Marine stainless steel clad plate welding process

Abstract

The present application relates to the technical field of stainless steel composite plate welding for ships, and discloses a welding process for stainless steel composite plate for ships, which comprises the following steps: step one, groove processing; step two, gasket mounting; step three, welding wire selection; step four, base layer bottoming welding; step five, base layer filling welding; step six, transition layer welding; and step seven, cladding welding: carbon dioxide gas shielded welding is adopted to perform cladding welding on the transition layer weld using the SFC-316L welding wire in a direct current reverse connection mode to form a cladding weld; the present application reduces the melting amount of the carbon steel base material through the design of the narrow gap at the root of the V-shaped groove; the ceramic gasket realizes single-sided welding and double-sided forming, thereby avoiding the thermal damage of back surface cleaning to the structure; the Cr element fixes the carbon in the weld, blocks the diffusion path of the carbon to the stainless steel side, and the comprehensive action of the multiple mechanisms controls the width of the decarburization layer and the carbon enrichment layer in the welded joint within a very small range, thereby reducing the welding cracks caused by carbon migration.

Description

Technical Field

[0001] This invention relates to the field of marine stainless steel composite plate technology, specifically a welding process for marine stainless steel composite plates. Background Technology

[0002] With the rapid development of the shipbuilding industry and technology, single materials cannot match the combined high strength and corrosion resistance of layered metal composite materials. Composite materials have gradually become an indispensable material in the shipbuilding and repair industry, and stainless steel composite plates are commonly used in the construction and repair of chemical tankers. However, when welding dissimilar materials, there are many factors that affect the welding quality due to significant differences in physical properties and chemical composition.

[0003] Specifically, carbon steel has a high carbon content and a low alloying element content, while stainless steel is the opposite. This significant difference in element concentration makes carbon migration in the weld fusion zone prone to occur during welding. Carbon diffuses from the carbon steel side to the stainless steel side, resulting in a decarburized layer on the carbon steel side and a carburized layer on the stainless steel side. The diffused carbon readily combines with chromium in the stainless steel to form chromium carbide, producing a hardened structure that can lead to weld cracks and other defects. Furthermore, calculations based on the Schaeffler microstructure diagram show that a mixture of Grade A steel and 316L steel may form a martensitic structure, which significantly affects the material's mechanical properties and corrosion resistance. Therefore, effectively suppressing carbon migration, preventing martensitic formation, and ensuring good mechanical and corrosion resistance in the welded joint are pressing technical challenges in the welding of stainless steel composite plates.

[0004] In view of this, the present invention addresses the shortcomings of the prior art by providing a welding process for marine stainless steel composite plates, aiming to solve technical problems such as welding cracks caused by carbon migration and the impact on joint performance due to the formation of martensite during the welding process of stainless steel composite plates, while achieving efficient and low-cost engineering applications. Summary of the Invention

[0005] The purpose of this invention is to provide a welding process for marine stainless steel composite plates to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a welding process for marine stainless steel composite plates, comprising the following steps: Step 1: Beveling: A V-shaped welding bevel is processed on the part of the stainless steel composite plate to be welded. The V-shaped welding bevel is opened from the stainless steel cladding side to the carbon steel base side, and the opening width of the V-shaped welding bevel gradually decreases from the stainless steel cladding side to the carbon steel base side. Step 2, Gasket Installation: Ceramic gaskets are installed on the reverse side of the stainless steel composite plate test plate. The reverse side is the outer surface of the carbon steel base layer. The ceramic gaskets are continuously arranged along the length of the weld to support the molten pool and ensure the formation of the reverse side of the weld. Step 3: Welding wire selection: Calculate the possible microstructure formed after mixing Grade A steel and 316L steel according to the Schaeffler microstructure diagram, and select welding materials based on the calculation results. Specifically: SFC-309MoL welding wire with higher Cr and Ni content than the cladding layer is used for transition layer welding; YCJ501-1 welding wire is used for base layer welding; and SFC-316L welding wire is used for cladding layer welding. Step 4, Base layer root pass welding: Carbon dioxide gas shielded welding is used to perform root pass welding on the carbon steel base layer in DC reverse polarity mode to form a root pass weld. Step 5, Base filler weld: Carbon dioxide gas shielded welding is used to perform base filler weld on the root weld in DC reverse polarity to form the base filler weld. Step 6, Transition Layer Welding: Using carbon dioxide gas shielded welding, the SFC-309MoL welding wire is used to perform transition layer welding on the base filler weld in DC reverse polarity to form a transition layer weld. During the welding process, the welding speed is controlled to reduce heat input, so that the transition layer weld metal meets the principle of equal performance matching to avoid the generation of martensite structure. Step 7, Coating Welding: Using carbon dioxide gas shielded welding, the SFC-316L welding wire is used to perform coating welding on the transition layer weld in DC reverse polarity to form a coating weld.

