High-wear-resistance Fe-based fine-grain laser cladding layer on nodular cast iron surface and preparation method thereof

Abstract

The invention relates to the field of laser cladding surface strengthening and remanufacturing, and discloses a spheroidal graphite cast iron surface high-wear-resistance Fe-based fine-grain laser cladding layer and a preparation method thereof.The cladding layer is prepared on the surface of a spheroidal graphite cast iron base material through a laser cladding method, and cladding alloy powder is composed of reduced iron powder and ferrovanadium powder which are different in particle size according to a certain proportion; and the high-wear-resistance Fe-based fine-grain laser cladding layer on the surface of the nodular cast iron is prepared. The alloy powder for laser cladding is only composed of reduced iron powder and ferrovanadium powder, the formula is simple, manufacturing is easy, a large amount of in-situ self-generated VC is successfully obtained through reverse transition of graphite in a nodular cast iron base material, and a cladding layer is composed of martensite, a large amount of eutectic structures distributed between crystals and the in-situ self-generated VC. The surface hardness and wear resistance of the nodular cast iron base material can be greatly improved under the condition that the simple alloy powder is adopted, and the cost for repairing or modifying the surface defects of the iron casting is low.

Description

Technical Field

[0001] The present invention relates to the field of laser cladding surface strengthening and remanufacturing, and in particular to a high-wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron and a preparation method thereof. Background Art

[0002] Ductile iron (Ductile iron) boasts excellent wear and impact resistance, capable of withstanding high pressure and high temperature environments. It is widely used in a variety of fields, including automotive, machinery, piping, and mining equipment. However, with the rapid development of industry and the demands of modern industry, ductile iron is increasingly exposed to extreme conditions, often experiencing severe wear and corrosion, leading to damage and failure of the workpiece. Repairing or modifying surface defects in cast iron parts is crucial to extend their service life and expand their applications. Currently, the industry primarily utilizes techniques such as arc spraying, electron beam welding, and inert gas shielded welding to repair ductile iron workpieces. However, due to the high carbon content of ductile iron, hard and brittle phases are easily formed at the interface during welding and cladding, reducing the tensile strength of the interface. During cooling, shrinkage of the weld and cladding layer also generates high residual stresses, leading to cracks at the interface.

[0003] Laser cladding is a surface modification technology gaining widespread application, producing high-performance cladding layers that are metallurgically bonded to the substrate. Compared to other welding processes, laser cladding offers greater precision and controllability, higher efficiency, and relatively low heat input, making the quality of the finished product more controllable when repairing ductile iron. Iron-based alloy powders are widely used due to their low cost, excellent wear resistance, and similar composition to the substrate, resulting in minimal residual stress.

[0004] Chinese Patent Publication No. CN115786907A discloses a laser cladding powder and a method for laser cladding on a ductile iron surface. The alloy powder used comprises: 30wt% to 65wt% of a first powder and 35wt% to 70wt% of a second powder. The first powder comprises 0.01wt% to 0.05wt% C, 1wt% to 3wt% Cr, 1wt% to 2.5wt% Si, 0.1wt% to 1wt% Fe, 0.5wt% to 1.5wt% B, 0.5wt% to 2wt% Co, 15wt% to 30wt% Cu, and the balance Ni. The second powder is tungsten carbide powder. Although the cladding layer can achieve a high hardness, the alloy powder formula is relatively complex, the alloy element content is high, and the overall powder cost is high. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron with low comprehensive cost, and a preparation method of the high wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron.

[0006] In order to solve the above technical problems, a method for preparing a highly wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron is proposed. The cladding layer is prepared on the surface of a ductile iron substrate by laser cladding, and the cladding alloy powder is composed of reduced iron powder and vanadium iron powder with different particle sizes in a certain proportion.

[0007] Preferably, the alloy powder comprises: 51.5 wt.% reduced iron powder, 48.5 wt.% ferrovanadium powder, and the ferrovanadium powder is FeV50.

[0008] Preferably, the alloy powder is a variable-size alloy powder, with the reduced iron powder having a particle size range of 100-200 mesh and the ferrovanadium powder having a particle size range of 400-600 mesh. Because the reduced iron powder and ferrovanadium powder use different particle size ranges, the alloy powder waste collected after laser cladding can be easily sieved to separate the reduced iron powder and ferrovanadium powder, allowing the recovered alloy powder to be reused.

[0009] Preferably, a synchronous powder feeding laser cladding method is adopted, and the cladding alloy powder is composed of reduced iron powder and vanadium iron powder of different particle sizes in a certain proportion, the laser power is 1000W, the pulse frequency is 4500Hz, the duty cycle is 95%, the spot diameter is 2.0mm, the scanning speed is 12mm / s, the overlap rate is 30%, the powder feeding amount is 6-7g / min, the powder feeding gas flow rate is 4.5L / min, and the coaxial shielding gas argon flow rate is 16L / min.

