KR101159433B1 - Low-hydrogen coated electrode - Google Patents

Abstract

In the low-hydrogen coated arc welding rod of the present invention, the steel core wire contains more than 0.05% and 0.10% or less, regulates P to 0.010% or less, S to 0.010% or less, and N to 0.005% or less. cloning, the 15 to 28%, metal fluoride with a metal carbonate as CO ₂ in terms of F in terms of 4 to 9%, 4.0 to 9.0% of SiO _2, 0.5 to 5.0% of TiO _2, with Mg as a metal body or the alloy Mg 0.5 to 3.0%, Si to 1.0 to 7.0%, Mn to 0.5 to 5.0%, Ni to 2.0 to 10.0%, Ti to 0.3 to 3.0%, B to 0.05 to 0.20%, Fe to 5.0 to 20.0% In addition, Al ₂ O ₃ is regulated to 2.0% or less, Mo to 0.1% or less, and Cr to 0.1% or less, and the coverage of the coating agent is 25 to 45%. By such a structure, the CTOD value at low temperature becomes high and it becomes suitable to weld 590 MPa class high tensile strength steel by a DC power supply.

Description

LOW-HYDROGEN COATED ELECTRODE}

The present invention relates to a low-hydrogen-based coated arc welding rod for high-strength steel that can ensure low temperature crack resistance and high toughness of weld metal when welded with high strength steel of 590 MPa or higher, in particular, welding by a DC power supply generally used abroad. The present invention relates to a low-hydrogen-based coated arc welding rod, which is suitable for, and excellent in low temperature fracture toughness up to about -40 ° C.

In recent years, as the structure becomes larger, attempts have been made to build the structure into high-strength steel for the purpose of weight reduction. In addition, in large offshore structures aimed at developing natural resources in cold regions such as Northern Europe, there is a high demand to improve fracture toughness at lower temperatures for welded metals in order to secure safety.

Conventionally, in large offshore structures, since it is difficult to secure both the strength and fracture toughness of a welded part, application of high strength steel is limited to a part, and it is produced only by low temperature steel of 490 MPa grade. For this reason, the development of the material which can weld this high tensile strength steel is strongly desired for the purpose of full application of the high tensile strength steel which is essential for weight reduction of a structure. Moreover, in recent years, marine structures are mainly built overseas, and there are still many applications for applying an electric arc rod as a solvent abroad. DC power is mostly used for Jeonbong Peak overseas. For this reason, the development of the high-strength low-hydrogen coated arc welding rod suitable for a DC power supply, especially the low-hydrogen coated arc welding rod excellent in low temperature fracture toughness is desired.

Conventionally, the following techniques have been developed as a high-hydrogen low-hydrogen coated arc welding rod. Japanese Patent No. 3154661 describes a low hydrogen-based coated arc welding rod suitable for use in welding steels sensitive to low temperature cracking, such as low Ni steel and high strength steel of 780 MPa or more. This prior art relates to an ultra-low hydrogen-based coated arc welding rod, which is particularly low oxygen based on fracture toughness and has a hydrogen content of 5 ml / 100 g or less. However, this prior art is not intended to improve the fracture toughness at the cryogenic temperature of -40 ° C, which is high (inadequate) to the temperature of the CTOD test, i. In addition, this prior art does not consider at all about the use of a DC power supply. That is, the low hydrogen system arc welding rod described in the said patent uses an AC power supply, and this low hydrogen system arc welding rod is not applicable to the welding using a DC power source as it is.

Further, Japanese Patent Application Laid-Open No. Hei 8-257791 relates to a coated arc welding rod for the purpose of obtaining a weld metal having excellent low temperature toughness and fracture toughness after stress relief annealing when welding high tensile strength steel, for example, high strength steel of 590 MPa or higher. will be. However, the temperature of the fracture toughness test (CTOD test) is high (inadequate) to -20 ° C and is not intended to improve the fracture toughness at cryogenic temperature of -40 ° C. Moreover, this prior art also does not consider the use of a DC power supply at all.

