JP2003236604A - Method for manufacturing titanium material, and lubricant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technique for making oxidized scale produced in the case that a titanium material is annealed in an oxidizing atmosphere thin as much as possible and easily descaling the oxidized scale after annealing. <P>SOLUTION: In the rolling lubricant for the titanium material containing a base and a surfactant to be added as necessary, the carbon content of the lubricant is defixed as ≤30 mass% and/or silicon content is defixed as ≥2 mass%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium material rolling lubricant and a method for producing a titanium material by rolling using the same.

[0002]

2. Description of the Related Art Titanium or a titanium alloy is a metal that is lighter and has better corrosion resistance than steel.
In recent years, its usage has been increasing as a structural material for aircraft, a roof material for building, and an exterior material for building. The titanium or titanium alloy (hereinafter collectively referred to simply as titanium) material used for such applications is usually produced by the method described below. As a titanium material,
Since a plate material is generally used, the present invention will be described below by taking a titanium plate as an example.

First, spongy titanium or titanium scrap is melted using a vacuum heating furnace and cooled to form an ingot. This ingot is heated, and forged or hot rolled into a strip (strip) with a plate thickness of 3 to 4 mm,
Further, this is subjected to an annealing treatment (annealing). afterwards,
After performing shot blasting treatment to remove oxide scale on the surface caused by hot rolling and annealing to some extent, it is completely descaled by pickling treatment with nitric hydrofluoric acid (mixed acid of nitric acid and hydrofluoric acid) ( (Scale removal). Next, after cold rolling (hereinafter, also simply referred to as "cold rolling") to a sheet thickness of about 0.4 to 1 mm, annealing is performed again.

The annealing at this time includes bright annealing and annealing in an oxidizing atmosphere. In the case of bright annealing, after annealing, the product is used as it is (bright annealed finished product) for various purposes. In addition, when annealed in an oxidizing atmosphere, oxide scale is generated on the surface, so molten alkali salt bath (also called salt bath) is used to heat alkali and salts such as sodium hydroxide and sodium nitrate to 450-500 ℃. After being descaled to some extent by immersion in a material that is heated and melted), it is completely descaled by pickling treatment with nitric hydrofluoric acid or the like to obtain a product (pickled finished product).

The bright annealing is usually performed in an inert gas such as argon or in a vacuum. Further, as the annealing in the oxidizing atmosphere, annealing in a combustion heating furnace using a hydrocarbon gas as a fuel is typical, and the annealing atmosphere in this case is a mixed gas of nitrogen, carbon dioxide, steam and oxygen. Therefore, it has an oxidizing power for titanium.

By the way, in the manufacturing process of a titanium plate, it is difficult to remove oxide scale formed on the surface when the titanium plate after cold rolling is annealed in an oxidizing atmosphere, as compared with stainless steel. It has been a problem from the past.

That is, in the case of stainless steel as well as titanium, descaling is carried out by immersion treatment in a salt bath. However, as compared with titanium, oxide scale is much easier to dissolve, so that it can be used at a relatively low temperature. Descaling is possible only by immersing it in a salt bath for a very short time.

However, compared with this, it is generally accepted that titanium oxide scale has a slow dissolution rate in a salt bath and therefore cannot be descaled unless it is immersed in a relatively high temperature salt bath for a long time. In order to save energy and improve productivity, or to reduce the defective rate of products due to insufficient descaling, it is required to develop an easier descaling technique.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to develop a technique for facilitating descaling after annealing by making the oxide scale produced when an titanium material is annealed in an oxidizing atmosphere as thin as possible. Is.

A more specific object of the present invention is to provide a lubricant for cold rolling of titanium material which can exhibit the above-mentioned effects.

[0011]

[Means for Solving the Problems] Oxide scale formed on the surface when a titanium plate is annealed in an oxidizing atmosphere has a higher annealing temperature and becomes thicker as the annealing time becomes longer, and descaling after annealing becomes difficult. This is generally known and can be understood by common sense. However, little was known about the relationship between the surface composition of titanium and oxide scale formation.

