JP2004306126A - Method of rolling base stock for titanium alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling method of a base stock for titanium alloy by which the rolling can be performed by a small number of processes without generating flaws such as cracks on the surface, and fuel and thermal energy can be reduced. <P>SOLUTION: This method is a rolling method of the base stock for titanium alloy which includes a heating stage S1 where the ingot ( base stock of the titanium alloy ) W1 is heated up to 1,200 °C, for example, and a first blooming stage S2 where such a heated ingot W1 is made into a bloom ( intermediated base stock ) W2 having a cross section which is reduced to the reduction of area of ≥ 80% by hot blooming of a plurality of times, a complementary heating stage S3 where the bloom W2 is heated to ≥ 1,150°C and a second blooming stage S4 where the complementarily heated bloom W2' is made into a billet ( titanium alloy material ) W3 having a cross section which is reduced to a reduction of area of ≥ 50% by hot blooming of a plurality of times. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for rolling a titanium alloy material for hot rolling into a billet having dimensions for processing an ingot or the like of a titanium alloy into various products.
[0002]
[Prior art]
BACKGROUND ART Titanium alloy materials such as billets having required dimensions and shapes for manufacturing various products made of titanium alloys are manufactured by hot rolling a titanium alloy material in a form such as an ingot. Such a conventional rolling method has been performed as follows.
For example, after a titanium alloy having a composition of Ti-6 wt% Al-4 wt% V is melted and cast into an ingot case (not shown), as shown in the upper part of FIG. An ingot (titanium alloy material) W1 having a shape is prepared. Next, as shown in FIGS. 4A and 4B, the ingot W1 is inserted into a soaking furnace in an atmosphere or an inert gas atmosphere and heated to 1150 ° C. over several hours. For about 5 hours to equalize the overall temperature (heating step s1).
[0003]
Next, the heated ingot W1 is passed between a pair of flat rolls (not shown), and hot slab rolling over several tens of passes is performed while gradually narrowing the gap between the pair of flat rolls. It is passed between grooved rolls having a concave cross section (first block rolling step s2: see FIG. 4A). In addition, the cross-sectional reduction rate in the entire hot slab rolling step s2 is 90% or more.
As a result, as shown in FIG. 4B, a long bloom W2 having a square cross section with a side of 170 mm is obtained. At both ends e, e of the bloom W2, approximately cross-shaped slits s, s accompanying plastic deformation by the flat roll during the hot rolling are located. By cutting both ends e and e of the bloom W2 and cutting the remaining portion to a predetermined length along the axial direction to divide the bloom W2, a plurality of slightly shorter blooms W2 'shown in FIG. Form.
[0004]
Further, as shown in FIGS. 4A and 4B, the entire surface layer of the bloom W2 'cooled to around room temperature is ground to a predetermined thickness by a grinder G, so that the surface associated with the hot slab rolling is formed. A surface grinding step s3 is performed to make the bloom W2 ″ from which flaws have been removed.
Next, as shown in FIGS. 4 (A) and 4 (B), the bloom W2 ″ having been subjected to surface grinding is reinserted into a soaking furnace, heated to 1100 ° C. over several hours, and brought to that temperature for several hours. Then, the heated bloom W2 ″ is passed between a pair of notched grooved rolls (not shown) and is gradually passed through a plurality of gradually smaller grooved rolls (not shown). The second bulk rolling step s5: see FIG. 4 (A)). Incidentally, the cross-sectional reduction rate in the entire hot slab rolling step s5 is about 70%.
[0005]
As a result, as shown in FIG. 4B, a long billet W3 having a square cross section with a minimum of 95 mm on one side is obtained. By cutting both ends e and e of the billet W3 in the same manner as described above, and cutting and dividing the remaining portion into a predetermined length in the axial direction, a slightly short billet W3 shown in the lower end of FIG. 'Can be obtained in plurality.
However, in the above-mentioned method of rolling the ingot (titanium alloy material) W1, the heating temperature in the initial heating step s1 is low, so that the hot workability in the first slab rolling (hot rolling) step s2 is insufficient. Thus, cracks are likely to occur near corners of the surface of the obtained bloom W2. In order to avoid this, it is necessary to cool the shortened bloom W2 'to room temperature and perform a complicated surface grinding step s3. In addition, since the ground bloom W2 ″ is reheated (step s4) and hot-rolled (step s5) to a required cross-sectional dimension, there is a problem in that the loss of fuel and heat energy is large. .
