A method for preparing a double-sided gradient-hardened structural metal sheet by low-temperature explosive hardening

Abstract

The application relates to a method for preparing a double-sided gradient-hardened structure metal plate by low-temperature explosive hardening, and belongs to the technical field of metal gradient hardening. First, liquid nitrogen is used to cool a plate to be hardened, and then an explosive explosion is used to generate a high-temperature and high-pressure shock wave to impact harden the plate to be hardened. Because a gap layer is arranged, the explosive shock wave is reflected to form a tensile wave and a compression wave, so that the metal plate with a double-sided gradient-hardened structure is obtained. The method can not only obtain a large-depth hardened layer by single-side explosive impact, but also realize the double-sided gradient-hardened structure.

Description

Technical Field

[0001] This invention relates to a method for preparing double-sided gradient hardened structural metal sheets by low-temperature explosive hardening, belonging to the field of metal gradient hardening technology. Background Technology

[0002] 304 austenitic stainless steel is a classic face-centered cubic stainless steel containing approximately 18% chromium and 8% nickel. It exhibits excellent corrosion resistance, low-temperature toughness, and machinability, making it widely used in industry, automotive, and construction. Due to its high toughness and low strength, 304 austenitic stainless steel requires various strengthening methods. Surface impact strengthening is a novel method that induces a nanogradient structure that can effectively break the strength-ductility balance of the metal, resulting in high-strength and high-toughness metallic materials.

[0003] Laser peening and mechanical peening are both effective methods for surface strengthening of metal sheets, thereby improving their strength and toughness. However, explosive shock waves, characterized by high pressure and high penetration, can effectively achieve deep strengthening of metal sheets compared to other surface treatment technologies. Furthermore, when an explosive shock wave propagates from a material with high wave impedance to a material with low wave impedance, it induces reflected tensile waves; when it propagates from a material with low wave impedance to a material with high wave impedance, it induces emitted compressive waves. However, there are currently no reports on how to achieve double-sided hardening through explosive shock. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for preparing double-sided gradient hardened structural metal sheets by low-temperature explosive hardening.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] A method for preparing double-sided gradient hardened structural metal sheets by low-temperature explosion hardening, the method steps include:

[0007] (1) Grind and polish the metal sheet and substrate to be hardened, and then clean them to obtain the pretreated metal sheet and substrate to be hardened. (2) Place the pretreated metal sheet to be hardened in liquid nitrogen and cool for 20-40 minutes; (3) In a static explosion site, place the substrate horizontally on the sand, place spacers on the four corners of the upper surface of the substrate, and place the cooled and hardened metal plate parallel above the substrate and support it on the spacers. (4) Place the high-explosive explosives that have been packed into the explosives frame and place the explosives frame on the surface of the metal plate to be hardened. Detonate the explosives to impact the metal plate to be hardened and achieve double-sided gradient hardening. The metal plate to be hardened is 304 austenitic stainless steel in a solid solution state; the spacer is a lightweight metal or polymer material; and the detonation velocity of the high-explosive is greater than or equal to 6800 m / s.

[0008] Furthermore, the thickness ratio of the substrate, the metal plate to be hardened, the spacer, and the high-velocity explosive is 20~30mm:5~15mm:0.1~0.5mm:1~7mm.

[0009] Furthermore, the thickness ratio of the metal plate to be hardened to the high-explosive explosive is 1:2.

[0010] Furthermore, in step (1), the metal plate and substrate to be hardened are ground and polished until the Ra is 2.5 μm.

[0011] Furthermore, in step (1), the substrate material is Q235 steel or #45 steel.

[0012] Furthermore, in step (3), the spacer is made of aluminum or rubber.

[0013] Furthermore, in step (4), a layer of butter with a thickness of 0.5~1mm is applied to the surface of the metal sheet to be hardened.

[0014] Furthermore, in step (4), the high-explosive velocity explosive is C4 explosive.

