Arc submerged welding wire and flux for 650 c supercritical steam turbine unit heat-resistant steel

Abstract

The application discloses a submerged-arc welding wire and flux for heat-resistant steel of a 650 DEG C ultra-supercritical thermal power unit, and the submerged-arc welding wire is used in combination with a fluorine-alkali type flux. The deposited metal after the submerged-arc welding wire and flux are welded has excellent high-temperature creep resistance and impact toughness. The submerged-arc welding wire and flux select high-quality raw materials, strictly control the P and S components in the welding wire and flux, and the flux selects a fluorine-alkali type slag system, so that the submerged-arc welding wire and flux have excellent welding process performance, a stable arc, strong resistance to blowhole, excellent deslagging performance and an attractive weld forming. The deposited metal after being treated at 770 DEG C for 4 hours has a tensile strength of greater than or equal to 680 MPa, an elongation of greater than or equal to 20%, and an RT impact of greater than or equal to 54 J, and is matched with the performance of G115 base metal.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of welding materials, and particularly relates to a submerged-arc welding wire and flux for 650 DEG C ultra-supercritical thermal power unit heat-resistant steel. BACKGROUND

[0002] Today, the society is developing rapidly, and the coal-fired power generation industry has become an indispensable part of social development. With the implementation of the global energy structure transformation, the "carbon neutralization" and "carbon standard" national strategies, high-parameter and large-capacity ultra-supercritical thermal power units have become an important development direction of future thermal power units. Under this background, the G115 new martensitic heat-resistant steel 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, so that the creep rupture strength of the material is 1.5 times that of P92 under a 650 DEG C steam environment, and the steam corrosion resistance is better than that of P92. The excellent performance of the G115 steel will be applied to the field of high-temperature and high-pressure parts of ultra-supercritical boilers, and the G115 steel plate has been engineered by the Chinese Academy of Engineering and Baosteel. Therefore, the research and development of matching welding materials are particularly important. Due to the difference between welding and steelmaking metallurgical processes, the development of a welding material matching the performance of G115 puts higher requirements on the research and development work. SUMMARY

[0003] To solve the above technical problems, the application provides a submerged-arc welding wire and flux for 650 DEG C ultra-supercritical thermal power unit heat-resistant steel, which adopts a fluorine-alkali type slag system and a low-P and S submerged-arc welding wire, and the deposited metal has excellent high-temperature creep resistance and impact toughness, and after 770 DEG C x 4h heat treatment, the tensile strength is greater than or equal to 680 MPa, the elongation is greater than or equal to 20%, and the RT impact is greater than or equal to 54 J, which is matched with the performance of the G115 base material.

[0004] The technical scheme of the application is: a submerged-arc welding wire and flux for 650 DEG C ultra-supercritical thermal power unit heat-resistant steel, which is used with a fluorine-alkali type flux and a submerged-arc welding wire;

[0005] (a) The components of the submerged-arc welding wire are as follows in percentage by weight based on the total weight of the submerged-arc welding wire: 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%, and Fe: balance;

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

[0007] The components of the deposited metal of the welding wire include, in percentage by weight: 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%, and Fe balance.

[0008] Preferably, the components of the submerged arc welding wire include, in percentage by weight and taking the total weight of the welding wire as the basis: 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%, and Fe balance.

[0009] Preferably, the components of the flux include, in percentage by weight and taking the total weight of the flux as the basis: fluorite 41-48%, calcite 3-8%, cryolite 3-8%, wollastonite 5-8%, bauxite 7-12%, sintered magnesite 12-17%, ferrosilicon 5-8%, and ferromanganese 6-8%.

[0010] Preferably, the components of the deposited metal after the submerged arc welding wire and the flux are welded include, in percentage by weight: 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%, and Fe balance.

