Ultralow-temperature stainless steel sheet argon tungsten-arc welding process

Abstract

According to the welding process for the 316LN austenitic stainless steel, the welding process is suitable for the ultralow temperature (-269 DEG C) environment, the multi-layer manual argon tungsten-arc welding (GTAW) technology is adopted, postweld heat treatment is not needed, the production process is simplified, and the cost is reduced. And by accurately controlling welding heat input, it is ensured that a welding joint has excellent toughness at the low temperature, and grain coarsening and harmful intermetallic phase precipitation are avoided. Nitrogen-strengthened 316LN base metal and a low-carbon and high-molybdenum GTS-316LM welding wire are selected, and the low-temperature strength and corrosion resistance of a welded joint are improved. Oxides and slag inclusion in the welding seam are reduced through high-purity argon protection, and the quality of the welding seam is optimized. Metallurgical bonding of welding seams is ensured through the interlayer cleaning process. Tests show that a welded joint shows excellent impact toughness and room-temperature mechanical properties at the temperature of-269 DEG C, and the ultralow-temperature application requirement is met. The process does not need postweld heat treatment, has the advantages of simplifying production, reducing cost and improving performance, and is suitable for equipment manufacturing and pipeline installation at the liquid helium temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding process in ultra-low temperature environment, and particularly relates to a welding process of 316LN austenitic stainless steel plate used at liquid helium temperature (-269 DEG C). BACKGROUND

[0002] Currently, in the field of ultra-low temperature (liquid helium temperature -269 DEG C) equipment manufacturing, 316LN austenitic stainless steel is widely used due to its excellent comprehensive mechanical properties at low temperature, for example, used for component manufacturing of the International Thermonuclear Experimental Reactor (ITER) program. For welding of 316LN stainless steel, the existing technology usually adopts tungsten inert gas welding (GTAW) and uses 316L or similar composition welding material.

[0003] The focus of the existing technology is generally as follows:

[0004] 1) Controlling the ferrite content in the weld: In order to obtain good low-temperature toughness, it is usually necessary to control the delta ferrite content in the weld at a very low level (for example, less than 2 FN), because ferrite will exhibit brittleness at low temperature, significantly reducing the impact toughness of the welded joint.

[0005] 2) Selecting low-carbon, high-nickel filler metal: Low-carbon (such as 316L) helps to prevent carbide precipitation during welding thermal cycle, thereby avoiding intergranular corrosion and toughness reduction. Higher nickel content helps to stabilize the austenitic structure and improve low-temperature toughness.

[0006] 3) Controlling welding heat input: Excessive heat input will cause the weld and heat-affected zone to coarsen, and harmful intermetallic phases may be produced, thereby deteriorating the low-temperature mechanical properties.

[0007] However, while achieving high impact toughness in an ultra-low temperature (-269 DEG C) environment, the existing technology still has room for further optimization in terms of simplifying production, reducing costs, and ensuring that the welded joint obtains stable and excellent comprehensive mechanical properties through a set of precise, stable, and post-weld heat treatment-free process parameter combinations. For example, patent CN110576273A proposes a welding material and process for the LNG (-170 DEG C) field, but does not fully address the application requirements at lower temperatures such as liquid helium. SUMMARY

[0008] The present application proposes an ultra-low temperature stainless steel sheet tungsten inert gas welding process that can simplify the production process, reduce production costs, and ensure the ultra-low temperature impact toughness and stability of the welded joint without reducing the mechanical properties by precisely controlling the welding heat input and without post-weld heat treatment.

[0009] In order to achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0010] An ultra-low temperature stainless steel sheet tungsten electrode argon arc welding process, comprising the following steps:

[0011] Step S1: Prepare the base material and the groove: use a stainless steel base material with a thickness of 5 mm and a groove angle of 60°, and use a single V-shaped groove butt joint for the welded joint; assemble the gap of 1-2 mm to ensure the back welding penetration, and weld the double side with single side.