[0010] Preferably, the alloy powder is mixed in a V-type powder mixer for 1.5-3 hours before laser cladding.

[0011] The high-wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron of the present invention is prepared by any of the above-mentioned methods for preparing the high-wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron.

[0012] The present invention has the following beneficial effects: the alloy powder for laser cladding, consisting solely of reduced iron powder and ferrovanadium powder, has a simple formulation and is easy to manufacture. Although graphite is not added to the cladding powder, by combining specific laser parameters and leveraging the reverse transition of graphite in the ductile iron substrate, a large amount of in-situ self-generated VC is successfully obtained. The cladding layer consists of martensite, a large amount of eutectic structure distributed between grains, and in-situ self-generated VC. Due to the increased consumption of carbon in the cladding layer, the generated cementite participates in the eutectic reaction, resulting in a large amount of uniformly distributed eutectic structure.

[0013] When laser cladding is performed on ductile iron substrates for surface strengthening and remanufacturing, no preheating and slow cooling steps are required. The resulting cladding layer is free of obvious crack defects and is composed of a large number of equiaxed crystals and some near-equiaxed crystals. The average hardness of the cladding layer can reach 950 HV0.2, approximately 3.25 times that of the ductile iron substrate, and the wear resistance of the cladding layer is approximately 48.8 times that of the ductile iron substrate. Compared with the existing technology, the present invention significantly improves the surface hardness and wear resistance of the ductile iron substrate while using a relatively simple alloy powder. This reduces the cost of repairing or modifying surface defects in cast iron parts, thereby extending their service life and broadening their application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The optical macroscopic topography image of the upper surface of the cladding layer obtained for the embodiment;

[0015] Figure 2 The cross-sectional morphology of the cladding layer obtained in control example 1;

[0016] Figure 3 The cross-sectional morphology of the cladding layer obtained for control example 2;

[0017] Figure 4 The cross-sectional morphology of the cladding layer obtained for the embodiment;

[0018] Figure 5 The optical microscopic morphology of the cladding layer obtained for control example 1;

[0019] Figure 6 The optical microscopic morphology of the cladding layer obtained for the embodiment;

[0020] Figure 7 The secondary electron morphology image of the cladding layer obtained in the embodiment is obtained by scanning electron microscope;

[0021] Figure 8 The microhardness distribution curves of the cladding layer and the ductile iron substrate obtained in Example and Comparative Example 1 are shown;

[0022] Figure 9 This is a cross-section of the friction and wear profile of the cladding layer and ductile iron in the embodiment;

[0023] Figure 10 The wear morphology of the cladding layer prepared in Example.

[0024] Figure 11 This is the wear morphology of ductile iron. DETAILED DESCRIPTION

[0025] Unless otherwise specified, the instruments, reagents, and materials used in the following examples are all conventional instruments, reagents, and materials available in the prior art and can be obtained through regular commercial channels. The experimental methods and detection methods used in the following examples are all conventional experimental methods and detection methods available in the prior art, unless otherwise specified.

[0026] The following examples and control examples were used to prepare the cladding layer:

[0027] Laser cladding was performed on a ductile iron substrate using a conventional synchronous powder feeding laser cladding method. The cladding alloy powder consisted of reduced iron powder and ferrovanadium powder of varying particle sizes. The laser power was 1000W, the laser pulse frequency was 4500Hz, the duty cycle was 95%, the spot diameter was 2.0mm, the scanning speed was 12mm / s, the overlap ratio was 30%, the powder feed rate was 6-7g / min, the feed gas flow rate was 4.5L / min, and the coaxial shielding gas flow rate was 16L / min. The alloy powders were variable in size: the reduced iron powder had a particle size range of 100-200 mesh, and the ferrovanadium powder had a particle size range of 400-600 mesh. The ferrovanadium powder was FeV50 with a vanadium content of 47.80 wt%. The alloy powders were mixed in a V-type powder mixer for 2 hours before laser cladding.

[0028] Example

[0029] The alloy powder comprises: 51.5 wt.% of reduced iron powder and 48.5 wt.% of ferrovanadium powder.

[0030] Comparative Example 1

[0031] The difference from the embodiment is that the alloy powder comprises: 67.6 wt. % reduced iron powder and 32.4 wt. % ferrovanadium powder.

[0032] Comparative Example 2

[0033] The difference from the embodiment is that the alloy powder includes: 66.42 wt.% reduced iron powder, 32.4 wt.% ferrovanadium powder, and 1.18 wt.% graphite.

[0034] See also Figure 1 , the optical macroscopic morphology of the upper surface of the cladding layer obtained in Example 1 shows that the surface of the cladding layer is smooth and the macroscopic formation is good.

[0035] See also Figure 2 From the cross-sectional morphology of the cladding layer obtained in control example 1, it can be seen that the cladding layer has obvious defects, namely, there are large and numerous pores accompanied by cracks.

[0036] See also Figure 3From the cross-sectional morphology of the cladding layer obtained in control example 2, it can be seen that the cladding layer has obvious defects, namely, there are large and numerous pores accompanied by cracks.

