JPS61103698A - Austenite stainless steel welding wire which is excellent in both high temperature creep breaking strength and creep breaking elongation - Google Patents

Abstract

PURPOSE:To obtain the welding wire of austenite stainless steel, which is excellent in both a high temperature creep breaking strength and a high temperature creep breaking elongation by setting the ratio N/P of N and P of the welding wire, to a specified range by a weight ratio. CONSTITUTION:0.02-0.1% (weight %, and so forth) C, 0.01-0.08% P, 0.01-0.4% V, <=0.2% N, and 0.1-1.0% Si are made to contain in a basic component of usual austenite stainless steel. Or <=0.6% Ti and <=0.1% B are also added to said component, the balance consists of iron and an inevitable impurity, and a ratio N/P of N and P is set to <=4.0 by weight %, by which a welding wire of austenite stainless steel, whose high temperature creep resistance is excellent, is manufactured.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an arc welding wire, particularly for welding austenitic stainless copper, which is mainly used as a component of pressure vessels or piping systems for the nuclear and chemical industries. This invention relates to an arc welding wire that produces an austenitic stainless steel weld metal with excellent high-temperature creep resistance.

(Prior Art) Pressure vessels and their piping systems are required to be resistant to cylinder temperature creep because they are used for long periods of time at cylinder temperatures and under stress. Since austenitic stainless steel weld metal has poorer temperature creep resistance than a base metal of the same composition, it is extremely important to improve the tube temperature creep resistance of bath-welded fluorite.

A material with excellent high-temperature creep resistance is a material with both high-temperature creep rupture strength and high-temperature creep rupture elongation.

In conventional austenitic stainless steel bath welding metals such as the 308 series, P, C, and N are added to the weld metal, which has improved high-temperature creep properties by adding ■ and teeth with single or striped composites. Or, Ti, B, P, C, N
Attempts have been made to further improve the tube temperature 1 Knope rupture properties of bath-welded metals by adding .

In addition, the two inventors previously published Japanese Patent Application Laid-Open No. 56-53897.
In JP-A-55-1909, it was revealed that the creep rupture strength of 308V weld metal increases as the amount of N increases. The creep rupture elongation of
■It was revealed that the effect was improved by addition.

The service life of materials that are used at high temperatures for long periods of time is estimated by the high-temperature creep rupture strength of the steel used. Rapid heating and cooling may occur due to failures, etc., which may generate shock thermal stress greater than in normal operating conditions, so material properties that can withstand such low-cycle thermal fatigue and have a long repeated life are also required.

The number of repetitions until rupture in low-cycle thermal fatigue is closely related to the ductility of the material, and the greater the ductility, the longer the life. Therefore, in order to strictly evaluate materials used at low temperatures, judgments should be made based on the results of high-temperature creep rupture tests and low-cycle thermal fatigue test areas, and both high-temperature creep rupture strength and creep rupture elongation should be evaluated. It is thought that it is not a big mistake to judge that a material with excellent low-cycle thermal fatigue properties also has better low-cycle thermal fatigue properties than a material with poorer properties. For the above reasons, high-temperature heat-resistant materials are required to have not only creep rupture strength but also creep rupture elongation.

However, in normal cases, when adding alloying elements to increase creep rupture strength, creep rupture elongation decreases. Therefore, developing a material that has both excellent creep rupture strength and excellent creep rupture elongation is a major problem facing heat-resistant material developers.

However, we focused on the creep rupture elongation as well as the high temperature creep rupture strength of 308V steel, and combined addition of P and N
Nothing has been shown to be extremely effective for this purpose.

(Problems to be Solved by the Invention) The present invention provides a heat-resistant stainless steel that can be used at high temperatures for long periods of time by setting the ratio N/P of N and P of the welding wire within a specific range by weight. Another object of the present invention is to provide an austenitic stainless steel welding wire that has both excellent high-temperature creep rupture strength and high-temperature creep rupture elongation.

(Means for Solving the Problems) The gist of the present invention is that ordinary austenite) M
Basic components include C0.02-0.10% (same as below by weight), P 0.01-0.08%, VO601-0.4%
, N02% or less, Si 0.1-1.0%, or further added with Ti 0.6% or less, B 0.01% or less, and the remainder consists of iron and unavoidable impurities, N and The present invention provides an austenitic stainless steel welding wire with excellent high temperature creep resistance, characterized in that the P ratio N/P is 4.0 or less per weight.

