JP3303344B2 - Method for producing cold-rolled sheet of titanium or titanium alloy with few surface defects - Google Patents

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 cold-rolled sheet of titanium and a titanium alloy having a small number of surface defects, and more particularly to a method of reducing the surface defects by performing descaling and heat treatment before cold rolling. And a cold rolled titanium alloy sheet.

[0002]

2. Description of the Related Art Thin sheets of titanium and titanium alloys (hereinafter sometimes referred to as titanium materials) are generally manufactured through hot rolling, heat treatment, descaling and cold rolling as shown in FIG. It is a target. In this case, the thin product 1
Surface flaw 2 on the surface as shown in FIG.
Occurs, which contributes to product failure. This scab is left without the high concentration oxygen solid solution layer (hereinafter referred to as oxygen rich layer) existing on the hot rolled sheet surface being sufficiently removed during descaling,
It is flawed due to the difference in ductility with the parent metal during the subsequent cold rolling. With the current technology, the residual oxygen-rich layer cannot be detected nondestructively (except for extreme cases such as residual scale), so that it is impossible to completely prevent flaws.

First, as shown in FIG. 2, the characteristics of the scab flaws are accompanied by minute cracks and a base metal (titanium material).
Is that there are harder parts. The high-hardness portion is a portion in which high-concentration oxygen is dissolved, that is, an oxygen-rich layer. From the hardness level, the oxygen concentration is estimated to be 1% or more.

This oxygen-rich layer is formed in a layered form as shown in FIG. 3 by heating a titanium material in an atmosphere containing oxygen. The thickness of the oxygen-rich layer 3 increases as the heating temperature increases and as the heating time increases. The oxygen-rich layer is divided while being slightly thinned in the hot rolling step, and is left in the concave portions on the sheet surface after hot rolling as shown in FIG. Since the oxygen-rich layer 3 remaining in the form of dots is harder than titanium as the base metal and has a different ductile behavior, it becomes a surface flaw in the cold rolling step. Therefore, it is necessary to remove all the oxygen-rich layer in the descaling step before the cold rolling step.

The thickness of the oxygen-rich layer is usually 20 to 50 μm.
However, since it is conceivable that the layer thickness is increased by heating conditions such as temperature and time at the time of formation, it is necessary to remove the surface layer of the titanium plate by at least 100 μm on both surfaces. The thickness of the hot-rolled plate (coil) supplied to the cold-rolled plate (coil) is 3 to 4 mm.
Therefore, the yield loss is 5 to 7% of the total thickness, which is a very large yield loss. Further, removing a plate surface as large as 100 μm by surface grinding or acid cleaning with nitric hydrofluoric acid is inefficient and cannot be said to be an industrial method.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to eliminate or reduce the residual oxygen-rich layer and to produce a titanium or titanium alloy cold-rolled plate free of bark defects.

[0007]

SUMMARY OF THE INVENTION The present invention, which has achieved the above-mentioned object, provides a process for producing a cold-rolled plate from a hot-rolled plate of titanium and a titanium alloy, after the hot-rolled plate is shot-blasted. Descaling with nitric hydrofluoric acid, then 6
The gist is that cold rolling is performed after annealing in a non-oxidizing atmosphere at 00 to 850 ° C. for 2 hours or more.

[0008]

After the hot rolling, it is impossible to measure the thickness of each of the oxygen-rich layers infinitely numerous in the state as shown in FIG. 4, and a non-destructive detection method has been established. It has not been. It is useless to remove the plate surface by 100 μm as in the conventional method.

Therefore, the present inventors have made it difficult to diffuse the oxygen in the residual oxygen-rich layer, which is difficult to detect, into the inside of the titanium plate by heat treatment, to eliminate or reduce the oxygen-rich layer, and then to carry out cold rolling. The present inventors have found that a cold-rolled sheet having no flaws (or a practically negligible incidence) can be obtained, and the present invention has been accomplished.

