Ultra-low-carbon high-si austenitic stainless steel welding wire for resisting high-temperature concentrated nitric acid corrosion and application thereof

Abstract

The application belongs to the field of welding materials, and particularly relates to an ultra-low-carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion and application thereof. The chemical composition of the welding wire is as follows (wt.%): C<=0.03%, Mn 0.3%-1.6%, Si 3.5%-4.5%, P<=0.01%, S<=0.01%, Cr 18.5%-20.5%, Ni 14.5%-16.0%, Mo<=1.1%, Nb<=0.15%, N 0.03%-0.12%, Cu<=0.1%, Co<=0.06%, Al<=0.05%, V<=0.05%, and the balance is iron. The welding wire is suitable for welding of austenitic stainless steel parts used in high-temperature concentrated nitric acid environments such as nuclear power or petroleum chemical industry, and the welding process is stable, the spatter is small, and the process performance is good. After welding by using the ultra-low-carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid environments, a weld with excellent mechanical properties can be obtained, the crack sensitivity is low, and the requirements of high-temperature concentrated nitric acid corrosion service environment can be met.

Description

Technical Field

[0001] This invention belongs to the field of welding materials, specifically a high-temperature resistant, high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion and its application. It is suitable for welding structural components used in high-temperature concentrated nitric acid environments in fields such as nuclear power and petrochemicals. Background Technology

[0002] Nuclear energy, as a highly efficient, clean, and economical energy source, has become one of the important development directions in my country's energy sector. However, with the continuous increase in my country's installed capacity, the large amount of spent fuel containing uranium, plutonium, and fission products generated during the operation of nuclear power plants will cause serious harm to the environment and human health if not treated in a timely and effective manner. Spent fuel reprocessing refers to the chemical treatment of nuclear fuel that has been irradiated (i.e., burned) in the reactor to remove fission products and recover unused and newly generated nuclear fuel materials. This reprocessing method can greatly improve the utilization rate of nuclear fuel and optimize the management and disposal of nuclear waste. The melter is one of the key pieces of equipment in the spent fuel reprocessing process. Being exposed to high concentrations and high radioactivity in boiling nitric acid for extended periods places extremely high demands on the mechanical properties and corrosion resistance of the materials. Corrosion-resistant high-Si austenitic stainless steel is key to improving the equipment's resistance to high-temperature concentrated nitric acid corrosion. Compared to the corrosion-resistant high-Si stainless steel base material, the development of its matching welding materials has lagged behind. The weld seam has a rapidly cooled, as-cast structure, which is significantly different from the structure of the base material after deformation and solution treatment. Many problems in engineering components originate from the failure of the weld joint. Welding materials are a crucial factor determining the performance of the weld joint; therefore, developing high-quality matching welding materials is the prerequisite and foundation for the further promotion and application of corrosion-resistant high-Si austenitic stainless steel.

[0003] While possessing good resistance to high-temperature concentrated nitric acid corrosion, weld metal should also exhibit excellent comprehensive mechanical properties and crack resistance. Generally, austenitic stainless steel weld metal containing approximately 4.0~5.0 wt.% Si can improve its resistance to nitric acid corrosion. Chinese patent application (publication number CN102319965A) reports an ultra-low carbon austenitic welding wire material for stainless steel welding, incorporating Cu and rare earth element Re. Cu-containing steel forms a Cu-rich precipitate phase under irradiation, a major mechanism causing embrittlement in nuclear power steel. Theoretically, the addition of rare earth elements can play a role in desulfurization, but they are prone to agglomeration during ingot smelting and fusion welding, forming inclusions, which is detrimental to improving the nitric acid corrosion resistance of the weld metal. Therefore, the content and use of Cu and rare earth element Re in nuclear power steel should be strictly limited. The literature (Yi Xiaoping, Yuan Shiwei; Welding Test and Application of 00Cr14Ni14Si4(C4) Steel, Welding 1997(9):17-20) reported an A012Si austenitic stainless steel welding wire with high weld metal strength and poor plasticity. In addition, the intergranular corrosion test results of the welded joint showed that the annual corrosion rate was as high as 1 mm / a. To improve the mechanical properties of the weld metal, it is advisable to add an appropriate amount of nitrogen element to the welding material and simultaneously control the δ-ferrite content in the weld metal to inhibit the generation of welding hot cracks. At present, there is relatively little research on austenitic stainless steel welding materials for high-temperature concentrated nitric acid corrosion resistance worldwide. Austenitic stainless steel welding materials with excellent mechanical properties, corrosion resistance and crack resistance, and applicable to nuclear power, petrochemical and other fields should be designed for high-temperature concentrated nitric acid corrosion environment. Summary of the Invention