[0012] Step S2: Select the filler material: use a welding wire with a diameter of Φ2.0mm;

[0013] Step S3: Select the welding equipment and electrical characteristics: use a direct current tungsten electrode argon arc welding equipment, adopt direct current positive connection (DCEN) connection, and connect the workpiece to the positive electrode. The tungsten electrode is a cerium tungsten electrode with a diameter of Φ3mm, and the nozzle diameter is Φ15mm;

[0014] Step S4: Select the protective gas: use argon with a purity of not less than 99.99% as the protective gas, control the gas flow of the welding gun nozzle at 10L / min, and control the back protective gas flow at 11L / min, which is used to isolate the harmful elements such as oxygen and nitrogen in the air from the molten pool, reduce the oxide inclusions in the weld, and improve the low temperature performance of the weld;

[0015] Step S5: Select the welding position and method: use the vertical welding upward welding method;

[0016] Step S6: Set the welding process parameters:

[0017] First layer (backing weld): welding current 85A, arc voltage 10V, welding speed 39mm / min, calculated heat input 13.076 KJ / cm;

[0018] Second layer (filler weld): welding current 101A, arc voltage 11V, welding speed 65mm / min, calculated heat input 10.255 KJ / cm;

[0019] Third layer (cover weld): welding current 101A, arc voltage 11V, welding speed 70mm / min, calculated heat input 9.522 KJ / cm;

[0020] From the first layer to the third layer, the welding heat input is gradually reduced, and the material organization and mechanical properties are matched by precise control to prevent problems such as organization coarsening, grain growth and intermetallic phase precipitation caused by excessive heat input;

[0021] Step S7: interpass treatment is performed: before welding each pass, the weld surface is cleaned by grinding with a grinding wheel to ensure that there are no defects such as oxide scale and slag, and the interpass temperature of each layer of welding is controlled to be no more than 100℃;

[0022] Step S8: after the welding is completed, no post-weld heat treatment is performed, and the manufacturing of the welded joint is directly completed.

[0023] Preferably, in the step S1, a 316LN austenitic stainless steel base material conforming to the ASTM A240 standard is used, and the nitrogen element in the 316LN austenitic stainless steel base material effectively stabilizes the austenitic structure.

[0024] Preferably, in the step S1, the impact absorption energy of the welded joint in a -269℃ ultra-low temperature environment is stabilized between 21J and 24J, the lateral expansion value is 0.98mm to 1.22mm, the impact absorption energy of the heat-affected zone is 36J to 37J, and the lateral expansion value is 1.31mm to 1.33mm.

[0025] Preferably, in the step S2, a GTS-316LM welding wire is used, and the low-carbon characteristic of the GTS-316LM welding wire reduces the risk of sensitization corrosion, and the molybdenum element improves the strength and corrosion resistance of the material.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] The key to obtaining an ultra-low temperature welded joint with excellent performance without post-weld heat treatment in the present application lies in the synergistic effect of the following points:

[0028] 1) Precise layered heat input control strategy: The core of the present application is to precisely control and optimally match the heat input of different weld passes. From the backing pass to the cover pass, the heat input presents a gradient decreasing trend (from about 13.1 KJ / cm to about 9.5 KJ / cm). This strategy not only ensures good penetration and root forming of the first weld pass, but also avoids excessive heating of the underlying weld and heat-affected zone through lower heat input of subsequent passes, effectively inhibiting grain coarsening and the precipitation of harmful intermetallic phases, which is the key to ensuring ultra-low temperature toughness.

[0029] 2) Optimized material matching: Nitrogen-reinforced 316LN base material is matched with low-carbon high-molybdenum GTS-316LM welding wire. The nitrogen element in 316LN effectively stabilizes the austenitic structure while providing solid solution strengthening and ensuring low temperature strength. The low-carbon characteristic of GTS-316LM welding wire minimizes the risk of sensitization corrosion, and the appropriate amount of molybdenum helps to improve the strength and corrosion resistance. The combination of the two lays the material foundation for obtaining excellent low temperature performance.

[0030] 3) Pure welding environment: high purity (≥99.99%) argon is used for sufficient protection, which effectively isolates the invasion of harmful elements such as oxygen and nitrogen in the air to the molten pool. This reduces the non-metallic inclusions such as oxides in the weld, improves the purity of the weld, and significantly improves the low temperature impact toughness.

[0031] 4) Strict interlayer processing process: through thorough mechanical cleaning (grinding), the oxide layer and possible defects on the surface of each weld are removed, ensuring good metallurgical bonding between multiple welds, eliminating interlayer defects, and ensuring the integrity and performance consistency of the entire welded joint. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A structure diagram of a welded joint group in a super-low-temperature stainless steel sheet tungsten argon arc welding process is provided.

[0033] Figure 2 A structure diagram of the number of layers of a welded joint in a super-low-temperature stainless steel sheet tungsten argon arc welding process is provided.

[0034] Figure 3 A process flow chart of a super-low-temperature stainless steel sheet tungsten argon arc welding process is provided.

[0035] Reference numerals in the drawings: DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all.

