CN117604327A - Protective material for boiler tube, preparation method of protective material and protective method of boiler tube - Google Patents
Protective material for boiler tube, preparation method of protective material and protective method of boiler tube Download PDFInfo
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- CN117604327A CN117604327A CN202311650185.6A CN202311650185A CN117604327A CN 117604327 A CN117604327 A CN 117604327A CN 202311650185 A CN202311650185 A CN 202311650185A CN 117604327 A CN117604327 A CN 117604327A
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- 239000000463 material Substances 0.000 title claims abstract description 62
- 238000002360 preparation method Methods 0.000 title claims abstract description 42
- 238000000034 method Methods 0.000 title claims abstract description 26
- 239000011253 protective coating Substances 0.000 claims abstract description 151
- 238000004372 laser cladding Methods 0.000 claims abstract description 50
- 239000010410 layer Substances 0.000 claims description 78
- 239000002994 raw material Substances 0.000 claims description 34
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 32
- 229910045601 alloy Inorganic materials 0.000 claims description 30
- 239000000956 alloy Substances 0.000 claims description 30
- 239000000843 powder Substances 0.000 claims description 30
- 239000007789 gas Substances 0.000 claims description 29
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 28
- 230000037452 priming Effects 0.000 claims description 23
- 230000033001 locomotion Effects 0.000 claims description 22
- 230000008018 melting Effects 0.000 claims description 21
- 238000002844 melting Methods 0.000 claims description 21
- 229910052757 nitrogen Inorganic materials 0.000 claims description 16
- 229910052786 argon Inorganic materials 0.000 claims description 14
- 239000013307 optical fiber Substances 0.000 claims description 14
- 230000001502 supplementing effect Effects 0.000 claims description 14
- 238000005253 cladding Methods 0.000 claims description 9
- 229910052804 chromium Inorganic materials 0.000 claims description 8
- 238000005303 weighing Methods 0.000 claims description 5
- 229910052726 zirconium Inorganic materials 0.000 claims description 5
- 230000008878 coupling Effects 0.000 claims description 3
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- 238000005859 coupling reaction Methods 0.000 claims description 3
- 239000004065 semiconductor Substances 0.000 claims description 2
- 239000011247 coating layer Substances 0.000 claims 1
- 230000007797 corrosion Effects 0.000 abstract description 46
- 238000005260 corrosion Methods 0.000 abstract description 46
- 230000035939 shock Effects 0.000 abstract description 10
- 239000000460 chlorine Substances 0.000 abstract description 8
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 abstract description 7
- 229910052801 chlorine Inorganic materials 0.000 abstract description 7
- 239000011159 matrix material Substances 0.000 abstract description 7
- 239000002028 Biomass Substances 0.000 abstract description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 abstract description 5
- 229910001514 alkali metal chloride Inorganic materials 0.000 abstract description 4
- 239000010813 municipal solid waste Substances 0.000 abstract description 3
- 230000002195 synergetic effect Effects 0.000 abstract description 3
- 229910052936 alkali metal sulfate Inorganic materials 0.000 abstract description 2
- 229910001119 inconels 625 Inorganic materials 0.000 description 11
- 238000012360 testing method Methods 0.000 description 10
- 238000010438 heat treatment Methods 0.000 description 9
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 8
- 230000003628 erosive effect Effects 0.000 description 8
- 238000009792 diffusion process Methods 0.000 description 7
- 229910052751 metal Inorganic materials 0.000 description 6
- 238000007254 oxidation reaction Methods 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
- 150000003839 salts Chemical class 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 238000000889 atomisation Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 5
- 238000011049 filling Methods 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
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- 238000003860 storage Methods 0.000 description 5
- 230000001360 synchronised effect Effects 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- BUKHSQBUKZIMLB-UHFFFAOYSA-L potassium;sodium;dichloride Chemical compound [Na+].[Cl-].[Cl-].[K+] BUKHSQBUKZIMLB-UHFFFAOYSA-L 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 238000005299 abrasion Methods 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 239000000835 fiber Substances 0.000 description 3
- 230000006698 induction Effects 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- 239000000758 substrate Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 2
- 229910008341 Si-Zr Inorganic materials 0.000 description 2
- 229910006682 Si—Zr Inorganic materials 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 239000002551 biofuel Substances 0.000 description 2
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- 239000003546 flue gas Substances 0.000 description 2
- 238000000227 grinding Methods 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 238000010248 power generation Methods 0.000 description 2
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- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 229910002515 CoAl Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 238000007792 addition Methods 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
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- 229910052742 iron Inorganic materials 0.000 description 1
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- 239000011156 metal matrix composite Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
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- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- -1 stress Substances 0.000 description 1
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- 229910000601 superalloy Inorganic materials 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C19/00—Alloys based on nickel or cobalt
- C22C19/03—Alloys based on nickel or cobalt based on nickel
- C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
- C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
- C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C24/00—Coating starting from inorganic powder
- C23C24/08—Coating starting from inorganic powder by application of heat or pressure and heat
- C23C24/10—Coating starting from inorganic powder by application of heat or pressure and heat with intermediate formation of a liquid phase in the layer
- C23C24/103—Coating with metallic material, i.e. metals or metal alloys, optionally comprising hard particles, e.g. oxides, carbides or nitrides
- C23C24/106—Coating with metal alloys or metal elements only
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
- F22B37/00—Component parts or details of steam boilers
- F22B37/02—Component parts or details of steam boilers applicable to more than one kind or type of steam boiler
- F22B37/06—Flue or fire tubes; Accessories therefor, e.g. fire-tube inserts
- F22B37/08—Fittings preventing burning-off of the tube edges
Abstract
The invention belongs to the technical field of surface engineering, and provides a protective material for a boiler tube, a preparation method thereof and a protective method for the boiler tube. The protective material for the boiler tube comprises the following components in percentage by mass: al:6 to 20wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance. The protective coating obtained by laser cladding of the protective material for the boiler tube is not easy to fall off when being metallurgically combined with a matrix, has good heat conduction performance and strong thermal shock resistance, can be used for working conditions of high-temperature chlorine corrosion or high-temperature chlorine corrosion-erosive wear synergistic action, and can also be used for corrosion protection under the working conditions that alkali metal chloride and sulfate coexist at high temperature; can be applied to but not limited to biomass boilers, garbage incineration boilers and biomass circulating fluidized bed boilers.