On the other hand, cold rolling of titanium is often carried out by small diameter multi-stage rolls like stainless steel.
Since titanium is generally a metal that is easily seized, many studies have been conducted on lubricants for preventing seizure on rolls during cold rolling. For example, "Plasticity and Processing" magazine,
Vol. 24, No. 264 (1983), pp. 59-67, discloses the results of research on the effect of rolling lubricants on the frictional properties of titanium sheets in cold rolling, among mineral oils, beef tallow, palm oil, etc. Describes that beef tallow has the best lubricating effect. Also, "Metal Progress" magazine, 65th
Vol. 2, No. 1 (1954), pp. 107-110, discloses the effect of lubricants on the friction coefficient of titanium. Liquid lubricants such as hydrocarbon compounds and silicone oil have no lubricating effect. It is described that solid lubricants such as graphite and molybdenum disulfide are effective.

However, since these studies were mainly conducted for the purpose of preventing the seizure of titanium, the composition of the titanium surface after cold rolling and the formation of oxide scale when it was annealed were investigated. It does not suggest anything about the impact.

The inventors of the present invention analyzed the surface of the titanium cold-rolled sheet produced in the usual process by glow discharge emission spectrometry, and as a result, as shown in FIG. It was found that there was a layer (carbon-enriched layer) that was converted to carbon. In the figure, curve 1 shows the change of the light intensity of the titanium atom, curve 2 shows the change of the light intensity of the carbon atom, and curve 3
Indicates the change in light intensity of oxygen atoms. As shown by the curve 2, the presence of a carbon atom-enriched layer at the start of sputtering, that is, in the surface layer, is observed in a region having a thickness of about 0.8 to 1.2 μm from the surface.

After degreasing this cold-rolled titanium plate with alkali,
Dip in 1 mass% hydrofluoric acid (30 ℃) for 30-60 seconds to dissolve the surface layer, scrub off the black particles adhering to the surface with water and dry, and then use X-ray diffraction and chemical analysis. As a result of the investigation, it was confirmed that the carbon-rich layer described above contained a large amount of TiC.

As described above, the reason why the carbon-enriched layer containing TiC is formed on the surface of the cold-rolled titanium plate is not clear at present, but the mineral oil (hydrocarbon-based compound) used as the lubricant for cold-rolling is not clear. It is speculated that) forms TiC by a mechanochemical reaction as shown in Eq. (1) with the active new surface of the titanium plate that appears after cold rolling.

C _n H _{2n + 2} + nTi → nTiC + (2n + 2) H (1) Furthermore, the inventors of the present invention used this titanium cold-rolled sheet at 30 ° C. for nitric hydrofluoric acid (nitric acid concentration 10 mass%, hydrogen fluoride). It was immersed in an aqueous solution with an acid concentration of 1 mass%) for 60 seconds to remove the carbon-enriched layer on the surface, then washed with water, dried, and annealed in a hydrocarbon gas combustion atmosphere. The thickness of the oxide scale produced by annealing is
1/3), it was found that descaling after annealing is much easier.

The reason why the oxide scale due to annealing is thinned by previously removing the carbon-enriched layer on the surface of the cold-rolled titanium material is not clear at this time.
It is presumed that it is due to the following reasons.

That is, when a titanium plate having a carbon enriched layer containing a large amount of TiC on its surface is annealed in an oxidizing atmosphere, the produced oxide scale becomes non-uniform and lacks in denseness. It is speculated that a thick oxide scale is formed due to the easy diffusion of oxygen into the gold. It is also considered that TiC is more likely to react with oxygen that has diffused than Ti, which is metallic, to form TiO ₂ (scale) by easily reacting as in Eq. (2).

TiC + 30 → TiO ₂ + CO (2) On the other hand, in the case of a titanium plate without a carbon-enriched layer on the surface, the oxide scale produced by annealing is dense and It is presumed that the scale becomes thin because it acts to prevent oxygen from diffusing.

