JPH06170569A - Composite heat source welding method for tube making - Google Patents

Abstract

PURPOSE:To provide a method to further improve the welding speed of the high frequency preheat laser beam welding method for tube making. CONSTITUTION:In a composite heat source welding method for tube making where the welding is completed by irradiating the laser beam onto the abutting part of a steel strip 1, a V-shaped groove 2 of the width a (mm) and of the depth b (mm) to meet all the following conditions is formed on the outer side of a tube at the abutting part before welding, and welding is executed thereto. (1) a>0, b>0, (2) (a/b)>(D/f), (3) (aXb)<=[ {3000/(Tm-Ti)}X(P/v)], (4) (t-b)<=-[4X{(P/v)+0.0005Ti}], (5) a <=[2X{(P/v)+0.0005Ti}]. Where, D: diameter (mm) of the laser beam before converging, f: focal distance (mm) of the converging optical system, P: output (kW) of the laser beam, v: welding speed (m/min), t: thickness (mm) of the steel strip to be welded, Tm: melting point ( deg.C) of the steel strip to be welded, Ti: preheat temperature ( deg.C) of the steel strip to be welded.

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 welded steel pipes such as steel pipes for general piping, steel pipes for machine structures and steel pipes for the chemical industry. Particularly, steel pipes having good mechanical properties such as bendability are improved. The present invention relates to a pipe-making welding method that is efficiently manufactured.

[0002]

2. Description of the Related Art As a welding method for manufacturing a welded pipe,
It is roughly classified into a fusion welding method such as TIG welding, plasma welding, and submerged arc welding, and a pressure welding method represented by ERW. The advantages of the fusion welding method are that welding defects are less likely to occur and the performance of the welded portion is excellent. Especially in TIG welding and plasma welding, the cleanliness of the weld metal is good, so the production of high-grade steel pipes such as stainless steel. Applied to the
Since the welding speed is slow, productivity is a problem. on the other hand,
ERW is quite excellent in terms of efficiency, which is completely opposite to the fusion welding method, but has the drawback that welding defects such as penetrators are likely to occur, so when this method is applied to the production of high-grade steel pipes, , The reliability of the performance of the weld becomes a problem.

Therefore, recently, the use of a carbon dioxide gas laser as a welding heat source has been studied, and a part thereof is being put to practical use for stainless welded pipes. Since laser welding is fusion welding, defects in the welded portion are less likely to occur, and since the energy density of the heat source is higher than in ordinary arc welding, deep penetration allows for high-speed welding, and the total heat input is Since it can be reduced, the characteristic of the welded portion is also good.

The present inventors have proposed a high-frequency preheating laser pipe welding method in which heating by high frequency and laser welding are combined for the purpose of further increasing the welding speed of laser welding (see Japanese Patent Laid-Open No. 2-70379). According to this, it is possible to obtain a welding speed about twice as high as that of the laser-only welding method and four times or more as high as that of the plasma welding method. However, there is a great demand for increasing the welding speed of laser welding, and further speeding up is required.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for further improving the welding speed in the high frequency preheat laser pipe welding method.

[0006]

Means for Solving the Problems The gist of the present invention is to feed a strip steel to a group of forming rolls and continuously form it into an open pipe shape, preheat using high frequency heating, and squeeze opposite. In the composite heat source pipe welding method in which both ends of this steel strip are butted against each other by pressing with a roll and the welding is completed by irradiating the butted part with a laser beam, the following is applied to the outer surface side of the tubular shape of the butted part before welding. There is provided a composite heat source pipe welding method characterized in that a V groove having a width a (mm) and a depth b (mm) satisfying all the conditions of is formed and welded.

[Conditions] a> 0, b> 0 (a / b)> (D / f) (axb) ≤ [{3000 / ( _Tm - _Ti )} x (P /
v)] (t−b) ≦ [4 × {(P / v) + 0.0005T _i }] a ≦ [2 × {(P / v) + 0.0005T _i }] where D is before focusing. Laser beam diameter (mm) f is the focal length of the focusing optical system (mm) P is the laser beam output (kW) v is the welding speed (m / min) t is the thickness of the steel strip to be welded (mm) T _m is the melting point of the steel strip to be welded (° C) T _i is the preheating temperature of the steel strip to be welded (° C)

[0008]

The present inventors applied a composite heat source welding method combining high-frequency heating and carbon dioxide laser as a welding method for bending and butt welding a strip steel, and various welding conditions and butt shapes Was appropriately changed to evaluate the performance of the welded portion.

