JP2007167937A - Steel sheet for welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel sheet for welding almost free from shape change even after welding. <P>SOLUTION: Compressive residual stress is applied to the inside in the width direction of a steel sheet 1 to be subjected to welding, and tensile residual stress is applied to both the edge parts in the width direction. Microscopically, compressive residual stress is preapplied to the vicinity of the part to be subjected to welding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a steel plate for welding.

As is well known, steel plates called thick steel plates are usually used as structural materials for bridges and ships.
When manufacturing such a thick steel plate, it is rolled to a predetermined size with a hot rolling mill and subsequently subjected to a cooling process by water cooling with an accelerated cooling device. However, the temperature at the time of hot rolling and the water cooling start temperature are non-uniform, and further, non-uniform cooling due to non-uniform cooling of the accelerating cooling device occurs, which causes residual stress in the thick steel plate after cooling. In some cases, the shape is poor, such as bending or undulation.

In the case of a thick steel plate with residual stress, when it is used after being cut into a number of strips by post-processing, the residual stress unevenly distributed in the thick steel plate is released by cutting, and the strip is cut. The problem of “curving” (cambering) that would be bent occurred.
As a technique for eliminating such “residual stress generated in a thick steel plate”, a method of applying a bending strain to the thick steel plate by a leveler has been adopted. The hot leveler has a high ability to correct the shape, and the cold leveler has a high ability to remove non-uniform residual stress, so the hot leveler or the cold leveler can be used depending on the situation of the thick steel plate that needs to be corrected. Selected and straightened the steel plate.

On the other hand, even if they are leveled steel plates, when they are used as welding structural materials (steel plates for welding) such as bridges and ships, material shrinkage due to welding occurs in the welding steel plates. However, it has been widely known among those skilled in the art that the shape is greatly deformed.
FIG. 16 shows the state of the deformation. For example, assuming that a steel plate for welding, which is manufactured by adopting a technique such as Patent Document 1 and the residual stress in the longitudinal direction of the steel plate is approximately 0 in the plate width direction, is used as a structural material such as a bridge or a ship, Consider performing rib attachment welding in the longitudinal direction (vertical direction in the figure) with respect to the inside in the width direction.

As a result, as shown in FIG. 16 (b), the welding steel plate, which was rectangular before welding, contracted greatly in the longitudinal direction in the longitudinal direction from the end in the width direction after the three strips were welded. The upper and lower sides of the steel plate are deformed into a concave shape. The reason for this is that, regarding the welded portion, the material once melts at the time of welding and then solidifies again, but at that time, the material shrinkage occurs in the solidified portion and tries to shrink.
That is, even if it is a thick steel plate with a residual stress of approximately 0 in order to suppress deformation after cutting, if it is used as a steel plate for welding, deformation due to material shrinkage may occur. It was a big problem.

  Conventionally, in order to avoid such deformation, dimensions have been taken in anticipation of such deformation, but depending on the shape of the welded rib or flange, the deformation amount of the steel plate for welding varies, and prediction is extremely difficult. It was difficult. In addition, even if the amount of deformation can be predicted, when welding steel plates greatly deformed from a rectangle are welded horizontally or perpendicularly to each other, a large gap (for example, 3 mm or more) is generated between the two steel plates, resulting in a welding operation. It became difficult, and the necessity to re-cut a steel plate had arisen. In particular, for a steel plate for welding having a plate thickness of 25 mm or less, material shrinkage due to welding is large, and re-cutting is required in most cases.

Patent Document 1 discloses a technique that focuses on the above-described deformation during welding. In this technology, the temperature distribution on the surface of a thick steel plate hot-corrected by a hot leveler is measured with a thermometer, and the residual stress distribution is calculated from the temperature distribution of the thick steel plate by a computer. A predetermined parameter representing the variation of the deformation amount is calculated. Further, the allowable value set in advance according to the welding conditions of the user and the parameter are compared, and if the parameter is not within the allowable range, the residual stress is reduced using a leveler or a heat treatment furnace.
JP 2001-316757 A

  However, Patent Document 1 is a technique for causing variation in deformation amount when welding is within a certain range, and is not intended to minimize or minimize the deformation amount associated with welding. Even if the variation in the amount of deformation can be within a certain range, as described above, when welding steel plates that have undergone deformation after welding, if there is a gap between them, re-cutting etc. There is no denying the need arises.

