Method for gas-electric vertical welding of quenched and tempered high-strength steel plate for large oil storage tank pressure vessel

Abstract

The application discloses a gas-electric vertical welding method of a quenched and tempered high-strength steel plate for a large oil storage tank pressure container, 1) during refining of the high-strength steel, Ca-Mg-Ce alloy blocks are added after refining; 2) during preparation of a welding test plate, a V-shaped groove is used for a thickness size of 25 mm or less, and an angle is 22.5°-34.5°; a non-symmetrical X-shaped groove is used for more than 25 mm, an outer side of the groove angle is 23°-33°, and an inner side is 48°-69°; 3) the welding test plate is matched and reserved gaps between the matched parts; 4) the opening surface of the V-shaped groove or the outer side of the non-symmetrical X-shaped groove is subjected to gas-electric vertical welding of one side, a side weld is formed, and the other side of the welding test plate is subjected to forced cooling; 5) the other side, i.e. the inner side of the non-symmetrical X-shaped groove, is subjected to gas-electric vertical welding, an inner back weld is formed, and the completed outer side weld is subjected to forced cooling by installing a copper water cooling test block with a notch. The welding joint has excellent low-temperature toughness; when linear energy welding is improved, the joint three areas have higher impact toughness reserves and safety margins.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy, and in particular to a gas-electric vertical welding method for quenched and tempered high-strength steel plates used in large oil storage tanks and pressure vessels, and a high heat input gas-electric vertical welding method for 12MnNiVR quenched and tempered high-strength steel plates used in large oil storage tanks and pressure vessels. Background Technology

[0002] 12MnNiVR steel plates possess wear resistance, heat resistance, and corrosion resistance, making them a commonly used material for large oil storage tanks and pressure vessels. The construction of large storage tanks and spherical tanks places higher demands on the structure, steel plates, and welding technology, including the use of high-efficiency welding with high heat input. Gas-electric vertical welding is one of the commonly used and efficient welding methods for 12MnNiVR steel thick plates to increase welding heat input. In the mid-to-late 1980s, China began to introduce gas-electric vertical welding equipment, which has been successfully applied in the manufacturing of various large oil and natural gas storage tanks.

[0003] However, gas-electric vertical welding is difficult to control in terms of welding quality, and the toughness of the heat-affected zone is relatively low. To improve the microstructure and properties of gas-electric vertical welded joints of 12MnNiVR steel, trace elements such as Ti, Nb, Ca, and Mg are added to the steel. These elements are utilized to precipitate at high temperatures, pinning austenite grains or forming intragranular structures to improve welding performance. The development has progressed from TiN to Ti2O3, and finally to the current method of controlling the spheroidization modification through the composite precipitation of Ca and Mg oxides or sulfides, thus achieving the goal of increasing the welding heat input.

[0004] Currently, the industrial production and application of high heat input welding steel plates in my country are mainly in the fields of crude oil storage tanks and shipbuilding, lacking the production of steel plates with welding heat input energy greater than 100 KJ / cm. The reason for this is that when developing high heat input welding steels, domestic enterprises typically employ the traditional mechanism of TiN particles pinning austenite and nucleating intragranular ferrite particles to avoid coarsening of austenite grains in the weld heat-affected zone. Simultaneously, acicular ferrite forms within the coarse-grained region of the heat-affected zone to improve the impact toughness of the coarse-grained weld region. Using this method, under effective production process control, although the steel plate can withstand heat input energy requirements of around 100 KJ / cm, during the welding thermal cycle, when the temperature reaches 1350℃, more than 50% of the TiN dissolves. When the temperature at the fusion line reaches or exceeds 1400℃, the volume fraction of dissolved TiN can even reach over 80%, significantly weakening the pinning effect. Furthermore, the composite precipitation with TiN as a particle is the key factor in the formation of intragranular ferrite. During welding, the dissolution and secondary precipitation of TiN during cooling further weakens the mechanism of TiN as a precipitate particle of composite particles such as MnS, affecting the formation of intragranular ferrite in the coarse-grained region and leading to fluctuations in welding performance.

