JPH07228958A - Production of pure titanium sheet for industry - Google Patents

Abstract

PURPOSE:To produce a pure Ti sheet for industry having beautiful surface and excellent press-formability by applying a heat treatment, hot-rolled plate annealing treatment and shot-blast treatment in the specific conditions to a Ti base stock in order and executing a cold-rolling and annealing. CONSTITUTION:In an electric heating furnace adjusted in the range of an oxygen concn. (y) in the atmosphere satisfying the inequality I by replacing the atmosphere in a furnace with inert gas of gaseous nitrogen or gaseous argon as the main component, the Ti base stock for hot-rolling is heated at 700-900 deg.C. Wherein, (x) in the inequality I is the index showing oxygen diffusion distance into the pure Ti and in the equation II, (t) is staying time (min) in the furnace at >=700 deg.C and T is heating temp. ( deg.C). Successively, the base stock is hot-rolled and the hot-rolled sheet is annealed at 450-650 deg.C and the shot blast treatment is executed so that the shot blast factor S shown in the equation III [wherein, rhois injection density (kg/m<2>), and (v) is injection velocity (m/min)] becomes 500-1200. After pickling so that the polishing quantity in the one side surface becomes 20mum, the cold-rolling and the annealing are applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plate material which has a beautiful surface free from surface roughness and scratches on the scale and surface and is excellent in press formability in the production of industrial pure titanium plate material. Is.

[0002]

2. Description of the Related Art Titanium has been used in recent years for heat exchangers, chemical plant members, coastal structural materials, etc. because of its excellent corrosion resistance and specific strength. Such a pure titanium plate material is usually produced by heating in the air to carry out hot rolling (hot rolling) and annealing to remove the scale of the generated surface to obtain a hot rolled product, or the plate material. Is further cold rolled (cold rolled) and annealed to obtain a cold rolled product.
However, since titanium is an active metal and has a particularly strong affinity with oxygen, it is extremely susceptible to oxidation at high temperatures, and during heating in the air or during hot rolling (hot rolling), oxidation or seizure with rolls causes the plate surface to There are problems such as rough skin and scratches.

In order to reduce the above-mentioned oxidation during heating and hot rolling, for example, a joint lecture of plastic working by K. Kimura et al. (198).
0) There is a method of heating and rolling titanium described in P419 in vacuum. However, it is difficult to secure a vacuum state as the material is larger, and it is industrially very difficult to secure a vacuum state not only for heating but also for rolling. On the other hand, it is conceivable to reduce the residual oxygen concentration in the furnace to near 0% in the gas heating furnace during heating. However, this is a problem that it is oxidized by H ₂ O or CO ₂ in the combustion exhaust gas to form a hardened layer, and when heated in a state where unburned gas is generated, hydrogen penetrates into the titanium material and becomes brittle, resulting in material property deterioration. There was a problem of significant deterioration.

As a method for removing the above-described surface roughness and flaws, for example, as described in JP-A-60-249535, after grinding with a belt grinder, a high-pressure liquid mixed with a polishing agent is projected. Then, a method of pickling with a mixed aqueous solution of nitric acid and hydrofluoric acid is known. However, although this method can remove surface flaws, it has a problem that the manufacturing process is complicated, and oxidation and surface flaws during heating, hot rolling and annealing are severe and the yield is large. Further, there is a method of completely removing surface roughness and scratches on the hot-rolled / pickled plate by grinding before cold rolling, but there have been problems of reduced yield and increased manufacturing cost due to the grinding process.

After the hot rolling, the annealing is omitted or the annealing is performed at a temperature higher than the recrystallization temperature. When the annealing is omitted, there is a problem that when the coil-shaped hot rolled sheet is unwound, workability is deteriorated due to curl and the flatness of the hot rolled sheet is poor. When annealed at a temperature higher than the recrystallization temperature, the base material is soft, and therefore during the subsequent mechanical descale treatment (for example, high-pressure blasting treatment), flaws due to the blasting material may be newly generated and the surface quality may be deteriorated.

The cold-rolled titanium product thus produced is
In many cases, it is press-molded into a product having a complicated uneven shape such as a plate heat exchanger. This plate heat exchanger needs to improve the heat transfer efficiency, and in recent years, the plate thickness has become thinner and the shape has become more complicated, and a material having more excellent press formability has been required. However, since titanium is a hexagonal crystal, it has a strong anisotropy and cracks occur when it is pressed. Therefore, for example, Japanese Patent Application Laid-Open No. 60-82227 discloses a method of reducing anisotropy by rolling at a right angle to the normal rolling direction. However, this method is extremely inefficient because it is necessary to cut the material plate rolled into a coil and roll it again.

