JPH0558835B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for welding joints of fully austenitic stainless steel or iron-based or nickel-based superalloy clad steel. [Conventional technology] Nickel content is 15~15% lower than that of general stainless steel.
So-called fully austenitic stainless steel or iron-based or nickel-based superalloys, which have been improved by more than 20%, have high corrosion resistance, stress corrosion cracking resistance,
It has heat resistance strength, etc., and is suitable for line pipes for oil and gas production, gas processing plants, general chemical plants,
It is beginning to be used for paper manufacturing plants, etc. Since these alloys are generally expensive and have lower strength than steel, clad steel, which is made of a mixture of these alloys to increase strength and is economically utilized, has come to be widely used. These clad steels are usually welded and used as structures. Since clad steel is made up of two or more materials with different properties, it is necessary to devise a welding method, but various welding methods that are economical and have sufficient joint performance have been proposed, and some have already been put into practical use. There is. Joint welding of clad steel for structures is generally carried out as shown in Figure 3 A and B. That is, in FIG. 3A, a V-shaped groove is provided with the opening on the composite material 1 side, and after welding the base material 2 with weld metal 3 having the same composition as the base material 2 from the bottom of the groove, Composite material 1 is welded onto weld metal 3 using a welding material whose alloy composition is equal to or higher than that of composite material 1, and the performance is equal to or higher than that of composite material 1. A composite weld metal 4 having the following properties was obtained. In addition, in Figure 3B, an X-shaped groove is created, and first the base material 2
From the side, weld base metal 3a equivalent to base metal 2.
Next, a base metal weld metal 3b that is equivalent to the base metal 2 is welded to the base metal 2 from the composite material 1 side, and a high alloy composite that is equivalent to or higher than the composite material 1 is welded onto the weld metal 3b. A good welded joint was obtained by welding with material weld metal 4. In this way, if the stainless clad steel joint welding work can be carried out from the composite material 1 side, then
However, it is possible to weld without any problem using the method explained in (b), but welding can be done in circumferential joints between clad steel pipes whose inner surfaces are made of superalloy, in closed vessels, or in clad steel plates that have a relatively large surface area and in which it is difficult to reverse the welding point. When welding, it is often necessary to provide an open weld groove on the base metal side and weld only from the base metal side. As a welding method in such a case, a method as shown in FIG. 4 has been conventionally used. That is, the composite material 1 or a welding material 4' substantially equivalent thereto was applied to the entire thickness from the composite material 1 side to the base metal 2 side. [Problems to be Solved by the Invention] In the conventional welding method shown in FIG. The weld metal melts the weld metal on the composite side and picks up a large amount of alloys such as chromium, nickel, molybdenum, etc., which causes hot cracking or cold cracking, and further reduces the ductility and toughness. Furthermore, although the conventional method shown in FIG. 4 is simple in that it uses one type of welding material, it has the following drawbacks. In other words, if welding is performed from the base metal side and the entire thickness of the clad steel is welded using super alloy high alloy steel, the welding material cost will be high, and the weld metal will be entirely composed of super alloy steel. Depending on the base metal, the strength of the welded joint may be lower than the base metal strength. Furthermore, superalloy clad steel structures are often used in thermal environments such as high temperature ranges or repeated temperature ranges between high temperatures and room temperature, and under such usage conditions,
If all the layers of the weld metal are made of superalloy, the difference in thermal expansion coefficient between the weld metal and the base metal will generate thermal stress, causing deformation of the weld joint, or carbon transfer from the base metal to the weld metal. There was a problem that the creep strength of the bond with the base metal decreased due to diffusion. [Means for Solving the Problems] The present invention has been made in view of the above circumstances, and
We attempted to solve the problem by welding the first layer with a superalloy alloy, then creating a special intermediate layer to prevent cracking and deterioration of ductility, and then welding a filler metal equivalent to the base metal on top of that. Ta. That is, in the present invention, the Ni content is 15% by weight.
When welding joints of stainless steel or superalloy clad steel made of Ni-based alloy and carbon steel or low-alloy steel as the base material, a groove with an opening on the base metal side is prepared and the joint is first welded. The composite part is welded using a filler metal with a high alloy chemical composition equivalent to that of the material, and the chemical composition is
The first step is to use additives in which Cr is more than 16% and less than 40%, and the remainder is Fe and unavoidable impurity elements.
After welding the intermediate layer, the chemical composition is C in weight%
0.02% or less, Si 0.1-0.3% and Ti 0.3-1.0%,
Contains one or two types of Nb 0.3-1.0%, with the remainder
