Heat treatment method for SLM forming gun steel product

Abstract

The invention discloses a heat treatment method of an SLM (selective laser melting) formed gun steel product, which comprises the following steps: S1, preheating: putting the SLM formed gun steel product into a preheating furnace, heating to 300-500 DEG C at a heating speed of 50-100 DEG C / h, and preserving heat for 1-2 hours; s2, quenching is conducted, specifically, the preheated gun steel product is rapidly put into a quenching medium, the quenching medium is water or oil or a polymer solution, and the quenching time is set to be 1-5 min according to the size and shape of the gun steel product; s3, tempering: putting the quenched gun steel product into a tempering furnace, heating to 200-400 DEG C at a heating speed of 50-100 DEG C / h, and preserving heat for 1-2 hours; s4, cooling is conducted, specifically, the tempered gun steel product is taken out and cooled to the room temperature; and S5, chemical plating: depositing a layer of metal or alloy on the surface of the gun steel product to increase the corrosion resistance and wear resistance of the gun steel product. The method has the beneficial effects that residual stress is effectively reduced, hardness and strength are improved, corrosion resistance and wear resistance are improved, performance is optimized, special requirements are met, and reliability is improved.

Description

Technical Field

[0001] The present invention relates to the field of heat treatment technology, and in particular to a heat treatment method for a SLM formed gun steel product. Background Art

[0002] With the continuous advancement of additive manufacturing technology, the application of selective laser melting (SLM) technology in the field of gun steel product manufacturing is increasing. SLM technology has the advantages of being able to manufacture parts with complex shapes and reduce material waste.

[0003] However, there are still some shortcomings in the performance of SLM-molded gun steel products. Among them, large residual stress is a more prominent problem, which may cause deformation and cracking of the product during use. In addition, low hardness and strength also limit its application in some high-strength requirements.

[0004] In order to overcome these problems and improve the performance of SLM-molded steel products, it is necessary to perform proper heat treatment on them. Traditional heat treatment methods may have some limitations when processing SLM-molded steel products. For example, traditional methods may not be able to effectively reduce residual stress, or while improving hardness and strength, lead to a decrease in other properties.

[0005] Therefore, in order to meet the needs of SLM-molded steel products in practical applications, it is particularly important to develop a heat treatment method specifically for this product. This method needs to be able to fully consider the characteristics of SLM-molded steel products, effectively improve their performance, and increase their reliability and service life in various applications. Summary of the invention

[0006] The object of the present invention is to provide a heat treatment method for SLM formed gun steel products to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above object, the present invention provides the following technical solution: a heat treatment method for SLM formed gun steel products, comprising the following steps:

[0008] S1. Preheating: Place the SLM-molded steel product into a preheating furnace, heat it to 300-500℃ at a heating rate of 50-100℃ / h, and keep it warm for 1-2h;

[0009] S2. Quenching: The preheated steel product is quickly placed in a quenching medium, which is water, oil or polymer solution. The quenching time is 1-5 minutes depending on the size and shape of the steel product.

[0010] S3, tempering: put the quenched gun steel product into the tempering furnace, heat it to 200-400℃ at a heating rate of 50-100℃ / h, and keep it warm for 1-2h;

[0011] S4, cooling: take out the tempered steel product and cool it to room temperature;

[0012] S5. Chemical plating: depositing a layer of metal or alloy on the surface of the steel product to increase its corrosion resistance and wear resistance.

[0013] Preferably, the preheating step:

[0014] Gradient heating: The preheating process is divided into multiple stages, each stage uses a different heating rate, in the initial stage, the heating is carried out at a slower heating rate of 50℃ / h, and then the heating rate is gradually increased to 80℃ / h-100℃ / h to reduce thermal stress;

[0015] Preheating atmosphere control: During the preheating process, specific inert gas is introduced to reduce the occurrence of oxidation and decarburization.

[0016] Preferably, the inert gas is selected from: nitrogen or argon with a purity of 99.9% or more;

[0017] Gas flow rate: range is 10-50 liters per minute;

[0018] Furnace pressure: range is 0.01-0.05MPa.

