Cr-fe alloy layer for barrel life extension and method of making the same

Abstract

The application belongs to the technical field of alloy materials, and relates to a Cr-Fe alloy layer for prolonging the service life of a barrel and a preparation method thereof. The Cr-Fe alloy layer comprises Cr: 45-85wt%, Fe: 14-54wt%, C: 0-1.2wt%, and O content is less than or equal to 0.3wt%; the Cr-Fe alloy layer is prepared by laser processing, the microstructure is mainly BCC phase, and 3-8% of Cr 23 strengthening phase is uniformly precipitated; the Cr-Fe alloy layer is metallurgically combined with the barrel substrate, the surface Vickers hardness is 400-600HV, and the mass loss is less than or equal to 0.01g in 500 high-temperature erosion wear cycle tests. The Cr-Fe alloy layer with specific components is formed by optimizing laser processing parameters, microcracks of the hard chromium plating layer are effectively repaired, the high-temperature erosion wear loss rate is reduced, and the service life of the barrel is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alloy materials, and relates to a Cr-Fe alloy layer for prolonging the service life of a barrel and a preparation method thereof. BACKGROUND

[0002] Hard chrome plating is widely used in gun barrel manufacturing due to its excellent wear resistance, corrosion resistance and ability to maintain ballistic performance. However, the barrel operates in an extremely variable use environment, and the plating layer needs to withstand severe high-pressure and high-temperature impact and chemical corrosion of high-temperature propellant gas. Although hard chrome plating is still the main process for this part, its inherent defects and limitations still lead to performance degradation, increased maintenance requirements and environmental compliance challenges.

[0003] Hard chrome plating layer has significant internal stress due to its microcrystalline structure, which makes it inherently brittle. As the thickness of the plating layer increases, stress accumulates, inevitably leading to the formation of microcracks. Although a controlled plating process can promote the formation of a dense and fine crack structure, the impact of such microcracks mainly manifests in two key aspects. First, in high-stress environments such as dynamic loading, these cracks can expand and propagate, eventually leading to coating peeling or catastrophic failure. Second, crack propagation during service weakens corrosion resistance. If the crack penetrates to the substrate, it can cause underlying corrosion or rusting under the coating. In addition, the adhesion between the plating layer and the substrate is weak, which can lead to adhesion failure in high-stress environments, thereby damaging the integrity of the plating layer. As the demand for increased range, velocity and muzzle velocity increases, the wear and corrosion problems of chrome-plated barrels become more prominent. Traditional single-layer chrome plating processes cannot meet the actual performance requirements. SUMMARY

[0004] The present application aims to solve the problems in the prior art, and provides a Cr-Fe alloy layer for prolonging the service life of a barrel and a preparation method thereof. The Cr-Fe alloy layer is metallurgically combined to repair hard chrome plating microcracks and improve high-temperature corrosion resistance.

[0005] One aspect of the present application provides a Cr-Fe alloy layer for prolonging the service life of a barrel, the composition of the Cr-Fe alloy layer includes, by mass percentage: Cr content of 45-85wt%, Fe content of 14-54wt%, C content of 0-1.2wt%, and O content of ≤0.3wt%;

[0006] The Cr-Fe alloy layer is made by laser processing, which melts the chrome plating layer on the surface of the barrel substrate and further melts the barrel substrate; the Cr-Fe alloy layer is metallurgically combined with the barrel substrate;

[0007] The microstructure of the Cr-Fe alloy layer is mainly body-centered cubic (BCC) phase, and the proportion of the BCC phase is greater than or equal to 85wt%, and the Cr 23 C6 strengthening phase, the Cr 23 The mass fraction of the C6 strengthening phase is 3-8wt%, and the size is 0.2-3.0μm.

[0008] The surface Vickers hardness of the Cr-Fe alloy layer is 400-600HV, and the mass loss is less than or equal to 0.01g in 500 high-temperature erosion and wear cycles.

[0009] Preferably, the content of Cr is 70-83wt%, and the content of Fe is 16-29wt%.

[0010] Further preferably, the content of Cr is 80-83wt%, and the content of Fe is 16.5-19wt%.

[0011] Preferably, the Cr-Fe alloy layer further comprises: the content of Mo is 0.2-0.8wt%, and the content of Ni is 0.1-0.5wt%. Whether the Cr-Fe alloy layer contains Mo and Ni elements depends on whether the barrel substrate contains Mo and Ni elements.

[0012] Preferably, the grain size of the BCC phase is 10-50μm, and there is Cr 23 C6 strengthening phase at the grain boundary.

[0013] Preferably, the Cr-Fe alloy layer is metallurgically combined with the barrel substrate, and the interface dislocation density is greater than or equal to 1×10 14 m -2 .

[0014] Preferably, in the high-temperature erosion and wear cycle test, the test conditions are: temperature 600℃, pressure 30MPa, and sliding speed 5m / s; after 500 cycles, the mass loss of the Cr-Fe alloy layer is less than or equal to 0.008g.

[0015] The second aspect of the present application provides a preparation method of the Cr-Fe alloy layer for barrel life extension, comprising the following steps:

[0016] (1) plating chromium on the surface of the barrel substrate;

[0017] (2) heating the barrel substrate plated with chromium to 300-500℃ under a protective atmosphere, and keeping warm for 10-60min, and then cooling to room temperature;

[0018] (3) performing laser remelting treatment on the barrel substrate obtained in step (2) under a protective atmosphere, and the laser power density is 4.95×10 4 ~9.20×10 4W / cm2, the scanning speed is 5-80 mm / s, the spot diameter is 120-180 μm, the scanning step distance is 40-60 μm, the laser melts the chromium plating layer on the surface of the body tube base, and the melting depth is further extended to the body tube base;

[0019] (4) cooling to obtain a Cr-Fe alloy layer.

