A submerged-arc welding method for improving performance of a welded joint of Q500qENH weather-resistant bridge steel

Abstract

The application discloses a submerged-arc welding method for improving the performance of a Q500qENH weather-resistant bridge steel welded joint, which optimizes the chemical composition of the Q500qENH weather-resistant bridge steel, and optimizes and controls the parameters of the submerged-arc welding method without preheating before welding and heat treatment after welding, so that the performance of the Q500qENH weather-resistant bridge steel welded joint is obviously improved, and the low-temperature impact toughness and the low-temperature fracture resistance are excellent.

Description

Technical Field

[0001] This invention belongs to the field of steel material welding technology, specifically relating to a submerged arc welding method for improving the performance of welded joints of Q500qENH weathering bridge steel. Background Technology

[0002] As a crucial control point in major transportation projects, steel bridges are trending towards multi-functionality, large-scale structures, and complex operating conditions, requiring bridge steel to possess comprehensive properties such as high strength and toughness, excellent weather resistance, and efficient weldability. Among these, Q500qENH weathering bridge steel, with its high strength (yield strength not less than 500MPa, tensile strength not less than 630MPa), high toughness (impact absorption energy at -40℃ not less than 120J), low yield-to-tensile ratio, easy weldability (impact absorption energy at -40℃ in the heat-affected zone not less than 54J), and weather resistance (weathering index not less than 6.5), is the preferred material. However, currently, with the increase of alloy content, the carbon equivalent of Q500qENH weathering bridge steel increases, leading to a deterioration in weldability. Furthermore, welding in high-altitude and frigid environments places more stringent requirements on preheating and post-weld heat treatment processes; conventional welding methods and measures are difficult to meet these standards.

[0003] Patent document CN 112222573 A (hereinafter referred to as Document 1) discloses a welding method for weathering steel Q500QENH, which includes the following steps: S1, a 60-degree angled groove is made at the welding joint of the two plates to be welded, and the groove wall is ground to remove loose rust and oxide scale; S2, the front and back welds are welded as root passes, and the groove is filled by solid wire welding, with the filled surface slightly higher than the original plane; S3, the surface is leveled with the original plane by planing. However, on the one hand, Document 1 only briefly introduces the welding method and welding process parameters, without detailing the welding materials and the mechanical properties and impact properties of the welded joint, resulting in poor guidance and applicability; on the other hand, the method in this document is a gas shielded welding method, which is not applicable to other welding methods.

[0004] Patent document CN 112620888 A (hereinafter referred to as Document 2) discloses a process for single-sided welding and double-sided forming of Q500qENH weathering steel in high-altitude and cold regions. This process overcomes the adverse effects of the high-altitude and cold environment on welding performance, improves the low-temperature toughness, crack resistance, and weather resistance of the welded joint, and thus obtains a welded joint with excellent mechanical and weather resistance properties. This enables the matching welding of large-span, heavy-load, high-strength, high-toughness, and high-weather-resistance bridge steel in high-altitude and cold regions, while eliminating the need for preheating before welding and post-weld heat treatment, thereby improving production efficiency and reducing energy consumption. However, Document 2 only provides the mechanical and impact properties of the welded joint, failing to provide the most crucial aspect: the low-temperature fracture resistance of the welded joint in high-altitude and cold environments.

[0005] Patent document CN 112756746 A (hereinafter referred to as Document 3) discloses a process for composite butt welding of Q500qENH weathering steel in high-altitude and cold regions. This process overcomes the adverse effects of the high-altitude and cold environment on welding performance, improving the low-temperature toughness, crack resistance, and weather resistance of the welded joint. This results in a welded joint with excellent mechanical and weather resistance properties, enabling the matching welding of large-span, heavy-load, high-strength, high-toughness, and high-weather-resistance bridge steel in high-altitude and cold regions. Furthermore, it eliminates the need for preheating before welding and post-weld heat treatment, improving production efficiency and reducing energy consumption. It is particularly suitable for welding thick-plate steel for high-strength bridge engineering. However, Document 3 only provides the mechanical and impact properties of the welded joint, failing to provide the most crucial aspect: its resistance to low-temperature fracture. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a submerged arc welding method for improving the performance of welded joints of Q500qENH weathering bridge steel. The chemical composition percentages of the Q500qENH weathering bridge steel are: C: 0.06–0.09%, Si: 0.20–0.40%, Mn: 1.40–1.50%, P≤0.015%, S≤0.005%, Nb: 0.04–0.06%, V: 0.04–0.06%, Ti: 0.010–0.020%, Cr: 0.45–0.60%, Ni: 0.30–0.40%, Cu: 0.30–0.40%, rare earth Ce: 0.0004–0.0015%, with the balance being Fe and associated inclusions.

