800MPa-grade high-toughness stainless steel welding rod and preparation method thereof

Abstract

The invention relates to the technical field of welding materials, in particular to an 800MPa-grade high-toughness stainless steel electrode and a preparation method thereof.The 800MPa-grade high-toughness stainless steel electrode comprises a core wire and a coating with specific ingredients, and the core wire is composed of, by mass, less than or equal to 0.05% of C, less than or equal to 0.50% of Si, 2.50%-5.00% of Mn, 16.50%-18.50% of Cr, 8.00%-10.00% of Ni, 3.00%-4.50% of Mo, 0.20%-0.50% of N, less than or equal to 0.010% of S, less than or equal to 0.012% of P and the balance Fe with the total weight of the core wire as the standard. By regulating and controlling the nitrogen content and the equivalent weight of Cr and Ni, an austenite and 3%-10% delta ferrite dual-phase structure is formed, matching of high strength, high plasticity and toughness and high crack resistance is achieved, the tensile strength is larger than or equal to 800 MPa, the ballistic work at the temperature of-20 DEG C is larger than or equal to 80 J, and the low-alloy high-strength steel welding method is suitable for welding of large-rigidity parts of low-alloy high-strength steel.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, and in particular to an 800MPa grade high-strength and high-toughness stainless steel welding electrode and its preparation method. Background Technology

[0002] Low-alloy high-strength steel is widely used in shipbuilding and marine equipment, engineering machinery, pressure vessels, and other fields, and is constantly developing towards higher strength levels and thicker specifications. With increasing strength, the hardenability of this type of steel increases. When using traditional ferritic low-alloy welding materials to weld large, rigid parts of thick-walled components, hydrogen-induced cooling cracks are prone to occur at the joint, adversely affecting structural safety and project progress. Austenitic stainless steel welding materials, due to their face-centered cubic lattice structure, have a stronger ability to adsorb and dissolve hydrogen, inhibiting hydrogen diffusion and accumulation. Combined with the higher plasticity of the weld, this effectively prevents hydrogen-induced cooling cracks. Due to limitations in the strengthening mechanism, the highest tensile strength of the weld metal of pure austenitic stainless steel welding materials currently reaches only about 750 MPa. Although this type of welding material possesses good plasticity and toughness, the joint strength mismatch when welded with higher-strength low-alloy steel is significant, which is detrimental to the joint's load-bearing capacity. Adding Cr and Mo can form more ferrite and obtain a duplex structure to further improve the strength of the weld metal, but this often severely deteriorates the weld's plasticity, toughness, and crack resistance, affecting the structural safety during service.

[0003] Publication No. CN102233489 B Duplex Stainless Steel Welding Electrode and Publication No. CN105537798 ACAP1400 Main Equipment Nuclear Grade Duplex Stainless Steel Welding Electrode, which introduce stainless steel welding electrodes with a tensile strength of up to 800MPa, both adopt a high ferrite content duplex structure technical approach. The weld microstructure contains fewer austenite-forming elements, and the content of nitrogen element, which can inhibit ferrite formation and play a significant strengthening role, does not exceed 0.15%. The ratio of ferrite to austenite is basically 1:1. This technical route is significantly different from the approach of the present invention, which is mainly austenite with only a small amount of ferrite in the duplex structure. Although it can guarantee the strength, the large amount of ferrite has a significant impact on plasticity, toughness, and crack resistance. Theoretically, it is difficult to achieve the plasticity and toughness level of its embodiment, and the crack sensitivity is greater when used for welding thick-walled components with high rigidity, making it difficult to give full play to the advantages of high plasticity, toughness, and high crack resistance of austenitic stainless steel welding materials.

[0004] Therefore, a new welding material is proposed to address the problems of insufficient strength in traditional pure austenitic welding materials and poor ductility and toughness in high-ferritic duplex welding materials. Summary of the Invention

[0005] In view of this, the present invention aims to propose an 800MPa grade high-strength and high-toughness stainless steel welding electrode and its preparation method, which solves the problems of insufficient strength of traditional pure austenitic welding materials and poor plasticity and toughness of high-ferritic duplex welding materials.