Japanese Patent Application Laid-open No. Hei 8-29431 discloses a low hydrogen-based coated arc welding rod for HT 60 class or higher high strength steel and low Ni steel for the purpose of obtaining good fracture toughness of weld metal. In this technique, however, the low temperature impact value at -20 ° C to -60 ° C is improved compared with the prior art, but the CTOD test at low temperature is not carried out, and whether the fracture toughness is good is unclear. This prior art also does not consider the use of a DC power supply at all.

Japanese Patent No. 3026899 discloses a low hydrogen coating arc welding rod for obtaining a high strength weld metal of HT 60 grade or higher for the purpose of improving low temperature toughness of a weld metal. However, even here, although the impact value of the V notch impact test at -40 degreeC improves compared with the conventional electrode, the CTOD test at low temperature is not performed and whether the fracture toughness is favorable is unclear. This prior art also does not consider the use of a DC power supply at all.

Japanese Patent No. 3154661 Japanese Patent Laid-Open No. 8-257791 Japanese Patent Publication No. 8-29431 Japanese Patent No. 3026899

As described above, in the prior art, a low-hydrogen-based coated arc welding rod having excellent low-temperature fracture toughness, which is intended to improve the CTOD value (breaking toughness value) at -40 ° C, has not yet been developed, and cold-destruction for DC power is not yet developed. A low hydrogen coated arc welding rod having excellent toughness has not been proposed. It is a fact that the problem which arises when using this DC power supply is not made conventionally at all.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has excellent CTOD value at low temperature, shows good low temperature fracture toughness, and is suitable as a welding material for high strength steel of 590 MPa or higher, and is preferably a low hydrogen coating based on DC welding material. It is an object to provide an arc welding rod.

The present invention is a low-hydrogen-coated arc welding rod coated with a coating material on a steel core wire, wherein the steel core wire contains C in an amount of 0.050% by mass or more and 0.10% by mass or less, and P is 0.010% by mass. % or less, regulating the below 0.010% by mass S, N to not more than 0.005 mass%, the coating agent is 15 to 28% by weight, metal fluoride to a total weight ratio of the coating agent, a metal carbonate as CO ₂ in terms of F conversion 4 to 9% by weight, SiO ₂ of 4.0 to 9.0 mass%, TiO ₂ 0.5 to 5.0 mass%, 0.5 to 3.0 mass% of Mg as a metal body or an alloy of Mg in terms of, 1.0 to 7.0% by weight of Si, the Mn 0.5 to 5.0% by mass, Ni to 2.0 to 10.0% by mass, Ti to 0.3 to 3.0% by mass, B to 0.05 to 0.20% by mass, Fe to 5.0 to 20.0% by mass, and Al ₂ O ₃ to 2.0% by mass Hereinafter, Mo is 0.1 mass% or less, Cr is 0.1 mass% or less, and also the arc stabilizer, slag generator, and a point other than the above are mentioned. Containing the (粘結劑), and the coating ratio of the coating agent is 25 to 45% by mass of the coating agent per total mass of the electrode.

The low hydrogen in the covered electrodes, it is preferred that the above coating agent, an acidic oxide, the SiO _2, the TiO _2, less than the total amount of the Al ₂ O ₃ 12% by weight.

In addition, C content per mass of the electrode is [C] (mass%), Si content is [Si] (mass%), Mn content is [Mn] (mass%), and Ni content is [Ni] (mass%), When Ti content is [Ti] (mass%), A = ([C] × 10 + 1.8 × [Si] + [Mn]) / {(1+ [Ni]) × (0.5+ [Ti]) } Is preferably 0.30 to 0.70.

