Submerged arc automatic welding process of high-strength steel S980CF for water and electricity in high-altitude, low-air-pressure and alpine regions

Abstract

The invention discloses an automatic submerged arc welding process of hydroelectric high-strength steel S980CF in high-altitude, low-air-pressure and alpine regions, and belongs to the technical field of high-strength steel welding. Comprising the following steps that welding is conducted in the high-altitude, low-air-pressure and alpine region environment, and high-strength steel S980CF for water and electricity is machined; selecting a welding wire according to an equal-strength matching principle, and preheating the combined test plate; carrying out backing welding on the preheated test panel, carrying out filling welding on the test panel subjected to backing welding, and carrying out covering slow cooling on the test panel by using an asbestos board after welding; and covering the welded test plate with an asbestos plate for slow cooling, controlling the cooling speed to be 3-15 DEG C / s, performing UT flaw detection after 24 hours, and performing mechanical property detection after the UT flaw detection meets the first-grade standard in NB / T47013. According to the method, welding is conducted through the large-diameter welding wire and large heat input, the requirement for construction in the hydropower steel plateau area can be met, the welding speed is high, a good welding joint can be obtained, and the welding work efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of high-strength steel welding, and specifically relates to a submerged arc automatic welding process for high-strength steel S980CF for hydropower in high-altitude, low-pressure and cold areas. Background Art

[0002] As my country's hydropower resources development gradually advances to the west, it has become a trend to build high-head, large-capacity hydropower stations in high-altitude, low-pressure, and cold regions. Water diversion penstocks, steel bifurcated pipes, and volutes are very important components of hydropower stations, and they are responsible for the normal production and safe operation of power stations. Therefore, in terms of technical and economic aspects such as structural safety, design optimization, and engineering construction, higher requirements are put forward for steel materials used in water diversion penstocks (including steel bifurcated pipes) and turbine volutes.

[0003] Due to the low temperature, long low temperature period, large temperature difference between day and night, and low oxygen content in the air under high altitude conditions, the welding process becomes complicated and the welding quality is difficult to guarantee. In order to meet the demand for reduction, the steel plates used for the pressure pipes of hydropower stations need to have the characteristics of large thickness, high strength, high toughness and easy welding. In this environment, the use of 600MPa and 800MPa steel to manufacture water diversion pressure steel pipes, steel bifurcated pipes, and volutes requires a lot of construction work, resulting in high costs and long production cycles, and also has a great impact on the safety of hydropower stations. Therefore, solving the welding of thick plate high-strength steel plates for hydropower is an important research and development topic.

[0004] At present, there is no development of submerged arc welding technology for high-strength steel for hydropower in high altitude, low pressure and cold regions in the prior art, and no development of submerged arc welding technology for thick plates of high-strength steel for hydropower. In addition, the invention patent with application publication number CN 112453662 A discloses a submerged arc welding process for 1000MPa grade high-strength steel, which can obtain good welded joints under certain conditions, but the welding process uses a thin steel plate thickness (≤38mm), does not specify the external welding environment, and uses a small wire diameter and welding heat input. At the same welding speed, more welding passes are required, and the welding work efficiency is low.

[0005] Therefore, there is an urgent need to design a submerged arc welding process for high-strength steel thick plates that can achieve welding under conditions of high altitude, low air pressure, and cold regions, while meeting welding quality standards and improving welding efficiency. Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the prior art and provide a submerged arc automatic welding process for high-strength steel S980CF for hydropower in high altitude, low air pressure and cold areas. The high-strength steel plates are welded by large-diameter welding wire and large heat input, which can meet the requirements of hydropower steel construction in plateau areas, and has a high welding speed, can obtain good welding joints, and improve welding work efficiency.