[0015] Furthermore, in step (4), the density of the high-explosive velocity explosive after compression is 1.5~1.7 g / cm³. 3 .

[0016] Furthermore, in step (4), the explosive frame is made of bakelite.

[0017] Beneficial effects This invention provides a method for preparing a double-sided gradient-hardened metal sheet through low-temperature explosive hardening. First, the sheet to be hardened is cooled with liquid nitrogen, then an explosive detonation generates a high-temperature, high-pressure shock wave, which hardens the sheet through impact. Due to the presence of a gap layer, the shock wave is reflected, forming tensile and compressive waves, thus obtaining a double-sided gradient-hardened metal sheet. This method, through single-sided explosive impact, not only achieves a deep hardened layer but also realizes a double-sided gradient-hardened structure. It has significant theoretical and practical value for the development and application of gradient hardening of metallic materials. Attached Figure Description

[0018] Figure 1 A schematic diagram of the apparatus for preparing double-sided gradient hardened structural metal sheets by low-temperature explosive hardening.

[0019] Figure 2Metallographic image of untreated 304 austenitic stainless steel.

[0020] Figure 3 Metallographic image of 304 austenitic stainless steel after low-temperature explosion hardening.

[0021] Figure 4 Hardness distribution diagrams of low-temperature explosion hardening 304 austenitic stainless steel and untreated 304 austenitic stainless steel.

[0022] Figure 5 This is a schematic diagram of a 2D simulation model for cryogenic explosive hardening.

[0023] Figure 6-7 The simulation data is shown in the figure. Detailed Implementation

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

[0025] A method for preparing double-sided gradient hardened structural metal sheets by low-temperature explosion hardening, the method steps include: (1) Grind and polish the metal sheet and substrate to be hardened, and then clean them to obtain the pretreated metal sheet and substrate to be hardened. (2) Place the pretreated metal sheet to be hardened in liquid nitrogen and cool for 20-40 minutes; (3) In a static explosion site, place the substrate horizontally on the sand, place spacers on the four corners of the upper surface of the substrate, and place the cooled and hardened metal plate parallel above the substrate and support it on the spacers. (4) Place the high-explosive explosives that have been packed into the explosives frame and place the explosives frame on the surface of the metal plate to be hardened. Detonate the explosives to impact the metal plate to be hardened and achieve double-sided gradient hardening. Among them, the metal plate to be hardened is solution-treated 304 austenitic stainless steel (such as SUS304, 304L, 304H); the spacer is a lightweight metal or polymer material; the detonation velocity of the high-explosive is greater than or equal to 6800m / s.

[0026] In some embodiments, the thickness ratio of the substrate, the metal plate to be hardened, the spacer and the high-explosive explosive is 20~30mm:5~15mm:0.1~0.5mm:1~7mm.

[0027] In some embodiments, the thickness ratio of the metal sheet to be hardened to the high-explosive explosive is 1:2.

[0028] In some embodiments, in step (1), grinding and polishing are performed until the Ra of the metal plate and substrate to be hardened is 2.5 μm.

[0029] In some embodiments, in step (1), the substrate material is Q235 steel or #45 steel.

[0030] In some embodiments, in step (3), the spacer is made of aluminum or rubber.

[0031] In some embodiments, in step (4), a layer of butter with a thickness of 0.5~1mm is applied to the surface of the metal sheet to be hardened.

[0032] In some embodiments, in step (4), the high-explosive velocity explosive is C4 explosive.

[0033] In some embodiments, in step (4), the density of the high-explosive velocity explosive after compression is 1.5~1.7 g / cm³. 3 .

[0034] In some embodiments, in step (4), the explosive frame is made of bakelite.

[0035] In the following embodiments: Metallographic images of low-temperature explosion-hardened 304 austenitic stainless steel and untreated 304 austenitic stainless steel: etched by a (HF:HNO3:H2O = 4:1:15) etchant and photographed by LEICA OM.

