JP5978064B2 - Weld metal, strip electrode, sintered flux and submerged arc welding method - Google Patents

Description

  The present invention relates to a weld metal, a strip electrode and a sintered flux used when forming the weld metal, and a submerged arc welding method. More specifically, a weld metal, a strip electrode, a sintered flux, and a submerged arc welding method suitable for a buffer layer (underlaying layer) provided between a base material and a surface layer (overlaying layer) in hardfacing welding About.

  When overlay welding is performed on a base material with high curability, such as low alloy steel, or when overlay welding is performed using an extremely hard material, it is caused by tensile stress generated in the base material and / or weld metal during welding. Therefore, cracks are likely to occur in the base material and the weld metal. Therefore, in general, when performing overlay welding, underlay welding by covering arc welding or the like is performed in order to suppress or reduce the above-described cracks. At that time, mild steel and austenitic stainless steel are mainly used as the welding material.

On the other hand, conventionally, fluxes for submerged arc overlay welding have also been developed (see Patent Documents 1 to 3). For example, Patent Document 1 discloses MgO / Al ₂ O ₃ and a flux with adjusted basicity in order to adapt to a wide range of welding conditions, have excellent welding workability, and obtain good mechanical performance. Yes. Further, in the technique described in Patent Document 2, the build-up layer is made tougher and stronger by adding alloy components such as Cr, Mo, Ni, and V from the sintered flux.

  On the other hand, Patent Document 3 proposes a flux that provides a weld metal with a low carbon content when combined with an austenitic stainless steel strip electrode. In the flux described in Patent Document 3, slag peelability and weld bead shape are improved by reducing the amount of carbon in the weld metal.

JP 58-128295 A JP-A-58-9795 Japanese Patent Laid-Open No. 2001-300765

  However, the above-described conventional overlay welding has a problem that, from the viewpoint of workability, the coating arc welding has a problem that the welding speed is low, and from the viewpoint of economy, the austenitic stainless steel welding material increases the cost. There's a problem. Regarding the improvement of construction efficiency, submerged arc welding using a strip electrode is effective, but even if the techniques described in Patent Documents 1 to 3 described above are applied to overlay welding, both construction efficiency and construction cost are reduced. It is difficult to improve.

  For example, Patent Document 1 mentions welding workability, but does not describe welding efficiency, composition of the weld metal, and mechanical performance. For this reason, when the flux described in Patent Document 1 is applied to underlay welding, what kind of weld metal is obtained, and the obtained weld metal exhibits excellent performance as a buffer layer in hardfacing welding. It is unknown.

  Moreover, since the flux described in Patent Document 2 contains alloy elements that contribute to high strength such as Cr, Mo, V, etc., a hardened structure is easily formed on the weld metal, and the presence and stress of diffusible hydrogen. There is concern about the occurrence of delayed cracking due to the overlapping of concentration. In order to suppress or reduce this delayed crack, not only the strict construction management at the time of welding but also the dehydrogenation treatment after the welding work is required, so that the construction efficiency is lowered.

  Further, when the flux described in Patent Document 2 is used, V is added to the weld metal. Therefore, when heat treatment after welding is performed, fine V carbide precipitates in the heat treatment stage, and the structure is remarkably hardened. SR cracking (reheat cracking) may occur. In addition, since the flux described in Patent Document 2 contains various alloy components, the cost increases.

  On the other hand, the flux described in Patent Document 3 is used in combination with a strip electrode made of austenitic stainless steel to form a build-up metal (surface layer) having corrosion resistance on the inner surface of a chemical reaction vessel or a reactor reaction vessel. Therefore, its usefulness when applied to a buffer layer (underlay layer) has not been studied and is unknown.

  Therefore, the present invention is excellent in construction efficiency and cost, and when applied to underlay welding, it is possible to suppress the occurrence of cracks in the overlay layer, a weld metal of a mild steel system, a strip electrode, a sintered flux, and The main object is to provide a submerged arc welding method.