[0007] To achieve the above object, the present invention adopts the following technical scheme: a submerged arc automatic welding process of high-strength steel S980CF for hydropower in high altitude, low pressure and cold areas, comprising the following steps:

[0008] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0009] Choose high altitude, low air pressure, and cold regions for welding, where the welding environment temperature is -10℃~5℃ and the air pressure is 0.05~0.07MPa;

[0010] Select high-strength steel S980CF for hydropower and machine it into test plates with a thickness of 30 to 120 mm. Open an X-shaped groove along the long side with a groove angle of 60°. Combine the two test plates without gaps and clean the impurities and oil stains on the groove and nearby areas.

[0011] S2. Select welding wire according to the equal strength matching principle and preheat the assembled test plate:

[0012] The diameter of the welding wire is selected to be 4mm. The assembled test plate is preheated with a remote infrared panel at a temperature of 90℃~100℃. The infrared thermometer is used for continuous measurement. When the predetermined temperature is reached, the heating is stopped.

[0013] S3, base welding process:

[0014] The preheated test plate is subjected to base welding, wherein the welding current is 420-480A, the arc voltage is 33-34V, the welding speed is 70-82cm / min, and the welding heat input is 15-18KJ / cm; after welding, the test plate is covered with an asbestos board for heat preservation and slow cooling, and the cooling speed is controlled at 3-15℃ / s. After base welding, the root is cleaned with an air planer, and after cleaning, the test plate is turned over for symmetrical welding, and the temperature of the test plate is measured with an infrared thermometer to ensure that the interlayer temperature is between 120℃ and 160℃;

[0015] S4, filling welding process:

[0016] Filling welding is performed on the test plate after base welding, wherein the welding current is 550-680A, the arc voltage is 33-35V, the welding speed is 45.7-57.75cm / min, and the welding heat input is 20-40KJ / cm; after each welding, the test plate is covered with asbestos board for heat preservation and slow cooling, and the cooling speed is controlled at 3-15℃ / s to prevent deformation of the test plate. Symmetrical welding is performed alternately on the front and back sides, and the temperature of the test plate is measured with an infrared thermometer to ensure that the interlayer temperature is between 120℃ and 160℃ before welding the next pass;

[0017] S5. After welding, the test plate cover is slowly cooled and the mechanical properties are tested:

[0018] When covering the surface, reduce the voltage, current and welding speed, and complete the covering with a heat input not less than that of the filling weld. Cover the welded test plate after covering with an asbestos board to keep warm and cool slowly. The cooling rate is controlled at 3-15℃ / s. After 24 hours, perform UT flaw detection. After meeting the Level 1 standard in NB / T47013, conduct mechanical property testing.

[0019] In the step S1, the composition of the high-strength steel S980CF includes, by mass percentage, C≤0.12%, Si≤0.30%, 0.70%≤Mn≤1.50%, P≤0.012%, S≤0.005%, Ti≤0.060%, 1.40%≤Ni≤2.20%, Cu≤0.50%, Mo≤0.70%, Vo≤0.060%, 0.02%≤Al, B≤0.004%, and the remainder is Fe and unavoidable impurities; the cold crack sensitivity index Pcm of the high-strength steel S980CF is ≤0.30.

[0020] The calculation formula of the cold crack sensitivity index Pcm is:

[0021] Pcm=(%C)+(%Si) / 30+(%Mn+%Cu+%Cr) / 20+(%Ni) / 60+(%Mo) / 15+(%V) / 10+5(%B)≤0.30.

[0022] In the step S2, the components of the welding wire include, by mass percentage, C≤0.09%, Si≤0.60%, 1.2%≤Mn≤2.0%, P≤0.020%, S≤0.020%, 3.0%≤Ni, 0.60%≤Mo≤0.90%, and the remainder is Fe and unavoidable impurities.

[0023] In step S4, the penetration depth H during welding affects the joint strength, and the penetration depth H is proportional to the welding current, and the proportionality coefficient is related to the wire diameter and the type of current. According to relevant tests, for welding with the same penetration depth, a larger current is required in high altitude, low air pressure, and cold regions than in plain areas. The welding arc voltage affects the weld width of each weld. When the arc voltage is increased, the weld penetration depth is slightly reduced and the weld width is increased. The final welding voltage is selected according to the welding current.

