Submerged-arc welding structure of dissimilar steel strip isolating layer

Abstract

The utility model provides a dissimilar steel strip isolating layer submerged-arc welding structure which comprises a first base material and a second base material, the edges of the first base material and the second base material are subjected to the same beveling operation, specifically, the front side and the back side of each plate end are each provided with a beveled edge, the plate ends are assembled to form an X-shaped beveled edge, and a truncated edge is reserved in the middle of each beveled edge; and surfacing the edge of the first base material to form a first welding body with the same thickness, butting the edges of the first base material and the second base material, and welding to obtain a second welding body. According to the method, subsequent submerged-arc welding is converted into similar steel welding through the isolation layer structure, and the risk of cracking caused by interaction of high residual stress and brittle structures after dissimilar steel welding is eliminated; and meanwhile, the problems that a wide recarburization and decarburization layer is generated due to carbon diffusion migration in direct welding of dissimilar steel, and cracking is caused due to serious ferrite embrittlement of a decarburized wide ferrite belt under long-time heat treatment and high-temperature operation are solved.

Description

Technical Field

[0001] The present invention relates to the field of welding technology, in particular to a submerged arc welding structure of a dissimilar steel strip isolation layer. Background Art

[0002] For the dissimilar steel welding joints of austenitic stainless steel + low alloy steel, in order to prevent post-weld cracking caused by excessive martensite content in the weld due to excessive fusion ratio and excessive dilution rate of the base material, improving the groove form, reducing the fusion ratio, and adopting welding methods with small parameters and small heat input have always been important control points in the dissimilar steel welding process. However, the above measures are exactly contrary to the welding characteristics of large penetration depth and high fusion ratio of submerged arc welding. Therefore, the application of submerged arc welding in dissimilar steel welding has been limited. However, for some large-structure thick plate dissimilar steel connection components, an efficient and stable welding method is urgently needed. To this end, the welding structure of the utility model solves the problem of limited application of dissimilar steel submerged arc welding due to excessive fusion ratio by pre-stacking an isolation layer before welding and then performing submerged arc butt welding, so that submerged arc welding can be applied to the welding of large-structure thick plate dissimilar steel, thereby improving production efficiency.

[0003] The utility model is aimed at the problems existing in the existing thick plate dissimilar steel welding, and provides a step-by-step welding method of pre-surfacing isolation layer + submerged arc welding butt welding. This technical solution can realize the application of submerged arc welding of large-diameter thick plate dissimilar steel, and improve production efficiency under the premise of ensuring the crack resistance and other performance properties of the welded joints after dissimilar steel welding. Summary of the Invention

[0004] To solve the above problems, the present invention discloses a submerged arc welding structure for a dissimilar steel strip isolation layer, comprising a first base metal and a second base metal, wherein the edges of the first base metal and the second base metal are subjected to the same beveling operation, specifically, beveling surfaces are provided on both the front and back sides of the plate ends, and the plate ends are paired to form an X-shaped bevel, with a blunt edge reserved between the two bevel surfaces on the front and back sides;

[0005] A first weld body with the same thickness is formed by surfacing welding on the edge of the first base material, and the edges of the first base material and the second base material are butted and welded to obtain a second weld body.

[0006] Preferably, the edges of the first base material and the second base material are butted together, and the groove angle formed by the groove surface is 60°.

[0007] Preferably, the first welded body is obtained by welding using 309L series welding rods.

[0008] Preferably, the second welded body is obtained by submerged arc double-sided welding using S308L welding wire and SJ601 flux.

[0009] The beneficial effects of the present invention are as follows: the present invention adopts an isolation layer structure to convert subsequent submerged arc welding into welding of similar steel materials, and also eliminates the risk of cracking caused by the interaction between high residual stress and brittle structure after welding of dissimilar steels; at the same time, compared with direct welding of dissimilar steels, there is carbon diffusion migration to produce wider carburization and decarburization layers. The wider ferrite band after decarburization will suffer from severe ferrite embrittlement and cracking under long-term heat treatment and high-temperature operation. The use of high Cr, Ni welding materials for pre-welding isolation layer can effectively inhibit the growth of decarburization layer and carburization layer and the precipitation of carbides, greatly reducing the risk of ferrite embrittlement during subsequent long-term thermal cycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a schematic diagram of the first parent material edge groove of the present invention;

[0011] Figure 2 This is a schematic diagram of the first parent material edge surfacing of the present invention;

[0012] Figure 3 This is a schematic diagram of the welding connection between the first base material and the second base material of the present invention.

