JPH02142677A - Method for welding steel - Google Patents

Abstract

PURPOSE:To weld steel without bead bottom cracking due to penetration of H2 by increasing heat gain of a postheating torch than that of a welding torch among a preheating torch, the welding torch and the postheating torch arranged at intervals in the welding direction. CONSTITUTION:The respective torches 4 whose mutual intervals are set like the formula are elevated by driving a supporting mechanism 9 and nozzles 2 are arranged in opposition at the proper intervals on a weld line W of material C to be welded. Inert gases are than supplied 11 to the respective nozzles 2 and spaces between the respective nozzles 2 tips and the material C to be welded are covered by the inert gases. A current is than carried between electrodes 3 of the respective nozzles 2 and the material C to be welded by a current supply means 10 and area are generated to start welding. Filler metal 5 is then supplied between the electrode 3 of the welding torch 4b and the material C to be welded and a traveling truck 8 is made to travel in the arrow direction and welding is performed along the weld line W. Namely, after the material C to be welded is preheated by the are generated by the preheating torch 4a, the filler metal 5 is molten by the welding torch 4b to form a bead B and further, the bead B is postheated by the postheating torch 4c having heat gain higher then the torch 4b.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method of welding steel materials, and in particular, suppresses the occurrence of under-bead cracking in a workpiece and suppresses hardened areas formed within the workpiece. It is intended to remove.

``Conventional technologyj'' Generally, when welding objects such as thick-walled carbon steel or low-alloy steel, as shown in Figure 1, hydrogen enters the lower part of the bead B formed during welding, causing damage to the objects. Under-bead cracks X are likely to occur in the welded product C, and hardened regions Y are likely to be formed near the bottom of the bead B.

When the under-bead crack X occurs or the hardened region Y is formed, the toughness of the welded object C decreases at the welded portion, so countermeasures are required.

Conventionally, one of the countermeasures has been to preheat the welded object C before welding, and after the welding work is completed, to apply postheat or to perform heat treatment such as tempering. ing.

"Problems to be Solved by the Invention" However, in such a conventional method, the following aWn remains to be improved.

That is, in the preheating and post-heat treatments described above, the cooling rate of the welded object C is slowed down, and each treatment such as heating the bead B and the welding object C, welding, and post-heating is performed by an individual heat source. Therefore, the temperature of the object to be welded C drops during each process, and hydrogen is not sufficiently released. Furthermore, if a tempering process is added to each of these processes, the welding process as a whole becomes complicated and the overall working time tends to increase.

On the other hand, as another method to prevent the occurrence of under-bead cracking Although it has been recognized that it has a protective effect, it has not yet been able to completely prevent its occurrence.

The present invention has been made in view of the above circumstances, and has the following objects: (i) To prevent the occurrence of under-bead cracking in a workpiece to be welded.

(ii) removing hardened areas within the workpiece;

(iii) These treatments should be carried out using simple equipment during and during the welding process.

The purpose is to

[Means for Solving the Problem] As a means for solving the problem, a preheating torch, a welding torch, and a postheating torch are arranged facing the workpiece at intervals in the welding direction, and each torch is A method of welding a workpiece by generating an arc and melting the filler metal with a welding torch, in which the heat input of the post-heating torch is larger than the heat input of the welding torch, and The distance between each torch is set in relation to the welding conditions.

"Function" If the interval between each torch is set in consideration of conditions such as the heat input of each torch and the temperature of the workpiece, the workpiece that has been raised to the required temperature by preheating will be in a high-temperature state. Welding and post-heat treatment are carried out while the material is maintained at a constant temperature, thereby reducing the intrusion of hydrogen and increasing the effect of expelling the intruded hydrogen, thereby reducing the occurrence of bead cracking.

By making the amount of heat input during the post-heat treatment larger than that during the welding process, the phenomenon of martensitic transformation of the welded object is suppressed, and the occurrence of bead cracking is prevented.

In addition, since heating by each torch is achieved by the generation of individual arcs, by using a welding machine with three torches, preheating, welding, and post-heat treatment can be performed in a continuous series without requiring any other equipment. The steps are carried out in order.

"Example" Hereinafter, based on FIGS. 2 to 4, an example of the method for welding steel materials according to the present invention will be described.

