JP7591964B2 - How to butt weld stainless steel plates - Google Patents

Description

The present invention relates to a method for butt welding stainless steel plates.

When stainless steel plates are butt welded together without using a filler metal, the base material may undergo welding deformation at the welded joint after welding, mainly due to thermal contraction in the direction of the weld line.

When viewed from the welding torch side, welding deformation of the base material can be a combination of so-called angular distortion, in which the weld line forms a V-shape as the valley line, and buckling deformation, in which the base material curves along the weld line so that it protrudes toward the welding torch. This type of welding deformation is likely to occur when the base material is a thin stainless steel plate.

In order to suppress welding deformation of the base material, it is possible to set the restraint position of the base material during welding as close as possible to the groove. However, when the restraint position of the base material is brought closer to the groove, when viewed from the welding torch side, a welding deformation that combines reverse angular deformation, which deforms in the opposite direction to the previous angular deformation, and buckling deformation, which causes the stainless steel plate to bend along the weld line so that it protrudes to the opposite side from the welding torch side, can occur.

When welding deformation occurs that is a combination of reverse angular distortion and buckling distortion, the area around the weld ends up with a complex shape. Even if the restraining position of the base material is kept constant, the direction of deformation may change as described above due to changes in the mechanical properties and plate thickness of the base material. It is possible to keep the direction of deformation constant by increasing the distance between the restraining devices that restrain each of a pair of base materials, but widening the distance between the restraining devices too much will increase the amount of welding deformation itself.

Such welding distortion problems are more likely to occur with austenitic stainless steel sheets, which have relatively lower yield strength and Young's modulus than ferritic stainless steel sheets. In addition, ferritic-austenitic dual-phase steel sheets, which have relatively higher strength than austenitic stainless steel sheets, are more likely to have welding distortion problems when the welding speed is low.

It is possible to obtain a welded joint with corrected welding distortion by performing correction on the welded joint after welding. However, as mentioned above, if the welded joint has a complex shape around the weld, if the direction of deformation of the base material changes for each joint, or if the amount of deformation is too large, it becomes necessary to individually adjust the correction conditions in the post-weld correction process according to the deformation state of the joint, which creates a problem of complicating the correction process. To prevent the correction process from becoming complicated, it is necessary to make the direction of welding deformation consistent for multiple welded joints manufactured, and further to reduce the amount of deformation itself.

Patent Document 1 describes a welding machine that uses a stage on which each plate material is placed, a first cooling body and a second cooling body that are respectively in contact with the upper surface of each plate material, a first pressing part and a second pressing part that press each cooling body, and a welding torch to butt weld different plate materials together. Patent Document 2 describes a method of preventing angular distortion caused by welding using a deformation suppression member formed of a gate-shaped member that is arranged to straddle the groove of the steel plate, a lifting plate that is inserted through the gate-shaped member and fixed to the steel plate, and a tapered pin that is inserted through approximately the center of the lifting plate to prevent deformation caused by welding heat when steel plates are butt welded on a backing metal.

However, even with the techniques described in Patent Documents 1 and 2, it is difficult to keep constant the welding deformation that occurs when butt welding stainless steel plates.

JP 2016-198822 A JP 2012-139702 A

The present invention was made in consideration of the above circumstances, and aims to provide a method for butt welding stainless steel plates that, when mass-producing welded joints, ensures that the welding deformation in each welded joint is in a consistent direction, making it possible to reduce the amount of deformation itself.

In order to solve the above problems, the present invention employs the following configuration.
[1] A preparation step of arranging two stainless steel plates having a thickness of 3 mm or less so that their ends face each other, and clamping and restraining the two stainless steel plates from the thickness direction with a pair of first restraining devices and a pair of second restraining devices;
and a welding process for butt-welding the ends of the opposed stainless steel plates without using a filler metal,
In the preparation step, when a predicted width of a weld portion formed by welding is w (mm) and a plate thickness of the stainless steel plate is t (mm), a distance between an end of the first restraint device and an end of the second restraint device is set in a range of {w+(40-10t)} mm or more and 2×{w+(40-10t)} mm or less ;
A method for butt welding stainless steel plates, wherein the distance between the end of the stainless steel plate restrained by the first restraint device and the end of the first restraint device, and the distance between the end of the stainless steel plate restrained by the second restraint device and the end of the second restraint device are aligned to within a range of ±5% based on half the distance between the end of the first restraint device and the end of the second restraint device .
[ 2 ] The method for butt welding stainless steel sheets according to [1] , wherein the stainless steel sheets are austenitic stainless steel sheets or ferritic-austenitic duplex stainless steel sheets.

