JP6282191B2 - First layer submerged arc welding method of high Cr CSEF steel - Google Patents

Description

  The present invention relates to a submerged arc welding method for high Cr-based CSEF (Creep Strength-Enhanced Ferritic Steel) steel, and more particularly to a first layer welding method.

  Thermal power boilers, turbines, and chemical reaction vessels (reactors) for desulfurization and reforming (heavy oil cracking) are all operated at high temperature and high pressure, so 1.25Cr-0.5Mo steel, 2.25Cr are used as materials. -1.0Mo steel, 2.25Cr-1.0Mo-V steel, etc. are applied. In recent years, there has been a demand for higher efficiency in the effective use of heavy oil and petroleum refining, and the application of high Cr-based CSEF steel containing 8% by mass or more of Cr has been studied. The high Cr-based CSEF steel includes SA387Gr. Stipulated in ASTM (American Society for Testing and Materials) standards and ASME (American Society of Mechanical Engineers) standards. 91, SA213Gr. T91 etc.

  Thermal power boilers, turbines, and reactors are assembled by appropriately combining forged rings, pipes, or bent steel sheets. Here, for example, the forging ring has a plate thickness of 150 to 450 mm, a maximum outer diameter of less than 7 m, and a total length of several to several tens of meters. As the welding method, covered arc welding, TIG welding, and submerged arc welding are used, and in particular, submerged arc welding is frequently used because it is more efficient than other welding methods. However, when submerged arc welding is performed on high Cr-based CSEF steel, hot cracking is likely to occur in the first layer welding.

  As a technique for preventing hot cracking in the first layer welding of the submerged arc welding, for example, in Patent Document 1, in narrow gap submerged arc welding of JIS SF50 and ASTM A148 having a C content of 0.27% by mass, which is a high carbon steel, Specifically, a foreign material or a foreign material made of low carbon steel or weld metal having a C content of 0.10% by mass or less is interposed as a spacer at the joint of the base metal at the first layer position of the V groove or X groove. Technology is disclosed. In this Patent Document 1, it is described that high-temperature cracking is likely to occur in the first layer weld bead in narrow gap welding of a high carbon steel material due to the pickup of the base metal to the weld metal of C by dilution of the base material. ing. That is, hot cracking is likely to occur when the C concentration of the weld metal increases and the melting point decreases. Therefore, in Patent Document 1, in the first layer welding, the influence of the C pickup from the base material is mitigated to prevent hot cracking by welding on a foreign material / foreign material spacer made of low carbon steel or weld metal. Is disclosed.

JP 58-68481 A

  Here, the high Cr-based CSEF steel has a C content of, for example, 0.08 to 0.12% by mass in ASTM A182 F91, that is, 0.12% by mass at the maximum, and the conventional 1.25Cr-0. It is comparable to 5Mo steel, 2.25Cr-1.0Mo steel, and 2.25Cr-1.0Mo-V steel. However, the welding wire composed of the high Cr-based CSEF steel and the co-material is more resistant to electric resistance than 1.25Cr-0.5Mo steel, 2.25Cr-1.0Mo steel, 2.25Cr-1.0Mo-V steel. Therefore, if the Joule heat generation is high and the magnitude of the welding current is the same, melting is easier. Therefore, in the welding of high Cr system CSEF steel, the amount of weld metal (deposition amount) is increased, and the solidification shrinkage of the weld metal is 1.25Cr-0.5Mo steel, 2.25Cr-1.0Mo steel, Since it is larger than 2.25Cr-1.0Mo-V steel, it is more difficult to suppress hot cracking.

  In order to weld thick plates with high efficiency, it is effective to increase the welding heat input, that is, increase the welding current, increase the arc voltage, and decrease the welding speed. However, when the welding heat input is increased, the bead shape tends to become a die, particularly in a narrow groove, and the risk of occurrence of hot cracking increases. The hot cracking that is a problem here is a crack that occurs when low melting point compounds such as P, S, Si, and Nb contained in the weld metal segregate between dendrites and austenite grain boundaries during solidification, and weld shrinkage strain is added. It is. Therefore, as one of the measures for suppressing the hot cracking, it is effective to suppress the components of the wire, specifically, impurities such as P, S, etc. to 100 ppm or less by dissolving with ultra high purity (EHP). . However, ultra high purity melting is economically difficult because it requires use of electron beam melting or a special furnace wall refractory material. For this reason, the technique which can suppress generation | occurrence | production of a hot crack even at a general impurity level is calculated | required.

