JPS6313692A - Wire for welding austenitic stainless steel - Google Patents

Abstract

PURPOSE:To improve high-temp. cracking resistance and elongation at creep rupture by incorporating Ni, Cr, Zr, etc., respectively at specific weight % into the titled wire, consisting the balance of Fe and further limiting Nb, Ti, etc., as impurities to prescribed % of below. CONSTITUTION:C is incorporated at 0.04-0.1wt%, Mn at 0.5-5%, Ni at 8-12%, Cr at 18-22%, N at 0.01-0.06%, and Zr at 0.01-0.5% as the component compsn. of the wire into said wire. The balance thereof is composed substantially of Fe and inevitable impurities. The inevitable impurities are so limited that P is incorporated therein at <=0.03%, S at <=0.02%, Nb at <=0.04%, V at <=0.2%, O at <=0.04%, Ti at <=0.05%, and Al at <=0.15. The components such as Mn and N of the above-mentioned component compsn. improve the high-temp. cracking resistance. The elongation at creep rupture is remarkably improved by limiting the Zr component and the limitation of the impurities.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an austenitic stainless steel welding wire, and more particularly to a weld metal that has good hot cracking resistance, creep rupture strength, and creep rupture elongation. The present invention relates to an austenitic stainless steel welding wire that provides the following properties.

[Prior Art] Stainless steel is an alloy steel that has significantly superior corrosion resistance and heat resistance compared to carbon steel, and also has excellent mechanical properties and workability. Stainless steels are classified into martensitic, ferritic, and austenitic stainless steels depending on their metal structure, and austenitic stainless steels in particular have extremely superior corrosion resistance and high-temperature strength compared to other stainless steels. . Therefore, austenitic stainless steel is widely used not only as a structural material that requires corrosion resistance, such as in various chemical equipment, but also as a structural material that requires both corrosion resistance and high-temperature strength, such as in power plants. It is used.

On the other hand, power generation plants are transitioning from conventional oil and coal-fired thermal power generation to nuclear power generation. Nuclear power generation is more economical than thermal power generation, and has achieved remarkable development as a stable energy source. There is. In nuclear power generation as well, development is progressing from light water reactors whose core is cooled with ordinary water to fast breeder reactors that use not only U235 but also PU239 as nuclear fuel to increase the breeding ratio.

In fast breeder reactors, liquid metals such as Na and Na- are used as heat transfer media, and in order to increase power generation efficiency, the core temperature is higher than that of conventional light water reactors ( (about 400-600℃). Therefore, in fast breeder reactors, both corrosion resistance and high temperature strength are taken into consideration.
Almost everything is made of austenitic stainless steel, with the exception of some parts such as the steam generator.

[Problems to be Solved by the Invention] As mentioned above, austenitic stainless steel is used as a structural material that requires excellent corrosion resistance and high-temperature strength, but some problems remain in weldability. ing. That is, when welding austenitic stainless steel as a base material, a welding wire having approximately the same chemical composition as the base material has conventionally been used as the welding material.
There was a problem in that the creep rupture strength and creep rupture elongation of the weld metal in the welded part were lower than that of the base metal.

As a result, especially in equipment such as the fast breeder reactor mentioned above, which is used in the creep region and where large strains are applied to the members due to thermal stress, there is a risk of strain concentrating on the welds, leading to failure accidents, and structural design considerations This was a major obstacle.

To solve these problems, various techniques have been proposed to add alloying elements such as C, Nb, Ti, V, and Mo to welding wires in order to increase the creep rupture strength of weld metal. ing. It is true that these techniques are considered to be effective to some extent if viewed only from the perspective of increasing creep rupture strength.

However, these technologies tend to significantly reduce creep rupture elongation while improving creep rupture strength, and are not suitable for applications such as fast breeder reactors that require excellent properties in both creep rupture strength and creep rupture elongation. However, these techniques are still insufficient.

Therefore, the object of the present invention is to develop the best austenitic stainless steel f which can provide a weld metal that has creep rupture strength comparable to that of the base metal and exhibits excellent creep rupture elongation.
14 welding wire.

[Means for Solving the Problems] The present invention provides C: 0.04 to 0.1% (weight%, same hereinafter), Si: 0.2 to 1%, Mn: 0.5 to 5.
%, Ni: 8-12%, Cr: 18-22%,
N: 0.01-0.06% and Zr: 0.0
Contains 1 to 0.5% as an essential component, with the remainder being substantially F.
e and unavoidable impurities, and as the unavoidable impurities, P
:50.03%, S: 0.02%, Nb:≦0,0
4%, V: 50.2%, 0: 50.04%, Ti: 50
．． The main point is that the content is limited to 0.05% and Al: 50.1%.

[Function] In order to obtain a weld metal that has creep rupture strength comparable to that of the base metal and exhibits excellent creep rupture elongation,
The effects of adding various alloying elements to welding wire were investigated in detail. As a result, when welding is performed using a welding wire with the above configuration, especially when 5US308 type austenitic stainless steel is used as the base material, the best values for both creep rupture strength and creep rupture elongation of the weld metal can be obtained. This led to the completion of the present invention.