  In order to reduce cracking of the base material or the built-up metal layer that occurs when forming a surface-hardened build-up layer, when using a highly curable base material or when forming a high-hardness build-up metal In order to improve the construction efficiency and construction cost, the idea of “(1) Introduction of a high-efficiency welding method” and “(2) Introduction of mild steel-based weld metal” was obtained. Then, it was concluded that the use of the strip electrode submerged arc welding method is effective for realizing (1), and the use of a mild steel welding material is effective for realizing (2).

  Furthermore, the present inventor has examined the deposited metal, found a composition having sufficient plastic deformability capable of withstanding the thermal stress during the overlay welding (tensile stress accompanying thermal shrinkage of the overlay deposited metal), The present invention has been reached.

That is, the weld metal according to the present invention is a weld metal formed by submerged arc welding using a strip electrode, and Si: 0.30 to 0.60 mass%, Mn: 1.00 to 1.50 mass. %, C: 0.20% by mass or less, the balance is composed of Fe and inevitable impurities, and the elongation at break as measured by a normal temperature tensile test in the as-welded state is 30% or more It is.
This weld metal may contain O: 0.05-0.10 mass%.
Moreover, you may regulate Bi to 0.005 mass% or less among the inevitable impurities.
Furthermore, among the inevitable impurities, the total content of Cr, Mo, Ti, Nb, V, Ni and Al may be regulated to 0.5% by mass or less.

  The strip electrode according to the present invention is a strip electrode used for submerged arc welding, contains Mn: 0.20 to 0.50 mass%, C: 0.10 mass% or less, Si: 0.10. % By mass or less, Cr, Mo, Ti, Nb, V, Ni and Al: The total is regulated to 1.0% by mass or less, and the balance is made of Fe and inevitable impurities.

The sintered type flux according to the present invention is a sintered type flux used for submerged arc welding using a strip electrode, and is SiO ₂ : 15 to 35% by mass, ZrO ₂ : 10 to 30% by mass, Al _2. O ₃ : 10 to 30% by mass, Mn (in terms of metal Mn): 5 to 15% by mass, metal carbonate (in terms of CO ₂ ): 5 to 10% by mass, fluorine compound (in terms of F): 0.5 to 3% by mass %, Bi ₂ O ₃ : 0.10% by mass or less, Cr, Mo, Ti, Nb, V, Ni, and Al: a total of 1.0% by mass or less.

The submerged arc welding method according to the present invention contains Mn: 0.20 to 0.50 mass%, C: 0.10 mass% or less, Si: 0.10 mass% or less, Cr, Mo, Ti , Nb, V, Ni and Al: The total amount is regulated to 1.0% by mass or less, and the balance is a strip electrode composed of Fe and inevitable impurities, SiO ₂ : 15 to 35% by mass, ZrO ₂ : 10 to 30% by mass %, Al ₂ O ₃ : 10 to 30% by mass, Mn (in terms of metal Mn): 5 to 15% by mass, metal carbonate (in terms of CO ₂ ): 5 to 10% by mass, fluorine compound (in terms of F): 0. 5 to 3% by mass and Bi ₂ O ₃ : 0.10% by mass or less, Cr, Mo, Ti, Nb, V, Ni and Al: having a composition regulated to 1.0% by mass or less in total Sintered flux and Si: 0.30-0.60 In addition to containing mass%, Mn: 1.00-1.50 mass%, C: regulated to 0.20 mass% or less, the balance is composed of Fe and unavoidable impurities, and remains welded A weld metal having a breaking elongation of 30% or more as measured by a normal temperature tensile test is obtained.

  According to the present invention, a weld metal having excellent plastic deformation performance can be obtained, so that it is possible to suppress the occurrence of cracks in the base material and the overlay layer when applied to underlay welding, and further, strip electrode welding Therefore, construction with high efficiency becomes possible.

It is a figure which shows typically the lamination | stacking method of overlay welding in the Example of this invention. It is a figure which shows the test piece collection position in the Example of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.

  The weld metal according to the embodiment of the present invention is formed by submerged arc welding using a strip electrode and contains Si: 0.30 to 0.60 mass% and Mn: 1.00 to 1.50 mass%. C: Restricted to 0.20% by mass or less, with the balance being composed of Fe and inevitable impurities. Further, this weld metal has a breaking elongation of 30% or more as measured by a normal temperature tensile test in a welded state.

