KR20080072937A - Steel plate for welding - Google Patents

Abstract

Provided is a steel plate in which a tensile residual stress is applied to an end portion of at least one side in the width direction and a portion to which compressing residual stress is applied exists in the inner portion in the width direction of the end portion to which the tensile residual stress is applied.

Description

Steel Plate for Welding {STEEL PLATE FOR WELDING}

The present invention relates to a steel sheet for welding.

As is well known, steel sheets commonly called thick steel sheets are used as structural materials such as bridges and ships.

When manufacturing such a thick steel plate, it rolls to predetermined dimension with a hot rolling mill, and then performs the cooling process by water cooling in an acceleration cooling apparatus. However, cooling unevenness occurs due to uneven temperature at the time of hot rolling, water cooling start temperature, and uneven water cooling of the accelerated cooling device, and causes residual stress on the thick steel plate after cooling, causing bending or bending ( There may be a shape defect such as undulation).

In the case of a thick steel plate having residual stress, when it is cut into a plurality of bars by post-processing and used for use, the residual stress unevenly distributed in the thick steel plate is opened by cutting, and the bar-cut steel is bent. The problem of "bar bend (camber)" occurred.

As a technique of eliminating such "residual stress generated in the thick steel sheet", a method of applying bending deformation to the thick steel sheet 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 stresses. Therefore, according to the situation of the thick steel sheet that needs to be corrected, the hot leveler or the cold leveler is selected to perform the steel sheet calibration. there was.

On the other hand, even if the steel sheet is subjected to leveler correction, when they are used as a welding structural material (welding steel sheet) such as a bridge or a ship, material shrinkage accompanying welding occurs in the steel sheet for welding, and its shape is greatly deformed. It is widely known among those skilled in the art.

16 shows the modified situation. For example, a welding steel sheet manufactured by employing techniques such as Patent Document 1 and having a residual stress in the steel sheet longitudinal direction being zero in the width direction of the plate is assumed to be used as a structural material such as a bridge or a ship. Consider welding with ribs in the longitudinal direction (up and down direction in the drawing).

As a result, as shown in Fig. 16 (b), the welding steel sheet, which was rectangular before welding, contracted larger in the longitudinal direction than the widthwise end portion after the three-bar welding, and the upper and lower edges of the steel sheet for welding were concave. Deformed into shape. The reason for this is that the welded part is melted once during welding and solidified again afterwards, but the shrinkage occurs in the solidified portion at that time, and tries to reduce it.

That is, even in the case of a steel sheet having a residual stress of approximately 0 in order to suppress deformation after cutting the bar, when it is used as a steel sheet for welding, deformation due to material shrinkage may occur, which is a significant problem.

Conventionally, in order to avoid such a deformation | transformation, although the dimension setting which predicted the said deformation | transformation was performed, the deformation amount of the steel plate for welding varied with the shape of the rib or flange to weld, and it was very difficult to predict. In addition, even if the deformation amount can be predicted, when welding welding steel sheets largely deformed from a rectangle to each other by welding them horizontally or at right angles, a large gap (for example, 3 mm or more) is formed between the two steel sheets, making welding work difficult. There is a need to recut steel sheets. In particular, for welded steel sheets having a plate thickness of 25 mm or less, material shrinkage accompanying welding was large, and recutting processing was required in most cases.

Patent Literature 1 discloses a technique focusing on the above-described deformation during welding. This technique measures the surface temperature distribution of a thick steel plate hot-calibrated by a hot leveler with a thermometer, calculates residual stress distribution, etc. from the temperature distribution of the thick steel plate by computer, and deforms the amount of deformation during welding from this residual stress distribution. It is supposed to calculate a predetermined parameter that indicates the deviation of. In addition, by comparing the parameters with the allowable values preset according to the welding conditions of the user, the residual stress is reduced by using a leveler or a heat treatment furnace when the parameters are not within the allowable range.

Patent Document 1: Japanese Unexamined Patent Publication No. 2001-316757

Disclosure of the Invention

Problems to be Solved by the Invention

However, Patent Document 1 is a technique in which the variation of the deformation amount at the time of welding is within a certain range, and is not intended to zero or minimize the deformation amount accompanying welding. For example, even if the variation of the deformation amount can be within a certain range, as described above, when welding the welded steel sheets with deformation after welding, if there is a gap between them, it is unclear that there is a need for re-cutting or the like. Can not.

