JP2013000784A - Submerge arc welding method of low alloy steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a submerge arc welding method for obtaining a weld metal exhibiting excellent corrosion resistance etc. under the environment of concentrated sulfuric acid and concentrated hydrochloric acid and having no welding defect.SOLUTION: Welding is performed by using the combination of a bond flux and a solid wire. The bond flux contains, by mass%, 5 to 21% of SiO, 15 to 44% of AlO, 7 to 32% of MgO, 0.5 to 10% of CaO, 5 to 35% of CaF, 5 to 33% of TiO, 0.2 to 5.0% of Si, 0.1 to 5.0% of Mn, and 0.5 to 9.0% of COin terms of metal carbonate. In bond flux, particles having a particle diameter exceeding 850 μm account for 20 to 55%, particles between 150 and 850 μm for 40 to 75%, and particles less than 150 μm for 6% or less, and the apparent density is 0.70 to 1.30 g/cm. The solid wire contains 0.005 to 0.2% of C, 0.01 to 1.5% of Si, 0.4 to 2.5% of Mn, 0.03 to 1.0% of Cu, 0.05 to 1.0% of Ni, 0.01 to 1.0% of Mo, and 0.01 to 0.25% of Sb.

Description

  The present invention relates to a submerged arc welding method for low alloy steel that provides excellent corrosion resistance in concentrated sulfuric acid and concentrated hydrochloric acid environments, and is particularly excellent in submerged arc welding of sulfuric acid dew point corrosion resistant low alloy steel applied in severe environments. The present invention relates to a submerged arc welding method for low alloy steel, which provides corrosion resistance and good weld metal mechanical performance, and forms a sound weld metal with no welding defects, and has good welding workability and excellent sulfuric acid resistance and hydrochloric acid resistance. It is.

  In recent years, with the development of industry, studies have been made on improving corrosion resistance from the viewpoint of increasing the toughness of steel materials and safety and economy, and among them, the application ratio of steel materials having excellent corrosion resistance is increasing year by year.

  For example, fossil fuels such as heavy oil and petroleum, gas fuels such as liquefied natural gas, general waste such as municipal waste, textile waste, woodworking waste, plastic, waste oil, waste tires, industrial waste such as medical waste, and sewage sludge Sulfur-resistant dew-point corrosion low alloy steel is used in smoke exhausting equipment such as boilers, and steel plating pickling tanks containing single or mixed pickling solutions such as hydrochloric acid and sulfuric acid. In particular, in the flue and chimney flue facilities such as coal-fired thermal power plants and garbage incineration facilities, sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion occur due to sulfur trioxide and hydrogen chloride in the exhaust gas. The need for is growing.

  Generally, when welded structures constructed by welding base materials such as sulfuric acid dew-point corrosion steel together by welding are used in a corrosive environment, the weld metal must have corrosion resistance equivalent to or higher than that of the base material. It is said. If there is a difference in corrosion resistance between the welded part and the base metal, the inferior corrosion resistance is selectively corroded, and the life of the structure is remarkably shortened. In addition, if the welded part is selectively corroded, stress may concentrate on the corroded holes and the structure may be destroyed. If the welded structure is used in a corrosive environment, the base material should be It is necessary to consider not only the dew point corrosion steel but also the corrosion resistance of the welding material constituting the welded portion.

  Conventionally, as a welding material for sulfuric acid dew-point corrosion steel, a material containing Cu or a Cu—Cr-based material as a corrosion-resistant element is applied. However, when these existing welding materials are used, they exhibit sufficiently excellent corrosion resistance under the sulfuric acid dew point corrosion environment generated by heavy oil fired boiler plant flue gas generators, but coal-fired boilers, garbage incineration or garbage gasification and melting facilities However, since sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion occur simultaneously, there was a problem that sufficient corrosion resistance of the welded portion could not be ensured.

  Considering these points, an attempt has been made to develop a welding material that can ensure sufficient corrosion resistance even in an environment in which sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion occur simultaneously.

