Welding method for preventing lamellar tearing of T and cross joints of medium and heavy plates

Abstract

This invention relates to a method for anti-lamellar tearing welding of T-joints and cross joints in medium-thick plates, applicable to T-joints and cross joints of Q355B or Q355C plates with a thickness of 14-32mm. The method includes: forming asymmetrical small bevels on the web and flanges; cleaning burrs and oxide scale; removing the hardened layer from the bevel edges and heat-affected zone; cleaning both sides of the weld; welding within 2 hours after cleaning; preheating one side of the weld to 80-150℃, and holding at that temperature; tack welding using CO2 gas shielded welding; welding the web and flanges using multi-layer, multi-pass, segmented back-welding, with submerged arc welding used for filler and capping welds, and welding in a segmented back-welding sequence from the middle to both ends, controlling the interpass temperature at 150-200℃; immediately after welding, performing post-heating hydrogen removal treatment at 250-350℃, holding for at least 2 hours, and performing non-destructive testing after the heat treatment is completed.

Description

Technical Field

[0001] This invention relates to the field of steel structure manufacturing technology, specifically to a method for anti-laminated tear welding of medium-thick plate T-joints and cross joints. Background Technology

[0002] In the welding of large steel structures, lamellar tearing in the near-weld zone of the base metal is a very dangerous defect when tensile stress, especially cyclic tensile stress caused by external loads, is applied in the thickness direction of the plate. Lamellar tearing differs from hot and cold cracks in the weld; it occurs in the heat-affected zone and adjacent base metal, and is a special type of crack. Lamellar tearing typically occurs in fillet welds, such as T-joints, cross joints, and corner welds.

[0003] The microscopic mechanism of lamellar tearing is as follows: During the rolling process of steel plates, non-metallic inclusions such as sulfides and oxides are distributed in strips along the rolling direction, resulting in significantly lower ductility in the thickness direction (Z-direction) compared to the rolling direction. During welding, the restraint stress and thermal stress are superimposed. When the tensile stress in the thickness direction exceeds the bonding strength between the inclusion and the matrix interface, the inclusion separates from the matrix, forming microcracks. Under stress, these microcracks propagate and coalesce along the rolling surface, eventually forming macroscopic lamellar tearing cracks. This process is sudden and difficult to detect early using conventional non-destructive testing methods.

[0004] Lamellar tears are difficult to detect and repair. Under cyclic tensile stress, microscopic lamellar tears can rapidly propagate and coalesce, forming macroscopic cracks and causing structural failure. This failure process is sudden and unpredictable. How to avoid lamellar tears and the serious hazards they cause has become a crucial issue in steel structure welding. To address this, anti-lamellar tear steel, namely Z-direction steel, has been developed. This type of steel requires higher ductility in the thickness direction and is 30% to 50% more expensive than ordinary steel.

[0005] In the steel structures of heavy industrial plants, steel columns, crane beams, and frame truss joints extensively use Q355B and Q355C thick plates for T-joints and cross joints, with plate thicknesses typically ranging from 14mm to 32mm. These joints have high restraint and bear significant tensile stress in the thickness direction, making them highly susceptible to fatal defects such as lamellar tearing, cold cracking, and delayed cracking during welding, which seriously affect structural safety.

[0006] Traditional welding processes for thick plate T-joints and cross joints have the following drawbacks: (1) With a large bevel angle and a lot of filler metal, the welding stress is concentrated and the risk of lamellar tearing is significantly increased; with conventional V-type or K-type bevels, the bevel angles of the web and flange plates are both 45-60°, the weld cross-sectional area is large, the welding heat input is high, and the restraint stress generated by cooling shrinkage is large. (2) The flame-hardened layer at the edge of the bevel was not removed, which became the origin of microcracks. After flame cutting, a quenched hardened layer with a thickness of 0.3-0.8 mm was formed at the edge of the cut. The hardness was as high as HV350 or more. It was brittle and easily generated microcracks under the action of welding thermal cycle. (3) Mismatch between preheating, interpass temperature, and post-heating regime can easily induce microcracks and lamellar tearing propagation; conventional processes have low preheating temperatures (usually only 50-80℃), no interpass temperature control, and lack of systematic post-heating hydrogen removal treatment after welding. (4) The welding sequence is unreasonable and the stress cannot be released evenly. Conventional processes often use continuous welding from one end to the other, which causes longitudinal shrinkage stress accumulation in the weld. The stress peak in the central area of ​​the cross joint with high restraint is high. (5) Relying on Z-direction steel plates, the plastic resistance of the steel plate thickness direction is increased to resist lamellar tearing, but Z-direction steel has high procurement costs, long supply cycle and poor versatility; for commonly used medium and thick plates with a thickness of 14-32mm, the economic efficiency of using Z-direction steel is poor.