[0007] The submerged arc welding method includes the following operations:

[0008] Step 1, beveling:

[0009] A V-shaped symmetrical bevel is made in the double butt joint of the substrate, with a bevel angle of 60° and a blunt edge of 2.0 mm.

[0010] Step 2, Preprocessing:

[0011] Grind and clean the V-shaped symmetrical bevel and the steel plate within 25-30mm on both sides;

[0012] Step 3, Welding:

[0013] Submerged arc welding is used, with multiple layers and multiple passes of continuous welding until the weld is filled. The welding current is 500±25A, the welding voltage is 32±2V, the welding speed is 40±2cm / min, the welding heat input is 25±2kJ / cm, and the interpass temperature is controlled below 120℃.

[0014] In some embodiments, the weld joint obtained by the submerged arc welding method has a weld zone low-temperature impact energy KV2 ≥ 75 J at -40℃, a fusion line low-temperature impact energy KV2 ≥ 110 J at -40℃, and a heat-affected zone low-temperature impact energy KV2 ≥ 95 J at -40℃. The weld joint has a tensile strength Rm ≥ 645 MPa, good bending performance at D = 3a 180°, a corrosion resistance index I ≥ 6.5, good low-temperature fracture toughness, a Vickers hardness HV10 < 250, and a CTOD fracture toughness characteristic value above 0.2 at -35℃. The weld joint microstructure consists of granular bainite + acicular ferrite + proeutectoid ferrite, and the heat-affected zone microstructure consists of granular bainite.

[0015] In some embodiments, in step 1, the base material is Q500qENH weathering bridge steel with a weather resistance index I ≥ 6.5, and the assembly is a butt joint with a thickness of 10-50mm.

[0016] In some implementations, in step 2, the surface is sanded with sandpaper and then cleaned with acetone to remove rust and oil.

[0017] In some implementations, step 3 involves no preheating before welding and no heat treatment after welding.

[0018] In some embodiments, in step 3, the welding wire used for submerged arc welding is a solid welding wire, the welding wire grade is OK Autrod13.40, the diameter is 4mm, the flux is OK Flux 10.62, and the weather resistance index I≥6.5.

[0019] In some embodiments, the Q500qENH weathering bridge steel is produced according to the following manufacturing process:

[0020] (1) Smelting is carried out using a low-carbon and low-crack-sensitivity composition design route;

[0021] (2) Steel billets were continuously cast using electromagnetic stirring and light pressure reduction processes;

[0022] (3) TMCP technology is used for two-stage rolling, and the rolled steel plate is air-cooled to room temperature;

[0023] (4) The tempering process is adopted, the tempering temperature is 550~580℃, the holding time is 20-40 minutes, and the furnace is air-cooled after being taken out of the furnace.

[0024] In some embodiments, the microstructure of the Q500qENH weathering bridge steel is fine and uniform bainitic ferrite + M / A islands + fine precipitates, with a yield strength Rel≥500MPa, tensile strength Rm≥630MPa, elongation after fracture A≥18%, and low-temperature impact energy KV2≥120J for a standard sample at -40℃.

[0025] The submerged arc welding method for improving the performance of welded joints of Q500qENH weathering bridge steel based on the above technical solutions has the following advantages:

[0026] (1) Using the welding method of the present invention, the microstructure of the weld seam of the submerged arc welded joint is granular bainite + acicular ferrite + proeutectoid ferrite, and the microstructure of the heat-affected zone is granular bainite.