[0024] In the step S5, the post-weld structure includes, by volume percentage, 3-10% acicular ferrite, 70-85% bainite and 5-10% carbide.

[0025] The beneficial effects of the present invention are:

[0026] 1) The present invention develops a submerged arc automatic welding process for high altitude, low air pressure and cold areas, which can meet the requirements for construction in hydropower steel plateau areas and solve the problem that the welding process becomes complicated and the welding quality is difficult to guarantee under high altitude conditions, such as low temperature, long low temperature period, large temperature difference between day and night and low oxygen content in the air.

[0027] 2) The present invention obtains a good welded joint by welding a 60 mm thick high-strength steel plate, selecting corresponding welding materials, and cooperating with the optimal welding process. The weld flaw detection meets the Level 1 standard in NB / T47013.

[0028] 3) The present invention utilizes a large diameter welding wire and a larger heat input, and requires fewer welding passes at the same welding speed, thereby improving welding work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the welding groove structure of the S980CF high-strength steel plate of the present invention;

[0030] Figure 2 This is a metallographic image of the weld at 1 / 4 of the plate thickness detected in Example 1 of the present invention;

[0031] Figure 3 This is a metallographic image of the weld at 1 / 4 of the plate thickness detected in Example 2 of the present invention;

[0032] Figure 4 This is a metallographic image of the weld at 1 / 4 of the plate thickness detected in Example 3 of the present invention;

[0033] Figure 5 This is a metallographic image of the weld at 1 / 4 of the plate thickness detected in Example 4 of the present invention;

[0034] Figure 6 This is a metallographic image of the weld at 1 / 4 of the plate thickness detected in Example 5 of the present invention;

[0035] Figure 7 This is a metallographic image of the weld at 1 / 4 of the plate thickness detected in Example 6 of the present invention;

[0036] Figure 8 This is a metallographic image of the weld at 1 / 4 of the plate thickness detected in Example 7 of the present invention;

[0037] Fig. 9 This is a metallographic image of the weld at 1 / 4 of the plate thickness detected in Example 8 of the present invention;

[0038] Fig.10 This is a metallographic image of the weld at 1 / 4 of the plate thickness detected in Example 9 of the present invention. DETAILED DESCRIPTION

[0039] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments.

[0040] Embodiment 1: The present invention provides a submerged arc automatic welding process for high-strength steel S980CF for hydropower in high altitude, low pressure and cold areas, comprising the following steps:

[0041] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0042] Welding was carried out in a high altitude, low air pressure and cold region environment, where the welding environment temperature was 5°C, the air pressure was 0.06MPa and the humidity was 52%.

[0043] Select high-strength steel S980CF for hydropower and machine it into a test plate with a width × length × thickness = 250mm × 500mm × 60mm, and open an X-shaped groove along the long side with a groove angle of 60°. Figure 1 As shown in the figure, the two test plates are combined without gap, and the impurities and oil stains on the groove and nearby areas are cleaned.

[0044] In terms of mass percentage, the composition of high-strength steel S980CF includes C: 0.12%, Si: 0.09%, Mn: 0.86%, P: 0.008%, S: 0.003%, Ti: 0.01%, Ni: 2.16%, Cu: 0.260%, Mo: 0.55%, V: 0.04%, Al: 0.036%, B: 0.001%, and the remainder is Fe and unavoidable impurities, Pcm = 0.29.

[0045] The mechanical properties of S980CF steel plate are as follows: tensile strength is 9880MPa, yield strength is 895MPa, and elongation is 21%; the impact energy Akv at -60℃ is: 137J, 166.5J, 154J at one quarter, and 126J, 142J, 138J at the core.

