JPS5910493A - Wire for pure argon shielded gas welding of austenitic stainless steel for cryogenic temperature service - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the toughness of the deposited metal at a cryogenic temp. by using a wire of the compsn. contg. a small amt. of a rare earth element as a wire for pure Ar shielded gas welding of austenitic stainless steels for cryogenic temp. service. CONSTITUTION:The metal which contains >17% Cr, 8-25% Ni, <0.010% C, 0.2-0.7% Si, 0.5-6.0% Mn, <0.03% P, <0.006% S, 0.02-0.30% rare earth element, <0.010% O, <0.10% N or further <3% Mo and consists of the balance Fe and of which the amt. of delta ferrite calculated by the equation [1] is 0<=delta<=5- 500[C%] is used as a wire for pure Ar shielded gas welding of austenitic stainless steel to be used for a storage vessel or the like of ultra low temp. liquid such as liquid hydrogen, liquid helium. The deposited metal which mainteins the original toughness without deterioration even at a cryogenic temp. is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wire for pure argon-covered gas arc welding of austenitic stainless steel for cryogenic use, and in particular to a wire for pure argon shielded gas arc welding of austenitic stainless steel for cryogenic use. This relates to a TIG arc bath contact wire.

Originally, austenitic stainless steel does not cause brittle fracture even at low temperatures, so it is widely used as a steel material for cryogenic pressure vessels for storing LNG plants, liquid hydrogen, and liquid helium.Recently, technology such as VOD refining has advanced. Yop
Improvements have been made in the quality of the steel material, and the absorbed energy at -196°0 has reached more than 80JC9f-m.

On the other hand, conventionally used welding materials are mainly c.
This is r-Ni austenitic stainless steel welding wire, and according to this, the absorbed energy of the bath-deposited metal part at -196°C is approximately 5 kgf-m or less, and welding is difficult due to the imbalance in low-temperature toughness with the base metal. Improvements in materials are strongly desired.

It is already known that low oxygen and low δ ferrite are effective in improving the toughness of weld metal.

First, the low oxygen content of the bath metallurgical dance was published in Japanese Patent Application Publication No. 55-114469.
As shown in the latest publication, arc stability can be achieved by adding a rare earth element such as mitshu metal to the wire and performing pure argon shield MIG welding.

However, if δ ferrite is reduced, high temperature cracking) is likely to occur, so it is usually necessary to precipitate 3 to 8% δ ferrite, and therefore a material with a completely ausbunite structure has not yet been put to practical use.

In an experiment conducted by the inventors, pure argon shield... Oxygen is present in narrow gap MIG weld metal! i′ to 0.01
If the amount of δ ferrite was suppressed to 0'% or less, high toughness could be obtained even if the amount of δ ferrite was present at about ]θ%. (vE-□oa = 15
．． 8 to 9f-m 1 1. 600~ for the same yukata metal
When a reproducible thermal cycle of 8F and 10°C is applied (using a reproducible thermal cycle test device), the absorbed energy at -196"C is significantly reduced. vE,,6=8#
(below f'-m), the cause of this was investigated using an electron microscope, etc., and δ
It turned out that this is because carbide precipitates in the ferrite part, which becomes the fracture path.

Also, for the same reason, pure argon shield multilayer distribution WI
It was found that in G bath welding, the absorbed energy of the welded metal part that actually underwent the reheating cycle of the next bath deteriorated significantly.

This is a new finding that cannot be ignored in an impact test even if it is not a problem in a static test such as the sulfuric acid-copper sulfate test; rather, the absolute value of absorbed energy is This is a problem that has become even more obvious as the price has increased.

For this reason, it is essential to develop a pure argon-shielded MIG arc welding wire that can prevent embrittlement, including in the reheated part, and obtain sound weld metal.

Now, in commonly practiced inert gas shielded MIG arc welding, Ar gas, H
Inert gas such as e gas, 02 gas or 00. Arc welding is carried out in a gas atmosphere to which an appropriate amount of active gas such as gas is added, but in this case the oxygen content in the weld metal increases and it is possible to obtain a low-oxygen weld metal as aimed at by this invention. Therefore, pure argon shielded MIG arc welding is only possible by adding rare earth elements as mentioned earlier to achieve low oxygen content and stabilize the arc. obtain.