A second intermediate layer is welded using a filler metal consisting of Fe and unavoidable impurity elements, and then a carbon steel or low alloy steel filler metal equivalent to the base metal is welded to the final layer on the second intermediate layer. This is a joint welding method for superalloy clad steel, which is characterized by the following. [Function] The details of the method for welding a superalloy clad steel joint according to the present invention will be explained with reference to the drawings. 1st
In the figure, a V-shaped groove is provided with openings on both base material 2 sides of the joint part, and both composite materials 1 are aligned. In addition to the V-shaped groove, a U-shaped groove can also be used. First, only the composite material 1 is welded and joined with the composite weld metal 4. In this case, composite material 1,
If only 1 can be welded, there is no need to use a filler metal, but if there is a risk of melting part of the base metals 2 and 2, use a filler metal with a higher alloy composition than composite material 1. It is necessary to weld the composite weld metal 4 so that the chemical composition falls within a predetermined composition range. Next, one or more first intermediate layers are welded onto the composite weld metal 4 using a high Cr filler metal. The microstructure of the first intermediate layer weld metal 5 obtained at this time is such that the amount of ferrite phase is 3% to 40% in terms of area ratio and the remainder is an austenite phase due to penetration from the base metal 2 and composite weld metal 4. must be done. In order to obtain such a first intermediate layer weld metal 5, it is necessary to use a filler metal having a weight percentage of more than 16% Cr and less than 40% Cr, with the balance being Fe and inevitable impurity elements. By controlling the microstructure of the first intermediate layer metal 5 within the above range, hot cracking or reduction in toughness can be prevented. Next, when a filler metal of carbon steel or low alloy steel equivalent to the base metal is welded onto this, the first intermediate layer weld metal 5
Ni, Cr, Mo, etc. are mixed in, causing cold cracking or a significant decrease in toughness of the carbon steel weld layer. Even if such alloying elements are mixed in, the filler metal must have a sufficiently low C to prevent cracking or a decrease in ductility.
It is necessary to stabilize the C content as a carbide, and for that purpose it is necessary to contain Ti or Nb. That is, C 0.02% or less, Si 0.1~0.3%, Ti 0.3~1.0%, Nb 0.3~
It must be welded using a filler metal containing 1.0% of type 1 or type 2, with the remainder consisting of Fe and unavoidable impurity elements. Next, on the second intermediate layer weld metal 6 obtained by welding the filler metal, a filler metal containing an alloying element equal to or higher than that of the base metal 2 is used to weld the entire thickness of both base metals 2. are joined by base metal weld metal 3. Welding methods applied to this, especially low-carbon intermediate overlay methods, are preferably low heat input and low dilution welding, and pulse-TIG welding, pulse-MIG welding, and shielded arc welding are suitable, but shielded arc welding In this case, the diameter of the welding rod should be 4 mmφ or less. Next, the reason for limiting the chemical composition of the filler metal for welding the first intermediate layer will be described. If the amount of Cr in the filler metal applied when welding the first intermediate layer weld metal 5 is 10% or less, the microstructure of the first intermediate layer weld metal 5 will be almost 100% austenite, which will prevent hot cracking. Occur. while 40
% or more, the first intermediate layer weld metal 5 has an extremely high Cr content, resulting in extremely low ductility and toughness. Next, the reasons for limiting the composition of the filler metal used when welding the second intermediate layer weld metal 6 will be explained. The lower the C, the lower the hardness of the second intermediate layer weld metal 6 and the better the toughness. However, when the C content exceeds 0.02%, the carbon in the second intermediate layer weld metal 6 becomes concentrated due to the movement of carbon contained in the base metal 2, and the hardness becomes extremely high, causing performance deterioration of the second intermediate layer weld metal 6. invite Si improves the fluidity of the additive when it is melted and also acts as a deoxidizing agent. As a deoxidizing agent
Si requires 0.1% or more, and adding more than 0.3% will cause a significant decrease in toughness, so the range should be 0.1 to 0.3.
%. Ti and Nb are elements necessary to fix C, and Ti requires at least 4 times the amount of C, and Nb requires at least 8 times the amount of C, but the addition of excessive Ti and Nb will reduce the toughness. In consideration of reduction and economic efficiency, each was set at 1.0% or less. Furthermore, since Ti and Nb are scattered into the air during welding and the effective amount decreases, the lower limit of each was set at 0.3%. [Example] Next, an example of the present invention will be described. The test materials used were superalloy clad steel plates consisting of Incoloy 825 material with a thickness of 2.5 mm as the composite material and API 5L-X60 material with a thickness of 19 mm as the base material. The groove shape is the second
As shown in Figure A, the groove angle α of the base material 2 is V-shaped.
α′=30°. First, a composite material 1 having the groove shape shown in FIG. 2A was welded using an Inconel 625 TIG welding rod as shown in FIG. 2B to obtain a composite weld metal. Next, a high Cr filler metal having the chemical composition shown in Table 1 was built up on the composite weld metal as a filler metal for the intermediate layer under the welding conditions shown in Table 2 (Test No. 1).
~No. 4). For comparison, ordinary carbon steel filler metal (test
No. 5), welding was performed on the Inconel 625 layer by the covered arc welding method under the welding conditions shown in Table 2 to the final layer of the full thickness on the base metal side (Test No. 5).