[Si: 0.30 to 0.60 mass%]
Si has a deoxidizing action that reacts with O in the weld metal, and has an effect of improving the cleaning degree of the weld metal. Si also has the effect of improving the conformability of the weld bead toes. However, when the amount of Si in the weld metal is less than 0.30% by mass, these effects are insufficient. On the other hand, excessive addition of Si reduces the elongation at break of the weld metal, so the amount of Si in the weld metal needs to be suppressed to 0.60% by mass or less. Therefore, in the weld metal of this embodiment, Si content shall be 0.30-0.60 mass%.

[Mn: 1.00-1.50 mass%]
Similar to Si, Mn is an element indispensable for deoxidation of the weld metal. However, when the amount of Mn in the weld metal is less than 1.00% by mass, a sufficient deoxidation effect cannot be obtained. On the other hand, when Mn is added excessively, the elongation at break of the weld metal is lowered, so the amount of Mn in the weld metal is suppressed to 1.50% by mass or less. Therefore, in the weld metal of this embodiment, the Mn content is 1.00 to 1.50 mass%.

[C: 0.20 mass% or less]
Excessive addition of C lowers the elongation at break of the weld metal and significantly increases the susceptibility to delayed cracking and hot cracking, so it is a limiting component in the weld metal of this embodiment. Specifically, if the amount of C in the weld metal exceeds 0.20% by mass, delayed cracking, high-temperature cracking, etc. are likely to occur in the overlay metal layer. Is controlled to 0.20 mass% or less. Moreover, it is preferable that C content in a weld metal shall be 0.15 mass% or less, and thereby, crack resistance can be improved.

[O: 0.05 to 0.10% by mass]
The weld metal of this embodiment may further contain O in addition to the components described above. O has the effect of lowering the viscosity of the molten metal composed of the electrode and flux melted by the arc heat, and improving the compatibility with the weld bead toe and the base material and the lap (overlap) portion of the previous pass. However, when O is added excessively, the toughness of the deposited metal is remarkably deteriorated.

  Specifically, when the amount of O in the weld metal is less than 0.05% by mass, the above-described addition effect may not be obtained, and when the amount of O in the weld metal exceeds 0.10% by mass. Toughness can be significantly reduced. Therefore, the O content is preferably 0.05 to 0.10% by mass.

[Balance: Fe and inevitable impurities]
The balance in the weld metal of this embodiment is Fe and inevitable impurities. The inevitable impurities mentioned here include P, S, Cu, B, Sn, Sb, As, and Pb. In addition, Bi, Cr, Mo, Ti, Nb, V, Ni, Al and the like are intentionally contained, it becomes difficult to achieve the object of the present invention. For this reason, in the weld metal of this embodiment, these elements are not added positively, and even when it is contained as an inevitable impurity, the content is restricted to the range shown below.

[Bi: 0.005 mass% or less]
Bi is an element that enhances the hot cracking susceptibility of the deposited metal. In addition, when PWHT (Post Weld Heat Treatment) is performed after welding the upper layer, or when preheating and temperature control between passes are required at the time of welding the upper layer, the weld metal When Bi is contained in a large amount, the SR cracking (reheat cracking) susceptibility of the deposited metal is increased. For this reason, from the viewpoint of improving crack resistance, the Bi content in the weld metal is preferably 0.005% by mass or less, and more preferably 0.003% by mass or less.

[[A]: 0.5% by mass or less]
Alloy elements such as Cr, Mo, Ti, Nb, V, Ni, and Al increase the strength of the deposited metal and decrease the elongation at break. Therefore, it is effective to reduce these alloy elements in order to improve the SR crack resistance of the underlayer. In particular, Ti, Nb, and V form fine carbides during PWHT after high-layer welding and high-temperature preheating / pass-to-pass control welding, and significantly increase the strength of the deposited metal. If it is contained, the SR cracking sensitivity becomes high.