[0006] In terms of alloy composition design, this invention uses C, Cr, Ni, N, Mn, and Mo as the main elements, giving full play to the strengthening effect of each element. A higher content of N is added to improve strength and prevent excessive ferrite formation. Through appropriate control of Cr and Ni equivalents, a dual-phase microstructure of austenite + 3%–10% δ-ferrite is obtained. A small amount of δ-ferrite can refine austenite grains and increase the surface area of ​​intergranular layers, further enhancing the strength of the weld metal on the basis of a single-phase austenite microstructure. Simultaneously, ferrite can dissolve more impurity elements such as S and P, preventing their aggregation at grain boundaries and improving the electrode's resistance to hot cracking. When the ferrite content is too high, the microstructure becomes brittle, and the plasticity and toughness of the weld metal are significantly reduced. Furthermore, ferrite acts as a channel for hydrogen diffusion and aggregation, increasing the susceptibility to hydrogen-induced cold cracking. Therefore, this invention controls the ferrite content of the weld metal between 3% and 10%. In terms of electrode coating design, an alkaline low-hydrogen coating is adopted, with a CaO-CaF2-SiO2 alkaline coating slag system as the framework. An appropriate amount of ferroalloy is added to ensure deoxidation and alloying. Titanium dioxide, soda ash, strontium carbonate and other additives are added to improve the pressure coating properties and prevent coating cracking, so that the electrode has good production and welding processability.

[0007] Traditional approaches to stainless steel welding electrodes aiming for 800MPa strength typically employ a balanced duplex microstructure with approximately 50% ferrite and 50% austenite. While this design achieves high strength, it sacrifices ductility, toughness, and crack resistance. Furthermore, the strength relies heavily on alloying (Cr, Mo, etc.) and two-phase strengthening, with very conservative (low) nitrogen (N) content. This invention takes the opposite approach, proposing a non-equilibrium duplex microstructure where austenite is absolutely dominant, retaining only 3%-10% δ-ferrite. This is equivalent to "precise strengthening" on a "flexible austenitic matrix," rather than "toughening" on "brittle ferrite." This design concept is a fundamental innovation. By elevating nitrogen (N) to the core strengthening element and precisely controlling the composition of the weld core, especially ensuring sufficient Mn content to improve nitrogen solubility, a high nitrogen content of 0.20%-0.50% is achieved in the weld metal. Nitrogen can not only directly and significantly improve strength through solid solution strengthening, but also act as a strong austenite stabilizing element, effectively suppressing the formation of excessive δ-ferrite during welding, thereby ensuring the realization of the microstructure design.

[0008] The specific inventive concept is as follows: Based on obtaining a large amount of austenitic phase with good plasticity, toughness, and crack resistance, the Cr and Ni equivalents are controlled with reference to the Schaeffer and Delong binary Cr-Ni phase diagram. This allows the weld microstructure to retain a small amount of δ-ferrite in the austenitic matrix, which improves strength by refining grain size and increasing the surface area of ​​intergranular layers, ultimately resulting in weld metal with excellent comprehensive properties such as strength, plasticity, toughness, and crack resistance. Specifically, the Cr equivalent is controlled by ferrite-forming elements such as Cr, Si, and Mo, while the Ni equivalent is controlled by austenite-forming elements such as Ni, N, C, and Mn. It should be noted that N and C are strong austenite-forming elements; according to the empirical formula of the Delong phase diagram, their contribution to the Ni equivalent is 30 times that of Ni. A small increase in these elements can significantly reduce the ferrite content in the weld and significantly improve strength through solid solution strengthening. This invention ensures good comprehensive properties of the weld metal by maintaining a certain N and C content to improve the strength of the deposited metal and suppress excessive retention of the ferrite phase. This invention retains the good ductility, toughness, and cold crack resistance of pure austenitic welds, and further improves weld strength. The tensile strength of the deposited metal is ≥800MPa, the elongation after fracture is ≥30%, and the impact absorption energy at -20℃ is ≥80J. The weld of this invention contains 3% to 10% δ-ferrite, which can dissolve more impurities such as S and P, disrupt the orientation of austenite dendrites, and effectively inhibit the generation of crystallization hot cracks.

[0009] The technical solution of this invention is implemented as follows:

[0010] One object of the present invention is to disclose an 800MPa grade high-strength and tough stainless steel welding electrode, comprising a welding core and a flux coating on the surface of the welding core, characterized in that, based on the total weight of the welding core, the welding core is composed of the following components in mass percentage: C≤0.05%, Si≤0.50%, Mn: 2.50%~5.00%, Cr: 16.50%~18.50%, Ni: 8.00%~10.00%, Mo: 3.00%~4.50%, N: 0.20%~0.50%, S≤0.010%, P≤0.012%, with the balance being Fe.

