Welding method of q690s high-strength steel for pressure conduit of hydropower station

Abstract

The present application relates to the technical field of steel material welding, and particularly relates to a welding method of Q690S high-strength steel for a hydropower station pressure pipeline. The present application comprehensively covers the welding joint form and thickness specification of the hydropower station pressure pipeline manufacturing and installation, solves the application problems of poor weldability of Q690S high-strength steel, low welding efficiency, difficult guarantee of welding joint performance, and easy generation of delayed cracks after welding, and the technical scheme is simple, has strong applicability, and the implementation effect meets the design technical conditions of large and super-large hydropower station pressure pipelines, and can be practically used for the welding manufacturing and welding installation in field environment of Q690S high-strength hydropower pressure pipeline.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel material welding, in particular to a welding method of Q690S high-strength steel for a pressure pipeline of a hydropower station. BACKGROUND

[0002] Hydropower is a renewable energy and a main force of clean energy. In order to meet the increasing demand for clean energy, hydropower stations develop towards high water head and large installed capacity. The pressure pipeline of a hydropower station is a core metal structure, with a diameter of several meters to tens of meters, and long-term bearing impact load of several hundred to thousands of meters drop. With the increase of water head and installed capacity of the hydropower station, the design material of the pressure pipeline is upgraded from Q355 strength level to Q690 level, and the low-temperature impact toughness requirement is upgraded from 0℃, KV2≥47J to-40℃, KV2≥47J. The proportion of use of ≥50mm thick steel plate is increased. The Q690 level thick plate and the high-strength steel have a large amount of Cr, Ni and Mo elements, and have a large tendency of welding quenching. Delayed cold cracks are prone to occur after welding. The welding material and the heat-affected zone are sensitive to welding heat input. In order to ensure the toughness of the welded joint, the welding heat input usually cannot exceed 30kJ / cm. However, in the field welding construction environment, some welding beads reach 40-50kJ / cm, which seriously affects the safe operation of the hydropower station. In addition, due to the large diameter of the hydropower pressure pipeline and the restriction of the field welding environment, the preheating temperature before welding cannot be higher than 100℃, and post-welding long-term dehydrogenation heat treatment cannot be carried out, which further increases the risk of occurrence of welding delayed cold cracks. SUMMARY

[0003] Therefore, the present application provides a welding method of Q690S high-strength steel for a pressure pipeline of a hydropower station. The welding method has the advantages of low preheating, post-heat treatment free and adaptation to large welding heat input, can adapt to the welding of Q690S high-strength thick plate and thick plate, the welded joint will not have cold cracks, has good low-temperature impact toughness and excellent joint performance.

[0004] In order to achieve the above-mentioned application purpose, the present application provides the following technical scheme:

[0005] The present application provides a welding method of Q690S high-strength steel for a pressure pipeline of a hydropower station, comprising the following steps: preheating or not preheating the Q690S high-strength steel, and then welding.

[0006] The cold crack sensitivity index Pcm of the Q690S high-strength steel is less than or equal to 0.22%.

[0007] The welding comprises at least one of pipe welding, pipe butt welding and welding of a pipe body and a stiffening ring.

[0008] When welding or pipe butt ring welding is made, whether preheating is determined according to the thickness of the Q690S high-strength steel:

[0009] If the thickness of the Q690S high-strength steel is ≤32mm, the Q690S high-strength steel is not preheated;

[0010] If the thickness of the Q690S high-strength steel is >32mm and ≤80mm, the Q690S high-strength steel is preheated before welding, and the preheating temperature is (H1+20)~100℃, wherein H1 is the thickness of the Q690S high-strength steel, mm;

[0011] When pipe body and stiffening ring welding is made, whether preheating is determined according to the ambient temperature of welding and the thickness of the pipe body:

[0012] If the ambient temperature of welding is ≥10℃ or the thickness of the pipe body is ≤32mm, the stiffening ring and the pipe body with the material of Q690S high-strength steel are not preheated;

[0013] If the ambient temperature of welding is <10℃ and the thickness of the pipe body is >32mm and ≤80mm, the stiffening ring and the pipe body are preheated; the preheating temperature is (H2+20)~100℃, wherein H2 is the thickness of the pipe body.

[0014] Preferably, when pipe welding is made, the welding method adopted is submerged arc welding; the conditions of the submerged arc welding include: opening a non-symmetrical X-shaped groove, leaving a blunt edge, the groove angle is 50~60°, the root 1~2 layers of welding beads and the root outer filling welding beads all adopt a diameter Φ4.0mm of submerged arc welding wire, the root 1~2 layers of welding beads welding current is 400~600A, the welding voltage is 18~30V, the welding speed is 300~500mm / min, and the welding heat input is 20~30kJ / cm; the filling welding bead outside the root welding bead welding current is 450~650A, the welding voltage is 20~32V, the welding speed is 200~500mm / min, and the welding heat input is 20~50kJ / cm; the small-groove side is welded first, then the large-groove side is filled, the interlayer temperature is not lower than the preheating temperature and not higher than 180℃; the diffusion hydrogen [H] of the welding material used in the submerged arc welding is ≤4mL / 100g.

[0015] Preferably, when the pipe butt ring is welded, the welding method used is shielded metal arc welding, and the conditions of the shielded metal arc welding include: opening a non-symmetrical X-shaped groove, leaving a bevel, the groove angle is 50-60°, short arc welding is used, a diameter Φ3.2mm electrode is used for the root 1-3 layers, the welding current is 90-130A for the flat welding position, the welding current is 80-120A for the vertical welding position and the overhead welding position, the welding voltage is 18-26V, the welding speed is 30-80mm / min, and the welding heat input is 10-30kJ / cm; a diameter Φ4.0mm electrode is used for the filling welding outside the root welding, the welding current is 130-180A for the flat welding position, the welding current is 120-160A for the vertical welding position and the overhead welding position, the welding voltage is 20-30V, the welding speed is 40-90mm / min, and the welding heat input is 10-50kJ / cm; the small-groove side welding is performed first, then the large-groove side welding is performed, the interpass temperature is not lower than the preheating temperature and not higher than 180℃.

[0016] Preferably, when the pipe body and the stiffening ring are welded, the welding method used is gas shielded welding, and the conditions of the gas shielded welding include: a T-shaped fillet weld is used without opening a groove, a solid wire is used, the welding current is 200-280A for the flat welding position, the welding voltage is 22-30V, the welding speed is 120-300mm / min, and the welding heat input is 10-25kJ / cm; the welding current is 150-200A for the vertical welding position and the overhead welding position, the welding voltage is 20-26V, the welding speed is 100-250mm / min, and the welding heat input is 12-25kJ / cm; the interpass temperature is not lower than the preheating temperature and not higher than 150℃.

[0017] Preferably, the chemical composition of the deposited metal of the electrode, in terms of mass percentage, is: C: 0.03-0.05%, Si: 0.3-0.6%, Mn: 1.5-1.8%, Ni: 3.0-4.0%, Cr: ≤0.10%, Mo: 0.60-0.80%, Ti: ≤0.03%, Nb: ≤0.02%, V: ≤0.02%, Cu: ≤0.10%, B: ≤0.001%, P: ≤0.015%, S: ≤0.01%, and the balance is Fe and unavoidable impurities; the diffusible hydrogen [H] of the electrode is ≤4mL / 100g.

[0018] Preferably, the chemical composition of the deposited metal of the welding material used in the submerged arc welding is: C: 0.05-0.10%, Si: 0.20-0.50%, Mn: 1.6-1.8%, Ni: 2.0-3.0%, Cr: 0.25-0.40%, Mo: 0.50-0.60%, Ti: ≤0.03%, Nb: ≤0.02%, V: ≤0.02%, Cu: ≤0.20%, B: ≤0.001%, P: ≤0.012%, S: ≤0.006%, and the balance is Fe and inevitable impurities.

