JPS6216745B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of welding a stainless steel joint. Iron-chromium (Fe-Cr) series, iron-chromium-nickel (Fe-Cr-Ni) series, iron-chromium-nickel-molybdenum (Fe-Cr-Ni) with excellent corrosion resistance, high-temperature oxidation resistance, high-temperature strength, etc. - Clad steel, which is made of stainless steel such as Mo) series, has been widely used in structures exposed to corrosive environments due to its economic efficiency. Joint welding of clad steel as a structure is generally carried out as shown in FIGS. 1A and 1B. That is, in FIG. 1A, a V-shaped groove is provided with the opening on the composite material 1 side, and after welding the base metal 2 with weld metal 3 having the same composition as the base metal 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 is equal to or higher than composite material 1.
Composite weld metal 4 with or better performance
I was getting . In addition, in Figure 1 B, an X-shaped groove is provided,
First, weld the base metal 2 from the base metal 2 side with a base metal weld metal 3a equivalent to the base metal 2, then weld the base metal 2 with a base metal weld metal 3b equivalent to the base metal 2 from the composite material 1 side, A good welded joint is obtained by welding a composite weld metal 4 of a high alloy equivalent to or higher than the composite material 1 on the weld metal 3b. In this way, if the stainless clad steel joint welding work can be carried out from the composite material 1 side, then
However, in the case of longitudinal welding or circumferential welding of small-diameter inner stainless steel clad steel pipes, welding equipment and welders cannot enter the inside of the steel pipe, so the outer base of the steel pipe must be welded without any problems. Welding work must be done from the material 2 side. In this case, as shown in Fig. 2, the commonly used welding method is to provide a V-shaped groove with the opening on the base metal 2 side, and to Comparing the total thickness of the clad steel up to the part with composite material 1, the total weld metal 4' was obtained using a welding material containing a large amount of alloying components. This is because when welding is performed on high alloy steel, which is the weld metal of composite material 1, using low carbon steel of the same type as base material 2 or welding material of low alloy steel, the weld metal of base material 2 will The components are concentrated by the weld metal of the composite material 1, which causes a part of the weld metal of the base material 2 to harden, resulting in a significant decrease in ductility and toughness, cracking, etc. This was because the entire thickness of the clad steel had to be welded with the entire weld metal 4' corresponding to composite material 1 due to the problem of. However, if welding is performed from the base metal side in this way and the entire thickness of the clad steel is welded using stainless steel high alloy steel, the welding material cost will be high, and the weld metal will be entirely made of stainless steel. Depending on the base metal, the strength of the welded joint may be lower than the base metal strength. Furthermore, stainless steel structures 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,
When all layers of the weld metal are made of austenitic stainless steel, the difference in thermal expansion coefficient between the weld metal and the base metal causes thermal stress, which can cause the weld joint to deform, or cause the weld metal to shift from the base metal. There was a problem in that the creep strength of the bond with the base metal decreased due to carbon diffusion. The applicant of the present application has published Japanese Patent Application Laid-Open No. 56-30081 entitled "Single-sided welding method for stainless steel clad steel joints," in which the chemical composition of the weld metal is in weight percent between the base metal weld metal layer and the composite weld metal layer. 1 so that C0.15% or less, Si1.0% or less, Mn2.0% or less, Cr12% or less, Ni12% or less, the balance being Fe and unavoidable impurity elements.
