Submerged-arc welding agent for T / P91 and T / P92 steel of ultra-supercritical thermal power generating unit and preparation method of submerged-arc welding agent

Abstract

The invention provides a submerged-arc welding flux for T / P 91 and T / P 92 steel of an ultra-supercritical thermal power generating unit. The submerged-arc welding flux comprises the following components: 36-42% of fluorite, 3-8% of aluminum fluoride, 0.6-2.2% of lanthanum fluoride, 1-6% of marble, 1-3% of magnesite, 3-8% of alpha-type aluminum oxide, 1-3% of bentonite, 2-5% of bauxite, 2-8% of cryolite, 5-15% of fused magnesite, 2-6% of wollastonite, 6-14% of manganese-silicon alloy and 1.2-2.8% of silicon-calcium alloy. When the submerged-arc welding flux is matched with T / P91 and T / P92 steel submerged-arc welding wires, the welding weldability is excellent, no iron particle bulge or undercut exists in a welding seam, a weld toe line is neat, deslagging is excellent, and the welding seam is attractive in forming. The obtained deposited metal is low in crack sensitivity and porosity, excellent in high-temperature creep property, good in impact toughness and low in temper brittleness.

Description

Technical Field

[0002] This invention belongs to the field of welding materials, and specifically relates to a submerged arc welding flux for T / P 91 and T / P 92 steels used in ultra-supercritical thermal power units. Background Technology

[0003] With the rapid development of the national economy and the resulting surge in electricity demand, there is an urgent need to improve the efficiency of power plant construction and operation, reduce costs, and simultaneously protect the environment. Increasing the main steam temperature and reheat steam temperature of thermal power units is the most effective way to improve their thermal efficiency and is also the core research and development direction for thermal power technology in the future. Ultra-supercritical technology is a mature and advanced power generation technology worldwide and a leading direction for power plant construction. It can effectively reduce pollution and save energy, and is also an inevitable path for my country's thermal power industry to achieve low-carbon electricity.

[0004] T / P 91 and T / P 92 steels are new types of fine-grained, toughened ferritic heat-resistant steels. Internationally, research and application of T / P 91 and T / P 92 steels are at the forefront. Well-known international welding material manufacturers such as Manchester, Bio-Rad, Olinkon, Kobe Steel, and Nippon Steel all have mature supporting welding materials and processes. T / P 91 steel and its supporting welding materials are widely used in thermal power plants. T / P 92 steel is the most widely used in high-temperature and high-pressure components such as main steam pipes of ultra-supercritical thermal power generating units, and it is currently the ferritic heat-resistant steel with the highest permissible steam parameters in production worldwide. Submerged arc welding is an important method for welding 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.

[0005] With the rapid development of steelmaking technology, large domestic welding material manufacturers such as Sichuan Atlantic, Kunshan Jingqun, and Xiye have successively carried out corresponding research and development of domestically produced welding materials and achieved certain results. 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); 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). However, for a long time, my country has mainly relied on imports for welding materials, especially submerged arc welding materials, for T / P 91 and T / P 92 steels. This is because submerged arc welding of T / P 91 and T / P 92 steels involves high heat input, and their low-temperature impact toughness and impact toughness stability are extremely sensitive to changes in the composition of the welding wire and flux, placing extremely high demands on welding materials and making development difficult. Importing from abroad is not only time-consuming and costly, but also currently lacks a universal submerged arc welding flux that can be used with submerged arc welding wires for both T / P 91 and T / P 92 steels, making it difficult to simultaneously achieve optimal welding process performance and mechanical properties. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a submerged arc welding flux for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units. This flux can be used in conjunction with submerged arc welding wires for both T / P 91 and T / P 92 steel, exhibiting excellent welding operability and consistently producing weld metal with superior mechanical properties.

[0007] To achieve the above-mentioned technical objectives, the technical solution of the present invention is a submerged arc welding flux for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units, which can be used in combination with submerged arc welding wire for T / P 91 and T / P 92 steel.

[0008] Based on the total weight of the welding flux, the specific composition (wt%) of the 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%, silicon-calcium alloy: 1.2-2.8%;

[0009] Meanwhile, the content of metal fluorides in the submerged arc welding flux, converted to F, is 18-26%;

[0010] All Mg in the submerged arc welding flux must be converted to MgO, all Al to Al2O3, and all Ca to CaO. The total content of Al2O3 and MgO must be 32-48%, and the total content of CaO and MgO must be 28-42%.