[0037] As shown in Figure 3 , a super-low-temperature stainless steel sheet tungsten argon arc welding process provided in the present embodiment includes the following steps:

[0038] Step S1: Prepare the base material and the groove: use a stainless steel base material with a thickness of 5mm and a groove angle of 60°, and a 316LN austenitic stainless steel base material that meets the ASTM A240 standard, and use a single V-shaped groove butt joint (as shown in Figure 1 ) for the welded joint; assemble the gap of 1-2mm to ensure back penetration, and single-sided welding with double-sided forming.

[0039] Step S2: Select the filler material: use a GTS-316LM brand welding wire with a diameter of Φ2.0mm, which meets the ASME SFA5.9 / 5.9M-2023 standard; the low-carbon characteristics of GTS-316LM welding wire minimize the risk of sensitization corrosion, and the molybdenum element improves the strength and corrosion resistance of the material.

[0040] Step S3: Selecting welding equipment and electrical characteristics: using a direct current tungsten argon arc welding (GTAW) equipment, adopting direct current positive connection (DCEN) connection, and connecting the workpiece to the positive electrode. The tungsten electrode is a cerium tungsten electrode (EWCe) with a diameter of Φ3 mm, and the nozzle diameter is Φ15 mm;

[0041] Step S4: Selecting protective gas: using argon (Ar) with a purity of not less than 99.99% as the protective gas, controlling the gas flow of the welding gun nozzle at 10 L / min, and controlling the back protective gas flow at 11 L / min, so as to isolate the harmful elements such as oxygen and nitrogen in the air from invading the molten pool, reduce the oxide inclusions in the weld, and improve the low-temperature performance of the weld;

[0042] Step S5: Selecting welding position and method: adopting vertical welding (3G) upward welding method;

[0043] Step S6: Setting the welding process parameters:

[0044] As shown in Figure 2 the first layer (the base welding bead): the welding current is 85 A, the arc voltage is 10 V, the welding speed is 39 mm / min, and the calculated heat input is 13.076 KJ / cm; by controlling a lower welding current (85 A) and a higher welding speed (39 mm / min) to ensure sufficient penetration and root shaping;

[0045] the second layer (the filler welding bead): the welding current is 101 A, the arc voltage is 11 V, the welding speed is 65 mm / min, and the calculated heat input is 10.255 KJ / cm;

[0046] the third layer (the cap welding bead): the welding current is 101 A, the arc voltage is 11 V, the welding speed is 70 mm / min, and the calculated heat input is 9.522 KJ / cm;

[0047] From the first layer to the third layer, the welding heat input is gradually decreased by progressive reduction, and the material organization and mechanical properties are matched by precise control to prevent problems such as organization coarsening, grain growth, and intermetallic phase precipitation caused by excessive heat input;

[0048] In the second layer (the filler welding bead) and the third layer (the cap welding bead), the welding heat input is gradually reduced by appropriately increasing the welding current (101 A) and appropriately increasing the welding speed (65 mm / min, 70 mm / min) to avoid overheating, reduce grain coarsening, and inhibit the precipitation of harmful intermetallic phases

[0049] The welding process avoids excessive heating of the weld and heat-affected zone by precisely controlling the heat input of each pass, effectively inhibiting grain coarsening and the precipitation of harmful intermetallic phases, ensuring excellent impact toughness and mechanical properties of the joint in ultra-low temperature environments.

[0050] Step S7: Interlayer treatment is performed: before welding each pass, the weld surface is cleaned by grinding with a grinding wheel to ensure that there are no defects such as oxidation scale and slag, and the interlayer temperature of each layer of welding is controlled to be no more than 100℃;

[0051] Step S8: After completing the welding, no post-weld heat treatment is performed, and the manufacturing of the welded joint is directly completed. Without post-weld heat treatment, the production process is simplified, the manufacturing cycle is shortened, and the production cost and energy consumption are significantly reduced.

[0052] The following will be described in detail in combination with specific experimental data:

[0053] According to the-269℃ impact performance requirements of austenitic stainless steel for liquid helium pressure vessels in GB / T 150.2-2024 "Pressure Vessels Part 2: Materials":

[0054] The average impact energy of the 3 standard samples KV2≥54J, and the average lateral expansion value LE≥0.53mm. Since the thickness of the base material of the present application is 5mm, it cannot be processed into standard samples (55mm×10mm×10mm), so it is processed into sub-size samples (55mm×10mm×2.5mm), and the qualified indicators are converted in proportion: the average impact energy KV2≥13.5J, and the average lateral expansion value LE≥0.53mm

[0055] 1) Excellent ultra-low temperature impact toughness: the V-notch impact test results at-269℃ ultra-low temperature environment show that:

[0056] The impact energy of the weld area is stable at 21J to 24J, and the lateral expansion value is 0.98mm to 1.22mm.

