Heat-resistant steel flux-cored wire with excellent low-temperature toughness

Abstract

The invention belongs to the technical field of special flux-cored wires, and relates to a heat-resistant steel flux-cored wire with excellent low-temperature toughness. The flux core powder comprises, by weight, 5-9 parts of micro-carbon ferrochrome powder, 4-8 parts of ferromolybdenum, 4-7 parts of ferrosilicon, 8-13 parts of electrolytic manganese, 0.6-1 part of ferrotitanium, 0.1-0.3 part of ferroboron, 35-45 parts of 95 # rutile, 6-10 parts of zircon sand, 6-12 parts of silicate, 3-6 parts of fluorite, 1-3 parts of aluminum oxide, less than 1.5 parts of magnesia, 0.1-0.3 part of rare earth oxide and 4-7 parts of fluoride. A proper amount of atomized iron powder is added until the total amount of the flux core powder is 100 parts. Through detection, the mechanical properties of deposited metal are as follows: the tensile strength is 580-740 Mpa, the yield strength is 500-590 Mpa, the percentage elongation after fracture is 20-28%, and the low-temperature toughness value at-30 DEG C is 115-140 J after heat treatment at 610 + / -10 DEG C.

Description

Technical Field

[0001] The present invention belongs to the technical field of special flux-cored wires, and relates to a heat-resistant steel flux-cored wire with excellent low-temperature toughness. Background Art

[0002] Heat-resistant steels are low and medium alloy steels based on chromium and molybdenum elements. They not only have good oxidation resistance and thermal strength, but also relatively good resistance to sulfuric acid and hydrogen corrosion. They are important metal materials for working under high-temperature conditions in industries such as power, petroleum, and chemical engineering. They are generally used in environments below 600 °C. However, in actual applications, the welds of heat-resistant steels may also encounter working conditions that require low-temperature toughness, such as low-temperature and high-temperature alternating environments: components of aeroengines, chemical reactors, and nuclear power plant cooling systems, which have to go through a cycle of high-temperature operation → rapid cooling (low temperature). Another example is high-temperature equipment in cold regions, including boilers, pipelines, etc. operating in extremely cold regions, where the working ambient temperature may be as low as below -40 °C. For example, high-pressure reactors in refineries and heat exchangers on deep-sea oil and gas platforms need to withstand combined load conditions of high temperature + mechanical shock or vibration. There are also some special industries, such as some nuclear-grade heat-resistant steel equipment (such as heat transfer tubes of steam generators), which need to meet the requirements of low-temperature toughness backup to cope with extreme temperature fluctuations under accident conditions.

[0003] The existing flux-cored wires for welding heat-resistant steels mainly focus on the study of process acidity and alkalinity, welding position, or shielding gas, as well as the mechanical properties at room temperature or 0 °C after heat treatment, without considering the low-temperature toughness at -30 °C after heat treatment. Through actual tests, the impact toughness of each heat-resistant steel flux-cored wire sample shows a cliff-like decrease after heat treatment at 610 °C, and it cannot meet the requirements of welding heat-resistant steels with low-temperature toughness.

[0004] Patent CN101450425A solves the problem from the aspect of processability that it uses CO2 gas shielded welding, has small spatter, easy slag removal, stable arc combustion, and the droplet transfer form is jet transfer, but does not mention mechanical properties, especially the low-temperature toughness at -30°C; Patent CA 113941799A features excellent welding process, stable arc, less spatter, beautiful forming, and can be welded in all positions. It has good mechanical properties and excellent low-temperature impact toughness. The impact value of the deposited metal at 0°C after heat treatment at 730±10°C x 2h is above 120J, but the low-temperature impact toughness drops severely. After heat treatment at 610°C * 10H, the impact toughness at -30°C is only less than 40J; After welding the vanadium-containing heat-resistant steel for low-alloy containers of 12Cr1MoVR type with a metal powder type flux-cored wire in Patent CN 102489895A, the tensile strength of the deposited metal is ≥550MPa, the yield strength is ≥470MPa, the elongation is ≥19%, the impact at 20°C reaches 70J, and the diffusible hydrogen content of the deposited metal is less than 4mL / 100g. There is also a severe drop in low-temperature impact toughness. After heat treatment at 610°C * 10H, the impact toughness value at -30°C is less than 28J. Summary of the Invention