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

Means to solve the problem

In order to achieve the above object, the following technical means have been devised in the present invention.

That is, in the steel sheet for welding according to the present invention, a tensile residual stress is applied to at least one end of the width direction, and a portion to which compression residual stress is applied is provided on the inner side of the width direction of the end to which the tensile residual stress is applied. It is characterized by.

In addition, tensile residual stress is applied to both ends in the width direction, and the compressive residual stress is provided on the inner side in the width direction of both ends provided with the tensile residual stress.

The inventors of the present invention conducted experiments and studies to develop a welded steel sheet (hereinafter sometimes referred to as a steel sheet) which has almost no rectangular shape change after welding, and deformations caused by welding exist inside the steel sheet to which welding is performed. It is believed that residual stress is related.

Therefore, first, the residual stress in the steel sheet was reduced by a thermal method, or a steel sheet uniformed to almost O was prepared by using a hot leveler or a cold leveler, and a welding experiment was conducted with a seam as shown in FIG.

By that experiment,

(i) Most steel sheets have a larger shrinkage in the longitudinal direction at the center portion thereof than at their ends,

(ii) The variation in shrinkage between the steel sheets was consistently small in the steel sheet with reduced residual stress.

From these results, the inventors of the present invention found that "the residual stress influences in relation to the amount of shrinkage accompanying welding."

Subsequently, the present inventors conducted a welding experiment from the viewpoint of the invariable degree of the steel sheet after welding (whether the rectangular shape before welding maintained the shape after welding). As a result, some of the steel sheets which did not control the residual stress were superior to the non-deformation degree than the steel sheets which controlled the residual stress to almost zero. As a result of investigating the residual stress distribution of the steel sheet having the desirable property, as shown in Fig. 1 (a), "the tensile stress remained at both ends in the width direction of the steel sheet and the compressive stress remained in the width direction".

Based on this result, the welding steel sheet which concerns on this invention is given the compressive residual stress in the width direction inside to which welding is performed, and the tensile residual stress is given to the both ends of the width direction. This steel sheet maintains a rectangular shape with little change in shape even after welding.

Since the residual stress distribution is macroscopic with respect to the steel sheet, the inventors of the present application have studied from a microscopic perspective. As a result, when welding with ribs or flanges is carried out, the molten material portion shrinks when it cools and solidifies again by a gas flame or an arc discharge, and a tensile stress due to the shrinkage occurs, resulting in deformation of the steel sheet in the longitudinal direction. The mechanism that caused this is revealed.

Thus, as shown in Fig. 2, it has come to the idea that a compressive residual stress that resists the tensile stress may be provided in the vicinity of the site where welding is performed. Later, it was found that shrinkage deformation occurred but the degree of deformation from the rectangle was small (keeping the rectangular shape).

Based on this idea, the tensile strength of the welded steel sheet according to the present invention is applied to both ends in the width direction, and the compressive residual stress is applied to the entire region in the width direction of both ends to which the tensile residual stress is applied. Doing. This steel sheet hardly undergoes a shape change even after welding.

In addition, the inventors of the present invention have found that the value of the compressive residual stress should be 0 MPa to 50 MPa through computer simulation experiments and the like.

Preferably, the deviation of the compressive residual stress may be ± 10 MPa or less. The deviation of the compressive residual stress as referred to herein means a deviation at the top of the compressive residual stress (for example, in the middle of the plate width direction in the case of FIG. 1A).

In addition, the value of residual stress as a whole of the said steel plate is O.

