JPH0356833B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is suitable for use in inert gas shielded arc welding of ferritic stainless steel, and particularly relates to a welding wire with excellent arc stability. Examples of ferritic stainless steel include
AISI405, 430, 434, 444 containing 11-35% Cr
etc. (see JIS Handbook of Steel, 1980 edition, pages 1210-1211). Traditionally, for example, SUS304 was mainly used for chemical industrial materials that particularly required corrosion resistance.
These austenitic stainless steels have been used, but these austenitic stainless steels have the drawbacks of poor stress corrosion cracking resistance and high prices because they contain a large amount of Ni. In contrast, ferritic stainless steel has excellent stress corrosion cracking resistance and is inexpensive, so it has recently replaced the austenitic stainless steel as a particularly useful material for applications that require corrosion resistance. It is starting to be used. This type of welding of ferritic stainless steel includes a dissimilar metal welding method using an austenitic welding material and a cometal welding method using a ferritic welding material. Among these, when austenitic welding materials are used, although the weld cracking resistance and properties of the deposited metal are good, they have the disadvantage of being susceptible to stress corrosion cracking and thermal fatigue cracking. When using the welding material of
Although it is inexpensive, it has the drawbacks of causing weld cracks and deteriorating the properties of the deposited metal, such as toughness and ductility. The reason for the disadvantages of the alloy welding method using ferrite-based welding materials is thought to be due to coarsening of ferrite crystal grains or precipitation of martensite during solidification after welding. On the other hand, the inert gas shielded arc welding method using inert gas shielded arc welding materials uses Ar,
Inert gas such as He or O ₂ or CO ₂
This is an arc welding method that uses a gas to which an appropriate amount of active gas such as 1.0% or more is added as a shielding gas, and is known as a welding method that allows automatic welding. This welding method is the MIG welding method, which uses a consumable electrode as the welding material,
It can be broadly divided into TIG welding, in which welding material is added to the arc of a non-consumable tungsten electrode. However, it is generally said that such inert gas shielded arc welding methods require a large amount of welding heat input or a large amount of penetration into the welded material (base material). For this reason, in the inert gas shielded arc welding method, the large heat input causes significant coarsening of ferrite crystal grains, and in the case of welded materials with a high C content, the amount of martensite precipitation increases due to dilution. The problem is that it tends to cause frequent weld cracking and large deterioration of toughness. Therefore, many studies have been conducted to solve the various problems mentioned above, but in general, it is necessary to add appropriate amounts of strong carbon/nitride forming elements such as Ti, Nb, and Al to make the weld metal ferrite. It has been considered to improve the performance of weld metal by preventing coarsening of crystal grains or by fixing C in steel and suppressing the precipitation of martensite. However, strong carbons such as Ti, Nb, Al, etc.
There is a limit to the improvement of the toughness of weld metal by adding nitride-forming elements;
Nitride increases the susceptibility to high-temperature welding cracking, making it easier for heat-affected zone cracking to occur in the deposited metal during multi-layer welding.Furthermore, the addition of strong carbides tends to make the arc unstable, making automatic welding possible. Gas-shielded arc welding, especially highly efficient MIG
Since this is a fatal drawback in welding, there has been a problem in that satisfactory results have not yet been obtained. The present invention has been made in view of the above-mentioned conventional problems, and is particularly excellent in arc stability and weld cracking resistance during inert gas shielded arc welding of ferritic stainless steel. The object of the present invention is to provide a welding wire that can improve the corrosion resistance and toughness of weld metal. As a result of repeated various experimental studies in accordance with the above-mentioned objectives, the present inventors have found that the toughness of weld metal can be improved by adding appropriate amounts of strong carbon/nitride-forming elements such as Ti, Nb, and Al. At the same time, by adding an appropriate amount of W as an essential element, we aimed to improve weld cracking resistance and arc stability, and found that the improved arc stability could make it suitable for continuous automatic welding. I found it. In particular, it has been found that by adding Ca, REM, and Mg in combination as necessary, hot workability can be improved, and at the same time, the toughness of the weld metal can be further improved. That is, the welding wire for inert gas shielded arc welding of ferritic stainless steel with excellent arc stability according to the present invention has C:
0.08% or less, N: 0.08% or less, Si: 2.0% or less,
Mn: 6.0% or less, P: 0.03% or less, S: 0.03% or less, Cr: 10-40%, W: 2.0% or less, Ti: 3.0% or less, Mo: 5.5% or less, Nb: 3.0% or less, V :
1.5% or less, Al: 0.5% or less, Zr: 0.5% or less, B:
One or more of 0.5% or less, Ca: 0.05% or less, REM: 0.05% or less, as required.