According to the present invention, excellent low temperature fracture toughness is obtained for high tensile strength steel of 590 MPa or higher by appropriately defining the composition of the steel core wire and the coating agent of the low-hydrogen coated arc welding rod. Thereby, the reliability of the welding joint with respect to various steel structures can be improved significantly.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail. Background Art Conventionally, AC power has been widely used in welding power sources for hand welding in Japan. Accordingly, a number of welding electrodes for AC power have been proposed. In general, when a welding rod designed for an AC power source is used as a DC power source, it has been found that retention of alloying elements such as Si, Mn, and C to the weld metal is lowered, and strength and toughness are lowered. Moreover, since it is easy to be influenced by magnetism, welding workability deteriorates. Therefore, the welding rod for AC power supply cannot be used for a DC power supply as it is. In order to solve these problems, the present inventors conducted a thorough experimental study on the balance between the core wire and the coating material component. It has been found to greatly affect the amount of oxygen. This is an unprecedented knowledge. That is, the present inventors found that the amount of oxygen in the weld metal is effectively lowered by defining the steel core C at more than 0.05% by mass and 0.10% by mass or less, thereby improving the welding workability and mechanical performance.

In addition, in order to ensure the CTOD value (low-temperature fracture toughness) at -40 degreeC in the welding part of high-strength steel of 590 MPa grade or more, after examining various alloy elements, the conditions shown below become essential. Found that. That is, firstly, it is necessary to further refine the weld metal structure in order to secure the strength of the weld metal without including the toughness reducing element as much as possible, and secondly, to secure the fracture toughness at -40 ° C.

Therefore, the inventors of the present invention have conducted various experimental studies on the coated arc welding rods capable of obtaining weld metals satisfying these conditions, and found that the following means are effective. First, in order to ensure the CTOD value (low temperature fracture toughness) at the -40 degreeC of a weld part, in a coating material component, 0.10 mass% or less of Cr and 0.10 mass% or less of Mo are regulated, and Si is 1.0-7.0 mass%. In addition, the toughness is prevented from being lowered, and high strength is secured by defining 0.5 to 5.0% by mass of Mn and 2.0 to 10.0% by mass of Ni. Further, by containing 0.05 to 0.20% by mass of B in the coating component and 0.3 to 3.0% by mass of Ti, the welded metal structure is fine acicular ferrite to be formed at -40 ° C. CTOD value (destructive toughness) was increased.

Hereinafter, the reason for the addition of the component contained in the steel core wire and the reason for composition limitation are demonstrated about the low hydrogen system arc welding rod in this invention.

`` C: 0.05% by mass or more and 0.10% by mass or less ''

C content in a steel core wire is one of the important elements in this invention. It was found that the carbon amount of the steel core wire to be used as the welding rod for DC power greatly influences the amount of oxygen in the weld metal as compared with the amount of C carbon contained in the coating material. That is, when C content in a steel core wire is high, the oxygen amount of a weld metal can be reduced and the toughness of a weld metal will improve. Conventionally, as described in the above-mentioned patent publication, it is considered that the lower the carbon content of the steel core is preferable for improving the toughness (0.05 mass% or less per mass of the steel core): Japanese Patent No. 3154661, Japanese Patent Publication 8-257791 and Japanese Patent Publication No. Hei 8-29431 have been used, but a steel core having a low carbon content has been used, but in welding in a DC power supply, it is preferable to contain a certain amount of carbon rather than to improve toughness. The inventors have discovered that. If the C content in the steel core is 0.05% by mass or less per total weight of the steel core, the effect of improving toughness is small, and the amount of C in the weld metal is reduced by decarburization in a DC power supply, so that the strength improvement does not occur. Moreover, when C exceeds 0.10 mass%, since C in a weld metal exceeds 0.08 mass% and produces high carbon martensite, the toughness of a weld metal falls. In addition, high temperature cracking of the weld metal is likely to occur. Therefore, C content in a steel core wire is prescribed | regulated to 0.05 mass% or more and 0.10 mass% or less per steel core wire total mass.

`` N: 0.005 mass% or less ''

When N, which is an unavoidable impurity in the steel core, exceeds 0.005% by mass per mass of the steel core, N in the weld metal exceeds 0.008% by mass, so that the internal deformation of the weld metal increases, so the toughness decreases. Therefore, N in the steel core wire per mass of steel core wire is regulated to 0.005 mass% or less.