It has been considered that the laser welding method requires an extremely high butt precision because the laser beam diameter is small, but in the experiments by the present inventors, some dents or gaps were formed on the outer surface side of the butt portion. It was clarified that the presence of the above does not adversely affect welding. According to the method of the present invention, the V-shaped groove is provided on the outer surface side of the pipe shape within a range that does not impair the weldability, so that the plate thickness of the strip steel in the welded portion is substantially reduced and the welding speed is increased. Is.

The method of the present invention will be described below with reference to the attached FIGS.

FIG. 1 (a) shows a state of a steel strip (hereinafter referred to as a material to be welded) being formed in the method of the present invention during the forming.
(B) is sectional drawing which respectively shows the state just before welding of the to-be-welded material in the method of this invention.

A material 1 to be welded having a plate thickness (wall thickness) t (mm) is formed into a tubular shape, and its end faces are abutted with each other, and a width a is formed on the outer surface side of the tubular shape.
(mm), V groove 2 of depth b (mm) is provided.

The method of providing the V-grooves 2 is to use the ones whose end face corners have been processed in advance so as to form the V-grooves 2 when the end faces of the material to be welded 1 are butted.
A method of continuously cutting or forming the end surface of the material to be welded 1 before the forming roll, a method of performing these processing immediately before welding after the material to be welded 1 is formed into an open pipe shape, or a forming roll Although there is a method of obtaining the V groove 2 by changing the roll hole type, the effect of the method of the present invention on the performance of the welded portion is the same. Further, the V groove 2 does not have to be exactly V-shaped, and even if the inclined surface has some unevenness or some curvature, it is allowed.

2 (a) and 2 (b) are sectional views showing the relationship between the shape of the V groove 2 and the laser beam 3. As shown in FIG.

The reasons for limiting the above conditions will be described below with reference to the symbols in FIGS. 1 and 2.

A> 0, b> 0: In the method of the present invention,
In order to reduce the wall thickness of the material to be welded 1 at the welded portion and increase the welding speed, it is necessary to provide the V-groove 2 having the width a and the depth b at the butt portion. That is, width a> 0, depth b>
Set to 0. In addition, the case where the width a = 0 and the depth b = 0 is the V groove 2
There is no conventional method.

(A / b)> (D / f): This expression is the focal length of a laser beam 3 having a beam diameter D (mm) with its optical axis aligned with the abutting portion of the end surface of the material 1 to be welded. This is a conditional expression for determining whether or not the laser beam 3 hits the shoulder portion 5 of the V groove 2 when it is focused at f (mm). FIG. 2A shows the case where (a / b) ≦ (D / f), which is outside the range defined by the present invention, and as is clear from the figure, the laser beam 3 hits the shoulder portion 5 of the V groove. As a result, metal plasma is generated at the shoulder portion 5, the laser beam 3 is absorbed by the plasma, and the penetration depth is reduced, which is not preferable. Figure 2
(B) is a proper condition defined by the present invention (a / b)>
In the case of (D / f), the laser beam 3 is concentrated on the bottom 6 of the V groove, and deep penetration can be efficiently obtained. That is, for high speed welding, it is a necessary condition that (a / b)> (D / f).

(A × b) ≦ [{3000 / (T_m−
T_i)} × (P / v)]: This formula is applied to the outer surface of the weld.
This is a conditional expression for preventing undercut. A
In order to prevent undercutting, the V groove 2 should be molten gold.
It needs to be fully filled with genera. Unit time in V groove 2
The amount of molten metal to be supplied per unit is the cross section of the V groove 2.
Product and welding speed v. The cross-sectional area of the V groove 2 is
It is represented by (1/2) x (axb). Average of welded material 1
Specific heat is C_p, The melting point of the welded material 1 is T_m, The material to be welded 1
Heat temperature to T_i, Ρ is the density of the material to be welded 1 and v is the welding speed.
Then, the molten metal required to fill the V groove 2 is formed.
The energy required per unit time is (1/2) × a × b × v × (T_m-T_i) × ρ × C_p It is represented by. If the output of the laser beam is P (W),
The energy supplied by the laser per unit time is P (J)
Is. Therefore, P ≧ {(1/2) × a × b × v × (T_m-T_i) × ρ
× C_p}  Therefore, (a × b) ≦ {2 / (C_p× ρ)} × [P / {v × (T
_m-T_i)}] Becomes. However, in practice, 2 / (C_p× ρ) is real
It is obtained experimentally, and a and b are calculated in each unit.
mm, P is kW, v is m / min, T_mAnd T_iIs ℃,
As will be described later, 3000 is suitable from many experimental results.
I'm sorry.