The present invention will be explained in detail below.

In order to improve creep rupture elongation, it is not preferable that creep deformation becomes localized in the temperature controlled creep process. To this end, it is necessary to cause uniform structural changes over as wide a range as possible without causing local structural changes even if there are slight differences in stress or temperature.

In order to make the structural changes uniform, it is necessary to make it easier for carbides and ferrides to precipitate to some extent in the austenite matrix and δ-ferrite, and once they are precipitated, even if the creep time elapses, the precipitates, etc. In order to prevent the second phase from being generated or grown locally, it is necessary to minimize areas where crystal grains and δ ferrite strength are uneven.

On the other hand, for leap rupture strength, fine precipitates must be uniformly dispersed and precipitated within the austenite matrix and do not disappear or coarsen even during the creep process at high temperatures and long periods of time. The creep rupture strength is strong.

The present inventors found from various experimental results that N in austenitic stainless steel weld metal has the effect of suppressing the formation and coarsening of precipitates during long-term holding at high temperatures, while P suppresses the formation of precipitates. It was confirmed that this method has the effect of uniformly precipitating precipitates both in areas with a lot of deformation and in areas with a little deformation during the high-temperature deformation process.

From these experimental results, we found that adding N and P appropriately allows precipitates to precipitate finely and uniformly during high-temperature creep deformation, and also suppresses the coarsening of precipitates even during long-term holding at high temperatures. It was inferred that the distribution shape of the precipitates was kept uniform and fine over time, and as a result, a weld metal with strong high-temperature creep rupture strength and large creep rupture elongation was obtained.

Therefore, the present inventors conducted various studies to find out in what range of combinations of P and N it is possible to obtain an austenitic stainless steel weld metal with extremely excellent high-temperature creep resistance.

Furthermore, when stainless steel is heated for a long time, it is known that the creep rupture elongation can be improved by suppressing the σ layer that is formed. We investigated whether it is possible to improve creep rupture elongation by bonding.

First, C0.03~0.06%, Si0.12~0.1
8%, Mn 1.5-2.0%, P 0.005-0.
05%, 30.002~0.004%, Ni 9.0~
11.0%, Cr19.0-21%, V 0.06-0
．． 15%, N 0.02-0.05%, 'Ti 0
．． Using a wire containing 0.01% or less and 0.01% or less of B, TIG welding was performed using SUS 304 with a plate thickness of 40111111 as a base material.

For welding, we used a wire of 5111111 da, and a current of 1
50A, voltage 13V, welding speed 15r! IMmin,
The interpass temperature was 150° C., the heat input was 7.8 KJloR, and argon gas was used. The longitudinal direction of the test piece is perpendicular to the bead direction as shown in Figure 3 (a = l
5 ram, 1) = 4 QwR, C: 301E+I
l, a=6mmmm, &=10”Rs R2=8MR
, θ=30°), 550°C, 25 Kq/ra
A creep rupture test was conducted under a load of n2.

The relationship between the creep rupture elongation determined from the test results and the weight ratio N/P of N and P in the weld metal is shown in Figure 1.

As can be seen from the figure, creep rupture elongation reaches its maximum when the weight ratio N/P of N and P is 1.5 inches, and when N/P is 4.0 inches.
In the above, the creep rupture elongation was 2/3 or less of the maximum value, and it was found that lowering N/P is more advantageous for creep rupture elongation. On the other hand, the leap rupture strength is Ni
As the number increases, the strength increases as shown in Figure 2. The figure is 55
This is the creep rupture strength at 0°C and 400 hours.

The present invention has been made based on the above findings.

In the present invention, the basic components of austenitic stainless steel include SUS 304.5US304L, 5US30
8. The composition of austenitic steel such as SUS 309,
Refers to what the alloy composition complies with, and the composition range is:
Mn 2.0% or less, Ni 8-16%, Cr18 in weight%
~27% etc.

Furthermore, in the present invention, the arc welding method refers to TIG# welding, submerged arc welding, MIG welding, and manual welding, and TIG welding refers to filler wire, and other welding methods include
The wire of the present invention is used as a welding electrode wire or a welding rod core wire.

