Submerged arc welding wire and welding flux for heat-resistant steel of 650 DEG C ultra-supercritical thermal power generating unit

Abstract

The invention discloses a submerged arc welding wire and a welding flux for heat-resistant steel of a 650 DEG C ultra-supercritical thermal power generating unit. A fluorine-alkali type welding flux is matched with the submerged arc welding wire for use. Deposited metal welded by the submerged-arc welding wire welding flux has excellent high-temperature creep resistance and impact toughness. According to the submerged-arc welding wire welding flux, high-quality raw materials are selected, components such as P and S in a welding wire and a welding agent are strictly controlled, a fluorine-alkali type slag system is selected for the welding flux, and the submerged-arc welding wire welding flux has the advantages of excellent welding process performance, stable electric arc, high porosity resistance, excellent slag detachability and attractive formed weld joint. After the deposited metal is subjected to 770 DEG C * 4 h heat treatment, the tensile strength is larger than or equal to 680 MPa, the ductility is larger than or equal to 20%, RT impact is larger than or equal to 54 J, and the performance of the deposited metal is matched with that of G115 base metal.

Description

Technical Field

[0001] The present application belongs to the field of welding materials, and in particular relates to a submerged arc welding wire and flux for heat-resistant steel of a 650°C ultra-supercritical thermal power unit. Background Art

[0002] Today's society is developing rapidly, and the coal-fired power generation industry has become an indispensable part of social development and progress. With the transformation of the global energy structure and the implementation of the national strategies of "carbon neutrality" and "carbon compliance", high-parameter and large-capacity ultra-supercritical thermal power units have become an important development direction for future thermal power units. Against this background, the new martensitic heat-resistant steel G115 invented by the Chinese Academy of Engineering team uses a variety of element composite strengthening theory to effectively improve the thermal strength of the material, making its endurance strength in a 650°C steam environment 1.5 times that of P92, and has better steam corrosion resistance than P92. The excellent performance makes G115 steel to be used in fields such as high-temperature and high-pressure components of ultra-supercritical boilers, and G115 steel plates have been jointly engineered by the Chinese Academy of Engineering and Baosteel. Therefore, the research and development of matching welding materials is particularly important. Due to the differences in welding and steelmaking metallurgical processes, the development of a welding material that matches the performance of G115 puts higher requirements on research and development work. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a submerged arc welding wire and flux for heat-resistant steel of 650℃ ultra-supercritical thermal power unit, which adopts fluorine-alkali type slag system and low P, S submerged arc welding wire. The deposited metal has excellent high-temperature creep resistance and impact toughness. After heat treatment at 770℃×4h, the tensile strength is ≥680MPa, the elongation is ≥20%, and the RT impact is ≥54J, which matches the performance of G115 base material.

[0004] The technical scheme of the present invention is: a heat-resistant steel submerged arc welding wire and flux for 650°C ultra-supercritical thermal power units, wherein the submerged arc welding wire is used in combination with a fluorine-alkali type flux;

[0005] (a) Based on the total weight of the submerged arc welding wire, the components of the submerged arc welding wire are as follows in terms of weight percentage: C: 0.08-0.14%; Si: ≤0.20%; Mn: 0.7-1.0%; P: ≤0.007%; S: ≤0.007%; P+S ≤0.012%; Cr: 8.5-9.5%, Ni ≤0.5%, V: 0.1-0.3%, W: 2.50-2.80%, Co: 2.6-3.0%, N ≤0.05%, Fe: balance;

[0006] The flux adopts a fluorine-alkali slag system. Based on the total weight of the flux, the components of the flux are as follows in weight percentage: fluorite: 30-50%, calcite: 1-10%, cryolite: 1-10%, wollastonite: 5-10%, bauxite: 4-13%, sintered magnesia: 10-20%, ferrosilicon: 4-10%, and ferromanganese: 5-10%.

