Self-shielded vertical down welding method for q420qD bridge structural steel

Abstract

The application provides a self-protection vertical downward welding method suitable for Q420qD bridge structure steel, and the welding groove is processed before welding, and then the welding joint to be welded is preheated, and if the plate thickness is less than or equal to 28 mm, the preheating is not needed; during welding, the self-protection flux-cored wire is used for vertical downward welding, and the carbon arc gouging is used for cleaning the root to ensure the root penetration. The bridge Q420qD material steel is welded by the method, the wind resistance is strong during the welding process, the appearance is well formed after welding, and the mechanical properties such as the low-temperature toughness of the joint are excellent, and the application is suitable for welding operations in the bridge site, mountainous areas and other outdoor harsh environments and high-altitude places where the gas is inconvenient.

Description

TECHNICAL FIELD

[0001] The present application relates to a bridge welding method, in particular to a self-protection vertical down welding method suitable for Q420qD bridge structure steel (steel tower commonly used material). BACKGROUND

[0002] Most of the main girder of long-span bridge adopts steel structure, and most of the tower adopts RC tower (reinforced concrete tower). The connection mode of the steel tower bridge site includes "metal contact + high bolt" and "full welding". Due to the modeling requirements of most steel towers, the curved special-shaped steel tower can only adopt the full welding form of bridge site connection. The construction of these steel towers brings great challenges to the bridge site welding construction. The height of the full-welded steel tower is generally about one hundred meters. The bridge site construction site belongs to special high-altitude operation. The environment is poor, and the welding is difficult. Especially, the wind speed is higher than that of the bridge deck and the ground.

[0003] At present, the bridge site welding of steel bridge (including steel tower) mostly adopts CO2 gas shielded welding process. During the welding process, strong wind will weaken the CO2 gas protection effect, causing air to enter the molten pool and causing porosity and other welding defects, affecting the internal quality of the weld, and further affecting the bridge erection progress. In addition, as the steel tower installation segment rises, the cost of gas cylinder hoisting increases linearly, and the safety hidden danger of gas cylinder storage at high altitude also increases. Similarly, the bridge erection in mountainous areas is inevitably disturbed by strong winds in valleys, and a series of gas inconvenience such as transportation, lifting and storage. If the gas shielded welding method is abandoned in the inconvenient gas place, there are not many welding methods to choose from. If submerged arc welding is used, it can only be used for flat position and some specific horizontal position welding operation, which is difficult to meet the full position welding requirements of the bridge site. If the shielded arc welding is used, the welding efficiency is too low, and the bridge erection period cannot be guaranteed.

[0004] Therefore, how to weld the bridge steel structure in the strong wind environment and the inconvenient gas condition and ensure the welding quality and efficiency is a problem to be solved. SUMMARY

[0005] The purpose of the present application is to provide a self-protection vertical down welding method suitable for Q420qD bridge structure steel in view of the problems in the background art.

[0006] Technical scheme: The present application provides a self-protection vertical down welding method suitable for Q420qD bridge structure steel, comprising:

[0007] Welding groove processing, preheating the welded joint, if the plate thickness is less than or equal to 28mm, no preheating;

[0008] Self-protection flux-cored wire is used for vertical down welding, and carbon arc gouging is used to ensure root penetration during the process.

[0009] The welding method of the present application does not need gas protection, relies on the flux of the flux-cored wire to form "self-protection" by gas and slag, and has excellent wind resistance (through tests, the weld quality welded by the self-protection flux-cored wire still meets the standard requirements under the action of 8-level strong wind with a wind speed of 17.2 m / s); the appearance after welding is well formed; the welding speed is fast by using the vertical downward welding method, the current and voltage values are relatively low, the corresponding heat input value is low, the welding deformation generated by using the welding method is small, which is beneficial to the control of welding deformation; the weld structure obtained by the self-protection flux-cored wire combined with the vertical downward welding method is fine and uniform acicular ferrite + granular bainite, the heat-affected zone structure is granular bainite + carbide-free bainite + pearlite + a small amount of ferrite, so that the weld has good strength index and excellent low-temperature impact toughness index, and the mechanical property data stably exceeds the requirements of the relevant standards. Therefore, the present application can effectively solve the welding problems in strong wind and harsh environment and in places where gas is not convenient to use.

[0010] Further, the self-protection flux-cored wire uses T553T8-1NA-N3 type, and the chemical composition is as follows in terms of mass percentage: C≤0.12%, Si≤0.80%, Mn≤1.75%, P≤0.030%, S≤0.030%, Cr≤0.15%, Ni=1.00%-2.00%, Mo≤0.35%, Al≤1.8%, V≤0.05%, and the balance is Fe.