[0020] The Cr-Fe alloy layer is preferably formed on the inner bore surface of the body tube, for improving the high-temperature corrosion resistance of the inner bore, and thus the inner bore of the body tube base is plated with chromium.

[0021] Preferably, the chromium plating process comprises: the plating solution comprises 100-500 g / L CrO3 and 1-5 g / L H2SO4, the temperature is 45-60 ℃, the current density is 40-60 A / dm2, and the electroplating time is 8-20 h.

[0022] Preferably, the laser power density is 6.0×10 4 ~8.0×10 4 W / cm2, the scanning speed is 5-60 mm / s, the spot diameter is 140-160 μm, and the scanning step distance is 45-55 μm.

[0023] Further preferably, the laser power density is 7.0×10 4 ~8.0×10 4 W / cm2, and the scanning speed is 40-60 mm / s. The protective atmosphere herein is nitrogen or argon.

[0024] Preferably, the cooling in step (4) is gradient cooling: rapid cooling to 150-300 ℃ at a rate of 300-500 ℃ / s, and then cooling to room temperature at a rate of 20-80 ℃ / s.

[0025] Preferably, a visual detection system is integrated in the laser remelting process, which comprises:

[0026] a three-light coordination module: laser scanner, visible light camera, and infrared thermal imager synchronously collect images of the molten pool region;

[0027] a dual acoustic feedback module: ultrasonic flaw detector and acoustic emission sensor real-time monitor crack signals;

[0028] an analysis unit: algorithm performs semantic segmentation on the surface cracks of the molten pool, locates the hollow areas, and outputs laser parameter adjustment instructions.

[0029] Preferably, the working process of the visual detection system comprises:

[0030] (1) before laser remelting, the substrate surface temperature uniformity is detected by an infrared thermal imager, and when the standard deviation of the temperature is >10 ℃, preheating compensation is triggered;

[0031] (2) During the remelting process, the visible light camera captures the molten pool morphology in real time, and the analysis unit calculates the crack width and the hollow area;

[0032] (3) When the crack width > 5 μm or the hollow area > 0.1 mm 2 , the laser power density is dynamically adjusted by ±5% or the scanning speed is dynamically adjusted by ±10%.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] (1) The present application optimizes the laser processing parameters, so that the chromium plating layer on the surface of the barrel body substrate is melted by laser, and part of the barrel body substrate is further melted, forming a Cr-Fe alloy layer with a specific composition and metallurgical bonding with the substrate (interface dislocation density ≥1×10 14 m -2 ), effectively repairing the microcracks of the hard chromium plating layer, and the mass loss is ≤0.01 g after 500 times of high temperature erosion and wear test.

[0035] (2) The BCC phase (≥85%) of the Cr-Fe alloy layer provided by the present application and the nanoscale Cr 23 C6 strengthening phase (0.2-3.0 μm) synergistically strengthen, and the Vickers hardness reaches 400-600 HV, and the high temperature wear resistance is improved.

[0036] (3) The present application performs preheating treatment before laser remelting to inhibit secondary cracks; and gradient cooling is performed after laser remelting to avoid phase change and reduce residual stress.

[0037] (4) The present application integrates a visual detection system during the laser remelting process, and dynamically adjusts the laser power density and the scanning speed in real time to ensure uniform distribution of the molten pool Cr and Fe.

[0038] (5) The method for prolonging the service life of the barrel body of the present application is simple and has strong industrial operability. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a surface morphology and cross-sectional view of a chromium plating layer.

[0040] Figure 2 is a relationship diagram of laser power density, scanning density and melting depth.

[0041] Figure 3 is a cross-sectional view of the plating layer under laser treatment at different laser power densities and scanning speeds.

[0042] Figure 4 is an XRD diffraction pattern of the plating layer after treatment at different scanning speeds.

[0043] Figure 5EBSD patterns of the laser treated plated layer under different laser processing parameters.

[0044] Figure 6 TEM analysis images of the interface between the laser processed layer and the steel substrate, wherein (a) is a bright field TEM image and element distribution of the sample; (b) is a bright field TEM image corresponding to (a); (c1), (d1), (e1) are high magnification bright field TEM images corresponding to different regions of (b); (c2), (d2), (e2) are SAED patterns corresponding to (c1), (d1), (e1).

[0045] Figure 7 Element distribution maps of the laser treated layer under different laser processing parameters.

[0046] Figure 8 Hardness distribution maps of the laser treated layer under different laser processing parameters.

[0047] Figure 9 A schematic diagram of laser processing the inner wall of a cylinder.

[0048] Figure 10 Surface and cross-sectional SEM images of the alloy layer of Example 2 and pictures of the cylinder of Example 2 and Comparative Example 1 after the semi-enclosed bomb test, wherein (a) is a cross-sectional SEM image of the alloy layer of Example 2, (b) is a surface SEM image of the alloy layer of Example 2, (c) is a picture of the cylinder of Comparative Example 1 after the semi-enclosed bomb test, (d) is a picture of the cylinder of Example 2 after the semi-enclosed bomb test (entry end), (e) is a picture of the cylinder of Example 2 after the semi-enclosed bomb test (exit end). DETAILED DESCRIPTION

[0049] In the description of the present application, unless otherwise specified, the numerical range "a~b" represents a shorthand notation for any real combination between a and b, and includes a and b. Various numbers include two, three, four, five, and more than five.

[0050] Hereinafter, embodiments of the Cr-Fe alloy layer for barrel life extension and the method for preparing the same according to the present application will be described in detail, however, these embodiments are exemplary, and the disclosure of the present application is not limited thereto. And the drawings used herein are merely for better illustrating the disclosed content of the present application, and do not have a limiting effect on the scope of protection.

