JP5289999B2 - Flux-cored wire for duplex stainless steel welding - Google Patents

Description

  The present invention is used for welding of duplex stainless steel, can obtain high strength weld metal performance similar to that of the base metal, has good toughness and corrosion resistance, has excellent defect resistance such as blowholes, and welding work The present invention relates to a flux cored wire for welding duplex stainless steel having good properties.

  Conventionally, duplex stainless steels represented by SUS329J3L and SUS329J4L are stainless steels having excellent corrosion resistance and strength characteristics. As the grade of this duplex stainless steel, the pitting corrosion resistance index PRE (Cr% + 3.3 Mo% + 16 N%) or PREW (Cr% + 3) is based on Cr, Mo, N, and W contained in the chemical composition. .3 (Mo% + 0.5 W%) + 1.6 N%). It is used as a corrosion resistant material for chemical plants, chemical equipment, oil wells, gas wells, etc. that require corrosion resistance, and because it has high strength, it is also used as a structural material for vehicles and the like.

  In recent years, inexpensive duplex stainless steels having a low pitting corrosion resistance index PRE have been developed. S32101 and S32304 have been put into practical use. The applied welding material has an index equal to or higher than the pitting corrosion resistance index of these steel materials, and is required to have good weld metal performance and welding workability at low cost.

  Under such circumstances, it is desired to develop a flux-cored wire that can be welded particularly efficiently and has good welding workability. However, there is a problem that welding defects such as blow holes occur when duplex stainless steel containing a large amount of N is welded. In addition, the bead shape tends to be convex, and there is a problem that it is necessary to add a reworking process using a grinder.

As a technique for solving this problem, for example, Cr, Mo, N is defined in Japanese Patent No. 3476125 (Patent Document 1), and TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ and MgO are used as slag agents. A flux-cored wire that has been regulated to improve pitting corrosion resistance, toughness, and welding workability is disclosed. However, in this flux cored wire, Mo is added more than conventional duplex stainless steel, and when applied to inexpensive duplex stainless steel, the cost of the welding material is high and the toughness of the weld metal is low. There was a problem.
Japanese Patent No. 3476125

  The present invention is used for welding inexpensive duplex stainless steel, and can provide a weld metal with high strength similar to that of the base material, good toughness and corrosion resistance, excellent resistance to defects such as blowholes, and welding An object is to provide a flux cored wire for welding duplex stainless steel with good workability.

The gist of the present invention is that, in a flux-cored wire for welding a duplex stainless steel, in which a stainless steel outer shell is filled with flux, the mass is based on the total mass of the wire, and the total of the stainless steel outer shell and the flux is C: 0. 0.06% or less, Si: 0.1 to 1.0%, Mn: 0.5 to 3.0%, Ni: 7 to 11%, Cr: 21 to 25%, Mo: 0.01 to 1%, N: 0.08 to 0.3% , metal fluoride: 0.2 to 1.5%, TiO ₂ as metal oxide : 3 to 8%, SiO ₂ : 0.5 to 5%, Al ₂ O ₃ And ZrO ₂ : 0.06% or less , and the other is characterized by Fe content of stainless steel outer shell, Fe content from iron alloy and inevitable impurities.

Moreover, it exists in the flux cored wire for welding of a duplex stainless steel characterized by C, Si, Mn, Ni, Cr, Mo, and N being 5-25 by the D value of a following formula.
D = 3Cr + 4.5Si + 3Mo-2.8Ni-84 (C + N) -1.4Mn-20 (formula)

  According to the flux-cored wire for welding duplex stainless steel of the present invention, a weld metal with high strength comparable to that of the base metal can be obtained in welding of inexpensive duplex stainless steel, toughness and corrosion resistance are good, and blowhole It is possible to provide a flux-cored wire for welding duplex stainless steel having excellent defect resistance and the like and excellent welding workability.

  In order to solve the above-mentioned problems, the present inventors have made trials of flux-cored wires having various component compositions and examined them in detail. As a result, it has been found that it is effective to add Mn in order to reduce the cost by reducing Mo, to achieve good welding workability, and to obtain corrosion resistance comparable to that of the base material.

  It has been clarified that Mn generates MnO on the droplet surface by a deoxidation reaction, thereby reducing the surface tension and improving the arc stability. Further, since Mn has the effect of increasing the N solid solubility in the deposited metal, it has been found that the yield of N is improved, austenite is stabilized at a low cost, and the strength is increased by solid solution strengthening.

  On the other hand, as the content of N increases, a problem arises that the defect resistance of blowholes and the like deteriorates. Moreover, since re-heating by welding produced Cr nitride in the austenite / ferrite grain boundary, resulting in deterioration of toughness and local corrosion, further studies were added. As a result, the ferrite-forming elements Cr, Mo and Si are adjusted, the crystallization of the ferrite is stabilized, and N is dissolved in the ferrite phase, thereby improving the slag removability and blow hole and other defect resistance, Moreover, it discovered that precipitation of Cr nitride could be reduced and deterioration of toughness and local corrosiveness could be suppressed.

