JPS63207482A - Electron beam welding method for thick steel plate - Google Patents

Abstract

PURPOSE:To weld thick steel plates without defects such as porosity, etc., even with the vertical welding by specifying component amounts of materials to be welded and projecting an electron beam at a push angle 2-10 deg. and confining the penetration to the inside of backing material. CONSTITUTION:The contents (weight %) of C, P, S and O of the materials to be welded are adjusted in the range of 0.20<=C<=0.60, P+S<=0.02, and O<=0.005 and the materials 1 to be welded are fitted so that the groove line becomes vertical to arrange the backing material 3. When the electron beam is projected on said groove line at the push angle 2-10 deg., the occurrence of the porosity due to the dropping of molten metal can be avoided. Further, when the welding is performed so that the penetration by the electron beam is confined to the inside of the backing material 3, the root porosity 8 exists in the backing material 3 and does not exist in the material 1 side to be welded and the thick steel plates can be welded without weld defects even with the vertical welding.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to vertically oriented steel plates containing a relatively large amount of carbon, such as carbon steel for mechanical structures and low alloy steel, and having a thickness of 100 IP or more. The present invention relates to an electron beam welding method for thick steel plates suitable for welding.

[Prior Art] Since electron beam welding has a high energy density, it is possible to obtain a penetration of 100 nun or more in one pass in terms of equipment capacity, and it is being widely applied in actual production.

By the way, in electron beam welding of thick plates, excessive molten metal is produced on the front or back side during welding, making it difficult to hold it in the welded area, resulting in the problem of dripping.

When this dripping occurs, the viscosity of the dripping molten metal draws out the molten metal near the center of the plate thickness, causing a shortage of molten metal inside the bead and causing defects such as porosity.

In this case, in horizontal welding, the molten metal tends to fall toward the relatively cold base metal side (lower side) due to the action of gravity, so the molten metal is easily cooled and solidified, and dripping is less likely to occur. In addition, the plate to prevent dripping can also be fixed to the material to be welded and easily installed. Therefore, in horizontal welding, dripping of the molten metal and internal defects such as porosity caused by the dripping can be prevented relatively easily.

There is also a report that even a thick plate with a thickness of 20011II11 was able to be penetrate-welded without any defects.

However, in penetration welding in a vertical position, the molten metal that comes out to the front and back sides as a surplus overlaps the heated surplus to form a bead, so the surplus tends to be too large and solidification is difficult. After a delay, it becomes difficult to hold the molten metal. For this reason, in vertical welding, dripping occurs and porosity is likely to occur inside. Therefore, it is difficult to perform vertical penetration welding of thick plates stably.

Conventional methods for preventing molten metal from dripping during vertical penetration welding of thick plates include using a copper dowel, or creating grooves on the front or back side of the groove to reduce the amount of molten metal that becomes excessive. A method of preventing molten metal from dripping is known.

[Problems to be Solved by the Invention] However, in the former method using a copper dowel, it is necessary to slide the welded material and the copper dot relative to each other as welding progresses; Fluctuations in the height of the overfill and sticking of the molten metal to the copper dowel occur, making it extremely difficult to slide the dowel smoothly, and this method cannot be said to be practical. In addition, in the method of forming grooves on the front or back side of the groove, when such grooves are provided, strong residual magnetism is likely to occur inside the groove, and the beam may bend horizontally or vertically due to the influence of this magnetism. And also,
There is a problem in that the strength of this residual magnetism fluctuates during welding. If the beam bends left and right in this way, a misalignment will occur. Also, when the beam bends upward, the molten metal is pushed toward the surface by gravity, causing dripping on the surface.
If the beam bends downward, dripping will occur on the back side.

Furthermore, gas components in the steel material are considered to be a factor in the generation of porosity during electron beam welding of thick plates. In other words,
When the oxygen content of the material to be welded is high, solidification is completed before the gas generated during welding is exhausted from the molten metal to the outside, and porosity occurs in that part.

Furthermore, as the carbon content increases, the amount of coagulation of the δ phase, which has the same capacity as P and S, decreases, and the amount of coagulation of the γ phase increases.
, the solid solution amount of S decreases, and solidification cracking becomes more likely to occur.

Generally, high carbon steel contains about 0.03% of (P+8>), and solidification cracking is likely to occur in high carbon steel, making it difficult to apply electron beam welding.

As described above, porosity caused by the oxygen content of the welded material and solidification cracking caused by the CI, P, and S content occur, but the relationship between the composition of the welded material and the frequency of occurrence of these various defects is has not yet been sufficiently investigated.

