JP2008105036A - Flux-cored wire for submerged arc welding for high-strength steel. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a weld metal having high strength and toughness of weld metal in high-speed submerged arc welding of high-strength steel, and capable of obtaining a weld metal having good wire productivity and bead shape and no weld defects. A flux cored wire for submerged arc welding of steel is provided.
The total of the steel outer sheath and the flux component is the total mass% of the wire, C: 0.05 to 0.30%, Si: 0.1 to 0.5%, Mn: 1.0 to 3.0. %, Ni: 2.0 to 9.0%, Cr: 1.5 to 3.5%, Mo: 1.0 to 4.0%, Ti: 0.02 to 0.10%, Mg: 0.0. 2 to 0.7% is contained, the balance is made of Fe and inevitable impurities, and the flux filling rate in the wire component is 10 to 30% by mass. Further, the filling flux is characterized by the total mass% of the flux, O: 0.2-1.0%. In addition, the steel outer skin is seamless.
[Selection] Figure 1

Description

  The present invention relates to a flux-cored wire for submerged arc welding for high-strength steel used in oil and natural gas line pipes, containers used for storage, and the like, and particularly excellent in high-speed welding conditions. The present invention relates to a flux-cored wire for submerged arc welding for high-strength steel capable of obtaining weld metal and bead shape with mechanical performance and welding workability.

  High-strength steel is used in line pipes used for the transportation of oil and natural gas, containers used for storage, etc. Recently, in order to reduce the amount of steel used by reducing the thickness, Strengthening of steel materials is underway. It is important to increase the strength and toughness of the weld metal as the strength of the steel increases.

  Conventionally, a solid wire containing an alloy component such as Ni, Cr, or Mo has been mainly used as a high-strength submerged arc welding wire for the purpose of increasing the strength of a weld metal part. However, when the alloy component amount of the wire is increased to increase the strength of the weld metal, the wire itself has high strength, and work hardening is added and the wire is further cured at the time of wire drawing in manufacturing the welding wire. When the wire is hardened, die wear and wire breakage increase, making manufacturing difficult. Therefore, in general, heat treatment is performed in the middle of wire drawing to reduce the strength of the wire, but when the alloy component is large, the transformation temperature of the wire is lowered. Retention is required. In addition, when softening is performed by a high-temperature normalizing treatment, the structure is easily transformed into a high-strength structure. Therefore, in order to soften, it is necessary to lower the heat treatment temperature and hold for a long time or gradually cool, and the productivity is very poor.

  Further, when welding is performed using a high-strength solid wire, it becomes difficult to correct the wire, and the center deviation from the groove center tends to occur, and a good bead cannot be obtained. As described above, the high-strength solid wire has a problem that productivity and weldability are lowered. Therefore, various flux cored wires have been developed, but in order to obtain a high strength and high toughness weld metal, it is necessary to reduce the oxygen content of the weld metal, which has been difficult with conventional flux cored wires. .

  In consideration of these points, attempts have been made to develop a wire for submerged arc welding which has good productivity and weldability and can provide high strength and high toughness. For example, a composite wire for submerged arc welding with low wire tensile strength is disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-142377 (Patent Document 1), which improves wire productivity and feedability. In the flux-cored wire, since the amount of oxygen in the wire is high, the amount of oxygen in the weld metal increases, and good low temperature toughness cannot be obtained. Furthermore, since the wire cross-sectional shape is a flux-cored wire having a seam, it absorbs moisture in the atmosphere. Therefore, it is not sufficient to reduce the moisture content of the flux, and the amount of diffusible hydrogen in the weld metal increases and delay cracking is likely to occur after welding.

  Further, JP-A-48-85443 (Patent Document 2) contains a strong basic slag forming component in the flux to be filled and is used in combination with a neutral flux or a weak basic flux. Disclosed is a submerged arc welding composite wire that can achieve excellent welding workability and high toughness. However, since the amount of oxygen in the weld metal is also affected by the combined flux, there is a limit to the significant reduction in the amount of oxygen in the method combining the neutral flux and the weakly basic flux. Further, since a large amount of slag forming components are contained in the flux to be filled, the alloy components are insufficient, which is insufficient for the demand for higher strength and higher toughness.