  Specifically, the total content ([A]) of Cr, Mo, Ti, Nb, V, Ni and Al in the weld metal is preferably 0.5% by mass or less, and 0.3% by mass or less. It is more preferable that Thus, SR cracking resistance can be further improved by reducing these alloy components contained in the weld metal.

[Elongation at break: 30% or more]
The elongation at break of the weld metal is an indicator of plastic deformability. The elongation at break of the weld metal can be measured by a normal temperature tensile test using a type IIA No. 2 test piece defined in JIS Z3111 in a state of being welded. And when the elongation at break of the weld metal is less than 30%, the thermal stress at the time of overlay welding cannot be reduced, and cracks may occur in the overlay metal layer. For this reason, in the weld metal of this embodiment, elongation at break shall be 30% or more.

  By using such a weld metal as the overlay layer, the tensile stress due to thermal shrinkage during welding of the overlay layer is reduced by plastic deformation of the overlay layer (welded metal), and the entire overlay metal layer is cracked. Sensitivity can be reduced. The elongation at break of the weld metal is preferably 35% or more, whereby the crack resistance can be further improved.

[Welding method]
Next, a welding method for obtaining the weld metal of this embodiment will be described. The weld metal of this embodiment is formed by submerged arc welding using a strip electrode. The component composition of the strip electrode used at that time is not particularly limited as long as it is a mild steel system from the viewpoint of the workability of the strip electrode and the yield of the alloy element in the weld metal. 20 to 0.50% by mass, C: 0.10% by mass or less, Si: 0.10% by mass or less, Cr, Mo, Ti, Nb, V, Ni and Al: 1.0 mass in total % Having a composition composed of Fe and inevitable impurities can be used.

Further, the flux used during welding may be either a sintered type or a fused type, but if a sintered type flux to which an iron powder-based raw material can be added is used, further improvement in welding efficiency is expected. _{Specifically,} SiO 2: 15 to 35 _wt%, ZrO 2: 10 to 30 _{wt%, Al} 2 O 3: 10 to 30 wt%, Mn (metal in terms of Mn): 5 to 15 wt%, metal carbonate (CO ₂ conversion): 5 to 10% by mass, fluorine compound (F conversion): 0.5 to 3% by mass, Bi ₂ O ₃ : 0.10% by mass or less, Cr, Mo, Ti, Nb V, Ni and Al: A sintered flux having a composition regulated to 1.0% by mass or less in total can be used.

(Strip electrode)
Hereinafter, the reason for limiting the numerical values of the respective components of the above-described strip electrode will be described.

<Mn: 0.20 to 0.50 mass%>
Mn contained in the strip electrode has an effect of increasing the amount of Mn in the weld metal and increasing the cleaning degree of the weld metal by a deoxidation effect. However, when the content is less than 0.20% by mass, the effect of addition is not sufficiently obtained, and when Mn is contained exceeding 0.50% by mass, the strength of the strip electrode is increased, and the rollability is increased. descend. Therefore, the amount of Mn in the strip electrode is preferably 0.2 to 0.50% by mass.

<C: 0.10% by mass or less>
When C is added excessively, the strength of the strip electrode is increased and the rollability is lowered. Therefore, it is preferable that the amount of C in the belt-like electrode is regulated to 0.1% by mass or less, thereby improving workability.

<Si: 0.10% by mass or less>
Si, like C, is an element that increases the strength of the strip electrode and decreases the rollability. For this reason, it is preferable from the viewpoint of workability improvement that the amount of Si in the strip electrode is regulated to 0.1 mass% or less.

<[A]: 1.0% by mass or less>
Alloy elements such as Cr, Mo, Ti, Nb and V also have an effect of increasing the strength of the strip electrode, and if added excessively, the rollability is lowered. Moreover, when Ni and Al are contained excessively in addition to these elements, the [A] value in the weld metal increases, and the SR cracking sensitivity of the weld metal increases. Therefore, from the viewpoint of improving the workability of the strip electrode and improving the crack resistance of the weld metal, the strip electrode has a total content of Cr, Mo, Ti, Nb, V, Ni, and Al ([A]) of 1. The content is preferably 0% by mass or less, and more preferably 0.5% by mass or less.