[0011] Furthermore, based on the total weight of the dried powder, the powder consists of the following components by mass percentage: marble 38.0%–54.0%, fluorite 21.0%–27.0%, titanium dioxide 1.5%–3.0%, metallic manganese 2.0%–5.0%, chromium powder 6.0%–10.0%, nickel powder 2.0%–4.0%, ferrotitanium 3.0%–8.0%, atomized ferrosilicon 3.0%–8.0%, ferromolybdenum 0.5%–1.0%, soda ash 1.0%–2.0%, strontium carbonate 2.0%–6.0%, and water glass 20.0%–25.0%.

[0012] Furthermore, the water glass is pure sodium water glass with a modulus of 2.8 to 3.0.

[0013] Furthermore, the chemical composition of the weld metal deposited by the welding electrode, by mass percentage, is as follows: C: 0.05%–0.08%, Si ≤ 0.60%, Mn: 2.50%–4.00%, Cr: 18.50%–21.50%, Ni: 9.00%–11.00%, Mo: 3.00%–4.50%, N: 0.20%–0.50%, S ≤ 0.010%, P ≤ 0.015%, with the balance being Fe.

[0014] Furthermore, the microstructure of the weld metal deposited by the welding electrode is austenite as the matrix and contains 3% to 10% δ-ferrite.

[0015] Furthermore, the tensile strength of the weld metal deposited by the welding electrode is ≥800MPa, the elongation after fracture is ≥30%, and the impact absorption energy at -20℃ is ≥80J.

[0016] Furthermore, when the welding electrode is used to weld large rigid joints of low alloy high-strength steel with a yield strength of 800MPa, no cracks are generated in the welded joint under conditions without preheating.

[0017] Another objective of this invention is to disclose a method for preparing an 800MPa-grade high-strength and high-toughness stainless steel welding electrode. This method involves preparing the 800MPa-grade high-strength and high-toughness stainless steel welding electrode as described in any of the above-mentioned methods. The core material is prepared by smelting, forging, wire rod rolling, diameter reduction drawing, and straightening and cutting. The components of the flux coating are mixed evenly, and then water glass binder is added and stirred until homogeneous. The flux coating is then evenly coated onto the core material using a hydraulic welding electrode production equipment. After grinding, low-temperature drying, high-temperature drying at 250℃~280℃ for 1~2 hours, and slow cooling, the finished welding electrode is obtained.

[0018] Furthermore, the welding rods, after being dried at high temperature, are slowly cooled to below 100°C before being removed from the furnace.

[0019] Compared with the prior art, the 800MPa-grade high-strength and high-toughness stainless steel welding electrode and its preparation method of the present invention have the following advantages:

[0020] 1. This invention introduces 3% to 10% δ-ferrite into the austenitic matrix by precisely controlling the nitrogen content (0.20% to 0.50%) and the synergistic effect of Cr and Ni equivalents. This constructs a microstructure design model with high strength, high plasticity and toughness, and high crack resistance as the core, which solves the inherent contradiction of insufficient strength of traditional pure austenitic welding materials and poor plasticity and toughness of high-ferrite duplex welding materials. It achieves excellent comprehensive performance matching with a tensile strength of ≥800MPa, elongation after fracture ≥30%, and impact absorption energy of -20℃ ≥80J.

[0021] 2. This invention, by integrating the service requirements of low-alloy high-strength steel welded joints with the analysis of material strengthening mechanisms, establishes an alloy design criterion dominated by austenite and controlled by a small amount of δ-ferrite. It fully leverages the dual effects of nitrogen element solid solution strengthening and austenite stabilization, and, in conjunction with the CaO-CaF2 low-hydrogen slag refining process, effectively suppresses the generation of hydrogen-induced cooling cracks and crystallization hot cracks, significantly improving the process reliability and structural safety of welding electrodes in the high rigidity parts of thick-walled components under non-preheating welding conditions.

[0022] 3. The welding arc of the electrode of the present invention is stable, with little spatter, beautiful weld formation, good slag removal, and good red-hot electrode during welding, thus exhibiting good welding processability. Detailed Implementation

[0023] To make the technical means and objectives and effects of the present invention easier to understand, the embodiments of the present invention will be described in detail below with reference to specific illustrations.