[0006]
In addition, the rolling material of the titanium alloy is heated, the inclined rolling is performed at a predetermined cross-sectional reduction rate corresponding to the heating temperature, and then the material after the inclined rolling is reheated or retained, and then the hole rolling mill is used. There has been proposed a method of manufacturing a rod or a wire of a titanium alloy by a hot rolling process (for example, see Patent Document 1).
However, the above-mentioned production method requires that a heated titanium alloy rolled material be rolled in a special rolling mill called tilt rolling, and has an object to produce a titanium alloy rod or wire. For this reason, the technical field cannot be applied directly or indirectly to the present invention for manufacturing a titanium alloy material such as a billet having a required size and shape for manufacturing various products made of a titanium alloy. Was something.
[0007]
[Patent Document 1]
JP-A-6-292906 (pages 1 to 6)
[0008]
[Problems to be solved by the invention]
The present invention solves the problems in the conventional technology described above, and provides a rolling method of a titanium alloy material that can be performed with a small number of steps without generating defects such as cracks on the surface and can reduce fuel and heat energy. That is the task.
[0009]
[Means for Solving the Problems]
The present invention, in order to solve the above problems, as a result of research and investigation by the inventors, to increase the temperature to initially heat the titanium alloy material and hot-rolling by effectively utilizing the heat energy, It was made with inspiration.
That is, the method for rolling a titanium alloy material in the present invention (claim 1) includes a heating step of heating the titanium alloy material to more than 1150 ° C., and a cross-section of the heated titanium alloy material by a plurality of hot slab rolling operations. A first bulk rolling step of forming an intermediate material having a cross section reduced to a reduction rate of 80% or more, a replenishment heating step of heating the intermediate material to 1150 ° C. or more, and a hot rolling of the replenished heated intermediate material a plurality of times; A second bulking step of forming a titanium alloy material having a cross-section reduced to a cross-sectional reduction rate of 50% or more by bulk-rolling.
[0010]
According to this, since the titanium alloy material is heated to a relatively high temperature exceeding 1150 ° C., the surface of the intermediate material obtained by the first sizing and rolling step is less likely to crack or split, and the heated state of the intermediate material is reduced. After the supplementary heating of the intermediate material to 1150 ° C. or higher, the process can be immediately shifted to the second block rolling step. Therefore, the number of steps and time can be remarkably reduced as compared with the above-described conventional technique, and the fuel and heat energy used can be considerably reduced. Therefore, it is possible to accurately and efficiently manufacture a titanium alloy material such as a billet having a required size and shape for manufacturing a product made of various titanium alloys.
[0011]
When the temperature of the heating step is 1150 ° C. or lower, cracks and tears due to hot working are likely to occur in the intermediate material in the first slab rolling step by hot slab rolling a plurality of times. For this reason, the temperature is set higher than 1150 ° C., and the desirable temperature range is 1200 to 1250 ° C. as described below. Further, when the temperature of the replenishment heating step is lower than 1150 ° C., cracks and the like easily occur in the titanium alloy material in the second bulk rolling step as described above. For this reason, the temperature is set to 1150 ° C. or more, and a desirable temperature range is 1150 to 1200 ° C. Furthermore, the reason why the cross-sectional reduction rate in the first bulk-rolling step is 80% or more and the cross-sectional reduction rate in the second bulk-rolling step is 50% or more is that the required cross-sectional shape and dimensions are less than these. This is because it becomes difficult to obtain a titanium alloy material by the above-mentioned small number of steps. % Range.
The titanium alloy material is, for example, an ingot that has been melted and cast, and the intermediate material is a long bloom that has been hot slab-rolled in the first slab-rolling step, and a cut bloom thereof. And the like, and the above-mentioned titanium alloy material includes a long billet hot-bulking-rolled in the second bulk-rolling step, and a cut billet thereof.
[0012]
Further, in the present invention, the heating step is to heat the titanium alloy material to 1200 to 1250 ° C. in a soaking furnace and hold it for several hours or more. A method of rolling a titanium alloy material in which at least the surface layer is heated to 1150 to 1200 ° C. (claim 2) is also included.
According to this, as described above, it is possible to reliably prevent cracks, tears, and the like due to hot working in the first and second bulking and rolling steps.
[0013]
Furthermore, the present invention also includes a method for rolling a titanium alloy material, wherein the temperature of the intermediate material at the time of final rolling in the second bulk rolling step is 800 ° C. or more (Claim 3). According to this, it is possible to further prevent a situation in which cracks, tears, and the like due to hot working in the second bulk rolling step occur on the surface of the titanium alloy material.
If the temperature is lower than 800 ° C., cracks and the like are likely to occur. Therefore, the temperature is excluded from the temperature range, and preferably 830 ° C. or higher. Further, the temperature may be at least 830 ° C. or more at least at the surface of the intermediate material where cracks and the like are likely to occur.