In addition to improving toughness by reducing oxygen as described above, the purpose of this invention is to prevent the precipitation of carbides due to the reheating cycle conventionally involved in this case, and to reduce the Charpy energy yield of the weld metal. We aim to provide an excellent cryogenic austenitic stainless steel wire for pure argon encapsulated gas arc welding! ...It's something.

The idea of this invention originates from the discovery that the decrease in toughness at extremely low temperatures due to the above-mentioned reheating cycle causes carbide precipitation in δ ferrite, which becomes the fracture path of the impact S test piece. ing.

This invention has image toughness even after undergoing a reheat cycle,
In order to obtain a melt-gradient metal sheet with good welding solidification and brittleness resistance,
The present invention provides a wire for pure argon encapsulated gas arc welding, which contains 1% by weight of pure argon gas encapsulated arc welding material of high toughness austenitic stainless steel for cryogenic use. 0.010% or less,
Si: O12-0.7%.

In: 0.5~f1. o%, P: 0.08%
Below, S: 0.006% or less, N1: 8-25%, rare earth element: 0.02-0.80% alloy Alloy 0: 0.0
10% or less, N: '・0.10% or more, containing at least 17% Or and furthermore 8% or less MO, with the remainder substantially consisting of Fe and unavoidable impurities,
And the amount of δ ferrite (%) calculated by the following formula is 0≦a
By satisfying the condition that ≦5-500 (0%), the problem in p1 above (7) is effectively solved.

Recorded δ ferrite-L2 (1,b・C81%']+[01%
)+[MO%])-2,5(ao-([0%]+[N%
) ) +0.5・CMn%〕10 [Ni%]) −24,
7 The inventors first conducted an experiment to clarify the acid accumulation in the steel necessary to maintain its toughness at extremely low temperatures.

That is, SUS 8] 6L steel plate (20tX
”'150 X8001ai+) with a depth of 18m
m, tip radius R = 4.5 mm, machined a U groove, 0:
0.005%, S, al%, Kn:
2.42%, P: 0.01
7%, S: (1,008%, Ni:
18.55%, Or: 18.19%1MO:1.
96%, rare earth elements: 0.050%, 0:0.
Ar +00° gas in pure argon atmosphere and 002 gas mixture ratio e1%, 8%, and 5% using 1,1174 ml wire with a chemical composition containing 0.060%, 1 N: 0.0818%. MIG arc welding is performed in an atmosphere, and the immersion liquid conditions are: current a i o A *
Eight passes of welding were performed at a voltage of 29■ and a welding speed of 20(8) degrees and 30α/min.

The Charpy absorbed energy at -196''0 of the welded wire mesh produced by the experiment was investigated, and the results are shown in Table 1 along with the oxygen content of the welded metal.

Table 1 Here, the standard values for cryogenic toughness are l”12.1 and 91.
f・m or more, but the absorbed energy of the steel material is -]96
``C has a characteristic of 80kflf-m or more, so in consideration of the safety of the welded part, it should be 1/8 or more of the base metal.
...10 kl? The criterion was f−m or higher. Table 1
The absorbed energy is 101c only when the oxygen content of the weld metal is 0.010% or less! 17 f-m or more, and has excellent low-temperature toughness.

It was found that the oxygen content of the deposited metal welded with a pure argon gas shield was the same as that in the wire.

Next, we conducted the following experiment to clarify the C content and δ ferrite content required in the wire to obtain high toughness without causing embrittlement even after being subjected to a reheat cycle. .

That is, 5US816L steel plate (20'X] 50wxa
0 (D
WIG arc welding was performed in a pure argon gas atmosphere using a 1.2-diameter welding wire.

Welding conditions are current 810A, voltage 29■, welding speed 1 degree 25
One bus welding was performed at cyn/min.

A half-size Charpy impact test piece (5 x 10 x 55 mm) which had been subjected to one welding cycle and an 850° 0 reproducible thermal cycle was taken, and an impact test was conducted at -196° 0.

This reproducible thermal cycle is a reproducible thermal cycle test rack fft, the temperature is raised to 85θ℃ in 6 seconds, and there is no holding time, 850℃
The test conditions were set such that the total cooling time from the temperature to 500'O was 24 seconds, and the cooling time to 800°C was 90 seconds.

To calculate the amount of δ ferrite, the formula listed above on page 8 from Tillon's organizational chart was introduced and used.

The absorbed energy (half size) at 196° C. of the deposited metal obtained through the experiment was investigated and is shown in Table 8.

