JP2005219079A - Method for welding casting member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for welding a casting member with which the removal of stress with a peening at repair-welding time can surely be performed without entrusting experiences of a skilled worker. <P>SOLUTION: This welding method is performed by providing with; a welding step S1 for welding the welding part 1a in the casting member 1 composed of a cast iron or a cast steel; a peening step S4 for peening the welded part 1a; and strain measuring steps S2, S5 for measuring the strain near the welded part developed with the welding. The strain near the welded part during welding and in the peening is continuously measured and the peening is started before the strain measured just after welding exceeds a prescribed maximum value and the peening is continued until the strain is lowered to not more than the minimum value of the prescribed value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for welding a cast member made of cast iron or cast steel.

Cast iron is a low-melting-point iron alloy mainly containing C2.5 to 4.0% and Si 0.5 to 3.0%. Moreover, as welding of cast iron, covering arc welding and oxygen acetylene gas welding are mainly performed. Cast iron welding is generally used for repairing casting defects, building up, welding repair of large machines, and the like.
However, cast iron has a problem of poor weldability. That is, when cast iron is welded, the heat-affected zone turns white. Birch is hard and brittle and has a significantly larger amount of shrinkage than the base metal base, and therefore, a large residual stress is generated during shrinkage and is easily cracked.

  On the other hand, cast steel is a cast product of steel and is easier to weld than cast iron, but similarly, there is a problem that a large residual stress is generated during shrinkage and is easily broken.

Conventionally, heat treatment (preheating and postheating) and peening have been mainly used to relieve thermal stress generated during welding of cast iron or cast steel.
By heat treatment (preheating, postheating), the thermal stress generated when the vicinity of the weld is locally heated can be reduced. However, in the case of welding repairs for large machines, it is possible to remove stress by heat treatment during manufacturing, but for large machines after installation on site, it is difficult to apply heat treatment, and peening with an air hammer or the like is applied to the weld repair part. Applied. Peening is to locally compress and deform the weld repair portion after welding.

  Note that non-patent documents 1 to 3 generally disclose welding of cast iron or cast steel. Patent Documents 1 and 2 are disclosed as means for relaxing thermal stress during welding.

  Patent Document 1 “Welding Repair Method for High Cr Cast Iron Products” preheats a high Cr cast iron product with casting defects to a temperature of 600 to 800 ° C., and maintains the temperature at 600 ° C. or higher when repairing the weld. Even after the end of welding, the heat treatment is immediately performed at a temperature of 600 ° C. or higher and then gradually cooled to room temperature at a cooling rate of 50 ° C. or lower per hour.

  In the method of overlaying welding a high-strength metal in multiple passes on the surface of a base material made of a material having high cracking sensitivity, the “building-up welding method” of Patent Document 2 is for forming an initial layer covering the surface of the base material. Using welding conditions that limit the heat input of each pass to a predetermined value or less and generate fine cracks in the weld beads of each pass, first separate the weld beads in parallel and the adjacent weld beads on the base metal surface. Then, a weld bead is formed so as to overlap the weld beads between adjacent weld beads.

Japanese Patent Application Laid-Open No. 07-214313, “Welding repair method for high Cr cast iron products” JP 2000-102866 A, “Overlay welding method”

“Basics of Welding Technology”, Welding Society, Industrial Bulletin Publishing, P115 “Cast Iron and Cast Steel”, Welding and Joining Handbook, Welding Society, Maruzen, P860-867 “Welding of cast iron”, technical guide from welding, Kobe Steel, 2000.11 No. 367, P1-8

  As described above, generally, when welding is performed on cast iron or cast steel, there is a concern about the occurrence of weld cracking due to deformation due to welding shrinkage, residual stress, or the like. In order to avoid this, in the case of large castings, stress can be removed by heat treatment using a large furnace at the time of manufacturing in the factory, but in the case of welding repair of large castings after installation, In many cases, peening with an air hammer or the like is performed on the weld repair portion in order to reduce welding shrinkage and prevent weld cracking.

  However, the peening needs to be performed at a high temperature in the welded portion, and the time until the peening starts after the end of welding and the degree of peening are important factors. However, peening at the time of repair welding is left to the experience of a skilled worker, and the result depends on the skill level of the worker, and even if peening is performed, a weld crack may occur. Therefore, it has been difficult to surely remove stress by peening by a general worker with low skill level.

  The present invention has been developed to solve such problems. That is, the objective of this invention is providing the welding method of the cast member which can perform reliably the stress removal by peening at the time of repair welding, without leaving to the experience of a skilled worker.