[0004] The purpose of this invention is to provide an ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance and its application. This welding wire has excellent mechanical properties, corrosion resistance and crack resistance, and can be applied to nuclear power, petrochemical and other fields.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A type of ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance has the following chemical composition by weight percentage: C≤0.03%, Mn 0.3%~1.6%, Si 3.5%~4.5%, P≤0.01%, S≤0.01%, Cr18.5%~20.5%, Ni 14.5%~16.0%, Mo≤1.1%, Nb≤0.15%, N 0.03%~0.12%, Cu≤0.1%, Co≤0.06%, Al≤0.05%, V≤0.05%, with the balance being iron.

[0007] The aforementioned high-temperature resistant, high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion has the following elemental composition content: any one or more of the following a~g:

[0008] a. The Cr content in the welding wire is further set to Cr: 18.5%~19.0%, or further set to Cr: 19.0%~19.6%, or further set to Cr: 19.6%~20.5%;

[0009] b. The Si content in the welding wire is further set to Si: 4.0%~4.4%;

[0010] c. The Ni content in the welding wire is further set to Ni: 14.5%~15.0%, or further set to Ni: 15.0%~16.0%;

[0011] d. The nitrogen content in the welding wire is further set to N: 0.03%~0.07%, or further set to N: 0.07%~0.10%, or further set to N: 0.10%~0.12%;

[0012] e. The Mn content in the welding wire is further set to Mn: 0.3%~0.9%, or further set to Mn: 0.9%~1.3%, or further set to Mn: 1.3%~1.6%;

[0013] f. The Nb content in the welding wire is further set to Nb≤0.02%;

[0014] g. The Mo content in the welding wire is further set to Mo≤0.02%.

[0015] The aforementioned high-temperature resistant, high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion has the following elemental composition content as one or more of the following a~f:

[0016] a. The Cu content in the welding wire is further set to Cu≤0.05%, or further set to Cu≤0.02%, or further set to Cu≤0.01%;

[0017] b. The Co content in the welding wire is further set to Co≤0.03%, or Co≤0.02%, or Co≤0.01%;

[0018] c. The Al content in the welding wire is further set to Al ≤ 0.02%, or further set to Al ≤ 0.01%;

[0019] d. The V content in the welding wire is further set to V≤0.02%, or further set to V≤0.01%;

[0020] e. The phosphorus (P) content in the welding wire is further set to P ≤ 0.005%;

[0021] f. The sulfur content in the welding wire is further set to S≤0.003%.

[0022] The application of the ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance is to apply the welding wire to austenitic stainless steel components used in high-temperature concentrated nitric acid environments in the nuclear power or petrochemical industries.

[0023] The application of the ultra-low carbon high Si austenitic stainless steel welding wire for high temperature resistant concentrated nitric acid corrosion is described. The welding process uses TIG welding, the joint type is butt joint, the welding current is 150~200A, the arc voltage is 10~15V, the current type / polarity is DC positive polarity, and the welding speed is 0.05~0.15m / min.

[0024] The application of the ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature resistant concentrated nitric acid corrosion involves welding test pieces using a multi-layer, multi-pass deposition method, with the interpass temperature during the welding process below 100℃.

[0025] The application of the ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance involves selecting a Φ2.0mm welding wire for the welding process.

[0026] In the application of the ultra-low carbon high Si austenitic stainless steel welding wire for high temperature resistance to concentrated nitric acid corrosion, during the welding process, high-purity argon gas with a volume purity ≥99.995% is used for arc protection, with an argon gas flow rate of 12~20L / min.

[0027] The application of the ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance, and the room temperature tensile properties of the weld metal obtained after welding: yield strength R p0.2 ≥210MPa, tensile strength R m ≥530MPa, elongation A≥30%; room temperature impact performance: Akv2≥35J; weld metal microstructure requirements: austenite + δferrite two-phase microstructure, FN value 1~10.

[0028] The application of the ultra-low carbon high Si austenitic stainless steel welding wire for high-temperature resistant concentrated nitric acid corrosion shows that, under simulated medium conditions of 95°C and 6M nitric acid solution, the corrosion rate of the weld metal after immersion until the corrosion rate stabilizes is ≤0.3mm / a.