[0011] The application also provides a preparation method of the submerged arc welding wire and the flux for the heat-resistant steel of the 650℃ ultra-supercritical thermal power unit, which comprises the following steps:

[0012] 1) according to the components and proportions of the welding wire, preparing materials, and through steelmaking, precision drawing, and volume division, the submerged arc welding wire is prepared;

[0013] 2) Mix the flux components in proportion;

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

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

[0016] In the present application, the submerged arc welding wire mainly provides the chemical components in the deposited metal, and the role of the submerged arc flux is mainly to generate gas, generate slag, deoxidize, and transition alloy, etc. Considering the loss of alloying elements during welding and the supplement of the alloy transition of the flux after welding, the metal chemical element components in the deposited metal after the final welding and the flux components are taken as examples, and the role of the main components in the present application in welding is analyzed as follows:

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

[0018] A small amount of Mn can reduce the content of S and promote the deoxidization of the weld, but too much Mn will reduce the stability of the high-temperature ferrite structure. Therefore, the content of Mn is preferably controlled within 0.7-1.2%;

[0019] Si, Cr and Ni are added in the core wire to jointly function. Si can promote the formation of Cr oxide film and improve the oxidation resistance. When Cr and Si exist at the same time, the high-temperature oxidation resistance of the alloy can also be improved. The addition of Ni can improve the heat resistance of the steel and inhibit the formation of high-temperature ferrite, thereby improving the tempering temperature of the heat-resistant steel structure. Therefore, the content of Si is generally controlled within ≤0.5%, the content of Cr is 8.5-9.5%, and the content of Ni is ≤0.5%;

[0020] P and S can form low-melting-point eutectic, which precipitates at the grain boundary during tempering, thereby reducing the strength of the material. Therefore, the content of P and S needs to be strictly controlled, and the content of P is ≤0.010% and the content of S is ≤0.010%;

[0021] Cr can improve the oxidation resistance and corrosion resistance of the heat-resistant steel, improve the high-temperature endurance strength and creep strength of the steel, and solid-solution strengthen the matrix. However, if the content of Cr is too high, the endurance strength will be reduced. Therefore, the content of Cr is preferably controlled within 8.5-9.5%;

[0022] Co element can play a solid solution strengthening effect, and can inhibit the generation of delta-ferrite, prevent performance degradation, so the Co content is preferably controlled at 2.5-3.5%;

[0023] W can also play a solid solution strengthening effect, and can improve the creep strength, but excessive W content can lead to the generation of delta-ferrite, which is not conducive to the mechanical properties of the weld, and thus is controlled at 2.30-2.80%;

[0024] V is a strong carbide forming element, and the addition of an appropriate amount of V in the steel can refine the grain, form dispersion strengthening, and significantly improve the weld strength, and the V is preferably controlled at 0.10-0.3%, and an appropriate amount of N is added, which can form stable nitrides with V, and play a solid solution strengthening effect in the weld, and the dispersion strengthening and solid solution strengthening are combined to achieve better strengthening effect, and the addition of N can further improve the creep strength and high-temperature endurance strength of the weld, but excessive N content can deteriorate the weldability and impact toughness, and thus the N is controlled at N≤0.05%.

[0025] In the present application, the fluoride mainly includes fluorite (CaF2), and barium fluoride and zirconium fluoride are added in combination, the addition of the fluoride can improve the basicity of the welding flux, thereby improving the impact toughness of the weld metal, and the addition of multiple fluorides can effectively reduce the content of H in the weld metal, thereby avoiding the generation of hydrogen embrittlement problems in the later period.

[0026] The main component of calcite is CaCO3, and the main function of calcite is to generate gas and slag, and the calcite is decomposed by welding heat to generate CO2 and CO, the CO2 can reduce the air partial pressure to reduce the O and H contents in the weld, and the CaO as an alkaline oxide can improve the basicity of the molten slag, and further improve the impact toughness of the weld metal, and the content of the calcite in the welding flux of the present application is 1-10%;

[0027] The addition of potassium cryolite can improve the fluidity of the molten slag, make the straightness of the weld edge better, and make the weld forming better, and the low ionization potential of the potassium cryolite can improve the arc stability during welding, and the content of the cryolite in the welding flux of the present application is 1-10%;

[0028] Wollastonite, mainly composed of CaSiO3, is a silicate mineral, and the addition of an appropriate amount of wollastonite in the welding flux can improve the acid-base degree of the welding flux, and the decomposition product CaO can also improve the basicity of the molten slag, thereby improving the impact toughness, and the wollastonite has needle-like and fibrous crystal morphology, and can increase the strength of the welding flux particles when used in the sintered welding flux, and can avoid excessive fine powder generation, and the content of the cryolite in the welding flux of the present application is 5-10%;

[0029] Bauxite, the main component is Al2O3, the main role is deoxidizer, the addition of Al2O3 can replace a part of SiO2, so as to ensure the basicity of the flux, avoid the basicity reduction caused by excessive addition of SiO2, so as to affect the impact toughness; the content of bauxite in the flux of the application is 4-13%;