FIGS. 2 and 3 show a welding machine suitable for carrying out the method of the present invention! 3&g torch 4 (preheating torch 4a, welding torch 4b, postheating torch 4) equipped with a nozzle 2 for inert gas injection and an electrode 3 for arc generation.
c) are provided at intervals in the welding direction, and the welding torch 4b
The basic configuration is provided with filler material supply means 6 for supplying filler material 5 into the arc generated thereby.

Further, the welding machine 1 includes a traveling rail 7 and a traveling trolley 8 provided along the welding 1w of the workpiece C, and the traveling trolley 8
is equipped with a support mechanism 9 for supporting each torch 4, current supply means 1° for supplying current to the torches 4, and gas supply means 11 for supplying inert gas to the nozzle 2.

The support mechanism 9 includes a support frame 12 that supports each torch 4 at intervals described in detail later, a lifting plate 13 attached to the support frame 12, a feed screw 14 attached to the lift plate 13, and a feed screw 14j. The electric motor 15 rotates to raise and lower the elevating plate 13 together with the torch 4.

The filler material supplying means 6 includes a filler material winding bobbin 16 attached to the traveling carriage 8, a guide tube 17 provided through the support frame 12 and projected near the tip of the welding torch 4b, and a guide tube 17 that can be moved up and down. The feed roller 18 is attached to the plate 13 and is rotated to feed the filler metal 5 pulled out from the filler metal winding bobbin 16 through the guide tube 17 and to the tip of the welding torch 4b. It is configured by an electric motor 19.

The current supply means 10 is operated by (1
(2) The power supply controller 20 adjusts the current to each torch 4 to set the welding heat input m.

The gas supply means 11 includes a cylinder 22 attached to the traveling cart 8 or placed separately, and a cylinder 22 that is connected to the support frame 12 from the cylinder 22.
The supply hose 23 supplies inert gas to the nozzle 2 of each torch 4 through the nozzle 2 of each torch 4.

The support frame 12 communicates with gas guide holes in each torch 4 and distributes inert gas to each nozzle 2.

Here, to explain the mutual spacing of each torch 4a, 4b, 4C, the mutual spacing of each torch 4a, 4b, 4C is as follows.
It is determined in consideration of the amount of heat input, the temperature of the object to be welded C (temperature before heating for each arbitrary torch = initial temperature, and temperature during cooling after heating = set temperature), etc.

When a semi-infinite solid is heated by a point heat source moving on its surface, the time ('I') required for the semi-infinite solid to cool down to temperature θ is expressed by the following equation.

However, thermal diffusivity welding efficiency heat input specific heat density θ per unit length: Set temperature (temperature) θ. : Initial temperature and mutual spacing of any adjacent torches is the above (
It is set by the following formula using the formula 1) and the welding speed V.

L=vT Example of calculation of torch spacing> By substituting the following conditions into the above equation (2), the mutual spacing (7(
The distance LX between the torches 4a and 4b and the distance Ly between the torches 4b and 4c were determined.

Substitution conditions k = 0.146 (cm'/5ec), C = 0.1
28 (cat/ga a(: ), ρ-7.79(g/a
m3), η=0.5, v=to(cI++/m1n), θ=300('
C) Q = 20 (k J / can): Preheating torch 4
Heat input θ due to a. = 25 ('C): Initial temperature at the time of heat input by preheating torch 4a, and Q = 10 (kJ 7 cm): Amount of heat input θ by welding torch 4b. -200 ('C): Initial temperature during heat input by welding torch 4b With these conditions, L X #1.6 (cm) and Ly valve 2.2 (Cm) are obtained.

In this way, by setting the mutual spacing between the torches 4 and driving the support mechanism 9 to raise and lower the torches 4, the nozzles 2 are arranged facing each other on the welding line W of the workpiece C at appropriate intervals. , the gas supply means [l supplies inert gas to each nozzle 2 to cover the space between the tip of each nozzle 2 and the workpiece C with the inert gas, and the current supply means 10
Welding is started by passing a current between the electrode 3 of each nozzle 2 and the workpiece C to generate an arc.

Then, from the welding start state, the filler metal supply means 6 is driven to supply the filler metal 5 between the electrode 3 of the welding torch 4b and the workpiece C, and the traveling carriage 8 is moved as shown in FIG. By running in the direction of the arrow, the
As shown in e), welding is performed along the welding line W.