[0007] Currently, there is an urgent need in this field for a lamellar tear-resistant welding process with reasonable process parameter matching, suitable for factory mass production, and independent of Z-direction steel. Summary of the Invention

[0008] To address the problems of high restraint and easy lamellar tearing in existing medium and thick plate T-joints and cross joints, and the high cost and unstable welding quality caused by traditional processes relying on Z-direction steel, this paper proposes a lamellar tear-resistant welding method for medium and thick plate T-joints and cross joints. This method can effectively suppress lamellar tearing without using Z-direction performance steel plates, improve the first-pass yield rate, reduce production costs, and meet the requirements of large-scale production.

[0009] A method for anti-lamellar tearing welding of T-joints and cross joints in medium-thick plates, applicable to welding T-joints and cross joints made of Q355B or Q355C material with a plate thickness of 14-32mm, comprising: Asymmetrical small bevels are machined on the web and flanges to remove burrs and oxide scale. Remove the hardened layer from the bevel edge and heat-affected zone, clean both sides of the weld, and weld within 2 hours after cleaning; Preheat one side of the weld at a temperature of 80-150℃, and then maintain the temperature after reaching the preheating temperature. CO2 gas shielded welding is used for tack welding; Multi-layer, multi-pass, segmented back-welding is used to weld the web and flange plates. Submerged arc welding is used for filler and cover welding. The welding sequence is segmented back-welding from the middle to both ends. The interpass temperature is controlled at 150-200℃ during welding. Immediately after welding, perform post-heating hydrogen removal treatment at a temperature of 250-350℃ for a holding time of not less than 2 hours. After the holding time is completed, conduct quality inspection. Among them, the welding materials used for tack welding and formal welding are low-strength matching welding materials.

[0010] Furthermore, the web bevel angle is 27.5-35°, the flange bevel angle is 5-10°, the blunt edge is 4-6 mm, the root gap is 2-3 mm, and the root corner of the bevel is transitioned by an arc with a radius of not less than 3 mm.

[0011] Furthermore, planing or grinding is used to remove a hardened layer of not less than 0.3 mm from the bevel edge and heat-affected zone to eliminate the origin of microcracks.

[0012] Furthermore, the cleaning range on both sides of the weld should be no less than 50 mm, and the surface cleanliness after cleaning should reach Sa2.5 level.

[0013] Furthermore, the entire temperature control process uses far-infrared electric heating, with the temperature measuring point located 50mm from the center of the weld, and dual-point monitoring on both sides, ensuring that the temperature fluctuation does not exceed ±5℃.

[0014] Furthermore, the preheating temperature before tack welding is 50°C higher than the interpass temperature during the actual welding. The tack welding length is 80-100mm, and the spacing is 400-500mm.

[0015] Furthermore, the weld metal strength of low-strength matching welding materials is 5-10% lower than that of the base metal.

[0016] Furthermore, the thickness of each weld layer during filler and capping welds shall not exceed 6 mm, and the weld beads between adjacent layers shall be staggered.

[0017] Furthermore, the preheating time is 10-15 min / 10mm plate thickness, and the temperature is maintained for 10-20 min after reaching the preheating temperature.

[0018] Furthermore, welded joints with a plate thickness of not less than 25 mm shall undergo UT testing within 48 hours after welding; welded joints with a plate thickness of less than 25 mm shall undergo UT testing within 24 hours after welding; Class I welds shall be 100% inspected, and Class II welds shall be randomly inspected according to specifications.

