Gun steel surface cr coating and method for preparing the same

Abstract

The application provides a gun steel surface Cr coating and a preparation method thereof, and relates to the technical field of surface modification of metal materials. The application uses pure Cr powder as cladding powder, and adopts a laser cladding coaxial powder feeding method to perform laser cladding on gun steel. The laser cladding coaxial powder feeding is to simultaneously and synchronously perform coating cladding by using a laser beam channel and an alloy powder channel of a coaxial powder feeding nozzle. The powder and the gun steel substrate are both melted. Cr2O3 reinforcing phases are synthesized by using in-situ reaction and atomic diffusion in a molten pool, so that the coating has stable wear resistance from room temperature to 600 DEG C. Meanwhile, the Fe in the substrate penetrates into the Cr to form a solid solution phase Cr-Fe, which increases the toughness of the substrate and reduces the crack tendency, and the coating is more compact. In addition, the application has high environmental protection and high efficiency, the equipment is simple, the quality is stable, and good economic benefits can be achieved.

Description

Technical Field

[0001] This invention relates to the field of surface modification technology for metallic materials, and in particular to a Cr coating on the surface of gun steel and its preparation method. Background Technology

[0002] In recent years, with the improvement of artillery range, power, and accuracy, severe high-temperature wear of the barrel has become a key problem hindering artillery development and urgently needs to be solved. Research on increasing the service life of artillery mainly focuses on aspects such as gun and cannon structural design, propellant ratio, and modification of the barrel's inner wall surface. Compared with barrel bore structure design and propellant ratio design, barrel inner wall surface modification is a more economical and environmentally friendly method to extend service life.

[0003] The main technologies used for surface modification of gun barrel inner walls both domestically and internationally include: arc ion plating, thermal spraying, explosive spraying, plasma spraying, chemical / physical vapor deposition, magnetron sputtering, electrospark deposition, laser surface strengthening, and electroplating. Currently, Cr plating is the most widely used and mature method for modifying artillery barrel surfaces. However, when applied to gun steel substrates, Cr plating suffers from a significant mismatch in thermal expansion coefficients, resulting in poor adhesion between the coating and the steel substrate, making it prone to microcracks and peeling after firing a certain number of projectiles. Furthermore, the electroplating process generates harmful Cr... 6+ Ions are difficult to handle and cause great pollution to the environment. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a Cr coating on the surface of gun steel and a method for preparing the same. The Cr coating prepared on the surface of gun steel by this invention has stable wear resistance from room temperature to 600°C, high bonding strength with the gun steel substrate, which is beneficial for stress relief and preventing crack propagation; and it is also environmentally friendly.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a Cr coating on a steel surface, comprising the following steps:

[0007] Pure Cr powder was used as the cladding powder to perform laser cladding on the surface of gun steel to obtain a pure Cr coating; the laser cladding was coaxial powder feeding laser cladding.

[0008] Preferably, the purity of the pure Cr powder is ≥99.99 wt%.

[0009] Preferably, the pure Cr powder is a spherical powder with a particle size of 100-200 mesh.

[0010] Preferably, the powder feeding rate of the laser cladding is 15-21 g / min, and the powder-carrying gas flow rate is 7-15 mL / min.

[0011] Preferably, the laser power of the laser cladding is 1.6 to 1.8 kW, the scanning speed is 400 to 600 mm / min, and the spot diameter is 2 to 5 mm.

[0012] Preferably, the laser power of the laser cladding is 1.6kW, the scanning speed is 600mm / min, and the spot diameter is 3mm.

[0013] Preferably, the laser cladding employs multiple overlaps with an overlap rate of 30-45%.

[0014] Preferably, the overlap ratio is 35%.

[0015] Preferably, the thickness of the Cr coating is 500–800 μm.

[0016] The present invention provides a Cr coating on the surface of gun steel prepared by the preparation method described above. The Cr coating includes a matrix phase and a reinforcing phase that are mutually doped. The matrix phase is a Cr-Fe solid solution phase, and the reinforcing phase includes Cr2O3.

