JPH07314178A - Gas shielded welding wire for austenitic stainless steel - Google Patents

Abstract

PURPOSE:To prevent generation of high-temp. crack without forming delta ferrite of welding metal by specifying the contents of C, Si, Mn, Cr, Ni, Cu, N and Mo, W, Zr, Ti, Nb and V in a wire compsn. and the value of pH. CONSTITUTION:The compsn. of the gas shielded welding wire for austenitic stainless steels is composed to contain, by weight %, <=0.03% C, 0.1 to 1.0% Si, 5 to 20% Mn, 12 to 20% Cr, 5 to 12% Ni, 0.02 to 5% Cu and 0.1 to 0.3% N, to contain one or >=2 kinds among 0.5 to 5.0% Mo, 0.5 to 5.0% W, 0.02 to 0.5% Zr, 0.02 to 0.5% Ti, 0.04 to 1.0% Nb, 0.08 to 2.0% V, is regulated to <=0.01% P and <=0.01% S and is composed of the balance inevitable impurities and Fe. Further, the value of pH expressed by formula: pH=Cr+Ni+Mo+30C +18N+1.5Si+0.5Nb is regulated to a range of 20 to 35. As a result, the service life at a high temp. is prolonged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding wire for austenitic stainless steel and high alloy steel for cryogenic applications such as nuclear fusion reactors, non-magnetic structures and fast breeder reactors, high temperature applications such as boiler vessels. . Further, these welding wires can also be used for general structures and for corrosion resistant steel.

[0002]

2. Description of the Related Art In the past, when austenitic stainless steel was welded, if the same composition as the base metal was welded completely, hot cracking would occur. It was usually generated. However, when δ ferrite is formed, there are problems such as deterioration of low temperature toughness due to δ ferrite itself, embrittlement due to σ phase generated at high temperature use, distribution of component elements, segregation, and deterioration of corrosion resistance. Therefore, the current situation is to reduce the harmful amount of δ-ferrite as much as possible and improve the characteristics while considering hot cracking.

For example, various welding wires have been proposed in which Mn is increased to 2 to 7%, P and S are reduced, or rare earth elements are added in order to improve hot crack resistance. (Japanese Patent Application Laid-Open Nos. 57-156894, 63-13692, and 59-10493). However, all of these techniques are premised on the formation of δ ferrite, and no consideration is given to cracks in the reheated portion of the weld metal. Further, since the applications are different, the characteristics of the weld metal cannot be satisfied in the prior art for thick plate welding for cryogenic temperatures or high temperatures, which is the object of the present invention. On the other hand, a completely austenitic weld metal has also been developed as a welding material for the purpose of improving cryogenic characteristics (Japanese Patent Laid-Open No. 58-58).
-97494), however, this was not sufficient in terms of welding construction of extremely thick material, since strength and weld hot cracking were not sufficiently considered.

On the other hand, a Ni-based alloy (for example, Inconel 625) having a small coefficient of thermal expansion and a low hot cracking property was also developed mainly for heat resistance, so that it has excellent toughness, but has sufficient yield strength for the purpose. There is a problem that it is not possible (for example, JP-A-47-42441 and 51-830).
31, ibid., 56-128696, etc.). Further, as a Ni-based welding material for high corrosion resistance and considering high temperature cracking property, a component containing 0.1 to 0.2% of nitrogen is disclosed (Japanese Patent Laid-Open No. 63-212091). Although it has a sufficient resistance to hot cracking when it has a relatively thin plate thickness, it does not have sufficient resistance to hot cracking for an extremely thick plate structure having a plate thickness of several tens of mm or more, which is the object of the present invention. Was enough.

[0005]

Claim 1 of the present invention
The structure targeted by the invention (hereinafter referred to as the first invention) relating to the present invention is mainly used in a cryogenic environment such as a liquefied gas storage container of 4K or 20K such as liquid He or liquid H ₂ or a superconducting device. In order to achieve high strength and high toughness at that temperature, nitrogen-containing austenitic stainless steels are mainly selected as candidates. However, since the plate thickness becomes extremely thick (100-400 mm) and the nitrogen content is large for improving the low temperature strength, the weld metal is in a state where welding hot cracking is very likely to occur. The first object of the present invention is to prevent hot cracking without forming δ ferrite in the weld metal in order to improve the toughness and non-magnetic properties of the weld metal at extremely low temperatures.