  Furthermore, in order to apply the spacer described in Patent Document 1, a great number of processes and labors such as buttering, spacer installation, fixing, and accuracy management are generated. In addition, since a foreign material or a different material whose component is significantly different from that of the base material is used as the spacer, there is a possibility that the required safety level of the joint performance including the welded portion may not be satisfied. In Patent Document 1, it is described that the backing metal is removed by gouging after welding, but it is not described that the weld metal is removed as well as the welded spacer. That is, Patent Document 1 is considered to be intended for applications that allow a foreign substance / different material to remain inside a joint of a spacer. Therefore, it is difficult to apply the welding method disclosed in Patent Document 1 using a foreign object / different material as a spacer to a thermal power generation boiler or the like from the viewpoint of the safety level of productivity, economy, and joint performance.

  The present invention has been made in view of the above-mentioned problems, and the problem is that, in submerged arc welding of high Cr system CSEF steel, it is the first that can suppress the occurrence of hot cracking in the first layer without increasing the process and labor. It is to provide a layer submerged arc welding method.

  As a result of diligent research, the present inventors have conceived that the melting point drop of the weld metal of the first layer is suppressed by filling the groove with a filler having a predetermined component.

That is, the first layer submerged arc welding method according to the present invention is based on high Cr-based CSEF steel, C: 0.10% by mass or less, Si: 0.50% by mass or less, Mn: 1.50% by mass or less. , P: 0.025 mass% or less, S: containing 0.025 mass% or less, and the balance Ri Do of Fe and unavoidable impurities, der Cr is 0.5 mass% contained as the inevitable impurities The metal powder or the cut wire is filled in the groove of the base material at a spray height of 1.0 to 4.0 mm and welded.

  According to this method, the base material dilution is suppressed by the filler whose C content is controlled to a predetermined value or less, and the initial layer hot cracking is prevented without lowering the melting point of the weld metal.

  According to the first layer submerged arc welding method according to the present invention, it is possible to suppress the occurrence of the first layer hot cracking in the welding of the high Cr system CSEF steel without increasing the process and labor.

It is a front view which shows the state of the single-type welding tip in the submerged arc welding method which concerns on this invention. It is a front view which shows the state of the single-type welding tip in the submerged arc welding method which concerns on this invention. It is a front view which shows the state of the single-type welding tip in the submerged arc welding method which concerns on this invention. It is a front view which shows the state of the welding tip of a tandem system in the submerged arc welding method which concerns on this invention. It is sectional drawing which shows the shape of the narrow groove | channel of the base material in the first layer submerged arc welding method which concerns on this invention, and a first layer weld metal. It is sectional drawing which shows the lamination | stacking procedure of the welding metal by the shape of the narrow groove | channel of a base material, and a tandem system in the submerged arc welding method which concerns on this invention. It is sectional drawing which shows the dispersion state of the filler before welding in the first layer submerged arc welding method which concerns on this invention, and is equivalent to the elements on larger scale of FIG. It is a front view of the welding tip used for the submerged arc welding method concerning the present invention. It is a side view of the welding tip shown in FIG. FIG. 10 is an end view of the welding tip shown in FIG. 8 on the side from which the inserted welding wire protrudes, and is a bottom view with respect to FIG. 9. It is a front view which shows the state of the single-type welding tip in the submerged arc welding method which concerns on this invention. It is a front view which shows the state of the single-type welding tip in the submerged arc welding method which concerns on this invention. It is a front view which shows the state of the single-type welding tip in the submerged arc welding method which concerns on this invention. It is a front view which shows the state of the single-type welding tip in the submerged arc welding method which concerns on this invention. It is a front view which shows the state of the single-type welding tip in the submerged arc welding method which concerns on this invention. It is a front view which shows the state of the single-type welding tip in the submerged arc welding method which concerns on this invention.

Hereinafter, embodiments of the present invention will be described in detail.
The first layer submerged arc welding method according to the present invention (hereinafter referred to as the first layer welding method according to the present invention) is a method of first layer welding in submerged arc welding of high Cr-based CSEF steel, which can be either single or tandem. Also applies. In the single submerged arc welding, for example, as shown in FIGS. 1 to 3, a base material 10 is welded by arc welding using a welding tip 11 in which a welding wire 12 is inserted. The angle 11 (tip angle) is tilted forward (FIG. 1) or backward (FIG. 2) or perpendicular (FIG. 3) with respect to the welding direction. On the other hand, in the tandem submerged arc welding, as shown in FIG. 4, welding is performed using two of the leading electrode (welding tip) 11a and the trailing electrode (welding tip) 11b in which the welding wires 12a and 12b are respectively inserted. To do. Further, the submerged arc welding uses a welding flux (not shown) for both single and tandem systems. Further, the chip / base material distance, the chip shape, and the chip angle will be described later.