[0007] The components of the deposited metal of the welding wire include, in weight percentage: C: 0.08-0.12%; Si: ≤0.50%; Mn: 0.7-1.2%; P: ≤0.010%; S: ≤0.010%; Cr: 8.5-9.5%; Ni≤0.5%; V: 0.1-0.3%; W: 2.30-2.80%; Co: 2.5-3.5%; N≤0.05%; Fe: balance.

[0008] Preferably, based on the total weight of the welding wire, the components of the submerged arc welding wire are as follows in weight percentage: C: 0.09-0.12%; Si: ≤0.18%; Mn: 0.78-0.95%; P: ≤0.006%; S: ≤0.005%; P+S≤0.011%; Cr: 8.7-9.3%, Ni≤0.4%, V: 0.20-0.30%, W: 2.55-2.75%, Co: 2.6-2.9%, N≤0.010%, Fe: balance.

[0009] Preferably, based on the total weight of the flux, the components of the flux, calculated by weight percentage, are as follows: fluorite: 41-48%, calcite: 3-8%, cryolite: 3-8%, wollastonite: 5-8%, bauxite: 7-12%, sintered magnesia: 12-17%, ferrosilicon: 5-8%, and ferromanganese: 6-8%.

[0010] Preferably, in terms of weight percentage, the components of the deposited metal after welding with the submerged arc welding wire and flux include: C: 0.085-0.110%; Si: 0.32-0.43%; Mn: 1.00-1.20%; P: ≤0.007%; S: ≤0.004%; Cr: 8.6-9.0%, Ni: 0.28-0.38%, V: 0.18-0.25%, W: 2.51-2.75%, Co: 2.75-3.11%, N≤0.05%, Fe: balance.

[0011] The present invention also provides a method for preparing a submerged arc welding wire and a flux for heat-resistant steel of a 650°C ultra-supercritical thermal power unit, comprising the following steps:

[0012] 1) preparing materials according to the composition and proportion of the welding wire, and manufacturing the submerged arc welding wire through steelmaking, fine drawing, and coiling;

[0013] 2) Mix the components of the flux evenly according to the proportion;

[0014] 3) Add 15-25% of the total weight of the flux component as a binder, stir and mix evenly, and then go through the production process of granulation, low-temperature drying, high-temperature sintering, and screening to complete the flux production.

[0015] Preferably, the flux is formed by low-temperature drying and high-temperature sintering, the low-temperature drying condition is 200-400°C×1-2h, and the high-temperature sintering condition is 550-700°C×1h.

[0016] The submerged arc welding wire in the present invention mainly provides the chemical composition in the deposited metal, and the submerged arc flux mainly functions as gasification, slag formation, deoxidation, transition alloy, etc. Considering the burning of alloy elements during welding and the supplement of flux alloy transition to deposited metal alloy after welding with flux, the metal chemical element components and flux components in the deposited metal after final welding are taken as examples, and the roles played by the main components in welding in the present invention are specifically analyzed as follows:

[0017] C has a strong strengthening effect, but it will significantly reduce the plasticity and toughness of the material. If the C content is too high, the weldability will deteriorate, and the impact toughness will also deteriorate due to the increase in strength. If the C content is too low, the strengthening effect will be reduced, which is not conducive to maintaining the strength of the welding material. Therefore, the C content should be limited to 0.08-0.12%;

[0018] A small amount of Mn can reduce the S content and promote weld deoxidation, but too much Mn will reduce the stability of the high-temperature ferrite of the organization, so its content should be controlled at 0.7-1.2%;

[0019] The core wire of the present invention is added with Si, Cr and Ni for combined effect. Si can promote the formation of Cr oxide film and improve oxidation resistance. When it exists together with Cr, it can also improve the high temperature oxidation resistance of the alloy. At the same time, the addition of Ni can improve the heat resistance of steel and inhibit the formation of high temperature ferrite, thereby increasing the tempering temperature of the heat-resistant steel structure. Therefore, it is generally controlled within Si≤0.5%, Cr: 8.5-9.5%, and Ni≤0.5%.

