JP2008126279A - Flux-cored wire for gas shielded arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flux-cored wire for gas shielded arc welding, when a hydrochloric acid and sulfuric acid dewpoint corrosion resistant steel is subjected to gas shielded arc welding, capable of obtaining a weld metal having excellent sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance and also having excellent strength and impact toughness while suppressing occurrence in the liquid metal embrittlement cracks of the weld metal caused by Cu and Sb as low melting point components. <P>SOLUTION: The flux-cored wire has a composition, in the whole steel wire, as metal or alloy, comprising, by mass, 0.01 to 0.2% C, 0.1 to 2.0% Si, 0.2 to 3.0% Mn and 0.05 to 1.0% Ni, and in which the content of P is limited to ≤0.03% and the content of S is limited to ≤0.03%, and, further comprising, in packed flux, an Fe-Cu alloy or an Fe-Cu-Si alloy having a Cu content of 10 to 30 mass% in such a manner that the Cu content is controlled to 0.1 to 1.0% per whole wire mass, and an Fe-Sb alloy having an Sb content of 40 to 60% in such a manner that the Sb content is controlled to 0.01 to 0.5% per whole wire mass, and the balance Fe with inevitable impurities. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an atmosphere in which low temperature corrosion is caused by sulfuric acid and hydrochloric acid, such as a flue and a chimney of a coal fired boiler and a garbage incineration facility, that is, hydrochloric acid resistant and excellent corrosion resistance in concentrated sulfuric acid and concentrated hydrochloric acid environments. The present invention relates to a flux-cored wire for gas shielded arc welding used when welding sulfuric acid dew-point corrosion steel.

  In general, when a welded structure is used in a corrosive environment, if there is a difference in corrosion resistance between the welded part and the base material, the one with lower corrosion resistance is selectively corroded, and the life of the structure is remarkably shortened. Further, when the welded portion is selectively corroded, stress concentration occurs in the corrosion hole, and in an extreme case, the structure may be destroyed. As described above, in the use of the welded structure, in the case where the corrosion deterioration cannot be ignored, it is necessary to sufficiently ensure not only the base material but also the corrosion resistance of the welded portion.

  Further, in flue gas facilities such as flues and chimneys in coal-fired thermal boilers and garbage incineration facilities, sulfuric acid dew point corrosion and / or hydrochloric acid dew point corrosion occur due to sulfur trioxide and hydrogen chloride in the exhaust gas. For this reason, in such an environment, generally, sulfuric acid dew point corrosion steel (see, for example, Non-Patent Document 1) is used. As the welding material for the sulfuric acid dew point corrosion steel, there are a material containing Cu alone as a corrosion resistant element and a material containing Cu-Cr. However, when welding using these existing welding materials, it shows sufficiently excellent corrosion resistance in the sulfuric acid dew point corrosion environment generated in the plant smoke exhaust system of heavy oil fired boilers, but in coal-fired boilers and waste incineration facilities, Since sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion occur simultaneously, there is a problem that the corrosion resistance of the welded portion is not sufficient.

  Therefore, conventionally, a welding material for obtaining a weld metal excellent in both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance has been proposed. Among them, in particular, in steel materials containing C, Si and Mn and restricting the contents of P and S, Cu is further added to improve both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance of the weld metal. A welding material in which Sb and Ni are added in combination is effective. As such a component-based welding material, a coated arc welding rod (see, for example, Patent Document 1), a solid wire for gas shielded arc welding (see, for example, Patent Document 2), and a gas shield, depending on the application. A flux-cored wire for arc welding (for example, see Patent Document 3) and a flux for submerged arc welding (for example, see Patent Document 4) have been proposed.