Description
Technical Field
The invention relates to the technical field of surface engineering, in particular to a protective material for a boiler tube, a preparation method thereof and a protective method for the boiler tube.
Background
The power generation by utilizing garbage, waste, biofuel and the like can play a key role in the aspects of energy safety and carbon dioxide emission reduction in the future, and is in a growing trend worldwide at present. However, these biofuels typically contain significant amounts of alkali metal chlorides (e.g., potassium chloride, sodium chloride, etc.), which produce very corrosive flue gases, and deposits formed on the heated surfaces of superheater tubes, etc., are typically rich in alkali metal chlorides. The presence of these deposits significantly enhances the high temperature corrosion of the boiler tubes, exacerbating the risk of boiler tube failure and even causing unplanned downtime of the unit. Therefore, high temperature corrosion of metals and alloys is a serious problem faced by safe and stable operation of boiler units. In general, maintaining a low steam temperature can reduce the corrosion rate of the boiler superheater. But at the same time, this results in poor power generation efficiency. Higher temperatures tend to lead to more severe corrosion. Therefore, it has become urgent to prevent the high temperature corrosion failure to maintain the operation of the boiler unit at high temperature and high pressure.
In addition, there is often a large amount of both corrosive gases and soot particles in the flue gas. Along with the improvement of the operation parameters of the unit, key parts such as boiler tubes, turbine blades, valves and the like often have serious high-temperature corrosion and mechanical damage such as abrasion, high-temperature erosion and the like due to the influences of high-temperature fluid, stress, impurities and the like. This can seriously jeopardize the safe operation of the boiler unit. For example, a circulating fluidized bed boiler using renewable energy such as biomass has a great prospect because the temperature of the fluidized bed can be easily controlled to realize stable biomass combustion. However, due to the impact of bed material particles (such as silica sand) in a severe chlorine-containing atmosphere, the pipe wall can be rapidly thinned or even burst under the synergistic effect of high-temperature corrosion-erosive wear, so that the normal operation of the power station boiler is seriously affected. It can be seen that corrosion and wear are one of the main causes of tube explosion in boilers.
The preparation of protective coatings on the surfaces of heated surfaces such as boiler tubes is an effective method. By adopting the laser cladding technology, a cladding layer with high quality, no crack and no hole which is metallurgically bonded with the matrix can be deposited on the surface of the boiler tube, thereby effectively avoiding losing the protective effect due to the falling off of the coating or the existence of pores and the like, and providing a channel for corrosive media. The choice of materials and the design of the components are one of the most critical factors determining the performance of the laser cladding layer. This complex service environment (thermal, chemical and mechanical interactions) makes it extremely difficult for most materials to meet all of the protective requirements placed on them today. For example, common superalloys are designed with a combination of strength, processing and welding properties, and even with good corrosion resistance, wear resistance is often not desirable. The ceramic-metal matrix composite material is selected to prepare the cladding layer, and the cladding layer has higher high-temperature wear resistance, but is not suitable for corrosion protection because the material system is easy to generate through cracks in the laser cladding process; moreover, when the heating surface of the boiler tube has ash deposition, molten salt corrosion often exists due to the factors of more complex components participating in corrosion reaction, local overheating and the like, so that the interface position of the ceramic particle reinforced phase and the metal matrix in the cladding layer is easily corroded preferentially.
Therefore, development of new materials suitable for laser cladding technology and capable of simultaneously playing roles in high temperature corrosion resistance and wear resistance is needed.
Disclosure of Invention
In view of the above, the present invention aims to provide a protective material for boiler tubes, a method for producing the same, and a method for protecting boiler tubes. The protective material for the boiler tube provided by the invention has high-temperature corrosion resistance and wear resistance.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a protective material for a boiler tube, which comprises the following components in percentage by mass:
al:6 to 20wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance.
The invention also provides a preparation method of the protective material for the boiler tube, which comprises the following steps:
weighing raw materials;
carrying out first melting on raw material Ni, then adding Cr, mo, co, si and Zr for second melting, and then adding Al for third melting to obtain alloy melt;
and atomizing the alloy melt to obtain the protective material for the boiler pipe.