"P: 0.010 mass% or less, S: 0.010 mass% or less"

P and S segregate during final solidification at the time of welding, deteriorating the toughness of the weld metal, and generating hot cracks. For this reason, it is preferable that P and S of a steel core wire are extremely low, but if it is going to reduce content of P and S, the manufacturing cost of a steel core wire will rise. For this reason, content of P and S is made into 0.010 mass% or less as a range with little influence on the low-temperature toughness of a weld metal, respectively.

On the other hand, a steel core wire usually uses a carbon steel core wire, but if necessary, an appropriate amount of deoxidizing elements such as Si, Mn, Ti, and elements such as Ni, Cu, Nb, and V can be added.

Next, the reason for addition of the components contained in the coating agent and the reason for composition limitation will be described.

Metal Carbonate (CO ₂ Conversion): 15-28 mass%

Metal carbonate is a component which can reduce the amount of N and hydrogen in a weld metal. If the metal carbonate in the coating is less than 15% by mass in terms of CO ₂ per mass of the coating, the shielding effect of CO ₂ is insufficient, and the amount of N in the weld metal cannot be made 0.008% by mass or less. Cracking and toughness cannot be obtained. That is, in order to obtain the outstanding crack resistance and toughness of a weld metal, it is necessary to make N amount in a weld metal into 0.008 mass% or less, but for this purpose, it is necessary to improve the sealing property at the time of welding. So, the content of the metal carbonate with at least 15% by mass in terms of CO ₂ per total mass of the coating agent. On the other hand, when the content of the metal carbonate in the coating agent exceeds 28% by mass in terms of CO ₂ , the viscosity of the slag becomes excessive, so that it is difficult to make directional welding. Therefore, the metal carbonate in the coating agent per mass of the coating agent is 15 to 28% by mass in terms of CO ₂ . Metal carbonate is added with calcium carbonate, barium carbonate, magnesium carbonate and the like.

Here, the metal carbonate (CO ₂ conversion) is, represents the mass of only the total number of CO ₂ part of the molecule from the metal carbonate as a% of the total mass of the coating agent is meant.

`` Metal fluoride (F equivalent): 4 to 9% by mass ''

Metal fluoride is a component which can obtain favorable welding workability by adjusting the viscosity of slag. If the metal fluoride in the coating agent is less than 4% by mass in terms of F, the viscosity of the slag becomes too high and the bead shape deteriorates. On the other hand, when the metal fluoride in a coating material exceeds 9 mass% in conversion of F, since an arc becomes unstable, it is unpreferable. Therefore, the metal fluoride in the coating agent per mass of the coating agent is 4 to 9% by mass in terms of F. The metal fluoride is added with calcium fluoride, sodium fluoride, barium fluoride, aluminum fluoride and the like.

Here, a metal fluoride (F conversion) means that the sum total of the mass of only the F part in a metal fluoride molecule is represented by% with respect to the coating material total mass.

"Mg (Mg equivalent): 0.5 to 3.0 mass% as a metal single substance or alloy"

Mg is an element having a very large effect of reducing oxygen in the weld metal and increasing the toughness of the weld metal as described above. When Mg (Mg equivalent) is less than 0.5 mass% per mass of the coating material as the metal single substance or alloy in the coating material, the amount of oxygen in the weld metal becomes less than 200 ppm, so the toughness is lowered. On the other hand, when Mg (Mg equivalent) exceeds 3.0 mass% as a metallic single substance or alloy in a coating agent, arc expansion will deteriorate and welding will become difficult. Therefore, Mg (Mg conversion) is made into 0.5-3.0 mass% as a metal single substance or an alloy in the coating material per mass of coating material. Mg may be added as metal magnesium, armag or nickel magnesium.

Here, Mg (Mg equivalent) as a single metal or an alloy means that the total of the Mg single mass and the mass of only the Mg part in an alloy is represented by% with respect to the coating material total mass.

