JP2006289377A - Titanium material hot rolling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium material hot rolling method by which flaws caused by the hot rolling, in particular, sticking flaw can be reduced. <P>SOLUTION: The titanium material hot rolling method is characterized in that when heated titanium material is hot-rolled, the first pass rolling is performed at a temperature of ≥ 750°C and a draft of > 8% without performing descaling before the rolling is started after the heating, then the heated titanium material is hot-rolled in a predetermined shape. Heated scale is uniformly depressed into the surface after the one pass rolling, and pressed into a base titanium. The adhesibility of heated scale is therefore increased, and the finely divided heated scales continuously remain in the surface even when the subsequent rolling is advanced, the sticking of a work to a rolling roll is suppressed and the flaw during the hot rolling can be reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for hot rolling of a titanium material, and more particularly to a method for hot rolling of a titanium material that can reduce hot rolling wrinkles caused by seizure between a material to be rolled and a roll.

  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, high-temperature oxidation forms a scale and an oxygen-enriched layer called α-case on the surface of the surface. It is known that the scale and α-case grow as the temperature increases and the time increases. From the viewpoint that this titanium scale may develop into defects such as rough skin and wrinkles on the surface of the material to be rolled after hot rolling (collectively, hereinafter referred to as scale wrinkles), the titanium scale has been conventionally used. In order to reduce soot, as a method of suppressing high temperature oxidation during hot rolling / heating, a method of heating at a relatively low temperature of 500 to 800 ° C. (see, for example, Patent Document 1), an oxygen partial pressure of the atmosphere Of 0.02 atm or less (for example, see Patent Document 2), a method of sealing a titanium material in a box and shutting it off from the atmosphere (for example, see Patent Document 3), a method of making the atmosphere argon or nitrogen gas (For example, refer patent document 4.), the method (for example, refer patent document 5) etc. which apply | coat antioxidant to a to-be-rolled material have been disclosed.

  In hot rolling of steel, the scale is reduced during hot rolling by de-scaling with high-pressure water or pressurizing by pressing down in the width direction of the slab and then spraying fluid or performing a brushing process. There is a method of removing (see, for example, Patent Document 6 and Patent Document 7).

  In stainless steel with a Cr content of 11% by mass or more, after being descaled after heating under a width reduction, etc., after the scale is regenerated in the part where the scale is peeled off, the next pass rolling is performed. There is a method of reducing surface wrinkles due to seizure with a rolling roll (collectively, hereinafter referred to as seizure flaws) (see, for example, Patent Document 8).

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 JP 05-057331 A JP 05-277543 A JP-A-60-170503

  As described above, in order to reduce the scale wrinkling that occurs during the hot rolling of titanium material, the method of suppressing the generation of the heating scale is easy on the rolling roll and metal titanium during the hot rolling because the heating scale is thin. May cause seizure defects. In addition, due to high-pressure water descaling and rolling in the width direction before rolling (particularly before rolling in the thickness direction), which is performed by hot rolling of steel, the heating scale on the heated titanium surface is removed in the same manner as described above. Burn-in defects may occur.

  In a rolling mill used for general industrial production, a material to be rolled is extracted from a heating furnace, conveyed by a conveying roll, and rolled by a rolling mill. In the hot rolling of titanium, the thermal conductivity of titanium is lower than that of steel, so the surface layer is cooled by contact with the transport roll and the scale becomes brittle. Partially peel off. For this reason, seizure flaws may occur at the portion where the scale is peeled off during subsequent hot rolling.

  On the other hand, in order to suppress seizure flaws, even in the hot rolling of titanium, after descaled after heating like the above-mentioned stainless steel, a method of maintaining the temperature at a high temperature before rolling to regenerate the scale can be considered. However, when the thickness of the heating scale formed during heating is compared between steel and titanium, it is about 0.5 to 3 mm (500 to 3000 μm) for steel, whereas it is on the order of several tens of μm for titanium. There is a difference of about 10 to 100 times between them, and it can be seen that the scale growth of titanium is much slower than that of steel. For this reason, in order to regenerate the scale in the middle of hot rolling with titanium, it takes about 10 to 100 times as long as steel to maintain the high temperature, and the efficiency is never good.

  Accordingly, an object of the present invention is to provide a method for hot rolling a titanium material that can reduce hot rolling, particularly seizure, in hot rolling of a titanium material.