[0030] Sintered magnesia, the main component is MgO, the main role is slagging, improving the basicity of the molten slag, so as to improve the impact toughness of the weld metal, when the raw material is selected, the loss on ignition and the particle size of the sintered magnesia should be paid attention to, and too large particle size or too small loss on ignition will cause segregation and weld bead pressure pit. The content of sintered magnesia in the flux of the application is 10-20%;

[0031] The addition of ferrosilicon and ferromanganese mainly plays the role of deoxidation, desulfurization, adjusting the viscosity of the molten slag, making the weld forming more beautiful, avoiding the appearance of too narrow and too wide weld, at the same time, reducing the content of S and O in the weld metal to avoid the occurrence of hot crack, improving the impact toughness of the weld, so the content of ferrosilicon is controlled in 4-10%, and the content of ferromanganese is controlled in 5-10%.

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

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

[0034] The submerged arc welding wire and flux for 650 DEG C ultra-supercritical thermal power unit heat-resistant steel of the application has excellent welding process performance, excellent deslagging performance, strong pore resistance, and beautiful weld forming. The fluorine-alkali type slag system and low P, S submerged arc welding wire are adopted, the deposited metal has excellent high temperature creep resistance and impact toughness, the tensile strength is greater than or equal to 660 MPa, the elongation is greater than or equal to 18%, and the RT impact is greater than or equal to 47 J after 770 DEG C x 4h heat treatment, which is matched with the performance of G115 base material. DETAILED DESCRIPTION

[0035] The technical scheme of the application will be further described below in combination with specific embodiments, but the application is not limited to these embodiments.

[0036] The application is composed of submerged arc welding wire and submerged arc flux, high-quality low P, S submerged arc welding wire is adopted, the welding wire is smelted according to the chemical composition of the welding wire in table 1, and the welding flux is prepared according to the welding flux formula in table 2, and the composition of the deposited metal is as shown in table 3.

[0037] The composition of the welding wire (weight percentage %) is as shown in table 1.

[0038] Table 1: Composition of welding wire (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 balance

[0040] The components of the low-P, S submerged arc flux of the fluoride base type (wt. %) are shown in Table 2.

[0041] Table 2: Components of the flux (wt. %)

[0042] fluorite calcite cryolite wollastonite bauxite sintered magnesite ferrosilicon ferromanganese 30～50 1～10 1～10 5～10 4～13 10～20 4～10 5～10

[0043] The components of the deposited metal after the submerged arc welding with the welding wire and the flux are shown in Table 3.

[0044] Table 3: Components of the deposited metal (wt. %)

[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 balance

[0046] Examples 1-5

[0047] The examples 1-5 are manufactured according to the manufacturing process commonly used in the submerged arc welding wire and flux manufacturing industry. The specific components of the examples 1-5 and the results and properties of the deposited metal are shown in Tables 4-1, 4-2, 4-3 and 4-4.

[0048] Table 4-1: Components of the submerged arc welding wire (wt. %)

[0049]

[0050]

[0051] Table 4-2: Components of the submerged arc flux (wt. %)

[0052] fluorite calcite cryolite wollastonite bauxite sintered magnesite 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 components of the deposited metal

[0054]

[0055]

[0056] Table 4-4: Mechanical properties

[0057]

[0058] From the above experiments, it can be seen that the submerged arc welding wire and the flux of the present application have excellent welding process properties, excellent deslagging property, strong resistance to porosity, and beautiful weld formation. Meanwhile, the deposited metal has excellent high-temperature creep resistance and excellent impact toughness, and after heat treatment at 770℃ for 4h, the tensile strength is ≥680MPa, the elongation is ≥20%, and the RT impact is ≥54J, which is matched with the properties of the G115 base material.

[0059] Example 6

[0060] The applicant has disclosed and obtained authorization for patent CN108213770 "650℃ ultra-supercritical thermal power unit metal powder core type heat-resistant steel submerged arc welding wire and flux" in 2017. The welding wire and flux of this type is a metal powder core, which has excellent yield strength, tensile strength and elongation at a temperature above 700℃, and is suitable for welding of steel for 650℃ and 700℃ ultra-supercritical thermal power units. Compared with the metal powder core type welding wire, the present application is matched with a submerged arc solid welding wire, which has stronger composition stability, better moisture resistance, more stable welding wire melting process and better arc stability during welding, so that a better weld formation can be obtained. At the same time, compared with the metal powder core type welding wire which is subject to steel strip, flux filling ratio and production process, the solid welding wire is easier to process into small diameter welding wire, and the welding heat input can be further controlled, so that the mechanical properties are more excellent and stable.