[0007] Preferably, in step one, the bevel angle of the V-shaped welding groove is 40°±2°, and the root gap of the V-shape is 6±1mm.

[0008] Preferably, in step two, the ceramic gasket is attached to the underside of the outer surface of the carbon steel base layer, and the ceramic gasket is in close contact with the outer surface of the carbon steel base layer to bear the molten metal during the welding process and form a full back weld.

[0009] Preferably, in step three, the SFC-309MoL welding wire used for the transition layer welding has a specification of φ1.2mm; the YCJ501-1 welding wire used for the base layer welding has a specification of φ1.2mm; and the SFC-316L welding wire used for the cladding layer welding has a specification of φ1.2mm.

[0010] Preferably, in step three, the YCJ501-1 welding wire used for the base layer welding meets the principle of equal strength, the SFC-309MoL welding wire used for the transition layer welding meets the principle of equal performance matching, and the SFC-316L welding wire used for the cladding layer welding matches the 316L stainless steel cladding material.

[0011] Preferably, in step six, the welding speed of each weld is controlled to be higher than that of the cladding weld during the transition layer welding process, so as to reduce heat input and reduce the risk of hot cracking.

[0012] Preferably, when welding in the flat welding position, the process parameters for each weld bead are as follows: Root pass welding: Welding current 182-208A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 13.8-16.9cm / min; Base filler welding: welding current 218-262A, welding voltage 25-27V, power supply polarity is DC reverse polarity, welding speed 20.0-36.6cm / min; Transition layer welding: welding current 205-235A, welding voltage 25-27V, power supply polarity is DC reverse polarity, welding speed 17.4-21.3cm / min; Clad welding: welding current 205-246A, welding voltage 24-27V, power supply polarity is DC reverse polarity, welding speed 25.7-33.0cm / min.

[0013] Preferably, when welding in a vertical welding position, the process parameters for each weld bead are as follows: Root pass welding: welding current 175-198A, welding voltage 21-23V, power supply polarity is DC reverse polarity, welding speed 11.0-13.5cm / min; Base filler welding: welding current 180-208A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 11.4-13.8cm / min; Transition layer welding: welding current 160-180A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 9.2-11.2cm / min; Clad welding: Welding current 150-170A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 6.8-8.4cm / min.

[0014] Preferably, in steps four to seven, the welding of each layer of weld bead adopts a multi-layer, multi-pass welding method, and the interpass temperature between adjacent weld bead is controlled below 150°C by natural cooling or forced cooling.

[0015] Preferably, in steps four to seven, the shielding gas used in carbon dioxide gas shielded welding is carbon dioxide gas, the volume purity of the carbon dioxide gas is not less than 99.5%, and the gas flow rate is 15L / min to 20L / min; during the welding process, the wire extension length is controlled between 15mm and 20mm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention suppresses carbon migration through multiple synergistic mechanisms: a narrow gap design at the root of the V-groove reduces the amount of carbon steel base metal melted into the weld; a ceramic backing enables single-sided welding with double-sided forming, avoiding thermal damage to the microstructure caused by back-side root cleaning; the transition layer uses high-Cr SFC-309MoL welding wire, where Cr elements fix the carbon in the weld, blocking the diffusion path of carbon to the stainless steel side; high welding speed and low heat input reduce the diffusion distance and time of carbon elements; and the interpass temperature is controlled below 150℃ to suppress carbon diffusion at high temperatures. The combined effect of these multiple mechanisms keeps the width of the decarburized and carburized layers in the weld joint within a very small range, thereby reducing welding cracks caused by carbon migration. Based on the calculation of the Schaeffler microstructure diagram, this invention precisely selects the welding material SFC-309MoL for the transition layer. The high Cr and high Ni content of the welding wire pushes the microstructure of the weld metal from the martensitic region to the austenitic or austenitic + ferrite region. Combined with a low heat input process and interpass temperature control, the final transition layer weld and cladding weld microstructure are mainly austenitic, without martensitic hardening, thus ensuring that the welded joint has sufficient plasticity, toughness, and resistance to intergranular corrosion. This invention employs carbon dioxide gas shielded welding throughout the entire process. Compared to traditional shielded metal arc welding (SMAW) and tungsten inert gas (TIG) welding, it offers advantages such as high deposition efficiency, low welding cost, and the ability to achieve automated or semi-automated operation, reducing labor intensity. Furthermore, with the addition of ceramic backing, it enables single-sided welding with double-sided forming, eliminating the need for workpiece flipping and back-side cleaning and repair welding, significantly shortening the construction cycle. The combined effect of these advantages allows this process to significantly improve welding efficiency and reduce manufacturing costs while ensuring welding quality, fully meeting the large-scale application needs of practical engineering projects such as the construction and repair of chemical tanker cargo holds.