For this reason, when performing vertical penetration welding on a thick steel plate having a thickness of 100 IllPJJ or more, there are many problems in terms of stability of welding quality.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for electron beam welding of thick steel plates that can obtain a sound welded part free from defects such as porosity, cold shut, and solidification cracking. do.

[Means for Solving the Problems] The electron beam welding method for thick steel plates according to the present invention is an electron beam welding method for thick steel plates in which the thick steel plates are upwardly welded in a vertical position. , s and O content (wt%
) to the range shown by the inequality below, place a backing material on the back side of the workpiece, and irradiate the workpiece with an electron beam at a receding angle of 2" to 10". It is characterized by partial penetration welding so that the penetration remains inside the backing material.

0.20≦C≦0.60 P+8≦0.020 0≦0.005 [Function] In the present invention, first, C, P, S and O of the material to be welded are
The content (weight %) of is adjusted to the range shown by the following inequality.

0.20≦C≦0.60 P+S≦0.020 O≦0. Since the material to be welded is irradiated with the electron beam at a receding angle of 2° to 10°, it is possible to avoid the occurrence of porosity caused by dripping of molten metal from the surface of the material to be welded. In addition, by using a backing material and performing partial penetration welding so that the penetration by the electron beam remains inside the backing material, defects such as root porosity and cold shut, as well as solidification cracking, can be prevented inside the welded material. It can be prevented.

Hereinafter, the operation of the present invention will be explained with reference to the accompanying drawings. FIGS. 1(a) and 1(b) are diagrams for explaining the electron beam welding method according to the present invention, with FIG. 1(a) being a plan view and FIG. 1(b) being a longitudinal sectional view. Align the workpiece 1 so that its mating surface (appearing on the top surface of the workpiece 1 as the groove line 2) is vertical, and place a backing material 3 behind the mating surface and on the back side of the workpiece. Then, as shown in Fig. 1(b), the electron beam 4 is irradiated onto the groove line 2 with a receding angle of θ. Adjust the beam strength so that the beam reaches the inside of the material 3, and weld upward from the bottom to the top of the material to be welded in a vertical position.Then, the part of the material to be welded near the groove line 2 will melt. A weld metal 6 is formed by cooling and solidifying the molten metal 5. In this case, droplets 7 of the molten metal 5 drip down on the surface side of the welded material 1. There is very little dripping.Furthermore, the root porosity 8 that occurs at the welding tip exists within the backing material 3 and does not exist as a defect inside the welded material 1.

Next, the reason for adopting the above-described configuration in the present invention will be explained. The inventors of the present application have conducted various experimental studies to develop a method for welding thick steel plates to be welded without causing internal defects, and have obtained the following findings.

As mentioned above, it is extremely difficult to obtain a welded part without internal defects by vertical penetration welding, so the inventors of the present invention
We considered welding by partial penetration welding using a horizontal electron beam 4 as shown in Figures (a) and (b).

In addition, FIG. 2(a) is a plan view, and FIG. 2(b) is a longitudinal cross-sectional view. Components that are the same as those in FIGS. 1(a) and (b) are given the same reference numerals and explanations are omitted. .

However, in partial penetration welding where the penetration depth exceeds 1100a, it is more difficult to obtain a defect-free weld than in the case of penetration welding.

The reason for this is that in penetration welding, the excess molten metal is shared and retained as excess metal on the front and back surfaces of the welded material, whereas in partial penetration welding as shown in Figures 2(a) and (b), Since the molten metal was held only on the surface, the molten metal was more likely to drip down, and large porosity 9 was generated near the center of penetration.

In addition, root porosity 8 and cold shut 10 occurred near the penetration tip, and furthermore, fine solidification cracks 11 occurred from the penetration tip to the center of the plate thickness.

Therefore, the inventors of the present invention studied a partial penetration welding method in which the electron beam 4 is given a sweepback angle θ, as shown in FIGS. 3(a) and 3(b). Note that in FIGS. 3(a) and 3(b), the same parts as in FIGS. 1(a) and 1(b) are designated by the same reference numerals, and the description thereof will be omitted.

By giving the beam a receding angle θ, the molten metal inside the beam hole is pushed toward the back of the beam hole by the action of gravity, and although excess molten metal drips from the surface as droplets 7, the plate The large porosity (porosity 9 shown in Figure 2) that had occurred near the center of the thickness no longer occurred.

A method for performing vertical advancement welding by giving a beam a sweepback angle is disclosed in Japanese Patent Laid-Open No. 31937/1983.

This publication targets aluminum alloys, and using this welding method, a clean bead appearance can be obtained without dripping of molten metal, and internal defects such as root porosity and cold shut can be avoided. It is said that this will completely prevent it.

