Root welding method for thick-specification ultrahigh-strength steel under high restraint condition

Abstract

The invention discloses a root welding method for thick ultra-high strength steel under a high restraint condition, which comprises the following steps of: processing an inclined Y-shaped groove in the center of a test piece by taking ultra-high strength steel as a welding base material, preheating at 140-180 DEG C before welding, performing root welding by adopting a gas metal arc welding method, and finally performing heat treatment. According to the welding property characteristics of the ultra-high strength steel, the technology of preheating before welding and heat treatment after welding is adopted when root welding is conducted on the thick ultra-high strength steel under the high constraint condition, and special control over welding current, voltage and welding speed is combined, so that welding cold cracks at the root position are avoided.

Description

Technical Field

[0001] The present invention belongs to the field of welding technology, and more specifically, relates to a root welding method for thick-gauge ultra-high-strength steel under high-constraint conditions. Background Art

[0002] With the rapid development of key industries such as aerospace, shipbuilding machinery, metallurgical engineering, and petrochemicals, the strength of steel materials used in some key welded structural parts has rapidly developed from 400MPa to more than 1300MPa, among which ultra-high-strength steel has attracted more and more attention in various engineering fields. Equipment made of ultra-high-strength steel has shown significant advantages such as high strength, low consumption, and high safety performance. Due to the high content of carbon and other alloying elements in ultra-high-strength steel, the tendency of welding cold cracks is very large, so welding cold cracks are very likely to occur at the root position during welding. Especially for welding with large thickness and high restraint conditions, due to the large residual tensile stress after welding, the cold crack tendency of the root weld is greatly increased.

[0003] In the existing welding technology, some root welding process technologies have been disclosed. For example, patent CN 103495797 B discloses a thick plate Y-type groove unequal gap non-clearing root welding method, patent CN 215509719 U discloses a steel structure efficient free root cleaning welding structure, CN 103317219 B discloses a medium and thick plate unequal gap I-type groove non-clearing root welding process, etc. The above-mentioned technologies are mainly aimed at how to achieve the process of non-clearing root. In addition, patent CN 105195866 B discloses a fully automatic root welding method for the pipe end of a bimetallic composite pipe, patent CN 101417364 B discloses a semi-automatic root welding method for a metal powder cored wire pipe, and patent CN 113231721 B discloses a non-clearing root welding process for a wind turbine tower tube section. The root welding processes involved in these patent technologies are mainly for tube-shaped structures. Patent CN105522262A discloses a welding method for 1100MPa grade low alloy ultra-high strength steel, which involves a thickness of only 4 to 30mm and does not involve a high degree of restraint. There is no record of a root welding method for thick ultra-high strength steel under high restraint conditions. Summary of the invention

[0004] The purpose of the present invention is to overcome the root weld cold crack problem that occurs when thick ultra-high strength steel is welded under high constraint conditions, and to propose a root welding method suitable for ultra-high strength steel with a thickness of 35 to 45 mm under high constraint conditions.

[0005] The technical purpose of the present invention is achieved through the following technical solutions.

[0006] A root welding method for thick gauge ultra-high strength steel under high restraint conditions is carried out according to the following steps:

[0007] Step 1, preheating the test piece to 140-180°C by flame spraying before root welding; ultra-high strength steel is used as welding base material, and its chemical composition mass percentage is C 0.18-0.30%, Si 0.20-0.5%, Mn 1.0-1.3%, Ni0.35-0.7%, Mo 0.20-0.40%, Cr 0.20-0.40%, Nb 0.020-0.035%, V 0.02-0.035%, Ti0.010-0.025%, and the rest is Fe and unavoidable impurity elements; the yield strength is 1320-1500MPa;

[0008] In step 1, the thickness of the ultra-high strength steel plate is 35-45 mm, and an oblique Y-shaped groove is processed in the center of the welding base material, with an upper groove angle of 60° and a lower end gap of 2.0±0.2 mm.

[0009] Before welding, clean the surface of the test piece and the inclined Y groove with a grinding wheel and sandpaper, then clean and dry with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned.

