JP2011206828A - Flux-cored welding wire for fine diameter wire multiple electrode submerged arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux-cored welding wire with a diameter of ≤3.2 mm which is favorably used for fine diameter wire multiple electrode submerged arc welding with three or more electrodes and excellent in the low-temperature toughness of a welded metal.SOLUTION: The flux-cored welding wire has the wire entire composition containing by mass, 0.04-0.22% C, 0.1-0.6% Si, 1.0-3.0% Mn, 0.01-0.25% Ti, 0.01-0.5% REM, and further containing one or two kinds of ≤10.0% Ni, ≤3.0% Mo, and further containing 0.1-0.5% BOand ≤0.5% Cu as necessary, and the balance Fe with inevitable impurities, wherein the mass ratio (the filling ratio) of the metallic flux component to the entire wire mass is 10-40%.

Description

  The present invention relates to a flux-cored welding wire used for pipe-making welding of a high-strength large-diameter welded steel pipe used for natural gas or the like, and is particularly suitable for use in small-diameter multi-electrode submerged arc welding with three or more electrodes. , Relating to a diameter of 3.2 mm or less.

 In recent years, in order to reduce the total cost of natural gas or crude oil transportation pipelines, the application of high-strength large-diameter steel pipes that can reduce the amount of steel used and reduce the cost of on-site welding as well as increasing the operating pressure has begun to be studied. . Such welded steel pipes are generally submerged due to their superior weld quality, beautiful bead appearance, and high-speed welding with high heat input. Manufactured by single-sided double-sided welding from inside and outside by arc welding. In addition, there is a strong demand for higher strength or thicker steel pipes to be applied, and development of steel pipes, welding methods, and welding materials to satisfy such demands are extremely important technologies.

  However, in the above-described high-strength material or thick-walled welded portion, there is an example in which it is difficult to ensure the mechanical properties, particularly the low temperature toughness of the weld heat affected zone (hereinafter referred to as HAZ). It is often scattered. This is because the steel plate must have a high chemical composition in order to satisfy the strength properties required for the material, and the thermal effect due to general multi-electrode double-sided submerged arc welding is relatively large. In order to solve this problem, many inventions related to the steel pipe composition and welding methods have been proposed.

  Among them, for example, a multi-electrode submerged arc welding method using a thin wire (hereinafter referred to as a thin SAW) disclosed in Patent Document 1, Patent Document 2 and the like is applied to a thin wire. This is a welding method capable of obtaining a predetermined HAZ toughness without changing the chemical composition of the steel pipe to be applied, due to the effect of increasing the current density and the effect of reducing the welding heat input obtained by the deep penetration characteristics. In addition to such high-strength / thick-walled steel pipes, even steel pipes that require severe low-temperature toughness even with relatively low-strength materials can be expected to have an improved toughness.

  As a welding material applied to the small-diameter SAW, either a solid solid wire or a flux-cored wire in which a flux component is filled in a hollow structure is used. Welding wires for steel pipes that require high-strength, thick-walled steel pipes or low-temperature toughness, alloy elements such as Ni and Mo are added to ensure their mechanical properties, especially low-temperature toughness. The solid wire generally has high strength. For this reason, the productivity of the drawing / reducing process is extremely poor, and a softening heat treatment must be performed in the middle of the diameter reducing process, and even when the heat treatment is performed, cracks, cracks, etc. may occur on the surface. In addition, the productivity and economy of the welding wire for small-diameter SAW, where the diameter reduction processing becomes more severe, are significantly reduced.

  On the other hand, the flux-cored wire is manufactured by filling a hollow steel outer shell with metal (alloy) powder, flux components, etc., so there is no problem of work hardening at the time of wire drawing like during solid wire production, The decrease in manufacturability associated with work hardening as in the production of solid wire is basically small even with a small diameter and high alloy wire, and is excellent in productivity and economy. A flux cored wire for welding is disclosed.

JP 2003-33876 A JP 2006-263814 A Japanese Patent Laid-Open No. 48-85443 JP 61-242791 A

  As described above, the high strength steel pipe welding wire that needs to contain a lot of alloy components is preferably a flux-cored wire from the viewpoint of productivity. In particular, the multi-electrode submerged arc welding method using a small-diameter (3.2 mm or less) welding wire is effective in increasing the thickness of the plate even when the welding heat input is reduced due to the effect of improving the current density by reducing the diameter of the wire. Since the penetration is obtained, it is easy to ensure the HAZ toughness even in the case of a high-strength steel pipe. Therefore, it is desirable to use a small-diameter flux-cored wire.