It is characterized by containing one or more of Mg: 0.05% or less, with the balance consisting of Fe and inevitable impurities. The reasons for limiting the component range (wt%) of the welding wire for inert gas shielded arc welding (TIG welding, MIG welding) of ferritic stainless steel with excellent arc stability according to the present invention will be described below. C (carbon): 0.08% or less If the C content is too high, martensite is generated and coarse carbides are formed, which deteriorates the toughness of the welded joint and deteriorates the intergranular corrosion resistance. It also deteriorates weldability and reduces weld cracking resistance. Therefore, the upper limit is set at 0.08%. N (nitrogen): 0.08% or less If the N content is too high, the weld cracking resistance will decrease and the toughness of the welded joint will deteriorate.
The upper limit is set at 0.08%. Si (silicon): 2.0% or less Si is an element that acts as a deoxidizer and arc stabilizer, but if it is too large, it causes coarsening of ferrite crystal grains, deteriorates the toughness of the weld and promotes its embrittlement. . Therefore, the upper limit
2.0%. Mn (manganese): 6.0% or less Mn acts as a deoxidizing agent, fixes S in steel, eliminates its harmful effects, and contributes to improving toughness even in small amounts. However, if contained in a large amount, martensite will precipitate, resulting in deterioration of toughness and ductility, so the upper limit is set at 6.0%. P (phosphorus), S (sulfur): 0.03% or less Too much P and S deteriorates hot cracking properties and toughness, and S in particular deteriorates corrosion resistance, so the upper limit for both needs to be 0.03%. There is. Cr (Chromium): 10-40% Cr is a basic component of ferritic stainless steel, and is an element necessary to increase the strength of welded joints and to provide corrosion resistance and oxidation resistance. 10% to obtain the same strength, corrosion resistance, and oxidation resistance as the welding material (base metal)
Add more. However, if the amount is too high, it will cause the welded part to become brittle and reduce the yield.
% or less. W (tungsten): 2.0% or less Although W is a carbide-forming element, it stabilizes the arc and eliminates defects in the weld zone, and by stabilizing the arc, it enables automatic welding that is continuously used.・It is an element that contributes to improving weld cracking resistance by suppressing the increase in weld cracking susceptibility when nitride-forming elements are added, improving arc stability, improving the toughness of weld metal, and intergranular corrosion resistance. It is a particularly necessary element for improvement. However, if it is contained in a large amount, it will actually deteriorate the toughness of the weld metal, so the upper limit is set at 2.0%. Ti (Titanium): 3.0% or less Ti acts as a deoxidizing agent, forms carbon and nitrides, and particularly refines the ferrite crystal grains of the weld metal, improving the toughness of the weld metal and improving intergranular corrosion resistance. It is an effective element for However, if it is contained in a large amount, the arc becomes unstable and the toughness of the welded part deteriorates, so the upper limit must be exceeded.
The rate shall be 3.0%. Mo (molybdenum): 5.5% or less, Nb (niobium): 3.0
% or less, V (vanadium): 1.5% or less, Al (aluminum): 0.5% or less, Zr (zirconium): 0.5%
Hereinafter, B (boron): 0.5% or less These are all effective elements for improving the corrosion resistance and toughness of weld metal, and one or more of the above elements can be selected as appropriate to each of the above. Add up to the maximum value. Among these, Mo improves intergranular corrosion resistance and contributes to improving toughness, especially at low temperatures, but if too much Mo is present, the arc becomes unstable, deteriorating the toughness and elongation of the weld and promoting its embrittlement. At the same time, the weld cracking resistance deteriorates, so the upper limit is set at 5.5%.
