JPH09314381A - Ni covered electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a covered electrode which is excellent in electrode heat damage resistance, free from any seizing phenomenon of slag, excellent in high temperature cracking resistance, and easy to obtain sound weld metal. SOLUTION: A core wire contains 55-75% Ni, 12-18% Cr, 1.0-4.5% Mo, 0.1-0.5% Ti, 0.9-2.7% Mn, and 0.7-2.5% Nb, and the coating flux contains 20-45% metal carbonate, 10-30% metal fluoride, 10-25% silicate and silicate compound, 0.9-4.0% Mn, 0.7-3.0% Nb relative to the total weight of the coating flux, and the ratio in content of the core to the coating flux is specified in terms of Mn and Nb.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a welding material of a high Ni alloy used for welding 9% Ni steel for LNG storage tanks. More specifically, it has good slag removability and excellent welding workability. The present invention relates to a Ni-based coated arc welding rod which can easily obtain a weld metal having good hot crack resistance.

[0002]

2. Description of the Related Art The consumption of natural gas is increasing rapidly as a clean energy alternative to petroleum, and the amount of natural gas transport / storage tanks is increasing accordingly. Cool natural gas for the purpose of simplifying transportation and storage of natural gas (-16
Liquefied natural gas (2 ° C.) is liquefied natural gas (LNG), and 9% Ni steel is mainly used as an LNG container. This steel is a ferritic alloy steel having excellent low temperature toughness, and has high strength and excellent weldability. Ni-Cr based welding materials with good bond toughness are most often used for welding 9% Ni steel, and in order to secure the required performance of the weld metal,
A coated arc welding rod is used in which alloy components such as Mn, Mo, Nb, and W are appropriately added in addition to Ni and Cr. For example, the inventors of the present invention described in JP-A-53-37555 disclose
Disclosed is a coated arc welding rod using a Cr-based core wire, containing Ta in one or both of the core wire and the coating material, and improving the microcrack resistance of the weld metal by controlling the total water content of the coating material. are doing.

In a coated arc welding rod using a Ni-Cr alloy for the core wire, the core wire is red-heated due to electric resistance heat during welding, the coating material is deteriorated, and welding workability is deteriorated. As a technique for improving the stick burning phenomenon, the present inventors have disclosed in Japanese Patent Publication No. 62-51716 that a Ni-Cr-based core wire is coated with a coating material containing a Li compound by controlling the particle size of limestone in the coating material. Thus, a coated arc welding rod in which the protective cylinder is strengthened and rod burning resistance is improved is disclosed.

In recent years, there has been a tendency to increase the welding current in order to improve the work efficiency. As the current value increases, the stick burning resistance of the conventional technique becomes insufficient, and the deterioration of the welding workability occurs due to the deterioration of the coating material. ing. Particularly in the vertical position where welding is performed with a large heat input, the slag seizure phenomenon is likely to occur, and the tendency is greater in the upper layer portion of the groove inner welding. In laminated welding such as in-groove and fillet welding, if seizure of the slag remains, the next layer welding is performed easily and soundly, so the removal of the slag becomes an essential work, and a lot of man-hours are required for that work, resulting in a decrease in work efficiency. To do. Not only that, in the color check inspection for inspecting the soundness of the welded part, a pseudo pattern of defects is generated on the bead surface, so it is necessary to shape the bead surface, which further increases man-hours and reduces the construction efficiency. There is a problem.

Further, when a large amount of alloy components are added to the coating material, if welding is performed at high current, the alloy components added from the coating material for the purpose of improving performance will not be sufficiently yielded and the target weld metal component cannot be obtained. In addition to the deterioration of the mechanical performance and crack resistance of the weld metal, depending on the alloy composition, the arc may become unstable and the slag may be mixed in the form of oxide to deteriorate the slag removability, thus improving welding workability. Also has an adverse effect. Therefore, there is a demand for the development of a covered arc welding rod which does not have a slag seizure phenomenon due to the stick burning phenomenon and has good welding workability and which can easily obtain sound weld metal performance.

[0006]

As described above, the Ni-based coated arc welding rod which has been used for welding 9% Ni steel for LNG storage tanks is accompanied by a burning phenomenon due to a change in working conditions due to use of high current. There was a problem that not only the welding work efficiency decreased due to slag baking but also the weld metal performance was likely to deteriorate. In view of these circumstances, the present invention has excellent welding workability without sticking phenomenon of slag when welding Ni-based alloy with a covered arc welding rod even if welding is performed under severe working conditions. However, it is an object of the present invention to provide a covered arc welding rod which can be efficiently welded, and which can easily obtain a sound weld metal having good high temperature crack resistance.