The reasons for specifying the types and contents of essential alloying elements in the present invention will be explained in detail below.

C: 0.04-0.1% C is an austenite-forming element and an essential element for increasing high temperature strength and creep rupture strength, and for this purpose, it is necessary to contain at least 0.04%.

However, too much C not only increases hot cracking susceptibility, but also significantly reduces corrosion resistance, which is an inherent characteristic of stainless steel, so it is necessary to suppress it to 0.1% or less.

Si: 0.2-1% Si addition is particularly effective on the wettability of weld metal, and 0.2% or more is necessary to prevent welding defects such as poor fusion even in narrow gap welding. . However, too much St tends to cause zero embrittlement and causes a decrease in ductility, so it is necessary to suppress it to 1% or less.

Mn: 0.5 to 5% Mn gi addition is effective for deoxidizing, and is also effective for fixing S and improving hot cracking resistance, and 0.5% or more is necessary. However, if there is too much Mn, the amount of δ-ferrite decreases and the hot cracking resistance decreases, so it is necessary to suppress it to 5% or less.

Ni: 8 to 12% Ni is an austenite-forming element and has the effect of increasing corrosion resistance, so 8% or more is required. However, if there is too much Ni, the amount of δ-ferrite in the weld metal decreases and the hot cracking resistance deteriorates, so it is necessary to suppress it to 12% or less.

Cr: 18-22% Cr is an austenite-forming element like Ni, and is the most effective element for obtaining high corrosion resistance of weld metal, and 18% or more is required. However, if the Cr content exceeds 22%, σ embrittlement tends to occur and the ductility decreases significantly, so it is necessary to suppress it to 22% or less.

N: 0.01-0.06% N has a great effect of forming nitrides and increasing high-temperature strength.
It also has the effect of increasing creep rupture strength, and
．． 01% or more is necessary. However, if N is too large, the creep rupture elongation and impact value will decrease, and welding defects such as blowholes will occur, so it is necessary to suppress the content to 0.06% or less.

Zr: 0.01-0.5% The present invention was made in order to obtain excellent creep rupture elongation of weld metal, and for this purpose, Zr is added to the welding wire.
It is necessary to include r as an essential component. Therefore, the greatest feature of the present invention is that the welding wire contains Zr. That is, Zr has a large deoxidizing effect and is effective in obtaining a highly clean weld metal, and also has the effect of making the crystal grains finer, so it is highly effective in improving the creep rupture elongation of the weld metal. In order to achieve such an effect, it is necessary to contain Zr at least 0.01%.

However, even if more than 0.5% of Zr is added, the effect commensurate with the amount added cannot be obtained, and on the contrary, the amount of slag generated increases, the conformability of the weld metal decreases, and poor fusion may occur. Become. Therefore, in the present invention, the amount of Zr added is from 0.01 to
It was defined as 0.5%.

The welding wire according to the present invention contains the above-mentioned alloying elements as essential components, and also contains P, S, Nb, V, and O as other inevitable impurities.

It is unavoidable that elements such as Ti and A1 are contained in minute amounts.

Regarding Nb, V, and Ti among these elements, as already mentioned, there is a technique for intentionally incorporating these elements to improve creep rupture strength. As already pointed out, although these elements are effective in improving creep rupture strength, they also have the disadvantage of decreasing creep rupture elongation.

As is clear from the above-mentioned purpose, the present invention has been made with the aim of improving not only the high temperature strength and creep rupture strength of weld metal, but also particularly the creep rupture elongation of weld metal. Therefore, in the present invention, elements such as Nb, V, Ti, etc. that cause a decrease in creep rupture elongation are regarded as impurities even if they are effective in improving creep rupture strength.

However, elements such as Nb, V, and Ti are originally impurities in stainless steel at 0.1% and 0.3%, respectively.

It was contained at about 0.1%. In other words, all of these elements are contained in the raw materials used during melting, and their amounts vary depending on the raw materials used, and their amounts are generally not controlled. Ta.

In the present invention, Nb and V are used for the reasons mentioned above.

It is necessary to reduce Ti, but in order not to have a negative effect on creep rupture elongation, Nb: 60.04%, ■: ≦0
．． It is necessary to limit the content to 2% and Ti: 50.05%, respectively.

In order to effectively achieve the effects of the present invention, the above Nb, V,
In addition to inevitable impurities such as Ti, p and s.

It is necessary to limit unavoidable impurities such as 0 and A1 to below a certain value. The effects of these unavoidable impurities on weld metal will be outlined.

P:≦0.03%, S:0.02% Both P and S are elements that tend to form low melting point compounds, and significantly reduce hot cracking resistance.

Therefore, in order to avoid such adverse effects, it is necessary to limit P to at least 0.03% or less and S to 0.02% or less.

0:50.04% O tends to form metal inclusions and significantly reduces creep rupture elongation, so it is necessary to limit it to 0.04% or less.