(]1) Table 8 The criteria for determining cryogenic toughness is that the test piece is of no size, so the above-mentioned %, or absorbed energy, is 5 kg.
Toughness of f-rn or higher was defined as high toughness.

All of the as-welded specimens exhibited absorbed energy of 9 f-m or more and exhibited excellent low-temperature toughness. However, when subjected to a simulated thermal cycle [7], the test specimens using wires other than the invention were significantly brittle.

As mentioned above, in the equilibration test, the carbide precipitated in the δ-ferrite part becomes the fracture path, so in order to prevent reheat embrittlement, it is necessary to reduce the C content at the same time as reducing the amount of δ-ferrite. becomes.

Carbide precipitation at δ ferrite grain boundaries in r/δ structure and γ/r
The time required for carbide precipitation to the r-grain boundaries of the structure is approximately 1/1° for the AiJ type and the latter type. Therefore, in the case of a short time period such as a bath welding reheat cycle, the reduction of δ ferrite 1' has a great effect in suppressing the precipitation of carbides.

Reducing the absolute value of the 1'cG content can reduce carbide precipitation and is effective in preventing reheat embrittlement.

In order to clarify this relationship, FIG. 1 shows the relationship between the absorbed energy, the C content, and the amount of δ ferra 2...ite after a simulated thermal cycle test. In Figure 1, the upper limit of the amount of δ ferrite that can obtain a sieving toughness of 5 to 9 f/m or more with 1 absorbed energy (half-size test piece) is determined by the relationship between the C content and the amount of δ ferrite (%). In addition, if the amount of δ ferrite becomes negative, solidification cracks occur, so the lower limit of the amount of δ ferrite (%) was limited to 0≦δ.

The range where particularly high toughness can be obtained is 0; 0.005%
and δ ferrite: 0 to 2%.
1Q Here, the inventors investigated the high temperature cracks in the region where the amount of δ ferrite is low from 0 to a%.
This was prevented by reducing the S1 content and simultaneously adding rare earth elements to form (MnRE)S.

As mentioned above, in order to put into practical use the limitation of the oxygen content and the amount of 0-containing 1-3 and δ ferrite in the welding wire, and to obtain a bath-deposited metal with excellent tenacity even after being subjected to a reheating cycle, welding wire Other compositional limitations are also necessary. The reason for this limitation is as follows.

For 0, as already mentioned, 0.010% is 20
If it exceeds 0.010%, it is impossible to avoid reheat embrittlement.
Upper limit.

Si is a deoxidizing element for welded gold implants, and if it is less than 0.2%, the yield of Qr will decrease, so the lower limit is set at 0.2% in the wire.
%. In addition, if the amount of δ ferrite is low, it is 0.7
If the content exceeds 0.7%, high-temperature cracks will occur, so to prevent this, the content is limited to 0.7% or less in the wire.

In is effective in preventing high temperature cracking, but has a low 0-Ni-Q
In the r-14n stainless steel phase diagram, Or is 1.
When Mn exceeds about 16%, Mn appears as a ferrite-forming element when Mn is 7 to 8% or more.
If it is less than 0%, the yield of Or will decrease.
．． It was limited to a range of 5 to 6.0%.

If P exceeds 0.0a%, high temperature fragility resistance deteriorates, so P is limited to 0.08% or less in the wire.

If S exceeds 0.006%, the high temperature brittleness resistance will deteriorate if the δ ferrite is low, so S should be 0.006% in the wire.
・Limited to below %.

N1 is a typical austenite stabilizing element and is effective in improving the settlement of the austenite grain matrix. Mn is 6
If the content is less than 8%, a large amount of δ ferrite will be produced in the case of martensite in the austenite, which will deteriorate the toughness, so the lower limit was set to 8% or more in the wire.

However, since it is also an element that increases sensitivity to cracking, the upper limit in the wire was set at 25%.

Rare earth elements of 0.02% or more are significantly effective in stabilizing the arc.
However, if it exceeds 0.30%, nonmetallic inclusions tend to increase and the toughness tends to deteriorate, so it was limited to 0.02 to 0.30% in the wire.

If N exceeds 0.10%, pores are likely to be generated, so N is limited to 0.10% or less in the wire.

