JP5657053B2 - Multi-layer overlay welding of thick steel plates by submerged arc welding - Google Patents

Description

  The present invention relates to submerged arc welding used when manufacturing a steel plate and steel plate column having a thickness exceeding 60 mm and used for steel structures such as steel frames and bridges. The present invention relates to a method for multi-layer welding using submerged arc welding.

  In recent years, with the increase in the height of buildings using steel structures, it has become a popular practice to form thick steel plates into boxes and form multi-layer welds with submerged arc welding to form steel columns. It has become.

Japanese Patent Laid-Open No. 11-138267

However, when multi-layer welding is performed on a corner joint portion of a thick steel plate assembled in a box shape using submerged arc welding to form a columnar steel frame, there may be a problem in the tensile properties of the weld metal.
This is presumed that the occurrence of weld defects (cold cracks) occurring in the weld metal even during multilayer welding has an adverse effect on the tensile strength.

  The present invention aims to establish a welding technique that is less likely to cause welding defects even when multi-layer welding is performed on corner joints of extremely thick steel plates assembled in a box shape by submerged arc welding, focusing on such points. To do.

  In order to achieve the above-mentioned object, the present invention performs diffusibility in the weld metal by covering the whole workpiece with a heat insulating material for a predetermined time after the initial layer welding of the corner welded portion by submerged arc welding. It is characterized by promoting a reduction in the amount of hydrogen and preventing low-temperature cracking that tends to occur in the second and subsequent layers.

In the present invention described in claim 1, when forming an extremely thick steel plate having a thickness of more than 60 mm in a box shape and forming a steel column by multi-layer welding of the joint portion by submerged arc welding, the first layer is welded after the first layer welding. while leaving between slag welds the entire workpiece is coated with fiberglass insulation material was kept for 6 hours or more, after the end of welding after a predetermined time, it performed the second layer welding, thereafter welding end after 6 hours or more It is characterized in that the next layer welding is performed after the lapse. Further, in the present invention described in claim 2, in forming an extremely thick steel plate having a thickness of more than 60 mm in a box shape and forming a steel column by multi-layer welding the joint portion by submerged arc welding, The entire workpiece is covered with glass fiber insulation with the slag left, and the weld is kept warm until the weld temperature drops below 100 ° C. After the warming time has elapsed, the second layer is welded. It is characterized in that the next layer welding is performed after the lapse.

In the present invention, without removing the slag after the first layer welding, the whole work is further covered with a glass fiber heat insulating material for 6 hours or more, or the welded part is kept warm until the temperature of the welded part decreases to 100 ° C. or lower. Since the heat is retained by the post-heating effect, it is possible to prevent the occurrence of weld defects (cold cracks) that occur in the weld metal during multi-layer welding. In particular, the effect can be seen in welding a long steel plate columnar body that is troublesome to control the temperature of the weld.

It is a front view which shows the test material which applies the multilayer overlay welding method of the thick steel plate by submerged arc welding. It is a front view which shows the state of the weld metal in each pass in a welding part. It is a front view of the test material in the state which has applied the method of the present invention. It is a figure which shows the temperature measurement point position which measures the temperature history at the time of welding. It is a figure which shows initial layer temperature history. It is the macro photograph of the longitudinal cross-section in the welding part of each test body, (a) is test body S8N, (b) is test body S8S, (c) is a cross section of test body S8I. It is a macro photograph of the diagonal longitudinal section in the welding part of each test body, (a) is test body S8N, (b) is test body S8S, (c) is a cross section of test body S8I. It is a perspective view which shows the diagonal longitudinal cross section used for a macro test. It is a macro photograph after carrying out the picric acid corrosion of the welding cross section of test body S8N, (a) is a diagonal vertical cross section of test body S8N, (b) is a vertical cross section of test body S8N. It is a graph which shows the result of a tension test. It is a graph which shows the result of an impact test.

  In the present invention, when a thick steel plate having a thickness of 60 mm or more is assembled in a box shape and the joint portion is joined using submerged arc welding (SAW) multi-layer welding, the first layer (first layer) welding is performed by SAW welding. The entire work is covered with a heat insulating material without removing the slag.

  As a welding base material, two SA440C steel skin plates (1) and (2) having a plate thickness of 80 mm are arranged in an L shape as shown in FIG. 1, and a groove (3) is formed on the outer surface side of the contact portion. And using a tandem submerged arc welder as shown in FIG. 2, a 25 mm square SN490B material arranged as a backing metal (4) inside the groove portion was used as a test material. Welding was performed with a layer 4 pass finish. In the figure, reference numeral (5) denotes a restraining plate, and reference numeral (6) denotes a through hole provided in the restraining plate.

  Table 1 shows the welding conditions for this three-layer four-pass finish.