First, in the present invention, after the hot rolled sheet is subjected to shot blasting to break the oxide scale film on the surface, pickling is performed with nitric hydrofluoric acid. The thickness of the plate to be removed by pickling is 5 to 30 μm in total on both sides, more preferably 5 to 1 μm.
A smaller value of 0 μm is better. The hot-rolled plate serving as a cold-rolled plate has a thickness of 3 to 4 mm, of which the oxygen-rich layer is 2 mm.
In the present invention, since the oxygen in the oxygen-rich layer is diffused by the heat treatment after the pickling step, it is not necessary to remove 100 μm as in the conventional method.

The pickled titanium sheet is annealed in a non-oxidizing atmosphere before the cold rolling step. Usually, the cold-rolled sheet (coil) is annealed in a vacuum or argon gas in the final step. Therefore, if annealing is performed before cold rolling using equipment for this step, no special equipment is required.

The above-mentioned annealing before cold rolling is performed for 2 hours or more. If it is less than 2 hours, the oxygen-rich layer may remain on the titanium plate surface, which is not preferable. Titanium or a titanium alloy is a metal having a strong affinity for oxygen, and is an effective oxygen absorbing medium to be used for removing impurity oxygen in a gas. For this reason, it is considered that by performing annealing while shutting off supply of oxygen from the outside, oxygen in the oxygen-rich layer diffuses into the titanium plate.

[0013] Therefore, the treatment of the method of the present invention of annealing in a non-oxidizing atmosphere following shot blasting and pickling can reduce the oxygen concentration and the hardness of the oxygen-rich layer. Even if the process is performed, no barbed flaw is generated.

[0014]

EXAMPLES The present invention will be described in more detail with reference to the following examples. However, the following examples do not limit the present invention, and all changes and modifications may be made without departing from the spirit of the preceding and following aspects. It is included in the technical scope of the present invention.

[0015] and titanium hot-rolled plate of Example thickness 3.5mm and sample. The thickness of the oxygen-rich layer was 20 to 30 μm and existed on the surface in a dotted manner.
First, after shot blasting, 2% HF and 15%
Pickling was performed with nitric hydrofluoric acid containing% HNO ₃ . Reduce the plate thickness (total amount on both sides) reduced by pickling to 10, 30, 60, 100 μm
Was changed. Examples 1-4, in which vacuum annealing was performed for 2 hours at 650 ° C. after pickling, and Comparative Examples 1, in which vacuum annealing was not performed.
4 was cold-rolled. 49% reduction in cold rolling
(From 3.5 mm to 1.8 mm in thickness), and observation of the surface state after cold rolling was carried out by an enlarged photograph. Table 1 shows the results.

[0016]

[Table 1]

From the results in Table 1, it can be seen that in the comparative example in which vacuum annealing was not performed, the surface flaw could not be prevented unless the plate surface was removed by 100 μm by pickling. In the example, no surface flaws were generated at all even by removing 10 μm alone, and it is clear that the oxygen-rich layer diffuses or disappears by vacuum annealing.

[0018]

The present invention is configured as described above.
By performing vacuum annealing, the removal amount of the hot-rolled sheet surface by pickling could be extremely reduced, and a cold-rolled sheet of titanium or a titanium alloy without any surface flaws could be produced.

[Brief description of the drawings]

FIG. 1 is a general manufacturing process diagram of a titanium thin plate.

FIG. 2 is a schematic diagram of a state in which a barb flaw on the surface of a titanium plate is viewed from above.

FIG. 3 is a schematic sectional view of a titanium sheet showing the presence of an oxygen-rich layer before hot rolling.

FIG. 4 is a schematic cross-sectional view of a titanium sheet showing the presence of an oxygen-rich layer after hot rolling.

[Explanation of symbols]

 1 Titanium (or titanium alloy) thin plate 2 Scratch flaw 3 Oxygen rich layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-42761 (JP, A) JP-A-61-284559 (JP, A) JP-A-62-280353 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C22F 1/00-3/02 B21B 45/06

Claims (1)

(57) [Claims] In a process of manufacturing a cold-rolled sheet from a hot-rolled sheet of titanium and a titanium alloy, the hot-rolled sheet is shot-blasted, descaled with nitric hydrofluoric acid, and then heated at 600 to 850 ° C. A method for producing a cold-rolled sheet of titanium or a titanium alloy having a small number of surface defects, wherein the sheet is subjected to annealing in a non-oxidizing atmosphere for at least one hour and then to cold rolling.