A stainless steel isolation layer welding wire for welding dissimilar materials 9Cr heat-resistant steel and austenitic stainless steel and its application.

Abstract

This invention discloses a stainless steel isolation layer welding wire for dissimilar welding of 9Cr heat-resistant steel and austenitic stainless steel, belonging to the field of welding materials technology. The welding wire comprises, by weight percentage: C: 0.05-0.15%, Cr: 15.0-16.0%, Ni: 23.0-27.0%, Mo: 3.5-5.5%, Mn: 1.0-2.0%, N: 0.10-0.20%, Si: ≤0.5%, with the balance being Fe. By controlling the content of Mo and C elements in the welding wire, and combining this with the synergistic matching of Cr and Ni element contents, a stable all-austenitic isolation layer metal is pre-deposited onto the 9Cr heat-resistant steel side. This welding wire is suitable for dissimilar metal welding of steam generators and loop pipelines in liquid sodium-cooled fast reactors, exhibiting good welding process performance and service stability.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, specifically to a stainless steel isolation layer welding wire used in liquid sodium-cooled fast reactors, which meets long-term performance requirements and effectively inhibits carbon migration in dissimilar welded joints of 9Cr heat-resistant steel and austenitic stainless steel. Background Technology

[0002] With the development of fourth-generation nuclear reactor technology, liquid sodium-cooled fast reactors have attracted widespread attention due to their high fuel utilization rate and good thermal performance. In this system, the steam generator and loop piping are usually made of materials such as 9Cr heat-resistant steel and austenitic stainless steel, which inevitably involves the problem of welding dissimilar metals.

[0003] Due to the significant differences in chemical composition, microstructure and thermophysical properties between 9Cr heat-resistant steel and austenitic stainless steel, carbon migration is prone to occur at the interface of welded joints under high-temperature service conditions. This may be accompanied by the formation of an interfacial martensitic layer and degradation of the properties of the isolation layer metal, thereby affecting the long-term service stability of the joint.

[0004] In existing technologies, nickel-based alloys are commonly used as isolation layer materials to alleviate the problems of welding dissimilar metals. However, in liquid sodium environments, nickel is prone to dissolution and corrosion, limiting its application. Therefore, developing a stainless steel isolation layer welding material suitable for liquid sodium environments, capable of inhibiting carbon migration, and possessing good microstructural stability has significant engineering application value. Summary of the Invention

[0005] The purpose of this invention is to provide a stainless steel isolation layer welding wire, which is suitable for welding joints of dissimilar materials such as 9Cr heat-resistant steel and austenitic stainless steel. Through composition design, a stable austenitic isolation layer structure is formed on the 9Cr heat-resistant steel side, thereby suppressing carbon migration behavior and ensuring that the isolation layer metal has good mechanical properties during high-temperature service.

[0006] The technical solution of the present invention is as follows: The welding wire of the present invention, by weight percentage, has the following chemical composition: C: 0.05-0.15%, Cr: 15.0-16.0%, Ni: 23.0-27.0%, Mo: 3.5-5.5%, Mn: 1.0-2.0%, N: 0.10-0.20%, Si: ≤0.5%, with the balance being Fe, and the total content of other impurities being <0.1%.

[0007] Smelted using a vacuum melting furnace or an electric furnace with ladle refining method, its basic chemical composition by weight percentage is as follows: C: 0.05-0.15%, Cr: 15.0-16.0%, Ni: 23.0-27.0%, Mo: 3.5-5.5%, Mn: 1.0-2.0%, N: 0.10-0.20%, Si: ≤0.5%, with the balance being Fe, and the total content of other impurities <0.1%.

[0008] The chemical composition of impurities in this welding wire contains P ≤ 0.003% (mass fraction) and S ≤ 0.006% (mass fraction).

[0009] The welding wire is a solid wire with a diameter of 1.2 mm. Welding is performed using tungsten inert gas (TIG) welding. The welding current is 140-170 A, the welding voltage is 10-15 V, the welding speed is 0.07-0.12 m / min, the wire feed speed is 0.7-1.2 m / min, and the arc protection uses high-purity argon gas with a purity ≥99.999% and a gas flow rate of 10-20 L / min.