[0051] In some embodiments of the present application, a Cr-Fe alloy layer for barrel life extension is provided, the composition of the Cr-Fe alloy layer includes, in mass percentage: Cr content of 45-85wt%, Fe content of 14-54wt%, C content of 0-1.2wt%, and O content ≤0.3wt%; the Cr-Fe alloy layer is made by laser processing, laser melting the chromium plating layer on the surface of the barrel substrate, and further extending the melting depth to part of the barrel substrate; the microstructure of the Cr-Fe alloy layer is mainly body-centered cubic (BCC) phase, the proportion of BCC phase ≥85wt%, and Cr 23 C6 strengthening phase, the Cr 23 The mass fraction of the Cr 14 C6 strengthening phase is 3-8wt%, and the size is 0.2-3.0μm; the Cr-Fe alloy layer is metallurgically combined with the barrel substrate, and the interface dislocation density ≥1×10 -2 m 6 The surface Vickers hardness of the Cr-Fe alloy layer is 400-600HV, and the mass loss is ≤0.01g in 500 high-temperature erosion and wear cycle tests.

[0052] The barrel refers to a tubular component that carries a projectile, withstands the pressure of gunpowder gas, and guides the flight direction of the projectile, i.e. a tubular launching component, including a barrel, a gun barrel, etc. The material of the barrel substrate is steel.

[0053] The Cr-Fe alloy layer is made by laser processing, the laser alloying technology irradiates the chromium plating layer on the surface of the barrel substrate with a high-energy-density laser beam, laser melts the chromium plating layer on the surface of the barrel substrate, and further extends the melting depth to the barrel substrate, inducing rapid melting of the chromium layer and the substrate, and forming a strengthened alloy layer. This process covers three stages of melting, liquid metal dynamics and rapid solidification, and the characteristic parameters and control mechanisms of each stage are as follows:

[0054] (1) After the laser energy is absorbed by the hard chromium coating, the surface temperature rises to the melting point (the melting point of Cr is 1907℃) within microseconds. Due to the high thermal conductivity (93.7W / m·K) of solid chromium, the melting depth is controlled by the ratio of laser power to scanning rate. When the energy density exceeds the threshold value (such as the critical flux of 1068nm laser is about 5×10 6 J / m 2 ), the Cr layer undergoes selective melting, and the substrate elements (Fe, C) diffuse into the molten pool to form an Fe-Cr-C ternary liquid alloy. The temperature gradient of the molten pool can reach 10 6 -10 7K / m induces Marangoni convection, promoting compositional homogenization. However, when the scanning rate exceeds 80 mm / s, the rapid solidification rate limits convection homogenization, leading to a decrease in alloying quality. Simultaneously, the viscosity of the liquid Fe-Cr-C alloy is significantly lower than that of solid chromium, and the molten pool expands under the drive of surface tension and recoil pressure.

[0055] (2) The morphology of the molten pool is determined by the energy distribution of the Gaussian beam. The central region has the highest temperature (>2200℃), forming a deep melting zone; the edge temperature is close to the solidus line (the solidus line is the critical temperature at which an alloy "completely solidifies from a liquid state to a solid state"), forming a shallow melting zone. The Cr element in the molten pool varies in density (Cr density is 7.2 g / cm³). 3 The density of Fe is 7.9 g / cm³. 3 Segregation can occur, but component separation can be suppressed by optimizing the laser process window (scanning speed, power density, etc.): for example, high power density can promote uniform mixing of Fe-Cr, while low power density can easily lead to banded segregation.

[0056] (3) Microstructure evolution and property regulation of rapid solidification: The solidification kinetics of laser-alloyed coatings in the mid-temperature region (where the supercooling ΔT ≈ 50-200℃) significantly affects the microstructure, which typically exhibits a nano-coupled structure (Cr). 23 (C6+ austenite or martensite). During the cooling process, Cr first precipitates in liquid Fe-Cr-C alloys. 23 C6 (M) 23 C6 type carbides), whose critical nucleation radius (r) is affected by supercooling: when ΔT≈100℃, based on classical nucleation theory, Cr 23 The crystal nucleus size of C6 is approximately 10~20 nm. Due to Cr... 23 C6 has a face-centered cubic (FCC) structure (lattice constant 1.06 nm) and a high Cr-C bond energy (~350 kJ / mol). Its precipitation significantly hinders dislocation movement and increases the material's yield strength. Cr 23 C6 has a hardness far exceeding that of common abrasives, effectively resisting the ploughing effect and significantly reducing wear rate. During molten pool cooling, metastable austenite (γ-Fe) forms in the Fe-rich regions of the matrix, but due to the solid solution strengthening of Cr, the austenite transforms into lath martensite during subsequent rapid cooling. The martensitic matrix reduces intermetallic adhesion, thus lowering the coefficient of friction. Cr 23 The C6 / martensite interface has a higher energy than the single phase, which forces cracks to bypass the phase and extends fatigue life.

[0057] In other embodiments of the present invention, a method for preparing a Cr-Fe alloy layer for extending the service life of the barrel is provided, comprising the following steps:

[0058] Step 1: Chrome plating on the surface of the barrel substrate:

[0059] The plating solution includes 100-500 g / L CrO3 and 1-5 g / L H2SO4, the temperature is 45-60 °C, the current density is 40-60 A / dm2, the barrel body substrate is electroplated for 8-20 h, and the inner bore surface of the barrel body substrate is pre-plated with a hard chromium layer with a thickness of 150-300 μm.

[0060] Step 2: Pre-heating treatment

[0061] After the barrel body substrate is plated with chromium, the barrel body substrate is placed in a pre-heating device, heated to 300-500 °C under a protective atmosphere, and maintained for 10-60 min, and then cooled to room temperature, so as to reduce the thermal stress in the subsequent laser remelting process, and inhibit secondary cracks and shrinkage cavities.

[0062] Step 3: Laser remelting process

[0063] The laser remelting is performed using a JPT continuous laser (wavelength 1064 nm) under a protective atmosphere. The key parameters are set as follows:

[0064] The laser power density is 4.95×10 4 ~9.20×10 4 W / cm2, the scanning speed is 5-80 mm / s, the spot diameter is 120-180 μm, and the scanning step distance is 40-60 μm.

