JPH01197073A - Method for welding joint of super alloy clad steel - Google Patents

Abstract

PURPOSE:To obtain an optimum welded joint from both sides of corrosion resistance and economicity by providing a particular intermediate layer for the purpose of preventing cracking and deterioration of ductile toughness after welding a first layer with a super alloy and welding its upper part with filler metal corresponding to base metal. CONSTITUTION:A groove with an opening at the base metal 2 side is provided and a cladding material part is first welded by the filler metal having almost equal chemical composition to cladding material 1. On the cladding material weld metal 4, the filler metal having the chemical composition consisting of, by weight, 10-40% Cr and the balance Fe with inevitable impurity elements is used to weld 5 a first intermediate layer. The filler metal having the chemical composition containing one kind or two kinds of <=0.02% C, 0.1-0.3% Si, 0.3-1.0% Ti, 0.3-1.0% Nb and the balance Fe with inevitable impurity elements is then used to weld (6) a second intermediate layer. Further, on this second intermediate layer weld metal 6, welding is performed up to a final layer with the carbon or low alloy steel filler metal equal to the base metal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a joint welding method for fully austenitic stainless steel or iron-based or nickel-based superalloy clad steel.

[Conventional technology]

15-20% nickel content compared to general stainless steel
The so-called fully austenitic stainless steels or iron-based and nickel-based super alloys that have been improved above have high corrosion resistance, stress corrosion cracking resistance, heat resistance strength, etc., and are used in line pipes for oil and gas production, gas processing plants, etc. It is beginning to be used in general chemical plants, paper manufacturing plants, etc.

Since these alloys are generally expensive and have lower strength than steel, clad steel, which is made from 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 as a structure is generally performed as shown in Figure 3 (a).
This is done as shown in (b). That is, in FIG. 3(a), a ■-shaped opening is provided with the opening on the composite material 1 side, and after welding the base material 2 with the weld metal 3 having the same composition as the base material 2 from the bottom of the groove, the base material 2 is welded from the bottom of the groove. Composite material 1 is welded to -F of material weld metal 3 using a welding material whose alloy composition is equal to or higher than that of composite material 1. A composite weld metal 4 having good performance was obtained.

In addition, in Fig. 3 (b), an X-shaped groove is provided, and the base metal 2 is first welded from the base metal 2 side with a base metal weld metal 3a that is equivalent to the base metal 2, and then the base metal 2 is welded from the composite material i side. A base metal weld metal 3b equivalent to the base metal 2 is welded, and a high-alloy composite weld metal 4 equivalent to or higher than the composite material 1 is welded onto the weld metal 3b to obtain a good welded joint. was.

In this way, stainless steel joint welding work is a composite material! If it can be carried out from the side, the method explained in Figures 3 (a) and (b) can be carried out without any problem, but if the inner surface is a superalloy clad steel pipe, it may be carried out at a circumferential joint between pipes, in a closed container, or in a comparatively When welding rad steel plates and the like because the area is large and it is difficult to reverse the welding location, 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 is applied to the entire thickness from the composite material 1 side to the base metal 2 side.

[Problem to be solved by the invention]

In the conventional welding method shown in Fig. 4, when the composite material side is welded with a welding material equivalent to the composite material, and then welded with a welding material equivalent to the base metal, the base metal weld metal is welded to the composite material side. When a large amount of melted alloys such as chromium, nickel, and molybdenum are picked up, hot cracking or cold cracking occurs, and the ductility is significantly reduced.

Further, although the conventional method shown in FIG. 4 is advantageous in that it uses only 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 superalloy high alloy steel, the cost of welding materials will be high, and since the weld metal is entirely made of superalloy, Depending on the base metal, the strength of the welded joint may be lower than the base metal strength. Furthermore, structures made of superalloy clad steel are often used in thermal environments such as high temperature ranges or repeated temperature ranges between high temperature and room temperature, and under such usage conditions, weld metal 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, and the diffusion of carbon from the base metal to the weld metal. Therefore, there was a problem in that the creep strength of the pound portion with the base metal decreased.