[0007]

Means for Solving the Problems The present invention is to solve the above-mentioned problems, and in a Ni-based coated arc welding rod, the weight% (hereinafter the same) with respect to the total weight of the core wire, Ni: 55-55.
75%, Cr: 12-18%, Mo: 1.0-4.5
%, Ti: 0.1 to 0.5%, Mn: 0.9 to 2.7
%, Nb: 0.7 to 2.5%, the balance consisting of Fe and inevitable impurities, to the total weight of the coating agent,
Metal carbonate: 20-45%, metal fluoride: 10-30
%, Silicates and silicate compounds: 10-25%, Mn:
0.9-4.0%, containing Nb: 0.7-3.0%,
Also, for Mn and Nb, the following formula (1),
It is a Ni-based coated arc welding rod characterized by satisfying the coefficient in the coating material shown in (2). Coefficient in coating material = 0.5 × (addition amount of Mn in coating material) / {addition amount of Mn in core wire + 0.5 × (addition amount of Mn in coating material)} ≦ 0.40 ... (1) Coefficient in coating material = 0.5 × (amount of Nb added in coating material) / {amount of Nb added in core wire + 0.5 × (amount of Nb added in coating material)} ≦ 0.35 (2)

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the above problems, the present invention coats various Ni-Cr core wires with a coating agent in which the type and amount of the alloying agent contained in the coating agent are changed. As a result of prototyping a coated arc welding rod and investigating the weld metal performance and welding workability, when adding alloy components, the degree of the effect differs depending on the alloy component from the core wire and the coating agent, and the welding workability Mn,
It was found that Nb has a great influence on the hot crack resistance.

With respect to Mn, which greatly affects the slag seizure phenomenon of welding workability, a test of welding work performance was carried out when both the core wire and the coating agent were added so that the weld metal components were the same. As a result, it was found that the amount of slag seizure is large when it is mainly added from the coating agent, and the degree of seizure of the slag and the peelability due to the brittleness of the slag are difficult depending on the addition ratio, and the protective cylinder formation status during welding is different. It was That is, Mn in the coating agent as shown in the above formula (1)
By controlling the coefficient to 0.40 or less, there is no slag seizure phenomenon, the slag is brittle and easy to remove, and the arc stability by improving and maintaining the protective cylinder is improved, and excellent welding workability is obtained. Got

Similarly, Nb was subjected to a high temperature cracking resistance investigation of the weld metal when added from both the core wire and the coating material so that the weld metal components were the same. In the cracking test, the crack resistance is not clear in the C-type jig restraint welding cracking test specified in JIS Z3115 for evaluating the high temperature cracking resistance, and therefore the restraint condition originally devised by the present inventors is rather severe. A test assuming repair welding was performed. That is, one-pass welding was performed in the U-groove in a sideways posture, the test beads were sequentially ground by about 1 mm from the surface, and the occurrence of cracks was examined several times. As a result, the resistance to high-temperature cracking is inferior when added mainly from the coating agent, and the number of cracks generated and the length of the cracks differ depending on the addition ratio, and the cracking resistance of the weld metal is as shown in equation (2) above. And the Nb coefficient in the coating is 0.3
We also obtained the finding that it is significantly improved by controlling to 5 or less.

The present invention has been made on the basis of the above findings, and a Ni--Cr type core wire is coated with a metal carbonate, a metal fluoride, a silicate and a silicate compound,
Further, by limiting the addition amount and the addition ratio of Mn and Nb from the core wire and the coating material, the arc stability, the slag peeling property, and the hot crack susceptibility of the weld metal can be remarkably improved. The reasons for limiting the components in the present invention will be described first from the core.

Ni is a main element constituting the matrix, and is required to be 55% or more in order to obtain various properties of the weld metal. However, in order to contain alloy components such as Cr, Mo and Nb as necessary, The limit is 75%. Therefore 55-
Limit to 75%.

[0013] Cr is a main element for maintaining strength characteristics and the like, and is required to be 12% or more in order to sufficiently bring out the effect, but if it exceeds 18%, toughness and ductility deteriorate. Therefore, it is limited to 12 to 18%.

Mo is effective in forming a solid solution in the matrix to improve the strength, but if it is less than 1.0%, the effect is small, and if it exceeds 4.5%, the toughness is lowered and the elongation is increased in the manufacturing process of the core wire. Linearity deteriorates. Therefore, it is limited to 1.0 to 4.5%.

Ti is required to be 0.1% or more in order to improve the porosity resistance of the weld metal, but if it exceeds 0.5%, the toughness deteriorates. Therefore, it is limited to 0.1 to 0.5%.

0.9% or more of Mn is necessary to improve toughness and porosity resistance, but if it exceeds 2.7%, the bead shape tends to be convex in vertical position welding. Therefore, it is limited to 0.9 to 2.7%.