[0019] Preferably, the chemical composition of the deposited metal of the solid wire is: C: 0.06-0.10%, Si: 0.50-0.80%, Mn: 1.6-1.7%, Ni: 1.3-1.5%, Cr: 0.2-0.40%, Mo: 0.45-0.55%, Ti: ≤0.03%, Nb: ≤0.02%, V: ≤0.02%, Cu: ≤0.10%, B: ≤0.001%, P: ≤0.012%, S: ≤0.01%, and the balance is Fe and inevitable impurities.

[0020] Preferably, the electrode comprises a coating and a core; the coating comprises, by mass percentage: marble: 35-45%, 97 fluorite: 10-20%, electrolytic manganese: 3-6%, 45 ferrosilicon: 7-12%, 55 ferromolybdenum: 2-5%, Ni60: 9-12%, barium carbonate: 2-6%, iron powder: 1-4%, cerium oxide: 0-1.5%, sodium carboxymethyl cellulose: 0-1.0%, zircon: 0-1.5%, and nickel-magnesium alloy: 0-1.5%; the core is H08C; the mass percentage of the coating in the electrode is 29-32%.

[0021] Preferably, the welding material used in the submerged arc welding comprises a flux and a welding wire; the flux comprises, by mass percentage: marble: 4-7%, lithium carbonate: 1-3%, magnesite: 30-40%, 95 fluorite: 25-35%, 83 bauxite: 20-30%, manganese ore powder: 0.5-2%, rutile: 0.5-2%, and silicon-calcium alloy: 1-4%.

[0022] Preferably, the environment temperature of the welding is >0℃, and the relative humidity is <90%.

[0023] This invention addresses the specific composition range and technical requirements of Q690S high-strength steel for water and electricity pressure pipelines, solving the welding technology problems of Q690S. Specifically, it includes the following aspects: (1) Under the premise of controlling the Pcm of Q690S high-strength steel, low preheating welding is achieved and the preheating temperature of steel plates of different thicknesses is determined to meet the requirements of field welding construction and avoid the occurrence of welding cold cracks; (2) By reasonably selecting and matching the welding heat input and interpass temperature, the welding heat-affected zone (2mm outside the fusion line) is guaranteed to be -40℃ and KV2≥47J; (3) According to the joint form and environmental characteristics of pipe welding, pipe butt ring welding, and pipe body and stiffening ring welding, the appropriate bevel form, welding method and welding sequence are determined; (4) For different joint forms, by controlling the composition of the welding materials and diffusing hydrogen used, post-weld dehydrogenation heat treatment is eliminated, and the weld metal is -40℃ and KV2≥47J is achieved under a heat input of ≤50kJ / cm for the butt joint. This invention comprehensively covers the welding joint types and thickness specifications for the manufacturing and installation of pressure pipelines in hydropower stations. It solves the application problems of poor weldability of Q690S high-strength steel, low welding efficiency, difficulty in ensuring the performance of welded joints, and easy occurrence of delayed cracks after welding. The technical solution is simple, highly applicable, and the implementation effect meets the design technical conditions of pressure pipelines in large and super-large hydropower stations. It can be practically used for the welding manufacturing of Q690S high-strength hydropower pressure pipelines and welding installation in field environments. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the welding bevel in Example 1;

[0025] Figure 2 This is a schematic diagram of the welding passes in Example 1;

[0026] Figure 3 This is a schematic diagram of the welding bevel in Example 3;

[0027] Figure 4 This is a schematic diagram of the welding passes in Example 3;

[0028] Figure 5 These are schematic diagrams of the welding bevels in Examples 4 and 5;

[0029] Figure 6 This is a schematic diagram of the welding passes in Example 4;

[0030] Figure 7 This is a schematic diagram of the welding passes in Example 5;

[0031] Figure 8 This is a schematic diagram of the welding passes in Example 6. Detailed Implementation

[0032] The application provides a welding method of Q690S high-strength steel for a pressure conduit of a hydropower station, which comprises the following steps: preheating or not preheating the Q690S high-strength steel, and then welding.

[0033] In the application, the cold crack sensitivity index Pcm of the Q690S high-strength steel is less than or equal to 0.22%. The cold crack sensitivity index of the Q690S high-strength steel is controlled in the above range, so that the low preheating welding requirement can be met, and the cold crack can be avoided in the case of preheating at a temperature less than or equal to 100 DEG C. In the application, the cold crack sensitivity index Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B(%) is used. In the formula, each element represents the mass percentage of each element.

[0034] In the application, the component range of the Q690S high-strength steel is preferably consistent with GB / T31946-2015 "Steel Plate for Pressure Steel Pipe of Hydropower Station". Specifically, the chemical components of the Q690S high-strength steel are as follows: C: less than or equal to 0.15%, Si: less than or equal to 0.50%, Mn: less than or equal to 2.0%, Ni: 0.20-2.0%, Cr: less than or equal to 0.80%, Mo: less than or equal to 0.60%, Ti: less than or equal to 0.05%, Nb: less than or equal to 0.12%, V: less than or equal to 0.08%, Cu: less than or equal to 0.30%, B: less than or equal to 0.003%, P: less than or equal to 0.018%, S: less than or equal to 0.008%, Al: greater than or equal to 0.015%, and the balance is Fe and inevitable impurities. However, in actual control, in order to meet the requirements of the steel plate for adapting to large heat input welding (adapting to 50 kJ / cm) and considering the economy, the main elements are preferably C: 0.05-0.1%, more preferably 0.07-0.09%, Mn: 1.4-1.6%, more preferably 1.4-1.5%, Ni: 0.4-0.6%, more preferably 0.4-0.5%, Cr: 0.15-0.4%, more preferably 0.2-0.35%, and Mo: 0.25-0.40%, more preferably 0.25-0.30%.

[0035] In the application, the welding comprises at least one of pipe manufacturing welding, pipe butt joint girth welding and pipe body and stiffening ring welding.

[0036] When the pipe manufacturing welding or the pipe butt joint girth welding is performed, whether preheating is performed is determined according to the thickness of the Q690S high-strength steel.

[0037] If the thickness of the Q690S high-strength steel is less than or equal to 32 mm, the Q690S high-strength steel is not preheated.

[0038] If the thickness of the Q690S high-strength steel is > 32 mm and ≤ 80 mm, the Q690S high-strength steel is preheated before welding, and the preheating temperature is (H1+20)~100℃, wherein H1 is the thickness of the Q690S high-strength steel, mm. For example, when the thickness of the Q690S high-strength steel is 40 mm, the preheating temperature is 60~100℃; when the thickness of the Q690S high-strength steel is 50 mm, the preheating temperature is 70~100℃; when the thickness of the Q690S high-strength steel is 60 mm, the preheating temperature is 80~100℃; when the thickness of the Q690S high-strength steel is 70 mm, the preheating temperature is 90~100℃; and when the thickness of the Q690S high-strength steel is 100 mm, the preheating temperature is 100℃.

[0039] When the pipe body and the stiffening ring are welded, whether preheating is needed is determined according to the ambient temperature of welding and the thickness of the pipe body:

[0040] If the ambient temperature of welding is ≥ 10℃ or the thickness of the pipe body is ≤ 32 mm, the stiffening ring and the pipe body made of Q690S high-strength steel are not preheated.

[0041] If the ambient temperature of welding is < 10℃ and the thickness of the pipe body is > 32 mm and ≤ 80 mm, the stiffening ring and the pipe body are preheated; the preheating temperature is (H2+20)~100℃, wherein H2 is the thickness of the pipe body, mm.

[0042] In the application, the material of the stiffening ring is preferably the same as that of the pipe body; and the thickness of the stiffening ring is preferably ≤ 25 mm.

[0043] The application preheats Q690S steel plates of different thickness specifications at different temperatures before welding, cooperates with Pcm, takes into account the requirements of plate production and quenching and tempering on hardenability, and can avoid the occurrence of welding cold cracks.

[0044] The pipe welding is first described below.