[Means to solve the problem]

The present invention was made in view of the above circumstances, and after welding the first layer with a superalloy alloy, a special intermediate layer is provided for the purpose of preventing cracking and deterioration of ductility, and a layer equivalent to the base metal is provided on top of the welding layer. We attempted to solve the problem by welding with filler metal.

That is, the present invention provides joint welding of stainless steel with a Ni content of 15% or more by weight, or a super alloy clad copper joint made of Ni-based alloy and carbon steel or low alloy steel as the base material. A groove with an opening on the side is provided, and the composite part is first welded with a filler metal having approximately the same chemical composition as the composite material, and the chemical composition of the composite weld metal is Cr 10% to 10% by weight. After welding the first intermediate layer using a filler metal consisting of 40% Fe, the balance being Fe and unavoidable impurity elements, the chemical composition is C0.02% or less in weight percent, Si 0.
1-0.3% and Ti 0.3-1.0%, Nb 0
．． A second intermediate layer is welded using a filler metal containing 3 to 1.0% of one or two types, with the remainder consisting of Fe and unavoidable impurity elements, and the second intermediate layer is further bonded to the base metal. This is a joint welding method for superalloy Clara 1 to steel, which is characterized by welding up to the final layer with equivalent carbon steel or low alloy steel filler metal.

[Effect]

The details of the super alloy clad steel joint welding method according to the present invention will be explained with reference to the drawings. In FIG. 1, a V-shaped opening is provided with openings on both sides of the joint 2, and the lily members 1 are butted together! 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, if only 1°1 of the composite material can be melted, there is no need to use a filler material, but
If there is a risk of partially melting the base metals 2, 2, welding is performed using a filler metal whose alloy composition is higher than that of the composite metal 1, so that the chemical composition of the composite weld metal 4 falls within the predetermined composition range. It is necessary to do so. 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 has a ferrite phase amount of 3% to 40% in terms of area ratio and the remainder is an austenite phase due to the infiltration from the base metal 2 and composite weld metal 4. You have to make it happen.

In order to obtain such a first intermediate layer weld metal 5, it is necessary to use a filler metal consisting of 10 to 40% Cr by weight, the balance being Fe and unavoidable impurity elements. By controlling the microstructure of the first intermediate layer metal 5 within the above range, hot cracking or deterioration of ductility can be prevented.

Next, when a filler metal of carbon steel or low alloy steel equivalent to the base metal is welded onto this, Ni and Cr of the first intermediate layer weld metal 5 are welded.
, Mo, etc. are mixed into the carbon steel weld layer, causing cold cracking or a significant decrease in ductility and toughness. Even if such alloying elements are mixed in, in order to prevent cracking or a decrease in ductility, the filler metal should have a sufficiently low C content and contain Ti or Nb to stabilize C as a carbide. need to be. That is, C0.02% or less in weight%, Si 0
．． 1-0.3% and Ti 0.3-1.0%, Nb
Contains 0.3 to 1.0% of one or two types, the balance being Fe
Welding must also be performed using a filler metal containing unavoidable impurity elements.

Next, on the second intermediate layer weld metal 6 obtained by welding the filler metal, a filler metal containing an alloy element equal to or higher than that of the base metal 2 is used to form the entire thickness of the double-open metal 2. are joined by base metal weld metal 3. Welding methods applied to this, especially low-carbon intermediate welding, are preferably low heat input and low dilution welding, and pulse-TIG welding, pulse-MIG welding, and shielded arc welding are suitable; 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 Cr content of the filler metal used when welding the first intermediate layer weld metal 5 is 10% or less, the microstructure of the first intermediate layer weld metal 5 becomes almost 100% austenite phase, resulting in hot cracking. do. On the other hand, when the Cr content is 40% or more, the first intermediate layer weld metal 5 has an extremely high Cr content and has extremely low ductility. 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 C exceeds 0.02%, the second
The carbon in the intermediate layer weld metal 6 is concentrated due to the movement of carbon contained in the base metal 2, and the hardness of the intermediate layer weld metal 6 becomes extremely high, causing performance deterioration of the second intermediate layer weld metal 6. Si improves the fluidity of the filler metal during melting and acts as a deoxidizing agent.

