JP2010201491A - Method for repairing heat-resistant steel casting by welding and heat resistant steel casting having part repaired by welding - Google Patents

Abstract

The present invention provides a method for repairing a heat-resistant steel product having excellent low-cycle fatigue characteristics and capable of being realized with simple equipment, and a heat-resistant steel product having a weld repair part.
In a first step, buttering welding using covering arc welding is performed on a groove formed in a weld repair target portion of a base material to form a buttering welded portion. In the second step, TIG remelt treatment is performed, and the buttering weld is melted and then solidified to form the TIG remelt treatment 30. In a 3rd process, buttering welding is performed by covering arc welding and the 1st main welding part 40 is formed on a TIG remelt processing part. In the fourth step, main welding is performed by covered arc welding, and the second main weld 50 is formed on the first main weld.
[Selection] Figure 1

Description

  The present invention relates to a heat-resisting steel product welding repair method and a heat-resisting steel product having a weld-repair portion, and more particularly to a heat-resisting steel product welding repair method suitable for heat-resistant steel products such as a steam turbine casing of a thermal power plant, and The present invention relates to a heat resistant steel product having a weld repair portion.

  Various techniques aimed at reducing the hardness and residual stress of welded parts have been proposed as techniques for repairing heat-resistant steel products.

  For example, in welding repair of a low alloy cast steel product used under high temperature, high pressure, and high stress for a long time, there is a method of performing preheating and stress relief annealing using a simple heating element (for example, see Patent Document 1).

  In addition, in the temper bead method in which a plurality of remaining layers are stacked on the first layer and welded, and the hardening region on the base material side generated in the first layer is tempered by the welding heat of the remaining layer and disappears. A method of gradually tempering the hardened zone by changing the supply amount of the welding wire that forms the remaining layer in response to the change in the welding speed (for example, refer to Patent Document 2), There is a method (for example, refer to Patent Document 3) in which a pad is arranged so as to surround the initial layer formation scheduled position, and the initial layer is formed along the pad.

  In addition, a welding metal having a transformation start temperature from austenite to martensite of 150 to 300 ° C. is formed, and the surface of the final layer is subjected to TIG remelt treatment (for example, see Patent Document 4) or by buttering welding. After the first layer is formed, a half bead method is performed, followed by a method of performing main welding by TIG welding (see, for example, Patent Document 5) or by forming a first layer by buttering welding so that adjacent beads overlap each other. There is a method of performing the main welding after applying the temper bead method for a long time (for example, see Patent Document 6).

JP 56-163091 A JP 2000-271742 A JP 2007-130654 A JP 2000-33480 A JP 2006-21206 A JP 2007-21530 A

  However, according to the method disclosed in Patent Document 1 described above, depending on the shape of the weld repair location, it may be impossible to set the simple heating element, or a uniform temperature state cannot be obtained. There is. Moreover, in stress relief annealing, since it will be in a local annealing state, there is a risk that the entire cast steel product will be distorted starting from the weld repair portion. In particular, when the vicinity of the mating surface of the casing is repaired by welding, it is necessary to make a surface by machining due to distortion, or in some cases, the casing cannot be regenerated.

  In addition, in the method disclosed in the above-mentioned Patent Document 2 or 3, since measures against residual stress are not taken, there is a possibility that the life is shortened. Furthermore, according to the method disclosed in Patent Document 3, depending on the shape of the weld repair location, the contact material may not be appropriately disposed.

  Further, a welding material having a transformation start temperature from austenite to martensite of 150 to 300 ° C. tends to be susceptible to low-temperature cracking, and in the method disclosed in Patent Document 4 described above, cracking occurs. Trouble is considered. Moreover, since it becomes a martensite structure, the hardness of a welded part increases and the hardness distribution including a base material has undulations. For this reason, there exists a possibility that low cycle fatigue strength may fall remarkably.