JP 2004-90044 A JP 2004-90045 A JP 2004-90042 A JP 2004-90051 A Nippon Steel Corporation, sulfuric acid corrosion resistant steel “S-TEN” technical data, 7th edition, Cat. No. Ac. 107, 2005

  However, the conventional techniques described above have the following problems. Based on the results of examinations such as confirmation tests conducted by the inventors of the present application, flux containing Cu and Sb effective for improving the hydrochloric acid resistance and sulfuric acid resistance of the weld metal as described in Patent Documents 1 to 4 When welding using a wire, when a part of Cu and Sb in the wire moves into the weld metal, it may remain on the surface of the weld metal and the weld heat affected zone together with the slag generated mainly by melting the flux. confirmed. Since Cu and Sb have a melting point lower than that of the slag component, the molten metal of Cu and Sb remains in the molten state even after the slag solidifies. It has been found that it penetrates into the coarsened austenite grain boundary in the vicinity and causes this to cause grain boundary embrittlement cracking (hereinafter referred to as liquid metal embrittlement cracking). When this liquid metal embrittlement crack occurs, the mechanical properties such as toughness and fatigue strength of the welded portion decrease, and the crack occurrence site becomes the starting point of corrosion. It becomes difficult to ensure mechanical properties and corrosion resistance.

  For the reasons described above, gas-shielded arc is resistant to hydrochloric acid and sulfuric acid dew-point corrosion steel using flux-cored wires containing low melting point components such as Cu and Sb, which are effective for improving the hydrochloric acid resistance and sulfuric acid resistance of weld metals. Gas shielded arc that can improve both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance of weld metal while suppressing liquid metal embrittlement cracking of welds due to these low melting point components when welded Development of a flux-cored wire for welding is desired.

  The present invention has been made in view of the above-mentioned problems of the prior art, and is caused by Cu and Sb, which are low melting point components, when hydrochloric acid resistant and sulfuric acid dew point corrosion steel is gas shielded arc welded. A flux-cored wire for gas shielded arc welding that provides weld metal with excellent sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance, as well as excellent strength and impact toughness, while suppressing the occurrence of liquid metal embrittlement cracks in weld metal. The purpose is to provide.

  The flux-cored wire for gas shielded arc welding according to the present invention is a flux-cored wire in which a filling flux is filled in a steel sheath. The entire wire, as a metal or an alloy, in mass%, C: 0.01 to 0 0.2%, Si: 0.1-2.0%, Mn: 0.2-3.0%, Ni: 0.05-1.0%, P: 0.03% or less, S Is limited to 0.03% or less, and only in the filling flux, as Fe-Cu alloy or Fe-Cu-Si alloy, Cu: 0.1 to 1.0% in terms of mass% with respect to the total mass of the wire. As a Fe-Sb alloy, the Fe-Cu alloy or Fe-Cu-Si containing Sb: 0.01 to 0.25% in mass% with respect to the total mass of the wire and contained in the filled flux Cu content in the alloy is 10-3 Wt%, Sb content in the Fe-Sb alloy is 40 to 60 wt%, characterized in that it is used in welding the steel excellent in hydrochloric acid and sulfuric acid.

  The flux-cored wire for gas shielded arc welding is preferably S: 0.005 to 0.03% by mass relative to the total mass of the wire.

  Moreover, Mo: 0.01-0.5% can also be contained in the mass as a metal or an alloy in the whole wire.

  Furthermore, the whole wire may contain Cr: 0.05 to 1.5% in mass% as a metal or alloy.

  Furthermore, the entire wire is composed of Al: 0.005 to 0.2%, Ti: 0.005 to 0.2%, and Zr: 0.005 to 0.2% in mass% as a metal or alloy. One or more elements selected from the group can also be contained.

  According to the present invention, in the filling flux in the steel outer shell, Cu is in the form of Fe-Cu alloy or Fe-Cu-Si alloy, and Sb is in the form of Fe-Sb alloy, each contained as metal powder. Furthermore, since the Cu content in the Fe-Cu alloy or Fe-Cu-Si alloy contained in the filling flux and the Sb content in the Fe-Sb alloy are within the appropriate ranges, it is used in concentrated sulfuric acid and concentrated hydrochloric acid environments. When gas-shielded arc welding is performed on hydrochloric acid and sulfuric acid dew-point corrosion steel, the occurrence of liquid metal embrittlement cracking of weld metal due to low melting point components is suppressed, and while maintaining good weldability, sulfuric acid corrosion resistance Weld metal with excellent strength and hydrochloric acid corrosion resistance, and excellent strength and impact toughness.

