Cu-induced passivation Fe-based high-corrosion-resistance laser cladding layer and cladding process thereof

Abstract

The invention discloses a Cu-induced passivation Fe-based high-corrosion-resistance laser cladding layer and a cladding process thereof, the cladding layer is prepared on a 27SiMn steel base material by adopting a laser cladding method, alloy powder adopted by laser cladding comprises 32.36-37.26 wt% of ferrovanadium powder, 6.10-6.70 wt% of graphite powder, 0.30-0.45 wt% of copper powder and the balance of spherical iron powder, and FeV50 is adopted as the ferrovanadium powder. A proper amount of Cu element promotes reduction of the equiaxed grain size and reduction of dendrites, but when the grain size is reduced, the grain boundary density is increased, the grain boundary position is prone to corrosion, rapid formation of a corrosion product Cu2O is facilitated, a more stable and compact passive film is formed on the surface of the Fe-based cladding layer, a corrosion medium can be effectively isolated, and the corrosion process is slowed down. And a corrosive medium is effectively prevented from permeating into the base body. And due to fine grain strengthening and dispersion strengthening, the hardness of the cladding layer is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser cladding, and specifically to Cu-induced passivation Fe-based laser cladding and its preparation method. Background Art

[0002] The corrosion resistance of the Fe-based cladding layer is relatively poor. Stainless steel has excellent corrosion resistance, mainly because of more than 12% Cr element and more than 8% Ni element in its composition. Thanks to the increase in corrosion potential and the formation of a dense oxide film on the surface, the progress of the corrosion reaction is effectively blocked. 27SiMn steel has a wide range of applications in the manufacturing fields such as excavator buckets, hydraulic supports of mining equipment, and ship rudder blades due to its high strength and good toughness. In order to extend its service life, improve comprehensive performance, and optimize costs at the same time, using laser cladding technology to prepare an Fe-based cladding layer is an effective method, but this cladding layer needs to have strong corrosion resistance to cope with complex working conditions. The corrosion resistance of the Fe-based cladding layer can be improved by adding a large amount of alloying elements, but this will cause a significant increase in cost.

[0003] Patent CN202310960215.7 discloses a self-passivating high-corrosion-resistance Fe-VC composite laser cladding layer and its preparation method. The method for obtaining this ultrafine-grained Fe-based laser cladding layer is to continuously perform follow-up water spray cooling on the back of the substrate molten pool during the cladding process. However, forced cooling may cause different grain sizes to form in different parts of the cladding layer, affecting the uniformity of the overall performance of the cladding layer, and the excessive temperature gradient is likely to cause the cladding layer to crack. Moreover, the follow-up water spray cooling makes the process complex and the cost increase.

[0004] Therefore, choosing a low-alloying method to improve the Fe-based cladding layer has obvious advantages. One is to reduce the process complexity, and the other is to reduce the production cost. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a Cu-induced passivation Fe-based high-corrosion-resistance laser cladding layer and its cladding process.

[0006] To solve the above technical problem, the Cu-induced passivation Fe-based high-corrosion-resistance laser cladding process of the present invention prepares a cladding layer on a 27SiMn steel substrate by laser cladding. The alloy powder used for laser cladding is composed of 32.36 - 37.26 wt.% of ferrovanadium powder, 6.10 - 6.70 wt.% of graphite powder, 0.30 - 0.45 wt.% of copper powder, and the balance is spherical iron powder, where the ferrovanadium powder uses FeV50.

[0007] Preferably, the alloy powder composition is 61.24 wt.% spherical iron powder, 32.36 wt.% ferrovanadium powder, 6.10 wt.% graphite powder, and 0.30 wt.% of copper powder.

[0008] Preferably, the particle size ranges of the spherical iron powder, ferrovanadium powder and graphite powder are all 100 - 200 mesh, and the particle size of the copper powder is 400 - 600 mesh. Copper powder with a smaller particle size is beneficial for uniform distribution in the alloy powder.

[0009] Preferably, the laser cladding is carried out by the synchronous powder feeding method.

