JPH07284988A - Coated electrode for high-nitrogen austenitic stainless steel - Google Patents

Abstract

PURPOSE:To improve the strength, high-temp. cracking resistance and corrosion resistance of a weld zone by coating a core wire consisting of a specific compsn. with a coating material controlled in the contents of a carbonate, SiO2, metal fluoride and metallic powder at a specific ratio. CONSTITUTION:The compsn. of the core wire of the coated arc electrode of for high-nitrogen austenitic stainless steels is composed, by the total weight of the compsn., of 0.01 to 0.12% C, 0.05 to 0.5% Si, 0.5 to 1.5% Mn, <=0.01% P, <=0.008% S, 22 to 28% Ni, 18 to 28% Cr, 0.5 to 2.5% Mo, 0.05 to 0.6% Nb, 0.02 to 0.2% Ti, 0.001 to 0.01% B, 0.1 to 0.3% N, 0.002 to 0.02% O, <=0.01% Mg and the balance Fe. The compsn. of the coating material is composed of 15 to 45% carbonate, 3 to 17% SiO2, 5 to 30% metal fluoride and 1 to 45% metallic powder. The C in the carbonate is confined to 2 to 5.5% and the C in the metallic powder to 0.001 to 0.2%. The core wire is coated with this coating material at a coating rate 20 to 40%.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is applicable to high temperature, such as in power plants.
The present invention relates to a coated arc welding rod applied to welding austenitic stainless steel used in a high pressure environment. Specifically, in welding of high nitrogen austenite / stainless steel in which crystallization of δ ferrite is suppressed, even if the welded part is exposed to a high temperature / high pressure environment, strength / hot cracking resistance /
The present invention relates to a coated arc welding rod having excellent characteristics such as corrosion resistance and excellent workability in all positions.

[0002]

2. Description of the Related Art In recent years, there has been an active movement to improve efficiency in thermal power generation from the viewpoint of energy saving. From such a background, high Cr with suppressed crystallization of δ ferrite is used for applications such as steel pipes for boilers that can improve thermal efficiency.
-High Ni-High N system and new austenitic stainless steel pipes containing Mo, Nb, Ti, B, etc. have been developed and are already in practical use. From such a trend, it is necessary to secure the same characteristics as steel materials in terms of welding material. As a welding material of this kind, a TIG wire of Japanese Patent Laid-Open No. 5-69187 "Welding material for high Cr high N austenitic steel" is disclosed, and this welding wire has crystallization suppression of δ ferrite and high temperature strength. 25Cr-20Ni-0.5% Nb-0.2 for securing
The N-0.06C system is used, and addition of Mg and P and S are restricted in order to prevent welding hot cracking.

On the other hand, since the coated arc welding rod is still under development, it is 21Cr-9Ni-0.2N-0.0 for conventional high nitrogen austenitic stainless steel.
4C system and 25Cr-14Ni-2.5Mo-0.3
The "high nitrogen Cr-Ni austenitic steel-coated arc welding rod" such as N-0.04C system is only disclosed in JP-A-53-37554. This coated arc welding rod has a 27Cr-22Ni-0.3N-0.04C system and a 25Cr-13Ni-2.5Mo-0.3N-0.04 system.
High-nitrogen austenitic stainless steel by coating a carbon-metal fluoride-based coating agent on a C-based core wire to suppress moisture in the coating agent and adding Al and Si to the core wire or the coating agent. It is described that the generation of blowholes can be prevented in the welding of No.

However, this coated arc welding rod is intended to prevent the formation of blowholes in the welding of high-nitrogen austenitic stainless steel, and it does not completely suppress the crystallization of δ-ferrite, and also has a core wire. Nb, T
Since neither i nor B is added nor O is controlled, and neither the carbonate of the coating agent nor the C in the metal powder is controlled, welding exposed to high temperature and high pressure as aimed at by the present invention is performed. Various properties such as strength, ductility, and corrosion resistance of the parts could not be obtained, and the variation was large.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems of the coated arc welding rod used for the high austenitic high nitrogen stainless steel used in a high temperature and high pressure environment. .

That is, the conventional covered arc welding rod disclosed in Japanese Patent Laid-Open No. 53-37554 is Cr, N.
From this point, it can be understood that it has high strength and excellent corrosion resistance by using a stainless steel core wire in which the amounts of i and N are controlled. It has been difficult to satisfy the high temperature crack resistance as well as to secure the high temperature strength and the corrosion resistance, which have recently been increasing in demand value. Further, the coating agent of this coated arc welding rod is a carbonate-metal fluoride system and is made of SiO ₂ or C.
Although metal powders such as r, Mn, and Al can be added, there is also a problem that C in the coating agent is not controlled and stable and stable metal deposition performance cannot be secured.