[0020] P and S will form low melting point eutectic, precipitate at grain boundaries during tempering, and reduce material strength, so their contents need to be strictly controlled, P≤0.010%, S≤0.010% respectively;

[0021] Cr can improve the oxidation resistance and corrosion resistance of heat-resistant steel, improve the high-temperature endurance strength and creep strength of steel, and solid-dissolve in the matrix to play a solid-solution strengthening role. However, too high Cr content will reduce the endurance strength, so it is appropriate to control the Cr content to 8.5-9.5%;

[0022] The Co element can play a role in solid solution strengthening and inhibit the formation of δ-ferrite to prevent performance degradation, so the Co content should be controlled at 2.5-3.5%;

[0023] W can also play a role in solid solution strengthening and can improve creep strength, but excessive W content will lead to the formation of δ-ferrite, which is not conducive to the mechanical properties of the weld, so it is controlled at 2.30-2.80%;

[0024] V is a strong carbide-forming element. Adding an appropriate amount of V to steel can refine the grains, form dispersion strengthening, and significantly improve the strength of the weld. The optimal control of V is 0.10-0.3%. At the same time, adding an appropriate amount of N can form stable nitrides with V, which plays a role of solid solution strengthening in the weld. The combined effect of dispersion strengthening and solid solution strengthening has a better strengthening effect. The addition of N can further improve the creep strength and high-temperature endurance strength of the weld, but too much N content will deteriorate the weldability and impact toughness, so N is controlled within N≤0.05%.

[0025] The fluoride in the present invention is mainly fluorite (CaF2), barium fluoride and zirconium fluoride. The addition of fluoride can increase the basicity of the flux, thereby improving the impact toughness of the weld metal. At the same time, the addition of multiple fluorides can effectively reduce the H content in the weld metal and avoid the occurrence of hydrogen embrittlement problems in the later stage. The content of fluoride in the flux of the present application is 30-50%;

[0026] The main component of calcite is CaCO3, and the main function of calcite is to generate gas and slag. The welding heat causes calcite to decompose and produce CO2 and CO. CO2 can remove the air partial pressure and reduce the O and H content of the weld to protect the weld. At the same time, CaO, as an alkaline oxide, can increase the alkalinity of the slag and further improve the impact toughness of the weld metal. The content of calcite in the flux of the present invention is 1-10%;

[0027] Cryolite: adding potassium cryolite can improve the fluidity of slag, make the edge of the weld straighter, and make the weld better. At the same time, potassium cryolite has a lower ionization potential, which can improve the arc stability during welding. The content of cryolite in the flux of this application is 1-10%;

[0028] Wollastonite, the main component of which is CaSiO3, is a silicate mineral. Adding an appropriate amount of wollastonite to the flux can improve the pH of the flux because it does not produce gas during welding. At the same time, the decomposition product CaO can also increase the alkalinity of the slag, thereby improving impact toughness. At the same time, wollastonite has needle-shaped and fibrous crystal forms. When used in sintered flux, it can increase the strength of the flux particles and avoid the generation of excessive fine powder. The content of cryolite in the flux of this application is 5-10%;

[0029] Bauxite, the main component of which is Al2O3, is mainly used as a deoxidizer. The addition of Al2O3 can replace part of SiO2, thereby ensuring the basicity of the flux and avoiding the reduction of basicity due to excessive addition of SiO2, thereby affecting the impact toughness; the content of bauxite in the flux of this application is 4-13%;

[0030] Sintered magnesia, the main component of which is MgO, is mainly used for slag formation and to increase the slag basicity, thereby increasing the impact toughness of the weld metal. When selecting raw materials, attention should be paid to the ignition loss and particle size of the sintered magnesia. If the particle size is too large or the ignition loss is too small, it will cause segregation and weld pitting. The content of sintered magnesia in the flux of this application is 10-20%;

[0031] The main functions of adding ferrosilicon and ferromanganese are deoxidation, desulfurization, and adjusting the viscosity of the slag to make the weld more beautiful and avoid the appearance of too narrow or too wide welds. At the same time, the S and O content in the weld metal is reduced to avoid the occurrence of thermal cracks and improve the impact toughness of the weld. Therefore, ferrosilicon is controlled at 4-10% and ferromanganese is controlled at 5-10%.