[0017] The parts of the device not covered herein are the same as or can be implemented using existing technologies. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the bevel structure for a welding process of marine stainless steel composite plate according to the present invention. Figure 2 This is a schematic diagram of the flat weld bead of a stainless steel composite plate according to a welding process for marine stainless steel composite plates of the present invention. Figure 3 This is a schematic diagram of the vertical welding bead of a stainless steel composite plate according to a welding process for marine stainless steel composite plates of the present invention. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0020] Example 1: Please refer to Figures 1-3 This invention provides a technical solution: a welding process for marine stainless steel composite plates, comprising the following steps: Step 1, Beveling: Process a V-shaped welding bevel at the welding area of ​​the stainless steel composite plate. The V-shaped welding bevel is opened from the stainless steel cladding side to the carbon steel base side, and the opening width of the V-shaped welding bevel gradually decreases from the stainless steel cladding side to the carbon steel base side. The V-groove's decreasing width from top to bottom allows the welding torch, applied from the stainless steel cladding side, to easily reach the bottom of the groove for root pass welding of the underlying carbon steel base layer. Simultaneously, the narrower lower groove allows the amount of molten metal to gradually increase from bottom to top, perfectly matching the welding sequence of this process: "weld the root base layer first, then fill the layers upwards to the cladding layer." More importantly, the V-groove's wider upper section and narrower lower section effectively controls the fusion ratio of the root pass and the fill pass, i.e., the proportion of the base metal in the weld metal. The narrower root region reduces the amount of carbon steel base metal melted, thereby reducing the total amount of carbon input into the weld and mitigating the carbon migration driving force during subsequent transition layer welding. Step 2, Ceramic Backing Installation: Ceramic backing is installed on the reverse side of the stainless steel composite plate test panel, which is the outer surface of the carbon steel base layer. The ceramic backing is continuously arranged along the length of the weld to support the molten pool and ensure the formation of the weld on the reverse side. The ceramic backing is a rigid backing made of high-alumina refractory material sintered at high temperature. It has the characteristics of high temperature resistance (above 1600℃), low thermal conductivity, and no chemical reaction with molten metal. During welding, the ceramic backing is tightly attached to the bottom outer surface of the carbon steel base layer. When the welding torch is applied from the cladding side, the arc energy penetrates the entire plate thickness and melts the root base material. As the molten metal flows downward under gravity, it is supported by the rigid surface of the ceramic backing and cools and solidifies under the constraint of the backing, forming a full and smooth back weld. Step 3: Welding Wire Selection: Based on the Schaeffler microstructure diagram, the possible microstructure formed after mixing Grade A steel and 316L steel is calculated. Welding materials are selected based on the calculation results: For the transition layer welding, SFC-309MoL welding wire with higher Cr and Ni content than the cladding layer is used; for the base layer welding, YCJ501-1 welding wire is used; and for the cladding layer welding, SFC-316L welding wire is used. According to the calculation results of the Schaeffler microstructure diagram, the transition layer welding uses SFC-309MoL welding wire with a φ1.2mm diameter and higher Cr and Ni content. This welding wire has a Cr content of approximately 23%–25% and a Ni content of approximately 12%–14%, significantly higher than the Cr content of 16%–18% and Ni content of 10%–14% in the 316L base material. When the SFC-309MoL welding wire melts into the transition layer, its high Cr and Ni content pushes the Cr and Ni equivalents of the weld metal towards the austenite or austenite + ferrite region in the Schaeffler microstructure diagram, thus preventing the formation of martensite. This welding wire selection principle is called the equal performance matching principle, which means that the properties of the transition layer weld metal, including corrosion resistance and mechanical properties, should be equivalent to those of the cladding base metal. Meanwhile, for the base layer welding, YCJ501-1 welding wire with a diameter of φ1.2mm was used. This welding wire is a