  For example, Japanese Patent Application Laid-Open No. 2004-90044 (Patent Document 1), Japanese Patent Application Laid-Open No. 2004-90045 (Patent Document 2), and Japanese Patent Application Laid-Open No. 2004-90042 (Patent Document 3) are respectively coated according to the welding method. Technology to add Cu, Sb and Ni to arc welding rods, solid wire for gas shielded arc welding, and flux-cored wire for gas shielded arc welding in order to obtain a weld metal with excellent resistance to sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion. There is a disclosure. In Patent Documents 1 to 3, Cu and Sb effective for improving sulfuric acid resistance and hydrochloric acid resistance are added. In the case of a coated arc welding rod or a flux-cored wire for gas shielded arc welding, Cu in the wire is used. And when a part of Sb moved into the weld metal, it was confirmed that it remained on the surface of the weld metal and the weld heat affected zone together with the slag generated by melting the flux. And since Cu and Sb have a melting point lower than that of the slag component, they remain in the molten state in the slag even after the slag solidifies, and the molten metals of Cu and Sb are weld metal and weld heat affected zone, particularly near the melting line. In some cases, the grains enter the coarsened austenite grain boundaries to cause grain boundary embrittlement cracks. When this grain boundary embrittlement crack occurs, the mechanical properties such as the toughness and fatigue strength of the welded portion are reduced, and the crack occurrence site becomes the starting point of corrosion. It becomes difficult to obtain corrosion resistance and mechanical properties.

  In addition to the various arc welding described above, various techniques for improving the corrosion resistance, that is, the sulfuric acid resistance and the hydrochloric acid resistance have also been proposed in the submerged arc welding method. In the submerged arc welding method, a granular flux is dispersed in advance along a welding line, an electrode wire is continuously supplied therein, and an arc is generated between the tip of the electrode wire and the base material. This is a method of performing welding continuously. Submerged arc welding is used in a wide range of fields such as steel frames, pipes, bridges, shipbuilding, and vehicles because it provides highly efficient and stable weld metal with excellent workability and mechanical performance. In order to improve productivity and ensure corrosion resistance, further quality improvement is required.

  Japanese Patent Application Laid-Open No. 2008-126279 (Patent Document 4) discloses a technique in which a flux-cored wire from which a weld metal excellent in sulfuric acid dew point corrosion resistance and hydrochloric acid dew point corrosion resistance is obtained is combined with a flux for submerged arc welding. In the disclosed technology, Cu to be added to the filled flux of the flux-cored wire is in the form of Fe-Cu alloy or Fe-Cu-Si alloy, Sb is contained in the form of Fe-Sb alloy, and grain boundary embrittlement cracking occurs. However, in the disclosed flux chemical composition, since a deoxidizer and a gas generator are not added, weld defects such as pits and blowholes are generated to obtain a sound weld metal. I can't.

  Japanese Unexamined Patent Application Publication No. 2004-90051 (Patent Document 5) discloses a technique related to a bond flux and a welding method for submerged arc welding of low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance. This is obtained by adding Sb to the flux in order to obtain a weld metal excellent in sulfuric acid resistance and hydrochloric acid resistance. However, since the amount of Sb added to the flux is small, it is easy to segregate and has a small particle size. In addition, since the raw material of the Sb compound is used, it is easy to peel off from the flux particles after granulation and to be pulverized, and there is a problem that Sb segregates in the weld metal and easily causes intergranular embrittlement cracking. .

JP 2004-90044 A JP 2004-90045 A JP 2004-90042 A JP 2008-126279 A JP 2004-90051 A

  Therefore, the present invention has been devised in view of the above-described problems, and in a submerged arc welding method of low alloy steel that provides excellent corrosion resistance in concentrated sulfuric acid and concentrated hydrochloric acid environments, excellent corrosion resistance and good An object of the present invention is to provide a submerged arc welding method for low-alloy steel with excellent weldability and sulfuric acid resistance and hydrochloric acid resistance, which can achieve weld metal mechanical performance and form a sound weld metal with no weld defects. And

  In order to solve the above problems, the present inventors have studied in detail the chemical composition of the flux, the particle size configuration, the apparent density, the chemical composition of the solid wire to be combined, and the like. As a result, by limiting the chemical composition, particle size composition and apparent density of the flux, and also by limiting the chemical composition of the solid wire to be combined, excellent corrosion resistance and good weld metal machine performance in concentrated sulfuric acid and concentrated hydrochloric acid environments It was also found that a submerged arc welding method with good welding workability can be achieved by forming a healthy weld metal free of welding defects.

That is, the gist of the present invention is mass%, SiO ₂ : 5 to 21%, Al ₂ O ₃ : 15 to 44%, MgO: 7 to 32%, CaO: 0.5 to 10%, CaF ₂ : 5 _{~35%, TiO 2: 5~33%} , Si: 0.2~5.0%, Mn: 0.1~5.0%, CO 2 minutes of metal carbonate: 0.5 to 9.0% The balance consists of FeO, alkali metal oxides and inevitable impurities, the particle size composition of the flux is 20% by mass, particles with a particle size of more than 850 μm are 20 to 55%, and particles with a particle size of 150 to 850 μm are 40 to 75. %, Particles having a particle diameter of less than 150 μm are 6% or less, and an apparent density is 0.70 to 1.30 g / cm ³ , and mass%, C: 0.005 to 0.2%, Si : 0.01-1.5%, Mn: 0.4-2.5%, Cu: 0.03-1.0%, Ni: 0.05- 1.0%, Mo: 0.01 to 1.0%, Sb: 0.01 to 0.25%, P: 0.03% or less, S: 0.03% or less, the balance being Fe And welding in combination with a solid wire made of inevitable impurities.