[0019] Preferably, multi-stage quenching is adopted:

[0020] The quenching process is divided into multiple stages, each stage using different quenching media or quenching conditions; a fast-cooling quenching medium is used in the first stage to quickly reduce the temperature of the gun steel product; a slower-cooling quenching medium is used in the second stage to reduce thermal stress and deformation.

[0021] Preferably, the first stage:

[0022] Quenching medium: cold water;

[0023] Temperature: room temperature;

[0024] Time: 1-3 minutes, depending on the size and shape of the steel product;

[0025] Phase 2:

[0026] Quenching medium: oil or polymer solution;

[0027] Temperature: 60-100℃;

[0028] Time: 3-5 minutes, depending on the size and shape of the steel product.

[0029] Preferably, the polymer includes any one of polyvinyl alcohol, polyacrylamide or polyethylene glycol.

[0030] Preferably, the specific steps of the chemical plating step are:

[0031] Surface preparation:

[0032] Use organic solvents or alkaline solutions to clean the surface of steel products to remove oil stains and impurities;

[0033] Use acidic solution or plasma to treat the surface of gun steel products to activate the surface and increase the adhesion of the coating;

[0034] Pre-plating a thin metal layer, such as nickel or copper, on the surface of the gun steel product to increase the uniformity and adhesion of the coating;

[0035] Chemical plating:

[0036] Select the plating solution according to your needs;

[0037] According to the composition of the plating solution and the material characteristics of the blasting steel product, the plating solution temperature is between 80-90°C;

[0038] According to the composition of the plating solution and the material properties of the blasting steel products, the pH value of the plating solution is between 4.5 and 5.5;

[0039] Select an appropriate deposition time between 1 and 2 hours according to needs.

[0040] Preferably, the plating solution is a nickel-phosphorus plating solution or a nickel-boron plating solution.

[0041] The heat treatment method of a SLM-formed gun steel product proposed in the present invention has the following beneficial effects:

[0042] 1. Effectively reduce residual stress:

[0043] Specific preheating, quenching and tempering processes: These process steps are designed to eliminate or reduce residual stress in steel products. Preheating can heat the material evenly and reduce the generation of thermal stress; quenching can quickly cool the material and change its structure, thereby reducing residual stress; tempering can further adjust the material's properties and reduce the impact of residual stress;

[0044] Reduced deformation and cracking risk: The reduction of residual stress helps to reduce the risk of deformation and cracking of the product during use. This is crucial to the reliability and safety of gun steel products and can ensure their normal operation in harsh environments.

[0045] 2. Improve hardness and strength:

[0046] Quenching and tempering steps: During the quenching process, the microstructure of the steel product changes to form high-strength phases such as martensite or bainite, which significantly improves hardness and strength. Tempering can adjust the balance between hardness and strength, while improving toughness and ductility;

[0047] Enhanced application capabilities: Improving hardness and strength enables artillery steel products to perform better in situations with high strength requirements, such as being able to withstand greater pressure and impact under extreme conditions such as artillery firing.

[0048] 3. Improve corrosion resistance and wear resistance:

[0049] Chemical plating step: By depositing a layer of metal or alloy, such as nickel, chromium, etc., on the surface of the steel product, a corrosion-resistant and wear-resistant protective layer can be formed. This protective layer can effectively prevent the external medium from corroding the steel product and improve its corrosion resistance and wear resistance;

[0050] Extend service life: Improving corrosion resistance and wear resistance can extend the service life of gun steel products, reduce maintenance and replacement costs, and improve their economic benefits.

[0051] 4. Optimize performance:

[0052] Comprehensive optimization of various properties: The heat treatment method of the present invention can not only improve key properties such as hardness, strength and corrosion resistance, but also optimize other performance indicators such as toughness, ductility, fatigue strength, etc. By comprehensively considering various properties, the gun steel products can perform better in practical applications;

[0053] Adapt to different application needs: Optimizing performance can make gun steel products better adapt to different application occasions and working conditions, meet various special requirements, and improve their versatility and applicability.