[0014]
In addition, the present invention includes a method for rolling a titanium alloy material (claim 4), wherein the titanium alloy is an α + β type titanium alloy. According to this, it is possible to more reliably prevent cracks and the like in the first and second block rolling processes, especially in the latter.
The α + β type titanium alloy includes Ti-6 wt% Al-4 wt% V, Ti-3 wt% Al-2 wt% V, Ti-6 wt% Al-7 wt% Nb, Ti-6 wt% Al-6 wt% V- 2 wt% Sn, Ti-6 wt% Al-2 wt% Sn-4 wt% Zr-6 wt% Mo, and the like. In particular, in the case of typical Ti-6wt% Al-4wt% V, if the temperature in the second bulking step is set to 830 ° C or more, cracks and the like can be reliably prevented.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings.
For example, a titanium alloy composed of Ti-6wt% Al-4wt% V is melted and then cast into an ingot case (not shown) to obtain a diameter: 600 mm × length: 1500 mm as shown at the upper end of FIG. An ingot (titanium alloy material) W1 having a cylindrical shape is prepared in advance.
First, as shown in FIGS. 1A and 1B, the ingot W1 is inserted into a soaking furnace in an atmosphere or in an atmosphere of an inert gas such as Ar and the like. After heating to 1200 to 1250 ° C., the temperature is maintained for about 5 to 6 hours to uniform the heating temperature of the entire ingot W1 (heating step S1).
[0016]
Next, the heated ingot W1 is passed between a pair of flat rolls R1 and R2 shown in FIG. 2A to obtain a material W1a having a substantially oval cross section as shown in FIG. 2B. The end e of the material W1a undergoes plastic deformation in which the contact surface with the rolls R1 and R2 is extended. The position orthogonal to the feed direction of the material W1a is alternately changed by 90 degrees, and hot slab rolling over about 40 passes is performed while gradually narrowing the gap between the flat rolls R1 and R2. As a result, as shown in FIG. 2C, the material W1b has a substantially square cross section and curved corners. Finally, as shown in FIG. 2 (D), the material W1b is passed between a pair of rolls R3, R4 having a rectangular section g1 with grooves g1 (first slab rolling step S2: see FIG. 1 (A)). The cross-sectional reduction rate by the entire hot slab rolling is 80% or more.
[0017]
As a result, as shown in FIG. 2E, a long bloom (intermediate material) W2 having a square cross section of 190 mm on a side is obtained. At both ends e, e of the bloom W2, as shown in FIG. 1 (B), substantially cross-shaped slits s, s accompanying plastic deformation of the flat rolls R1, R2 and the like during the hot rolling are located. ing. By cutting the bloom W2 at both ends e and e and hot-cutting the remaining portion along the axial direction to divide the bloom W2, a bloom W2 ′ having a length of 5000 mm is formed as shown in FIG. For example, two are formed.
Next, as shown in FIGS. 1A and 1B, the two blooms W2 'in a heating state of about 850 to 950 ° C. are inserted into an intermediate heat retaining furnace, and are taken for about 10 to 20 minutes. Then, supplementary heating for supplementing thermal energy is performed so that at least the surface temperature is 1150 to 1200 ° C. (supplementary heating step S3).
[0018]
Further, as shown in FIG. 2 (F), each bloom W2 'taken out of the intermediate heat preserving furnace is passed between rolls R5 and R6 having a right-angled triangular groove g2 as shown in FIG. Are passed between the grooved rolls Rn, Rn, which become smaller in order, by 5 to 8 passes. Lastly, as shown in FIG. 2 (G), hot slab rolling (the second slab rolling step S4: see FIG. 1 (A)) is performed by passing through the rolls R7 and R8 having the grooves g3 of the final dimensions. The cross-sectional reduction rate in the entire process S4 is 50% or more, preferably 60% or more.
As a result, as shown in the lower part of FIG. 1B, a long billet W3 having a square cross section with a minimum side of 95 mm is obtained. By cutting both ends of the billet W3 similar to the above and cutting the remaining portion along the axial direction to divide the billet W3, a billet (titanium) having a length of 4000 to 6500 mm as shown in the lower end of FIG. (Alloy material) W3 '.
[0019]
The obtained plurality of billets W3 'are inspected and subjected to necessary surface grinding by a grinder (not shown) or the like, thereby forming a titanium alloy material (titanium product processing) for processing into a titanium alloy product such as a wire. Material).
