JP2000052089A - Austenite system stainless steel filler rod with excellent high temperature characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a filler rod with excellent high temperature characteristic by coating a coating agent around a core wire containing carbonate, silica, and SiO2 around a core wire at specific weight proportion against the overall weight of a coating agent, and composing the rod of Mo, W, Cu, Nb, V, N, and the balance of Fe and inevitable impurities at the core wire weight ratio of total of one or both of the core wire and the coating agent. SOLUTION: A coating agent containing 20-45% carbonate, 10-30% silica, and 3-18% SiO2 at weight % against the overall weight of the coating agent is coated on this filler rod. Furthermore, the rod is composed of 0.2-5% Mo, 1-5% W, 0.1-2.5% Cu, 0.1-2.0% Nb, 0.1-2% V 0.05-0.3% N, and the balance of Fe and inevitable impurities, at the core wire weight ratio of total of one or both of the core wire and the coating agent. It is preferable that 0.016-0.05% P is contained, Nb/V is 0.1-0.5, and Mo is 0.2-1.1% at the core wire weight ratio of total of one or both of the core wire and the coating agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated arc welding rod applied to welding of austenitic stainless steel used in a high temperature and high pressure environment such as a power plant.

[0002]

_2. Description of the Related Art In recent years, from the viewpoint of energy saving and suppression of CO ₂ emission, the power generation efficiency has been improved by increasing the temperature and pressure of steam conditions, and there has been an active movement to apply a high-strength heater tube material. ing. So 18Cr-8
W based on Ni-based austenitic stainless steel,
A new austenitic stainless steel tube has been developed that has been strengthened by adding Nb, V, and N, and has the advantage that it can be used as a boiler tube in a wide range of power plants, from industrial to electric and commercial use. Have.

As a welding material for such austenitic stainless steel, JIS D of high Ni alloy is used.
It is considered that NiCr-3 or a base material processed into a wire is used. However, the performance of a weld metal obtained from a welding material obtained by directly processing a base material of high-temperature, high-strength austenitic stainless steel into a wire is inferior to that of the base material. The base metal can obtain high strength by hot working such as melting, forging, rolling, heat treatment tempering, etc., whereas the weld metal is often used as a solidified structure, and the same composition as the base material Various properties such as sufficient high-temperature strength, toughness after aging, and high-temperature corrosion resistance cannot be obtained. In addition, a high Ni alloy welding material can provide sufficient performance but is expensive.

[0004] Japanese Patent No. 2622530 discloses 18Cr-8Ni as a welding material excellent in high-temperature strength of this kind.
There has been proposed a welding material for austenitic steel excellent in high-temperature strength in which high-temperature strength is improved by adding Nb, N, Ti, Mo, or the like to a system base. However, in the above technology,
Although high-temperature strength is ensured, there has been a problem that the toughness after aging and the high-temperature corrosion resistance, which are properties necessary for high-temperature and high-pressure power plant materials, are not sufficient.

[0005]

SUMMARY OF THE INVENTION The present invention provides an 18Cr-
When welding 8Ni-based high-temperature high-strength austenitic stainless steel, high-temperature strength, ductility,
An object of the present invention is to provide a coated arc welding rod having toughness, high-temperature corrosion resistance, and good hot crack resistance.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a weld metal having high temperature strength, ductility, toughness and high temperature corrosion resistance equal to or higher than that of a base material as welded and having good hot crack resistance is obtained. For this reason, various investigations were carried out from the viewpoint of the composition of the core wire of the coated arc welding rod and the coating agent. The mechanism of strengthening the high-temperature strength of each alloy element is as follows: solid solution strengthening of Mo, W, Cu, solid solution strengthening of Nb, V and precipitation strengthening by carbonitride precipitation, solid solution strengthening of N and precipitation strengthening by nitride precipitation There is. Even if these alloy elements are added alone, the high-temperature strength can be improved by the above-mentioned strengthening mechanism, but the high-temperature strength can be further improved by a synergistic effect of adding Mo, W, Cu, Nb, V, and N in an appropriate amount in combination, It has been found that toughness can be improved.

