JPH06248404A - Production of titanium sheet excellent in press formability - Google Patents

Abstract

PURPOSE:To produce a titanium sheet improved in press formability, by heating a cold rolled sheet to an annealing temp. in a nonoxidizing atmosphere, thereafter cooling it under specified conditions and forming an oxidized film on the surface of the sheet in final annealing for a titanium sheet. CONSTITUTION:In the final annealing stage of a titanium sheet, the cold rolled sheet is heated to a prescribed annealing temp. in a nonoxidizing atmosphere (vacuum or inert atmosphere of Ar, He or the like). Then, in the cooling stage from the same heating temp., this titanium sheet is cooled from the temp. range of 200 to 500 deg.C in an oxidizing atmosphere (about 0.01 to 20% oxygen concn.) to form an oxidized film having >=250Angstrom thickness. In this way, the titanium sheet excellent in press formability is obtd., and press working into a complicated shape is enabled.

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 titanium plate which enables high press forming by forming an oxide film on the surface of the titanium plate.

[0002]

2. Description of the Related Art Titanium is used in seawater heat exchangers because it has excellent corrosion resistance and does not corrode in particular to seawater. Among them, plate materials are often used in plate heat exchangers. There is. In order to improve the heat transfer efficiency, this plate heat exchanger is press-formed to make the surface uneven. In recent years, in order to further improve heat transfer efficiency, due to needs such as thinning of plate thickness and complication of surface irregularity shape, from the viewpoint of preventing local constriction or cracking at the time of press molding, more excellent moldability Things have come to be demanded.

In order to prevent press cracking, it is necessary to sufficiently lubricate the surface. Regarding this point, for example, Japanese Patent Laid-Open No. Sho 63-63
No. 174749 is disclosed, but this method requires a number of steps such as forming an iron / zinc alloy layer of a lubricant carrier, followed by zinc phosphate treatment and lubricant application. From the viewpoint of the material of the titanium plate, one of the causes of cracking is anisotropy because titanium is a hexagonal crystal. Therefore, for example, in JP-A-60-82227,
There is a method of reducing anisotropy by rolling at a right angle to the normal rolling direction. However, in this method, there is no choice but to take a very inefficient method of cutting the material plate rolled into a coil shape and rolling it again.

Further, generally, as a method of improving cold workability, it is reported that an oxide film by heating in the atmosphere is effective in preventing seizure with a tool (Proceedings of the 13th Spring Lecture Meeting of Japan Society for Plasticity Processing). 143). This report is a lubrication technique in the intermediate step of manufacturing a plate and a wire rod by cold working, and is inefficient because it involves an extra step of heating in the atmosphere. Further, in this report, there is no mention of the relationship between the thickness of the surface oxide film and the press formability.

[0005]

SUMMARY OF THE INVENTION According to the present invention, a simple treatment is added in the final annealing step of a titanium plate to form an oxide film on the surface without performing an inefficient method as in the prior art. The purpose is to improve high press formability.

[0006]

Means for Solving the Problems As a result of various studies to improve the press formability of a titanium plate, the present inventors have found the following findings. (1) Necking and cracking occur during press forming because deformation is locally concentrated due to poor lubrication between the titanium plate and the press die. Therefore, even if the formability is improved in terms of material, there is a limit in preventing cracking. (2) After annealing a cold-rolled titanium plate at a predetermined temperature in an non-oxidizing atmosphere, and subsequently cooling from a relatively low temperature in the cooling process in an oxidizing atmosphere, the material is recrystallized and evenly surfaced. If a dense oxide film is applied to a predetermined thickness, surface lubricity is improved and press formability is improved. (3) When the thickness of the surface oxide film is 250 angstroms, the press formability is remarkably improved, and when the thickness is 600 angstroms, the effect tends to be saturated. The present invention is based on the above findings, and the gist thereof is as follows. (1) In the final annealing step of the titanium plate, the cold rolled plate is heated to a predetermined annealing temperature in a non-oxidizing atmosphere, and then the titanium plate is heated from a temperature range of 200 to 500 ° C. in a cooling process from the heating temperature. It is characterized in that it is cooled in an oxidizing atmosphere to form an oxide film on the plate surface. (2) Oxidizing atmosphere is 0.01 atmosphere or inert gas.
A mixed gas containing -20% oxygen is desirable. (3) The thickness of the oxide film described in (1) above is preferably 250 angstroms or more. The thickness of the oxide film referred to here was defined as the thickness of the oxygen-enriched layer on the surface containing 2% or more of oxygen concentration in atomic%.

The present invention will be described in detail below. The target titanium plate is a material equivalent to industrial pure titanium JIS type 1 to 3 or a material obtained by adding Pd to them, or Ti-.
3Al-2.5V, Ti-15V-3Cr-3Sn-3
It is a material of all kinds used for press molding, such as a titanium alloy having excellent workability such as Al. Further, although the manufacturing history is not particularly limited, it can be applied to a sheet cold-rolled by a conventional method.