According to the method for rolling a titanium alloy material in the present invention as described above, since the titanium alloy material W1 is heated to a relatively high temperature in the heating step S1, the surface of the intermediate material W2 obtained in the first slab rolling step S2 is obtained. After the supplementary heating (S3) of the heated intermediate material W2 'to 1150 ° C. or more, the process can immediately proceed to the second bulking step S4. Therefore, the number of steps and time can be remarkably reduced as compared with the related art, and the loss of fuel and heat energy can be reduced.
[0020]
【Example】
Hereinafter, specific examples of the present invention will be described together with comparative examples.
Two cylindrical ingots (titanium alloy material) W1 made of a titanium alloy of Ti-6 wt% Al-4 wt% V and having a diameter of 600 mm × length: 1500 mm are prepared, and one of the ingots W1 is an embodiment and the other is ingot. Was used as a comparative example.
The ingot W1 of the example was inserted into the soaking furnace, heated to 1200 ° C. over 2 hours as shown by the solid line in the graph of FIG. 3, and then maintained at that temperature for 6 hours (heating step S1). On the other hand, the ingot W1 of the comparative example was also inserted into the same soaking furnace and heated to 1150 ° C. over 2 hours as shown by the dashed line in FIG. 3, and then kept at that temperature for 5 hours (heating step). s1).
[0021]
Next, as shown by a solid line in FIG. 3, the ingot W1 of the example was passed between the flat rolls R1 and R2 shown in FIG. 2A, and the obtained material W1a was gradually narrowed in the gap. Hot slab rolling with 40 passes between the flat rolls R1 and R2 was performed. The obtained material W1b having a substantially square cross section was passed between the rolls R3 and R4 with the groove g1 (first slab rolling step S2). The cross-sectional reduction rate of the entire process S2 was 87.2%. By cutting the both ends e and e of the obtained bloom W2 having a square cross section and a side of 190 mm in the embodiment, and cutting the remaining portion by hot cutting along the axial direction, the embodiment is divided. And two blooms W2 'having a length of 5000 mm.
[0022]
On the other hand, as for the heated ingot W1 of the comparative example, as shown by the one-dot chain line in FIG. 3, the hot slab rolling which is passed between the flat rolls R1 and R2 and the like and the rolls R3 and R4 with the groove g1 as described above. The first blooming step s2 was performed to obtain a bloom W2 of a comparative example having a square cross section and a side of 170 mm. The cross-sectional reduction rate in the entire process s2 was 89.8%. By cutting both ends e and e of the bloom W2 and cutting the remaining portion by hot cutting along the axial direction, three blooms W2 'having a length of 4000 mm in the comparative example were formed.
As shown by the one-dot chain line in FIG. 3, after the three blooms W2 'are air-cooled to room temperature, their surface layers are ground over four layers by the grinder G (surface layer grinding s3) and located on the surface. Flaws such as cracks were removed.
[0023]
Next, after inserting the two blooms W2 'of the embodiment in a heating state of about 900 ° C. into an intermediate heat-retaining furnace, as shown by a solid line in FIG. Heated (replenishment heating step S3).
Further, as shown by the solid line in FIG. 3, the two blooms W2 'taken out of the intermediate heat preserving furnace are continuously rolled between the rolls R5 and R6 with the grooves g2 and the grooved rolls Rn which become smaller sequentially. , Rn in a total of 8 passes. Lastly, hot rolling was performed by passing through rolls R7 and R8 with grooves g3 of product dimensions (second bulk rolling step S4), and a long titanium alloy material W3 having a square section of 95 mm on a side was obtained. The area reduction rate during this period was 75.0%.
By cutting both end portions of the two titanium alloy materials W3 and hot cutting the remaining portion along the axial direction to divide the titanium alloy material W3 into three sections, each of the sections has a square section of 95 mm and a length of 6500 mm. In total, six titanium alloy materials W3 ′ were obtained.
[0024]
On the other hand, the three blooms W2 'of the comparative example subjected to the surface layer grinding were respectively inserted into the soaking furnace, heated to 1100 ° C. over 2 hours as shown in FIG. 3, and then held for 2 hours (reheating). Step s4).
Further, as shown by the one-dot chain line in FIG. 3, the three blooms W2 'taken out of the soaking furnace are passed between the rolls R5 and R6 with the groove g2 as described above for a total of 13 passes. Hot slab rolling (the second slab rolling step s5) of passing through the rolls R7 and R8 with the groove g3. As a result, a long titanium alloy material W3 having a square cross section of 95 mm on a side was obtained. The area reduction rate during this period was 68.8%.