It was proposed to provide an intermediate weld metal layer of more than one layer. However, the intermediate weld metal layer as described above still had a high hardness of 350 to 400 Hv and a low toughness value. Also, in the bending test, the intermediate weld metal layer had no ductility and was hardly bent. When a clad pipe having such a stainless clad steel joint was used in a high temperature environment containing a large amount of hydrogen sulfide, cracks occurred in the joint. It was recognized that this was due to cracks occurring in the intermediate weld metal layer, which propagated into the base weld metal, leading to fracture. If the weld metal contains areas of high hardness and low toughness, even locally, there is a high possibility that cracks will occur under harsh usage environments, causing problems in the safe design of the structure. occured. For this reason, it became necessary to take measures to reduce the hardness and increase the toughness of the intermediate weld metal. The present invention has been made in view of the above circumstances, and employs a low dilution welding method to prevent carbon from penetrating from the base metal of stainless clad steel into the intermediate weld metal when welding the intermediate weld metal. , and also titanium (Ti) or niobium (Nb), or Ti and Nb
The object of the present invention is to solve the above-mentioned problems by fixing carbon in the weld metal using a low carbon steel filler metal containing . The details of the stainless clad steel joint welding method according to the present invention will be explained with reference to the drawings. In FIG. 3, a V-shaped groove is provided with openings on both base material 2 sides of the joint portion, and both composite materials 1 are butted.
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 melted, 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 content 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 intermediate layers are welded onto the composite weld metal 4 using a filler metal such as low carbon steel. The components of the intermediate weld metal 5 obtained at this time are C<0.1%, Si<1.0%, Mn<2.0%,
Cr<12%, Ni<10%, Mo<1.0% and either one of Ti or Nb, or the sum of them
The upper limit is 1.0%, and in the case of Ti alone, it is 4 times the amount of C,
In the case of Nb alone, 8 times the amount of C, in the case of both coexisting
The sum of the amount of Ti and twice the amount of Nb must be contained as a lower limit of four times the amount of C, and the balance must be made of Fe and unavoidable impurity elements. In order to obtain such an intermediate weld metal 5, in weight %,
C0.02% or less, Si0.1~0.3% and Ti0.5~1.0%,
Contains one or two types of Nb0.5~1.0% and the balance is Fe
In addition, it is necessary to use a filler metal consisting of unavoidable impurity elements. Next, a filler metal containing an alloying element equal to or higher than that of the base metal 2 is used on the intermediate weld metal 5 to join the entire thickness of both base metals 2 with the base metal weld 3. Welding methods applied to this, especially low carbon intermediate overlay methods, are preferably low heat input and low dilution welding, such as pulse-TIG welding, pulse-MIG welding,
Covered arc welding is suitable, but in the case of covered arc welding, the diameter of the welding rod should be 4 mmφ or less. Next, we will discuss the reasons for limiting the chemical composition of the filler metal for welding the intermediate layer. The lower the carbon C content, the lower the hardness of the intermediate weld metal 5 and the better the toughness. However, when the content exceeds 0.02%, carbon in the intermediate weld metal 5 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 intermediate weld metal 5. Silicon improves the fluidity of the filler metal during melting and acts as a deoxidizing agent. Si as a deoxidizer
requires 0.1% or more, and adding more than 0.3% will cause a significant decrease in toughness, so the range should be reduced to 0.1 to 0.3%.
And so. Titanium (Ti) and neobium (Nb) are elements necessary to fix C. 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 excess Ti and Nb improves toughness. Considering the decrease in and economic efficiency,
Each was set to 1.0% or less. Also, during welding, Ti, Nb
The lower limit for each was set at 0.5%, as these substances disperse into the air and reduce the effective amount. Next, embodiments of the present invention will be described. The test materials used were stainless clad steel plates with a 2.5 mm thick SUS316L material as the composite material and a 12.5 mm thick SB42 material as the base material. The groove shape is 4th
As shown in the figure, the groove angle α of the base material 2 is V-shaped.
α′=15°. First, a composite material 1 having the groove shape shown in FIG. 4A was welded using a Type 309 MoL coated arc welding rod as shown in FIG. 4B to obtain a composite weld metal 4. Next, using a 1.6 mm diameter low carbon steel filler metal having the chemical composition shown in Table 1 as the filler metal for the intermediate layer on the composite weld metal 4, welded the intermediate weld metal 5 by pulse TIG welding under the following conditions. Single layer welding was performed. Pulse current: current 190A, voltage 12V, time 0.3sec Base current: current 80A, voltage 9V, time 0.3sec Welding speed: 8cm/min, Ar shielding gas flow rate 10/min