Therefore, (a × b) is [{3000 /
(T _m −T _i )} × (P / v)] or less.

(T−b) ≦ [4 × {(P / v) +0.00
05T _i }]: This expression is a conditional expression for obtaining the dosage energy required to melt the plate thickness (t−b) with the width a.

By providing the V groove 2 in the abutting portion, the plate thickness that must be melted by the laser is reduced to (tb), and the welding speed can be increased. The penetration depth by the laser is proportional to the heat input (P / v), but when preheating is performed, it is necessary to convert the administration energy by the laser and the administration energy by the preheating into heat input. .

As described above, the plate thickness that must be melted by the laser is (t-b), but in reality, the melting of the depth (t-b) is as wide as the V groove width a. Need to get Therefore, the contribution of the administration energy due to the preheating may be taken into consideration for the rectangular region of a × (t−b). When a rectangular region having a width a and a depth (t-b) is heated to a temperature T _i by high-frequency heating, the energy administered to this region per unit time is a × (t-b) × C _p × ρ × v × T _i . Therefore, the total heat input of the heat input by the laser and the heat input by the high frequency preheating is (P / v) + {a x (t-b) x C _p x p x v x (T
_i / v)} = (P / v) + {a * (t-b) * _Cp * [rho] * _Ti >. Therefore, the V-groove is provided to reduce the substantial plate thickness (t
-B), the heat input condition necessary for welding when preheating the temperature T _i is described as follows, where k ₂ is a proportional coefficient.

(T−b) ≦ k ₂ × [(P / v) + {a
(T−b) × C _p × ρ × T _i }] Here, in practice, k ₂ and {a (t−b) × C _p × ρ} are experimentally obtained, and each unit is as described above. Then, from a number of experimental results described later, k ₂ = 4,
It is appropriate that {a (t−b) × C _p × ρ} = 0.0005.

Therefore, (t−b) is [4 × {(P /
v) + 0.0005T _i }] or less.

A ≦ [2 × {(P / v) +0.0005
T _i }]: This expression is a conditional expression for preventing undercut in the welded portion.

FIG. 3 is a sectional view showing an undercut 4 which occurs when the width a of the V groove 2 is excessively larger than the bead width Ba. In order not to cause the undercut 4 in the welded portion, the groove width a of the V groove 2 needs to be smaller than the bead width Ba. If the welding speed v (m / min) is constant, the bead width Ba is proportional to the heat input (P / v). Therefore, if k ₃ is taken as a proportional coefficient and considered in the same manner as in the above equation, the following equation is obtained.

A ≦ k ₃ × [(P / v) + {a (t−b)
XC _p × ρ × T _i }] Here, practically, k ₃ , {a (t−b) × C _p × ρ} is obtained experimentally, and if each unit is as described above, From a number of experimental results described later, k ₃ = 2,
It is appropriate that {a (t−b) × C _p × ρ} = 0.0005.

Therefore, a is [2 × {(P / v) +0.
0005T _i }] or less.

Next, the results of some experiments conducted by the present inventors and the grounds for the above four coefficients obtained therefrom will be described with reference to FIGS. 4 to 11.

FIG. 4 is a diagram showing an appropriate range of a and b values at a plate thickness of 3 mm and a welding speed of 10 m / min.

FIG. 5 is a diagram showing an appropriate range of a and b values at a plate thickness of 3 mm and a welding speed of 20 m / min.

FIG. 6 is a diagram showing an appropriate range of a and b values at a plate thickness of 3 mm and a welding speed of 30 m / min.

As experimental conditions, the laser beam diameter before focusing D = 30 mm, the focal length f of the mirror (parabolic mirror) f = 150 mm
, And the laser output P was fixed at 5 kW, and the focus position was set at the bottom 6 of the V groove. Preheating temperature T due to high frequency
_i was set to 1000 ° C. The material to be welded 1 is SUS 304.
, Melting point T _m is 1450 ° C., average specific heat C _p is 650 (J / kg.
K).

The range of the a and b values of the V groove 2 in which a normal bead is obtained is the shaded area shown in each drawing which satisfies the above conditions (1) to (4). In the case of the welding speed of 10 m / min shown in FIG. 4 and the case of the welding speed of 20 m / min shown in FIG. 5, the shaded area is relatively large, so that the method of the present invention can be applied to a wide range. Further, even when a = 0 and b = 0, that is, in the conventional method in which the V groove 2 is not provided, a normal bead can be obtained. However, when the welding speed in FIG. 6 is 30 m / min, the appropriate range of the a and b values is narrowed, and in the case of the conventional method in which the V groove 2 is not provided, that is, the points of a = 0 and b = 0 are It can be seen that welding cannot be performed because the area deviates from the proper area of the shaded area.