[0065] By optimizing the parameters of the laser remelting, the chromium plating layer on the surface of the barrel body substrate is melted by the laser, and the melting depth can be further extended to the barrel body substrate, so as to obtain a Cr-Fe alloy layer which can be metallurgically combined with the substrate and has a specific composition and structure.

[0066] Step 4: Gradient cooling control

[0067] After the laser remelting, a segmented cooling process is adopted:

[0068] First stage: rapidly cooled to 150-300 °C at a rate of 300-500 °C / s;

[0069] Second stage: cooled to room temperature at a rate of 20-80 °C / s to reduce residual stress.

[0070] After the laser processing is completed, the alloy layer sample is taken for characterization and performance testing, and the specific characterization means are as follows:

[0071] The surface morphology and cross-section microstructure of the material were characterized by field emission scanning electron microscopy-energy spectrum analysis (SEM / EDX) combined with electron backscatter diffraction (EBSD) technology, and scanning transmission electron microscopy (Talos F200X). Element composition analysis was completed by electron probe X-ray microanalysis (EPMA). Phase analysis was completed by X-ray diffractometer (XRD), using a Cu target, a scanning range of 20-90°, a test voltage of 40 kV, and a scanning speed of 10° / min. TEM analysis of the interface morphology of the alloy layer and the matrix layer.

[0072] Hardness testing was performed using a Vickers hardness tester (Wilson VH3100), with a test load of 100 grams and a loading time of 15 seconds.

[0073] High temperature erosion and wear test: 20# low alloy steel was used as the friction matching material to simulate the relative movement between the rotating band and the inner wall of the barrel. The sample was heated to 600°C to simulate the heat accumulation on the bore surface after multiple shots, a constant normal pressure of 30 MPa was applied to the friction surface, and the punch was accelerated to 5 m / s at a distance of 2 meters to reproduce the peak pressure at the bottom of the bullet in a typical shooting cycle. A precision piezoelectric balance was used to measure the mass loss at intervals of 100 cycles.

[0074] Semi-closed explosive cartridge test: under the action of electric shock, 2g±0.05g of C-class nitrocellulose was ignited, and then 40g±2g of propellant was ignited. The propellant burns in the chamber to produce high temperature and high pressure gas, which pushes the copper projectile forward. The high temperature gas penetrates the sample and causes high temperature and high pressure ablation damage to the sample. After multiple shots, the inner surface morphology of the sample was observed and compared.

[0075] Figure 1 The surface morphology and cross-sectional view of the chromium electroplated layer are shown, showing fine nodular surface texture and dense microcrack network. The microcracks in the hard chromium plating layer are caused by tensile stress residual stress generated during deposition. Specifically, chromium hydride with hexagonal close-packed (HCP) microstructure is first formed during electroplating, and then phase transformation occurs to form pure chromium with body-centered cubic (BCC) structure. The volume difference between the two phases causes tensile stress inside the plating layer. As the thickness of the plating layer increases, stress accumulation is inevitable, and eventually microcracks are formed. The laser processing method provided by the present application can effectively remove microcracks, thereby providing the performance of the alloy layer.

[0076] Example 1

[0077] The effects of laser parameters on the alloy layer were studied, and the specific steps were as follows:

[0078] (1) The 30CrNi2MoVA high-strength steel was used as the substrate, and a 200 μm hard chromium layer was pre-plated in a plating solution containing 250 g / L CrO3 and 2.5 g / L H2SO4 at a temperature of 53±1 ℃ and a current density of 50 A / dm2 for 13 hours. 2

[0079] (2) The chromium-plated substrate was heated to 400 ℃ in a nitrogen atmosphere, and after holding for 30 min, it was cooled to room temperature.

[0080] (3) Laser remelting: A JPT continuous laser (wavelength 1064 nm) was used for laser remelting under a protective atmosphere. The key parameters were set as follows:

[0081] The spot diameter was 150 μm, and the scanning step distance was 50 μm.

[0082] The laser power density was 4.95×10 4 W / cm 2 , and the scanning speeds were 5, 20, 35, 50, 65 and 80 mm / s, respectively;

[0083] The laser power density was 5.66×10 4 W / cm 2 , and the scanning speeds were 5, 20, 35, 50, 65 and 80 mm / s, respectively;

[0084] The laser power density was 6.37×10 4 W / cm 2 , and the scanning speeds were 5, 20, 35, 50, 65 and 80 mm / s, respectively;

[0085] The laser power density was 7.08×10 4 W / cm 2 , and the scanning speeds were 5, 20, 35, 50, 65 and 80 mm / s, respectively;

[0086] The laser power density was 7.78×10 4 W / cm 2 , and the scanning speeds were 5, 20, 35, 50, 65 and 80 mm / s, respectively;

[0087] The laser power density was 8.49×10 4 W / cm 2 , and the scanning speeds were 5, 20, 35, 50, 65 and 80 mm / s, respectively;

[0088] The laser power density was 9.20×10 4 W / cm 2 , and the scanning speeds were 5, 20, 35, 50, 65 and 80 mm / s, respectively. ​

[0089] (4) Gradient cooling: Two-stage cooling was applied: rapid cooling to 200 °C at a rate of 300 °C / s, followed by slow cooling to room temperature at a rate of 50 °C / s.