[0011] The T / P 91 and T / P 92 steel submerged arc welding wires used in conjunction with the submerged arc welding flux must meet the following requirements: P≤0.005%, S≤0.005% and P+S≤0.008%; Sb≤0.003%, Sn≤0.003% and As≤0.003%.

[0012] The present invention also provides a method for preparing submerged arc welding flux for T / P 91 and T / P 92 steels of ultra-supercritical thermal power units, the preparation method comprising the following steps:

[0013] 1) Weigh and mix the components of the submerged arc welding flux according to their respective weight proportions, and dry mix them evenly; the dry mixing time can be 0.25~0.5h;

[0014] 2) Add 15-28% of the total weight of flux, a lithium-sodium mixed water glass with a modulus of 2.6-31 and a concentration of 40±2Be as a binder to the uniformly mixed powder, stir and mix evenly and granulate;

[0015] 3) After granulation, the flux is produced through a process of low-temperature drying, high-temperature sintering, and sieving. The low-temperature drying conditions are 300-380℃ for 1-2 hours, the high-temperature sintering conditions are 500-650℃ for 1-2 hours, and the flux is sieved through a 10-60 mesh screen to obtain the finished flux.

[0016] Preferably, the amount of lithium silicate water glass added to the binder is 5-8%.

[0017] Regarding the particle size of the flux, if the particle size is too coarse, the reaction will not be sufficient during the welding process, resulting in poor weld bead formation or defects such as cratering and porosity. On the other hand, if the particle size is too fine, recycling will be difficult, leading to increased usage costs. Therefore, in this invention, the particle size should be controlled between 10 and 60 mesh.

[0018] When using the above-mentioned submerged arc welding flux in combination with T / P 91 and T / P 92 submerged arc welding wires to weld T / P 91 and T / P 92 steel, the weld metal can achieve optimal welding process performance and mechanical properties at the same time. It not only has excellent welding process performance, but also excellent high-temperature creep performance, good impact toughness, and low temper brittleness and crack sensitivity.

[0019] The main functions of the submerged arc welding flux of this invention are deoxidation, gas generation, slag formation, and micro-alloying of the weld. This is taken into account the loss of alloying elements during welding and the replenishment of the weld metal alloy after welding with welding wire. In the above-mentioned submerged arc welding flux formulation, the specific roles of the main components in welding are analyzed as follows:

[0020] In this invention, fluoride is mainly composed of fluorite (CaF2), with the addition of aluminum fluoride, lanthanum fluoride, and cryolite. The addition of this multi-component composite fluoride adjusts the melting point, viscosity, and surface tension of the slag, improving its fluidity. It is an important slag-forming agent and a foundation for ensuring good weldability and weld formation. It can also react with SiO2 in the slag, effectively reducing the diffusible hydrogen content in the weld, decreasing porosity, and improving resistance to low-temperature cracking. Simultaneously, it increases the basicity of the slag, having dephosphorizing and desulfurizing effects. The small amount of rare earth elements in lanthanum fluoride further purifies and micro-alloys the weld, reducing weld crack sensitivity and improving the impact toughness of the weld metal. Furthermore, cryolite significantly improves the fluidity of the slag, resulting in a neater weld toe and better weld formation. Cryolite also acts as a strong arc stabilizer, with K... + and Na + The low ionization potential improves arc stability during welding. The flux in this application contains 40-60% fluoride, and the value of the metal fluoride converted to F is 18-26%. When the conversion value of fluoride is lower than 18, the weld has a high diffusible hydrogen content and poor impact toughness. When the conversion value of fluoride is higher than 26, the weld formation deteriorates.

[0021] In this invention, the carbonates are marble and magnesite. The main component of marble is CaCO3, and the main component of magnesite is MgCO3. The main functions of the carbonates are slag formation and gas generation. On the one hand, the CO2 gas produced during the welding process can protect the molten pool and expel air from it. It can also react with hydrogen protons in the molten pool, reducing the O and H content in the weld. On the other hand, it can increase the stirring of the liquid molten pool, which is conducive to a more complete metallurgical reaction and allows the slag to float. In addition, the CaO and MgO produced by its decomposition are alkaline oxides, which can increase the alkalinity of the slag and react with S impurities in the molten pool, further removing S and impurities and improving the impact toughness of the weld metal. However, unlike welding rods, the carbonate content in submerged arc welding flux should not be too high, otherwise the weld will develop indentations or iron particle protrusions due to excessive molten pool activity. The flux design in this application has a marble content of 1-6% and a magnesite content controlled at 1-3%.

