JPS60240386A - Welding method with broad electrode - Google Patents

Abstract

PURPOSE:To prevent a peeling crack by applying magnetic oscillation to a molten metal by an AC excitation coil to weld a cladding metal and base metal and forming the cladding metal so as to have the same groove depth as the sheet thickness or smaller groove depth than said thickness. CONSTITUTION:A broad electrode 23 is fed by feed rollers 24 to a steel sheet 21 which is a base metal. A ferromagnetic material 27 and the excitation coil 29 are disposed around the end of the electrode 23. The molten pool of a molten metal 35 is made between the steel sheet 21 and the electrode 23 when DC welding current flows to the electrode 23. The molten metal 35 moves laterally and generates the excited flow on account of the alternating field when 1-20Hz AC magnetizing current is passed to the coil 29 in this stage. The finer crystal grains of the molten metal 35 are thus formed and the density of the grain boundary to be precipitated in the stage of a heat treatment is extremely decreased. The peeling crack of the weld metal is prevented by such decrease coupled with the formation of the cladding sheet to the small groove depth.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in merged arc welding and electroslag welding.

Stainless clad steel is used for reactors, heat exchangers, etc. used in oil refining plants and fertilizer plants, taking into account its hydrogen erosion resistance, corrosion resistance, and erosion resistance. As a method for highly efficient overlay welding of welded joints of clad steel, a wide electrode (width 25 mm) is generally used.
Submerged arc welding and electroslag welding using 75 m) have been adopted.

Conventionally, in the wide electrode welding method, as shown in FIG. A power supply tip 6 connected to a feed roller 4 and a welding power source 5 is provided on the wide electrode 3, and a current (I) is passed between the wide electrode 3 and the steel plate 1, while feeding the wide electrode 3 in the direction of the steel plate 1. It is to be welded. 7ll-1 in the figure. flux, 8 is stainless steel overlay weld metal, 9 is solidified slag,
10 is a molten metal, 11 is a welded part of a steel plate, and 12 is a slag energized melted part (or arc). Moreover, the groove shape of the overlay welding is cut into the steel plate 1 by about IWa, as shown in FIG. 2, and the angle (θ) is 30 degrees.

In this wide electrode welding method, a rotating magnetic field B is generated around the wide electrode 3, a proximity force is generated by a parallel current flowing in the molten metal 10, and the molten metal 1o flows inward from the molten pool side end.

However, according to the manufacturing method described above, as shown in FIG. 3, there is a crack (hereinafter referred to as
13 (referred to as peeling cracks) occurs. Further, this peeling crack 13 has a drawback that it tends to occur at the position P. There are three possible reasons for this:

■ As shown in Fig. 4, coarse grain boundaries 15 exist in the overlay weld metal 8 near the boundary (overlay weld boundary) 14 between the base steel plate 1 and the overlay weld metal 8, and post-weld heat treatment Carbon diffuses and moves from the steel sheet 1, and carbide 1511C is precipitated at the grain boundaries. As a result, the boundary portion 14 has a structure highly susceptible to hydrogen cracking.

■ Residual stress exists.

■ When the equipment is stopped, the stored hydrogen during operation
Accumulate in

In addition, in FIG. 3, the angle between the tangent of the boundary line between the steel plate 1 and the overlay weld metal 8 at the position P and the horizontal angle is α.

However, in recent years, the environments in which various reactors and heat exchangers are used have become more severe, and it has become necessary to completely prevent peeling cracks in overlay welds.

The present invention was made in view of these circumstances, and it is possible to weld by providing an excitation coil around the end of a wide electrode and applying magnetic vibration to the molten metal under predetermined conditions.
An object of the present invention is to provide a wide electrode welding method that can prevent peeling cracks. That is, the present inventors have proposed TIG welding and MI
As a result of investigating the influence of magnetic vibration on G welding, they found the effect of refining crystal grains, and tried to apply this magnetic vibration to internal welding using a wide electrode to prevent exfoliation cracking.

Hereinafter, the present invention will be explained with reference to the drawings.

In the present invention, as shown in FIG. 5, a stainless steel mating material 22 and a wide electrode 23 are arranged on a base steel plate 21. The groove shape of the laminate 22 is such that the depth of the groove is the same as the thickness of the laminate 22, as shown in FIG. This wide electrode 23 is
A power supply tip 26 having a plate thickness of 0.4 mm is sent toward the base steel plate 21 by a feed roller 24, and is connected to a welding power source 25.
is in contact with. Further, the wide electrode 23 has a ferromagnetic core 27 around its end. An excitation coil 29 is arranged via a non-magnetic reel 28. This excitation coil 29 is connected to a variable AC power source 30 for excitation. In this case, exciting coil 2
9 is preferably 1 to 20 Hz. In the figure, 31 is flux, and 32 is stainless steel overlay weld metal 3.
3 is a cold water steel pipe, and 34 is a welded portion.