[0005] In view of the problem that the impact toughness of traditional heat-resistant steel flux-cored wires drops steeply after heat treatment and cannot meet the welding requirements of heat-resistant steels with low-temperature toughness requirements, the present invention proposes a new type of heat-resistant steel flux-cored wire with excellent low-temperature toughness.

[0006] To achieve the above object, the present invention is realized by the following technical solutions: The flux-cored wire with excellent low-temperature toughness of the present invention uses a low-carbon steel strip (HS1) with a thickness of 0.4 - 0.6mm and a width of 10 - 14mm on the outside, and various alloy powders and mineral powders are wrapped inside the strip as the flux-cored powder, and it is processed according to a filling ratio of 13 - 18%.

[0007] The flux-cored powder contains the following substances in parts by weight: 5 - 9 parts of micro-carbon ferrochromium powder, 4 - 8 parts of ferromolybdenum, 4 - 7 parts of ferrosilicon, 8 - 13 parts of electrolytic manganese, 0.6 - 1 part of ferrotitanium, 0.1 - 0.3 part of ferroboron, 35 - 45 parts of 95# rutile (main component TiO2), 6 - 10 parts of zircon sand, 6 - 12 parts of silicate (the silicate refers to one of potassium silicate, sodium silicate, and calcium silicate), 3 - 6 parts of fluorite (main component CaF2), 1 - 3 parts of alumina, <1.5 parts of magnesia, 0.1 - 0.3 part of rare earth oxide (one or two of cerium oxide and lanthanum oxide), 4 - 7 parts of fluoride (the fluoride is any one or two of CaF2, NaF, and LiF), and the rest is an appropriate amount of atomized iron powder added to make the total weight of the flux-cored powder 100 parts (that is, an equilibrium amount of iron powder is added to make the total weight of the flux-cored powder 100 weight parts).

[0008] For low-carbon steel strip HS1, the contents of the following elements are required to meet the following requirements: C: ≤0.03%, Si: ≤0.01%, Mn: ≤25%, Alt: <0.03%, N <0.003%, S: ≤0.023%, P: ≤0.025%. The mechanical properties of the steel strip need to meet: yield strength 160 - 200 Mpa, tensile strength ≥300 Mpa, elongation ≥43%.

[0009] The functions of each substance in the flux-cored powder are as follows: Micro-carbon ferrochrome + ferromolybdenum: Cr can strengthen by solid solution to inhibit dislocation migration at low temperature and reduce the ductile-brittle transition temperature. Mo can enhance high-temperature strength and tempering stability. Cr and Mo cooperate to refine grain boundary carbides, reduce low-temperature crack sensitivity, and improve toughness.

[0010] Ferrotitanium: Added in trace amounts to keep the content of the deposited metal at 0.02 - 0.05%, which can play a role in refining grains (pinning effect of TiN) and improving impact toughness.

[0011] Ferroboron: Added in trace amounts (content of the deposited metal 0.002 - 0.005%), forming BN second-phase particles to pin the austenite grain boundary and inhibit grain coarsening.

[0012] Ferrosilicon + electrolytic manganese: Deoxidize, strengthen by solid solution, and improve the fluidity of the molten pool. Strictly control the composite deoxidation ratio of silicon and manganese within the range proposed in the present invention to control the morphology of MnS inclusions and avoid low-temperature brittle fracture caused by strip-shaped sulfides.

[0013] Rutile: The main component of slag-making, improving slag coverage and slag detachment property, and can also stabilize the arc, improve the stiffness of the arc, and reduce spatter.