  Hereinafter, the best mode for carrying out the present invention will be described. In the following description, mass% in the composition is simply expressed as%.

  The inventor of the present application is likely to occur when welding using a flux-cored wire containing low melting point components such as Cu and Sb effective in improving the hydrochloric acid resistance and sulfuric acid resistance of the weld metal. A weld metal with excellent mechanical properties such as toughness, excellent in both sulfuric acid resistance and hydrochloric acid corrosion resistance, while preventing the occurrence of liquid metal embrittlement cracks in the welds and suppressing the occurrence of liquid metal embrittlement cracks in the welds. The earnest experiment was examined about the component composition of the obtained flux cored wire.

  As a result, in the flux-cored wire, (1) in the filled flux in the steel outer shell, Cu is in the form of Fe-Cu alloy or Fe-Cu-Si alloy, Sb is in the form of Fe-Sb alloy, Each is contained as a metal powder, and (2) Cu content in the Fe-Cu alloy or Fe-Cu-Si alloy contained in the filling flux, and Sb content in the Fe-Sb alloy within an appropriate range, Cu And Sb can be stabilized as an alloy having a higher melting point, and the resistance to sulfuric acid corrosion and hydrochloric acid corrosion can be improved while suppressing liquid metal embrittlement cracking of weld metal caused by molten Cu and Sb. As a result, the present invention has been achieved.

  That is, the flux-cored wire for gas shielded arc welding according to the present invention (hereinafter also simply referred to as a flux-cored wire) is one in which a filling flux is filled in a steel outer sheath, and C: 0.01 to 0.2%, Si: 0.1-2.0%, Mn: 0.2-3.0% and Ni: 0.05-1.0%, P: 0.03% or less and S: It is limited to 0.03% or less. Further, in the filled flux, as Fe—Cu alloy or Fe—Cu—Si alloy, Cu: 0.1 to 1.0% is added per total mass of the wire, and as the Fe—Sb alloy, the total mass of the wire is added. Sb: 0.01 to 0.25% is added. Furthermore, the Cu content of the Fe—Cu alloy or the Fe—Cu—Si alloy contained in the filled flux is 10 to 30% by mass, and the Sb content of the Fe—Sb alloy is 40 to 60% by mass. In addition, the remainder in the steel outer sheath of the flux-cored wire of the present invention and the remainder in the metal or alloy component contained in the filled flux are Fe and inevitable impurities. Moreover, in addition to the metal or alloy component described above, for example, a slag forming agent such as an oxide, a fluoride and a carbonate or an arc stabilizer may be contained in the filled flux.

  As described above, the flux-cored wire of the present invention is formed by filling a steel outer shell with a filling flux, and is a basic component for obtaining a weld metal having required characteristics. C, Si, Mn, Ni , P and S, and optional components Mo, Cr, Al, Ti, and Zr may be contained in one or both of the steel outer shell and the filling flux. On the other hand, Cu and Sb are contained in the filling flux as metal powder of Fe alloy as will be described later.

  Further, the content Mw of each component with respect to the total mass of the wire defined in the present invention is obtained by the following mathematical formula (1). In the following mathematical formula (1), Mc is the content (mass%) in the steel outer sheath, Mf is the content (mass%) in the filling flux, and R is the ratio (mass%) of the total mass of the filling flux to the total mass of the wire. ) Respectively.

  Hereinafter, the reasons for limiting the component composition in the flux-cored wire of the present invention will be described.

C: 0.01 to 0.2%
C is an element necessary for ensuring the strength of the welded structural steel as a welded joint. However, if the content is less than 0.01%, sufficient joint strength cannot be obtained. On the other hand, when the C content exceeds 0.2%, the sulfuric acid corrosion resistance decreases, the elongation and impact toughness of the weld metal decrease, and the crack resistance also deteriorates. Therefore, the C content is limited to 0.01 to 0.2%. In addition, from the viewpoint of sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance, the smaller the C content, the more preferable, and 0.1% or less is more preferable.