  The first layer welding method according to the present invention is a submerged arc welding method applied to the first pass, that is, the first layer welding. By the first layer welding, as shown in FIG. 5, the first layer weld metal 21 is solidified at the groove bottom in the groove. Thereafter, by repeating the pass, a new weld metal 22 is laminated upward (in the direction of the white arrow in the figure) as shown in FIG.

(Base material)
The first layer welding method according to the present invention is intended for high Cr system CSEF steel as a base material (material to be welded). There are various standards for high Cr-based CSEF steel. For example, SA387Gr. There are T10, X10CrMoVNb9-1 defined in EN standards (European standards), fire SFVAF28, fire SFVAF29, fire STBA28, fire STPA28, and fire SCMV28 defined in thermal power technical standards.

  As components of the base material, C: 0.07 to 0.14 mass%, Si: 0.50 mass% or less, Mn: 0.70 mass% or less, Ni: 0.50 mass% or less, Cr: 8. 00 to 11.50 mass%, Mo: 0.25 to 1.10 mass%, V: 0.15 to 0.35 mass%, Nb: 0.04 to 0.10 mass%, P: 0.025 mass% % Or less, S: 0.015% by mass or less, N: 0.03 to 0.10% by mass, the balance being made of Fe and inevitable impurities is preferable, and Cu: 1.70% by mass or less B: 0.060% or less, W: 2.50% or less, Co: 3.0% by mass or less.

  In the first layer welding method according to the present invention, it is preferable to combine a base metal having the above components with a welding wire and a welding flux described later. Furthermore, in the first layer welding method according to the present invention, as shown in FIG. 7, a filler 21f having the following predetermined components is filled into the groove at a predetermined spraying height h and welded.

(filler)
In the first layer welding method according to the present invention, C: 0.10% by mass or less, Si: 0.50% by mass or less, Mn: 1.50% by mass or less, P: 0.025% by mass or less, S: 0.0. Filled with a metal powder or cut wire containing 025 mass% or less, the balance being Fe and inevitable impurities, as a filler, filling the groove of the base material to a height of 1.0 to 4.0 mm and welding. . Hereinafter, the filler will be described in more detail.

(C: 0.10 mass% or less)
C causes a high temperature crack in the weld metal by lowering the melting point. In order to prevent the melting point of the weld metal from lowering, the C content of the filler is 0.10% by mass or less, preferably 0.05% by mass or less, including the dilution of the base material.

(Si: 0.50 mass% or less)
Si has the effect of adjusting the viscosity of the molten metal to adjust the bead shape. On the other hand, when it exceeds 0.50 mass%, slag seizure occurs and slag removal becomes difficult. Therefore, the Si content of the filler is 0.50 mass% or less, preferably 0.30 mass% or less.

(Mn: 1.50 mass% or less)
Mn has the effect of adjusting the viscosity of the molten metal to adjust the bead shape. On the other hand, when it exceeds 1.50 mass%, slag seizure occurs and slag removal becomes difficult. Therefore, the Mn content of the filler is 1.50% by mass or less, preferably 1.30% by mass or less.

(P: 0.025 mass% or less, S: 0.025 mass% or less)
P and S each cause a high temperature crack in the weld metal by lowering the melting point. Therefore, each content of P and S in the filler is 0.025% by mass or less, and preferably less than 0.025% by mass.

  The filler may contain Cu, Cr, Mo, Ni, Nb, V, W, Co, N, etc. as unavoidable impurities, each 0.5 mass% or less, and 0.8 mass% or less in total. .

(Spray height: 1.0-4.0mm)
When the spraying height is less than 1.0 mm, the filler is insufficient in the amount of the filler and cannot suppress the concentration of C in the weld metal in the first layer. As a result, the C concentration in the weld metal is excessive. Thus, hot cracking cannot be suppressed. Therefore, the filler has a spraying height of 1.0 mm or more, preferably 1.5 mm or more. On the other hand, if the filler is filled in excess of the spray height of 4.0 mm, the amount of the filler becomes excessive and the weld bead shape becomes a convex bead, causing poor fusion and slag entrainment. Therefore, the filler has a spray height of 4.0 mm or less, preferably 3.5 mm or less.

  As the filler, either the metal powder of the above component or a cut wire may be applied. The metal powder preferably has an average particle size of 1 mm or less, and the cut wire preferably has a wire diameter and length (cut length) of 1 mm or less, respectively.

  It should be noted that the welded portion (the first layer weld metal 21 shown in FIG. 5) using the filler may be removed according to the required safety level of the joint performance after all the welding including the second and subsequent passes are completed. . As the removal method, a known method such as gouging or machining can be applied.