"Si: 1.0-7.0 mass%"

Si is a deoxidizing element. In addition, Si has an effect of improving the wettability of the molten pool and the base metal during welding, thereby improving the welding workability. If the content of Si is less than 1.0% by mass, the deoxidation effect is weak, and pores easily occur in the weld metal, and the effect of improving welding workability cannot be obtained. On the other hand, when Si content exceeds 7.0 mass%, a low melting-point oxide will precipitate at a grain boundary, and it will degrade crack resistance and toughness. Therefore, Si content is made into 1.0 to 7.0 mass%. Si is added by Fe-Si etc.

"Mn: 0.5-5.0 mass%"

Mn is an element that deoxidizes and at the same time lowers the ferrite transformation temperature to refine the ferrite particles, thereby increasing the strength and toughness. If the Mn content is less than 0.5% by mass, high strength and high toughness cannot be obtained. On the other hand, when Mn content exceeds 5.0 mass%, a weld metal will show a lath phase structure, and will rather deteriorate the toughness of a weld metal. Therefore, Mn content is made into 0.5 to 5.0 mass%. This Mn is added with a metal Mn, Fe-Mn, Fe-Si-Mn, or the like.

"Ni: 2.0-10.0 mass%"

 Ni is an element which raises strength and toughness. If Ni content is less than 2.0 mass%, a highly tough weld metal cannot be obtained. On the other hand, when Ni content exceeds 10.0 mass%, the intensity | strength of a weld metal will become high too much and toughness will fall. Therefore, content of Ni is made into 2.0-10.0 mass%. This Ni is added to the metal Ni, Ni-Mg, Fe-Ni and the like.

"Ti: 0.3-3.0 mass%"

Ti is a deoxidizing element and is effective for improving the strength of the weld metal. In addition, Ti produces a fine spherical oxide, and is effective for miniaturizing the structure of a weld metal. When Ti content is less than 0.3 mass%, sufficient deoxidation property and the strength improvement effect of a weld metal do not express. On the other hand, when Ti content exceeds 3.0 mass%, since the amount of Ti in a weld metal will become large too much, strength and hardness will become excessively high, and the toughness of a weld metal will fall. Therefore, Ti content is made into 0.3-3.0 mass%. Ti is added as Fe-Ti, metal Ti, or the like.

"B: 0.05-0.20 mass%"

B is an element effective for suppressing grain boundary ferrite and having a hardenability. When B content is less than 0.05 mass%, the suppression effect of the grain boundary ferrite by B does not arise, and the metal structure of a weld metal becomes coarse. On the other hand, when content of B exceeds 0.20 mass%, weld metal will show coarse lath-like structure, and toughness will deteriorate. Therefore, B content is prescribed | regulated to 0.05-0.20 mass%. B is added as Fe-B, Fe-Si-B, metal B, or the like.

`` Cr: 0.1% by mass or less ''

When Cr exceeds 0.1 mass%, hardening hardening of a weld metal and crystal precipitation of (delta) ferrite phase generate | occur | produce, and deterioration of low-temperature toughness becomes remarkable, Cr content is regulated to 0.1 mass% or less.

`` Mo: 0.1% by mass or less ''

Mo, like Cr, crystallizes the δ ferrite phase and deteriorates low temperature toughness, so Mo content is regulated to 0.1 mass% or less.

"Fe: 5.0-20.0 mass%"

Fe is an element that affects welding workability and welding efficiency. When the Fe content is less than 5.0% by mass, the welding efficiency is lowered, the arc flutters, and the welding workability is lowered. Moreover, when Fe content exceeds 20.0 mass%, a shielding effect will fall and welding workability will fall. For this reason, Fe content is 5.0-20.0 mass%, Preferably you may be 5.0-15.0 mass%. Fe is added as Fe-Mn, Fe-Si or iron powder.

"SiO ₂ : 4.0-9.0 mass%"

In the coating agent, it is necessary to add SiO ₂ which is an acidic oxide as a caking additive and a slag aid. If the SiO ₂ in the coating agent exceeds 9.0 mass% per the total mass of the coating agent, the slag is to shape the glass, this ends up in the slag removability deteriorate. On the other hand, if the SiO ₂ in the coating agent is less than 4.0% by mass per the total mass of the coating agent can not be obtained the effect as a binder. Thus, SiO ₂ content of the coating agent per total mass of the coating agent is set at 4.0 to 9.0% by weight.

