JPH0428475B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method of welding thick-walled steel materials, and in particular,
The present invention relates to a method for welding thick-walled steel materials that suppresses the occurrence of under-bead cracking in the weld zone and effectively removes the hardened area formed within the weld zone.

Generally, when welding thick-walled steel materials such as thick-walled carbon steel or low-alloy steel, hydrogen generated during welding enters between the weld bead and the steel material, causing the first
As shown in the figure, under-bead cracks X tend to occur in the steel material S below the weld bead B, and hardened areas Y tend to form as shown by the chain lines in the same figure, and these under-bead cracks X and hardening tend to occur. Since the area Y may cause a decrease in the stiffness of the steel material S, countermeasures are required.

Conventionally, therefore, the steel material S is preheated before welding, postheated after welding, and further subjected to heat treatment such as tempering.

However, such conventional methods still have the following problems that need to be improved.

In other words, the preheating, welding, postheating, and tempering heat treatments described above are each performed individually, and in particular, the tempering process is performed independently of other heat treatments, so the welding work as a whole is can become complicated.

On the other hand, in order to prevent the occurrence of the above-mentioned under-bead cracks By simply decreasing
It has not yet been possible to completely prevent its occurrence.

The present invention has been made in view of the above-mentioned conventional circumstances, and its purpose is to preheat a welded part of a thick steel material and then form a first layer weld bead on the welded part. Next, the weld bead is heated and softened to make the thickness uniform, and post-heating is performed, and a second layer is applied onto the uniform weld bead with a heat input larger than each heat input in the previous process. It is an object of the present invention to provide a method for welding thick-walled steel materials, which can form a molten heat bead, effectively suppress the occurrence of under-bead cracking, and remove a hardened region with a simple operation.

Hereinafter, an example in which the present invention is applied to welding of normal thick-walled steel materials will be described.

A special welding device is used to carry out the present invention. First, the welding device will be explained with reference to FIG. 2. The welding device 1 is installed along a welding line W of a steel material S. The welding direction (direction of the arrow in Fig. 2) is
Three torches 3 spaced apart along
(3a, 3b, 3c) and the three torches 3 (3
a, 3b, 3c) and the steel material S, and a power source 4 for generating an arc between the torches 3 (3
a, 3b, 3c) for supplying an inert gas to cover the space between each torch tip and the steel material S and the arc, and the three torches 3
Torch 3b located in the middle among a, 3b, and 3c
and a filler material supplying means 7 for supplying the filler material 6 to the filler material 6 .

Next, to explain the welding method for thick-walled steel material S, first, a second
As shown in the figure, three torches 3 of welding device 1
(3a, 3b, 3c) are arranged facing each other, a coating gas consisting of an inert gas is supplied from the coating gas supply means 5 to each of the three torches 3 (3a, 3b, 3c), and each torch By injecting gas into the gap between the tips of 3a, 3b, and 3c and the thick steel material S, the welded portion of the thick steel material S, that is, the vicinity of the weld line W is covered with gas.

Next, as shown in FIG. 3a, an electric current is supplied between the torch 3a located forward in the welding direction (in the direction of the arrow in FIG. 3) and the thick steel material S to generate an arc in the above-mentioned coating gas. The area near the welding line W is preheated to near the melting point by the heat of the arc. The amount of heat input used during the preheating is, for example, 15 kilojoules/cm.

Each torch 3a, 3b,
3c in the welding direction, an arc is generated by the torch 3b located in the middle, and the filler metal 6 is supplied into the arc and melted. As shown in FIG. 3b, a first layer of weld bead _B1 is formed on the preheated welding part. The formation of the weld bead B ₁ in the first layer is performed with almost the same amount of heat input as the amount of heat input during the preheating, and the surface temperature of the thick steel material S after preheating is 100°C to 600°C. It will be implemented once the scope of This temperature range is 100℃
Welding at a surface temperature below will reduce the preheating effect mentioned above, and if the surface temperature exceeds 600℃, microcracking due to transformation stress will easily occur.
This is set because the appearance of the formed bead becomes poor.

Next, as shown in FIG. 3c, the first layer of weld bead _B1 formed as described above is
By heating and softening with a torch 3c located at the rear in the welding direction, the surface is flattened and the thickness is made uniform, and the welded portion is post-heated. The heat input in this step is 15 kilojoules/cm, which is almost the same as in both of the above steps,
And, similarly to the step of forming the first layer weld bead _B1 , the surface temperature of the thick steel material S is 100°C to 600°C.
This step is carried out when the range is reached.

Thereafter, as shown in FIG. 3d, on the first layer weld bead _B1 whose thickness has been made uniform,
A second layer of weld bead _B2 is formed by the intermediate torch 3b. The amount of heat input in the step of forming the second layer weld bead _B2 is set higher than the amount of heat input in each of the steps described above, and is, for example, 20 kilojoules/cm or more.