[0010] By weight percentage, the final weld isolation layer metal chemical composition is: C: 0.05-0.15%, Cr: 15.0-16.0%, Ni: 23.0-27.0%, Mo: 3.5-5.5%, Mn: 1.0-2.0%, N: 0.10-0.20%, Si: ≤0.5%, P≤0.003%, S≤0.006%, with the balance being Fe, and the total content of other impurities <0.1%.

[0011] The yield strength R of the isolation layer metal formed after welding under as-welded conditions and tensile conditions at 550 °C. p0.2 ≥300 MPa, tensile strength R m It has an impact strength of ≥450 MPa, an elongation at break of ≥25%, and a room temperature impact performance of KV2 ≥150 J.

[0012] The insulating layer metal is subjected to tempering at 750 °C for 2.5 h and aging at 550 °C for 5000 h. The yield strength R under tensile conditions at 550 °C is... p0.2 ≥300 MPa, tensile strength R m It has an impact strength of ≥450 MPa, an elongation at break of ≥20%, and a room temperature impact performance of KV2 ≥100 J.

[0013] After welding with this welding wire, the formation of the martensite layer at the interface between the insulating metal and the 9Cr heat-resistant steel is effectively suppressed; furthermore, after sequential tempering at 750 °C for 2.5 h and aging at 550 °C for 5000 h, the carbon migration behavior at the interface is inhibited, thereby reducing the amount of martensite near the 9Cr heat-resistant steel side interface.23 The amount of C6 carbide precipitated was significantly reduced.

[0014] The Mo content is adjusted to enhance the high-temperature strength of the isolation layer metal within the 550 ℃ service temperature range, while the C content is adjusted to reduce the carbon chemical potential difference between the isolation layer metal and 9Cr heat-resistant steel. The synergistic effect of Cr and Ni elements ensures the stability of the austenitic structure of the isolation layer under compositional dilution conditions, thereby suppressing carbon migration and reducing the formation of the interfacial martensite layer during high-temperature service. This welding wire is suitable for dissimilar metal welding of steam generators and loop pipelines in liquid sodium-cooled fast reactors, exhibiting good welding process performance and service stability.

[0015] The present invention has the following advantages: 1. The welding wire is made of stainless steel and is suitable for use in liquid sodium environments; 2. By focusing on the control of Mo and C element content and combining it with the synergistic design of Cr and Ni elements, the isolation layer on the 9Cr heat-resistant steel side forms a stable all-austenitic structure, good high-temperature strength and excellent impact toughness. 3. Under high-temperature service conditions, it can reduce the risk of interfacial carbon migration and improve the long-term service stability of the microstructure of dissimilar material welded joints; 4. It has good adaptability to welding processes and is suitable for engineering applications. Attached Figure Description

[0016] Figure 1 This is a schematic diagram showing the position of the isolation layer metal in the dissimilar alloy welded joint of 9Cr heat-resistant steel and austenitic stainless steel under actual working conditions.

[0017] Figure 2 This is a schematic diagram illustrating the preparation of the initial material for the isolation layer metal performance test sample. To facilitate the preparation of the mechanical properties of the weld metal surfacing with the welding wire of this invention, the original material for the mechanical sample was prepared by beveling a hot-rolled Fe-16Cr-25Ni-6Mo-1.5Mn-2Si-0.1C-0.1N austenitic stainless steel base material and a backing plate.

[0018] Figure 3 This diagram illustrates the preparation of a sample of the interface between the isolation layer metal and 9Cr heat-resistant steel. To verify the effect of the welding wire of this invention on inhibiting carbon migration after being deposited on the surface of 9Cr heat-resistant steel, the interface sample shown in the figure was prepared and subsequently subjected to tempering at 750 °C for 2.5 h and aging at 550 °C for 5000 h after welding.

