A type of submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units

Abstract

This invention provides a submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units, comprising the following components: C: 0.08%-0.13%, Mn: 0.40%~0.80%, Si: 0.05%~0.25%, P≤0.005%, S≤0.005% and P+S≤0.008%, Cr: 8.5%~10.5%, Mo: 0.35%~0.60%, Ni: 0.4%~0.6%, W: 1.3%~2.0%, V: 0.15%~0.25%, Nb: 0.02%~0.1%, N: 0.02%~0.06%, with the remainder being Fe and other unavoidable impurities. When used with the matching submerged arc welding flux, it exhibits excellent weldability, with no iron particles protruding or undercut in the weld, and a neat weld toe line. The resulting deposited metal has low crack sensitivity and porosity, and also possesses excellent high-temperature creep performance, good impact toughness, and low temper brittleness.

Description

Technical Field

[0001] This invention belongs to the field of welding materials, and specifically relates to a submerged arc welding wire for T / P 92 steel used in ultra-supercritical thermal power units. Background Technology

[0002] T / P92 steel is a new type of martensitic heat-resistant steel obtained by adding a certain amount of tungsten and appropriately reducing the molybdenum content based on T / P91 steel. T / P92 steel is the most widely used high-temperature and high-pressure component in ultra-supercritical thermal power generating units, such as the main steam pipes. It is also currently the ferritic heat-resistant steel with the highest permissible steam parameters in production worldwide. It is widely used in thick-walled pipes such as main steam pipes and headers in ultra-supercritical units, as well as heating surface pipes such as superheaters and reheaters. Its casting material (C92) is also used to manufacture cylinders and valves. Submerged arc welding is an important welding method for ultra-supercritical boilers, offering high production efficiency and good working conditions. It has significant advantages in large-scale, high-efficiency circumferential weld welding in boiler construction. The comprehensive performance of the submerged arc welding flux often determines the welding efficiency and final weld quality, requiring the flux to possess both good welding process performance and welding metallurgical performance.

[0003] With the rapid development of steelmaking technology, before 2010, the State Grid Corporation of China, the Electric Power Research Institute, and universities took the lead in researching P92 steel welding materials and achieved certain academic results. Subsequently, large domestic welding material manufacturers such as Sichuan Atlantic, Kunshan Jingqun, and Xi'an Metallurgical Group successively carried out corresponding research and development of domestically produced welding materials and promoted the application of domestically produced welding materials. For example: In 2013, Sichuan Atlantic Welding Materials Co., Ltd. disclosed a new type of ultra-supercritical ferritic heat-resistant steel welding electrode (providing a T / P 92 steel hand welding electrode with good welding process performance and mechanical properties, as well as good 100,000-hour creep strength and high-temperature creep performance, but in fact only the core composition was shown and the composition of the deposited metal was not disclosed); In 2015, Kunshan Jingqun took the lead in passing the localization appraisal of T / P 91 and T / P 92 steel welding electrodes; In 2017, Wuhan University disclosed patent number CN1071388876 A "A low-nickel copper-containing T / P 92 steel welding material with high temperature creep resistance" (disclosing a P92 steel electric welding electrode with excellent room temperature mechanical properties and excellent high-temperature creep resistance); In 2023, Sichuan Xiye New Materials Co., Ltd. disclosed "P92 steel submerged arc welding flux" (disclosing a P92 steel submerged arc welding flux with good weldability, which can effectively inhibit welding cracks and porosity, and can also obtain weld metal with good impact toughness).

[0004] However, for a long time, my country has mainly relied on imports for welding materials, especially submerged arc welding materials, for T / P 92 steel. This is because submerged arc welding has a large heat input, and the temper brittleness, crack resistance, low-temperature impact toughness, and impact toughness stability of the welding materials are extremely sensitive to changes in the composition of the welding wire and flux, placing extremely high demands on the welding materials and making development difficult. On the one hand, importing from abroad is time-consuming and costly; secondly, with the deepening of international academic research, in recent years, ASME (American Society of Mechanical Engineers) standards have also made certain limitations and adjustments to the composition and performance indicators of T / P 92 steel and welding materials. Many patented technologies before 2017 are no longer able to meet the current technical requirements for the construction of T / P 92 ultra-supercritical thermal power units; furthermore, to date, it is difficult for existing domestic submerged arc welding technologies to simultaneously achieve optimal welding process performance and mechanical properties. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units. It exhibits excellent welding operability and can stably produce weld metal with superior mechanical and high-temperature properties, making it suitable for the construction of T / P 92 steel ultra-supercritical thermal power units.