[0036] Model FM The test conditions for the 700 micro Vickers hardness tester are: pressure 1.5N, holding time 15s.

[0037] 2D simulation of cryogenic explosive hardening: numerical simulation was performed using the commercial software ANSYS Autodyn.

[0038] Example 1 like Figure 1 As shown, a method for preparing double-sided gradient hardened structural metal sheets by low-temperature explosion hardening includes the following steps: Step 1: The outer surfaces of the 304 austenitic stainless steel plate 2 and the Q235 steel substrate plate 1 to be hardened are ground and polished to Ra 2.5μm using a grinding machine to remove surface oxides. They are then wiped and cleaned with a 95% ethanol solution to remove oil and other impurities, and dried for later use to obtain the pretreated samples. Both the 304 austenitic stainless steel and the Q235 steel are in a solution-treated state, with thicknesses of 10mm and 20mm respectively.

[0039] Step 2: Place the 304 austenitic stainless steel plate 2 to be hardened in a liquid nitrogen environment and cool for 30 minutes. If no more bubbles are generated around the metal, it indicates that the overall temperature of the 304 austenitic stainless steel plate 2 to be hardened has reached approximately -196℃.

[0040] Step 3: Place the pretreated Q235 steel substrate 1 horizontally on the fine sand base 6 of the static blasting site, place the spacer 5 (thickness of 0.3mm) on the upper surface of the Q235 steel substrate 1, and place the 304 austenitic stainless steel plate 2 to be hardened obtained in Step 2 parallel above it.

[0041] Step 4: Press C4 explosive 4 into a sheet with the same length and width as the 304 austenitic stainless steel plate to be hardened using a bakelite explosive frame (explosive thickness 5mm, density 1.6g / cm³). 3 Apply a 1mm thick layer of grease evenly to the surface of the 304 austenitic stainless steel sheet to be hardened to protect the surface, and then lay C4 explosive fragments parallel to the surface of the metal sheet to be hardened.

[0042] Step 5: Place detonator 3 at the center of the edge of the explosive layer and connect it to the detonation circuit.

[0043] Step 6: After the safety protection measures are complete, remotely detonate detonator 3, and the explosive impact hardens the 304 austenitic stainless steel plate, thereby obtaining a double-sided gradient hardened 304 austenitic stainless steel plate.

[0044] Hardened and untreated 304 austenitic stainless steel sheets were cut to a depth of 3×5×10mm using a wire EDM machine. 3 The small sample (10mm is the thickness of the plate) was then used to mount the small sample into a 22mm diameter mounting block using a metallographic mounting machine. The block was then ground for 5 minutes at each of the following grits: #600, #800, #1000, #1500, #2000, and #3000. Finally, it was polished for 10 minutes each using felt, velvet, and 3µm and 0.5µm diamond polishing solutions, respectively.

[0045] like Figure 2 As shown, the untreated 304 austenitic stainless steel is in a coarse-grained state after solution treatment, with a small amount of annealed twins within the coarse grains. Figure 3 As shown, after low-temperature explosive impact hardening, the hardened layer is as high as 6mm from the hardened surface to the core, and there is also a 2mm hardened layer from the back to the core.

[0046] like Figure 4 As shown, compared to the hardness of untreated 304 austenitic stainless steel (187.2 HV), the hardness of the hardened outermost layer increased by 111.6%, and the hardness gradually decreased with increasing depth. A secondary peak appeared in the central region, followed by a gradual decrease in hardness, and a gradual increase in hardness was observed again in the last 2 mm depth. This confirms the formation of a double-sided gradient hardening structure. The formation of the double-sided gradient hardening structure is mainly attributed to the special propagation of the explosive shock wave.