"TiO ₂ : 0.5-5.0 mass%"

In the coating agent, TiO ₂ which is an acidic oxide can be added as a slag aid. When the TiO ₂ in the coating agent is less than 0.5% by mass per the total mass of the coating agent, the welding operability deteriorates. In addition, if TiO ₂ is more than 5.0 mass%, the viscosity of the slag is lowered and workability is deteriorated. Therefore, when the addition of TiO ₂ in the coating agent, the TiO ₂ content of blood per total mass of replication is from 0.5 to 5.0 mass%.

`` Al ₂ O ₃ : 2.0 mass% or less ''

In the coating agent, Al ₂ O ₃ which is an acidic oxide can be added as a slag aid. If the Al ₂ O ₃ in the coating agent exceeds 2.0 mass% per the total mass of the coating agent, the slag is to shape the glass, this ends up in the slag removability deteriorate. Thus, if the addition of Al ₂ O ₃ in the coating agent, the coating agent total weight Al ₂ O ₃ content of sugar is at most 2.0% by mass.

"An acidic oxide, SiO _2, TiO _2, the total amount of Al ₂ O _3: 12.0% by mass or less."

In the coating agent, in addition to SiO ₂ , TiO ₂ , Al ₂ O ₃ , and the like, which are acid oxides, may be added as the slag aid. When the total amount of acidic oxides of SiO ₂ , TiO ₂ , Al ₂ O _{3 in} the coating agent exceeds 12.0 mass% per mass of the coating material, the basicity of the slag is insufficient, and the amount of oxygen in the weld metal is less than 200 ppm. Becomes difficult. When the amount of oxygen in the weld metal exceeds 200 ppm, the impact test performance (toughness) of the weld metal decreases. Thus, the total amount of blood, when added to the acidic oxide in duplicate, covering agent per total mass of _{SiO 2, TiO 2, Al 2} O 3 is at most 12.0 mass%.

Next, the coverage of the coating material of the coating arc welding rod in this invention is demonstrated.

`` Coat rate: 25 to 45% ''

The coverage of the covered arc welding rod is calculated by the formula [(mass of welding cloth / total welding rod mass) × 100]. If the coverage is less than 25%, the shield will be insufficient and the N content and the hydrogen content in the weld metal will increase, leading to a decrease in toughness and crack resistance of the weld metal. On the other hand, when the coverage exceeds 45%, the arc length becomes long, resulting in arc fragments. Therefore, the coverage of the covering arc welding rod shall be 25 to 45%.

"A = ([C] x 10 + 1.5 x [Si] + [Mn]) / {(4 + [Ni]) x (0.5 + [Ti])}: 0.30 to 0.70"

C, Si, and Mn are elements that increase the strength of the welded portion. In addition, Ni is an element which raises toughness of a weld and improves fracture toughness. In addition, Ti is an element which refines welded structure and improves toughness. Then, C content per mass of the welding rod is [C] (mass%), Si content is [Si] (mass%), Mn content is [Mn] (mass%), and Ni content is [Ni] (mass%), When Ti content is [Ti] (mass%), A-value determined by content of these elements = ([C] x10 + 1.5x [Si] + [Mn]) / {(4+ [Ni]) x ( 0.5+ [Ti])} is less than 0.30, the strength of the weld metal is lowered and the CTOD value (destructive toughness) is also lowered. Moreover, when A value exceeds 0.70, CTOD value (destructive toughness) will fall by the toughness fall by the strength rise by C, Si, Mn, Ti, and the relative lack of Ni content. For this reason, it is preferable that A value is 0.30 to 0.70.

This A value is taken in consideration of the balance between strength and toughness. As the denominator of the A value, an element that increases toughness was selected, and an element that increased the strength of the welded part was selected for the molecule, and the relationship between the A value and the CTOD value was summarized. As a result, a very clear correlation was obtained. In other words, when the A value is 0.30 to 0.70, the CTOD value is excellent.