  Moreover, in the method disclosed in the above-mentioned Patent Document 5, since TIG welding is performed after the half bead method is performed, the penetration depth by TIG welding may exceed the metal thickness of the first layer weld, It is possible to form a hardened layer, which requires a very high skill.

  In the method disclosed in Patent Document 6 described above, temper bead welding is performed with a predetermined short bead length so that adjacent beads overlap each other for each unit region. This technique requires high skill, and the welding speed and turn-up speed are likely to vary depending on the welder, so the quality of the welded part can be stabilized, including techniques to prevent the occurrence of weld defects between adjacent unit weld areas. Issues remain in terms of sex.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a heat repair method and weld repair portion for heat-resistant steel products that are excellent in low cycle fatigue characteristics and can be realized with simple equipment. It is providing the heat-resistant steel goods which have this.

  In order to achieve the above-described object, the welding repair method for heat-resistant steel products of the present invention includes the following first to fourth steps.

  In the first step, buttering welding using covered arc welding is performed on the groove formed in the weld repair target portion of the base material to form a buttering weld portion. In the second step, TIG remelt treatment is performed, and the buttering weld is melted and then allowed to cool and solidify to form a TIG remelt treatment. In the third step, buttering welding using covered arc welding is performed to form a first main weld on the TIG remelt treated part. In the fourth step, main welding is performed by covered arc welding, and a second main weld is formed on the first main weld.

  In carrying out the above-described welding repair method, preferably, the first to fourth steps are performed with the weld repair target portion at a temperature within the range of 300 to 400 ° C.

  Further, according to a preferred embodiment of the welding repair method of the present invention, after the fourth step, it is preferable to peening the weld repair portion including the TIG remelt treatment portion, the first main weld portion, and the second main weld portion. . At this time, it is preferable to apply a metal mesh to the region of the base material including the weld repair portion and perform the peening process through the metal mesh.

  According to another preferred embodiment of the welding repair method of the present invention, after the fourth step, the surface of the weld repair portion may be heated and held at a temperature in the range of 600 to 800 ° C. for at least 10 minutes. .

  Further, according to another preferred embodiment of the welding repair method of the present invention, after the fourth step, after the peening treatment of the weld repair portion, the surface of the weld repair portion is brought to a temperature in the range of 500 to 800 ° C. It is good to heat and hold for at least 10 minutes.

  In order to achieve the above-described object, the heat-resistant steel product having the weld repaired portion of the present invention uses covered arc welding with respect to the base material and the groove formed in the weld repair target portion of the base material. The buttering weld formed by the buttering welding was melted by the TIG remelt treatment and then allowed to cool and solidified, and the buttering welding using the coated arc welding on the TIG remelt treated portion. The first main welded part formed by the above-mentioned method and the second main welded part formed by the main welding using the covered arc welding on the first main welded part.

  According to a preferred embodiment of the heat-resistant steel product having the weld repair portion described above, the Vickers hardness of the base material is in the range of 160 to 230, the Vickers hardness of the second welded portion, and the Vickers hardness of the base material. The maximum difference is 120, and the residual stress on the surface of the second main weld is preferably in the range of +100 MPa to −300 MPa. Further, when the difference between the Vickers hardness of the second weld zone and the Vickers hardness of the base material is 100 at the maximum, and the residual stress on the surface of the second weld zone is in the range of +50 MPa to −150 MPa, Is preferred.

  According to the welding repair method of the present invention, the tempering process is effectively performed for the hardening of the base material generated during the buttering welding by performing the TIG remelting process without cutting and removing the buttering weld. Is called. Further, by performing temper bead welding by the buttering method, an effective tempering effect of the base material can be obtained.

  Moreover, the tempering effect and the reduction of residual stress become more remarkable by performing the 1st-4th process as a temperature within the range of 300-400 degreeC for a welding repair object part.

  Moreover, a compressive residual stress can be provided to the surface of a weld repair part by performing a peening process to a weld repair part. At this time, since the tempering effect is obtained in the third step, uniform compressive residual stress can be applied to the welded portion and the base material by the peening process.