FIG. 7 is a diagram showing an appropriate range of a and b values at a plate thickness of 6 mm and a welding speed of 7 m / min.

FIG. 8 is a diagram showing an appropriate range of a and b values at a plate thickness of 6 mm and a welding speed of 12 m / min.

FIG. 9 is a diagram showing an appropriate range of a and b values at a plate thickness of 9 mm and a welding speed of 20 m / min.

Other experimental conditions in the above example are shown in FIG.
This is the same as the case of FIG.

The shaded area in these figures where normal beads are obtained is similar to the case of a plate thickness of 3 mm,
As the welding speed increases, the appropriate range of the a and b values is narrowed and the shaded area becomes smaller. In the case of FIG. 9, there is no hatched portion indicating the proper region, but this is because normal welding is impossible under the conditions of FIG. This indicates that a measure such as raising the preheating temperature or raising the laser output is necessary to carry out.

FIG. 10 is a diagram showing an appropriate range of a and b values at a plate thickness of 8 mm and a welding speed of 5 m / min.

FIG. 11 is a diagram showing an appropriate range of a and b values at a plate thickness of 8 mm and a welding speed of 8 m / min.

In these examples, the other experimental conditions are exactly the same as above.

It is apparent from FIGS. 10 and 11 that the same tendency as in the case of the plate thickness of 3 mm or 6 mm is exhibited even when the plate thickness is 8 mm.

Here, a conditional expression and a method of determining each coefficient in the conditional expression will be described.

Fixing heat input conditions such as plate thickness, preheating temperature, laser output, and welding speed, welding is performed while changing the V groove shape, and the conditions of the V groove shape for obtaining a sound weld bead are arranged. Then, the area shown by the hatched portion in FIGS. Comparing the conditional expressions and with the boundary of this region, recursively, {2 / (C _p × ρ)} = 30 in the expression
00, k ₂ = 4 in the formula, k ₃ = in the formula
2, {a (t-b) × C _p × ρ} = 0 in the equation.
0005 were obtained respectively.

The above is the austenitic stainless steel SU.
It is the result of examination on S 304, but it was confirmed that in the case of carbon steel, low alloy steel or ferritic stainless steel, if the above conditional expressions are satisfied, a normal bead can be obtained as in this case. Was done.

[0047]

Example A steel strip having the chemical composition and melting point (T _m ) shown in Table 1 was used as the material to be welded. A is an austenitic stainless steel, B is a ferritic stainless steel, and C is a 50 kg class low alloy steel.

A butt welding test was performed using the method shown in FIGS. 1 and 2B, that is, using a carbon dioxide gas laser oscillator with a maximum output of 5 kW as a welding heat source and a high frequency heating device with a frequency of 450 kHz. The beam diameter D of the laser beam before focusing was set to 30 mm, and the focus position f was set to the bottom of the V groove. Table 2-1 and Table 2-2 show other welding conditions at this time. The conventional example is a method in which the V groove is not provided.

The welds were evaluated by visually observing the bead shape. Table 2 also shows the evaluation results. The white circles represent normal beads.

[0050]

[Table 1]

[0051]

[Table 2-1]

[0052]

[Table 2-2]

No. 1, 2, 3, 7, 10, 11, 15, 19, 2
3, 27, 31 and 35 are conventional examples which do not satisfy the conditional expression performed without providing the V groove, and are Nos. 4, 8, 12, 16, 20, 2
4, 28, 32 and 36 are examples of the present invention, and others are comparative examples.

In all of the examples of the present invention in which all conditions were within the range defined by the present invention, a normal bead shape was obtained, and normal welding was possible even when the welding speed was 30 m / min.

With A steel having a plate thickness of 3 mm, insufficient melting occurred under the welding speed of 30 m / min of the conventional example No. 3, so that the welding speed of 20 m / min of the conventional example No. 2 was normal. It was found to be the limit speed at which the shape can be obtained. However, for example, in the case where the welding speed of Inventive Example No. 4 is 30 m / min,
No insufficient penetration was observed, and it was possible to speed up welding by providing an appropriate V groove. Comparative example No. 5 is a
= 0.2 mm, b = 2.0 mm, D = 30 mm, f = 150 mm, the condition (a / b)> (D / f) is not satisfied as shown in FIG. Insufficient melting occurred because it did not concentrate on the bottom of the groove. Comparative example No.6
Is a conditional expression (a × b) ≦ [{3000 / (T _m −T _i ).
} (P / v)] is not satisfied, and the V groove is too large to generate molten metal enough to fill the groove, resulting in undercut.