Si: 0.1 to 2.0%
Si is added as a deoxidizing element and an element that suppresses the surface tension of the droplet. However, when the content is less than 0.1%, the effect of addition cannot be sufficiently obtained, so Si needs to be added by 0.1% or more. Thereby, it can coexist with Cu and can improve the corrosion resistance especially in a sulfuric acid concentration range of about 40%. On the other hand, if the Si content exceeds 2.0%, the improvement in corrosion resistance is saturated, and the toughness is greatly reduced as the ductility is lowered. Therefore, the Si content is limited to 0.1 to 2.0%.

Mn: 0.2 to 3.0%
In addition to acting as a deoxidizing element, Mn is an element effective for improving the strength and impact toughness of the weld metal. However, when the content is less than 0.2%, a sufficient effect cannot be obtained, and when Mn is added over 3.0%, the hardenability is increased and the hardness of the weld metal is increased. , Crack resistance deteriorates. Therefore, the Mn content is limited to 0.2 to 3.0%.

Ni: 0.05-1.0%
Ni is added as an element that improves hydrochloric acid corrosion resistance. However, if its content is less than 0.05%, sufficient effects cannot be obtained. On the other hand, even if Ni is added in an amount exceeding 1.0%, the corrosion resistance is almost saturated and an excessive increase in strength is caused to increase the weld crack sensitivity. Therefore, the Ni content is limited to 0.05 to 1.0%.

P: 0.03% or less P is an impurity element, and since it significantly inhibits sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance, the smaller the amount, the better. Specifically, when the P content exceeds 0.03%, the sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance deteriorate. Therefore, the P content is 0.03% or less.

S: 0.03% or less S is an impurity element, and excessive content exceeding 0.03% lowers the corrosion resistance and promotes hot welding cracking. Therefore, it is necessary to limit the corrosion resistance and cracking resistance. There is. Therefore, the S content is 0.03% or less. S has the effect of improving sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance by coexisting with Cu, Sb, and Mo, and the effect becomes remarkable at 0.005% or more. Thus, from the viewpoint of corrosion resistance, since a small amount is effective, the S content is preferably S: 0.005 to 0.03%.

Cu: 0.1 to 1.0%
Cu is added to improve sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance. However, when the content is less than 0.1%, a sufficient effect cannot be obtained. On the other hand, even if Cu is added in excess of 1.0%, the corrosion resistance is almost saturated and an excessive increase in strength is caused, resulting in an increase in weld crack sensitivity. Therefore, the Cu content is limited to 0.1 to 1.0%.

  However, since Cu is a low melting point component, if it is contained in the wire as a pure metal, even after the slag generated during welding solidifies, it remains in the molten state in the slag, and the molten Cu remains in the weld metal and weld. This is not preferable because it enters the heat-affected zone, particularly the coarsened austenite grain boundary in the vicinity of the melting line and causes liquid metal embrittlement cracking. Therefore, in the flux-cored wire of the present invention, during welding, Cu in the weld metal and the weld heat affected zone is stabilized as a higher melting point alloy, and the liquid metal embrittlement of the weld metal due to the molten Cu. In order to improve sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance while suppressing cracking, Cu is in the form of an Fe-Cu alloy or Fe-Cu-Si alloy having a melting point higher than that of pure metal, and in the filling flux as metal powder. Add to. At that time, when the Cu content in the Fe—Cu alloy and the Fe—Cu—Si alloy is less than 10 mass%, the effect of improving the sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance by Cu cannot be stably obtained. On the other hand, when the Cu content in the Fe—Cu alloy and the Fe—Cu—Si alloy exceeds 30% by mass, the liquid metal embrittlement cracking of the weld metal caused by the molten Cu can be suppressed during welding. become unable. Therefore, the Cu content of the Fe—Cu alloy and the Fe—Cu—Si alloy contained in the flux is 10 to 30% by mass.

Sb: 0.01 to 0.25%
Sb is an element that coexists with Cu and further improves sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance. However, when the Sb content is less than 0.01%, the effect cannot be obtained. On the other hand, when the Sb content exceeds 0.25%, the arc becomes unstable, the welding workability is deteriorated, and the weld crack sensitivity is increased. Therefore, the Sb content is limited to 0.01 to 0.25%.