  Therefore, in view of the above problems, an object of the present invention is to clarify a technique in which a rectangular shape change hardly occurs after welding, and to provide a welding steel plate to which the technique is applied.

In order to achieve the above object, the present invention takes the following technical means.
That is, the steel plate for welding according to the present invention is a steel plate for welding that is welded in the width direction inside in the longitudinal direction, and is provided with a compressive residual stress in the width direction inside in advance. A tensile residual stress is applied to both ends in advance.
The inventors of the present application conducted experiments and research in order to develop a steel plate for welding (hereinafter sometimes referred to as a steel plate) that hardly changes in rectangular shape even after welding, and the deformation caused by welding is subjected to welding. It came to be thought that the residual stress existing inside the steel plate is related.

Therefore, first, the residual stress in the steel sheet is reduced by a thermal method, or a steel sheet that is made uniform to almost zero using a hot leveler or a cold leveler is prepared, and the trace as shown in FIG. A welding experiment was conducted.
From that experiment,
(i) Most steel sheets have a greater amount of contraction in the longitudinal direction at the center than at their edges,
(ii) The variation in the amount of shrinkage between the steel plates is uniformly smaller in the steel plates with reduced residual stress,
And got the result.

From this result, the present inventors have come to ascertain that “the residual stress has some influence on the amount of shrinkage accompanying welding”.
Next, the inventors of the present application conducted a welding experiment from the viewpoint of the degree of non-deformation of the steel sheet after welding (whether the shape was rectangular before welding but does not maintain its shape after welding). . As a result, some of the steel sheets whose residual stress was not controlled were more excellent in non-deformation than the steel sheets whose residual stress was controlled to approximately zero. As a result of investigating the residual stress distribution of the steel sheet having the desirable properties, as shown in FIG. 1 (a), "the tensile stress remains at both ends in the width direction of the steel sheet and the compressive stress remains inside the width direction".

Based on this result, the steel sheet for welding according to the present invention is such that compressive residual stress is applied to the inside in the width direction where welding is performed, and tensile residual stress is applied to both ends in the width direction. This steel plate maintains a rectangular shape with little change in shape after welding.
Since the residual stress distribution is macroscopic with respect to the steel sheet, the inventors of the present application have repeatedly studied from a microscopic viewpoint. As a result, when the rib or flange is welded, the material part melted by the gas flame or arc discharge is cooled and solidified again, and tensile stress resulting from the shrinkage is generated. Clarified the mechanism of longitudinal deformation.

Therefore, as shown in FIG. 2, the inventors have reached the idea that a compressive residual stress against the tensile stress should be provided in the vicinity of a portion to be welded, and such residual stress distribution is expressed as follows. It has been clarified that the welded steel sheet has a small degree of deformation from the rectangle (maintains the rectangular shape) after the welding, although shrinkage deformation occurs.
Based on this idea, the steel sheet for welding according to the present invention is preliminarily provided with compressive residual stress in the vicinity of the portion to be welded. This steel plate hardly changes in shape after welding.

  In addition, the inventors of the present application, through computer simulation experiments, and the like, when the site to be welded is located at a location 100 mm or more away from the end in the width direction, both sides in the width direction of the site to be welded. It is clear that compressive residual stress is applied in advance to the region of 50 mm to 100 mm, and the value of the compressive residual stress is preferably 0 MPa to 50 MPa.

Moreover, when the site | part to which the said welding is performed is located in the place within 50 mm from the width direction edge part, it is a compression inside in the area | region of 50 mm-100 mm inside the width direction of the site | part to which the said welding is performed. It is clarified that stress is applied and the value of the residual stress of compression is preferably 0 MPa to 50 MPa.
In addition, when the part to be welded is located at a position of 50 mm to 100 mm from the end in the width direction, the region on the inner side in the width direction of the part to be welded and a region of 50 mm to 100 mm and welding are performed. It has been clarified that compressive residual stress is applied in advance to a region of 50 mm or more on the width direction end portion side of the portion to be formed, and the value of the compressive residual stress is 0 MPa to 50 MPa.

  Preferably, the variation in the residual stress of the compression is ± 10 MPa or less.