In this case, desirable bath contact conditions include, for example, TIG m
Regarding contact, when using 1.6Mg wire,
Current: 150-200A, pressure: 10-15V, bath contact speed: 12-15%/min, interpass temperature: room temperature - 150°C, using pure argon gas as shielding gas, flow rate: 20-15V
The speed is set at 25t/min.

In addition, for submerged arc welding, 5iO21 is used as a flux.
0-30%, At20320-30%, CaO10-2
0%, Vig014-24% as the main components, and one or both of CaF2 and AlF2 as metal fluorides,
When using a wire containing 3 to 30% deoxidizing agent and 40% or less alloy material, etc., and using a wire of 1.61E+Ilφ, the current is 150 to 200A, the voltage is 23 to 30V, and the welding speed is 5 Q citb/min
, an interpass temperature chamber of 1 to 150°C, and a current of 550 to 600 in the case of submerged arc welding using a 4.Qsng wire.
A. It is standard that the voltage is 30 to 35 V, the welding speed is 20 cpm, and the interpass temperature is room temperature to 150°C.

For lviIGm contact, when using t, 6+mm wire, current 200-250A, voltage 28-33
■, welding speed 20~25 e/mib, interpass temperature room temperature ~ 150℃, 7-rud gas (argon + 2% 0
, ) at a flow rate of 15 to 20 t/min.

Hand welding rod, lime titania coated rod, 4 m
When using an m-chain welding rod, the current is 130 to 1soA.
, the pressure 20-30V, welding speed 15-25 cpm.

It is standard that the interpass temperature is between room temperature and 150°C.

Next, the limitations of each component in the present invention will be explained.

If C= is high, the high temperature creep rupture strength of the weld metal will be high (but the amount of δ ferrite will be small, making inter-vessel cracking more likely to occur, and the amount of carbides will increase, resulting in embrittlement. Therefore, the amount of C in the wire will increase) The upper limit of 0.1% was set in consideration of hot cracking during welding and cracking due to deformation after welding.The lower limit of wire 〇〇 content weight was set at 0.1% in order to maintain the creep strength of the weld metal. 02%.

Since P improves the high temperature creep strength and elongation of the weld metal, it is necessary to contain 0.01% or more in the wire. However, if the content of P in the weld metal is too high, it will easily break.
The upper limit of P in the wire was 0.10 inch.

(2) increases the high-temperature creep rupture elongation of the weld metal, so it is necessary to add 0.01% or more to the wire. However, even if the amount added exceeds 0.4%, the effect is small, so the upper limit was set at 0.4%.

N is an important element that forms crabmides with V, Cr, Ti, etc., and thereby directly or indirectly determines the creep rupture strength. Creep rupture stress 30Kg at 550℃
/mm20 condition, if a creep rupture time of 100 hr or more is required, 0. An amount of N of oos% or more is required. Therefore, 0. oos% or more must be added. However, if the amount added is too large, δ ferrite in the weld metal will decrease and hot cracking will occur, so it is necessary to limit the amount to 0.4% or less.

Since Sl acts as a deoxidizing agent during submerged arc welding, it increases the yield of Ti. Moreover, since it increases the high temperature creep rupture strength of the weld metal, it is necessary to contain 0.1% or more in the wire. However, if the amount added is too large, the ductility of the #welt metal will deteriorate, so the Si content in the wire must be kept at 1.0% or less.

As shown in Figure 1 above, the weight ratio of N and P (N/P) has a close relationship with the creep elongation at rupture, and when this value is 1.5, the elongation at creep reaches its maximum. As the thickness increases, the creep rupture elongation decreases to 2/3 of the maximum value.If N is added, the creep rupture strength increases by 5, but the creep rupture strength To obtain a material with excellent creep rupture elongation,
Even if N is high (N/P weight ratio must be kept at 4 or less).

Among austenitic stainless steels, those with particularly high Cr content tend to form a σ phase during the high-temperature creep process, which becomes a starting point for cracking during creep and reduces creep rupture elongation. For such things, Ti and B have a suppressing effect during high temperature creep of weld metal, and Ti <:
Sufficient effects are observed even at 0.053% and B<0.0067%. Furthermore, if these elements are added in excess of the σ suppression effect, the ductility will deteriorate, so in consideration of the yield during bath welding, the upper limits of Ti in the wire are 0.6% and 0.6%, respectively.
B was set to 0.01%.