In this configuration, when a welding current (direct current) is passed through the wide electrode 231C power supply chip 26 (Fig. 7), the arc between the wide electrode 21 and the base steel plate 21 or the slag current conduction resistance heat is applied to the wide electrode 2. is melted, and a molten pool of molten metal 35 is formed. Here, 1 to 20 Hz is applied to the excitation coil 29.
When a magnetizing current (alternating current) of
They rotate alternately as shown in Figures (A) and (C).

That is, when a magnetizing current (alternating current) is passed, an alternating magnetic field B is generated by the excitation coil 29 in the vertical direction (FIGS. 10(a) and 10(b)), and the welding current IK flowing through the molten metal 35 causes a Lorentz force. F occurs, and the molten metal 35 moves from side to side (Fig. 4).

11(A) and 11(B)), excitation is generated.

As a result, the crystal grains of the molten metal 35 are made finer, and even if carbon diffuses from the base steel plate 21 and precipitates at the grain boundaries during post-weld heat treatment, its density is significantly lower, reducing susceptibility to peeling. be done.

Specifically, if the groove shape of the mating material 22 as shown in FIG. 12 is used, the penetration shape after overlay welding will be as shown in FIG. 13. Therefore, the angle α between the tangent to the boundary line between the steel plate 21 and the weld bead 33 and the horizontal line at the position P where peeling cracks are likely to occur is smaller than the conventional angle α. From this K, there is a tensile residual stress in the X direction after welding, but when considering the stress in the Y direction that promotes peel cracking, the first
As shown in Fig. 4, 17I: The stress α in the X direction becomes αY (= α × αX) in the Y direction. From the above, the angle α
In the case of the groove shape according to the present invention having a small value, peeling cracks can be prevented.

Next, examples of the present invention will be described.

Overlay welding was performed using a base steel plate of clad steel having the chemical composition shown in Table 1, a cladding material, and a wide electrode of YB347 with a width of 25 m while varying the magnetic field frequency and magnetic field strength. The welding test pieces shown in Fig. 15(a) and (
b) and those shown in FIG. 16 were used. Here, the 15th
Figure (a) is a plan view, Figure (b) is a front view, Figure 16 is a partially enlarged view of Figure 15 (b), and 41 in the figure is a vertical (L)
) 200tan, width (W) 400 steel, thickness (Ts
) The base material steel plate is 53 mm thick, and 42 is a laminated material with a thickness (T2) of 3 mm. For comparison, a welding test piece corresponding to the conventional method was also prepared in which the base material of the steel plate was cut down by about 1 mm, as shown in FIG.

When the above-mentioned overlay welding was carried out and the metallographic structure of the cross section of the molten metal was observed, a characteristic diagram shown in FIG. 18 was obtained. Here, the welding conditions are welding current 400 A (DCRP)
, welding voltage 27~29v1 welding speed 150 tea/
Suppose you want to perform strip-shaped electrode tactile welding with mln. As shown in the figure, the range where crystal grains are refined (shaded area) is clear. In addition, as shown in the same figure, the magnetic field frequency is 5 Hz, and the magnetic field strength is 2.
Selecting the conditions of 50 fus, ■ When magnetic vibration is not applied with the conventional groove shape (Fig. 17), ■ When magnetic vibration is applied with the conventional groove shape (Fig. 17), ■ When the magnetic vibration is applied with the conventional groove shape (Fig. 17), ■ New groove Clad steel using the welding conditions shown in Table 2 for each welding method when magnetic vibration is not applied with the new groove shape (Fig. 16), and when magnetic vibration is applied with the new groove shape (Fig. 16). Overlay welding was performed on the welded joint.

Figure 19 (a3
, Cut out a test piece with the shape shown in (h), and heat it at 691°C.
× After 24 hours of welding and heat treatment, various temperatures,
After exposure to hydrogen under hydrogen pressure for 48 hours and a cooling rate of 2001:/hr, the presence or absence of exfoliation cracks was investigated by ultrasonic flaw detection. In addition, 51 in the figure is the base material steel plate, and 52 is the vertical (L) 1o
otten, width (W) 40WIII+ stainless steel laminated material, 53 is stainless steel overlay weld metal, overall height H) is 50 mm. The results are shown in Table 3.