According to the method for butt welding stainless steel plates of the present invention, the distance between the end of the stainless steel plate and each of the ends of the first and second restraining devices is adjusted to within a range of ±5% based on half the distance between the end of the first restraining device and the end of the second restraining device, and the distance between the end of the first restraining device and the end of the second restraining device is set to be equal to or greater than {w+(40-10t)} mm. This allows the unrestrained portion to deform toward the opposite side of the welding torch during the welding process, and ensures that a V-shaped angular deformation with the weld line as the valley line as viewed from the welding torch side is generated in the welded joint. In addition, the occurrence of such angular deformation causes the cross-sectional neutral axis to move toward the welding torch side, and buckling deformation that protrudes toward the welding torch side can be generated. This allows the direction of welding deformation in the welded joint after welding to be consistent for each welded joint, and further reduces the amount of deformation itself.

Therefore, according to the present invention, when mass-producing welded joints, the welding deformation in each welded joint is in a uniform direction, and the amount of deformation itself can be reduced. Furthermore, in the correction process after welding, correction can be performed without changing the correction conditions for each welded joint.

FIG. 1 is a schematic cross-sectional view showing a preparation step of a method for butt welding stainless steel plates according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a welding process of a method for butt welding stainless steel plates according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing a welded joint produced by the method for butt welding stainless steel plates according to an embodiment of the present invention. FIG. 4 is a schematic diagram showing a preparation step of the method for butt welding stainless steel plates according to an embodiment of the present invention, and is a schematic plan view seen from the welding torch side. FIG. 5 is a schematic diagram illustrating angular deformation and reverse angular deformation. FIG. 6 is a schematic diagram illustrating the amount of deformation of a welded joint.

The method for butt welding stainless steel plates, which is an embodiment of the present invention, will be described with reference to the drawings.

The welding target of the welding method of this embodiment is stainless steel plate. In particular, when austenitic stainless steel plate or ferritic-austenitic duplex stainless steel plate is used to mass-produce welded joints by the welding method of this embodiment, the welding deformation in each welded joint will be in a uniform direction, and the amount of deformation itself can be reduced. Note that the welding method of stainless steel plate of this embodiment is not limited to austenitic stainless steel plate or ferritic-austenitic duplex stainless steel plate, but can also be suitably applied to other stainless steel plates such as ferritic stainless steel plate.

The stainless steel plate to be welded is a thin steel plate with a thickness of 3 mm or less. Thin steel plates are prone to welding deformation, and are therefore particularly suitable for use as the welding object of the welding method of this embodiment. More preferably, the plate thickness is 1 to 3 mm, and may be 1 to 2 mm. By making the plate thickness 1 mm or more, the temperature gradient in the plate thickness direction at the welded portion during welding does not become too small, and buckling deformation does not become complicated. Furthermore, by making the plate thickness 3 mm or less, the penetration depth during welding is sufficient, making it possible to weld without using a filler metal.

A groove may be provided on the end face of the stainless steel plate to be welded. The shape of the groove formed by butting the grooves together is preferably an I-groove. Alternatively, no groove preparation may be performed and the end face of the stainless steel plate may be left as is. In the case of an I-groove, the root spacing is 0 mm.

The method for welding stainless steel sheets in this embodiment includes a preparation process and a welding process. Each process is described below.

(Preparation process)
1 and 4, in the preparation step, two stainless steel plates 1 and 2 are arranged so that their respective ends 1a and 2a face each other, and then the stainless steel plates 1 and 2 are restrained. As described above, a groove may be provided at each of the ends 1a and 2a.

In this embodiment, a first restraining device 3 and a second restraining device 4 are used to restrain each of the stainless steel plates 1 and 2. The first restraining device 3 is composed of a pair of two block-shaped restraining bodies 3a and 3b, which sandwich and restrain one of the stainless steel plates 1 in the thickness direction. The second restraining device 4, like the first restraining device 3, is composed of a pair of two block-shaped restraining bodies 4a and 4b, which sandwich and restrain the other stainless steel plate 2 in the thickness direction.