As described above, in order to thin the oxide scale produced by annealing and facilitate descaling after annealing, the carbon-enriched layer on the surface of the titanium plate before annealing should be removed, or
I found it effective to make it as thin as possible,
It is not preferable to add a step of pickling or rinsing before annealing because it increases the production cost. Therefore, a lubricant that does not form a carbon-enriched layer on the titanium surface in the process of cold rolling as much as possible, or even if a carbon-enriched layer is formed, a lubricant that thins the oxide scale formed by subsequent annealing cannot be obtained. As a result of various studies, a titanium plate was cold-rolled with a lubricant containing 20 mass% or less of carbon or a lubricant containing 2 mass% or more of silicon, so that the oxide scale produced by annealing was reduced. The present invention has been completed by finding that it can be made significantly thinner.

FIG. 2 shows a conventional mineral oil type lubricant, a lubricant containing carbon of 30 mass% or less,
Alternatively, the titanium material was cold-rolled using a lubricant containing 2 mass% or more of silicon, and the surface of the titanium plate annealed in an oxidizing atmosphere after degreasing with alkali was subjected to GDS analysis.

FIG. 2 (a) is a normal mineral oil-based lubricant (carbon content is about 86%), and FIG. 2 (b) is a lubricant having a carbon content of about 9% (mixture of mineral oil, water and surfactant). , (C) is cold rolled using a lubricant (silicone oil) with a silicon content of about 20%,
The result of analyzing the surface degreased with alkali by the same glow discharge emission spectrometry as in the case of FIG. 1 is shown in a graph.

FIGS. 2D, 2E, and 2F are similar to the surface of the titanium plate in FIGS. 2A, 2B, and 2C annealed in an oxidizing atmosphere. It is a graph which shows the analysis result of.

As can be seen from these analysis results, FIG.
Comparing (d), (e) and (f), cold rolling using a lubricant containing 30 mass% or less of carbon or a lubricant containing 2 mass% or more of silicon instead of the usual mineral oil type lubricant. After that, by performing annealing, the thickness of the produced oxide scale can be significantly reduced.

Of particular note in these analytical results are:
Comparing Fig. 2 (b) and Fig. 2 (c), although Fig. 2 (e) and Fig. 2 (f) were compared, although the carbon concentration on the surface after cold rolling was similar, Later scale thickness is much thinner in the latter. That is, it is found that it is effective to use the silicon-containing lubricant.

The reason for this is not clear at present,
In the case of FIG. 2 (c), silicon is concentrated on the surface together with carbon, which is presumed to have suppressed the growth of scale during the annealing process.

The reference numerals in FIG. 2 are the same as those in FIG. 1, but the reference numeral 4 is a graph showing changes in the light intensity of silicon atoms. Here, the present invention is as follows.

(1) A titanium material is characterized in that a titanium material is cold-rolled using a lubricant having a carbon content of 30 mass% or less, annealed in an oxidizing atmosphere after rolling, and then descaled. Manufacturing method by rolling.

(2) A titanium material is characterized in that a titanium material is cold-rolled using a lubricant having a silicon content of 2 mass% or more, annealed in an oxidizing atmosphere after rolling, and then descaled. Manufacturing method by rolling.

(3) A lubricant for rolling a titanium material having a carbon content of 30 mass% or less. (4) A lubricant for rolling a titanium material, which has a carbon content of 85 mass% or less and a silicon content of 2 mass% or more.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION The rolling of the titanium plate according to the present invention may be carried out by a commonly used method and equipment, and the lubricant according to the present invention is supplied to the gap between the titanium plate to be rolled and the rolling roll. By this, the oxide scale generated by annealing can be thinned, and descaling after annealing can be facilitated.

The commonly used method and equipment are, for example, a rolling mill having one work roll each having a diameter of about 50 to 200 mm (two rolls in total) and two or more work rolls for backing up the work roll. Use the rolling reduction of one rolling
A typical method is 10 to 50% of rolling with several to ten or more passes.

The material to be rolled is an industrial pure titanium or titanium alloy strip or cut plate having a plate thickness of about 2 to 5 mm, which is generally rolled to a plate thickness of about 0.3 to 2 mm.