[0017] This invention provides a method for preparing a Cr coating on a steel surface. The method uses pure Cr powder as the cladding powder and employs a laser cladding coaxial powder feeding method to perform laser cladding on gun steel. This method utilizes the simultaneous and synchronous cladding of the laser beam channel and the alloy powder channel in a coaxial powder feeding nozzle. Both the powder and the gun steel substrate melt, and atoms in the molten pool redisperse, leading to an in-situ formation reaction and the in-situ formation of a reinforcement. This invention utilizes the in-situ reaction and atomic diffusion in the molten pool to synthesize a Cr2O3 reinforcing phase. The in-situ generated Cr2O3 is uniformly distributed in the Cr coating. This hard Cr2O3 phase provides the coating with stable wear resistance from room temperature to 600℃, exhibiting superior wear resistance compared to electroplated Cr. Simultaneously, the infiltration of Fe into the gun steel substrate forms a solid solution phase Cr-Fe with Cr, increasing the toughness of the substrate, reducing cracking tendency, and making the coating more dense. Furthermore, due to the high energy density of the laser, the coating and substrate are metallurgically bonded, resulting in high interfacial bonding strength, which is beneficial for stress relief and prevents crack propagation. Furthermore, this invention utilizes laser cladding to prepare Cr coatings, which is clean, environmentally friendly, efficient, requires simple equipment, produces stable quality, and can achieve good economic benefits. Attached Figure Description

[0018] Figure 1 The image shows the XRD pattern of the Cr composite coating after laser cladding treatment in Example 1.

[0019] Figure 2 This is a microstructure morphology diagram of the Cr composite coating in Example 1;

[0020] Figure 3 The wear traces of the Cr composite coating at different temperatures in Example 1 are shown.

[0021] Figure 4 The wear marks of the electroplated Cr layer formed on the surface of gun steel by electroplating at different temperatures;

[0022] Figure 5 The above are the EDS line scan results of the Cr composite coating in Example 1. Figure 5 In Figure a, the cross-sectional morphology of the Cr composite coating is shown; in Figure b, the EDS line scan result is shown along the path of the arrow in Figure a.

[0023] Figure 6 The hardness test results are for the workpiece with Cr coating obtained in Example 1;

[0024] Figure 7 These are cross-sectional morphology diagrams of the coatings in Example 1 and Comparative Examples 1-2. Figure 7 In the middle, (a), (b), and (c) correspond to Example 1, Comparative Example 1, and Comparative Example 2, respectively. Detailed Implementation

[0025] This invention provides a method for preparing a Cr coating on a steel surface, comprising the following steps:

[0026] Pure Cr powder was used as the cladding powder to perform laser cladding on the surface of gun steel to obtain a Cr coating; the laser cladding was coaxial powder feeding laser cladding.

[0027] This invention does not have specific requirements for the material of the gun steel; any gun steel well-known to those skilled in the art, such as PCrNi3MoVQ, can be used. Before laser cladding, this invention preferably involves sequentially cleaning and preheating the gun steel. The cleaning method is preferably as follows: sandblasting the gun steel to remove the oxide layer on the surface, then cleaning the surface with anhydrous ethanol and drying it to remove oil and residual sandblasting particles; the preheating temperature is preferably 300–400°C, more preferably 350°C, and the preheating time is preferably 1–3 hours, more preferably 2 hours. Preheating is preferably carried out in a muffle furnace. This invention, through preheating, alters the metal structure and physical properties, reduces residual stress and temperature gradient, and improves the metal's toughness and ductility, thereby effectively reducing the risk of crack formation during cladding and ensuring the quality and reliability of the cladding layer.

[0028] In this invention, the purity of the pure Cr powder is preferably ≥99.99 wt%, and the pure Cr powder is preferably spherical powder with a particle size of 100-200 mesh. Before laser cladding, the pure Cr powder is preferably dried. The drying temperature is preferably 70-110°C, more preferably 80-100°C, and the drying time is preferably 20-60 min, more preferably 50-60 min. The drying is preferably carried out in an oven. After drying, cladding powder with satisfactory flowability for laser cladding is obtained.

[0029] In this invention, the preferred powder feeding speed for laser cladding is 15-21 g / min, the preferred powder carrier gas flow rate is 7-15 mL / min, the preferred powder carrier gas is high-purity Ar gas, and the preferred purity of the high-purity Ar gas is 99.99 wt%.

[0030] In this invention, the laser power of the laser cladding is preferably 1.6 to 1.8 kW, more preferably 1.6 kW; the scanning speed is preferably 400 to 600 mm / min, more preferably 600 mm / min; the spot diameter is preferably 2 to 5 mm, more preferably 3 mm; in this invention, the laser cladding preferably employs multi-layer overlapping, and the overlapping rate is preferably 30 to 45%, more preferably 35%.

[0031] The present invention does not have any particular requirements for the specific operation method of the laser cladding. The operation method known to those skilled in the art can be used. Specifically, pure Cr powder is loaded into a powder hopper with coaxial powder feeding, and powder is fed by a powder feeding mechanism. The gun steel plate is placed on the worktable, and coaxial powder feeding laser cladding is performed under the above-mentioned laser cladding parameters. In the embodiment of the present invention, the powder feeding plate of the powder feeding mechanism is based on a rotating metering plate with grooves.

