JPH04288991A - Welding method - Google Patents

Abstract

PURPOSE:To execute the welding work with high efficiency, and to prevent the deterioration of toughness of a welding zone and a welding metal and the generation of a microcracking. CONSTITUTION:At the time of welding a steel base material, the cooling time DELTAT800-500 is shortened by injecting a low temperature refrigerant of liquefied gas of liquid nitrogen, liquid argon, etc., to a high temperature bead part in the vicinity of a molten pool and cooling forcibly and quickly the bean part by following a movement of a welding position.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding steel frames, bridges, shipbuilding and other steel structures.

0002

[Prior art and problems to be solved by this invention] In order to improve the efficiency of arc welding work, it is necessary to
It is necessary to increase the amount of melting per unit time. To achieve this, it is necessary to increase the input welding arc thermal energy per unit length of welding line. This energy

0003

[Math 1]

It is shown as 0004.

[0005] Generally, however, as this heat input increases, the toughness of the weld metal and weld heat affected zone of steel tends to decrease.

[0006] In other words, as shown in the welding thermal cycle diagram of the welded part in Figure 7, many studies have revealed that the cooling time ΔT800-500 during the process of cooling from 800°C to 500°C affects the toughness. There is. As shown in the correlation graphs of heat input and cooling time in FIGS. 7 and 8, as the heat input increases, ΔT800-500 also increases. Furthermore, as shown in the correlation graph between cooling time and toughness in FIG. 9, high-strength steel has a remarkable tendency for toughness to deteriorate due to large heat input. Therefore, for example, HT-60 steel requires 50Kjoule/
cm, and for HT-80 steel, a heat input limit of 45Kjoule/cm or less is considered the manufacturing standard. In other words, the efficiency of welding work has been reduced accordingly.

[0007] In addition, welding with a long cooling time of ΔT800-500 tends to induce fine weld cracks (cracks caused by diffusible hydrogen) at the grain boundaries of the weld metal, so to avoid this, it is necessary to shorten the cooling time. was desired.

[0008] As a means of shortening the cooling time, the applicant of the present application attached a cooling box to the weld base material along the welded part, and supplied cooling water to this cooling box to directly forcedly cool the weld base material. We have previously proposed a method (Patent Application No. 156934/1999)
.

The present invention has a more direct cooling effect than the above-mentioned means for cooling the weld base metal, further shortens the cooling time, improves the efficiency of welding work, and improves the welding area and weld metal. The purpose of the present invention is to propose a welding method that can prevent the deterioration of toughness and the occurrence of microcracks.

0010

[Means for solving the problem] (1) The welding method is as follows:
When welding steel base metals, it moves following the movement of the welding position and injects a low-temperature refrigerant into the high-temperature bead near the molten pool to forcibly cool it.

[0011] In the welding method (2), which is another invention, a low-temperature coolant is injected into the high-temperature bead part to forcibly cool it, and a cooling box is attached to the steel base material along the welded part. The steel base material is directly forcedly cooled by supplying cooling water to the steel base material.

0012

[Operation] This welding method involves injecting a low-temperature refrigerant such as non-reactive liquefied gas such as liquid nitrogen, liquid helium, liquid air, or liquid carbon dioxide into the high-temperature bead immediately after welding near the molten pool. The bead section is rapidly forcedly cooled in a short period of time by heat absorption commensurate with the heat of vaporization and the specific heat of the low-temperature gas.

[0013] To give an example of the test results, the heat input is 42.0
00 Joule/cm, (welding current 700A, arc voltage 35V, welding speed 35cm/min), ΔT8
00-500 = 53 seconds (air cooling), but by injecting liquid nitrogen into the high temperature bead part, it was possible to shorten it to 22 seconds. Note that this result was obtained in an example described later.

In the welding method according to the invention (2), the steel base metal is directly forcedly cooled with cooling water at the same time as the bead portion is rapidly forcedly cooled, so that the cooling time can be further shortened.

[0015]

Embodiment FIGS. 1 and 2 show an embodiment in which a steel base material 1 is welded by shielded gas arc welding using this welding method. The electrode wire 2 is surrounded by a gas nozzle 3 that injects shielding gas, and moves in the direction of the arrow (leftward in the drawing) to perform welding. This welding apparatus has a screen plate 4, a liquefied nitrogen gas injection pipe 5, and a tunnel cover 6 installed in this order on the opposite side in the welding direction. The screen plate 4 and the injection pipe 5 hang down with a slight inclination in the direction opposite to welding, and their tips reach nearly the height of the bead portion 7 on the steel base material 1. The tunnel cover 6 has a length of about 50-100 mm, has a substantially arcuate cross section, is open at both ends, has both edges close to the surface of the steel base material 1, covers the upper part of the bead portion 7, and has one end at the tip of the injection pipe 5. A rectifying plate 8 is attached adjacent to the spray plate and extending along the injection direction.