[0046] S2. Select welding wire according to the equal strength matching principle and preheat the assembled test plate:

[0047] The welding wire diameter is selected to be 4 mm. The components of the welding wire, in mass percentage, include C: 0.079%, Si: 0.30%, Mn: 1.63%, P: 0.007%, S: 0.003%, Ni: 3.11%, Mo: 0.82%, and the remainder is Fe and inevitable impurities.

[0048] Use a remote infrared plate to preheat the assembled test plate at a temperature of 90°C and use an infrared thermometer to measure continuously. When the predetermined temperature is reached, stop heating and keep warm for a period of time to ensure that the steel plate is heated evenly.

[0049] S3, base welding process:

[0050] The preheated test plate was subjected to base welding, wherein the welding current was 420A, the arc voltage was 33V, the welding speed was 74.3cm / min, and the welding heat input was 15KJ / cm; after base welding, the root was cleaned with an air planer, and after cleaning, the test plate was turned over and symmetrically welded, and the temperature of the test plate was measured with an infrared thermometer to ensure that the interlayer temperature was 130℃±10℃; due to welding in a low temperature environment, the test plate was covered with an asbestos board after welding for insulation and slow cooling, and the cooling rate was controlled at 3℃ / s to avoid cold cracks caused by too fast cooling.

[0051] S4, filling welding process:

[0052] The test plate after the base welding is filled with welding, in which the welding current is 550A, the arc voltage is 35V, the welding speed is 57.75cm / min, and the welding heat input is 20KJ / cm; to prevent the test plate from deformation, symmetrical welding with alternating front and back sides is adopted, and the temperature of the test plate is measured with an infrared thermometer to ensure that the interlayer temperature is at 130℃±10℃ before welding the next pass; due to welding in a low temperature environment, the welded test plate should be covered with asbestos board after each welding to keep it warm and cool slowly, and the cooling rate is controlled at 3℃ / s to avoid cold cracks caused by too fast cooling.

[0053] S5. After the test plate is covered, it is slowly cooled and the mechanical properties are tested:

[0054] When covering, the welding current is 550A, the arc voltage is 35V, the welding speed is 57.75cm / min, and the welding heat input is 20KJ / cm. The welded test plate after covering is covered with asbestos board for insulation and slow cooling. The cooling rate is controlled at 3℃ / s to prevent excessive cooling rate and cold cracks. After 24 hours, UT flaw detection is carried out to meet the Level 1 standard of NB / T47013, and then mechanical properties are tested.

[0055] Analysis of the microstructure and mechanical properties of the metal after welding: The metallographic structure of the weld is 78% bainite + 8% carbide + 4% ferrite. Figure 2 shown.

[0056] The mechanical properties of the welded parts are shown in Table 1:

[0057]

[0058] Embodiment 2: The present invention provides a submerged arc automatic welding process for high-strength steel S980CF for hydropower in high altitude, low pressure and cold areas, comprising the following steps:

[0059] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0060] Welding was carried out in a high altitude, low air pressure and cold region environment, where the welding environment temperature was 5°C, the air pressure was 0.06MPa and the humidity was 64%.

[0061] Select high-strength steel S980CF for hydropower and machine it into a test plate with a width × length × thickness = 250mm × 500mm × 60mm, and open an X-shaped groove along the long side with a groove angle of 60°. Figure 1 As shown, the two test plates are combined without gaps, and impurities and oil stains on the groove and nearby areas are cleaned.

[0062] In terms of mass percentage, the composition of high-strength steel S980CF includes C: 0.12%, Si: 0.09%, Mn: 0.86%, P: 0.008%, S: 0.003%, Ti: 0.01%, Ni: 2.16%, Cu: 0.260%, Mo: 0.55%, V: 0.04%, Al: 0.036%, B: 0.001%, and the remainder is Fe and unavoidable impurities, Pcm = 0.29.

[0063] The mechanical properties of S980CF steel plate are as follows: tensile strength is 9880MPa, yield strength is 895MPa, and elongation is 21%; the impact energy Akv at -60℃ is: 137J, 166.5J, 154J at one quarter, and 126J, 142J, 138J at the core.