[0010] Preferably, pulsed laser is used for cladding, with a laser power of 800 - 1000 W, the distance from the cladding head to the substrate surface being 24 mm, the overlapping rate being 35%, the laser pulse frequency being 4400 - 4500 Hz, the duty cycle being 95%, the cladding speed being 10 - 12 mm / s, using pure argon with a flow rate of 5.5 - 6 L / min as the powder feeding gas, the powder feeding amount being 5.5 - 6 g / min, and using pure argon with a flow rate of 16 L / min as the shielding gas.

[0011] The Cu - induced passivated Fe - based high - corrosion - resistant laser cladding layer of the present invention is prepared by using any one of the foregoing cladding processes.

[0012] The beneficial effects of the present invention are as follows: When no Cu element is added, the microstructure morphology of the cladding layer is composed of dendritic crystals and equiaxed grains. When the Cu addition amount is 0.3 - 0.45 wt.%, the dendritic crystals in the cladding layer decrease, and the fine equiaxed grains increase. The high thermal conductivity of Cu can increase the temperature gradient and cooling rate of the molten pool, increase the undercooling degree of the molten pool, inhibit the growth of grains, and promote grain refinement. Therefore, at this time, the average grain size of the cladding layer is the smallest, reaching the sub - micron ultrafine grain scale. Due to fine - grain strengthening and dispersion strengthening, the average micro - hardness of the cladding layer reaches a maximum of 920 HV. 0.2 . When the Cu addition amount is 0.6 wt.%, the average grain size increases. The reason is that more Cu elements are added, latent heat is released during the formation of compounds, and the thermal expansion coefficient of Cu is higher than that of Fe and V. This difference causes additional thermal stress introduced by the addition of copper powder, making it easier for atoms at grain boundaries to diffuse, resulting in grain growth, reducing the undercooling degree, and relatively reducing the degree of grain refinement. When an excessive amount of Cu is added, due to the coarsening of carbides, the grain size increases, the fine - grain strengthening effect weakens, and the hardness decreases.

[0013] An appropriate amount of Cu element promotes the reduction of the equiaxed grain size and the decrease of dendritic crystals. However, while the grain size decreases, the grain boundary density increases. Grain boundaries are more prone to corrosion, but it is beneficial for the rapid formation of the corrosion product Cu2O, and a more stable and dense passivation film is formed on the surface of the Fe - based cladding layer, which can effectively isolate the corrosion medium and slow down the corrosion process. It effectively prevents the corrosion medium from penetrating into the substrate interior. And due to fine - grain strengthening and dispersion strengthening, the hardness of the cladding layer is increased. Low - content copper powder can not only avoid the problem of high laser reflectivity of copper, but also obtain high performance at low cost. Only natural cooling is required during the cladding process. Description of the Drawings

[0014] Figure 1 Optical micrograph of the clad layer a obtained in Example 1 of the present invention;

[0015] Figure 2 Optical micrograph of the clad layer b obtained in Example 2 of the present invention;

[0016] Figure 3 Optical micrograph of the clad layer c obtained in Example 3 of the present invention;

[0017] Figure 4 Optical micrograph of the clad layer d obtained in Example 4 of the present invention;

[0018] Figure 5 Optical micrograph of the clad layer e obtained in Comparative Example 1 of the present invention;

[0019] Figure 6 Optical micrograph of the clad layer f obtained in Comparative Example 2 of the present invention;

[0020] Figure 7 Optical micrograph of the clad layer g obtained in Comparative Example 3 of the present invention;

[0021] Figure 8 Average grain size diagram of the clad layers a, b, c, d, e, f, g;

[0022] Figure 9 Average microhardness diagram of the clad layers a, b, c, d, e, f, g;

[0023] Figure 10 Potentiodynamic polarization curves measured for the clad layers a, b, c, d, e, f, g in 3.5 wt.% NaCl solution. Detailed Description of the Invention

[0024] The specific examples and comparative examples were all prepared for the clad layer according to the following method:

[0025] The clad layer was prepared on a 27SiMn steel substrate by means of pulsed laser cladding with synchronous powder feeding. The laser power was 1000 W, the distance between the cladding head and the substrate surface was 24 mm, the overlapping rate was 35%, the laser pulse frequency was 4500 Hz, the duty cycle was 95%, the cladding speed was 12 mm / s, pure argon with a flow rate of 6 L / min was used as the powder feeding gas, the powder feeding amount was 5.5 g / min, and pure argon with a flow rate of 16 L / min was used as the shielding gas.