(Welding wire)
The welding wire used in the first layer welding method according to the present invention is C: 0.03 to 0.13 mass%, Si: 0.05 to 0.50 mass%, Mn: 0.50 to 2.20 mass%. Ni: more than 0.20% by mass and 1.00% by mass or less, Cr: 8.00 to 10.50% by mass, Mo: 0.20 to 1.20% by mass, V: 0.05 to 0.45 N%: 0.020-0.080 mass%, P: 0.015 mass% or less, S: 0.010 mass% or less, N: 0.02-0.08 mass%, the balance being Those composed of Fe and inevitable impurities are preferable, and further Cu: 1.70% by mass or less, B: 0.005% by mass or less, W: 2.0% by mass or less, Co: 3.0% by mass or less May be.

  C, together with N, is combined with Cr, Mo, W, V, Nb, and B to precipitate various carbonitrides, and has the effect of improving the creep rupture strength. In order to sufficiently obtain this effect, the C content of the welding wire is preferably 0.03% by mass or more, and more preferably 0.04% by mass or more. On the other hand, when C is added excessively, specifically, when the C content exceeds 0.13% by mass, the hot cracking resistance deteriorates. Therefore, the C content of the welding wire is preferably 0.13% by mass or less, and more preferably 0.12% by mass or less.

  Si acts as a deoxidizer and has an effect of improving the toughness of the weld metal by reducing the amount of oxygen in the deposited metal. In order to sufficiently obtain this effect, the Si content of the welding wire is preferably 0.05% by mass or more, more preferably more than 0.05% by mass. On the other hand, Si is a ferrite-forming element. When it is added in excess, specifically, when the Si content exceeds 0.50% by mass, δ-ferrite remains in the weld metal and the toughness of the weld metal deteriorates. . Therefore, the Si content of the welding wire is preferably 0.50% by mass or less, more preferably 0.48% by mass or less, and further preferably 0.45% by mass or less.

  Mn acts as a deoxidizer and has the effect of reducing the amount of oxygen in the deposited metal and improving toughness. Mn is an austenite-forming element and has an effect of suppressing toughness deterioration due to residual δ-ferrite in the weld metal. In order to sufficiently obtain these effects, the Mn content of the welding wire is preferably 0.50% by mass or more, and more preferably 0.55% by mass or more. On the other hand, even if the Mn content exceeds 2.20% by mass, the toughness of the weld metal deteriorates. Therefore, the Mn content of the welding wire is preferably 2.20% by mass or less, and more preferably 2.15% by mass or less.

  Ni is an austenite-forming element like Mn, and has the effect of suppressing toughness deterioration due to residual δ-ferrite in the weld metal. In order to sufficiently obtain this effect, the Ni content of the welding wire is preferably more than 0.20% by mass, more preferably 0.25% by mass or more, and further preferably 0.30% by mass or more. On the other hand, even if the Ni content exceeds 1.00% by mass, the toughness of the weld metal deteriorates. Therefore, the Ni content of the welding wire is preferably 1.00% by mass or less, and more preferably 0.95% by mass or less.

  Furthermore, if the total content of Mn and Ni exceeds 1.50% by mass, the toughness of the weld metal deteriorates, and the Ac1 transformation point of the weld metal decreases, making high temperature tempering impossible, and the structure stabilization treatment becomes impossible. become unable. Therefore, the total content of Mn and Ni in the welding wire is more preferably 1.50% by mass or less.

  Cr is a main element of high Cr-based CSEF steel, which is a material to be welded (base material) of the first layer welding method according to the present invention, and is an essential element for ensuring oxidation resistance and high temperature strength. In order to sufficiently obtain this effect, the Cr content of the welding wire is preferably 8.00% by mass or more, and more preferably 8.05% by mass or more. On the other hand, Cr is a ferrite-forming element. When it is added excessively, specifically, if the Cr content exceeds 10.50 mass%, δ-ferrite remains and the toughness of the weld metal deteriorates. Therefore, the Cr content of the welding wire is preferably 10.50% by mass or less, and more preferably 10.45% by mass or less.

  Mo is a solid solution strengthening element and has an effect of improving the creep rupture strength. In order to sufficiently obtain this effect, the Mo content of the welding wire is preferably 0.20% by mass or more, and more preferably 0.22% by mass or more. On the other hand, since Mo is a ferrite-forming element, if added in excess, specifically, if the Mo content exceeds 1.20% by mass, δ-ferrite remains in the weld metal and the toughness of the weld metal. Deteriorates. Therefore, the Mo content in the welding wire is preferably 1.20% by mass or less, and more preferably 1.18% by mass or less.

  V is a precipitation strengthening element and has the effect of improving the creep rupture strength by being precipitated as carbonitride. In order to sufficiently obtain this effect, the V content of the welding wire is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more. On the other hand, V is also a ferrite-forming element, and when added excessively, specifically, if the V content exceeds 0.45 mass%, δ-ferrite remains in the weld metal and the toughness of the weld metal deteriorates. To do. Therefore, the V content of the welding wire is preferably 0.45% by mass or less, and more preferably 0.40% by mass or less.

