JP2006281285A - Method for hot-rolling titanium material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for hot-rolling a titanium material, which can be executed in general steel-manufacturing facilities, and can reduce scale defects. <P>SOLUTION: By the method of hot-rolling a heated titanium material, following steps are performed or repeated two or more times, and thereafter the titanium material is rolled into a prescribed size. The steps are: a step in which surface scales are peeled off and crushed by passing the material through reduction rolls with a reduction rate of ≤8% as a first rolling pass; and a step in which the surface scales peeled off and crushed are removed by spraying either of a water stream and a gas stream, or by spraying a mixed fluid of water and gas against a material to be rolled after the rolling pass, or between the rolling passes and after the rolling pass. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for hot rolling a titanium material, and more particularly to a method for hot rolling a titanium material that can reduce hot rolling wrinkles.

  When a titanium material is hot-rolled, it is generally heated to 700 to 900 ° C. with pure titanium for industrial use, and further to 1000 ° C. or more with a titanium alloy having a high hot deformation resistance. On the other hand, when titanium is exposed to an oxidizing atmosphere such as air at a high temperature of 700 to 1000 ° C. or higher, a high-temperature oxidation forms a scale and an oxygen-enriched layer called α-case on its surface on its surface. It is known that the scale and α-case grow as the temperature increases and the time increases. Titanium scales are less prone to delamination than steel scales at high temperatures, and during hot rolling where either or both of high-pressure water and / or slab width reduction as in hot rolling of steel is performed. Since this is difficult to remove by the descaling method (for example, refer to Patent Document 1 and Patent Document 2), defects such as rough skin and wrinkles on the surface of the rolled material after hot rolling (collectively, hereinafter referred to as scale wrinkles). ) May develop.

  Until now, in order to reduce the scale wrinkle of titanium material, as a method of suppressing high temperature oxidation during heating or hot rolling, a method of heating at a relatively low temperature of 500 to 800 ° C. (for example, see Patent Document 3) ), A method of setting the oxygen partial pressure of the atmosphere to 0.02 atm or less (for example, see Patent Document 4), a method of sealing a titanium material in a box and shutting it off from the atmosphere (for example, see Patent Document 5), atmosphere Has been disclosed, for example, a method of using an argon or nitrogen gas (see, for example, Patent Document 6), a method of applying an antioxidant to a material to be rolled (see, for example, Patent Document 7), and the like.

JP 05-057331 A JP 05-277543 A JP-A 64-005606 JP 61-108407 A Japanese Patent Laid-Open No. 61-270361 Japanese Patent Laid-Open No. 06-170410 JP-A-61-133054

  In order to reduce the scale wrinkles generated during the hot rolling of the titanium material, the method for controlling the heating atmosphere as described above to suppress the heating scale requires heating equipment for that purpose. On the other hand, since steel is generally heated in an oxidizing atmosphere such as the atmosphere, if special heating equipment for titanium is required, the advantage that the titanium material can be hot-rolled with the steel production equipment as it is cannot be utilized. .

  Moreover, the method of sealing and heating a titanium material in a box adds a work of sealing in the box, a work of taking out from the box before hot rolling after heating, and a complicated process.

  The method of lowering the heating temperature to suppress the heating scale is because the rolling temperature is also lowered, so when rolling a large size material with large deformation resistance, the load on the rolling mill becomes excessive, and general hot rolling The mill may have insufficient capacity. This is particularly a problem with titanium alloys having high deformation resistance at high temperatures. Furthermore, in the temperature range of about 700 to 800 ° C., the heating scale of titanium cannot be sufficiently suppressed, and scale wrinkles may occur due to hot rolling.

  Therefore, the present invention, in hot rolling of titanium material, without using a heating facility that can control the atmosphere to suppress the heating scale, and without heating in a low temperature region where the hot deformation resistance is excessive, An object of the present invention is to provide a method for hot rolling titanium material, which can reduce scale wrinkles that can be carried out in a general steel production facility.