Next, even if the knowledge of the TIG wire component, which essentially requires Mg, disclosed in JP-A-5-69187 is applied to the design of the core wire component of the welding rod, the stability of the arc is significantly impaired and the welding is performed. It was difficult to put it into practical use in terms of workability. As described above, the case of adding Mg to the core wire is extremely small in the conventional welding rod, and generally, the deterioration of the welding workability due to the addition of Mg is not known at all.

In view of the above situation, the present invention has been made to solve the problem of "securing high temperature strength, ductility, corrosion resistance and high temperature crack resistance" which cannot be achieved only by conventional knowledge and techniques.

[0009]

The inventors of the present invention secure a weld metal which has high strength and excellent corrosion resistance under a high temperature and high pressure environment, but is less likely to be embrittled and has good hot crack resistance. With the aim of ensuring good workability that facilitates backside welding of steel pipes, various studies were conducted from the viewpoint of the composition of the core wire of the coated arc welding rod and the coating agent. As a result, the following findings have been obtained.

In order to make various properties such as strength, corrosion resistance and embrittlement under high temperature and high pressure excellent, first, the basic component of the weld metal is 25% Ni-20% Cr-1% Mo-0.
It is necessary to suppress the crystallization of δ ferrite by using 2N system.

In the coated arc welding rod, in order to obtain such a weld metal component, addition of these alloy components is mainly performed from the core wire, but Ni in the core wire is added.
The amount of Mo added may be approximately the same as the target value of the deposited metal. However, the amount of Cr, which easily oxidizes during welding, must be determined in consideration of the consumption amount thereof.

In this basic component system, it is effective to add C, Nb, Ti and B as components for further enhancing high temperature strength.

The present invention is constructed on the basis of the above findings, and the gist of the present invention is that the C is 0.01 to 0. 12
%, Si 0.05 to 0.5%, Mn 0.5 to 1.5
%, P is 0.01% or less, S is 0.008% or less, Ni
22-28%, Cr 18-28%, Mo 0.5-
2.5%, Nb 0.05-0.6%, Ti 0.02
~ 0.2%, B is 0.001-0.01%, N is 0.1
.About.0.3%, O 0.002 to 0.025%, Mg 0.01% or less, and the balance Fe and unavoidable impurities around the core wire with a carbonate, based on the total weight of the coating material. 15 ~
45%, SiO ₂ 3-17%, metal fluoride 5-30
%, 1 to 45% of metal powder is contained, C in the carbonate is 2 to 5.5%, and C in the metal powder is 0.001 to 0.
A coating arc welding rod for high nitrogen austenitic stainless steel is characterized in that a coating agent of 2% is coated at a coating rate of 20 to 40%.

[0014]

The function of the high-nitrogen austenitic stainless steel coated arc welding rod of the present invention is to ensure excellent corrosion resistance, strength, and embrittlement resistance under high temperature and high pressure environment, as well as good hot crack resistance. Security and welding workability. In order to satisfy all of these welding performances, by adjusting the composition of the core wire of the coated arc welding rod and the composition of the coating agent, while ensuring good welding workability, the weld metal composition of high nitrogen austenitic stainless steel Based on C, Si, Mn, P, S, Ni, Cr, Mo,
It is necessary to control each of Nb, Ti, B, N, O, and Mg within an appropriate amount range.

First, the reason for limiting each component in the core wire will be described. C added to the core wire yields to the weld metal together with the C addition source in the coating material to enhance the high temperature strength, but if it exceeds the proper amount, the deterioration of the hot crack resistance is remarkably promoted. Therefore, the appropriate amount of C in the core should be 0.01 to 0.12%.

Si can be added as a deoxidizing agent to obtain a clean weld metal without blowholes, but if added in a large amount, it promotes the occurrence of hot cracking. Therefore, the appropriate amount range to be added to the core wire must be controlled to 0.05 to 0.5%.

Mn can be expected to have an effect as a deoxidizing agent like Si and is easily nitrided, so that the amount of N dissolved can be increased while maintaining a sound weld metal without blowholes. It also effectively prevents hot cracking, but if it is added in a large amount, the peelability of the slag will be impaired, so it must be made 0.5 to 1.5%.

It is generally known that P and S increase the hot cracking susceptibility, but in the weld metal of the complete austenite structure as in the present invention, P is 0.01% or less,
It is necessary to limit S to 0.008% or less.