According to the same table, the method of applying only magnetic vibration and the method of improving only the groove shape are effective in preventing peeling cracks, but the method according to the present invention, which improves the groove shape by applying magnetic vibration, has a more severe hydrogen No peeling cracks occurred even under exposure conditions, confirming that it is effective in preventing peeling cracks. This is considered to be due to the following two points.

■ The micrographs of the metal structures of the cross-sections of the test pieces corresponding to the conventional method (without magnetic vibration) and the method of the present invention (with magnetic vibration) are shown in Figures 20 (a) and (b). It is. As shown in the figure, it can be confirmed that the crystal grains of the stainless steel overlay weld metal 53 are made finer by adding magnetic imaging.

Even if carbon diffuses through the base metal during heat treatment after welding and precipitates at grain boundaries, its density is extremely low, reducing cracking susceptibility.

■ Macrophotographs of cross-sections of overlay weld metal 53 of test pieces corresponding to the conventional method (without magnetic vibration) and the method of the present invention (with magnetic vibration) are shown in FIGS. 21(a) and (b) K. That's right. In the case of the method of the present invention (fb in the same figure)
), the angle α at the position P described above is calculated using the conventional method (the same figure (
It can be confirmed that the stress in the Y direction, which promotes peeling, can be reduced by making it smaller than in a)).

As detailed above, according to the present invention, peeling cracks in overlay weld metal are prevented by applying magnetic vibration and by making the depth of the groove of the composite material of cracked steel to be equal to or less than its thickness. Therefore, it is possible to provide a wide electrode welding method that is extremely effective when using stainless steel or other materials such as pressure vessels.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the conventional wide electrode welding method, Figure 2 is an explanatory diagram showing the groove shape of overlay welding in the same welding method, and Figure 3 is a perspective view showing the conventional wide electrode welding method.
4 and 4 are explanatory views showing exfoliation cracks in the welding method, FIG. 5 is an explanatory view showing a wide electrode welding method according to an embodiment of the present invention, and FIG. 6 is an explanatory view of the action of the welding method, 7th
Figure 8 shows the DC welding current in the same welding method.
The figure shows the magnetizing current, Figure 9 (A) and Figure C) show the rotational direction of the molten pool that changes depending on the magnetizing current, Figure 10 (A) 1 and Figure 10 (B). ) is a diagram showing the direction of the alternating magnetic field B that changes as the magnetizing current changes, No. 11
Figures (a) and (b) are diagrams showing the direction of the Lorentz force F that changes with changes in the alternating magnetic field B, and Figure 12 is the groove shape of overlay welding of a clad steel welded joint using the method of the present invention. FIG. 13 is an explanatory diagram showing the penetration shape after overlay welding, and FIG. 14 is an explanatory diagram showing the stress in the X and Y directions at a position P where exfoliation cracking is likely to occur by the method of the present invention. , FIG. 15(a) is a plan view of a welded test piece according to an example of the present invention, FIG. 15(b) is a front view of the same welded test piece, and FIG. 16 is an enlarged view of FIG. 15(b). Fig. 17 is a front view of a welding test piece corresponding to the conventional method, Fig. 18 is a characteristic diagram showing the relationship between magnetic field frequency and magnetic field strength, and Fig. 19 (a) is a side view of a test piece according to the method of the present invention. , FIG. 20(b) is a front view of the same test piece, FIG. 20(a) is a microscopic photograph of the cross-sectional metal structure of the test piece according to the conventional method, and FIG. 20(b) is a test piece according to the method of the present invention. FIG. 21 ( ) is a true view of overlay weld metal of a test piece according to the conventional method. 21.41.51...Base material steel plate, 22,42°52.
・・Stainless steel cladding material, 23・・Wide electrode, 24・
... Feed roller, 25... Welding power source, 26... Power supply chip, 27... Ferromagnetic core, 28... Non-magnetic material reel, 29... Excitation coil, 30... Excitation Variable AC power supply for, 31...Flux, J 2, 5;?
... Stainless steel overlay weld metal, 33... Cold water steel pipe, 34... Welded part, 35... Molten metal. Applicant Sub-Agent Patent Attorney Takehiko Suzue Item 1 Figure 4 Figure 7 Figure 9 (A) (B) Figure 10 (A) (0) Figure 11 (A) (0) Figure 12 Fig. 13 Fig. 14 Fig. 16 Prisoner Fig. 17 Fig. 41, 41 Fig. 18

Claims (1)

[Claims] In the wide electrode welding method for overlay welding of clad steel weld joints, an excitation coil is placed around the end of the wide electrode,
Welding is performed while applying magnetic vibration to the molten metal in the molten pool by passing an alternating current through the coil, and the groove depth of the clad steel laminate is made equal to or smaller than the thickness of the clad steel. Characteristic wide electrode welding method.