Further, a high-toughness composite wire for submerged arc welding is disclosed in Japanese Patent Laid-Open No. 49-103858 (Patent Document 3), and a large-diameter seamless flux-cored wire for large heat input submerged arc welding of low-temperature steel is disclosed in Japanese Patent Laid-Open No. 61-242791. Although it is disclosed by the gazette (patent document 4), there exists a problem that the yield strength and intensity | strength of a weld metal are insufficient in the described wire component.
JP 2006-142377 A Japanese Patent Laid-Open No. 48-85443 JP-A 49-103858 JP 61-242791 A

  An object of the present invention is to provide a flux cored wire for submerged arc welding for high-strength steel capable of obtaining a weld metal and bead shape having excellent mechanical performance even under high-speed welding conditions and welding workability.

  The gist of the present invention is that, in a flux cored wire for submerged arc welding for high-strength steel, the total of the steel outer sheath and flux components is the total mass% of the wire, C: 0.05 to 0.30%, Si: 0.00. 1-0.5%, Mn: 1.0-3.0%, Ni: 2.0-9.0%, Cr: 1.5-3.5%, Mo: 1.0-4.0% Ti: 0.02 to 0.10%, Mg: 0.2 to 0.7%, the balance is made of Fe and inevitable impurities, and the flux filling rate of the flux in the wire component is 10 to 10. It is 30 mass%. Further, the filling flux is characterized by the total mass% of the flux, O: 0.2-1.0%. Further, the present invention is a flux-cored wire for submerged arc welding for high-strength steel, characterized in that the steel outer skin is seamless.

  According to the submerged arc welding wire for high-strength steel of the present invention, in high-speed submerged arc welding of high-strength steel, it is easy to manufacture a wire containing a large amount of alloy components, and a high-strength, high-toughness weld metal is formed. In addition, it is possible to obtain a better welding workability and bead shape, and to reduce the amount of oxygen and the amount of diffusible hydrogen in the weld metal.

In order to solve the above-mentioned problems, the present inventors have made various studies on the wire component, which is the sum of the steel outer shell and the flux, the flux filling rate, the oxygen content of the filling flux, and the like.
As a result, the wire contains an appropriate amount of C, Si, Mn, Ni, Cr, Mo, Ti, Mg, and by limiting the flux filling rate, the wire productivity is good and a high strength weld metal is obtained. It has also been found that a tough weld metal can be obtained by adjusting the amount of O in the filling flux to an appropriate amount. Furthermore, it has been found that by eliminating the seam in the steel outer shell, good welding workability can be obtained and the amount of diffusible hydrogen in the weld metal can be reduced.

The reasons for limiting the components of the flux-cored wire for submerged arc welding for high-strength steel of the present invention will be described below.
(C of the whole wire: 0.05 to 0.30 mass% (hereinafter referred to as%))
C is an important element for ensuring the strength of the weld metal by solid solution strengthening, and has an effect of reducing the arc atmosphere and oxygen of the weld metal by reacting with oxygen in the arc. If the C of the total of the steel outer shell and the flux component (hereinafter referred to as the wire component) is less than 0.05%, the effect of deoxidation and securing the strength is insufficient, and if it exceeds 0.30%, the weld metal contains Since C of the steel becomes high, it becomes a structure mainly composed of martensite, and the strength is increased, but the proof stress and toughness are lowered.

(Si: 0.1-0.5%)
Si is an important element for improving the strength and toughness of the weld metal, and since it combines with oxygen during welding to become a slag component, it has an effect of reducing oxygen in the weld metal. If the wire component Si is less than 0.1%, the effects of improving the strength, toughness and reducing oxygen cannot be obtained. On the other hand, if it exceeds 0.5%, the matrix in the weld metal is strengthened by solid solution, and the toughness is remarkably lowered.

(Mn: 1.0-3.0%)
Mn is an effective component for improving the hardenability and increasing the strength. If the Mn of the wire component is less than 1.0%, the hardenability is insufficient and the strength is insufficient. If it exceeds 3.0%, the hardenability becomes excessive, the strength of the weld metal increases, and the toughness decreases.

(Ni: 2.0-9.0%)
Ni aims at ensuring the strength and toughness of the weld metal. If the wire component Ni is less than 2.0%, the effect is insufficient, and if it exceeds 9.0%, the austenite fraction becomes excessive, the weld metal strength decreases, and the effect of improving toughness is saturated. In addition, hot cracking occurs during welding.

(Cr: 1.5-3.5%)
Cr aims at ensuring the strength of the weld metal. If the Cr content of the wire component is less than 1.5%, the effect cannot be obtained, and if it exceeds 3.5%, the strength becomes excessive and the toughness decreases.
(Mo: 1.0-4.0%)
Mo aims at ensuring the yield strength and strength of the weld metal. If the Mo content of the wire component is less than 1.0%, the effect cannot be obtained, and if it exceeds 4.0%, an intermetallic compound is generated in the weld metal, the weld metal is remarkably hardened, and the toughness is lowered.