[0013] List of reference numerals:

[0014] 1. First base material; 2. Groove surface; 3. Blunt edge; 4. First weld body; 5. Second weld body; 6. Second base material. DETAILED DESCRIPTION

[0015] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, and the terms "inward" and "outward" refer to directions toward or away from the geometric center of a particular component, respectively.

[0016] The equipment in this example is C221312 dissolving kettle, inner cylinder S30408, equipment flange 16MnII, equipment flange + inner cylinder annular butt joint B2-20mm thick, the welding operation includes the following steps:

[0017] Step 1: For the neck equipment flange and the connected cylinder butt joint, pre-open a double-sided asymmetric submerged arc welding groove according to the subsequent submerged arc welding process requirements, that is, open the groove surface 2, and the length of the blunt edge 2 is 6mm.

[0018] Step 2: First, use 309L series welding rod E309L-16 to pre-build an isolation layer on the groove of the 16MnII flange. Before cladding, remove impurities such as water, rust, and oil from the 16MnII flange groove surface and the surrounding 20mm area. The cladding electrode diameter should be ≤ Φ3.2. Use non-oscillating, straight-line, rapid welding with a current of ≤ 120A. Control the cladding depth and dilution rate, and keep the interpass temperature ≤ 150°C.

[0019] Step 3: After surfacing, measure the thickness of the surfacing layer. The thickness of the surfacing layer is required to be ≥10mm. Then the surface of the surfacing layer is turned into the final groove for submerged arc welding. After processing, the thickness of the surfacing layer is guaranteed to be ≥8mm.

[0020] Step 4: Perform visual inspection and 100% PT inspection on the groove surface after the cladding layer is processed. The PT inspection must pass Level I. Any defects exceeding the standard are repaired and polished to a smooth surface.

[0021] Step 5: Clean the groove surface after the buildup isolation layer processing and the final submerged arc weld groove surface of the S30408 base material on the other side, as well as the surrounding 20mm area, to remove any water, rust, and oil. Polish to a metallic luster, and then perform submerged arc welding with S308L / SJ601. The welding current should be controlled within the range of 400-500A.

[0022] Step 6: After the front side submerged arc welding is completed, when cleaning the back side, the thickness of the removed isolation layer should first be surfacing with E309L-16 welding rod to the specified thickness (i.e. ≥8mm after surfacing) and then filled with submerged arc welding.

[0023] In summary: 1. This method solves the problem of excessive fusion ratio and dilution rate in submerged arc welding of dissimilar steels, leading to post-weld cracking. Traditional submerged arc welding, due to its deep penetration and thick blunt edge, eliminates the need for a bevel for thin plate welding. For thick plate welding, a 5-6mm blunt edge and a Y-shaped bevel are typically reserved. However, both bevel configurations result in excessive incorporation of the base metal into the weld metal. Directly welding Q345R and S30408, excessive incorporation of the low-alloy Q345R base metal into the weld metal, significantly diluting elements like Cr and Ni. This results in the formation of a large amount of martensite in the weld microstructure, leading to post-weld cracking. The structure of pre-applying a weld overlay isolation layer avoids the direct welding of Q345R and S30408, and transforms the original welding of dissimilar steels into the welding of 309 weld overlay isolation layer and subsequent S30408 austenitic stainless steel of the same type. It fundamentally eliminates the occurrence of martensite-induced cracking due to excessive fusion ratio after submerged arc welding of dissimilar materials.

