JPH07180012A - Production of titanium sheet having beautiful surface - Google Patents

Abstract

PURPOSE:To produce a Ti sheet having a beautiful surface by subjecting the ingot, forged material or bloomed material of Ti to hot rolling and annealing at temps. lower than those in the conventional ways, thereafter removing surface scales by mechanical descaling and pickling and executing cold rolling. CONSTITUTION:The ingot of pure Ti for industrual use or the forged material or bloomed material obtd. by working the same ingot is heated to a relatively low temp. of 650 to 780 deg.C and is subjected to hot rolling. This hot rolled sheet is subjected to low temp. annealing at 420 to 650 deg.C to improve the flatness and descaling properties of the hot rolled sheet. After that, the surface is subjected to mechanical descaling treatment such as shot blasting under the conditions in which the shot blast coefficient S expressed by the formula 1 (where rho in the formula denotes the projection density of shots; Kg/m<2> and V denotes the projection rate of shots; m/min) is regulated to 500 to 1200. Then, it is subjected to pickling treatment so as to regulate the amt. of a pickling solvent expressing the average solvent depth per side of the Ti sheet to >=30mum, is thereafter subjected to cold rolling, is worked to regulate its thickness into prescribed one and is subsequently subjected to finish annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium plate, and more particularly to a method for manufacturing a plate material having a beautiful surface free of scale and flaws.

[0002]

2. Description of the Related Art Since titanium plates have excellent corrosion resistance and specific strength, the fields of use such as heat exchangers have expanded in recent years and the demand for them has increased significantly. As a method for producing such a titanium plate, usually, a hot rolled product is obtained by pickling and removing the surface scale generated after hot rolling-annealing in air, or the plate material is further cold rolled-annealed. As a result, it is made into a cold rolled product. However, since titanium is an active metal, there is a problem that surface defects occur due to oxidation or seizure during hot rolling.

To remove this surface flaw, for example,
As disclosed in Japanese Patent Application Laid-Open No. 60-249535, a method is known in which after grinding with a belt grinder, a high-pressure liquid mixed with a polishing agent is projected and then pickled with a mixed aqueous solution of nitric acid and hydrofluoric acid. However, although this method can remove the surface flaw, it has a problem that the manufacturing process is complicated and the yield is increased.

[0004]

SUMMARY OF THE INVENTION According to the present invention, rolling is performed at a low temperature without performing the conventional hot rolling at a high temperature without performing the conventional inefficient method, and then the shot is performed. The purpose of the present invention is to produce a titanium plate having a beautiful surface by removing surface flaws and scale generated during hot rolling by a simple treatment of blasting-pickling.

[0005]

DISCLOSURE OF THE INVENTION In order to solve the above problems associated with the production of industrial pure titanium rolled material, the present inventors have
As a result of investigating a method of manufacturing while minimizing the generation of surface oxide scale, the steps of forging, slabbing or hot rolling, and the subsequent annealing treatment were performed at a heating temperature lower than the heating temperature conventionally used. As for the temperature range, rolling is performed at a temperature of 780 ° C. or lower and 650 ° C. or higher, and subsequent annealing is performed at a temperature of 650 ° C. or lower and 420 ° C. or higher, mechanical descale-pickling, and excellent surface properties with little oxide layer. It was clarified that the above was obtained, and the present invention was completed.

In the present invention, industrial pure titanium means J
These are materials such as IS type 1, 2 type, and 3 type. The ingot material is a material as it is cast, and the forging material is a material obtained by forging the ingot material hot, warm or cold,
The slab material is an ingot material, a forged material, or a slab material. Further, the rolled material obtained in the present invention is a slab, a thick plate,
The intermediate plate and the thin plate are obtained by hot rolling of the strip-shaped intermediate plate or thin plate.

In the present invention, the rolling and annealing steps of an industrial pure titanium ingot material or a forged material or a slab material obtained by processing the ingot material are heated and rolled at a relatively low temperature. If the material temperature is too low or the rolling reduction is high, surface cracks such as edge cracks will occur, and there is a high possibility that yields will decrease and breaks during rolling will occur. It needs to be within the range. Therefore, the present inventors have investigated in detail the influence of the heating temperature and annealing temperature of hot rolling on the surface properties of the hot rolled sheet, using an ingot material of industrial pure titanium and its forged material. As a result, in the conventional heating in air (for example, 870 ° C.), the surface texture of the rolled plate is
When the material is heated, the surface oxide layer remains on the surface in a granular form, and in order to obtain a good surface, mechanical descale (shot blasting, liquid honing, bending, etc.)-Pickling and surface grinding are performed as in the normal process. It was often necessary. However, when the heating temperature is 780 ° C. to 650 ° C., the surface oxide layer is considerably smaller than that in the conventional method, and surface cracks such as ear cracks do not occur at all at this heating temperature. It was The finishing temperature at this time is
For the purpose of reducing the rolling load of cold rolling which is a subsequent step, it is desirable to lower the strength of the hot rolled sheet by raising the temperature as high as possible (for example, 650 ° C. or higher).