[0054] 5. Meet special requirements:

[0055] Developed in accordance with the characteristics of SLM-molded cannon steel products: This invention fully considers the special properties and manufacturing process of SLM-molded cannon steel products, and designs a targeted heat treatment method. This specialized development can better meet the needs of cannon steel products in special applications, such as in aerospace, defense and other fields;

[0056] Improve product competitiveness: Meeting special requirements can make gun steel products more competitive in the market and bring more business opportunities to the enterprise.

[0057] 6. Improve reliability:

[0058] Improved product performance: By improving hardness, strength, corrosion resistance and other properties, the reliability of gun steel products has been significantly improved. This means that the product is less likely to fail during use and can operate more stably;

[0059] Reduce the risk of failure: Improved reliability can reduce the risk of failure during use and reduce losses and safety hazards caused by product failure. This is particularly important for some key application areas, such as military and aviation.

[0060] In summary, the beneficial effects of the present invention include effectively reducing residual stress, improving hardness and strength, improving corrosion resistance and wear resistance, optimizing performance, meeting special requirements, and improving reliability. These beneficial effects enable SLM-formed gun steel products to have better performance and reliability in practical applications, meet various special needs, and provide strong support for the development of related fields. DETAILED DESCRIPTION

[0061] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] The present invention provides a technical solution: a heat treatment method for a SLM-formed gun steel product, comprising the following steps:

[0063] S1. Preheating: Place the SLM-molded steel product into a preheating furnace, heat it to 300-500℃ at a heating rate of 50-100℃ / h, and keep it warm for 1-2h;

[0064] Gradient heating: The preheating process is divided into multiple stages, each stage uses a different heating rate, in the initial stage, the heating is carried out at a slower heating rate of 50℃ / h, and then the heating rate is gradually increased to 80℃ / h-100℃ / h to reduce thermal stress;

[0065] Preheating atmosphere control: During the preheating process, specific inert gas is introduced to reduce the occurrence of oxidation and decarburization;

[0066] Inert gas selection: including nitrogen or argon with an atmosphere purity of more than 99.9%;

[0067] Gas flow rate: range is 10-50 liters per minute;

[0068] Furnace pressure: range is 0.01-0.05MPa.

[0069] S2. Quenching: The preheated steel product is quickly placed in a quenching medium, which is water, oil or polymer solution. The quenching time is 1-5 minutes depending on the size and shape of the steel product.

[0070] Using multi-stage quenching:

[0071] Divide the quenching process into multiple stages, using different quenching media or quenching conditions in each stage; use a fast-cooling quenching medium in the first stage to quickly reduce the temperature of the steel product; use a slower-cooling quenching medium in the second stage to reduce thermal stress and deformation;

[0072] The first stage: Quenching medium: cold water; temperature: room temperature; time: 1-3 minutes depending on the size and shape of the steel product;

[0073] The second stage: quenching medium: oil or polymer solution; temperature: 60-100°C; time: 3-5 minutes depending on the size and shape of the steel product, the polymer includes any one of polyvinyl alcohol, polyacrylamide or polyethylene glycol.

[0074] S3. Tempering: Put the quenched artillery steel product into the tempering furnace, heat it to 200-400℃ at a heating rate of 50-100℃ / h, and keep it warm for 1-2h.

[0075] S4. Cooling: Take out the tempered steel product and cool it to room temperature.

[0076] S5. Chemical plating: depositing a layer of metal or alloy on the surface of the steel product to increase its corrosion resistance and wear resistance;

[0077] Specific steps of chemical plating:

[0078] Surface pretreatment: Use organic solvents or alkaline solutions to clean the surface of steel products to remove oil and impurities; use acidic solutions or plasma to treat the surface of steel products to activate the surface and increase the adhesion of the coating; pre-plate a thin metal layer, such as nickel or copper, on the surface of steel products to increase the uniformity and adhesion of the coating;

[0079] Chemical plating: select nickel-phosphorus plating solution or nickel-boron plating solution according to needs; according to the composition of the plating solution and the material properties of the blasted steel product, the plating solution temperature is between 80-90°C; according to the composition of the plating solution and the material properties of the blasted steel product, the plating solution pH value is between 4.5-5.5; select the appropriate deposition time between 1-2 hours according to needs.