[0007]

According to the present invention, industrial pure titanium material is heated in an atmosphere in an electric heating furnace-hot rolling-annealing-without performing the conventional complicated, poor-yielding and inefficient methods. The simple process of shot blasting-pickling-cold rolling-annealing removes scale and surface roughening and scratches that occur during heating and hot rolling with good yield, and has a beautiful surface and press formability. It is an object to provide a method for producing an excellent industrial pure titanium plate.

[0008]

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention uses a raw material for hot rolling in the production of an industrial pure titanium plate, and the atmosphere in the furnace contains nitrogen gas or argon gas as a main component. It is heated to 700 to 900 ° C. in an electric heating furnace in which the atmosphere is replaced with an inert gas and the oxygen concentration y in the atmosphere is adjusted to satisfy the formula (1), and then hot rolling is performed to obtain a hot rolled plate, Subsequently, the hot-rolled sheet is annealed at a temperature of 450 to 650 ° C., followed by shot blasting treatment under the condition that the shot blasting coefficient S represented by the formula (3) is 500 to 1200, and then one surface A method for producing a pure titanium plate for industrial use, which comprises pickling under the condition that the amount of fusing is 20 μm or more, followed by cold rolling, and then annealing. Oxygen concentration y (ppm) ≤ 168.5x ^-1 (1) However, x is an index showing the oxygen diffusion distance in pure titanium,
It is shown by the following equation (2). x = t ^0.5 · exp {−5597 / (T + 273)} (2) t: time in furnace at 700 ° C. or higher (minutes) T: heating temperature (° C.) shot blast coefficient S = ρ × v ² / ( 3.6 × 10 ⁶ ) (3) However, ρ: Projection density (kg / m ² ) v: Projection speed (m / min) Here, industrial pure titanium is JIS Class 1, Class 2, Class 3 It is a material corresponding to a seed. The amount of fusing by pickling is the average fusing depth of the base metal per one side of the plate.

[0009]

The present invention will be described in detail below. In order to solve the above-mentioned problems relating to the method for producing a pure titanium plate for industrial use, the present inventors have proposed a method for suppressing the production of a surface scale or an oxidation hardened layer of a titanium material, and a rough surface of the scale or surface generated during hot rolling. As a result of various studies on a method for effectively removing defects and flaws and a method for improving press formability of a cold rolled product, the following (1) to (5) were found. (1) Generation of an oxide scale or a hardened layer by heating an industrial pure titanium material in an electric heating furnace by replacing the atmosphere in the furnace with an inert gas whose main component is nitrogen gas or argon gas to suppress oxygen concentration and heating. Is reduced, surface roughness and defects during hot rolling are reduced, and the depth is also reduced. (2) By annealing the hot-rolled sheet at a relatively low temperature at which residual strain is removed, densification of the scale inside the surface flaw generated during hot-rolling is suppressed, and then shot blasting-acid treatment. The flaws are easily removed by washing. Further, the unevenness of the plate surface due to the shot blast treatment is small, the surface properties of the plate after pickling are very beautiful, and the flatness is also good.

(3) By the above-mentioned annealing at a relatively low temperature,
In terms of material, the value is improved and the press formability is improved. (4) By subjecting the surface defects of the hot rolled / annealed plate to shot blasting under the specified conditions, the metal covering of the defects is deformed A beautiful plate surface can be obtained because the scale is modified and the flaws are easily abraded in the subsequent pickling, but if the shot blasting treatment is too strong, the effect of removing the surface flaws will be large, but Since the processed layer is formed on the smooth surface with no irregularities and has no flaws, and this processed layer remains after pickling, it causes surface cracking during cold rolling or press forming. In some cases, the above-mentioned modification of the internal scale is not sufficiently achieved, and after the pickling, surface flaws may remain or surface roughness may not be completely removed. (5) (1) reduces surface roughness and flaws Though
If the fusing depth after pickling after shot blasting is insufficient, the oxide layer around the flaw or the layer processed by shot blasting remains, causing surface cracks during cold rolling or press forming.