Further, B ₂ O ₃ in the bonded flux: it is in the submerged arc welding method of low alloy steel with excellent resistance to sulfuric acid and hydrochloric acid, characterized containing 0.05 to 3.0%.

  According to the submerged arc welding method of the low alloy steel to which the present invention is applied, excellent corrosion resistance and good weld metal mechanical performance can be obtained in a concentrated sulfuric acid and concentrated hydrochloric acid environment, and a sound weld metal free from welding defects can be formed. In addition, it is possible to provide a submerged arc welding method for low alloy steel having excellent welding workability and excellent sulfuric acid resistance and hydrochloric acid resistance.

It is a figure which shows the groove shape of the multilayer pile-welding test board used in the Example of this invention.

  The present inventors prevent intergranular embrittlement cracking that is likely to occur when welding is performed using a welding material containing Cu and Sb, which is effective in improving the sulfuric acid resistance and hydrochloric acid resistance of the weld metal, and concentrated sulfuric acid. Excellent corrosion resistance in a concentrated hydrochloric acid environment, good weld metal mechanical performance, sound weld metal free of weld defects, and submerged arc welding with good welding workability Various studies were made on the chemical composition, particle size composition, apparent density, and chemical composition of the solid wire to be combined.

  In order to obtain a weld metal excellent in both sulfuric acid dew point corrosion resistance and hydrochloric acid dew point corrosion resistance, addition of Cu and Sb is indispensable, and it is necessary to add to either the flux or the solid wire to be combined. Therefore, first, addition to the flux was examined. Two types of fluxes were studied: melt flux and bond flux. As a result, when added to the molten flux, there was no segregation of the Cu compound and Sb compound in the flux, and a weld metal excellent in both sulfuric acid dew point corrosion resistance and hydrochloric acid dew point corrosion resistance could be obtained. However, when the element is added to the molten flux, the alloying agent and the metal carbonate cannot be added, so that welding defects of pits and blowholes frequently occur due to insufficient deoxidation and shielding gas during welding. On the other hand, when Cu and Sb are added to the bond flux, Cu and Sb are easily added to the flux because they are added in a small amount, and are easily peeled off from the granulated flux particles and easily pulverized. Segregation occurred and grain boundary embrittlement cracking occurred.

  From the above results, addition of Cu and Sb to the flux is difficult, so addition to a solid wire was examined. Conventionally, a solid wire for gas shielded arc welding to which Cu and Sb are added is welded with a large current when applied to submerged arc welding, so that Sb added to the wire is easily boiled and gasified by arc heat, It was considered difficult to apply a solid wire with Sb added to submerged arc welding.

  Therefore, it was examined whether or not Sb can be stably contained in the weld metal by adding an appropriate amount of Sb to the solid wire and optimizing the chemical composition, particle size configuration, and apparent density of the flux.

First, bond flux corresponding to high heat input welding with high current is applied, and in order to adjust the softening melting point of the flux and the viscosity, fluidity, solidification rate of the molten slag, SiO ₂ , Al ₂ O ₃ , The slag composition of MgO, CaO, CaF ₂ and TiO ₂ was optimized. In order to stably contain Sb in the weld metal, it is important to prevent Sb from boiling and being gasified by arc heat, increasing the softening and melting point of the flux and increasing the solidification rate of the molten slag. By increasing the speed, there was a tendency that Sb was stably contained in the weld metal.

  However, only by optimizing the slag composition of the bond flux, Sb could not be contained in the weld metal completely stably. Therefore, what has been newly found in order to completely and stably contain Sb in the weld metal is optimization of the particle size configuration and apparent density of the flux. This could be improved by increasing the fraction of the larger flux particles and limiting the apparent density. The flux is melted by the arc heat during welding, but the flux in the arc atmosphere is reduced by increasing the amount of flux particles with a larger particle size to slow the flux melting rate and concentrating the amount of heat on the flux melting. Thus, Sb could be stably contained in the weld metal.