gas-shielded welding wire for carbon steel, and the strength of its deposited metal matches the strength of the carbon steel base material, satisfying the principle of equal strength. For the cladding layer welding, SFC-316L welding wire with a diameter of φ1.2mm was used. Its chemical composition is consistent with that of the 316L stainless steel cladding base material, satisfying the principle of material matching. Through the differentiated selection of the three layers of welding wire, the transition layer uses SFC-309MoL welding wire with high Cr and high Ni content, which effectively suppresses the formation of martensite. The corrosion resistance and mechanical properties of the transition layer weld metal are comparable to those of the cladding base metal, achieving equal performance matching. The strength of the base weld matches that of the base metal, ensuring the load-bearing capacity of the joint. The composition of the cladding weld is consistent with that of the base metal, ensuring the corrosion resistance of the cladding surface. The synergistic effect of the three layers of welding wire systematically solves the problem of microstructure matching in dissimilar steel welding from a material perspective. Step 4, Base layer root pass welding: Carbon dioxide gas shielded welding is used to perform root pass welding on the carbon steel base layer in DC reverse polarity mode to form a root pass weld. Step 5, Base filler weld: Carbon dioxide gas shielded welding is used to perform base filler weld on the root weld in DC reverse polarity to form the base filler weld. Steps four and five involve root pass welding and filler welding, respectively, both performed using CO2 gas shielded welding with DC reverse polarity. The basic working principle of CO2 gas shielded welding is as follows: the welding wire is continuously fed as the electrode, generating an arc between the wire tip and the workpiece. The high temperature of the arc, approximately 5000-6000℃, melts the welding wire and base material to form a molten pool. Simultaneously, CO2 gas ejected from the welding torch nozzle forms a protective gas flow, displacing air from the arc zone and molten pool zone to prevent oxidation and nitriding of the molten metal. DC reverse polarity, with the workpiece connected to the negative electrode and the welding wire to the positive electrode, is characterized by greater penetration, a stable arc, and less spatter, making it suitable for root pass welding and filler welding of thick plates. Step 6, Transition Layer Welding: Using carbon dioxide gas shielded welding, SFC-309MoL welding wire is used to weld the transition layer on the base filler weld in DC reverse polarity to form the transition layer weld. During the welding process, the welding speed is controlled to reduce heat input and ensure that the transition layer weld metal meets the principle of equal performance matching to avoid the formation of martensite structure. The transition layer welding uses SFC-309MoL welding wire (φ1.2mm). This wire contains a high content of Cr (23%–25%) and Ni (12%–14%), with added Mo (2%–3%). During welding, the arc simultaneously melts the SFC-309MoL welding wire and a portion of the carbon steel filling the weld surface layer, forming a transition layer molten pool. This pool contains Fe and C elements from the carbon steel, as well as a large amount of Cr, Ni, and Mo elements from the welding wire. The addition of these alloying elements makes Cr and Ni strong austenitizing elements, pushing the weld metal microstructure from the martensitic region to the austenitic or austenitic + ferrite region, thereby inhibiting the formation of martensitic hardened structures. Cr has a strong affinity for C, preferentially combining with C to form stable carbides, thus fixing the carbon elements in the weld and preventing their continued diffusion to the stainless steel side. The addition of Mo further improves the weld metal's resistance to pitting and crevice corrosion. As welding speed increases, heat input decreases. Reducing heat input is significant because it decreases the high-temperature dwell time, thereby reducing the diffusion distance and amount of carbon, inhibiting carbon migration; it reduces carbide precipitation at grain boundaries, preventing intergranular corrosion; it lowers the level of residual welding stress, reducing the driving force for hot and cold cracking; and it refines the grain structure of the weld metal, improving plasticity and toughness. Furthermore, step six requires the welding speed of the transition layer to be higher than that of the cladding layer, because the transition layer is more sensitive to heat input. Carbon migration and martensitic transformation mainly occur in the transition layer region, therefore, this region requires stricter heat input control.