[0029] The rationale for determining the chemical composition of the ultra-low carbon, high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance in this invention is as follows:

[0030] In high-temperature concentrated nitric acid service environments, the formation and coarsening of carbides within the weld are significant factors contributing to the deterioration of the weld's mechanical properties and corrosion resistance. Reducing the carbon (C) content can significantly decrease the tendency for carbide formation and coarsening. Nitrogen (N) is an austenite-forming element that can inhibit the formation of δ-ferrite. Excessive δ-ferrite is a harmful microstructure, deteriorating the impact toughness and corrosion resistance of austenitic steel weld metal. Nitrogen can also form carbides with v, which helps improve the high-temperature strength and stable microstructure of heat-resistant steel welds. Therefore, in this invention, C ≤ 0.03%; N: 0.03%~0.12%, preferably 0.03%~0.07%, or 0.07%~0.10%, or 0.10%~0.12%.

[0031] The addition amount of silicon (Si) in austenitic stainless steel is typically 0.3% to 0.6%, playing a deoxidizing role during alloy smelting. As a welding material, silicon improves the fluidity of the molten pool; however, excessive silicon content increases the tendency for hot cracking and promotes the formation of harmful phases, deteriorating the mechanical properties of the weld metal. In high-temperature, high-concentration nitric acid service environments, Si is a key element for improving the nitric acid corrosion resistance of austenitic stainless steel; however, increasing the Si content significantly affects weld metal segregation and phase precipitation. Therefore, the Si content in the welding material should be reasonably controlled within a range; in this invention, Si is 3.5% to 4.5%.

[0032] Mn is an austenitizing element. Increasing the Mn content in heat-resistant steel can inhibit the formation of high-temperature δ-ferrite, but it also lowers the Al transformation temperature and reduces the high-temperature stability of the ferrite matrix. When the Mn content is too high, Mn segregation will occur, forming MnS defects and deteriorating performance. A suitable amount of Mn can ensure that the material has high strength while also possessing high low-temperature impact toughness and strong crack resistance. Therefore, Mn is an indispensable alloying element. In this invention, the Mn content is 0.30%~1.6%, preferably 0.3%~0.9%, or 0.9%~1.3%, or 1.3%~1.6%.

[0033] Cr is one of the essential elements for the resistance of austenitic stainless steel to high-temperature oxidation and corrosion. Cr can improve the oxidation resistance and corrosion resistance of the material. Cr is dissolved in the matrix and plays a role in solid solution strengthening. At the same time, it improves the hardenability of heat-resistant steel and reduces the critical cooling rate of heat-resistant steel, allowing it to obtain a full martensitic structure at a lower cooling rate. However, if the Cr content in the steel is too high, it will promote the formation of high-temperature δ-ferrite and cause coarsening of the corresponding carbide precipitates, thus having adverse effects. Therefore, in this invention, the Cr content is 18.5%~20.5%, preferably 18.5%~19.0%, or 19.0%~19.6%, or 19.6%~20.5%.

[0034] Ni is an austenitizing element, similar to Mn. Increasing the Ni content in heat-resistant steel can suppress the formation of high-temperature δ-ferrite, but it also lowers the Al transformation temperature and reduces the high-temperature stability of the ferrite matrix. Increasing Ni content can improve toughness, but it reduces the stability of carbonitrides, accelerates the coarsening of precipitates, reduces tempering resistance (tempering stability, tempering resistance), and leads to deterioration of creep retardation properties. Furthermore, under irradiation, Ni is also an important source of helium formation. Therefore, in this invention, Ni content is 14.5%~16.0%, preferably 14.5%~15.0%, or 15.0%~16.0%.

[0035] Nitrogen (Nb) is a common microalloying element in austenitic stainless steel. It can fix free carbon atoms in the matrix, thereby inhibiting the growth of nitrogen (M). 23 C6 precipitates at grain boundaries and improves resistance to intergranular corrosion. Furthermore, Nb significantly improves high-temperature strength through solid solution strengthening and precipitation strengthening of NbX and Z phases. However, some reports indicate that Nb strongly segregates between dendrites during weld pool solidification and promotes the precipitation of second phases such as Nb(C,N), which negatively impacts impact toughness. Therefore, in this invention, Nb ≤ 0.15%, and preferably Nb ≤ 0.02%.