As shown in the schematic plan view of FIG. 4, the first restraining device 3 and the second restraining device 4 extend along the longitudinal direction of the ends 1a, 2a of the stainless steel plates 1, 2. In addition, the first restraining device 3 and the second restraining device 4 are positioned relative to the stainless steel plates 1, 2 so that the ends 3c, 4c of the first restraining device 3 and the second restraining device 4 on the steel plate end side are parallel to the ends 1a, 2a of the steel plates.

The lengths D1, D2 of the first restraining device 3 and the second restraining device 4 are longer than the length of the ends 1a, 2a or are the same as the length of the ends 1a, 2a, as shown in Figure 4. If the lengths D1, D2 of the first restraining device 3 and the second restraining device 4 are shorter than the length of the ends 1a, 2a, there will be areas where the stainless steel plates 1, 2 are not restrained, which can cause unexpected welding deformation, which is not preferable.

The widths h1 and h2 of the first restraining device 3 and the second restraining device 4 are not particularly limited as long as they are wide enough to reliably restrain the stainless steel plates 1 and 2, respectively.

Each of the stainless steel plates 1 and 2 is restrained by a first restraining device 3 and a second restraining device 4 at a position away from the ends 1a and 2a of the stainless steel plates 1 and 2. As shown in FIG. 4, the distance L1 between the tip of the end 1a of one of the stainless steel plates 1 restrained by the first restraining device 3 and the end 3c of the first restraining device 3, and the distance L2 between the tip of the end 2a of the other stainless steel plate 2 restrained by the second restraining device 4 and the end 4c of the second restraining device 4 are set to half the distance (L1+L2) between the end 3c of the first restraining device 3 and the end 4c of the second restraining device 4, and are aligned within a range of ±5% of this standard. If the distances L1 and L2 are outside this range, it becomes difficult to control the welding deformation after welding to the expected deformation state.

In the preparation process, the distance M between the end 3c of the first restraining device 3 on the steel plate end side and the end 4c of the second restraining device 4 on the steel plate end side is set to {w+(40-10t)} mm or more, where w (mm) is the predicted width of the weld to be formed in the next welding process, and t (mm) is the thickness of the stainless steel plate. The upper limit of the distance M may be set to 2×{w+(40-10t)} mm or less. More preferably, the distance M between the end 3c of the first restraining device 3 and the end 4c of the second restraining device 4 is set to {w+(40-10t)} mm or more. The distance M may be set to 1.1×{w+(40-10t)} mm or less. Most preferably, the distance M is set to {w+(40-10t)} mm.

The smaller the plate thickness t of the stainless steel plates 1 and 2 that are the base material, the smaller the gradient of the temperature distribution in the plate thickness direction of the welded part that receives the welding heat input becomes, and angular distortion becomes less likely to occur. Therefore, by increasing the distance M between the end 3c of the first restraining device 3 and the end 4c of the second restraining device 4, it is possible to suppress unexpected welding deformation. On the other hand, if the distance M between the end 3c of the first restraining device 3 and the end 4c of the second restraining device 4 is too wide, the restraining force by the first and second restraining devices 3 and 4 at the ends 1a and 2a becomes weak, and the amount of deformation becomes large. In addition, the distance M between the end 3c of the first restraining device 3 and the end 4c of the second restraining device 4 needs to be at least equal to or greater than the width w of the welded part. Based on the above knowledge, the inventor conducted experiments and came to find the above range.

If the distance between the end 3c of the first restraint 3 on the steel plate end side and the end 4c of the second restraint 4 on the steel plate end side is less than {w + (40 - 10t)} mm, angular deformation (reverse angular deformation (see Figure 5 (b))) may occur in which the weld line is bent when viewed from the welding torch side, and buckling deformation may occur in which the stainless steel plates 1 and 2 bend along the weld line so that they protrude toward the opposite side to the welding torch side. The combination of such unexpected deformations causes more complex deformation near the weld line, making post-welding correction difficult.

If the distance M between the end 3c of the first restraining device 3 on the steel plate end side and the end 4c of the second restraining device 4 on the steel plate end side exceeds 2 x {w + (40 - 10t)} mm, the distance between the first restraining device 3 and the second restraining device 4 and the ends 1a, 2a of the steel plate will widen, which will weaken the restraining force on the ends 1a, 2a and increase the amount of welding deformation.

The predicted width w (mm) of the weld is the predicted value of the width of the weld metal on the welding torch side of the weld formed by the welding process. This predicted width w is determined by conducting a preliminary test. In the preliminary test, welding conditions are the same as those in the welding process, and welding is performed using a stainless steel plate that has the same material, plate thickness, and end shape as the stainless steel plate to be welded. The width of the weld formed in the preliminary test is the predicted width w.