[0024] It should be noted that all directional and positional terms used in this invention, such as "up," "down," "left," "right," "front," "back," "vertical," "horizontal," "inner," "outer," "top," "lower," "lateral," "longitudinal," and "center," are only used to explain the relative positional relationships and connections between components in a specific state. They are merely for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0025] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0027] Low-alloy steels are generally welded using low-alloy welding materials. Only in highly rigid areas, due to high structural stress, is there a risk of cracking even with traditional low-alloy welding materials employing high preheating, high pass temperatures, and post-weld heating. In such cases, stainless steel welding materials are preferred. This is because austenitic stainless steel welding materials have a face-centered cubic crystal structure, which has a stronger ability to adsorb and dissolve hydrogen, inhibiting hydrogen diffusion and accumulation. Combined with the high plasticity of the weld, this effectively prevents hydrogen-induced cooling cracks.

[0028] This invention provides an 800MPa grade high-strength and high-toughness stainless steel welding electrode, which aims to solve the problems of insufficient strength of existing pure austenitic stainless steel welding electrodes and poor plasticity and toughness of traditional duplex stainless steel welding electrodes. It is particularly suitable for welding high-rigidity parts of low alloy high-strength steel with a yield strength of 800MPa.

[0029] This invention creatively combines the strengthening approach of high-nitrogen austenitic stainless steel with the microstructure control approach of duplex stainless steel. Through a unique technical path of strengthening with austenite as the main component plus a small amount of ferrite plus high nitrogen, a new type of stainless steel welding electrode that can maintain excellent ductility, toughness, crack resistance and processability at a high strength of 800MPa has been successfully developed. This is to further improve the load-bearing capacity of joints in high rigidity parts of thick-walled low-alloy high-strength steel components and ensure the safety of structural service.

[0030] The welding electrode consists of a core and a coating on the outer periphery of the core, with the coating accounting for 30%-45% of the total weight of the electrode.

[0031] Preparation and mechanism of action of welding core: The welding core is smelted in an electric furnace and is made through processes such as billet forging, wire rod rolling, diameter reduction drawing, straightening and cutting.

[0032] Preferably, the welding core is made by electric furnace smelting, billet forging, wire rod rolling, diameter reduction drawing, straightening and cutting; the components are mixed evenly according to the aforementioned coating formula, a binder (water glass) is added and stirred evenly, and then coated evenly on the welding core according to the specified outer diameter using a hydraulic welding electrode production equipment. After grinding out the clamping end and the arc-starting end, it is air-dried at low temperature, and then dried at high temperature in a welding electrode drying oven at 250℃~280℃ for 1.5 hours. After slow cooling to below 100℃, it is removed from the oven, thus obtaining the welding electrode of the present invention.

[0033] Based on the total weight of the weld core, its chemical composition by mass percentage is as follows: C≤0.05%, Si≤0.50%, Mn: 2.50%~5.00%, Cr: 16.50%~18.50%, Ni: 8.00%~10.00%, Mo: 3.00%~4.50%, N: 0.20%~0.50%, S≤0.010%, P≤0.012%, with the balance being Fe. Among them, nitrogen (N), as a strong austenite forming element and solid solution strengthening element, is the key to achieving high strength of 800MPa. Its high content design (0.20%~0.50%) can significantly improve the strength of the weld metal through solid solution strengthening and grain boundary strengthening without significantly impairing plasticity and toughness. At the same time, N works synergistically with C, Mn, and Ni to stabilize the austenite structure and inhibit the formation of excessive δ-ferrite. Cr and Mo, as ferrite-forming elements, work with austenite-forming elements to regulate the Cr and Ni equivalents, ensuring the formation of a dual-phase microstructure in the weld with an austenite matrix and 3%–10% δ-ferrite. This small amount of δ-ferrite refines the grains, disrupts dendrite orientation, effectively suppresses hot crystallization cracking, and improves strength. Mn not only acts as an austenite stabilizing and strengthening element but also combines with S to form MnS, reducing the tendency for hot cracking and significantly increasing the solubility of nitrogen in the steel, providing a foundation for the smelting of high-nitrogen weld cores. C, within a suitable range (≤0.05%), can further strengthen austenite, but excessive content easily forms carbides, thus requiring strict control. S and P are harmful impurities; strictly limiting their content (S≤0.010%, P≤0.012%) ensures weld purity and improves toughness and crack resistance.