  Nb is an element that contributes to stabilization of creep rupture strength by precipitation as solid solution strengthening and nitride. In order to sufficiently obtain this effect, the Nb content of the welding wire is preferably 0.020% by mass or more, and more preferably 0.022% by mass or more. On the other hand, Nb is also a ferrite-forming element. When it is contained in excess, specifically, when the Nb content exceeds 0.080 mass%, δ-ferrite remains in the weld metal and the toughness of the weld metal deteriorates. To do. Therefore, the Nb content of the welding wire is preferably 0.080% by mass or less, and more preferably 0.078% by mass or less.

  P and S are elements that increase the hot cracking susceptibility. When the P content exceeds 0.015% by mass, or when the S content exceeds 0.010% by mass, the hot cracking resistance deteriorates. Therefore, the P content of the welding wire is preferably regulated to 0.015% by mass or less, and more preferably 0.010% by mass or less. Moreover, it is preferable to regulate S content of a welding wire to 0.010 mass% or less, and 0.009 mass% or less is more preferable.

  N, together with C, combines with Cr, Mo, W, V, Nb, and B to precipitate various carbonitrides and has the effect of improving the creep rupture strength. In order to sufficiently obtain this effect, the N content of the welding wire is preferably 0.02% by mass or more, and more preferably 0.03% by mass or more. On the other hand, when N is contained excessively, specifically, when the N content exceeds 0.08% by mass, the slag removability deteriorates. Therefore, the N content of the welding wire is preferably 0.08% by mass or less, and more preferably 0.07% by mass or less.

  Cu is an austenite generating element and has an effect of suppressing toughness deterioration due to residual δ-ferrite in the weld metal. On the other hand, when it contains excessively, specifically, when Cu content exceeds 1.70 mass%, a hot crack will be caused. Therefore, the Cu content of the welding wire is preferably 1.70% by mass or less, more preferably 1.00% by mass or less, and further preferably 0.50% by mass or less. Cu may be contained on the surface of the welding wire by plating.

  B has the effect of increasing the creep rupture strength by dispersing and stabilizing carbides when contained in a trace amount. On the other hand, when it contains excessively, specifically, when B content exceeds 0.005 mass%, a hot crack will be caused. Therefore, the B content of the welding wire is preferably 0.005% by mass or less, more preferably 0.003% by mass or less, and further preferably 0.0015% by mass or less.

  W is an element that contributes to stabilization of the creep rupture strength by solid solution strengthening of the matrix and precipitation of fine carbides. On the other hand, since W is also a ferrite-forming element, if it is contained in excess, specifically, if the W content exceeds 2.0 mass%, δ-ferrite remains in the weld metal, and the toughness of the weld metal is reduced. to degrade. Accordingly, the W content of the welding wire is preferably 2.0% by mass or less, more preferably 1.8% by mass or less, and even more preferably 1.7% by mass or less.

  Co is an element that suppresses residual δ ferrite. On the other hand, when Co is excessively contained, specifically, when the Co content exceeds 3.0 mass%, the Ac1 point is lowered, so that high-temperature tempering is impossible and the structure cannot be stabilized. Therefore, the Co content of the welding wire is preferably 3.0% by mass or less, more preferably 2.0% by mass or less, and further preferably 1.8% by mass or less.

  The welding wire may contain 0.02% by mass or less of Ti, Al, etc. as inevitable impurities, and 0.04% by mass or less in total.

  The welding wire preferably has a wire diameter of 3 to 5 mm. If the wire diameter is less than 3 mm, a sufficient amount of welding cannot be obtained, and the welding efficiency is impaired. On the other hand, when the wire diameter exceeds 5 mm, the amount of welding becomes excessive, and even with the first layer welding method according to the present invention, it is difficult to suppress high temperature cracking of the first layer.

(Welding flux)
The welding flux used in the first layer welding method according to the present invention preferably has a basicity represented by the following formula of 1.0 to 3.3.
Basicity = [CaF ₂ + CaO + MgO + SrO + Na ₂ O + Li ₂ O + 1/2 (MnO + FeO)] / [SiO ₂ +1/2 (Al ₂ O ₃ + TiO ₂ + ZrO ₂ )]
Here, each compound in the above formula represents the content (mass%) of the compound in the welding flux.