The invention also provides a protection method of the boiler tube, which comprises the following steps:
preparing a protective coating on the boiler tubes;
the protective coating is obtained by laser cladding of the protective material for the boiler pipe or the protective material for the boiler pipe prepared by the preparation method of the technical scheme.
Preferably, a primer layer is arranged between the boiler tube and the protective coating; the priming layer is obtained by cladding priming material through laser; the priming material comprises the following components in percentage by mass:
al: 4-6 wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance.
Preferably, the thickness of the primer layer is 300-500 μm.
Preferably, the laser cladding parameters of the priming layer include: the powder supplementing gas is high-purity nitrogen, the shielding gas is high-purity argon, the laser is an optical fiber laser, the rated output power of the laser is 3-8 kW, the diameter of a laser beam focus spot is 1-3 mm, the relative movement speed of the laser spot and a workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm.
Preferably, the protective coating comprises a first protective coating or a second protective coating;
the preparation raw materials of the first protective coating comprise the following components in percentage by mass: al:6 to 20wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance;
the laser cladding parameters of the first protective coating comprise: the powder supplementing gas is high-purity nitrogen, the shielding gas is high-purity argon, the laser is an optical fiber laser, the rated output power of the laser is 3-8 kW, the diameter of a laser beam focus spot is 1-3 mm, the relative movement speed of the laser spot and a workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm;
the thickness of the first protective coating is 400-650 mu m.
Preferably, the second protective coating comprises a first gradient protective coating and a second gradient protective coating which are sequentially stacked; the first gradient protective coating is in contact with the primer layer;
the preparation raw materials of the first gradient protective coating comprise the following components in percentage by mass: al: 8-12 wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance;
the preparation raw materials of the second gradient protective coating comprise the following components in percentage by mass: al: 15-20 wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance.
Preferably, the thickness of the first gradient protective coating and the second gradient protective coating is independently 400-600 μm.
Preferably, the laser cladding parameters of the first gradient protective coating include: the powder supplementing gas is high-purity nitrogen, the shielding gas is high-purity argon, the laser is an optical fiber laser, the rated output power of the laser is 3-8 kW, the diameter of a laser beam focus spot is 1-3 mm, the relative movement speed of the laser spot and a workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm;
the laser cladding parameters of the second gradient protective coating comprise: the powder supplementing gas is high-purity nitrogen, the shielding gas is high-purity argon, the laser is an optical fiber coupling output semiconductor laser or an optical fiber laser, the rated output power of the laser is 3-8 kW, the diameter of a laser beam focus spot is 1-3 mm, the relative movement speed of the laser spot and a workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm.
The invention provides a protective material for a boiler tube, which comprises the following components in percentage by mass: al:6 to 20wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance. The protective coating obtained by laser cladding of the protective material for the boiler tube is not easy to fall off when being metallurgically combined with a matrix, has good heat conduction performance and strong thermal shock resistance, can be used for working conditions of high-temperature chlorine corrosion or high-temperature chlorine corrosion-erosive wear synergistic action, and can also be used for corrosion protection under the working conditions that alkali metal chloride and sulfate coexist at high temperature; can be applied to but not limited to biomass boilers, garbage incineration boilers and biomass circulating fluidized bed boilers.
The invention also provides a protection method of the boiler tube, which comprises the following steps: preparing a protective coating on the boiler tubes; the protective coating is obtained by laser cladding of the protective material for the boiler pipe or the protective material for the boiler pipe prepared by the preparation method of the technical scheme.
Furthermore, a priming layer is arranged between the boiler tube and the protective coating, fe in the boiler tube matrix is isolated by the priming layer, the influence of dilution of Fe element on the performance of the protective coating is prevented, and the protective coating can be better applied to the environment with high-temperature corrosion, almost no erosive wear or with a certain degree of wear.
Further, the second protective coating comprises a first gradient protective coating and a second gradient protective coating which are sequentially stacked; the first gradient protective coating is in contact with the primer layer. According to the invention, the protective coating is a multilayer protective coating with gradient change of aluminum content, so that the inner layer of the protective coating is free from cracks, the substrate is ensured not to be corroded, and the final protective coating can be in service in a high-temperature corrosion environment with serious high-temperature abrasion.
Drawings
FIG. 1 is a graph of the surface morphology of the protective coating obtained in example 1 after 100 thermal shock tests, wherein the left graph is a picture of the protective coating after the thermal shock test without applying the flaw detector, and the right graph is a picture of the protective coating after the thermal shock test with applying the flaw detector;
FIG. 2 is a cross-sectional profile of the principal elements in the protective coating obtained in example 1;
FIG. 3 is a graph showing the weight loss per unit area of the protective coating and the Inconel625 alloy laser cladding layer obtained in example 1 after being exposed to a NaCl-KCl mixed salt at 700 ℃ for 144 hours;
FIG. 4 is a cross-sectional morphology diagram of the protective coating obtained in example 1 and the Inconel625 alloy laser cladding layer after being exposed to a 700 ℃ NaCl-KCl mixed salt for 144 hours, wherein the left diagram is the Inconel625 alloy laser cladding layer, and the right diagram is the protective coating obtained in example 1;
FIG. 5 is a cross-sectional profile of the principal elements in the protective coating obtained in example 2;
FIG. 6 is a graph showing the mass loss of the protective coating and the Inconel625 alloy laser cladding obtained in example 2 after a high-temperature erosion test at 900℃for 8 minutes.