Effects of the Invention

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

1 is a conceptual diagram showing the residual stress distribution of the steel sheet for welding and the contracted state after welding (macro),

2 is a conceptual diagram showing the residual stress distribution of the steel sheet for welding according to the present invention (microscopic),

3 is a diagram illustrating a target model in a simulation experiment;

4 is a diagram showing results obtained in a simulation experiment;

5 is a conceptual diagram showing the residual stress distribution of the steel sheet for welding according to the present invention (another embodiment),

6 is a view showing a rectangular deformation amount of the steel sheet subjected to welding (plate thickness 12 mm),

7 is a view showing a rectangular deformation amount of the steel sheet subjected to welding (plate thickness 16 mm),

8 is a view showing a rectangular deformation amount of a steel plate subjected to welding (plate thickness 22 mm),

9 is a view showing a rectangular deformation amount of the steel sheet subjected to welding (plate thickness 28 mm),

10 is a view showing a rectangular deformation amount of the steel sheet for welding (plate thickness 34 mm),

11 is a view showing a relationship between an average residual stress value and a rectangular deformation degree;

12 is a view showing the relationship between the plate thickness and the rectangular deformation degree,

13 is a view showing a relationship between the number of rib bars and a rectangular deformation degree;

14 is a view showing a relationship between the number of rib bars and a rectangular deformation degree in the steel sheet for welding of the present invention;

15 is a schematic view of a rolling apparatus,

16 is a conceptual diagram showing a residual stress distribution of the steel sheet according to the prior art and the contracted state after welding.

Explanation of the sign

1: steel plate for welding 2: rib

3: rolling equipment 8: jaw rolling mill

11: finishing mill 12: accelerated cooling device

16: Multi-function Leveler 17: Leveling Roll (Multi-Function Leveler)

18: Back up roll (multifunctional leveler) W: Welded part

Implement the invention  Best form for

EMBODIMENT OF THE INVENTION Hereinafter, the steel plate for welding which concerns on this invention is demonstrated based on drawing.

1 and 2 show a welding steel sheet 1 according to the invention.

As shown in Fig. 1 (a), when the welded steel sheet 1 (hereinafter sometimes referred to simply as a steel sheet) is measured with a residual stress in the cross section in the width direction, a compressive residual stress is applied to the inside of the width direction. Tensile residual stress is applied to both sides in the width direction. The stress distribution curve has a trapezoidal shape that is convex downward.

Residual stress prescribed | regulated by this steel plate 1 is an average value of the plate | board thickness direction, and what kind of residual stress distribution of a plate | board thickness direction may be sufficient.

The integrated value of the tensile residual stress and the integrated residual stress are the same, and the residual stress value in the entire steel sheet 1 is zero.

FIG. 2 (a) shows a situation in which the ribs 2 are welded in the longitudinal direction (steel plate rolling direction) to the inside of the width direction of the steel sheet 1 having such a residual stress distribution.

The microscopic view of this situation (only the vicinity of the weld portion W) is shown in FIG. 2 (b). As can be seen from this figure, the weld portion W is once melted by a gas flame or an arc, so that the residual compressive stress originally existed is lost. Thereafter, material shrinkage occurs as the welded portion W solidifies. Since the welded portion W is constrained by the steel plate around it, the tensile residual stress remains as a site where the material shrinkage and residual material shrinkage. Due to the tensile stress, deformation in the longitudinal direction of the steel sheet occurs.

By the way, the compressive residual stress is previously given to the width direction outer side of the welding part W and the shrinkage | contraction part, and it is in the situation which does not produce the said material shrinkage. Therefore, the shrinkage of the longitudinal direction does not occur even as the whole steel plate 1.

[Simulation experiments and results]

Next, the specific value of the compressive residual stress previously given to the steel plate 1 of this embodiment is demonstrated.

The inventors of the present invention have specifically investigated the deformation behavior of the steel sheet 1 when rib welding using a thermoelastic three-dimensional FEM model in order to obtain a steel sheet with less deformation during welding.

As shown in FIG. 3, the size of the steel sheet 1 used in the model experiment is 16 mm thick, 2000 mm wide, and 500 mm long. The shape of the attached ribs 2 was 15 mm in thickness, 150 mm in width (height), and 500 mm in length, and the number of attachment ribs was varied in the range of 1 to 5.

As the steel sheet 1 to be welded, (i) normal steel (no residual stress control), (ii) residual stress reduction steel (residual stress value in the width direction is 5 MPa), and (iii) no residual stress steel ( Three of the ideal steel plates with no residual stress were used.