[0047] To describe the propagation process of the explosion shock wave in 304 austenitic stainless steel during cryogenic explosive hardening, the commercial software ANSYS Autodyn was used to numerically simulate cryogenic explosive hardening. Figure 5 As shown, the simulation employed a coupled method of two-dimensional smoothed particle hydrodynamics (SPH) and Lagrange grids. The SPH particle size for C4 explosive was set to 0.2 mm, and the grid size for both 304 austenitic stainless steel and Q235 steel was set to 0.2 mm × 0.2 mm, with a 0.3 mm gap between them. The red dots represent the detonation positions (detonator insertion locations). The C4 explosive material was modeled using the JWL model, the 304 austenitic stainless steel using the Steinberg Guinan model, and the Q235 steel using the Johnson-Cook model.

[0048] Figure 6 (a) shows the pressure change curve along the depth direction of 304 austenitic stainless steel during a low-temperature explosion impact. The compression wave generated by the high-velocity explosive initially forms a high pressure of approximately 21.6 GPa at the outermost surface, inducing plastic deformation in the 304 austenitic stainless steel. Subsequently, the compression wave gradually decreases to approximately 10.8 GPa. Then, due to the air gap layer (spacer support) between the 304 austenitic stainless steel and Q235 steel, reflected tensile and anti-compression waves are induced. Figure 7 As shown, the reflected tensile wave is mainly concentrated in the middle region, and the tensile stress gradually decreases from the center to both ends; while the reflected compressive wave is concentrated in the back region, and the anti-compressive stress gradually decreases from the backmost part (9.18 GPa) to the core.

[0049] This invention utilizes the strong penetrating power and unique propagation characteristics of explosive shock waves to create a spacer of a specific thickness between the plate to be hardened and the substrate plate, thereby obtaining a 304 austenitic stainless steel plate with a double-sided gradient hardening structure after an explosive impact.

[0050] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A method for preparing double-sided gradient hardening structural metal sheets by low-temperature explosion hardening, characterized in that: The method steps include: (1) Grind and polish the metal sheet and substrate to be hardened, and then clean them to obtain the pretreated metal sheet and substrate to be hardened. (2) Place the pretreated metal sheet to be hardened in liquid nitrogen and cool for 20-40 minutes; (3) In a static explosion site, place the substrate horizontally on the sand, place spacers on the four corners of the upper surface of the substrate, and place the cooled and hardened metal plate parallel above the substrate and support it on the spacers. (4) Place the high-explosive explosives that have been packed into the explosives frame and place the explosives frame on the surface of the metal plate to be hardened. Detonate the explosives to impact the metal plate to be hardened and achieve double-sided gradient hardening. The metal plate to be hardened is 304 austenitic stainless steel in a solid solution state; the spacer is a lightweight metal or polymer material; and the detonation velocity of the high-explosive is greater than or equal to 6800 m / s.

2. The method as described in claim 1, characterized in that: The thickness ratio of the substrate, the metal plate to be hardened, the spacer and the high-explosive explosive is 20~30mm:5~15mm:0.1~0.5mm:1~7mm.

3. The method as described in claim 1, characterized in that: The thickness ratio of the metal sheet to be hardened to the high-explosive explosive is 1:

2.

4. The method as described in claim 1, characterized in that: In step (1), the metal plate and substrate to be hardened are ground and polished until the Ra is 2.5 μm.

5. The method as described in claim 1, characterized in that: In step (1), the substrate material is Q235 steel or #45 steel.

6. The method as described in claim 1, characterized in that: In step (3), the material of the spacer is aluminum or rubber.

7. The method as described in claim 1, characterized in that: In step (4), a layer of 0.5~1mm thick grease is applied to the surface of the metal sheet to be hardened.

8. The method as described in claim 1, characterized in that: In step (4), the high-explosive velocity explosive is C4 explosive.

9. The method as described in claim 1, characterized in that: In step (4), the density of the high-explosive velocity explosive after compression is 1.5~1.7 g / cm³. 3 .

10. The method as described in claim 1, characterized in that: In step (4), the explosive frame is made of bakelite.

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