[Example]

Hereinafter, the Example of the low-hydrogen-based clad arc welding rod which concerns on this invention is demonstrated concretely compared with the comparative example.

First, the coating agent which has various chemical components was apply | coated to the steel core wire which has a composition shown in following Table 1, and the coating arc welding rod was produced. In addition, in the present Example, the diameter of the steel core wire was 4 mm. The composition of the steel core wire used by each Example and the comparative example is shown in following Table 1. In addition, Table 2-Table 4 show the kind of steel core wire, the coverage, the composition of the coating agent, and A value which were used for the welding rod of the Example of this invention and a comparative example, respectively. In Tables 3 and 5, the components of the other columns are BaO, Na ₂ O, Li ₂ O, Fe ₂ O ₃ , ZrO _2, and the like.

Subsequently, it welded using this covered arc welding rod, evaluated the welding workability at that time, and evaluated the mechanical performance of the weld metal. In this embodiment, as a welding base material, a steel plate having a plate thickness of 60 mm with X improvement is used, and after preheating the steel plate to a temperature of 100 ° C., the welding heat input is performed in a downward welding position with respect to the improved part. Welded at 25 kJ / cm. The power supply used the DC power supply, and welded on condition of welding current 150A and arc voltage 23V-25V. At this time, a tensile strength 610 MPa grade steel sheet was used as the steel sheet.

The mechanical performance was evaluated by 0.2% yield strength, tensile strength, transition temperature vTrs, and CTOD value (breaking toughness) at -40 ° C of the weld metal. The strength and tensile strength of the weld metal were evaluated by taking a tensile test piece from the obtained weld metal, measuring the load against 0.2% elongation, and measuring the maximum tensile strength. In addition, according to BS (British standard) 5762, the CTOD (Crack Tip Opening Displacement) at -40 ℃ was measured.

These test results and evaluation results are shown in Tables 6 and 7 below. On the other hand, in the evaluation result column of welding workability, (circle) shows that it is good, (triangle | delta) is a little bad, and x is bad. The comprehensive determination was performed based on welding workability and CTOD value.

As shown in Table 2 to Table 7, Examples E1 to E26 are excellent in welding workability and the number of weld metals, because the chemical composition and coverage in the steel core wire and the coating agent are within the scope of the present invention. Since the small amount and the oxygen amount are sufficiently reduced, the strength and the fracture toughness are excellent. Moreover, the CTOD value in -40 degreeC was also sufficiently high that it is 0.28 mm or more.

In contrast, Comparative Example T1 stopped the CTOD test because the coverage was less than the lower limit of the present invention and the strength was insufficient. In the comparative example T2, since a coverage was more than the upper limit of the range of this invention, and weldability fell, the test was stopped. In Comparative Example T3, the metal carbonate in the coating material was below the prescribed range of the present invention, and the amount of oxygen in the weld metal increased, resulting in a decrease in fracture toughness. In Comparative Example T4, the metal carbonate in the coating agent exceeded the upper limit of the prescribed range of the present invention, and the bead shape became convex.

In Comparative Example T5, the fluoride in the coating was less than the lower limit of the prescribed range of the present invention, and the bead shape became convex. In Comparative Example T6, since the fluoride in the coating exceeded the upper limit of the prescribed range of the present invention, the arc became unstable and the weldability deteriorated.

In Comparative Example T7, Mg in the coating agent was less than the lower limit of the prescribed range of the present invention, the oxygen content of the weld metal was high, and good fracture toughness was not obtained. In Comparative Example T8, since the Mg in the coating material exceeded the upper limit of the prescribed range of the present invention, the arc was strong and the weldability deteriorated.

In Comparative Examples T9, T11, T13, and T15, Si, Mn, Ni, and Ti in the coating were less than the lower limit of the prescribed range of the present invention, respectively, and the tensile strength was insufficient. In Comparative Examples T10, T12, T14, and T16, respectively, Si, Mn, Ni, and Ti in the coating agent exceeded the upper limit of the specified range of the present invention, so that the tensile strength increased and the fracture toughness deteriorated.