[0036] Mo is a key element that synergistically enhances the resistance to localized corrosion of austenitic stainless steel with Cr. It is also a substitutional strengthening element, improving high-temperature strength but impairing ductility. In austenitic stainless steel weld metal, Mo segregates in the interdendritic region, promoting the formation of interdendritic precipitates, and exhibits strong interactions with Si. Therefore, the influence of Mo-rich phases should be considered in studies of weld metal microstructure and property stability. Thus, in this invention, Mo ≤ 1.1%, and preferably Mo ≤ 0.02%.

[0037] Under irradiation, Cu forms a Cu-rich precipitate phase, which is a major mechanism causing embrittlement of steel used in nuclear power plants. Therefore, the Cu content should be strictly limited. In this invention, Cu ≤ 0.1%, preferably Cu ≤ 0.05%, or Cu ≤ 0.02%, or Cu ≤ 0.01%.

[0038] Co has a large neutron absorption cross section, which easily causes Co-containing materials to fail under neutron irradiation. Furthermore, the radioactive isotope of Co, 60Co, has a long half-life of 5.26 years, and its impact will increase with the reactor's operating time. This not only introduces radioactivity into reactor equipment and components but also makes pipelines, pumps, valves, and other equipment in the primary coolant system radioactive. This will bring many difficulties to the maintenance of nuclear reactor equipment and components and waste disposal, and may even endanger personal safety. Therefore, the Co content should be strictly limited. In this invention, Co ≤ 0.06%, preferably Co ≤ 0.03%, or Co ≤ 0.02%, or Co ≤ 0.01%.

[0039] Sulfur (S) and phosphorus (P) are harmful impurities in steel, mostly introduced during steelmaking from raw materials, and should be minimized. During welding, inadequate cleaning of the bevel can also increase S content. Excessive P content increases the tendency for cold cracking, while excessive S content increases the tendency for hot cracking. Therefore, the S and P content in the chemical composition of welding wire should be strictly controlled. In this invention, S ≤ 0.01%, preferably S ≤ 0.003%; P ≤ 0.01%, preferably P ≤ 0.005%.

[0040] The present invention has the following advantages and beneficial effects:

[0041] 1. The ultra-low carbon, high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion environments of this invention possesses excellent mechanical properties, resistance to concentrated nitric acid corrosion, and crack resistance, and can be used for welding key structural components in fields such as nuclear power or petrochemicals. The welding wire of this invention contains ≤0.03% C, which inhibits the formation of carbides and the tendency for coarsening in the weld. The addition of 0.03%~0.12% N compensates for the strength decrease caused by the reduced C content and inhibits the formation of δ-ferrite. These two points are crucial for improving the mechanical properties, corrosion resistance, and crack resistance of heat-resistant steel welds.

[0042] 2. In addition to strictly controlling the content of C and Cr in the welding wire composition and proportion, this invention also precisely controls the content of Ni, Mn, Nb, and Mo: by limiting the Ni content in the welding wire to 14.5%~16.0% and the Mn content to 0.3%~1.6%, the δ-ferrite content in the weld metal is controlled to improve the weld metal's resistance to nitric acid corrosion and crack susceptibility. This invention controls the Nb content in the welding wire to ≤0.15% and the Mo content to ≤1.1%, ensuring that the weld metal maintains excellent corrosion resistance while possessing good mechanical properties.

[0043] Furthermore, considering nuclear applications, the welding wire of this invention does not contain Co or Cu, and reduces the generation of the long-lived radioactive isotope 60Co by limiting the content of impurity Co to no more than 0.06%, and suppresses the irradiation embrittlement of the weld metal by limiting the content of impurity Cu to no more than 0.1%.

[0044] 3. This invention provides a solid ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion environments. When welding under inert gas protection, it effectively prevents weld oxidation, reduces inclusions in the weld, and improves weld quality. It also effectively avoids slag contamination and quality degradation of the weld during welding with electrodes or flux-cored wires. Experiments show that when using this stainless steel welding wire in conjunction with the welding process defined in this invention, spatter is minimal, the process is stable, and the process performance is good. Furthermore, it can obtain austenitic weld metal that meets the required mechanical properties, resistance to concentrated nitric acid corrosion, and crack resistance.