[0006] To achieve the above-mentioned technical objectives, the technical solution of the present invention is a submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units, wherein the specific chemical composition of the welding wire is as follows:

[0007] C: 0.08%-0.13%, Mn: 0.40%~0.80%, Si: 0.05%~0.25%, P≤0.005%, S≤0.005% and P+S≤0.008%, Cr: 8.5%~10.5%, Mo: 0.35%~0.60%, Ni: 0.4%~0.6%, W: 1.3%~2.0%, V: 0.15%~0.25%, Nb: 0.02%~0.1%, N: 0.02%~0.06%, with the remainder being Fe and other unavoidable impurities.

[0008] Preferably, by weight percentage, the submerged arc welding wire has Mn+Ni≤1.20% and Sb≤0.003%, Sn≤0.003%, and As≤0.003%.

[0009] Preferably, by weight percentage, the submerged arc welding wire further contains Al: 0.008~0.020%, Ti≤0.005%, and O≤0.005%.

[0010] The main functions of each alloy in this invention are analyzed in detail below:

[0011] Carbon: C is an added component to ensure the room temperature strength, creep rupture strength, and toughness of the weld metal. To improve the hot strength of steel, a stable carbide phase needs to be formed. The creep resistance of the material can be improved through dispersion strengthening. Therefore, to improve hot strength, the carbon content needs to be appropriately increased; adding strong carbide-forming elements such as Nb and V simultaneously is even more effective. When the C content is too low, the weld is prone to forming δ-ferrite, and the number of carbides is small, which is detrimental to creep strength. However, if the C content is too high, it will increase the susceptibility to weld cracking and reduce the plasticity and weldability of the steel. Therefore, the C content in this invention is controlled within the range of 0.08-0.13%.

[0012] Manganese (Mn) is a good deoxidizer and desulfurizer, which can increase the strength and toughness of welds. Its ability to form and stabilize austenitic structures in steel is second only to nickel. Although manganese improves the instantaneous strength of steel at high temperatures, excessive Mn content will significantly reduce the AC1 point (i.e., the heating phase transformation point or lower critical point) of the weld and reduce creep strength, which is detrimental to endurance strength and creep strength. It will also reduce the stability of high-temperature ferrite in the microstructure, cause weld grain embrittlement, and lead to a significant tendency for temper embrittlement. Therefore, the Mn content in this invention is controlled at 0.40~0.80%.

[0013] Nickel: Ni is also an austenite-forming element, which can improve the impact toughness of the weld and inhibit the formation of δ-ferrite in T / P 92 steel welds. However, increasing the Ni content significantly reduces the AC1 point and decreases creep performance. To ensure excellent high-temperature rupture and high-temperature creep performance of the weld, the Ni content of the welding wire in this invention is controlled at 0.4%~0.6%, and the Mn+Ni content is controlled within the range of ≤1.2%.

[0014] Silicon (Si) dissolves in ferrite and austenite, increasing the strength and hardness of steel and improving the oxidation resistance of welds. It is a beneficial element for resisting high-temperature corrosion in heat-resistant steels. However, excessive Si content reduces the weldability of steel, causing spattering, and also reduces the toughness and plasticity of the weld, affecting weld quality. Therefore, the Si content should not be too high. Considering that water glass and silicon deoxidizers in the flux have a certain Si-enhancing effect on the weld, the Si element in this invention is controlled at a low level, with a mass fraction of 0.05-0.25%.

[0015] Phosphorus and sulfur: P and S are impurity elements that readily form low-melting-point compounds during welding, increasing the tendency for hot cracking in the weld joint. P easily forms low-melting-point phosphides in the weld, increasing hot cracking susceptibility, while S is more likely to segregate at grain boundaries, increasing the hot cracking susceptibility of the weld heat-affected zone. Therefore, their levels should be controlled as low as possible. To ensure the safety of the welding material, the mass fractions of P and S in this invention are controlled to be below 0.005%, and the total P+S content is controlled to be below 0.008%.

[0016] Reducing impurities that easily form low-melting-point compounds, such as Sn, Sb, and As, in addition to P and S, also helps to improve the temper embrittlement characteristics and SR crack susceptibility of the weld metal. Therefore, it is preferable to control the Sn, Sb, and As content in the welding wire to be below 0.003%.

[0017] Chromium (Cr): At high temperatures, Cr promotes the formation of a dense passivation film on the metal surface, preventing further oxidation. It improves the oxidation resistance and high-temperature gas corrosion resistance of steel, and enhances the thermal strength of heat-resistant steel. It is the most important element for ensuring resistance to steam oxidation and hot corrosion. However, Cr is a ferrite-forming element; when its content is too high, it will produce δ-ferrite, reducing the impact toughness, high-temperature creep strength, and durability of the weld. In this invention, the Cr content is controlled at 8.5~10.5%.