[0034] Preparation and Mechanism of Action of the Medicated Coating: Based on the total weight of the dried powder of the medicated coating, the following components were weighed according to the following mass percentages: marble 38.0%–54.0%, fluorite 21.0%–27.0%, titanium dioxide 1.5%–3.0%, metallic manganese 2.0%–5.0%, chromium powder 6.0%–10.0%, nickel powder 2.0%–4.0%, ferrotitanium 3.0%–8.0%, atomized ferrosilicon 3.0%–8.0%, ferromolybdenum 0.5%–1.0%, soda ash 1.0%–2.0%, and strontium carbonate 2.0%–6.0%. After the above dry powders were mixed evenly, pure sodium silicate with a modulus of 2.8–3.0, accounting for 20.0%–25.0% of the total weight of the dried powder of the medicated coating, was added as a binder and stirred evenly to prepare the medicated coating coating. Marble and fluorite constitute a CaO-CaF2 low-hydrogen slag system. This slag system has weak oxidizing properties and high alkalinity, effectively deoxidizing, desulfurizing, and dephosphorizing, reducing inclusions and gas content in the weld, and improving the purity of the deposited metal. Simultaneously, its low-hydrogen characteristic is a fundamental guarantee against hydrogen-induced cooling cracking. Titanium dioxide is used to increase the plasticity of the flux coating and improve its pressure coating performance. Metallic manganese, ferrotitanium, and atomized ferrosilicon act as deoxidizers, combining with oxygen in the flux coating to prevent porosity in the weld and promote the transition of alloying elements. Chromium powder, nickel powder, and ferromolybdenum are used to supplement the weld with Cr, Ni, and Mo elements, ensuring the alloy composition of the deposited metal. Ferrottinium and ferrosilicon also have the effect of refining grains. Soda ash and strontium carbonate are used to improve the pressure coating performance and prevent cracking of the flux coating during manufacturing and drying.

[0035] The stainless steel welding electrode of this invention primarily transfers alloying elements to the weld metal through the core and coating. The coating slag system adopts a CaO-CaF2 low-hydrogen slag system mainly composed of marble and fluorite. This slag system has weak oxidizing properties and a high alloying element transition coefficient, which can refine the weld metal, giving it high comprehensive mechanical properties and good crack resistance. The main roles of the coating and alloying components in the welding electrode of this invention are as follows:

[0036] Marble: Used for slag formation, gas generation, and arc stabilization; increases slag basicity; reduces the content of oxygen, nitrogen, sulfur, phosphorus, and inclusions in the weld metal; and improves the purity of the weld metal. When the marble content in the flux coating is low, the arc blowing force is small; when it is too high, the flux coating melting point is too high, and spatter increases. The amount added in this invention is 38.0%–54.0%.

[0037] Fluorite: Used for slag formation, improving slag fluidity, and enhancing weld bead formation. When the fluorite content in the flux coating is low, weld bead formation is poor and porosity is likely to occur; when the content is too high, arc stability deteriorates, worsening welding process performance. The amount added in this invention is 21.0%–27.0%.

[0038] Titanium dioxide: Used to increase the plasticity of the electrode coating and improve the coating performance of welding electrodes. The amount added in this invention is 1.5%–3.0%.

[0039] Titanium iron: It works synergistically with Si and Mn elements to deoxidize the weld and promote the transition of alloying elements such as Si and Mn, thus refining the grain size. The amount added in this invention is 3.0% to 8.0%.

[0040] Soda ash: Used to improve the coating properties of welding electrodes; excessive addition can cause the coating to absorb moisture. The dosage in this invention is 1.0%–2.0%.

[0041] Strontium carbonate: Used to improve slag properties and prevent flux coating cracking; excessive amounts deteriorate welding processability. The dosage in this invention is 2.0%–6.0%.

[0042] C: An austenite-forming element, it can significantly improve the strength of weld metal. However, high content is detrimental to weldability and toughness, and it easily forms carbides with Cr, reducing the corrosion resistance of the weld. In this invention, the C content in the deposited metal is controlled at 0.05% to 0.08%.

[0043] Si: Primarily used for deoxidation and improving weld fluidity. Adding an appropriate amount of ferrosilicon to the flux coating improves weld spread. High Si content in the weld is detrimental to toughness and easily forms a low-melting-point Ni-Si phase, which is unfavorable for the weld's resistance to hot cracking. In this invention, the Si content in the deposited metal is controlled below 0.6%.

[0044] Mn: A strengthening element and austenite stabilizer, it is also a good deoxidizer and desulfurizer, refining welds. It combines with sulfur to form MnS, inhibiting the formation of low-melting-point FeS eutectic at grain boundaries and reducing the tendency for hot cracking in welds. Furthermore, Mn increases the solubility of nitrogen in stainless steel, facilitating the smelting of nitrogen-containing weld cores. To ensure the addition of nitrogen to the weld, a certain Mn content must be maintained. In this invention, the Mn content of the deposited metal is controlled between 2.50% and 4.00%.