With the steel A having a plate thickness of 6 mm, it is impossible to weld at a welding speed of 7 m / min as in the case of the conventional example No. 7, whereas a proper V groove is provided as in the example of the present invention No. 8. By providing it, normal welding became possible. Comparative example No. 9 is a case where the conditional expression (t−b) ≦ {4 × (P / v + 0.0005T _i )} is not satisfied, and insufficient melting occurred due to the shallow V groove. Comparative example No. 10 is conditional expression a ≦ [2 × {(P
/ V) + 0.0005T _i }] is not satisfied, and the groove width is too wide and undercut occurs.

Nos. 15 to 22 are the results in the case of A steel having a plate thickness of 8 mm. Nos. 23 to 30 are the results in the case of B steel (ferritic stainless steel) having a plate thickness of 3 mm and 6 mm. As shown in Table 2, the results of the high-speed welding by the method of the present invention were the same as those in the case of the A steel having the plate thicknesses of 3 mm and 6 mm.

Nos. 31 to 38 are the results in the case of C steel (low alloy steel) having a plate thickness of 3 mm and 6 mm.

Also in these cases, the results of high speed welding by the method of the present invention were similar to those of the above-mentioned A steel, as is clear from Table 2.

[0060]

According to the composite heat source pipe welding method of the present invention which uses both laser beam and high frequency heating, it is possible to obtain a normal welding bead and to achieve a significantly high speed. As a result, a high-performance welded steel pipe can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a V-groove shape before welding in the welding method of the present invention. (A) shows the state in the middle of forming of a strip steel, (b) shows the state just before welding, respectively.

FIG. 2 is a cross-sectional view showing the relationship between the shape of a V groove and a laser beam. (A) shows an inappropriate case, and (b) shows an appropriate case.

FIG. 3 is a cross-sectional view showing a state of occurrence of undercut when the V groove width is excessively large.

FIG. 4 is a diagram showing an example of an appropriate range of a and b values at a plate thickness of 3 mm and a welding speed of 10 m / min.

FIG. 5 is a diagram showing an example of an appropriate range of a and b values at a plate thickness of 3 mm and a welding speed of 20 m / min.

FIG. 6 is a diagram showing an example of an appropriate range of a and b values at a plate thickness of 3 mm and a welding speed of 30 m / min.

FIG. 7 is a diagram showing an example of an appropriate range of a and b values at a plate thickness of 6 mm and a welding speed of 7 m / min.

FIG. 8 is a diagram showing an example of an appropriate range of a and b values at a plate thickness of 6 mm and a welding speed of 12 m / min.

FIG. 9 is a diagram showing an example of an appropriate range of a and b values at a plate thickness of 9 mm and a welding speed of 20 m / min.

FIG. 10 is a diagram showing an example of an appropriate range of a and b values at a plate thickness of 8 mm and a welding speed of 5 m / min.

FIG. 11 is a diagram showing an example of an appropriate range of a and b values at a plate thickness of 8 mm and a welding speed of 8 m / min.

[Explanation of symbols]

1: welded material, 2: V groove, 3: laser beam, 4: undercut, 5: shoulder of V groove, 6: bottom of V groove, a: V
Groove width, b: V groove depth, t: plate thickness (wall thickness), D: laser beam diameter, f: focal length, Ba: bead width when undercut occurs

Claims (1)

[Claims] 1. A steel strip is fed to a forming roll group to be continuously formed into an open pipe shape, preheated by high-frequency heating, and pressed by opposite squeeze rolls to press both ends of the steel strip. In the composite heat source pipe welding method in which the surfaces are butted and the welding is completed by irradiating the butted portion with a laser beam, the following is applied to the outer surface side of the pipe shape of the butted portion before welding.
A method for welding a composite heat source pipe, characterized in that a V groove having a width a (mm) and a depth b (mm) satisfying all of the above conditions is formed and welded. [Conditions] a> 0, b> 0 (a / b)> (D / f) (axb) ≤ [{3000 / ( _Tm - _Ti )} x (P /
v)] (t−b) ≦ [4 × {(P / v) + 0.0005T _i }] a ≦ [2 × {(P / v) + 0.0005T _i }] where D is before focusing. Laser beam diameter (mm) f is the focal length of the focusing optical system (mm) P is the laser beam output (kW) v is the welding speed (m / min) t is the thickness of the steel strip to be welded (mm) T _m is the melting point of the steel strip to be welded (° C) T _i is the preheating temperature of the steel strip to be welded (° C)