  When the basicity of the welding flux is less than 1.0, the amount of oxygen in the weld metal is not sufficiently reduced, and the toughness of the weld metal is lowered. Therefore, the welding flux preferably has a basicity of 1.0 or more, and more preferably 1.3 or more. On the other hand, if the basicity of the welding flux exceeds 3.3, the appearance and shape of the beads are likely to be poor. Therefore, the welding flux preferably has a basicity of 3.3 or less, and more preferably 3.2 or less. In addition, as long as the basicity of the welding flux used in the first layer welding method according to the present invention satisfies this range, the other components such as the respective contents of the compounds constituting the welding flux are specifically defined. It is not something.

[Single submerged arc welding conditions]
In the first layer welding method according to the present invention, the following conditions are preferably applied in the case of single welding.

(Chip / base metal distance)
As shown in FIGS. 1 to 3 and FIGS. 11 to 16, the tip / base material distance is a distance L between the base material 10 and a portion where the welding wire 12 finally protrudes from the welding tip 11. As described above, a welding wire made of a base material and a co-material, that is, a high Cr-based CSEF steel has a higher electric resistance than a low Cr-based CSEF steel, and therefore has a large Joule heat generation, and has the same size. Even with current, the amount of welding increases. Here, the Joule heat generation increases as the distance between the tip and the base material increases. Specifically, when the tip / base metal distance exceeds 40 mm, the amount of welding becomes excessive. On the other hand, if the tip / base metal distance is less than 20 mm, there is a risk that the tip of the tip may be melted by the arc. Therefore, the distance between the tip and the base material is preferably managed in the range of 20 to 40 mm, and more preferably in the range of 25 to 35 mm.

(Chip shape)
The tip shape is a straight tube shown in FIGS. 1 to 3, a bend square shape shown in FIGS. 8 to 10, or FIG. The shape as shown in 3b may be used, and is appropriately selected from the viewpoint of ensuring the welding wire feedability and feeding position stabilization. In particular, as shown in FIGS. 8 to 10, a bend square member that is bent in a range in which the tip end portion (the lower end in FIGS. 8 and 9) that protrudes the welding wire 12 (see FIGS. 11 to 16) does not hinder wire feeding. In the shaped chip, the feeding position is stabilized, and as a result, the wire feeding speed is stabilized.

(Chip angle)
As shown in FIGS. 1 to 3 and FIGS. 11 to 16, the tip angle includes a line perpendicular to the surface of the base material 10 and an axis at a portion where the welding wire 12 finally protrudes from the welding tip 11. The angle to make. The tip angle affects the degree of heating of the wire by the welding arc, and as a result, increases or decreases the welding wire feed speed. Specifically, if the same welding current and the same tip / base metal distance L are used, the tip angle is the receding angle α (see FIGS. 1, 11, and 15) when the tip angle is β (see FIGS. 2, 12, and 15). 14)), the wire feeding speed is increased. For this reason, in order to stabilize the wire feeding speed, it is preferable to manage the tip angle within the range of the receding angle α up to 60 ° and the forward angle β up to 60 °.

(Welding wire feed speed V: 50 to 120 g / min)
If the welding wire feed speed is less than 50 g / min, the welding current is too low, the arc becomes unstable, and penetration defects are likely to occur. Therefore, the feeding speed of the welding wire is preferably 50 g / min or more, and more preferably 55 g / min or more. On the other hand, when the feeding speed of the welding wire exceeds 120 g / min, the amount of welding becomes excessive, and hot cracking is likely to occur, and the slag peelability is also deteriorated. Accordingly, the feeding speed of the welding wire is preferably 120 g / min or less, and more preferably 115 g / min or less.

(Welding speed v: 20 to 60 cm / min)
If the welding speed is less than 20 cm / min, the amount of welding becomes excessive and hot cracking is likely to occur. Therefore, the welding speed is preferably 20 cm / min or more, and more preferably 25 cm / min or more. On the other hand, when the welding speed exceeds 60 cm / min, the molten metal cannot be supplied in time, the bead shape becomes unstable, and fusion failure and slag winding are likely to occur. Therefore, the welding speed is preferably 60 cm / min or less, and more preferably 55 cm / min or less.

(Welding amount per unit weld length: 1.8 to 4.5 g / cm)
The amount of deposition per unit weld length is the welding wire feed speed / welding speed. If the welding amount per unit weld length is less than 1.8 g / cm, the welding amount is insufficient, the bead shape becomes unstable, and poor fusion or slag entrainment occurs. Therefore, the deposition amount per unit weld length is preferably 1.8 g / cm or more, and more preferably 2.0 g / cm or more. On the other hand, if the amount of welding per unit weld length exceeds 4.5 g / cm, the amount of welding becomes excessive, and the amount of solidification shrinkage of the molten metal becomes excessive and the shape of the weld is indefinite. However, it becomes perpendicular to the final solidified part and hot cracks are likely to occur. Therefore, the deposition amount per unit weld length is preferably 4.5 g / cm or less, and more preferably 4.3 g / cm or less.