The invention according to claim 2 (hereinafter referred to as the second invention) is mainly intended for austenitic stainless steel for high temperature applications, but like the first invention, the weld metal has a σ phase when used at high temperatures. By eliminating the δ-ferrite that transforms and causes embrittlement, the use limitation of the structure, which has been limited by the properties of the weld metal, is improved, and the present invention prolongs the service life at high temperature. The second purpose is to raise the operating temperature in time.

[0007]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems, in which C: 0.03% or less by weight%,
Si: 0.1-1.0%, Mn: 5-20%, Cr: 1
2-20%, Ni: 5-12%, Cu: 0.02-5.
0%, N: 0.1 to 0.3%, Mo: 0.
5 to 5.0%, W: 05 to 5.0%, Zr: 0.02
~ 0.5%, Ti: 0.02-0.5%, Nb: 0.0
4 to 1.0%, V: 0.08 to 2.0%, one or more of P, 0.01% or less, S:
It is regulated to 0.01% or less, and PH shown in formula (1)
Is in the range of 20 or more and 35 or less, and the balance consists of unavoidable impurities and iron, which is a gas shield welding wire for austenitic stainless steel. PH = Cr + Ni + Mo + 30C + 18N + 1.5Si + 0.5Nb ・ ・ ・ ・ ・ ・ ・ ・ (1)

Further, in% by weight, C: 0.02%
Hereinafter, Si: 0.01 to 1.0%, Mn: 5 to 20, P
: 0.005-0.02%, Cr: 12-20%, N
i: 6 to 10%, Cu: 0.02 to 5.0%, Mo:
0.5 to 3.0%, N: 0.05 to 0.2%, W: 0.1 to 1.0%, Zr: 0.01 to 0.1
%, Ti: 0.01 to 0.1%, Nb: 0.02 to 0.
2%, V: 0.04 to 0.4%, one or more kinds are contained, and S: 0.01% or less is regulated, and PH shown in the formula (1) is 20 or more and 35 or more. A gas shield welding wire for austenitic stainless steel, characterized in that the balance is in the following range and the balance is inevitable impurities and iron.

[0009]

There are two types of cracks that occur in the weld metal of completely austenitic stainless steel: cracks during solidification and cracks in the reheated portion during multilayer welding, and both must be prevented during welding. Therefore, the present inventors have studied solidification cracking properties and reheat cracking of multi-layer welds, and have obtained the following findings.

First, in order to prevent cracking during solidification, if the amount of δ ferrite can be increased at the end of solidification, segregation and local solidification shrinkage can be reduced and cracking can be prevented. The present inventors have found that the Ni equivalent of the weld metal excluding Mn and Cr
It has been found that by limiting the sum of equal amounts and adding an appropriate amount of Mn, the amount of δ during solidification can be increased and austenite can be stabilized during cooling to eliminate δ ferrite.

Next, as a result of investigating cracks in the reheated portion by changing the composition of the welding wire, it was found that excessive nitrogen, carbon, etc. were accumulated and precipitated at the grain boundaries to cause the cracks. It was However, N is an essential element for improving strength at low and high temperatures, and as a result of further studies, the addition of carbonitride-forming elements such as Ti, Nb, and W results in the formation of intragranular precipitates. It was found that cracks can be prevented without significantly reducing nitrogen if the grain boundary precipitates are generated and reduced.

The reasons for limiting the components of the first invention of the present invention will be described below. First, C is an element that forms a solid solution in austenitic stainless steel weld metal to improve strength (proof stress), but combines with Cr, Mo or Nb and precipitates as carbides at grain boundaries to impair ductility and toughness. Since it is also harmful to hot cracking, 0.03% is made the upper limit, and the lower the range is, the more desirable.

Si is added as a deoxidizing element in the wire in an amount of 0.1% or more, but a large amount of Si promotes the formation of Fe--Cr--Mo intermetallic compound σ phase or carbide with Nb, Mo, etc. It is harmful to ductility, toughness and hot crack resistance. Therefore, the upper limit is set to 1.0%.

