JP2003311322A - Titanium welded tube of excellent workability, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium welded tube for preventing degradation of workability by welding and having the workability of a welded part of the tube close to that of a base material, and a titanium welded tube manufacturing method. <P>SOLUTION: In this titanium welded tube, the ratio of a weld bead width W (mm) of a weld zone to the thickness t (mm) satisfies inequalities 6.5>t/W≥1/3. In this titanium welded tube manufacturing method, butt welding is performed by rolling a flat plate into a cylinder, and irradiating laser beam to a butted part so that the ratio of the weld bead width W (mm) of the weld zone to the thickness t (mm) satisfies inequalities 6.5>t/W≥1/3. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-walled titanium welded pipe which is required to have workability and is particularly used for automobile exhaust system pipes, corrosion resistant pipes and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Titanium (titanium alloy) has excellent corrosion resistance,
It has excellent features such as light weight, rich metallic luster color, and large plastic anisotropy. Therefore, it is used for corrosion-resistant pipes, automobile exhaust system pipes, parts and the like. In particular, for parts, not only corrosion resistance is required, but also thinning for weight reduction or pipe workability is required. That is, in order to be used as a part, it is required to have a thin wall and high secondary workability of the pipe including the welded portion.

Conventionally, methods of forming a pipe by hot extrusion have been used because of the problem of workability of the welded portion. However, these methods cannot produce a thin wall, and the manufacturing cost is very high. I have a problem. In addition, as a method of manufacturing at a low price, roll forming from a coil,
A method of joining by welding after bending in the circumferential direction is used. Generally, TIG welding is performed, but since the workability of the welded portion is poor as a product, there is a problem in the deformability of the pipe during secondary processing.

[0004]

Regarding other laser welding, Japanese Patent Application Laid-Open No. 11-114684 discloses a β-type titanium alloy welded pipe excellent in weld toughness and a manufacturing method by laser welding. It is a thick-walled tube with a plate thickness of 6.5 mm where toughness is a problem, and the relationship between the bead width (W) at the seam and the penetration depth (d) d / W
There is an example of β-type titanium alloy welded pipe characterized by ≧ 6.5, but the weldability is not specified at all.

Further, when the relational expression defined in the above-mentioned known invention is modified, W ≦ d / 6.5, and when laser welding is performed on a thin material, for example, t
= 1.0 mm, the penetration depth d becomes equal to the plate thickness t, so that the bead width W (mm) is 1 /
6.5mm or less will be required. However, obtaining such a narrow bead width actually requires a very small welding beam width, which is 0.2 m even when considering the upset.
A beam diameter of m or less is required. In this case, it is impossible to obtain a sound welded portion that can withstand high machining, because the plate edge is formed with precision and shakes due to vibration of the plate edge. An object of the present invention is to provide a titanium welded pipe which prevents deterioration of workability due to welding and is excellent in workability of not only the base material but also the welded portion of the pipe, and a method for producing the same.

[0006]

That is, the gist of the present invention is as follows. (1) A thin-walled titanium welded pipe characterized in that a ratio of a weld bead width W (mm) and a plate thickness t (mm) of a welded portion is 6.5> t / W ≧ 1/3. (2) A flat plate is roll-formed into a cylindrical shape, a laser beam is irradiated to the abutting portion, and the ratio of the weld bead width W (mm) to the plate thickness t (mm) at the welded portion is 6.5> t / W ≧. A method for producing a titanium welded pipe, which comprises performing butt welding so as to satisfy 1/3.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
In general, the workability of welded pipes is not clear about the relationship between weld cracking and the thermal effect of laser welding. The present inventor applies the stress at a constant ratio in the pipe axis direction and the pipe circumferential direction of the relationship between the weld width and the pipe workability, so that the pipe is deformed and the history until it breaks in a certain strain state is obtained. The following findings were obtained using the method of measurement.

That is, the crystal grains become coarse and soften by the time the weld metal is solidified and cooled, and fracture occurs at the weld heat affected zone. In commonly used TIG welding etc., the heat input width is large and the welding speed is slow, so the welding heat effect width is large, and when the pipe is expanded by applying internal pressure to the pipe, it breaks at the welded part and the expansion ratio is high. Workability cannot be obtained. These are problems in processing such as claw expansion that expands the pipe diameter at the end of the pipe, cone expansion that pushes in a tapered tool to expand, and pipe expansion molding processing such as hydroforming.