Nb forms carbon/nitrides, refines the structure and improves toughness, and also improves intergranular corrosion resistance and stress corrosion resistance. However, if too much Nb is present, the arc becomes unstable and the toughness of the weld zone is reduced. As it deteriorates, the weld cracking resistance also deteriorates, so the upper limit for Nb is set at 3.0%. V forms carbon/nitrides, refines the structure, improves the toughness of the weld, and improves intergranular corrosion resistance, but too much V makes the arc unstable and deteriorates the toughness of the weld. As the weld cracking resistance deteriorates, the upper limit of
The rate shall be 1.5%. Al is an element that acts as a deoxidizing agent and contributes to improving the toughness and heat resistance of the weld, but if it is too much, the arc becomes unstable, deteriorating the toughness of the weld and weld cracking resistance. The upper limit shall be 0.5% or less. Furthermore, Zr,
Hf and B both fix C and N in steel and contribute to improving toughness and pitting corrosion resistance, but if too much, the arc becomes unstable, deteriorating the toughness of the weld and reducing weld cracking resistance. The upper limit for both Zr and B is 0.5%, as this will cause deterioration and hot workability.
shall be. Ca (calcium): 0.05% or less, REM (rare earth element): 0.05% or less, Mg (magnesium): 0.05% or less These are all elements that remove S in steel and act as deoxidizers, and especially The combined addition with W improves the toughness of the weld metal and contributes to improving hot workability. REM also contributes to hydrogen removal and improves weld cracking resistance. Therefore, it is desirable to add one or more of these elements as necessary, but if they are added in large amounts, arc instability increases and defects are likely to occur in the weld, and at the same time, hot processing becomes difficult. The upper limit is set at 0.05% for each. In addition, Ni of 0.50% or less and Cu of 0.30% or less as impurity elements do not adversely affect the properties of the material of the present invention. The present invention will be explained below with reference to Examples. Example 1 First, steel with a chemical composition corresponding to the steel type of the test material is melted, then rolled and drawn into a wire rod with a diameter of 1.6 mm, wound on a reel, and each with a chemical composition shown in Table 1. Consumable electrode welding wires for MIG welding were manufactured using a comparative material and an inventive material.

[Table] Next, when performing MIG welding using welding wires made of comparative materials and inventive materials of each chemical composition shown in Table 1 above and using these as consumable electrodes, The base material shown in Table 2 with a size of 25 mm was used, and the bevel was set at 40°.
In addition, the welding conditions are: total current 320A, arc voltage
Five-layer MIG welding was performed at 27 V and a welding speed of 20 cm/min, with Ar + 1% O ₂ gas flowing as a shielding gas at a flow rate of 25/min. Thereafter, the toughness and corrosion resistance of the welded joint were tested. These results are shown in Table 2.

[Table] In Table 2, arc disturbance and spatter generation were visually observed, and defects other than cracks were examined by X-ray transmission testing. In addition, the weld cracking rate was determined by macroscopic cross-sectional observation of the welded part on 20 cross sections, and calculated by (number of cracked cross sections/20 step surfaces) x 100 (%). Furthermore, the Charpy impact value was measured as a toughness evaluation test. In this case, a No. 4 test piece (2 mm V notch) specified in JIS Z 3112 was cut out as welded and tested at 20°C. Furthermore, intergranular cracking resistance was investigated as an evaluation test for corrosion resistance. In this case, according to the regulations of JIS Z 0575, thickness 2 mm, L = 1
A specimen of mm in diameter was taken from a defect-free area and bent at an angle of 180°.