[0022] The Al2O3 in this invention is derived from α-alumina, bentonite, bauxite, and cryolite. Al2O3 is an amphoteric oxide and an important slag-forming agent, which improves the fluidity of molten slag and adjusts the weld bead shape. An appropriate proportion of Al2O3 also helps improve slag removal. However, excessive alumina content will lead to an excessively high melting point of the molten slag, causing pitting and convexity on the weld surface, thus resulting in poor weld formation.

[0023] Fused magnesia is composed of MgO, an important slag-forming agent. Compared to sintered magnesia, it has advantages such as ultra-high purity and extreme high-temperature resistance, and extremely low content of harmful elements such as P, Pb, Sb, Sn, As, and S. MgO can adjust the melting point of slag, improve slag fluidity, and has the effect of adjusting weld bead shape. MgO is an alkaline slag-forming agent, which increases the basicity of slag and is beneficial to improving the impact toughness of weld metal. However, its high melting point, in alkaline slag systems, excessive content will increase the solidification temperature of slag, increase slag viscosity, increase the surface tension of molten iron, worsen weld wettability, and cause "slag dust" to adhere to the weld surface, or even cause slag to press against molten iron, forming indentations on the weld surface and affecting weld formation. Therefore, the content of fused magnesia in the flux of this application is controlled at 5-15%.

[0024] Wollastonite, with the chemical formula CaSiO3, is a calcium-based metasilicate mineral. During welding, it decomposes to produce CaO, thereby adjusting the basicity of the slag and improving both welding process performance and weld metal toughness. Furthermore, wollastonite has needle-like and fibrous crystal forms; when used in sintered fluxes, it can increase the strength of the flux particles, thus regulating the flux particle size. In this application, the wollastonite content is controlled at 2-6%.

[0025] The deoxidizer uses high-purity manganese-silicon alloy and silicon-calcium alloy combined with rare earth fluorides. On one hand, it deoxidizes, desulfurizes, and adjusts the viscosity of the slag; on the other hand, it effectively purifies the weld seam and reduces the content of harmful elements such as Pb, Sb, Sn, As, and S, thereby improving the toughness of the weld metal and reducing the tendency for temper embrittlement and reheat cracking. The manganese-silicon alloy content in this application is 6-14%.

[0026] Furthermore, when converting all Mg in the flux to MgO, all Al to Al2O3, and all Ca to CaO, the total content of Al2O3 and MgO must be between 32% and 48%, and the total content of CaO and MgO must be between 28% and 42%. This is a conclusion reached through extensive experimental research in this application. If the proportions are exceeded, the welding performance and mechanical properties cannot be optimized simultaneously.

[0027] The above explains the reasons for the compositional limitations of the submerged arc welding flux used in T / P 91 and T / P 92 steels for ultra-supercritical thermal power units according to this application. The remaining components are iron and unavoidable impurities.

[0028] The submerged arc welding flux binder for ultra-supercritical thermal power units T / P 91 and T / P 92 steel of this invention is a lithium-sodium mixed water glass, with an addition amount of 15-28% of the total weight of the added flux components. The sodium water glass has a modulus of 2.6-3.1 and a concentration of 38-42°Bé, while the lithium silicate water glass contains 1.8-2.8% LiO2. Li acts as an arc stabilizer, making the welding arc more stable and resulting in better weld formation. Furthermore, Li can suppress the moisture absorption of the flux and reduce the hydrogen content in the weld metal, thereby inhibiting the occurrence of low-temperature cracks. Insufficient Li addition will not effectively resist moisture absorption and reduce diffusive hydrogen. However, Li water glass is expensive and has poor viscosity; excessive addition will increase costs and affect flux granulation and formation. Therefore, the addition amount of Li water glass in this application is controlled between 5-8% of the total binder weight.