[0011] Further, when welding vertically downward, the downward inclination angle of the welding wire is 65°-80°.

[0012] Further, when the plate thickness is 28 mm≤plate thickness≤50 mm, the preheating temperature is 60°C-100°C; when the plate thickness is >50 mm, the preheating temperature is 80°C-120°C.

[0013] Further, when the plate thickness is >20 mm, the groove form is X-type groove, the groove angle of the first welding side is 44°-50°, the groove angle of the root cleaning side is 49°-55°, the blunt edge is 2 mm, and the groove root gap is controlled to be 0-2 mm; when the plate thickness is ≤20 mm, the groove form is V-type groove, the groove angle is 39°-45°, the blunt edge is 0-1 mm, and the groove root gap is controlled to be 4-6 mm.

[0014] Further, for the X-type groove, the backing welding, vertical down welding of the filling layer are sequentially carried out first, and the slag is polished and cleaned every welding; when the welding of the first welding side groove reaches half depth, the other groove side is changed to carbon arc air gouging to clean the root; after the cleaning, the groove surface is polished and cleaned, and the backing welding, filling and surface layer of the cleaned groove are sequentially vertically down welded; the first welding side groove is changed again, and the filling and surface layer of the remaining groove are sequentially vertically down welded.

[0015] Further, for the V-type groove, a ceramic backing pad is pasted on the back, and then the backing welding, filling and surface layer are vertically down welded; then the ceramic backing pad on the back is removed, and the backing layer is cleaned by carbon arc air gouging, and the cleaned part is re-welded to fill.

[0016] In the technical solution, since the alkalinity of the internal components of the ceramic backing pad is low and the acidic oxide is more, the ceramic backing pad is prone to chemical reaction with the alkaline self-protection welding wire during welding, and the residual slag on the back of the weld after welding affects the appearance forming and penetration rate of the weld, therefore, after the welding of the back of the ceramic backing pad is completed and removed, the backing layer is cleaned by carbon arc air gouging, and the cleaned part is re-welded to fill, so as to ensure the root penetration and back forming.

[0017] Further, for the X-type groove, the welding current of all welding passes is 190-220A, the welding voltage is 18-20V, the welding speed is 240-280mm / min, the power polarity is direct current positive connection, the wire feeding speed is 90-110in / min, the dry elongation is 19-25mm, the swing range is 1-2mm, and the heat input is 7.3-11.0KJ / cm.

[0018] Further, for the V-type groove, the welding current of the backing layer is 150-170A, the welding voltage is 16-18V, the welding speed is 180-220mm / min, and the heat input is 6.5-10.2KJ / cm; the welding current of the filling and surface layer is 190-220A, the welding voltage is 18-20V, the welding speed is 240-280mm / min, and the heat input is 7.3-11.0KJ / cm; the power polarity is direct current positive connection, the wire feeding speed is 90-110in / min, the dry elongation is 19-25mm, and the swing range is 1-2mm.

[0019] Beneficial effects: compared with the prior art, the present application has the following obvious advantages: the present application can solve the welding problem of the bridge steel structure in the strong wind and harsh environment and the place where gas is not convenient, and the appearance forming of the welded weld is good, and the mechanical properties such as low-temperature toughness of the joint are excellent. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application are briefly introduced as follows. Obviously, the drawings described below only are the embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0021] Figure 1 is a schematic diagram of a joint groove in the embodiment 1 of the present application;

[0022] Figure 2 is a schematic diagram of welding bead deposition in the embodiment 1 of the present application, wherein 1-20 are the welding bead sequence;

[0023] Figure 3 is a schematic diagram of vertical down welding operation in the embodiment of the present application, wherein the angle shown in the diagram is the wire downward inclination angle;

[0024] Figure 4 is a schematic diagram of a joint groove in the embodiment 2 of the present application;

[0025] Figure 5 is a schematic diagram of welding bead deposition in the embodiment 2 of the present application, wherein 1-13 are the welding bead sequence. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely in the embodiments of the present application in combination with the drawings. Obviously, the described embodiments are not all the embodiments. All other embodiments obtained by those skilled in the art without any creative effort on the basis of the embodiments of the present application belong to the protection scope of the present application.

[0027] Embodiment 1

[0028] The chemical composition of the Q420qD bridge structure steel used is shown in Table 1, and the mechanical properties are shown in Table 2.