[0045] 4. Experiments show that the weld metal of the ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion environment of the present invention meets the following performance requirements: yield strength R p0.2 ≥210MPa, tensile strength R m ≥530MPa, elongation A≥30%; room temperature impact performance requirement: Akv2≥35J; corrosion rate of weld metal after immersion in simulated medium conditions (95℃, 6M nitric acid solution) until the corrosion rate stabilizes ≤0.3mm / a; weld metal microstructure requirement: austenite + δferrite two-phase microstructure, FN value 1~10. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the welding joint type used in this invention.

[0047] Figure 2 The image shows the macroscopic morphology of the weld metal cross-section in Comparative Example 1. The upper right image is a magnified view of a local crack in the left image, and the lower right image is a magnified view of a local crack in the upper right image. Detailed Implementation

[0048] Taking Φ2.0mm welding wire as an example, a multi-layer, multi-pass TIG (manual tungsten inert gas welding) method is used to prepare the weld metal of the Φ2.0mm welding wire. The base material is corrosion-resistant high-Si austenitic stainless steel, and the joint type is a 12mm thick plate butt weld. The welding parameters are: welding current 150A~200A (specifically 180A in this case), arc voltage 10V~15V (specifically 12V~13V in this case), DC positive polarity, welding speed 0.06m / min~0.15m / min (specifically 0.10m / min in this case), arc protection using high-purity argon gas with a volume purity ≥99.995%, and argon gas flow rate 12L / min~20L / min (specifically 15L / min in this case); the interpass temperature during the welding process is below 100℃, and samples are then taken from the weld metal for mechanical property analysis. Of course, the welding process of this invention can be adjusted for different welding wire diameters.

[0049] The chemical composition (weight percentage) of the ultra-low carbon high-Si austenitic stainless steel welding wires of Examples 1-5 and Comparative Examples 1-2 is shown in Table 1.

[0050] Table 1 Chemical composition of welding wire (wt.%)

[0051] chemical composition C Mn Si Cr Ni Mo Nb N Example 1 0.0068 1.47 3.88 18.66 14.7 1.04 0.11 0.047 Example 2 0.0041 1.53 3.85 20.0 16.0 0.31 0.09 0.045 Example 3 0.0066 1.44 4.02 19.90 15.9 0.74 0.11 0.088 Example 4 0.0036 0.49 4.11 19.37 15.7 ＜0.005 ＜0.005 0.12 Example 5 0.0034 0.96 4.12 19.37 15.7 0.01 ＜0.005 0.12 Comparative Example 1 0.0066 1.40 3.90 18.97 18.9 1.02 0.1 0.047 Comparative Example 2 0.0072 1.53 3.88 18.91 16.9 1.03 0.11 0.062 chemical composition P S Cu Co V Al Fe Example 1 ＜0.005 0.0010 ＜0.03 ＜0.03 ＜0.03 ＜0.03 margin Example 2 ＜0.005 0.0044 ＜0.03 ＜0.03 ＜0.03 ＜0.03 margin Example 3 ＜0.005 ＜0.001 ＜0.03 ＜0.03 ＜0.03 0.056 margin Example 4 ＜0.005 ＜0.001 ＜0.03 ＜0.03 ＜0.03 ＜0.03 margin Example 5 ＜0.005 ＜0.001 ＜0.03 ＜0.03 ＜0.03 ＜0.03 margin Comparative Example 1 ＜0.005 ＜0.001 ＜0.03 ＜0.03 ＜0.03 ＜0.03 margin Comparative Example 2 ＜0.005 ＜0.001 ＜0.03 ＜0.03 ＜0.03 0.049 margin

[0052] The results of the room temperature tensile and impact properties of the weld metals of the ultra-low carbon high-Si austenitic stainless steel welding wires of Examples 1-5 and Comparative Examples 1-2 are shown in Table 2.

[0053] Table 2. Results of room temperature tensile and impact properties of weld metal

[0054] <![CDATA[Yield strength Rp 0.2 , MPa]]> Tensile strength Rm, MPa Elongation after fracture A, % <![CDATA[Impact energy A KV2 , J <!-- 5 -->]]> Example 1 449 754 45.8 102 Example 2 493 765 39.3 61 Example 3 476 762 33 45 Example 4 451 717 46.3 84 Example 5 425 700 52.8 62 Comparative Example 1 382 457 6.5 35 Comparative Example 2 405 606 16.2 29

[0055] The tensile properties of the weld metal of ultra-low carbon high-Si austenitic stainless steel welding wires in Examples 1-5 and Comparative Examples 1-2 at 100°C are shown in Table 3.