In the present invention, as a result of various studies on the annealing process of the hot-rolled sheet or hot-rolled strip hot-rolled at such a relatively low temperature, the annealing temperature ( For example, by performing an annealing treatment at a temperature lower than 740 to 650 ° C., that is, 650 ° C. or less and 420 ° C. or more, the shape such as flatness of the plate is improved, and the mechanical descaling property thereafter is also improved, It was found that a good surface can be obtained after pickling. That is, the hot rolled plate or hot rolled strip thus hot rolled is
When annealed at a temperature of 420 ° C or lower and 420 ° C or higher, the bending of the plate in the direction perpendicular to the rolling direction (when the coil is unwound, warpage occurs in the plate width direction, hereinafter referred to as C warp) is reduced, and the thin plate thereafter. It has been found that the handling workability of the is improved.

Further, as a result of various investigations for the purpose of removing surface flaws and scale produced during hot rolling, the following findings were found. (1) If the hot-rolled sheet is annealed at a relatively low temperature such that the residual strain of the hot-rolled sheet is removed, the densification of the internal scale of the flaw is suppressed, and the flaw is removed by the subsequent shot blasting / pickling treatment. It becomes easy to be removed. Further, the plate or strip that has been hot rolled and annealed at a low temperature has its surface irregularities reduced by shot blasting, the plate surface after pickling becomes very beautiful, and the flatness of the plate also becomes good. (2) If the flaws after hot rolling / annealing are shot blasted under the specified conditions, the metal cover of the flaws will be deformed and the internal scale will be modified, and the pickling after that will remove the flaws. It is easy to be done. However, if the shot blasting treatment is made too strong, the effect of removing the defects will be large, but the surface irregularities will become severe and a processed layer will be formed on the smooth surface part without any defects, and the processed layer will remain even after pickling. By doing so, it may cause surface cracking during cold rolling. (3) If the depth of hot-dip cutting is insufficient in the pickling after shot blasting, the hot-rolled flaws are removed, but the oxidation-hardened layer around the flaws or the layer processed by shot blasting remains, and May cause surface cracks.

The present invention is constructed on the basis of the above findings, and the gist thereof is as follows.
After annealing the hot-rolled sheet hot-rolled at a low temperature at a temperature of 420 to 650 ° C., the shot blast coefficient S represented by the following formula (1) is applied to the surface of the titanium plate under the condition of 500 to 1200. Shot blasting is performed, followed by pickling under the condition that the amount of fusing is 30 μm or more, followed by cold rolling and annealing. S = ρ × v ² /(3.6×10 ⁶ ) ………………………… (1) where ρ: Projection density (kg / m ² ), v: Projection speed (m / min) The amount of pickling and fusing mentioned here is the average fusing depth of the base metal per one side of the plate.

The present invention will be described in detail below. INDUSTRIAL APPLICABILITY By hot rolling at a low temperature of 650 to 780 ° C., the present invention suppresses the oxide scale in the hot rolled sheet produced thereby as much as possible compared with the conventional method, thereby removing scale in the next step. It is about to reduce the load.

Conventionally, after hot rolling, the hot rolled sheet or strip is not annealed or is recrystallized at about 700 ° C. to be annealed, and then mechanical descale-pickling is performed. If the former is hot rolled, the surface hardness is high, and a plate, especially a coiled one due to internal strain, will have C-screw and will be rubbed when the thin plate is passed through the manufacturing equipment, causing many problems in work.

On the other hand, when annealing is carried out to completely recrystallize it at 700 ° C. or more, the plate is softened and internal strain is removed and the shape is improved, but the original oxide scale is suppressed even if hot rolling is performed at low temperature. Even if it is done, since a fine scale is generated inside the hot-rolled flaw, the flaw removability in the subsequent shot blast-pickling treatment is deteriorated. Further, even if the mechanical descale in the next step, for example, a flaw such as an oxide scale during hot rolling due to shot blasting or the like is removed by softening, there is a possibility that unevenness of the surface due to shot may be added to the flat portion. That is, the oxide scale can be removed, but in addition, new unevenness is generated on the surface.