[0032] The above is the reason for limiting the composition of the submerged arc welding wire and flux for heat-resistant steel of a 650°C ultra-supercritical thermal power unit in this application. The remaining part is iron and unavoidable impurities.

[0033] The main component of the deposited metal is provided by the submerged arc welding wire. The submerged arc welding flux is a fluorine-alkali type flux, which can ensure good welding processability while obtaining good mechanical properties.

[0034] The submerged arc welding wire and flux for heat-resistant steel of 650°C ultra-supercritical thermal power unit of the present invention have excellent welding process performance, excellent slag removal performance, strong porosity resistance, and beautiful weld formation. Fluorine-alkali type slag system and low P, S submerged arc welding wire are adopted, and the deposited metal has excellent high-temperature creep resistance and impact toughness. After heat treatment at 770°C × 4h, the tensile strength is ≥660MPa, the elongation is ≥18%, and the RT impact is ≥47J, which matches the performance of G115 parent material. DETAILED DESCRIPTION

[0035] The technical solution of the present application is further described below in conjunction with specific embodiments, but the present application is not limited to these embodiments.

[0036] The present invention is composed of submerged arc welding wire and submerged arc flux. High-quality low P, S submerged arc welding wire is used. The welding wire is smelted according to the chemical composition of the welding wire in Table 1 and is prepared according to the flux formula in Table 2. The deposited metal components are shown in Table 3.

[0037] The welding wire components (weight percentage) are shown in Table 1.

[0038] Table 1: Welding wire composition (weight percentage)

[0039] C Si Mn P S P+S Cr 0.08～0.14 ≤0.20 0.7～1.0 ≤0.007 ≤0.007 ≤0.012 8.5～9.5 Ni V W Co N Fe ≤0.5 0.1～0.3 2.50～2.80 2.6～3.0 ≤0.05 margin

[0040] The components (weight percentage) of fluorine-alkali type low P, S submerged arc welding flux are shown in Table 2.

[0041] Table 2: Flux composition (weight %)

[0042] fluorite Calcite cryolite Wollastonite Bauxite Sintered magnesia Ferrosilicon Ferromanganese 30～50 1～10 1～10 5～10 4～13 10～20 4～10 5～10

[0043] The composition (weight percentage) of the deposited metal after welding with submerged arc welding wire and flux is shown in Table 3.

[0044] Table 3: Deposited metal composition (weight percentage)

[0045] C Si Mn P S Cr 0.08～0.12 ≤0.50 0.7～1.2 ≤0.010 ≤0.010 8.5～9.5 Ni V W Co N Fe ≤0.5 0.1～0.3 2.30～2.80 2.5～3.0 ≤0.05 margin

[0046] Embodiments 1 to 5

[0047] Manufactured according to the common manufacturing process in the submerged arc welding wire flux production industry, the specific composition, deposited metal results and properties of Examples 1 to 5 are shown in Tables 4-1, 4-2, 4-3 and 4-4.