[0090] Figure 2 The relationship between laser power density, scanning density and melt depth is shown, and the secondary crack formation zone and crack-free zone are marked. The results show that when the melting is limited to the coating, crack formation is inevitable; otherwise, when the melting extends to the steel substrate, alloying occurs and no cracks are observed. Figure 3 The cross-sectional view of the coating under laser treatment at different laser power densities and scanning speeds is shown. From Figures 2-3 it can be seen that at a low power density of 4.95 x 10 4 W / cm 2 , when the scanning speed is in the range of 20 to 80 mm / s, only the chromium coating melts, and cracks appear in the treated area after solidification. When the scanning speed drops to 5 mm / s, the melting depth extends to the steel substrate, and a crack-free alloy layer is formed after subsequent solidification. When the power density increases to 6.37 x 10 4 W / cm 2 , similar trends are observed. When the power density reaches 9.20 x 10 4 W / cm 2 , the processing temperature rises to the vaporization temperature of chromium, resulting in material loss and the formation of cavities.

[0091] Based on the above observations, the red dashed box in Figure 3 is defined as the appropriate laser processing window, which can eliminate micro-cracks and achieve alloying between the chromium layer and the steel substrate, achieving a metallurgical bond with minimal defects.

[0092] Figure 4 The XRD diffraction patterns of the coating treated at different scanning speeds are shown. XRD analysis shows that the detected phase after laser treatment is still a body-centered cubic structure, and the characteristic peaks correspond to (110), (200) and (211) crystal planes. According to the Fe-Cr phase diagram, Fe and Cr form a continuous solid solution in the body-centered cubic structure. In addition, the XRD peaks of the laser-processed coating show a characteristic shift to higher 2θ angles, which is due to lattice distortion caused by solute atoms. As the Fe content increases, the 2θ angle shifts to a higher angle. Figure 4 The trend is clearly shown: the laser alloy layer treated at a scanning speed of 5 mm / s and a power density of 7.78 x 10 4 W / cm 2 , its (220) diffraction peak shows a more significant high-angle shift compared to the layer treated at the same power density and a scanning speed of 50 mm / s.

[0093] Figure 5EBSD maps of laser treated hard chrome coating under different laser processing parameters are shown. When low laser power density and high scanning speed are used, the hard chrome layer only undergoes surface remelting, resulting in grain coarsening of the hard chrome layer in the heat-affected zone (e.g. Figure 5 (a1) ). With the increase of laser power density, laser processing leads to the simultaneous melting of the hard chrome layer and the steel substrate, i.e. the alloying phenomenon occurs (e.g. Figure 5 (b1)-(c1) ). After alloying, the alloyed layer presents significant grain coarsening compared to the nanoscale grain size of the original hard chrome layer. Through IPF and grain boundary distribution maps, it can be clearly observed that a large number of low-angle grain boundaries are formed in the heat-affected zone, and the grain size is refined.

[0094] Figure 6 The TEM analysis diagram of the laser processed layer (50 mm / s, 7.78x10 4 W / cm 2 ) and the steel substrate interface shows that the molten pool is mainly composed of Cr and Fe elements, and only contains a small amount of carbon-rich and oxygen-rich compounds. Carbon element may come from the steel substrate, and insufficient protection of the processing atmosphere also leads to the penetration of oxygen into the molten pool. Inside the molten pool, Cr-Fe phase with BCC structure is mainly formed, and a small amount of Cr 23 C6 strengthening phase is precipitated. As shown in Figure 6 (d1, d2), there are a large number of short dislocations, and in Figure 6 (e1, e2), dislocations are observed, indicating that there is obvious metallurgical bonding at the interface between the laser processed layer and the steel substrate. The dislocation density at the interface between the laser processed layer and the steel substrate is 1.5x10 14 m -2 .

[0095] Figure 7 Element distribution maps of the laser treated layer under different laser processing parameters are shown, Figure 8 Hardness distribution maps of the laser treated layer under different laser processing parameters are shown. Based on the observation results of Figure 7 and Figure 8 , combined with the cross-sectional morphology of the laser treated layer in Figure 3 , the best laser processing parameters are determined under the premise of taking into account the highest hardness alloy layer, the highest processing efficiency, and the optimal morphology, i.e. laser power density 7.78x10 4 W / cm 2 , scanning speed 50 mm / s.

[0096] Example 2

[0097] The alloy layer of this example is obtained by the following steps:

[0098] (1) A cylinder (10 mm in diameter and 7.5 mm in wall thickness) made of 30CrNi2MoVA high-strength steel was prepared, and a 210 μm hard chromium layer was pre-plated on the inner wall of the cylinder in a plating solution containing 260 g / L Cr03 and 2.8 g / L H2S04 at a temperature of 53 ± 1 °C and a current density of 45 A / dm2 for 13 hours. 2

[0099] (2) The chromium-plated substrate was heated to 400 °C in a nitrogen atmosphere, and held for 30 min before cooling to room temperature.

[0100] (3) Laser remelting: A JPT continuous laser (wavelength 1064 nm) was used for laser remelting under a protective atmosphere. The key parameters were set as follows: spot diameter 150 μm, scanning step distance 50 μm, laser power density 7.78 x 10 4 W / cm 2 , scanning speed 50 mm / s, and laser head rotation speed 1.59 rpm. The laser beam configuration for processing the inner wall is shown in Figure 9 .

[0101] (4) Gradient cooling: Two-stage cooling was adopted: rapid cooling to 200 °C at a speed of 300 °C / s, and then slow cooling to room temperature at a speed of 50 °C / s.

[0102] Example 3

[0103] Example 3 differs from Example 2 only in that the cylinder made of 42CrMo steel was used in Example 3, and the other conditions were the same as in Example 2.

[0104] Comparative Example 1

[0105] Comparative Example 1 only plated chromium without laser remelting, and the specific steps were as follows:

[0106] (1) A cylinder (10 mm in diameter and 7.5 mm in wall thickness) made of 30CrNi2MoVA high-strength steel was prepared, and a 210 μm hard chromium layer was pre-plated on the inner wall of the cylinder in a plating solution containing 260 g / L Cr03 and 2.8 g / L H2S04 at a temperature of 53 ± 1 °C and a current density of 45 A / dm2 for 13 hours. 2

[0107] (2) The chromium-plated substrate was heated to 400 °C in a nitrogen atmosphere, and held for 30 min before cooling to room temperature.