  However, in the case of a flux-cored wire, the chemical component variation due to the homogeneity of the filler is slightly larger than that of the solid wire manufactured by melting, and due to the alloy component / flux component being filled. The oxygen content of the weld metal tends to be slightly higher, and there is a concern that the low-temperature toughness will decrease with an increase in the oxygen content of the weld metal.

  As a feature of the flux-cored wire, there is a tendency that the initial oxygen amount tends to be higher than that of the solid wire due to the influence of oxides and water of crystallization contained in the filler, and also a feature of the small diameter SAW. Reduction of heat input increases the solidification rate of the molten part compared with general SAW welding, so the deoxidation reaction in the molten pool and the rise of the deoxidized product are not sufficiently promoted, and oxygen in the weld metal part The amount tends to increase.

  Although there is a craving for a flux-cored wire having a composition that can ensure toughness even in a situation where the weld metal part is low-oxygenated or oxygen is somewhat high to some extent, no examples have been achieved yet.

  Accordingly, an object of the present invention is to provide a flux cored wire for thin multi-electrode multi-merged submerged welding which has excellent weld metal part characteristics and is excellent in economic productivity in thin multi-electrode submerged welding.

  Generally, the toughness of the high strength steel weld metal part tends to be improved by reducing the amount of oxygen. The amount of oxygen in the weld metal part varies depending on the composition of the base metal and welding wire to be applied, the amount of deoxidizing element contained, the composition ratio / basicity of the applied flux, welding conditions (current, voltage, speed, etc.) Since it is determined under the control factors, it is extremely difficult to control.

  In order to solve the above-mentioned problems, the present inventors have intensively studied and are able to manufacture by utilizing the feature of the flux-cored wire manufacturing process that does not require a furnace melting process in manufacturing the welding wire. In the case of a flux-cored wire containing a relatively large amount, a new finding has been found that low temperature toughness can be ensured even in a weld metal containing a certain amount of oxygen.

The present invention has been made by further study based on the above knowledge, that is, the present invention,
1. It is a metal-based flux-cored wire used for multi-electrode submerged arc welding of 3 or more electrodes, the diameter is 3.2 mm or less, and the total of the steel outer sheath and flux components is the total mass% of the wire, C: 0.04 -0.22%, Si: 0.1-0.6%, Mn: 1.0-3.0%, Ti: 0.01-0.25%, REM: 0.01-0.5%, In addition, Ni: 10.0% or less, Mo: 3.0% or less, one or two of the balance, Fe and unavoidable impurities, the mass ratio of the metal-based flux component to the total mass of the wire (filling The flux-cored welding wire for small-diameter multi-electrode submerged arc welding, characterized in that the ratio is 10 to 40%.
2. The total of the steel outer sheath and the flux component is the total mass% of the wire, and further, the mass%, B ₂ O ₃ ; 0.1 to 0.5%, Cu: 0.5% or less, Cr: 1.0% or less V: 0.1% or less, Nb: 0.05% or less, 1 or 2 or more types, The flux-cored welding wire for small diameter multi-electrode submerged arc welding of 1 characterized by the above-mentioned.
3. A thin multi-electrode submerged arc welding method using the flux-cored welding wire for thin multi-electrode submerged arc welding according to 3.1 or 2.
4). A welded steel pipe manufactured using the flux-cored welding wire for thin multi-electrode submerged arc welding described in 1 or 2 for pipe making welding.

  According to the present invention, it is possible to obtain a welding wire for thin multi-electrode submerged arc welding having excellent toughness of the weld metal part. Therefore, natural gas, high-strength line pipe for crude oil transportation, structural high-strength steel pipe, etc. It is possible to manufacture welded steel pipes that require low-temperature toughness and low-diameter multi-electrode submerged arc welding with excellent productivity and economy, which is extremely useful industrially.

The figure which shows the groove shape for evaluation joint preparation, (a) shows the groove shape when a thin wire is used, and (b) shows the groove shape when a 4.0 mmφ wire is used. The figure explaining the collection point of a Charpy impact test piece.

In the present invention, the total component composition of the steel-based flux-cored wire and the steel outer sheath and the metal flux (hereinafter referred to as the wire total component composition) and the mass ratio of the metal flux component to the total mass of the wire (filling rate%) Stipulate.
[Total composition of wire components]
In the following description, “%” means “mass%”.
C: 0.04 to 0.22%
C is a strengthening element for securing the strength of the weld metal part, and by the effect of reducing the oxygen content of the weld metal part by the CO gas generation reaction under an arc atmosphere and the shielding effect of the generated CO gas, the weld metal part It is an extremely important element having a combined effect of preventing the inclusion of N into the metal.