[0056] Table 3. Tensile properties of weld metal at 100℃

[0057] <![CDATA[Yield strength Rp 0.2 , MPa]]> Tensile strength Rm, MPa Elongation after fracture A, % Example 1 372 652 46.8 Example 2 372 621 39.0 Example 3 366 620 38.3 Example 4 307 577 52.8 Example 5 390 625 40.8 Comparative Example 1 303 370 7.5 Comparative Example 2 308 438 7.5

[0058] The weld metal microstructure and FN value (FN is the δ-ferrite content, and its value represents the volume percentage of δ-ferrite in the weld wire of ultra-low carbon high Si austenitic stainless steel in Examples 1-5 and Comparative Examples 1-2)

[0059] Table 4 Weld microstructure type and FN value

[0060] Organization type FN value Example 1 Austenitic structure + δ-ferrite structure 9.6 Example 2 Austenitic structure + δ-ferrite structure 8.2 Example 3 Austenitic structure + δ-ferrite structure 7.1 Example 4 Austenitic structure + δ-ferrite structure 1.8 Example 5 Austenitic structure + δ-ferrite structure 1.3 Comparative Example 1 All-austenitic structure 0 Comparative Example 2 Austenitic structure + δ-ferrite structure 0.5

[0061] The corrosion properties of the weld metals from the ultra-low carbon high-Si austenitic stainless steel welding wires of Examples 1-5 are shown in Table 5. The corrosion solution was a 6M nitric acid solution. After immersing the weld metal at 95°C for 120 hours, it was removed, cleaned, weighed, and the corrosion rate was calculated.

[0062] Table 5 Corrosion rate of weld metal

[0063]

[0064] The welding test conditions for the above embodiments and comparative examples are shown in Table 6, and the weld joint types used are as follows: Figure 1 As shown, the thickness of the workpiece to be welded is 12mm, the V-groove angle is 45º, and the weld bottom distance is 12mm.

[0065] Table 6 Welding Test Conditions

[0066] Process method Welding wire specifications (mm) Current intensity (A) Arc voltage (V) Types / Polarity of Current Welding speed (m / min) Protective gas and flow rate (L / min) TIG Φ2.0 180 11~13 DCEN 0.1 99.999%Ar，15

[0067] The performance design requirements of this invention for the weld metal of ultra-low carbon high-Si austenitic stainless steel welding wire used in high-temperature concentrated nitric acid corrosive environments are as follows:

[0068] Room temperature tensile property requirements for weld metal: Yield strength R p0.2 ≥210MPa, tensile strength R m≥530MPa, elongation A≥30%; room temperature impact performance requirement: Akv2≥35J; corrosion rate of weld metal after immersion in simulated medium conditions (95℃, 6M nitric acid solution) until the corrosion rate stabilizes ≤0.3mm / a; weld metal microstructure requirement: austenite + δ-ferrite two-phase structure, FN value 1~10. The room temperature tensile performance test standard is GB / T 2652-2008, the high temperature tensile performance test standard is GB / T228.2-2015, the room temperature impact performance test standard is GB / T 2650-2008, and the corrosion performance test standard is JB / T 7901-1999.

[0069] As can be seen from Examples 1-5, Comparative Examples 1-2 and Tables 1-5:

[0070] The chemical composition of the welding wire designed using this invention, as shown in Examples 1-5, is within the scope of the technical solution of this invention, and the weld metal meets the performance design requirements of this invention. In Comparative Examples 1 and 2, the Ni content of the welding wire was 18.9% and 16.9%, respectively, which is outside the scope of the technical solution of this invention (14.5%~16.0%). Increased Ni content leads to a lower δ-ferrite content (see Table 4, FN values ​​are all less than 1.0), increased crack susceptibility, and the appearance of cracks in the weld metal (see Table 4). Figure 2 Therefore, the toughness and ductility of the weld metal were deteriorated, resulting in room temperature elongation of only 6.5% and 16.2%, respectively, and elongation at 100°C of only 7.5%. The room temperature impact energy was 35J and 29J, respectively. It can be seen that the room temperature elongation and impact energy of the weld metal did not meet the design requirements of this invention (room temperature elongation A≥30%; room temperature impact energy Akv2≥35J). As can be seen from Table 5, the corrosion rate of the weld metal of welding wires in Examples 1 to 5 is less than 0.3mm / a, which fully meets the performance design requirements.