(Sintered flux)
Hereinafter, the reason for limiting the numerical value of each component of the sintered flux will be described.

<SiO ₂ : 15 to 35% by mass>
SiO ₂ is an acidic substance that reacts with other basic substances contained in the flux during welding to form glass-like slag, protecting the molten metal in the arc atmosphere, and welding metal and weld beads. This prevents the oxidation and nitridation of the bead and improves the bead shape. However, the above-described effects may not be obtained with a sintered flux having a SiO ₂ content of less than 15% by mass.

On the other hand, since SiO ₂ causes a reduction reaction during welding, excessive addition increases the amount of Si in the deposited metal and reduces the elongation at break. Specifically, the addition of SiO ₂ exceeds 35 mass%, elongation at break of the welded metal may decrease. Therefore, the SiO ₂ content of the sintered flux is preferably 15 to 35% by mass.

<ZrO ₂ : 10 to 30% by mass>
ZrO ₂ is added to the flux as a slag forming agent, but a sufficient effect may not be obtained with a sintered flux whose content is less than 10% by mass. On the other hand, when ZrO ₂ is added excessively, the viscosity of the molten slag increases and the molten slag tends to precede, so that the conformability of the weld bead decreases, and welding defects such as slag entrainment are induced. Specifically, with a sintered flux with ZrO ₂ exceeding 30 mass%, welding defects are likely to occur. Therefore, the ZrO ₂ content of the sintered flux is preferably 10 to 30% by mass.

<Al ₂ O ₃ : 10 to 30% by mass>
Al ₂ O ₃ is a basic substance, and reacts with other acidic substances contained in the flux during welding to form glass-like slag, thereby protecting the molten metal in the arc atmosphere and welding metal In addition to preventing oxidation of the weld bead and the effect of improving the bead shape. However, the above-described effects may not be obtained with a sintered flux having an Al ₂ O ₃ content of less than 10% by mass.

On the other hand, since Al ₂ O ₃ causes a reduction reaction during welding, excessive addition increases the amount of Al in the weld metal and the [A] value. Specifically, when Al ₂ O ₃ is added in excess of 30% by mass, the [A] value in the weld metal increases, and the SR cracking susceptibility of the weld metal may increase. Accordingly, the Al ₂ O ₃ content of the sintered flux is preferably 10 to 30% by mass.

<Mn (metal Mn conversion): 5 to 15% by mass>
Mn is added as an alloy element additive or a slag forming agent, for example, in the form of metal Mn, Fe—Mn alloy or the like. However, when the amount of Mn in the flux is less than 5% by mass, the effect of addition may not be obtained. On the other hand, for example, when Mn is added excessively exceeding 15% by mass, the amount of Mn in the deposited metal increases, and the elongation at break decreases. Therefore, the Mn content of the sintered flux is preferably 5 to 15% by mass. When Mn is added in the form of an Fe—Mn alloy, an Fe—Si—Mn alloy, or the like, the amount of Mn here refers to the amount converted to metal Mn.

<Metal carbonate (CO ₂ conversion): 5 to 10% by mass>
Metal carbonate is decomposed into metal oxide and CO ₂ by arc heat. The metal oxide forms a slag to protect the weld bead, and CO ₂ has an effect of lowering the hydrogen partial pressure in the arc atmosphere and reducing the amount of diffusible hydrogen in the deposited metal. Carbonate, but are not particularly limited, for example MgCO _3, CaCO _3, can be added in the form of such BaCO _{3, Na} 2 CO _3.

However, when the total content of the metal carbonate is less than 5% by mass in terms of CO ₂ , the above-described effects may not be obtained. Moreover, when metal carbonate is added excessively, the viscosity of the molten slag increases and the molten slag tends to precede, so the conformability of the weld bead toe is reduced and welding defects such as slag entrainment are induced. . Specifically, a welding defect is likely to occur in a sintered flux in which the total content of metal carbonate exceeds 10% by mass in terms of CO ₂ . Therefore, the total content of metal carbonate sintered flux is preferably 5 to 10% by mass in terms of CO _2.