[0019] Actual production has shown that after a quenched and hardened layer of 0.3-0.8 mm thickness is formed at the cut edge of the base material, the hardness reaches over HV350, resulting in high brittleness and a high susceptibility to microcracks under welding thermal cycling. To address this issue, this invention innovatively employs a combination of processes including asymmetric small-angle beveling, removal of the beveling hardened layer, pre-weld cleaning, low-strength matching welding materials, full-process temperature control, enhanced tack welding, multi-layer, multi-pass, segmented back-welding, and post-weld non-destructive testing. This process suppresses lamellar tearing and cold cracking, and reduces welding stress.

[0020] The beneficial effects of the above scheme are: 1) With the synergistic effect of low-strength matching welding materials and full-process temperature control, the incidence of lamellar tearing is zero and the incidence of cold cracking is less than 0.1% when Z-direction performance steel plates are not used; 2) The use of asymmetrical small bevels (web bevel angle 27.5-35°, flange bevel angle 5-10°) combined with multi-layer, multi-pass, segmented back welding reduces the amount of filler in the bevel weld by more than 25%, reduces welding stress, and reduces deformation. 3) By removing a flame-hardened layer of not less than 0.3 mm, combined with the synergistic effect of pre-welding Sa2.5 level cleaning, the crack source is eliminated from the source; 4) Use low-strength matching welding materials (the strength of the weld metal is 5-10% lower than that of the base metal) so that plastic deformation occurs preferentially in the weld metal, reducing the risk of stress in the thickness direction of the base metal. In conjunction with the temperature control throughout the process, it effectively inhibits the initiation and propagation of lamellar tears. 5) Effectively inhibits lamellar tearing and cold cracking, reduces welding stress, achieves a first-pass yield of no less than 99.5%, has stable process, is suitable for large-scale production, and is economically viable; 6) Applicable to common medium-thick plates ranging from 14-32mm, covering key nodes such as heavy steel structure workshops, crane beams, and steel column shoulder beams. The process parameters are clear and the feasibility is strong. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the welding process provided in an embodiment of the present invention; Figure 2 This is a cross-sectional view of the asymmetrical bevel of the T-joint in Embodiment 1 of the present invention; Figure 3 This is a cross-sectional view of the asymmetrical K-type bevel of the cross-shaped joint in Embodiment 2 of the present invention; Figure 4 This is a schematic diagram of the multi-layer, multi-pass, segmented unsoldering sequence in this invention; Figure 5 This is a schematic diagram of post-weld heat dissipation and heat preservation in this invention.