As a condition of rib welding, the heat input by welding was 1.7 kJ / mm (320A x 32V x 24 cm / min.), And the welding length (weaving width) was made into the general thing of 8 mm. This welding condition is almost the same even if the thickness of the steel sheet or the thickness of the ribs 2 is changed.

Under these conditions, the value of the residual stress generated when the ribs 2 were welded, the influence on the circumference of the weld portion W after the rib welding, and the like were confirmed.

As a result,

(Iii) By rib welding, a tensile residual stress of about 300 MPa is generated in the weld portion W,

(Ii) By rib welding, the area where the initial residual stress is changed (heat affected area) is ± 50 mm on both sides of the rib welding position,

(Iii) The influence of the shrinkage of the material of the welded portion W on the periphery is an increase in the compressive stress, and the influence is changed by the number of ribs (6 MPa / piece).

In view of the above, the present inventors simulated the conditions for obtaining the steel plate with few shape changes after welding, changing experimental conditions.

As a result, when the position of the rib welding is an inner side (width direction inner side) of 100 mm or more from the end of the steel plate 1, the area of -100 to -50 mm and 50 to 100 mm based on the position of the rib welding. In (the area | region of 50-100 mm of both sides of the welding part W), the compressive residual stress was previously given and it turned out that the value should just exist in the range of 0 MPa-50 MPa.

Therefore, in the case of the steel sheet having the initial residual stress distribution as shown in Fig. 4A, the above conditions are satisfied after the rib welding, and the steel sheet is less in shape change after the welding. In addition, since the weld portion W is once melted and the residual stress disappears, even if the initial residual stress at the rib welding position is -50 MPa or less (for example, -70 MPa) as shown in FIG. none. However, since the position to which the rib 2 adheres does not need to be determined strictly, it is preferable to set it as the residual stress distribution of FIG.

When the position of the rib welding is within 50 mm from the end of the steel plate 1, the compressive residual stress is applied in advance to an area of 50 to 100 mm in the inner side (width direction inner side) than the position of the rib welding, and the value It turned out that it should just be in the range of 0 MPa-50 MPa. Therefore, if the steel sheet has an initial residual stress distribution such as a solid line or broken line shown in Fig. 4 (c), the above conditions are satisfied after the rib welding, and the steel sheet with less shape change after welding is obtained.

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, the area | region of 50-100 mm of an inner side (width direction inner side) rather than the attachment position of the rib 2 The compressive residual stress in the range of 0 MPa to 50 MPa is previously given to the film, and at the same time, the compressive residual stress of 0 MPa to 50 MPa in an area of 50 mm or more outside of the steel sheet (the widthwise end side) than the attachment position of the rib 2 If it is given in advance, it came to discover what is good. Therefore, if the steel sheet has an initial residual stress distribution such as a solid line or broken line shown in Fig. 4 (d), the above conditions are satisfied after welding, and the steel sheet with less shape change after welding is obtained.

In addition, since the welding portion W is once melted and the initial residual stress disappears, the initial residual stress at the rib welding position is -50 MPa or less (for example, -70 MPa) as shown in the solid line of FIG. ) Does not matter.

The inventors have found that a fairly good result (less deformation after welding) can be obtained if the deviation of the compressive residual stress is ± 10 MPa or less.

Although FIG. 4 mentioned above microscopically looked at the residual stress distribution initially given to the steel plate with few deformation | transformation, FIG. 5 shows the macroscopic view of the initial residual stress distribution (distribution in the whole width direction of a steel plate). Similarly, Figure 1 (a) is a macroscopic view of the initial residual stress distribution.

In the steel sheet according to the present invention, the compressive residual stress is applied to the vicinity of the site where the welding is performed in advance, and as shown in Figs. 5 (a) to 5 (c), the conditions described above corresponding to the rib 2 attachment position are shown. The compressive stress (initial residual compressive stress of 0 MPa to 50 MPa in the region of 50 to 100 mm on both sides of the welded portion W) is given. In addition, since the value of residual stress is 0 as the whole steel plate 1, the tensile residual stress which removes a compressive residual stress is also provided. Therefore, the residual stress distribution has an uneven shape in the width direction.

