JP2007160314A - Flux cored wire for welding high-strength stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flux-cored wire for welding high-strength stainless steel which ensures the high-strength weld joint performance as high as that of austenitic stainless steel SUS304, and has excellent bending performance, high low-temperature toughness and excellent welding workability. <P>SOLUTION: In the flux-cored wire for welding high-strength stainless steel with flux filled inside a shell consisting of austenitic stainless steel, the total components contained in the shell and the flux are, by mass, based on the total wire weight, 8.0-10.0% Ni, 17.0-22.0% Cr, 0.5-2.0% Ti, ≤ 0.10% Bi, 0.05-0.70% fluoride, and 5-10% the total slag agent, and the balance including deoxidizing agent, Fe and inevitable impurities. The amount of O in the weld metal is 0.07-0.20% by adjusting the amount of the component of the deoxidizing agent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stainless steel flux cored wire, and particularly applied to austenitic stainless steel SUS304, which can provide high strength welded joint performance similar to that of the base material, good bending performance, high low temperature toughness, and The present invention relates to a flux cored wire for welding high-strength stainless steel having good welding workability.

  Austenitic stainless steel SUS304 is applied to LNG storage tanks and building structural members because of its excellent corrosion resistance and good mechanical performance such as strength and low temperature toughness. However, although the tensile strength of the austenitic stainless steel SUS304 is high, the JIS Z3323 YF308 welding material, which is a co-metal, has low tensile strength. When a bending test is performed on a welded joint, a weld metal with low strength is selectively used. Due to the deformation, there was a problem that the weld metal part was cracked. Furthermore, the flux-cored wire has low low temperature toughness compared to other welding methods, and there are cases where sufficient performance for quality requirements cannot be obtained for applications to cryogenic steels.

  As a technique for solving this problem, for example, in Japanese Patent Laid-Open No. 8-267282 (Patent Document 1), austenitic stainless steel that can obtain high strength and high toughness by optimizing the total amount of alloy components, particularly C + N. Flux-cored wires have been proposed. However, in the case of in-situ welding with insufficient gas shielding, N and O in the atmosphere are mixed into the weld metal and become high, and sufficient toughness is often not obtained.

  In addition, JP 2003-136280 A (Patent Document 2) discloses a flux-cored wire for welding austenitic stainless steel that is refined in austenite structure and has excellent toughness and ductility by appropriately adding Mg and Ti. Proposed. However, since the tensile strength is low, a weld metal having low strength is selectively deformed in a bending test of a welded joint, so that there is a problem that a weld is easily cracked and welding workability is poor.

JP-A-8-267282 JP 2003-136280 A

  The present invention provides a high-strength stainless steel welding flux-cored wire that provides weld joint performance as high as austenitic stainless steel SUS304, has good bending performance, high low-temperature toughness, and good workability. The purpose is to provide.

  In order to solve the above problems, the present inventors have made various studies on alloy components. As a result, it has been found that Ti and O in the weld metal have a great influence on the mechanical properties of the weld metal. As shown in FIG. 1 showing the relationship between Ti and mechanical properties, Ti has a tendency to greatly improve the tensile strength and toughness as it increases. However, on the other hand, when the amount of O is small, it has become clear that the effect of Ti cannot be sufficiently obtained and the mechanical properties cannot be improved.

Therefore, the present inventors conducted a detailed investigation on the relationship between Ti and O. As a result, it was found that a large amount of TiO ₂ was dispersed as inclusions in the weld metal, thereby suppressing coarse growth of the austenite solidified structure. Further, it has been found that by adding Ti, fine ferrite can be obtained, the microstructure can be refined, a weld metal having high tensile strength and high toughness can be obtained. Since the tensile strength is increased, it was confirmed that there was no crack in the bending test of the welded joint and that good performance was obtained.

  This invention is made | formed by the above knowledge, The place made into the summary is as follows. In a high-strength stainless steel welding flux-cored wire in which a flux is filled inside the austenitic stainless steel outer sheath, the total amount of components contained in the outer sheath and the flux is expressed by mass% with respect to the total mass of the Ni: 8.0 to 8.0 10.0%, Cr: 17.0 to 22.0%, Ti: 0.5 to 2.0%, Bi: 0.10% or less, Fluoride: 0.05 to 0.70%, of slag agent Total: 5 to 10% is contained, the other is a deoxidizer, Fe and inevitable impurities, and the amount of O in the weld metal is 0.07 to 0.20 mass% by adjusting the deoxidizer component. Features.

  Moreover, a deoxidizer component is the mass% with respect to the total mass of a wire, Si: 0.2-0.7%, Mn: 0.5-2.5%, 1 type or 2 types of Al and Mg is 0.00. It exists in the flux cored wire for high-strength stainless steel welding characterized by adjusting in the range of 01 to 0.40%.

  According to the austenitic high strength stainless steel welding flux cored wire of the present invention, a high strength, high toughness weld metal is obtained, bending performance is good, welding workability is good, and so on. Part is obtained.