[0045] In the present application, when the pipe is welded, the welding method adopted is submerged arc welding; the conditions of the submerged arc welding include: opening a non-symmetrical X-shaped groove, leaving a root face, the groove angle is 50-60°, the root 1-2 layers of welding beads and the filling welding beads outside the root both adopt a submerged arc welding wire with a diameter of Φ4.0 mm, the welding current of the root 1-2 layers of welding beads is 400-600 A, the welding voltage is 18-30 V, the welding speed is 300-500 mm / min, and the welding heat input is 20-30 kJ / cm; the welding current of the filling welding beads outside the root is 450-650 A, the welding voltage is 20-32 V, the welding speed is 200-500 mm / min, and the welding heat input is 20-50 kJ / cm; the small-groove side is welded first and then the large-groove side is filled, the interpass temperature is not lower than the preheating temperature and not higher than 180℃; the diffusion hydrogen [H] of the welding material used in the submerged arc welding is ≤4 mL / 100 g.

[0046] In specific embodiments, the root face is preferably left 2-4 mm. The purpose of leaving the root face in the present application is to prevent the occurrence of welding-through defects when the root welding bead is welded. In specific embodiments, the groove angle can be 50°, 55° or 60°; the welding current of the root 1-2 layers of welding beads can be 400 A, 450 A, 500 A, 550 A or 600 A, the welding voltage can be 18 V, 20 V, 24 V, 26 V, 28 V or 30 V, the welding speed can be 300 mm / min, 350 mm / min, 400 mm / min, 450 mm / min or 500 mm / min, and the welding heat input can be 20 kJ / cm, 23 kJ / cm, 25 kJ / cm, 27 kJ / cm or 30 kJ / cm; the welding current of the filling welding beads outside the root welding bead can be 450 A, 500 A, 550 A, 600 A or 650 A, the welding voltage can be 20 V, 24 V, 26 V, 28 V, 30 V or 32 V, the welding speed can be 200 mm / min, 250 mm / min, 300 mm / min, 350 mm / min, 400 mm / min, 450 mm / min or 500 mm / min, and the welding heat input can be 20 kJ / cm, 25 kJ / cm, 30 kJ / cm, 35 kJ / cm, 40 kJ / cm, 45 kJ / cm or 50 kJ / cm.

[0047] In the present application, the groove angle is selected to be 50-60°, which is easier to remove slag; the welding current, the welding voltage, the welding speed and the welding heat input are controlled within the above ranges, which can guarantee the welding forming and the low-temperature toughness of the welded joint. The interpass temperature has a relatively significant influence on the impact energy of the heat-affected zone, and the present application controls the interpass temperature to be not lower than the preheating temperature and not higher than 180℃, which ensures that the KV2 of the heat-affected zone is ≥47 J under a heat input of 50 kJ / cm.

[0048] In order to facilitate the root operation, the present application preferably firstly carries out the outer weld welding, and then carries out the inner weld welding. In the present application, the submerged arc welding inner weld root is preferably located at 2 / 3 of the plate thickness. In the submerged arc welding, the present application preferably firstly carries out the carbon arc air gouging after the small groove side welding is completed, and then carries out the large groove side welding after the formed carburized layer is polished and removed, until the welding is completed.

[0049] The pipe welding bead is straight seam welding, flat welding position, and the submerged arc automatic welding is high in efficiency. According to the pipe welding characteristics, the outer weld adopts the gantry submerged arc welding mechanism welding, and the inner weld adopts the submerged arc welding track trolley welding. Since the gantry welding mechanism is high-altitude operation, in order to reduce the high-altitude operation amount, the present application selects the asymmetric X type groove form, and the root position is located at 2 / 3 of the inner weld side plate surface, so that the welding efficiency can be improved.

[0050] In the present application, the chemical composition of the deposited metal of the welding material used in the submerged arc welding preferably comprises, in mass percentage: C: 0.05-0.10%, Si: 0.20-0.50%, Mn: 1.6-1.8%, Ni: 2.0-3.0%, Cr: 0.25-0.40%, Mo: 0.50-0.60%, Ti: ≤0.03%, Nb: ≤0.02%, V: ≤0.02%, Cu: ≤0.20%, B: ≤0.001%, P: ≤0.012%, S: ≤0.006%, and the balance is Fe and inevitable impurities; the diffusion hydrogen [H] of the welding material is ≤4 mL / 100g.

[0051] In the present application, the welding material preferably comprises a flux and a welding wire; the welding wire preferably comprises C: 0.07-0.10%, Si: 0.20-0.35%, Mn: 1.6-1.85%, Ni: 2.0-3.0%, Cr: 0.25-0.40%, Mo: 0.50-0.60%, Ti: 0.01-0.02%, Nb: ≤0.01%, V: ≤0.01%, Cu: ≤0.20%, B: ≤0.001%, P: ≤0.01%, S: ≤0.005%, and the balance is Fe and inevitable impurities; the diameter of the welding wire is preferably 4.0 mm. The flux preferably comprises, in mass percentage: marble 4-7%, lithium carbonate 1-3%, magnesia 30-40%, 95 fluorite 25-35%, 83 bauxite 20-30%, manganese ore powder 0.5-2%, rutile 0.5-2%, and silicon calcium alloy 1-4%.

[0052] In the present application, the marble is preferably 95 marble, the particle size of the marble is preferably less than 40 mesh, in specific embodiments, the chemical composition and particle size composition of the marble are shown in Table 1 and Table 2 respectively; the particle size of the lithium carbonate is preferably less than 60 mesh, in specific embodiments, the chemical composition and particle size composition of the lithium carbonate are shown in Table 3 and Table 4 respectively; the particle size of the magnesite is preferably less than 80 mesh, in specific embodiments, the chemical composition and particle size composition of the magnesite are shown in Table 5 and Table 6 respectively; the particle size of the 95 fluorite is preferably less than 40 mesh, in specific embodiments, the chemical composition and particle size composition of the 95 fluorite are shown in Table 7 and Table 8 respectively; the particle size of the 83 bauxite is preferably less than 80 mesh, in specific embodiments, the chemical composition and particle size composition of the 83 bauxite are shown in Table 9 and Table 10 respectively; the particle size of the manganese ore powder is preferably less than 80 mesh, in specific embodiments, the chemical composition and particle size composition of the manganese ore powder are shown in Table 11 and Table 12 respectively; the particle size of the rutile is preferably less than 70 mesh, in specific embodiments, the chemical composition and particle size composition of the rutile are shown in Table 13 and Table 14 respectively; the particle size of the calcium-silicon alloy is preferably less than 70 mesh, in specific embodiments, the chemical composition and particle size composition of the calcium-silicon alloy are shown in Table 15 and Table 16 respectively.

[0053] Note: In the following tables, +40 represents the proportion of oversize on a 40 mesh screen; -200 represents the proportion of undersize on a 200 mesh screen, and so on.

[0054] Table 1 Chemical composition of marble in the flux (wt%)

[0055]

[0056] Table 2 Particle size composition of marble in the flux

[0057]

[0058] Table 3 Chemical composition of lithium carbonate (wt%)

[0059]

[0060] Table 4 Particle size composition of lithium carbonate

[0061]

[0062] Table 5 Chemical composition of magnesite (wt%)

[0063]

[0064] Table 6 Particle size composition of magnesite

[0065]

[0066] Table 7 Chemical composition of 95 fluorite (wt%)

[0067]

[0068] Table 8 Particle size composition of 95 fluorite (wt%)

[0069]

[0070] Table 9 Chemical composition of 83 bauxite (wt%)

[0071]

[0072] Table 10 Particle size composition of 83 bauxite

[0073]

[0074] Table 11 Chemical composition of manganese ore powder (wt%)

[0075]

[0076] Table 12 Particle size composition of manganese ore powder

[0077]

[0078] Table 13 Chemical composition of rutile

[0079]

[0080] Table 14 Particle size composition of rutile

[0081]

[0082] Table 15 Chemical composition of silicon calcium alloy

[0083]

[0084] Table 16 Particle size composition of silicon calcium alloy

[0085]

[0086] In the present application, the marble, magnesite, fluorite and bauxite are slag forming agents, which are used to form a molten slag with suitable viscosity and spreadability to cover the molten pool, thereby protecting the weld metal. The fluorite mainly reduces the diffusible hydrogen in the weld. An increase in the content of fluorite reduces the diffusible hydrogen but also reduces the arc stability. To solve this problem, the addition of appropriate amount of lithium carbonate with low ionization can improve the arc stability. In addition, rutile is added to improve the viscosity and fluidity of the molten slag. In addition, the manganese ore powder deoxidizes and compensates for the ablation of manganese elements in the cladding metal. The silicon calcium alloy deoxidizes and desulfurizes, thereby purifying the weld and improving the toughness of the weld metal.