<Fluorine compound (F conversion): 0.5 to 3% by mass>
The fluorine compound acts as a slag forming agent like ZrO ₂ described above. The fluorine compound added to the sintered flux is not particularly limited, and not only metal fluorides typified by BaF ₂ , CaF ₂ , KF, NaF, AlF _3, etc., but also K ₂ SiF _6, etc. Fluorine resin such as composite metal fluoride or PTFE (polytetrafluoroethylene) may be used.

  However, when the total content of these fluorine compounds is less than 0.5% by mass in terms of F, the above-described effects may not be obtained. If the fluorine compound is added excessively, specifically, if the total content of the fluorine compound exceeds 3% by mass in terms of F, the bead shape may be deteriorated. Therefore, the total content of fluorine compounds in the sintered flux is preferably 0.5 to 3% by mass in terms of F.

<Bi ₂ O ₃ : 0.10% by mass or less>
Bi ₂ O ₃ improves the slag removability during welding and has the effect of forming a beautiful weld bead, which contributes to the reduction of construction costs. The amount of Bi ₂ O ₃ in the flux is preferably regulated to 0.10% by mass or less. If the amount of Bi ₂ O ₃ in the flux exceeds 0.10% by mass, the amount of Bi in the weld metal increases, which may increase the high temperature crack sensitivity and SR crack sensitivity of the weld metal. Note that the Bi ₂ O ₃ content in the sintered flux may be zero.

<[A]: 1.0% by mass or less>
When the total content ([A]) of Cr, Mo, Ti, Nb, V, Ni, and Al in the flux exceeds 1.0% by mass, the SR cracking susceptibility of the deposited metal may be increased. Therefore, the sintered flux also has a total content of Cr, Mo, Ti, Nb, V, Ni and Al ([A]) of 1 as in the case of the strip electrode from the viewpoint of improving the crack resistance of the deposited metal. It is preferable to regulate to 0.0 mass% or less, and it is more preferred to regulate to 0.5 mass% or less.

  As described above in detail, the weld metal of the present embodiment has a breaking elongation of 30% or more in the as-welded state. The tensile stress resulting from the shrinkage can be reduced by plastic deformation of the overlay layer (welded metal). As a result, the tensile residual stress and crack susceptibility of the lower layer and the upper layer are reduced, so that the occurrence of cracks in the welded portion can be suppressed.

  In addition, the weld metal of this embodiment is a mild steel system and does not contain alloy elements that increase the self-hardness of the weld metal such as Cr, Mo, Ti. Temperature management becomes unnecessary, and it becomes possible to improve the construction cost and the melting material cost.

  Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention. FIG. 1 is a diagram schematically showing the laminating method of overlay welding performed in this example. In this example, a steel plate (JIS G3101 SS400) having a thickness of 30 mm is used as a base material 1, and overlay welding shown in FIG. 1 is performed by using a sintered flux by a strip electrode submerged arc welding method. The function of layer 2 as a buffer layer was evaluated. At that time, the size of the strip electrode was 0.4 mm in thickness and 50 mm in width, and the particle size of the sintered flux was 12 × 65 mesh.

  Table 1 below shows the component composition of the base material subjected to the test, Table 2 shows the component composition of the strip electrode, and Table 3 shows the component composition of the sintered flux. In addition, the remainder in the component composition of the base material and the strip electrode shown in Table 1 and Table 2 below is Fe and inevitable impurities. Moreover, the component composition of the strip electrode shown in Table 2 below and the component composition of the sintered flux shown in Table 3 below are based on “Iron and Steel—Inductively Coupled Plasma Emission Spectroscopy Method” defined in JIS G1258 and JIS G1257. It is a value analyzed by a wet chemical analysis method represented by the prescribed “iron and steel—atomic absorption analysis method”.

  Further, the underlayer 2 was formed with a distance between the tip (electrode) and the base material of 45 mm, a preheating / interpass temperature of 250 ° C., a bead and lap (overlap) width of the previous pass of 5 mm, and a stacking number of 5 layers. . Other welding conditions are shown in Table 4 below.