This effect is thought to be due to the relatively thin thickness of the target plate and the low melting point of aluminum.

However, the object of the present invention is a thick steel plate having a thickness of 1001111 mm or more. Also, steel has a higher melting point than aluminum. For this reason, in the case of thick steel plates, unlike in the case of thin aluminum plates, it is difficult to completely prevent defects in the root part, and the problem of solidification cracking of the weld metal, which does not occur in the case of aluminum, occurs. .

Furthermore, since aluminum has a low specific gravity, the
It is thought that a large receding angle of 0° was required, but
In the case of thick steel plates, if the receding angle exceeds 10'', the penetration depth will be extremely reduced.

Therefore, the inventors of the present application conducted various studies to find the optimal beam sweep angle for electron beam welding of thick steel plates, and as a result, they found that for thick steel plates, the beam sweep angle should be set between 2° and 10". I found it.

The reason why this beam recession angle is set in the range of 2° to 10° is as follows. First, if the receding angle is less than 2°, the force of gravity that pushes the molten metal in the beam hole toward the back of the beam hole becomes small, and the molten metal tends to drip from the surface. For this reason, the molten metal inside the beam hole is drawn out due to viscosity, causing a shortage of molten metal at the center of the welding area and generating porosity. On the other hand, when the receding angle exceeds 10°, the molten metal within the beam hole gathers toward the back of the beam hole due to the action of gravity, filling the beam hole near the root. In this case, it becomes necessary for the beam to form a beam hole while removing this molten metal, which reduces the penetration depth and increases the variation in the penetration depth.
Not suitable for welding thick plates. For this reason, in the case of thick steel plates, the beam recession angle is set in the range of 2° to 10°.

In this case, as shown in FIG. 2, the root porosity 8 and cold shut 10 that occur near the penetration tip and the minute solidification cracks 11 that occur from the penetration tip to the center of the plate thickness are as shown in FIG. Even with the method shown in Figure 2, the problem could not be prevented, and the problem occurred in the same way as in the case shown in Figure 2.

The cold shut that occurs near the welding tip is caused by the narrow bead width at the welding tip, and the surrounding base metal receives less heat from the electron beam and molten metal, so the temperature of the base metal does not rise sufficiently. This occurs because the molten metal is rapidly solidified.

On the other hand, root porosity occurs when a cavity is created by the explosion of metal vapor, and as in the case of cold shut, the molten metal is rapidly cooled and solidified, and solidification proceeds without the molten metal sufficiently filling the cavity.

In order to prevent this cold shut and root porosity from occurring, it is possible to widen the bead width at the penetration tip, but in the case of partial penetration welding where the penetration depth is deep, the bead width may be increased. If it is widened, vertical cracks will occur, and it is very difficult to prevent defects at the tip of the penetration.

For this reason, as shown in FIG. 4, a groove shape in which a convex portion 12 was previously formed on the back side of the welded material 1 was studied. By using such a groove, all defects such as root porosity at the penetration tip can be generated in the convex portion 12. After welding, by cutting and removing the convex portion 12, a welded portion free of these defects can be obtained.

However, even with this method, fine solidification cracks are caused by secondary
Similar to the method shown in Figures and Figure 3, the cracks occurred near the center of the plate thickness.

This solidification cracking hardly occurs in the case of penetration welding,
Occurs during partial penetration welding. In the case of penetration welding, parallel beads penetrate the entire material to be welded. but,
In partial penetration welding, there is some material to be welded that does not melt on the back side, so it is thought that the restraining force caused by this part acts on the entire material to be welded in a complex manner, causing solidification cracking. .

Therefore, in order to reduce the influence of stress generated during welding near the penetration tip on the welded material, a backing material 3 independent from the welded material 1 was used as shown in FIG. 1.

As a result, all the defects at the penetration tip could be kept inside the backing material 3, and by limiting (P+S)l, it was possible to obtain a welded part without solidification cracks in the welded material. . For this reason, a backing material is used in the present invention.

Note that the range in which defects occur near the penetration tip varies depending on the penetration depth. For example, the penetration depth is 150
In the case of um, defects occurred in a range of about 20nun from the penetration tip, and in the case of a penetration depth of 2501, defects occurred in a range of about 30IIIll. Therefore, the thickness of the backing material is approximately 30 II when the thickness of the material to be welded is approximately 150 II.
1 or more, and when the plate thickness of the material to be welded is about 2501111n, it is preferably about 50Il111 or more.

Since the components of the backing material will mix with the weld metal, it is desirable to use a co-material with the same composition as the welded material, but it should be used as long as it does not adversely affect weld defects or joint performance, depending on the required characteristics of the welded part. It is also possible to use a material having a composition similar to that of the material to be welded.