[0064] S2. Select welding wire according to the equal strength matching principle and preheat the assembled test plate:

[0065] The welding wire diameter is selected to be 4 mm. The components of the welding wire, in mass percentage, include C: 0.079%, Si: 0.30%, Mn: 1.63%, P: 0.007%, S: 0.003%, Ni: 3.11%, Mo: 0.82%, and the remainder is Fe and inevitable impurities.

[0066] Use a remote infrared plate to preheat the assembled test plate at a temperature of 90°C and use an infrared thermometer to measure continuously. When the predetermined temperature is reached, stop heating and keep warm for a period of time to ensure that the steel plate is heated evenly.

[0067] S3, base welding process:

[0068] The preheated test plate was subjected to base welding, wherein the welding current was 450A, the arc voltage was 34V, the welding speed was 82cm / min, and the welding heat input was 16KJ / cm; after base welding, the root was cleaned with an air planer, and after cleaning, the test plate was turned over and symmetrically welded, and the temperature of the test plate was measured with an infrared thermometer to ensure that the interlayer temperature was 130℃±10℃; due to welding in a low temperature environment, the test plate was covered with an asbestos board after welding for insulation and slow cooling, and the cooling rate was controlled at 8℃ / s to avoid cold cracks caused by too fast cooling.

[0069] S4, filling welding process:

[0070] The test plate after the base welding was filled with welding, in which the welding current was 600A, the arc voltage was 34V, the welding speed was 40.80cm / min, and the welding heat input was 30KJ / cm; to prevent the test plate from deforming, symmetrical welding with alternating front and back sides was adopted, and the temperature of the test plate was measured with an infrared thermometer to ensure that the interlayer temperature was at 130℃±10℃ before welding the next pass; due to welding in a low temperature environment, the test plate was covered with an asbestos board after each welding pass for insulation and slow cooling, and the cooling rate was controlled at 8℃ / s to avoid cold cracks caused by too fast cooling.

[0071] S5. After the cover welding, the test plate is slowly cooled and the mechanical properties are tested:

[0072] When covering, the welding current is 450A, the arc voltage is 33V, the welding speed is 55.69cm / min, and the welding heat input is 16KJ / cm. The welded test plate after covering is slowly cooled to prevent the cooling speed from being too high, which will produce hardened structure, increase internal stress and produce cold cracks. The welded test plate is covered with asbestos board for insulation and slow cooling, and the cooling rate is controlled at 8℃ / s. After 24 hours, UT flaw detection is carried out and mechanical properties are tested after meeting the Level 1 standard of NB / T47013.

[0073] Analysis of the microstructure and mechanical properties of the welded metal: The weld metallographic structure is 81% bainite + 6% carbide + 5% ferrite. Figure 3 shown.

[0074] The mechanical properties of the welded parts are shown in Table 2:

[0075]

[0076] Embodiment 3: The present invention provides a submerged arc automatic welding process for high-strength steel S980CF for hydropower in high altitude, low pressure and cold areas, comprising the following steps:

[0077] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0078] Welding was carried out in a high altitude, low air pressure and cold region environment, where the welding environment temperature was 5°C, the air pressure was 0.06MPa and the humidity was 64%.

[0079] Select high-strength steel S980CF for hydropower and machine it into a test plate with a width × length × thickness = 250mm × 500mm × 60mm, and open an X-shaped groove along the long side with a groove angle of 60°. Figure 1 As shown, the two test plates are combined without gaps, and impurities and oil stains on the groove and nearby areas are cleaned.

[0080] In terms of mass percentage, the composition of high-strength steel S980CF includes C: 0.12%, Si: 0.09%, Mn: 0.86%, P: 0.008%, S: 0.003%, Ti: 0.01%, Ni: 2.16%, Cu: 0.260%, Mo: 0.55%, V: 0.04%, Al: 0.036%, B: 0.001%, and the remainder is Fe and unavoidable impurities, Pcm = 0.29.