[0022] In the attached diagram: 1. Web plate; 2. Flange plate; 3. Bevel; 4. Blunt edge; 5. Root gap; 6. De-hardened layer area (≥0.3mm); 7. Weld; 8. Far-infrared electric heating plate heater; 9. Aluminum silicate needle-punched blanket fiber cotton insulation blanket; 10. Temperature measuring point. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0026] Example 1 This embodiment takes a T-joint of a steel column shoulder beam in the main plant of a metallurgical steel plant as an example. The component material is Q355B, the web thickness t1=25mm, and the flange thickness t2=25mm. This joint bears the load transmitted by the crane beam and requires high welding quality, without allowing lamellar tearing or cold cracking. The specific welding steps are as follows (e.g.) Figure 1 , Figure 2 , Figure 4 , Figure 5 (as shown) A single-sided V-shaped bevel is machined on the web plate using CNC flame cutting, with the bevel angle controlled at 32°. The flange plate is not beveled, and the gap between the flange plate and the web plate is no more than 0.5 mm. The blunt edge is 5 mm, and the root gap is 2.5 mm, and the gaps should be uniform. The bevel root corner is transitioned with a 5 mm radius arc. After machining, the arc transition area is ground with an angle grinder to remove the sharp edges. After beveling, cutting burrs and oxide scale are removed, and the surface roughness of the bevel is Ra=18 μm. Using an angle grinder with a 120-grit grinding wheel, grind the bevel edge surface and the hardened layer of the heat-affected zone (extending outwards by 8mm) to a depth of 0.35mm until a metallic luster is exposed to eliminate microcrack origin points; then use sandblasting (80-grit quartz sand as the sandblasting medium, sandblasting pressure controlled at 0.5MPa, sandblasting time 3min / m) to clean it. 2 Clean the area 55 mm on both sides of the weld, including the bevel surface and the mating surface of the web and flange, to ensure that the cleanliness of the weld area reaches Sa2.5 level after cleaning, with no visible rust, oxide scale, or oil stains on the surface, and presenting a uniform metallic color; the cleaning work shall be completed within 1.5 hours before welding, and after cleaning, the quality inspector shall visually inspect to confirm that there are no impurities that will affect the welding quality; A far-infrared electric heating plate heater is used to preheat one side of the weld seam (temperature measuring points are set at the weld seam location, and a thermocouple thermometer is used for continuous monitoring, recording the temperature every 5 minutes). Both sides of the weld seam are then covered with an aluminum silicate needle-punched blanket / fiber cotton insulation blanket for heat preservation. In this embodiment, the plate thickness is 25mm, greater than 24mm, and the preheating temperature is controlled at 120℃ (fluctuation not exceeding ±5℃). The preheating time is calculated based on 15 minutes for every 10mm of plate thickness, so the theoretical preheating time for a 25mm plate thickness is 37.5 minutes (for ease of operation, the actual preheating time is rounded to 40 minutes). After reaching the preheating temperature, the plate is held at that temperature for 12 minutes before welding. ER50-6 welding wire with a diameter of φ1.2mm (low-strength matching welding material, weld metal strength 8% lower than Q355B base metal) was used for tack welding. Before welding, the welding wire was placed in a drying oven and dried at 180℃ for 1.5 hours, and used immediately. CO2 gas shielded welding (FCAW) was used for tack welding (the tack welding area was cleaned before tack welding). The welding current was controlled at 210A, the welding voltage at 28V, and the welding speed at 31cm / min. The tack welding length was 90mm, the spacing was 450mm, and the weld leg size was 4.5mm. During tack welding, the weld formation was controlled to be uniform, avoiding defects such as incomplete penetration and porosity, and ensuring that the tack weld had sufficient strength. The preheating temperature for tack welding was 50℃ higher than the interpass temperature for the formal welding. After the tack welding was completed, a visual inspection was performed. H10Mn2 welding wire with a diameter of φ5.0mm and SJ101 flux were selected for the formal welding. The flux was dried at 320℃ for 2.5 hours before use to remove moisture and prevent porosity in the weld. The formal welding employed multi-layer, multi-pass, segmented back-welding: 1) Root pass welding: CO2 gas shielded welding (FCAW) was used, with welding current controlled at 235A, welding voltage at 29V, welding speed at 34cm / min, and gas flow rate at 20L / min. During the root pass welding, root penetration and uniform weld formation were ensured, with a root pass thickness of 5mm. 2) Filler pass welding: Submerged arc welding (SAW) was used, with multi-layer, multi-pass welding. The thickness of each weld layer was controlled at 5mm, and the width of each weld pass at 12mm. The welding sequence was segmented back-welding from the middle to both ends, with each segment length controlled at 250mm. The middle segment was welded first, followed by the segments towards both ends. Step-by-step welding ensures uniform stress distribution. After each weld pass is completed, promptly clean the slag and spatter with a wire brush. Only proceed with the next weld pass after inspection for defects. Stagger the weld passes by 60mm to avoid stress concentration caused by overlapping weld passes. A total of 4 filler welds are performed. 3) Cover weld: Submerged arc welding (SAW) is used. The welding current is controlled at 550A, the welding voltage at 33V, and the welding speed at 46cm / min. During the cover weld, the weld surface is kept flat, with a weld reinforcement of 3mm. After the cover weld is completed, clean the slag and spatter and perform a visual inspection. During the formal welding process, the interpass temperature is strictly controlled at 160℃. Continuously monitor the temperature with a thermometer and record the temperature every 5 minutes. If the temperature rises to 170℃, stop welding and wait for the temperature to drop below 160℃ before resuming welding. After each weld pass is completed, clean the slag with a wire brush within 1 minute. Immediately after welding, the weld is subjected to post-heating hydrogen removal treatment (using a far-infrared electric heating plate heater to heat one side of the weld, and covering both sides of the weld with aluminum silicate needle-punched blanket fiber cotton insulation blanket for insulation). The post-heating hydrogen removal temperature is controlled at 300℃, the heating rate is 80℃ / h, and the temperature is maintained for 2h after reaching 300℃. After the insulation is completed, the weld area is covered with aluminum silicate needle-punched blanket fiber cotton insulation blanket and cooled to room temperature at a cooling rate of 40℃ / h. During the post-heating hydrogen removal process, the temperature is recorded every 20 minutes and the temperature is controlled between 295-305℃.