[0087] In the present application, the flux is preferably prepared by a method well known in the art. Specifically, the components are mixed in the above proportions, and then granulated with water glass corresponding to 15-30% of the total mass of the components. After low-temperature drying, the final sintering is performed at 800-900°C. In the present application, the particle size of the flux is preferably 10-60 mesh.

[0088] In the present application, the basic principle for selecting the flux is to match the strength and -40°C Charpy impact energy with the base material, and to satisfy the post-welding hydrogen heat treatment exemption. To ensure the -40°C Charpy impact energy under high heat input, the weld structure is selected to match the flux with low-carbon martensite and lower bainite structure as the main structure. To achieve the structure control, the weld material composition adopts a high-Ni, high-Mo, low-C, and low-Cr component system, effectively avoiding the occurrence of grain boundary ferrite and upper bainite structures which are not conducive to toughness under high heat input. To achieve high purity of the weld metal, a high-alkalinity, low-hydrogen slag system is used to reduce the toughness reduction caused by large inclusion size or impurity element segregation, and to reduce the diffusible hydrogen content, thereby reducing the occurrence of delayed cold cracking, and ensuring that the process performance and use performance of the weld material meet the requirements.

[0089] Before the submerged arc welding, the used flux is preferably baked in the present application. The baking temperature is preferably 300-400°C, and the time is preferably 0.5-2 hours. In specific embodiments, the baking temperature can be 300°C, 330°C, 350°C, 380°C, or 400°C, and the time can be 0.5 hours, 1 hour, 1.5 hours, or 2 hours. The purpose of baking in the present application is to reduce the diffusible hydrogen of the cladding metal.

[0090] The pipe butt circumferential welding is described below.

[0091] In the present application, when the pipe butt circumferential welding is performed, the welding method used is shielded metal arc welding.

[0092] The conditions of the stick arc welding include: opening a non-symmetrical X-shaped groove, leaving a root face, preferably leaving a 2-4mm root face; the groove angle is 50-60°, and in specific embodiments, it can be 50°, 55° or 60°; short arc welding is adopted, the root 1-3 layers adopt a Φ3.2mm electrode, the welding current is 90-130A in the flat welding position, and in specific embodiments, it can be 90A, 100A, 110A, 120A or 130A; the welding current is 80-120A in the vertical welding position, and in specific embodiments, it can be 80A, 90A, 100A, 110A or 120A; the welding voltage is 18-26V, and in specific embodiments, it can be 18V, 20V, 22V, 24V or 26V; the welding speed is 30-80mm / min, and in specific embodiments, it can be 30mm / min, 40mm / min, 50mm / min, 60mm / min, 70mm / min or 80mm / min; the welding heat input is 10-30kJ / cm, and in specific embodiments, it can be 10kJ / cm, 15kJ / cm, 20kJ / cm, 25kJ / cm or 30kJ / cm; the root pass outside the root adopts a Φ4.0mm electrode, the welding current is 130-180A in the flat welding position, and in specific embodiments, it can be 130A, 140A, 150A, 160A, 170A or 180A; the welding current is 120-160A in the vertical welding position, and in specific embodiments, it can be 120A, 130A, 140A, 150A or 160A; the welding voltage is 20-30V, and in specific embodiments, it can be 20V, 22V, 24V, 26V, 28V or 30V; the welding speed is 40-90mm / min, and in specific embodiments, it can be 40mm / min, 50mm / min, 60mm / min, 70mm / min, 80mm / min or 90mm / min; the welding heat input is 10-50kJ / cm, and in specific embodiments, it can be 10kJ / cm, 20kJ / cm, 30kJ / cm, 40kJ / cm or 50kJ / cm.

[0093] The small groove side welding is first completed, and then the large groove side welding is performed until it is filled; the interlayer temperature is not lower than the preheating temperature and not higher than 180℃; preferably, after the small groove side welding is completed, carbon arc gouging is first performed, the formed carburized layer is polished and removed after gouging, and then the large groove side welding is performed until it is filled.

[0094] The pipe-to-pipe butt welding is usually welded in the field environment in the rock mass, and the pipe diameter is usually several meters to tens of meters, so the electrode arc welding with flexible operation is selected; since the distance between the steel pipe and the rock mass is less than 1 meter, in order to facilitate manual operation, the filling amount of the outer weld should be small, so the asymmetric X-shaped groove form is selected, and the root part is located at 2 / 3 of the inner weld side steel plate surface. In order to reduce the welding filling amount and improve the welding efficiency, the groove angle is selected to be 50-60°; in order to facilitate the cleaning operation, the outer weld is welded first, and then the inner weld is welded.

[0095] Since the welding operation is manual operation, the process execution of the welder cannot be monitored in real time, the welding rod with specific components is selected to ensure the toughness of the weld under the limit process (50 kJ / cm) and to realize the post-welding hydrogen heat treatment without producing delayed cold cracks.

[0096] In the present application, the chemical composition of the deposited metal of the welding rod is: C: 0.03-0.05%, Si: 0.3-0.6%, Mn: 1.5-1.8%, Ni: 3.0-4.0%, Cr: ≤0.10%, Mo: 0.60-0.80%, Ti: ≤0.03%, Nb: ≤0.02%, V: ≤0.02%, Cu: ≤0.10%, B: ≤0.001%, P: ≤0.015%, S: ≤0.01%, and the balance is Fe and unavoidable impurities, in terms of mass percentage; the diffusible hydrogen [H] of the welding rod is ≤4 mL / 100g. In specific embodiments, the content of C can be 0.03%, 0.04% or 0.05%, the content of Si can be 0.3%, 0.4%, 0.5% or 0.6%, the content of Mn can be 1.5%, 1.6%, 1.7% or 1.8%, the content of Ni can be 3.0%, 3.2%, 3.4%, 3.6%, 3.8 or 4.0%, and the content of Mo can be 0.6%, 0.7% or 0.8%.

[0097] In the present application, the welding rod preferably includes a coating and a welding core; the coating includes marble: 35-45%, 97 fluorite: 10-20%, electrolytic manganese: 3-6%, 45 ferrosilicon: 7-12%, 55 ferromolybdenum: 2-5%, Ni60: 9-12%, barium carbonate: 2-6%, iron powder: 1-4%, cerium oxide: 0-1.5%, sodium carboxymethyl cellulose: 0-1.0%, zircon: 0-1.5%, and nickel-magnesium alloy: 0-1.5%, in terms of mass percentage; the welding core is preferably H08C (S: ≤0.005%, P ≤0.008); the mass percentage of the coating in the welding rod is preferably 29-32%, and in specific embodiments, it can be 29%, 30%, 31% or 32%.