Therefore, heat input such as laser welding is small,
The welding method in which the width of the heat-affected zone is narrow is advantageous because the cooling rate of the weld metal also increases. However, in the case where the pipe wall thickness is small as in the present invention, when the irradiation width of the welded portion is reduced, the welding heat affected width is reduced due to the welding stability due to the weld end plate edge accuracy, but the forming limit is significantly reduced. I understood it. Figure 2 shows the outer diameter D welded by CO ₂ laser
= 60.5 mm, plate thickness t = 1.0 mm, ratio t / W between weld bead width W and wall thickness t, and outer diameter until pipe end is restrained and internal pressure is applied D / initial outer diameter D ₀ ratio D /
The relationship with D ₀ is shown.

Black coating indicates the fracture of the welded portion, and white coating indicates the fracture of the base metal. When t / W is smaller than 1/3, the welded part is broken, but the welded state becomes unstable due to the shape difference of the plate end and the influence of heat input fluctuation. On the other hand, when t / W is 6.5 or more, unwelding occurs in the fusion zone in the pipe axis direction, resulting in fracture of the weld zone. Therefore, the ratio of the weld bead width (W) and the plate thickness (t) of the welded portion is defined as 6.5> t / W ≧ 1/3. The relationship between the plate and the laser beam during laser irradiation is shown in Fig. 3. In order to perform stable welding, the SQ roll (welding roll) before the SQ roll (welding roll) is almost in contact with the end of the plate or is nearly parallel. It is necessary to mold so that it will be in a state. The weld bead width shall include the heat affected zone.
The laser used for welding may be a carbon dioxide laser, YAG, or a semiconductor. A solid-state element (LD) laser has high heat conversion efficiency and can reduce manufacturing cost.

[0011]

[Example] As a tube material, a steel plate having a tensile strength of 390 MPa and a plate thickness of 1.0 mm was formed into a substantially cylindrical shape by multi-stage SQ rolls (welding rolls), and as an example of the present invention, CO
₂ Laser irradiation, t / W at welding speed 3.0m / min
A pipe having an outer diameter of 60.5 mm was welded so that the outer diameter became 1.0.
As a comparative example, T should be the same material and have the same dimensions.
IG welding was performed to produce a tube having a wide weld portion with t / W = 1/6. In both methods, welding was performed in an inert gas with an argon shield.

FIG. 4 shows a forming limit diagram of the TIG welded pipes of the present invention example and the comparative example. FIG. 4 shows forming limits when hydroforming is performed under various conditions, in which the vertical axis represents circumferential strain (logarithmic strain) and the horizontal axis represents axial strain (logarithmic strain). In the example of the present invention, when the deformation under the uniaxial stress was applied, the pipe diameter could be expanded up to twice at the pipe diameter ratio (expansion ratio), and the working ratio higher than 60% could be achieved as compared with the comparative example. On the other hand, in the comparative example, the maximum pipe expansion ratio was 1.4 times because of the weldability.

[0013]

As described in detail above, according to the present invention, it is possible to obtain a titanium welded pipe having excellent workability not only in the base metal but also in the welded portion of the pipe, and a thin-walled pipe having improved weldable workability. The above can provide a beneficial effect in industry.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a state of a welded portion of an example of the present invention.

FIG. 2 is a diagram showing a welding method in the embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between t / W and a pipe expansion ratio D / D _{0 according} to the embodiment of the present invention.

FIG. 4 is a diagram comparing molding limits of the present invention and a conventional TIG pipe.

Claims (2)

[Claims] 1. A weld bead width W (mm) and a plate thickness t of a welded portion.
(Mm) ratio is 6.5> t / W ≧ 1/3, a titanium welded pipe. 2. A flat plate is roll-formed into a cylindrical shape, a laser beam is irradiated to the abutting portion, and the weld bead width W (m
A method for producing a titanium welded pipe, which comprises performing butt welding so that a ratio of m) to a plate thickness t (mm) satisfies 6.5> t / W ≧ 1/3.