[0019] Figure 4The microstructures of the weld interfaces between the isolation layer metals and 9Cr steel in Examples 1-2 and Comparative Examples 1-3, after sequential tempering at 750°C for 2.5 h and aging at 550°C for 5000 h following welding, are shown. These microstructures were used to observe the presence of martensite layer formation and carbon migration at the interface. Detailed Implementation

[0020] The welding wire of this invention can be prepared using conventional smelting methods in the art, including but not limited to vacuum melting or ladle refining, as long as the final chemical composition meets the scope defined by this invention. The following are preferred embodiments of this invention. The welding wires in the following embodiments and comparative examples are prepared using a process route of vacuum induction furnace smelting-forging-hot rolling-drawing. The alloy raw materials are first melted into steel ingots in a vacuum induction furnace. After melting, the steel ingots are de-scaled and subjected to chemical composition analysis and quality inspection to ensure that their chemical composition and purity meet the design requirements. The qualified steel ingots are heated and forged into square bars, and the surface of the square bars is subjected to necessary grinding and flaw detection. Subsequently, the square bars are heated to the rolling temperature range and hot-rolled multiple times to prepare wire rods. The wire rods are air-cooled and pickled to remove surface oxide scale. After pickling, the wire rods are drawn multiple times combined with intermediate annealing to finally obtain a solid welding wire with a diameter of 1.2 mm. Tungsten inert gas (TIG) welding is used, and the welding method is butt welding. Figure 2 ) and surface fusion welding ( Figure 3 The former is used to analyze the mechanical properties of weld metal, while the latter is used to analyze the inhibitory effect of the isolation layer metal on martensite formation and carbon migration, as shown below. Figure 2 and Figure 3 As shown. The welding parameters are: welding current 170 A, DC positive polarity, welding voltage 14 V, welding speed 0.09 m / min, wire feed speed 0.9 m / min, arc shielding atmosphere argon with purity ≥99.999%, shielding gas flow rate 15 L / min, and interpass temperature 80℃.

[0021] Tensile and impact test specimens of the weld after welding were prepared in accordance with GB / T 25774.1-2010 "Inspection of Welding Materials - Part 1: Preparation and Inspection of Mechanical Properties of Deposited Metals of Steel, Nickel and Nickel Alloys". The tensile test specimen size was M6. 3. Parallel to the weld metal; impact dimensions are 10 mm × 10 mm × 55 mm, with the specimen notch located at the centerline of the weld cross-section. Tensile tests at room temperature and 550 °C were conducted according to GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Tests at room temperature" and GB / T 228.2-2015 "Metallic materials, tensile testing—Part 2: Tests at high temperature," respectively. Impact tests were conducted according to GB / T229–2020 "Metallic materials, Charpy impact test method."

[0022] The analysis of the interfacial martensite layer and carbon migration in the surface fused samples after welding was performed using scanning electron microscopy.

[0023] Example 1: The basic chemical composition (by weight) of the stainless steel isolation layer welding wire for welding dissimilar materials of 9Cr heat-resistant steel and austenitic stainless steel is as follows: C: 0.08%, Cr: 16.0%, Ni: 25.5%, Mo: 4.3%, Mn: 1.5%, N: 0.16%, Si: ≤0.5%, P≤0.003%, S≤0.006%, with the remainder being Fe and unavoidable impurities (including H, O, B, Cu, W, Al, V, Co, Nb, Zr, and Ti, etc.).

[0024] Example 2: The basic chemical composition (by weight) of the stainless steel isolation layer welding wire for welding dissimilar materials of 9Cr heat-resistant steel and austenitic stainless steel is as follows: C: 0.066%, Cr: 16.0%, Ni: 25.4%, Mo: 4.3%, Mn: 1.5%, N: 0.17%, Si: ≤0.5%, P≤0.003%, S≤0.006%, with the remainder being Fe and unavoidable impurities (including H, O, B, Cu, W, Al, V, Co, Nb, Zr, and Ti, etc.).

[0025] Comparative Example 1: The basic chemical composition of the welding wire (by weight) is as follows: C: 0.092%, Cr: 15.8%, Ni: 25.5%, Mo: 6.3%, Mn: 1.5%, N: 0.18%, Si: ≤0.5%, P≤0.003%, S≤0.006%, with the remainder being Fe and unavoidable impurities (including H, O, B, Cu, W, Al, V, Co, Nb, Zr, and Ti, etc.).