The present invention can be achieved by the synergistic effect of the individual and coexistence of each component composition of the stainless steel shell and the filling flux. The reasons for addition and limitation of each component composition will be described below.
Since C produces carbides with Cr, Mo, etc. and deteriorates corrosion resistance and toughness, the C content is set to 0.06 mass% (hereinafter referred to as%) or less.

  Si has the effect of improving slag encapsulation and bead shape. If Si is less than 0.1%, the amount of slag is small and the slag encapsulation is impaired, and the bead surface is oxidized and the temper color is adhered. On the other hand, if it exceeds 1.0%, the viscosity of the molten metal is lowered and the bead shape is deteriorated. Therefore, Si is 0.1 to 1.0%.

  Mn lowers the surface tension of the molten metal, stabilizes the arc, and has the effect of improving the yield by increasing the N solid solubility in the deposited metal. If Mn is less than 0.5%, the arc becomes unstable. Further, the N solid solubility is lowered and nitride is deposited, so that the corrosion resistance is deteriorated. On the other hand, if it exceeds 3.0%, the amount of spatter generated increases. Therefore, Mn is 0.5 to 3.0%.

  Ni has the effect of stabilizing the austenite phase and improving toughness and adjusting strength. If Ni is less than 7%, the amount of crystallization of austenite decreases and the toughness deteriorates. On the other hand, if it exceeds 11%, the amount of austenite crystallized increases and the strength decreases. Therefore, Ni is 7 to 11%.

Cr has the effect of forming a passive film and improving the corrosion resistance. If Cr is less than 21%, sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 25%, the amount of ferrite crystallized increases and the toughness deteriorates. Therefore, Cr is 21 to 25%.
Mo has the effect of improving corrosion resistance and toughness. If Mo is less than 0.01%, sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 1.0%, the cost increases. Therefore, Mo is set to 0.01 to 1.0%.

  N stabilizes the austenite structure and is a solid solution strengthening element and has the effect of increasing the strength of the deposited metal. When N is less than 0.08%, the strength of the deposited metal is lowered. On the other hand, if it exceeds 0.30%, blow holes frequently occur and toughness deteriorates. Note that N is an amount converted to N when contained in the form of a nitrogen compound in the flux.

Furthermore, by making the C, Si, Mn, Ni, Cr, Mo and N 5 to 25 with the D value of the following formula, an appropriate amount of austenite is crystallized from the ferrite phase, and the balance between the ferrite phase and the austenite phase is balanced. In particular, the elongation of the weld metal can be improved. If the D value is less than 5, the amount of austenite crystallized increases and the strength decreases. On the other hand, if the D value exceeds 25, the amount of ferrite crystallized increases and the elongation decreases.
D = 3Cr + 4.5Si + 3Mo-2.8Ni-84 (C + N) -1.4Mn-20 (formula)

The metal oxide is necessary for adjusting the arc stability, and is added for the purpose of improving the concentration of the arc by smoothing the droplet transfer. As the metal oxide, TiO ₂ , SiO ₂ , Al ₂ O ₃ , ZrO _2, etc. can be used, TiO ₂ is 3 to 8%, SiO ₂ is 0.5 to 5%, and the total of Al ₂ O ₃ and ZrO ₂ It is preferable that it is 0.06% or less of range.

Metal fluoride is necessary for adjusting the melting point of slag, and is added for the purpose of improving the bead shape and slag removability. As the metal fluoride, NaF, LiF, CaF ₂ , AlF ₃ , K ₂ ZrF ₆ , K ₂ SiF _{6 and the} like can be used. Even if any metal fluoride is used, the same effect can be obtained. The total content is preferably 0.2 to 1.5%. Further, P is preferably 0.040% or less and S is 0.030% or less from the viewpoint of securing strength and toughness.

  As mentioned above, the reason for limiting the component composition of the flux cored wire for welding the duplex stainless steel of the present invention has been described. The filled flux that has been stirred and dried is filled into a U-shaped groove, then formed into a round shape, and drawn to a predetermined wire diameter. At this time, a seamless type flux-cored wire can be obtained by welding the shaped outer seam. When the outer skin is a pipe, the pipe is vibrated to be filled with a flux and drawn to a predetermined wire diameter. The filling flux can be granulated by adding a fixing agent (aqueous solution of potassium silicate and sodium silicate) so that supply and filling can be performed smoothly.

Hereinafter, the present invention will be described in detail by way of examples.
Using the austenitic stainless steel skin having chemical components shown in Table 1, flux-cored wires for welding duplex stainless steels having various compositions shown in Table 2 were produced. The wire diameter was 1.2 mm. The metal oxide was TiO ₂ : 4 to 7%, SiO ₂ : 0.9 to 3.5%, and Al ₂ O ₃ and ZrO ₂ were 0.01 to 0.06% in total. As the metal fluoride, one or more of NaF and K ₂ SiF ₆ were used.