[0061] The submerged arc solid welding wire of the present application is smelted by a steel plant, and compared with the mechanical mixing of flux particles of the metal powder core type welding wire, the composition of molten iron for steelmaking is more uniform. It has been verified that the chemical composition stability of the head and tail of the same furnace is better. The results are shown in Table 5-1, and it can be seen that the chemical composition of the welding wire of the present application 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 sample 0.11 0.06 0.92 0.006 0.005 0.011 8.9 tail sample 0.11 0.08 0.92 0.006 0.005 0.011 8.8 Ni V W Co N Fe head sample 0.34 0.21 2.6 2.9 0.004 balance tail sample 0.35 0.21 2.7 2.9 0.003 balance

[0064] Moisture resistance test.

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

[0066] Table 5-2 Test results of moisture resistance

[0067]

[0068]

[0069] Welding stability test.

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

[0071] Therefore, the present application not only has excellent welding process performance, high temperature creep resistance of the deposited metal and excellent impact toughness which can match the performance of G115 base material, but also has significant improvement and improvement in quality and performance compared with the corresponding prior art which has been on the market.

[0072] The above-described embodiments are merely preferred embodiments of the present application, and it should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A combination of submerged arc welding wire and flux for heat-resistant steel in 650℃ ultra-supercritical thermal power units, characterized in that, The submerged arc welding wire and flux for the heat-resistant steel of the 650℃ ultra-supercritical thermal power unit are used in conjunction with fluorine-alkali type flux. (a) Based on the total weight of the submerged arc welding wire, the composition of the submerged arc welding wire, by weight percentage, is as follows: 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 composition of the flux is as follows by weight percentage: fluorite: 30-50%, calcite: 1-10%, cryolite: 1-10%, wollastonite: 5-10%, bauxite: 4-13%, sintered magnesia: 10-20%, ferrosilicon: 4-10%, ferromanganese: 5-10%.

2. The combination of submerged arc welding wire and flux for heat-resistant steel of 650℃ ultra-supercritical thermal power units according to claim 1, characterized in that, By weight percentage, the composition of the deposited metal after welding with the submerged arc welding wire and flux includes: 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 combination of submerged arc welding wire and flux for heat-resistant steel of 650℃ ultra-supercritical thermal power units according to claim 1, characterized in that, Based on the total weight of the welding wire, the composition of the submerged arc welding wire, expressed as a percentage by weight, is as follows: 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 combination of submerged arc welding wire and flux for heat-resistant steel of 650℃ ultra-supercritical thermal power units according to claim 1, characterized in that, Based on the total weight of the flux, the composition of the flux is as follows by weight percentage: fluorite: 41-48%, calcite: 3-8%, cryolite: 3-8%, wollastonite: 5-8%, bauxite: 7-12%, sintered magnesia: 12-17%, ferrosilicon: 5-8%, ferromanganese: 6-8%.

5. The combination of submerged arc welding wire and flux for heat-resistant steel of 650℃ ultra-supercritical thermal power units according to claim 1, characterized in that, By weight percentage, the composition of the deposited metal after welding with the submerged arc welding wire and flux includes: 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 preparation method of the combination of submerged arc welding wire and flux for heat-resistant steel of 650℃ ultra-supercritical thermal power units as described in claim 1, characterized in that, The preparation method includes the following steps: 1) Prepare materials according to the composition and proportion of the welding wire, and manufacture submerged arc welding wire through steelmaking, precision drawing, and slitting; 2) Mix all components of the flux evenly according to the specified proportions; 3) Add 15-25% of the total weight of the flux components as binder, stir and mix evenly, and then complete the flux production process through granulation, low-temperature drying, high-temperature sintering and sieving.

7. The preparation method of the combination of submerged arc welding wire and flux for heat-resistant steel of 650℃ ultra-supercritical thermal power units according to claim 6, characterized in that, The flux is produced by low-temperature drying and high-temperature sintering. The low-temperature drying conditions are 200-400℃×1-2h, and the high-temperature sintering conditions are 550-700℃×1h.

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