Detailed Description
The invention provides a protective material for a boiler tube, which comprises the following components in percentage by mass:
al:6 to 20wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance.
The protective material for the boiler tube provided by the invention comprises the following components: from 6 to 20wt.%, preferably from 8 to 18wt.%, more preferably from 10 to 15wt.%. According to the invention, the proper content of Al element can simultaneously improve the high-temperature wear resistance and corrosion resistance of the protective coating obtained by laser cladding of the protective material for the boiler tube. First, al forms gamma' -Ni 3 Basic constituent elements of Al phase. Al is added into the protective coating to play a solid solution strengthening role and also can form Ni with Ni 3 Al, carrying out precipitation strengthening. Second, the protective coating surface may form Al 2 O 3 And (5) an oxide layer. Compared with the oxide of Fe or Ni, the growth speed is high, so that the oxide layer is thick and easy to peel, al 2 O 3 The oxide layer has low forming speed, thin oxide layer, good adhesiveness, difficult peeling, high-temperature hardness and stronger protection effect on the matrix in a high-temperature erosion and abrasion environment. And Cl - At Al 2 O 3 The diffusion activation energy in the oxide layer is about Cr 2 O 3 Twice as many as that of the other. In a high temperature corrosive environment containing chloride,destruction of Al 2 O 3 Oxide layer ratio Cr 2 O 3 It is much more difficult to significantly improve the high temperature chlorine corrosion resistance of the protective coating.
The protective material for the boiler tube provided by the invention comprises Cr:18 to 24wt.%, preferably 19 to 23wt.%, more preferably 20 to 22wt.%, and even more preferably 21wt.%. In the invention, cr is added to cause lattice distortion in the protective coating formed by laser cladding, so that elastic stress field reinforcement is generated, and solid solution reinforcement is realized. However, cr content should not be too high, which would lead to increased brittleness of the protective coating and to cracking. The invention controls the Cr content between 18 and 24 weight percent, which not only ensures that Cr atoms in solid solution can produce short-range ordered strengthening effect. In a high-temperature environment, continuous and compact protective Cr can be formed on the surface of the protective coating 2 O 3 The oxidation layer delays outward diffusion of metal elements and inward diffusion of corrosive media such as O, cl, S and the like, so that the high-temperature corrosion resistance of the protective coating is effectively improved.
The protective material for the boiler tube provided by the invention comprises Mo:5 to 7wt.%, preferably 5.5 to 6.5wt.%, more preferably 6wt.%. According to the invention, mo can reduce the high-temperature diffusion speed of Al, cr and other elements in the protective coating obtained by laser cladding of the protective material for the boiler pipe, strengthen the binding force of atoms in solid solution and improve the corrosion resistance, strength and high-temperature processability of the protective coating. In addition, mo can further accelerate θ -Al 2 O 3 To alpha-Al 2 O 3 Thereby obtaining a slowly growing dense oxide layer. Mo and Cr coupling also makes the oxide/metal interface flatter and more complete. However, the Mo content is not too high. Firstly, the excessive Mo content is easy to form volatile refractory metal oxide, which affects the integrity of the oxide layer; secondly, due to the nature of the laser cladding technique, too high Mo content is liable to cause severe segregation of the protective coating.
The protective material for the boiler tube provided by the invention comprises Co:1 to 5wt.%, preferably 2 to 4wt.%, more preferably 3wt.%. In the invention, co can reduce the protective material for the boiler tube to be obtained by laser claddingThe stacking fault energy of the protective coating makes dislocation movement difficult, and the strength of the material is improved, thereby causing solid solution strengthening. Also, it has been shown that Co sulfides are relatively stable and can effectively inhibit internal sulfidation. The invention can improve the high-temperature corrosion performance of the protective coating in the presence of alkali chloride and sulfate simultaneously by the action of Co and Cr. In addition, co promotes protection of oxides such as CoAl 2 O 4 Thereby making the etch layer denser with fewer point defects. The out-diffusion of metal atoms can be further suppressed, slowing down the corrosion rate. However, co is expensive and should not be added in excessive amounts. For protective coatings, co additions can be minimized if only high temperature chlorine corrosion is present in the corrosive environment.
The protective material for the boiler tube provided by the invention comprises Si:0.5 to 1wt.%, preferably 0.6 to 0.9wt.%, more preferably 0.7 to 0.8wt.%. In the invention, si can reduce the content of oxide in the protective coating obtained by laser cladding of the protective material for the boiler tube. In addition, si can change the growth mechanism of the oxide layer, improve the adhesiveness of the oxide layer and obviously improve the anti-stripping capability of the oxide layer. Small amounts of Si promote protective continuity of Al 2 O 3 The formation of the oxide layer does not deteriorate the stability of the gamma' phase. Small amounts of Si can also promote surface densification of Cr 2 O 3 And an oxidation layer is generated, so that the oxidation resistance, high-temperature corrosion resistance and high-temperature erosive wear resistance of the protective coating are improved.