[0029] Table 1 Chemical composition of Q420qD bridge structure steel (t32) base material

[0030]

[0031] Table 2 Mechanical properties of Q420qD bridge structure steel (t32) base material

[0032]

[0033] The test steel plate to be welded has a thickness of 32 mm, a size of 32×200×600 mm, and a joint groove form shown in Figure 1The groove is X type. The welding material is T553T8-1NA-N3, and the diameter of welding wire is 2.0 mm. The welding equipment is DC-500IIe type welding machine of Outee, and the power polarity is direct current positive connection.

[0034] The chemical composition of the welding core of T553T8-1NA-N3 (Φ2.0) self-shielded flux-cored wire is shown in Table 3, and the mechanical properties of the fusion cladding metal of the welding wire are shown in Table 4.

[0035] Table 3 Chemical composition of welding core of T553T8-1NA-N3 (Φ2.0) self-shielded flux-cored wire

[0036]

[0037] Table 4 Mechanical properties of fusion cladding metal of T553T8-1NA-N3 (Φ2.0) self-shielded flux-cored wire

[0038]

[0039] Example 1 is welded according to the following steps:

[0040] (a) Groove processing

[0041] As Figure 1 , the rust, oil stains and other impurities within 20 mm range on both sides of the groove of the two butt plates after machining or flame cutting are polished and cleaned to expose the metal luster of the groove area;

[0042] The groove form is X type, and the groove angle formed by the two steel plates is 44°-50° on the first welding side and 49°-55° on the root cleaning side, and the bevel is 2 mm.

[0043] (b) The gap of 0-2 mm is pulled at the root of the groove, and the positioning welding assembly is performed.

[0044] (c) The at least 100 mm range on both sides of the welded joint is preheated to 60-100℃ by using electric heating equipment.

[0045] (d) The self-shielded flux-cored wire without gas protection is used to sequentially perform the backing welding of the first welding side groove and the vertical downward welding of the filling layer, and the welding operation is as shown in Figure 3 .

[0046] When the self-shielded vertical downward welding is performed, the angle between the welding wire extending in the welding gun and the vertical plane below (i.e. the downward angle of the welding wire) is 65°-80°. When the self-shielded vertical downward welding is performed, the weld appearance is well formed, but in order to prevent the molten iron from falling downward, a high welding speed needs to be maintained and the swing range needs to be as small as possible, so as to prevent the welding defects such as incomplete penetration and incomplete fusion.

[0047] The droplet transfer mode of the self-shielded flux-cored wire during vertical down welding is mainly arc bridge coexisting surface tension transfer and arc bridge coexisting explosive transfer, especially the explosive transfer makes part of the droplet transfer into the molten pool and another part of the droplet fly away from the arc as dispersed particles, thereby producing large particles splashing in different directions along the upper and lower front and back, which macroscopically causes the interlayer deslagging of the self-shielded welding to be weak and the splashing to be large. Therefore, the grinding and cleaning process between each pass (layer) should be paid special attention to during the welding process, and the slag can be cleaned by using a small hammer + steel brush assisted grinding machine to avoid the slag inclusion defect as much as possible.

[0048] The self-shielded flux-cored wire adopts T553T8-1NA-N3, and the diameter is 2.0 mm. The chemical composition of the self-shielded flux-cored wire core is as follows in terms of mass percentage: C≤0.12%, Si≤0.80%, Mn≤1.75%, P≤0.030%, S≤0.030%, Cr≤0.15%, Ni=1.00%-2.00%, Mo≤0.35%, Al≤1.8%, V≤0.05%, and the balance is Fe.

[0049] During the welding of the base, filling and cover layers of the self-shielded wire, the welding current is 190-220 A, the welding voltage is 18-20 V, the welding speed is 240-280 mm / min, the power polarity is direct current positive connection, the wire feeding speed is 90-110 in / min, the dry elongation is 19-25 mm, the swing range is 1-2 mm, and the heat input is 7.3-11.0 KJ / cm. Because the welding speed of the self-shielded vertical down welding is fast, the current and voltage values are relatively low, and the corresponding heat input value is low, the welding deformation produced by this welding method is small; and compared with the vertical up welding, the number of weld seams (layers) is more, and the weld seam lines are more dense and uniform, which is more conducive to obtaining excellent weld mechanical properties on the basis of multi-layer and multi-pass welding.

[0050] (e) When the welding of the first welding side groove is performed to about half the depth, the other side of the groove is changed to carbon arc gouging to clean the root (if the welding stays for a long time, preheating treatment should also be performed before cleaning the root); after the cleaning of the root is completed, the groove surface is polished and cleaned, and the self-shielded flux-cored wire is used to sequentially perform vertical down welding on the base, filling and cover layers of the cleaned groove.