  In addition, since Sb is a low melting point component as in the case of Cu described above, when Sb is added to the wire as a pure metal, even after the slag produced during welding solidifies, it remains in the molten state in the slag and is in a molten state. This is not preferable because the Sb intrudes into the weld metal and the weld heat affected zone, particularly the coarsened austenite grain boundary near the melting line, and causes liquid metal embrittlement cracks. Therefore, in the flux-cored wire of the present invention, during welding, Sb in the weld metal and the weld heat-affected zone is stabilized as a higher melting point alloy, and the liquid metal embrittlement of the weld metal due to molten Sb. In order to improve sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance while suppressing cracking, Sb is added to the filling flux as metal powder in the form of an Fe—Sb alloy having a melting point higher than that of pure metal. Thus, when Sb is contained in the filled flux in the form of an Fe—Sb alloy having a high melting point, the bead formability is deteriorated and the Sb is deteriorated particularly when used as a welding wire in submerged arc welding having a high heat input. The problem of the decrease in the yield of Sb in the weld metal due to the dissipation of can also be improved.

  However, when the Sb content in the Fe—Sb alloy is less than 40% by mass, the effect of improving the sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance by Sb cannot be stably obtained. On the other hand, when the Sb content in the Fe—Sb alloy exceeds 60% by mass, liquid metal embrittlement cracking of the weld metal due to Sb in the molten state cannot be suppressed during welding. Therefore, the Sb content of the Fe—Sb alloy contained in the flux is 40 to 60%. The melting point of this Fe—Sb alloy is more preferably 1000 ° C. or higher.

  In addition to the above components, the flux-cored wire of the present invention may contain Mo in the steel outer sheath and / or the filling flux.

Mo: 0.01 to 0.5%
Mo is an element that significantly improves hydrochloric acid corrosion resistance in the presence of Cu, and is added as necessary. The effect is further increased by the combined effect of Cu and Sb. However, when the Mo content is less than 0.01%, the effect of addition cannot be obtained. On the other hand, when Mo is added exceeding 0.5%, not only hydrochloric acid corrosion resistance but also sulfuric acid corrosion resistance is lowered. Therefore, when adding Mo, the content is made 0.01 to 0.5%.

  Furthermore, in the flux-cored wire of the present invention, Cr may be added to the steel outer sheath and / or the filled flux in addition to the above components.

Cr: 0.05 to 1.5%
Cr is an element that generally reduces hydrochloric acid corrosion resistance, but conversely is an element that improves sulfuric acid corrosion resistance. Therefore, the flux-cored wire of the present invention is added as necessary, for example, when ensuring corrosion resistance in a sulfuric acid dew point corrosion environment generated in a plant having a large amount of sulfur oxide in exhaust gas. However, when the Cr content is less than 0.05%, the sulfuric acid corrosion resistance improving effect cannot be obtained. On the other hand, when Cr is added exceeding 1.5%, the sulfuric acid corrosion resistance is inhibited. Therefore, when adding Cr, the content is made 0.05 to 1.5%.

  Furthermore, in the flux-cored wire of the present invention, one or more elements selected from the group consisting of Al, Ti and Zr can be added to the steel outer sheath and / or the filled flux.

Al: 0.005-0.2%, Ti: 0.005-0.2% and Zr: 0.005-0.2%
Al is added as a deoxidizing element and, if necessary, as an element effective for improving impact toughness. However, if the Al content is less than 0.005%, the effect is not sufficient. On the other hand, if the Al content exceeds 0.2%, welding workability is hindered. Therefore, when adding Al, the content is made 0.005 to 0.2%. Ti is a deoxidizing element like Al, and also forms an Ti oxide, refines the microstructure of the weld metal, and is an element effective in improving toughness, and is added as necessary. However, when the Ti content is less than 0.005%, the effect is not sufficient. On the other hand, when the Ti content exceeds 0.2%, seizure of slag increases and impact toughness decreases. Therefore, when adding Ti, the content is made 0.005 to 0.2%. Furthermore, Zr is a deoxidizing element like Al and Ti, and is an element effective for improving toughness by being added in combination with these elements, so is added as necessary. However, if the Zr content is less than 0.005%, the effect is not sufficient. On the other hand, if the Zr content exceeds 0.2%, the seizure of slag increases as in the case of Al and Ti, and the impact toughness is reduced. Reduce. Therefore, when adding Zr, the content is made 0.005 to 0.2%.