By continuing to carry out each of the above steps,
Two layers of weld beads B ₁ over the entire length of the weld line W,
B ₂ is formed to complete the welding of the thick steel material S.

In the process of such molten heat, the preheating treatment, the formation of the first layer weld bead _B1 , and the post-heat treatment can be performed in a series of operations, so that the thickness of the thick steel material S after each treatment can be It is possible to suppress the temperature drop, maintain the thick steel material S at a high temperature, for example, 200° C. or higher, and slow down its cooling rate. Therefore, it is possible to ensure sufficient time for the hydrogen that has entered under the weld bead B to scatter, thereby preventing the occurrence of under-bead cracking X. In addition, by slowing down the cooling rate, martensitic transformation of thick steel material S heated to high temperatures (for example, 900°C or higher) can be prevented,
The occurrence of under-bead cracking X is further prevented.

On the other hand, when the first layer weld bead B ₁ is formed, as shown in FIGS. 4 and 5, a hardened region Y is formed in the thick steel material S under the weld bead B ₁ . However, the hardened region Y is removed in the above-mentioned post-heating step and the step of forming the second layer weld bead _B2 .

That is, since the heat input when forming the second layer weld bead _B2 is set higher than the individual heat input in the previous steps, the heat input causes the thick steel material to A temperature distribution shown by curve a in FIG. 6b is generated in S, and as is clear from the comparison with FIG. By gradually cooling the thick steel material S, the hardened region Y can be removed (in Fig. 6a, the part Y' where the chain line is interrupted is
This is the hardened area removed during the formation of two rows of weld beads _B2 ). Since the thickness of the first layer weld bead B ₁ is made uniform during the post-heating process, the second layer weld bead B ₂ is formed in many rows. In this case, the above-mentioned temperature distribution can be uniformly generated, and the hardened region Y can be reliably removed. Since such a removal operation of the hardened area Y is carried out during a series of welding operations,
Easy to operate.

In addition, although the case where two layers of weld beads were formed was explained in the said Example, it is also possible to laminate three or four layers of weld beads. However, when forming weld beads in the third and subsequent layers, there is no need to impose restrictions on the type or conditions of welding. This is the third
This is because the influence of the weld bead formed after the layer on the thick steel material S is extremely small. Further, the heat input amount described above is just an example, and can be changed in various ways based on the material of the thick steel material S, etc.

As explained above, according to the method for welding thick-walled steel materials according to the present invention, after preheating the welded portion of the thick-walled steel material, a first layer weld bead is formed in the welded portion, and the weld bead of the first layer is The weld bead is heated and softened to make its thickness uniform, and post-heating is performed, and a second layer is applied on the uniformized first layer weld bead with a heat input larger than each of the heat inputs in the above steps. This method slows down the cooling rate of thick-walled steel materials to sufficiently disperse hydrogen at the bottom of the weld bead to prevent under-bead cracking.
It is possible to uniformly heat thick-walled steel materials to reliably remove hardened regions, prevent deterioration in the ductility of thick-walled steel materials during welding, and prevent the occurrence of under-bead cracking and remove hardened regions. This operation can be performed during a series of welding operations, and has excellent effects such as simplifying the operation.

[Brief explanation of drawings]

Among the drawings, Fig. 1 is a schematic diagram showing under-bead cracks and hardened areas that occur in welds during general welding, and Fig. 2 is a structural example of a welding device used to carry out the present invention. Front view showing, Figure 3~
Fig. 6 shows one embodiment of the present invention, Fig. 3 is a diagram of one process, Fig. 4 is a schematic diagram showing the state in which the first layer weld bead is formed, and Fig. 5 is a schematic diagram showing the state in which the weld bead of the first layer is formed. FIG. 6 is a schematic diagram showing a state in which the weld bead thickness of the second layer is made uniform, and FIG. 6 is a schematic diagram showing a state in which a second layer of weld beads is formed. B...Weld bead, S...(thick wall) steel material, X...
...Crack under the bead, Y...hardened area, W...weld line,
1... Welding device, 3 (3a, 3b, 3c)... Torch, 6... Filler metal.

Claims (1)

[Scope of Claims] 1. A method for welding thick-walled steel materials, which includes: (a) preheating a welded portion of the thick-walled steel material; (b) melting a filler metal into the preheated welded portion to form a first layer. (c) a step of uniformizing the thickness of the weld bead of the first layer by heating and softening the weld bead of the first layer; (d) a step of forming a uniform weld bead of the first layer; above,
(e) a step of forming a second layer weld bead by melting the melting material; (e) including these steps (a) to (d); (f) The heating operation in each step is performed by coating the part to be heated with gas and generating an arc in the gas coating. A method of welding thick-walled steel materials.