[0018] Molybdenum (Mo) improves the hardenability of steel, enhances the creep strength of heat-resistant alloys, and improves corrosion resistance. In this invention, the Mo content is controlled at 0.35~0.60%.

[0019] Tungsten: W plays a solid solution strengthening role, which can improve the stability of carbides and increase creep strength. However, excessive W content will lead to the formation of δ-ferrite, which is not conducive to the mechanical properties of the weld. Therefore, the W content in this invention is controlled at 1.3-2.0%.

[0020] Vanadium and niobium: Both V and Nb are strong carbide-forming elements, capable of forming stable second-phase precipitates, refining grains, and improving the high-temperature creep strength of the weld. They are added to ensure room-temperature strength and creep rupture strength. However, excessive V and Nb content can reduce the impact toughness of the weld. Therefore, in this invention, the V content is controlled at 0.15–0.25%, and the Nb content is controlled at 0.02–0.10%.

[0021] Aluminum: A small amount of Al can deoxidize, refine grains, inhibit the aging of steel, and improve low-temperature toughness, oxidation resistance and fatigue strength. However, a high amount of Al will lead to a significant reduction in high-temperature strength and toughness. Therefore, the Al content in this invention is controlled at 0.008~0.020%.

[0022] Titanium: Ti is a strong deoxidizer, but in ultra-supercritical welds, Ti may generate brittle hard phases, leading to age hardening and embrittlement, and reducing weld toughness. Therefore, the Ti content in this invention is controlled at ≤0.005%.

[0023] Nitrogen: N can form fine, dispersed nitride precipitates with Nb and V, significantly improving the high-temperature creep strength of the weld. To ensure the weld's resistance to high-temperature creep, the N content in this invention is controlled at 0.02%-0.06%.

[0024] Oxygen: A low O content is an important guarantee for obtaining a clean weld and good impact toughness. Therefore, the O content of the submerged arc welding wire of this invention is designed to be below 0.005%.

[0025] The above explains the reasons for the compositional limitations of the submerged arc welding wire for T / P 92 steel used in ultra-supercritical thermal power units according to the present invention. The remaining portion consists of iron and unavoidable impurities.

[0026] In addition, the matching submerged arc welding flux used in the T / P 92 steel submerged arc welding wire for ultra-supercritical thermal power units of the present invention also adopts high-purity raw materials with extremely low P, S, Sb, Sn and As content in raw material development and design; to ensure that the obtained deposited metal has low temper brittleness and low crack sensitivity.

[0027] The aforementioned submerged arc welding flux is a submerged arc welding flux for T / P 91 and T / P 92 steels of ultra-supercritical thermal power units developed by the applicant. By weight percentage, the composition of the aforementioned submerged arc welding flux is as follows: fluorite: 36-42%, aluminum fluoride: 3-8%, lanthanum fluoride: 0.6-2.2%, marble: 1-6%, magnesite: 1-3%, α-alumina: 3-8%, bentonite: 1-3%, bauxite: 2-5%, cryolite: 2-8%, fused magnesia: 5-15%, wollastonite: 2-6%, manganese silicon alloy: 6-14%, and silicon-calcium alloy: 1.2-6.8%.

[0028] The beneficial effects of this invention based on its technical solution are:

[0029] This invention provides a submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units. When used in combination with a matching submerged arc welding flux, ① the weld metal has a Mn+Ni content ≤1.2%, which avoids the reduction of the AC1 point and ensures good high-temperature creep performance and high high-temperature endurance strength; ② the content of impurity elements is low, the temper brittleness index X coefficient and J coefficient of the weld metal are low, and the temper brittleness and crack sensitivity of the weld are low; ③ by reasonably adjusting the content of various alloying elements, it has good operability in the welding process when used in combination with the matching flux, so that the weld metal after welding has good mechanical properties (tensile strength after 760℃×4h heat treatment >750MPa, room temperature impact >75J) and excellent high-temperature creep performance (creep strength at 625℃ for 100,000 hours >85MPa).

[0030] This invention relates to submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units. Through precise design and control of chemical element ratios, and strict control and limitation of wire purity and impurity elements, when used in combination with a matching submerged arc welding flux, it exhibits excellent weldability, no iron particle protrusions or undercut in the weld, neat weld toe line, excellent slag removal, and aesthetically pleasing weld formation. The resulting deposited metal has low crack sensitivity and porosity, and possesses excellent high-temperature creep performance, impact toughness, low temper brittleness, and low crack sensitivity, achieving optimal welding process performance and mechanical properties simultaneously. Detailed Implementation

[0031] To better understand the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0032] A submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units, the chemical composition of which is shown in Table 1 by mass fraction, and the specific content of each embodiment is shown in Table 2.