  In the flux-cored wire of the present invention, the filling rate of the filling flux is not particularly limited. Further, the cross-sectional shape of the wire may be a joint type such as a C cross-section and an overlapping cross-section, or a seamless type without a seam. Further, the thickness of the steel outer sheath and the wire diameter are not particularly limited, and can be appropriately selected. Furthermore, the flux-cored wire of the present invention can be applied to gas shielded arc welding such as MIG and MAG, or submerged arc welding.

  As described above, in the flux-cored wire of the present invention, Cu and Sb are stabilized as an alloy having a higher melting point, thereby suppressing liquid metal embrittlement cracking of weld metal caused by molten Cu and Sb. The sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance can be improved. In particular, it has a high heat input and is effective in suppressing liquid metal embrittlement cracking in weld metal and in improving sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance in submerged arc welding using a flux filled in the groove together with the welding wire. is there. Therefore, it is possible to ensure the long-term reliability of hydrochloric acid and sulfuric acid dew-point corrosion steel structures used in thermal power boilers and smoke incinerators, and to improve the economic effect by improving the maintainability of welds. The present invention contributes greatly to the development of the industry.

  However, in submerged arc welding, in order to more stably exert the above-mentioned effect of suppressing the above-mentioned body metal embrittlement cracking by the flux-cored wire of the present invention, pure metal is contained in the flux filled in the groove of the material to be welded. It is desirable to limit the contents of Cu and Sb contained as 0.005% or less. At that time, the flux filled in the groove to be welded may be either a melt-type flux or a bond-type flux.

  The flux-cored wire of the present invention is used when welding steel having excellent hydrochloric acid resistance and sulfuric acid resistance, and is applied to manufacture of welded structures, and repair welding or overlaying of the structures. It can also be applied to. Specifically, hydrochloric acid that exhibits excellent corrosion resistance in an environment that causes low-temperature corrosion by sulfuric acid and hydrochloric acid, such as flues and chimneys of coal-fired boilers and waste incineration facilities, that is, concentrated sulfuric acid and concentrated hydrochloric acid environment Used in welding construction of sulfuric acid dew point corrosion low alloy steel. More specifically, for example, fossil fuels such as heavy oil and coal, gas fuels such as liquefied natural gas, general waste such as municipal waste, woodworking waste, textile waste, waste oil, plastic, waste tires, medical waste, and other industrial waste Hydrochloric acid and sulfuric acid dew points that are applied to smoke exhaust facilities such as boilers that burn waste and sewage sludge, etc., or steel pickling tanks that contain single or mixed pickling solutions such as hydrochloric acid and sulfuric acid Can be used for gas shielded arc welding of corroded steel.

  Hereinafter, the operation and effect of the present invention will be described in more detail with reference to examples of the present invention. In this example, a V groove with a groove angle of 50 ° was prepared on a base material of hydrochloric acid and sulfuric acid dew point corrosion steel having a thickness of 160 mm and a composition shown in Table 1 below. Also, a flux-cored wire of an example and a comparative example in which the diameter of the wire is 4.0 mm or 1.2 mm by combining a steel outer sheath having the composition shown in Table 2 below and a filling flux having the composition shown in Table 3 below. Was made. The details of each flux cored wire are shown in Table 4 below. In addition, the remainder in the chemical composition of the whole flux cored wire shown in Table 4 below is Fe and inevitable impurities. Moreover, the underline in the following Table 3 and Table 4 shows that it is outside the scope of the present invention.

  Next, using each of the flux-cored wires of Examples and Comparative Examples shown in Table 4 above, MAG welding of hydrochloric acid and sulfuric acid dew-point corrosion resistant steel having the composition shown in Table 1 was performed under the welding conditions shown in Table 5 below. Alternatively, submerged arc welding (SAW) was performed. At that time, in the case of submerged arc welding, welding was performed using a flux for submerged arc welding shown in Table 6 below.

