JPH0431787B2 - - Google Patents

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.

``Prior Art'' Generally, when welding objects such as thick-walled carbon steel or low-alloy steel, hydrogen enters the lower part of the bead B formed during welding, as shown in Figure 1.
Under-bead cracks X are likely to occur in the workpiece C to be welded, and a hardened region Y is 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, and therefore countermeasures are required.

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

"Problems to be Solved by the Invention" However, with such conventional methods, the following problems remain to be improved.

That is, the above-mentioned preheating and post-heat treatment are performed on the welded object C.
The purpose is to slow the cooling rate of the bead B and release the hydrogen between the bead B and the workpiece C, but each process such as preheating, welding, and postheating is performed by an individual heat source. As a result, the temperature of the welded object C drops during each process, and hydrogen is not sufficiently released. moreover,
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 be long.

On the other hand, as another method to prevent the occurrence of under-bead cracking
The use of under-bead cracks X has also been considered, but although it has been found to be effective in reducing the amount of under-bead cracking X, the occurrence has not yet been completely prevented.

The present invention has been made in view of the above circumstances, and has the following objects: (1) To prevent under-bead cracks from occurring in a workpiece to be welded.

() To remove the hardened area within the workpiece.

() These treatments should be carried out using simple equipment at the same time as 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 of the torches is Along with generating an arc,
A method of welding objects to be welded by melting the filler metal with a welding torch, in which the heat input of the post-heating torch is greater than the heat input of the welding torch, and the interval between each torch is These settings are set in association with the conditions.

"Function" If the distance 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 heated to the required temperature by preheating will Welding and post-heat treatment are performed while being maintained at high temperatures to reduce hydrogen intrusion.
In addition, the effect of expelling the trapped hydrogen is increased to reduce 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 continuously without the need for other equipment. It is carried out in a series of steps.

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

FIGS. 2 and 3 show an example of a welding machine 1 suitable for implementing the method of the present invention. torches 4 (preheating torch 4a, welding torch 4b, postheating torch 4c) are provided at intervals in the welding direction, and filler metal 5 is supplied to the welding torches 4b into the arc generated thereby. This is a basic configuration in which a filler metal supply means 6 is provided.

The welding machine 1 also includes a traveling rail 7 and a traveling truck 8 provided along the welding line W of the workpiece C, and the traveling truck 8 includes a support mechanism 9 that supports each torch 4, and a supporting mechanism 9 for supporting each torch 4. A current supply means 10 for supplying current to the nozzle 2 and a gas supply means 11 for supplying an inert gas to the nozzle 2 are mounted.

The support mechanism 9 includes a support frame 12 that supports each torch 4 at intervals described in detail later, an elevating plate 13 attached to the supporting frame 12, a feed screw 14 attached to the elevating plate 13, and a feed screw 14. The electric motor 15 rotates and drives the elevating plate 13 up and down 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 protruding near the tip of the welding torch 4b provided through the support frame 12, A feed roller 18 is attached to the lifting plate 13 and feeds the filler metal 5 pulled out from the filler metal winding bobbin 16 through the guide cylinder 17 to the tip of the welding torch 4b, and the feed roller 18 is rotationally driven. It is configured by an electric motor 19 that operates.

The current supply means 10 includes a power supply controller 20 attached to the traveling cart 8 and a power supply cable 21 for supplying current between each torch 4 and the workpiece C. 20 is used to adjust the current to each torch 4 and set the amount of welding heat input.

The gas supply means 11 includes a cylinder 22 attached to the traveling truck 8 or placed separately;
and a supply hose 23 that supplies inert gas to the nozzle 2 of each torch 4 via the support frame 12.

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 between each torch 4a, 4b, 4c, each torch 4a, 4b, 4c
The mutual spacing is determined in consideration of the amount of heat input, the temperature of the object to be welded C (temperature before heating = initial temperature for each arbitrary torch, 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 (T) required for the semi-infinite solid to cool down to temperature θ is expressed by the following equation.

T=1/2πk(ηQ/Cρ)1/θ−θ ₀ …(1) where k: thermal diffusivity η: welding efficiency Q: heat input per unit length C: specific heat ρ: density θ: set temperature (Temperature) θ ₀ : Initial temperature The case of welding low alloy steel will be explained below.

Then, the mutual distance L between any adjacent torches
is set by the following formula using the above formula (1) and the welding speed v.

L=vT =v×1/2πk(ηQ/Cρ)1/θ−θ ₀ ...(2) <Example of calculation of torch spacing> Substitute the following conditions into equation (2) above to calculate the mutual spacing L
(distance Lx between torches 4a and 4b, torches 4b and 4c
The interval Ly) was calculated.

Substitution conditions k=0.146 (cm ² /sec), C=0.128 (cal/g℃), ρ=7.79 (g/cm ³ ), η=0.5, v=10 (cm/min), θ=300 (℃) ) Q = 20 (kJ/cm): Amount of heat input by preheating torch 4a θ ₀ = 25 (℃): Initial temperature at the time of heat input by preheating torch 4a and Q = 10 (kJ/cm): Amount of heat input by welding torch 4b θ ₀ =200 (°C): Initial temperature during heat input by welding torch 4b With these conditions, Lx≒1.6 (cm) and Ly≒2.2 (cm) are obtained.

To further explain the above, the reference temperature before heat input by the preheating torch 4a is 25°C even if the workpiece to be welded is kept at room temperature, and the reference temperature before heat input by the welding torch 4b is 25°C.
After being heated by 2/3 of surface temperature
That's about it.