As a treatment method having both of the above-mentioned good properties, a hot-rolled sheet or a hot-rolled strip hot-rolled at a relatively low temperature has a higher working strain than the conventional hot-rolled sheet hot-rolled. Since much of the accumulated softening, recovery softening, and some recrystallization start at a rather low temperature, annealing at a temperature lower than the annealing temperature of conventional hot rolled materials, that is, 650 ° C or less and 420 ° C or more, must be performed. As a result, although it is not completely recrystallized, the recovery state is such that the C z is flattened to the extent that it does not cause a problem in manufacturing, and the internal strain can be removed to adjust the shape. Since hot rolling and annealing are performed at a lower temperature, the scale of the surface is small and it is easy to crush the oxide scale during the mechanical descaling in the next process or to raise the scab-like defects during hot rolling. To reduce the amount of fusing, that is, 30μ
A good plate shape and surface can be obtained with an amount of ablation of m or more. Therefore, in the present invention, the annealing temperature is set in the range of 420 to 650 ° C. The holding time in this temperature range is not particularly limited, but in order to stably eliminate the C-strain of the plate, 3
0 seconds or more is desirable.

Oxide scale produced on the hot rolled titanium plate is
It is removed by mechanical descaling method and pickling method with acid. The shot blasting method is generally used for the mechanical descaling method.However, shot blasting removes the oxide scale on the surface by crushing or removing it, or lifts up the defects such as a cap during hot rolling, and then removes the defects by pickling. Although it can be easily removed, the increase in hardness of the hot-rolled sheet material is an important factor at this time.

Regarding shot blasting conditions,
If the coefficient S represented by the equation (1) is less than 500, hot-rolling defects cannot be sufficiently removed. Further, when the coefficient S exceeds 1200, the effect of removing flaws becomes large, but the surface irregularities become severe and a processed layer is formed on a smooth surface without flaws, and the processed layer remains even after pickling, which results in cold work. Surface cracking occurs during rolling. Therefore, the range of the coefficient S is 5
It was set to 00-1200. Here, the projection density and the projection speed, which are the components of the coefficient S, are not particularly limited, and the coefficient S
Should be determined so as to satisfy the above range, but as the industrially feasible range, the projection density is 150 to 350 kg.
/ M ² , and the projection speed is preferably about 2000 to 4000 m / min. The size of the shot particles is not particularly limited and may be about 0.1 to 1 mm which is usually used.

For the titanium plate treated in this way, the amount of pickling and shaving may be at least 30 μm. That is, when the thickness is less than 30 μm, the hot rolling defects are removed, but the oxidatively hardened layer around the defects or the processed layer by shot blast remains, which causes surface cracking during cold rolling. Therefore,
The amount of pickling and shaving was 30 μm. The pickling conditions are not particularly limited, and may be carried out using a mixed aqueous solution of nitric acid and hydrofluoric acid, which is usually applied to descaling of titanium plates, sulfuric acid, or the like. Further, the subsequent cold rolling / annealing conditions are not particularly limited, and may be the conditions generally applied to the production of titanium plates.

[0018]

EXAMPLES Examples of the present invention will be shown below. JIS 2 class slab (thickness 130mm) is machined to surface grinding, and heating temperature is 3 levels in the range of 650 ° C to 780 ° C and heating under normal conditions. Final plate thickness is 6mm (reduction rate 95%). ), No ear cracking was found to be a problem in any case. This is performed within the annealing conditions of the present invention, shot-blasted under various conditions, and then pickled, and the results of evaluation of the surface of the material obtained by further cold rolling the material by 60% are shown in Table 1.

From Table 1, hot rolling was performed at a low temperature of 780 to 650.
It can be seen that a titanium plate having a beautiful surface can be obtained by carrying out annealing at 650.degree.

[0020]

[Table 1]

[0021]

EFFECTS OF THE INVENTION According to the present invention, a titanium plate having a beautiful surface can be manufactured by removing surface flaws by a simple process without using an inefficient method as in the prior art. Effect is remarkable.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiaki Nishida 3434 Shimada, Hikari-shi, Yamaguchi Prefecture Nippon Steel Corporation Hikari Steel Works (72) Inventor Tomohiro Nishijima 3434 Shimada, Hikari-shi, Yamaguchi Prefecture New Japan (80) Inventor Hidenori Masuoka 3434 Shimada, Hikari City, Yamaguchi Prefecture Nippon Steel Co., Ltd. Hikari Steel Co., Ltd.

Claims (1)

[Claims] 1. An ingot material of industrial pure titanium, or a forged material or a slab material obtained by processing the ingot material,
A hot rolled plate is produced by heating to 0 ° C. or lower and 650 ° C. or higher, followed by hot rolling, followed by annealing the hot rolled plate at a temperature of 650 to 420 ° C. The following (1) on the surface
The shot blast coefficient S represented by the formula is 500 to 120.
A method for producing a titanium plate having a beautiful surface, which comprises performing shot blasting treatment in a condition of 0 range, followed by pickling under a condition of ablation amount of 30 μm or more, followed by cold rolling and annealing. . S = ρ × v ² /(3.6×10 ⁶ ) ………………………… (1) where ρ is the projection density (kg / m ² ), v is the projection speed (m /
Minutes)