[0045] Cr: A strong ferrite-forming element, it is a fundamental component of the corrosion resistance of stainless steel and can significantly improve weld strength. Low Cr content in the weld metal results in insufficient strength, while excessive Cr content is detrimental to plasticity and toughness. This invention controls the Cr content in the weld metal to 18.50%–21.50% to ensure an appropriate ferrite content.

[0046] Ni: A strong austenite-forming element that can improve the plasticity and toughness of metals. This invention controls the Ni content within the range of 9.00% to 11.00%, and controls the Ni equivalent through synergistic effects with austenite-forming elements such as Mn and N, to ensure a weld metal structure dominated by austenite.

[0047] Mo: Ferrite forming element, which can improve the strength of weld metal and improve pitting corrosion resistance. Adding an appropriate amount of Mo can improve the crack resistance of welding. When there is too much, carbides are easily precipitated at the austenite grain boundaries, which reduces the strength and toughness of the weld. In this invention, the content is controlled at 3.00% to 4.50%.

[0048] Nitrogen (N): A strong austenite-forming element, it can suppress the formation of δ-ferrite in high-temperature regions and significantly improve the strength of the weld metal through solid solution strengthening, grain boundary strengthening, and reduction of austenite stacking fault energy, while having a relatively small impact on ductility and toughness. This invention primarily utilizes nitrogen to achieve higher strength in the weld metal without sacrificing toughness. Excessive nitrogen content makes the core difficult to smelt and easily leads to nitrogen porosity during welding. Experiments have verified that the nitrogen content in the weld metal should be controlled between 0.20% and 0.50%.

[0049] S and P: Impurity elements in welds, which are detrimental to weld performance and crack resistance. Their content should be reduced as much as possible. Considering the manufacturing cost of welding electrodes, the upper limits of S and P content in the deposited metal should be controlled at 0.010% and 0.015%, respectively.

[0050] The deposited metal of this invention has a high alloy content (high Cr, Ni, Mo, N), and the liquid metal has poor fluidity, making it prone to porosity. Designing a coating formula that can effectively form slag, deoxidize, and dehydrogenate (low-hydrogen slag system), and can also smoothly transition high contents of alloying elements such as Cr, Ni, and Mo to the weld, while ensuring arc stability, minimal spatter, and good coating formation, requires extensive experimental exploration and experience accumulation, making it extremely difficult.

[0051] Electrode manufacturing: Using hydraulic electrode production equipment, the flux coating is evenly applied to the core electrode. The clamping end and arc-starting end are ground out. After low-temperature air drying, the electrode is dried at 250℃~280℃ for 1~2 hours in an electrode drying oven. Then, it is slowly cooled to below 100℃ before being removed from the oven to obtain the finished electrode. Preferably, the drying time is 1.5 hours.

[0052] To verify the effectiveness of the present invention, welding electrodes with a diameter of 4.0 mm were prepared using the core material formulation shown in Table 1 and the coating material formulation shown in Table 2 (Examples 1-3), and their performance was tested.

[0053] Table 1 Chemical composition of the solder core in the examples (wt%)

[0054] Table 2. Composition of the drug coating in the examples (wt%)

[0055]

[0056] Table 3 Chemical composition (wt%) of the weld metal deposited by the welding electrode in the examples

[0057]

[0058] Table 4. Test results of hydrogen diffusion and mechanical properties of electrode deposited metal

[0059]

[0060] Using the core material formulations shown in Table 1 and the coating formulations shown in Table 2, φ4.0mm welding electrodes were prepared using existing hydraulic electrode production equipment. Test plates were welded in a flat welding position at a welding current of 120A–140A, a welding speed of 15cm / min–20cm / min, without preheating, and a pass temperature of 80℃–120℃. Samples of the weld metal were taken after welding for chemical composition and mechanical property testing.

[0061] According to the above welding parameters, low alloy high-strength steel with a yield strength of 800MPa (panel thickness 80mm, through-part wall thickness 80mm) was used to conduct a cup-shaped pipe section welding crack test in a high temperature and high humidity environment of 30℃×80%RH to assess the crack condition of the welded joint.

[0062] The cup-shaped pipe section welding crack test was completed using welding electrodes from three different embodiments. No cracks were found during the dissection of the welded joint. The specific results are shown in Table 5.