Nb is effective in improving the strength of the weld metal and is 0.7
% Is required, but if it exceeds 2.5%, the toughness deteriorates. Therefore, it is limited to 0.7 to 2.5%.

Next, the reasons for limiting the coating agent will be described. Metal carbonate shields the arc from the atmosphere by the evolved gas decomposed at high temperature, and also maintains a healthy welding metal by keeping the welding atmosphere highly basic, and excellent work by optimizing the viscosity and fluidity of the slag. It is effective for securing the property and is required to be 20% or more, but if it exceeds 45%, the slag removability and the bead appearance are deteriorated. Therefore, it is limited to 20 to 45%. The metal carbonate refers to barium carbonate, strontium carbonate, lithium carbonate, manganese carbonate, magnesium carbonate, etc. in addition to limestone.

Similar to the metal carbonate, the metal fluoride shields the arc from the atmosphere by the generated gas decomposed at high temperature, and is effective in improving the toughness and ductility by reducing the amount of oxygen in the weld metal. In addition, it is necessary to secure excellent workability in all postures by optimizing the viscosity and fluidity of slag and to improve deterioration of slag removability, and 10% or more is necessary, but if it exceeds 30%, the arc becomes unstable. The welding workability deteriorates. Therefore 10-
Limit to 30%. The term "metal fluoride" refers to fluorite, aluminum fluoride, magnesium fluoride, cryolite, sodium fluoride, zirconium fluoride, and the like.

Silicates and silicate compounds are effective in forming a strong protective cylinder and stabilizing the arc. In addition, it is effective in giving a suitable fluidity to the slag and encapsulating the bead, and improving the bead appearance.
If it exceeds 25%, the slag removability deteriorates. Therefore 10
Limit to ~ 25%.

As described above, Mn is required to be 0.9% or more in order to improve toughness and porosity resistance.
If it exceeds 0%, the slag is vitrified and the slag removability is extremely deteriorated, and the seizure phenomenon is not improved even if the coating agent coefficient is 0.4 or less. Therefore, it is limited to 0.9 to 4.0%.

Nb is effective in improving the strength of the weld metal and is 0.7
% Is required, but if it exceeds 3.0%, the crack resistance is deteriorated, and it is not improved even if the coating agent coefficient is 0.35 or less.
Therefore, it is limited to 0.7 to 3.0%.

The Mn coefficient in the coating agent represented by the formula (1) has a great relationship with the stick burn resistance and the slag seizure prevention. The smaller the coefficient value, the smaller the slag seizure amount, and the slag becomes brittle and the slag is removed. It is easy and peelability is improved. In addition, the protection tube tends to be strengthened and stick burn resistance tends to be improved. When the coefficient value exceeds 0.40, the slag vitrifies to cause a seizure phenomenon and deteriorates the slag releasability. Further, the phenomenon of stick burning becomes remarkable, the protective cylinder becomes weak, and the arc state becomes unstable. Therefore, Mn in the coating agent
The coefficient is limited to 0.40 or less within the range of the amount of Mn added.

The Nb coefficient in the coating agent represented by the formula (2) has a great relationship with the hot cracking of the weld metal, and the smaller the value is, the more the crack resistance is improved. When the coefficient value exceeds 0.35, the number of cracks and crack length of the weld metal increase, and the hot crack resistance is significantly deteriorated. Therefore, the Nb coefficient in the coating material is limited to 0.35 or less within the range of the amount of Nb added.

In order to obtain a sound weld metal, Fe-A
1, the metal Al, Fe-Si, etc. are added as deoxidizing agents, and the metal powder is appropriately added to obtain a weld metal according to the required characteristics, without impairing the characteristics of the present invention. However, the alloying agent should be 30% or less because the components of the weld metal tend to become nonuniform when the compounding amount is large. In addition, the metal powder other than the deoxidizing agent mentioned here means metal Cr, Fe-Cr,
This refers to powders of metal Ni, metal W, and the like.

[0026]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples. The core wire used in the experiment was made into a size of 4.0 mm diameter × 350 mm by melting, forging, rolling and drawing. Table 1 shows the core wire compositions. W1 to W5 are the core wires used in the present invention, and W6 to W8 are the core wires used in the comparative example. Table 2 shows the composition of the coating agent coated on the core wire of Table 1. F1 to F4 are coating agents used in the present invention, and F5 to F8.
Is the coating material used in the comparative example.

[0027]

[Table 1]

[0028]

[Table 2]

The coated arc welding rod is manufactured by adding water glass such as potassium silicate or sodium silicate to the coating material shown in Table 2 in an amount of about 20% of the weight of the coating material, and coating the wet mixture with a coating rate of about 30%. The core wire of Table 1 is coated so that
It was prepared by firing for about 60 minutes.