  From the above, by optimizing the chemical composition, particle size composition, apparent density of the bond flux, and the chemical composition of the solid wire to be combined, it is possible to obtain a weld metal that is superior in both sulfuric acid dew point corrosion resistance and hydrochloric acid dew point corrosion resistance. In addition, the flux chemical composition, particle size composition, and apparent density are taken into account in consideration of welding workability, so that good welding workability and bead shape can be obtained, and alloying agents such as Si and Mn are added. It has been found that good weld metal mechanical performance can be obtained.

  In the submerged arc welding method of low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance to which the present invention is applied, the bond flux and the solid wire are welded in combination.

The bonded flux is the _{mass%, SiO 2: 5~21%,} Al 2 O 3: 15~44%, MgO: 7~32%, CaO: 0.5~10%, CaF 2: 5~35% _{, TiO 2: 5~33%, Si} : 0.2~5.0%, Mn: 0.1~5.0%, CO 2 minutes of metal carbonate: contain 0.5 to 9.0% The balance consists of FeO, alkali metal oxides and inevitable impurities, the particle size composition of the flux is 20% by mass, particles with a particle size of more than 850 μm are 20-55%, particles with a particle size of 150-850 μm are 40-75%, The particles having a diameter of less than 150 μm are 6% or less, and the apparent density is 0.70 to 1.30 g / cm ³ . About the bond flux which concerns, a component composition, a particle size structure, and the reason for limitation of an apparent density are demonstrated. In addition, the following% shows the mass%.

SiO ₂ : 5 to 21%
SiO ₂ is an important component for forming a good weld bead, but if it is excessive, the amount of oxygen in the weld metal increases and the toughness deteriorates. If the SiO ₂ content is less than 5%, the conformity of the end portion of the bead heel becomes poor and the bead shape becomes poor, resulting in poor slag removability. On the other hand, if it exceeds 21%, the oxygen content of the weld metal increases and the toughness decreases. Thus, SiO ₂ is set to 5-21%.

Al ₂ O ₃ : 15 to 44%
Al ₂ O ₃ is an important component for obtaining good slag peelability and bead appearance. In addition, there is an effect that Sb is stably contained in the weld metal. If Al ₂ O ₃ is less than 15%, the effect cannot be obtained. On the other hand, if it exceeds 44%, it becomes a convex bead and the bead cannot be flattened, and the slag removability becomes poor. Accordingly, Al ₂ O ₃ is set to 15 to 44%.

MgO: 7 to 32%
MgO has the effect of improving the fire resistance and basicity of the slag. It is also the most important component for stably containing Sb in the weld metal. If MgO is less than 7%, the basicity of the flux decreases, the amount of oxygen in the weld metal increases, the toughness decreases, and Sb is not stably contained in the weld metal. On the other hand, if it exceeds 32%, the softening and melting point of the flux becomes high, the wave surface of the bead surface becomes rough, and the slag peelability and the bead appearance become poor. Therefore, MgO is 7 to 32%. In addition, MgO contains the MgO content of MgCO ₃ .

CaO: 0.5 to 10%
CaO is an important component for adjusting the melting point and fluidity of the slag. If CaO is less than 0.5%, the bead collar is not well adapted and the bead appearance is poor. On the other hand, if it exceeds 10%, the slag fluidity will be poor, the bead height will be uneven and the slag peelability will be poor. Therefore, CaO is 0.5 to 10%. Note that CaO includes the CaO content of CaCO ₃ .

CaF ₂ : 5 to 35%
CaF ₂ is effective in improving toughness, but since the melting point is low, if it is excessive, the smoothness of the bead is impaired. When CaF ₂ is less than 5%, there is no effect of improving toughness, and when it exceeds 35%, the bead appearance is poor. Therefore, CaF ₂ is 5 to 35%.

TiO _2: 5~33%
TiO ₂ is effective in obtaining the smoothness of the bead surface and is also effective in improving toughness. If TiO ₂ is less than 5%, there is no effect of improving the smoothness and toughness of the bead surface. If it exceeds 33%, the rising angle of the bead heel end portion becomes large and the bead shape and slag peelability become poor. Therefore, TiO ₂ is set to 5-33%.

Si: 0.2-5.0%
Si is a deoxidizing element and reduces the oxygen content of the weld metal. If Si is less than 0.2%, the deoxidizing effect cannot be obtained and the toughness is lowered. On the other hand, if it exceeds 5.0%, the hardness of the weld metal becomes excessive and the toughness decreases. Therefore, Si is 0.2 to 5.0%.

Mn: 0.1 to 5.0%
Mn is a deoxidizing element like Si, and reduces the oxygen content of the weld metal. If Mn is less than 0.1%, the deoxidizing effect cannot be obtained and the toughness is lowered. On the other hand, if it exceeds 5.0%, the hardness of the weld metal becomes excessive and the toughness decreases. Therefore, Mn is set to 0.1 to 5.0%.