[0108] Comparative Example 2

[0109] Comparative Example 2 differs from Example 2 only in that no preheating treatment was performed in Comparative Example 2, and the specific steps were as follows:

[0110] ​​(1) A cylinder (10 mm in diameter and 7.5 mm in wall thickness) made of 30CrNi2MoVA high-strength steel was pre-plated with a 210 μm hard chromium layer on the inner wall. The plating was performed in a plating solution containing 260 g / L Cr03 and 2.8 g / L H2S04 at a temperature of 53 ± 1 °C and a current density of 45 A / dm2 for 13 hours. 2

[0111] (2) Laser remelting: Laser remelting was performed using a JPT continuous laser (wavelength 1064 nm) under a protective atmosphere. The key parameters were set as follows: spot diameter 150 μm, scanning step 50 μm, laser power density 7.78 x 10 4 W / cm 2 , scanning speed 50 mm / s, and laser head rotation speed 1.59 rpm.

[0112] (3) Gradient cooling: Two-stage cooling was performed at a rate of 300 °C / s to 200 °C and then at a rate of 50 °C / s to room temperature.

[0113] Comparative Example 3

[0114] Comparative Example 3 differs from Example 2 in that Comparative Example 3 was not subjected to gradient cooling. The specific steps are as follows:

[0115] (1) A cylinder (10 mm in diameter and 7.5 mm in wall thickness) made of 30CrNi2MoVA high-strength steel was pre-plated with a 210 μm hard chromium layer on the inner wall. The plating was performed in a plating solution containing 260 g / L Cr03 and 2.8 g / L H2S04 at a temperature of 53 ± 1 °C and a current density of 45 A / dm2 for 13 hours. 2

[0116] (2) The chromium-plated substrate was heated to 400 °C in a nitrogen atmosphere, held for 30 min, and then cooled to room temperature.

[0117] (3) Laser remelting: Laser remelting was performed using a JPT continuous laser (wavelength 1064 nm) under a protective atmosphere. The key parameters were set as follows: spot diameter 150 μm, scanning step 50 μm, laser power density 7.78 x 10 4 W / cm 2 , scanning speed 50 mm / s, and laser head rotation speed 1.59 rpm.

[0118] (4) Cooling to room temperature at a rate of 300 °C / s.

[0119] Comparative Example 4

[0120] ​​The difference between Comparative Example 4 and Example 2 is that Comparative Example 4 did not undergo gradient cooling. The specific steps are as follows:

[0121] (1) A cylinder (10 mm in diameter and 7.5 mm in wall thickness) made of 30CrNi2MoVA high-strength steel was pre-plated with a 210 μm hard chromium layer on the inner wall of the cylinder. Electroplating was carried out in a plating solution containing 260 g / L CrO3 and 2.8 g / L H2SO4 at a temperature of 53 ± 1 °C and a current density of 45 A / dm³. 2 It lasted for 13 hours.

[0122] (2) The chromium-plated substrate is heated to 400°C in a nitrogen atmosphere, held for 30 minutes, and then cooled to room temperature.

[0123] (3) Laser remelting: Laser remelting was performed using a JPT continuous laser (wavelength 1064nm) under a protective atmosphere. Key parameters were set as follows: spot diameter 150μm, scanning step size 50μm, and laser power density 7.78×10⁻⁶. 4 W / cm 2 The scanning speed is 50 mm / s, and the laser head rotation speed is 1.59 rpm.

[0124] (4) Cool to room temperature at 50℃ / s.

[0125] Table 1 Performance data of Examples 2-3 and Comparative Examples 1-4

[0126]

[0127] In Example 2, Cr 23 The C6 phase had a mass fraction as high as 4.9% and a size of 0.5~2μm. In Example 3, Cr 23 The C6 phase had a mass fraction as high as 4.8% and a size of 0.5~2μm. Compared with the hard chrome plating substrate, the laser-alloyed surfaces of Examples 2 and 3 exhibited superior wear resistance and corrosion resistance. In the high-temperature corrosion wear test, after 500 test cycles, the mass loss of the laser-alloyed surfaces of Examples 2 and 3 was 0.006g and 0.008g, respectively, and no significant wear damage was observed, while the mass loss of the hard chrome plating in Comparative Example 1 was as high as 0.027g.

[0128] Compared with Example 2, Comparative Example 2 did not undergo preheating treatment before laser remelting, and the precipitated Cr 23 The C6 phase decreased, and the high-temperature wear loss increased to 0.021g; in Comparative Examples 3 and 4, no gradient cooling was used, and the Cr... 23 C6 phase precipitation decreased, and high-temperature wear loss increased.

[0129] Example 2, the roughness of the laser alloyed inner surface was measured to be 1.20 pm, as shown in Figure 10 (b). Compared to the roughness of the as-plated hard chromium surface of Comparative Example 1 (2.21 pm), the laser alloying process significantly smoothed the surface texture, which has a positive impact on the barrel performance. The laser treated cylindrical bullet was tested in a semi-enclosed bomb test device. As shown in Figure 10 (c)-(e), after 40 shots, the untreated hard chromium plating (Comparative Example 1) flaked off, while the laser treated plating (Example 2) remained intact after 45 shots.

[0130] Example 5

[0131] In this example, a visual inspection system was also integrated during the laser remelting process, and the system hardware configuration is as follows:

[0132] Three-light synergy module:

[0133] Laser scanner: a galvanometer scanning system with the model of SCANLAB intelliSCAN de20 was used, equipped with a 1068 nm coaxial pilot light, for precise positioning of the laser focal point and assisting in molten pool profile capture. The scanning accuracy is ±5 pm.