However, it is often not known exactly at which point in the steel sheet 1 the rib welding is performed at the time of producing the steel sheet 1 according to the present invention. This is because most of the time, the user cuts and trims the steel sheet 1, and there are few cases where the steel sheet 1 is used as a member as it is in the factory. Therefore, the compressive stress that satisfies the above-described condition is given corresponding to the position where the rib 2 is attached, and as shown in Fig. 1 (a), the compressive residual stress is applied to the inside of the width direction in which the welding in the longitudinal direction is performed. It is very preferable that the steel sheet 1 have a stress distribution with tensile residual stress at both ends in the width direction. On the other hand, the inside of the width direction of the steel plate 1 is a site | part where rib welding is performed, and as mentioned above, although inside may be 100 mm or more from the edge part of the steel plate 1, even if it is inside 200 mm or more from the edge part of the steel plate 1, There is no problem.

[Method of measuring residual stress]

In addition, in measuring the residual stress of the steel plate 1, various methods can be adopted as the measuring method. For example, a method of (i) punching a steel sheet to be subjected to a target, and attaching a strain gauge directly to the site, and measuring the residual stress value using the strain gauge (punching, puncturing), (ii) hot Based on the surface temperature distribution of the steel sheet at the point of completion of the calibration, the amount of indentation by the cold leveler, and the like, there is a method of obtaining an average value of the residual stress in the sheet thickness direction.

In the present embodiment, the initial residual stress is measured by the drilling method. Specifically, a split test piece (bar piece) is considered to have a pitch of 100 mm from both ends in the width direction of the target steel sheet, and from the end of the split test piece on the center line and in the longitudinal direction, "between the roll centers of the cold leveler which corrected the steel plate. A strain gauge is to be attached at a position of +100 mm.

Experimental Example

6 to 10, ribs 2 made of five bars in the longitudinal direction of the steel sheet 1 (sometimes referred to as the steel 1 of the present invention) to which the residual stress distribution is satisfied are satisfied. The test result which welded and attached and calculated | required the rectangular deformation degree (delta) of the board length direction at that time is shown. 6 indicates a residual stress value measured using a drilling method, and a solid line indicates a calculated residual stress value calculated in consideration of the temperature distribution and the calibration conditions of the steel sheet 1.

The steel 1 of this invention is the same as each figure (d), and the residual stress value of 100 mm or more inside from both ends of a width direction is 0 MPa--50 MPa. As a comparative example, conventional steels (usually steels, control of residual stress, each drawing (a)], residual stress reduction steels (each drawing (b)), and ordinary straightening steels (traditional steels calibrated with a leveler or the like) , (C) is rib welding.

The steel plate 1 which welded the rib 2 has five types, and the board thickness is 12, 16, 22, 28, and 34 mm, the width is 2000 mm, and the length is 9000 mm. The shape of the attached rib 2 was 15 mm in thickness, 150 mm in width (height), and 9000 mm in length similarly to the simulation experiment.

The rectangular deformation degree δ of the steel sheet 1 is, for example, in the steel sheet 1 of FIG. 1B based on one of the cross sections of the left and right (width direction) of the shrinkage amount of one edge portion of the upper and lower sides (rolling direction). It measures and supposes that it converted into the value per 10m in length. In this experimental example, the upper limit of rectangular deformation degree (delta) shall be 1.2 mm. This is because the steel sheet gap that can be welded is about 3 mm (about 1.5 mm per sheet) is clear from the field results.

As can be seen from the results in Figs. 6 to 10, it can be seen that, in all the plate thicknesses, the steel 1 of the present invention has a rectangular deformation degree δ of 1.2 mm or less.

In conventional steel, in which the compressive stress remains in the center portion and both ends in the width direction, and the tensile stress remains in the region between the center portion and the both ends, a rectangular deformation degree δ of 1.5 mm or more occurs in all the plate thicknesses. It became clear that it was inappropriate.

In residual stress reducing steel or ordinary straightening steel where residual tensile stress of 50 MPa or less exists in the plate width direction, the rectangular strain degree δ is 1 mm to 3 mm, and the shrinkage in the longitudinal direction is large, which is not suitable for welding. .