[0029] In addition, the submerged arc welding flux for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units of the present invention adopts high-purity raw materials with extremely low P, S, Sb, Sn and As content in raw material development and selection; and the submerged arc welding wire for T / P 91 and T / P 92 steel used in conjunction with it must meet the following requirements: P≤0.005%, S≤0.005% and P+S≤0.008%; Sb≤0.003%, Sn≤0.003% and As≤0.003%, to ensure that the obtained deposited metal has low temper brittleness and low crack sensitivity.

[0030] The beneficial effects of this invention based on its technical solution are:

[0031] This invention improves slag fluidity by selecting raw materials, designing and adjusting the formula, controlling the surface tension of slag and molten iron, adjusting slag basicity, controlling slag and molten iron, and adjusting the types and proportions of fluorides, oxides and their deoxidizers; improves weldability, arc stability, slag removal and weld formation by controlling flux basicity, adding raw and auxiliary materials and specific dehydrogenation materials; reduces the water content and diffusible hydrogen content of flux by controlling the purity of flux raw materials, purifying the weld with rare earth elements, and limiting impurities in the matching welding wire; and ensures that the deposited metal has good high-temperature creep performance and low temper brittleness and low crack sensitivity by controlling the purity of flux raw materials, supplementing with rare earth elements to purify the weld, and limiting impurities in the welding wire.

[0032] The submerged arc welding flux for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units of the present invention can be used simultaneously with submerged arc welding wires for both T / P 91 and T / P 92 steel. This flux, when used with T / P 91 and T / P 92 steel submerged arc welding wires, exhibits excellent weldability, with no iron particles protruding or undercut in the weld, neat weld toe lines, excellent slag removal, and aesthetically pleasing weld formation. The resulting deposited metal has low crack sensitivity and porosity, and possesses excellent high-temperature creep resistance, impact toughness, low temper brittleness, and low crack sensitivity. Detailed Implementation

[0033] 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.

[0034] A submerged arc welding flux for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units is an alumina-fluorine-alkali slag system. Based on the total weight of the flux, the flux formulation consists of the following components by weight percentage: 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%.

[0035] The specific composition and content of the submerged arc welding flux used in T / P 91 and T / P 92 steels for ultra-supercritical thermal power units in the embodiments are shown in Table 1 (weight percentage %).

[0036] Table 1: Composition of Submerged Arc Welding Flux for T / P 91 and T / P 92 Steel in Ultra-Supercritical Thermal Power Units

[0037] (by weight %)

[0038]

[0039] The submerged arc welding flux for T / P 91 and T / P 92 steel used in ultra-supercritical thermal power units is used in combination with the matching submerged arc welding wire for T / P 91 and T / P 92 steel used in ultra-supercritical thermal power units. The chemical composition (wt%) of the matching submerged arc welding wire for T / P 91 and T / P 92 steel used in the unit is shown in Tables 2 and 3 below.

[0040] Table 2 Composition of T / P 91 steel submerged arc welding wire for ultra-supercritical thermal power units

[0041]

[0042] Table 3 Composition of T / P 92 steel submerged arc welding wire for ultra-supercritical thermal power units

[0043]

[0044] The submerged arc welding fluxes for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units, as described in each embodiment, were used in conjunction with the submerged arc welding wire for T / P 91 steel in ultra-supercritical thermal power units as described in Table 2. The corresponding results are shown in Tables 4, 5, and 6. The submerged arc welding fluxes for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units, as described in each embodiment, were used in conjunction with the submerged arc welding wire for T / P 92 steel in ultra-supercritical thermal power units as described in Table 3. The corresponding results are shown in Tables 7, 8, and 9.

[0045] Table 4: Evaluation Table of Welding Process of T / P 91 Steel

[0046]

[0047] 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.

[0048] 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.

[0049] Table 5: Specific elemental chemical composition of various T / P 91 steel welding examples

[0050] (weight percentage wt%)

[0051]

[0052] Table 6: Performance Test Results of Various Examples of Welding of T / P 91 Steel

[0053]

[0054] Note: Due to the long time and high cost of high-temperature creep testing, only Example 5 was selected for high-temperature creep testing.

[0055] Table 7: Evaluation Table of Welding Process of T / P 92 Steel

[0056]

[0057] Table 8: Specific elemental chemical composition of various examples of welding of T / P 92 steel

[0058] (weight percentage wt%)

[0059]

[0060] Table 9: Performance Test Results of Various Examples of Welding of T / P 92 Steel

[0061]

[0062] Note: ① Due to the long time and high cost of high-temperature creep testing, only Example 3 was selected for high-temperature creep testing.