[0005] Therefore, it is necessary to develop a new high-energy gas-electric vertical welding method for quenched and tempered high-strength steel plates (12MnNiVR) used in large oil storage tanks and pressure vessels to overcome the above problems. Summary of the Invention

[0006] Objective of the invention: To address the shortcomings and defects of existing technologies, this invention provides a gas-electric vertical welding method for quenched and tempered high-strength steel plates used in large oil storage tank pressure vessels. The welded joint Rm ≥ 540 MPa, joint cold bending d = 3a, 180° pass, weld impact energy -20℃ KV2 ≥ 57 J, fusion line impact energy -20℃ KV2 ≥ 70 J, and heat-affected zone (fusion line + 1 mm).

[0007] -20℃ KV2≥66J; the joint has excellent low-temperature toughness; when welding with increased line energy, the joint has a high impact toughness reserve and safety margin in three zones.

[0008] Technical solution: The present invention provides a gas-electric vertical welding method for quenched and tempered high-strength steel plates used in large oil storage tank pressure vessels, characterized by comprising the following steps:

[0009] 1) Before welding, in order to meet the performance requirements of high heat input gas electric vertical welding of tempered high-strength steel plate 12MnNiVR, Ca-Mg-Ce alloy blocks are added after refining the high-strength steel 12MnNiVR so that the weight percentage of Ca, Mg and Ce in the molten steel is ≤0.0005%.

[0010] 2) When preparing welding test plates, V-grooves are used for thicknesses below 25mm, with an angle of 22.5° to 34.5°; for thicknesses above 25mm, asymmetrical X-grooves are used, with an outer bevel angle of 23° to 33° and an inner bevel angle of 48° to 69°. The outer bevel depth t is set according to the steel plate thickness as t = 1 / 2a + 2mm to 4mm, where a is the steel plate thickness. No blunt edge is left on the bevel.

[0011] 3) Assemble the welding test plates, leaving an assembly gap of 3mm to 6mm;

[0012] 4) Perform gas-electric vertical welding on one side of the V-groove opening or the outer side of the asymmetrical X-groove to form a side weld. Add a copper triangular water-cooled test block to the other side of the welding test plate for forced cooling.

[0013] 5) Perform gas-electric vertical welding on the other side of the asymmetric X-shaped bevel, i.e. the inner side, to form the inner back weld. The completed outer side weld is fitted with a copper water-cooled test block with a notch for forced cooling; complete the gas-electric vertical welding of 12MnNiVR high-strength steel plate for large oil storage tank pressure vessels.

[0014] The thickness of the 12MnNiVR high-strength steel plate used for the large oil storage tank pressure vessel is 20mm to 40mm.

[0015] The chemical composition of the 12MnNiVR high-strength steel plate for large oil storage tank pressure vessels, by weight percentage, is as follows: C: 0.08%–0.11%, Si: 0.20%–0.30%, Mn: 1.37%–1.53%, P: ≤0.015%, S: ≤0.0050%, Ni: 0.20%–0.50%, Mo: 0.10%–0.30%, V: 0.02%–0.06%, Ti: 0.01%–0.025%, Alt: 0.025%–0.035%, with the balance being Fe and unavoidable impurities. During the refining of the 12MnNiVR high-strength steel, Ca-Mg-Ce alloy blocks are added after refining to ensure that the weight percentages of Ca, Mg, and Ce in the molten steel are all ≤0.0005%.

[0016] The 12MnNiVR high-strength steel plate used for the large oil storage tank pressure vessel requires a tempering treatment after hot rolling: the steel plate at room temperature is heated to 900℃~920℃ in the furnace, and the holding time is extended by 15min~30min after the steel billet is thoroughly heated. After being taken out of the furnace, it is immersed in a water tank for quenching. The tempering heat treatment is heated at 620℃~650℃ and the furnace time is 3.3t+30min, where t is the thickness of the steel plate. After the tempering heat treatment, the microstructure is tempered sorbite.

[0017] In step 2), the roughness of the bevel surface of the welding test plate is ≤ Ra20.

[0018] In step 3), after the assembly is completed, the two ends and the middle position of the assembled welding test plate are tack welded by manual arc welding, CO2 gas shielded welding or hydrogen arc welding. The weld length of each tack weld is ≥15mm, the weld height is ≥4mm, and the interval between adjacent tack welds is no more than 300mm.