[0010] Step 2, root welding is performed by using a consumable electrode gas shielded welding method, the ambient temperature is above 5°C, the humidity is below 90%; the wire extension length is 10-20mm, the gas supply is set to be 2s in advance, the gas is stopped 2s later, the root welding shielding gas flow rate is 20-25L / min, the welding current is 240-280A, the welding voltage is 20-25V, the welding speed is 0.1-0.3m / min, and the shielding gas is a mixture of carbon dioxide and argon;

[0011] In step 2, the shielding gas is a mixture of 20% CO2 and 80% Ar by volume, the wire extension length is 10-20 mm, the gas supply is set to be 2s in advance, the gas stop is set to be 2s later, the root welding shielding gas flow rate is 20-25L / min, the welding current is 250-260A, the welding voltage is 21-24V, and the welding speed is 0.2-0.3m / min.

[0012] In step 2, the root welding environment temperature is 10-38° C. and the humidity is 20-85%.

[0013] Step 3, after welding, perform post-weld heat treatment at a temperature of 150-160°C for 1-3 hours, followed by air cooling to room temperature of 20-25°C.

[0014] In step 3, the heat treatment temperature is 150-160° C., and the heat treatment time is 2-3 hours.

[0015] According to the weldability characteristics of ultra-high strength steel, the present invention adopts a process of preheating before welding and heat treatment after welding when performing root welding of thick ultra-high strength steel under high constraint conditions, combined with the control of welding current, voltage and welding speed to avoid welding cold cracks at the root position. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the shape of the high-constraint specimen in the present invention.

[0017] Figure 2 Schematic diagram of sampling of cross-sectional crack observation specimens after welding in the embodiment.

[0018] Figure 3 This is a photo of the weld flaw detection appearance of the welding sample in Example 1 after it was left to stand for 48 hours.

[0019] Figure 4 This is a cross-sectional morphology photograph of the welding sample of Example 1 after being dissected after being left to stand for 48 hours.

[0020] Figure 5 This is a photo of the weld flaw detection appearance of the welding sample in Example 2 after it was left to stand for 48 hours.

[0021] Figure 6 This is a cross-sectional morphology photograph of the welding sample of Example 2 after being dissected after being left to stand for 48 hours.

[0022] Figure 7 This is a photo of the weld flaw detection appearance of the welding sample in Example 3 after it was left to stand for 48 hours.

[0023] Figure 8 This is a cross-sectional morphology photograph of the welding sample of Example 3 after being dissected after being left to stand for 48 hours.

[0024] Fig. 9 This is a photo of the weld flaw detection appearance of the welding sample in Example 4 after it was left to stand for 48 hours.

[0025] Fig.10 This is a cross-sectional morphology photograph of the welded sample of Example 4 after being left to rest for 48 hours.

[0026] Fig.11 This is a photo of the weld flaw detection appearance of the welding sample in Example 5 after it was left to stand for 48 hours.

[0027] Fig.12 This is a cross-sectional morphology photograph of the welded sample of Example 5 after being left to rest for 48 hours.

[0028] Fig.13 This is a photo of the weld flaw detection appearance of the welding sample in Example 6 after it was left to stand for 48 hours.

[0029] Fig.14 This is a cross-sectional morphology photograph of the welding sample of Example 6 after being dissected after being left to stand for 48 hours.

[0030] Fig.15 This is a photo of the weld flaw detection appearance of the welding sample in Example 7 after it was left to stand for 48 hours.

[0031] Fig.16 This is a cross-sectional morphology photograph of the welding sample of Example 7 after being dissected after being left to stand for 48 hours.

[0032] Fig.17 It is a schematic diagram of flame spray preheating in the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0034] The welding base material used in the embodiment of the present invention has the following composition (mass percentage wt%): C 0.18-0.30%, Si 0.20-0.5%, Mn 1.0-1.3%, Ni 0.35-0.7%, Mo 0.20-0.40%, Cr 0.20-0.40%, Nb 0.020-0.035%, V 0.02-0.035%, Ti 0.010-0.025%, and the rest is Fe and inevitable impurity elements; the yield strength is 1320-1500MPa. The ultra-high strength steel of this composition has a high tendency of welding cold cracks due to its high carbon equivalent and alloy content. Hydrogen-induced cracks, i.e. welding cold cracks, are easily generated at the weld root during root welding. The welding base material is ultra-high strength steel, and the thickness of the steel plate is 35-45mm. For welding of thick steel plates, the degree of restraint is relatively large, which aggravates the tendency of root welding cold cracks. The steel plate is processed into a full-thickness specimen of 150×200mm for manufacturing high-constraint specimens. An inclined Y-shaped groove is processed in the center of the specimen, with an upper groove angle of 60° and a lower end gap of 2.0±0.2mm. Through this processing form of the specimen, that is, a groove is processed in the full-thickness specimen for welding, so that the constraint is better and can better reflect the high-constraint welding conditions. Figure 1 As shown, a is 60mm, b is 80mm, c is 200mm, d is 150mm, the test weld is located in the center of the full thickness specimen, f is the up-bevel angle of 60°, δ is the thickness, in the thickness direction, the up-bevel depth reaches half of the thickness, and a lower end gap e is formed on the other half of the thickness, e is 2.0±0.2mm, one side is processed along the opening direction of the up-bevel and penetrates the entire thickness; the other side is processed along the opening direction of the up-bevel to half of the thickness, and then processed in a direction parallel to the other side and penetrates the remaining half of the thickness. At this time, a lower end gap is formed between the two parallel sides.

[0035] Before welding, the surfaces of the test piece and the inclined Y groove are cleaned with a grinding wheel and sandpaper, and then cleaned and dried with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned. The process purpose of the present invention is to avoid the introduction of hydrogen during welding and prevent the introduction of excessive hydrogen from causing welding cold cracks.

[0036] The root welding environment temperature is 10-38℃ and the humidity is 20-85% before welding. When the temperature is lower, the cooling rate after welding is too fast, which may lead to the formation of brittle martensite structure with high cold crack sensitivity. Therefore, the ambient temperature during root welding should be above 5℃, and 10-38℃ is the best. Excessive humidity can easily lead to the introduction of excessive hydrogen during welding, causing welding cold cracks. Therefore, the humidity during root welding should be below 90%, and 20-85% is the best. Preheat the specimen to 140-180℃ before root welding. Preheating is mainly to reduce the cooling rate of the specimen after welding, which is conducive to the escape of hydrogen in the joint, while reducing the cooling rate of the joint and reducing the formation of brittle martensite with high hydrogen embrittlement sensitivity.

[0037] The root welding is performed by using the metal arc gas shielded welding method (MAG welding), and ER50-6 or ER80-G solid welding wire is used. The root welding shielding gas is a mixture of 20% CO2 + 80% Ar (volume percentage), the wire extension length is 20mm, the gas supply is set to 2s in advance, the gas is stopped 2s later, and the root welding shielding gas flow rate is 20-25L / min. The welding current is 240-280A, the welding voltage is 21-24V, and the welding speed is 0.2-0.3m / min.

[0038] After welding, post-weld heat treatment is carried out in a heating furnace at a temperature of 150-160°C for 1-3 hours, followed by air cooling to room temperature of 20-25°C. The main purpose of post-weld heat treatment is to further expel the diffused hydrogen from the joint.

[0039] Example 1

[0040] 1. Welding base material composition: C 0.18%, Si 0.22%, Mn 1.0%, Ni 0.54%, Mo 0.20%, Cr0.25%, Nb0.025%, V 0.03%, Ti 0.015%, the rest are Fe and unavoidable impurity elements; the yield strength is 1323MPa.

[0041] 2. The welding base material is ultra-high strength steel, the steel plate thickness is 45mm, and the steel plate is processed into a full-thickness test piece of 150×200mm for manufacturing high-constraint test pieces. An oblique Y-shaped groove is processed in the center of the test piece, see the attached Figure 1 .

[0042] 3. Before welding, clean the surface of the test piece and the inclined Y groove with a grinding wheel and sandpaper, then clean and dry with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned.

[0043] 4. The root welding environment temperature is 10℃ and the humidity is 25%.

[0044] 5. Preheat the specimen to 165°C by flame spraying before root welding.

[0045] 6. Root welding was performed by MAG welding, using ER50-6 solid wire. The root welding shielding gas was a mixture of 20% CO2 + 80% Ar, the wire extension length was 20 mm, the gas supply was set to start 2s in advance, the gas was stopped 2s later, and the root welding shielding gas flow rate was 25 L / min. The welding current was 280 A, the welding voltage was 22.5 V, and the welding speed was 0.3 m / min.

[0046] 7. After welding, post-weld heat treatment is carried out in a heating furnace (the furnace temperature has been raised to the heat treatment temperature), the heat treatment temperature is 150°C, the heat treatment time is 2 hours, and then air-cooled to room temperature.

[0047] After completing the above process, place the welded specimen for 48 hours and then perform weld surface flaw detection and joint cross-section dissection. The interception position of the observation surface of the cross-section dissection is shown in the attached Figure 2 , where A is 35 mm, B is 9 mm, C is 80 mm, D is 35 mm, E is 5 mm, and F is 60°, the same below. The weld flaw detection results and cross-sectional crack observation pictures of this embodiment are shown in the attached Figure 3 and attached Figure 4 As shown, no cracks were found in the effective weld of the weld, and no cracks were observed in the five sections.

[0048] Example 2

[0049] 1. The composition of the welding base material is: C 0.29%, Si 0.5%, Mn 1.15%, Ni 0.69%, Mo 0.33%, Cr0.38%, Nb0.034%, V 0.035%, Ti 0.020%, and the rest are Fe and unavoidable impurity elements; the yield strength is 1495MPa.

[0050] 2. The welding parent material is ultra-high strength steel, the steel plate thickness is 35mm, and the steel plate is processed into a full-thickness test piece of 150×200mm for manufacturing high-constraint test pieces. An oblique Y-shaped groove is processed in the center of the test piece, see the attached Figure 1 .

[0051] 3. Before welding, clean the surface of the test piece and the inclined Y groove with a grinding wheel and sandpaper, then clean and dry with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned.

[0052] 4. The root welding environment temperature is 25℃ and the humidity is 67%.

[0053] 5. Preheat the specimen to 150°C by flame spraying before root welding.

[0054] 6. Root welding was performed by MAG welding, using ER80-G solid wire. The root welding shielding gas was a mixture of 20% CO2 + 80% Ar, the wire extension length was 20 mm, the gas supply was set to start 2s in advance, the gas was stopped 2s later, and the root welding shielding gas flow rate was 20 L / min. The welding current was 270 A, the welding voltage was 21.5 V, and the welding speed was 0.3 m / min.

[0055] 7. After welding, post-weld heat treatment is carried out in a heating furnace (the furnace temperature has been raised to the heat treatment temperature), the heat treatment temperature is 160°C, the heat treatment time is 1 hour, and then air-cooled to room temperature.

[0056] After completing the above process, the welded specimen was placed for 48 hours for weld surface flaw detection and joint cross-section dissection. The weld flaw detection results and cross-section crack observation pictures of this embodiment are shown in the attached figure. Figure 5 and attached Figure 6 As shown, no cracks were found in the effective weld of the weld, and no cracks were observed in the five sections.

[0057] Example 3

[0058] 1. The composition of the welding base material is: C 0.26%, Si 0.45%, Mn 1.2%, Ni 0.35%, Mo 0.40%, Cr0.22%, Nb0.020%, V 0.035%, Ti 0.021%, and the rest are Fe and unavoidable impurity elements; the yield strength is 1410MPa.

[0059] 2. The welding base material is ultra-high strength steel, the steel plate thickness is 40mm, and the steel plate is processed into a full-thickness test piece of 150×200mm for manufacturing high-constraint test pieces. An oblique Y-shaped groove is processed in the center of the test piece (see attached). Figure 1 .

[0060] 3. Before welding, clean the surface of the test piece and the inclined Y groove with a grinding wheel and sandpaper, then clean and dry with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned.

[0061] 4. The root welding environment temperature is 38°C and the humidity is 85%.

[0062] 5. Preheat the specimen to 145°C by flame spraying before root welding.

[0063] 6. Root welding was performed using the metal arc gas shielded welding method (MAG welding) and ER80-G solid welding wire. The root welding shielding gas was a mixture of 20% CO2 + 80% Ar, the wire extension length was 20 mm, the gas supply was set to start 2s in advance, the gas was stopped 2s later, and the root welding shielding gas flow rate was 20 L / min. The welding current was 268 A, the welding voltage was 24 V, and the welding speed was 0.3 m / min.

[0064] 7. After welding, post-weld heat treatment is carried out in a heating furnace (the furnace temperature has been raised to the heat treatment temperature), the heat treatment temperature is 150°C, the heat treatment time is 3 hours, and then air-cooled to room temperature.

[0065] After completing the above process, the welded specimen was placed for 48 hours for weld surface flaw detection and joint cross-section dissection. The weld flaw detection results and cross-section crack observation pictures of this embodiment are shown in the attached figure. Figure 7 and attached Figure 8 As shown, no cracks were found in the effective weld of the weld, and no cracks were observed in the five sections.

[0066] Example 4

[0067] 1. The composition of the welding base material is: C 0.28%, Si 0.39%, Mn 1.3%, Ni 0.44%, Mo 0.26%, Cr0.28%, Nb0.031%, V 0.030%, Ti 0.025%, and the rest are Fe and unavoidable impurity elements; the yield strength is 1455MPa.

[0068] 2. The welding parent material is ultra-high strength steel, the steel plate thickness is 40mm, and the steel plate is processed into a full-thickness test piece of 150×200mm for manufacturing high-constraint test pieces. An oblique Y-shaped groove is processed in the center of the test piece (see attached Figure 1 .

[0069] 3. Before welding, clean the surface of the test piece and the inclined Y groove with a grinding wheel and sandpaper, then clean and dry with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned.

[0070] 4. The root welding environment temperature is 30℃ and the humidity is 57%.

[0071] 5. Preheat the specimen to 140°C by flame spraying before root welding.

[0072] 6. Root welding was performed using the metal arc gas shielded welding method (MAG welding) and ER80-G solid welding wire. The root welding shielding gas was a mixture of 20% CO2 + 80% Ar, the wire extension length was 20 mm, the gas supply was set to start 2s in advance, the gas was stopped 2s later, and the root welding shielding gas flow rate was 20 L / min. The welding current was 240 A, the welding voltage was 21.2 V, and the welding speed was 0.2 m / min.

[0073] 7. After welding, post-weld heat treatment is carried out in a heating furnace (the furnace temperature has been raised to the heat treatment temperature), the heat treatment temperature is 155°C, the heat treatment time is 2 hours, and then air-cooled to room temperature.

[0074] After completing the above process, the welded specimen was placed for 48 hours for weld surface flaw detection and joint cross-section dissection. The weld flaw detection results and cross-section crack observation pictures of this embodiment are shown in the attached figure. Fig. 9 and attached Fig.10 As shown, no cracks were found in the effective weld of the weld, and no cracks were observed in the five sections.

[0075] Example 5

[0076] 1. The composition of the welding base material is: C 0.27%, Si 0.41%, Mn 1.05%, Ni 0.37%, Mo 0.31%, Cr 0.24%, Nb 0.028%, V 0.035%, Ti 0.011%, and the rest are Fe and unavoidable impurity elements; the yield strength is 1413MPa.

[0077] 2. The welding base material is ultra-high strength steel, the steel plate thickness is 40mm, and the steel plate is processed into a full-thickness test piece of 150×200mm for manufacturing high-constraint test pieces. An oblique Y-shaped groove is processed in the center of the test piece (see attached). Figure 1 .

[0078] 3. Before welding, clean the surface of the test piece and the inclined Y groove with a grinding wheel and sandpaper, then clean and dry with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned.

[0079] 4. The root welding environment temperature is 32°C and the humidity is 48%.

[0080] 5. Preheat the specimen to 170°C by flame spraying before root welding.

[0081] 6. Root welding was performed using the metal arc gas shielded welding method (MAG welding), and ER80-G solid welding wire was used. The root welding shielding gas was a mixture of 20% CO2 + 80% Ar, the wire extension length was 20 mm, the gas supply was set to start 2s in advance, the gas was stopped 2s later, and the root welding shielding gas flow rate was 20 L / min. The welding current was 265 A, the welding voltage was 23.6 V, and the welding speed was 0.3 m / min.

[0082] 7. After welding, post-weld heat treatment is carried out in a heating furnace (the furnace temperature has been raised to the heat treatment temperature), the heat treatment temperature is 150°C, the heat treatment time is 2 hours, and then air-cooled to room temperature.

[0083] After completing the above process, the welded specimen was placed for 48 hours for weld surface flaw detection and joint cross-section dissection. The weld flaw detection results and cross-section crack observation pictures of this embodiment are shown in the attached figure. Fig.11 and attached Fig.12 As shown, no cracks were found in the effective weld of the weld, and no cracks were observed in the five sections.

[0084] Example 6

[0085] 1. The composition of the welding base material is: C 0.24%, Si 0.50%, Mn 1.28%, Ni 0.42%, Mo 0.25%, Cr 0.38%, Nb 0.034%, V 0.029%, Ti 0.022%, and the rest are Fe and unavoidable impurity elements; the yield strength is 1465MPa.

[0086] 2. The welding base material is ultra-high strength steel, the steel plate thickness is 40mm, and the steel plate is processed into a full-thickness test piece of 150×200mm for manufacturing high-constraint test pieces. An oblique Y-shaped groove is processed in the center of the test piece, see the attached Figure 1 .

[0087] 3. Before welding, clean the surface of the test piece and the inclined Y groove with a grinding wheel and sandpaper, then clean and dry with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned.

[0088] 4. The root welding environment temperature is 27℃ and the humidity is 74%.

[0089] 5. Preheat the specimen to 145°C by flame spraying before root welding.

[0090] 6. Root welding was performed using the metal arc gas shielded welding method (MAG welding), and ER80-G solid welding wire was used. The root welding shielding gas was a mixture of 20% CO2 + 80% Ar, the wire extension length was 20 mm, the gas supply was set to start 2s in advance, the gas was stopped 2s later, and the root welding shielding gas flow rate was 23 L / min. The welding current was 255 A, the welding voltage was 23.1 V, and the welding speed was 0.28 m / min.

[0091] 7. After welding, post-weld heat treatment is carried out in a heating furnace (the furnace temperature has been raised to the heat treatment temperature), the heat treatment temperature is 160°C, the heat treatment time is 3 hours, and then air-cooled to room temperature.

[0092] After completing the above process, the welded specimen was placed for 48 hours for weld surface flaw detection and joint cross-section dissection. The weld flaw detection results and cross-section crack observation pictures of this embodiment are shown in the attached figure. Fig.13 and attached Fig.14 As shown, no cracks were found in the effective weld of the weld, and no cracks were observed in the five sections.

[0093] Example 7

[0094] 1. The composition of the welding base material is: C 0.27%, Si 0.21%, Mn 1.30%, Ni 0.7%, Mo 0.27%, Cr 0.29%, Nb 0.030%, V 0.035%, Ti 0.023%, and the rest are Fe and unavoidable impurity elements; the yield strength is 1465MPa.

[0095] 2. The welding base material is ultra-high strength steel, the steel plate thickness is 40mm, and the steel plate is processed into a full-thickness test piece of 150×200mm for manufacturing high-constraint test pieces. An oblique Y-shaped groove is processed in the center of the test piece, see the attached Figure 1 .

[0096] 3. Before welding, clean the surface of the test piece and the inclined Y groove with a grinding wheel and sandpaper, then clean and dry with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned.

[0097] 4. The root welding environment temperature is 10℃ and the humidity is 66%.

[0098] 5. Preheat the specimen to 180°C before root welding by flame spraying.