[0098] In the present application, the marble is preferably 95 marble (i.e. mass content of calcium carbonate > 95%), which is preferably composed of 60 mesh marble and 40 mesh marble at a mass ratio of 1:1, in specific embodiments, the chemical composition of the marble is shown in Table 17, and the particle size composition is shown in Table 18; the particle size of the 97 fluorite is preferably 60 mesh, in specific embodiments, the chemical composition of the 97 fluorite is shown in Table 19, and the particle size composition is shown in Table 20; the particle size of the electrolytic manganese is preferably less than 40 mesh, in specific embodiments, the chemical composition of the electrolytic manganese is shown in Table 21, and the particle size composition is shown in Table 22; the particle size of the 45 ferrosilicon is preferably less than 40 mesh, in specific embodiments, the chemical composition of the 45 ferrosilicon is shown in Table 23, and the particle size composition is shown in Table 24; the particle size of the 55 molybdenum iron is preferably less than 60 mesh, in specific embodiments, the chemical composition of the 55 molybdenum iron is shown in Table 25, and the particle size composition is shown in Table 26; in specific embodiments, the chemical composition of the Ni60 is shown in Table 27, and the particle size composition is shown in Table 28; the particle size of the barium carbonate is preferably less than 100 mesh, in specific embodiments, the chemical composition of the barium carbonate is shown in Table 29, and the particle size composition is shown in Table 30; in the present application, the particle size of the iron powder is preferably less than 40 mesh, in specific embodiments, the chemical composition of the iron powder is shown in Table 31, and the physical parameters are shown in Table 32; the particle size of the cerium oxide is preferably less than 80 mesh, in specific embodiments, the chemical composition of the cerium oxide is shown in Table 33, and the particle size composition is shown in Table 34; in specific embodiments, the chemical composition of the zircon is shown in Table 35, and the particle size composition is shown in Table 36; in specific embodiments, the chemical composition of the nickel-magnesium alloy is shown in Table 37, and the particle size composition is shown in Table 38.

[0099] Table 17 Chemical composition of marble in coating (wt%)

[0100]

[0101] Table 18 Particle size composition of marble in coating

[0102]

[0103] Table 19 Chemical composition of 97 fluorite (wt%)

[0104]

[0105] Table 20 Particle size composition of 97 fluorite

[0106]

[0107] Table 21 Chemical composition of electrolytic manganese (wt%)

[0108]

[0109] Table 22 Particle size composition of electrolytic manganese

[0110]

[0111] Table 23 Chemical composition of 45 ferrosilicon (wt%)

[0112]

[0113] Table 24 Particle size composition of 45 ferrosilicon

[0114]

[0115] Table 25 Chemical composition of 55 ferromolybdenum (wt%)

[0116]

[0117] Table 26 Particle size composition of 55 ferromolybdenum

[0118]

[0119] Table 27 Chemical composition of Ni60 (wt%)

[0120]

[0121] Table 28 Particle size composition of Ni60

[0122]

[0123] Table 29 Chemical composition of barium carbonate (wt%)

[0124]

[0125] Table 30 Particle size composition of barium carbonate

[0126]

[0127] Table 31 Chemical composition of iron powder (wt%)

[0128]

[0129] Table 32 Physical parameters of iron powder

[0130]

[0131] Table 33 Chemical composition of cerium oxide (wt%)

[0132]

[0133] Table 34 Particle size composition of cerium oxide

[0134]

[0135] Table 35 Chemical composition of zircon (wt%)

[0136]

[0137] Table 36 Particle size composition of zircon

[0138]

[0139] Table 37 Chemical composition of nickel-magnesium alloy (wt%)

[0140]

[0141] Table 38 Particle size composition of nickel-magnesium alloy

[0142]

[0143] In the present application, all elements in the deposited metal of the welding rod basically play a strengthening role, and Si and Mn also play a deoxidizing role. The overall welding rod component system is designed to obtain a low-carbon martensite structure with high toughness (medium-high carbon martensite has poor toughness), and for this purpose, the carbon content is controlled at 0.03-0.05%, and the traditional welding material is 0.06-0.1%; in order to make up for the reduction of strength caused by the reduction of C content, the Mo content is increased from 0.5% in the traditional to 0.6-0.8%, and it is traditionally believed that Mo is not conducive to low-temperature toughness, but through the research of the present application, it is found that appropriate increase does not reduce the toughness; the Ni content is controlled at 3-4% in order to reduce the phase transition temperature of the weld metal, so as to avoid the appearance of high-temperature transition structure which is not conducive to low-temperature toughness under 50kJ / cm large heat input, including grain boundary ferrite and granular bainite (the traditional same grade welding material has Ni content of 2-3%).

[0144] The present application adopts a welding rod system with high Ni, high Mo, low C, low Cr and high purity, which effectively avoids the appearance of grain boundary ferrite and upper bainite structure which is not conducive to toughness under large heat input, reduces the toughness reduction caused by impurity element segregation, adopts an ultra-low hydrogen welding material slag system, reduces the occurrence of delayed cold cracking, so as to ensure that the process performance and use performance of the welding rod meet the requirements.

[0145] The present application does not have special requirements for the preparation method of the welding rod, and can be prepared by using the methods well known in the art, specifically, the flux is mixed according to the above components, 15-30% water glass of the mass of the flux is added and mixed, then the flux is coated on the surface of the H08C welding core by using an oil press, and after baking at 300-400℃, the welding rod manufacturing is completed.

[0146] Before the electrode arc welding, the electrode used in the present application is preferably baked first, the baking temperature is preferably 300-400℃, and the baking time is 0.5-2 hours. In specific embodiments, the baking temperature can be 300℃, 330℃, 350℃, 380℃ or 400℃, and the baking time can be 0.5 hour, 1 hour, 1.5 hours or 2 hours. The purpose of baking in the present application is to reduce the diffusion hydrogen of the cladding metal.

[0147] The welding of the pipe body and the stiffening ring is described below.

[0148] In the present application, when the pipe body and the stiffening ring are welded, the welding method used is gas shielded welding. The shielding gas used in the gas shielded welding is 80% Ar + 20% CO2 by volume percentage.

[0149] The conditions of the gas shielded welding include: T-type fillet weld without beveling, solid wire is used, the welding current is 200-280A in flat position, which can be 200A, 220A, 240A, 260A or 280A in specific embodiments; the welding voltage is 22-30V, which can be 22V, 24V, 26V, 28V or 30V in specific embodiments; the welding speed is 120-300mm / min, which can be 120mm / min, 150mm / min, 200mm / min, 250mm / min or 300mm / min in specific embodiments; the welding heat input is 10-25kJ / cm, which can be 10kJ / cm, 12kJ / cm, 14kJ / cm, 16kJ / cm, 18kJ / cm, 20kJ / cm, 23kJ / cm or 25kJ / cm in specific embodiments; the welding current is 150-200A in vertical and overhead positions, which can be 150A, 160A, 170A, 180A, 190A or 200A in specific embodiments; the welding voltage is 20-26V, which can be 20V, 22V, 24V or 26V in specific embodiments; the welding speed is 100-250mm / min, which can be 100mm / min, 150mm / min, 200mm / min or 250mm / min in specific embodiments; the welding heat input is 12-25kJ / cm, which can be 12kJ / cm, 15kJ / cm, 20kJ / cm or 25kJ / cm in specific embodiments; the interpass temperature is not lower than the preheating temperature and not higher than 150℃.

[0150] In the present application, when the ambient temperature of the welding is ≥10℃, the stiffening ring and the pipe body are not preheated.

[0151] The connection between the stiffening ring and the pipe body is designed as a non-beveled T-type fillet weld, the stiffening ring is welded in the pipe factory, the solid gas shield welding is adopted, the welding efficiency is high, the operation is flexible, and the diffusible hydrogen content can generally reach ≤3 mL / 100g. The thickness of the stiffening ring plate is mostly less than 25 mm, which can greatly reduce the probability of occurrence of welding cold cracks. According to the provisions of GB4675.2-84 "Weldability Test Butt Joint (CTS) Welding Crack Test Method", CTS tests are carried out on the stiffening ring plate with a thickness of 10 mm, 20 mm and 25 mm, and the base plate with a thickness of 32 mm, 60 mm and 80 mm, respectively, to simulate the possibility of cold cracks in the fillet weld at an ambient temperature of 10℃. The results show that in the range of 10-25 mm of the stiffening ring plate and 32-80 mm of the base plate, no cracks are found in the test weld before welding, so the stiffening ring and the pipe body can be welded without preheating when the ambient temperature is ≥10℃. In addition, according to the different size requirements of the fillet weld, the process parameters can be adjusted to obtain a workpiece that meets the welding quality.

