A method for composite spraying of corrosion and wear resistant stainless steel parts

Abstract

This invention discloses a composite spraying process for corrosion-resistant and wear-resistant stainless steel parts, comprising the following steps: S1, pretreatment: degreasing and sandblasting roughening treatment of the stainless steel parts surface to achieve a surface roughness Ra of 5-15 μm; S2, spraying the base layer: preparing an alloy base layer on the pretreated stainless steel parts surface using a supersonic flame spraying process, with a base layer thickness of 80-150 μm; S3, spraying the intermediate layer: preparing a composite metal intermediate layer on the base layer surface using a supersonic flame spraying process, with an intermediate layer thickness of 150-250 μm; S4, spraying the top layer: preparing a composite metal top layer on the intermediate layer surface using a supersonic flame spraying process, with a top layer thickness of 100-200 μm; S5, sealing treatment: sealing the composite coating using a vacuum pressure impregnation process; the thermal expansion coefficients of the base layer, intermediate layer, and top layer in this invention exhibit a gradient transition, resulting in low thermal stress between layers and making them less prone to cracking and peeling under thermal cycling and temperature change conditions.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, and in particular to a composite spraying method for corrosion-resistant and wear-resistant stainless steel parts. Background Technology

[0002] Stainless steel is widely used in petrochemical, marine engineering, food machinery, medical devices, and aerospace industries due to its excellent corrosion resistance and mechanical properties. However, under harsh working conditions such as chloride ion content, acidic media, high-temperature oxidation, and abrasive erosion, ordinary stainless steel parts still face serious localized corrosion (such as pitting corrosion, crevice corrosion, and stress corrosion cracking) and wear damage, leading to shortened equipment lifespan, increased safety risks, and higher maintenance costs.

[0003] Currently, the main technical means to improve the corrosion resistance and wear resistance of stainless steel parts include electroplating, chemical plating, thermal spraying, vapor deposition, laser cladding, and anodizing.

[0004] Electroplating hard chrome is a traditional surface strengthening process with advantages such as high hardness and good wear resistance, but it has the following prominent problems: the electroplating process generates waste liquid and waste gas containing hexavalent chromium, which seriously pollutes the environment and has been subject to increasingly stringent environmental regulations; the coating and the substrate are mechanically bonded, and the bonding strength is limited, making it easy to peel off under heavy load or impact conditions; microcracks exist inside the electroplated layer, and corrosive media can easily penetrate along the cracks, reducing corrosion resistance; the uniformity of the coating thickness is difficult to control, and the coating thickness varies greatly on workpieces with complex shapes.

[0005] Electroless nickel-phosphorus alloy plating has good uniformity and corrosion resistance, but the coating hardness is relatively low (it can reach HV800-900 after heat treatment), and the wear resistance is insufficient to meet the requirements of high wear conditions; the plating solution has poor stability, high cost, and short service life; phosphorus-containing waste liquid is difficult to treat and faces great environmental pressure.

[0006] Conventional thermal spraying technologies (flame spraying, arc spraying, and plasma spraying) can prepare ceramic and cermet coatings with large coating thickness and wide applicability. However, they have the following drawbacks: flame spraying and arc spraying coatings have high porosity (typically 5%-15%), allowing corrosive media to easily penetrate the coating and reach the substrate interface, causing interfacial corrosion and coating peeling; plasma spraying equipment is expensive, energy-intensive, complex to operate, and has low spraying efficiency; single ceramic coatings (such as alumina and chromium oxide) have high hardness but poor toughness, making them prone to cracking and peeling under impact loads; single metal coatings (such as nickel-based alloys) have good corrosion resistance but insufficient wear resistance, making it difficult to meet the dual requirements of corrosion resistance and wear resistance. Summary of the Invention

[0007] This invention proposes a composite spraying method for corrosion-resistant and wear-resistant stainless steel parts to solve the problems mentioned in the background art.