[0026] Comparative Example 2: The basic chemical composition of the welding wire (by weight) is as follows: C: 0.084%, Cr: 15.8%, Ni: 25.4%, Mo: 2.3%, Mn: 1.5%, N: 0.16%, Si: ≤0.5%, P≤0.003%, S≤0.006%, with the remainder being Fe and unavoidable impurities (including H, O, B, Cu, W, Al, V, Co, Nb, Zr, and Ti, etc.).

[0027] Comparative Example 3: The basic chemical composition of the welding wire (by weight) is as follows: C: 0.042%, Cr: 15.9%, Ni: 25.4%, Mo: 4.3%, Mn: 1.5%, N: 0.18%, Si: ≤0.5%, P≤0.003%, S≤0.006%, with the remainder being Fe and unavoidable impurities (including H, O, B, Cu, W, Al, V, Co, Nb, Zr, and Ti, etc.).

[0028] The composition design of the welding wire of this invention aims to "inhibit carbon migration, ensure the stability of the all-austenitic microstructure of the isolation layer, and take into account the service strength and toughness at 550℃". The functions of each alloying element are as follows: Carbon is used to regulate the carbon chemical potential difference between the isolation layer metal and 9Cr heat-resistant steel, thereby reducing the driving force of carbon migration at the interface. At the same time, an appropriate amount of carbon can improve the strength of the isolation layer metal through the effects of precipitated phases and solid solution strengthening. However, too low a carbon content will lead to insufficient high-temperature strength of the isolation layer metal and a decrease in its ability to inhibit carbon migration.

[0029] Mo is a key strengthening element used to improve the high-temperature strength of the isolation layer metal in the service temperature range of 550 °C and enhance its microstructure stability under long-term service conditions; however, when the Mo content is too high, it may lead to a decrease in the impact toughness of the isolation layer metal after long-term aging.

[0030] Cr and Ni elements work together to stabilize the austenitic structure and regulate the Cr and Ni equivalents, so that the isolation layer maintains a fully austenitic structure even under the dilution of the 9Cr side composition, thereby reducing the risk of interfacial martensite layer formation.

[0031] Mn and N elements are used to improve the stability of austenite and enhance the solid solution strengthening effect.

[0032] The Si content is controlled at a low level to reduce inclusions and oxidation tendency, thereby improving weld purity and weld formation quality.

[0033] The tensile properties at 550 ℃ and the room temperature impact properties of the welded isolation layer metal are shown in Table 1 and Table 2, respectively. After tempering at 750 ℃ ​​for 2.5 h, the welded isolation layer metal was then aged at 550 ℃ for 5000 h. The tensile properties at 550 ℃ and the room temperature impact properties are shown in Table 3 and Table 4, respectively.

[0034] The present invention provides a method for using stainless steel isolation layer welding wire for dissimilar welding of 9Cr heat-resistant steel and austenitic stainless steel, comprising the following steps: Specific operation method for welding the isolation layer metal: First, using TIG welding, the welding wires of Examples 1-2 and Comparative Examples 1-3 are deposited onto the bevel surface of the 9Cr heat-resistant steel. The total deposit thickness is >5mm (3mm in this case). The welding current is 170A, the welding voltage is 14V, the welding speed is 0.09 m / min, the shielding gas is 99.99% argon, the gas flow rate is 15 L / min, and the interpass temperature is <100℃ (80℃ in this case). After deposition, the isolation layer metal is tempered at 750℃ for 2.5 h along with the heat-affected zone of the 9Cr heat-resistant steel to eliminate heat-affected zone hardening. Then, the surface of the isolation layer metal is re-beveled. Subsequently, austenitic stainless steel welding wire is used to complete the welding of the isolation layer metal to the austenitic stainless steel base material, with welding parameters identical to the isolation layer welding process. No post-weld heat treatment is required after welding. Figure 1 This is a schematic diagram showing the position of the isolation layer metal in the dissimilar alloy welded joint of 9Cr heat-resistant steel and austenitic stainless steel under actual working conditions.

[0035] Figure 2 This is a schematic diagram of the preparation of the initial material for the isolation layer metal performance test sample. In order to facilitate the preparation of the mechanical properties of the welding wire surfacing metal of this invention, the original material of the mechanical sample is prepared by beveling hot-rolled Fe-16Cr-25Ni-6Mo-1.5Mn-2Si-0.1C-0.1N austenitic stainless steel base material and the same base material of the backing plate.