Tables 3 to 5 show the chemical composition of the weld metal welded with a welding rod in which the core wire of Table 1 and the coating material of Table 2 are combined, and Tables 6 and 7 show the mechanical properties of the weld metal and joint welding. The mechanical properties of the metal, the X-ray test result, the welding workability test result and the split resistance hot crack test result are shown.

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

[Table 5]

[0034]

[Table 6]

[0035]

[Table 7]

The weld metal performance test was carried out in accordance with JIS Z3225. The weld metal performance of the joint is 9% Ni steel with the groove shape shown in Fig. 1, and the welding current: 13 in the vertical position.
Double-sided butt welding was performed under welding conditions of 0 A and speed: 50 to 100 mm / min, and a short gauge tensile test, an impact test, and an X-ray performance test were performed. X-ray transmission test (J
After performing IS Z3106), a joint tensile test piece (JIS Z3121 No. 1) and an impact test piece (JIS
Z3111, No. 4) was collected and investigated for mechanical properties.
The impact test was conducted at -196 ° C to determine the absorbed energy.

The welding workability evaluation test was judged during joint welding. In the hot cracking resistance test, the groove shape of 9% Ni steel was formed, and the test plate 1 was welded 3 to the constraining plate 2 as shown in FIG. 3 to constrain it. Welding current: 145 A, welding speed: 20 cm / m
Weld the test bead in a horizontal position under the condition of in, grind the bead surface 3 times by 1mm each, and perform color check inspection, measure the number and length of cracks, and measure the high temperature cracking resistance by 3 times in total. evaluated.

No. 1 of the present invention example. 1 to No. No. 12 was excellent in weld metal mechanical performance, crack resistance, X-ray performance, and good welding workability.

On the other hand, in Comparative Example No. 13 is Cr in the core
Excessive amount, insufficient Ti, excessive amount of metal fluoride in coating agent, insufficient amount of silicate compound, excessive amount of Nb in coated arc welding rod, and excessive Mn coating agent coefficient. No. No. 14 has excessive Cr in the core wire, insufficient Ti, insufficient silicate compound in the coating agent, excessive Nb in the coated arc welding rod, and excessive Mn coating agent coefficient.

No. 15 is lack of Ni in the core wire, Cr, M
o, excessive Ti, excessive Mn in the coated arc welding rod, No.
No. 16 has excessive Ni in the core wire, insufficient Cr and Mo, insufficient silicate compound in the coating agent, and excessive Mn and Nb coating agent coefficients.

No. 17 is excessive Ni, Cr, M in the core wire
o Shortage, No. No. 18 is insufficient metal carbonate in the coating material, metal fluoride, excess silicate compound, No. No. 19 is an excess of metal fluoride in the coating material, a silicate compound is insufficient, and No. 19 No. 20 is in excess of metal carbonate and metal fluoride in the coating agent. For each of these reasons, in Comparative Examples, there are problems such as mechanical properties of weld metal, deterioration of cracking resistance, poor X-ray performance, arc state that is particularly unstable in welding workability, poor seizure of slag, and the like. is there.

[0042]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, in a coated arc welding rod of Ni-based alloy, the rod burntability is excellent even at a high current, the welding workability, particularly the arc state is stable, and there is no slag seizure and good peelability. And also has good high temperature crack resistance,
It is intended to provide a covered arc welding rod which can easily obtain a sound weld metal having no welding defects, and contributes greatly to efficiently and economically perform welding of TSNi-based alloys.

[Brief description of drawings]

FIG. 1 is a sectional view showing a groove shape for joint welding used in Examples.

FIG. 2 is a cross-sectional view showing a groove shape for a crack test used in Examples.

FIG. 3 is a diagram showing a restrained state of a crack test material used in Examples.

Claims (1)

[Claims] 1. In a Ni-based coated arc welding rod, in weight% with respect to the total weight of the core wire, Ni: 55-75%, Cr: 12-18%, Mo: 1.0-4.5%, Ti: 0.1 to 0.5%, Mn: 0.9 to 2.7%, Nb: 0.7 to 2.5%, with the balance being Fe and inevitable impurities, the total weight of the coating agent % By weight, metal carbonate: 20 to 45%, metal fluoride: 10 to 30%, silicate and silicate compound: 10 to 25%, Mn: 0.9 to 4.0%, Nb: Ni-based coated arc welding containing 0.7 to 3.0% and satisfying the coefficients of Mn and Nb in the coating agent represented by the following formulas (1) and (2), respectively. rod. Coefficient in coating material = 0.5 × (addition amount of Mn in coating material) / {addition amount of Mn in core wire + 0.5 × (addition amount of Mn in coating material)} ≦ 0.40 ... (1) Coefficient in coating material = 0.5 × (amount of Nb added in coating material) / {amount of Nb added in core wire + 0.5 × (amount of Nb added in coating material)} ≦ 0.35 (2)