  Similarly, a 13Cr-4Ni weld metal was overlay welded by a strip electrode submerged welding method to form an overlay layer (surface hardened overlay layer) 3 on the overlay layer 2. Note that the number of the upper layers 3 was three.

  By the above-mentioned welding test, the presence or absence of delayed cracking, high temperature cracking, and SR cracking of the bottom layer 2 and the top layer 3 before and after PWHT was confirmed. Various cracks are detected by an X-ray transmission test, and the total length of cracks generated per 100 mm weld length is 3.0 mm or less, “Good”, longer than 3.0 mm and 5.0 mm or less Were evaluated as “ordinary (Δ)” and those longer than 5.0 mm as “defective (×)”. For SR cracks, the same X-ray transmission test was conducted before and after SR (reheating). Cracks detected for the first time after SR were “SR cracks”, and other cracks were “delayed cracks” or “hot cracks”. It was judged. The SR conditions were a holding temperature of 600 ° C. and a holding time of 1 hour.

  The breaking elongation and toughness of the underlayer 2 were evaluated by a room temperature tensile test and a Charpy impact test using a type IIA No. 2 tensile test piece and a 2 mm-V notch test piece specified in JIS Z3111. FIG. 2 is a diagram showing the evaluation specimen collection position. As shown in FIG. 2, the Charpy impact test piece 10 and the room temperature tensile test piece 20 were cut out from a position 6 mm from the outermost surface of the underlayer 2.

  On the other hand, for welding workability, visual sensory evaluation was performed for “bead shape”, “bead alignment” and “slag peelability”, and “slag entrainment property” was evaluated by a cross-sectional macro observation test of the overlay layer. . Specifically, for the “bead shape”, the quality of the appearance was judged in two stages by visual observation, and “good” was evaluated as “good”, and “bad” was evaluated as “poor”.

  In addition, “bead alignment” is classified into four stages according to the tendency of undercut occurrence. ◎ indicates that the undercut occurrence tendency is extremely weak, ◎ indicates that the undercut occurrence tendency is weak, and ○ indicates that the undercut occurrence tendency is slightly strong. The case where the tendency of undercut occurrence is strong is indicated as x. Furthermore, “slag peeling peelability” is classified into 4 stages according to the tendency of seizure of slag to the surface of the weld bead. The thing was made into (triangle | delta) and the thing with a strong slag seizure tendency was made into x.

  On the other hand, “slag entrainment” is classified into 4 stages according to the tendency of slag entrainment to the overlap with the previous weld bead. Slightly strong ones were indicated by Δ, and those having a strong tendency to involve slag were indicated by ×.

  The overall evaluation is “◎” when the results of the evaluation of welding workability are all good (◯ or ◎), the toughness is 50 J or more, and the crack resistance evaluation before and after SR is good (◯). If the evaluation result of welding workability is normal (△), the toughness is less than 50J, or the crack resistance evaluation before and after SR is normal (△), “○” The evaluation result was evaluated as “×” if there was a defect (×) or there was a defect (×) in the crack resistance evaluation before and after SR.

  The above evaluation results are summarized in Table 5 below. In addition, the component composition of the weld metal shown in Table 5 below is a value analyzed in accordance with “Iron and Steel—Spark Discharge Emission Analysis Method” and JIS Z2613 “General Oxygen Determination Method for Metal Materials” defined in JIS G1253. It is.

  As shown in Table 5 above, the weld metal of Comparative Example 1 in which the C content exceeds the range of the present invention and the elongation at break is less than 30% is high in crack sensitivity, and both the overlay layer 2 and the overlay layer 3 In addition, delayed cracking or hot cracking occurred before SR, and SR cracking occurred after SR. Moreover, the weld metal of Comparative Example 2 whose Si content is less than the range of the present invention has poor conformability, poor slag entrainment property (x), and has a problem in terms of construction efficiency. On the other hand, in the weld metal of Comparative Example 3 in which the Si content exceeded the range of the present invention and the elongation at break was less than 30%, delayed cracking or hot cracking occurred in the overlay layer 3.