  If the content is less than 0.04%, an effect due to the generation of CO gas cannot be obtained, and when application to high-strength steel is assumed, insufficient strength is caused. On the other hand, when the content exceeds 0.22%, the weld metal part structure becomes a quenched structure such as martensite, and the toughness decreases. Therefore, it is specified to be 0.04 to 0.22%.

Si: 0.1-0.6%
Si has the effect of reducing the oxygen content of the weld metal part as a strengthening element in order to ensure the strength of the weld metal part and to have a deoxidizing ability. If the content is less than 0.1%, this effect is insufficient. On the other hand, if the content exceeds 0.6%, the formation of MA (Martensite-Austenite constituent) in the weld metal is promoted, and the toughness decreases. Therefore, it is specified to be 0.1 to 0.6%.

Mn: 1.0-3.0%
Mn contributes to securing the strength of the weld metal by improving the hardenability. Since it is cheaper than other alloy components, it can be actively added to ensure the strength of the weld metal. If it is less than 1.0%, the hardenability is insufficient, so the strength of the weld metal part is lowered. On the other hand, if it exceeds 3.0%, the hardenability becomes excessive and the toughness decreases. Therefore, it is specified to be 1.0 to 3.0%.

1 type or 2 types of Ni: 10.0% or less and Mo: 3.0% or less Ni contributes to securing the strength of the weld metal part by improving hardenability, and effectively acts to improve toughness. If the content exceeds 10.0%, the effect of improving toughness is saturated, and depending on the welding conditions, etc., it may promote high temperature cracking of the weld metal part. .

  Mo improves the strength of the weld metal part by improving the hardenability, but if it exceeds 3.0%, the hardenability becomes excessive and may promote toughness reduction. % Or less.

Ti: 0.01 to 0.25%
Ti is effective as a deoxidizing element for reducing oxygen in the weld metal part. Moreover, in order to produce | generate Ti oxide and Ti nitride in a weld metal, and to contribute to toughness improvement, 0.01% or more is contained. On the other hand, when it contains exceeding 0.25%, generation | occurrence | production of Ti carbide | carbonized_material is encouraged and it comes to reduce a toughness remarkably, Therefore It prescribes | regulates to 0.01 to 0.25%.

REM: 0.01 to 0.5%
REM is the most important element in the present invention, and its effects and reasons for limitation are as follows. REM is mainly composed of alkaline earth metals such as Ce and La, and has a relatively strong deoxidizing ability. Further, it is known that a deoxidation product of REM is finely generated as an oxysulfide, unlike an oxide that easily aggregates such as Al oxide. An attempt has been made to improve the toughness by adding tens of ppm of REM to a steel sheet for high heat input welding, for example, using the effect of refining the microstructure by the finely dispersed oxysulfide.

  On the other hand, in order to achieve the same effect with the weld metal, it is necessary to add a large amount of REM to the welding wire in advance because the yield of REM is extremely low in the process of melting and resolidifying the welding wire. In the case of a general solid wire, adding a large amount of REM at the melting stage promotes various manufacturability reductions such as nozzle clogging and billet cracking promotion during steelmaking, and thus is not very realistic. On the other hand, in the case of a flux-cored wire, since REM can be directly contained in the filler, it is possible to leave sufficient REM oxysulfide in the weld metal even at a low yield rate during welding. It becomes. However, if the content is less than 0.01%, REM does not yield in the weld metal. On the other hand, if it exceeds 0.5% and is added excessively, the amount of oxysulfide is excessively increased and the toughness is reduced. Therefore, the REM content is specified to be 0.01 to 0.5%.

Metal flux filling rate: 10-40%
When the filling rate of the metal-based flux component is less than 10%, molding becomes difficult and an alloy component for ensuring strength toughness is insufficient. On the other hand, when the filling rate exceeds 40%, the drawability of the welding wire is lowered, and the manufacturability such as disconnection during the process is hindered. The filling rate (%) is a mass ratio of the metal-based flux component to the total mass of the wire, and is defined as metal-based flux / total mass of the wire (= steel outer shell + metal-based flux) × 100 (%).

The above is the basic configuration of the present invention. In the case where the characteristics are further improved, B ₂ O ₃ ; 0.1 to 0.5%, Cu: 0.5% or less, Cr: It is possible to contain one or more of 1.0% or less, V: 0.1% or less, and Nb: 0.05% or less.