[0063] ②X coefficient = 10P + 5Sb + 4Sn + As × 10 -2 The general technical requirement for boilers is ≤15ppm, while the requirement for this invention is <10ppm.

[0064] ③ J coefficient = (Si + Mn) × (P + S) × 10 4 The general technical requirement for boilers is ≤150%, while the requirement for this invention is <100%.

[0065] Therefore, 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.

[0066] The experimental results above show that the submerged arc welding flux of the present invention can be used with both T / P 91 steel and T / P 92 steel submerged arc welding wires. Tables 4 and 7 show that the submerged arc welding flux of the present invention, when used with T / P 91 and T / P 92 steel submerged arc welding wires, exhibits excellent weldability, with no iron particles protruding or undercut in the weld, neat weld toe lines, excellent slag removal, and aesthetically pleasing weld formation. As can be seen from Tables 6 and 9, the diffusible hydrogen content of the weld metal obtained by welding with submerged arc welding flux of the present invention and T / P 91 and T / P 92 steel submerged arc welding wires can meet H4 (i.e., diffusible hydrogen < 4 ml / 100g weld metal), and the crack sensitivity and porosity are low. The high-temperature creep performance at 625℃ for 100,000 hours is excellent, and its high-temperature creep strength is much higher than the maximum allowable stress value of T / P 91 and T / P 92 steel at 625℃ in the ASME standard and the recommended data of GB for the 100,000-hour creep strength of T / P 91 and T / P 92 steel at 625℃. The weld metal has low temper brittleness index X coefficient and J coefficient, and low temper brittleness and crack sensitivity. The weld metal has excellent impact toughness, with room temperature impact toughness of T / P 91 steel weld metal > 115J and room temperature impact toughness of T / P 92 steel weld metal > 75J. The submerged arc welding flux of this invention is a general-purpose submerged arc welding flux that can be used with both T / P 91 and T / P 92 steel submerged arc welding wires, and can simultaneously achieve optimal welding process performance and mechanical properties.

[0067] 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 flux for T / P 91 and T / P 92 steels in ultra-supercritical thermal power units, characterized in that, The submerged arc welding flux for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units can be used in conjunction with submerged arc welding wire for both T / P 91 and T / P 92 steel. Based on the total weight of the welding flux, the composition of the submerged arc welding flux, by weight percentage, 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%, silicon-calcium alloy: 1.2-6.8%; Meanwhile, the content of metal fluorides in the submerged arc welding flux, converted to F, is 18-26%; All Mg in the submerged arc welding flux must be converted to MgO, all Al to Al2O3, and all Ca to CaO. The total content of Al2O3 and MgO must be 32-48%, and the total content of CaO and MgO must be 28-42%.

2. The submerged arc welding flux for T / P 91 and T / P 92 steel in ultra-supercritical thermal power units as described in claim 1, characterized in that, The submerged arc welding wires for T / P 91 steel and T / P 92 steel used in conjunction with the submerged arc welding flux must meet the following requirements: P≤0.005%, S≤0.005% and P+S≤0.008%; Sb≤0.003%, Sn≤0.003% and As≤0.003%.

3. The method for preparing submerged arc welding flux for T / P 91 and T / P 92 steels of ultra-supercritical thermal power units as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: 1) Weigh and mix the components of the submerged arc welding flux according to their respective weight proportions, and dry mix them evenly; 2) Add 15-28% of the total weight of flux, a lithium-sodium mixed water glass with a modulus of 2.6-31 and a concentration of 40±2Be as a binder to the uniformly mixed powder, stir and mix evenly and granulate. 3) After granulation, the flux is produced through a process of low-temperature drying, high-temperature sintering, and sieving. The low-temperature drying conditions are 300-380℃ for 1-2 hours, the high-temperature sintering conditions are 500-650℃ for 1-2 hours, and the flux is sieved through a 10-60 mesh screen to obtain the finished flux.

4. The method for preparing submerged arc welding flux for T / P 91 and T / P 92 steels of ultra-supercritical thermal power units according to claim 3, characterized in that, The amount of lithium silicate water glass in the binder is 5-8%.

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