  In the welding method according to the present invention, as shown in FIG. 3, the flux (7) and slag (8) are not recovered until the next pass construction after each pass construction, and the whole work is wrapped with a heat insulating material (9). Covered and kept warm. In the embodiment of the present invention, the second pass welding is performed when 6 hours have elapsed after the end of the first pass welding or when the temperature of the workpiece near the welded portion becomes 100 ° C. or less. Thereafter, the welding of the next pass was performed after 2 hours from the end of welding in the previous pass. Hereinafter, the test body by this welding method is referred to as S8I.

  A conventional submerged arc welding method for producing a thick steel plate column collects flux and slag immediately after each pass. After the end of one pass, when the temperature of the workpiece near the welded portion becomes 250 ° C. or lower, the next pass is welded and this operation is repeated. Hereinafter, the test body by this welding method is referred to as S8N.

  In addition, as a different submerged arc welding method for producing thick steel plate columnar bodies, after each pass construction, the flux and slag are not collected until the next pass construction, and 6 hours have passed after the first pass welding, or welding The second pass was welded when the temperature of the workpiece in the vicinity of the part became 100 ° C. or less, and the second pass was welded after 2 hours from the end of welding in the previous pass after the third pass. Hereinafter, the test body by this welding method is referred to as S8S.

  FIG. 4 shows the arrangement of measurement points for measuring the temperature history when corner welding is performed by each welding method. The measurement points are 100 mm and 550 mm from the end of the web side skin plate (1) in the direction along the weld line, and from the open end on the surface side in the direction perpendicular to the weld line. 20mm position, 200mm position, 20mm position from the open end on the web side skin plate (1) on the back side, and 10mm position on the flange side skin plate (2), 40mm position and 100mm position from the corner, Measurement was performed at intervals of 10 seconds from the start of welding to the next welding.

  At the 550mm position on the surface side from the edge of the web-side skin plate (1) in the S8I specimen that covers the workpiece with a heat insulating material after welding in each pass and the S8S specimen that does not collect flux and slag after each pass. And at the measuring point 40mm from the flange side corner, the temperature maintenance time of 150 ° C or more is about 1.7 times in the first layer and about 50 minutes in time, and the total time is about 1.4 times. The difference was about 80 minutes.

  From the surface-side open tip in the direction perpendicular to the weld line on the web side, with the S8I specimen that coats the workpiece with a heat insulating material after welding in each pass and the S8S specimen that does not collect flux and slag after each pass construction At the measuring point at 20 mm and 40 mm from the corner on the flange side, the temperature maintenance time of 150 ° C. or more is about 1.4 times that of the first layer, and the time is about 35 minutes. A difference of about 100 minutes over 5 times was seen.

  In the comparison of the temperature history for each measurement point in the S8I test specimen in which the work is covered with a heat insulating material after welding in each pass, the temperature history is low at a position 200 mm from the surface-side open tip in the direction perpendicular to the weld line. However, there was no significant difference in the 150 ° C. maintenance time in the other welding vicinity (range of 20 to 60 mm). From this, it was found that controlling the temperature of the welded end of the box flange (20 mm position from the open end on the web surface side and 40 mm position from the flange side corner) is effective in confirming the autothermal effect. .

  Each of the S8I specimen that covers the work with a heat insulating material after welding in each pass, the S8S specimen that does not collect flux and slag after each pass, and the S8N specimen that collects flux and slag after welding in each pass The time for maintaining 100 ° C. and the time for maintaining 150 ° C. after each pass is set at a position 100 mm from the edge of the web side skin plate (1) in the direction along the weld line and 40 mm from the corner on the flange side. Table 2 shows the measurement results at the position measurement points.

The temperature history of the first layer is shown in FIG.
From this temperature history, it is confirmed that the S8I specimen that coats the workpiece with heat insulating material can maintain the workpiece temperature for a longer time than the S8S specimen that does not collect flux and slag and the S8N specimen that collects flux and slag after welding. did it.

6, 7 and 9 show macro photographs of the welds of each specimen. FIG. 6 is a macro photograph of a longitudinal section at the welded portion of each specimen, and FIG. 7 is a macro photograph of an oblique longitudinal section at the welded section of each specimen, with (a) representing the specimen S8N and (b) representing the specimen S8N. Specimen S8S, (c) is the result of the cross section of specimen S8I.
Here, as shown in FIG. 8, the oblique longitudinal section is a longitudinal section cut along an inclined surface that changes in the depth direction along the weld line.

  From this macrophotograph, in the specimen S8N, as shown in FIGS. 6 (a) and 7 (a), cracks were visually observed in the circled portions. In the oblique cross section macro, the crack width was about 15 mm and the depth was 20 to 25 mm. Moreover, according to the longitudinal section macro, cracks occurred at a depth of 15 to 25 mm and occurred at a pitch of about 30 mm. No cracks could be confirmed in the S8S specimen and the S8I specimen.

  With respect to the cracking of the S8N specimen, a macro test by picric acid corrosion was performed for the purpose of confirming a more detailed cracking position. Picric acid corrosion has a feature that the solidification structure of each pass can be clearly confirmed, and it was confirmed whether the origin of the crack penetrated into the weld metal part (DEPO) or the heat affected zone (HAZ).