(Welding process)
Next, as shown in Fig. 2, in the welding process, a welding torch 10 is placed against the opposed ends 1a, 2a, and butt welding is performed without using a filler metal. The welding method is laser welding or non-consumable electrode gas shielded arc welding, preferably TIG welding. The welding is performed on one side. Other welding conditions are not particularly limited.

In this embodiment, backing is not required. If backing is performed, the periphery of the ends 1a and 2a will be constrained more strongly than necessary, and buckling deformation may become large due to thermal contraction of the welded portion after welding.

Figure 3 shows the state after welding is completed. The weld 20 is formed by welding. This results in a welded joint 30 in which the stainless steel plates 1 and 2 are joined by the weld. As mentioned above, the predicted width w of the weld 20 used to determine the spacing M is determined based on the width of the weld of the welded joint obtained by the preliminary test. For reference, Figure 3 shows the measurement range of the width of the weld measured in the preliminary test by a dimension line along with the symbol w.

When the weld joint 30 obtained by the welding method of this embodiment is released from the constraint by the first and second constraint parts 3 and 4, it undergoes a welding deformation that is a combination of so-called angular distortion, which deforms into a V-shape with the weld line as the valley line, and buckling distortion, which bends the base material along the weld line so that it protrudes toward the welding torch, when viewed from the welding torch side during welding. This welding deformation is a planned deformation. Even if the weld joints 30 are mass-produced by the welding method of this embodiment, the direction of the angular distortion and buckling deformation does not change for each weld joint. Furthermore, the amount of deformation in each weld joint 30 is also small. As a result, when performing the correction process after welding, it is not necessary to adjust the correction conditions for each weld joint 30 according to the deformation state of the weld joint 30.

As described above, according to the method for butt welding stainless steel plates of this embodiment, the distance between the ends 1a, 2a of the stainless steel plates 1, 2 and the ends 3c, 4c of the first restraining device 3 and the second restraining device 4 is adjusted to within a range of ±5% based on half the distance between the end 3c of the first restraining device 3 and the end 4c of the second restraining device 4, and the distance M between the end 3c of the first restraining device 3 and the end 4c of the second restraining device 4 is set to {w + (40 - 10t)} mm or more, so that during the welding process, there is room for the unrestrained portion to deform on the side opposite the welding torch 10, and this ensures that a V-shaped angular deformation with the weld line as the valley line can be generated in the weld joint 30 when viewed from the welding torch 10 side. In addition, the occurrence of such angular deformation causes the cross-sectional neutral axis to move toward the welding torch 10 side, and buckling deformation that protrudes toward the welding torch 10 side along the weld line can be generated. As a result, in this embodiment, when mass-producing welded joints 30, the direction of welding deformation in the welded joints 30 after welding can be made constant for each welded joint 30, and the amount of deformation itself can be made small. Then, in the post-weld straightening process, straightening can be performed without adjusting the straightening conditions for each welded joint 30.

Two stainless steel plates with a length of 200 mm, a width of 75 mm and a thickness of 1.5 mm (steel type: SUS316L), two stainless steel plates with a length of 200 mm, a width of 75 mm and a thickness of 2.0 mm (steel type: SUS316L), two stainless steel plates with a length of 200 mm, a width of 75 mm and a thickness of 2.0 mm (steel type: NSSC2351, manufactured by Nippon Steel Stainless Steel Corporation), and two stainless steel plates with a length of 200 mm, a width of 75 mm and a thickness of 2.0 mm (steel type: NSSC2120, manufactured by Nippon Steel Stainless Steel Corporation) were prepared. SUS316L is an austenitic stainless steel plate, and NSSC2351 and NSSC2120 are ferritic-austenitic duplex stainless steel plates.

Next, as a preparation step, the two stainless steel plates were arranged so that their end faces (200 mm long ends) parallel to the longitudinal direction faced each other, and then each stainless steel plate was restrained. In addition, when arranging the two stainless steel plates to be welded, they were arranged so that they were horizontal.

To restrain each stainless steel plate, a first restraining device and a second restraining device as shown in Figures 1 and 4 were used. As shown in the schematic plan view of Figure 4, the first restraining device and the second restraining device were extended along the longitudinal direction of the end of the stainless steel plate parallel to the longitudinal direction. In addition, the first restraining device and the second restraining device were placed on each stainless steel plate so that the ends of the first restraining device and the second restraining device on the steel plate end side were parallel to the steel plate end.