  The welding current and the arc voltage are adjusted as one means for controlling the welding wire feeding speed within an appropriate range. The power supply characteristic may be either a drooping characteristic or a constant voltage characteristic. Here, the drooping characteristic is a characteristic of a power source that can perform stable welding with little change in current even if the arc length varies. Specifically, when the arc length becomes long, the wire feed speed is temporarily increased, and when the arc length becomes short, the wire feed speed is slowed to stabilize the current. Turn into. Either DCEP or AC may be applied as the power polarity.

[Tandem submerged arc welding conditions]
The first layer welding method according to the present invention is applicable also to tandem welding, and it is preferable to apply the following conditions. Note that the tip shape is the same as that of single welding, such as a straight tube shape shown in FIG. 4, a bend square shape shape shown in FIGS. 8 to 10, or FIG. The shape is appropriately selected from the shapes shown in 3b.

(Chip / base metal distance)
As shown in FIG. 4, the tip / base material distance is the distance between the base material 10 and the portion where the welding wire 12 a (12 b) finally protrudes from the welding tip 11 a (11 b), as in the case of single welding. L, and a range of 20 to 40 mm is preferable. The tip / base material distance may not be the same between the leading electrode 11a and the trailing electrode 11b. Further, the tip / base metal distance when the tip shape of the welding tips 11a and 11b is the bend square shape shown in FIGS. 8 to 10 is indicated by a distance L between the welding tip 11 and the base material 10 in FIGS. Street.

(Chip angle)
As shown in FIG. 4, the tip angle is a line perpendicular to the surface of the base material 10 and a portion where the welding wire 12a (12b) finally protrudes from the welding tip 11a (11b) as in the case of single welding. An angle α (β) formed by the axis of. For both the leading pole 11a and the trailing pole 11b, the tip angle (receding angle α, advancing angle β) is managed within a range of ± 60 ° (from the receding angle 60 ° to the advancing angle 60 °). Preferred for stabilization. The tip angles α and β when the tip shape of the weld tips 11a and 11b is the bend square shape shown in FIGS. 8 to 10 are as shown by the tip angles α and β of the weld tip 11 in FIGS.

(Feeding speed of the welding wire leading electrode V _L: 45~90g / min, the trailing electrode V _T: 60~110g / min)
If the welding wire feed speed is less than 45 g / min at the leading electrode or less than 60 g / min at the trailing electrode, the welding current is too small, the arc becomes unstable, and penetration defects tend to occur. On the other hand, if the feeding speed of the welding wire exceeds 90 g / min at the leading electrode or exceeds 110 g / min at the trailing electrode, the amount of welding becomes excessive and high temperature cracking is likely to occur, and slag peelability It gets worse. In tandem welding, it is preferable that the feeding speed of the welding wire of the leading electrode is slower than that of the trailing electrode. By reducing the amount of metal deposited by the leading electrode, the bead depth can be reduced, the bead width can be increased, and hot cracking is difficult. Therefore, the feeding speed of the welding wire is preferably in the range of 45 to 90 g / min for the leading electrode and 60 to 110 g / min for the trailing electrode.

(Welding speed v: 30 to 55 cm / min)
If the welding speed is less than 30 cm / min, the amount of welding becomes excessive and hot cracking is likely to occur. On the other hand, when the welding speed exceeds 55 cm / min, the molten metal cannot be supplied in time, the bead shape becomes unstable, and fusion failure and slag winding are likely to occur. Therefore, the welding speed is preferably in the range of 30 to 55 cm / min.

(Welding amount per unit weld length: 2.8 to 3.8 g / cm)
The amount of welding per unit weld length is (feeding speed of the welding wire of the leading electrode + feeding speed of the welding wire of the trailing electrode) / welding speed. When the welding amount per unit weld length is less than 2.8 g / cm, the welding amount is insufficient and the welding efficiency is lowered. On the other hand, if the amount of welding per unit weld length exceeds 3.8 g / cm, the amount of welding becomes excessive, and the amount of solidification shrinkage of the molten metal becomes excessive and the shape of the penetration is not formed. However, it becomes perpendicular to the final solidified part and hot cracks are likely to occur. Therefore, the amount of deposition per unit weld length is preferably in the range of 2.8 to 3.8 g / cm.

  The power supply characteristic may be either a drooping characteristic or a constant voltage characteristic as in the case of single welding. Further, either DCEP or AC may be applied as the polarity. Moreover, you may apply V connection and Scott connection.