[0036] Table 1. Tensile properties of the weld-fit isolation layer metals in the examples and comparative examples at 550 °C.

[0037] Table 2. Room temperature impact performance test results of the welded isolation layer metals in the examples and comparative examples.

[0038] Table 3. Tensile properties at 550 °C after sequential tempering at 750 °C for 2.5 h and aging at 550 °C for 5000 h for the isolation layer metals of the examples and comparative examples.

[0039] Table 4. Room temperature impact performance test results of the isolation layer metals in the examples and comparative examples after being tempered at 750 °C for 2.5 h and aged at 550 °C for 5000 h respectively.

[0040] Figure 4The microstructures of the weld interfaces between the isolation layer metal and 9Cr steel in Examples 1-2 and Comparative Examples 1-3 after sequential tempering at 750 °C for 2.5 h and aging at 550 °C for 5000 h are shown in the figures. As can be seen from the figures, no obvious martensite layer formed at the interface in any of the samples. However, due to the weak ability of Comparative Examples 1 and 3 to suppress carbon migration during aging, martensite formed near the 9Cr heat-resistant steel side interface. 23 There were significantly more C6 carbides.

[0041] Table 5 Welding test conditions

[0042] The performance design requirements for the isolation layer metal in this invention are: The weld-bonded isolation layer metal has a tensile property of yield strength R at 550 ℃. p0.2 >300MPa, tensile strength R m ≥450MPa, elongation after fracture A≥25%, room temperature impact resistance KV2≥150 J; after the welded isolation layer metal is tempered at 750 ℃ ​​for 2.5 h, and then aged at 550 ℃ for 5000 h, its tensile properties at 550 ℃ are: yield strength R p0.2 ≥300MPa, tensile strength R m ≥450MPa, elongation after fracture A≥20%, room temperature impact performance KV2≥100J.

[0043] From Examples 1-2, Comparative Examples 1-3, Tables 1-4 and Figure 4 It can be seen that: The chemical composition of the welding wire designed using this invention, as shown in Examples 1-2, is within the range defined by the technical solution of this invention. The isolation layer metal formed therefrom, in the as-welded state and after sequential tempering at 750 °C for 2.5 h and aging at 550 °C for 5000 h, exhibits strength, plasticity, and impact toughness that meet the comprehensive performance design requirements of this invention. Simultaneously, the weld interface sample between the isolation layer metal and 9Cr heat-resistant steel, after tempering and aging at 550 °C for 5000 h, demonstrates good carbon migration inhibition ability.

[0044] In Comparative Example 1, the Mo content of the welding wire was 6.3%, exceeding the Mo content range (3.5-5.5%) specified in this invention. Excessive Mo content resulted in a significant decrease in the impact toughness and elongation after fracture of the tempered isolation layer metal after aging at 550 °C for 5000 h, failing to meet the performance design requirements of this invention. Simultaneously, the increased Mo content lowered the carbon chemical potential on the isolation layer metal side, enhancing the driving force for carbon migration towards the interface on the 9Cr heat-resistant steel side, thereby forming more Mo near the interface on the 9Cr heat-resistant steel side. 23 C6 carbides.

[0045] In Comparative Example 2, the Mo content of the welding wire was 2.3%, which is lower than the Mo content range (3.5-5.5%) specified in this invention. Due to the insufficient Mo content, the strength of the resulting isolation layer metal under tensile conditions at 550 °C in the weld state was insufficient; furthermore, even after being tempered at 750 °C for 2.5 h and then further aged at 550 °C for 5000 h, its elongation after fracture under tensile conditions at 550 °C still failed to meet the performance design requirements of this invention.

[0046] In Comparative Example 3, the carbon content of the welding wire was 0.042%, which is lower than the carbon content range (0.05-0.15%) specified in this invention. Due to the excessively low carbon content, the strength of the resulting isolation layer metal under tensile conditions at 550 °C was insufficient in the as-welded state and after sequential tempering at 750 °C for 2.5 h followed by aging at 550 °C for 5000 h, making it difficult to meet the performance design requirements of this invention. Simultaneously, the reduced carbon content lowers the carbon chemical potential on the isolation layer metal side, thereby increasing the driving force for carbon migration to the interface from the 9Cr heat-resistant steel side. Therefore, after further aging at 550 °C for 5000 h on the tempered interface sample, more methyl groups (M) tend to precipitate and accumulate near the interface on the 9Cr heat-resistant steel side. 23 C6 carbides.