[0071] The results show that the welding wire of this invention is suitable for welding austenitic stainless steel components used in high-temperature concentrated nitric acid environments such as nuclear power plants or petrochemical plants. The welding process is stable, with minimal spatter and good process performance. Welding with the ultra-low carbon, high-Si austenitic stainless steel welding wire of this invention in high-temperature concentrated nitric acid corrosion environments yields welds with excellent mechanical properties and low crack sensitivity, meeting the requirements of high-temperature concentrated nitric acid corrosion service environments.

Claims

1. A welding wire for ultra-low carbon, high-Si austenitic stainless steel resistant to high-temperature concentrated nitric acid corrosion, characterized in that, The chemical composition of this welding wire, by weight percentage, is as follows: C≤0.03%, Mn 0.3%~1.6%, Si 3.5%~4.5%, P≤0.01%, S≤0.01%, Cr 18.5%~20.5%, Ni 14.5%~16.0%, Mo≤1.1%, Nb≤0.15%, N 0.03%~0.12%, Cu≤0.1%, Co≤0.06%, Al≤0.05%, V≤0.05%, with the balance being iron; The welding process uses TIG welding, with a butt joint, a welding current of 150~200A, an arc voltage of 10~15V, a current type / polarity of DC positive polarity, and a welding speed of 0.05~0.15m / min. Room temperature tensile properties of the weld metal obtained after welding: yield strength R p0.2 ≥210MPa, tensile strength R m ≥530MPa, elongation A≥30%; room temperature impact performance: Akv2≥35J; weld metal microstructure requirements: austenite + δferrite two-phase microstructure, FN value 1~10; The corrosion rate of the weld metal after immersion in a 6M nitric acid solution at 95℃ until the corrosion rate stabilizes is ≤0.3mm / a.

2. The ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance according to claim 1, characterized in that, The content of each element in the welding wire is one or more of the following a~g conditions: a. The Cr content in the welding wire is further set to Cr: 18.5%~19.0%, or further set to Cr: 19.0%~19.6%, or further set to Cr: 19.6%~20.5%; b. The Si content in the welding wire is further set to Si: 4.0%~4.4%; c. The Ni content in the welding wire is further set to Ni: 14.5%~15.0%, or further set to Ni: 15.0%~16.0%; d. The nitrogen content in the welding wire is further set to N: 0.03%~0.07%, or further set to N: 0.07%~0.10%, or further set to N: 0.10%~0.12%; e. The Mn content in the welding wire is further set to Mn: 0.3%~0.9%, or further set to Mn: 0.9%~1.3%, or further set to Mn: 1.3%~1.6%; f. The Nb content in the welding wire is further set to Nb≤0.02%; g. The Mo content in the welding wire is further set to Mo≤0.02%.

3. The ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance according to claim 1, characterized in that, The content of each element in the welding wire is any one or more of the following conditions a to f: a. The Cu content in the welding wire is further set to Cu≤0.05%, or further set to Cu≤0.02%, or further set to Cu≤0.01%; b. The Co content in the welding wire is further set to Co≤0.03%, or Co≤0.02%, or Co≤0.01%; c. The Al content in the welding wire is further set to Al ≤ 0.02%, or further set to Al ≤ 0.01%; d. The V content in the welding wire is further set to V≤0.02%, or further set to V≤0.01%; e. The phosphorus (P) content in the welding wire is further set to P ≤ 0.005%; f. The sulfur content in the welding wire is further set to S≤0.003%.

4. The application of the ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance as described in any one of claims 1 to 3, characterized in that, This welding wire is used for welding austenitic stainless steel components used in high-temperature concentrated nitric acid environments in the nuclear power or petrochemical industries.

5. The application of the ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance according to claim 4, characterized in that, The specimen was welded using a multi-layer, multi-pass welding method, with the interpass temperature during the welding process being below 100℃.

6. The application of the ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance according to claim 4, characterized in that, Welding wire with a specification of Φ2.0mm was selected for the welding process.

7. The application of the ultra-low carbon high-Si austenitic stainless steel welding wire for high-temperature concentrated nitric acid corrosion resistance according to claim 4, characterized in that, During the welding process, high-purity argon gas with a volume purity of ≥99.995% is used for arc protection, with an argon gas flow rate of 12~20L / min.

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