According to the present invention, a welding step of welding a welded portion of a cast member made of cast iron or cast steel;
A peening step of peening the weld;
A strain measuring step for measuring strain in the vicinity of the weld where strain is generated by the welding, and
Continuously measure the strain near the weld during welding and peening,
A method for welding a cast member, characterized in that peening is started before the strain measured immediately after welding exceeds a predetermined maximum value and peening is continued until the strain falls below a minimum value of the predetermined value. Is provided.

According to the method of the present invention, the strain in the vicinity of the welded part during welding and peening is continuously measured, and peening is performed based on the measured value. It is possible to reliably perform peening based on highly objective data.
In addition, peening is started before the strain measured immediately after welding exceeds a predetermined maximum value, and peening is continued until the strain drops below the minimum value of the predetermined value. It is possible to suppress the stress by peening during repair welding.

According to a preferred embodiment of the present invention, in the strain measurement step, the temperature in the vicinity of the weld is measured simultaneously, and the temperature correction of the strain measurement value is performed.
By this method, temperature correction can be performed and distortion can be accurately measured.

In the strain measurement step, two strains orthogonal to each other are measured using a strain gauge, and after temperature correction, the strain is converted into stress.
By this method, the internal stress of the welded portion can be grasped by the stress conversion after temperature correction, and peening can be surely performed based on objective stress data with high reproducibility.

In the strain measurement step, it is preferable that a plurality of strain gauges are provided at positions symmetrical to the welded portion at positions where strain is generated by welding, and the maximum value, minimum value, or average value thereof is used.
By this method, it is possible to reduce the influence of variation in characteristics for each strain gauge and perform highly reliable measurement.

The predetermined maximum value of the strain is preferably set to a value whose stress converted value is sufficiently lower than the breaking strength of the cast member.
Thereby, since the generated stress of the welded portion is higher than that of the measuring portion, the generated stress of the welded portion can be suppressed to a value sufficiently lower than the breaking strength of the cast member.

Further, the predetermined minimum value of the strain is preferably set to a value immediately before welding or an intermediate value between the value immediately before welding and the predetermined maximum value.
Thereby, even when welding is repeated, the generated stress of the welded portion can be kept low.

Moreover, when welding of the said welding part consists of multiple passes and / or multiple layers, it is preferable to perform the said peening for every single pass or single layer welding.
By this method, even when multi-layer welding is performed, the generated stress in the welded portion can be kept low.

  As described above, the casting member welding method of the present invention has excellent effects such as the ability to reliably remove stress by peening during repair welding without leaving the experience of skilled workers.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

The method of the present invention makes it possible to weld a cast member more easily than in the past by quantitatively grasping the following items.
(1) Strain reduction management by peening based on data (2) Time from the end of welding to the start of peening (3) Time of peening

FIG. 1 is an apparatus configuration diagram for carrying out the method of the present invention. As shown in this figure, in the present invention, a strain detection sensor (a strain gauge 2 and a thermocouple 3) is attached in the vicinity of the welded portion 1a of the cast member 1, and during welding by the welding device 4 and during peening by the peening device 5. The strain is measured and the change is constantly monitored using the measurement recording device 6.
In this figure, the welding device 4 comprises a welding power source 4a and a welding torch 4b. Welding is preferably shielded metal arc welding (SMAW) or MAG welding (Metal Active Gas Welding), but the present invention is not limited to these and may be other welding.
Moreover, in this figure, although the peening apparatus 5 consists of the compressor 5a and the air hammer 5b, this invention is not limited to these, Other means may be sufficient.

FIG. 2 is a flow diagram of the method of the present invention. As shown in this figure, the method of the present invention includes a welding step S1, a peening step S4, and strain measurement steps S2 and S5.
In the welding step S <b> 1, the welded portion 1 a of the cast member 1 made of cast iron and cast steel is welded using the welding device 4. In the peening step S4, the welded portion 1a is peened using the peening apparatus 5. In the strain measurement steps S <b> 2 and S <b> 5, the measurement recording device 6 is used to measure the strain in the vicinity of the weld where strain is generated by welding.

Further, the measurement recording device 6 is used to continuously measure the strain in the vicinity of the weld during welding and peening, and the strain measured immediately after welding after the welding step S1 is compared with a predetermined maximum value. Peening is started before exceeding a predetermined maximum value (S3, S4).
Further, the peening is continued until the measured strain falls below a predetermined minimum value (S6, S4).

Furthermore, in the strain measurement step S2, the residual stress (internal stress) generated in the welded portion can be grasped by measuring the strain of two orthogonal axes using the strain gauge 2, correcting the temperature, and converting it to stress. Therefore, peening can be performed reliably based on objective stress data with high reproducibility.
Further, by analyzing the strain measurement data using the measurement recording device 6, it is possible to determine whether or not a crack has occurred in the welded portion.

