JPS5897494A - Submerged arc welding method for austenitic stainless steel for ultra-low temperature service - Google Patents

Abstract

PURPOSE:To obtain deposited metal having excellent low temp. toughness by specifying the components in a welding flux and deposited metal. CONSTITUTION:The components of a flux contain, by weight %, 40-60% CaF2, 20-30%Al2O3, 5-15% CaO or MgO, and 5-15% SiO2 and further contain <=5% MnO and <=10% Cr2O3. By using such flux and an austenitic stainless steel electrode, the deposited metal which contains <=0.08% C, 0.2-0.7% Si, 0.5-6% Mn, <=0.03% P, <=0.006% S, >=17% Cr, <=3% Mo, <=0.035% oxygen, and <=0.1% nitrogen and of which the content of delta ferrite calculated by the equation Iis negative is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a submerged arc welding method for cryogenic austenitic stainless steel, and more particularly to a welding method that exhibits excellent absorbed energy in the Charpy impact test of weld metal.

Since austenitic stainless steel does not cause brittle fracture even at low temperatures, the same welding materials as at room temperature have been used when used at extremely low temperatures.

However, in recent years, due to improvements in the material of steel sheets, the relatively low absorbed energy of welded metal has become a noticeable problem.

Table 1 shows the absorbed energy at 196℃ for each part of 5US316L, 200m thick silver copper welded by submerged arc welding. Compared to this, the weld metal is only 3
It is only kgf-m.

Table 1 On the other hand, there is a research report on the toughness of weld metal that shows that high toughness can be obtained with low oxygen and low δ ferrite. It has not yet been put to practical use because the properties of this material decrease, and reducing the amount of δ ferrite tends to cause high-temperature cracking.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a submerged arc welding method for austenitic stainless steel for ultra-low grooves in which the Charpy absorbed energy of the weld metal is excellent.

The gist of the present invention is as follows.

That is, CaF2: 40 to 60% by weight, Ago,
:20-30%, CaO or MgO: 5-15%,
Sin: 5 to 15%, further 5% if necessary
C:0 using a flux containing the following Mn0110% or less Cr, 03 and an austenitic stainless steel electrode.
．． 08% or less, Si: 0.2-0.7%, Mn: 0
5-6%, P: 0.03% or less, S: 0.006. % or less, Cr: 17% or more, MO: 3% or less, oxygen: 0
．． Submerged austenitic stainless steel for cryogenic use characterized by obtaining a deposited metal containing 0.035% U, nitrogen: 0.1% or less, and having a negative δ ferrite amount calculated by the following formula (1). This is an arc welding method.

Recorded δ'7z light - 3.2 (1,5Si% + Cr%) -
2,4(30(C%+N%)+0.5 Mn%+Ni%
)-24,7-(1) The present inventors conducted experiments to clarify the amount of oxygen in steel and the degree of δ ferrite required to obtain a high-toughness weld metal. That is, C: o, o2%
, Si: 0.32%, Mn: 2.4%, p: o, o
2%, S: 0.004%, Ni: 11.0%, Cr: 1
9.2%, N: 0.04% chemical composition, 4 to The amount of δ ferrite was changed by changing B, and the amount of δ ferrite was calculated by introducing the following relational expression (1) from the Tillon organization chart and using this.

δ ferrite-3,2 (1,5Si%+Cr%)-2
, 4 (30 (cj% + N%) + 0.5 Mn% + Ni%
) -24,7-(1) For test material layers 5 to 7, the amount of CaF2 and basicity of the flux were changed in order to change the oxygen content in the weld metal. In this case as well, metal N1 was added to the flux to adjust the δ ferrite R.

The absorbed energy at -196°C of the weld metal produced by the experiment was investigated, and the results are shown in Table 2 along with the chemical composition of the weld metal and the amount of δ ferrite.

Table 2 In Table 2, only in the case of sample material layers 1.2 and 5, where the oxygen in the deposited metal is 0.035% or less and the amount of δ ferrite determined by equation (1) is negative. The absorbed energy is 10 kgf-m or more, and it has excellent low-temperature toughness. Based on this result, the present invention limits the oxygen content of the weld metal to 0.035% or less, so that the amount of δ ferrite calculated by equation (1) becomes negative.

As mentioned above, the oxygen content of the weld metal and the δ ferrite f4
In order to put this limitation into practical use and obtain a weld metal with excellent toughness, it is necessary to also limit other compositions of the weld metal, and the reason for this limitation is as follows.

Although there is no effect, if it exceeds 0.08%, the corrosion resistance due to water during the water pressure test will deteriorate, so it was limited to 0.08% or less.

Si and S: If the weld metal does not contain δ ferrite, Si and S are
Since an upper limit is necessary to prevent high temperature cracking, the upper limit was determined through experiments. That is, a groove as shown in FIG. 1 was welded by mixing iron sulfide and ferrosilicon with the flux used in sample material A1, and using the same electrode as in sample material &1.

Welding current: 600A, voltage: 38V, speed: 30m/mi
The test was carried out under the conditions of n. The groove 2 shown in Fig. 1 is the restraint base plate 4.
SUS 3 restrained by restraint plate 6 and restraint welding 8
08 base material 10 was processed. After cutting the welded cross section, high temperature cracks were investigated by penetrant testing, and the results are shown in Table 3.

Table 3 From the results in Table 3, S is 0.0 to prevent high temperature cracks.
The content of Si was limited to 0.06% or less, and Si was limited to 0.7% or less. Note that if Si is less than 0.2%, the yield of Cr decreases, so the lower limit was limited to 0.2%.