Moreover, in conventional steel etc., the shrinkage amount in the width direction inside is very large compared with the both ends. On the other hand, in the steel 1 of the present invention, since the rectangular deformation degree δ in the width direction is substantially the same value, and thus maintains a rectangular shape, the welded steel sheet 1 when the welding of the steel 1 of the present invention is performed by welding. And 1) it is difficult to produce a problem that the gap between 1 and 2 varies depending on the position in the width direction, so that welding is quite easy.

In addition to the above experiments, the inventors of the present invention have ribs made of five bars in the longitudinal direction with respect to the inventive steel 1 having various sheet thicknesses or the inventive steel 1 having substantially the same distribution of residual stress but different stress values. (2) was welded and affixed, and rectangular deformation degree (delta) was calculated | required. The results are shown in FIGS. 11 and 12.

As can be seen from FIG. 11, in order to achieve a rectangular deformation degree δ (<1.2 mm) which is practically not a problem, the compressive residual stress applied inside the width direction of the steel sheet 1 is 0 MPa to 70 MPa, preferably 0. It may be MPa to 50 MPa. This is consistent with the results of computer simulations.

12 shows a plurality of results of the welding experiment, the average residual stress of (i) -40 to -20 MPa, (ii) -20 to 0 MPa, (iii) 0 to 20 MPa, and (iii) 20 to 40 MPa It is divided into four types of phosphorus, and is a figure which showed the relationship of the plate | board thickness and rectangular deformation degree (delta). As is clear from this figure, the steel sheet belonging to the steel 1 of the present invention (the residual stress value in the width direction of -50 MPa to 0 MPa, i.e. and (ii)) is surely provided that the sheet thickness is 10 mm or more. In this way, the rectangular deformation degree δ is 1.2 mm or less, which is a steel sheet suitable for welding.

Furthermore, even if the residual stress value in the width direction is 0 to 20 MPa, the sheet thickness is 25 mm or more, or the sheet thickness is 35 mm or more even if the residual stress value in the width direction is 20 to 40 MPa, so that the rectangular deformation degree δ is surely 1.2. It turned out that it will be mm or less, and it becomes a steel plate suitable for welding.

FIG. 13 and FIG. 14 show that 2, 3, 5, and 7 bar ribs 2 are welded and attached to each of the steel 1, the conventional steel, the residual stress reducing steel, and the ordinary straightening steel of this embodiment, and then The result of having obtained the rectangular deformation degree (delta) of the plate length direction of is shown.

As the number of bars of the ribs 2 attached by welding increases, the rectangular deformation degree δ increases in all steel sheets. However, the steel 1 of the present invention has a smaller degree of increase, and if the ribs 2 are within 7 bars, the rectangular shape The deformation degree δ does not exceed 1.2 mm.

[Steel Sheet Manufacturing Equipment]

15 schematically shows a rolling apparatus 3 for welding steel sheet 1, thick steel sheet according to the present invention. On the upstream side of the rolling apparatus 3, a heating furnace 5 for heating the slab 4 is provided, and on the downstream side of the heating furnace 5, a pair of work rolls 6 and 6 and a working roll are provided. A roughing mill 8 with back up rolls 7, 7 and back up rolls is provided. Moreover, the finishing rolling mill 11 which has a pair of work rolls 9 and 9 and a pair of back up rolls 10 and 10 is provided downstream of the rough mill 8. As shown in FIG.

On the downstream side of the finish rolling mill 11, an accelerated cooling device 12 (cooling device) for cooling the steel sheet 1 on which the rolling is finished in the finish rolling mill 11 is provided. The accelerated cooling device 12 forcibly cools the steel sheet 1 by spraying cooling water on the steel sheet 1 to realize a predetermined plate temperature.

In the vicinity of the outlet side of the accelerated cooling device 12, an outlet plate thermometer 13 such as a radiation thermometer or a thermo viewer is provided, and the temperature distribution on the surface of the steel sheet can be measured. For this reason, the surface temperature distribution of the steel plate 1 immediately after cooling can be known. Since it is clear from past results that the surface temperature distribution and the residual stress distribution in the steel sheet 1 have a predetermined relationship, the residual stress distribution in the steel sheet 1 can be estimated from this measurement result.