  FIG. 3 is a schematic diagram of data obtained by the present invention. In this figure, the horizontal axis represents elapsed time, and the vertical axis represents strain. Further, the thin line A in the figure is the strain in the Y direction (direction perpendicular to the weld line) at a position 30 mm from the groove center, and the thick line B is the Y direction strain at a position 50 mm from the groove center.

In this figure, when welding is started, strains in both A and B become negative (compressed state) due to thermal expansion of the welded portion. Next, it can be seen that the strains of both A and B become positive (tensile state) as the weld shrinks due to cooling.
Moreover, the magnitude | size of the distortion of A and B is so large that it is close to a groove center, and it turns out that the actual distortion of a welding part can be estimated from the magnitude | size of the distortion of A and B, and becomes larger than the distortion of the thin wire | line A.
Therefore, it can be seen that by performing the peening immediately after welding by the method of the present invention, the strains A and B can be reduced, and the actual strain of the welded portion can also be reduced.

    In cold welding of cast iron or cast steel, short bead method (bead length: 10 to 15 mm) + peening immediately after welding is usually performed by covering arc welding. Conventionally, the welding time (bead length) and peening conditions (time until peening is started after the end of welding, peening strength, peening time, etc.) are left to the management of the worker, and as described above, highly skilled Skill was necessary.

    On the other hand, in the present invention, strain can be monitored and managed. This makes it possible to stabilize welding time and peening conditions, and repair work can be performed without requiring advanced skills. Moreover, welding quality can be improved by stabilizing welding time and peening conditions.

  Examples of the present invention will be described below.

FIG. 4 shows the shape of the specimen used and the measurement location of strain. In this figure, (A) is a plan view and (B) is a cross-sectional view taken along the line AA.
The test specimen was a cast steel material having the chemical composition shown in Table 1 (hereinafter referred to as SC480), and after cutting the cast steel material to a plate thickness of 40 mm, a groove groove simulating a groove for repairing was processed.

  In addition, in order to measure local strain due to welding, biaxial high-temperature strain gauges are attached to both sides of the 30 mm position (E1, E1 ′) and 50 mm (E2, E2 ′) from the groove center. It was. In addition, a biaxial general strain gauge was attached to a position (E3, E3 ') 100 mm from the groove in order to measure the strain of the entire test specimen. That is, the strain was measured at both the top and bottom symmetrical positions and both the front and back sides with the groove as the center.

  The temperature was measured at a position (not shown) adjacent to the strain gauge at the center of the specimen using a thermocouple. The strain and temperature were measured continuously from the start of welding until the specimen was cooled to room temperature. Regarding the amount of shrinkage, the amount of change in the distance between two points across the groove before and after welding and in the weld line direction was measured.

  As a welding material for coated arc welding (SMAW), a coated arc welding rod of JIS Z 3212 D5016 was used. Table 2 shows the chemical composition of the coated arc welding rod.

  In the covering arc welding, the multi-layer welding shown in FIG. 5A was performed. In this welding, preheating was not performed, and the interpass temperature was controlled to 50 ° C. or lower. The peening was tested under two conditions, one for each layer (with peening) and no peening (without peening).

  The welding conditions were the same with 19 passes, a current of 145 to 160 A, and a speed of 15 to 17 cm / min.

  FIG. 6 shows the strain measurement results of the coated arc welding. In this figure, (A) shows the case with peening, and (B) shows the case without peening. In each figure, the horizontal axis represents elapsed time, and the vertical axis represents strain. Also, thin lines A and A 'in the figure are strains in the Y direction (direction perpendicular to the weld line) at a position 30 mm from the groove center, and thick lines B and B' are strains in the Y direction at a position 50 mm from the groove center. It is.

From FIG. 6B, it can be seen that in the case of no peening, the amount of tensile strain in the vicinity of the weld increases for each welding pass, and eventually exceeds 3000 μs. Therefore, it can be seen that, without peening, the actual strain of the welded portion is larger than the strain of the thin wire A, so that a weld crack may occur.
In contrast, from FIG. 6A, when peening is performed, the tensile strain reduction due to peening can be clearly measured, particularly from a thin line A 30 mm from the groove, and finally can be suppressed to less than 3000 μs. Understand.

  As a welding material for MAG welding, a solid wire of JISZ 3312 YSW15 was used. Table 2 shows the chemical composition of the solid wire for MAG welding.

  In MAG welding, multi-layer welding shown in FIG. 5B was performed. In this welding, preheating was not performed, and the interpass temperature was controlled to 50 ° C. or lower. The peening was tested under two conditions, one for each layer (with peening) and no peening (without peening).

  The welding conditions were the same as the number of passes 26, current 155 to 160 A, voltage 22 to 23 V, and speed 20 to 45 cm / min.