  In addition, when performing peening treatment on the weld repair part, if a wire mesh is applied in the vicinity including the weld repair part and peening treatment is performed via this wire mesh, the level of compressive residual stress applied can be confirmed by the shape of the wire mesh. And grant level can be controlled.

  Further, when the surface of the weld repaired portion is heated and held at a temperature in the range of 600 to 800 ° C. for at least 10 minutes, the tempering effect of the weld repaired portion can be promoted and the residual stress of the welded portion can be removed. Similarly, after peening the weld repaired portion, the surface of the weld repaired portion is heated and held at a temperature in the range of 500 to 800 ° C. for at least 10 minutes, and the tempering effect of the weld repaired portion can be promoted. Residual stress can be reduced.

  Further, according to the heat-resistant steel product having the weld repair part of the present invention, the difference in Vickers hardness between the base material and the weld repair part can be kept small, so that the low cycle fatigue life of the weld repair part including the base material is improved. The Further, since the residual stress in the weld repair portion is a compressive stress or a low level tensile stress, the risk of cracking is reduced.

It is process drawing for demonstrating the welding repair method of 1st Embodiment. It is process drawing (1) for demonstrating a peening process. It is process drawing (2) for demonstrating a peening process. It is a schematic diagram of the restraint state of a test body. It is a schematic diagram of a groove to be tested.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

  Moreover, in each figure, the hatching which shows a cross section may be partly omitted.

(First embodiment)
With reference to FIG. 1, the welding repair method of 1st Embodiment is demonstrated. 1A to 1E are process diagrams for explaining a welding repair method according to the first embodiment. 1A to 1E are views showing cut end surfaces of main parts of a base material including a weld repair target part.

  The welding repair method according to the first embodiment is a method for repairing defects such as cracks generated in a steam turbine casing material used for a long period of time. Examples of the steam turbine casing material include Cr—Mo—V cast steel and Cr—Mo cast steel.

  The welding repair method of 1st Embodiment is performed with respect to the groove | channel 14 formed in the welding repair object part 12 of the base material 10 which consists of cast steel products (it may be called a heat-resistant steel product) (FIG. 1 ( A)).

  First, in a 1st process, buttering welding is performed with respect to the groove | channel 14 formed in the welding repair object part 12 of the base material 10, ie, the first layer buttering welding is performed, and the buttering welding part 20 is formed. Buttering welding is performed using covered arc welding (SMAW). In this covered arc welding, for example, a welding rod having a diameter of 3.2 mm and corresponding to JIS Z3223 DT2315 is used (FIG. 1B).

  Next, in the second step, TIG remelt treatment is performed, and the buttering weld 20 is melted and then allowed to cool and solidify to form the TIG remelt treatment 30. The TIG remelt process is a process that melts the buttering weld 20 using the arc heat of the TIG torch without using a welding rod, and gives a temper effect to the weld heat affected zone of the base material 10. This TIG remelt treatment is performed subsequent to the buttering welding in the first step, that is, without performing bead cutting on the buttering welded portion 20 formed in the first step (FIG. 1C).

  Next, in the third step, the first main welding part 40 is formed on the TIG remelt treatment part 30 by buttering welding. This welding is by buttering welding similar to the first step, and is so-called temper bead welding in which a temper effect is obtained. That is, unlike the normal method of sequentially stacking on the bottom surface of the groove, welding is performed so as to cover the exposed surface of the groove. This temper bead welding is performed, for example, by SMAW using a welding rod corresponding to JIS Z3223 DT2315 having a diameter of 4 mm (FIG. 1D).