The protective material for the boiler tube provided by the invention comprises the following components; zr:1 to 3wt.%, preferably 1.5 to 2.5wt.%, more preferably 2wt.%. In the present invention, zr is contained in the protective oxide layer (Al 2 O 3 、Cr 2 O 3 ) Is segregated at the grain boundaries of (a). Since the diffusion path of Zr ions is similar to, but not exactly the same as, al ions can be significantly inhibited from continuing to diffuse outward by the "blocking effect". In addition, zr ions can also effectively delay the peeling of the protective oxide layer by inhibiting the growth of interface pores and improving the interface strength between the oxide layer and the protective coating obtained by laser cladding of the protective material for the boiler tube. Zr can be rapidly diffused in a high-temperature corrosion environmentS which directly enters the protective coating or is released by sulfide oxidation is captured in time on the surface of the cladding layer, so that internal vulcanization-oxidation cycle reaction of the protective coating can be effectively prevented, and the high-temperature corrosion resistance of the protective coating when sulfate or chloride and sulfate coexist is further improved. However, once the Zr content is too high, zrO formation at the oxide grain boundaries is caused 2 Particles, which in turn, accelerate the transport of O and S, promoting internal oxidation and sulfidation. In addition, zrO 2 Will grow on the oxide layer (Cr 2 O 3 、Al 2 O 3 ) The larger local internal stress is introduced, and finally the oxide layer is cracked and peeled off, so that the adding amount of Zr is not excessively high. The proper amount of Zr not only can enhance the interfacial adhesion of the protective oxide layer, but also can enable the oxide layer to have higher high-temperature corrosion resistance and lower growth rate, which are very important for improving the durability of the protective coating in a high-temperature corrosion environment.
The protective material for the boiler tube provided by the invention comprises Ni: the balance. In the present invention, ni has a face-centered cubic structure, and is transformed from room temperature to a high Wen Moyi structure. In addition, the third layer of electronic shell layer of Ni atoms is basically filled, so that more alloy elements can be dissolved for alloying, the stability of gamma austenite phase is still maintained, and multiple ways are provided for improving the high-temperature corrosion and wear resistance of the protective coating formed after laser cladding. In addition, ni itself can prevent the inward diffusion of corrosive media by accumulating under the oxide layer, which contributes to the excellent corrosion resistance of the protective coating formed after laser cladding.
The invention also provides a preparation method of the protective material for the boiler tube, which comprises the following steps:
weighing raw materials; carrying out first melting on raw material Ni, then adding Cr, mo, co, si and Zr for second melting, and then adding Al for third melting to obtain alloy melt;
and atomizing the alloy melt to obtain the protective material for the boiler pipe.
The invention is characterized by weighing raw materials; and (3) carrying out first melting on raw material Ni, then adding Cr, mo, co, si and Zr for second melting, and then adding Al for third melting to obtain alloy melt.
In the invention, the mass fraction of the raw materials in the weighed raw materials is preferably carried out according to the mass fraction of the components of the protective material for the boiler tube according to the technical scheme. In the present invention, the purity of the raw material is preferably not less than 99.9%.
In the present invention, the first melting, the second melting and the third melting are preferably performed in a vacuum medium frequency induction furnace, and the model of the vacuum medium frequency induction furnace is preferably YC-2016028#. The temperature and time of the first melting, the second melting, and the third melting are not particularly limited as long as the raw materials can be melted.
After the third melting, the invention preferably further comprises heat preservation treatment; the temperature of the heat preservation treatment is preferably 1400-1500 ℃ and the time is preferably 10-30 min.
After the alloy melt is obtained, the protective material for the boiler tube is obtained by atomizing the alloy melt.
In the present invention, the atomized medium is preferably nitrogen. In the present invention, the atomization is preferably performed in an atomization rapid condensing apparatus. In the present invention, the alloy melt is preferably placed in a crucible of the atomizing rapid condensing device. In the present invention, the flow rate of the alloy melt during atomization is preferably 6 to 10kg/min.
After the atomization, the invention preferably further comprises sieving, wherein the pore diameter of the sieving screen is preferably 140-325 meshes.
In the present invention, the particle size of the protective material for a boiler tube is preferably 53 to 105. Mu.m.
The invention also provides a protection method of the boiler tube, which comprises the following steps:
preparing a protective coating on the boiler tubes;
the protective coating is obtained by laser cladding of the protective material for the boiler pipe or the protective material for the boiler pipe prepared by the preparation method of the technical scheme.
The present invention preferably further includes derusting the boiler tubes prior to preparing the protective coating. The operation of the rust removing treatment is not particularly limited in the present invention, and a rust removing operation well known to those skilled in the art may be employed.
In the present invention, a primer layer is preferably provided between the boiler tubes and the protective coating. In the present invention, the thickness of the primer layer is preferably 300 to 500 μm. In the present invention, the primer layer is preferably obtained by laser cladding a primer material. In the invention, the priming material preferably comprises the following components in parts by weight: al: 4-6 wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance.
In the present invention, the laser cladding parameters of the primer layer include: the powder supplementing gas is preferably high-purity nitrogen, the shielding gas is preferably high-purity argon, the laser is preferably an optical fiber laser, the rated output power of the laser is preferably 3-8 kW, the diameter of a laser beam focus spot is preferably 1-3 mm, the relative movement speed of the laser spot and a workpiece is preferably 5-25 cm/s, and the axial stepping distance is preferably 0.5-2.5 mm.