By cutting both end portions of the three titanium alloy materials W3 and hot-cutting the remaining portion along the axial direction and dividing into two, a comparative example having a square section of 95 mm on a side and a length of 6000 mm In total, six titanium alloy materials W3 ′ were obtained.
[0025]
The relationship between the temperature histories and the required time in the examples and comparative examples as described above is schematically illustrated by a graph in FIG. According to this, it was found that the working time of the working example was clearly shorter and the loss of heat energy was smaller in the working example than in the comparative example.
Further, with respect to all of the six titanium alloy materials W3 'of the above-described embodiment and the six titanium alloy materials W3' of the comparative example, the entire surfaces thereof were visually inspected, and slight surface flaws that could be repaired with a grinder or the like were found. Except for surface defects such as cracks and tears having a depth of 5.0 mm or more that are not suitable for product processing and cannot be repaired.
As a result, in the titanium alloy material W3 'of the example, only minor surface flaws that could be repaired by all six were observed. On the other hand, in the titanium alloy material W3 'of the comparative example, at least one crack that could not be repaired was recognized in two out of six pieces. This is presumably because, in the comparative example, since the heating step s1 and the reheating step s4, particularly the heating temperature of the latter were low, cracks were induced in the subsequent hot working in the second block rolling step s5.
The operation and effect of the present invention are supported by the results of the above examples.
[0026]
The present invention is not limited to the embodiments and examples described above.
For example, in the first slab rolling step S2, the flat rolls R1 and R2 are initially only a few passes, and all subsequent tens of passes are hot slab rolled using the grooved rolls R3 and R4. Is also good.
Further, the intermediate heat retaining furnace can be used also as the soaking furnace.
Further, the titanium alloy material is not limited to the cylindrical ingot W1, but may be a quadrangular prism-shaped ingot.
It should be noted that the titanium alloy that is the subject of the present invention is not limited to the above-mentioned α + β-type titanium alloy, but also includes an α-type titanium alloy and a β-type titanium alloy.
[0027]
【The invention's effect】
According to the method for rolling a titanium alloy material of the present invention (claim 1), since the titanium alloy material is heated to a relatively high temperature in the heating step, cracks may occur on the surface of the intermediate material obtained in the first slab rolling step. Tear and the like are less likely to occur. In addition, since the intermediate material in the heated state is refilled and heated so as to have the temperature or more, the process can immediately proceed to the second block rolling step, so that the man-hour and time can be remarkably reduced as compared with the related art, and the fuel and heat energy can be reduced. Loss can also be reduced.
According to the method for rolling a titanium alloy material of claims 2 to 4, both cracks and tears associated with the hot working in at least the first bulking step and the second bulking step and at least the latter are ensured. Can be prevented.
[Brief description of the drawings]
FIG. 1A is a flowchart of each step showing a manufacturing method of the present invention, and FIG. 1B is a flowchart showing an outline of each step corresponding to FIG.
FIGS. 2A to 2G are schematic views showing first and second sizing and rolling steps in the manufacturing method.
FIG. 3 is a graph schematically showing a relationship between temperature history and time in Examples and Comparative Examples.
4A is a flowchart of each step showing a conventional manufacturing method, and FIG. 4B is a flowchart showing an outline of each step corresponding to FIG.
[Explanation of symbols]
S1... Heating step S2... First lumping and rolling step S3... Replenishing heating step S4... Second lumping and rolling step W1... Ingot (titanium) Alloy material)
W2, W2 '… Bloom (intermediate material)
W3, W3 '... billet (titanium alloy material)

Claims (4)

A heating step of heating the titanium alloy material to over 1150 ° C.,
A first bulk rolling step of converting the heated titanium alloy material into an intermediate material having a cross-section reduced to a cross-section reduction rate of 80% or more by a plurality of hot-rolling operations;
A supplementary heating step of heating the intermediate material to 1150 ° C. or higher,
A second bulking step of turning the supplementary-heated intermediate material into a titanium alloy material having a cross section reduced to a cross-sectional reduction rate of 50% or more by a plurality of hot slab rolling operations;
A method for rolling a titanium alloy material, comprising: The heating step is to heat the titanium alloy material to 1200 to 1250 ° C. in a soaking furnace and hold it for several hours or more. The method for rolling a titanium alloy material according to claim 1, wherein the method is heated to 1200 ° C. The temperature of the intermediate material at the time of final rolling in the second bulk rolling step is 800 ° C. or more.
The method for rolling a titanium alloy material according to claim 1 or 2, wherein: The method for rolling a titanium alloy material according to any one of claims 1 to 3, wherein the titanium alloy is an α + β type titanium alloy.

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