[0134] Visible light camera: a Basler acA2440-75um industrial camera was used, with a resolution of 2448x2048 pixels, equipped with a 500 nm band-pass filter to suppress the strong light interference of the molten pool, and a frame rate of 75 fps. The Computar M1614-MP2 lens was selected, with a focal length of 16 mm and a working distance of 200 mm.

[0135] Infrared thermal imager: a FLIR A6751scMWIR camera was used, with a spectral range of 3-5 pm, a resolution of 640x512 pixels, a temperature measurement range of 300-2500 °C, and an accuracy of ±1.5 °C. It was equipped with a 25 mm germanium lens, with a sampling rate of 100 Hz.

[0136] Dual acoustic feedback module:

[0137] Ultrasonic flaw detector: an Olympus EPOCH 650 portable ultrasonic flaw detector was used, equipped with a 10 MHz focused probe, to monitor the crack initiation signals in the area below the molten pool (depth 0-2 mm) in real time in a water film coupling mode. The sampling rate was 1 kHz.

[0138] Acoustic emission sensor: a Physical Acoustics Micro80 sensor was used, with a bandwidth of 100-1000 kHz and a sensitivity of >80 dB, which was fixed to the back of the substrate through a magnetic attraction device, to collect the acoustic emission signals of micro-crack propagation during the solidification process of the molten pool in real time. The sampling rate was 2 MHz.

[0139] Analysis unit: Industrial control computer (Intel Xeon E3-1275v6, 32GB RAM) running a dedicated image processing and control software developed in C++. The software integrates OpenCV library (v4.5) for core image processing operations.

[0140] System workflow and algorithm implementation:

[0141] Temperature uniformity detection in preheating stage:

[0142] Infrared thermal camera acquires temperature distribution map of the substrate surface (100mm x 100mm area) at 10Hz frequency before laser firing.

[0143] Analysis unit calculates the standard deviation σ of all pixel temperatures in the area.

[0144] If σ > 10℃, software triggers preheating compensation instruction: control preheating device to locally compensate the low-temperature area until σ ≤ 10℃. The compensation process usually takes <2 minutes.

[0145] Real-time monitoring and defect identification of molten pool during remelting process:

[0146] Molten pool morphology capture: visible light camera synchronously captures molten pool area (viewing field ~3mm x 2.5mm) at 75fps frame rate. Coaxial indicator light of laser scanner assists in outlining the molten pool edge.

[0147] Crack detection and width calculation:

[0148] Analysis unit pre-processes each frame of molten pool image: median filter (5x5 kernel) for noise reduction, adaptive threshold segmentation (Otsu method) to extract bright area of molten pool, Canny edge detection algorithm to strengthen the boundary profile of bright and dark areas.

[0149] Identify potential crack features (thin, high-curvature dark lines) in the edge image.

[0150] For the identified crack, select several point pairs (Pi, Pj) along its length direction. Calculate the pixel distance between point pairs .

[0151] Convert pixel distance to actual physical width W actual = d pixel x 1.22(μm) according to camera calibration parameters (1 pixel = 1.22μm).

[0152] Take the maximum value of width calculated from all point pairs on this crack as Wmax of the crack.

[0153] Hollow area positioning and area calculation:

[0154] Connectivity analysis is performed on the preprocessed binary image (with the bright area of ​​the molten pool as the foreground).

[0155] Identify holes (i.e., hollow candidate areas) within the foreground region.

[0156] Calculate the area A of the connected region of each hole. pixel (Number of pixels).

[0157] According to the calibration parameters (1 pixel = 1.488 μm) 2 ), calculate the actual area A actual =A pixel ×1.488(μm 2 ).

[0158] Infrared temperature field monitoring: The infrared thermal imager outputs a real-time temperature distribution map of the molten pool and heat-affected zone, and the analysis unit records the maximum temperature Tmax and temperature gradient.

[0159] Real-time feedback control: The analysis unit continuously judges the following conditions:

[0160] Does the Wmax of any crack > 5 μm?

[0161] A of any hollow drum actual Is it >0.1mm? 2 ,

[0162] The ultrasonic or acoustic emission module detected a crack signal exceeding a set threshold.

[0163] If any of the conditions are met, the software will immediately generate laser parameter adjustment instructions:

[0164] If the laser power density is adjusted due to abnormal temperature or excessive defects, adjust it within ±5% of the set value.

[0165] If abnormal molten pool flow occurs or if you wish to change the heat input, adjust the scanning speed: within ±10% of the set value.

[0166] The adjustment commands are sent to the laser controller in real time via the Modbus TCP protocol.

[0167] The system records all adjustment events and the corresponding image, temperature, and acoustic data.

[0168] Multimodal image fusion technology implementation:

[0169] The analysis unit performs spatiotemporal registration on the data from the three-light synergy module:

[0170] Spatial registration: Based on the known hardware installation location and calibration board data, establish a rigid transformation matrix (translation + rotation) from each sensor coordinate system to the molten pool coordinate system.

[0171] Time synchronization: Utilize hardware trigger signal (from laser Q-switch) to ensure three optical data acquisition within the same laser pulse cycle (synchronization error <1 ms).

[0172] Fusion processing:

[0173] Overlay the point cloud data of the laser scanner onto the visible light image to accurately define the molten pool boundary.

[0174] Map the temperature data of the infrared thermal imager to the corresponding area of the visible light image (after registration) in pseudo-color, forming a temperature-topography overlay.

[0175] Element segregation area identification:

[0176] In the visible light image, the molten pool area may cause slight changes in color or texture (such as segregation band color slightly darker or different reflection) due to element differences (Cr / Fe ratio) after solidification.

[0177] The analysis unit processes the visible light image of the molten pool solidification area as follows:

[0178] Extract the region of interest (ROI).

[0179] Convert to HSV color space and analyze the local variance of the saturation (S) and lightness (V) channels.

[0180] Apply the Sobel operator to calculate the gradient amplitude and identify texture mutation areas.