With respect to the annealing conditions, the atmosphere may be a vacuum or an inert gas atmosphere such as argon or helium which is usually used as an unoxidized atmosphere in which an oxide film is not formed during annealing. The temperature and time are not particularly limited as long as the material is recrystallized.

Regarding the temperature range in which the cooling is started in the oxidizing atmosphere during the cooling process, if the temperature is less than 200 ° C., an oxide film having a target thickness cannot be applied. If the temperature exceeds 500 ° C., the target oxide film application can be controlled. Since it becomes difficult and non-uniform, the temperature range is set to 200 to 500 ° C. The oxidizing atmosphere is preferably atmospheric air or a mixed gas containing oxygen in an inert gas, and the oxygen concentration in the mixed gas is 0.
If it is less than 01%, an oxide film having a desired thickness cannot be applied, and if it exceeds 20%, it becomes difficult to control the application of an intended oxide film and becomes non-uniform.
An oxygen concentration range of 20% is desirable. The specific method of cooling in the oxidizing atmosphere in the cooling process from the annealing is not particularly limited, and a coil or a cut plate-shaped titanium plate is annealed in a batch type annealing furnace in a non-oxidizing atmosphere, or strip-shaped. After the titanium plate is annealed in a continuous annealing furnace in a non-oxidizing atmosphere, the titanium plate may be taken out of the furnace in the cooling process, or the inside of the furnace may be replaced with an air atmosphere or a mixed gas atmosphere of oxygen and an inert gas. Further, when the atmosphere is replaced with these oxidizing atmospheres, if the inside of the furnace is once evacuated and then replaced, the target oxide film can be applied more uniformly.

Regarding the thickness of the oxide film on the surface, if the thickness is less than 250 Å, the press formability is not improved, and
Since it is remarkably improved from 0 angstrom, it is set to 250 angstrom or more. The thicker the oxide film is, the higher the press formability is. Therefore, the upper limit is not particularly limited, but the effect tends to be saturated from 600 angstrom.

[0011]

【Example】

Example 1 Using a cold-rolled cut plate having a plate thickness of 0.5 mm, which is equivalent to industrial pure titanium JIS Class 1, annealed at 630 ° C. for 8 hours in vacuum, and then at various temperatures in the atmosphere in the cooling process. After forming an oxide film by cooling, that is, by removing the furnace, the press formability of the titanium plate is evaluated by the Erichsen test method (J
It was evaluated by the IS B method). The results are shown in Table 1. It can be seen from Table 1 that the Erichsen value is remarkably improved when the surface coating thickness is 250 Å or more in the cooling start temperature range of 200 to 500 ° C.

[Table 1]

Example 2 Using a cold-rolled sheet having a thickness of 0.5 mm, which is equivalent to industrial pure titanium JIS Class 1, annealed in argon gas at 650 ° C. for 3 hours, and then at various temperatures in the cooling process. Therefore, after reducing the pressure in the furnace to 100 Torr or less, the inside of the furnace was replaced with argon gas having various oxygen concentrations and cooled to form an oxide film. The press formability of these titanium plates was evaluated by the Erichsen test method (JIS B method). The results are shown in Table 2. From Table 2, the cooling start temperature is 200-
In the range of 500 ° C., and the oxygen concentration in Ar gas was 0.
In the case of 01 to 20%, it can be seen that the Erichsen value is remarkably improved when the surface coating thickness is 250 angstroms or more.

[0013]

[Table 2]

[0014]

According to the present invention, the press formability is remarkably improved by simply performing a simple process in the final annealing of the titanium plate without performing the conventional inefficient method.
It enables press processing of complicated shapes that could not be done before,
Its industrial effect is remarkable.

[Brief description of drawings]

FIG. 1 is a chart of pressability evaluation results by an Erichsen test of a material provided with an oxide film by the treatment of the present invention.

Front page continuation (72) Inventor Akihiko Kusano 3434 Shimada, Hikari-shi, Nippon Steel Co., Ltd., Hikari Works, Ltd. In-house (72) Inventor Katsuhiro Osafune 3434 Shimada, Hikari-shi, Nippon Steel Co., Ltd.

Claims (4)

[Claims] 1. In the final annealing step of a titanium plate, the cold-rolled plate is heated to a predetermined annealing temperature in a non-oxidizing atmosphere, and subsequently in the cooling process from the heating temperature, the titanium is heated from a temperature range of 200 to 500 ° C. A method for producing a titanium plate having excellent press formability, which comprises cooling the plate in an oxidizing atmosphere to form an oxide film on the surface of the plate. 2. The method for producing a titanium plate having excellent press formability according to claim 1, wherein the oxidizing atmosphere is atmospheric air. 3. The oxidizing atmosphere is 0.01 to 2 in the inert gas.
The method for producing a titanium plate having excellent press formability according to claim 1, wherein the mixed gas contains 0% oxygen. 4. The method for producing a titanium plate having excellent press formability according to claim 1, wherein the thickness of the oxide film is 250 angstroms or more.