In order to solve the above problems, the gist of the present invention is as follows.
(1) Upon hot rolling of the heated titanium material, after heating, as a first rolling pass, a step of peeling and pulverizing the surface scale by passing under a rolling roll at a rolling reduction rate of 8% or less; and After the rolling pass, either a water stream or an air flow or a mixed fluid of water and gas is sprayed on the material to be rolled, and a scale removing step is arranged which includes a step of removing the peeled and crushed surface scale, A method of hot rolling a titanium material, characterized by rolling to a size.
(2) The hot rolling method for a titanium material according to (1), wherein the scale removing step is repeated a plurality of times after the heating.
(3) Further, during the rolling pass for peeling and crushing the surface scale, either the water stream or the airflow or the mixed fluid of water and gas is sprayed on the material to be rolled to remove the peeled and crushed surface scale. The method for hot rolling a titanium material as described in (1) or (2) above.

  Here, titanium is a metal having titanium as a main constituent element, including industrial pure titanium, α-type titanium alloy, α + β-type titanium alloy, and β-type titanium alloy.

  Moreover, titanium here can take arbitrary cross-sectional shapes, such as plate shape and rod shape, as the cross-sectional shape.

  According to the present invention, it can be carried out in a general steel production facility without using a heating facility capable of controlling the atmosphere to suppress the heating scale, and without heating in a low temperature range where the hot deformation resistance is excessive. Since it is possible to provide a hot rolling method for titanium material that can reduce scale wrinkles, the industrial effects are immeasurable.

  As a result of intensive research on a hot rolling method for reducing scale wrinkles caused by heating scales in titanium materials, the present inventors passed titanium materials after heating under a rolling roll at a reduction rate of 8% or less. As a result, the heating scale partially peels off on the surface after passing the material, and the heating scale is finely pulverized, and then can be almost removed simply by spraying either a water stream or an air current or a mixed fluid of water and gas. I found out that On the other hand, if a material with a rolling reduction of more than 8% is passed before adding a material with a rolling reduction of 8% or less after heating, the heating scale is pushed into the surface of the titanium material and printed, and the heating scale peels off very much. After that, it was found that about 70% or more remains even when either a water flow or an air flow or a mixed fluid of water and gas is sprayed on the material to be rolled. Then, depending on the heating scale remaining rate after first passing under the rolling roll and spraying either water flow or air flow or a mixed fluid of water and gas, the frequency of occurrence of wrinkles on the surface of the material on which the rolling has been performed subsequently changes. Accordingly, the frequency of occurrence of wrinkles after the final rolling increases in response to the heating scale remaining rate.

  The rolling behavior of the heating scale described above is considered as the following process. When the heating scale comes into contact with the roll, the temperature is lowered, so that the heating scale becomes brittle and is divided even by a slight stress load. When the rolling reduction after heating is as low as 8% or less, since the rolling reduction is small, the heated scale divided on the surface of the material to be rolled comes out of the rolling roll without being crimped to the base material, It can be almost removed by spraying either a water stream or an air stream or a mixed fluid of water and gas. In addition, if the fluid is not sprayed, when the rolling reduction ratio of the next rolling is high, the heating scale whose surface is divided is pushed in and pressed onto the surface of the material to be rolled. On the other hand, when the rolling reduction after heating exceeds 8%, the divided heating scale is pushed in as it is by a rolling roll, and is embedded in a soft base material and pressed. Therefore, a heating scale with a high adhesion and a low peelability remains.