[0057] The impact energy of the heat-affected zone is as high as 36J to 37J, and the lateral expansion value is 1.31mm to 1.33mm.

[0058] This result far exceeds the impact energy requirements of conventional low-temperature pressure vessels, indicating that the welded joint has extremely high resistance to brittle fracture at liquid helium temperature, ensuring the safety of the equipment under extreme low-temperature working conditions.

[0059] 2) Excellent room temperature mechanical properties:

[0060] Tensile strength: The tensile strengths of the joints reached 624 MPa and 613 MPa respectively, far exceeding the minimum value required by the base material standard (≥515 MPa), achieving equal strength matching. The fracture locations were all at the weld seam, indicating that the weld metal possesses excellent strength and toughness.

[0061] Bending performance: Transverse face bending and back bending tests were conducted under the conditions of 4a mandrel diameter and 180°. No cracks were found in any of the specimens, indicating that the welded joint has good plasticity.

[0062] 3) Reliable welding quality: No defects were found in the appearance inspection, and the RT (radiological inspection) test result was Grade I qualified, proving that the weld is dense inside and free from volume defects such as porosity, slag inclusion, and incomplete penetration.

[0063] 4) Simplified process and cost-effectiveness: This process eliminates the need for post-weld heat treatment, simplifies the production process, shortens the manufacturing cycle, and significantly reduces energy consumption and production costs.

[0064] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low-temperature stainless steel thin plate tungsten inert gas welding process, characterized in that, Includes the following steps: Step S1: Prepare the base material and bevel: Use a 5mm thick stainless steel base material with a 60° bevel angle, and use a single V-groove butt joint for welding; the assembly gap is 1-2mm to ensure back-side penetration and single-sided welding with double-sided forming; Step S2: Select filler material: Use welding wire with a diameter of Φ2.0mm; Step S3: Select welding equipment and electrical characteristics: Use DC tungsten inert gas welding equipment, with DC positive connection (DCEN) and the workpiece connected to the positive terminal; the tungsten electrode is a cerium tungsten electrode with a diameter of Φ3mm, and the nozzle diameter is Φ15mm; Step S4: Select shielding gas: Use argon gas with a purity of not less than 99.99% as shielding gas. Control the gas flow rate of the welding torch nozzle at 10L / min and the back shielding gas flow rate at 10L / min. This is used to isolate harmful elements such as oxygen and nitrogen in the air from intruding into the molten pool, reduce oxide inclusions in the weld, and improve the low-temperature performance of the weld. Step S5: Select welding position and method: Use vertical welding upward welding method; Step S6: Set welding process parameters: First layer (root pass): Welding current 85A, arc voltage 10V, welding speed 39mm / min, calculated heat input is 13.076 KJ / cm; Second layer (filler weld): Welding current 101A, arc voltage 11V, welding speed 65mm / min, calculated heat input 10.255 KJ / cm; Third layer (cover weld): Welding current 101A, arc voltage 11V, welding speed 70mm / min, calculated heat input is 9.522 KJ / cm; From the first weld bead to the third weld bead, the welding heat input is gradually reduced. Through precise control, the optimal material structure and mechanical properties are matched, preventing problems such as coarsening of structure, grain growth and precipitation of intermetallic phases caused by excessive heat input. Step S7: Perform interpass treatment: Before each weld, grind and clean the weld surface with a grinding wheel to ensure that there are no defects such as oxide scale and slag inclusions, and control the interpass temperature of each weld to not exceed 100℃. Step S8: After welding is completed, no post-weld heat treatment is performed; the manufacturing of the welded joint is completed directly.

2. The ultra-low temperature stainless steel thin plate tungsten inert gas welding process according to claim 1, characterized in that, In step S1, 316LN austenitic stainless steel base material conforming to ASTM A240 standard is used, and the nitrogen element in the 316LN austenitic stainless steel base material effectively stabilizes the austenitic structure.

3. The ultra-low temperature stainless steel thin plate tungsten inert gas welding process according to claim 1, characterized in that, In step S1, the impact absorption energy of the welded joint in the -269℃ ultra-low temperature environment is stable between 21J and 24J, and the lateral expansion value is between 0.98mm and 1.22mm. The impact absorption energy of the heat-affected zone reaches 36J to 37J, and the lateral expansion value is between 1.31mm and 1.33mm.

4. The ultra-low temperature stainless steel thin plate tungsten inert gas welding process according to claim 1, characterized in that, In step S2, GTS-316LM welding wire is used. The low carbon content of GTS-316LM welding wire reduces the risk of sensitization corrosion, and the molybdenum element improves the strength and corrosion resistance of the material.

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