[0063] Table 5. Test results of weld cracks in cup-shaped pipe sections

[0064]

[0065] Example 1

[0066] A high-strength and high-toughness stainless steel welding electrode of 800MPa grade has the following chemical composition (by mass percentage): C 0.027%, Si 0.30%, Mn 2.77%, Cr 18.32%, Ni 9.92%, Mo 3.10%, N 0.25%, S 0.007%, P 0.008%, with the balance being Fe. The coating composition (by mass percentage) is: marble 38%, fluorite 21%, titanium dioxide 3%, metallic manganese 5%, chromium powder 6%, nickel powder 2%, ferrotitanium 8%, atomized ferrosilicon 8%, ferromolybdenum 1%, soda ash 2%, strontium carbonate 6%, and water glass 20%. After using this core and coating to make a φ4.0mm welding electrode, welding was performed in a flat welding position. The chemical composition (by mass percentage) of the deposited metal was measured as follows: C 0.056%, Si 0.57%, Mn 3.45%, Cr 19.58%, Ni 10.64%, Mo 3.22%, N 0.23%, S 0.006%, P 0.010%, with the balance being Fe. Mechanical property tests showed that its tensile strength was 804 MPa, elongation after fracture was 34.5%, and the impact absorption energy at -20℃ reached 110 J.

[0067] Furthermore, a cup-shaped pipe section welding crack test was conducted on 80mm thick low-alloy high-strength steel with a yield strength of 800MPa under high temperature and high humidity conditions of 30℃×80%RH (without preheating). No cracks were found after joint dissection, and the crack rate was 0%, indicating that the welding electrode of this embodiment has excellent comprehensive performance and excellent crack resistance.

[0068] Example 2

[0069] A high-strength and high-toughness stainless steel welding electrode of 800MPa grade has the following chemical composition (by mass percentage): C 0.046%, Si 0.34%, Mn 4.49%, Cr 16.67%, Ni 9.03%, Mo 3.88%, N 0.45%, S 0.008%, P 0.009%, with the balance being Fe. The coating composition (by mass percentage) is: marble 45%, fluorite 24%, titanium dioxide 1.5%, metallic manganese 4%, chromium powder 8%, nickel powder 3%, ferrotitanium 6%, atomized ferrosilicon 5%, ferromolybdenum 0.5%, soda ash 2%, strontium carbonate 4%, and water glass 23%. After using this core and coating to make a φ4.0mm welding electrode, welding was performed in a flat welding position. The chemical composition (by mass percentage) of the deposited metal was measured as follows: C 0.077%, Si 0.49%, Mn 3.74%, Cr 18.96%, Ni 9.81%, Mo 3.72%, N 0.41%, S 0.005%, P 0.012%, with the balance being Fe. Mechanical property tests showed that its tensile strength was 816MPa, elongation after fracture was 32.5%, and the impact absorption energy at -20℃ reached 108J.

[0070] In the cup-shaped pipe section welding crack test (without preheating) conducted in a high temperature and high humidity environment of 30℃×80%RH, no cracks were found in the joint, and the crack rate was 0%, which further verified the excellent characteristics of the welding electrode of the present invention that can maintain high strength, high toughness and high crack resistance under different formulations.

[0071] Example 3

[0072] A high-strength and high-toughness stainless steel welding electrode of 800MPa grade has the following core chemical composition (by mass percentage): C 0.035%, Si 0.46%, Mn 3.25%, Cr 17.50%, Ni 8.21%, Mo 4.44%, N 0.36%, S 0.008%, P 0.010%, with the balance being Fe. The coating composition (by mass percentage) is: marble 54%, fluorite 27%, titanium dioxide 2%, metallic manganese 2%, chromium powder 10%, nickel powder 4%, ferrotitanium 3%, atomized ferrosilicon 3%, ferromolybdenum 0.5%, soda ash 1%, strontium carbonate 2%, and water glass 25%. After using this core and coating to make a φ4.0mm welding electrode, welding was performed in a flat welding position. The chemical composition (by mass percentage) of the deposited metal was measured as follows: C 0.065%, Si 0.44%, Mn 2.70%, Cr 21.15%, Ni 9.06%, Mo 4.31%, N 0.32%, S 0.007%, P 0.011%, with the balance being Fe. Mechanical property tests showed that its tensile strength reached 820MPa, elongation after fracture was 31.0%, and the impact absorption energy at -20℃ was 89J.