[0021] If the heat input of the transition layer is too high, i.e. the welding speed is too slow, the high temperature duration is prolonged, and carbon elements have more time to diffuse from the carbon steel side to the stainless steel side, resulting in thicker decarburized and carburized layers. A large amount of network carbides precipitate in the carburized layer, making the joint embrittled. At the same time, excessive heat input will also lead to coarse weld grains, reducing plasticity and toughness.

[0022] Step 7, Coating Welding: Using carbon dioxide gas shielded welding, SFC-316L welding wire is used to perform coating welding on the transition layer weld in DC reverse polarity to form the coating weld.

[0023] The cladding welding uses SFC-316L welding wire with a diameter of φ1.2mm. Its chemical composition is exactly the same as that of the 316L stainless steel cladding base material: Cr approximately 16%–18%, Ni approximately 10%–14%, Mo approximately 2%–3%, and C ≤ 0.03%. Since the transition layer provides a buffer zone with high Cr and high Ni, there is no dilution problem of carbon steel to the weld during cladding welding. The arc only melts the SFC-316L welding wire and the SFC-309MoL weld metal on the surface of the transition layer. Both have similar compositions, being austenitic stainless steel. Therefore, the chemical composition of the cladding weld can remain consistent with that of the 316L base material.

[0024] During the welding process, the SFC-316L welding wire melts into the transition layer surface, forming the final cladding weld. This weld has an austenitic microstructure, exhibiting excellent corrosion resistance. The cladding weld is the surface of a chemical tanker's cargo hold that directly contacts corrosive media, and its corrosion resistance directly determines the ship's service life and safety. The SFC-316L welding wire contains molybdenum (Mo), further enhancing the weld metal's resistance to pitting corrosion in chloride-containing environments.

[0025] In step one, the bevel angle of the V-groove is 40°±2°, and the root gap is 6±1mm. The size of the bevel angle directly affects the filler metal, fusion ratio, and accessibility of the welding torch. A 40° bevel angle is considered a small V-groove angle, reducing the filler metal: the smaller the bevel angle, the less filler metal is required, which improves welding efficiency and reduces the total heat input, thus helping to suppress carbon migration. The root gap of 6±1mm is considered a large root gap, ensuring full root penetration: a larger root gap allows the arc to fully penetrate to the root during the first root pass, achieving good back-side formation with the ceramic backing; it also facilitates torch insertion: since this process uses CO2 gas shielded welding, the torch nozzle has a certain size, and the larger root gap allows the torch to easily extend into the root of the bevel for the root pass. In step two, a ceramic backing is installed below the outer surface of the carbon steel base layer. The ceramic backing adheres tightly to the outer surface of the carbon steel base layer and is used to bear the molten metal during welding and form a full back weld. By installing the ceramic backing, single-sided welding with double-sided forming is achieved, eliminating the need to flip the workpiece and perform back root cleaning and repair welding, significantly shortening the construction cycle. The back weld is full, without depressions or weld beads, ensuring the integrity of the entire cross-section of the welded joint. It avoids the thermal damage and stress concentration caused to the base layer structure by carbon arc gouging. The thermal insulation effect of the ceramic backing also reduces heat loss on the back side, which is beneficial for the heat preservation and slow cooling of the molten pool, reducing the risk of hardened structure caused by excessively rapid cooling.