[0081] The mechanical properties of S980CF steel plate are as follows: tensile strength is 9880MPa, yield strength is 895MPa, and elongation is 21%; the impact energy Akv at -60℃ is: 137J, 166.5J, 154J at one quarter, and 126J, 142J, 138J at the core.

[0082] S2. Select welding wire according to the equal strength matching principle and preheat the assembled test plate:

[0083] The welding wire diameter is selected to be 4 mm. The components of the welding wire, in mass percentage, include C: 0.079%, Si: 0.30%, Mn: 1.63%, P: 0.007%, S: 0.003%, Ni: 3.11%, Mo: 0.82%, and the remainder is Fe and inevitable impurities.

[0084] Use a remote infrared plate to preheat the assembled test plate at a temperature of 90°C and use an infrared thermometer to measure continuously. When the predetermined temperature is reached, stop heating and keep warm for a period of time to ensure that the steel plate is heated evenly.

[0085] S3, base welding process:

[0086] The preheated test plate is subjected to base welding, wherein the welding current is 480A, the arc voltage is 33V, the welding speed is 70.00cm / min, and the welding heat input is 18KJ / cm; after base welding, the root is cleaned with an air planer, and after cleaning, the test plate is turned over and symmetrical welding is adopted, and the temperature of the test plate is measured with an infrared thermometer to ensure that the interlayer temperature is 130℃±10℃; since welding is carried out in a low temperature environment, the test plate should be covered with an asbestos board after welding for insulation and slow cooling, and the cooling rate is controlled at 15℃ / s to avoid cold cracks caused by too fast cooling, which will affect the strength of the welded joint.

[0087] S4, filling welding process:

[0088] The test plate after the base welding is filled with welding, in which the welding current is 680A, the arc voltage is 33V, the welding speed is 45.70cm / min, and the welding heat input is 40KJ / cm; to prevent the test plate from deformation, symmetrical welding of alternating front and back sides is adopted, and the temperature of the test plate is measured with an infrared thermometer to ensure that the interlayer temperature is at 130℃±10℃ before welding the next pass; due to welding in a low temperature environment, the test plate should be covered with asbestos board after each welding to keep it warm and cool slowly, and the cooling rate is controlled at 15℃ / s to avoid cold cracks caused by too fast cooling, which will affect the strength of the welded joint.

[0089] S5. After the cover welding, the test plate is slowly cooled and the mechanical properties are tested:

[0090] When covering the surface, the welding current is 480A, the arc voltage is 33V, the welding speed is 52.80cm / min, and the welding heat input is 18KJ / cm. The test plate after welding is covered with asbestos board for insulation and slow cooling. The cooling rate is controlled at 15℃ / s to prevent the cooling rate from being too high, resulting in hardened structure, increasing internal stress and causing cold cracks. After 24 hours, UT flaw detection is carried out to meet the Level 1 standard of NB / T47013, and then mechanical properties are tested.

[0091] Analysis of the microstructure and mechanical properties of the welded metal: The weld metallographic structure is 77% bainite + 8% carbide + 4% ferrite. Figure 4 shown.

[0092] The mechanical properties of the welded parts are shown in Table 3:

[0093]

[0094] Embodiment 4 is different from Embodiment 1 in that:

[0095] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0096] Welding was carried out in a high altitude, low air pressure and cold region environment, where the welding environment temperature was -5°C, the air pressure was 0.05MPa and the humidity was 62%.

[0097] Analysis of the microstructure and mechanical properties of the welded metal: The weld metallographic structure is 82% bainite + 7% carbide + 5% ferrite. Figure 5 shown.

[0098] The mechanical properties of the welded parts are shown in Table 4:

[0099]

[0100]

[0101] Embodiment 5 is different from Embodiment 1 in that:

[0102] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0103] Welding was carried out in a high altitude, low air pressure and cold region environment, where the welding environment temperature was -5°C, the air pressure was 0.05MPa and the humidity was 62%.