[0032] When pure Cr is used for cladding, the linear expansion coefficients of the gun steel plates differ, and a large temperature gradient exists during the solidification of the cladding layer. This results in high stress in the solidified coating, making it prone to cracking, reducing coating performance, and causing coating peeling. This invention mitigates the impact of the difference in linear expansion coefficients by preheating the gun steel substrate. By adjusting the laser cladding process parameters, especially the laser power and scanning speed, the energy input of the laser cladding is adjusted, thereby regulating the temperature gradient during solidification and solving the above-mentioned technical problems.

[0033] In this invention, the thickness of the coating formed by laser cladding is preferably 500–800 μm. After the laser cladding is completed, the surface of the resulting coating is preferably polished smooth, and the thickness of the polished Cr coating is preferably 400–700 μm.

[0034] Gun steel plates are made of medium-high carbon low-alloy steel, with a carbon content generally around 0.2% to 0.3%. Carbon combines with strong carbide-forming elements such as Mo and V to form alloy carbides for second-phase strengthening, ensuring a good balance of strength and toughness. The gun steel plates contain approximately 3% Ni and 1% Cr to achieve high hardenability and low-temperature toughness. After final quenching and tempering, the room temperature strength σ0.1 of the gun steel is 1104–1172 MPa, but the strength drops drastically at high temperatures, causing softening of the inner wall layer of the barrel, leading to deformation and ablation of the anode wires, and serious problems such as peeling. This invention can effectively solve the technical problems of poor adhesion between the electroplated Cr coating and the substrate, high brittleness, numerous cracks, poor adhesion, and serious environmental pollution.

[0035] This invention provides a Cr coating on the surface of gun steel prepared by the preparation method described above. The Cr coating includes a matrix phase and a reinforcing phase that are mutually doped. The matrix phase is a Cr-Fe solid solution phase, and the reinforcing phase includes Cr2O3. In this invention, the Cr coating is a high-performance Cr coating, which is resistant to high temperatures and wear. The hard phase of Cr2O3 is generated in situ in the coating, which gives the composite coating stable wear resistance from room temperature to 600℃. Compared with the electroplated Cr layer, its wear resistance is more outstanding (the electroplated Cr layer lacks Cr2O3 at room temperature, resulting in a large amount of wear). At the same time, in this composite coating, the infiltration of Fe in the matrix forms a Cr-Fe solid solution phase with Cr, which increases the toughness of the matrix, reduces the tendency to crack, and makes the coating more dense. This can effectively solve the performance problems of the electroplated Cr coating and improve its performance.

[0036] To further illustrate the present invention, the Cr coating on the surface of gun steel and its preparation method provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of protection of the present invention.

[0037] Example 1

[0038] A 10×100×150mm gun steel sample was selected. First, the plate was sandblasted to remove the oxide layer on its surface. Then, the surface was cleaned with anhydrous ethanol and dried to remove oil and residual sandblasting particles. The cleaned plate was then placed in a muffle furnace and preheated to 350℃ for 2 hours. The cladding powder, pure Cr powder (99.99wt% purity, 100-200 mesh spherical powder), was placed in a drying oven and dried at 80℃ for 30 minutes.

[0039] Place the dried powder into a powder hopper. Place the preheated plate onto a fixture with a heat insulation plate. Start the laser cladding system. The laser surface treatment process parameters are: laser power 1.6kW, scanning speed 600mm / min, spot diameter 3mm, multi-pass overlap, overlap rate 35%; the powder feeding device process parameters are: powder feeding speed 21g / min, powder-carrying gas flow rate 7mL / min, and powder-carrying gas 99.99% high-purity Ar gas.

[0040] Remove the workpiece after laser cladding (coating thickness 700μm), grind the workpiece flat, and obtain a workpiece with Cr coating (coating thickness 550μm).

[0041] Figure 1 The image shows the XRD pattern of the Cr composite coating after laser cladding treatment in this embodiment. It shows the phase analysis results of the coating in this embodiment, which determines that the Cr coating in this embodiment is composed of a Cr-Fe solid solution phase (mainly Cr element) and CrO3 and Cr2O3 second phases.

[0042] Figure 2 This is a microstructure image of the Cr composite coating in this embodiment. Figure 2 It can be seen that the Cr coating has a dense structure, fine grains, and Cr oxides are evenly distributed inside the grains.