Ni stabilizes the austenite structure of the deposited metal and enhances the mechanical properties of ductility and toughness. But,
When the amount of Ni in the core wire becomes high, the rod burn resistance of the coated arc welding rod is significantly deteriorated, so it must be controlled to 22 to 28%.

Cr is essential for improving the corrosion resistance and high temperature strength. Further, like the above Mn, it increases the amount of N dissolved and acts as a deoxidizing agent, but on the other hand, if added too much, the mechanical properties of ductility and toughness are impaired. Therefore, 18 to 28% is an appropriate amount.

Mo enhances high-temperature strength, but accelerates deterioration of toughness, so it is controlled to 0.5 to 2.5%.

Nb, Ti, and B all adversely affect the hot crack resistance, but have the advantage of increasing the high temperature strength. In order to bring out the advantages while suppressing these disadvantages, all of these ingredients are essential and N
b is 0.05 to 0.6%, Ti is 0.02 to 0.2%,
B must be controlled to 0.001-0.01%.

The amount of N added to the weld metal from the core wire can prevent the invasion of N in the atmosphere if the shield during welding is perfect, so that the amounts of N in the core wire and the weld metal are almost equivalent.
However, there is a limit to the upper limit addition amount of N, and it is inevitably determined by the contents of Cr, Mn, etc., which have a strong affinity with N. N
Is 0.1 in the core wire to improve high temperature strength and corrosion resistance.
%, But the maximum amount of N that can be solid-dissolved in the core wire is about 0.3%.

O (oxygen) decreases the yield rate of Cr, Mn, Nb, Ti, B, C, etc. added to the weld metal from the core wire or the coating agent, so it is indirect but high temperature strength. Since it affects various welding performances such as corrosion resistance and corrosion resistance, 0.002 to 0.
It is necessary to control to 025%.

Although Mg has an effect as a deoxidizing agent, if Mg is contained in the core wire in a predetermined amount or more, the melting rate of the core wire is increased, and as a result, arc breakage occurs frequently, so that welding is stably maintained. It becomes difficult to make it. Therefore, it is necessary to limit it to 0.01% or less.

The remaining components contained in the other core wires include Fe and unavoidable impurities.

Next, the reasons for limiting each component in the coating material will be described. C added to the weld metal is C in the core wire.
At the same time, it comes from C contained as an impurity in the coating agent and C contained in the carbonate. Therefore, if the addition sources of these C are not controlled to the proper ranges, the C of the weld metal
The content becomes unstable. For example, C increases the high-temperature strength, but when it exceeds the proper addition amount, the hot-cracking resistance remarkably deteriorates. Therefore, the control of the C amount is essential to stabilize the performance of the deposited metal.

The carbonate in the coating agent generates CO ₂ during welding to strengthen the spraying of the arc and improve the fluidity of the slag, but if too much, spatter frequently occurs and the bead shape also deteriorates. Therefore, it must be controlled to 15 to 45%. As the carbonate, calcium carbonate, magnesite, dolomite, barium carbonate or the like can be added.

SiO ₂ gives the molten slag an appropriate viscosity and improves the bead shape in all position welding, but if it is too much, the bead shape in the vertical position becomes convex, so 3 to 17%.
Need to The addition source of SiO ₂ is silica sand,
Potassium feldspar, sericite, water glass used as a fixing agent, etc.

Metal fluoride lowers the melting point and viscosity of slag,
Moreover, since the penetration is deepened, it is effective in preventing defective fusion and blowhole defects. However, if the amount is excessive, spatter frequently occurs, and the bead shape becomes convex, so it must be controlled to 5 to 30%.

The metal powder is added as an alloying agent and a deoxidizer for the purpose of adjusting the composition of the deposited metal.
r, Ni, Mn, Mo, Ti, Fe-Nb, Fe-B,
A powder having a particle size of 350 μm or less, such as Fe-Al. 1
% Or more, but if it exceeds 45%, the heat resistance of the coating material is significantly deteriorated, so the upper limit must be limited.

Since C in the carbonate is related to the amount of CO ₂ generated that protects the molten metal during welding, it is effective for shutting off the atmosphere and obtaining a stable weld metal component. Since the amount of CO ₂ generated by the carbonate during welding is proportional to the amount of C in the carbonate, it also affects the amount of C in the weld metal and the contents of other components. Therefore, control it to 2 to 5.5%. There must be.

C in the metal powder refers to the amount of C contained in the alloying agent or deoxidizing agent, and these C are easily retained in the deposited metal like C in the core wire, and the action thereof is also the same. And must be controlled to 0.001 to 0.2%.