[0008] This invention proposes a composite spraying method for corrosion-resistant and wear-resistant stainless steel parts, comprising the following steps: S1. Pretreatment: The stainless steel parts are degreased and sandblasted to roughen the surface, so that the surface roughness Ra reaches 5-15μm. S2. Spraying underlayer: An alloy underlayer is prepared on the surface of the pretreated stainless steel parts using a supersonic flame spraying process, and the thickness of the underlayer is 80-150μm. S3. Spraying intermediate layer: A composite metal intermediate layer is prepared on the surface of the bottom layer using a supersonic flame spraying process. The thickness of the intermediate layer is 150-250μm. S4. Sprayed surface layer: A composite metal surface layer is prepared on the surface of the intermediate layer using a supersonic flame spraying process, and the surface layer thickness is 100-200μm. S5. Sealing treatment: Vacuum pressure impregnation process is used to seal the pores of the composite coating;

[0009] The total thickness of the bottom layer, intermediate layer and top layer is 330-600μm, with the bottom layer accounting for 15%-25% of the total thickness, the intermediate layer accounting for 35%-55% of the total thickness, and the top layer accounting for 25%-40% of the total thickness.

[0010] Preferably, in step S1, the specific steps for degreasing are as follows:

[0011] Use an alkaline cleaning agent to ultrasonically clean at 50-70℃ for 10-20 minutes, then wash with hot water and pure water in sequence, and dry at 100-120℃.

[0012] The roughening treatment uses brown or white fused alumina abrasive with a particle size of 30-60 mesh, a blasting pressure of 0.5-0.8 MPa, a blasting angle of 75°-90°, and a blasting distance of 150-250 mm. The surface cleanliness after blasting reaches the Sa2.5 standard.

[0013] Preferably, in step S2, the alloy base layer has the following composition by mass percentage: Cr 18%-25%, with the balance being Ni and unavoidable impurities, powder particle size 15-45μm, and purity ≥99.5%.

[0014] Preferably, in step S3, the composite metal interlayer is composed of 60%-75% chromium carbide and 25%-40% NiCr alloy by mass percentage, with a powder particle size of 15-45 μm.

[0015] Preferably, in step S4, the composite metal surface layer is composed of 85%-92% alumina and 8%-15% titanium dioxide by mass percentage, with a powder particle size of 15-45μm and a purity of ≥99.5%.

[0016] Preferably, in step S5, the sealing agent is selected from silicone resin sealing agents or nano-sized sealing agents. Sol-gel sealing agent.

[0017] Preferably, it also includes post-processing and inspection, with specific steps as follows:

[0018] The workpieces that have been sprayed and sealed are then precision machined to achieve a surface roughness Ra≤1.6μm;

[0019] The coating bonding strength was tested using the scratch test or tensile test, and the coating bonding strength was ≥70MPa.

[0020] The corrosion resistance was tested by salt spray test, and no red rust was observed after ≥1000 hours of neutral salt spray test;

[0021] Abrasive wear test was used to test wear resistance, with wear volume ≤ 0.5 mm³.

[0022] Preferably, after the sandblasting roughening treatment is completed, the base coat is applied within 4-6 hours; the base coat, intermediate coat and top coat are all applied continuously in the same spray booth, with the temperature of the spray booth controlled at 15-30℃ and the relative humidity ≤60%.

[0023] The present invention proposes a composite spraying method for corrosion-resistant and wear-resistant stainless steel parts, the advantages of which are as follows: 1. This invention forms an anchoring structure on the stainless steel surface through sandblasting roughening treatment, and combined with the high kinetic energy particle impact of supersonic flame spraying, so that the NiCr alloy bottom layer and the stainless steel substrate form a strong mechanical locking and diffusion bond with a bonding strength ≥70MPa, which is more than 40% higher than that of conventional thermal spray coating. 2. The bottom layer of this invention provides an excellent barrier against corrosion; the NiCr alloy phase in the intermediate layer further blocks corrosion channels; the top layer has high chemical inertness and strong corrosion resistance; the vacuum pressure impregnation and sealing treatment seals the micropores remaining in the coating, forming a complete and dense protective barrier. The corrosion resistance of the composite coating is more than twice that of the single coating. 3. The thermal expansion coefficients of the bottom layer, middle layer and top layer in this invention are gradient transitions, the thermal stress between each layer is small, and it is not easy to crack and peel off under thermal cycling and temperature change conditions. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments.