[0026] In step three, the SFC-309MoL welding wire used for the transition layer welding has a specification of φ1.2mm; the YCJ501-1 welding wire used for the base layer welding has a specification of φ1.2mm; and the SFC-316L welding wire used for the cladding layer welding has a specification of φ1.2mm. In step three, the YCJ501-1 welding wire used for the base layer welding meets the principle of equal strength, the SFC-309MoL welding wire used for the transition layer welding meets the principle of equal performance matching, and the SFC-316L welding wire used for the cladding layer welding is matched with the 316L stainless steel cladding material. Through the differentiated selection of the three layers of welding wire, the transition layer uses SFC-309MoL welding wire with high Cr and high Ni content, which effectively suppresses the formation of martensite. The corrosion resistance and mechanical properties of the transition layer weld metal are comparable to those of the cladding base metal, achieving equal performance matching. The strength of the base weld matches that of the base metal, ensuring the load-bearing capacity of the joint. The composition of the cladding weld is consistent with that of the base metal, ensuring the corrosion resistance of the cladding surface. The synergistic effect of the three layers of welding wire systematically solves the problem of microstructure matching in dissimilar steel welding from a material perspective. In step six, the welding speed of each weld pass during the transition layer welding process is controlled to be higher than that of the cladding layer welding to reduce heat input and lower the risk of hot cracking. The welding speed of the transition layer is higher than that of the cladding layer because the transition layer is more sensitive to heat input. Carbon migration and martensitic transformation mainly occur in the transition layer region, therefore, this region requires stricter heat input control.

[0027] When welding in a flat position, the process parameters for each weld bead are as follows: Root pass welding: Welding current 182-208A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 13.8-16.9cm / min; Base filler welding: welding current 218-262A, welding voltage 25-27V, power supply polarity is DC reverse polarity, welding speed 20.0-36.6cm / min; Transition layer welding: welding current 205-235A, welding voltage 25-27V, power supply polarity is DC reverse polarity, welding speed 17.4-21.3cm / min; Clad welding: welding current 205-246A, welding voltage 24-27V, power supply polarity is DC reverse polarity, welding speed 25.7-33.0cm / min.

[0028] Table 1 Flat Welding Process Parameters Flat welding utilizes higher current and faster welding speed to leverage the high efficiency advantages of CO2 gas shielded welding.

[0029] In steps four through seven, the welding of each layer of weld bead adopts a multi-layer, multi-pass welding method, and the interpass temperature between adjacent weld bead is controlled below 150℃ through natural cooling or forced cooling.

[0030] Interpass temperature refers to the measured temperature of the previous weld before the next weld is applied during multi-layer, multi-pass welding. Steps four through seven require that the interpass temperature be controlled below 150℃, which can be achieved through natural cooling or forced cooling. The necessity of interpass temperature control stems from the sensitization phenomenon in stainless steel. When austenitic stainless steels, including 316L, remain in the temperature range of 450-850℃ for extended periods, chromium (Cr) at the grain boundaries combines with carbon (C) to form carbides that precipitate along the grain boundaries. This causes the Cr content near the grain boundaries to decrease below the critical value required for passivation, resulting in a loss of resistance to intergranular corrosion. This temperature range is known as the sensitization temperature range. If the interpass temperature is too high, exceeding 150℃, the combined heat from the previous weld and the new weld will prolong the residence time of the weld metal within the sensitization temperature range during subsequent weld passes, leading to a large amount of carbide precipitation and a severe decrease in resistance to intergranular corrosion.

[0031] Furthermore, excessively high interpass temperatures can: increase the grain size of the weld metal, reducing plasticity and toughness; increase the level of residual stress in welding; and provide higher temperatures and longer times for carbon diffusion, thus exacerbating carbon migration. Controlling the interpass temperature below 150°C ensures that each weld pass has cooled to a temperature well below the sensitization temperature range before the next pass is welded, thereby avoiding excessively long cumulative residence time of the weld metal within the sensitization temperature range.

[0032] In steps four through seven, the shielding gas used in carbon dioxide gas shielded welding is carbon dioxide gas, the volume purity of which is not less than 99.5%, and the gas flow rate is 15L / min to 20L / min; during the welding process, the wire extension length is controlled between 15mm and 20mm.

[0033] After CO2 gas is ejected from the welding torch nozzle, it forms a protective gas shield around the electric arc, displacing air from the arc zone and the molten pool. If the CO2 purity is insufficient, the protective effect will decrease, and the molten metal will be oxidized or nitrided, resulting in defects such as porosity and inclusions. If the gas flow rate is too low (<15L / min), the protective gas flow will be insufficient to displacing air; if the flow rate is too high (>20L / min), turbulence will occur, entraining air into the molten pool.