[0048] Table 4-1: Example of Submerged Arc Welding Wire Composition (Weight Percentage %)

[0049]

[0050]

[0051] Table 4-2: Example of Submerged Arc Welding Flux Composition (Weight Percentage %)

[0052] fluorite Calcite cryolite Wollastonite Bauxite Sintered magnesia Ferrosilicon Ferromanganese Example 1 42 7 4 7 10 16 6 8 Example 2 45 8 8 5 7 14 5 8 Example 3 48 5 5 8 10 12 5 7 Example 4 41 3 6 7 12 17 6 6 Example 5 45 3 3 8 10 15 8 8

[0053] Table 4-3: Chemical composition of deposited metal

[0054]

[0055]

[0056] Table 4-4: Mechanical properties

[0057]

[0058] It can be seen from the above experiments that the submerged arc welding wire and flux of the present invention have excellent welding process performance, excellent slag removal, strong porosity resistance, and beautiful weld formation. At the same time, the deposited metal has excellent high temperature creep resistance and excellent impact toughness. After heat treatment at 770℃×4h, the tensile strength is ≥680MPa, the elongation is ≥20%, and the RT impact is ≥54J, which matches the performance of G115 base material.

[0059] Example 6

[0060] The applicant had disclosed the patent CN108213770 "A Metal Powder Core Heat-resistant Steel Submerged Arc Welding Wire and Flux for 650℃ Ultra-supercritical Thermal Power Units" in 2017 and was authorized. The flux of this type of welding wire is a metal powder core, which has excellent yield strength, tensile strength and elongation at temperatures above 700℃, and is suitable for welding steel for 650℃ and 700℃ ultra-supercritical thermal power units. Compared with this type of metal powder core welding wire, the present invention is equipped with a submerged arc solid welding wire. The submerged arc solid welding wire has stronger component stability, better moisture absorption resistance, more stable welding wire melting process during welding, better arc stability, so that better weld formation can be obtained. At the same time, compared with the metal powder core welding wire, which is subject to the steel strip, flux filling ratio and production process, the solid welding wire is easier to process into a small wire diameter welding wire, which can further control the welding heat input, so that the mechanical properties obtained are more excellent and stable.

[0061] The submerged arc solid welding wire of the present invention is smelted in a steel mill. Compared with the mechanical mixing of flux particles of metal powder cored welding wire, the composition of molten iron in steelmaking is more uniform. It has been verified that the chemical composition stability of the head and tail samples of the same furnace number is better. The results are shown in Table 5-1, which shows that the chemical composition of the welding wire of the present invention is very stable and uniform.

[0062] Table 5-1 Test results of chemical composition stability of welding wire head and tail

[0063] C Si Mn P S P+S Cr Head sampling 0.11 0.06 0.92 0.006 0.005 0.011 8.9 Tail sampling 0.11 0.08 0.92 0.006 0.005 0.011 8.8 Ni V W Co N Fe Head sampling 0.34 0.21 2.6 2.9 0.004 margin Tail sampling 0.35 0.21 2.7 2.9 0.003 margin

[0064] Moisture absorption resistance test.

[0065] The diffusible hydrogen content of the deposited metal of the submerged arc solid welding wire and the metal powder cored welding wire was tested before and after standing in humid air for 24 hours, and the results are shown in 5-2. It can be seen that the submerged arc solid welding wire of the present invention has less diffusible hydrogen increase and better moisture absorption resistance.

[0066] Table 5-2 Moisture absorption resistance test results

[0067]

[0068]

[0069] Welding stability test.

[0070] By observing the current and voltage meter during the welding process, it was found that when welding with submerged arc solid wire, the current and voltage meter fluctuated less and the arc was more stable.

[0071] Therefore, the present invention not only has excellent welding process performance, the high temperature creep resistance and excellent impact toughness of the deposited metal can match the performance of the G115 base material, but also has significant improvements and enhancements in quality and performance compared with the corresponding existing technologies already on the market.

[0072] The above-described embodiments are only preferred implementation modes of the present application. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present application, and these modifications and improvements all fall within the protection scope of the present application.