[0043] Figure 3 The wear track profiles of the Cr composite coating in this embodiment are shown at different temperatures: room temperature (RT) wear track depth: 13.202 μm; 200℃ wear track depth: 20.625 μm; 400℃ wear track depth: 18.814 μm; 600℃ wear track depth: 17.377 μm. The composite coating prepared by laser cladding has a dense structure, strong adhesion between the coating and the substrate, high coating hardness, and stable tribological properties at different temperatures, with virtually no change in wear morphology from room temperature to 600℃. Figure 4 The wear marks are depicted at different temperatures on a Cr-plated layer (65 μm thick) formed on the surface of gun steel using an electroplating method. Figure 4 It can be seen that the maximum wear depth reaches 40.1239 μm at room temperature. As the wear temperature increases, the wear depth of the electroplated Cr coating gradually decreases (wear depth of 26.025 μm at 200℃, 9.4483 μm at 400℃, and 9.6278 μm at 600℃). However, the wear difference between room temperature and high temperature electroplated Cr is large, and stable friction and wear effect cannot be guaranteed in a wide temperature range.

[0044] Figure 5 This is the EDS line scan result of the Cr composite coating in this embodiment. Figure 5 Image a shows the cross-sectional morphology of the Cr composite coating; image b shows the EDS line scan results along the path indicated by the arrow in image a. Figure 5It can be seen that the substrate element Fe penetrates into the coating, and the Cr coating and the substrate undergo a metallurgical reaction to achieve element diffusion and metallurgical bonding. Compared with the mechanical bonding of electroplated Cr, the bonding force is better, and the Cr and Fe elements are relatively uniformly distributed from the coating surface to the substrate.

[0045] Figure 6 The hardness test results are for the gun steel plate workpiece substrate and the Cr-coated workpiece prepared in Example 1. Figure 6 It can be seen that the hardness (HV) of the gun steel matrix 0.2 The average hardness of the workpiece with Cr coating in Example 1 is about 514 HV, which is 2.1 times higher than that of the gun steel substrate.

[0046] Comparative Example 1

[0047] The laser power was 1.5kW, the scanning speed was 900mm / min, the spot diameter was 3mm, and multiple overlaps were used with an overlap rate of 35%. The rest was the same as in Example 1.

[0048] Comparative Example 2

[0049] The laser power was 1.5kW, the scanning speed was 1200mm / min, the spot diameter was 3mm, the multi-channel overlap was 35%, and the rest was the same as in Example 1.

[0050] Figure 7 These are cross-sectional morphology diagrams of the coatings in Example 1 and Comparative Examples 1-2. Figure 7 In the figures (a), (b), and (c), corresponding to Example 1, Comparative Example 1, and Comparative Example 2, respectively,... Figure 7 It can be seen that Example 1 has good forming, with no defects such as pores or cracks, and the Cr coating hardening depth can reach 500μm to 800μm; Comparative Example 1 has incomplete forming and microcracks appear; Comparative Example 2 has a large dilution rate, and the coating height does not meet the forming requirements.

[0051] The above test results show that the laser cladding method for preparing Cr composite coatings provided by this invention can improve the microhardness, strength, and wear resistance of gun steel plates. The hardening depth of the Cr coating can reach 500μm to 800μm, and the microstructure is uniform and dense. Furthermore, the surface treatment process of this invention is convenient to operate, uses simple equipment, is economical and practical, technically reliable, highly efficient, and produces stable quality, thus achieving good economic benefits.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a Cr coating on the surface of gun steel, characterized in that, Includes the following steps: Pure Cr powder was used as the cladding powder to perform laser cladding on the surface of gun steel to obtain a Cr coating; the laser cladding was coaxial powder feeding laser cladding; the pure Cr powder was spherical powder with a particle size of 100-200 mesh. The laser cladding process involves a powder feeding rate of 21 g / min and a powder-carrying gas flow rate of 7 mL / min; the laser power is 1.6 kW, the scanning speed is 600 mm / min, and the spot diameter is 3 mm; the laser cladding employs multi-pass overlapping with an overlap rate of 35%. Before laser cladding, the gun steel is cleaned and preheated in sequence, with the preheating temperature being 350°C. The Cr coating comprises a matrix phase and a reinforcing phase that are mutually doped. The matrix phase is a Cr-Fe solid solution phase, and the reinforcing phase comprises Cr2O3.

2. The preparation method according to claim 1, characterized in that, The purity of the pure Cr powder is ≥99.99wt%.

3. The preparation method according to claim 1, characterized in that, The thickness of the Cr coating is 500~800μm.

4. The Cr coating on the surface of gun steel prepared by the preparation method according to any one of claims 1 to 3, wherein the Cr coating comprises a matrix phase and a reinforcing phase that are mutually doped, wherein the matrix phase is a Cr-Fe solid solution phase, and the reinforcing phase comprises Cr2O3.

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