  And from each welded joint welded by the method mentioned above, the corrosion test piece, the tensile test piece, the impact test piece, and the surface bending test piece were sampled by the method shown below, and tested and evaluated. In the corrosion test, test pieces having a length of 25 mm, a width of 25 mm, and a thickness of 4 mm were taken from the weld metal part of each joint, and the entire surface was wet-polished with No. 400 emery paper and then immersed in 50% sulfuric acid at 70 ° C. for 24 hours. Or immersed in 10.5% hydrochloric acid at 80 ° C. for 24 hours, and the amount of decrease in the corrosion plate thickness per side was measured. The tensile test was evaluated with a No. 1A test piece in accordance with the weld joint tensile test method of JIS Z 3121. The impact test was based on JIS Z 3128, and a full-size V-notch test piece defined in JIS Z 2202 was sampled so that a notch was located in the weld metal, and a Charpy impact test was performed at a test temperature of 0 ° C. The surface bending test was performed according to JIS Z 3122 and R = 2t (32 mm).

  In addition, the appearance of the bead after welding and the presence or absence of undercut were investigated, and the welding workability was also evaluated. The above results are summarized in Table 7 below. In the joint tensile test results shown in Table 7 below, the fractures with the base metal were evaluated as ◯, and the fractures at other parts were evaluated as x. In addition, the corrosion test result shows that the corrosion plate thickness reduction amount of the base material is 0.12 to 0.15 mm, so that the test piece (welded metal) corrosion plate thickness reduction amount is less than 0.15 mm did. Furthermore, the impact test result was acceptable when the Charpy absorbed energy was 50 J or more. These tests were comprehensively evaluated including the results of surface bending tests and welding workability evaluation results.

  As shown in Table 7 above, no. The joints 1 to 9 are examples using flux-cored wires (No. A to No. I) produced within the scope of the present invention. 2, No. 5, no. 8 and no. The joint of No. 9 was subjected to MAG welding, No. 9 1, no. 3, no. 4, no. 6 and no. Further, the joint of No. 7 is obtained by submerged arc welding using the flux for submerged arc welding shown in Table 6 above. All of the joints of these examples have no liquid metal embrittlement cracking, good welding workability, excellent sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance, and strength, impact toughness and bending characteristics. A good weld metal part was obtained.

  On the other hand, comparative example No. which carried out submerged arc welding using the flux cored wire (No.J-No.X) which remove | deviates from the scope of the present invention, and using MAG welding or the welding flux shown in Table 6 above. The joints 10 to 24 were unsuitable for any one or more of corrosion resistance, impact toughness, crackability and welding workability, and were rejected as a comprehensive evaluation. Specifically, Comparative Example No. The joint (wire No. J) of No. 10 has a Si content less than the component range of the present invention, so is poor in sulfuric acid corrosion resistance and uses pure Sb as the Sb source in the flux. Brittle cracks occurred. Comparative Example No. The joint No. 11 (Wire No. K) had a Cu content that was less than the component range of the present invention, and therefore was poor in both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance. Comparative Example No. The joint of No. 12 (wire No. L) had a Cu content higher than the range of the present invention, and therefore caused an excessive increase in hardness, resulting in deterioration of toughness and weld cracking. Comparative Example No. The joint (wire No. M) No. 13 has an Sb content that is less than the component range of the present invention, so both the sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance are inferior. Furthermore, the C content and Al content are low. Since there are more than the range of this invention, toughness and welding workability | operativity were inferior.