The present invention can be achieved by a single effect and a synergistic effect due to the coexistence of each component composition of the outer skin and the filling flux. The reasons for addition and limitation of each component composition will be described below.
Ni is required to be 8.0% by mass (hereinafter referred to as%) or more for the purpose of stabilizing the austenite structure and obtaining excellent toughness. On the other hand, if added over 10.0%, austenite grows coarsely, and the tensile strength decreases. Therefore, Ni needs to be 8.0 to 10.0%.

  Cr is a main element that causes ferrite to crystallize, and is required to be 17.0% or more in order to obtain an appropriate austenite / ferrite amount balance and to obtain ferrite required for securing high-temperature crack resistance. On the other hand, if added over 22.0%, the ferrite becomes excessive and the toughness is lowered. Therefore, Cr needs to be 17.0 to 22.0%.

Ti is dispersed as an inclusion of TiO _{2 in} the weld metal, and suppresses the growth of the austenite structure, and part of the solution dissolves to crystallize fine ferrite, thereby obtaining a weld metal having high strength and high toughness. For the purpose, 0.5% or more is necessary. On the other hand, if it is added over 2.0%, the amount of spatter generated increases and welding workability deteriorates. Therefore, Ti needs to be 0.5 to 2.0%.

  Bi is added for the purpose of improving slag releasability, but if added over 0.10%, it segregates at austenite grain boundaries, weakens the grain boundary bonding force, and deteriorates toughness. Therefore, it is necessary to make it 0.10% or less. On the other hand, when Bi is made free, good toughness can be obtained, but since the slag peelability deteriorates, it is preferably made 0.01% or more. Bi can use metal bismuth and bismuth oxide. In the case of bismuth oxide, the Bi conversion value is used.

Fluoride needs to be 0.05% or more for the purpose of improving the detachability of droplets and reducing the amount of spatter generated. On the other hand, if added over 0.70%, the droplets grow greatly, which causes an increase in the amount of spatter generated. Therefore, the fluoride must be 0.05 to 0.70%. As the type of fluoride, AlF ₃ , NaF, K ₂ ZrF ₆ , LiF, or the like can be used.

The total amount of the slag agent is added in an amount of 5% or more for the purpose of reducing the amount of spatter generated by making the difference in melting rate between the outer sheath of the wire tip near the arc generation point and the protruding flux appropriate. On the other hand, when the content exceeds 10%, the outer shell melts quickly and the protruding flux is long, so that the detachment of the droplets is performed at a high position and the amount of spatter generated increases. This indicates that the melting timing of the outer shell and the protruding flux is too far apart, and the molten droplet of the outer shell is detached from the upper part of the arc, which causes an increase in the amount of spatter. Therefore, the total amount of the slag agent needs to be 5 to 10%. The slag agent includes the above-mentioned fluorides, and is a total of oxides such as TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ , FeO, Fe ₂ O ₃ , K ₂ O, Na ₂ O, CaO and MgO. Say.

The amount of O in the weld metal is 0 for the purpose of obtaining good toughness by generating a part of the added Ti in the weld metal as TiO ₂ inclusions, inhibiting the growth of austenite grains, refining the structure. Adjust to 07% or more. However, if the amount of O exceeds 0.20%, weld defects such as blow holes are generated, so the amount of O of the weld metal is adjusted to 0.07 to 0.20%. At this time, the deoxidizers Si, Mn, Al, and Mg are appropriately adjusted according to the slag agent component so as to obtain an appropriate amount of O.

Of the deoxidizer, Si is required to be 0.2% or more in order to stabilize the arc, reduce the amount of spatter generated, and adjust the amount of oxygen in the weld metal. On the other hand, if it exceeds 0.7%, the amount of oxygen in the weld metal becomes too low and the toughness becomes low. Therefore, Si is 0.2 to 0.7%.
Mn is required to be 0.5% or more in order to dissolve in austenite and improve the tensile strength and adjust the amount of oxygen in the weld metal. On the other hand, if it exceeds 2.5%, the amount of spatter generated increases and the amount of oxygen in the weld metal becomes too low, resulting in low toughness.

Al and Mg are strong deoxidizers, and adjust the amount of oxygen in the weld metal. If the total of one or two of Al and Mg is less than 0.01%, the amount of oxygen in the weld metal is less than 0.01%. It becomes too high and blow holes are likely to occur. On the other hand, if the total of one or two of Al and Mg exceeds 0.40%, the amount of oxygen in the weld metal decreases, the amount of TiO ₂ required for the weld metal decreases, and the strength and toughness also decrease. . Further, the amount of spatter generated increases.
As mentioned above, although the reason for limitation of the flux cored wire constituent requirements for stainless steel welding of the present invention was described, as another component, C is preferably 0.01 to 0.05% from the viewpoint of ensuring strength and toughness, and further Mo, Alloying agents such as V and Nb can be added in combination for adjusting the mechanical performance.