[0014] Zircon sand: Slag-making, improving the weld shape, and used in combination with magnesite and alumina to improve slag coverage and increase slag viscosity Fluorite: Slag-making, reducing arc voltage, improving slag detachment property, and enhancing desulfurization Fluoride + alumina + magnesite: The proportion range provided by the present invention can provide a high-purity fluoride system, reduce the oxygen content in the weld, and reduce the damage of inclusions to toughness.

[0015] Silicate: Has the effect of stabilizing the arc.

[0016] Rare earth oxide: Refine the solidification structure of the molten pool, purify the weld bead (desulfurize and remove inclusions), and improve low-temperature toughness.

[0017] The flux-cored wire for heat-resistant steel in CO2 shielded gas welding with excellent low-temperature toughness provided by the present invention has a final product wire diameter of 1.0 - 1.6 mm after processing. The tensile strength of its as-welded deposited metal is ≥550 MPa, the yield strength is ≥470 MPa, the elongation is ≥20%, the impact value at 0°C is ≥140 J, and it has excellent low-temperature toughness after heat treatment at 610 ± 10°C, with the impact energy at -30°C > 110 J. It is especially suitable for working conditions with requirements for low-temperature impact toughness in the nuclear power industry, chemical industry, etc.

[0018] During its preparation process, first, by using the vacuum-sealed powder-making process, the oxygen content of the flux powder is controlled within 100 ppm to reduce the influence of oxide inclusions on toughness. During the subsequent use of the wire, in-situ deoxidation is realized by introducing an Al-Mg-Ca composite deoxidizer to achieve dynamic deoxidation of the molten pool, which can effectively improve the purity of the weld.

[0019] In the alloy composition of the present invention, the Cr content is increased to inhibit the dislocation migration at low temperature through solid solution strengthening and reduce the ductile-brittle transition temperature. By controlling the ratio of elements Mo and Cr, the synergistic effect of Cr and molybdenum (Mo) is realized to refine the grain boundary carbides, reduce the low-temperature crack sensitivity, and improve toughness. Then, through the microalloying of titanium (Ti) and boron (B), Ti and B are added and their ratio is strictly controlled to form TiN and BN second-phase particles to pin the austenite grain boundaries and inhibit grain coarsening.

[0020] The flux-cored formula design adopts a high-purity fluoride system of a fluoride-Al2O3-MgO composite slag system to reduce the oxygen content of the weld (≤200 ppm) and reduce the damage of inclusions to toughness.

[0021] Rare earth oxides are added to the formula and their ratio is strictly controlled to refine the solidification structure of the molten pool and improve low-temperature toughness. The composite deoxidation ratio of silicon (Si) and manganese (Mn) is strictly controlled to control the morphology of MnS inclusions and avoid low-temperature brittle fracture caused by strip sulfides.

[0022] The production process is as follows: First, the required flux powders are baked according to their respective characteristics to remove residual moisture or other volatile impurities. This part is the same as the existing wire processing technology and will not be elaborated here. Then, the flux powders that need to be deoxidized (such as ferrosilicon, electrolytic manganese, ferrotitanium, 95# rutile, zircon sand, silicate, fluorite) are loaded into a vacuum melting furnace. After being evacuated under a vacuum of 10 -2 -10 -5 Pa, subsequent melting is carried out.

[0023] After the steel strip is ultrasonically cleaned, it is rolled into a U-shape by the rollers on the forming machine. The mixed and pretreated powder is added to the U-shaped steel strip at a filling ratio of 13-18%. After multiple rollings, the U-shaped groove is changed into an O-shape, and then through multiple drawings, a welding wire with a diameter of 1.0-1.6 mm is made. Finally, the finished welding wire is obtained after surface cleaning.