(Ti: 0.02-0.10%)
Since Ti combines with oxygen during welding to become a slag component, it has an effect of reducing oxygen in the weld metal. If Ti of the wire component is less than 0.02%, the effect cannot be obtained, and if it exceeds 0.10%, a large amount of Ti compound such as TiC precipitates in the weld metal and the toughness deteriorates.

(Mg: 0.20 to 0.70%)
Mg has a large ionization tendency and acts as a powerful deoxidizer in the arc. If the wire component Mg is less than 0.20%, a sufficient deoxidation effect cannot be obtained, and if it exceeds 0.70%, a reaction of Mg + 2H ₂ O → Mg (OH) ₂ + H ₂ occurs during welding, and hydrogen Gas is generated and blow holes and pits are generated frequently.

(Flux filling rate: 10-30%)
The flux filling rate of the above-mentioned wire component is 10 to 30%. When the flux filling rate is less than 10%, the alloy components necessary for the intended increase in strength and toughness are insufficient, and sufficient mechanical performance cannot be obtained. On the other hand, if it exceeds 30%, the seamless flux-cored wire is welded at the seam part after molding to eliminate the seam. However, the flux component tends to enter during welding of the seam part, resulting in weld defects and production. Deteriorates. Further, when the filling flux is increased, the amount of oxygen in the wire is increased and the amount of oxygen in the weld metal is also increased, so that the toughness is lowered.

(O of flux total mass%: 0.2 to 1.0%)
O is 0.2 to 1.0% in the total mass% of the flux to be filled. When O is less than 0.2%, Mg and Al in inevitable impurities become very fine oxides of Mg and Al, and these have good lattice matching with TiN, and thus become TiN precipitation nuclei. Similarly, MnS and the like are precipitated together using Mg or Al oxides as nuclei. TiN, MnS, etc., in a normal ferrite-based structure, can inhibit the austenite grain boundary growth and refine the structure due to the pinning effect, but can improve toughness, but in the high-strength steel bainite-based structure, Serves as a starting point of fracture, and decreases the strength and toughness of the weld metal. On the other hand, if it exceeds 1.0%, the amount of oxygen in the weld metal increases, and a large amount of coarse oxides such as Al ₂ O ₃ and Ti oxide are generated in the weld metal. In ordinary ferrite-based structures, small amounts of these oxides serve as nuclei for the formation of fine ferrite (acicular ferrite) in the austenite grains and improve toughness. In this structure, a coarse oxide becomes a starting point of fracture, and strength and toughness are lowered.

The amount of O of the flux to be filled is adjusted in advance by measuring the amount of oxygen in the filling flux material and calculating the amount of oxygen in the alloy component from the amount of alloy component.
The alloy component in the flux is a flux-cored wire in accordance with the components of various high-strength steels (base materials) by adjusting the compounding components within each limited range in consideration of the components and content of the steel outer shell. It can be.

In order to reduce the amount of oxygen in the weld metal, it is desirable that the main component of the filling flux is metal powder and no oxide or the like serving as a slag forming agent is added. In addition, both P and S are preferably as low as possible because they produce a low melting point compound and reduce toughness.
The wire of the present invention preferably has a wire outer diameter of 3.2 to 6.4 mm in order to enable stable arc welding even when welding with a high current.

  The flux-cored wire for submerged arc welding of the high strength steel of the present invention has a seamless cross-sectional shape (hereinafter referred to as seamless) in the steel outer shell, and therefore has excellent moisture absorption performance, and the diffusible hydrogen content of the weld metal. Can be reduced as much as possible. In addition, with a normal seamed flux-cored wire that is formed from strip steel and does not weld the seam, the wire cross-section is asymmetrical, the wire itself is easily twisted, and is easily misaligned with the center of the groove during welding. However, according to the present invention, the wire cross section is formed of concentric circles, is symmetric in all directions, can be easily handled, and a wire that is not easily twisted can be obtained. In addition, since the arc at the time of welding is further stabilized by performing copper plating on the wire surface, it is preferable.

  In the method of manufacturing a flux cored wire for submerged arc welding of high strength steel according to the present invention, a steel pipe is vibration-filled with flux, and then reduced in diameter and annealed to form a strand. Alternatively, the steel strip is formed into a U-shape in a molding process and filled with flux, and then molded into an O-shape and welded to the seam portion, and then reduced in diameter and annealed to form a strand. Those wires are plated as necessary, and then drawn to obtain a product having a predetermined diameter.

