A welding method for annealed pickled line heavy gauge 409 stainless steel

Abstract

The present application belongs to the technical field of annealing and pickling line strip steel welding, and particularly relates to a welding method for thick specification 409 stainless steel of an annealing and pickling line, comprising the following contents: (1) water-cooled copper back plate clamping and inducing micro V-shaped gap; (2) first MIG main connection welding; (3) back shallow concave forced forming and defect observation; (4) second low linear energy swing MIG remelting shaping; (5) weld quality closed loop observation. The method is characterized in that the arc-shaped protrusions of the water-cooled copper back plate cooperate with the clamping platform to form a micro V-shaped gap with a large upper part and a small lower part in the clamped state of the non-grooving I-shaped joint, thereby reducing the grooving processing time, and the double MIG welding is adopted, the first pass completes the main connection, the second pass is rapidly remelted and shaped under the condition of low linear energy, the second MIG pass has the metal filling capacity, the transition flatness of the upper surface of the weld and the weld toe is more quickly improved, and meanwhile, the thick specification joint root fusion, the front low excess height, the intact weld and the rapid rhythm of the unit are considered.

Description

Technical Field

[0001] This invention belongs to the field of welding technology for annealed pickling line strip steel, and particularly relates to a welding method for 409 stainless steel with a thickness specification in annealed pickling lines. Background Technology

[0002] In the continuous production process of stainless steel annealing and pickling lines, the tail and head of the front and rear coils need to be rapidly welded at the entrance section to ensure continuous operation of the unit. For 8-12mm thick 409 stainless steel, the welded joints must not only meet the requirements of connection strength, but also the requirements of the unit's fast pace, tension operation, roller passage, subsequent annealing and pickling, and post-weld defect observation. In actual production, the welding time of the unit is usually required to be controlled within 4 minutes, resulting in a significant contradiction between welding efficiency and weld quality.

[0003] 409 stainless steel is a ferritic stainless steel. When thick strip steel is subjected to MIG welding with an I-joint without beveling, problems such as insufficient root fusion, localized burn-through and collapse, excessive weld reinforcement on the front side, obvious weld toe angle, and unstable back side formation are prone to occur. Simply increasing the heat input may improve fusion but increases the risk of weld reinforcement and coarsening of the heat-affected zone; decreasing the heat input may result in incomplete penetration and lack of fusion. Existing welding processes have the following defects: (1) Existing MIG welding solutions for annealing and pickling lines mostly rely on measures such as adding stiffening plates after welding, cutting off the starting and ending arc sections, opening vertical seams, or air cooling, mainly to solve the problem of weld breakage; (2) Traditional grooved copper backing plates or copper pads can easily cause liquid metal to accumulate on the back of the weld, forming a bulge or covering the back fusion line. This morphology is not conducive to the strip passing through the roller system, nor is it conducive to judging whether there is incomplete penetration or incomplete fusion at the root. (3) In the type I butt joint of thick 409 stainless steel without beveling, the root fusion requires sufficient energy, but the weld reinforcement on the front and the weld toe transition need to be controlled. A single weld pass is difficult to simultaneously achieve root fusion, back forming and low reinforcement on the front. (4) Although TIG remelting can improve the weld surface, it has a small heat input and no metal filling ability, making it difficult to meet the rapid processing requirements of the upper surface and weld toe of thick 409 stainless steel welds under a production rhythm of less than 4 minutes.

[0004] In summary, simply adjusting the MIG welding parameters based on traditional solutions makes it difficult to simultaneously achieve root fusion of thick joints, low excess weld on the front side, high weld quality, and fast unit operation. Summary of the Invention