[0034] The wire extension length refers to the length of the welding wire extending from the tip of the welding torch to the surface of the workpiece. The principle behind controlling the extension length to 15mm-20mm is that the welding wire itself has resistance; when welding current passes through the extended section of the wire, it generates resistance heat to preheat the wire. The longer the extension length, the greater the resistance heat, the higher the preheating temperature of the wire, and the higher the deposition efficiency. However, if the extension length is too long, the wire will glow red and soften in the extended section due to excessive resistance heat, leading to unstable wire feeding and arc drift; if the extension length is too short, the preheating is insufficient, reducing deposition efficiency. 15mm-20mm is the optimal extension length range for φ1.2mm welding wire in CO2 gas shielded welding.

[0035] Example 2: In this example, everything else is the same as in Example 1. The difference is that vertical welding is used, and the process parameters for each weld are as follows: Root pass welding: welding current 175-198A, welding voltage 21-23V, power supply polarity is DC reverse polarity, welding speed 11.0-13.5cm / min; Base filler welding: welding current 180-208A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 11.4-13.8cm / min; Transition layer welding: welding current 160-180A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 9.2-11.2cm / min; Clad welding: Welding current 150-170A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 6.8-8.4cm / min.

[0036] Table 2 Vertical welding process parameters: By reducing current and speed, the vertical welding parameters overcome the problem of molten pool flow and ensure the welding quality of the vertical welding position.

[0037] This invention suppresses carbon migration through multiple synergistic mechanisms: a narrow gap design at the root of the V-groove reduces the amount of carbon steel base metal melted into the weld; a ceramic backing enables single-sided welding with double-sided forming, avoiding thermal damage to the microstructure caused by back-side root cleaning; the transition layer uses high-Cr SFC-309MoL welding wire, where Cr elements fix the carbon in the weld, blocking the diffusion path of carbon to the stainless steel side; high welding speed and low heat input reduce the diffusion distance and time of carbon elements; and the interpass temperature is controlled below 150℃ to suppress carbon diffusion at high temperatures. The combined effect of these multiple mechanisms keeps the width of the decarburized and carburized layers in the weld joint within a very small range, thereby reducing welding cracks caused by carbon migration. Based on the calculation of the Schaeffler microstructure diagram, this invention precisely selects the welding material SFC-309MoL for the transition layer. The high Cr and high Ni content of the welding wire pushes the microstructure of the weld metal from the martensitic region to the austenitic or austenitic + ferrite region. Combined with a low heat input process and interpass temperature control, the final transition layer weld and cladding weld microstructure are mainly austenitic, without martensitic hardening, thus ensuring that the welded joint has sufficient plasticity, toughness, and resistance to intergranular corrosion. This invention employs carbon dioxide gas shielded welding throughout the entire process. Compared to traditional shielded metal arc welding (SMAW) and tungsten inert gas (TIG) welding, it offers advantages such as high deposition efficiency, low welding cost, and the ability to achieve automated or semi-automated operation, reducing labor intensity. Furthermore, with the addition of ceramic backing, it enables single-sided welding with double-sided forming, eliminating the need for workpiece flipping and back-side cleaning and repair welding, significantly shortening the construction cycle. The combined effect of these advantages allows this process to significantly improve welding efficiency and reduce manufacturing costs while ensuring welding quality, fully meeting the large-scale application needs of practical engineering projects such as the construction and repair of chemical tanker cargo holds.

[0038] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A welding process for marine stainless steel composite plates, characterized in that: Includes the following steps: Step 1: Beveling: A V-shaped welding bevel is processed on the part of the stainless steel composite plate to be welded. The V-shaped welding bevel is opened from the stainless steel cladding side to the carbon steel base side, and the opening width of the V-shaped welding bevel gradually decreases from the stainless steel cladding side to the carbon steel base side. Step 2, Gasket Installation: Ceramic gaskets are installed on the reverse side of the stainless steel composite plate test plate. The reverse side is the outer surface of the carbon steel base layer. The ceramic gaskets are continuously arranged along the length of the weld to support the molten pool and ensure the formation of the reverse side of the weld. Step 3: Welding wire selection: Calculate the possible microstructure formed after mixing Grade A steel and 316L steel according to the Schaeffler microstructure diagram, and select welding materials based on the calculation results. Specifically: SFC-309MoL welding wire with higher Cr and Ni content than the cladding layer is used for transition layer welding; YCJ501-1 welding wire is used for base layer welding; and SFC-316L welding wire is used for cladding layer welding. Step 4, Base layer root pass welding: Carbon dioxide gas shielded welding is used to perform root pass welding on the carbon steel base layer in DC reverse polarity mode to form a root pass weld. Step 5, Base filler weld: Carbon dioxide gas shielded welding is used to perform base filler weld on the root weld in DC reverse polarity to form the base filler weld. Step 6, Transition Layer Welding: Using carbon dioxide gas shielded welding, the SFC-309MoL welding wire is used to perform transition layer welding on the base filler weld in DC reverse polarity to form a transition layer weld. During the welding process, the welding speed is controlled to reduce heat input, so that the transition layer weld metal meets the principle of equal performance matching to avoid the generation of martensite structure. Step 7, Coating Welding: Using carbon dioxide gas shielded welding, the SFC-316L welding wire is used to perform coating welding on the transition layer weld in DC reverse polarity to form a coating weld.