[0027] Taking the T-joint as the first-level weld, 100% UT flaw detection is carried out 48 hours after welding is completed, as required. The testing instrument is a digital ultrasonic flaw detector with a probe frequency of 4MHz and a probe angle of 45° to ensure that the detection covers the entire weld area.

[0028] The test results show that the weld in this embodiment has no defects such as lamellar tearing, cold cracking, incomplete penetration, or lack of fusion. There are only a few scattered pores. The defect level meets the requirements of Level II. The weld is rated as Level I qualified and can meet the design and use requirements.

[0029] Example 2 This embodiment focuses on a cross joint of a crane beam in the main heavy-duty plant of a scientific research and experimental building. The component material is Q355B, and the plate thickness is 32mm. This joint bears both dynamic and static loads and has high welding restraint. The specific welding steps are as follows (e.g.) Figure 1 , Figure 3 , Figure 4 , Figure 5 (as shown) Asymmetrical K-shaped bevels were machined on both sides of the cross joint using plasma cutting; the blunt edge was 4mm and the root gap was 3mm; the root corner of the bevel was transitioned with an arc of 3mm radius, and the edges were removed by grinding after machining; after beveling, cutting burrs and oxide scale were removed, and the surface roughness of the bevel was Ra=20 μm. The plate is relatively thick with a large bevel area. The bevel edges (including the bevel surface and the edge of the heat-affected zone extending outwards by 10mm) are planed using an edge planer to a depth of 0.4mm. After planing, the bevel surface is polished with an angle grinder until a metallic luster is exposed. Finally, sandblasting is used for cleaning (80-mesh quartz sand is used as the sandblasting medium, the sandblasting pressure is controlled at 0.6MPa, and the sandblasting time is 4min / m). 2 Clean the area 60 mm on both sides of the weld, including the bevel surface and the component contact surface, ensuring that the cleanliness of the weld area reaches Sa2.5 level after cleaning. The cleaning work should be completed within 1 hour before welding, and the quality inspector should visually inspect it after cleaning. Use a far-infrared electric heating plate heater to cover one side of the weld for preheating (the temperature measuring point is set at the weld position, and a thermocouple thermometer is used for continuous monitoring, recording the temperature every 5 minutes), and cover both sides of the weld with aluminum silicate needle-punched blanket fiber cotton insulation blanket for insulation. In this embodiment, the plate thickness is 32 mm, which is greater than 24 mm. The preheating temperature is controlled at 140℃ (fluctuation not exceeding ±5℃). The preheating time is calculated based on 15 minutes for every 10 mm of plate thickness. The theoretical preheating time for a 32 mm plate thickness is 48 minutes (for ease of operation, the actual preheating time is rounded to 40 minutes). After reaching the preheating temperature, hold for 15 minutes before welding. ER50-6 welding wire with a diameter of φ1.2mm (low-strength matching welding material, the weld metal strength is 7% lower than that of Q355B base metal) was used for tack welding. Before welding, the welding wire was placed in a drying oven and dried at 190℃ for 1.5 hours, and used immediately. CO2 gas shielded welding (FCAW) was used for tack welding (the tack welding area was cleaned before tack welding). The welding current was controlled at 220A, the welding voltage at 29V, and the welding speed at 32cm / min. The tack welding length was 100mm, the spacing was 500mm, and the weld leg size was 5mm. During the tack welding process, the weld formation was controlled to be uniform. After the tack welding was completed, a visual inspection was performed. Any unqualified parts were removed and re-tack welded. After the formal welding was completed, the tack welds that affected the formation of the cap weld were ground off. H10Mn2 welding wire with a diameter of φ5.0mm and SJ101 flux were selected for the formal welding. The