B ₂ O ₃ ; 0.1-0.5%
B ₂ O ₃ dissociates in the arc and supplies B to the weld metal. In order to improve the hardenability of the weld metal part to increase the strength and improve the toughness by suppressing the formation of intergranular ferrite, it is included as a flux component. However, if it is less than 0.1%, the yield is low, so B is welded. The above effect cannot be obtained without remaining in the metal. On the other hand, if the content exceeds 0.5%, the B of the weld metal becomes excessive and promotes toughness reduction and hot cracking. ˜0.5%.

Cu: 0.5% or less, Cr: 1.0% or less, V: 0.1% or less, Nb: 0.05% or less Cu, Cr, V, and Nb are contained when improving the strength of the weld metal part. However, if it is contained excessively, the toughness will decrease, so Cu: 0.5% or less, Cr: 1.0% or less, V: 0.1% or less, Nb: 0.05% or less . Hereinafter, the effects of the present invention will be described in detail with reference to examples.

  Mild steel strip was formed into a U shape, filled with metal fluxes having various component compositions that had been adjusted in advance, and lap-molded into an O shape, and then a welding wire was prepared by wire drawing and annealing processes. Note that the wire diameter is basically a thin wire having a diameter of 2.4 or 3.2 mm within the scope of the present invention, and a diameter of 4.0 mm, which is often applied in general submerged arc welding as a comparative example. Added. Table 1 shows the dimensions and composition of the mild steel strip steel, and Table 2 shows the total composition of the wires (total composition of the steel outer sheath and the metal flux).

  By combining the obtained welding wire and the melt type flux, a joint of a thick steel plate (plate thickness 25.4 mm) provided with a groove shape shown in FIG. 1 was welded by double-sided single-layer submerged arc welding. Table 3 shows the composition of the melt type flux, and Table 4 shows the welding conditions. When a thin wire is applied, since the penetration depth in the plate thickness direction is increased, the groove cross-sectional area can be reduced and the welding heat input can be reduced even with the same plate thickness.

  The weld joint toughness of the obtained welded joint was evaluated by a Charpy impact test. In the Charpy impact test, as shown in FIG. 2, a Charpy impact test piece (JIS Z22024) was sampled around a position 7 mm below the outer steel plate surface, and the notch position was (a) the center of the weld metal part and ( b) The absorbed energy (average value of 10 pieces) at a test temperature of −30 ° C. was determined with the melt line part (position where the ratio of the weld metal and the heat-affected part was 50% each). The absorbed energy was defined as good if it was 100 J or more. The evaluation results are summarized in Table 5.

  From Table 5, it is clear that in the joints (A1 to A22) using the welding wire for small diameter SAW welding according to the present invention, the low temperature toughness of the weld metal part and the melt line part is very good.

  On the other hand, in the case of the comparative examples (B1 to B12) in which the chemical composition of the welding wire or the filling rate of the flux deviates from the range defined in the present invention, the welding heat input is reduced by the application of the small diameter multi-electrode welding. For this reason, although the low temperature toughness of the molten wire portion is good, the toughness of the weld metal portion is low (B1 to B10), the manufacturability of the wire is lowered, and the wire is being manufactured or being welded. Wire bending (B11) or disconnection occurred (B12).

  Furthermore, in the case of the comparative examples (B13 to B15) using the normal 4.0 mmφ wire, the weld metal part toughness satisfies the predetermined performance, but the heat input is excessive, so the low temperature toughness of the melt line part is low. Results were obtained.

Claims (4)

  It is a metal-based flux-cored wire used for multi-electrode submerged arc welding of 3 or more electrodes, the diameter is 3.2 mm or less, and the total of the steel outer sheath and flux components is the total mass% of the wire, C: 0.04 -0.22%, Si: 0.1-0.6%, Mn: 1.0-3.0%, Ti: 0.01-0.25%, REM: 0.01-0.5%, In addition, Ni: 10.0% or less, Mo: 3.0% or less, one or two of the balance, Fe and unavoidable impurities, the mass ratio of the metal-based flux component to the total mass of the wire (filling The flux-cored welding wire for small-diameter multi-electrode submerged arc welding, characterized in that the ratio is 10 to 40%. The total of the steel outer sheath and the flux component is the total mass% of the wire, and further, the mass%, B ₂ O ₃ ; 0.1 to 0.5%, Cu: 0.5% or less, Cr: 1.0% or less V: 0.1% or less, Nb: 0.05% or less, or one or more of them, containing a flux cored welding wire for small-diameter multi-electrode submerged arc welding according to claim 1.   A thin multi-electrode submerged arc welding method using the flux-cored welding wire for thin multi-electrode submerged arc welding according to claim 1 or 2.   A welded steel pipe manufactured by using the flux-cored welding wire for thin multi-electrode submerged arc welding according to claim 1 or 2 for pipe making welding.

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