[0181] Mark high-variance and / or high-gradient-amplitude areas as suspected segregation areas.

[0182] Combine with infrared temperature map: If the temperature gradient of a suspected segregation area is abnormal (too high or too low) during solidification, increase its confidence as a real segregation area.

[0183] Output the position coordinates and range of suspected segregation areas, prompting the operator or for subsequent process parameter fine-tuning (such as local adjustment of scanning strategy).

[0184] Implementation effect verification (integrate the system under the parameters of Example 2):

[0185] During the continuous processing of 10 samples, the system successfully detected: 3 times of preheating compensation triggered by insufficient local preheating (temperature difference >15℃); 2 times of small cracks (Wmax≈6-7μm) caused by molten pool fluctuation, triggering a 4% reduction in laser power; 1 suspected air pocket (Aactual≈0.12mm 2 ), triggering an 8% increase in scanning speed.

[0186] After adjustment, no excessive defects (crack <5 μm, no hollow) were formed in the molten pool of all samples.

[0187] The EPMA line scanning results of the Cr / Fe element distribution of the molten pool showed that the standard deviation was controlled between 3.8-4.5%.

[0188] Compared with the traditional unmonitored process, the product qualified rate is increased from about 85% to more than 98% after using the system, and the performance (hardness, wear loss) consistency is significantly improved.

[0189] Aspects, embodiments, features of the present invention are to be considered illustrative only and not restrictive in all aspects. The scope of the present invention is defined only by the claims. Other embodiments, modifications, and uses can be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.

[0190] In the preparation method of the present invention, the order of each step is not limited to the order listed, and for those skilled in the art, the order of each step can be changed without creative labor, which is within the protection scope of the present invention. In addition, two or more steps or actions can be performed simultaneously.

[0191] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace them. Here, it is not necessary and also impossible to fully exemplify all embodiments. However, any obvious changes or variations derived from the essential spirit of the present invention still belong to the protection scope of the present invention, and any additional limitation is contrary to the spirit of the present invention.

Claims

1. Cr-Fe alloy layer for life extension of a barrel, characterized in that, The composition of the Cr-Fe alloy layer includes, in percentage by mass, Cr content of 45-85 wt%, Fe content of 14-54 wt%, C content of 0-1.2 wt%, and O content of ≤0.3 wt%; The Cr-Fe alloy layer is made by laser processing, laser melting the chrome plating layer on the surface of the barrel substrate, and further melting the barrel substrate; the Cr-Fe alloy layer is metallurgically combined with the barrel substrate; The microstructure of the Cr-Fe alloy layer is mainly BCC phase, the proportion of BCC phase is ≥ 85wt%, and Cr is uniformly precipitated 23 C6 strengthening phase, the Cr 23 The mass fraction of the C6 strengthening phase is 3~8wt%, and the size is 0.2~3.0μm; The surface Vickers hardness of the Cr-Fe alloy layer is 400-600 HV, and the mass loss is ≤0.01 g in 500 high-temperature erosion and wear cycle tests; The barrel substrate is made of steel.

2. The Cr-Fe alloy layer according to claim 1, characterized by The Cr content is 80-83 wt%, and the Fe content is 16.5-19 wt%.

3. The Cr-Fe alloy layer according to claim 1, characterized by In the high-temperature erosion and wear cycle test, the test conditions are: temperature 600℃, pressure 30MPa, sliding speed 5m / s; after 500 cycles, the mass loss of the Cr-Fe alloy layer is ≤0.008g.

4. The method for preparing a Cr-Fe alloy layer for life extension of a barrel according to claim 1, characterized by, The method comprises the following steps: (1) chrome plating on the surface of the barrel substrate; (2) heating the barrel substrate after chrome plating to 300-500℃ under a protective atmosphere, maintaining for 10-60min, and then cooling to room temperature; (3) Under a protective atmosphere, the barrel base body obtained in step (2) is subjected to laser remelting treatment, the laser power density is 4.95×10 4 9.20×10 4 W / cm2, the scanning speed is 5-80 mm / s, the spot diameter is 120-180 μm, the scanning step distance is 40-60 μm, the laser melts the chromium plating layer on the surface of the barrel base body, and the melting depth is further extended to the barrel base body; (4) gradient cooling: rapidly cooling to 150-300℃ at 300-500℃ / s, and then cooling to room temperature at 20-80℃ / s, to obtain the Cr-Fe alloy layer.

5. The preparation method according to claim 4, characterized in that, The laser power density is 6.0*10 4 4 The laser power density is 6.0*10The scanning speed is 5-60 mm / s, the spot diameter is 140-160 μm, and the scanning step is 45-55 μm.

6. The preparation method according to claim 4, characterized in that, The laser power density was 7.0 x 10 4 8.0 x 10 4 W / cm2, and the scanning speed was 40-60 mm / s.

7. The preparation method according to claim 4, characterized in that, A visual detection system is integrated in the laser remelting process, which comprises: Three-light coordination module: laser scanner, visible light camera, and infrared thermal imager synchronously collect images of the molten pool area; Dual acoustic feedback module: ultrasonic flaw detector and acoustic emission sensor monitor crack signals in real time; Analysis unit: algorithm performs semantic segmentation on surface cracks of the molten pool, locates hollow areas, and outputs laser parameter adjustment instructions.

8. The preparation method according to claim 7, characterized in that, The working process of the visual detection system comprises: (1) before laser remelting, the substrate surface temperature uniformity is detected by the infrared thermal imager, and when the standard deviation of the temperature is >10℃, preheating compensation is triggered; (2) during the remelting process, the visible light camera captures the molten pool morphology in real time, and the analysis unit calculates the crack width and hollow area. (3) When the crack width > 5 μm or the hollow area > 0.1 mm 2 dynamic adjustment of the laser power density ± 5% or the scanning speed ± 10%.

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