  Next, in the fourth step, main welding is performed to form the second main welding part 50 on the first main welding part 40. This main welding is usually performed by SMAW in a lamination system. This main welding is performed by using, for example, a welding rod corresponding to JIS Z3223 DT2315 having a diameter of 4 mm by SMAW. By this main welding, the groove portion remaining in each step up to the third step is embedded. In the first to fourth steps, the temperature between the preheating passes is preferably 300 to 400 ° C. That is, it is preferable to perform welding in each process in a state where the welding repair target portion 12 is heated and held at 300 to 400 ° C. (FIG. 1E).

  In the following description, the TIG remelt processing section 30, the first main welding section 40, and the second main welding section 50 may be collectively referred to as a welding repair section. Moreover, the 1st main welding part 40 and the 2nd main welding part 50 may be named generically a main welding part.

(Second Embodiment)
The welding repair method of 2nd Embodiment is equipped with the process of carrying out the peening process of this welding part after the 4th process of the welding repair method of 1st Embodiment demonstrated with reference to FIG. This peening process is performed using an air chisel.

  In performing this peening process, it is preferable to apply a wire mesh to the weld repair part including the main weld part formed in the fourth step and perform the peening process through the wire mesh. With reference to FIG.2 and FIG.3, the peening process performed via a wire mesh is demonstrated. 2 and 3A and 3B are process diagrams for explaining the peening process.

  For example, as the wire mesh 60, a mesh made of SUS304 having a wire diameter of 0.6 mm and a distance between wires of 2.3 mm is applied to the weld repair portion 16 using a magnet (FIG. 2). Thereafter, peening is performed through the wire mesh 60 using the air chisel 70 (FIG. 3A). In this case, by visually checking the degree of deformation of the wire mesh 60, the level of residual stress applied can be controlled. For example, if the peening is strong enough to break the wire mesh, the stress level is about −350 MPa, and if the medium peening is enough to flatten the wire mesh 62 (FIG. 3B), the stress level is about −200 MPa. There is a stress level of about −150 MPa as long as it can be confirmed that the wire of the wire mesh is deformed.

  In addition, when the peening process is performed via the wire mesh 60, it is possible to easily determine the peened portion and the unprocessed portion by visually confirming the surface state of the wire mesh. As a result, variation in the peening degree depending on the place can be suppressed.

(Third embodiment)
The welding repair method of 3rd Embodiment is equipped with the process which heat-holds the welding repair part containing this welding part after the 4th process of the welding repair method of 1st Embodiment mentioned above.

  This heating and holding is performed by locally heating the surface of the main welded portion and its periphery using a heating burner. While measuring the temperature with a surface thermometer, it is heated and held at a temperature in the range of 600 to 800 ° C. for at least 10 minutes and then allowed to cool.

(Fourth embodiment)
The welding repair method of the fourth embodiment includes a step of peening the main welded portion and a step of heating and holding the weld repaired portion including the main welded portion after the fourth step of the weld repair method of the first embodiment described above. It has.

  The peening process is performed using an air chisel as in the second embodiment. The heating and holding is performed using a heating burner as in the third embodiment. In this heating and holding, the surface of the main welded portion and its periphery are heated and held at a temperature in the range of 500 to 800 ° C. for at least 10 minutes and then allowed to cool.

(Example)
1. Evaluation test 1
The test method will be described with reference to FIG. FIG. 4 is a schematic diagram of the restrained state of the specimen. As a test body (base material) 10, a rectangular parallelepiped Cr—Mo—V cast steel having lengths L11, L12, and L13 of 300 mm, 200 mm, and 25 mm, respectively, was used. A groove-like groove having a depth of 15 mm was formed in the weld repair target portion, and the width of this groove was 12 mm. The angle formed by both side surfaces of the groove was 70 degrees. On the back surface of the test body 10, a mild steel restraint plate 90 having side lengths L21, L22, and L23 of 20 mm, 200 mm, and 100 mm was fillet welded to restrain elongation in the L12 direction during welding.

  Tables 1 and 2 show welding repair methods of Examples and Comparative Examples. Table 1 shows steps corresponding to the first to third steps described above. Table 2 shows steps after the fourth step.