The distance L1 between the end of one stainless steel plate restrained by the first restraining device and the end of the first restraining device, and the distance L2 between the end of the other stainless steel plate restrained by the second restraining device and the end of the second restraining device, were the same length. In addition, the distance between the end of the first restraining device on the steel plate end side and the end of the second restraining device on the steel plate end side was as shown in Table 1.

Next, the opposed ends were butt-welded without using a filler metal. The welding method was TIG welding, and the welding speed and welding heat input were as shown in Table 1. One-sided welding was used for the welding procedure. In this manner, welded joints were produced. Three welded joints were produced for each condition number.

No backing was performed.

The direction of angular distortion was checked for the welded joints obtained. Three welded joints were produced for each condition, and all welded joints were marked as "○" if they were deformed into a V-shape with the weld line as a valley line when viewed from the welding torch side during welding. On the other hand, some or all of the welded joints were marked as "×" if they were deformed in the opposite direction so that the weld line became a crest line when viewed from the welding torch side during welding. The results are shown in Table 1. An example of deformation in the case of "○" is shown in Figure 5(a), and an example of deformation in the case of "×" is shown in Figure 5(b).

In addition, the amount of deformation after welding was evaluated for those welded joints for which the direction of angular distortion was evaluated as "○". The amount of deformation was evaluated by measuring the deformation angle θ centered on the weld in a cross section in the plate thickness direction perpendicular to the longitudinal direction of the welded joint. Figure 6 shows the deformation angle θ. The deformation angle θ was defined as the inclination angle of the stainless steel plate on one side relative to the horizontal plane M when the welded joint was placed on the horizontal plane M. When the deformation angle θ was 0 to 2° or less, the amount of deformation was small and was evaluated as "○", and when the deformation angle θ was more than 2°, the amount of deformation was large and was evaluated as "×". The results are shown in Table 1.

As shown in Table 1, all three welded joints manufactured under conditions where the spacing of the restraining devices satisfied the present invention were deformed into a V-shape with the weld line as the valley line when viewed from the welding torch side during welding, as shown in Figure 5(a). In this way, welded joints whose manufacturing conditions satisfied the present invention had a consistent direction of welding deformation in the welded joint after welding, and the deformation angle θ of the lateral bending could be kept in the range of 0 to 2°.

On the other hand, as shown in Table 1, in the welded joints manufactured under conditions where the spacing of the restraining devices did not satisfy the requirements of the present invention, some of the three welded joints were deformed so that the weld line became a crest line when viewed from the welding torch side during welding, as shown in Figure 5 (b). As a result, the direction of the welding deformation was different for each welded joint.

As a result, while the correction conditions for correcting the deformation of the welded joint were consistent for all welded joints in the examples of the invention, the correction conditions had to be adjusted for each welded joint in the comparative examples, which reduced the productivity of the welded joints.

1...one stainless steel plate (stainless steel plate), 2...other stainless steel plate (stainless steel plate), 1a, 2a...end, 3...first restraint, 4...second restraint, 3c...end of first restraint, 4c...end of second restraint, 10...welding torch, 30...welding joint, M...spacing.

Claims (2)

A preparation step of arranging two stainless steel plates each having a thickness of 3 mm or less so that their ends face each other, and clamping and restraining the two stainless steel plates from the thickness direction using a pair of first restraining devices and a pair of second restraining devices;
and a welding process for butt-welding the ends of the opposed stainless steel plates without using a filler metal,
In the preparation step, when a predicted width of a weld portion formed by welding is w (mm) and a plate thickness of the stainless steel plate is t (mm), a distance between an end of the first restraint device and an end of the second restraint device is set in a range of {w+(40-10t)} mm or more and 2×{w+(40-10t)} mm or less ;
A method for butt welding stainless steel plates, wherein the distance between the end of the stainless steel plate restrained by the first restraint device and the end of the first restraint device, and the distance between the end of the stainless steel plate restrained by the second restraint device and the end of the second restraint device are aligned to within a range of ±5% based on half the distance between the end of the first restraint device and the end of the second restraint device. 2. The method for butt welding stainless steel plates according to claim 1 , wherein the stainless steel plates are austenitic stainless steel plates or ferritic-austenitic duplex stainless steel plates.

Images