The gist of the present invention for solving the above problems is as follows.
(1) During the hot rolling of the heated titanium material, after the heating, the first pass rolling is performed at a temperature of 750 ° C. or more and a reduction ratio of more than 8% without being descaled until the start of rolling. A method for hot rolling of a titanium material, characterized in that the rolling is performed in the following manner.

  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. Here, descaling is a process that actively removes the heating scale, such as generally used fluid spraying such as high-pressure water, brushing process, slab width reduction, etc. It does not include the process of transporting the material with a roll or the like.

  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, in the hot rolling of a titanium material, it is possible to provide a method for hot rolling of a titanium material, which can advantageously reduce defects due to hot rolling, particularly seizure defects. The above effect is immeasurable.

  In the hot rolling of titanium material, the present inventors have conducted extensive research on a hot rolling method for reducing surface flaws caused by seizure with a rolling roll. As a result, the heating scale is stably applied to the surface of the material to be rolled. By making it exist, it is found that the contact between the rolling roll and the metal titanium is suppressed and seizure defects are reduced, and as a method of stably presenting the heating scale on the surface of the material to be rolled, without descale after heating, It has been found that it is effective to perform rolling at a temperature of 750 ° C. or higher at the first pass at a rolling reduction of more than 8%, preferably 10% or more. By this method, the heating scale is uniformly pushed into the surface after one-pass rolling, and it is in a state where it is pressure-bonded to the base material titanium, the adhesion of the heating scale is increased, and it is finely divided even if the rolling proceeds thereafter. The heating scale remains on the surface and suppresses the seizure of the rolling roll and the material to be rolled, and as a result, seizure flaws are reduced.

FIG. 1 shows the relationship between the rolling reduction ratio of the first pass after heating and the heating scale remaining ratio after the first pass rolling (evaluation in the following step 1), and further cold rolling using a plate that has continued hot rolling thereafter. The relationship with the frequency of wrinkles (evaluated in the following, step 2) is shown. In addition, the used titanium material is industrial pure titanium JIS1 type.
[Step 1]: (1) Heating a 60 mm thick slab at 850 ° C. for 4 hours → (2) Heating furnace extraction → (3) One pass rolling at various reduction ratios at 800 ° C. → (4) Heating of the material to be rolled Evaluation of scale residual ratio [Step 2]: (1) Heating 60 mm thick slab at 850 ° C. for 4 hours → (2) Heating furnace extraction → (3) One pass rolling at various reduction ratios at 800 ° C. → (4) Continues hot rolling and rolls to a thickness of about 4 mm → (5) Shot blasting, nitric hydrofluoric acid pickling (about 50 μm thickness cutting) → (6) Cold rolling to a thickness of 2 mm → (7) 疵 frequency Evaluate

  Here, the surface of the slab was smoothed by machining, and each of the eight chamfers was prepared by chamfering 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 wrinkle frequency in step 2 was evaluated by a percentage by dividing the cold-rolled plate 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. That is, although the wrinkle after cold rolling is evaluated as an observation method, evaluation here is equivalent to evaluating the wrinkle by hot rolling, that is, the surface as hot rolled.

  From FIG. 1, as described above, the remaining ratio of the heating scale corresponds to the drought frequency after cold rolling, and the heating scale remaining ratio is 50% when the rolling reduction ratio of the first pass after heating exceeds 8%. % And the frequency of wrinkles decreases to 20% or less. Further, when the rolling reduction ratio in the first pass is 10% or more, the heating scale remaining rate is increased to 70% or more and the wrinkle frequency is reduced to 10% or less. More preferably, when the rolling reduction of the first pass is 20% or more, the wrinkle frequency is stabilized to less than 10%.