Other components that can be added to the coating agent include
CaO, MgO, Al ₂ O ₃ , Na ₂ O, K ₂ O, Fe
O, MnO, TiO _{2 and the} like can be used alone or in combination of two or more types depending on the purpose of workability such as stability of arc, fluidity of slag, etc., but in any case, it is acceptable It is necessary that the range is 10% or less based on the total weight of the coating material so that the composition ratio of the essential components is not impaired.

The coverage means the ratio of the total weight of the coating agent to the total weight of the coated arc welding rod, which is too small,
If the amount is too large, the arc during welding will be unstable and the composition of the deposited metal will also vary. On the other hand, if the amount is too small, the welding rod will burn, and if the amount is too large, the amount of slag will be excessive. Therefore, it must be controlled within the range of 20 to 40%.

As described above, the coated arc welding rod for high nitrogen austenitic stainless steel according to the present invention has C and M in the core wire.
In a coating material in which components such as n, Ni, Cr, Mo, Nb, Ti, B, N, and O are controlled within appropriate amounts and at a predetermined ratio, carbonate, SiO ₂ , metal in the coating material By controlling the amount of C contained in carbonates and metal powders as well as controlling the amount of fluoride and metal powders within the proper range, a weld metal with high strength, high corrosion resistance and high temperature cracking resistance can be obtained even under high temperature and high pressure. Therefore, welding workability in all positions can be improved.

Here, referring to the method for producing a coated arc welding rod, a coating material mixed and mixed with a core wire is prepared and then a wet coating method is performed while adding a fixing agent (an aqueous solution of potassium silicate and sodium silicate) to the coating agent. Mix and paint around the core. After coating, drying and baking are performed at 150 to 400 ° C. for about 1 to 3 hours.

[0038]

EXAMPLES Examples of the present invention will be described below. The applicable steel type of the coated arc welding rod of the present invention is a high nitrogen austenitic stainless steel used in a high temperature environment, and other welding execution conditions are general ones which are not particularly different from those of a commercially available general-purpose stainless welding rod. Table 1 shows the chemical composition of the test core wire. Tables 2 to 5 show the compositions of coated arc welding rods obtained by combining the test core wire and the coating material. Table 6 shows the chemical composition of the base material used.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

[Table 6]

Tables 7 to 10 show the results of analysis, tensile test results, impact test results, side bending test results and hot cracking test results of the weld metal welded using the coated arc welding rods of Tables 2 to 5 and the base metal. , Corrosion resistance test results, X-ray test results, and welding workability test results are shown.

[0046]

[Table 7]

[0047]

[Table 8]

[0048]

[Table 9]

[0049]

[Table 10]

The welding method used was a welding rod having a rod diameter of 3.2 mm, a welding current of 70 to 100 A (AC), and an arc voltage of 21.
〜25V, welding speed 100〜250mm / min Fig. 1
The groove-shaped test plate shown in (1) was constrained by a jig, then the first pass was backside welded, and the top was laminated. In FIG.
The plate thickness t = 16 mm, the groove angle θ = 60 °, and the root face r = 1.5 mm. The welding workability test was performed in each of the downward and upright postures, but other tests were performed only in the downward direction.

In the hot cracking test, six macro test pieces for the cross section of the welded portion were sampled, wet-polished and etched, and then 100-2.
The presence or absence of cracks was observed with a microscope of 00 magnification. As the tensile test piece, a JIS Z3111 A2 test piece was sampled as shown in FIG. Impact test is 700 ° C x 1000 and 30
From the weld metal that has been aged for 00 hours, JI
A SZ3111 No. 4 test piece was collected. In the side bending test, a test piece having a thickness of 9.5 mm was sampled from the welded portion, and the bending ductility of the cross section of the welded portion was investigated under the conditions of a bending radius of 18 mm and a bending angle of 180 °.

In the corrosion resistance test, a test piece was sampled according to the procedure shown in FIG. 4, and a mixed gas (0.5%) assuming the environment of a coal-fired boiler was used.
SO ₂ + 5% O ₂ + 15% CO ₂ + bal. Artificial synthetic ash (1.5 mol K ₂ SO ₄ + under N ₂ atmosphere
1.5 mol Na ₂ SO ₄ +1.0 mol Fe ₂ O
_The corrosion weight loss was investigated under the condition of 700 ° C. × 100 hr in ₃ ). 2 to 4, 1 is a base material, 2 is a weld metal, and 3 is a test piece sampling position. For the X-ray test, take an X-ray transmission photograph of the weld and
It was evaluated according to the criteria of IS Z3104.