[0019] In steps 4) and 5), the protective gas is carbon dioxide gas, with a CO2 gas volume percentage ≥ 98% and a gas flow rate controlled at 26 L / min to 28 L / min.

[0020] In steps 4) and 5), the welding current is 360A to 420A, the welding voltage is 36V to 41V, and the welding speed is 5cm / min to 17cm / min.

[0021] In steps 4) and 5), the welding line energy of the gas-electric vertical welding is ≥100KJ / cm; the welding test plates are assembled, leaving a gap for assembly, and the front gas-electric vertical welding is performed to form the front weld. A copper triangular water-cooled test block is installed on the back of the welding test plate for forced cooling; the back gas-electric vertical welding is performed to form the back weld. The completed front weld is then installed with a copper water-cooled test block with a notch for forced cooling.

[0022] Among them, the welded joint Rm≥540MPa, the joint cold bending d=3a, 180° qualified, the weld impact energy -20℃KV2≥57J, the fusion line impact energy -20℃KV2≥70J, and the heat-affected zone -20℃KV2≥66J.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0024] In the refining of high-strength steel 12MnNiVR of this invention, a Ca-Mg-Ce alloy block is added after refining to ensure that the weight percentages of Ca, Mg, and Ce in the molten steel are all ≤0.0005%. This block is used for secondary weak deoxidation and microalloying, in addition to aluminum deoxidation. Utilizing the strong affinity of Ca-Mg-Ce for O and S in steel, it readily forms Ca-Mg-Ce oxides, sulfides, and their composite compounds. These compounds have melting points exceeding 3000℃ and good thermal stability. The resulting finely dispersed Ca-Mg-Ce oxygen-sulfur compound second-phase particles can suppress the coarsening of austenite at high temperatures during high heat input welding, increase the nucleation rate of intragranular ferrite, promote the formation of fine acicular ferrite structures, and improve the impact performance of the coarse-grained zone of the weld, thereby enhancing high heat input welding performance.

[0025] The high-strength 12MnNiVR steel plate used in the large oil storage tank pressure vessel of this invention requires tempering treatment after hot rolling. The measured mechanical properties of the steel plate are ReL≥600MPa, Rm≥670MPa, A≥19%, and KV2 impact energy at -20℃≥270J, exhibiting excellent performance. The welded joint has Rm≥540MPa, and the joint cold bending d=3a, 180° is qualified. The weld impact energy at -20℃KV2≥57J, the fusion line impact energy at -20℃KV2≥70J, and the heat-affected zone (fusion line +1mm) at -20℃KV2≥66J. The joint has excellent low-temperature toughness; when welding with increased heat input, the three zones of the joint have high impact toughness reserves and safety margins. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the welding bevel structure of the present invention. Figure 1 ;

[0027] Figure 2 This is a schematic diagram of the welding bevel structure of the present invention. Figure 2 ;

[0028] Figure 3 This is a particle diagram of the dispersed precipitates of 12MnNiVR in the quenched and tempered high-strength steel plate of the present invention.

[0029] Figure 4 This is a diagram of the dispersed composite precipitated particles of the present invention;

[0030] Figure 5 The microstructure of 12MnNiVR high-strength steel plate according to the present invention. Figure 1 ;

[0031] Figure 6 The microstructure of 12MnNiVR high-strength steel plate according to the present invention. Figure 2 ;

[0032] Figure 7 The microstructure of the asymmetric X-groove weld joint of the present invention Figure 1 ;

[0033] Figure 8 The microstructure of the asymmetric X-groove weld joint of the present invention Figure 2 ;

[0034] Figure 9 This is a microstructure diagram of the cladding metal cladding line and coarse-grained region of the present invention, wherein the coarse-grained region is an intragranular acicular ferrite structure. Detailed Implementation

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0036] This invention discloses a gas-electric vertical welding method for quenched and tempered high-strength steel plate 12MnNiVR used in large oil storage tank pressure vessels. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the same result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0037] For general arc welding, the formula for calculating welding heat input is:

[0038] E=ηUI / V(1)

[0039] In the formula, E is the heat input, U is the voltage, I is the current, V is the welding speed, and η is the thermal efficiency.