FIG. 2 shows the relationship between the temperature of the material to be rolled in the first pass and the heating scale remaining rate (evaluated in Step 3 below), and the frequency of drought when cold rolling is performed using a plate that has been hot-rolled thereafter. (Evaluation in step 4 below). In addition, all are the evaluation results on the back side of the slab. Here, the surface and shape of the slab used, the evaluation of the heating scale remaining rate, and the evaluation of the wrinkle frequency are the same as described above.
[Step 3]: (1) Heating a slab having a thickness of 60 mm for 4 hours at 850 ° C. → (2) Extraction in a heating furnace → (3) Repetitively moving on a transport roll until the surface of the slab reaches various temperatures → (4) Reduction 1 pass rolling at a rate of 20% → (5) Evaluate the heating scale remaining rate on the back side of the material to be rolled [Step 4]: (1) Heat a 60 mm thick slab at 850 ° C. for 4 hours → (2) Extraction from the heating furnace → (3 ) Repeated movement on the transport roll until the surface of the slab reaches various temperatures → (4) One pass rolling with a rolling reduction of 20% → (5) Continued hot rolling and rolled to a thickness of about 4 mm → (6) Shot Descaling by blasting and nitric acid hydrofluoric acid pickling (about 50μm thickness cutting) → (7) Cold rolling to thickness 2mm → (8) Evaluation of the frequency of wrinkles on the back of the plate

  FIG. 2 shows that the peeling of the heating scale during slab conveyance is related to the temperature. When the temperature is as high as 750 ° C. or higher, the heating scale remaining rate is 60% or more and the soot frequency is stable to 10% or less, but when the temperature is lowered to 700 ° C. or lower, the heating scale remaining rate decreases to 20% or less. The wrinkle frequency exceeds 40%. Therefore, it is necessary to carry out the first pass rolling at a temperature of 750 ° C. or higher after heating. This result is considered to be because when the surface of the roll is transported while the temperature is lowered, the heating scale on the back surface side is peeled off during transportation.

  In addition, when the descaling is performed by spraying high-pressure water before rolling in the first pass, or when the slab is reduced by 5% in the width direction, the heating scale is removed by these descaling steps, and the thickness is increased thereafter. Even when rolling was performed at a rolling reduction of 20% in the direction, the heating scale remaining rate was as low as 7% or less, and accordingly, the wrinkle frequency was as high as 60%.

  The same effects as described above can be obtained with a titanium alloy.

  From the above, in order to carry out the first pass rolling with the heating scale remaining for the purpose of reducing seizure flaws during hot rolling, in the present invention, without descaling the heated titanium material, In addition, in order to suppress peeling of the heating scale during conveyance, the temperature of the material to be rolled in the first pass was set to 750 ° C. or higher. In the present invention, the titanium material is rolled at a reduction ratio of more than 8% in the first pass, and then rolled into a predetermined shape. Note that the reduction rate is preferably 10% or more because the seizure defects can be more stably reduced, and when the reduction rate is further required, the reduction ratio is more preferably 20% or more. .

  In the present invention, since the heating scale is pressure-bonded to the surface of the material to be rolled in the first pass and the adhesion is increased, the descaling by the light rolling or the high-pressure water with a reduction rate of 8% or less after the first pass, the slab width direction Even if this reduction is applied, the heating scale remains stably on the surface of the material to be rolled, and the effect of reducing seizure flaws remains unchanged.

  The invention is explained in more detail using the following examples.

  First, in Table 1, the heating conditions when the plate is hot-rolled, the descaling conditions after extraction, the rolling temperature in the first pass, the rolling schedule (the reduction rate of each pass), the heating scale remaining rate after one pass, The frequency of wrinkles after cold rolling is shown. 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 slab had a smooth surface finished by machining, and each of the eight chamfers was a 1 mm chamfered one. The heating atmosphere was all air, and the slab was kept on standby while repeatedly moving on the transport roll until the slab reached the rolling temperature in the first pass of Table 1 after extraction. In rolling, the slab was reduced in the thickness direction with a horizontal roll to obtain a hot rolled plate having a thickness of 4 mm.

  The heating scale remaining rate after one pass in Table 1 is a sample in which rolling was stopped in one pass, and the surface of the sample was visually observed to evaluate the remaining state of the heating scale. Evaluation of the hot rolling mill was performed by hot rolling according to the rolling schedule shown in Table 1, then shot blasting and scouring with nitric hydrofluoric acid pickled to a thickness of about 50 μm, descaling, and then cold rolling to a thickness of 2 mm Was used to evaluate the wrinkle frequency on the surface. In addition, the evaluation method of the heating scale residual rate and the wrinkle frequency after cold rolling is the same as the above-mentioned.