When using low-alloy steel and performing the preheating process and welding process consecutively, an effective temperature of approximately 200°C is required, so the surface temperature should be set taking this into account). The reference temperature before heat input by welding torch 4c is 200℃ at the part heated by welding torch 4b (the heat is transferred to the workpiece by the heat input from welding torch 4b, and the temperature near the surface layer is naturally 200℃). (Since the temperature is higher than room temperature, it may be lower than the aforementioned temperature of 300°C.)

In this way, the mutual spacing of each torch 4 is set,
Further, by driving the support mechanism 9 to raise and lower each torch 4, the nozzles 2 are arranged facing each other at appropriate intervals on the welding line W of the workpiece C, and then the gas supply means 11 is used to inject each nozzle 2 into the welding line W of the workpiece C. Activated gas is supplied to cover the space between the tip of each nozzle 2 and the workpiece C with inert gas, and the current supply means 10 is used to cover the space between the electrode 3 of each nozzle 2 and the workpiece C to be welded. Welding is initiated by passing a current through and generating an arc.

Then, from the welding start state, the filler metal supply means 6
is driven to connect the electrode 3 of the welding torch 4b and the workpiece C.
By supplying the filler metal 5 between the welding line W and moving the carriage 8 in the direction of the arrow in FIG. 3, as shown in FIGS.
Welding is performed along the

That is, as shown in FIG. 4a, the workpiece C to be welded is preheated by the arc generated by the preheating torch 4a located forward in the welding direction of the arrow, and then the welding torch is placed on the preheated workpiece C. By melting the filler metal 5 at 4b, a bead B is formed as shown in FIG. 4b, and further, as shown in FIG. Postheat is applied to B and the object to be welded C. 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 temperature drop of the welded object C after each process is suppressed. For example, by maintaining the workpiece C 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,
can be prevented from occurring. Furthermore, by slowing the cooling rate, it is possible to prevent the welded object C, which has been 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 meaning of making the amount of heat input by the post-heating torch 4c larger than the amount of heat input by the welding torch 4b will be explained below.

In a typical welding operation, a weld is formed by overlapping multiple layers of weld beads. In this case, by forming the first layer of weld beads, a hardened region Y (first
(see figure), there is a possibility that the hardened region Y may be heated and tempered to a softened state by the heat input when forming the second layer weld bead.

Therefore, in addition to the heat input from the preheating torch and the welding torch, the heat input from the postheating torch is made larger than the heat input from the welding torch, and adjustments are made to create a state that satisfies the above-mentioned conditions.

For example, in low alloy steel, Heat input during preheating 20 (kJ/cm), Heat input during welding 10 (kJ/cm), Heat input during post-heating 11-13 (kJ/cm) This is how it is operated.

When superimposing the next weld bead on top of the previous weld bead, the temperature of the welding area due to the formation of the previous weld bead will drop by the time of the next welding, so heat input under these conditions must be repeated. become.

By performing each of these heat inputs, the hardened region Y can be removed.

In the embodiment of the welding machine 1, the number of each torch 4a, 4b, 4c for preheating, welding, and heat treatment is one, but it may be plural. Further, the heat input amount and the torch spacing shown in <Calculation example of torch spacing> can be changed depending on the materials of the workpiece C and the filler metal 5, etc. Furthermore, the shape of the object to be welded C is not limited to a flat plate shape, and can also be applied to circumferential welding of a pipe.

"Effects of the Invention" As explained above, the method for welding steel materials according to the present invention involves arranging a preheating torch, a welding torch, and a postheating torch at intervals in the welding direction, and generating an arc with each torch. In addition to preheating, welding, and post-heat treatment, the method also involves making the heat input of the post-heating torch larger than the heat input of the welding torch, and setting the interval between each torch in relation to the welding conditions. Therefore, the mutual spacing between the preheating torch, welding torch, and postheating torch is set based on the welding conditions and the temperature desired to be applied to the surface of the workpiece, and welding is performed while maintaining the spacing between each torch during a series of welding operations. Because the work is carried out, the heat generated by the preheating torch and welding torch keeps the welding target part of the workpiece at a high temperature from the preheating treatment to the start of the postheating treatment. Therefore, it is possible to suppress the phenomenon that hydrogen enters the workpiece to be welded and to reduce the occurrence of bead cracking.

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 is suppressed and the workpiece is welded. The hardened region formed inside the product 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 simultaneously with the welding process, the process can be easily performed without requiring any special equipment other than a welding machine.

Effects such as this can be obtained.

[Brief explanation of drawings]

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;
The figure is a front view thereof, and FIG. 4 is a schematic diagram of the processing state by each torch. B...bead, C...work to be welded, ,4
b, 4c)...torch, 5...melt material, 6...melt material supply means, 7...travel rail, 8...traveling trolley, 9...support mechanism, 10...current supply means, 1
1...Gas supply means.

Claims (1)

[Claims] 1. A preheating torch, a welding torch, and a postheating torch are arranged facing the workpiece at intervals in the welding direction,
This is a method of welding workpieces by generating an arc from each of the torches in a gas-covered environment and melting the filler metal with a welding torch. A method for welding steel materials, characterized in that the amount of heat input is increased and the interval (L) between arbitrary torches has the following relationship. L=v×1/2πk(ηQ/Cρ)1/θ−θ _0where v: Welding speed k: Thermal diffusivity η: Welding efficiency Q: Heat input per unit length C: Specific heat ρ: Density θ: Setting Temperature θ ₀ : Initial temperature