In the present invention, the atmosphere in the heating furnace is replaced with an inert gas containing nitrogen gas or argon gas as a main component to reduce the oxygen in the furnace to a predetermined amount or less, and the industrial pure titanium material is heated to a predetermined temperature in the atmosphere. Since it heats up to, the heating furnace is preferably an electric heating furnace whose atmosphere is easy to control,
An electromagnetic induction furnace, a resistance heating furnace, a direct current heating furnace, etc. may be properly used. The purity of the inert gas containing nitrogen gas or argon gas as the main component is 99.99%, which is commonly used industrially.

Even if the atmosphere in the furnace is replaced with an inert gas mainly containing such nitrogen gas or argon gas, oxygen contained as impurities in the gas and air intruding from the seal portion of the furnace are completely eliminated. Since it is extremely difficult to do so, by controlling the oxygen concentration in the furnace according to the above equation (1), it is possible to reduce the thickness of the scale and the oxidative hardening layer produced during heating.

The heating temperature of the pure titanium material for industrial use is 700 ° C.
If it is less than the range, the deformation resistance for processing the material is large and the rolling load is large, so that it is necessary to have a rolling function force for that purpose, which is difficult. If it exceeds 900 ° C,
Oxygen diffusion is very fast because the temperature is above or near the β-transformation point, and oxidation in a controlled atmosphere furnace is likely to occur, especially when hot rolling in the atmosphere and formation of scales and oxidative hardening layers occur, causing surface roughness. The flaw becomes severe. Therefore, the range of the heating temperature is set to 700 to 900 ° C. Preferably 800
Is in the range of to 890 ° C.

Expression (1) is an expression representing the relationship between the index representing the oxygen diffusion distance in pure titanium expressed by Expression (2) and the oxygen concentration in the furnace within the scope of the present invention. Here, the equation (2) is an index x that represents the diffusion distance of oxygen in consideration of diffusion of oxygen into pure titanium.
Is a relational expression of the in-furnace time t after the material to be heated reaches 700 ° C. or higher and the finally reached heating temperature T. When the in-furnace time t is less than 700 ° C., the diffusion of oxygen is slow and the formation of the oxidation hardened layer is extremely small.
The time is over. Also, the time spent in the furnace at 700 ° C or higher is
Considering the work efficiency and the formation of the oxidation-hardened layer, about 30 to 60 minutes is desirable. Further, FIG. 1 is a graph showing the above formula (1), and as can be seen from this figure, an index x indicating the oxygen diffusion distance into pure titanium obtained from the above t and T within the range of the formula (1). According to the method, when the oxygen concentration in the heating furnace is suppressed, the scale and the oxidative hardening layer generated during heating are reduced, and after hot rolling, annealing within the scope of the present invention-shot blasting treatment-pickling gives a beautiful surface. It is possible to produce a pure titanium plate for industrial use, which has excellent press formability. Outside the range of the formula (1), the scale and the oxidatively hardened layer generated at the time of heating become thicker, which easily cause surface roughening and scratches due to hot rolling, and also promote the degree of skin roughening and scratches. Blasting-Not completely removed by pickling.

When the annealing temperature of the hot-rolled sheet is less than 450 ° C., the generation of internal scales of surface defects during hot-rolling is suppressed and the press formability of the cold-rolled product is improved, but the rolling direction of the hot-rolled sheet is improved. Bending by a method at right angles to (a warpage occurs in the plate width direction when the coil is expanded. Hereinafter referred to as C warping) remains, and the subsequent handling workability is poor. When it exceeds 650 ° C, a dense scale is generated inside the surface flaw during hot rolling,
Subsequent shot blasting-pickling makes it difficult to remove surface flaws, and since the surface hardness of the plate is low, unevenness due to shot blast remains or the effect of improving the press moldability of the product is lost. Therefore, the annealing temperature of the hot rolled sheet is set to the range of 450 to 650 ° C. Preferably 50
It is in the range of 0 to 630 ° C. The holding time in this temperature range is not particularly limited, but is preferably 30 seconds or more in order to eliminate C warpage of the plate.