  FIG. 7 shows the strain measurement results of MAG welding. In this figure, (A) shows the case with peening, and (B) shows the case without peening. In each figure, the horizontal axis represents elapsed time, and the vertical axis represents strain. In the figure, thin lines A and A ′ are strains in the Y direction (direction perpendicular to the weld line) at a position 30 mm from the groove center, and thick lines B and B ′ are strains in the Y direction at a position 50 mm from the groove center. It is.

From FIG. 7B, it can be seen that in the case without peening, the amount of tensile strain in the vicinity of the weld increases for each welding pass, and eventually exceeds 2000 μs. Therefore, it can be seen that, without peening, the actual strain of the welded portion is larger than the strain of the thin wire A, so that a weld crack may occur.
In contrast, from FIG. 7A, when peening is performed, the tensile strain reduction due to peening can be clearly measured, particularly from a thin line A 30 mm from the groove, and finally can be suppressed to less than 2000 μs. Understand.

The above-mentioned clad arc welding and MAG welding were under substantially the same conditions, but the total number of passes was 19 passes compared with 26 passes of MAG welding.
Table 3 summarizes the strain amount (Y direction) of 30 mm from the groove center after each layer welding. When peening was performed, two values before and after peening were shown.

  From this table, it can be seen that both the coated arc welding and the MAG welding reduce the strain amount to about half by performing peening. Also, the amount of strain after completion of welding was about half when the peening was performed compared to when the peening was not performed.

  Table 4 shows the measurement results of the contraction amount.

From this table, when peening was not performed, the shrinkage was 0.45 mm for MAG welding and 0.68 mm for coated arc welding. The amount of shrinkage was larger in the case of the coated arc welding in which the amount of welding in one pass was larger (the total number of passes was smaller).
In addition, when peening was performed, it was found that the shrinkage amount was about half, 0.27 mm for MAG welding and 0.40 mm for coated arc welding.

From the test results described above, the following was confirmed.
(1) Strain and temperature can be measured at a measurement position of about 30 mm from the groove center near the weld.
(2) Increase in strain due to welding and reduction in strain due to peening can be measured.
(3) Temperature can also be measured at a position adjacent to the strain gauge.
(4) As an effect of peening, an effect of reducing strain and shrinkage was confirmed.
(5) Compared to the case where peening is not performed, both the amount of strain and the amount of shrinkage are about half.
(6) As a management method for temperature, stress, and strain, measure strain and temperature near the weld (about 30 mm from the center of the groove), measure the temperature at the position adjacent to the strain gauge, and measure the measured strain value. Temperature correction should be performed.
(7) Strain is measured biaxially, corrected for temperature, converted to stress, and welding is performed while confirming that the stress is below the set value.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

It is an apparatus block diagram for enforcing the method of this invention. FIG. 3 is a flow diagram of the method of the present invention. It is a schematic diagram of the data obtained by this invention. It is an external view of the sample material in the Example of this invention. It is a figure which shows the lamination | stacking of the welding pass in the Example of this invention. It is a figure which shows the result of 1st Example of this invention. It is a figure which shows the result of 2nd Example of this invention.

Explanation of symbols

1 cast member, 1a weld, 2 strain gauge, 3 thermocouple,
4 welding equipment, 4a welding power source, 4b welding torch,
5 Peening device, 5a Compressor, 5b Air hammer,
6 Measurement recording device

Claims (7)

A welding step of welding a weld of a cast member made of cast iron or cast steel;
A peening step of peening the weld;
A strain measuring step for measuring strain in the vicinity of the weld where strain is generated by the welding, and
Continuously measure the strain near the weld during welding and peening,
A method for welding a cast member, characterized in that peening is started before the strain measured immediately after welding exceeds a predetermined maximum value and peening is continued until the strain falls below a minimum value of the predetermined value. .   The method for welding a cast member according to claim 1, wherein, in the strain measurement step, the temperature in the vicinity of the welded portion is simultaneously measured, and the temperature of the measured strain value is corrected.   2. The method for welding cast members according to claim 1, wherein, in the strain measurement step, two orthogonal strains are measured using a strain gauge, the temperature is corrected, and then converted into stress.   2. The strain measurement step, wherein a plurality of strain gauges are provided at positions symmetrical with respect to a welded portion at a position where strain is generated by welding, and a maximum value, a minimum value, or an average value thereof is used. A method for welding a cast member as described in 1.   The method for welding a cast member according to claim 1, wherein the predetermined maximum value of the strain is set such that a stress conversion value is sufficiently lower than a fracture strength of the cast member.   2. The casting member welding method according to claim 1, wherein the predetermined minimum value of the strain is set to a value immediately before welding or an intermediate value between the value immediately before welding and the predetermined maximum value. 2. The method for welding a cast member according to claim 1, wherein, when welding of the welded portion includes a plurality of passes and / or a plurality of layers, the peening is performed for each single pass or single layer welding.

Images