Mn is an element that plays a major role in preventing hot cracking, which is the main purpose of the present invention. A detailed study of the effect of Mn on the phase stability has revealed that it has an effect of increasing δ ferrite during solidification. An increase in the amount of δ ferrite in the weld metal during solidification is advantageous for solidification cracking. This effect becomes remarkable when Mn is added by 5% or more.
Further, Mn is an element that acts to stabilize austenite at normal temperature and low temperature range. However, excessive addition causes problems such as welding workability and fume problems, so the upper limit is made 20%.

Cr is added in an amount of 12% or more for the purpose of ensuring corrosion resistance, stabilizing austenite after low temperature processing, and forming a solid solution of N. However, if excessive, it stabilizes the δ phase during cooling from the solidification temperature to room temperature, In the present invention, the upper limit is set to 20% because the effect of γ-phase stabilization due to Mn at low temperatures is lost.

Ni is a stabilizing element of the austenite matrix and is added in an amount of 5% or more from the viewpoint of ensuring ductility and toughness. However, if it is excessive, δ ferrite is not formed during solidification and the hot cracking property is deteriorated. And

Cu, like Ni, is a stabilizing element of the austenite matrix. Usually, about 0.02% is mixed as an impurity. There is a case where it is added for stabilizing austenite, but when it is excessive, there is a risk that δ ferrite is not formed during solidification and the hot crack resistance is lowered, so the upper limit is made 5.0%.

N, like C, forms a solid solution in the matrix to improve the strength at low and high temperatures, but has a larger amount of solid solution than C and is an element which is hard to precipitate. In order to secure the strength, which is the main object of the present invention, 0.1% or more is necessary. However, since it is an austenite stabilizing element during solidification, it is limited to 0.3% or less from the viewpoint of hot cracking of the weld metal. However, Nb,
When nitrogen-fixing elements such as Ti, V and Mo are not added, precipitates are likely to occur at grain boundaries, so it is desirable that the content not exceed 0.25%.

Since Mo, W, Zr, Ti, Nb and V are all carbonitride forming elements, their main purpose is to prevent precipitation of carbon and nitrogen at grain boundaries and prevent reheat cracking. Seed or two or more types are added. It is also an element that has the effect of forming a solid solution in the matrix or forming a precipitate with C and N to improve the strength. However, excessive addition causes deterioration of toughness due to coarsening of precipitates and intermetallic compounds. Therefore, the range of the added amount of each element is Mo: 0.
5 to 5.0%, W: 0.5 to 5.0%, Zr: 0.02
~ 0.5%, Ti: 0.02-0.5%, Nb: 0.0
4 to 1.0% and V: 0.08 to 2.0%.

Since P and S are unavoidable impurities and promote high-temperature welding cracking, they are preferably as small as possible, and are each made 0.01% or less.

In addition to the above components and iron as the balance, Al, Ca, REM (rare earth element), etc. added as a deoxidizing agent and oxygen remain as inevitable impurities, but the deoxidizing agent has a workability of welding. It is preferable that the total amount is 0.1% or less because it lowers, and oxygen is 0.01% or less because it serves as a source of inclusions and lowers toughness.

PH defines the range in which the effect of preventing hot cracking and the effect of stabilizing austenite by the addition of Mn are remarkable. That is, when this PH value is small, Mn
However, even if Mn is added, it is difficult to stabilize the austenite phase against processing and external force. On the contrary, if Mn is added too much, the hot cracking property cannot be improved even if Mn is added. Therefore, P
The range of H is 20 to 35.

The base material of the first aspect of the present invention contains 0.02% or more of nitrogen in order to obtain a high yield strength at a low temperature, and has a plate thickness number such that solidification cracking and reheat cracking become a problem. 10 mm
The above austenitic stainless steels can be applied to ordinary stainless steel plates. Further, the welding method is intended for the TIG welding method having a low oxygen content and excellent toughness because the wire of the present invention is for cryogenic use, but if the main purpose is only hot crack prevention, it is generally used for MIG or the like. It can also be applied to gas shield welding.

Next, the reasons for limiting the components of the second invention will be described. C is an element that solid-dissolves and precipitates in the weld metal of austenitic stainless steel to improve the strength (proof stress), but since it has a low solubility, it is often added as Cr, Mo or Nb during aging (during use). They combine with each other and precipitate as carbides at grain boundaries, which impairs ductility and toughness, and is also harmful to hot cracking. Therefore, the upper limit is 0.02
%, And the lower the value is within the normal range, the more desirable.