As for the shot blasting condition, when the coefficient S represented by the equation (3) is less than 500, it is impossible to sufficiently remove the surface roughness and flaws of the hot rolled sheet. Coefficient S is 12
If it exceeds 00, the effect of removing surface roughness and scratches becomes large, but the unevenness of the plate surface becomes severe by shot blasting, and a processed layer is formed on the smooth surface part of the plate, and this processed layer remains after pickling. Surface cracking occurs during cold rolling or press forming. Therefore, the range of the shot blast coefficient S is set to 500 to 1200. Here, the projection density ρ and the projection speed v in the equation (3) are not particularly limited, and may be set so that the coefficient S satisfies the above range.
However, as the industrially feasible range, the projection density ρ is 1
50 to 350 kg / mm ² , projection speed v is 2000 to 4
About 000 m / min is desirable.

When the pickling and shaving amount is less than 20 μm, surface roughening and scratches during hot rolling are removed, but an oxidatively hardened layer around the surface flaws or a layer processed by shot blast remains.
Surface cracking occurs during subsequent cold rolling or press forming. Therefore, the amount of pickling and shaving was set to 20 μm or more. Desirable conditions are ablation amount 25 to 35 μm. Other pickling conditions are not particularly limited, and pickling may be performed using a mixed aqueous solution of nitric acid and hydrofluoric acid, which is generally applied for descaling of industrial pure titanium plates, sulfuric acid and the like. The cold rolling and annealing conditions after pickling are not particularly limited, and the conditions generally applied to the production of titanium plates may be used.

[0018]

The present invention will be described in more detail with reference to the following examples. Test numbers 1-27 in Table 1 are 60 Hz, 120
A kW electromagnetic induction furnace was used, and the inside of the furnace was replaced with an inert gas containing 99.99% pure nitrogen gas as a main component, and a material equivalent to industrial pure titanium JIS Class 1 (120 mm thick x 200 mm wide)
X length 250 mm), the oxygen concentration in each furnace shown in Table 1
(ppm), in-furnace time t (minutes) of 700 ° C or higher, and finally heated at the heating temperature T (° C) that is reached, and hot-rolled in the atmosphere to form a hot-rolled sheet with a thickness of 3.0 mm. That is the case. Test No. 28 in Table 1 is the same material and shape as the above, heated by gas heating under the conditions shown in Table 1 and hot-rolled in the atmosphere to obtain a hot-rolled sheet having a thickness of 3.0 mm. This is the case. Here, the rolling end temperature of any of the above test materials is 550 to 6
It was about 00 ° C.

Subsequently, Test Nos. 1 to 28 were annealed at various temperatures for 2 minutes in the air, and then shot blasted under various conditions (shot blast coefficient S) to prepare a mixed aqueous solution of nitric acid and hydrofluoric acid. Pickled with. Further, the pickled plate was cold rolled to a plate thickness of 0.5 mm and then annealed at 630 ° C. for 5 hours in an argon gas atmosphere.

With respect to Test Nos. 1 to 28, the evaluation of the production conditions and the pickled plate was as follows: surface flaw residual ratio, surface roughness, flatness, and evaluation of surface properties and press formability as evaluation of cold rolled / annealed plate. Table 1 shows the values (JIS B method). Table 1 also shows the overall evaluation (◯: good, ×: bad) of each test material based on the above evaluations of surface and press moldability. Further, FIG. 1 shows the relationship between the comprehensive evaluation in Table 1 and the heating conditions.

[0021]

[Table 1]

[0022]

[Table 2]

From Table 1 and FIG. 1, when heating at 720, 800, 850 and 880 ° C., which is in the range of 700 to 900 ° C., the atmosphere in the furnace of the electromagnetic induction furnace is an inert gas mainly composed of nitrogen gas. And the oxygen concentration in the furnace is below a predetermined amount,
After hot rolling, after atmospheric annealing at 450 to 650 ° C., shot blasting treatment with shot blasting coefficient S in the range of 500 to 1200 and pickling and shaving by 20 μm or more Test Nos. 1 to 14
Is good on both the surface of the pickled plate, the surface of the cold rolled / annealed plate and the Erichsen value. This is to control the atmosphere in the furnace and the oxygen concentration during heating to suppress the generation of scales and oxidatively hardened layers, reduce the surface roughness and flaws that occur during hot rolling, and further reduce the annealing temperature after hot rolling. By making it relatively low, the internal scale of the surface flaws is prevented from becoming dense, and subsequent shot blasting treatment-pickling makes it easier to remove the surface flaws, so that the surface roughness and flaws are removed, and it has a beautiful surface. This is the result of obtaining a plate having excellent formability.