  According to the result of the macro test by picric acid corrosion shown in FIG. 9, it is predicted that the crack is generated near the boundary portion of the third pass, and this crack is caused by the heat-affected zone in the second pass (in the one-pass weld metal). ) And the weld metal part and the weld metal part in the third pass.

  The weld metal of each test body was subjected to a tensile test according to JIS Z2241. Two test samples were formed at positions 10 mm (U), 25 mm (M), and 40 mm (L) from the upper surface of the skin plate of the weld metal of each test specimen. The result of the tensile test is shown in FIG.

In the S8N test specimen that had not been kept warm, cracks were confirmed in the test piece at a position 25 mm (NTM1, NTM2) from the top. On the other hand, in the S8S test body in which slag heat insulation was carried out, a test body in which the test piece at a position of 40 mm (STL1, STL2) from the upper part broke early and the tensile strength did not satisfy the target performance was confirmed.
On the other hand, in the S8I test body which performed heat insulation heat insulation, all showed the high yield strength value compared with the other test body.

  An impact test based on JIS Z2202 is performed on the metal at the welded connection of each specimen. Each test piece was sampled at a position of 7 mm from the upper surface and the lower surface in each of the weld metal portion (DEPO), bond portion (BOND), and heat affected zone (HAZ) of each test specimen. The result of the impact test is shown in FIG.

  As is clear from FIG. 11, the weld metal part (DEPO) showed the highest result with the S8I test body subjected to heat insulation. In the bond part (BOND), the S8I test body with heat insulation was stable in both the upper and lower parts, but the S8N test body without heat insulation and slag heat insulation were implemented. The S8S specimen was high at the top and low at the bottom. In the heat affected zone (HAZ), all the specimens showed high values.

  The difference in the impact value between the upper part and the lower part in the S8N test body and the S8S test body at the bond part (BOND) is considered to be due to the difference in the heat insulation situation compared to S8I. In the lower part, the effect of slag heat insulation is low and there is not much difference depending on the presence or absence of heat insulation. If the whole specimen is kept warm with the heat insulation material, S8I has a large heat insulation effect on the whole specimen, so good impact characteristics can be obtained even in the lower part. Predicted.

  From the above results, in SAW multi-layer welding (4 pass continuous welding) with a thickness of 80 mm with SA440 material, if no heat retention is performed, transverse cracks due to hydrogen occur in the weld metal, but slag It was confirmed that the generation of hydrogen cracking can be suppressed by further diffusing hydrogen, which is the cause, due to the heat retention effect by the heat insulating material.

  In addition, the thermal insulation effect by the heat insulating material is more effective than the thermal insulation effect by the slag, and the holding time of 150 ° C. or 100 ° C. at which the autothermal effect capable of reducing the amount of hydrogen in the weld metal is obtained is the thermal insulation heat insulation. It was confirmed that can be held for a longer time than slag insulation.

  It was confirmed that the tensile strength performance and impact performance of the weld metal were improved by the self-heating effect of the heat insulating material compared with the slag heat insulation.

  Furthermore, in the implementation of SAW multi-layer welding of SA440 steel with a plate thickness of 80 mm, the post-weld heat insulating material shall be used for one day after one pass welding under temperature control at the position of 40 mm on the surface of the web surface. It was found that the occurrence of cold cracking can be avoided by managing the holding time at 105 ° C. or higher as 5.0 hours and the holding time at 100 ° C. or higher as 8.5 hours or more.

  INDUSTRIAL APPLICABILITY The present invention can be used for welding thick steel plate columns having a thickness of more than 60 mm, in which corner welding portions of skin plates are multilayered by submerged arc welding.

  DESCRIPTION OF SYMBOLS 1 ... Web side skin plate, 2 ... Flange side skin plate, 3 ... Groove, 4 ... Back metal, 5 ... Restraint plate, 6 ... Through-hole provided in restraint plate, 7 ... Flux, 8 ... Slag, 9 ... Insulation.

Claims (2)

When forming an extremely thick steel plate with a wall thickness of more than 60mm in a box shape and forming a steel column by multi-layer welding the joints by submerged arc welding,
The entire workpiece while leaving the initial layer welding after the slag was kept covered to more than 6 hours at fiberglass insulation, does its incubation time second layer after welding, after subsequent welding completion after 6 hours or more following A method of multi-layer welding of thick steel plates by submerged arc welding, wherein layer welding is performed. When forming an extremely thick steel plate with a wall thickness of more than 60mm in a box shape and forming a steel column by multi-layer welding the joints by submerged arc welding,
After the first layer welding, the entire workpiece is covered with glass fiber insulation with the slag remaining, and the temperature is kept until the weld temperature drops to 100 ° C or lower. A multilayer overlay welding method for thick steel plates by submerged arc welding, wherein the next layer welding is performed after a lapse of a certain time after completion.