The preferred range of basic components of austenitic stainless steel is as follows.

If there is too much austenite-forming element in the austenite-forming element, δ ferrite will decrease and hot cracking will easily occur during bath welding, so it is preferable that the content in the wire is 2% or less.

Ni is required to be at least 8% in the wire in order to provide high temperature creep resistance and heat resistance, but Ni is an austenite-forming element, and when it is in excess, δ ferrite decreases and hot cracking occurs during welding. It becomes easier. Also, in order to reduce manufacturing costs, the content in the wire is preferably 16% or less.

Cr is a ferrite-forming element, and in order to produce δ ferrite in the weld metal, it must be contained in the wire in an amount of 18% or more as an alloying component. Further, since Cr improves heat resistance and oxidation resistance and strengthens high-temperature creep strength, from this point of view as well, 18% or more is necessary. Further, Cr is an element that promotes the formation of intermetallic compounds such as carbides and σ phase, and if it is too large, the ductility decreases and it becomes easy to crack, so the content in the wire is preferably 27% or less.

In addition, in the case of submerged arc welding, S is transferred from the flux to the weld metal and promotes embrittlement of the weld metal, so the S content in the wire is preferably 0.03% or less.

(Example) The effects of the present invention will be illustrated in more detail by Examples below.

SUS 304 with a plate thickness of 40IlOi was used as the base material, a U groove (angle of 30°) with a depth of 30fi was made in it, and welding was performed using the wire shown in Table 1 and the welding conditions shown in Table 2. . The welding direction is the longitudinal direction of the test piece, and the shape shown in Fig. 4 (a = 13 gourd, b = 7M, C = 30ffl) is made from the weld metal.
+II, d=7 Q++on, 6=14m, f=
A creep rupture specimen of 6+++n+t3, G=10gIIIR) was collected. A creep rupture test was conducted on Tanizuki welding metal at 550°C.

As an example of the results of the creep rupture test, Table 1 shows the rupture time at 550° C. and 27 homs/1111112, the elongation at break, and the N/P weight ratio.

As can be seen from the same table, the creep rupture elongation of Comparative Examples A, °B, C, D, and E whose N/P weight ratio is greater than 4 is small, but the N/P weight ratio is 4 or less. The present invention F
-0 means the same level of creep 4i as the comparative example! i-off time A
-E has a larger creep rupture elongation and is superior in both creep rupture elongation and creep rupture strength.

Table 2 (Effects of the Invention) As described above, the wire of the present invention guarantees an austenitic stainless steel welded joint with excellent high-temperature creep rupture strength and creep rupture elongation, which have not been clarified in the past. This makes it possible to achieve this and has extremely significant industrial effects.

[Brief explanation of the drawing]

Figure 1 shows 550℃ 25Kff/It! Figure 2 is a graph showing the relationship between creep rupture strength at 550°C and 400 hours and Ni, and Figure 3 is the exploratory test. FIG. 4 is an explanatory diagram showing the shape and dimensions of the test piece used in Examples.

Claims (1)

[Claims] 1. In the basic components of ordinary austenitic stainless steel, C
0.02-0.10% (weight%, same below) P0.01
~0.10%, V0.01~0.4%, N0.2% or less, Si0.1~1.0%, the remainder consists of iron and unavoidable impurities, and the ratio of N and P is N/ An austenitic stainless steel welding wire having excellent high-temperature creep rupture strength and creep rupture elongation, characterized in that P is 4.0 or less in weight%. 2 In addition to the basic components of normal austenitic stainless steel, C
0.02-0.10% (weight%, same below) P0.01
~0.10%, V0.01-0.4%, N0.2% or less, Si0.1-1.0%, Ti0.6% or less, B0.0
1% or less, the remainder consists of iron and unavoidable impurities, and the high temperature creep rupture strength and creep rupture elongation are characterized by the ratio N/P of N and P being 4.0 or less in weight%. Both are excellent austenitic stainless steel welding wires.