[0073] In a cup-shaped pipe section welding crack test (without preheating) at a high temperature and humidity of 30℃×80%RH, the welded joint of this embodiment still showed no cracks, with a crack rate of 0%. This result indicates that even with significant adjustments to the coating composition, the electrode of this invention can still stably achieve a high strength of 800MPa while maintaining good ductility, toughness, and complete crack resistance.

[0074] In summary, the experimental data from Examples 1 to 3 demonstrate that the 800MPa-grade high-strength and high-toughness stainless steel welding electrode provided by this invention exhibits a tensile strength in its weld metal consistently exceeding 800MPa, an elongation after fracture greater than 30%, and an impact absorption energy at -20℃ far exceeding the design target of 80J. More importantly, in harsh high-temperature and high-humidity environments, no cracks were observed in the joints of all examples during welding without preheating. This fully demonstrates that the welding electrode of this invention not only possesses excellent mechanical properties but also outstanding resistance to cold and hot cracking, excellent welding process performance, and is particularly suitable for efficient and high-quality welding of thick-walled, high-rigidity low-alloy high-strength steel components, exhibiting significant engineering application value.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength and high-toughness stainless steel welding electrode of 800MPa grade, comprising a welding core and a flux coating on the surface of the welding core, characterized in that, Based on the total weight of the welding core, the welding core is composed of the following components by mass percentage: C≤0.05%, Si≤0.50%, Mn: 2.50%~5.00%, Cr: 16.50%~18.50%, Ni: 8.00%~10.00%, Mo: 3.00%~4.50%, N: 0.20%~0.50%, S≤0.010%, P≤0.012%, with the balance being Fe.

2. The 800MPa grade high-strength and high-toughness stainless steel welding electrode according to claim 1, characterized in that, Based on the total weight of the dried powder, the powder consists of the following components by mass percentage: marble 38.0%–54.0%, fluorite 21.0%–27.0%, titanium dioxide 1.5%–3.0%, metallic manganese 2.0%–5.0%, chromium powder 6.0%–10.0%, nickel powder 2.0%–4.0%, ferrotitanium 3.0%–8.0%, atomized ferrosilicon 3.0%–8.0%, ferromolybdenum 0.5%–1.0%, soda ash 1.0%–2.0%, strontium carbonate 2.0%–6.0%, and water glass 20.0%–25.0%.

3. The 800MPa grade high-strength and high-toughness stainless steel welding electrode according to claim 2, characterized in that, The water glass is pure sodium water glass with a modulus of 2.8 to 3.

0.

4. The 800MPa grade high-strength and high-toughness stainless steel welding electrode according to claim 1, characterized in that, The chemical composition of the weld metal deposited by the welding electrode, by mass percentage, is as follows: C: 0.05%–0.08%, Si ≤ 0.60%, Mn: 2.50%–4.00%, Cr: 18.50%–21.50%, Ni: 9.00%–11.00%, Mo: 3.00%–4.50%, N: 0.20%–0.50%, S ≤ 0.010%, P ≤ 0.015%, with the balance being Fe.

5. The 800MPa grade high-strength and high-toughness stainless steel welding electrode according to claim 4, characterized in that, The microstructure of the weld metal deposited by the welding electrode is austenite matrix containing 3% to 10% δ-ferrite.

6. The 800MPa grade high-strength and high-toughness stainless steel welding electrode according to claim 5, characterized in that, The welding electrode has a tensile strength ≥800MPa, an elongation after fracture ≥30%, and an impact absorption energy ≥80J at -20℃.

7. The 800MPa grade high-strength and high-toughness stainless steel welding electrode according to claim 1, characterized in that, When the welding electrode is used to weld large rigid joints of low alloy high-strength steel with a yield strength of 800MPa, no cracks are generated in the welded joint without preheating.

8. A method for preparing 800MPa grade high-strength and high-toughness stainless steel welding electrodes, used to prepare 800MPa grade high-strength and high-toughness stainless steel welding electrodes as described in any one of claims 1-7, characterized in that, The core material is made by smelting, forging, rolling, reducing diameter, drawing, straightening and cutting. The components of the coating are mixed evenly, and then water glass binder is added and stirred evenly. The coating is evenly coated on the core material using a hydraulic electrode production equipment. After grinding, low-temperature drying, high-temperature drying at 250℃~280℃ for 1~2 hours, and slow cooling, the finished electrode is obtained.

9. The method for using 800MPa grade high-strength and high-toughness stainless steel welding electrodes according to claim 1, characterized in that, The welding rods, after being dried at high temperature, are slowly cooled to below 100°C before being removed from the furnace.

Images