P is an element that improves high-temperature strength and ductility. However, P forms a low-melting point eutectic such as Fe ₃ P at the time of solidification and tends to cause high-temperature cracking.
The addition amount was limited as follows. In the present invention, Nb and V
By adjusting the addition amount of P, 0.0
Even if added up to 5%, it does not cause hot cracking,
It has been found that high-temperature strength and ductility can be improved.

Further, the high-temperature strength is secured by the synergistic effect of the addition of Mo in an amount of 0.1 to 1.1% and the combined addition of W, Cu, Nb, V and N, and after further aging. It has been found that the improvement of toughness and the high temperature corrosion resistance can be ensured.

The present invention has been made on the basis of the above findings. The gist of the present invention is as follows. (1) Austenitic stainless steel is used as a core wire, and the core is surrounded by the core material with respect to the total weight of the coating agent. And coated with a coating containing ₂₀ to 45% of carbonate (wt%, hereinafter the same), 10 to 30% of fluorite, and ₃ to 18% of SiO2. Or, by adding both, Mo is 0.2 to 5 in terms of core weight ratio.
%, W 1 to 5%, Cu 0.1 to 2.5%, Nb 0.1 to 2.0%, V 0.1 to 2.0%, N 0.0
An austenitic stainless steel welding rod excellent in high-temperature characteristics, containing 5 to 0.3%, with the balance being Fe and inevitable impurities. (2) Austenitic stainless steel is used as a core wire, and TiO ₂ is surrounded by 25 to 65% (% by weight, hereinafter the same) based on the total weight of the coating agent around the core wire,
It is coated with a coating agent containing 5 to 35% of carbonate and 1 to 15% of fluorite. %, W is 1 to 5%, C
u is 0.1 to 2.5%, Nb is 0.1 to 2.0%, V is 0.1 to 2.0%, N is 0.05 to 0.3%, and the balance is Fe and An austenitic stainless steel welding rod with excellent high-temperature properties characterized by being inevitable impurities.
(3) In the welding rod according to (1) or (2), one or both of the core wire and the coating agent are added up, and the total weight of the core wire and P
Austenitic stainless steel welding rod excellent in high-temperature properties, characterized by containing 0.016% to 0.05% of Nb / V and Nb / V of 0.1 to 1.5. (4) (1)
The welding rod according to any one of (1) to (3), wherein one or both of the core wire and the coating agent are added and Mo is 0.2 to
An austenitic stainless steel welding rod excellent in high-temperature characteristics characterized by being made 1.1%.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting various numerical values of the austenitic stainless steel welding rod excellent in high-temperature strength according to the present invention will be described below. Among the components added to the coating agent of claim 1, the carbonate is calcium carbonate, magnesite, dolomite,
There are lithium carbonate, barium carbonate, etc., which are added for the purpose of improving arc stability. If it is less than 20%, the effect cannot be sufficiently obtained. If added in excess of 45%, spatter will increase. Therefore, the total of one or more carbonates needs to be 20 to 45%.

Fluorite is added because it improves the fluidity of the slag, smoothes the edge of the bead, and prevents welding defects such as poor fusion and slag entrainment. If it is less than 10%, the effect cannot be sufficiently obtained. If added in excess of 30%, the amount of spatter generated will increase. Therefore, the fluorite needs to be 10 to 30%.

[0012] SiO ₂ is made to have an appropriate viscosity to the molten slag, but to improve the bead shape in all position welding, since becomes excessively large bead shape of vertical position becomes convex 3-18%
Need to be Examples of the addition source include silica sand, potassium feldspar, mica, and water glass used as a fixing agent.

[0013] Of the components added to the coating agent of claim 2, T
iO ₂ is added for the purpose of improving the stability of the arc and forming a slag having good encapsulation property, and particularly for improving the bead shape in the downward posture. If it is less than 25%, the effect cannot be sufficiently obtained. If it exceeds 65%, the bead shape in the vertical position becomes convex. Therefore, TiO ₂
Should be 25-65%.

The carbonate includes calcium carbonate, magnesite, dolomite, lithium carbonate, barium carbonate, etc., and is added for the purpose of improving the fluidity of the slag and improving the bead shape in the upright posture. If it is less than 5%, the effect cannot be sufficiently obtained. If added in excess of 35%, spatter will increase. Therefore, the total of one or more carbonates needs to be 5 to 35%.