  Example 1 is repaired by the method of the first embodiment described above. Example 2 is repaired by the method of the second embodiment described above. Example 3 was repaired by the method of the second embodiment described above, and a peening process was performed by applying a wire mesh. Example 4 is repaired by the method of the third embodiment described above. Example 5 is repaired by the method of the fourth embodiment described above.

  In Comparative Example 1, after performing the first layer buttering welding using the same welding material as in the first step of the first embodiment, without performing the TIG remelt treatment, the normal lamination type temper bead welding is performed. The main welding was performed. In Comparative Example 1, the temperature between the preheating passes was set to 200 to 250 ° C.

  In Comparative Example 2, the first layer buttering welding was performed in the same manner as in Comparative Example 1, and then half bead cutting was performed, and then the normal lamination type temper bead welding and main welding were performed without performing the TIG remelt treatment. is there. In Comparative Example 2, the first layer buttering welding was performed at a temperature between preheating passes of 200 to 250 ° C.

  The temper bead welding and the main welding are performed by TIG welding (GTAW) using a welding rod corresponding to JIS Z3316 WGTIG1CM having a diameter of 2.4 mm. In temper bead welding and main welding, the temperature between preheating passes was set to 350 to 400 ° C.

  In Comparative Example 3, after performing buttering welding in the same manner as in Comparative Example 1, bead cutting and TIG remelt treatment were not performed, and divided short bead type temper bead welding and main welding were performed. In Comparative Example 3, the buttering welding was performed with the temperature between the preheating passes set to 200 to 250 ° C.

  Further, the temper bead welding and the main welding were performed by SMAW using a welding rod corresponding to JIS Z3223 DT2315 having a diameter of 4 mm at a temperature between preheating passes of 350 to 400 ° C.

  Comparative Example 4 is different from Comparative Example 3 in that half bead cutting is performed after initial layer buttering welding, and the others are the same. In Comparative Examples 1 to 4, peening and burner heating after the main welding are not performed.

  A low cycle fatigue test was performed on Examples 1 to 5 and Comparative Examples 1 to 4. Table 3 shows the fatigue test conditions.

Table 4 shows the test results. Table 4 shows the residual stress (MPa), the maximum hardness (HV) of the weld repair portion, and the low cycle fatigue life (times) for each of Examples 1 to 5 and Comparative Examples 1 to 4. The maximum hardness is expressed as Vickers hardness (HV) and is given by HV = 1.8544 × P / d ² . Here, P is a weighted kgf, and d is the length of the diagonal line of the indentation. The residual stress is a tensile residual stress (+) of 100 MPa or less, or a compressive residual stress (−), and the low cycle fatigue life is 60% or more of 672 times of the base material life. To pass.

  As a result, in all of Examples 1 to 5, the residual stress and the low cycle fatigue life reached the acceptance criteria. In particular, in Examples 4 and 5, the residual stress is a compressive residual stress (−) and has a value close to 0, which indicates a more excellent quality characteristic of the weld repair portion.

  In Comparative Examples 3 and 4, the low cycle fatigue life is 60% or more of the base material, but the residual stress is high.

2. Evaluation test 2
Table 5 shows the results of evaluation tests on different base materials. Table 5 shows the low cycle fatigue life results for Examples 1, 4 and 5 and Comparative Example 1.

  Here, as a base material, each of Cr-Mo-V cast steel and Cr-Mo cast steel was subjected to deterioration treatment and then subjected to welding repair. This deterioration process is a so-called step cool process, and is performed by gradually cooling from 590 ° C. in a furnace.

  The base metal hardness after the deterioration treatment was 220 in terms of Vickers hardness (HV) for Cr—Mo—V cast steel and 175 in terms of Vickers hardness (HV) for Cr—Mo cast steel.

  The low cycle fatigue life of Examples 1, 4, and 5 was 60% or more of the base metal regardless of the cast steel. On the other hand, Comparative Example 1 had a value smaller than 60% of the base material in any cast steel.