2. The welding process for marine stainless steel composite plates according to claim 1, characterized in that: In step one, the bevel angle of the V-shaped welding groove is 40°±2°, and the root gap of the V-shape is 6±1mm.

3. The welding process for marine stainless steel composite plates according to claim 1, characterized in that: In step two, the ceramic gasket is attached to the underside of the outer surface of the carbon steel base layer. The ceramic gasket is in close contact with the outer surface of the carbon steel base layer and is used to carry molten metal during the welding process and form a full back weld.

4. The welding process for marine stainless steel composite plates according to claim 1, characterized in that: In step three, the SFC-309MoL welding wire used for the transition layer welding has a specification of φ1.2mm; the YCJ501-1 welding wire used for the base layer welding has a specification of φ1.2mm; and the SFC-316L welding wire used for the cladding layer welding has a specification of φ1.2mm.

5. The welding process for marine stainless steel composite plates according to claim 1, characterized in that: In step three, the YCJ501-1 welding wire used for the base layer welding meets the principle of equal strength, the SFC-309MoL welding wire used for the transition layer welding meets the principle of equal performance matching, and the SFC-316L welding wire used for the cladding layer welding matches the 316L stainless steel cladding material.

6. The welding process for marine stainless steel composite plates according to claim 1, characterized in that: In step six, the welding speed of each weld is controlled to be higher than that of the cladding weld during the transition layer welding process, so as to reduce heat input and reduce the risk of hot cracking.

7. The welding process for marine stainless steel composite plates according to claim 1, characterized in that: When welding in a flat position, the process parameters for each weld bead are as follows: Root pass welding: Welding current 182-208A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 13.8-16.9cm / min; Base filler welding: welding current 218-262A, welding voltage 25-27V, power supply polarity is DC reverse polarity, welding speed 20.0-36.6cm / min; Transition layer welding: welding current 205-235A, welding voltage 25-27V, power supply polarity is DC reverse polarity, welding speed 17.4-21.3cm / min; Clad welding: welding current 205-246A, welding voltage 24-27V, power supply polarity is DC reverse polarity, welding speed 25.7-33.0cm / min.

8. The welding process for marine stainless steel composite plates according to claim 1, characterized in that: When welding in a vertical position, the process parameters for each weld bead are as follows: Root pass welding: Welding current 175-198A, welding voltage 21-23V, power supply polarity is DC reverse polarity, welding speed 11.0-13.5cm / min; Base filler welding: welding current 180-208A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 11.4-13.8cm / min; Transition layer welding: welding current 160-180A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 9.2-11.2cm / min; Coating welding: Welding current 150-170A, welding voltage 23-25V, power supply polarity is DC reverse polarity, welding speed 6.8-8.4cm / min.

9. The welding process for marine stainless steel composite plates according to claim 1, characterized in that: In steps four through seven, the welding of each layer of weld bead adopts a multi-layer, multi-pass welding method, and the interpass temperature between adjacent weld bead is controlled below 150℃ through natural cooling or forced cooling.

10. The welding process for marine stainless steel composite plates according to claim 1, characterized in that: In steps four through seven, the shielding gas used in carbon dioxide gas shielded welding is carbon dioxide gas, the volume purity of which is not less than 99.5%, and the gas flow rate is 15L / min to 20L / min; during the welding process, the wire extension length is controlled between 15mm and 20mm.

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