On the other hand, in the test No. 27, the heating temperature is as high as 920 ° C. even when the oxygen concentration is controlled to be 500 ppm and thus the scale and the oxidative hardening layer are easily generated, and the surface is subjected to hot rolling in the atmosphere. Since the defects were remarkable and relatively large surface roughness and many defects were generated, the defects could not be removed by the subsequent shot blasting treatment-pickling. Exam number 2
In Nos. 1 to 26, since the oxygen concentration in the electromagnetic induction furnace was a predetermined amount or more, it was relatively easy to oxidize at the time of heating and surface roughening and scratches were significantly generated by hot rolling, so that subsequent shot blasting-pickling Although the flaws were removed, the oxidation-hardened layer around the flaws remained, and as a result, microcracks occurred during cold rolling.

Test No. 28 uses a gas heating furnace, and due to the influence of combustion gas components, oxidation during heating was intense and a thick oxidatively hardened layer was formed. Therefore, hot rolling caused rough surface and scratches on the surface. The result was that the flaw could not be removed by the subsequent shot blasting treatment-pickling.

In Test No. 15, since the annealing temperature is as low as 400 ° C., distortion and bending of the hot rolled sheet remain, so that the pickled sheet and cold rolled
The shape of the annealed plate is very bad. Test No. 16 had an annealing temperature as high as 700 ° C., so the internal scale of the surface flaws became dense during annealing, and the flaws were difficult to remove by subsequent shot blasting-pickling, and the material was softened, so cold rolling and Even after annealing, the unevenness of shot blasting remains and the surface quality is poor.

Since the shot blast coefficient of Test No. 17 is as high as 1284, the processed layer in the shot blast process was thick and could not be removed by the subsequent pickling, resulting in microcracks during cold rolling. Test No. 18 has a low shot blasting coefficient of 429, so the surface flaws were not sufficiently modified by shot blasting. As a result, the surface flaws were not completely removed by the subsequent pickling, and the flaws remained after cold rolling. did.

In Test No. 19, the pickling and shaving amount was as small as 15 μm, so that the oxidation hardened layer around the surface flaw and the processed layer of shot blasting remained, and as a result, microcracks were generated in the subsequent cold rolling. . Test No. 20 has a pickling and smelting amount of 10
Since it was as small as μm, surface defects remained after cold rolling.

[0029]

As described above, by applying the present invention, the industrial pure titanium material is heated in the atmosphere by the electric heating furnace without using the conventional complicated, poor yield and inefficient method. A simple process of hot rolling-annealing-shot blasting-pickling-cold rolling-annealing removes the scale and surface roughening and flaws generated during heating and hot rolling with good yield, and has a beautiful surface. An industrial pure titanium plate having excellent press formability can be manufactured.

[Brief description of drawings]

1] Formula (1) and test numbers 1 to 6 and 22 to 27 in Table 1
It is the figure which illustrated the comprehensive evaluation (○: good, ×: bad).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiaki Nishida 3434 Shimada, Hikari City, Yamaguchi Prefecture Shin Nippon Steel Co., Ltd.

Claims (1)

[Claims] 1. In the production of a pure titanium plate for industrial use, the material for hot rolling is replaced with an inert gas containing nitrogen gas or argon gas as the main component in the furnace atmosphere so that the oxygen concentration y in the atmosphere is ( It is heated to 700 to 900 ° C. in an electric heating furnace adjusted to satisfy the formula (1), and then hot rolled into a hot rolled plate, and then the hot rolled plate is heated to 450 to 650 ° C.
Annealing at a temperature of, followed by shot blasting treatment under the condition that the shot blasting coefficient S represented by the formula (3) is 500 to 1200, followed by pickling under the condition that the amount of ablation on one side is 20 μm or more. A method for producing a pure titanium plate for industrial use, which is characterized by performing cold rolling and then annealing. Oxygen concentration y (ppm) ≤ 168.5x ^-1 (1) However, x is an index showing the oxygen diffusion distance in pure titanium,
It is shown by the following equation (2). x = t ^0.5 · exp {−5597 / (T + 273)} (2) t: time in furnace at 700 ° C. or higher (minutes) T: heating temperature (° C.) shot blast coefficient S = ρ × v ² / ( 3.6 × 10 ⁶ ) (3) where ρ: Projection density (kg / m ² ) v: Projection speed (m / min)