Fluorite is added for the purpose of improving the stability of the arc at a low current such as in a vertical position. If it is less than 1%, the effect cannot be sufficiently obtained. If it is added in excess of 15%, the amount of spatter generated will increase. Therefore, fluorite is 1
Need to be ~ 15%.

In the present invention, Mo, among the elements added by adding one or both of the core wire and the coating agent, improves the high-temperature strength mainly by solid solution strengthening. If it is less than 0.2%, the effect cannot be sufficiently obtained. If added in excess of 5%, the toughness after aging is reduced. Therefore, Mo needs to be 0.2 to 5%. In addition, Mo
By setting it to 1.1%, the toughness after aging is further improved,
Good high temperature corrosion resistance.

W is, like Mo, mainly by solid solution strengthening.
Improve high temperature strength. If it is less than 1%, the effect cannot be sufficiently obtained. Even if added in excess of 5%, the effect of improving the high-temperature strength by solid solution strengthening is reduced, and a large amount of carbides is precipitated to lower the ductility. Therefore, W is 1-5
It needs to be%.

Cu improves the high-temperature strength by solid solution strengthening. Further, the toughness is improved by stabilizing the austenite structure. If it is less than 0.1%, the effect cannot be sufficiently obtained. Addition of more than 2.5% causes precipitation of intermetallic compounds and impairs the mechanical properties of ductility and toughness. Therefore, Cu must be 0.1-2.5%.

Nb improves high-temperature strength by solid solution strengthening and precipitation strengthening (mainly precipitation of carbides). If it is less than 0.1%, the effect cannot be sufficiently obtained. 2.0%
When added in excess of, not only the effect of improving the high-temperature strength is saturated, but also a large amount of carbide is precipitated, toughness and ductility are deteriorated, and the toughness after aging is significantly reduced. Therefore, Nb needs to be 0.1 to 2.0%.

V improves the high-temperature strength by solid solution strengthening and precipitation strengthening (mainly nitride precipitation). If it is less than 0.1%, the effect cannot be sufficiently obtained. When added in excess of 2.0%, not only does the effect of improving high-temperature strength saturate, but also a large amount of nitrides precipitate, and toughness and ductility deteriorate.
Significantly reduces toughness after aging. Therefore, V is 0.1 to
Must be 2.0%.

N enhances high-temperature strength by solid solution strengthening by interstitial solid solution and precipitation strengthening of nitrides such as VN. 0.0
If it is less than 5%, the effect cannot be sufficiently obtained. If added in excess of 0.3%, defects such as blowholes are generated, and furthermore, the workability of welding, particularly the slag peeling property, is deteriorated. Therefore, N needs to be 0.05 to 0.3%.

By the simultaneous presence of Mo, W, Cu, Nb, V, and N, an appropriate amount of carbonitride is precipitated, solid solution strengthening is sufficiently promoted, and both high-temperature strength and toughness can be improved. . Therefore, it is necessary to add each alloy in the above-mentioned appropriate range.

As described above, various properties such as high-temperature strength, ductility, toughness, and high-temperature corrosion resistance can be improved by adding each alloy in an appropriate amount in a complex manner. And ductility can be further improved. 0.01
If it is less than 6%, the effect cannot be sufficiently obtained. If it exceeds 0.05%, it becomes difficult to prevent hot cracking even if Nb / V is an appropriate value. Therefore, P must be 0.016 to 0.05%.

Nb / V is an indicator of the easiness of formation of a eutectic having a low melting point of P. If it is less than 0.1, nitrides precipitate more than carbides, so that the crystal grains can be refined. This is not sufficient, so that segregation of P is likely to occur and hot cracking is likely to occur. If it exceeds 1.5, carbides precipitate more than nitrides, so that the crystal grains are not sufficiently refined, P segregation is likely to occur, and hot cracking is liable to occur. Therefore, the region where the ratio of carbide to nitride is desirable is
Nb / V is 0.1 to 1.5, and makes the crystal grains particularly fine to prevent segregation of P and to improve the hot cracking resistance.