'As a deoxidizing agent, Si requires o.i% or more, and 0.
Addition of 3% or more causes a significant decrease in toughness, so the range was set to 0.1 to 0.3%. Ti and Nb are elements necessary to fix C, and Ti is more than 4 times the amount of C.
Nb requires at least 8 times the amount of C, but excessive Ti and N
In consideration of the decrease in toughness and economic efficiency caused by the addition of b, each content was set at 1.0% or less. Also, Ti, Nb during welding
Since these particles scatter into the air and the effective amount decreases, the lower limit for each was set at 0.3%.

〔Example〕

Next, the present invention will be explained in detail. As a test material, Incoloy 825 material with a thickness of 2.5 mm was used as a composite material, and a thickness of 1 mm was used as a base material.
A superalloy clad steel plate made of 9n+m API 5L-X60 material was used. The groove shape is shown in Figure 2 (a)
As shown in the figure, the groove angle α=α'=30 of the base material 2 in the V shape.
”. First, the composite material 1 with the groove shape shown in Fig. 2 (a)
were welded using an Inconel 625 TIG welding rod as shown in FIG. 2 (b) to obtain a composite weld metal. Next, a high Cr type filler material having the chemical composition shown in Table 1 was built up on the composite weld metal as a filler material for the intermediate layer under the welding conditions shown in Table 2. Test No. 1 to No. 4). For comparison,
Using 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 1 Chemical composition of filler metal for intermediate layer (wt%) Next, in Test No. 1, as shown in Figure 2 (d), on the first intermediate layer weld metal, the second intermediate layer was welded by pulse TIG welding. One layer of weld metal was welded.

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. 2(E).

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 integrity test of the joint weld are shown in Table 4.

As shown in Table 4, the Inconel 625 weld layer is directly overlaid with carbon steel welding material equivalent to the base material (Test No.
Regarding 5), the carbon steel weld layer caused a significant decrease in ductility, and it was observed that many hot cracks had already occurred in the carbon steel weld layer immediately above the Inconel 625 weld layer immediately after welding.

Table 3 Chemical composition of filler metal for intermediate layer Table 4 of 0 cedar
Mechanical test results for welded joints The joints welded using the method according to the invention showed sufficient ductility, no cracks were observed, and mechanical properties almost equivalent to those of welded joints made of carbon steel pipes.

(Effects 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 the welding material also has the characteristics of a clad material. I can do it. 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 the drawing]

Fig. 1 is a cross-sectional view of an embodiment of the welded joint according to the present invention, and Fig. 2 (a), (b), (c), (d), and (e) show an embodiment of the welding procedure of the present invention. A sectional view shown in Fig. 3 (a),
(B) and FIG. 4 are sectional views of conventional welded joints, respectively. 1...Mixture 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 Patent applicant The Japan Steel Works, Ltd.

Claims (1)

[Claims] (1) When welding joints of stainless steel with a Ni content of 15% or more by weight, or super alloy clad steel with a Ni-based alloy composite and carbon steel or low alloy steel as the base material, the base metal side is opened. A groove is prepared, and the composite part is first welded with a filler metal having approximately the same chemical composition as the composite material.
After welding the first intermediate layer using a filler metal consisting of 0% Fe and unavoidable impurity elements, the chemical composition is 0% by weight.
with C0.02% or less, Si0.1-0.3% and Ti
The second intermediate layer is welded using a filler metal containing one or two of 0.3 to 1.0% Nb and 0.3 to 1.0% Nb, with the remainder consisting of Fe and unavoidable impurity elements, and A method for welding a joint of superalloy clad steel, characterized by welding carbon steel or low alloy steel filler metal equivalent to the base metal onto the second intermediate layer up to the final layer.