[0025] This invention proposes a composite spraying method for corrosion-resistant and wear-resistant stainless steel parts, comprising the following steps:

[0026] Step 1: Preprocessing

[0027] The stainless steel parts are degreased to remove oil and organic contaminants. Specifically, the parts are ultrasonically cleaned for 10-20 minutes at 50-70℃ with an alkaline cleaning agent, then washed with hot water and pure water in sequence, and finally dried at 100-120℃.

[0028] After degreasing, the workpiece undergoes sandblasting roughening treatment, specifically as follows: Brown or white fused alumina abrasive is used, with a particle size of 30-60 mesh; the sandblasting pressure is 0.5-0.8 MPa; the sandblasting angle is 75°-90°; and the sandblasting distance is 150-250 mm. After sandblasting, the workpiece surface roughness Ra reaches 5-15 μm, and the surface cleanliness reaches Sa2.5 standard, in order to remove the surface passivation film and form an anchoring structure.

[0029] After sandblasting, apply a coating within 4-6 hours to prevent the surface from oxidizing or becoming contaminated again.

[0030] Step 2: Apply the primer

[0031] An alloy underlayer was prepared on the surface of pretreated stainless steel parts using a high-velocity oxygen flame spraying (HVOF) process. The material formulation of the underlayer was as follows (by mass percentage): Cr 18%-25%, with the balance being Ni and unavoidable impurities. The powder particle size was 15-45 μm, and the purity was ≥99.5%.

[0032] The spraying process parameters are as follows: oxygen flow rate 800-1000L / min, kerosene flow rate 20-30L / h, powder feeding rate 40-60g / min, spraying distance 300-400mm, spraying angle 75°-90°, spray gun moving speed 500-800mm / s, and overlap rate of 30%-50% per coat. The thickness of the base coat is controlled at 80-150μm.

[0033] Step 3: Spray the intermediate layer

[0034] A composite metal intermediate layer is prepared on the surface of the base layer using a high-velocity oxygen flame spraying (HVOF) process. The material formulation of the intermediate layer consists of 60%-75% chromium carbide by mass percentage. It consists of 25%-40% NiCr alloy and powder particle size of 15-45μm.

[0035] The spraying process parameters are as follows: oxygen flow rate 900-1100 L / min, kerosene flow rate 22-32 L / h, powder feeding rate 35-55 g / min, spraying distance 280-380 mm, spraying angle 75°-90°, spray gun moving speed 400-700 mm / s, and overlap rate of 30%-50% per coat. The thickness of the intermediate layer is controlled at 150-250 μm.

[0036] Step 4: Spray the topcoat

[0037] A composite metal topcoat is prepared on the surface of the intermediate layer using a high-velocity oxygen flame (HVOF) spraying process. The topcoat material formulation consists of 85%-92% alumina by mass percentage. ) and 8%-15% titanium dioxide ( It consists of powder particles of 15-45μm and a purity of ≥99.5%.

[0038] The spraying process parameters are as follows: oxygen flow rate 1000-1200L / min, kerosene flow rate 24-34L / h, powder feeding rate 30-50g / min, spraying distance 250-350mm, spraying angle 75°-90°, spray gun moving speed 300-600mm / s, and overlap rate of 30%-50% per coat. The surface layer thickness is controlled at 100-200μm.

[0039] Step 5: Sealing the holes

[0040] Vacuum pressure impregnation is used to seal the surface layer. The sealing agent selected is either silicone resin or nano-sized silicone resin. The vacuum pressure impregnation process parameters for the sol-gel sealing agent are: vacuum degree ≤ -0.095MPa, pressure holding time 10-30 minutes, pressure 0.3-0.6MPa, and impregnation time 20-40 minutes.

[0041] After sealing, a curing process is performed at a temperature of 120-180℃ for 1-3 hours.

[0042] Step Six: Control of Total Thickness of Composite Coating

[0043] The total thickness of the bottom layer, intermediate layer and top layer is controlled between 330-600μm, and the proportion of each layer thickness is as follows: the bottom layer accounts for 15%-25% of the total thickness, the intermediate layer accounts for 35%-55% of the total thickness, and the top layer accounts for 25%-40% of the total thickness.