[0040] Gas-fired vertical welding, as a welding method, requires high current density, equal wire feeding, and high arc voltage during the welding process. The melting rate is proportional to the rate at which metal is filled into the weld bevel and should be equal to the equal wire feeding rate. Therefore, through derivation, the formula for calculating the welding heat input of gas-fired vertical welding can also be expressed as:

[0041] E = kiUS(2)

[0042] In the formula, ki is the welding wire melting coefficient, and S is the bevel cross-sectional area.

[0043] The chemical composition of the 12MnNiVR high-strength steel plate for large oil storage tank pressure vessels of the present invention, by weight percentage, is as follows: C: 0.08%~0.11%, Si: 0.20%~0.30%, Mn: 1.37%~1.53%, P: ≤0.015%, S: ≤0.0050%, Ni: 0.20%~0.50%, Mo: 0.10%~0.30%, V: 0.02%~0.06%, Ti: 0.01%~0.025%, Alt: 0.025%~0.035%, with the balance being Fe and unavoidable impurities. During the refining of the high-strength steel 12MnNiVR, Ca-Mg-Ce alloy blocks are added after refining to ensure that the weight percentages of Ca, Mg, and Ce in the molten steel are all ≤0.0005%. High-strength 12MnNiVR steel plates for large oil storage tank pressure vessels require quenching and tempering treatment after hot rolling: the steel plates at room temperature are reheated in a furnace to 900℃~920℃, and after the billet is thoroughly heated, the holding time is extended by 15min~30min. After being removed from the furnace, they are immersed in a water tank for quenching. The tempering heat treatment is carried out at a heating temperature of 620℃~650℃, with a furnace time of 3.3t+30min, where t is the thickness of the steel plate. After quenching and tempering heat treatment, a tempered sorbite microstructure is obtained. The properties of the steel plate are shown in Table 1.

[0044] Table 1 Mechanical properties of 12MnNiVR steel plate

[0045]

[0046] High-energy heat input gas-electric vertical welding (EGW) was developed for typical dimensions and thicknesses of quenched and tempered high-strength steel plate 12MnNiVR: 21.5mm, 32mm, and 40mm. The test plate dimensions were 800mm (rolling direction) × 200mm (width) × 21.5 / 32 / 40mm (thickness). EGW was performed using Φ1.6mm diameter DW-S60G welding wire from Kobe Steel, Japan, with CO2 as the shielding gas. The chemical composition and mechanical properties of the deposited metal are shown in Tables 2 and 3.

[0047] Table 2 Chemical composition of deposited metal (Wt%)

[0048]

[0049] Table 3 Mechanical properties of deposited metal

[0050]

[0051] The gas-electric vertical welding (EGW) conditions are shown in Table 4. After the welding method described above, the welded joint was subjected to manual ultrasonic testing and mechanical property testing. The ultrasonic testing results were Class I qualified. The tensile test performance of the 21.5mm / 32mm / 40mm thick 12MnNiVR steel plate EGW welded joint is shown in Table 5. The impact test performance of various parts of the 21.5mm / 32mm / 40mm thick 12MnNiVR steel plate EGW welded joint is shown in Table 6. The side bending test of the welded joint was conducted with a bending diameter D = 4a (thickness) and a bending angle of 180°. The bending test results showed that the test specimen was intact and there were no cracks or defects.

[0052] Table 4 Welding conditions for test plates

[0053]

[0054] Table 5 Tensile test results of welded joints

[0055]

[0056] Table 6 Impact test results of welded joints

[0057]

[0058]

[0059] As can be seen, the welded joint obtained from the 11.5mm / 32mm / 40mm thick 12MnNiVR steel plate in Example 2 not only possesses excellent comprehensive mechanical properties but also exhibits no welding defects. The welding process is stable and rapid, meeting the welding construction requirements for metal structures with high-performance welded joints. The above examples are merely illustrative of the technical concept of this invention and should not be construed as limiting the scope of protection of this invention. Any modifications made to the technical solution based on the technical concept proposed in this invention fall within the scope of protection of this invention.