[0033] Table 1. Composition of T / P 92 steel submerged arc welding wire for ultra-supercritical thermal power units

[0034] (by weight %)

[0035]

[0036] Table 2 Examples of Composition of Submerged Arc Welding Wire for T / P 92 Steel (Weight Percentage %)

[0037]

[0038] The submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units is used in combination with the matching submerged arc welding flux. The matching submerged arc welding flux is the submerged arc welding flux for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units developed by the applicant, and its specific composition is shown in Table 3.

[0039] Table 3: Composition of Submerged Arc Welding Flux for T / P 91 and T / P 92 Steel in Ultra-Supercritical Thermal Power Units

[0040] (by weight %)

[0041]

[0042] The test results of the weld metal obtained by welding the T / P 92 steel submerged arc welding wire of the ultra-supercritical thermal power unit with the submerged arc welding flux described in Table 3 are shown in Tables 4, 5 and 6.

[0043] Table 4: Evaluation Table of Welding Process of T / P 92 Steel

[0044]

[0045] Note: ① Weld within the given welding parameter range, visually observe and evaluate the uniformity of weld slag coverage, weld surface condition, and weld formation.

[0046] ② Ensure the slag coverage is complete and uniform; evaluate the slag removal performance according to GB / T25776 Welding Material Welding Process Performance Evaluation Method. Mark welds with easy slag removal, no slag adhering to the weld surface, uniform and delicate weld ripples, and neat weld toe lines with a √. The same applies below.

[0047] Table 5: Chemical composition of weld metal in each embodiment and with matching flux

[0048] (weight percentage wt%)

[0049]

[0050] Table 6: Performance Test Results of Various Examples of Welding of T / P 92 Steel

[0051]

[0052] Note: ① Due to the long time and high cost of high-temperature creep testing, only Example 4 was selected for high-temperature creep testing.

[0053] ②X coefficient = 10P + 5Sb + 4Sn + As × 10 -2 The general boiler industry technical requirement is ≤15ppm, while this invention is <10ppm;

[0054] ③ J coefficient = (Si + Mn) × (P + S) × 10 4 The general boiler industry technical requirement is ≤150%, while this invention is <100%.

[0055] ④ It can be seen that the weld metal obtained by combining the flux of the present invention with T / P 91 and T / P 92 submerged arc welding wires has a low sensitivity to temper embrittlement.

[0056] As can be seen from the above experimental results, the submerged arc welding wire and matching flux of the present invention have excellent welding operability and can produce weld metal with excellent mechanical properties and high-temperature performance, which can be used in the construction of T / P 92 steel ultra-supercritical thermal power units.

[0057] As shown in Table 4, the submerged arc welding wire of this invention, when used in combination with the matching submerged arc welding flux, exhibits excellent weldability, no iron particle protrusions or undercut in the weld, neat weld toe line, excellent slag removal, and aesthetically pleasing weld formation. Tables 5 and 6 show that the submerged arc welding wire of this invention, when used in combination with the matching submerged arc welding flux, results in weld metal with low crack sensitivity and porosity; excellent high-temperature creep performance at 625℃ for 100,000 hours, with its high-temperature creep strength far exceeding the maximum allowable stress value for T / P 92 steel at 625℃ in the ASME standard and the recommended data for the 100,000-hour creep strength of T / P 92 steel at 625℃ in GB standards; low temper brittleness index (X coefficient and J coefficient) in the weld metal, indicating low temper brittleness and crack sensitivity; and after tempering heat treatment at 760℃ for 4 hours, the weld metal exhibits high strength (>750MPa) and excellent impact toughness (>75J). When used with the submerged arc welding flux for T / P91 and T / P92 steels of ultra-supercritical thermal power units developed by the applicant, it can simultaneously achieve optimal welding process performance and mechanical properties.

[0058] The embodiments described above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units, characterized in that, The specific chemical composition of the welding wire, by weight percentage, is as follows: C: 0.08%-0.13%, Mn: 0.40%~0.80%, Si: 0.05%~0.25%, P≤0.005%, S≤0.005% and P+S≤0.008%, Cr: 8.5%~10.5%, Mo: 0.35%~0.60%, Ni: 0.4%~0.6%, W: 1.3%~2.0%, V: 0.15%~0.25%, Nb: 0.02%~0.10%, N: 0.02%~0.06%, with the remainder being Fe and other unavoidable impurities.

2. The submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units according to claim 1, characterized in that, By weight percentage, the submerged arc welding wire contains Mn+Ni≤1.20% and Sb≤0.003%, Sn≤0.003%, and As≤0.003%.

3. The submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units according to claim 1 or 2, characterized in that, By weight percentage, the submerged arc welding wire also contains Al: 0.008~0.020%, Ti≤0.005%, and O≤0.005%.

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