Next, the relationship between the composition of the material to be welded and the occurrence of various defects will be explained. Figure 5 shows the groove shape and the C content (wt%) and (P+S) content (wt%) of the welded material.
FIG. 3 is a graph diagram showing the relationship between the occurrence of cracking and the occurrence of cracking.

However, the groove A has the shape shown in FIG. 1, the groove B has the shape shown in FIG. 4, and the groove C has the shape shown in FIG. 3.

In Fig. 5, a steel material with a plate thickness of 150 to 300 μ is used, the acceleration voltage is 150 V, and the beam current is 3
00 to 400111A, welding speed 0.6 to 1.5
The data are plotted at n+m/sec with the beam recession angle varied from 2 to 10 degrees.

As is clear from this figure, the groove is A type, the C content is 0.60% or less, and the (P+S) content is 0.020%.
% or less, electron beam welded parts free of defects can be obtained.

Figure 6 is a graph showing the relationship between plate thickness and recession angle and the presence or absence of defects, and Figure 7 is a graph showing the relationship between oxygen content (wt%) and plate thickness and the presence or absence of porosity. It is. Conditions such as accelerating voltage, beam current, and welding speed are the same as in the case of FIG. 5.

As is clear from Figures 6 and 7, defects can be eliminated by setting the receding angle to 2''' to 10° and the oxygen content to 0.005% by weight or less, regardless of the plate thickness. A clean welded area can be obtained.

For this reason, the contents (wt%) of cSp, s, and 0 components in the welded material are set within the range shown by the following inequality.

0.20≦C≦0.60 P+S≦0.020 0≦0.005 [Example] Next, Examples 1 to 26 in which welding was performed by the method of the present invention
This will be explained together with Comparative Examples 1 to 41 in which welding was performed under conditions that deviate from the conditions specified in the claims of the present application.

Table 1 below shows the composition, welding conditions, presence or absence of welding defects, etc. of each example and comparative example.

As shown in Table 1, the test materials were carbon steel with various contents of C, (P1S> and O) or Cr and Mo
Contains low alloy steel.

There are three types of groove shapes: A (as shown in Figure 1), B (as shown in Figure 4), and C (as shown in Figure 3). have a tip. In addition, A
The backing material in the case of this type had a thickness of 100 mm, and was a common material having the same composition as the welded member.

Further, in Table 1, O indicates a case where there is no defect, and × indicates a case where a defect occurs.

As is clear from Table 1, cracks occurred inside the welded material when the groove shape was Type 8 or C, whereas when the groove type A used a backing material, cracks occurred inside the welded material. In case, C content is 0.20-0.60%, (P+S)
No cracking or porosity occurred when the content was 0.020% or less and the zero content was 0.005% or less.

In addition, porosity occurred when the beam recession angle was less than 2°, but porosity did not occur when the beam recession angle was 2° or more.

[Effects of the Invention] According to the present invention, the occurrence of porosity due to dripping of molten metal during electron beam welding can be avoided, and a sound welded part without defects such as root porosity and cold shut, as well as solidification cracks, etc. can be achieved. Obtainable.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are diagrams showing an electron beam welding method according to an embodiment of the present invention, and FIG. 2(a) is a diagram showing an electron beam welding method according to an embodiment of the present invention. (b) shows the groove shape in the case of a horizontal beam, Fig. 3 (a) and (b) show the groove shape without a backing material, and Fig. 4 shows the groove shape in the case where the back side has a convexity. is a graph showing the relationship between C1 (P+8) content, groove shape, and presence or absence of cracks, No. 6
The figure is a graph showing the relationship between plate thickness and receding angle and the presence or absence of defects, and FIG. 7 is a graph showing the relationship between C content and plate thickness and the presence or absence of porosity. 1: Material to be welded, 2: Groove line, 3: Backing material, 4: Electron beam, 5: Molten metal, 6: Weld metal, 7: Dripping molten metal, 8-nil topology, 9: Porosity, 10: Cold Shut, 11: Solidification Cracking Applicant Kobe Steel Co., Ltd. Representative Patent Attorney Tadashi Fujimaki Kengo Rouchi (°)

Claims (1)

[Claims] In an electron beam welding method for thick steel plates in which the steel plates are welded upward in a vertical position, the content (% by weight) of C, P, S, and O in the material to be welded is expressed by the following inequality. A backing material is placed on the back side of the material to be welded, and the electron beam is irradiated onto the material at a receding angle of 2° to 10°. A method for electron beam welding of thick steel plates, which is characterized by partial penetration welding so that the welding stays inside. 0.20≦C≦0.60 P+S≦0.020 O≦0.005