In the present invention, the protective coating preferably includes a first protective coating or a second protective coating.
In the invention, the preparation raw materials of the first protective coating preferably comprise the following components in percentage by mass: al:6 to 20wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance.
In the present invention, the laser cladding parameters of the first protective coating layer include: the powder supplementing gas is preferably high-purity nitrogen, the shielding gas is preferably high-purity argon, the laser is preferably an optical fiber laser, the rated output power of the laser is preferably 3-8 kW, the diameter of a laser beam focus spot is preferably 1-3 mm, the relative movement speed of the laser spot and a workpiece is preferably 5-25 cm/s, and the axial stepping distance is preferably 0.5-2.5 mm.
In the present invention, the thickness of the first protective coating is preferably 400 to 650 μm.
In the present invention, the first protective coating can be used for high temperature corrosion protection, typically high temperature wear.
In the present invention, the second protective coating preferably includes a first gradient protective coating and a second gradient protective coating which are sequentially stacked; the first gradient protective coating is preferably in contact with the primer layer.
In the present invention, the thickness of the first gradient protective coating layer and the second gradient protective coating layer is independently preferably 400 to 600 μm.
In the invention, the mass fraction of aluminum in the protective material for preparing the raw material boiler tube of the first gradient protective coating is preferably 8-12 wt%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance. In the invention, the laser cladding parameters of the first gradient protective coating comprise: the powder supplementing gas is preferably high-purity nitrogen, the shielding gas is preferably high-purity argon, the laser is preferably an optical fiber laser, the rated output power of the laser is 3-8 kW, the focal spot diameter of the laser beam is 1-3 mm, the relative movement speed of the laser spot and the workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm.
In the invention, the mass fraction of aluminum in the protective material for preparing the raw material boiler tube of the second gradient protective coating is preferably 15-20 wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance. In the present invention, the laser cladding parameters of the second gradient protective coating layer include: the powder supplementing gas is preferably high-purity nitrogen, the shielding gas is preferably high-purity argon, the laser is preferably an optical fiber laser, the rated output power of the laser is 3-8 kW, the diameter of a laser beam focus spot is 1-3 mm, the relative movement speed of the laser spot and a workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm.
In the present invention, the second protective coating can be applied to environments where high temperature corrosion and severe high temperature wear occur.
In the invention, when the laser cladding is carried out, the laser head is preferably fixed for the tubular sample, and the tubular sample performs rotary-stepping compound motion; for a plate-like sample, it is preferable that the steel plate is stationary and the laser head performs a linear reciprocating-stepping combined motion.
The protective material for boiler tubes, the method for producing the same, and the method for protecting boiler tubes according to the present invention will be described in detail with reference to examples, but they should not be construed as limiting the scope of the present invention.
Example 1 preparation of high temperature Corrosion resistant laser cladding protective coating on superheater tube heating surface
1. Powder composition and preparation
1. Alloy powder composition:
the preparation raw materials of the priming layer comprise the following components in percentage by mass: al:5wt.%; cr:22wt.%; mo:5wt.%; co:2wt.%; si:0.5wt.%; zr:1.25wt.%; ni: the balance.
The preparation raw materials of the first protective coating (high-temperature corrosion-resistant laser cladding protective coating) comprise the following components in percentage by mass: al:10wt.%; cr:20wt.%; mo:7wt.%; co:1wt.%; si:0.75wt.%; zr:1.5wt.%; ni: the balance.
2. Preparation of the preparation raw materials of the priming layer and the first protective coating:
weighing Ni, cr, al, mo, co, si and Zr according to the mass fraction in 1, firstly adding metal Ni into a vacuum intermediate frequency induction furnace, heating and melting, and adding Cr, mo, co, zr and Si after the Ni is completely melted; after Cr, mo, co, zr, ni and Si are completely melted, adding Al for melting; and (3) preserving the temperature of the melted alloy at 1400-1500 ℃ for 20min to obtain alloy melt.
Pouring the prepared alloy melt into a crucible of an atomization rapid condensing device, and atomizing and pulverizing by using the device to obtain Ni-Cr-Al-Mo-Co-Si-Zr alloy powder serving as a preparation raw material of the protective coating, wherein the particle size is 53-105 mu m; the atomizing medium was nitrogen and the alloy melt flow rate was 6kg/min.
2. Preparing a priming layer and a high-temperature corrosion-resistant laser cladding protective coating on a heating surface of a superheater tube
The superheater tubes were made of TP347H stainless steel having an outer diameter of 30mm and a length of 6m.
1. Preparation of a primer layer
(1) And derusting the outer surface of the superheater tube by using an electric grinding wheel.
(2) Filling the preparation raw materials of the priming layer into a powder storage container of a pneumatic synchronous powder feeding system, and selecting high-purity nitrogen as powder supplementing gas and high-purity argon as protective gas. The method of laser head static and superheater tube spiral motion relative to laser head, overlap cladding is adopted to prepare the priming layer.