That is, as shown in FIG. 4(a), the workpiece C is preheated by the arc generated by the preheating torch 4a located forward in the welding direction of the arrow, and then, on the preheated workpiece C, By melting the filler metal 5 with the welding torch 4b, a bead B is formed as shown in FIG. 4(b), and further, as shown in FIG.
After-heat is given to the bead B and the workpiece C by the generated arc. By sequentially repeating these steps, welding is performed over the entire length of the weld line W.

The preheating, welding, and postheating processes in such welding work are performed in a continuous series of steps in which each torch 4 is sequentially moved in the welding direction, so that the workpiece C after each process is
For example, by keeping the object C to be welded at a high temperature of 200°C or higher to delay cooling, and ensuring sufficient time for the hydrogen that has entered under the weld bead B to diffuse, we can prevent under-bead cracking. Generation of X can be prevented. Furthermore, by slowing down the cooling rate, it is possible to prevent the welded object p heated to a high temperature of, for example, 900° C. or higher, from undergoing martensitic transformation, and it is possible to prevent the occurrence of under-bead cracks X from a structural standpoint.

Furthermore, the amount of heat input by the post-heating torch 4C is calculated from the welding torch 4b.
By making the amount of heat input larger than the heat input amount, the hardened region Y in the welded object C formed after welding can be heated to the tempering temperature via the beads, and the hardened region Y can be removed.

In the embodiment of the welding machine 1, there is one torch 4a, 4b, and 4C for preheating, welding, and post-heat treatment, but a plurality of torches 4a, 4b, and 4C may be provided. Also, <Example of calculation of torch spacing>
The amount of heat input and the torch interval shown in can be changed depending on the material of the workpiece C and the filler metal 5, etc. Furthermore, the object to be welded C
The shape is not limited to a flat plate shape, and can also be applied to circumferential welding of pipes.

"Effects of the Invention" As explained above, the method for welding steel materials according to the present invention has the following effects:
In addition to preheating, welding, and postheating by arranging a preheating torch, a welding torch, and a postheating torch at intervals in the welding direction and generating an arc with each torch,
The heat input of the post-heating torch is made larger than the heat input of the welding torch, and the interval between each torch is set in relation to the welding conditions. Since welding and post-heat treatment are carried out while being maintained at a high temperature, the intrusion of hydrogen can be reduced and the occurrence of under-bead cracking can be reduced.

■ By maintaining a high temperature state during each process from preheating to post-heat treatment, and by increasing the amount of heat input during post-heat treatment compared to the welding process, the phenomenon of martensitic transformation of the welded object can be suppressed and the welded object can be welded. The hardened region formed inside the steel can be removed by heating to the tempering temperature, thereby preventing a decrease in toughness and increasing the effect of preventing bead cracking.

■ By performing preheating, welding, and post-heat treatment at the same time as the welding process, it can be easily performed without requiring special equipment other than a welding machine.

Effects such as this can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing under-bead cracks and hardened areas that occur in the weld during general welding, and FIGS. 2 to 4 show an example of the method for welding steel materials according to the present invention. FIG. 2 is a side view showing an example of a welding machine suitable for carrying out the method of the present invention, FIG. 3 is a front view thereof, and FIG. 4 is a schematic diagram of processing states using each torch. B... Bead, C... Work to be welded, X... Crack under the bead, Y... New area, W... Welding. Wire, l... Welding machine, 2... Nozzle, 3... Electrode, 4 (4a, 4b, 4c)... Torch, 5...
... filler metal, 6 ... filler metal supply means, 7 ... traveling rail, 8 ... traveling trolley, 9 ... support mechanism, IO ... Current supply means, 11 ... Gas supply means.

Claims (1)

[Scope of Claims] A preheating torch, a welding torch, and a postheating torch are arranged facing the workpiece at intervals in the welding direction, and an arc is generated from each of the torches in a gas coating, and the welding torch is used to perform welding. This is a method for welding workpieces by bringing the materials into a molten state, in which the amount of heat input from the post-heating torch is greater than the amount of heat input from the welding torch, and the distance between arbitrary torches (L
) has the following relationship: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ where v: Welding speed k: Thermal diffusivity η: Welding efficiency Q: Heat input per unit length C: Specific heat ρ: Density θ: Set temperature θ_0: Initial temperature