[0051] (f) The first welding side groove is changed again, and the self-shielded flux-cored wire is used to sequentially perform vertical down welding on the filling and cover layers of the remaining groove which is not filled.

[0052] The schematic diagram of the weld bead deposition is shown in Figure 2 . The welding process parameters are shown in Table 5, and the mechanical properties of the welded joint are shown in Table 9.

[0053] Table 5 Welding process parameters of Example 1

[0054]

[0055] Example 2

[0056] The difference from Example 1 is that the test steel plate to be welded has a thickness of 20 mm, a size of 20 x 200 x 600 mm, and the joint groove form is as shown in Figure 4 , which is a V-shaped groove. The chemical composition of the test steel plate is shown in Table 6, and the mechanical properties are shown in Table 7. No preheating is performed before welding.

[0057] The remaining conditions are basically the same as in Example 1.

[0058] Table 6 Chemical composition of Q420qD bridge structural steel (t20) base material

[0059]

[0060] Table 7 Mechanical properties of Q420qD bridge structural steel (t20) base material

[0061]

[0062] Example 2 is welded according to the following steps:

[0063] (a) Welding groove machining

[0064] The impurities such as rust and oil within 20 mm range on both sides of the groove of the two machined or flame-cut butt joint steel plates are polished and cleaned to expose the metal luster of the groove area;

[0065] The groove form is a V-shaped groove, and the groove angle formed by the two steel plates is 39° to 45°, and the root face is 0 to 1 mm.

[0066] (b) The gap of 4 to 6 mm is pulled at the root of the groove (because the arc penetration of self-protection welding is strong, the gap should not be too large), the back is pasted with ceramic backing, and positioning welding assembly is performed using a plate.

[0067] (c) Vertical down welding is performed using self-protection flux-cored wire for backing, filling and cap layer.

[0068] The self-protection flux-cored wire uses T553T8-1NA-N3, and the diameter is 2.0 mm. The chemical composition of the self-protection flux-cored wire core is as follows in terms of mass percentage: C≤0.12%, Si≤0.80%, Mn≤1.75%, P≤0.030%, S≤0.030%, Cr≤0.15%, Ni=1.00%-2.00%, Mo≤0.35%, Al≤1.8%, V≤0.05%, and the balance is Fe.

[0069] When the backing layer is welded by the self-shielded welding wire, the welding current is 150-170 A, the welding voltage is 16-18 V, the welding speed is 180-220 mm / min, the power polarity is direct current positive connection, the wire feeding speed is 90-110 in / min, the dry elongation is 19-25 mm, the swing is 1-2 mm, and the heat input is 6.5-10.2 KJ / cm. When the filling and cover layers are welded by the self-shielded welding wire, the welding current is 190-220 A, the welding voltage is 18-20 V, the welding speed is 240-280 mm / min, the power polarity is direct current positive connection, the wire feeding speed is 90-110 in / min, the dry elongation is 19-25 mm, the swing is 1-2 mm, and the heat input is 7.3-11.0 KJ / cm.

[0070] (d) The backing layer is cleaned by the carbon arc gouging, and the cleaned area is refilled by the self-shielded welding wire. When the refilled layer is welded by the self-shielded welding wire, the welding current is 190-220 A, the welding voltage is 18-20 V, the welding speed is 240-280 mm / min, the power polarity is direct current positive connection, the wire feeding speed is 90-110 in / min, the dry elongation is 19-25 mm, the swing is 1-2 mm, and the heat input is 7.3-11.0 KJ / cm.

[0071] The schematic diagram of the weld bead deposition is shown in Figure 5 The welding process parameters are shown in Table 8, and the mechanical properties of the welded joint are shown in Table 9.

[0072] Table 8 Welding process parameters of Example 2

[0073]

[0074] Table 9 Mechanical properties of the welded test plate of Examples 1 and 2

[0075]

[0076] The self-protection welding method is adopted to vertically downward weld butt welds of Q420qD bridge structure steel, the welds are well formed, and the appearance quality meets the requirements of Table 4.9.12 in Railway Steel Bridge Manufacturing Specification (Q / CR9211-2015); after UT ultrasonic flaw detection, the internal quality of the welds meets the requirements of Grade I in Railway Steel Bridge Manufacturing Specification (Q / CR9211-2015). The yield strength, tensile strength, elongation after fracture of the welds and the tensile strength of the butt joint are all greater than the standard values of the base material (refer to GB / T714-2015 standard); the joint bending test welds are intact (refer to Q / CR9211-2015 standard); the Charpy impact energy of the welds and the heat affected zone of the joint at-20 DEG C is all greater than or equal to 47J (refer to Q / CR9211-2015 standard), and the average value is about 3 times greater than the standard value, with a high low-temperature impact reserve; the maximum hardness HV10 of the three zones of the welded joint is all less than or equal to 380 (refer to Q / CR9211-2015 standard).