[0005] The purpose of this invention is to provide a welding method for annealed and pickled 409 stainless steel of thicker specifications, which solves the problem that simply adjusting the MIG welding parameters based on traditional solutions makes it difficult to simultaneously achieve root fusion of thick-specification joints, low excess material and high burr on the front side, intact welds, and a fast-paced production line.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A welding method for annealed and pickled 409 stainless steel of wire thickness includes the following: (a) Water-cooled copper backplate clamping induces micro-V-shaped gap Before welding, the ends of the front and rear steel coils are cut, ground, or trimmed. A type I butt joint without beveling is used, and the butt gap is controlled to be 3-5mm. A water-cooled copper back plate is installed below the joint. The upper surface of the water-cooled copper back plate has an arc-shaped protrusion, and a water-cooling channel is installed inside the water-cooled copper back plate. The arc-shaped protrusion is located below the center line of the weld. When the clamping platform presses the end and head of the strip, the arc-shaped protrusion provides support to the lower surface of the joint, causing the edges of the end and head of the strip joint to be slightly raised. This makes the original type I butt joint actually present a micro-V-shaped gap that is larger at the top and smaller at the bottom when clamped.

[0007] (ii) First MIG main connection weld The first MIG weld is used to complete the main weld connection and root fusion. It is the main weld that bears the joint strength. During the first welding process, the water-cooled copper backplate supports and cools the root of the molten pool.

[0008] (iii) The shallow concave forced forming on the back and the defects can be observed. The arc-shaped protrusion on the upper surface of the water-cooled copper backplate causes a shallow concave area to form on the back of the weld during solidification.

[0009] (iv) Second low-line energy swing MIG remelting and shaping The second MIG weld is not a regular cover pass high-density weld, but a low-energy oscillating MIG remelting and shaping weld. Its functions include: rapidly remelting the front and toe areas of the first weld; spreading the toe area through serrated oscillation; generating a secondary heat cycle for the first weld to temper; and improving the smoothness of the weld surface and toe transition through a small amount of filler.

[0010] Because the voltage, current, and wire feed speed need to be matched in MIG welding, the parameters for the second MIG welding pass cannot simply aim for low heat input. Using too high a voltage and too low a current may result in a long arc, leading to arc drift, spatter, undercut, or insufficient remelting.

[0011] The second MIG weld uses a sawtooth oscillation with an oscillation amplitude of 3.5-4.5 mm and an oscillation frequency of 1.5-2 times / s. The dwell time on both sides is 0.15-0.2 s. During the oscillation process, the electric arc is periodically applied to the center of the weld and the weld toe areas on both sides. The dwell time on both sides promotes the remelting and spreading of the weld toe, reduces the reinforcement height and stress concentration at the weld toe.

[0012] (v) Closed-loop observation of weld quality After welding is completed, the key points to check are the front reinforcement height, weld toe transition, shallow concave depth on the back and the condition of the root fusion line.

[0013] Preferably, the height of the arc-shaped protrusion of the water-cooled copper backplate in (a) is 1.5-2.5mm; the diameter of the protrusion arc is 8-12mm.

[0014] Preferably, in step (ii), the first MIG weld uses 309L welding wire with a diameter of 1.6 mm, and the shielding gas is Ar and 3% O2.

[0015] Preferably, the parameters for the first MIG weld in (ii) are: voltage 28-32V, current 400-420A, wire feed speed 7-8m / min, and welding speed 0.5-0.7m / min.

[0016] Preferably, in the first MIG welding process in (ii), the water cooling flow rate is 18-22 L / min, which is used to control the shape of the back molten pool and the width of the heat-affected zone.

[0017] Preferably, the concave depth of the shallow concave area in (iii) is 1-2 mm, and the two sides of the concave area are smoothly transitioned to the back of the base material. This back morphology avoids the bulge from affecting the passage of the roller system, and makes the back fusion line easier to expose and observe. When there is incomplete welding or incomplete fusion, the shallow concave area can more directly show the abnormal boundary.

[0018] Preferably, the second MIG welding parameters in (iv) are: voltage 32-35V; current 220-250A; wire feed speed 4.5-5.2m / min; welding speed 0.9-1.1m / min.

[0019] Preferably, the linear energy in (ii) and (iv) is calculated using the following formula: q = 60 × U × I / (1000000 × v), where q is the linear energy without thermal efficiency, in kJ / mm; U is the welding voltage, in V; I is the welding current, in A; and v is the welding speed, in m / min.