Claims

1. A stainless steel isolation layer welding wire for welding dissimilar materials of 9Cr heat-resistant steel and austenitic stainless steel, characterized in that, The chemical composition of this welding wire, by weight percentage, is as follows: C: 0.05-0.15%, Cr: 15.0-16.0%, Ni: 23.0-27.0%, Mo: 3.5-5.5%, Mn: 1.0-2.0%, N: 0.10-0.20%, Si: ≤0.5%, with the balance being Fe and unavoidable impurities.

2. The welding wire according to claim 1, characterized in that, Its chemical composition by weight percentage includes: C: 0.06-0.08%, Cr: 15.8-16.0%, Ni: 25.0-25.8%, Mo: 4.0-4.5%, Mn: 1.3-1.8%, N: 0.15-0.18%, Si: ≤0.5%, with the balance being Fe and unavoidable impurities.

3. An application of the welding wire according to claim 1 or 2, characterized in that, This welding wire is used in dissimilar welding joints of 9Cr heat-resistant steel and austenitic stainless steel. The welding wire is used for pre-surfacing welding on the bevel surface of the 9Cr heat-resistant steel base material. Then, the 9Cr steel with the weld overlay isolation layer metal is subjected to tempering treatment at 750℃ for 2.5 h to soften the heat-affected zone of the 9Cr heat-resistant steel. Subsequently, the isolation layer metal is beveled again, and finally, the welding of the isolation layer metal and austenitic stainless steel is completed by using austenitic stainless steel welding wire (austenitic stainless steel weld metal).

4. The application according to claim 3, characterized in that, The 9Cr heat-resistant steel base material has a V-shaped bevel with an angle of 20°-35° to the vertical plane. The isolation layer metal is a transition metal between the 9Cr heat-resistant steel and the austenitic weld metal, used to reduce carbon migration at the 9Cr heat-resistant steel side interface of the welded joint and inhibit the formation of the martensite layer. The isolation layer metal thickness is >5mm.

5. The application according to claim 3, characterized in that, The welding wire is a solid welding wire with a diameter of 1.2 mm.

6. The application according to claim 3, 4, or 5, characterized in that, The welding process is as follows: a solid welding wire with a diameter of 1.2 mm is used, and tungsten inert gas (TIG) welding is employed. The welding method is deposition welding. The welding parameters are: welding current 140-170 A, DC positive polarity, welding voltage 10-15 V, welding speed 0.07-0.12 m / min, wire feed speed 0.7-1.2 m / min, arc shielding atmosphere is argon with a purity ≥99.999%, shielding gas flow rate is 10-20 L / min, and interpass temperature during welding is <100 ℃.

7. The application according to claims 3 and 6, characterized in that, The yield strength R of the isolation layer metal formed after welding under as-welded conditions and tensile conditions at 550 °C. p0.2 ≥300 MPa, tensile strength R m ≥450 MPa, elongation after fracture A≥25%; and the room temperature impact resistance KV2 of the isolation layer metal under weld conditions is ≥150 J.

8. The application according to claims 3 and 6, characterized in that, The isolation layer metal formed after welding, after being tempered at 750 °C for 2.5 h and aged at 550 °C for 5000 h in the as-welded state, exhibits a yield strength R under tensile conditions at 550 °C. p0.2 ≥300 MPa, tensile strength R m ≥450 MPa, elongation after fracture A≥20%; and the room temperature impact performance KV2≥100 J after the insulating layer metal is successively tempered at 750 ℃ ​​for 2.5 h and aged at 550 ℃ for 5000 h.

9. The application according to claim 3, characterized in that, The insulating layer metal formed after welding can inhibit the formation of martensite at the interface with 9Cr heat-resistant steel. Furthermore, after sequential tempering at 750 °C for 2.5 h and aging at 550 °C for 5000 h, it can inhibit the formation of martensite near the side interface of 9Cr heat-resistant steel. 23 Precipitation of C6 carbides.

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