[Table] Furthermore, base metal weld metal 3 was welded to the final layer on intermediate weld metal 5 by mild steel covered arc welding as shown in FIG. 4D. Note that preheating before welding and heat treatment after welding were not performed at all. The chemical composition of the intermediate weld metal 5 obtained by the above procedure is shown in Table 2, and the results of the mechanical test of the joint weld are shown in Table 3.

【table】

[Table] From the above results, weld metal with extremely low hardness and high toughness can be obtained in the joint regardless of which filler metal for the intermediate layer is used. With this level of hardness,
It has been empirically confirmed that there is almost no possibility of cracking during use as a structure. In order to clarify the effects of Ti and Nb addition, welded metals with chemical components equivalent to intermediate weld metals, such as Ti alone, Nb alone, Ti, Nb, and neither Ti nor Nb, were welded using a welding arc. The hardness of the remelted and solidified weld metal simulant test material was measured and the Charpy test was performed. The results are shown in Table 4.

[Table] Of course, the thermal history is different from the intermediate weld metal obtained in the example, and the chemical composition is also slightly different.
The hardness is higher than the hardness shown in Table 3. However, it is known that metals containing Ti, Nb, or both have lower hardness and higher toughness than metals containing no additives. This is because the addition of Ti and Nb fixed carbon to Ti and Nb, reducing the amount of solid solution carbon. As can be understood from the above explanation, in the welding method for stainless clad steel joints according to the present invention, Fe-Cr type, Fe-Cr-Ni type or Fe-
When welding a stainless clad steel joint using Cr-Ni-Mo stainless steel as a composite material and mild steel or low-alloy steel as the base material, a groove with an opening on the base metal side is created and the composite material is first welded. The composite part is welded using a filler metal with approximately the same chemical composition, and the chemical composition is 0.02% or less by weight, and Si0.1~ on top of this composite weld metal.
TIG welding or
One or more intermediate layers are welded using the MIG welding method, and a filler metal containing alloy elements equal to or higher than that of the base metal is welded onto this intermediate layer, so the welded joint is equivalent to a composite material. corrosion resistance, high-temperature oxidation resistance, etc., and mechanical strength equivalent to that of the base metal. By containing Ti and Nb in the intermediate weld metal, the hardness is reduced and a joint weld with high toughness is created. Therefore, it is possible to provide a stainless-clad steel structure that is free from cracking even when used as a pipe under severe conditions.

[Brief explanation of the drawing]

Figures 1A and 2B are explanatory diagrams of the conventional welding method for stainless clad steel joints from the composite material side, Figure 2 is an explanatory diagram of the conventional welding method from the base metal side, and Figure 3 is an explanatory diagram of the present invention. Explanatory diagram of the welding method according to Figure 4 A, B,
C and D are explanatory diagrams of embodiments of the present invention. 1...Mixture material, 2...Base metal, 3...Base metal weld metal, 4...
Composite weld metal, 5...Intermediate weld metal.

Claims (1)

[Claims] 1 Fe-Cr system, Fe-Cr-Ni system or Fe-Cr
- When welding stainless clad steel joints using Ni-Mo stainless steel as a composite material and mild steel or low-alloy steel as the base material, a groove with an opening on the base metal side is created and the composite material is first welded. The composite part is welded with filler metal of the same chemical composition, and the chemical composition is 0.02% or less by weight, Si0.1~0.3 on top of this composite weld metal.
% and one or two of Ti0.5~1.0% and Nb0.5~1.0%, with the remainder consisting of Fe and unavoidable impurity elements, using the TIG welding method or
A stainless steel club characterized by welding one or more intermediate layers using the MIG welding method, and then welding the final layer on the intermediate layer with a filler metal containing an alloy element equal to or higher than that of the base metal. How to weld joints made of Tsudo steel.