Combined welding method for Q420qD thick plate

Abstract

The invention discloses a combined welding method, particularly discloses a combined welding method for Q420qD thick plates, and belongs to the technical field of high-strength steel welding processes. According to the combined welding method for the Q420qD thick plate, the welding quality meets the requirement, and the production efficiency is relatively high. Comprising the steps that a Q420qD thick plate is adopted for machining, a qualified to-be-welded weld joint is assembled, the welding work of the to-be-welded weld joint is completed in a CO2 gas shielded welding bottoming, submerged arc automatic welding seam filling and capping combined welding mode, and the specific operation process is as follows: firstly, oil stains, splashes and burrs of the to-be-welded weld joint and accessories of the to-be-welded weld joint are cleaned, and then the to-be-welded weld joint and the accessories of the to-be-welded weld joint are cleaned; the method comprises the following steps: firstly, welding a Q420qD thick plate, preheating a weld joint to be welded and a base material in a range of 80-120mm nearby the weld joint, performing baking and heat preservation on an automatic submerged arc welding protective flux at the same time, and after the preheating, baking and heat preservation are qualified, completing the welding work of the Q420qD thick plate by adopting a CO2 gas shielded welding bottoming and automatic submerged arc welding capping combined welding mode according to the welding process requirements of multi-layer and multi-pass welding.

Description

TECHNICAL FIELD

[0001] The present application relates to a combined welding method, in particular to a combined welding method for Q420qD thick plate, belonging to the technical field of welding process of low alloy high strength steel. BACKGROUND

[0002] With the rapid development of bridge construction in China, bridges have been developing towards longer span, longer, larger and more flexible, and bridge structures have been developing towards lightness, which puts forward higher requirements on bridge steel, such as strength, plasticity, toughness and welding performance. Q420qD high strength steel is a kind of low alloy high strength structural steel with yield strength ≥ 420 MPa, which has high strength, low temperature toughness and impact performance of bearing the load of locomotive vehicles, and has good fatigue resistance and atmospheric corrosion resistance, so it is widely used in steel for railway, highway bridge, cross-river and cross-sea bridge. However, Q420qD has high strength, and welding is prone to crack, increasing the difficulty of welding; in order to obtain good welding quality of Q420qD steel, the welding process is very important in steel structure engineering.

[0003] The existing patent technology CN201810478724.5 provides a gas shielded welding method for low-carbon Q420q bridge steel, which realizes a welding process without preheating before welding and without heat treatment after welding in the manufacturing process of a low-carbon Q420q bridge steel medium plate structure under the new national standard, and realizes a simple, efficient and economical welding method in the construction process of the bridge steel medium plate. However, the patent technology adopts gas shielded welding method, uses 20% CO2+80% Ar mixed gas as protective gas, and compared with the traditional welding method, the welding performance is good, but the construction cost is high. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a combined welding method for Q420qD thick plate, which has stable welding arc, meets the requirements of welding quality, has relatively high production efficiency and significantly reduced construction cost.

[0005] The technical scheme adopted to solve the above technical problems is: a combined welding method for Q420qD thick plate, which comprises a Q420qD thick plate processing and assembly qualified weld seam, and the combined welding method adopts CO2 gas shielded welding backing, automatic submerged arc welding filling and covering of the weld seam, and the specific operation process is as follows, First, clean the oil, splash, burr of the weld and its accessories, then preheat the base material of the weld and its nearby 80-120mm range, at the same time, bake and keep warm the protective flux for submerged arc automatic welding, after the preheating and baking and keeping warm are qualified, use the combination of CO2 gas shielded welding and submerged arc automatic welding to complete the welding of Q420qD thick plate according to the welding process requirements of multi-layer and multi-pass welding, Wherein, the thickness of each layer of weld metal in multi-layer and multi-pass welding is not more than 8mm, and the temperature difference between layers is controlled between 150-200℃. The welding wire of CO2 gas shielded welding is copper-plated gas shielded welding wire for 550-600Mpa low alloy high strength steel, or is 550Mpa low temperature steel gas shielded flux-cored welding wire; the welding wire of submerged arc automatic welding is 550Mpa Mn-Mo series heat-resistant steel high-strength copper-plated submerged arc welding wire, and the protective flux is GXL-125 low alloy steel submerged arc sintered flux, and the particle size of the flux is selected as 1.43-0.28mm.