[0024] Compared with the prior art, the advantages and positive effects of the present invention are as follows: After testing, the mass percentages of the following elements in the welding wire prepared by the present invention meet the requirements: C: <0.1%, Cr: 0.3-0.5%, Mo: 0.4-0.6%, Si: 0.3-0.6%, Mn: 0.6-1.0%, S: ≤0.025%, P: ≤0.03%. The mechanical properties of the deposited metal are as follows: tensile strength 580-740 Mpa, yield strength 500-590 Mpa, elongation after fracture 20-28%. After heat treatment at 610±10°C, the low-temperature toughness value at -30°C is 115-140 J. Specific embodiments

[0025] In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be further described below with reference to specific embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0026] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the present invention is not limited by the specific embodiments disclosed in the following specification.

[0027] In the following embodiments, the specifications of some materials are as follows. These materials can be obtained through commercial customization. For the remaining materials not specifically described, common commercially available products in the field of welding wires are used.

[0028] Ferrosilicon: Comply with GB / T 2272, grade FFeSi75-A, mesh size requirement 80-300 mesh.

[0029] Micro-carbon ferrochrome, particle size 80-280 mesh, Cr>65%, C<0.1%, P<0.035%, S<0.1%.

[0030] The fluoride refers to one or two of CaF2, NaF, and LiF: the main component content is greater than 98%, and the water-insoluble matter is less than 0.5%.

[0031] The rare earth oxide refers to one or two of cerium oxide and lanthanum oxide, and the particle size is controlled at 240-300 mesh.

[0032] The silicate is one of potassium silicate, sodium silicate, and calcium silicate, and the particle size requirement is 200 - 330 mesh.

[0033] Example 1 Select low - carbon steel strip HS1 with a thickness of 0.4 mm and a width of 10 mm. The strip contains the following components by weight percentage: C: 0.022%, Si: 0.005%, Mn: 0.22%, Alt: 0.026%, N: 0.0016%, S: 0.003%, P: 0.006%. Mechanical properties: yield strength 184 Mpa, tensile strength 315 Mpa, elongation ≥ 47%. The flux - cored composition is by weight percentage. The flux - core accounts for 15% of the weight of the welding wire, and the weight percentages of the flux - core components are: Micro - carbon ferrochrome powder 7%, ferromolybdenum 7%, ferrosilicon 4%, electrolytic manganese 11%, ferro - titanium 0.7%, ferro - boron 0.3%, 95# rutile 36%, zircon sand 9%, sodium silicate 7%, fluorite 6%, alumina 3%, magnesia 1%, lanthanum oxide 0.2%, calcium fluoride 5%, and the balance is iron powder, totaling 100%.

[0034] After each flux powder is baked at high temperature to remove moisture (a typical process is baking at 8℃ for 1 h), the flux powders are mixed and evacuated at 10 -5 Pa for 1 h and then mixed evenly, added to the U - shaped steel strip, and made into a welding wire with a diameter of 1.2 mm through rolling and drawing.

[0035] Verification: Using CO2 gas shielded welding, the chemical composition of the deposited metal of the obtained finished welding wire (by weight percentage) is: C: 0.06%, Mn: 1.15, Si: 0.41, S: 0.008%, P: 0.010, Mo: 0.58, Cr: 0.43, and the balance is Fe. The mechanical properties of the deposited metal are: tensile strength 677 MPa, yield strength 580 Mpa, elongation 20%, average impact energy at 0℃ is 166 J. After heat treatment at 610 ± 10℃, three points are detected, and the low - temperature toughness values at - 30℃ are 122 J, 126 J, and 130 J respectively.

[0036] Example 2 Unless otherwise specified, this example is the same as Example 1. Select low - carbon steel strip HS1 with a thickness of 0.4 mm and a width of 12 mm. The strip contains the following components by weight percentage: C: 0.023%, Si: 0.004%, Mn: 0.25%, Alt: 0.021%, N: 0.0017%, S: 0.003%, P: 0.007%. Mechanical properties: yield strength 182 Mpa, tensile strength 312 Mpa, elongation ≥ 47%. The flux - cored composition is by weight percentage. The flux - core accounts for 17% of the weight of the welding wire, and the weight percentages of the flux - core components are: 7% of micro-carbon ferrochrome powder, 6% of ferromolybdenum, 4.5% of ferrosilicon, 9% of electrolytic manganese, 0.6% of ferro-titanium, 0.3% of ferro-boron, 40% of 95# rutile, 8.5% of zircon sand, 6% of calcium silicate, 6% of fluorite, 3% of alumina, 1% of magnesia, 0.2% of cerium oxide, 6% of lithium fluoride, with the balance being iron powder, totaling 100%.