flux was dried at 340℃ for 2.5 hours before use to remove moisture and prevent porosity in the weld. The formal welding employed multi-layer, multi-pass, segmented back-welding: 1) Root pass: CO2 gas shielded welding (FCAW) was used, with welding current controlled at 245A, welding voltage at 30V, welding speed at 33cm / min, and gas flow rate at 22L / min. During the root pass, root penetration and uniform weld formation were ensured, with a root pass thickness of 4mm. 2) Filler pass: Submerged arc welding (SAW) was used, with multi-layer, multi-pass welding. Each weld layer thickness was controlled at 5.5mm, and each weld pass width at 14mm. The welding sequence was segmented back-welding from the middle to both ends, with each segment length controlled... The weld length is 280mm. After each weld is completed, the slag is cleaned and the weld is inspected for defects before proceeding to the next weld. The weld beads are staggered by 55mm between layers to avoid stress concentration caused by weld bead overlap. A total of 5 layers of filler welds are performed. 3) Cover weld: Submerged arc welding (SAW) is used. The welding current is controlled at 580A, the welding voltage is controlled at 34V, and the welding speed is controlled at 47cm / min. During the cover weld, the weld surface is kept flat and the weld reinforcement is 3.2mm. After the cover weld is completed, the slag and spatter are cleaned and the appearance is inspected. During the formal welding process, the interpass temperature is strictly controlled at 180℃ and continuously monitored with a thermometer. The temperature is recorded every 5 minutes. If the temperature rises to 170℃, welding is paused and resumed when the temperature drops below 160℃. After each layer of welding is completed, the slag is cleaned with a wire brush within 1 minute. Immediately after welding, the weld was subjected to post-heating hydrogen removal treatment (using a far-infrared electric heating plate heater to heat one side of the weld, and covering both sides of the weld with aluminum silicate needle-punched blanket fiber cotton insulation blanket for insulation). The post-heating hydrogen removal temperature was controlled at 320℃, the heating rate was 70℃ / h, and the temperature was maintained for 2.5h after reaching 320℃. After the insulation was completed, the weld area was covered with aluminum silicate needle-punched blanket fiber cotton insulation blanket and cooled to room temperature at a cooling rate of 35℃ / h. During the post-heating hydrogen removal process, the temperature was recorded every 20 minutes and controlled between 295-305℃.

[0030] Taking the cross joint as a primary weld, 100% UT flaw detection was carried out 48 hours after the welding was completed, as required. The testing instrument used was a digital ultrasonic flaw detector with a probe frequency of 3MHz and a probe angle of 60° to ensure that the detection covered the entire weld area.

[0031] The test results show that the weld in this embodiment has no defects such as lamellar tearing, cold cracking, incomplete penetration, or lack of fusion, and meets the Class II qualification standard, thus being deemed qualified and meeting the load-bearing requirements.

[0032] Comparative Example 1 To verify the technical effect of this invention, a comparative experiment was conducted between the method of this invention and the conventional process. Experimental conditions: material Q355B, plate thickness 25mm, T-joint type, 50 pieces per test group. The conventional process uses a symmetrical 45° V-groove, does not remove the hardened layer, does not use low-strength matching welding materials, and lacks systematic post-heating hydrogen removal treatment. The experimental results are shown in the table below:

[0033] The results of the above comparative tests show that the method of the present invention has significant advantages in eliminating lamellar tearing and cold cracking, increasing the first-pass yield rate from 92.5% to over 99.5%, while reducing the weld filler volume by over 28% and reducing the overall material cost by over 35% (mainly due to the elimination of Z-direction steel).