CO ₂ minutes of CO ₂ partial metal carbonates metal carbonate is an important element in improving toughness of the weld metal, the nitrogen content of the metal carbonate is decomposed CO The CO ₂ gas arc atmosphere during the welding It has the effect of reducing the pressure and reducing the nitrogen content of the weld metal. If the CO ₂ content is less than 0.5%, the amount of nitrogen in the weld metal increases and the toughness decreases. On the other hand, if it exceeds 9.0%, welding defects such as pock marks, pits, and undercuts occur on the surface of the weld bead. Therefore, the CO ₂ content of the metal carbonate is 0.5 to 9.0%. The metal carbonate may be used _{CaCO 3, BaCO 3, MgCO 3} , MnCO 3.

B ₂ O ₃ : 0.05 to 3.0%
B ₂ O ₃ is effective in improving toughness. However, even if B ₂ O ₃ is not added, good weld metal toughness can be obtained by the addition of Si and Mn and the deoxidizing element and the hardenability improving element contained in the combined solid wire. When welding with a high heat input is performed as described above, the grain structure tends to be coarsened due to a decrease in the cooling rate. Therefore, from the viewpoint of preventing the coarsening of the grain structure, the content of B ₂ O ₃ is set to 0. It is desirable to add 05% or more. On the other hand, if it exceeds 3.0%, the hardenability becomes excessive, the strength of the weld metal increases, and the toughness decreases. Therefore, B ₂ O ₃ is made 0.05 to 3.0%.

  Next, the particle size configuration of the flux will be described. In the particle size constitution of this flux,% means mass%.

Particles with a particle size greater than 850 μm: 20-55%
Particles having a particle size of more than 850 μm in the particle size configuration are extremely important particles that stably contain Sb in the weld metal. If the particle size is more than 850 μm and less than 20%, Sb is not stably contained in the weld metal, the bead shape is convex, the gas escape is poor, and welding defects such as pits and pock marks also occur. On the other hand, if the particle size exceeds 850 μm, the bead width becomes too wide and the penetration becomes shallow, resulting in poor penetration and poor fusion in the case of slag entrainment defects and butt welding. Accordingly, the particle size exceeding 850 μm is set to 20 to 55%.

Particles having a particle size of 150 to 850 μm: 40 to 75%
Particles having a particle size of 150 to 850 μm with a flux particle size composition are also extremely important particles that stably contain Sb in the weld metal. When the particle size is less than 40%, the Sb is not stably contained in the weld metal, the bead shape is convex, the gas escape is poor, and welding defects such as pits and pock marks are generated. On the other hand, when the particle size of 150 to 850 μm exceeds 75%, the width of the bead is excessively widened and the penetration becomes shallow, and in the case of slag entrainment defects or butt welding, poor penetration and poor fusion occur. Therefore, the particle size of 850 μm or more is 40 to 75%.

Particles with a particle size of less than 150 μm: 6% or less Particles with a particle size of less than 150 μm with a flux particle size composition are particles that make the bead shape and slag peelability poor. If the particle size is less than 150 μm, the slag tends to stick and the slag peelability is poor, the bead width is narrowed and the shape is poor, and the gas is poor and welding defects such as pits and pock marks. Is generated. Therefore, the particle size of less than 150 μm is 6% or less.

Apparent density: 0.70 to 1.30 g / cm ³
The apparent density of the flux is an important factor for forming a stable bead, and is also important for stably incorporating Sb into the weld metal. When the apparent density of the flux is less than 0.70 g / cm ³ , the arc blowing during welding is intense and the arc becomes unstable and the bead shape is poor. Sb is boiled and gasified by arc blowing, and Sb is stabilized. Not contained in weld metal. Further, the bead width becomes too wide and the penetration becomes shallow, and in the case of slag entrainment defects or butt welding, poor penetration and poor fusion also occur. On the other hand, when the apparent density of the flux exceeds 1.30 g / cm ³ , the flux becomes heavy and the arc atmosphere is crushed, the bead width becomes narrow and convex, resulting in undercut. Therefore, the apparent density of the flux is 0.70 to 1.30 g / cm ³ .

Others are alkali metal oxides such as Na ₂ O, K ₂ O and Li ₂ O, and inevitable impurities such as iron oxide (FeO, etc.), P, S, etc. Both P and S produce low melting point compounds. Lowering the toughness is preferable.