[0027] (2) The submerged arc welded joint of this invention exhibits excellent low-temperature impact toughness. The low-temperature impact energy KV2 of the standard specimen at -40℃ in the weld zone of the weld joint is ≥75J, the low-temperature impact energy KV2 of the standard specimen at -40℃ in the fusion line is ≥110J, and the low-temperature impact energy KV2 of the standard specimen at -40℃ in the heat-affected zone is ≥95J. The tensile strength Rm of the welded joint is ≥645MPa, and the bending performance of D=3a at 180° is intact. The hardness (HV10) of the welded joint is much lower than 350 (<250), and there is no tendency for hardening cracking.

[0028] (3) The submerged arc welding joint of the present invention has good resistance to low temperature fracture, and the CTOD fracture toughness characteristic value at -35℃ is above 0.2.

[0029] (4) The welding technology of the present invention realizes that there is no preheating before welding and no heat treatment after welding, and the resulting welded joint has excellent microstructure and corrosion resistance. Attached Figure Description

[0030] Figure 1 A schematic diagram of the welding process used in this invention.

[0031] Figure 2 Macroscopic photograph of the welded joint in Embodiment 1 of the present invention.

[0032] Figure 3 The microstructure of the weld zone of the welded joint in Embodiment 1 of the present invention is shown at 400x magnification.

[0033] Figure 4 The microstructure of the fusion zone of the welded joint in Example 1 of this invention is shown at 400x magnification.

[0034] Figure 5 The microstructure of the coarse-grained region of the welded joint in Example 1 of this invention is shown at 400x magnification.

[0035] Figure 6 Example 1 of the present invention: tensile specimen of welded joint.

[0036] Figure 7 Example 1 of the present invention: Impact specimen of the heat-affected zone of the welded joint.

[0037] Figure 8 Example 1 of the present invention: a bending specimen of a welded joint.

[0038] Figure 9Example 1 of the present invention: CTOD sample of welded joint at -35℃. Detailed Implementation

[0039] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0040] In Examples 1-3 below, the chemical composition percentages of Q500qENH weathering bridge steel are as follows: C: 0.06-0.09%, Si: 0.20-0.40%, Mn: 1.40-1.50%, P≤0.015%, S≤0.005%, Nb: 0.04-0.06%, V: 0.04-0.06%, Ti: 0.010-0.020%, Cr: 0.45-0.60%, Ni: 0.30-0.40%, Cu: 0.30-0.09%. 0.40%, rare earth Ce: 0.0004~0.0015%, balance Fe and accompanying inclusions, weather resistance index of steel plate I≥6.5; the production process of the bridge steel is as follows: (1) smelting is carried out using a low carbon and low crack sensitivity composition design route; (2) steel billets are continuously cast using electromagnetic stirring and light pressure process; (3) TMCP technology is used for two-stage rolling, and the rolled steel plate is air-cooled to room temperature; (4) tempering process is used, tempering temperature is 550~580℃, holding time is 20-40 minutes, and air-cooled after exiting the furnace.

[0041] The microstructure of Q500qENH weathering bridge steel consists of fine and uniform bainitic ferrite grains + M / A islands + dispersed precipitates, with a yield strength R... el ≥500MPa, tensile strength Rm≥630MPa, elongation after fracture A≥18%, low-temperature impact energy KV2≥120J for standard specimen at -40℃.

[0042] In Examples 1 to 3 below, the welding wire used for submerged arc welding is a solid welding wire, the welding wire grade is OK Autrod 13.40, the diameter is 4mm, and the flux is OK Flux 10.62.

[0043] The submerged arc welding butt joint bevel diagrams used in Examples 1-3 below are shown below. Figure 1 As shown, the microstructure and properties of the welded joint are described in [reference needed]. Figures 2-9 .

[0044] Example 1

[0045] A submerged arc welding method for improving the performance of welded joints of Q500qENH weathering bridge steel, the specific steps of which are as follows:

[0046] S1 Beveling: When two boards with a thickness of 16+16mm are joined together, a V-shaped symmetrical beveling is made on the double-jointed substrate with a beveling angle of 60° and a blunt edge of 2.0mm.

[0047] S2 pretreatment: Use sandpaper to grind the V-shaped symmetrical bevel and the steel plate within 25-30mm on both sides, and then clean with acetone to remove rust and impurities.