The term "core weight ratio" as used herein refers to a ratio represented by the following formula, and the coating compounding ratio in the formula means the mixing ratio of the added material to the total weight of the coating agent. The term "covering ratio" means the ratio of the coating weight to the total weight of the welding rod. Core wire weight ratio = content in core wire (% by weight) + mixing ratio in coating agent (% by weight) × coverage / (100−coverage)

In addition, referring to a method of manufacturing a coated arc welding rod, a coating material mixed and mixed with a core wire is prepared, and then wet-mixing is performed while a fixing agent (aqueous solution of potassium silicate and sodium silicate) is added to the coating material. , A coating agent is applied around the cord, and after coating, drying and firing are performed at 150 to 420 ° C. for about 1 to 3 hours.

[0027]

EXAMPLES Table 1 shows the main chemical components of the test core wire. Tables 2 to 11 show the compositions of the coated arc welding rods by the combination of the test core wire and the coating agent. Table 12 shows the chemical components of the base material used. Tables 13 to 22 show the analytical test results, tensile test results, impact test results, hot cracking test results, hot corrosion resistance test results, and welding workability test results of the deposited metal welded using the coated arc welding rod and the base metal. Is shown.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

[Table 5]

[0033]

[Table 6]

[0034]

[Table 7]

[0035]

[Table 8]

[0036]

[Table 9]

[0037]

[Table 10]

[0038]

[Table 11]

[0039]

[Table 12]

[0040]

[Table 13]

[0041]

[Table 14]

[0042]

[Table 15]

[0043]

[Table 16]

[0044]

[Table 17]

[0045]

[Table 18]

[0046]

[Table 19]

[0047]

[Table 20]

[0048]

[Table 21]

[0049]

[Table 22]

The welding method used was a welding rod having a rod diameter of 4.0 mm, a welding current of 100 to 140 A (AC), and an arc voltage of 2.
The test pieces having a groove shape shown in FIG. 1 were stacked at 0 to 25 V at a welding speed of 100 to 250 mm / min. In FIG. 1, the plate thickness t is 12 mm, the groove angle α is 45 °, and the root interval a is 12 mm. In addition, the welding workability test was performed in each of a downward position and a vertical position, while other tests were performed in a downward position.

In the hot cracking test, six macro test pieces of the cross section of the welded portion were collected, and after wet polishing and etching, 100 to 20
The presence or absence of cracks was observed under a microscope of 0 magnification, and the presence or absence of defects such as blow holes was also observed. As the tensile test piece, a JIS Z3111A2 test piece was sampled as shown in FIG. The impact test was performed on the as-welded metal and the weld metal aged at 600 ° C. for 1000 hours in accordance with JIS Z31 as shown in FIG.
No. 114 test piece was collected.

In the high-temperature corrosion test, a test piece was sampled as shown in FIG. 4 and a mixed gas (5% O
₂ + 15% CO ₂ + 0.5% SO ₂ + balN ₂ ) artificial synthetic ash (1.5 mol NaSO ₄ +
1.5mol K ₂ SO ₄ + 1.0mol Fe ₂ O
_{In 3} ), corrosion weight loss was investigated under the conditions of 650 ° C. × 100 hours. 2 to 4, 1 is a base material, 2 is a weld metal, and 3 is a position where each test piece is collected.

Tables 6, 7 and 8 show the results of each test. In the table, welding rod symbol No. Nos. 16 to 30 are examples of the present invention, and welding rod symbols No. 1 to 15 are comparative examples. N which is an example of the present invention
o. Nos. 16 to 30 had good welding workability, high-temperature strength, elongation, toughness, high-temperature cracking resistance, and high-temperature corrosion resistance.

In the comparative example, welding rod No. In No. 1, since the carbonate in the coating agent was low and the fluorite was high, the arc was unstable and the amount of spatter generated was large. Welding rod No. In No. ₂ , since the carbonate in the coating agent is high and SiO ₂ is low, the amount of spatter generated is large and the bead shape is poor.

The welding rod No. 3 has low fluorite in the coating agent,
Further, since the SiO ₂ content is high, the fluidity of the slag is poor, and the bead shape in a vertical position becomes convex. Welding rod No. Sample No. 4 has low Mo in terms of core wire weight ratio and high Cu, so that high-temperature strength is low and ductility and toughness are low.