  By using the steel plate for welding of the present invention, material shrinkage after welding can be made substantially uniform along the plate width direction of the steel plate.

Hereinafter, the steel sheet for welding concerning this invention is demonstrated below based on a figure.
1 and 2 show a steel plate 1 for welding according to the present invention.
As shown in FIG. 1 (a), the welding steel plate 1 (hereinafter sometimes simply referred to as a steel plate) is provided with compressive residual stress in the width direction when the residual stress in the cross section in the width direction is measured. Tensile residual stress is applied to both sides in the width direction. The stress distribution curve has a downward trapezoidal shape.

The residual stress defined by the steel plate 1 is an average value in the plate thickness direction, and the residual stress distribution in the plate thickness direction may be anything. Further, the integrated value of the tensile residual stress and the integrated value of the compressive residual stress are substantially equal, and the residual stress value in the entire steel sheet 1 is substantially zero.
FIG. 2A shows a situation in which the rib 2 is welded in the longitudinal direction (steel plate rolling direction) with respect to the inside in the width direction of the steel plate 1 having such residual stress distribution.

  FIG. 2B shows a microscopic view of this situation (only the vicinity of the weld W is seen). As can be seen from this figure, the weld W is once melted by a gas flame or an arc, and the compressive residual stress from the beginning is canceled. Thereafter, as the melted portion W solidifies, material shrinkage occurs. However, since the welded portion W is constrained by the surrounding steel plate, it becomes a portion where residual tensile stress remains, and this material shrinkage and residual tensile stress remain. Due to the above, deformation in the longitudinal direction of the steel sheet occurs.

However, a compressive residual stress is applied in advance to the outer side in the width direction of the welded portion W (shrinkage portion), and the material shrinkage is not caused. Therefore, contraction in the longitudinal direction does not occur in the steel plate 1 as a whole.
[Simulation experiments and results]
Next, the specific value of the compressive residual stress given beforehand to the steel plate 1 of this embodiment is demonstrated.

The inventors of the present application examined in detail the deformation behavior of the steel sheet 1 when rib-welded using a thermoelastic-plastic three-dimensional FEM model in order to obtain a steel sheet with little deformation during welding.
As shown in FIG. 3, the steel plate 1 used in the model experiment has a thickness of 16 mm, a width of 2000 mm, and a length of 500 mm. The shape of the attached rib 2 was 15 mm in thickness, 150 mm in width (height), and 500 mm in length, and the number of attachment ribs was variable in the range of 1 to 5.

As steel plate 1 to be welded, (i) normal steel (no residual stress control), (ii) residual stress reduced steel (residual stress value in the width direction is 5 MPa), (iii) no residual stress steel (no residual stress) Three ideal steel plates without stress) were used.
As conditions for rib welding, the heat input by welding was set to 1.7 kJ / mm (320 A × 32 V × 24 cm / min.), And the welding leg length (weaving width) was set to 8 mm. This welding condition is almost the same even if the thickness of the steel plate and the thickness of the rib 2 are changed.

Under these conditions, the value of residual stress generated when the rib 2 was welded, the influence on the periphery of the weld W after the rib welding, and the like were confirmed.
as a result,
(i) A tensile residual stress of about 300 MPa is generated in the weld W by rib welding.
(ii) The area where the initial residual stress changes due to rib welding (heat affected area) is ± 50 mm on both sides of the rib welding position.
(iii) The effect of material shrinkage of the welded portion W on the surroundings is an increase in compressive stress, and the degree of influence varies depending on the number of ribs (6 MPa / piece).
In view of the above, the inventors of the present invention performed a simulation by changing the experimental conditions to obtain a steel sheet with little shape change after welding.

As a result, when the position of the rib welding is 100 mm or more inside (width direction inner side) from the end of the steel plate 1, regions of −100 to −50 mm and 50 to 100 mm (welded portion W) with respect to the position of the rib welding. In the region of 50 to 100 mm on both sides), a compressive residual stress was previously applied, and it was found that the value should be in the range of 0 MPa to 50 MPa.
Therefore, if it is a steel plate which has an initial residual stress distribution as shown to Fig.4 (a), it will satisfy | fill the said conditions after rib welding, and will become a steel plate with few shape changes after welding. Further, since the welded portion W is once melted and the residual stress is canceled, as shown in FIG. 4B, even if the initial residual stress at the rib welding position is −50 MPa or less (for example, −70 MPa). I do not care. However, since the position to which the rib 2 is attached is not strictly determined, it is preferable that the residual stress distribution shown in FIG.