  In the weld metal of Comparative Example 4 whose Mn content is less than the range of the present invention, delayed cracking or hot cracking occurred in the underlay layer 2. On the other hand, in the weld metal of Comparative Examples 5 and 6 in which the Mn content exceeds the range of the present invention and the elongation at break is less than 30%, delayed cracking or hot cracking occurred in the overlay layer 3. In addition, although the component composition is within the range of the present invention, the weld metal of Comparative Example 7 having a breaking elongation of less than 30% has delayed cracking or hot cracking in the overlay layer 3.

  On the other hand, the weld metal of Examples 1 to 13 having a component composition within the scope of the present invention and having an elongation at break of 30% or more is more cracked than the weld metal of Comparative Examples 1 to 7. There was little generation and welding workability and toughness were also excellent. Among them, the weld metals of Examples 1 to 8 that satisfy not only claim 1 but also the requirements of claims 2 to 4 were particularly excellent in properties as a buffer layer and welding workability.

  From the above results, according to the present invention, it was confirmed that a buffer layer (underlay layer) capable of suppressing the occurrence of various cracks in the build-up layer can be efficiently formed.

DESCRIPTION OF SYMBOLS 1 Base material 2 Bottom layer 3 Top layer 10 Charpy impact test piece 20 Room temperature tensile test piece

Claims (7)

A weld metal for the buffer layer of overlay welding ,
Si: 0.30-0.60 mass%,
Mn: 1.00-1.50 mass%,
And containing
C: 0.20 mass% or less,
Regulated by
The balance has a composition consisting of Fe and inevitable impurities,
A weld metal having an elongation at break of 30% or more as measured by a normal temperature tensile test in a welded state.   Furthermore, O: 0.05-0.10 mass% is contained, The weld metal of Claim 1 characterized by the above-mentioned.   The weld metal according to claim 1 or 2, wherein Bi is controlled to 0.005 mass% or less among the inevitable impurities.   The total content of Cr, Mo, Ti, Nb, V, Ni and Al among the inevitable impurities is regulated to 0.5% by mass or less. The weld metal described in 1. A band-shaped electrode for producing the weld metal according to any one of claims 1 to 4 ,
Mn: 0.20 to 0.50% by mass,
And containing
C: 0.10 mass% or less,
Si: 0.10% by mass or less,
Cr, Mo, Ti, Nb, V, Ni and Al: 1.0% by mass or less in total,
Regulated by
A strip electrode characterized in that the balance is Fe and inevitable impurities. A sintered flux used for submerged arc welding using a strip electrode for producing the weld metal according to any one of claims 1 to 4,
SiO ₂ : 15 to 35% by mass,
ZrO ₂ : 10 to 30% by mass,
Al ₂ O ₃ : 10 to 30% by mass,
Mn (in terms of metal Mn): 5 to 15% by mass,
Metal carbonate (CO ₂ equivalent): 5 to 10% by mass,
Fluorine compound (F conversion): 0.5 to 3% by mass,
And containing
Bi ₂ O ₃ : 0.10% by mass or less,
Cr, Mo, Ti, Nb, V, Ni and Al: 1.0% by mass or less in total,
Sintered flux with a composition regulated to Mn: 0.20 to 0.50% by mass, C: 0.10% by mass or less, Si: 0.10% by mass or less, Cr, Mo, Ti, Nb, V, Ni and Al: in total A band-shaped electrode which is regulated to 1.0% by mass or less and the balance is made of Fe and inevitable impurities;
SiO _2: 15 to 35 _wt%, ZrO 2: 10 to 30 _{wt%, Al} 2 O 3: 10 to 30 wt%, Mn (metal in terms of Mn): 5 to 15 wt%, metal carbonate (CO ₂ equivalent) : 5 to 10% by mass, fluorine compound (F conversion): 0.5 to 3% by mass and Bi ₂ O ₃ : 0.10% by mass or less, Cr, Mo, Ti, Nb, V, Ni and Al: a sintered flux having a composition regulated to 1.0% by mass or less in total;
Use
A submerged arc welding method for obtaining the weld metal according to claim 1.

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