the plate subjected to pickling after hot rolling has a rough surface flaw. Observed.

  No. Example 16 uses industrial pure titanium two-type material, and after grinding and removing the casting surface of the ingot, the surface layer is melted and re-solidified, and the surface is ground to make the thickness of the melt-resolidified layer 0.5 mm The depth is adjusted and then hot rolled. A slightly coarse surface flaw was observed, but no surface melting occurred. Compared to 15, it was improved.

  No. In Example 17, two types of industrial pure titanium were used to grind and remove the casting surface of the ingot, then the surface layer was melted and re-solidified, and the surface was further ground to give a thickness of 1 mm from the surface. The depth is adjusted and then hot rolled. The surface wrinkles were slight and greatly improved, and the level was the same as that of the conventional method of passing through the lump process.

  No. The 18 comparative example is a case where it manufactures by the method of passing through the conventional lump process using Ti-3% Al-2.5% V alloy.

  No. In 19 examples, a casting surface of an ingot was ground and removed using a Ti-3% Al-2.5% V alloy, and then the surface layer was melted and re-solidified, and the surface was further ground to form a molten re-solidified layer. The thickness is adjusted to a depth of 0.5 mm, and then hot rolled. A slightly coarse surface flaw was observed, but no surface melting occurred. Compared to 18, it was improved.

  No. In the 20th embodiment, the casting surface of the ingot was ground and removed using a Ti-3% Al-2.5% V alloy, the surface layer was melted and re-solidified, and the surface was further ground to form a molten re-solidified layer. The thickness is adjusted from the surface to a depth of 1 mm, and then hot rolled. The surface wrinkles was slight and was at the same level as the method through the conventional lump process.

It is a figure which shows typically a structure by a sectional view with a cast titanium ingot. It is sectional drawing which shows the structure | tissue which melted and resolidified the surface layer of the titanium ingot.

Explanation of symbols

  1 Ingot surface

Claims (6)

  A method for producing a titanium material, comprising performing hot rolling after melting and re-solidifying a surface layer corresponding to at least a rolling surface of an ingot.   2. The method for producing a titanium material according to claim 1, wherein the depth of the melt-resolidified layer of the surface layer is 1 mm or more from the outermost surface of the ingot.   The titanium material according to claim 1 or 2, wherein melting of the surface layer is performed by combining one or more of induction heating, arc heating, plasma heating, electron beam heating, and laser heating. Production method.   The method for producing a titanium material according to any one of claims 1 to 3, wherein the melting part is set to a vacuum or an inert gas atmosphere.   The method for producing a titanium material according to any one of claims 1 to 4, wherein an ingot that is heated to a temperature lower than the melting point from the β transformation point and then cooled at a cooling rate equal to or higher than air cooling is used.   At least 1 mm deep from the surface layer corresponding to the rolling surface is a melted and re-solidified structure, and the lower part is a structure as cast or a structure cooled after heating to the β zone after casting, Rolling material.

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