In Comparative Examples T17 and T18, B in the coating agent was below the lower limit and above the upper limit, respectively, of the prescribed range of the present invention, and the structure refining effect was not exhibited, and fracture toughness was deteriorated. In Comparative Examples T19 and T21, SiO ₂ and TiO ₂ in the coating agent were respectively less than the lower limit of the prescribed range of the present invention, the amount of slag was small, and the welding workability was poor. In addition, in Comparative Examples T20 and T23, since the SiO ₂ and Al ₂ O ₃ in the coating agent exceeded the upper limit of the prescribed range of the present invention, the peelability of the slag worsened and the weldability deteriorated. In addition, in Comparative Example T22, since the TiO ₂ in the coating agent exceeded the upper limit of the prescribed range of the present invention, the bead shape became convex and the weldability deteriorated. In Comparative Example T24, since the total amount of acidic oxides in the coating agent exceeded the upper limit of the prescribed range of the present invention, the amount of oxygen in the weld metal increased, and fracture toughness deteriorated.

In Comparative Examples T24 and T25, the low-temperature toughness and the fracture toughness were low because Cr and Mo in the coating material exceeded the upper limit, respectively. In Comparative Example T26, since the C in the steel core was below the lower limit of the present invention, the tensile strength was insufficient, and the amount of oxygen in the weld metal increased, the CTOD test was stopped. Further, in Comparative Examples T27 to T30, the low temperature toughness and fracture toughness deteriorated because C, P, S and N in the steel core wire exceeded the upper limit of the present invention, respectively. In Comparative Examples T1 to T30 described above, the CTOD value at -40 ° C was at most 0.14 mm, which was much lower than the CTOD value at -40 ° C of the present invention.

Five examples of E9, E10, E13, E16, and E24 are those in which the comprehensive evaluation is Δ. These CTOD values are 0.36 mm or less. The reason for this is that E24 is excessive in the total amount of acidic oxides, E10 and E16 are in excess of A value, E9 is in excess of A value, and E13 is A value in the upper limit of the preferred range.

Claims (3)

As a low hydrogen coated arc welding rod coated with a steel core wire,
The steel core wire contains C in excess of 0.05% by mass and 0.10% by mass or less, and regulates P to 0.010% by mass or less, S to 0.010% by mass or less, and N to 0.005% by mass or less,
The coating agent is 15 to 28% by weight of metal carbonate in terms of CO ₂ , 4 to 9% by weight of metal fluoride in terms of F, 4.0 to 9.0% by weight of SiO ₂ , and 0.5 to 0.5 in terms of TiO ₂ , based on the total weight of the coating material. 5.0 mass%, a metal single substance or alloy, 0.5-3.0 mass% in conversion of Mg, 1.0-7.0 mass% of Si, 0.5-5.0 mass% of Mn, 2.0-10.0 mass% of Ni, 0.3-3.0 mass of Ti It contains 0.05 to 0.20% by mass of B, 5.0 to 20.0% by mass of Fe, regulates 2.0% by mass or less of Al ₂ O ₃ , 0.1% by mass or less of Mo, and 0.1% by mass or less of Cr. It contains an arc stabilizer, slag generator, caking agent other than the above,
The coating ratio of the coating material is 25 to 45% by mass ratio of the coating material per mass of the welding rod, the low hydrogen-based coated arc welding rod. The method of claim 1,
A low-hydrogen-based coated arc welding rod in which the total amount of SiO ₂ , TiO ₂ , and Al ₂ O ₃ is 12 mass% or less in the coating agent. The method according to claim 1 or 2,
C content per mass of welding rod is [C] (mass%), Si content is [Si] (mass%), Mn content is [Mn] (mass%), Ni content is [Ni] (mass%), Ti content When [Ti] (mass%) is set to A = ([C] × 10 + 1.8 × [Si] + [Mn]) / {(1+ [Ni]) × (0.5+ [Ti])} A low hydrogen coating arc welding rod having an A value of 0.30 to 0.70.