FIG. 1 shows the relationship between the rolling reduction ratio in the first pass (when the material passes once under the rolling roll) and the residual ratio of the heating scale after spraying the water flow after the first pass (evaluated in step 1 below) and further hot The relationship with the frequency of wrinkle generation after cold rolling using a plate that has continued to be rolled (evaluated in step 2 below) is shown. In addition, the used titanium material is industrial pure titanium JIS1 type.
[Step 1]: (1) Heating 60 mm thick slab at 850 ° C. for 4 hours → (2) Heating furnace extraction → (3) Feeding material under rolling roll at various rolling reductions once → (4) Spraying water flow → (5) Evaluate the heat scale remaining rate of the material to be rolled [Step 2]: (1) Heat 60 mm slab at 850 ° C. for 4 hours → (2) Extraction from heating furnace → (3) Roll at various reduction ratios Pass the material under the roll once and spray with water flow → (4) Furthermore, continue the hot rolling with a reduction rate of 10% or more in each pass and roll to a thickness of about 4 mm → (5) Shot blasting and nitric hydrofluoric acid Descaling by washing (approx. 50μm thickness) → (6) Cold rolling to thickness 2mm → (7) Evaluation of flaw occurrence frequency

  Here, the surface of the slab was smoothed by machining, and each of the eight chamfers was one that was cared for 1 mm. The heating scale remaining rate in step 1 was obtained by visually observing a total of 30 locations obtained by dividing the rolled surface into 3 equal parts in the width direction and 10 equal parts in the length direction, and counting the number of places where the heat scale remained. And evaluated as a percentage. The remaining heating scale can be identified by the color, the portion where the heating scale remains is the whitish color of titanium oxide, which is the heating scale, and the portion where the heating scale does not remain is dark gray. is doing. The occurrence frequency of wrinkles in step 2 was evaluated by a percentage by dividing the plate after cold rolling into 30 equal parts in the length direction, counting the number of wrinkles in the 30 places. The presence or absence of a heel was first determined by visual observation, and then visually observed again where the work gloves were caught on the surface.

  Shot blasted and pickled surface skin is rough and may overlook small wrinkles. By performing cold rolling, the surface becomes smooth and the wrinkles extend in the length direction, so that wrinkles can be easily observed. Therefore, wrinkles were evaluated after cold rolling. In other words, as an observation method, wrinkles are evaluated after cold rolling, but the evaluation here is evaluation of wrinkles by hot rolling, that is, hot-rolled surfaces.

  From FIG. 1, as described above, the residual ratio of the heating scale and the frequency of wrinkle generation after cold rolling correspond to each other, and when the reduction ratio of the first pass after heating is 8% or less, When the wrinkle occurrence frequency is both low, 20% or less, and when the rolling reduction is 5% or less, these are stably reduced to 10% or less.

  Moreover, FIG. 2 shows the relationship between the rolling reduction rate when the material is passed under the rolling roll twice after heating (two passes), the heating scale residual rate, and the frequency of wrinkling after cold rolling. In this case, too, water flow was sprayed as in step 1 and step 2 in the same manner as in FIG. Compared to the one-pass material (one pass) in FIG. 1, when the reduction rate is 8% or less, the remaining ratio of heating scale and the frequency of wrinkles are reduced to about 10% or less, and the reduction rate is 5% or less. These are stable to 3% or less. Therefore, wrinkles can be stably reduced by passing a plurality of passes at a rolling reduction of 8% or less.

  The same effects as described above can be obtained with a titanium alloy. In addition, although the water flow was sprayed in the example shown in FIG. 1, FIG. 2, the same effect is acquired even if it sprays airflow or the mixed fluid of water and gas.

  Further, in the case of steel, hot rolling of plates and strips using slabs, in the case of steel, a reduction in the width direction is applied at the beginning of rolling, but in the present invention, the reduction in the width direction is applied before the reduction in the thickness direction or in the same manner as steel. Even if it implements later, since the effect which reduces a hot rolling wrinkle does not change, you may provide the reduction | decrease of the width direction in this invention.

  The invention will now be described in more detail using the following examples.

  First, Table 1 shows the heating conditions, rolling schedule (reduction rate of each pass), the remaining rate of the heating scale, and the frequency of wrinkling after cold rolling when the plate is hot-rolled. In addition, the slab used as a raw material has the same shape with a thickness of 60 mm, a width of 120 mm, and a length of 150 mm, and industrial pure titanium JIS type 1, JIS type 4, JIS 61 type (Ti-3Al-2.5V) which is an α + β type titanium alloy, Four types of Ti-15V-3Cr-3Sn-3Al, which are β-type titanium alloys, were used. The surface of the slab was smoothed by machining, and each of the eight chamfers was one that was maintained at 1 mm. All the heating atmospheres were air | atmosphere, and rolling rolled the slab in the thickness direction with the horizontal roll, and made it the hot rolled sheet of thickness 4mm. No. in Table 1 When the rolling reduction ratio in the first pass is 1%, it means that the material passes through the same rolling roll gap as the slab thickness of 60 mm.