溶接は、表３に示す成分の二相ステンレス鋼（Ｂ１）を用いてＪＩＳ Ｚ ３３２３に基づいて溶着金属試験を行った。溶接後ＪＩＳ Ｚ ３１０６に基づいてＸ線透過試験を実施し、溶接継手部の割れおよびブローホール発生状況の確認を行った。溶着金属性能は、ＪＩＳ Ｚ ３１１１に準拠し、引張試験および衝撃試験を行った。また腐食試験は、ＪＩＳ Ｇ ０５７７に準拠した。

For welding, a weld metal test was performed based on JIS Z 3323 using duplex stainless steel (B1) having the components shown in Table 3. After welding, an X-ray transmission test was performed based on JIS Z 3106, and cracks in the welded joint and blowhole generation were confirmed. The weld metal performance was based on JIS Z 3111, and a tensile test and an impact test were performed. The corrosion test was based on JIS G 0577.

Ｘ線透過試験は、第１種の疵点数３点未満を良好とした。溶着金属性能は、引張試験の引張強さ：６５０ＭＰａ以上、伸び：１５％以上、衝撃試験の−２０℃における吸収エネルギー（ｖＥ−２０℃）：２７Ｊ以上、腐食試験の孔食電位：３５０ｍＶ以上を良好とした。

In the X-ray transmission test, the number of saddle points of the first type was less than 3 points. The weld metal performance was as follows: tensile strength in tensile test: 650 MPa or more, elongation: 15% or more, absorbed energy at −20 ° C. in impact test (vE-20 ° C.): 27 J or more, pitting potential in corrosion test: 350 mV or more. It was good.

For welding workability, horizontal fillet welding was performed using the duplex stainless steel (B2) shown in Table 3, and the arc stability, spatter generation state, slag encapsulation, and bead shape were examined. In addition, the welding current of the welding metal test and the investigation of the welding workability was carried out with 180 to 250 A and shield gas: CO ₂ . The results are summarized in Table 4.

表２および表４中のワイヤＮｏ．１〜１２が本願発明例、ワイヤＮｏ．１３〜２４は比較例である。

In Table 2 and Table 4, the wire No. 1 to 12 are examples of the present invention, wire No. 13 to 24 are comparative examples.

  Wire No. which is the present invention. 1 to 12, since C, Si, Mn, Ni, Cr, Mo, N and D values are appropriate, the X-ray transmission test is good, and the tensile strength, elongation, absorbed energy and pitting potential are high, The welding workability was also good, and the result was extremely satisfactory. In the comparative example, the wire No. No. 13 had low C and high absorbed energy and pitting potential. Wire No. No. 14 had a low Si content, so the slag encapsulation was poor and the temper color was adhered.

  Wire No. No. 15 had a poor bead shape because of high Si. Wire No. No. 16 had a low pitting potential because Mn was low. Moreover, the arc was unstable. Wire No. No. 17 was sputtered frequently because of high Mn. Moreover, since D value was low, tensile strength was low. Wire No. No. 18 had a low absorbed energy because Ni was low. Wire No. No. 19 had a low tensile strength because Ni was high.

Wire No. No. 20 had a low pitting corrosion potential because Cr was low. Wire No. No. 21 had low absorbed energy because Cr was high. Moreover, since D value was high, elongation was low. Wire No. Since No. 22 had low Mo, the pitting corrosion potential was low. Wire No. No. 23 had a low tensile strength because N was low. Wire No. No. 24 had 5 points because N was high and the X-ray transmission test could not be performed. Also, the absorbed energy was low.

Applicant Nippon Steel & Sumikin Welding Industry Co., Ltd.
Attorney Attorney Shiina and others 1

Claims (2)

In the flux-cored wire for welding a duplex stainless steel, in which the inside of the stainless steel outer shell is filled with flux, the mass is based on the total mass of the wire, and the total of the stainless steel outer shell and the flux is C: 0.06% or less, Si : 0.1-1.0%, Mn: 0.5-3.0%, Ni: 7-11%, Cr: 21-25%, Mo: 0.01-1%, N: 0.08- 0.3% , metal fluoride: 0.2 to 1.5%, TiO ₂ as metal oxide : 3 to 8%, SiO ₂ : 0.5 to 5%, total of Al ₂ O ₃ and ZrO ₂ : A flux-cored wire for welding two-phase stainless steel, characterized by containing 0.06% or less , the other being the Fe content of the stainless steel skin, the Fe content from the iron alloy, and inevitable impurities. The flux cored wire for welding a duplex stainless steel according to claim 1, wherein C, Si, Mn, Ni, Cr, Mo, and N have a D value of 5 to 25 in the following formula. D = 3Cr + 4.5Si + 3Mo-2.8Ni-84 (C + N) -1.4Mn-20 (formula)