[0020] Preferably, the second line energy in (iv) and (ii) is 35%-50% of the first line energy. Therefore, the second line achieves rapid shaping with low heat input, while reducing the risk of overheating in the heat-affected zone of 409 ferritic stainless steel.

[0021] Preferably, in step (v), the front excess height is no more than 2mm, and the back concave depth is 1-2mm. If discontinuous fusion lines, black lines, abnormal grooves, or local non-fusion boundaries appear in the shallow concave area on the back, they can be used as the basis for observing defects such as incomplete penetration or non-fusion.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: (1) Double-pass MIG welding is adopted. The first pass completes the main connection, and the second pass is rapidly remelted and shaped under low line energy conditions. It is suitable for welding rhythms within 4 minutes and adapts to the rapid production rhythm of annealing and pickling lines. Compared with TIG remelting, the second pass of MIG has metal filling ability, which can improve the smoothness of the transition at the weld surface and weld toe more quickly; (2) By using the arc-shaped protrusion of the water-cooled copper back plate to cooperate with the clamping platform, the I-type joint without beveling forms a micro-V-shaped gap with a larger upper part and a smaller lower part in the clamping state, which reduces the beveling time and improves the root fusion conditions of thick-gauge joints. It does not require mechanical beveling but obtains micro-V-shaped beveling fusion conditions. The slightly wider upper part is conducive to the entry of MIG arc and the filling of welding wire. The lower gap is controlled by the protruding copper back plate, which helps to suppress burn-through, collapse and root morphology loss. (3) The arc-shaped raised copper back plate makes the back of the weld seam form a shallow concave shape of 1-2mm and a smooth transition, avoiding the accumulation of liquid metal and back bulge caused by traditional grooved pads, which is conducive to the stable passage of the annealing pickling line roller system, tension section and subsequent processes. (4) Since the back fusion line is not covered by the deposited metal, root defects such as incomplete penetration and incomplete fusion are more likely to be found in the shallow concave area on the back, making root defects easier to observe and improving the efficiency of on-site quality judgment. (5) The second low-energy oscillating MIG welding remelts and spreads the weld toe area by serrated oscillation and stopping on both sides, which reduces the weld face height and makes the weld toe transition smooth. The second line energy is 35%-50% of the first line energy, which reduces the risk of overheating and grain coarsening in the heat-affected zone and avoids stress concentration and overheating risk in the weld toe. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process of an embodiment of the present invention; Figure 2 This is a schematic diagram of the water-cooled copper backplate structure in an embodiment of the present invention; Figure 3 This is a schematic diagram of the clamping platform and the water-cooled copper backplate clamping pre-forming in an embodiment of the present invention; Figure 4 This is a schematic diagram of the weld cross-sectional morphology after using the welding method of the present invention.

[0024] Explanation of reference numerals in the attached drawings: 1. 409 steel coil; 2. Clamping platform; 3. Water-cooled copper backplate; 4. Water-cooling channel; 5. Arc-shaped protrusion; 6. Slightly upturned strip edge area with a micro-V-shaped gap that is larger at the top and smaller at the bottom; 7. 409 stainless steel base material; 8. First MIG main connection weld metal; 9. Second MIG remelting and shaping layer; 10. Smooth weld toe transition area; 11. Shallow concave area. Detailed Implementation

[0025] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] A welding method for annealed and pickled 409 stainless steel of a certain thickness, such as... Figure 1 As shown, it includes the following: (a) Water-cooled copper backplate clamping induces micro-V-shaped gap like Figure 3 As shown, before welding, the ends and heads of the front and rear 409 steel coils 1 are cut, ground, or trimmed. A type I butt joint without beveling is used, and the butt gap is controlled to be 3mm. A water-cooled copper backplate 3 is installed below the joint. Figure 2 As shown, the upper surface of the water-cooled copper back plate 3 is provided with an arc-shaped protrusion 5, the height of which is 2mm and the diameter of the arc is 10mm. The water-cooled copper back plate 3 is provided with a water-cooling channel 4. The arc-shaped protrusion 5 is located below the center line of the weld. When the clamping platform 2 presses the tail and head of the strip, the arc-shaped protrusion 5 provides support to the lower surface of the joint, causing the edges of the tail and head of the strip joint to be slightly raised. This makes the original I-type butt joint actually present a micro-V-shaped gap 6 that is larger at the top and smaller at the bottom when clamped.