  The heating scale remaining rate in Table 1 is obtained by making a sample in which rolling was stopped with the number of observation passes described in the column, and visually observing the surface of the sample to evaluate the remaining state of the heating scale. Evaluation of the hot rolling mill was carried out by hot rolling according to the rolling schedule shown in Table 1, then shot blasting, slicing by about 50 μm in thickness with nitric hydrofluoric acid, descaling, and then cold rolling to a thickness of 2 mm. The frequency of wrinkle occurrence on the surface was evaluated using a plate. In addition, the evaluation method of the heating scale residual rate and the flaw occurrence frequency after cold rolling is the same as that described above.

  In industrial pure titanium JIS type 1 and JIS type 4 in Table 1, No. 1 which is a comparative example. 7, 8, 12 and 18 have a reduction ratio in the first pass of 10% or more, which is outside the range of the present invention, so that the heating scale residual ratio is 70% or more. The soot generation rate is as high as 40% or more. On the other hand, Example No. whose heating temperature is 850 ° C. 1, 2, 3, 4, 5, 6, 13, 14, 15, 16, 17, and Example No. 800 ° C. 9, 10 and 11 are in the range of the present invention, the reduction ratio of the first pass is 0 to 8%, the residual ratio of the heating scale is as low as less than 20%, and the occurrence frequency of wrinkles after cold rolling is 20% or less. Low.

  Among them, Example No. 1 in which the rolling reduction in the first pass is 5% or less. 1, 2, 3, 4, 5, 9, 10, 13, 14, 15, 16, and 17 have a heating scale residual rate of 7% or less, and the frequency of occurrence of wrinkles after cold rolling is further lower than 10%. I understand that.

  Example No. different only in the spraying conditions of the fluid. When comparing four of 4, 13, 14, and 15, there is almost no difference in the remaining ratio of the heating scale and the frequency of occurrence of wrinkles after cold rolling.

  In the case of titanium alloys Ti-3Al-2.5V and Ti-15V-3Cr-3Sn-3Al in Table 1, the same effects as those of industrial pure titanium JIS type 1 and JIS type 4 are obtained, and the first pass is reduced. In Examples where the rate is as low as 3% or 5%, No. 19, 20, 22, 23 and comparative example No. as high as 30%. Comparing 21 and 24, both the heat scale remaining rate and the flaw occurrence frequency after cold rolling are lower in the example, at 10% or less.

  Further, Example No. 2 which passed 2 or 3 passes at 3% or 5% with a rolling reduction of 8% or less. 25, 26, 27, 28, 29, and 30 have a heating scale remaining rate of 3% or less and a flaw occurrence frequency after cold rolling of 3% or less as compared with the case where only one pass is performed. Recognize. The effect is the same for industrial pure titanium and titanium alloys (Ti-3Al-2.5V, Ti-15V-3Cr-3Sn-3Al).

  Next, Table 2 shows the heating conditions, rolling schedule (reduction rate of each pass), the remaining rate of the heating scale, and the frequency of wrinkling after descaling when the bar wire is hot-rolled. Here, the rolling reduction is indicated by the cross-sectional reduction rate. In addition, billet used as a material has the same shape with a diameter of 60 mm and a length of 300 mm, industrial pure titanium JIS type 1, JIS type 4, JIS 61 type (Ti-3Al-2.5V) which is an α + β type titanium alloy, β type titanium. Four types of alloys, Ti-15V-3Cr-3Sn-3Al, were used. The heating atmosphere was all air, and the rolling was reduced by a perforated upper and lower roll to a bar wire having a diameter of 20 mm.