[0152] In the present application, the solid wire has a chemical composition of the deposited metal in mass percentage: C: 0.06-0.10%, Si: 0.50-0.80%, Mn: 1.6-1.7%, Ni: 1.3-1.5%, Cr: 0.2-0.40%, Mo: 0.45-0.55%, Ti: ≤0.03%, Nb: ≤0.02%, V: ≤0.02%, Cu: ≤0.10%, B: ≤0.001%, P: ≤0.012%, S: ≤0.01%, and the balance being Fe and unavoidable impurities.

[0153] In the present application, the solid wire can be a commercially available product or can be prepared by a method well known in the art. In the present application, the above-mentioned solid wire composition meets the national standard GB / T8110 ER80-G and the American standard AWS A5.28ER110S-G, and the required product can be THQ80-1 of Tianjin Daqiao Welding Material Group Co., Ltd., JQ•MG80-G of Tianjin Jinqiao Welding Material Group Co., Ltd., and CHW-80CF of Sichuan Dawan Welding Material Co., Ltd.

[0154] In the present application, the diameter of the solid wire is preferably 1.2 mm.

[0155] In the present application, the environmental temperature for welding is preferably >0℃ and the relative humidity is preferably <90%, regardless of the welding method.

[0156] The application is aimed at different joint forms, uses different welding methods, welding process parameters and welding materials, more comprehensively covers the welding joint forms and thickness specifications of the manufacturing and installation of the penstock of the hydropower station, and solves the application problems of poor weldability of the Q690S high-strength steel, low welding efficiency, difficult guarantee of the performance of the welded joint, and easy to produce delayed cracks after welding. In the implementation process of the application, the performance of the welded joint meets the technical requirements, low welding preheating can be realized, post-welding hydrogen heat treatment is avoided, and 50 kJ / cm large heat input welding is adapted, which has the characteristics of high efficiency, safe and reliable service, strong practicability, easy to use and the like. Therefore, the application has important role in promoting the application of Q690S in the penstock of the hydropower station and promoting the design upgrade of the hydropower station, and can be popularized in the fields of marine engineering, military industry and the like.

[0157] The welding method of the Q690S high-strength steel plate for the penstock of the hydropower station provided by the application will be described in detail below in combination with the examples, but they cannot be understood as the limitation of the protection scope of the application.

[0158] The chemical composition of the Q690S high-strength steel plate for the penstock of the hydropower station involved in the following examples 1-8 and comparative examples 1-2 is shown in Table 39. The preparation method of the Q690S steel plate involved is well known in the art, specifically, a converter is used for smelting, in order to further improve the purity of the molten steel, the molten steel after smelting is refined in a LF furnace and vacuum treated in a VOD furnace, and the refined molten steel is processed to the required specification size through continuous casting and rolling process. In order to meet the mechanical properties of the steel plate, the steel plate after continuous casting and rolling is subjected to quenching and tempering treatment, and the mechanical properties of the Q690s steel plate after the quenching and tempering treatment are shown in Table 40.

[0159] Table 39 Chemical composition of steel of examples 1-8 and comparative examples 1-2 (wt%)

[0160]

[0161] Table 40 Mechanical properties of steel plate of examples 1-8 and comparative examples 1-2

[0162]

[0163] Note: In Table 40, the Charpy impact energy test is carried out three times in parallel, so there are three values.

[0164] According to the conventional joint forms of the penstock of the hydropower station, such as butt joint and T-type joint, the application arranges steel plates of different thickness, welding materials and process parameter combinations for welding, which are the embodiments of the application, and the specific welding conditions are as follows:

[0165] The equipment used in the following examples and comparative examples is DC-1000 submerged arc welding machine, ZX7-500 stick electrode arc welding machine or 350GL5 gas shielded welding machine, and the welding all adopts direct current reverse connection.

[0166] Example 1

[0167] 32mm+32mm thick Q690S steel plate submerged arc welding butt welding, welding steel plate is 2 block 600x200x32mm Q690S steel plate, welding groove and welding pass schematic diagram as shown in Figure 1 and Figure 2 ;

[0168] The asymmetric X-shaped groove form is selected, the root part is 2 / 3 away from the inner welding side steel plate surface, leaving 2mm root face, the groove angle is selected as 60°, no preheating before welding, the flux is baked at 350℃ for 2 hours before use, the welding environment is 20℃, the relative humidity is 50%, the welding sequence is to weld the small groove side first, then back carbon arc gouging, after cleaning, use the grinder to polish and remove the carburized layer, then weld the large groove side;

[0169] The chemical composition of the submerged arc welding material used is: C: 0.07, Si: 0.30, Mn: 1.73, Ni: 2.5, Cr: 0.28, Mo: 0.55, Ti: 0.01, Nb: 0.005, V: 0.004, Cu: 0.04, B: 0.0003, P: 0.01, S: 0.005, the balance is Fe and unavoidable impurities; the diffusion hydrogen [H] of the submerged arc welding material is 3.2mL / 100g;

[0170] The composition of the flux used is: marble 6%, lithium carbonate 2%, magnesia 36%, 95 fluorite 29%, 83 bauxite 24%, manganese ore powder 1%, rutile 0.8%, silicon calcium alloy 1.2%. After mixing the above proportions, add water glass equivalent to 25% of the total mass of the powder, granulate, dry at low temperature, and finally sinter at 880℃ to form, the diameter of the submerged arc welding wire used is Φ4.0mm, the chemical composition of the submerged arc welding wire is C: 0.08, Si: 0.25, Mn: 1.78, Ni: 2.5, Cr: 0.28, Mo: 0.55, Ti: 0.012, Nb: 0.004, V: 0.003, Cu: 0.04, B: 0.0006, P: 0.008, S: 0.003, the balance is Fe and unavoidable impurities.

[0171] Example 2

[0172] Compared with example 1, the difference is that the welding parameters and interpass temperature control are different, and the welding material is the same.

[0173] Example 3

[0174] 60mm+60mm thick Q690S steel plate shielded arc welding butt welding, using vertical welding position, the welding steel plate is 2 block 600x200x60mm Q690S steel plate, the welding groove and welding pass schematic diagram as shown inFigure 3 and Figure 4 as shown in the drawings;

[0175] The asymmetric X-shaped groove form is selected, the root position is 2 / 3 from the inner welding side steel plate surface, 2mm root face is left, the electrode arc welding groove angle is 50°, the preheating is 80℃ according to the plate thickness before welding, the welding sequence is that the small groove side is welded first, the back carbon arc air gouging is performed to clear the root, the grinding is performed to clear the root after the root is cleared, and then the large groove side is welded to fill; the root 1~3 layers adopt the diameter Φ3.2mm electrode, the filling weld outside the root adopts the diameter Φ4.0mm electrode, the electrode is baked at 350℃ for 2 hours before use, and the welding environment is 20℃ and the relative humidity is 50%;

[0176] The percentage of the chemical composition of the cladding metal is: C: 0.04, Si: 0.45, Mn: 1.6, Ni: 3.5, Cr: 0.03, Mo: 0.70, Ti: 0.006, Nb: 0.004, V: 0.005, Cu: 0.03, B: 0.0006, P: ≤0.008, S: ≤0.005, and the balance is Fe and inevitable impurities; the electrode diffusion hydrogen [H]=2.8mL / 100g. The coating ratio of the electrode is 30%, and the composition of the coating is: marble: 42%, 97 fluorite: 17%, electrolytic manganese: 5%, 45 ferrosilicon: 10%, 55 ferromolybdenum: 4%, Ni60: 11%, barium carbonate 5%, iron powder: 3%, cerium oxide 0.5%, sodium carboxymethyl cellulose 0.5%, zircon 1%, nickel-magnesium alloy 1%. The electrode core used by the electrode is H08C (S: ≤0.005%, P≤0.008%). After the coating of the electrode is mixed according to the above components, 22% water glass is added and mixed, and then the coating is coated on the surface of the H08C core by using an oil press, and after baking at 400℃, the electrode manufacturing is completed. The electrode diameter is Φ3.2mm, Φ4.0mm, Φ3.2mm is used for the backing welding, and Φ4.0mm is used for the filling welding.