  Comparative Example No. In the joint (wire No. N) No. 14, the Sb content exceeded the component range of the present invention, so that weld cracks occurred. Comparative Example No. Since the Ni content was less than the component range of the present invention, the joint (wire No. O) 15 was inferior in sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance. Moreover, since the Cu content of the Fe—Cu—Si alloy added as a Cu source in the flux exceeds the component range of the present invention, the melting point was lowered and liquid metal embrittlement cracking occurred. Comparative Example No. Since the joint of 16 (wire No. P) had Ni and Ti exceeding the component range of the present invention, it caused an excessive increase in hardness and was inferior in toughness and welding workability. Comparative Example No. Since the Sb content of the Fe-Sb alloy added as an Sb source in the flux is less than the component range of the present invention, the joint No. 17 (wire No. Q) is resistant to sulfuric acid corrosion and hydrochloric acid. Was inferior. Comparative Example No. Since the Cu content of the Fe-Cu alloy added as a Cu source in the flux is less than the component range of the present invention, the joint No. 18 (wire No. R) has sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance. It was inferior.

  Comparative Example No. In the joint No. 19 (wire No. S), since the Sb content of the Fe—Sb alloy added as the Sb source in the flux exceeds the component range of the present invention, the melting point is lowered and the liquid metal becomes brittle. Cracked. Comparative Example No. The joint (wire No. T) 20 has a lower melting point and a liquid metal embrittlement because the Cu content of the Fe-Cu alloy added as a Cu source in the flux exceeds the component range of the present invention. Cracked. Comparative Example No. Since the S content of the joint (wire No. U) 21 exceeded the component range of the present invention, the sulfuric acid corrosion resistance was inferior and weld solidification cracking occurred. Comparative Example No. In the joint No. 22 (wire No. V), since Mo exceeds the component range of the present invention, both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance deteriorate, and the Mn content also falls within the component range of the present invention. Therefore, the weld metal hardness increased and weld cracking occurred. Comparative Example No. In the joint No. 23 (wire No. W), since the Cr content exceeds the component range of the present invention, both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance are deteriorated, and added as an Sb source in the flux. Since the Sb content of the Fe—Sb alloy exceeds the component range of the present invention, the melting point was lowered and liquid metal embrittlement cracking occurred. Comparative Example No. Since the joint (wire No. X) 24 uses pure Cu as a Cu source in the flux, liquid metal embrittlement cracking occurred.

  As described above, by welding using the flux-cored wire of the present invention, while suppressing the occurrence of liquid metal embrittlement cracking, it has excellent corrosion resistance in sulfuric acid environment and hydrochloric acid environment, and strength and impact toughness In addition, an excellent weld metal can be obtained, and a remarkable effect can be obtained in improving the welding workability.

Claims (5)

In the flux-cored wire in which the filling flux is filled in the steel outer sheath,
In the whole wire, as metal or alloy, in mass%,
C: 0.01 to 0.2%
Si: 0.1 to 2.0%,
Mn: 0.2 to 3.0%
Ni: 0.05-1.0%
And containing
P: 0.03% or less,
S: limited to 0.03% or less,
Furthermore, only in the filling flux, as Fe-Cu alloy or Fe-Cu-Si alloy, in a mass% with respect to the total mass of the wire, containing Cu: 0.1 to 1.0%, and as an Fe-Sb alloy, In mass% with respect to the total mass of the wire, containing Sb: 0.01 to 0.25%,
And the Cu content in the Fe-Cu alloy or Fe-Cu-Si alloy contained in the filled flux is 10 to 30% by mass, the Sb content in the Fe-Sb alloy is 40 to 60% by mass,
A flux-cored wire for gas shielded arc welding, which is used when welding steel with excellent hydrochloric acid resistance and sulfuric acid resistance.   2. The flux-cored wire for gas shielded arc welding according to claim 1, wherein S is 0.005 to 0.03% by mass% with respect to the total mass of the wire.   The flux-cored wire for gas shielded arc welding according to claim 1 or 2, further comprising Mo: 0.01 to 0.5% by mass as a metal or alloy as a whole of the wire.   The gas shielded arc welding according to any one of claims 1 to 3, further comprising Cr: 0.05 to 1.5% in mass% as a metal or alloy as a whole wire. Flux cored wire.   Furthermore, the group consisting of Al: 0.005 to 0.2%, Ti: 0.005 to 0.2%, and Zr: 0.005 to 0.2% in mass% as a metal or alloy as the whole wire 5. The flux-cored wire for gas shielded arc welding according to claim 1, comprising one or more elements selected from the group consisting of: