Submerged-arc welding method for 9Ni steel

Abstract

The invention relates to a 9Ni steel submerged-arc welding method, and belongs to the technical field of welding. According to the method, 9Ni steel with the tensile strength of 690-750 MPa and the thickness of 50 mm is used as a splicing base material; the matched welding material is characterized in that the tensile strength of the welding material is 630-710 MPa, the diameter phi of a welding wire is 2.4 mm or above, the brand is OK Auto NiCrMo-4, and the welding flux is OK Flux 10.90; (2) an asymmetric K-shaped groove is adopted for splicing base metal; (3) according to submerged-arc welding parameters, the welding line energy is 10-30 KJ / cm, butt joints of the spliced base metal with the same plate thickness are continuously welded till a welding seam is filled, and a welding bead is cleaned through a steel wire brush after each pass of welding; and the interlayer temperature is controlled to be less than or equal to 120 DEG C. The impact absorption energy values of the tensile strength of a welding joint, a welding seam of the welding joint, a fusion line, a heat affected zone and the like of submerged arc welding reach a higher level, and the welding joint has excellent low-temperature impact toughness and cold bending performance.

Description

Technical Field

[0001] The present invention belongs to the welding method of steel plates, and particularly relates to the submerged arc welding method of 9Ni steel. Background Art

[0002] With the increasing demand for natural gas in industry and life, as the main steel used to build liquefied gas storage tanks, liquefied gas carriers, fuel tanks for large ships, natural gas receiving stations, etc., the demand for 9Ni steel has been increasing year by year. The Ni content of 9Ni steel is 8.8 - 9.3%. The high Ni content not only brings a series of production problems but also brings operation problems to welding. At present, there are already a few enterprises that have the ability to produce 50 mm thick 9Ni steel that meets the requirements of classification society specifications, and the steel is slowly being put on the market. For the welding of 9Ni steel, currently, manual arc welding and gas shielded welding are still used. If the submerged arc welding method is used, there are situations where the low-temperature toughness and cold bending performance of the welded joint are unstable, and it is difficult to meet the weldability test requirements of the classification society.

[0003] After retrieval, Chinese Patent Publication No. CN 115740706 A discloses a butt joint welding method for 9Ni steel according to the thickness of the 9Ni steel plate, which involves the X-shaped groove grinding process and does not involve important welding parameters such as welding materials and welding line energy. Chinese Patent Publication No. CN104625359A discloses a welding process for the bottom plate of an LNG cryogenic tank, which uses two 9Ni steel plates with a thickness of 6 - 9 mm for horizontal lapping, and the overlapping part forms a lap joint welding method, which does not involve the performance of the joint after welding and cannot evaluate the welding effect.

[0004] In summary, the prior art has not disclosed an ideal submerged arc welding method for 9Ni steel. Summary of the Invention

[0005] The purpose of the present invention is to provide a submerged arc welding method for 9Ni steel, select 9Ni steel plates, design welding materials and submerged arc welding processes that match the 9Ni steel plates, and the welded joint is tested for weldability mechanical properties. The results show that the performance of the welded joint of the 50 mm thick 9Ni steel after submerged arc welding of the present invention fully meets the weldability requirements of the classification society.

[0006] The technical solution of the present invention is as follows: A submerged arc welding method for 9Ni steel, the base metal does not need to be preheated before welding and does not need to be heat-treated after welding, specifically as follows: (1) Selection of base metal and welding materials: Use 9Ni steel with a tensile strength of 690 - 750 MPa as the splicing base metal; the tensile strength of the welding material is 630 - 710 MPa, the wire diameter of the welding wire is ≥2.4 mm, the welding wire grade is OK Autrod NiCrMo-4 (AWS A5.14 ERNiCrMo-4), and the welding flux is OK Flux 10.90; (2)The welding groove for butt joint of base metal is an asymmetric K-type groove. The height from the first welding surface to the groove is 35 mm, the groove angle is 45°, and the root face is 5 mm. The use of an asymmetric K-type groove can effectively reduce welding deformation, but it will increase the welding stress of the welded joint.

[0007] (3)Submerged arc welding parameters: welding current is 350 ± 10 A, welding voltage is 30 ± 1 V, welding speed is 40 ± 2 cm / min, and welding line energy is 15 ± 3 KJ / cm; and welding current is 410 ± 10 A, welding voltage is 32 ± 1 V, welding speed is 26 ± 2 cm / min, and welding line energy is 30 ± 3 KJ / cm. Continuously weld the butt joint of the butt-welded base metal with the same plate thickness until the weld is filled, and clean the weld bead with a wire brush after each pass of welding; the baking temperature of the welding flux is 250 °C, and the baking time is 1 h; the interpass temperature is controlled at ≤120 °C.

[0008] The welding method is applicable to base metal with a thickness of 50 mm.

[0009] The chemical components and mass percentages of the welding wire in the welding method are as follows: C: ≤0.03%, Si: 0.10 - 0.30%, Mn: 0.4 - 0.6%, P: ≤0.010%, S: ≤0.010%, Cr: 14 - 18%, Ni: 61 - 63%, Al: 0.04 - 0.08%, Fe: 6.0 - 7.0%, Mo: 12.0 - 15.0%, and the balance is inevitable impurity elements.

[0010] The ultrasonic flaw detection result of the weld of the welded joint of the two butt-welded base metals obtained by the above-mentioned submerged arc welding method for 9Ni steel meets the requirements of Grade I specified in the standard of GB / T 11345 - 1989.

[0011] By the above-mentioned submerged arc welding method for 9Ni steel, the tensile strength of the welded joint of the two butt-welded base metals with a thickness of 50 mm is 690 - 730 MPa, the bending mandrel diameter D = 6a, and the 180 °C forward and reverse cold bending is qualified. The extremely low temperature transverse impact toughness value at -196 °C: ≥100 J at the weld, ≥90 J at the fusion line, ≥110 J in the heat affected zone HAZ of the weld, and ≥200 J for the base metal, meeting the weldability certification and production requirements of the classification society. It is significantly higher than the extremely low temperature transverse impact toughness value of ≥27 J required by the classification society specification at -196 °C.

[0012] The microstructure of the weld zone of the welded joint obtained by the above-mentioned submerged arc welding method for 9Ni steel is austenite structure, and the microstructure of the heat affected zone is acicular bainite structure. The acicular bainite structure is the guarantee of the toughness of the welded joint.

[0013] Compared with the prior art, the advantages of the present invention are as follows: (1)SAW welding method for 50 mm thick 9Ni steel. The tensile strength of the welded joint, the impact toughness values of the weld, fusion line, and heat affected zone of the welded joint all reach a relatively high level, and the welded joint has excellent low-temperature impact toughness and cold bending performance.

[0014] (2)The microstructure of the heat affected zone (HAZ) of the welded joint is mainly acicular bainite, with fine and uniform grains. The weld metal is mainly fine austenite, thus endowing the weld with excellent strength, low-temperature toughness, and cold bending performance.

[0015] (3)A welding process is achieved where the base metal does not require preheating before welding and post-weld heat treatment. The multi-layer and multi-pass continuous welding process is adopted, which is simple, efficient, energy-saving in welding operation, and convenient for the popularization and application of the method. Description of the Drawings

[0016] Figure 1 This is the SAW welding groove composed of two 50 mm thick base metals of the present invention.

[0017] Figure 2 This is the tensile specimen of the welded joint in Example 3 of the present invention.

[0018] Figure 3 This is the impact specimen of the welded joint in Example 3 of the present invention.

[0019] Figure 4 This is the face bend and root bend specimens of the welded joint in Example 3 of the present invention.

[0020] Figure 5 This is the macrostructure specimen of the welded joint in Example 4 of the present invention.

[0021] Figure 6 This is the weld microstructure of the welded joint in Example 1 of the present invention, which is austenite.

[0022] Figure 7 This is the microstructure of the fusion line of the welded joint in Example 1 of the present invention. One side is austenite, and the other side is acicular bainite, with fine and uniform bainite grains.

[0023] Figure 8 This is the microstructure of the HAZ zone 3 mm away from the fusion line of the welded joint in Example 1 of the present invention, which is acicular bainite with fine and uniform grains. Detailed Embodiments

[0024] The following further describes the present invention in detail with reference to embodiments. The embodiments are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention. Example 1

[0025] Base material: 50-mm thick 9Ni steel with a tensile strength of 704 MPa, a very low temperature transverse impact toughness value of ≥200 J at -196 °C, thick plate combination of 50 mm + 50 mm. The dimensions of the base material in length × width × thickness are 1300 mm × 300 mm × 50 mm. The welding groove of the splicing material uses an asymmetric K-type groove. The height from the first welding surface to the groove is 35 mm, the groove angle is 45°, and the root face is 5 mm, as Figure 1 shown.

[0026] Welding materials: Welding wire: The chemical components and mass percentages are as follows: C: 0.008%, Si: 0.18%, Mn: 0.45%, P: 0.006%, S: 0.003%, Cr: 15.1%, Ni: 61.8%, Fe: 6.4%, Mo: 13.5%, Al: 0.06%, and the balance is inevitable impurity elements.

[0027] The diameter of the welding wire is φ2.4 mm, and it is welded in combination with the sintered welding flux INCOFLUX 10.90. The mechanical properties of the deposited metal: yield strength Rp 0.2 : 456 MPa, tensile strength Rm: 684 MPa, elongation A: 44.0%, Z-directional cross-sectional shrinkage rate: 47%, AKv impact absorption energy values at -196 °C are 91 J, 89 J, and 104 J.

[0028] The welding process parameters are as follows: welding current 350 ± 10 A, welding voltage 30 ± 1 V, welding speed 40 ± 2 cm / min, welding line energy 15 ± 3 KJ / cm; the baking system of the welding flux is 250 °C × 1 h; the interlayer temperature is controlled at 50 - 100 °C. Example 2

[0029] The welded plate of Example 1 is further subjected to stress relief heat treatment. The stress relief treatment process is as follows: place the welded plate in a heating furnace for tempering treatment, the tempering temperature is 580 °C, the holding time in the furnace is 100 min, start timing when the furnace temperature reaches the set temperature, and cool in air after taking out of the furnace. Example 3

[0030] Base material: 50-mm thick 9Ni steel with a tensile strength of 719 MPa, base material splicing combination of 50 mm + 50 mm. The dimensions of the base material in length × width × thickness are 1300 mm × 300 mm × 40 mm, using an asymmetric K-type groove, the groove angle is 45°, and the root face is 5 mm, as Figure 1 shown.

[0031] Welding materials: Welding wire: The chemical components and their mass percentages are as follows: C: 0.006%, Si: 0.20%, Mn: 0.50%, P: 0.007%, S: 0.002%, Cr: 17.2%, Ni: 62.4%, Fe: 6.30%, Mo: 13.9%, and the balance is inevitable impurity elements.

[0032] The diameter of the welding wire is φ2.4 mm, the grade is OK Autrod NiCrMo-4 (AWS A5.14 ERNiCrMo-4), and it is welded in combination with OK Flux 10.90. The mechanical properties of the deposited metal are as follows: yield strength Rp 0.2 : 513 MPa, tensile strength Rm: 690 MPa, elongation A: 34.0%, Z-directional reduction of area: 46%, impact absorption energy value AKv at -196 °C: 93 J, 109 J, 84 J.

[0033] The welding process parameters are as follows: welding current 410 ± 10 A, welding voltage 32 ± 1 V, welding speed 26 ± 2 cm / min, welding line energy 30 kJ / cm; the baking system of the welding flux is 250 °C × 1 h; the interlayer temperature is controlled at 50 - 100 °C. Example 4

[0034] The welded plate of Example 3 is further subjected to stress relief heat treatment. The stress relief treatment process is as follows: place the welded plate in a heating furnace for tempering treatment, the tempering temperature is 560 °C, the holding time in the furnace is 100 min, start timing when the furnace temperature reaches the specified temperature, and cool in air after taking out of the furnace.

[0035] The ultrasonic flaw detection result of the weld of the 50-mm-thick 9Ni steel plate welded by the above welding method meets the requirements of Grade I specified in the standard of GB / T 11345-1989.

[0036] For the 50-mm-thick 9Ni steel welded by the above welding method, after detecting the mechanical properties of the welded joint, the results of the tensile test, impact test and cold bending test are shown in Tables 1 - 3 respectively. From the performance of the examples, the tensile strength of the steel plate welded joint is between 690 - 730 MPa, the bending core diameter D = 6a, the 180 °C forward and reverse cold bending is qualified, and the extremely low temperature transverse impact toughness values of the weld, fusion line and HAZ area at -196 °C are stable, fully meeting the weldability certification requirements of the classification society and production requirements.

[0037] Table 1 Tensile test results of the welded joint

[0038] Table 2 Tensile test results of the welded joint

[0039] Table 3 Impact test results of welded joints

[0040] Note: The value after " / " is the average value of this group.

[0041] It shows that the heat-affected zone of the weld has extremely low low-temperature toughness.

[0042] In addition to the above embodiments, the present invention also includes other implementation manners. Any technical solutions formed by equivalent transformation or equivalent substitution shall fall within the protection scope of the claims of the present invention.

Claims

1. Submerged arc welding method for 9Ni steel plate, characterized in that: Including, Step 1. Select base material and welding materials: Use 9Ni steel with a tensile strength of 690 - 750 MPa as the spliced base material; the tensile strength of the welding materials is 630 - 710 MPa, the wire diameter is ≥2.4 mm, the submerged arc welding wire grade is OK AutrodNiCrMo-4 (AWS A5.14 ERNiCrMo-4), and the welding flux is OK Flux 10.

90. Step 2. The submerged arc welding groove of the spliced material adopts an asymmetric K-shaped groove. The height from the first welding surface to the groove is 35 mm, the groove angle is 45°, and the root face is 5 mm. Step 3. Submerged arc welding process: The welding current is 350 ± 10 A, the welding voltage is 30 ± 1 V, the welding speed is 40 ± 2 cm / min, and the welding line energy is 15 ± 3 KJ / cm; or the welding current is 410 ± 10 A, the welding voltage is 32 ± 1 V, the welding speed is 26 ± 2 cm / min, and the welding line energy is 30 ± 3 KJ / cm; Continuously weld the butt joint of the spliced base material with the same plate thickness until the weld is filled, and the interpass temperature ≤ 120°C.

2. The method according to claim 1, wherein: Step 3. During the submerged arc welding process, use a wire brush to clean the weld bead after each pass of welding.

3. The method according to claim 1, characterized in that: Step 3. Bake the welding flux at 250°C for 1 h.

4. The method according to claim 1, wherein: The thickness of the base material is 50 mm.

5. The method according to claim 1, characterized in that: The chemical components and mass percentages of the wire are as follows: C: ≤0.03%, Si: 0.10 - 0.30%, Mn: 0.4 - 0.6%, P: ≤0.010%, S: ≤0.010%, Cr: 14 - 18%, Ni: 61 - 63%, Al: 0.04 - 0.08%, Fe: 6.0 - 7.0%, and the balance is inevitable impurity elements.

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