  When the position of rib welding is within 50 mm from the end of the steel plate 1, compressive residual stress is applied in advance to the region 50 to 100 mm on the inner side (inner side in the width direction) from the position of rib welding. Has been found to be in the range of 0 MPa to 50 MPa. Therefore, if the steel sheet has an initial residual stress distribution as shown by a solid line or a broken line in FIG. 4 (c), the above condition is satisfied after rib welding, and the steel sheet has little shape change after welding.

  Moreover, when the attachment position of the rib 2 exists in the range of 50 mm-100 mm from the edge part of the steel plate 1, it is the range of 0-50 MPa beforehand in the area | region of 50-100 mm inside (width direction inner side) from the attachment position of the rib 2. The compressive residual stress of 0 MPa to 50 MPa is preferably applied in advance to a region of 50 mm or more outside the steel plate (width direction end side) from the attachment position of the rib 2. I came to find out. Therefore, if the steel sheet has an initial residual stress distribution such as a solid line or a broken line shown in FIG. 4 (d), the above condition is satisfied after welding, and the steel sheet has little shape change after welding.

Since the welded portion W is once melted and the initial residual stress is canceled, the initial residual stress at the rib welding position is −50 MPa or less (for example, −70 MPa) as shown by the solid line in FIG. It doesn't matter.
The inventors of the present application have revealed that very good results (less deformation after welding) can be obtained when the variation in compressive residual stress is ± 10 MPa or less.

FIG. 4 described above is a microscopic view of the residual stress distribution initially applied to a steel plate with little deformation, but FIG. 5 is a macro view of the initial residual stress distribution (in the entire width direction of the steel plate). Distribution). FIG. 1A also shows the macroscopic view of the initial residual stress distribution.
The steel sheet according to the present invention is preliminarily provided with compressive residual stress in the vicinity of the portion to be welded, and corresponds to the attachment position of the rib 2 as shown in FIGS. 5 (a) to 5 (c). Compressive stress satisfying the above conditions (initial residual compressive stress of 0 MPa to 50 MPa in the region of 50 to 100 mm on both sides of the weld W) is applied. In addition, since the residual stress value of the steel plate 1 as a whole is substantially 0, a tensile residual stress that cancels the compressive residual stress is also applied. Therefore, the residual stress distribution is uneven in the width direction.

  However, it is often not exactly known at which point of the steel plate 1 the rib welding is performed at the time of manufacturing the steel plate 1 according to the present invention. This is because the majority of cases where the user performs trimming cutting of the steel sheet 1 and there are few cases where the factory shipment is used as it is as a member. Accordingly, a compressive stress that satisfies the above-described conditions is applied corresponding to the attachment position of the rib 2, and as shown in FIG. It is very preferable that the steel sheet 1 has a residual stress and a stress distribution that is a tensile residual stress at both ends in the width direction. The inside in the width direction of the steel plate 1 is a portion where rib welding is performed, and may be inside 100 mm or more from the end of the steel plate 1 as described above, but 200 mm or more from the end of the steel plate 1. There is no problem even inside.

[Method of measuring residual stress]
In measuring the residual stress of the steel sheet 1, a number of measuring methods can be employed. For example, (i) a method of drilling holes in a target steel plate, attaching a strain gauge directly to the part, and measuring the residual stress value with this strain gauge (drilling method), (ii) when hot straightening is completed There is a method for obtaining an average value of residual stress in the thickness direction based on the surface temperature distribution of the steel plate and the amount of indentation by a cold leveler.
In the present embodiment, the initial residual stress is measured using a drilling method. Specifically, considering split test pieces (strips) at 100 mm pitches from both ends in the width direction of the target steel plate, from the end in the longitudinal direction on the center line of the split test piece, A strain gauge is affixed at a position “roll center distance + 100 mm”.
[Experimental example]
In FIGS. 6 to 10, five ribs 2 are attached by welding in the longitudinal direction to a steel sheet 1 (sometimes referred to as the present invention steel 1) provided with a residual stress distribution that satisfies the above-described conditions. The experimental results of obtaining the rectangular deformation degree δ in the plate longitudinal direction at that time are shown. 6 to 10 are residual stress values actually measured using the drilling method, and a solid line indicates a calculated residual stress value calculated in consideration of the temperature distribution of the steel sheet 1 and the correction conditions.