The covered arc welding rod symbol Nos. In Tables 2 to 5 and 7 to 10 1 to 21 are comparative examples,
No. 22 to 36 are the present invention. As is clear from Tables 7 to 10, No. 1 is 0.01% C in the core
And the C of the carbonate in the coating is less than 2%, the high temperature strength is too low. In addition, No. 2 has 0.12% C in the core
%, The carbon content of the carbonate in the coating material exceeded 5.5%, and the carbon content of the metal powder also exceeded 0.2%, so that high temperature cracking is likely to occur. In addition, No. 3 is 0.05 in the core wire
%, And Mn is also less than 0.5%, blow holes are likely to occur.

No. 4 is 0.5% Si in the core wire, T
Since i exceeds 0.2% and B exceeds 0.01%, hot cracking is likely to occur. In addition, No. 5 is M in the core
Since n exceeds 1.5%, the peelability of the slag is poor. In addition, No. In No. 6, since P in the core wire exceeds 0.01% and S exceeds 0.008%, hot cracking easily occurs. No. 7 is less than 22% Ni and 28% Cr
And toughness is low because Mo also exceeds 2.5%.

No. In No. 8, since Ni exceeds 28%, the stick burn resistance is poor. 9 is less than 18% Cr, M
Since o is also less than 0.5%, the high temperature strength is low. In addition, No. 1
In No. 0, Nb exceeds 0.6%, so high temperature cracking is likely to occur, and No. No. 11 has a low high temperature strength because N is less than 0.1%. In addition, No. In the case of No. 12 in which O was less than 0.002%, the yields of C, Si, Nb, Ti, and B were high, and thus hot cracking was likely to occur, and conversely O was more than 0.025%. No. 13 has low high temperature strength.

No. In No. 14, since Mg exceeds 0.01%, the arc is easily broken and it is unstable. Also N
o. In No. 15, since the carbonate content in the coating material is less than 15%, the arc is weak, and the fluidity of the slag is poor, so that a convex bead is easily formed. In addition, No. In No. 16, since the carbonate content exceeds 45%, there are many spatters and uniform beads cannot be obtained. In addition, No. No. 17 has a bad bead shape because SiO ₂ is less than 3%. Since 18 is over 17%, the workability in the vertical posture is poor.

No. No. 19 has poor slag fluidity because the metal fluoride content is less than 5%, and No. 19 exceeding 30%. 20 has a lot of spatter. In addition, No. In No. 21, since the metal powder exceeds 45%, the stick burn resistance is poor. On the other hand, N of the present invention
o. All of Nos. 22 to 36 have good strength, toughness and corrosion resistance, and have excellent X-ray performance, high temperature crack resistance and welding workability.

[0058]

As described above, the coated arc welding rod for high nitrogen austenite / stainless steel of the present invention is suitable for welding high nitrogen austenite / stainless steel used in high temperature / high pressure environments such as power plants. It is easy to prevent defects such as high temperature cracks, blowholes, and poor fusion, and the welded part has excellent strength, ductility, toughness, and corrosion resistance. Therefore, the work efficiency of the coated arc welding of high nitrogen austenitic stainless steel is improved, and a sound and high quality welded portion can be secured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a groove shape in a welding test of an example.

FIG. 2 is a sectional view showing a position where a tensile test piece of the deposited metal is taken.

FIG. 3 is a cross-sectional view showing an impact test piece sampling position of a weld metal.

FIG. 4 is a cross-sectional view showing a position where a corrosion test piece of a deposited metal is collected.

Claims (1)

[Claims] 1. C is 0.0 in% by weight based on the total weight of the core wire.
1 to 0.12%, Si 0.05 to 0.5%, Mn 0.5 to 1.5%, P 0.01% or less, S 0.00
8% or less, Ni is 22 to 28%, Cr is 18 to 28%,
Mo is 0.5 to 2.5%, Nb is 0.05 to 0.6%,
Ti is 0.02 to 0.2%, B is 0.001 to 0.01
%, N 0.1-0.3%, O 0.002-0.02
5%, Mg 0.01% or less, the balance Fe and the composition of unavoidable impurities around the core wire, 15 to 45% of carbonate, 3 to 17% of SiO ₂ , metal based on the total weight of the coating material. It contains 5 to 30% of fluoride and 1 to 45% of metal powder, and C in the carbonate is 2 to 5.5% and C in the metal powder is 0.
A coating arc welding rod for high nitrogen austenitic stainless steel, characterized in that a coating material of 001 to 0.2% is coated at a coating rate of 20 to 40%.