In the present specification, the term "cold rolling (cold rolling)" generally refers to rolling performed at normal temperature, but lubrication is also performed in so-called warm rolling performed while heating to a maximum of several hundreds of degrees. Since the formation of titanium carbide and the formation of the surface carbon-enriched layer by the mechanochemical reaction between the agent and titanium may occur, warm rolling that causes the mechanochemical reaction is also included.

The lubricant for limiting the carbon content according to the present invention includes, as a base, a compound of carbon and hydrogen such as hydrocarbon, carbon such as ester, alcohol or fatty acid, hydrogen and oxygen. It is recommended that one or more of the following compounds be mixed with water and optionally a surfactant.

In another embodiment, a mineral oil-based rolling oil to which a surfactant is added if necessary is commercially available. By using this as a base material and mixing it with water, the carbon content becomes 30 mass% or less. You may use what was prepared in this way.

In another embodiment, an aqueous solution containing 8 to 15% of a phosphate (potassium phosphate, sodium phosphate, etc.) may be used as a base. To adjust the carbon content of the lubricant,
In any case, it can be carried out by selecting the type of the base material and blending it, or by diluting it with water.

As the lubricant for limiting the silicon content according to the present invention, silicone oil (general formula: (-R ₂ SiO-)) is used.
_n ), an alkoxide containing silicon (general formula: Si (OR) ₄ ).
It is recommended to use one kind or a mixture of two or more kinds of organosilicon compounds (R is an alkyl group etc.) such as a silane coupling agent (general formula: RSi (OR) ₃ ). Further, a mixture of these organosilicon compounds with a normal mineral oil-based lubricant or water can also be used. However, when mixing with water, it is desirable to add a surfactant for assisting the mixing.

Also in the lubricant which defines the silicon content,
The silicon content can be adjusted by selecting the base material (including dilution with water) as in the case of adjusting the carbon content.

In any type of lubricant according to the present invention, a water-soluble compound containing silicon in an organic silicon compound mixed with water and a surfactant, for example, sodium metasilicate (Na ₂ SiO ₃ ). It is also possible to use the one to which water glass is added.

By setting the silicon content to 2 mass% or more, the allowable range of the carbon content is widened, and the scale formation is effectively suppressed even if the carbon content is expanded to 85% or less.

In a preferred embodiment of the present invention, the lubricant used preferably has a carbon content of 30 mass% or less and a silicon content of 2 mass% or more. In the present invention, after the completion of cold rolling, annealing is carried out in an oxidizing atmosphere, which is usually carried out at 700 to 830 ° C. for about 1 to 3 minutes while continuously passing a titanium strip through a heating furnace. It suffices to perform the annealing conditions.

After annealing in an oxidizing atmosphere, since oxide scale is formed on the surface, the molten scale is soaked and pickled with a nitric hydrofluoric acid aqueous solution for descaling. The molten salt dipping treatment may be a commonly used treatment, such as a molten alkali salt bath at 450 to 520 ° C. (for example, 90 mass% sodium hydroxide,
It may be immersed for 5 to 30 seconds in a melt of sodium nitrate (10 mass%). The pickling is preferably performed by dipping in a nitric hydrofluoric acid pickling solution (aqueous solution having a nitric acid concentration of 8 to 15 mass% and a hydrofluoric acid concentration of 2 to 5 mass%) at 30 to 50 ° C. for about 60 to 200 seconds.

On the other hand, in order to anneal the titanium strip while wound in a coil, a batch type heating furnace is used in a non-oxidizing atmosphere at 680 to 720 ° C. for 12 to 24 hours. In this case, since the oxide scale is hardly generated by the annealing, it is not necessary to perform descaling thereafter.

[0046]

[Example] (Example 1) Plate thickness 3 mm, width 120 mm, length 200 mm
A sheet of industrial pure titanium (JIS type 1) was rolled to a sheet thickness of 0.8 mm using a small experimental 4-stage rolling mill (work roll diameter: 150 mm). The 7 kinds of lubricants shown in Table 1 were applied to the work rolls for each pass, and each lubricant was rolled for a total of 15 passes.