  The solid wire to be welded in combination with the bond flux composed of the components as described above is C: 0.005-0.2%, Si: 0.01-1.5%, Mn: 0.4-2. 0.5%, Cu: 0.03-1.0%, Ni: 0.05-1.0%, Mo: 0.01-1.0%, Sb: 0.01-0.25% , P: 0.03% or less, S: 0.03% or less, with the balance being Fe and inevitable impurities. Hereinafter, the component composition of the solid wire will be described in detail.

C: 0.005-0.2%
C is an important element that ensures the strength of the weld metal by solid solution strengthening, and has an effect of reacting with oxygen in the arc to reduce the arc atmosphere and the amount of oxygen in the weld metal. If C is less than 0.005%, the effect of deoxidizing the weld metal and securing the strength is insufficient, and the toughness is also lowered. On the other hand, if it exceeds 0.2%, C of the weld metal becomes high, so that it becomes a structure mainly composed of martensite, and the strength is high and the toughness is lowered. Therefore, C is 0.005 to 0.2%.

Si: 0.01 to 1.5%
Si is a deoxidizing element and reduces the oxygen content of the weld metal. If Si is less than 0.01%, the deoxidizing effect cannot be obtained and the toughness is lowered. On the other hand, if it exceeds 1.5%, the hardness of the weld metal becomes excessive and the toughness decreases. Therefore, Si is set to 0.01 to 1.5%.

Mn: 0.4 to 2.5%
Mn is an effective component for improving the hardenability and increasing the strength. If Mn is less than 0.4%, the hardenability is insufficient, the strength is lowered, and the toughness is lowered. On the other hand, if it exceeds 2.5%, the hardenability becomes excessive, the strength of the weld metal increases, and the toughness decreases. Therefore, Mn is set to 0.4 to 2.5%.

Cu: 0.03-1.0%
Cu is an important component that improves sulfuric acid dew point corrosion resistance and hydrochloric acid dew point corrosion resistance. If Cu is less than 0.03%, the effect of improving corrosion resistance cannot be obtained sufficiently. On the other hand, even if added over 1.0%, the corrosion resistance is almost saturated, and an excessive increase in strength of the weld metal is caused to cause toughness reduction and grain boundary embrittlement cracking. Therefore, Cu is 0.03 to 1.0%.

Ni: 0.05-1.0%
Ni improves the toughness of the weld metal. If Ni is less than 0.05%, the effect cannot be obtained and the toughness decreases. On the other hand, if it exceeds 1.0%, since Ni is an austenite stabilizing element, the austenite grain size is coarsened and the toughness of the weld metal is lowered. Therefore, Ni is set to 0.05 to 1.0%.

Mo: 0.01 to 1.0%
Mo is an important component as an element for increasing the hardenability of the weld metal. If Mo is less than 0.01%, the strength of the weld metal is lowered and there is no effect in improving toughness. If it exceeds 1.0%, the hardenability of the weld metal becomes excessive, the hardness becomes excessive, and the toughness is increased. descend. Therefore, Mo is set to 0.01 to 1.0%.

Sb: 0.01 to 0.25%
Sb is the most important component for improving sulfuric acid dew point corrosion resistance and hydrochloric acid dew point corrosion resistance in combination with Cu. If Sb is less than 0.01%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.25%, grain boundary embrittlement cracking occurs. Therefore, Sb is set to 0.01 to 0.25%.

P: 0.03% or less, S: 0.03% or less Both P and S are preferably as low as possible because they both generate a low melting point compound and reduce toughness. Therefore, both P and S are made 0.03% or less.

  In addition, the submerged arc welding method of the low alloy steel excellent in sulfuric acid resistance and hydrochloric acid resistance according to the present invention is a solid wire to be combined in order to perform welding that enables stable arc, wire feedability, and improved welding efficiency. The wire diameter is 2.0 to 4.8 mm and is applied to multi-electrode submerged arc welding of one electrode or two or more electrodes.

  Hereinafter, the effect of the present invention will be described in more detail with reference to examples.

  Table 3 shows the weld metal mechanical performance evaluation and weld workability evaluation of multi-layer welding, using various flux components and particle sizes, bond fluxes adjusted to the apparent density shown in Table 1, and solid wires of chemical composition shown in Table 2. As shown in FIG. 1, a sulfuric acid dew point corrosion-resistant low alloy steel sheet having a thickness of 25 mm and a groove angle of 30 ° and a root interval of 13 mm as shown in FIG. No. 10 was processed, and a multi-layer welding test was carried out under the welding conditions shown in Table 4 with the backing metal 15 applied.

  The bond flux shown in Table 1 was granulated with water glass as a fixing material, and then calcined at 400 to 550 ° C. for 2 hours, and sized to various particle size configurations and apparent densities.