The welding rod No. In No. 5, Mo in the core wire weight ratio is high and W is low, so that the toughness after aging is low and the high-temperature strength is low. Welding rod No. No. 6 has low high-temperature strength and ductility due to high W in core wire ratio and low Nb.

The welding rod No. No. 7 has high ductility, toughness, and low aging toughness due to high Nb and low V in core wire weight ratio. Welding rod No. 8 has a high V in terms of core weight ratio, and C
Since u is low, high-temperature strength, ductility, toughness, and toughness after aging are low.

The welding rod No. No. 9 has a low high-temperature strength because N in the core wire weight ratio is low. Welding rod No. In No. 10, since N in the core wire weight ratio is high, the removability of the slag is poor. Blowholes also occurred.

The welding rod No. In No. 11, a high-temperature crack occurred because of high P in the core wire weight ratio. Welding rod No. In No. 12, since the TiO ₂ in the coating agent was low, the arc was unstable and the bead shape in the downward direction was poor.

The welding rod No. In No. 13, since the TiO ₂ in the coating agent is high and the carbonate is low, the bead shape in the vertical position is poor. Welding rod No. In No. 14, since the carbonate in the coating material is high and the fluorite is low, the amount of spatter generated is large, and the arc stability in the vertical position is poor. Welding rod No. In No. 15, since the fluorite in the coating agent is high, the amount of spatter generated is large.

[0061]

As described above, according to the present invention, coated arc welding which is excellent in high-temperature strength, ductility, toughness, high-temperature cracking resistance and high-temperature corrosion resistance of a weld metal and excellent in workability in all-position welding. A rod can be provided, which contributes to improving the quality of an austenitic stainless steel weld having excellent high-temperature properties.

[Brief description of the drawings]

FIG. 1 Test piece

FIG. 2 Test piece

FIG. 3 Test piece

FIG. 4 Test piece

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Toshiyuki Miyake 20-1 Shintomi, Futtsu-shi, Chiba F-term in the Technology Development Division of Nippon Steel Corporation (reference) 4E001 AA03 BB01 CA03 DB05 DC05 EA07 4E084 AA02 AA03 AA09 AA20 AA25 AA26 AA27 BA06 BA09 BA11 BA23 CA02 CA03 CA08 CA13 DA01 FA03 GA07

Claims (4)

[Claims] 1. An austenitic stainless steel core wire, around which the carbonate is 20 to 45% (% by weight, the same applies hereinafter) and the fluorite is 10 to 30% based on the total weight of the coating agent.
%, And a coating agent containing ₃ to 18% of SiO2, and one or both of the core wire and the coating agent are added, and Mo is 0.2 to 5% by weight of the core wire and W is 1%. -5%, Cu 0.1-2.5%, Nb 0.1-2.0%, V 0.
An austenitic stainless steel welding rod excellent in high-temperature properties, characterized by containing 1 to 2.0% and 0.05 to 0.3% of N, with the balance being Fe and inevitable impurities. 2. A core made of austenitic stainless steel, and TiO ₂ around the core with respect to the total weight of the coating agent.
25-65% (% by weight, the same applies hereinafter), and carbonates 5-3
5% and a coating agent containing 1 to 15% of fluorite, and one or both of the core wire and the coating agent are combined to give a Mo content of 0.2 to 5% and a W of 1 ~ 5%, Cu is 0.1 ~
2.5%, Nb is 0.1 to 2.0%, and V is 0.1 to 2.
An austenitic stainless steel welding rod excellent in high-temperature characteristics, containing 0% and 0.05 to 0.3% of N, with the balance being Fe and inevitable impurities. 3. The welding rod according to claim 1, wherein one or both of the core wire and the coating agent are added and P is 0.016% to 0.05% by weight of the core wire. An austenitic stainless steel welding rod having excellent high-temperature properties, containing Nb / V of 0.1 to 1.5. 4. The welding rod according to any one of claims 1 to 3, wherein one or both of the core wire and the coating agent are added to make the Mo 0.2 to 1.1% by weight of the core wire. An austenitic stainless steel welding rod with excellent high-temperature properties.