(3) The fiber laser with rated power of 5kW is selected for laser cladding, and the parameters are as follows: the output power of the laser is 4kW, the diameter of a laser beam focus spot is 2mm, the relative movement speed of the laser spot and a workpiece is 15cm/s, the axial stepping distance is 1.2mm, and the priming layer with the average thickness of 400 mu m is obtained.
2. Preparation of high-temperature corrosion-resistant laser cladding protective coating
(1) Filling the Ni-Cr-Al-Mo-Co-Si-Zr alloy powder serving as a preparation raw material of the first protective coating into a powder storage container of a pneumatic synchronous powder feeding system, and preparing the protective coating on the surface of the priming layer by adopting the same method; the fiber laser with rated power of 3.3kW is selected for laser cladding, and the parameters are as follows: the output power of the laser is 4kW, the diameter of a laser beam focus spot is 2mm, the relative movement speed of the laser spot and a workpiece is 10cm/s, the axial stepping distance is 1.2mm, and the high-temperature corrosion-resistant laser cladding protective coating with the average thickness of about 600 mu m is obtained.
Example 2 preparation of high temperature Corrosion and wear resistant gradient laser cladding protective coating on Water wall tube heating surface
1. Powder composition and preparation
1. Alloy powder composition
The preparation raw materials of the priming layer comprise the following components in percentage by mass: al:5wt.%; cr:18wt.%; mo:5wt.%; co:2wt.%; si:0.5wt.%; zr:1.25wt.%; ni: the balance.
The preparation raw materials of the first gradient protective coating comprise the following components in percentage by mass: al:10wt.%; cr:18wt.%; mo:5wt.%; co:2wt.%; si:0.5wt.%; zr:1.2wt.%; ni: the balance.
The preparation raw materials of the second gradient protective coating comprise the following components in percentage by mass: al:20wt.%; cr:20wt.%; mo:6wt.%; co:2wt.%; si:0.5wt.%; zr:1.25wt.%; ni: the balance.
The preparation of the base layer, the preparation of the raw material for the preparation of the first gradient protective coating and the preparation of the raw material for the preparation of the second gradient protective coating are the same as in example 1.
2. And sequentially preparing a priming layer, a first gradient protective coating and a second gradient protective coating on the heating surface of the water wall pipe.
The water wall tube is made of 15CrMo steel, and has an outer diameter of 60mm and a length of 8m.
(1) And derusting the outer surface of the water wall pipe by using an electric grinding wheel.
(2) Filling the preparation raw materials of the priming layer into a powder storage container of a pneumatic synchronous powder feeding system, and selecting high-purity nitrogen as powder supplementing gas and high-purity argon as protective gas. Preparing a first gradient protective coating by adopting a method that a laser head is static, a water wall pipe performs spiral motion relative to the laser head and overlapping cladding is adopted; the fiber laser with rated power of 5kW is selected for laser cladding, and the parameters are as follows: the output power of the laser is 5kW, the focal spot diameter of the laser beam is 2mm, the relative movement speed of the laser spot and the workpiece is 15cm/s, the axial stepping distance is 1.6mm, and the bottom layer with the average thickness of about 400 mu m is obtained.
(3) Filling the preparation raw materials of the first gradient protective coating into a powder storage container of a pneumatic synchronous powder feeding system, and continuously preparing the first gradient protective coating on the surface of the prepared priming layer by adopting the same method; the main parameters are as follows: the output power of the laser is 5kW, the focal spot diameter of the laser beam is 2mm, the relative movement speed of the laser spot and the workpiece is 10cm/s, the axial stepping distance is 1.6mm, and the second protective coating with the average thickness of about 400 mu m is obtained.
(4) Filling the preparation raw materials of the second gradient protective coating into a powder storage container of a pneumatic synchronous powder feeding system, and continuously preparing the second gradient protective coating on the surface of the prepared first protective coating by adopting the same method; the main parameters are as follows: the output power of the laser is 5kW, the diameter of a laser beam focus spot is 2mm, the relative movement speed of the laser spot and a workpiece is 8cm/s, the axial stepping distance is 1.5mm, and the third gradient protective coating with the average thickness of about 400 mu m is obtained.
Performance testing
Carrying out a thermal shock test on the heating surface of the superheater tube provided with the priming layer and the protective coating, which is obtained in the embodiment 1, wherein the specific process is as follows: and heating the heating surface of the superheater tube provided with the priming layer and the protective coating to 750 ℃, preserving heat for 10min, rapidly quenching in water of 20-25 ℃ for quenching, and repeating 100 times. The results are shown in FIG. 1. Fig. 1 is a surface topography diagram of the protective coating obtained in example 1 after 100 thermal shock tests, wherein the left graph is a picture of the protective coating after the thermal shock test without applying the flaw detector, and the right graph is a picture of the protective coating after the thermal shock test with applying the flaw detector. As can be seen from fig. 1: after flaw detection, the protective coating is proved to have no cracks after 100 times of thermal shock experiments, and has excellent protective effect.
FIG. 2 is a cross-sectional profile of the principal elements in the protective coating obtained in example 1. As can be seen from fig. 2: fe from the substrate drops sharply after entering the protective coating, which is already negligible at the surface; cr and Mo elements are uniformly distributed in the protective coating; the Al content increased sharply after 500 μm from the matrix, and met the desired Al content range at the near-surface location.