A test piece having a size of 100 mm × 150 mm was cut out from the rolled titanium plate and degreased with a commercially available alkaline degreasing agent (Daiichi Kogyo Seiyaku Co., Ltd. “methacryl CP3200” 3 mass% aqueous solution at 60 ° C.). After soaking for 10 minutes, wash with water and dry)
After that, annealing was performed at 800 ° C. for 160 seconds in an oxidizing gas atmosphere (composition: 75 vol% nitrogen, 11 vol% carbon dioxide, 10 vol% steam, 4 vol% oxygen) simulating a hydrocarbon gas combustion atmosphere.

A 50 × 75 mm test piece was cut out from the annealed titanium plate, and a 480 ° C. salt bath (composition: 82 mass
_{% NaOH-10mass% NaNO 3 -7mass} % Na 2 CO 3 -1mass%
(NaCl) for 20 seconds, then washed with water, immersed in a nitric hydrofluoric acid pickling solution (composition: 10 mass% HNO ₃ -2 mass% HF) at 40 ° C for 60 seconds, washed with water and dried.

The surface of the test piece was observed with an optical microscope, and the degree of descaling was evaluated by the descaling area ratio (percentage of the descaled area to the total surface area). The results are shown in Table 1.

As can be seen from the table, the carbon content is 30 mass.
% Or less or a lubricant having a silicon content of 2 mass% or more was used to descale the annealed titanium plate, and the descaled area ratio in the case of the present invention examples (No. 1 to 7) was 82 to
It was 100%. On the other hand, a titanium plate rolled with a lubricant having a carbon content of more than 30 mass% and a silicon content of less than 2 mass% was annealed and descaled in Comparative Examples (No. 8 to 1).
In the case of 0), the descaling area ratio was as low as 7 to 27%.

[0051]

[Table 1]

[0052]

EFFECTS OF THE INVENTION According to the present invention, it is possible to reduce the scale of oxide produced when an titanium plate is annealed in an oxidizing atmosphere and facilitate descaling after annealing. Not only can the rate be reduced, but the thermal energy required for descaling and the acid used for pickling can be saved, which is a great practical effect.

[Brief description of drawings]

FIG. 1 is a graph showing the results of analyzing the surface of a titanium cold-rolled sheet manufactured by a conventional rolling method by glow discharge emission spectrometry.

FIG. 2 is a graph showing the results of surface analysis when using a normal lubricant, a lubricant according to the present invention containing 30 mass% or less of carbon, and a lubricant containing 2 mass% or more of silicon. Figure 1 (a) shows a conventional mineral oil-based lubricant,
Is a lubricant with a carbon content of about 9%, and (c) is a lubricant with a silicon content of about 20%. , Same (e), same (f)
2A is a graph showing the results of surface analysis after annealing the titanium plates obtained in FIGS. 1A, 1B, and 1C in an oxidizing atmosphere.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C10M 105/24 C10M 105/24 105/32 105/32 105/76 105/76 107/02 107/02 107 / 50 107/50 171/00 171/00 173/00 173/00 C22F 1/18 C22F 1/18 H // C22F 1/00 685 1/00 685Z 686 686Z C10N 20:00 C10N 20:00 Z 30: 00 30:00 Z 40:24 40:24 Z 70:00 70:00 (72) Inventor ▲ Takahashi Masanori 4-533 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. F-term ( Reference) 4E002 AA08 AD05 BC08 CB03 CB08 4H104 BB01A BB14A BB31A BJ02A BJ03A CJ10A DA02A EA21A LA20 PA23 PA32

Claims (4)

[Claims] 1. A titanium material which is characterized in that a titanium material is cold-rolled by using a lubricant having a carbon content of 30 mass% or less, annealed in an oxidizing atmosphere after rolling, and then descaled. Manufacturing method. 2. A titanium material which is characterized in that a titanium material is cold-rolled using a lubricant having a silicon content of 2 mass% or more, annealed in an oxidizing atmosphere after rolling, and then descaled. Manufacturing method. 3. A lubricant for rolling titanium material having a carbon content of 30 mass% or less. 4. A lubricant for rolling a titanium material, which has a carbon content of 85 mass% or less and a silicon content of 2 mass% or more.