[0026] Example 1:

[0027] The alloy powder used in laser cladding consists of 61.24 wt.% spherical iron powder, 32.36 wt.% ferrovanadium powder, 6.10 wt.% graphite powder, and 0.30 wt.% copper powder. Among them, FeV50 is used for the ferrovanadium powder, the mass content of vanadium in the ferrovanadium powder is 48%, the particle size ranges of the ferrovanadium powder, graphite powder, and spherical iron powder are all 100 - 200 mesh, and the particle size of the copper powder is 400 - 600 mesh, resulting in the cladding layer a.

[0028] Example 2:

[0029] The alloy powder used in laser cladding consists of 61.09 wt.% spherical iron powder, 32.36 wt.% ferrovanadium powder, 6.10 wt.% graphite powder, and 0.45 wt.% copper powder. Among them, FeV50 is used for the ferrovanadium powder, the mass content of vanadium in the ferrovanadium powder is 48%, the particle size ranges of the ferrovanadium powder, graphite powder, and spherical iron powder are all 100 - 200 mesh, and the particle size of the copper powder is 400 - 600 mesh, resulting in the cladding layer b.

[0030] Example 3:

[0031] The alloy powder used in laser cladding consists of 55.74 wt.% spherical iron powder, 37.26 wt.% ferrovanadium powder, 6.70 wt.% graphite powder, and 0.3 wt.% copper powder. Among them, FeV50 is used for the ferrovanadium powder, the mass content of vanadium in the ferrovanadium powder is 48%, the particle size ranges of the ferrovanadium powder, graphite powder, and spherical iron powder are all 100 - 200 mesh, and the particle size of the copper powder is 400 - 600 mesh, resulting in the cladding layer c.

[0032] Example 4:

[0033] The alloy powder used in laser cladding consists of 55.59 wt.% spherical iron powder, 37.26 wt.% ferrovanadium powder, 6.70 wt.% graphite powder, and 0.45 wt.% copper powder. Among them, FeV50 is used for the ferrovanadium powder, the mass content of vanadium in the ferrovanadium powder is 48%, the particle size ranges of the ferrovanadium powder, graphite powder, and spherical iron powder are all 100 - 200 mesh, and the particle size of the copper powder is 400 - 600 mesh, resulting in the cladding layer d.

[0034] Control Example 1:

[0035] The alloy powder used in laser cladding consists of 61.54 wt.% spherical iron powder, 32.36 wt.% ferrovanadium powder, 6.10 wt.% graphite powder, without copper powder. Among them, FeV50 is used for the ferrovanadium powder, the mass content of vanadium in the ferrovanadium powder is 48%, the particle size ranges of the ferrovanadium powder, graphite powder, and spherical iron powder are all 100 - 200 mesh, resulting in the cladding layer e.

[0036] Control Example 2:

[0037] The alloy powder used in laser cladding consists of 61.39 wt.% spherical iron powder, 32.36 wt.% ferrovanadium powder, 6.10 wt.% graphite powder, and 0.15 wt.% copper powder. Among them, the ferrovanadium powder is FeV50, and the mass content of vanadium in the ferrovanadium powder is 48%. The particle size ranges of the ferrovanadium powder, graphite powder, and spherical iron powder are all 100 - 200 mesh, and the particle size of the copper powder is 400 - 600 mesh, obtaining the cladding layer f.

[0038] Comparative Example 3:

[0039] The alloy powder used in laser cladding consists of 60.94 wt.% spherical iron powder, 32.36 wt.% ferrovanadium powder, 6.10 wt.% graphite powder, and 0.60 wt.% copper powder. Among them, the ferrovanadium powder is FeV50, and the mass content of vanadium in the ferrovanadium powder is 48%. The particle size ranges of the ferrovanadium powder, graphite powder, and spherical iron powder are all 100 - 200 mesh, and the particle size of the copper powder is 400 - 600 mesh, obtaining the cladding layer g.