[0037] See also Figure 4 , the cross-sectional morphology of the cladding layer obtained in Example 1 shows that no obvious cracks or pore defects are found in the cladding layer.

[0038] See also Figure 5 The optical microscopic morphology of the cladding layer obtained in the control example is composed of a large number of equiaxed crystals and some nearly equiaxed crystals.

[0039] See also Figure 6 The optical microscopic morphology of the cladding layer produced in Example 1 shows that it is composed of a large number of equiaxed crystals and some near-equiaxed crystals, with a dense distribution of eutectic structures, similar to a skeleton, between the crystals. The average grain size of the cladding layer is 1.84 μm. The large undercooling during the cladding process inhibits grain growth. The cladding layer also contains a large amount of in-situ self-generated VC, which can serve as a nucleus for heterogeneous nucleation and is distributed along grain boundaries, hindering grain growth.

[0040] See also Figure 7 A scanning electron microscope secondary electron topography image of the cladding layer obtained in Example 1 shows that, despite the absence of graphite in the cladding powder, a large amount of in-situ self-generated VC was successfully obtained through the reverse transition of graphite in the ductile iron substrate. The cladding layer consists of martensite, a large amount of eutectic structure distributed between grains, and in-situ self-generated VC. Due to the increased consumption of carbon in the cladding layer, the generated cementite participates in the eutectic reaction, resulting in a large amount of uniformly distributed eutectic structure.

[0041] See also Figure 8 The microhardness distribution curves of the cladding layers obtained in the embodiment and the control example show that the average microhardness of the cladding layer obtained in the embodiment is 950HV0.2, and the hardness of the cladding layer is greatly improved compared with the ductile iron substrate, which is about 3.25 times that of the ductile iron substrate.

[0042] See also Figure 9 , the friction and wear profile cross section of the embodiment cladding layer and the ductile iron substrate. The wear loss of the embodiment cladding layer and the ductile iron substrate was measured to be 0.126mm 3 and 6.15mm 3 It can be inferred that the wear resistance of the cladding layer in the embodiment is about 48.8 times that of the ductile iron substrate. Due to its high average hardness, the protection of the eutectic structure and the dispersion strengthening effect of in-situ autogenous VC, it exhibits extremely excellent wear resistance.

[0043] See also Figure 10 and Figure 11, respectively, are the wear morphologies of the cladding layer and the ductile iron substrate prepared in the embodiment. Analysis shows that a large number of grooves appear on the surface wear morphology of the ductile iron substrate, showing stratification and severe matrix peeling, which means that there is obvious plastic deformation. This is mainly due to the low hardness of ductile iron and the presence of graphite particles resulting in uneven hardness distribution. Therefore, under the continuous friction between the grinding balls and the sample surface, obvious peeling and stratification phenomena occur. The wear of ductile iron is mainly the combined effect of adhesive wear, fatigue wear and abrasive wear. The wear surface of the cladding layer of the embodiment is relatively smooth, with only a small amount of adhesion marks, showing a typical abrasive wear morphology. This is because the hardness of the cladding layer of the embodiment is more outstanding, a large number of eutectic structures are densely arranged between the grains, and a large number of in-situ self-generated VC pinned therein, acting as a wear-resistant skeleton to jointly prevent the occurrence of wear.

[0044] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a highly wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron, characterized in that: A cladding layer is prepared on the surface of a ductile iron substrate by a laser cladding method. The cladding alloy powder is composed of reduced iron powder and ferrovanadium powder with different particle sizes in a certain proportion.

2. The method for preparing a high wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron according to claim 1, characterized in that: The alloy powder comprises: 51.5wt.% reduced iron powder and 48.5wt.% ferrovanadium powder, wherein the ferrovanadium powder is FeV50.

3. The method for preparing a high wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron according to claim 2, characterized in that: The alloy powder is a variable-size alloy powder, the particle size range of the reduced iron powder is 100-200 meshes, and the particle size range of the vanadium iron powder is 400-600 meshes.

4. The method for preparing a high wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron according to claim 2, characterized in that: The synchronous powder feeding laser cladding method is adopted. The cladding alloy powder is composed of reduced iron powder and vanadium iron powder with different particle sizes in a certain proportion. The laser power is 1000W, the pulse frequency is 4500Hz, the duty cycle is 95%, the spot diameter is 2.0mm, the scanning speed is 12mm / s, the overlap rate is 30%, the powder feeding amount is 6-7g / min, the powder feeding gas flow rate is 4.5L / min, and the coaxial protective gas argon flow rate is 16L / min.

5. The method for preparing a high wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron according to claim 1, characterized in that: The alloy powders were mixed in a V-type powder mixer for 1.5-3 hours before laser cladding.

6. A highly wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron, characterized in that: The high wear-resistant Fe-based fine-grained laser cladding layer on the surface of ductile iron is prepared by the preparation method of any one of claims 1-5.

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