3. Evaluation test 3
The test was conducted using actual casing waste. The actual casing waste material used here is Cr-Mo-V cast steel having a weight of about 1000 kg.

  With reference to FIG. 5, the groove to be tested will be described. FIG. 5 is a schematic diagram of a groove to be tested.

  A groove of the bottom of the ship is formed on the surface of the casing material using gouging and a grinder. The groove has a depth D of 30 mm, a long portion L1 of the opening 100 mm, and a short portion L2 of 50 mm. Welding repair was performed on the groove by the methods of Example 3 and Example 5, respectively.

  When welding was performed by the method of Example 3, the residual stress was +75 MPa in the state before performing the peening treatment, that is, in the state of being welded in the same manner as in Example 1. On the other hand, after performing a peening process, it was -190 MPa. Moreover, the weld repair part constructed by the method of Example 5 was −15 MPa.

  As described above, an excellent weld repair portion was obtained even in a test piece of actual size.

10 Base material
12 Welding repair target part 14 Groove 16 Welding repair part
20 Buttering weld
30 TIG remelt treatment section
40 First welded portion 50 Second welded portion 60, 62 Wire mesh 70 Air chisel 90 Mild steel restraint plate

Claims (9)

A first step of performing buttering welding using covered arc welding on the groove formed in the weld repair target portion of the base metal to form a buttering weld portion;
Performing a TIG remelt treatment, solidifying after melting the buttering weld, and forming a TIG remelt treatment,
A third step of performing buttering welding using covered arc welding and forming a first main weld on the TIG remelt treated portion;
A welding repair method for heat-resistant steel products, comprising: a fourth step of performing main welding by covered arc welding and forming a second main welding portion on the first main welding portion. 2. The method for repairing a heat-resistant steel product according to claim 1, wherein the first to fourth steps are performed at a temperature within a range of 300 to 400 ° C. of the welding repair target portion. After the fourth step,
The welding repair method for heat-resistant steel products according to claim 1 or 2, wherein a peening process is performed on a weld repair portion including the TIG remelt treatment portion, the first main weld portion, and the second main weld portion. In peening the weld repair part,
4. The method for repairing a heat-resistant steel product according to claim 3, wherein a wire mesh is assigned to a region of the base material including the weld repair portion, and peening is performed through the wire mesh. After the fourth step,
2. The surface of the weld repair portion comprising the TIG remelt treatment portion, the first main weld portion, and the second main weld portion is heated and held at a temperature in the range of 600 to 800 ° C. for at least 10 minutes. Or the welding repair method of the heat-resistant steel products of 2. After performing the peening process,
The method of repairing a heat-resistant steel product according to claim 3, wherein the surface of the weld repair portion is heated and held at a temperature in the range of 500 to 800 ° C for at least 10 minutes. With the base material,
TIG remelt formed by melting a buttering weld formed by buttering welding using covered arc welding to a groove formed in the weld repair target portion of the base metal and then solidifying the melted portion by TIG remelt treatment. A processing unit;
On the TIG remelt treated part, a first main weld part formed by buttering welding using covered arc welding,
A heat-resisting steel product having a weld repair portion, comprising: a second main weld portion formed by main welding using covered arc welding on the first main weld portion. The Vickers hardness of the base material is in the range of 160-230,
The difference between the Vickers hardness of the second welded portion and the Vickers hardness of the base material is at most 120;
The heat resistant steel product having a weld repair portion according to claim 7, wherein a residual stress on the surface of the second main weld portion is in a range of +100 MPa to −300 MPa. The Vickers hardness of the base material is in the range of 160-230,
The difference between the Vickers hardness of the second welded portion and the Vickers hardness of the base material is at most 100,
The heat-resisting steel product having a weld repair portion according to claim 7, wherein the residual stress on the surface of the second main weld portion is in the range of +50 MPa to -150 MPa.

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