  The heating scale remaining rate in Table 2 was evaluated by evaluating the remaining state of the heating scale by making a sample in which rolling was stopped with the number of observation passes indicated in the column and visually observing the surface of the sample. The heating scale remaining rate was expressed as a percentage by observing a total of 30 places where the observation sample was divided into 10 equal parts in the longitudinal direction and 3 parts in the circumferential direction, and measuring the number of remaining heating scale parts. The hot rolling mill was evaluated by performing hot rolling according to the rolling schedule shown in Table 2, then removing the scale by shot blasting and nitric hydrofluoric acid pickling to remove approximately 50 μm in diameter, and then dividing into 30 equal parts in the longitudinal direction. The number of spots with wrinkles at 30 locations was measured and indicated as a percentage as the frequency of occurrence of wrinkles on the surface. The determination of the remaining heating scale and the presence or absence of wrinkles was carried out in the same manner as in the case of the above-mentioned plate, and the heating scale was in color and the wrinkles were visually and manually touched.

  In the bar in Table 2, the comparative example No. 1 in which the rolling reduction in the first pass is as high as 10% or more. 37, 38, 40, 42, and 44 have a heating scale residual rate of 60% or more and a soot generation frequency after descaling of 43% or more. On the other hand, in Example 1 of the present invention, the rolling reduction of the first pass or the first pass and the second pass is 8% or less. 31, 32, 33, 34, 35, 36, 39, 41, 43, 45, 46, 47 are industrial pure titanium JIS type 1, JIS type 4, Ti-3Al-2.5V, Ti-15V-3Cr-3Sn. It can be seen that in any of the -3Al varieties, the heating scale residual rate is 13% or less and the occurrence frequency of wrinkles after descaling is as low as 17% or less.

  Among them, Example No. 1 in which the rolling reduction in the first pass is 5% or less. 31, 32, 33, 34, 35, 39, and 43 have a heating scale remaining rate of 7% or less, and the occurrence frequency of wrinkles after cold rolling is 10% or less. It should be noted that Example No. 1 differs only in the fluid spraying conditions. When 34 and 35 are compared, there is no difference in the heating scale remaining rate and the occurrence frequency of wrinkles after descaling.

  Moreover, Example No. 2 which passed 2 passes at 5% of 8% or less rolling reduction. 45, 46 and 47 show that the heating scale remaining rate is 3% or less and the frequency of soot generation after descaling is 3% or less, compared with the case where only one pass is performed. The effect is the same for industrial pure titanium and titanium alloys (Ti-3Al-2.5V, Ti-15V-3Cr-3Sn-3Al).

  As described above, the present invention has been described using the examples of industrial pure titanium and titanium alloy plates and rods, but the same effect can be obtained in other titanium varieties and shapes.

The figure which shows the relationship between the reduction ratio of the 1st pass after heating, the heating scale residual rate after spraying a water flow after 1 pass, and the frequency of wrinkling after cold rolling using the plate which continued the hot rolling further It is. It is a figure which shows the relationship between the rolling reduction rate at the time of passing a rolling roll under 2 times after a heating, a heating scale residual rate, and the flaw occurrence frequency after cold rolling.

Claims (3)

  In the hot rolling of the heated titanium material, after heating, as a first rolling pass, a step of peeling and pulverizing the surface scale by passing under the rolling roll at a reduction rate of 8% or less, and further after the rolling pass , Spraying either a water stream or an air stream or a mixed fluid of water and gas onto the material to be rolled, and providing a scale removal step comprising removing the exfoliated and crushed surface scale, and then rolling to a predetermined size A method for hot rolling a titanium material.   The method for hot rolling titanium material according to claim 1, wherein the scale removing step is repeated a plurality of times after the heating.   Further, during the rolling pass for peeling and crushing the surface scale, either the water stream or the air flow or the mixed fluid of water and gas is sprayed on the material to be rolled to remove the peeled and crushed surface scale. A method for hot rolling a titanium material according to claim 1 or 2.

Images