  In industrial pure titanium JIS type 1 and JIS type 4 in Table 1, No. 1 which is a comparative example. A1, A2, A3, A11, and A18 have a rolling reduction ratio of the first pass of 8% or less, which is outside the scope of the present invention. A15 and A16 are heating because the first-pass rolling temperature (hereinafter referred to as the first-pass rolling temperature) after waiting while moving on the transport roll after heat extraction is less than 750 ° C., which is outside the scope of the present invention. The scale remaining rate is as low as 20% or less, and accordingly, the frequency of wrinkles after cold rolling is as high as 40% or more. On the other hand, Example No. whose heating temperature is 850 ° C. A4, A5, A6, A7, A8, A9, A10, A17, A19, A20, and Example No. A12, A13, and A14 are within the range of the present invention, in which the rolling reduction in the first pass is 9 to 40%, which exceeds 8%, and the rolling temperature in the first pass is 750 to 800 ° C., which is 750 ° C. or higher. The residual rate is as high as 50% or more, and the frequency of wrinkling after cold rolling is as low as 20% or less.

  Among them, Example No. 1 in which the rolling reduction of the first pass is 10% or more. As for A5, A6, A7, A8, A9, A10, A13, A14, A17, A19, A20, it can be seen that the residual ratio of the heating scale is 63% or more and the wrinkle frequency after cold rolling is further lower, 10% or less. . In addition, Example No. In A7 and A8, rolling is performed at 20% and 30% reduction in the first pass, so the heating scale remains in contact even when light rolling is performed at 5% reduction in the second pass. Therefore, the same effect is obtained.

  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 reduction No. which is a comparative example having a low rate of 3%. A21, A24, No. 10 which is 10% and 20%, which is a high example. When A22, A23, A25, and A26 are compared, the heat scale remaining rate is higher in the examples, and the frequency of wrinkling after cold rolling is as low as 10% or less.

  In addition, Comparative Example No. descaled with high pressure water after extraction in the heating furnace. A27, A28, and A29 are industrial pure titanium JIS type 1, Ti-3Al-2.5V, Ti-15V-3Cr-3Sn-3Al, and the heating scale remaining rate is as low as 7% or less, and the frequency of defects after cold rolling. Is as high as 60% or more.

  Next, Table 2 shows the heating conditions, the descaling conditions after extraction, the rolling temperature of the first pass, the rolling schedule (the rolling reduction ratio of each pass), and the heating scale remaining rate after the first pass when the bar wire is hot rolled. The frequency of wrinkles after descaling is shown. 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 billet was kept on standby while repeatedly moving on the transport roll until the billet reached the rolling temperature in the first pass in Table 2. Rolling was reduced with a perforated upper and lower roll to form a bar with a diameter of 20 mm.

  For the heating scale remaining rate in Table 2, a sample in which rolling was stopped in one pass was made, and the surface of the sample was visually observed to evaluate the remaining state of the heating scale. 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 performed by the same method as in the case of the above-described plate, and the heating scale was colored 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 low as 5% or less. B1, B2, B10, B12, B14, the rolling temperature of the first pass is as low as 650 ° C. B8 has a heating scale remaining rate of 10% or less and a wrinkle frequency after descaling of 60% or more. On the other hand, Example No. of the present invention in which the rolling reduction in the first pass is 10% or more and the rolling temperature in the first pass is 750 ° C. or more. B3, B4, B5, B6, B7, B9, B11, B13, B15 are industrial pure titanium JIS type 1, JIS type 4, Ti-3Al-2.5V, Ti-15V-3Cr-3Sn-3Al Also, it can be seen that the residual rate of heating scale is as high as 70% or more and the soot frequency after descaling is as low as 10% or less.

  Comparative Example No. descaled with high-pressure water after extraction. B16, B17, and B18 are industrial pure titanium JIS type 1, Ti-3Al-2.5V, Ti-15V-3Cr-3Sn-3Al, and the heating scale residual rate is as low as 7% or less. % And higher.

  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.

It is a figure which shows the relationship between the rolling reduction rate of the 1st pass after heating, the heating scale residual rate after 1 pass rolling, and also the drought frequency at the time of cold rolling using the board which continued the hot rolling. It is a figure which shows the relationship between the to-be-rolled material temperature of the 1st path | pass at the time of making it wait while moving on a conveyance roll after heat extraction, and a heating scale residual rate.

Claims (1)

  During the hot rolling of the heated titanium material, after the heating, the first pass rolling is performed at a temperature of 750 ° C. or more and a reduction rate of more than 8% without being descaled until the start of rolling, and then rolled into a predetermined shape. A method for hot rolling a titanium material.

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