The steel 1 of the present invention is as shown in each figure (d), and the residual stress value 100 mm or more inside from both ends in the width direction is 0 MPa to −50 MPa. As comparative examples, conventional steel (regular steel with no residual stress control, each figure (a)), residual stress reduced steel (each figure (b)), and regular straightened steel (conventional steel is straightened with a leveler, etc.) Steel, each figure (c)) is rib welded.
There are five types of steel plates 1 to which the ribs 2 are welded. The plate thicknesses are 12, 16, 22, 28, 34 mm, the width is 2000 mm, and the length is 9000 mm. The shape of the attached rib 2 was the same as in the simulation experiment, and was 15 mm thick, 150 mm wide (height), and 9000 mm long.

  The rectangular deformation degree δ of the steel plate 1 is, for example, in the steel plate 1 of FIG. 1B, with the shrinkage amount of either one of the upper and lower (rolling direction) edges as the reference on either the left or right (width direction) end surface. Measured and converted to a value per 10 m length. In this experimental example, the upper limit value of the rectangular deformation degree δ is 1.2 mm. This is because it is clear from the actual results of the field that the steel plate gap that can be welded is about 3 mm (about 1.5 mm per one steel plate).

As can be seen from the results of FIGS. 6 to 10, it can be understood that the rectangular deformation degree δ of the steel 1 of the present invention is 1.2 mm or less at all plate thicknesses.
In the conventional steel in which compressive stress remains in the center and both ends in the width direction and tensile stress remains in the region between the center and both ends, a rectangular deformation δ of 1.5 mm or more is obtained in all plate thicknesses. It was revealed that it was inappropriate for welding.

Residual stress-reduced steel or normal straightened steel having a residual tensile stress of 50 MPa or less in the plate width direction has a rectangular deformation degree δ of 1 mm to 3 mm and a large amount of shrinkage in the longitudinal direction, which is inappropriate for welding.
Further, in the conventional steel or the like, the amount of contraction inside the width direction is very large compared to both end portions. On the other hand, in the steel 1 of the present invention, the rectangular deformation degree δ in the width direction is substantially the same value and maintains the rectangular shape. Inconvenience that the gap between the steel plates 1 and 1 differs depending on the position in the width direction hardly occurs, and welding is very easy to perform.

In addition to the above experiments, the inventors of the present invention have 5 in the longitudinal direction for the steel 1 of the present invention having various thicknesses and the steel 1 of the invention in which the residual stress distribution shape is substantially the same but the stress value is different. The rib 2 of the strip was attached by welding to obtain a rectangular deformation degree δ. The results are shown in FIGS.
As can be seen from FIG. 11, in order to achieve a rectangular deformation degree δ (<1.2 mm) that is not problematic in practice, the compressive residual stress applied to the inside in the width direction of the steel plate 1 is 0 MPa to 70 MPa, preferably 0 MPa to It is good that it is 50 MPa. This is consistent with the results of computer simulation.

  FIG. 12 shows a plurality of results of welding experiments, in which the average residual stress is (i) −40 to −20 MPa, (ii) −20 to 0 MPa, (iii) 0 to 20 MPa, and (iv) 20 to 40 MPa. FIG. 6 is a diagram showing the relationship between the plate thickness and the rectangular deformation degree δ. As is clear from this figure, a steel sheet belonging to the steel 1 of the present invention (with a residual stress value in the width direction of −50 MPa to 0 MPa, that is, (i), (ii)) and a thickness of 10 mm or more is reliable. Further, the degree of rectangular deformation δ is 1.2 mm or less, and the steel sheet is suitable for welding.