[0177] Example 4

[0178] The 80mm+80mm thick Q690S steel plate is butt welded by electrode arc welding, the welding position is flat, the welded steel plates are two 600×200×80mm Q690S steel plates, the welding groove and the welding pass schematic diagram are shown in Figure 5 and Figure 6 , and the filling welding heat input is controlled at 30kJ / cm. The electrode is the same as that in example 3.

[0179] Example 5

[0180] The 80mm+80mm thick Q690S steel plate is butt welded by electrode arc welding, the welding position is flat, the welded steel plates are two 600×200×80mm Q690S steel plates, the welding groove and the welding pass schematic diagram are shown in Figure 5and Figure 7 The filler bead heat input is controlled at 50 kJ / cm as shown. The welding rod is the same as in Example 3.

[0181] Example 6

[0182] 20mm+32mm thick Q690S steel plate solid gas shielded welding T type corner welding, the protective gas is 80% Ar+20% CO2, using flat welding position, the steel plate size is 600x200x20mm, 600x200x32mm Q690S steel plate, the welding pass schematic diagram is shown in 8, without opening the groove;

[0183] The solid wire used in Example 6 is a THQ80-1 brand wire produced by Tianjin Daqiao Welding Material Group Co., Ltd., the chemical composition of the wire is: C: 0.07, Si: 0.60, Mn: 1.65, Ni: 1.35, Cr: 0.36, Mo: 0.51, Ti: 0.008, Nb: 0.003, V: 0.004, Cu: 0.05, B: 0.0007, P: 0.008, S: 0.007, the balance is Fe and unavoidable impurities, the wire diameter is Φ1.2mm, and it is a copper-plated wire.

[0184] Example 7

[0185] 20mm+32mm thick Q690S steel plate solid gas shielded welding T type corner welding, the protective gas is 80% Ar+20% CO2, using flat welding position, the steel plate size is 600x200x20mm, 600x200x32mm Q690S steel plate, without opening the groove;

[0186] The solid wire used in Example 7 is a JQ•MG80-G brand wire produced by Sichuan Dawan Welding Material Co., Ltd., the chemical composition of the wire is: C: 0.08, Si: 0.56, Mn: 1.6, Ni: 1.4, Cr: 0.32, Mo: 0.50, Ti: 0.01, Nb: 0.005, V: 0.003, Cu: 0.02, B: 0.0005, P: 0.01, S: 0.006, the balance is Fe and unavoidable impurities, the wire diameter is Φ1.2mm, and it is a copper-plated wire.

[0187] Example 8

[0188] 20mm+32mm thick Q690S steel plate solid gas shielded welding T type corner welding, the protective gas is 80% Ar+20% CO2, using flat welding position, the steel plate size is 600x200x20mm, 600x200x32mm Q690S steel plate, without opening the groove, and preheating at 80℃ before welding;

[0189] The solid welding wire used in Example 8 is a JQ•MG80-G brand welding wire produced by Sichuan Dayang Welding Material Co., Ltd., and the chemical composition of the welding wire is as follows: C: 0.08, Si: 0.56, Mn: 1.6, Ni: 1.4, Cr: 0.32, Mo: 0.50, Ti: 0.01, Nb: 0.005, V: 0.003, Cu: 0.02, B: 0.0005, P: 0.01, S: 0.006, and the balance is Fe and inevitable impurities. The diameter of the welding wire is Φ1.2 mm, and the welding wire is a copper-plated welding wire.

[0190] Comparative Example 1

[0191] The difference from Example 3 is only that the interpass temperature of the filler bead layer is controlled to be 200-250°C, so as to compare the influence of the interpass temperature of the welding process parameter on the performance of the welded joint.

[0192] Comparative Example 2

[0193] The difference from Example 3 is only that the welding rod used is a traditional Q690S grade welding material, so as to compare the influence of the selection of the welding material on the performance of the welded joint under a large heat input of 50 kJ / cm, especially the impact energy at -40°C.

[0194] The welding rod used in Comparative Example 2 is a TENACITO 80 CL brand electric welding rod of OERLIKON brand, and the chemical composition of the cladding metal is as follows: C: 0.059%, Si: 0.42%, Mn: 1.61%, Ni: 2.49%, Cr: 0.34%, Mo: 0.44%, Cu: 0.019%, Nb: 0.003%, and V: 0.01%. The diameter of the welding rod is Φ3.2 mm and Φ4.0 mm, and Φ3.2 mm is used for the backing bead, and Φ4.0 mm is used for the filler bead.

[0195] Comparative Example 3

[0196] The welding rod arc welding butt joint of the 60 mm+60 mm thick Q690S steel plate is carried out in a vertical welding position, and the welded steel plates are two 600×200×60 mm Q690S steel plates. The difference from Example 3 is only that a 60 mm thick Q690S steel plate with Pcm=0.24% is used, and the chemical composition of the steel plate is as follows: C: 0.10%, Si: 0.19%, Mn: 1.04%, Ni: 0.67%, Cr: 0.55%, Mo: 0.33%, Cu: 0.28%, Nb: 0.023%, and V: 0.041%, and the rest is the same as in Example 3.

[0197] For the welding combination of the above different plate thicknesses, joint forms and welding methods, welding is carried out according to the welding technical solution of the present application. The groove form, joint form and welding sequence are as follows: Figures 1-8The welding process parameters are shown in Table 41. Examples 1 and 2 are submerged arc welding, Examples 3 and Comparative Examples 1-3 are vertical welding of shielded arc welding, Examples 4 and 5 are flat welding of shielded arc welding, and Examples 6, 7 and 8 are T-type fillet welding.

[0198] Table 41 Welding process parameters of examples and comparative examples

[0199]

[0200] Referring to “Metallic Materials Tensile Test Part 1: Room Temperature Test Method” GB / T 228.1-2021, “Welded Joints Bending Test Method” GB / T 2653-2008, “Metallic Materials Charpy Pendulum Impact Test Method” GB / T 229-2020, “Pressure Equipment Nondestructive Testing Part 2: Radiographic Testing” NB / T 47013.2-2015 / XG1-2018, the welded joints of each example and comparative example are tested for performance and radiographic testing, and the results are shown in Table 42.

[0201]

[0202] Table 42 Performance test results of welded joints of examples and comparative examples

[0203]

[0204] As can be seen from Tables 41-42, the welded joints obtained from the examples and comparative examples except Comparative Example 3 meet the I-grade weld requirement of ultrasonic testing, and Comparative Example 3 has welding cold cracks after welding at 80°C due to the Pcm exceeding the requirement of ≤0.22% defined in the present application.

[0205] The tensile strength of the welded joints of Examples 1-5 welded according to the welding method of the present application meets the requirement of ≥780MPa, the KV2 of the weld and the heat-affected zone at -40°C is ≥47J, meeting the performance requirement of the base material specified in the national standard (GB / T 31946-2015 “Steel for Water and Pressure Pipe”) and satisfying the design requirement of the pressure pipe of the hydropower station. The results of the radiographic testing of Examples 6 and 7 meet the requirements of the stiffening ring testing, and according to the relevant standards, the stiffening ring does not need to be tested for mechanical properties.

[0206] In Comparative Example 1, the interlayer temperature exceeds the process parameter control range of the present application, resulting in a -40°C impact energy of the welding heat-affected zone of less than 47J.