Claims

1. A submerged arc welding wire and flux for heat-resistant steel of 650°C ultra-supercritical thermal power unit, characterized in that: The submerged arc welding wire and flux for heat-resistant steel of 650°C ultra-supercritical thermal power unit are used with fluorine-alkali type flux and submerged arc welding wire; (a) Based on the total weight of the submerged arc welding wire, the components of the submerged arc welding wire are as follows in terms of weight percentage: C: 0.08-0.14%; Si: ≤0.20%; Mn: 0.7-1.0%; P: ≤0.007%; S: ≤0.007%; P+S ≤0.012%; Cr: 8.5-9.5%, Ni ≤0.5%, V: 0.1-0.3%, W: 2.50-2.80%, Co: 2.6-3.0%, N ≤0.05%, Fe: balance; (b) The flux adopts a fluorine-alkali slag system. Based on the total weight of the flux, the components of the flux, calculated by weight percentage, are as follows: fluorite: 30-50%, calcite: 1-10%, cryolite: 1-10%, wollastonite: 5-10%, bauxite: 4-13%, sintered magnesia: 10-20%, ferrosilicon: 4-10%, and ferromanganese: 5-10%.

2. The submerged arc welding wire and flux for heat-resistant steel of 650°C ultra-supercritical thermal power unit according to claim 1, characterized in that: Measured in weight percentage, the components of the deposited metal after welding with the submerged arc welding wire and flux include: C: 0.08-0.12%; Si: ≤0.50%; Mn: 0.7-1.2%; P: ≤0.010%; S: ≤0.010%; Cr: 8.5-9.5%, Ni≤0.5%, V: 0.1-0.3%, W: 2.30-2.80%, Co: 2.5-3.5%, N≤0.05%, Fe: balance.

3. The submerged arc welding wire and flux for heat-resistant steel of 650°C ultra-supercritical thermal power unit according to claim 1, characterized in that: Based on the total weight of the welding wire, the components of the submerged arc welding wire are as follows in weight percentage: C: 0.09-0.12%; Si: ≤0.18%; Mn: 0.78-0.95%; P: ≤0.006%; S: ≤0.005%; P+S≤0.011%; Cr: 8.7-9.3%, Ni≤0.4%, V: 0.20-0.30%, W: 2.55-2.75%, Co: 2.6-2.9%, N≤0.010%, Fe: balance.

4. The submerged arc welding wire and flux for heat-resistant steel of 650°C ultra-supercritical thermal power unit according to claim 1, characterized in that: Based on the total weight of the flux, the components of the flux are as follows in weight percentage: fluorite: 41-48%, calcite: 3-8%, cryolite: 3-8%, wollastonite: 5-8%, bauxite: 7-12%, sintered magnesia: 12-17%, ferrosilicon: 5-8%, and ferromanganese: 6-8%.

5. The submerged arc welding wire and flux for heat-resistant steel of 650°C ultra-supercritical thermal power unit according to claim 1, characterized in that: Measured in weight percentage, the components of the deposited metal after welding with the submerged arc welding wire and flux include: C: 0.085-0.110%; Si: 0.32-0.43%; Mn: 1.00-1.20%; P: ≤0.007%; S: ≤0.004%; Cr: 8.6-9.0%, Ni: 0.28-0.38%, V: 0.18-0.25%, W: 2.51-2.75%, Co: 2.75-3.11%, N≤0.05%, Fe: balance.

6. The method for preparing a submerged arc welding wire and flux for heat-resistant steel of a 650°C ultra-supercritical thermal power unit according to claim 1, characterized in that: The preparation method comprises the following steps: 1) preparing materials according to the composition and proportion of the welding wire, and manufacturing the submerged arc welding wire through steelmaking, fine drawing, and coiling; 2) Mix the components of the flux evenly according to the proportion; 3) Add 15-25% of the total weight of the flux component as a binder, stir and mix evenly, and then go through the production process of granulation, low-temperature drying, high-temperature sintering, and screening to complete the flux production.

7. The method for preparing submerged arc welding wire and flux for heat-resistant steel of 650°C ultra-supercritical thermal power unit according to claim 6, characterized in that: The flux is formed by low-temperature drying and high-temperature sintering, the low-temperature drying condition is 200-400°C×1-2h, and the high-temperature sintering condition is 550-700°C×1h.

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