  In addition, the solid wires shown in Table 2 were used by reducing the diameter of the original wires, annealing, pickling, and plating to make the wires, and drawing those wires to a diameter of 4.0 mm.

  Table 5 shows combinations of various prototype bond fluxes and various prototype solid wires. The evaluation of each test is to investigate the appearance of the bead after multi-layer welding, bead shape, slag peelability and the presence or absence of welding defects by X-ray transmission test, and further, the tensile strength, toughness, sulfuric acid corrosion resistance and hydrochloric acid resistance of the weld metal Corrosion was investigated.

  The mechanical performance of weld metal is evaluated by collecting Charpy impact test pieces (JIS Z2242 V-notch test pieces) and tensile test pieces (JIS Z2241 No. 10) around the center of the steel plate thickness of the multi-layer welded specimen. Further, a corrosion test piece having a thickness of 4 mm, a length of 20 mm, and a width of 20 mm was taken from the same position, and in a sulfuric acid solution having a temperature of 70 ° C. and a concentration of 50% by volume for 24 hours, a temperature of 80 ° C. and a concentration of 10% by volume. Was subjected to a 24 hour immersion corrosion test in a hydrochloric acid solution to measure the weight loss.

  The toughness was evaluated by a Charpy impact test at −20 ° C., and evaluated by the average of 3 repetitions. The absorbed energy in the Charpy impact test was 50 J or more. The tensile strength was evaluated as good as 400 MPa or more. In addition, the evaluation of sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance is based on the fact that the corrosion plate thickness reduction amount of the base material of sulfuric acid dew point corrosion low alloy steel plate is 0.20 to 0.25 mm. A plate thickness reduction amount of 0.25 mm or less was considered good. These survey results are summarized in Table 5.

  In Table 5, test symbols T1 to T10 are examples of the present invention, and test symbols T11 to T31 are comparative examples.

The test symbols T1 to T10, which are examples of the present invention, have good resistance to sulfuric acid and hydrochloric acid of the weld metal because the flux symbols BF1 to BF10 and the combined wire symbols W1 to W5 satisfy the constituent requirements of the present invention. In addition, the welding workability was good, there was no defect in the welded part, and the mechanical performance of the weld metal was excellent, which was a very satisfactory result. In addition, since the test symbol T5 has a small amount of B ₂ O ₃ of the flux symbol BF8, the absorbed energy of the weld metal was slightly low.

  Since the test symbol T11 in the comparative example has many particles having a flux particle size of 150 μm or less of the flux symbol BF22, the slag peelability and the bead shape were poor and pits were generated. Moreover, since there are many Cs of the combined wire symbol W9, the tensile strength of the weld metal was high and the absorbed energy was low.

Test symbol T12 had poor bead shape and slag removability because of the small amount of SiO _{2 in} flux symbol BF11. Moreover, since Mn is large, the tensile strength of the weld metal was high and the absorbed energy was low. Further, since there are many particles having a flux particle size of 850 μm or more, the width of the bead is excessively widened, so that the penetration becomes shallow and slag entrainment occurs.

In test symbol T13, the amount of Al ₂ O _{3 in} flux symbol BF12 was small, so the slag peelability and bead appearance were poor, and the corrosion plate thickness was reduced. Moreover, since there is much Si, the tensile strength of the weld metal was high and the absorbed energy was low.

  In test symbol T14, the flux apparent density of flux symbol BF21 is small, so that the arc blowing during welding is severe and the arc becomes unstable and the bead shape is poor. Sb is boiled and gasified by arc blowing, and Sb is stable. As a result, it was not contained in the weld metal, so that the corrosion plate thickness was reduced. Further, the width of the bead was excessively widened, so that the penetration became shallow and slag entrainment occurred. Furthermore, since the C of the combined wire symbol W8 is small, the tensile strength of the weld metal is low and the absorbed energy is also low.

In test symbol T15, the amount of SiO _{2 of} flux symbol BF13 is large, and thus the absorbed energy of the weld metal was low. In addition, since the CaF ₂ is large, the bead appearance was poor. Furthermore, since there are many particles with a flux particle size of 150 to 850 μm, the width of the bead is excessively widened, so that the penetration becomes shallow and slag entrainment occurs.

Test symbol T16 had a poor bead shape and slag peelability because of the large amount of Al ₂ O ₃ of flux symbol BF14. Moreover, since there was little CaO, the conformity of the bead collar part was bad and the external appearance was bad. Furthermore, since there is little Si, the absorbed energy of the weld metal was low.