[0104] Analysis of the microstructure and mechanical properties of the welded metal: The weld metallographic structure is 84% ​​bainite + 6% carbide + 3% ferrite. Figure 6 shown.

[0105] The mechanical properties of the welded parts are shown in Table 5:

[0106]

[0107] Embodiment 6 is different from the comparative document 1 in that:

[0108] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0109] Welding was carried out in a high altitude, low air pressure and cold region environment, where the welding environment temperature was -5°C, the air pressure was 0.05MPa and the humidity was 62%.

[0110] Analysis of the microstructure and mechanical properties of the metal after welding: The metallographic structure of the weld is 73% bainite + 9% carbide + 8% ferrite. Figure 7 shown.

[0111] The mechanical properties of the welded parts are shown in Table 6:

[0112]

[0113] Embodiment 7 is different from the comparative document 1 in that:

[0114] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0115] Welding was carried out in a high altitude, low air pressure and cold region environment, where the welding environment temperature was -10°C, the air pressure was 0.07MPa and the humidity was 75%.

[0116] Analysis of the microstructure and mechanical properties of the welded metal: The weld metallographic structure is 82% bainite + 4% carbide + 5% ferrite. Figure 8 shown.

[0117] The mechanical properties of the welded parts are shown in Table 7:

[0118]

[0119]

[0120] Embodiment 8 is different from the comparative document 1 in that:

[0121] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0122] Welding was carried out in a high altitude, low air pressure and cold region environment, where the welding environment temperature was -10°C, the air pressure was 0.07MPa and the humidity was 75%.

[0123] Analysis of the microstructure and mechanical properties of the welded metal: The weld metallographic structure is 79% bainite + 6% carbide + 5% ferrite. Fig. 9 shown.

[0124] The mechanical properties of the welded parts are shown in Table 8:

[0125]

[0126] Embodiment 9 is different from the comparative document 1 in that:

[0127] S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower:

[0128] Welding was carried out in a high altitude, low air pressure and cold region environment, where the welding environment temperature was -10°C, the air pressure was 0.07MPa and the humidity was 75%.

[0129] Analysis of the microstructure and mechanical properties of the welded metal: The weld metallographic structure is 81% bainite + 7% carbide + 7% ferrite. Fig.10 shown.

[0130] The mechanical properties of the welded parts are shown in Table 9:

[0131]

[0132]

[0133] For welding of S980 high-strength steel in high-altitude, low-pressure and cold areas, a preheating temperature of 90-100°C is adopted; the base welding process is: current 420-480A, arc voltage 33-34V, welding speed 70-82cm / min, welding heat input 15-18KJ / cm; ensure the interlayer temperature at 120°C-160°C; the filling welding process is: welding current 550-680A, arc voltage 33-35V, welding speed 45.7-57.75cm / min, welding heat input 20-40KJ / cm, ensure the interlayer temperature at 120°C-160°C. The cooling rate is controlled at 3-15℃ / s. If the cooling rate is less than 3℃ / s, more ferrite and precipitated carbides will be produced in the weld structure, reducing the tensile strength of the welded joint. If the cooling rate is greater than 15℃ / s, more martensite will be generated in the weld structure, resulting in cold cracks. m ≥980MPa, fracture in base metal or weld; weld and heat affected zone -40℃ impact absorption energy KV 2 ≥80J.

[0134] The performance test results of the above embodiments 1 to 9 show that after the submerged arc automatic welding of the high-strength steel S980CF for hydropower, the mechanical properties of the welded joints of the present invention have reached the performance requirements of S980 strength level welding.

[0135] The present invention utilizes large diameter welding wire and large heat input to weld 60mm thick high-strength steel plates, which can meet the requirements of hydropower steel construction in plateau areas, and has a high welding speed, can obtain good welding joints, and improve welding work efficiency.