[0034] Furthermore, the process stability of the method of this invention was verified in batches. In the steel structure manufacturing project of the main plant of a metallurgical steel plant, the method of this invention was used to weld 320 T-joints and 186 cross joints, all made of Q355B steel with a thickness ranging from 16 to 30 mm. 100% UT (Undertested Test) results after welding showed no cases of lamellar tearing, a 0% cold cracking rate, and a 99.7% first-pass yield rate, fully meeting the engineering design and usage requirements.

[0035] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for welding T-shaped and cross-shaped joints of a medium plate against lamellar tearing, which is suitable for welding T-shaped joints and cross-shaped joints of Q355B or Q355C material and a plate thickness of 14-32 mm, characterized in that, include: Asymmetrical small bevels are machined on the web and flanges to remove burrs and oxide scale. Remove the hardened layer from the bevel edge and heat-affected zone, clean both sides of the weld, and weld within 2 hours after cleaning; Preheat one side of the weld at a temperature of 80-150℃, and then maintain the temperature after reaching the preheating temperature. CO2 gas shielded welding is used for tack welding; Multi-layer, multi-pass, segmented back-welding is used to weld the web and flange plates. Submerged arc welding is used for filler and cover welding. The welding sequence is segmented back-welding from the middle to both ends. The interpass temperature is controlled at 150-200℃ during welding. Immediately after welding, post-heating hydrogen removal treatment is performed at a temperature of 250-350℃ and a holding time of not less than 2 hours. Quality inspection is carried out after the holding time is completed. Among them, the welding materials used for tack welding and formal welding are low-strength matching welding materials.

2. The method for anti-laminated tearing welding of medium-thick plate T-joints and cross joints according to claim 1, characterized in that, The web bevel angle is 27.5-35°, the flange bevel angle is 5-10°, the blunt edge is 4-6 mm, the root gap is 2-3 mm, and the root corner of the bevel is transitioned by an arc with a radius of not less than 3 mm.

3. The method of claim 1, wherein the method is a method of welding a T- or cross joint of a plate having a thickness of 20 mm or more. By planing or grinding, remove the flame-hardened layer of at least 0.3 mm from the bevel edge and heat-affected zone to eliminate the origin of microcracks.

4. The method for anti-lamellar tearing welding of medium-thick plate T-joints and cross joints according to claim 1, characterized in that, The cleaning range on both sides of the weld should be no less than 50 mm, and the surface cleanliness should reach Sa2.5 level after cleaning.

5. The method for anti-laminated tearing welding of medium-thick plate T-joints and cross joints according to claim 1, characterized in that, The entire temperature control process uses far-infrared electric heating, with the temperature measuring point located 50mm from the center of the weld. Dual-point monitoring is conducted on both the front and back sides, and the temperature fluctuation does not exceed ±5℃.

6. The method for anti-laminated tearing welding of medium-thick plate T-joints and cross joints according to claim 1, characterized in that, The preheating temperature before tack welding is 50°C higher than the interpass temperature during the actual welding. The tack welding length is 80-100mm and the spacing is 400-500mm.

7. The method for anti-laminated tearing welding of medium-thick plate T-joints and cross joints according to claim 1, characterized in that, The weld metal strength of low-strength matching welding materials is 5-10% lower than that of the base metal.

8. The method for anti-lamellar tearing welding of medium-thick plate T-joints and cross joints according to claim 1, characterized in that, When performing filler and cover welds, the thickness of each weld layer should not exceed 6 mm, and the weld beads between adjacent layers should be staggered.

9. The method for anti-lamellar tearing welding of medium-thick plate T-joints and cross joints according to claim 1, characterized in that, Preheating time is 10-15 min for a 10mm thick plate. After reaching the preheating temperature, maintain the temperature for 10-20 min.

10. The method for anti-laminated tearing welding of medium-thick plate T-joints and cross joints according to claim 1, characterized in that, For welded joints with a plate thickness of not less than 25 mm, UT testing shall be performed within 48 hours after welding; for welded joints with a plate thickness of less than 25 mm, UT testing shall be performed within 24 hours after welding; 100% inspection of Class I welds and random inspection of Class II welds according to specifications.

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