[0027] (ii) First MIG main connection weld The first MIG weld is used to complete the main weld connection and root fusion, and is the main weld pass that bears the joint strength. During the first weld pass, the water-cooled copper backing plate 3 supports and cools the root of the molten pool. The first MIG weld uses 309L welding wire with a diameter of 1.6mm, shielding gas of Ar and 3% O2, voltage of 30V, current of 410A, wire feed speed of 7.5m / min, and welding speed of 0.6m / min. Based on the thermal efficiency line energy estimation, q = 60 × U × I / (1000000×v), where q is the linear energy without thermal efficiency, in kJ / mm; U is the welding voltage, in V; I is the welding current, in A; v is the welding speed, in m / min. The first pass linear energy = 60×30×410 / (1000000×0.6) = 1.23 kJ / mm. The water cooling flow rate during the first pass of MIG welding is 20 L / min, used to control the shape of the back weld pool and the width of the heat-affected zone. Figure 4As shown, the first MIG main connection weld metal 8 is formed at the bottom between the 409 stainless steel base material 7.

[0028] (iii) The shallow concave forced forming on the back and the defects can be observed. The arc-shaped protrusion 5 on the upper surface of the water-cooled copper backplate 3 causes a shallow concave area 11 to be formed on the back of the weld during the solidification process. The concave depth is 1.5mm, and the two sides of the concave area are smoothly transitioned to the back of the base material.

[0029] (iv) Second low-line energy swing MIG remelting and shaping The second MIG weld uses a sawtooth oscillation with an amplitude of 4 mm and an oscillation frequency of 1.5 times / s. The dwell time on both sides is 0.15s. During the oscillation process, the arc periodically acts on the center of the weld and the weld toe areas on both sides. The dwell time on both sides promotes the remelting and spreading of the weld toe, reduces the reinforcement height and stress concentration of the weld toe. The voltage is 32V; the current is 220A; the wire feed speed is 5.0m / min; the welding speed is 1.0m / min. The first pass line energy is 60×32×220 / (1000000×1.0)=0.4224kJ / mm. The second MIG remelting shaping layer 9 and the smooth weld toe transition zone 10 are formed on the top of the 409 stainless steel base material 7.

[0030] (v) Closed-loop observation of weld quality After welding is completed, focus on checking the front reinforcement height, weld toe transition, back shallow concavity depth, and root fusion line condition, such as... Figure 4 As shown, the weld cross-section exhibits an ideal shape with a low front reinforcement height, a smooth transition at the weld toe, and a shallow concave back. The front reinforcement height is no more than 2mm, and the weld toe and the base material have a smooth transition to avoid sharp angles and obvious stress concentration. The concave depth on the back is 1-2mm, and the two sides of the concave transition smoothly with the back of the base material.

[0031] The shallow concave structure formed by the welding method of this invention is different from the back metal accumulation morphology formed by traditional grooved backing plates, making the root fusion line easier to expose and observe, facilitating on-site identification of defects such as incomplete penetration and incomplete fusion. At the same time, it eliminates the mechanical beveling process before welding thick 409 stainless steel, reducing the time for beveling, grinding and centering adjustment. The second low-energy oscillating MIG welding has the functions of remelting and shaping, secondary thermal cycling and a small amount of filling. The weld surface treatment can be completed within 4 minutes in the production rhythm of the annealing and pickling line, reducing the amount of post-weld grinding and rework.