A hot leveler 14 is provided downstream of the accelerated cooling device 12. The hot leveler 14 is provided with a plurality of leveling rolls 15, 15.

In addition, the multifunctional leveler 16 is provided at an offline position of the present rolling line. The multifunctional leveler 16 is provided with a plurality of leveling rolls 17, 17... Which are arranged in a zigzag manner at the top and bottom, and each leveling roll 17 is a back-up roll for reinforcing the leveling roll 17. 18 is arrange | positioned. This backup roll 18 is comprised by the continuous multiple back-up roll (not shown) in the axial direction (for example, 3-5 pieces), and each divided back-up by a rolling reduction device (not shown). A roll can be rolled independently. Therefore, only a part of the leveling roll 17 can be pressed toward the steel sheet 1 to correct a part of the shape of the steel sheet 1 or to impart the residual stress in the width direction to the steel sheet 1.

The procedure to manufacture the steel plate 1 for welding which concerns on this invention using the rolling apparatus 3 mentioned above is demonstrated.

First, the slab 4 heated at a predetermined temperature (about 1200 ° C) by the heating furnace 5 is introduced into the finishing rolling mill 11 via the rough rolling mill 8, and a predetermined pass schedule is set. Reverse rolling is accordingly. The steel sheet 1 after finish rolling is introduced into the accelerated cooling apparatus 12, and cooled to the target plate temperature, for example, under a condition where the cooling rate is constant.

The surface temperature of the cooled steel plate 1 is measured by the outlet side plate thermometer 13, and the residual stress distribution remaining in the steel plate 1 is calculated from the result.

Usually, when residual stress exists in the steel sheet 1, deformation occurs when the product is subjected to post-processing (bar cutting), so that the hot leveler 14 or the multifunctional leveler 16 functions as a cold leveler, By repeatedly applying the steel sheet 1 in the longitudinal direction in order to repeatedly bend and deflect, the stress state in the steel sheet is corrected, so that the residual stress is almost zero. In addition, the shape of the steel sheet 1 is modified to remove the medium wave or edge wave generated after rolling.

Then, in order to make the steel plate 1 into the steel plate for welding which concerns on this invention, the steel plate 1 is introduce | transduced into the multifunctional leveler 16 again.

In detail, the rolling reduction amount of each divided backup roll of the multifunctional leveler 16 is set individually, and the residual stress distribution of the board width direction is adjusted like FIG. 1 (a). For example, in the case of five divided back-up rolls in the width direction, the rolling reduction amount of one to three divided back-up rolls in the center is increased to increase the amount of bending in the center of the steel sheet 1 by the leveling roll 17. . By passing the steel sheet 1 through the multifunctional leveler 16 under such a setting, the compressive residual stress can be added inside the width direction.

On the other hand, in the case of providing stress distribution as shown in Figs. 5 (a) to 5 (c), the back-up roll is composed of about 10 divided back-up rolls, and the division corresponding to the position at which the compressive stress is to be applied. What is necessary is just to reduce a backup roll and to give compressive residual stress to the steel plate 1.

In addition, this invention is not limited to the said embodiment.

That is, it belongs to this invention to have the technical idea of providing compressive residual stress in the vicinity of the site | part to which welding in the longitudinal direction is performed previously, and suppressing or equalizing shrinkage (plate shrinkage) of the longitudinal direction of a steel plate for welding.

Claims (5)

A steel sheet having a tensile residual stress applied to at least one end in the width direction, and a portion provided with a compression residual stress on the inner side in the width direction of the end portion provided with the tensile residual stress. The method of claim 1, The steel sheet which has tensile residual stress applied to the both ends of the width direction, and the part provided with the compression residual stress in the width direction inner side of the both ends to which the said tensile residual stress was provided. The method of claim 2, A steel sheet in which tensile residual stress is imparted to both ends in the width direction, and compressive residual stress is imparted to the entire inner side of the width direction of both ends to which the tensile residual stress is applied. The method according to any one of claims 1 to 3, Steel sheet having a value of the compressive residual stress is 0 MPa to 50 MPa. The method according to any one of claims 1 to 3, A steel sheet having a deviation of the compressive residual stress of ± 10 MPa or less.

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