[0048] S3 welding: Submerged arc welding is used, with multiple layers and multiple passes of continuous welding until the weld is filled. The welding current is 500A, the welding voltage is 32V, the welding speed is 40cm / min, the welding heat input is 25kJ / cm, and the interpass temperature is controlled below 120℃.

[0049] Using the welding method of the present invention, the microstructure of the submerged arc welded joint is granular bainite + acicular ferrite + proeutectoid ferrite, and the microstructure of the heat-affected zone is granular bainite; the tensile, impact, bending, hardness, and CTOD fracture toughness characteristic values ​​of the welded joint are shown in Tables 1 to 3.

[0050] Example 2:

[0051] A submerged arc welding method for improving the performance of welded joints of Q500qENH weathering bridge steel, the specific steps of which are as follows:

[0052] S1 Beveling: When two boards with a thickness of 32+32mm are joined together, a V-shaped symmetrical beveling is made on the double-jointed substrate. The beveling angle is 60° and the blunt edge is 2.0mm.

[0053] S2 pretreatment: Use sandpaper to grind the V-shaped symmetrical bevel and the steel plate within 25-30mm on both sides, and then clean with acetone to remove rust and impurities.

[0054] S3 welding: Submerged arc welding is used, with multiple layers and multiple passes of continuous welding until the weld is filled. The welding current is 500A, the welding voltage is 32V, the welding speed is 40cm / min, the welding heat input is 23kJ / cm, and the interpass temperature is controlled below 120℃.

[0055] Using the welding method of the present invention, the microstructure of the submerged arc welded joint is granular bainite + acicular ferrite + proeutectoid ferrite, and the microstructure of the heat-affected zone is granular bainite; the tensile, impact, bending, hardness, and CTOD fracture toughness characteristic values ​​of the welded joint are shown in Tables 1 to 3.

[0056] Example 3:

[0057] A submerged arc welding method for improving the performance of welded joints of Q500qENH weathering bridge steel, the specific steps of which are as follows:

[0058] S1 Beveling: When two boards with a thickness of 40+40mm are joined together, a V-shaped symmetrical beveling is made on the double-jointed substrate with a beveling angle of 60° and a blunt edge of 2.0mm.

[0059] S2 pretreatment: Grind the V-shaped symmetrical bevel and the steel plate within 25-30mm on both sides with sandpaper, and clean with acetone to remove rust and impurities to ensure the quality of the welded joint;

[0060] S3 welding: Submerged arc welding is used, with multiple layers and multiple passes of continuous welding until the weld is filled. The welding current is 500A, the welding voltage is 32V, the welding speed is 40cm / min, the welding heat input is 24kJ / cm, and the interpass temperature is controlled below 120℃.

[0061] Using the welding method of the present invention, the microstructure of the submerged arc welded joint is granular bainite + acicular ferrite + proeutectoid ferrite, and the microstructure of the heat-affected zone is granular bainite; the tensile, impact, bending, hardness, and CTOD fracture toughness characteristic values ​​of the welded joint are shown in Tables 1 to 3.

[0062] Table 1: Tensile, Impact, and Bending Properties of Welded Joints

[0063]

[0064] Table 2: Vickers hardness (HV10) of welded joints

[0065]

[0066] Table 3: CTOD toughness characteristic values ​​of welded joints (-35℃)

[0067] 1 20.00 40.02 / 0.267 / 2 19.98 40.00 0.224 3 19.98 40.00 / 0.205 / Technical Requirements ≥0.13