Claims

1. A welding method for annealed and pickled 409 stainless steel of wire thickness, characterized in that, Includes the following: (a) Water-cooled copper backplate clamping induces micro-V-shaped gap Before welding, the ends of the front and rear steel coils are cut, ground or trimmed. A type I butt joint without beveling is adopted, and the butt gap is controlled to be 3-5mm. A water-cooled copper back plate is set below the joint. An arc-shaped protrusion is set on the upper surface of the water-cooled copper back plate, and a water-cooling channel is set inside the water-cooled copper back plate. The arc-shaped protrusion is located below the center line of the weld. When the clamping platform presses the end and head of the strip, the arc-shaped protrusion provides support to the lower surface of the joint, causing the edges of the end and head of the strip joint to be slightly raised. This makes the original type I butt joint actually present a micro-V-shaped gap that is larger at the top and smaller at the bottom when clamped. (ii) First MIG main connection weld The first MIG weld is used to complete the main connection of the weld and the root fusion. It is the main weld that bears the strength of the joint. During the first welding process, the water-cooled copper back plate supports and cools the root of the molten pool. (iii) The shallow concave forced forming on the back and the defects can be observed. The arc-shaped protrusion on the upper surface of the water-cooled copper back plate causes a shallow concave area to form on the back of the weld during solidification. (iv) Second low-line energy swing MIG remelting and shaping The second MIG weld is a low-line-energy oscillating MIG remelting and shaping weld, which includes: rapidly remelting the front and toe areas of the first weld; spreading the toe area through serrated oscillation; generating a secondary heat cycle of weld tempering in the first weld; and improving the smoothness of the weld surface and toe transition through a small amount of filler. The second MIG weld uses a sawtooth oscillation with an oscillation amplitude of 3.5-4.5 mm and an oscillation frequency of 1.5-2 times / s. The dwell time on both sides is 0.15-0.2 s. During the oscillation process, the electric arc is periodically applied to the center of the weld and the weld toe areas on both sides. The dwell time on both sides promotes the remelting and spreading of the weld toe, reduces the reinforcement height and stress concentration at the weld toe. (v) Closed-loop observation of weld quality After welding is completed, the key points to check are the front reinforcement height, weld toe transition, shallow concave depth on the back and the condition of the root fusion line.

2. The welding method for annealed and pickled 409 stainless steel of wire thickness according to claim 1, characterized in that, The height of the arc-shaped protrusion of the water-cooled copper backplate in (a) is 1.5-2.5mm; the diameter of the protrusion arc is 8-12mm.

3. The welding method for annealed and pickled 409 stainless steel of wire thickness according to claim 1, characterized in that, In step (ii), the first MIG weld uses 309L welding wire with a diameter of 1.6 mm, and the shielding gas is Ar and 3% O2.

4. The welding method for annealed and pickled 409 stainless steel of wire thickness according to claim 1, characterized in that, The parameters for the first MIG weld in (II) are: voltage 28-32V, current 400-420A, wire feed speed 7-8m / min, and welding speed 0.5-0.7m / min.

5. The welding method for annealed and pickled 409 stainless steel of wire thickness according to claim 1, characterized in that, In the first MIG welding process described in (II), the water cooling flow rate is 18-22 L / min, which is used to control the shape of the back molten pool and the width of the heat-affected zone.

6. The welding method for annealed and pickled 409 stainless steel of wire thickness according to claim 1, characterized in that, The concave depth of the shallow concave area in (iii) is 1-2 mm, and the two sides of the concave area are smoothly transitioned to the back of the parent material.

7. The welding method for annealed and pickled 409 stainless steel of wire thickness according to claim 1, characterized in that, The parameters for the second MIG welding in section (iv) are as follows: voltage 32-35V; current 220-250A; wire feed speed 4.5-5.2m / min; welding speed 0.9-1.1m / min.

8. The welding method for annealed and pickled 409 stainless steel of wire thickness according to claim 1, characterized in that, The linear energy in (ii) and (iv) is calculated using the following formula: q = 60 × U × I / (1000000 × v), where q is the linear energy without thermal efficiency, in kJ / mm; U is the welding voltage, in V; I is the welding current, in A; and v is the welding speed, in m / min.

9. The welding method for annealed and pickled 409 stainless steel of wire thickness according to claim 1, characterized in that, In (iv) and (ii), the energy of the second line is 35%-50% of the energy of the first line.

10. The welding method for annealed and pickled 409 stainless steel of wire thickness according to claim 1, characterized in that, In the fifth part, the height of the front side is no more than 2mm, and the depth of the concave side is 1-2mm.

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