I did it at As shown in Table 2, comparative material No. 1 that does not contain W
-6 have poor arc stability and are highly susceptible to weld cracking due to the addition of carbon/nitride forming elements, especially comparative materials Nos. 2, 4 and 4 containing a large amount of carbon/nitride forming elements. It is clear that No. 6 had a high weld cracking rate and was extremely poor in toughness. On the other hand, good results were obtained for all of the present invention materials Nos. 7 to 14 containing W and carbon/nitride forming elements. Example 2 First, a steel with a chemical composition corresponding to the steel type of the test material was melted, then rolled and drawn into a wire rod with a diameter of 1.6 mm, wound on a reel, and made into a wire rod with a chemical composition shown in Table 3. Consumable electrode welding wires for MIG welding were manufactured using a comparative material and an inventive material.

[Table] Next, MIG welding was carried out under the same welding conditions as in Example 1 using welding wires made of comparative materials and inventive materials with each chemical composition shown in Table 2 above, and using these as consumable electrodes. We then conducted welding workability and post-weld toughness evaluation tests. The results are shown in Table 4. In addition, in the toughness evaluation test, the test was conducted not only at 20°C as in Example 1 but also at 0°C.

[Table] As shown in Table 4, in comparison materials 21 to 25, which do not contain W and contain carbon/nitride forming elements and one or more of Ca, REM, and Mg, the arc stability is The welding area is extremely poor, defects in the welded area become large, and the toughness is considerably degraded, making automatic welding by MIG welding difficult. In contrast, the present invention material contains an appropriate amount of carbon/nitride-forming elements and has a composite addition of W and at least one of Ca, REM, and Mg.
Nos. 26 to 31 all had good arc stability, no welding defects, and excellent toughness. As detailed above, in the welding wire for inert gas shield welding (TIG welding, MIG welding) of ferritic stainless steel with excellent arc stability according to the present invention, strong carbon such as Ti, Nb, Al, etc. Add appropriate amounts of nitride-forming elements, add appropriate amounts of W as an essential element, and add Ca, REM,
Since one or more types of Mg are added, it is possible to improve the toughness of the weld metal due to the strong carbon/nitride forming elements, and at the same time, it is possible to improve the weld cracking susceptibility due to the addition of carbon/nitride forming elements. By suppressing the increasing tendency of welding by the essential addition of W, weld cracking resistance and arc stability are improved, and the improved arc stability makes it suitable for automatic welding that is continuously used, resulting in welding without welding defects. Joints can also be obtained by continuous automatic welding, and
The combined addition of Mg and W has very excellent effects such as improving hot workability and further improving the toughness of the weld metal.

Claims (1)

[Claims] 1. C: 0.08% or less, N: 0.08% or less, Si: 2.0% or less, Mn: 6.0% or less, P: 0.03%
Below, S: 0.03% or less, Cr: 10-40%, W: 2.0
% or less, Ti: 3.0% or less, and Mo: 5.5% or less,
Nb: 3.0% or less, V: 1.5% or less, Al: 0.5% or less,
An inert ferritic stainless steel with excellent arc stability, containing one or more of Zr: 0.5% or less, B: 0.5% or less, and the remainder consisting of Fe and unavoidable impurities. Welding wire for gas shielded arc welding. 2 In weight%, C: 0.08% or less, N: 0.08% or less, Si: 2.0% or less, Mn: 6.0% or less, P: 0.03%
Below, S: 0.03% or less, Cr: 10-40%, W: 2.0
% or less, Ti: 3.0% or less, and Mo: 5.5% or less,
Nb: 3.0% or less, V: 1.5% or less, Al: 0.5% or less,
Zr: 0.5% or less, B: one or more of 0.5% or less, Ca: 0.05% or less, REM:
An inert gas shield made of ferritic stainless steel with excellent arc stability, characterized by containing one or more of the following: 0.05% or less, Mg: 0.05% or less, and the remainder consisting of Fe and unavoidable impurities. Welding wire for arc welding.