  The first layer welding method according to the present invention may be applied to a base material having a plate thickness of less than 150 mm. Further, application to the X groove is not excluded. When applied to the X groove, in the welding to the back side, the first layer welding is performed by filling the groove with the filler in the same manner as the front side. Further, after the first pass after the first layer welding by the first layer welding method according to the present invention, it can be welded by submerged arc welding in the same manner as the welding conditions except for the filler or under different conditions, Alternatively, a welding method such as gas shield arc welding may be applied.

  As mentioned above, although the form for implementing this invention has been described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. It should be noted that the present invention is not limited by this embodiment, and can be implemented with modifications within the scope shown in the claims, all of which are included in the technical scope of the present invention.

[Test specimen preparation]
A plate material having a thickness of 250 mm made of high Cr-based CSEF steel having the components shown in Table 1 is prepared. By machining, the radius of curvature R of the groove groove bottom is 10 mm, and the groove angle θ is 4 °. A narrow groove was formed as a base material (see FIG. 5). Moreover, the shape (metal powder, cut wire) and the filler of a component shown in Table 4 were prepared, and it filled with the spraying height h (refer FIG. 7) shown in Table 4 in the groove | channel of the base material. As for the filler, the metal powder has an average particle diameter of 75 μm, the cut wire has a wire diameter of 1 mm, and a cut length of 1 mm.

  Using a welding wire having a wire diameter of 4 mm with the components shown in Table 2 and a welding flux with the particle size and components shown in Table 3, submerged arc welding is performed on the groove of the base metal with a tip bent tip (see FIGS. 8 to 10). The test body 20 shown in FIG. 5 was produced by performing one pass for each layer under the following conditions.

(Welding conditions)
Tip / base material distance: 30 mm
Tip angle: 0 °
Electrode characteristics: Drooping characteristics Electrode polarity: AC single Welding posture: downward Welding current: 400A
Welding voltage: 31V
Welding wire feed speed: 80 g / min
Welding speed: 40 cm / min
Welding amount per unit weld length: 2.0 g / cm

[Evaluation]
(Health of welds)
In the prepared specimen, within a range of 300 mm excluding the start and end of the weld bead, the macro structure was visually observed in cross sections every 50 mm, and weld defects (slag entrainment, slag peelability, slag seizure) The presence or absence of poor fusion and poor penetration) was observed. The slag peelability was determined by passing the flux adhering to the bead surface after welding three times with a hammer and passing the slag easily peeled, and rejecting the one not peeled off. Those having no welding defects are indicated by “◯” in Table 4, and those having welding defects are shown in Table 4.

  After observation of the weld defect, the bead shape was visually observed. Specifically, in the evaluation of slag peelability, the surface appearance of the trace of the slag was peeled off, and when the bead shape was stable, “○” was passed, and when unstable, “×” was rejected. 4 shows.

(High temperature crack resistance)
The test specimen was cut at 5 locations every 50 mm in a range of 300 mm in length excluding the start and end portions of the weld bead, and the macrostructure of the cross section was observed. Table 5 shows that no cracks occurred in all of the five cross-sections as “good” as acceptable, and “x” as those where one or more cracks occurred as unacceptable.

  As shown in Table 4, the test specimen No. In Nos. 1 to 3, the filler component and the spread height of the groove were within the scope of the present invention, and the soundness and hot crack resistance of the welded portion were good.

  In contrast, the test specimen No. In No. 4, since the C content of the filler was excessive, hot cracking occurred due to the concentration of C in the weld metal. Test material No. No. 5 shows that the Si content of the filler is the test material No. In No. 6, slag seizure occurred because the Mn content of the filler was excessive. Test material No. No. 7 has a P content of the filler of test material No. In No. 8, since the S content of the filler was excessive, hot cracking occurred.

  Specimen No. In No. 9, since the spraying height of the filler was excessive, the weld bead shape became a convex bead, which resulted in poor fusion and slag entrainment. Specimen No. In No. 10, since the spraying height of the filler was insufficient, concentration of C in the weld metal could not be suppressed, and hot cracking occurred.

10 Base material (material to be welded)
11 Welding tip 11a Leading electrode (welding tip)
11b trailing electrode (welding tip)
12, 12a, 12b Welding wire 20 Specimen 21 First layer weld metal 21f Filler 22 Weld metal

Claims (1)

A first layer submerged arc welding method using a high Cr-based CSEF steel as a base material,
C: 0.10% by mass or less, Si: 0.50% by mass or less, Mn: 1.50% by mass or less, P: 0.025% by mass or less, S: 0.025% by mass or less, the balance being Ri Do of Fe and unavoidable impurities, the metal powder or cut wire Cr is Ru der 0.5 mass% contained as the inevitable impurities, spraying height to the open destination within the base material from 1.0 to 4 A first layer submerged arc welding method characterized by filling and welding to 0.0 mm.

Images