Referring to the method for manufacturing the flux-cored wire, for example, when the outer skin is formed into a tubular shape from a steel strip, the filled flux that has been blended, stirred, and dried is filled into a U-shaped groove and then formed into a round shape. The wire diameter is drawn. 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 used in the form of a bond flux by adding a fixing agent (an 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.
An austenitic stainless steel welding flux-cored wire having the composition shown in Table 2 was manufactured using the austenitic stainless steel outer skin having chemical components shown in Table 1. The wire diameter was 1.2 mm. The flux filling rate was 20-23%.

  Austenitic stainless steel SUS304 having the components shown in Table 3 was used for each test as a base material. The weld metal performance was a tensile test according to JIS Z 3323. The impact test conformed to JIS Z 3111. As for the weld joint performance, a weld joint (sheet thickness 12 mm, groove angle 45 °, gap 12 mm with backing metal) conforming to the test material for corrosion test of JIS Z 3323 was prepared. Thereafter, in accordance with JIS Z 3106, an X-ray transmission test was carried out to confirm cracks in the welded joint and occurrence of blowholes. The mechanical properties of the welded joint include tensile test of butt welded joint using JIS Z 3121 No. 1A test piece, bending test of butt joint using JIS Z 3122 surface bending test piece (20R, 180 ° bending), JIS Z 3128 An impact test of a welded joint using a V-notch test piece (steel thickness center, notch position: sampled at the weld metal center) was performed.

In the evaluation, both the weld metal and the welded joint had good tensile strength: 600 MPa or more, bending performance: no defect, absorbed energy at −196 ° C. (vE-196 ° C.): 30 J or more. In the X-ray transmission test, type 1 without blowholes (type 1 flaws) and cracks (type 3 flaws) was considered good. Welding workability was determined by sensory evaluation when creating a welded joint. In addition, the welding current of the weld metal test, the welded joint test, and the investigation of the welding workability was 180 to 250 A, downward welding, and shielding gas: CO ₂ . The results are summarized in Table 4.

In Table 4, wire No. 1 to 8 are examples of the present invention, wire Nos. 9 to 16 are comparative examples.
Wire No. which is an example of the present invention. 1-8, Ni, Cr, Ti, Bi, fluoride, slag agent total, Si, Mn, Al, Mg and the amount of O in the weld metal are appropriate, so the tensile strength is high and the bending performance is high The results were very satisfactory, with good absorption energy, excellent crack resistance and blowhole resistance, and good welding workability.

In the comparative example, the wire No. No. 9 had low absorption energy because Ni was low. Moreover, since the fluoride was high, the amount of spatter generated was large.
Wire No. No. 10 had high Ni, so the tensile strength was low and the bending performance of the joint was poor. Moreover, since Si is high, O of the weld metal is low and the absorbed energy is low. Further, since the fluoride was low, the amount of spatter generated was large.
Wire No. No. 11 had a large amount of spatter because the total amount of slag agent was low.

Wire No. No. 12 had low absorption energy because Cr was high. Moreover, since the sum total of the slag agent was high, there was much spatter generation amount.
Wire No. No. 13 had low Bi because of its high Bi. Moreover, since Al and Mg were not contained, O in the weld metal was increased and blow holes were generated.
Wire No. No. 14 was cracked because Cr was low. Moreover, since the total amount of Al and Mg was high, O of the weld metal was low, and the absorbed energy was low. Also, the amount of spatter generated was large. Since this wire was cracked in the weld metal test, the joint performance was not investigated.

Wire No. Since No. 15 had low Ti, its tensile strength was low and the bending performance of the joint was poor. Also, the absorbed energy was low.
Wire No. No. 16 had a large amount of spatter because Ti was high. Moreover, since Mn was high, O of the weld metal was low and the absorbed energy was low.

It is a figure which shows the relationship between Ti amount of a weld metal, and a mechanical property.

Claims (2)

In the high-strength stainless steel welding flux cored wire filled with flux inside the austenitic stainless steel outer sheath, as a total of the components contained in the outer sheath and the flux, in mass% with respect to the total mass of the wire,
Ni: 8.0 to 10.0%,
Cr: 17.0 to 22.0%,
Ti: 0.5 to 2.0%,
Bi: 0.10% or less,
Fluoride: 0.05-0.70%
Total of slag agent: contains 5-10%,
The other is a deoxidizer, Fe, and inevitable impurities, and the amount of oxygen in the weld metal is 0.07 to 0.20 mass% due to the deoxidizer component, and a high-strength stainless steel welding flux cored wire . The deoxidizer component is in mass% with respect to the total mass of the wire, Si: 0.2 to 0.7%, Mn: 0.5 to 2.5%, and one or two of Al and Mg are 0.01 to The flux-cored wire for high-strength stainless steel according to claim 1, which is adjusted within a range of 0.40%.

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