In addition, even if the residual stress value in the width direction is 0 to 20 MPa, the plate thickness is 25 mm or more, or even if the residual stress value in the width direction is 20 to 40 MPa, the plate thickness is 35 mm or more. If it exists, it turned out that rectangular deformation degree (delta) becomes 1.2 mm or less, and becomes a steel plate suitable for welding.
FIGS. 13 and 14 show the steel plate 1, the conventional steel, the residual stress-reducing steel, and the normal straightened steel according to the present embodiment, with 2, 3, 5, and 7 (main) ribs 2 attached by welding. The result of obtaining the rectangular deformation degree δ in the plate longitudinal direction is shown.
As the number of ribs 2 attached by welding increases, the degree of rectangular deformation δ increases in all the steel plates. However, the degree of increase in the steel 1 of the present invention is small, and the degree of rectangular deformation is less if the rib 2 is within 7 threads. δ does not exceed 1.2 mm.

[Steel plate manufacturing equipment]
FIG. 15 shows an outline of a rolling device 3 for a welding steel plate 1 (thick steel plate) according to the present invention. A roughing mill provided with a heating furnace 5 for heating the slab 4 on the upstream side of the rolling apparatus 3 and provided with a pair of work rolls 6 and 6 and a pair of backup rolls 7 and 7 on the downstream side of the heating furnace 5. 8 is provided. Further, a finish rolling mill 11 having a pair of work rolls 9 and 9 and a pair of backup rolls 10 and 10 is provided on the downstream side of the rough rolling mill 8.

On the downstream side of the finish rolling mill 11, an accelerated cooling device 12 (cooling device) for cooling the steel sheet 1 that has been rolled by the finish rolling mill 11 is provided. The accelerated cooling device 12 forcibly cools the steel plate 1 by spraying cooling water onto the steel plate 1 to achieve a predetermined plate temperature.
An exit side plate thermometer 13 such as a radiation thermometer or a thermoviewer is installed in the vicinity of the exit side of the accelerated cooling device 12 so that the temperature distribution on the surface of the steel plate can be measured. Thereby, the surface temperature distribution of the steel plate 1 immediately after cooling can be known. Since it is clear from the past results that the surface temperature distribution and the residual stress distribution in the steel plate 1 have a predetermined relationship, the residual stress distribution in the steel plate 1 can be estimated from this measurement result. .

A hot leveler 14 is provided on the downstream side of the acceleration cooling device 12. This hot leveler 14 is provided with a plurality of leveling rolls 15, 15,.
In addition, a multifunctional leveler 16 is provided at a position that is off-line from the main rolling line. The multi-function leveler 16 includes a plurality of leveling rolls 17, 17,... Arranged in a staggered manner in the top and bottom, and each leveling roll 17 has a backup roll 18 that backs up the leveling roll 17. Has been deployed. The backup roll 18 is constituted by a plurality of (for example, 3 to 5) continuous backup rolls (not shown) connected in the axial direction, and each of the backup backup rolls is moved by a reduction adjusting device (not shown). It can be independently reduced. Therefore, only a part of the leveling roll 17 can be pressed against the steel plate 1 to correct a partial shape of the steel plate 1 or to apply a residual stress in the width direction to the steel plate 1.

A procedure for manufacturing the welding steel plate 1 according to the present invention using the rolling apparatus 3 described above will be described.
First, the slab 4 heated to a predetermined temperature (about 1200 ° C.) by the heating furnace 5 is introduced into the finishing mill 11 through the roughing mill 8, and reverse-rolled according to a preset pass schedule. The The steel plate 1 after the finish rolling is introduced into the accelerated cooling device 12, and is cooled to the target plate temperature, for example, under the condition of a constant cooling rate.

The cooled steel plate 1 is measured for the surface temperature by the outlet plate thermometer 13, and the residual stress distribution remaining on the steel plate 1 is calculated from the result.
Usually, when residual stress is present in the steel plate 1, deformation occurs when post-processing (strip cutting) of the product. Therefore, the hot leveler 14 and the multifunctional leveler 16 function as a cold leveler, and after rolling. The steel plate 1 is subjected to repeated bending and unbending deformations in the longitudinal direction in order to correct the stress state in the steel plate so that the residual stress becomes substantially zero. At the same time, the shape of the steel plate 1 is corrected so as to eliminate medium waves and ear waves generated after rolling.