[0037] After high-temperature baking, vacuum powder making and uniform mixing, it is added to the U-shaped steel strip and rolled and drawn to make a welding wire with a diameter of 1.6 mm.

[0038] Verification: Using CO2 gas shielded welding, the chemical composition of the deposited metal of the finished welding wire (calculated by weight percentage) is: C: 0.06, Mn: 0.82, Si: 0.40, S: 0.008, P: 0.011, Mo: 0.53, Cr: 0.44, with the balance being Fe. The mechanical properties of the deposited metal are: tensile strength is 683 MPa, yield strength is 582 Mpa, elongation is 20%, the average impact energy at 0 °C is 158 J, after heat treatment at 610 ± 10 °C, three points are detected, and the low-temperature toughness values at -30 °C are 118 J, 124 J, and 129 J respectively.

[0039] Example 3 Unless otherwise specified in this example, it is the same as Example 1. Low-carbon steel strip HS1 is selected, with a thickness of 0.5 mm and a width of 12 mm. The strip includes the following components by weight percentage: C: 0.021%, Si: 0.006%, Mn: 0.28%, Alt: 0.020%, N: 0.0014%, S: 0.005%, P: 0.008%. Mechanical properties: yield strength is 185 Mpa, tensile strength is 322 Mpa, elongation ≥ 46%. The flux-cored composition is calculated by weight percentage. The flux core accounts for 18% of the weight of the welding wire, and the weight percentage of the flux-cored composition is: 6% of micro-carbon ferrochrome powder, 5% of ferromolybdenum, 4% of ferrosilicon, 9% of electrolytic manganese, 0.8% of ferro-titanium, 0.1% of ferro-boron, 41% of 95# rutile, 7% of zircon sand, 10% of silicate, 4.5% of fluorite, 2.2% of alumina, 0.6% of magnesia, 0.2% of rare earth oxide, 5% of fluoride, with the balance being iron powder, totaling 100%.

[0040] After high-temperature baking, vacuum powder making and uniform mixing, it is added to the U-shaped steel strip and rolled and drawn to make a welding wire with a diameter of 1.6 mm.

[0041] Verification: Using CO2 gas shielded welding, the chemical composition of the deposited metal of the finished welding wire (calculated by weight percentage) is: C: 0.06, Mn: 0.78, Si: 0.35, S: 0.007, P: 0.012, Mo: 0.55, Cr: 0.41, and the balance is Fe. The mechanical properties of the deposited metal are: tensile strength is 696 MPa, yield strength is 588 Mpa, elongation is 21%, average impact energy at 0 °C is 154 J. After heat treatment at 610 ± 10 °C, three points are detected, and the low-temperature toughness values at -30 °C are 125 J, 131 J, and 133 J respectively.

[0042] Example 4 For the parts not specifically described in this example, they are the same as those in Example 1. Low-carbon steel strip HS1 is selected, with a thickness of 0.5 mm and a width of 14 mm. The strip includes the following components by weight percentage: C: 0.027%, Si: 0.007%, Mn: 0.32%, Alt: 0.021%, N: 0.0011%, S: 0.006%, P: 0.010%. Mechanical properties: yield strength is 178 Mpa, tensile strength is 306 Mpa, elongation ≥ 48%. The flux cored composition is calculated by weight percentage. The flux core accounts for 15% of the weight of the welding wire, and the weight percentages of the flux core components are: Micro-carbon ferrochrome powder 7%, ferromolybdenum 8%, ferrosilicon 5%, electrolytic manganese 13%, ferrotitanium 1%, ferroboron 0.3%, 95# rutile 40%, zircon sand 6%, silicate 6%, fluorite 3%, alumina 1%, magnesia 0.5%, rare earth oxide 0.1%, fluoride 5%, and the balance is iron powder, totaling 100%.