[0207] In Comparative Example 2, 50kJ / cm high heat input welding is performed using welding materials not within the component range defined in the present application, resulting in a -40°C impact energy of the weld of less than 47J.

[0208] ​Comparative Example 3 appeared welding cold cracks after welding due to Pcm of Q690s exceeding the invention.

[0209] Examples 1-8 involve four specifications of 20, 32, 60, 80 mm in different joint forms and combination modes. According to the engineering practice experience, the relevant tests are representative, and can cover the welding of Q690S high-strength steel with thickness ≤32 mm and 32 mm < thickness ≤80 mm. It can be seen that the welding method proposed in the present application covers the joint form and thickness specification of the welding of the water and electricity pressure pipeline, and the implementation effect conforms to the relevant standards and design regulations, and can be used for the pipe manufacturing and installation welding of the Q690S grade water and electricity pressure pipeline.

[0210] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled persons in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A welding method for Q690S high-strength steel for a pressure conduit of a hydropower station, characterized in that, The method comprises the following steps: Preheating or not preheating the Q690S high-strength steel before welding; The cold crack sensitivity index Pcm of the Q690S high-strength steel is less than or equal to 0.22%; The welding comprises pipe-making welding, pipe butt girth welding and pipe body and stiffening ring welding; When the welding is pipe-making welding or pipe butt girth welding, whether preheating is needed is determined according to the thickness of the Q690S high-strength steel: If the thickness of the Q690S high-strength steel is less than or equal to 32 mm, the Q690S high-strength steel is not preheated; If the thickness of the Q690S high-strength steel is greater than 32 mm and less than or equal to 80 mm, the Q690S high-strength steel is preheated before welding, and the preheating temperature is (H1+20)~100℃, wherein H1 is the thickness of the Q690S high-strength steel, mm; When the welding is pipe body and stiffening ring welding, whether preheating is needed is determined according to the ambient temperature of the welding and the thickness of the pipe body: If the ambient temperature of the welding is greater than or equal to 10℃ or the thickness of the pipe body is less than or equal to 32 mm, the stiffening ring and the pipe body made of the Q690S high-strength steel are not preheated; If the ambient temperature of the welding is less than 10℃ and the thickness of the pipe body is greater than 32 mm and less than or equal to 80 mm, the stiffening ring and the pipe body are preheated; the preheating temperature is (H2+20)~100℃, wherein H2 is the thickness of the pipe body; When the welding is pipe-making welding, the welding method adopted is submerged arc welding; the conditions of the submerged arc welding comprise the following: an asymmetric X-shaped groove is opened, a bevel is left, the groove angle is 50~60°, the root 1~2 layers of welding beads and the root outer filling welding beads all adopt a submerged arc welding wire with a diameter of Φ4.0 mm, the welding current of the root 1~2 layers of welding beads is 400~600A, the welding voltage is 18~30V, the welding speed is 300~500mm / min, and the welding heat input is 20~30kJ / cm; the welding current of the filling welding beads outside the root welding beads is 450~650A, the welding voltage is 20~32V, the welding speed is 200~500mm / min, and the welding heat input is 20~50kJ / cm; the small-groove side is welded first, then the large-groove side is welded, the interlayer temperature is not lower than the preheating temperature and not higher than 180℃; the diffusible hydrogen [H] of the welding material used in the submerged arc welding is less than or equal to 4mL / 100g. When the pipe butt joint ring is welded, the welding method is shielded arc welding, and the welding conditions of the shielded arc welding include the following: an asymmetric X-shaped groove is opened, a bevel is reserved, the groove angle is 50-60 DEG, short arc welding is used, a diameter of the welding rod is 3.2 mm, the welding current is 90-130 A in the flat welding position, the welding current is 80-120 A in the vertical welding position and the overhead welding position, the welding voltage is 18-26 V, the welding speed is 30-80 mm / min, and the welding heat input is 10-30 kJ / cm; a diameter of the welding rod is 4.0 mm, the welding current is 130-180 A in the flat welding position, the welding current is 120-160 A in the vertical welding position and the overhead welding position, the welding voltage is 20-30 V, the welding speed is 40-90 mm / min, and the welding heat input is 10-50 kJ / cm; the small-groove side is welded first, then the large-groove side is welded, the interpass temperature is not lower than the preheating temperature and not higher than 180 DEG C; When the pipe body and the stiffening ring are welded, the welding method is gas shielded welding, and the welding conditions of the gas shielded welding include the following: a T-shaped fillet is not opened, a solid wire is used, the welding current is 200-280 A in the flat welding position, the welding voltage is 22-30 V, the welding speed is 120-300 mm / min, and the welding heat input is 10-25 kJ / cm; the welding current is 150-200 A in the vertical welding position and the overhead welding position, the welding voltage is 20-26 V, the welding speed is 100-250 mm / min, and the welding heat input is 12-25 kJ / cm; the interpass temperature is not lower than the preheating temperature and not higher than 150 DEG C.

2. The welding method according to claim 1, characterized in that, The chemical composition of the deposited metal of the welding rod is as follows in terms of mass percentage: C: 0.03-0.05%, Si: 0.3-0.6%, Mn: 1.5-1.8%, Ni: 3.0-4.0%, Cr: ≤0.10%, Mo: 0.60-0.80%, Ti: ≤0.03%, Nb: ≤0.02%, V: ≤0.02%, Cu: ≤0.10%, B: ≤0.001%, P: ≤0.015%, S: ≤0.01%, and the balance is Fe and inevitable impurities; the diffusible hydrogen [H] of the welding rod is ≤4 mL / 100 g.

3. The welding method of claim 1, wherein, The chemical composition of the deposited metal of the welding material used in the submerged arc welding is as follows in terms of mass percentage: C: 0.05-0.10%, Si: 0.20-0.50%, Mn: 1.6-1.8%, Ni: 2.0-3.0%, Cr: 0.25-0.40%, Mo: 0.50-0.60%, Ti: ≤0.03%, Nb: ≤0.02%, V: ≤0.02%, Cu: ≤0.20%, B: ≤0.001%, P: ≤0.012%, S: ≤0.006%, and the balance is Fe and inevitable impurities.

4. The welding method of claim 1, wherein, The solid welding wire has a deposited metal chemical composition in mass percentage: C: 0.06-0.10%, Si: 0.50-0.80%, Mn: 1.6-1.7%, Ni: 1.3-1.5%, Cr: 0.2-0.40%, Mo: 0.45-0.55%, Ti: ≤0.03%, Nb: ≤0.02%, V: ≤0.02%, Cu: ≤0.10%, B: ≤0.001%, P: ≤0.012%, S: ≤0.01%, and the balance of Fe and inevitable impurities.

5. The welding method of claim 1, wherein, The welding rod comprises a coating and a core; the coating comprises, in mass percentage: marble: 35-45%, 97 fluorite: 10-20%, electrolytic manganese: 3-6%, 45 ferrosilicon: 7-12%, 55 ferromolybdenum: 2-5%, Ni60: 9-12%, barium carbonate: 2-6%, iron powder: 1-4%, cerium oxide: 0-1.5%, sodium carboxymethyl cellulose: 0-1.0%, zircon: 0-1.5%, and nickel-magnesium alloy: 0-1.5%; the core is H08C; the mass percentage of the coating in the welding rod is 29-32%.

6. The welding method of claim 1, wherein, The welding material for the submerged arc welding comprises a flux and a welding wire; the flux comprises, in mass percentage: marble: 4-7%, lithium carbonate: 1-3%, magnesite: 30-40%, 95 fluorite: 25-35%, 83 bauxite: 20-30%, manganese ore powder: 0.5-2%, rutile: 0.5-2%, and silicon-calcium alloy: 1-4%.

7. The welding method according to any one of claims 1 to 6, characterized in that, The welding environment has a temperature >0℃ and a relative humidity <90%.

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