Si is 0.01% as a deoxidizing element of the wire.
Although added as described above, a large amount of addition promotes the formation of Fe-Cr-Mo-based intermetallic compound σ phase or carbides with Nb and Mo, and is harmful to ductility, toughness, and hot crack resistance. Therefore, the upper limit is set to 1.0%.

Mn is an element that plays a major role in the prevention of hot cracking, which is the gist of the present invention. A detailed study of the effect of Mn on the phase stability has revealed that it has an effect of increasing δ ferrite during solidification. An increase in the amount of δ ferrite in the weld metal during solidification is advantageous for solidification cracking. This effect becomes remarkable when Mn is added by 5% or more.
Further, Mn is an element that works in the direction of stabilizing austenite in normal and low temperature regions. However, excessive addition causes problems such as welding workability and fume problems, so the upper limit is made 20%.

Like S, P is an element that promotes high temperature cracking, but at the same time, it has an effect of improving creep strength.
It is added in the range of 0.005% to 0.02%.

Cr is added in an amount of 12% or more for the purpose of ensuring corrosion resistance, stabilizing austenite after low-temperature working, and forming a solid solution of N. However, if excessive, it stabilizes the δ phase during cooling from solidification to normal temperature, The upper limit is set to 20% because the effect of Mn in stabilizing the austenite phase is lost.

Ni is a stabilizing element of the austenite matrix and is added in an amount of 6% or more from the viewpoint of ensuring ductility and toughness. However, if it is excessive, δ ferrite is not formed during solidification and the hot cracking resistance is deteriorated. Below.

Cu, like Ni, is a stabilizing element of the austenite matrix. Usually, about 0.02% is mixed as an impurity. It may be added for stabilizing austenite, but if it is excessive, δ-ferrite is not formed during solidification and there is a risk of decreasing hot crackability, so 5.0% is made the upper limit.

Mo is a solid solution in the matrix or C,
It is an element that has the effect of forming a precipitate with N and improving the strength. In the present invention, 0.5% or more is added to improve the high temperature creep strength. However, if excessive, it forms brittle intermetallic compounds such as LAVES phase during use at high temperature, resulting in deterioration of toughness and decrease in creep rupture strength.
The upper limit is 0%.

N, like C, forms a solid solution or precipitates in the matrix and improves the strength at high temperatures. Further, N is an austenite stabilizing element and has a larger amount of solid solution than C, and is an element that can be effectively utilized in various applications. In the present invention, 0.0 to improve high temperature strength and creep strength.
5% or more is added, but is 0.2% or less due to restrictions such as deterioration of toughness due to aging precipitation and deterioration of creep ductility.

W, Zr, Ti. Since Nb and V are both carbonitride-forming elements, one or more of them are added for the main purpose of preventing grain boundary precipitation of carbon and nitrogen and preventing reheat cracking. Further, both solid solution and precipitation also have the effect of improving strength. However, in order to prevent deterioration of toughness due to coarsening of precipitates and intermetallic compounds, the range of addition amount of each element is W: 0.1 to 1.0%, Zr: 0.
01-0.1%, Ti: 0.01-0.1%, Nb:
0.02-0.2% and V: 0.04-0.4%.

Since S is an unavoidable impurity and promotes high temperature cracking in welding, the smaller the content, the more desirable and 0.01% or less.

In addition to the above components and iron as the balance, Al, Ca, REM and the like added as deoxidizing agents and oxygen remain as unavoidable impurities, but deoxidizing agents reduce welding workability. The total is preferably 0.1% or less, and oxygen is preferably 0.01% or less because it serves as a source of inclusions.

PH defines a range in which the effect of preventing hot cracking by the addition of Mn and the effect of stabilizing austenite are remarkable. That is, when this PH value is small, Mn
However, even if Mn is added, it is difficult to stabilize the austenite phase against processing and external force. On the contrary, if Mn is added too much, the hot cracking property cannot be improved even if Mn is added. Therefore, P
The range of H is 20 to 35.

The base material to which the second invention is applied is such that nitrogen and Mo are added to obtain high temperature creep strength, and solidification cracking and reheat cracking become a problem.
The above austenitic stainless steels can be applied to ordinary stainless steel plates. Further, the welding method is intended for the TIG welding method, which has a low oxygen content and excellent toughness, since the wire of the present invention is an important structure such as a fast breeder reactor, but it is only intended to prevent hot cracking. Then, it can be applied to general gas shield welding such as MIG.