Claims

1. A gas-electric vertical welding method for quenched and tempered high-strength steel plates used in large oil storage tank pressure vessels, characterized in that: Includes the following steps: 1) Before welding, when refining high-strength steel 12MnNiVR, add Ca-Mg-Ce alloy blocks after refining to ensure that the weight percentage of Ca, Mg, and Ce in the molten steel is ≤0.0005%; 2) When preparing the welding test plate, the thickness is 40mm and an asymmetrical X-shaped bevel is used. The bevel angle is 23°~33° on the outside and 48°~69° on the inside. The bevel depth of the outer side is set according to the thickness of the steel plate, t=1 / 2a+2mm~4mm, where a is the thickness of the steel plate. No blunt edge is left on the bevel. 3) Assemble the welding test plates, leaving an assembly gap of 3mm to 6mm; 4) Perform gas-electric vertical welding on one side of the asymmetrical X-shaped groove to form a side weld. Add a copper triangular water-cooled test block to the other side of the welding test plate for forced cooling. 5) Perform gas-electric vertical welding on the other side, i.e. the inner side, of the asymmetric X-shaped bevel to form the inner back weld. The completed outer side weld is fitted with a copper water-cooled test block with a notch for forced cooling; complete the gas-electric vertical welding of 12MnNiVR high-strength steel plate for large oil storage tank pressure vessels. The chemical composition of the quenched and tempered high-strength steel plate 12MnNiVR used in this large oil storage tank pressure vessel, by weight percentage, is as follows: C: 0.08%–0.11%, Si: 0.20%–0.30%, Mn: 1.37%–1.53%, P: ≤0.015%, S: ≤0.0050%, Ni: 0.20%–0.50%, Mo: 0.10%–0.30%, V: 0.02%–0.06%, Ti: 0.01%–0.025%, Alt: 0.025%–0.035%, with the balance being Fe and unavoidable impurities. During the refining of the high-strength steel 12MnNiVR, Ca-Mg-Ce alloy blocks are added after refining to ensure that the weight percentages of Ca, Mg, and Ce in the molten steel are all ≤0.0005%. The 12MnNiVR high-strength steel plate used for the large oil storage tank pressure vessel requires quenching and tempering treatment after hot rolling: the steel plate at room temperature is heated in the furnace to 900℃~920℃, and the holding time is extended by 15min~30min after the billet is thoroughly heated. After being taken out of the furnace, it is immersed in a water tank for quenching. The tempering heat treatment is heated at 620℃~650℃ and the furnace time is 3.3t+30min, where t is the thickness of the steel plate. After quenching and tempering heat treatment, the microstructure is tempered sorbite. In steps 4) and 5), the protective gas is carbon dioxide, with a CO2 gas volume percentage ≥ 98% and a gas flow rate controlled at 26 L / min to 28 L / min. The welded joint has an Rm ≥ 540MPa, a cold bending d = 3a, and a 180° pass rate. The weld impact energy at -20℃ is KV2 ≥ 57J, the fusion line impact energy at -20℃ is KV2 ≥ 70J, and the heat-affected zone impact energy at -20℃ is KV2 ≥ 66J. When the test plate thickness is 40mm, the welding parameters are as follows: For the first pass (positive), EGW welding method is used, with DWS-60G welding wire of diameter Φ1.6mm as filler metal, current of 400±10A, voltage of 40±2V, welding speed of 8cm / min, and welding heat input of 120kJ / cm; For the first pass (reverse), EGW welding method is used, with DWS-60G welding wire of diameter Φ1.6mm as filler metal, current of 390±10A, voltage of 39±2V, welding speed of 14cm / min, and welding heat input of 65kJ / cm.

2. The gas-electric vertical welding method for quenched and tempered high-strength steel plates for large oil storage tank pressure vessels according to claim 1, characterized in that: In step 2), the roughness of the bevel surface of the welding test plate is ≤ Ra20.

3. The gas-electric vertical welding method for quenched and tempered high-strength steel plates for large oil storage tank pressure vessels according to claim 1, characterized in that: After the assembly is completed in step 3), the two ends and the middle position of the assembled welding test plate are tack welded using manual arc welding, CO2 gas shielded welding or hydrogen arc welding. The weld length of each tack weld is ≥15mm, the weld height is ≥4mm, and the interval between adjacent tack welds does not exceed 300mm.

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