[0006] Further, before welding, the welding performance of the steel plate to be welded is evaluated according to the following calculation formula of welding crack sensitivity index Pcm, and after the welding performance evaluation is qualified, the welding process evaluation test piece is made according to the requirements, and the test is qualified, and then the product welding is carried out, Pcm (%) = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B = 0.2154 ≤ 0.22; The welding process evaluation test piece includes butt joint test piece and corner joint test piece, and the test results are as follows, The test results of the butt joint test piece are as follows, The test results of the corner joint test piece are as follows, .

[0007] The preferred mode of the above scheme is that the preheating temperature of the base material on both sides of the weld is 80-100℃, the baking temperature of the welding protective agent is 250℃, the baking time is 1-2h, the CO2 gas shielded welding wire is GML-W60 or GFR-81K2, and the submerged arc automatic welding wire is GWR-WEA4M1.

[0008] Further, before assembling the weld to be welded, a V-shaped groove is prepared on the base material, the groove pure edge is 2-4mm, and the root gap is 0-3mm; the welding power source adopts direct current reverse polarity connection method.

[0009] The preferred mode of the above scheme is that the process parameters of the multi-layer and multi-pass welding process for welding butt joint are controlled according to the following table, .

[0010] Further, the process parameters for welding the corner joint by using the multi-layer multi-pass welding process are controlled according to the following table, .

[0011] The chemical composition of the welded base metal is controlled according to the following table in the preferred mode of the above scheme: C≤0.11, S≤0.007, P≤0.025, Mn 1.0-1.7, Si≤0.55, Cr≤0.50, Mo≤0.25, V 0.01-0.08, Ni≤0.30, Cu≤0.30, and the rest is Fe.

[0012] The beneficial effects of the present application are that the combined welding method provided by the present application directly uses CO2 gas shielded welding for backing and automatic submerged arc welding for covering, thereby solving the technical problem of high welding cost in the prior art when 20% CO2+80% Ar mixed gas is used as the protective gas for welding the medium-thick to thick low-alloy high-strength steel such as Q420qD. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The figure is a schematic diagram of the bevel of the butt joint involved in the combined welding method for Q420qD thick plates according to the present application. Figure 2 The figure is a schematic diagram of the bevel of the corner joint involved in the combined welding method for Q420qD thick plates according to the present application. DETAILED DESCRIPTION

[0014] As shown in Figure 1 , Figure 2 The combined welding method for Q420qD thick plates according to the present application has stable welding arc, meets the requirements of welding quality, has relatively high production efficiency, and significantly reduces construction cost. The combined welding method includes using Q420qD thick plates that meet the requirements of processing and assembly to form a weld seam to be welded. First, clean the oil, splash, burr of the weld and its accessories, then preheat the base metal of the weld and its nearby 80-120mm range, at the same time, bake and keep warm the protective flux for submerged arc automatic welding, after the preheating and baking and keeping warm are qualified, use the combination of CO2 gas shielded welding and submerged arc automatic welding to complete the welding of Q420qD thick plate according to the welding process requirements of multi-layer and multi-pass welding, In the multi-layer and multi-pass welding, the thickness of each layer of weld metal is not more than 8mm, and the temperature difference between layers is controlled between 150-200℃. The welding wire of CO2 gas shielded welding is copper-plated gas shielded welding wire for 550-600Mpa low alloy high strength steel, or 550Mpa low temperature steel gas shielded flux-cored welding wire; the welding wire of submerged arc automatic welding is 550Mpa Mn-Mo series heat-resistant steel high-strength copper-plated submerged arc welding wire, the protective flux is GXL-125 low alloy steel submerged arc sintered flux, and the particle size of the flux is selected as 1.43-0.28mm. The technical scheme provided in the application directly uses the combination of CO2 gas shielded welding and submerged arc automatic welding, thereby solving the technical problem of high welding cost in the prior art when welding similar Q420qD low alloy high strength steel of medium thickness to thick, and using 20% CO2+80% Ar mixed gas as protective gas. By using the combined welding method of the application, CO2 gas shielded welding is only used for backing, and submerged arc automatic welding is used for subsequent fillet welding and cap welding, thereby effectively ensuring the stability of the welding arc, meeting the welding quality requirements, effectively improving the production efficiency, and significantly reducing the production cost.