[0038]

【Example】

Example 1 First, an example of the first invention will be described. 1 shown in Table 1
9 kinds of austenitic stainless steel welding wires (1.
2 mm diameter) was created. No. in the table Nos. 1 to 10 are wires of the present invention, and 11 to 19 are welding wires for comparison.

[0039]

[Table 1]

As the base material, a stainless steel plate having the components shown in Table 2 and a plate thickness of 200 mm was used. Welding uses the TIG welding method,
Processed at an angle of 8.5 ° on one side and a root gap of 10 m
250A, 1 in the trapezoidal groove that is abutted as m
Lamination was performed under the conditions of 0 V and 12 cpm. The wire feed rate was 12 gr / min.

[0041]

[Table 2]

Table 3 shows the weldability of each studied wire and the result of the tensile test at 77K. With the wire of the present invention, it is possible to obtain a good weld without cracking, and to obtain a sufficiently large value in yield strength, tensile strength and toughness at low temperatures.

[0043]

[Table 3]

Embodiment 2 Next, the present invention will be explained with reference to an embodiment of the second invention. Table 4
16 types of austenitic stainless steel welding wires (1.2 mm diameter) shown in Table 1 were prepared. No. in the table Nos. 1 to 9 are the wires of the present invention. 10 to 16 are welding wires for comparison.

[0045]

[Table 4]

As the base material, a stainless steel plate having a plate thickness of 50 mm and having the components shown in Table 5 was used. For welding, a U-groove with a width of 12 mm and a depth of 25 mm is processed from one side on a steel plate with a depth of 50 mm, and 250
Lamination was performed with one pass per layer under the conditions of A, 10 V, and 12 cpm. The wire feed rate was 10 gr / min.

[0047]

[Table 5]

Table 6 shows the results of the evaluation of the weldability and the toughness after aging of each studied wire. With the wire of the present invention, a good weld having no cracks was obtained, and the toughness after aging at high temperature and the creep rupture strength were sufficiently large.

[0049]

[Table 6]

[0050]

As can be seen from the above examples, the welding of extremely thick cryogenic structures and the structures requiring creep strength can be performed without the formation of δ ferrite. As a result, a weld metal having excellent strength and toughness at extremely low temperatures and a weld metal having excellent creep strength at high temperatures and toughness after aging can be obtained. Further, the present invention is applicable not only to extremely low temperature and high temperature applications but also to all welding of austenitic steel materials, and the effect is very large.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Miyake 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division

Claims (2)

[Claims] 1. By weight%, C: 0.03% or less, Si: 0.1 to 1.0%, Mn: 5 to 20%, Cr: 12 to 20%, Ni: 5 to 12%, Cu : 0.02-5.0%, N: 0.1-0.3%, Mo: 0.5-5.0%, W: 0.5-5.0%, Zr: 0 0.02 to 0.5%, Ti: 0.02 to 0.5%, Nb: 0.04 to 1.0%, V: 0.08 to 2.0%, and one or more types are contained. P: 0.01% or less, S: 0.01% or less, and PH shown in the formula (1) is in the range of 20 or more and 35 or less, and the balance consists of inevitable impurities and iron. Gas shield welding wire for austenitic stainless steel, characterized by. PH = Cr + Ni + Mo + 30C + 18N + 1.5Si + 0.5Nb ・ ・ ・ ・ ・ ・ ・ ・ (1) 2. In% by weight, C: 0.02% or less, Si: 0.01 to 1.0%, Mn: 5 to 20%, P: 0.005 to 0.02%, Cr: 12 to 12. 20%, Ni: 6 to 10%, Cu: 0.02 to 5.0%, Mo: 0.5 to 3.0%, N: 0.05 to 0.2%, W: 0 1 to 1.0%, Zr: 0.01 to 0.1%, Ti: 0.01 to 0.1%, Nb: 0.02 to 0.2%, V: 0.04 to 0.4. %, S: 0.01% or less, and PH in the formula (1) is in the range of 20 or more and 35 or less, with the balance being unavoidable impurities and iron. A gas shield welding wire for austenitic stainless steel, which is characterized by comprising: PH = Cr + Ni + Mo + 30C + 18N + 1.5Si + 0.5Nb ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (1)