[0016] To weld with this welding method, the gas nozzle 3
While blowing out shielding gas, an arc 9 is generated between the steel base material 1 and the electrode wire 2, and the welding is performed by moving. At the same time, liquefied nitrogen gas is injected from the tip of the injection pipe 5. 1 in Figure 1
0 is the molten pool directly below the electrode wire 3 and the molten metal at its periphery, and the tip of the injection pipe 5 is located on the high-temperature bead portion 7' close to the molten pool 10. Liquefied nitrogen gas (LN2) is injected onto the high-temperature bead portion 7' from the injection pipe 5 tilted in the opposite direction to welding, absorbs heat from the bead portion 7, vaporizes it, cools the bead portion, and welds the inside of the tunnel cover 6. It flows in the opposite direction, further comes into contact with the bead portion 7, absorbs heat and heats up, forcibly cools the bead portion 7, and then is discharged from the open end of the tunnel cover 6.

FIG. 3 shows the cooling time ΔT800-500 of the welded part by the welding method of the above embodiment, which was significantly shorter than the cooling time ΔT800-500 by conventional air cooling. Note that this cooling time was based on the temperature-time measured by inserting a thermocouple 11 into a hole drilled directly below the bead portion 7 of the steel base material 1, as shown in FIG. 3(b).

Furthermore, in FIG. 1, when the distance between the electrode wire 2 and the tip of the injection tube 5 is S, the correlation between S and the cooling time reduction effect is as shown in FIG. It is highly effective to inject refrigerant into the area. Usually S=
It is about 20 to 40 mm, and if it is longer than this, the cooling effect will be reduced.

[0019] If the refrigerant mixes into the molten metal, welding defects such as blowholes will occur, so it is necessary to take measures to prevent this. The screen plate 4 of the embodiment is effective in preventing contamination.

Although not shown, when welding is performed by tilting the steel base material so that the welding direction is upwardly sloped, the low-temperature refrigerant liquid and gas flow downward within the tunnel cover and mix with the molten pool. This is effective in increasing cooling efficiency.

FIG. 5 A cooling box 12 with one side open along the welded joint with an L-shaped groove is attached to one side of the steel base materials 1, 1 to be edge welded, and a water supply pipe 13 is installed in the cooling box 12. , the drain pipe 14 is connected to supply cooling water, and the cooling water is directly supplied to the steel base material 1.
This is a device that forcibly cools the air by bringing it into contact with the air. Figure 6 shows an example of the welding method (2) in which the steel base metal is forcibly cooled using the cooling device shown in Fig. 6, and liquefied nitrogen gas is injected from the injection pipe 5 to the high-temperature bead part that has been welded by shield gas arc welding to rapidly cool it. show.

[0022]

Effects of the Invention: The welding method (1) rapidly cools the high-temperature bead immediately after welding and can significantly shorten the cooling time ΔT800-500, improving welding efficiency and reducing the deterioration of the welded part's toughness and microscopic welding. It has the effect of preventing cracking. The welding method (2) involves rapid cooling of the high-temperature bead and, at the same time,
The steel base material is also forcedly cooled, further reducing cooling time.
The effect can be increased.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a cross section of an embodiment of a welding method.

FIG. 2 is a sectional view taken along line AA in FIG. 1;

FIG. 3(a) is a cooling curve of a welded part in an example. (b) is an explanatory diagram showing means for measuring the temperature of the welded part.

FIG. 4 is a correlation graph between the distance S between the electrode wire and the tip of the injection tube and the cooling time reduction effect.

FIG. 5 is a partially sectional perspective view of a cooling device for a steel base material.

FIG. 6 is an explanatory diagram of an embodiment of the welding method (2).

FIG. 7 shows cooling curves of welds with different amounts of heat input.

FIG. 8 is a correlation graph between heat input amount and cooling time.

FIG. 9 is a correlation graph between cooling time and weld zone toughness.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Steel base material, 2... Electrode wire, 3... Gas nozzle, 4... Screen plate, 5... Liquefied nitrogen gas injection pipe, 6... Tunnel cover, 7
...bead part, 8...straightening plate, 9...arc, 10...molten pool,
11... Thermocouple, 12... Cooling box, 13... Water supply pipe, 14... Drain pipe.

Claims (2)

[Claims] 1. A welding method characterized in that, when welding steel base metals, the welding position is moved to follow the movement of the welding position, and a low-temperature refrigerant is injected into the high-temperature bead near the molten pool for forced cooling. 2. The welding method according to claim 1, wherein a cooling box is attached to the steel base material along the welded part, and cooling water is supplied to the cooling box to directly forcibly cool the steel base material.