As is clear from Schiefler's phase diagram, less than 17% of Or produces martensite and deteriorates toughness, so it is necessary to contain at least 17% in the wire.
In addition, if it exceeds 26%, it will promote the precipitation of carbides.
6% or less is desirable. ...MO is effective in increasing room temperature strength, but if it exceeds 3%, the toughness decreases, so it is limited to 8% or less in the wire E7.

Next, an example will be described.

Example] The chemical component is O: 0,005% by weight (therefore, (6-5
oo・Co%]=2.5)), Si: 0
．． 82%, Mn:z, 81%, P: 0.01
6%, s: o, ooa%, Ni: 10.88%
, Or: 18.410%, rare earth element: 0.0
515%, N: 0.0478%, o: o,
Using a 1.21 AIip wire with a
The groove 1 shown in the figure was heated to a current of 8] OA.

Voltage 29v, welding speed 3Q CTI /□1o 3rd
As shown in the figure, pure argon shielded gas arc welding was performed on the multilayer welding, and the metal deposited in the bath was investigated. In FIG. 1..., 2 is the welding base material, 8 is each pass of multilayer distribution, and 4 is the impact test piece sampling position. Table 4 lists the chemical composition of the deposited metal and the Charpy absorbed energy for the notch positions f&l shown in Figure 8, 5.6.

From Table 4, the Charpy absorbed energy is at the notch position 2.1.
When placed in position 6, which was subjected to multiple electric reheating cycles, the result was 14.7 kgf-m, indicating excellent low-temperature toughness.

Example 2 Welding was carried out under the same conditions as in Example 1 using the flat 7 wire (δ ferrite content: 1.6%) shown in Table 1. The investigation results of the weld metal are also shown in Table 4, and the Charpy absorbed energy is 14.1 kf-m even when the notch position txt is placed at position 6, which has undergone multiple reheat cycles, indicating excellent low-temperature toughness. I have a meeting.

As is clear from the above embodiments, this invention stabilizes the arc by adding components, particularly rare earth elements, to the welding wire, enables pure argon shielded gas arc welding, and limits the oxygen content in the wire to a low level. In addition, by introducing a relational expression between the amount of δ ferrite and C content that can prevent reheat embrittlement due to carbide precipitation5, and by limiting this, the low temperature toughness of welds of austenitic stainless steel for cryogenic use is greatly improved. can.

In the embodiments, pure argon shielded WIG arc welding is described, but the present invention is not limited to this and can be similarly applied to TIG arc welding.

[Brief explanation of drawings]

Figure 1 is a chart showing the relationship between absorbed energy 15-, 0 content, and δ ferrite amount after a simulated thermal cycle test, Figure 2 is a cross-sectional view showing the groove shape, and Figure 8 is the procedure for collecting Charpy test pieces. FIG.

Claims (1)

[Claims] L O: 0.010% or less, Si; 0.
2-067 weight 1%, In: o, 5-6.0 weight %
, P: 0.08%, S: 0.00
6% by weight or less, N18-25% by weight, rare earth elements:
Contains 1% by weight of 0.02-0.80, O: 0.0101
0 heavy lid, N: 11 □ 0.10 heavy lid % or less ■ has an austenitic stainless steel composition containing at least 17 heavy yield of Or, and δ divided by the following formula (1) A wire for pure argon encapsulated gas welding of austenitic stainless steel for extremely low temperatures, with ferrite it (%) of 0≦δ≦5-500 [0%]. δ −8,2−(1,5−[81%'] + [Or
%] ) -2,5-(80-((0%) 10 [N%) )
+ o, 5-(:Mn%] + [N soil%) J-24,7
...(1) Long 0: 0.010 insect cover% or less,
si-: 0.2~0°7 heavy lid%, In: 0
．． 5-6.0% by weight, P: 0. Oa weight% or less, S: 0.006 weight% or less, N1:8
~25% by weight, rare earth elements: O,02~0.8G l
"Including weight%, O: 0.010% by weight or less, N: 0
．． 10% by weight or less and at least 17% by weight of Or
The composition is an austenitic stainless steel containing 8% by weight or less of MO, and δ ferrite 1. calculated by tt using the following formula (2). A wire for pure argon encapsulated gas welding of austenitic stainless steel for cryogenic use, in which (%) 1 is 0≦δ≦5-500·[C%]. δ= 8.2- (1,5-[Si%] 10[Cr%'E
+CIO%])=2.5・(8011([C%]+[
N%)) +0.5・[Mn%]+[Ni%]) -24
,7-(2)