FIG. 3 is a graph showing the weight loss per unit area of the protective coating and the Inconel625 alloy laser cladding layer obtained in example 1 after being exposed to a NaCl-KCl mixed salt at 700℃for 144 hours. As can be seen from fig. 3: in the high temperature corrosive environment of chloride deposited salts, the protective coating of the present invention can be about 15 times as corrosion resistant as commonly used in boiler tube corrosion protective materials (Inconel 625).
FIG. 4 is a cross-sectional morphology diagram of the protective coating obtained in example 1 and the Inconel625 alloy laser cladding layer after being exposed to a 700 ℃ NaCl-KCl mixed salt for 144 hours, wherein the left graph is the Inconel625 alloy laser cladding layer, and the right graph is the protective coating obtained in example 1. As can be seen from fig. 4: the thickness of the corrosion product on the surface of the Inconel625 alloy laser cladding layer can reach about 110 mu m, and the thickness of the corrosion product on the surface of the protective coating layer is only 2 mu m.
FIG. 5 is a cross-sectional profile of the principal elements in the protective coating obtained in example 2. As can be seen from fig. 5: the elemental content of Fe from the substrate drops sharply after entering the protective coating, which is already negligible at the surface. The Al element content is increased in a gradient manner in the protective coating.
FIG. 6 is a graph showing the mass loss of the protective coating and the Inconel625 alloy laser cladding obtained in example 2 after a high-temperature erosion test at 900℃for 8 minutes. As can be seen from fig. 6: in a high temperature erosive wear environment, the high temperature erosive wear resistance of the protective coating can be up to about 2.8 times that of the corrosion protective material (Inconel 625) commonly used in boiler tubes.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (10)
1. The protective material for the boiler tube is characterized by comprising the following components in percentage by mass:
al:6 to 20wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance.
2. The method for preparing the protective material for the boiler tubes according to claim 1, comprising the following steps:
weighing raw materials;
carrying out first melting on raw material Ni, then adding Cr, mo, co, si and Zr for second melting, and then adding Al for third melting to obtain alloy melt;
and atomizing the alloy melt to obtain the protective material for the boiler pipe.
3. A method of protecting boiler tubes, comprising the steps of:
preparing a protective coating on the boiler tubes;
the protective coating is obtained by laser cladding of the protective material for the boiler pipe according to claim 1 or the protective material for the boiler pipe prepared by the preparation method according to claim 2.
4. A protection method according to claim 3, wherein a primer layer is provided between the boiler tubes and the protective coating; the priming layer is obtained by cladding priming material through laser; the priming material comprises the following components in percentage by mass:
al: 4-6 wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance.
5. The method of claim 4, wherein the primer layer has a thickness of 300 to 500. Mu.m.
6. The method of claim 4 or 5, wherein the parameters of laser cladding of the primer layer include: the powder supplementing gas is high-purity nitrogen, the shielding gas is high-purity argon, the laser is an optical fiber laser, the rated output power of the laser is 3-8 kW, the diameter of a laser beam focus spot is 1-3 mm, the relative movement speed of the laser spot and a workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm.
7. A method of protecting according to claim 3, wherein the protective coating comprises a first protective coating or a second protective coating;
the preparation raw materials of the first protective coating comprise the following components in percentage by mass: al:6 to 20wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance;
the laser cladding parameters of the first protective coating comprise: the powder supplementing gas is high-purity nitrogen, the shielding gas is high-purity argon, the laser is an optical fiber laser, the rated output power of the laser is 3-8 kW, the diameter of a laser beam focus spot is 1-3 mm, the relative movement speed of the laser spot and a workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm;
the thickness of the first protective coating is 400-650 mu m.
8. The method of claim 7, wherein the second protective coating comprises a first gradient protective coating and a second gradient protective coating stacked in sequence; the first gradient protective coating is in contact with the primer layer;
the preparation raw materials of the first gradient protective coating comprise the following components in percentage by mass: al: 8-12 wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance;
the preparation raw materials of the second gradient protective coating comprise the following components in percentage by mass: al: 15-20 wt.%; cr: 18-24 wt.%; mo: 5-7 wt.%; co:1 to 5wt.%; si:0.5 to 1wt.%; zr: 1-3 wt.%; ni: the balance.
9. The protective coating for boiler tubes according to claim 8, wherein the first and second gradient protective coatings independently have a thickness of 400-600 μm.
10. The protection method according to claim 8 or 9, wherein the laser cladding parameters of the first gradient protection coating layer include: the powder supplementing gas is high-purity nitrogen, the shielding gas is high-purity argon, the laser is an optical fiber laser, the rated output power of the laser is 3-8 kW, the diameter of a laser beam focus spot is 1-3 mm, the relative movement speed of the laser spot and a workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm;
the laser cladding parameters of the second gradient protective coating comprise: the powder supplementing gas is high-purity nitrogen, the shielding gas is high-purity argon, the laser is an optical fiber coupling output semiconductor laser or an optical fiber laser, the rated output power of the laser is 3-8 kW, the diameter of a laser beam focus spot is 1-3 mm, the relative movement speed of the laser spot and a workpiece is 5-25 cm/s, and the axial stepping distance is 0.5-2.5 mm.
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