[0099] 6. Root welding was performed by MAG welding, using ER50-6 solid wire. The root welding shielding gas was a mixture of 20% CO2 + 80% Ar, the wire extension length was 20 mm, the gas supply was set to start 2s in advance, the gas was stopped 2s later, and the root welding shielding gas flow rate was 25 L / min. The welding current was 242 A, the welding voltage was 23.8, and the welding speed was 0.3 m / min.

[0100] 7. After welding, post-weld heat treatment is carried out in a heating furnace (the furnace temperature has been raised to the heat treatment temperature), the heat treatment temperature is 150°C, the heat treatment time is 2 hours, and then air-cooled to room temperature.

[0101] After completing the above process, the welded specimen was placed for 48 hours for weld surface flaw detection and joint cross-section dissection. The weld flaw detection results and cross-section crack observation pictures of this embodiment are shown in the attached figure. Fig.15 and attached Fig.16 As shown, no cracks were found in the effective weld of the weld, and no cracks were observed in the five sections.

[0102] By adjusting the process parameters according to the content of the present invention, root welding of ultra-high strength steel under high constraint conditions can be achieved, and the performance shown by the test is basically consistent with the present invention. The above is an exemplary description of the present invention. It should be noted that any simple deformation, modification or other equivalent replacement that can be made by other technicians in this field without spending creative labor falls within the protection scope of the present invention without departing from the core of the present invention.

Claims

1. A root welding method for thick-gauge ultra-high-strength steel under high-constraint conditions, characterized in that: Follow the steps below: Step 1, preheating the test piece to 140-180°C by flame spraying before root welding; ultra-high strength steel is used as welding base material, and its chemical composition mass percentage is C 0.18-0.30%, Si 0.20-0.5%, Mn 1.0-1.3%, Ni0.35-0.7%, Mo 0.20-0.40%, Cr 0.20-0.40%, Nb 0.020-0.035%, V 0.02-0.035%, Ti0.010-0.025%, and the rest is Fe and unavoidable impurity elements; the yield strength is 1320-1500MPa; Step 2, root welding is performed by using a consumable electrode gas shielded welding method, the ambient temperature is above 5°C, the humidity is below 90%; the wire extension length is 10-20mm, the gas supply is set to be 2s in advance, the gas is stopped 2s later, the root welding shielding gas flow rate is 20-25L / min, the welding current is 240-280A, the welding voltage is 20-25V, the welding speed is 0.1-0.3m / min, and the shielding gas is a mixture of carbon dioxide and argon; Step 3, after welding, perform post-weld heat treatment at a temperature of 150-160°C for 1-3 hours, followed by air cooling to room temperature of 20-25°C.

2. A root welding method for thick-gauge ultra-high strength steel under high-constraint conditions according to claim 1, characterized in that: In step 1, the thickness of the ultra-high strength steel plate is 35-45 mm, and an oblique Y-shaped groove is processed in the center of the welding base material, with an upper groove angle of 60° and a lower end gap of 2.0±0.2 mm.

3. A root welding method for thick-gauge ultra-high strength steel under high-constraint conditions according to claim 1, characterized in that: Before welding, clean the surface of the test piece and the inclined Y groove with a grinding wheel and sandpaper, then clean and dry with alcohol to ensure that the oxide scale, rust, water and oil stains near the groove surface are cleaned.

4. A root welding method for thick-gauge ultra-high strength steel under high-constraint conditions according to claim 1, characterized in that: In step 2, the shielding gas is a mixture of 20% CO2 and 80% Ar by volume, the wire extension length is 10-20 mm, the gas supply is set to be 2s in advance, the gas stop is set to be 2s later, the root welding shielding gas flow rate is 20-25L / min, the welding current is 250-260A, the welding voltage is 21-24V, and the welding speed is 0.2-0.3m / min.

5. A root welding method for thick-gauge ultra-high strength steel under high-constraint conditions according to claim 1, characterized in that: In step 2, the root welding environment temperature is 10-38° C. and the humidity is 20-85%.

6. A root welding method for thick-gauge ultra-high strength steel under high-constraint conditions according to claim 1, characterized in that: In step 3, the heat treatment temperature is 150-160° C., and the heat treatment time is 2-3 hours.

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