Mn: Mn is effective in preventing high temperature cracking, but if it exceeds 6%, the Si in the flux is reduced and the Si in the weld metal is reduced.
Since Cr exceeds 0.7%, the upper limit was set at 6%, and since the yield of Cr decreases below 0.5%, it was limited to a range of 0.5 to 6%.

P: If P exceeds 0.03%, high temperature fragility resistance deteriorates, so P is limited to 0.03% or less.

Cr: Cr is <17% as is clear from Schiffler's phase diagram.
If it is less than 1, martensite will be formed and the toughness will deteriorate.
Limited to 7% or more.

Mo: Mo is effective in increasing room temperature strength, but if it exceeds 3%, toughness decreases, so it is limited to 3% or less.

N: - If □゛N exceeds 0.1%, pores are likely to occur, so 0.
Limited to 1% or less.

In order to achieve the above-mentioned weld metal composition, it is necessary to use a flux that reduces the oxygen content in the weld metal to 0.035% or less and improves workability. Next, the reason for limiting the composition of the flux will be explained.

CaF2: There are two ways to reduce the amount of oxygen in the weld metal: increasing the basicity of the flux and adding large amounts of fluorides such as CaF2. It is undesirable because it makes the condition worse. CaF
, to investigate the effect of A40゜: Sin, : C
A flux of a0=2:1:1 was mixed with varying amounts of CaF2, and this flux was used for welding under the same welding conditions as in Table 3 to investigate the acid capacity and workability. The results are shown in Table 4. If CaF2 is 40% or more, the oxygen content can be reduced to 0.035% or less, but 6
If it exceeds 0%, the stability of the arc will be impaired and short-circuit energization will occur repeatedly, so the amount of CaF was limited to a range of 40 to 60%.

AA03: A403 has the effect of improving slag peelability, but
If it is less than 20%, there is no effect, and if it exceeds 30%, unevenness will occur on the surface of the bead, so it is limited to a range of 20 to 30%.

CaO, MgO: Both basic oxides such as CaO and MgO have 5i
Lower the activity of n2, Sin, +CaF, -+SiF,
It has the effect of suppressing the production of fluoride gas due to the reaction of +CaO, so it is necessary to have a content of 5% or more.
If it exceeds 5%, the slag will seize, so the
% range.

Sin: 5in2 has the effect of improving the bead shape, especially the alignment of the dance edges, but if it is less than 5%, the effect is small, so the lower limit is set at 5%, and if it exceeds 15%, Si in the weld metal
The upper limit is 5-15, as it becomes high and impairs high temperature resistance.
%.

The above CaF2, At, 0. , CaO, MgO, Si
The basic components of the flux of the present invention are limited amounts of Mn0% Cr30. The purpose of the present invention can be achieved more effectively when the following amount is contained below. The reasons for these limitations are as follows.

MnO: MnO has the effect of improving the wettability of Be-F, but 5
If it exceeds 5%, oxygen in the weld metal will increase, so it was limited to 5% or less.

Cr, 03: Cr2O3 is effective in preventing oxidation loss of Cr in the electrode.If it exceeds 10%, slag peeling becomes poor, so it was limited to 10% or less.

Example I C: 0°03%, S! =0.4%, Mn: 2.5%
, P: 0.020%, S2 0.004%, Ni: 1
3.4%, Cr: 19.2%, rlo, 03% electrode and CaF2: 45%, A-e-tos' 25%, C
The groove 2 shown in Figure 2 was welded using a melting flux consisting of aO: 15% and 5in2:15%, and the deposited metal was investigated, and the chemical composition and Charpy absorbed energy are shown in Table 5. . From Table 5, it can be seen that the Charpy absorbed energy (Table 5) is 10.3 krf·m, indicating that it has excellent low temperature toughness.

Example 2 C: o, o4%, Si: 0.2%, Mn: 4%, P
: 0.020%, s: o, oo5%, Ni: 15.0%
, Cr: 19.5%, Mo: 2.2%, N: 0.06%
electrode and CaF: 54. %, AM O,: 20
%, MgO: 10%, 5in2: 8%, Cr, 0.
Welding was carried out under the same conditions as in Example 1 using a melting flux containing: 5% MnO and 3% MnO. The results of the investigation of the weld metal are also shown in Table 5 above, and the Charpy absorbed energy is 8.2 to 9 f·m (t), and it has excellent low-temperature toughness.

As is clear from the above examples, the present invention was able to obtain a weld metal with excellent low-temperature toughness by limiting the components of the welding flux and the weld metal, particularly the oxygen needles and the amount of δ ferrite in the weld metal.

Note that the weld metal composition of the present invention can be widely applied not only to submerged arc welding but also to MIG welding and covered arc welding.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the groove used in the high temperature cracking test of weld metal, and FIG. 2 is a front view showing the groove used in the Charpy test of weld metal. Agent Takeo Nakaji No. 1 [71

Claims (1)

[Claims] (1) Weight ratio of CaF2:40-60%, Atρ,:2
0-30%, CaO or MgO: 5-15%, 8i
02: Contains 5 to 15%, and if necessary, 5% or less MnO, 10% or less Cr, 0. Using a flux containing C: 0.08% and an austenitic stainless steel electrode
Below, Si: 0.2-0.7%, MrI: 0.5-0.5%
6%, p: o, o 3% or less, S: o, oo 6% or less, C
r: 17% or more, Mo: 3% or less, oxygen: 0.
0.035% or less, nitrogen = 0.1% or less, and the following (
1) A method for submerged arc welding of austenitic stainless steel for cryogenic use, characterized by obtaining a deposited metal having a negative amount of δ ferrite calculated by the formula. Recorded δ ferrite-3,2 (1,5Si%+Cr%)-2,
4'(30(C%+N%)+0.5Mn%+Ni%)
-24,7・(1)