[0068] As shown in Tables 1-3 above, the tensile strength of the welded joint produced by the welding method of this invention is much greater than 630 MPa (Rm≥645 MPa), and the fracture occurs in the base material region. The impact energy of the weld zone, fusion zone, and heat-affected zone of the welded joint is much greater than 54 J, meeting the requirements of bridge design specifications. Specifically, the low-temperature impact energy KV2 of the standard specimen at -40℃ for the weld zone of the welded joint is ≥75 J, KV2 of the standard specimen at -40℃ for the fusion line is ≥110 J, and KV2 of the standard specimen at -40℃ for the heat-affected zone is ≥95 J. The welded joint remains intact without cracks after bending in both directions, demonstrating good bending performance. The hardness (HV10) of different locations of the welded joint is distributed between 183 and 241 (<250), which is much lower than 350, indicating a low tendency for crack initiation in the welded joint. The CTOD toughness characteristic value of the welded joint at -35℃ is above 0.20. While Chinese standards have not yet specified a minimum CTOD value for bridge steel, the minimum CTOD values ​​specified by DNV-OS-C401-2014 (DNV GL) and API RP 2Z-2005 (API RP 2Z-2005) are 0.15mm and 0.13mm respectively, indicating that the welded joint exhibits good resistance to low-temperature fracture. In conclusion, this invention fully meets the actual service conditions requirements of the Q500qENH bridge in high-altitude and cold regions (such as the Sichuan-Tibet Railway), and has strong guiding significance for welding applications in large-span, heavy-load bridge engineering.

[0069] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A submerged arc welding method for improving the performance of welded joints of Q500qENH weathering bridge steel, wherein the chemical composition percentage of the Q500qENH weathering bridge steel is: C: 0.06-0.09%, Si: 0.20-0.40%, Mn: 1.40-1.50%, P≤0.015%, S≤0.005%, Nb: 0.04-0.06%, V: 0.04-0.06%, Ti: 0.010-0.020%, Cr: 0.45-0.60%, Ni: 0.30-0.40%, Cu: 0.30-0.40%, rare earth Ce: 0.0004-0.0015%, with the balance being Fe and associated inclusions; The submerged arc welding method includes the following operations: Step 1, beveling: The base material has a V-shaped symmetrical bevel with a bevel angle of 60° and a blunt edge of 2.0 mm. The base material is Q500qENH weathering bridge steel with a weathering index I ≥ 6.5, and the assembly is a 10-50 mm thick butt joint. The microstructure of the Q500qENH weathering bridge steel is fine and uniform bainitic ferrite + M / A islands + fine precipitates, with a yield strength Rel ≥ 500 MPa, tensile strength Rm ≥ 630 MPa, elongation after fracture A ≥ 18%, and low-temperature impact energy KV2 ≥ 120 J for a standard sample at -40℃. The Q500qENH weathering bridge steel mentioned above is produced according to the following manufacturing process: (1) Smelting is carried out using a low-carbon and low-crack-sensitivity composition design route; (2) Steel billets are continuously cast using electromagnetic stirring and light pressure reduction processes; (3) The TMCP technology is used for two-stage rolling, and the rolled steel plate is air-cooled to room temperature; (4) The tempering process is adopted, the tempering temperature is 550-580℃, the holding time is 20-40 minutes, and the furnace is air-cooled after being taken out of the furnace; Step 2, Preprocessing: Grind and clean the V-shaped symmetrical bevel and the steel plate within 25-30mm on both sides, and then clean with acetone to remove rust and oil. Step 3, Welding: Submerged arc welding is used, with multiple layers and multiple passes of continuous welding until the weld is filled. No preheating is required before welding and no heat treatment is required after welding. The welding current is 500±25A, the welding voltage is 32±2V, the welding speed is 40±2 cm / min, the welding heat input is 25±2kJ / cm, and the interpass temperature is controlled below 120℃. In step 3, the welding wire used for submerged arc welding is a solid welding wire, with the wire grade OK Autrod 13.40, a diameter of 4mm, and the flux is OK Flux 10.62 with a weather resistance index I≥6.5; The weld joint obtained by the submerged arc welding method has a low-temperature impact energy (KV2) of ≥75J for the weld zone at -40℃, ≥110J for the fusion line at -40℃, and ≥95J for the heat-affected zone at -40℃. The weld joint has a tensile strength (Rm) ≥645MPa, good bending performance at D=3a 180°, a corrosion resistance index (I) ≥6.5, good low-temperature fracture toughness, a Vickers hardness (HV10) <250, and a CTOD fracture toughness characteristic value above 0.2 at -35℃. The weld microstructure consists of granular bainite + acicular ferrite + proeutectoid ferrite, and the heat-affected zone microstructure consists of granular bainite.

2. In the submerged arc welding method according to claim 1, step 2 involves polishing with sandpaper.

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