[0077] In conclusion, the self-protection welding method is adopted to vertically downward weld butt welds of Q420qD bridge structure steel, by designing reasonable welding groove and welding process parameters and measures, and adapting the self-protection flux-cored wire with model T553T8-1NA-N3 (Φ2.0), the appearance formation and internal quality of the obtained welded joint are good, and the mechanical properties of the welded joint can all meet the requirements of the relevant standard (Q / CR9211-2015), verifying the operability and applicability of the proposed self-protection vertically downward welding method.

[0078] The application will be popularized and applied in the bridge site construction of Changtai Yangtze River Bridge steel tower and Zhangjingao Yangtze River Bridge steel tower, and has important demonstration and reference significance for solving the welding problems in strong wind and bad environment and places where gas is inconvenient to use.

[0079] The above merely describes specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any changes or alternative solutions that can be easily thought of by those skilled in the art within the technical range disclosed by the present application should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A self-shielded vertical down welding method suitable for Q420qD bridge structure steel, characterized in that, Comprise: Welding groove processing, preheating the joint to be welded, if the plate thickness ≤28mm, then no preheating; 28mm < plate thickness ≤50mm, preheating temperature is 60℃ ~ 100℃; plate thickness > 50mm, preheating temperature is 80℃ ~ 120℃; Using self-protection flux-cored wire for vertical down welding, using carbon arc air gouging to ensure root penetration in the process; Self-protection flux-cored wire uses T553T8-1NA-N3 type, the chemical composition is as follows: C ≤0.12%, Si ≤0.80%, Mn ≤1.75%, P ≤0.030%, S ≤0.030%, Cr ≤0.15%, Ni =1.00% ~ 2.00%, Mo ≤0.35%, Al ≤1.8%, V ≤0.05%, the balance is Fe; When the plate thickness > 20mm, the groove form is X type groove; For X type groove, first in turn, the bottom of the first welding side groove, filling layer vertical down welding, each weld will be slag polished clean; when the first welding side groove is welded to half depth, change to the other side of the groove to root carbon arc air gouging; after the root cleaning, the groove surface is polished clean, and the bottom, filling and cap layer of the cleaned groove are welded in turn; change to the first welding side groove again, and fill and cap layer of the remaining groove are welded in turn; For X type groove, welding current is 190 ~ 220A, welding voltage is 18 ~ 20V, welding speed is 240 ~ 280mm / min, power polarity is direct current positive connection, wire feeding speed is 90 ~ 110in / min, dry elongation is 19 ~ 25mm, swing is 1 ~ 2mm, heat input is 7.3 ~ 11.0KJ / cm; When the plate thickness ≤20mm, the groove form is V type groove; For V type groove, ceramic pad is pasted on its back, and then the bottom, filling and cap layer are welded by vertical down welding; then the back ceramic pad is removed, and the bottom layer is re-welded by carbon arc air gouging, and the cleaned root is filled; For V type groove, the welding current of the bottom layer is 150 ~ 170A, the welding voltage is 16 ~ 18V, the welding speed is 180 ~ 220mm / min, the heat input is 6.5 ~ 10.2KJ / cm; the welding current of the filling and cap layer is 190 ~ 220A, the welding voltage is 18 ~ 20V, the welding speed is 240 ~ 280mm / min, the heat input is 7.3 ~ 11.0KJ / cm; the power polarity is direct current positive connection, the wire feeding speed is 90 ~ 110in / min, the dry elongation is 19 ~ 25mm, the swing is 1 ~ 2mm.

2. The self-protecting vertical down welding method according to claim 1, characterized by, When vertical down welding, the wire inclination angle is 65° ~ 80°.

3. The self-protecting vertical down welding method according to claim 1, characterized by, For X type groove, the first welding side groove angle is 44° ~ 50°, the root cleaning side groove angle is 49° ~ 55°, the bevel is 2mm, and the groove root gap is controlled in 0 ~ 2mm; for V type groove, the groove angle is 39° ~ 45°, the bevel is 0 ~ 1mm, and the groove root gap is controlled in 4 ~ 6mm.

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