In test symbol T17, the amount of MgO in flux symbol BF15 was small, so the absorbed energy of the weld metal was low, and the corrosion plate thickness loss was large. Further, since TiO ₂ is large, the bead shape and the slag removability was poor. Further, since CO ₂ is large, a pock mark is formed on the surface of the weld bead, the bead appearance is poor, and pits are also generated.

  In test symbol T18, since there was much MgO of flux symbol BF16, the wavy surface of the bead surface became rough, and the slag peelability and bead appearance were poor. Moreover, since Mn is small, the weld metal absorption energy was low. Further, since there are few particles having a flux particle size of 850 μm or more, Sb is not stably contained in the weld metal, the corrosion plate thickness is reduced, the bead becomes convex, the bead shape is poor, and pits are generated.

  In test symbol T19, since the Mn of the combined wire symbol W6 was large, the tensile strength of the weld metal was high and the absorbed energy was low. Moreover, since there was little Cu, the corrosion board thickness reduction amount was many.

Since the test symbol T20 contained a large amount of CaO of the flux symbol BF17, the bead height was uneven and the bead appearance and slag peelability were poor. Further, since CaF ₂ is small, the absorbed energy of the weld metal was low. Furthermore, since there are few particles with a flux particle size of 150 to 850 μm, Sb is not stably contained in the weld metal, the corrosion plate thickness is reduced, the bead becomes convex, the bead shape is poor, and pits are generated.

Since the test symbol T21 has a large amount of B ₂ O ₃ of the flux symbol BF18, the tensile strength of the weld metal was high and the absorbed energy was low. Moreover, since the apparent density of the flux was large, the bead width was narrow and became a convex shape, resulting in undercutting. Furthermore, since Sb was not added to the combined wire symbol W7, the corrosion plate thickness was greatly reduced.

The test symbol T22 had a low value of absorbed energy of the weld metal because the CO _{2 of the} flux symbol BF19 was small. Moreover, since there was much Sb of the wire symbol W18 combined, the crack arose.

  In test symbol T23, since the Mn of the combined wire symbol W10 was small, the tensile strength of the weld metal was low and the absorbed energy was also low.

  In test symbol T24, the amount of Si in the combined wire symbol W11 was large, so the tensile strength of the weld metal was high and the absorbed energy was low.

  In the test symbol T25, since the combined wire symbol W12 does not contain Si, the absorbed energy of the weld metal was low.

Test symbol T26 had a small bead shape and a low absorbed energy of the weld metal because TiO _{2 of} flux symbol BF20 was small.

  The test symbol T27 was cracked because of the large amount of Cu in the combined wire symbol W13. Moreover, the tensile strength of the weld metal was high and the absorbed energy was low.

  In test symbol T28, the amount of Ni in the combined wire symbol W14 was small, so the absorbed energy of the weld metal was low.

  Since the test symbol T29 has a large amount of Ni in the combined wire symbol W15, the absorbed energy of the weld metal was low.

  In test symbol T30, since there was much Mo of the wire symbol W16 combined, the tensile strength of the weld metal was high and the absorbed energy was low.

  In the test symbol T31, since the Mo of the combined wire symbol W17 is small, the tensile strength of the weld metal is low and the absorbed energy is also low.

Claims (2)

% By mass
SiO _2: 5~21%,
Al ₂ O ₃ : 15 to 44%,
MgO: 7 to 32%,
CaO: 0.5 to 10%,
CaF ₂ : 5 to 35%,
TiO _2: 5~33%,
Si: 0.2 to 5.0%,
Mn: 0.1 to 5.0%,
Metal carbonate CO ₂ min: 0.5-9.0%
The balance consists of FeO, alkali metal oxides and inevitable impurities,
The particle size composition of the flux is mass%,
20% to 55% of particles having a particle size of more than 850 μm,
40-75% of particles with a particle size of 150-850 μm,
6% or less of particles with a particle size of less than 150 μm
A bond flux having an apparent density of 0.70 to 1.30 g / cm ³ ;
% By mass
C: 0.005-0.2%,
Si: 0.01 to 1.5%,
Mn: 0.4 to 2.5%
Cu: 0.03-1.0%,
Ni: 0.05 to 1.0%,
Mo: 0.01 to 1.0%,
Sb: 0.01 to 0.25%
And P: 0.03% or less, S: 0.03% or less, and a combination of a solid wire consisting of Fe and inevitable impurities in the balance, and welding with a low alloy steel, a submerged arc welding method . Furthermore, the bond flux, B ₂ O _3: 0.05~3.0% submerged arc welding method of low alloy steel according to claim 1, characterized in that it contains.

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