Al: 50.1% If AI exceeds 5, the amount of slag generated will increase, reducing welding workability and decreasing creep rupture elongation, so 0.1
% or less.

[Example] Welding wires (1, 2) with various chemical compositions shown in Table 1 below
Perform TIG welding under the following welding conditions using
A creep rupture test was conducted at 550° C., and the 1000 hour creep rupture strength and 1000 hour elongation at break were determined. The results are also listed in Table 1. 5 used as the test base material
The chemical composition of US304 steel is shown in Table 2 below. Further, the groove shape during welding is shown in FIG. 4, and the test piece sampling position is shown in FIG. 4 by a broken line.

[Welding conditions] Test base material: 5US304 (20mmt) Welding current:
20OA (DC3P) Welding voltage: 11v Welding speed: 10 cm/min Shielding gas: Ar Based on the results in Table 1 above, the following considerations can be made.

(1) Wire No. 1.2 shows the influence of C. When wire No. 2 having a C content lower than 0.04% was used, good values were obtained for creep rupture elongation, but only low values for creep rupture strength were obtained. Furthermore, when wire No. 2 with a C content higher than 0.1% was used, the creep rupture elongation decreased significantly.

(2) Wire No. 3. 4 shows the influence of St. Wire No. whose St content is lower than 0.2%,
When No. 3 was used, the bead conformability was poor and welding workability was poor. Further, when wire No. 4 having a St content higher than 1% was used, there was no problem in welding workability, but only a low creep rupture elongation was obtained.

(3) Wire No. 5. 6 shows the influence of Mn. Wire N0 with Mn content lower than 0.5%
When No. 15 was used, blowholes were generated during horizontal welding because a sufficient deoxidizing effect could not be obtained.

Furthermore, when wire No. 6 with a Mn content higher than 5% was used, hot cracking occurred during welding.

(4) Wire No. 7.8 shows the effect of Ni. Wire No. with Ni content lower than 8%.

When No. 7 was used, an abnormal metal structure was obtained in which martensite was generated in the weld metal. Furthermore, when wire No. 8 with a Ni content higher than 12% was used, hot cracking occurred during welding.

(5) Wire No. 7.9 shows the influence of Cr. When wire N017 with a Cr content lower than 18% was used, martensite was generated in the weld metal. Further, when wire No. 19 with a Cr content higher than 22% was used, only a low creep rupture elongation was obtained.

(6) Wire No. 10.11 shows the influence of N. Wire No. 1 with N content lower than 0.01%
When 0 was used, sufficient leap rupture strength could not be obtained. Also, wire N with a higher N content than 0.06%
When using No. 0 and No. 11, only a low creep rupture elongation was obtained.

(7) Wire No. 12.13 shows the influence of Zr. Wire No. with Zr content lower than 0.01%
, 12, no effect of Zr on creep rupture elongation improvement was observed. In addition, the Zr content is 0.5
When wire No. 13 having a higher than % was used, although the effect of improving creep rupture elongation was found to be excellent, the amount of slag generated during welding was large and welding workability was poor.

(8) Wire No. 14 shows the effect of Nb. Wire No. with Nb content higher than 0.04%.

When No. 14 was used, a decrease in creep rupture elongation was observed.

(9) In contrast to the comparative examples described in (1) to (8) above, wire Nos. 15 to 18 are examples that satisfy all the component composition ranges defined by the present invention. These wires N0115
- 18, weld metals comparable in creep rupture strength and creep rupture elongation to the base metal were obtained in all cases.

(lO) Furthermore, when comparing the creep characteristics after solution treatment with wire No. 12.15, wire No.

It is understood that when No. 15 was used, a relatively good leap elongation at break was obtained even after the solution treatment.

In the above embodiment, TI using Ar as the shielding gas was used.
Although we considered the case of G welding, wire No.
15 to 18 as shielding gas (Ar+2%0
2) or (Ar + 5% 02), submerged arc welding using sintered flux, and coated arc welding coated with lime titania type coating material. Creep rupture tests were also conducted for each case. In each case, effects almost the same as those shown in Table 1 were obtained.

[Effects of the Invention] As described above, according to the present invention, by employing the above-described structure, an austenitic weld metal that is excellent in hot cracking resistance, creep rupture strength, and creep rupture elongation can be obtained. A wire for stainless steel welding has been realized.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the groove shape and the test piece sampling position.

Claims (1)

[Claims] C: 0.04 to 0.1% (weight%, same below), Si:
0.2-1%, Mn: 0.5-5%, Ni: 8-12%
, Cr: 18-22%, N: 0.01-0.0
6% and Zr: 0.01 to 0.5% as essential components, and the remainder is substantially Fe and unavoidable impurities, and the unavoidable impurities include P: ≦0.03% and S: 0.02%.
, Nb:≦0.04%, V:≦0.2%, O:≦0.0
4%, Ti: ≦0.05%, and Al: ≦0.1%.