Then, in order to make the steel plate 1 into the welding steel plate according to the present invention, the steel plate 1 is again introduced into the multifunctional leveler 16.
Specifically, the reduction amount of each divided backup roll of the multi-function leveler 16 is individually set, and the residual stress distribution in the plate width direction is adjusted as shown in FIG. For example, in the case of five divided backup rolls in the width direction, the amount of reduction of the central one to three divided backup rolls is increased so that the bending amount at the center of the steel sheet 1 by the leveling roll 17 is increased. By passing the steel plate 1 through the multi-function leveler 16 under such setting, compressive residual stress can be applied to the inside in the width direction.

When applying the stress distribution as shown in FIGS. 5A to 5C, the backup roll is composed of about 10 divided backup rolls, and the division corresponding to the position to apply the compressive stress is performed. It is preferable to compress only the backup roll and to apply a compressive residual stress to the steel sheet 1.
The present invention is not limited to the above embodiment.

  That is, those having the technical idea of pre-applying compressive residual stress in the vicinity of the part to be welded facing in the longitudinal direction to suppress or equalize longitudinal contraction (sheet shrinkage) of the steel sheet for welding Belongs to the present invention.

It is a conceptual diagram which shows the residual stress distribution of the steel plate for welding concerning this invention, and the shrinkage | contraction state after welding (macro view). It is a conceptual diagram which shows the residual stress distribution of the steel plate for welding concerning this invention (micro view). It is a figure which shows the object model in a simulation experiment. It is a figure which shows the result obtained by the simulation experiment. It is a conceptual diagram which shows the residual stress distribution of the steel plate for welding concerning this invention (another embodiment). It is the figure which showed the rectangular deformation amount of the steel plate which gave welding (plate | board thickness 12mm). It is the figure which showed the rectangular deformation amount of the steel plate which gave welding (plate thickness of 16 mm). It is the figure which showed the rectangular deformation amount of the steel plate which gave welding (plate | board thickness 22mm). It is the figure which showed the rectangular deformation amount of the steel plate which gave welding (plate | board thickness 28mm). It is the figure which showed the rectangular deformation amount of the steel plate for welding (plate thickness 34mm). It is the figure which showed the relationship between an average residual stress value and a rectangular deformation degree. It is the figure which showed the relationship between plate | board thickness and a rectangular deformation degree. It is the figure which showed the relationship between the number of rib strips, and a rectangular deformation degree. It is the figure which showed the relationship between the rib strip number and the rectangular deformation degree in the steel plate for welding of this invention. It is the schematic of a rolling apparatus. It is a conceptual diagram which shows the residual stress distribution of the steel plate concerning a prior art example, and the shrinkage state after welding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate for welding 2 Rib 3 Rolling device 8 Coarse rolling mill 11 Finishing rolling mill 12 Accelerated cooling device 16 Multifunctional leveler 17 Leveling roll (multifunctional leveler)
18 Backup roll (multi-function leveler)
W weld

Claims (6)

  A steel sheet for welding, wherein a compressive residual stress is preliminarily applied in the vicinity of a portion to be welded. A steel plate for welding that is welded facing in the longitudinal direction inside the width direction,
A welding steel sheet, wherein compressive residual stress is applied in advance to the inside in the width direction, and tensile residual stress is applied in advance to both ends in the width direction. When the site to be welded is located at a location 100 mm or more away from the end in the width direction,
A compressive residual stress is preliminarily applied to a region of 50 mm to 100 mm on both sides in the width direction of a portion to be welded, and the value of the compressive residual stress is 0 MPa to 50 MPa. Item 3. A steel sheet for welding according to item 1 or 2. When the part to be welded is located at a location within 50 mm from the end in the width direction,
A compressive residual stress is preliminarily applied to an area of 50 mm to 100 mm on the inner side in the width direction of the portion to be welded, and the value of the compressive residual stress is 0 MPa to 50 MPa. The steel plate for welding according to claim 1 or 2. When the site to be welded is located at a location 50 mm to 100 mm from the end in the width direction,
Compressive residual stress is applied in advance to the region on the inner side in the width direction of the part to be welded and 50 mm to 100 mm and to the region on the end in the width direction of the part to be welded and 50 mm or more. The steel sheet for welding according to claim 1 or 2, wherein a value of the compressive residual stress is 0 MPa to 50 MPa.   The welding steel plate according to any one of claims 3 to 5, wherein a variation in the compressive residual stress is ± 10 MPa or less.

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