Electric heating – Metal heating – By arc
Reexamination Certificate
1998-12-09
2001-05-15
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121350, C228S235200
Reexamination Certificate
active
06232573
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a titanium alloy sheet which has excellent workability and small anisotropy with respect to mechanical properties such as bending properties and a production method thereof.
2. Description of Related Art
Generally, a titanium alloy sheet is produced as a coil by hot rolling that uses a tandem mill, and such a coil is cut to a predetermined length for sheet forming. With respect to titanium alloys that have relatively poor workability such as &agr;+&bgr; type titanium alloys, a so-called “pack rolling” is performed, mainly using a reverse mill, in which a titanium alloy slab is packed with carbon steels, for example, by covering the upper and down sides of a slab with carbon steels or by inserting a slab in a carbon steel box before rolling, so that a decrease in temperature during rolling is suppressed and rolling is performed in a high temperature range where the titanium alloy has relatively good workability.
In any one of the methods described above, hot rolling is performed in the air, and then, oxide scales which are formed on surfaces during heating or rolling and oxygen-enriched layers underneath are removed in a grinding process, for example, using a coil grinder or a sheet grinder.
It is an essential step for improving the quality of a titanium alloy sheet to remove oxide scales on surfaces and oxygen-enriched layers underneath. The reason is that, if oxide scales and oxygen-enriched layers remain, the appearance of a product deteriorates, and since the areas near the surfaces are significantly hardened by the oxide scales and the oxygen-enriched layers, the workability such as bending properties' deteriorates.
The workability, such as bending properties, is sensitively influenced by surface conditions such as surface roughness, and thus, in a grinding process, a grindstone, an abrasive belt and abrasive grains are appropriately combined in order to control the surface roughness of the finish.
However, since grinding is performed in one direction, there is a difference in surface conditions such as surface roughness between the grinding direction and a direction transversal to it. Thereby, the workability is good in the grinding direction, however, significantly bad in the direction transversal to the grinding direction, resulting in a large anisotropy with respect to mechanical properties.
In actually forming a titanium alloy sheet into a certain component, a step of bending or the like is performed, and the bending direction is not limited to the grinding direction. The bending may be performed in any direction, for example, in the direction transversal or diagonal to the grinding direction. Although excellent workability is desired in all directions of a sheet plane, the current titanium alloy sheet which is ground in one direction cannot meet this requirement.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a titanium alloy sheet which has excellent workability, small anisotropy with respect to mechanical properties such as bending properties, and also excellent appearance after it is formed into a component, and a production method thereof.
According to the present invention, there is provided a titanium alloy sheet having a surface roughness that satisfies the relationship Ra≦2 &mgr;m in all directions and a surface waviness that satisfies the relationship W
CA
≦10 &mgr;m.
This titanium alloy sheet can be produced by a method which comprises the steps of rolling a titanium alloy slab, and then acid pickling the rolled titanium alloy sheet, for example, with 1 to 10% HF and 1 to 40% HNO
3
, whereby a surface roughness satisfying the relationship Ra≦2 &mgr;m in all directions and a surface waviness satisfying the relationship W
CA
≦10 &mgr;m are achieved.
The method can further comprise a step of grinding the rolled titanium alloy sheet before acid pickling.
In the method, rolling may be replaced by pack rolling, preferably by packing a titanium alloy slab with carbon steels in a vacuum by an electron beam welding method and then rolling it. Here, the titanium alloy slab signifies not only its as-cast slab, but also its rolled semi-product having a certain thickness.
When cross rolling, for example, with a cross ratio 0.2 to 5 is applied to rolling, it is more effective to obtain the surface conditions described above.
DETAILED DESCRIPTION OF THE INVENTION
A titanium alloy sheet in accordance with the present invention has a surface roughness that satisfies the relationship Ra≦2 &mgr;m in all directions and has a surface waviness that satisfies the relationship W
CA
≦10 &mgr;m. By setting the surface roughness of the sheet at Ra≦2 &mgr;m in all directions, the sheet exhibits excellent workability even when forming such as bending is performed in any direction. Also, when a sheet with the surface waviness at W
CA
≦10 &mgr;m is formed into a component, a rough surface appearing at forming can be suppressed.
In such a case, by performing acid pickling as surface finishing after rolling, a titanium alloy sheet having low surface roughness, small anisotropy, and low a surface waviness can be produced.
Also, by performing grinding and acid pickling as surface finishing after rolling, such surface conditions can be easily obtained, because the surface roughness of the sheet is reduced by grinding before acid pickling.
A titanium alloy slab may be packed with carbon steels before rolling in the air to maintain a high rolling temperature, more preferably packed in a vacuum by an electron beam welding method to suppress the deposition of oxide scales and the formation of oxygen-enriched layers during heating. Therefore, the surface finishing treatment can be simplified, and also the titanium alloy sheet having a surface roughness that satisfies Ra≦2 &mgr;m in all directions and a surface waviness that satisfies W
CA
≦10 &mgr;m can be more easily obtained.
Cross rolling is preferably applied to rolling. By cross rolling, anisotropy with respect to mechanical properties resulting from the texture formation during rolling can be significantly suppressed. By performing acid pickling, or grinding and acid pickling, as subsequent surface treatment, the surface roughness can be more easily and securely set at Ra≦2 &mgr;m in all directions, and the surface waviness can be set at W
CA
≦10 &mgr;m. The cross ratio at cross rolling should be set at 0.2~5 to obtain much smaller anisotropy with respect to mechanical properties.
Mixed acid of 1~10% HF+1~40% HNO
3
should be preferably used for the acid pickling described above, because this mixed acid enables oxide scales to be removed without absorption of much hydrogen into a titanium alloy sheet.
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patent: 3579800 (1971-05-01), Packard
patent: 3711937 (1973-01-01), Emley
patent: 3798747 (1974-03-01), Lalwaney
patent: 4406761 (1983-09-01), Shimogori et al.
patent: 4826605 (1989-05-01), Doble et al.
patent: 5060845 (1991-10-01), Suenaga et al.
patent: 5415336 (1995-05-01), Stenard et al.
patent: 5513791 (1996-05-01), Rowe et al.
patent: 402192804 (1990-07-01), None
Fukai Hideaki
Iizumi Hiroshi
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Heinrich Samuel M.
NKK Corporation
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