【table】

【table】

[Table] Next, in test Nos. 1 to 4, one layer of second intermediate layer weld metal was welded on top of the first intermediate layer weld metal by pulse TIG welding, as shown in FIG. 2D. Furthermore, the base metal weld metal was welded to the final layer on the second intermediate layer weld metal by mild steel covered arc welding as shown in FIG. 2E. Note that no preheating before welding and no heat treatment after welding were performed. The chemical composition of the intermediate layer weld metal obtained by the above procedure is shown in Table 3, and the results of the mechanical test of the joint weld are shown in Table 4. In the case where the Inconel 625 weld layer shown in Table 4 was directly built up with carbon steel welding material equivalent to the base metal (Test No. 5), the carbon steel weld layer caused a significant decrease in ductility, and the Inconel 625 weld layer was already welded immediately after welding. It was observed that many hot cracks had occurred in the carbon steel close layer directly above the 625 weld layer.

【table】

【table】

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to use a welding material equivalent to the composite material for the composite material, and a welding material equivalent to the base material for the base material, and it is possible to give the welding material also the characteristics of the clad material. In addition, the present invention does not require reversing in the case of wide and large-area clad steel plates, and in the case of closed containers, welding can be performed only from the base material on the carbon steel side, so the inner cladding material is not contaminated and has a great economic effect. Furthermore, when buried underground or under the sea like clad steel pipes, if the circumferential joint is made of superalloy, there is a risk of corrosion due to the corrosion potential difference with the base metal, and superalloys generally have poor resin coating properties. However, it can be said that the welding method according to the present invention can provide an optimal welded joint in terms of both corrosion resistance and economy.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of an embodiment of a welded joint according to the present invention, Fig. 2 A, B, C, D, and H are cross-sectional views showing an embodiment of the welding procedure of the present invention; and FIG. 4 are sectional views of conventional welded joints, respectively. 1...Mixture material, 2...Base metal, 3...Base metal weld metal, 4, 4'...Mixture weld metal, 5...First intermediate layer weld metal, 6...Second intermediate layer weld metal .

Claims (1)

[Claims] 1 When welding a superalloy clad steel joint with stainless steel or Ni-based alloy having a Ni content of 15% or more by weight and carbon steel or low-alloy steel as the base material, the base metal side is opened. First, the composite part is welded using a filler metal with a high alloy chemical composition equivalent to that of the composite material. , 40
After welding the first intermediate layer using a filler metal with a chemical composition of C 0.02 or less and Si 0.1 or less in weight %, the balance is Fe and unavoidable impurity elements.
The second intermediate layer is welded using a filler metal containing 0.3% Ti, 0.3% to 1.0% Ti, and 0.3% to 1.0% Nb, with the remainder consisting of Fe and unavoidable impurity elements; A joint welding method for superalloy clad steel, characterized by welding carbon steel or low alloy steel filler metal equivalent to the base metal onto the intermediate layer up to the final layer.