Moreover, as a flux combined with the flux cored wire for submerged arc welding of the high strength steel of the present invention, in order to reduce the oxygen content of the weld metal, the basicity represented by the following formula is 1.3 or more. preferable.
Basicity = [CaO + MgO + CaF ₂ + BaO + 0.5 × (MnO + FeO)] / [SiO ₂ + 0.5 × (Al ₂ O ₃ + TiO ₂ + ZrO ₂ )]
However, each component represents mass%.
Hereinafter, the effects of the present invention will be described in detail by way of examples.

Hereinafter, the effect of the present invention will be described in detail with reference to examples.
Using the steel outer sheath shown in Table 1, flux-cored wires having various components shown in Table 2 were made as trial products. The steel pipe of F1 shown in Table 1 was subjected to vibration filling with a flux and then reduced in diameter and annealed to form a strand. The steel strip of F2 was formed into a U-shape in a molding process, filled with flux, formed into an O-shape, welded to the seam portion, and then reduced in diameter and annealed to form a strand. The steel strip of F3 was formed into a U-shape in a molding process and filled with a flux, and after forming into a wrap shape, it was reduced in diameter and annealed to form a strand. Furthermore, those strands were drawn to a diameter of 4.0 mm. The amount of O in the flux was measured using an inert gas melting-infrared absorption method before filling the flux.

表２に示す各種フラックス入りワイヤにつき表３に示す溶融型フラックスとを組合わせて表４に示す板厚２０ｍｍ、長さ１５００ｍｍの鋼板を、図１に示す開先角度：９０°、開先深さ７．５ｍｍのＸ型開先形状に加工し、表５に示す溶接条件および図２に示す電極配置の溶接施工条件で、３電極による表側と裏側の両面１パスの溶接を実施した。

A steel sheet having a thickness of 20 mm and a length of 1500 mm shown in Table 4 in combination with the melt-type flux shown in Table 3 for various flux-cored wires shown in Table 2 and a groove angle shown in FIG. 1: 90 °, groove depth. It was processed into an X-shaped groove shape with a thickness of 7.5 mm, and 1-pass welding on both the front side and the back side with 3 electrodes was performed under the welding conditions shown in Table 5 and the welding conditions of the electrode arrangement shown in FIG.

各試作ワイヤの評価は、ワイヤ製造時の生産性、拡散性水素量、溶接後のビード形状および溶接欠陥の有無、溶接金属の引張強さ、靭性および酸素量を調査した。
ワイヤの生産性はシームレスのフラックス入りワイヤを製造する時のシーム部を溶接する時に、充填フラックスが溶接部への入り込みの有無および伸線時の断線の有無を調査した。拡散性水素量の測定はＪＩＳ Ｚ ３１１８に準拠して表３に示すフラックスと組合わせて測定し、８ｍｌ／１００ｇ以下を良好とした。

Each prototype wire was evaluated by examining the productivity at the time of wire production, the amount of diffusible hydrogen, the bead shape after welding and the presence or absence of weld defects, the tensile strength, the toughness, and the oxygen content of the weld metal.
As for the productivity of the wire, when welding the seam portion when manufacturing a seamless flux-cored wire, the presence or absence of the filler flux entering the welded portion and the presence or absence of breakage during wire drawing were investigated. The amount of diffusible hydrogen was measured in combination with the flux shown in Table 3 according to JIS Z 3118, and 8 ml / 100 g or less was considered good.

  The bead shape was examined for undercut and overlap. The weld defects were examined for the presence of blowholes, pits and hot cracks by visual inspection and X-ray transmission test. As for the mechanical performance of the weld metal, tensile test pieces (JIS Z 3111 A2) and impact test pieces (JIS Z 3111 No. 4) were sampled around 7 mm below the surface of the steel plate on the front side as shown in FIG. The test was conducted. The mechanical performance was evaluated as good when the tensile strength was 900 MPa or more and the absorbed energy at −20 ° C. was 80 J or more. These results are summarized in Table 6.