[0024] 2. It greatly reduces the width of the decarburized layer and the carburized layer formed by carbon migration during the welding of dissimilar steels, and reduces the risk of brittle cracking of the fusion line accessories due to the transformation of the decarburized layer into ferrite and embrittlement at high temperatures. When dissimilar steels are directly welded by butt welding, due to the diffusion of carbon, a decarburized layer is formed on the side of the pearlite steel with low Cr and Ni, and a carburized layer is formed on the side of the austenitic stainless steel with high Cr and Ni. In addition to the carbon element in the carburized layer being melted into the base material, the remaining carbon element precipitates as carbon and chromium carbides, which increases the brittle and hard tendency of the structure. The carbon content on the decarburized layer side is too low, and the pearlite structure will be transformed into ferrite. Under the subsequent long-term high-temperature operation and heat treatment, the ferrite will produce 475℃ embrittlement and other problems, causing cracking of the joint. The use of high fusion ratio submerged arc welding to directly weld dissimilar steels will further... This tendency toward brittle cracking is further exacerbated. Using high-Cr and high-Ni 309L welding consumables pre-clad on the Q345R side significantly inhibits carbon diffusion and migration, suppressing the growth of both decarburized and recarburized layers. Because the width of the decarburized layer formed within the barrier layer 309L is much smaller than that formed when conventional Q345R and S30408 are directly butt-welded, even with the same prolonged high-temperature and heat treatment cycles, the resulting ferrite embrittlement zone is too narrow, significantly reducing the ductility and toughness of the welded joint. Physical and chemical testing shows that welding with the barrier layer, after a subsequent 7-hour heat treatment, shows little change in ductility and toughness compared to the as-welded state. However, the ductility and toughness of the S30408+Q345R alloy significantly decreases after the prolonged heat treatment, essentially failing the bend test. Furthermore, the higher Ni content in the barrier layer, through graphitization, inhibits subsequent carbide formation, reducing the subsequent brittle-hard tendency of the microstructure.

[0025] Due to the significant differences in the linear expansion coefficient and thermal conductivity between austenitic stainless steel and low-alloy pearlite steel (the linear expansion coefficient of austenitic steel is 30%-50% higher than that of low-alloy pearlite steel, but its thermal conductivity is only 1 / 3 of that), direct welding of the two will inevitably result in large welding thermal stresses and post-weld residual stresses. Excessive welding residual stresses interact with the martensitic structure formed in the weld due to the excessive fusion ratio and the ferrite embrittlement caused by subsequent heat treatment, inevitably increasing the risk of cracking. However, the use of a pre-surfacing isolation layer transforms the original welding of dissimilar steels during docking into welding of the same type of steel with an isolation layer and subsequent austenitic stainless steel, thereby eliminating the factor of excessive welding residual stress caused by the difference in material and physical parameters on both sides and the direct welding of dissimilar materials. This eliminates the risk of cracking caused by the interaction of high residual stress and brittle structure.

[0026] The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above-mentioned embodiment, but also include technical solutions composed of any combination of the above technical features.

Claims

1. A submerged arc welding structure with a dissimilar steel strip isolation layer, characterized in that: The plate comprises a first mother material (1) and a second mother material (8), and the edges of the first mother material (1) and the second mother material (8) are subjected to the same beveling operation, specifically, beveling surfaces (2) are provided on both the front and back sides of the plate end, and the plate ends are paired to form an X-shaped beveling, and a blunt edge (3) is reserved between the two beveling surfaces (2) on the front and back sides; A first weld body (4) having the same thickness is formed by surfacing welding on the edge of the first parent material (1), and the edges of the first parent material (1) and the second parent material (8) are butted and welded to obtain a second weld body (5).

2. The submerged arc welding structure with a dissimilar steel strip isolation layer according to claim 1, characterized in that: The edges of the first parent material (1) and the second parent material (8) are butted together, and the groove angle formed by the groove surface (2) is 60°.

3. The submerged arc welding structure with a dissimilar steel strip isolation layer according to claim 1, characterized in that: The first welded body (4) is obtained by welding using 309L series welding rods.

4. The submerged arc welding structure with a dissimilar steel strip isolation layer according to claim 1, characterized in that: The second welded body (5) is obtained by submerged arc double-sided welding using S308L welding wire and SJ601 flux.

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