[0015] Correspondingly, in combination with the prior art, in order to avoid cracks in the weld during welding and after welding, and to ensure the quality of the weld, the application first evaluates the welding performance of the steel plate to be welded according to the following calculation formula of welding crack sensitivity index Pcm before welding, then performs welding process evaluation test piece according to the requirements after the welding performance evaluation is qualified, and then performs product welding after the test piece is tested and qualified, Pcm (%) = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B = 0.2154 ≤ 0.22; The welding process evaluation test piece includes butt joint test piece and corner joint test piece, and the test results are as follows, The test results of the butt joint test piece are as follows, The test results of the corner joint test piece are as follows, More is, in the welding, the temperature of the base material preheating on both sides of the weld is 80-100℃, the temperature of the welding protective agent baking is 250℃, the baking time is 1-2h, the CO2 gas shielded welding wire is GML-W60 or GFR-81K2, and the submerged arc automatic welding wire is GWR-WEA4M1. Before the welding of the weld assembly, a V-shaped groove is prepared on the base material, the groove pure edge is 2-4mm, and the root gap is 0-3mm; the welding power supply adopts the direct current reverse polarity connection method. The process parameters of the multi-layer multi-pass welding process for welding the butt joint are controlled according to the following table, The process parameters of the multi-layer multi-pass welding process for welding the corner joint are controlled according to the following table, In summary, the technical scheme provided by the application also has the following advantages, The steel plate Q420qD is selected as the base material, and the steel material adopts the delivery state of the thermal mechanical control rolling (TMCP) process. The comprehensive performance of the welding is equivalent to the base material by using the submerged arc automatic welding process, which can completely meet the welding quality requirements, and the line energy is large, the production efficiency is high, and the quality is stable.

[0016] The technical scheme of the application will be further described below through specific examples: Example 1 Taking high-strength alloy steel 420qD with a thickness of 50mm as an example.

[0017] Welding process: the base material preheating temperature before welding is 80-100℃, the multi-layer multi-pass welding process is adopted, the interlayer temperature is 150-200℃, and the welding parameters are shown in the following table. The welding agent should be strictly baked before use, the baking temperature is 250℃, and the baking time is 1-2h.

[0018] Table 3 Steel chemical composition performance analysis table 1 (%) Table 4 Steel chemical composition performance analysis table 2 (%) Note: The judgment technical standard of the chemical composition detection index of Q420qD-Z25 steel material is GB / T714-2015 and GB / T5313-2010.

[0019] According to the above various parameter indexes of the steel material, combined with the technical requirements in the specification GB / T714-2015, when the carbon content is not greater than 0.12%, the welding crack sensitivity index (Pcm) is used instead of the carbon equivalent (Ceq) to evaluate the welding performance of the steel material.

[0020] Pcm (%) = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B = 0.2154 The Pcm (%) of the welding crack sensitivity index meets the specification requirements, and the steel has good weldability.

[0021] Table 5 Steel mechanical property analysis table (%) Note: The technical standard for judging the mechanical property detection index of Q420qD-Z25 steel is GB / T714-2015.