[0136] The above description is only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A submerged arc automatic welding process for high-strength steel S980CF for hydropower in high altitude, low pressure and cold areas, characterized by: The following steps are involved: S1. Determine the welding environment and machine the high-strength steel S980CF for hydropower: Choose high altitude, low air pressure, and cold regions for welding, where the welding environment temperature is -10℃~5℃ and the air pressure is 0.05~0.07MPa; High-strength steel S980CF for hydropower was selected for machining into test plates with a thickness of 30-120 mm, and an X-shaped groove was opened along the long side with a groove angle of 60°. The two test plates were combined without gaps, and impurities and oil stains in and around the groove were cleaned; S2. Select welding wire according to the equal strength matching principle and preheat the assembled test plate: The diameter of the welding wire is selected to be 4mm. The assembled test plate is preheated with a remote infrared panel at a temperature of 90℃~100℃. An infrared thermometer is used for continuous measurement. When the predetermined temperature is reached, heating is stopped. S3, base welding process: The preheated test plate is subjected to base welding, wherein the welding current is 420~480A, the arc voltage is 33~34V, the welding speed is 70~82cm / min, and the welding heat input is 15~18KJ / cm; after welding, the test plate is covered with an asbestos board for heat preservation and slow cooling, and the cooling speed is controlled at 3~15℃ / s. After base welding, the root is cleaned with an air planer, and after cleaning, the test plate is turned over for symmetrical welding, and the temperature of the test plate is measured with an infrared thermometer to ensure that the interlayer temperature is 120℃~160℃; S4, filling welding process: Filling welding is performed on the test plate after base welding, wherein the welding current is 550~680A, the arc voltage is 33~35V, the welding speed is 45.7~57.75cm / min, and the welding heat input is 20~40KJ / cm; after each welding, the test plate is covered with asbestos board for insulation and slow cooling, and the cooling speed is controlled at 3~15℃ / s to prevent deformation of the test plate. Symmetrical welding is performed alternately on the front and back sides, and the temperature of the test plate is measured with an infrared thermometer to ensure that the interlayer temperature is 120℃~160℃ before welding the next pass; S5. After welding, the test plate cover is slowly cooled and the mechanical properties are tested: When covering the surface, reduce the voltage, current and welding speed, and complete the covering with a heat input not less than that of the filling weld. Cover the welded test plate after covering with an asbestos board to keep it warm and cool it slowly. The cooling rate is controlled at 3~15℃ / s. After 24 hours, perform UT flaw detection. After meeting the Level 1 standard in NB / T47013, conduct mechanical property testing.

2. According to claim 1, a submerged arc automatic welding process for high-strength steel S980CF for hydropower in high altitude, low pressure and cold areas, characterized in that: In the step S1, the composition of the high-strength steel S980CF includes, by mass percentage, C≤0.12%, Si≤0.30%, 0.70%≤Mn≤1.50%, P≤0.012%, S≤0.005%, Ti≤0.060%, 1.40%≤Ni≤2.20%, Cu≤0.50%, Mo≤0.70%, Vo≤0.060%, 0.02%≤Al, B≤0.004%, and the remainder is Fe and unavoidable impurities; the cold crack sensitivity index Pcm of the high-strength steel S980CF is ≤0.

30.

3. The submerged arc automatic welding process of high-strength steel S980CF for hydropower in high altitude, low pressure and cold areas according to claim 2 is characterized by: In the step S2, the components of the welding wire include, by mass percentage, C≤0.09%, Si≤0.60%, 1.2%≤Mn≤2.0%, P≤0.020%, S≤0.020%, 3.0%≤Ni, 0.60%≤Mo≤0.90%, and the remainder is Fe and unavoidable impurities.

4. The submerged arc automatic welding process of high-strength steel S980CF for hydropower in high altitude, low pressure and cold areas according to claim 1 is characterized by: In step S5, the post-weld structure includes, by volume percentage, 3-10% acicular ferrite, 70-85% bainite and 5-10% carbide.

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