[0040] See Figure 1-7 , the optical micrographs of the cladding layers a, b, c, d, e, f, g. The average grain sizes of the cladding layers a, b, c, d, e, f, g are 0.87 μm, 0.89 μm, 0.89 μm, 0.93 μm, 1.18 μm, 1.11 μm, and 1.05 μm respectively.

[0041] See Figure 8 , the average grain size diagrams of the cladding layers a, b, c, d, e, f, g.

[0042] See Figure 9 , the average microhardness of the cladding layers a, b, c, d, e, f, g. The average microhardness of the cladding layers a, b, c, d, e, f, g are 920 HV 0.2 , 863 HV 0.2 , 900 HV 0.2 , 861 HV 0.2 , 793 HV 0.2 , 830 HV 0.2 and 827 HV 0.2 . When adding 0.30 wt.% in the Fe - based powder, the microhardness of the cladding layer is the highest. Among them, the microhardness of the cladding layer a is increased by 127 HV compared with that of the cladding layer e 0.2 , and the microhardness of the cladding layer a is about 4.8 times that of 27SiMn steel.

[0043] See Figure 10, The potentiodynamic polarization curves of the clad layers a, b, c, d, e, f, and g measured in a 3.5 wt.% NaCl solution. Table 1 shows the fitting results of the polarization curves. It can be seen that obvious passivation phenomena appear in the potentiodynamic polarization curves of clad layer a, clad layer b, clad layer c, and clad layer d. During the electrochemical corrosion process, the grain boundaries are corroded first. As the grains become finer and the grain boundary area increases, the formation of corrosion products becomes faster. When 0.30 - 0.45 wt.% of Cu is added to the Fe-based powder, a passivation phenomenon appears in the potentiodynamic polarization curve. The corrosion current density of clad layer a is the smallest, the passivation range is the largest, and the corrosion resistance is the best. When an excessive amount of Cu element is added, the passivation phenomenon disappears and the corrosion resistance decreases. This is mainly because when the carbides aggregate and coarsen, the galvanic corrosion is aggravated, resulting in an increase in the cathode area of a single corrosion unit and further enhancing the galvanic corrosion.

[0044] Table 1 Fitting Results of Polarization Curves

[0045]

[0046] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A Cu-induced passivation Fe-based high corrosion resistance laser cladding process, characterized in that: A cladding layer is prepared on a 27SiMn steel substrate by laser cladding. The alloy powder used for laser cladding consists of 32.36 - 37.26 wt.% of ferrovanadium powder, 6.10 - 6.70 wt.% of graphite powder, 0.30 - 0.45 wt.% of copper powder, and the balance being spherical iron powder. Among them, the ferrovanadium powder is FeV50.

2. The Cu-induced passivation Fe-based high corrosion resistance laser cladding process according to claim 1, wherein: The alloy powder composition is 61.24 wt.% spherical iron powder, 32.36 wt.% ferrovanadium powder, 6.10 wt.% graphite powder, and 0.30 wt.% copper powder.

3. The Cu-induced passivation Fe-based high corrosion resistance laser cladding process according to claim 2, characterized in that: The particle size ranges of the spherical iron powder, ferrovanadium powder, and graphite powder are all 100 - 200 mesh, and the particle size of the copper powder is 400 - 600 mesh.

4. The Cu-induced passivation Fe-based high corrosion resistance laser cladding process according to claim 3, characterized in that: Laser cladding is carried out by the synchronous powder feeding method.

5. The Cu-induced passivation Fe-based high corrosion resistance laser cladding process according to claim 4, characterized in that: Pulsed laser is used for cladding. The laser power is 800 - 1000 W, the distance from the cladding head to the substrate surface is 24 mm, the overlapping rate is 35%, the laser pulse frequency is 4400 - 4500 Hz, the duty cycle is 95%, the cladding speed is 10 - 12 mm / s, pure argon with a flow rate of 5.5 - 6 L / min is used as the powder feeding gas, the powder feeding amount is 5.5 - 6 g / min, and pure argon with a flow rate of 16 L / min is used as the shielding gas.

6. A Cu-induced passivated Fe-based high corrosion-resistant laser cladding layer, characterized in that: It is prepared by using the cladding process according to any one of claims 1 - 5.

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