表２および表６中、ワイヤ記号Ｗ１〜Ｗ１０が本発明例、ワイヤ記号Ｗ１１〜Ｗ２６は比較例である。本発明例であるワイヤ記号Ｗ１〜Ｗ１０は、ワイヤ成分のＣ、Ｓｉ、Ｍｎ、Ｎｉ、Ｃｒ、Ｍｏ、ＴｉおよびＭｇ量が適正で、充填フラックス中のＯ量も適正であるので、引張強さが十分得られ、溶接金属中の酸素量が低いので吸収エネルギーも良好であった。また、フラックス充填率が適正で、シームレスのフラックス入りワイヤであるため、ワイヤの生産性、ビード形状が良好で、拡散性水素量が低く、溶接欠陥もないなど、極めて満足な結果であった。

In Tables 2 and 6, wire symbols W1 to W10 are examples of the present invention, and wire symbols W11 to W26 are comparative examples. The wire symbols W1 to W10 as examples of the present invention have appropriate amounts of C, Si, Mn, Ni, Cr, Mo, Ti, and Mg as wire components, and the amount of O in the filling flux is also appropriate. Was sufficiently obtained, and since the amount of oxygen in the weld metal was low, the absorbed energy was also good. Moreover, since the flux filling rate was appropriate and the wire was seamless, it was a very satisfactory result such as good wire productivity, good bead shape, low diffusible hydrogen content, and no welding defects.

  In the comparative example, the wire symbol W11 has a small amount of C and a large amount of O in the filling flux, so deoxidation is insufficient, the amount of oxygen in the weld metal is high, and a coarse oxide is precipitated in the weld metal. The tensile strength and absorbed energy were low. Since the wire symbol W12 has a large amount of C, the weld metal has a martensite-based structure, the tensile strength is high, and the absorbed energy is low.

  The wire symbol W13 had a low flux filling rate, a shortage of alloy elements, and a low tensile strength. Moreover, since the amount of Si was not contained in the filling flux, deoxidation was insufficient, the amount of oxygen in the weld metal was increased, and the absorbed energy was low. Since the wire symbol W14 has a large amount of Si, the tensile strength was high and the absorbed energy was low.

  Since the wire symbol W15 has a small amount of Mn, the hardenability is insufficient, and since the amount of O in the filling flux is small, inclusions are generated in the weld metal, and the tensile strength and absorbed energy are low. It was. Since the wire symbol W16 has a large amount of Mn, the wire symbol W16 was excessively quenched, resulting in high tensile strength and low absorption energy.

  Since the wire symbol W17 has a small amount of Ni, its tensile strength and absorbed energy were low. Since the wire symbol W18 has a large amount of Ni, hot cracking occurred, and the tensile strength and the absorbed energy were remarkably reduced. The wire symbol W19 had a low tensile strength because of a small amount of Cr.

  Since the wire symbol W20 had a large amount of Cr, the tensile strength was high and the absorbed energy was low. Further, since the flux filling rate was high, the flux entered during welding of the seam part during wire production, and the productivity deteriorated. Since the wire symbol W21 has a small amount of Mo, the tensile strength was low. Further, since the amount of O in the filling flux was small, inclusions were precipitated and the absorbed energy was low.

  Since the wire symbol W22 has a large amount of Mo, the tensile strength was high and the absorbed energy was low. Since the wire symbol W23 has a small amount of Ti, the amount of oxygen in the weld metal is high, and the absorbed energy is low. Since the wire symbol W24 has a large amount of Ti, inclusions precipitated in the weld metal and the absorbed energy was low.

  Since the wire symbol W25 has a seamed flux-cored wire shape, the wire twisted during welding and a meandering bead occurred. Moreover, since the flux in the wire absorbed moisture, the amount of diffusible hydrogen increased. Furthermore, since the amount of Mg is small, the deoxidation effect is insufficient, the amount of oxygen in the weld metal is high, and the absorbed energy is low. Since the wire symbol W26 has a large amount of Mg, hydrogen gas was generated, and blow holes and pits were generated frequently. Therefore, mechanical performance evaluation was not performed.

It is a figure which shows the groove shape of the test plate used in the Example of this invention. It is a figure which shows arrangement | positioning of the welding electrode in the Example of this invention. It is the figure which showed the sampling position of the test piece in the Example of this invention.

Claims (3)

In a flux cored wire for submerged arc welding for high-strength steel with a steel sheath filled with flux, the total of the steel sheath and flux components is the total mass% of the wire, C: 0.05 to 0.30%, Si : 0.1-0.5%, Mn: 1.0-3.0%, Ni: 2.0-9.0%, Cr: 1.5-3.5%, Mo: 1.0-4 0.0%, Ti: 0.02 to 0.10%, Mg: 0.2 to 0.7%, the balance is made of Fe and inevitable impurities, and the flux filling rate of the flux in the wire component Is a flux cored wire for submerged arc welding for high-strength steel, characterized by being 10-30% by mass. 2. The flux-cored wire for submerged arc welding for high-strength steel according to claim 1, wherein the flux is the total mass% of the flux and is O: 0.2 to 1.0%. The flux-cored wire for submerged arc welding for high-strength steel according to claim 1 or 2, wherein the steel outer shell has no seam.

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