[0022] Table 6 CO2 gas shielded welding backing + submerged arc welding cover joint test results Table 7 CO2 gas shielded welding backing + submerged arc welding angle test results .

[0023] According to the above table, the detection results of the welding process of Q420qD-Z25 show that the welding method of CO2 gas shielded welding backing and submerged arc welding filling and covering can effectively guarantee the welding quality, and can meet the welding requirements of relevant specifications and design.

Claims

1. A combined welding method for Q420qD thick plates, comprising processing and assembling qualified weld seams from Q420qD thick plates, characterized in that: The combined welding method described above employs a combination of CO2 gas shielded welding for the root pass, submerged arc welding for the filler pass, and capping weld to complete the welding work of the seam to be welded. The specific operation process is as follows. First, clean the oil, spatter, and burrs from the weld seam and its accessories. Then, preheat the weld seam and the base material within an 80-120mm radius around it. Simultaneously, bake and maintain the temperature of the flux used for submerged arc welding. After the preheating, baking, and temperature maintenance are satisfactory, use a combination welding method of CO2 gas shielded welding for the root pass and submerged arc welding for the cover pass, following the welding process requirements of multi-layer, multi-pass welding, to complete the welding of the Q420qD thick plate. Among them, the thickness of each layer of weld metal in multi-layer multi-pass welding shall not exceed 8mm, and the temperature difference between layers shall be controlled between 150 and 200℃. The welding wire for CO2 gas shielded welding is a copper-plated solid welding wire for low-alloy high-strength steel of 550-600 MPa grade, or a flux-cored welding wire for low-temperature steel of 550 MPa grade; the welding wire for submerged arc welding is a copper-plated submerged arc welding wire for high-strength Mn-Mo heat-resistant steel of 550 MPa grade, and the protective flux is GXL-125 low-alloy steel submerged arc sintered flux, with a flux particle size of 1.43-0.28 mm.

2. The combined welding method for Q420QD thick plates according to claim 1, characterized in that: Before welding, the welding performance of the steel plate to be welded is evaluated using the welding crack sensitivity index Pcm calculated according to the following formula. After the welding performance evaluation is qualified, a welding procedure qualification test piece is made according to the requirements, consisting of CO2 gas shielded welding for the root pass and submerged arc welding for the cover pass. Only after the test is qualified can the product welding be carried out. Pcm (%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B=0.2154≤0.22; The welding procedure qualification test specimens include butt joint specimens and corner joint specimens, and the test results are as follows. The test results of the butt joint specimens are shown in the table below. The test results of the corner joint specimens are shown in the table below. 。 3. The combined welding method for Q420QD thick plates according to claim 1 or 2, characterized in that: The preheating temperature of the base metal on both sides of the weld is 80-100℃, the baking temperature of the welding shielding agent is 250℃, the baking time is 1-2 hours, the CO2 gas shielded welding wire is GML-W60 or GFR-81K2, and the submerged arc automatic welding wire is GWR-WEA4M1.

4. The combined welding method for Q420QD thick plates according to claim 3, characterized in that: Before assembling the weld, prepare a V-shaped groove on the base material with a pure edge of 2-4 mm and a root gap of 0-3 mm; use DC reverse polarity connection for welding power.

5. The combined welding method for Q420QD thick plates according to claim 2, characterized in that: The process parameters for welding butt joints using multi-layer, multi-pass welding technology are controlled according to the table below. 。 6. The combined welding method for Q420QD thick plates according to claim 2, characterized in that: The process parameters for welding corner joints using a multi-layer, multi-pass welding process are controlled according to the table below. 。 7. The combined welding method for Q420QD thick plates according to claim 1, characterized in that: The chemical composition of the base material to be welded shall be controlled according to the following table: C≤0.11, S≤0.007, P≤0.025, Mn1.0~1.7, Si≤0.55, Cr≤0.50, Mo≤0.25, V0.01~0.08, Ni≤0.30, Cu≤0.30, with the remainder being Fe.

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