[0044] Step 7: Post-processing and Inspection

[0045] The workpieces after spraying and sealing are then precision machined to remove spraying flash and surface burrs, achieving a surface roughness Ra ≤ 1.6 μm. The total thickness of the composite coating and the thickness of each layer are measured using an eddy current thickness gauge. The coating bonding strength is tested using the scratch method or tensile method, with a bonding strength ≥ 70 MPa. Corrosion resistance is tested using a salt spray test, with no red rust observed after ≥ 1000 hours of neutral salt spray testing. Abrasive wear resistance is tested using an abrasive wear test, with a wear volume ≤ 0.5 mm³.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite spraying method for corrosion-resistant and wear-resistant stainless steel parts, characterized in that, Includes the following steps: S1. Pretreatment: The stainless steel parts are degreased and sandblasted to roughen the surface, so that the surface roughness Ra reaches 5-15μm. S2. Spraying underlayer: An alloy underlayer is prepared on the surface of the pretreated stainless steel parts using a supersonic flame spraying process, and the thickness of the underlayer is 80-150μm. S3. Spraying intermediate layer: A composite metal intermediate layer is prepared on the surface of the bottom layer using a supersonic flame spraying process. The thickness of the intermediate layer is 150-250μm. S4. Sprayed surface layer: A composite metal surface layer is prepared on the surface of the intermediate layer using a supersonic flame spraying process, and the surface layer thickness is 100-200μm. S5. Sealing treatment: Vacuum pressure impregnation process is used to seal the pores of the composite coating; The total thickness of the bottom layer, intermediate layer and top layer is 330-600μm, with the bottom layer accounting for 15%-25% of the total thickness, the intermediate layer accounting for 35%-55% of the total thickness, and the top layer accounting for 25%-40% of the total thickness.

2. The composite spraying method for corrosion-resistant and wear-resistant stainless steel parts according to claim 1, characterized in that, In step S1, the specific steps for degreasing are as follows: Use an alkaline cleaning agent to ultrasonically clean at 50-70℃ for 10-20 minutes, then wash with hot water and pure water in sequence, and dry at 100-120℃. The roughening treatment uses brown or white fused alumina abrasive with a particle size of 30-60 mesh, a blasting pressure of 0.5-0.8 MPa, a blasting angle of 75°-90°, and a blasting distance of 150-250 mm. The surface cleanliness after blasting reaches the Sa2.5 standard.

3. The composite spraying method for corrosion-resistant and wear-resistant stainless steel parts according to claim 1, characterized in that, In step S2, the alloy base layer has the following composition by mass percentage: Cr 18%-25%, with the balance being Ni and unavoidable impurities, powder particle size 15-45μm, and purity ≥99.5%.

4. The composite spraying method for corrosion-resistant and wear-resistant stainless steel parts according to claim 1, characterized in that, In step S3, the composite metal interlayer is composed of 60%-75% chromium carbide and 25%-40% NiCr alloy by mass percentage, with a powder particle size of 15-45 μm.

5. The composite spraying method for corrosion-resistant and wear-resistant stainless steel parts according to claim 1, characterized in that, In step S4, the composite metal surface layer is composed of 85%-92% alumina and 8%-15% titanium dioxide by mass percentage, with a powder particle size of 15-45μm and a purity of ≥99.5%.

6. The composite spraying method for corrosion-resistant and wear-resistant stainless steel parts according to claim 1, characterized in that, In step S5, the sealing agent is selected from silicone resin sealing agents or nano-sized sealing agents. Sol-gel sealing agent.

7. The composite spraying method for corrosion-resistant and wear-resistant stainless steel parts according to claim 1, characterized in that, It also includes post-processing and inspection, with specific steps as follows: The workpieces that have been sprayed and sealed are then precision machined to achieve a surface roughness Ra≤1.6μm; The coating bonding strength was tested using the scratch test or tensile test, and the coating bonding strength was ≥70MPa. The corrosion resistance was tested by salt spray test, and no red rust was observed after ≥1000 hours of neutral salt spray test; Abrasive wear test was used to test wear resistance, with wear volume ≤ 0.5 mm³.

8. The composite spraying method for corrosion-resistant and wear-resistant stainless steel parts according to claim 1, characterized in that, After the sandblasting roughening treatment is completed, the base coat is applied within 4-6 hours. The base coat, intermediate coat and top coat are all applied continuously in the same spray booth, with the temperature controlled at 15-30℃ and the relative humidity ≤60%.