[0043] After high-temperature baking, vacuum powder making and uniform mixing, it is added to the U-shaped steel strip and made into a welding wire with a diameter of 1.2 mm through rolling and drawing.

[0044] Verification: Using CO2 gas shielded welding, the chemical composition of the deposited metal of the finished welding wire (calculated by weight percentage) is: C: 0.07, Mn: 0.74, Si: 0.36, S: 0.006, P: 0.010, Mo: 0.55, Cr: 0.43, and the balance is Fe. The mechanical properties of the deposited metal are: tensile strength is 711 MPa, yield strength is 567 Mpa, elongation is 22%, average impact energy at 0 °C is 149 J. After heat treatment at 610 ± 10 °C, three points are detected, and the low-temperature toughness values at -30 °C are 122 J, 127 J, and 130 J respectively.

[0045] Comparative Example 1 The difference between this comparative example and Example 1 is that the weight fraction of micro-carbon ferrochrome powder is adjusted to 4%, ferro-molybdenum is adjusted to 3%, and the reduced parts of the two component contents are supplemented with iron powder. The contents of the remaining substances and the preparation process are the same as those in Example 1. After testing, after reducing the Cr and Mo components, the mechanical properties of the finally obtained deposited metal are as follows: the tensile strength is 671 MPa, the yield strength is 578 Mpa, the elongation is 22%, the average impact energy at 0 °C is 172 J. After heat treatment at 610 ± 10 °C, three points are tested, and the low-temperature toughness values at -30 °C are 45, 48, and 52 J respectively.

[0046] Comparative Example 2 The difference between this comparative example and Example 2 is that the ferro-titanium and ferro-boron components are omitted, and the omitted components are supplemented with iron powder. The dosages of the remaining substances and the preparation process remain unchanged. After testing, the mechanical properties of the deposited metal are as follows: the tensile strength is 633 MPa, the yield strength is 524 Mpa, the elongation is 21%, the average impact energy at 0 °C is 137 J. After heat treatment at 610 ± 10 °C, three points are tested, and the low-temperature toughness values at -30 °C are 22, 34, and 38 J respectively.

[0047] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, as long as it does not depart from the technical content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A flux-cored wire for heat-resistant steel with excellent low-temperature toughness, characterized in that, HS1 steel strip is adopted, and the flux-cored powder contains the following substances in parts by weight: 5-9 parts of micro-carbon ferrochrome powder; 4-8 parts of ferromolybdenum; 4-7 parts of ferrosilicon; 8-13 parts of electrolytic manganese; 0.6-1 part of ferro-titanium; 0.1-0.3 part of ferro-boron; 35-45 parts of 95# rutile; 6-10 parts of zircon sand; 6-12 parts of silicate; 3-6 parts of fluorite; 1-3 parts of alumina; less than 1.5 parts of magnesia and not zero; 0.1-0.3 part of rare earth oxide; 4-7 parts of fluoride; a certain amount of atomized iron powder.

2. The flux cored wire for heat-resistant steel with excellent low-temperature toughness according to claim 1, wherein, The thickness of the steel strip is 0.4-0.6 mm, the width is 10-14 mm, and the filling ratio is 13-18%.

3. The flux cored wire for heat resistant steel with excellent low temperature toughness according to claim 2, characterized in that, The element content in the steel strip meets the following requirements: C: ≤0.03%, Si: ≤0.01%, Mn: ≤25%, Al: <0.03%, N <0.003%, S: ≤0.023%, P: ≤0.025%; the mechanical properties need to meet the following requirements: yield strength 160-200 Mpa, tensile strength ≥300 Mpa, elongation ≥43%.