[0080] Preheating experiment operation:

[0081] S1. Preheating:

[0082] Heating rate: 50℃ / h in the initial stage, and 100℃ / h in the middle and late stages;

[0083] Target temperature: 450℃;

[0084] Keep warm time: 1.5 hours;

[0085] Preheating atmosphere: Use 99.9% pure argon as inert protective gas;

[0086] Gas flow rate: 30 liters per minute;

[0087] Pressure inside the furnace: 0.03MPa.

[0088] Experimental setup:

[0089] Control group: SLM-formed gun steel products without any heat treatment.

[0090] Experimental group: SLM-formed gun steel products processed according to the above steps.

[0091] Testing and analysis

[0092] 1. Thermal stress test: Thermal stress is measured using an X-ray diffractometer.

[0093] 2. Microstructure observation: Observe the changes in the internal microstructure of the material using a scanning electron microscope (SEM).

[0094] 3. Hardness test: Use Vickers hardness tester to carry out hardness test.

[0095] 4. Corrosion resistance test: The corrosion resistance of the samples was evaluated through salt spray test.

[0096] result:

[0097] Thermal stress test:

[0098] The thermal stress value of the control group was about 150MPa.

[0099] The thermal stress value of the experimental group was significantly reduced to 35MPa.

[0100] Microstructural evaluation:

[0101] There are uneven grains and larger melting marks in the control group.

[0102] The grains in the experimental group are more refined and evenly distributed, and the melting marks are significantly improved.

[0103] Hardness test:

[0104] The hardness of the control group was about 300 HV.

[0105] The hardness of the experimental group increased to 400 HV, indicating that heat treatment effectively increased the hardness of the material.

[0106] Corrosion resistance:

[0107] The salt spray test showed that the experimental group extended the time for corrosion to begin, from 48 hours in the control group to 72 hours, indicating that heat treatment enhanced the corrosion resistance of the material.

[0108] Quenching experiment operation:

[0109] Experimental setup:

[0110] Control group: SLM-formed steel products without heat treatment.

[0111] Experimental group A: heat treatment was performed only by preheating and a single quenching medium (water or oil).

[0112] Experimental Group B: Heat treatment was performed according to the multi-stage quenching process you described.

[0113] Implementation steps:

[0114] All samples were first subjected to the S1 stage preheating treatment.

[0115] Experimental Group A

[0116] Single quenching: Immerse the preheated product directly in room temperature cold water for 3 minutes or in oil for 5 minutes.

[0117] Experimental Group B

[0118] Multi-stage quenching:

[0119] Stage 1: Immerse the preheated product in room temperature cold water for 1 to 3 minutes (depending on the specific size and shape).

[0120] Second stage: Immediately transfer the product to oil or polyacrylamide solution at a temperature of 60-100°C and continue quenching for 3 to 5 minutes.

[0121] Testing and analysis:

[0122] Internal stress analysis: using X-ray diffractometer.

[0123] Microstructure: Scanning electron microscopy (SEM).

[0124] Hardness assessment: Tested using a Vickers hardness tester.

[0125] Tensile strength determination: completed by universal material testing machine.

[0126] Corrosion resistance evaluation: salt spray test.

[0127] Result analysis:

[0128] Internal Stress: It is expected that the products of Experimental Group B have significantly lower internal stress than those of the Control Group and Experimental Group A, since the multi-stage quenching process optimizes the cooling process and reduces stress accumulation.

[0129] Microstructure: The materials in experimental group B are expected to show a more uniform and refined grain structure than those in other groups, as the gradual decrease in temperature helps promote more uniform crystal growth.

[0130] Hardness: The hardness values ​​of Experimental Group B are expected to be between Experimental Group A and the Control Group because multi-stage quenching provides a better balance of hardness and toughness.

[0131] Tensile Strength: The multi-stage quenching process may lead to the higher tensile strength of experimental group B due to the combined effects of internal stress reduction and grain refinement.

[0132] Corrosion resistance: Experimental group B is expected to have better corrosion resistance, and the more uniform microstructure and lower internal stress help reduce the probability of corrosion.

[0133] Embodiment 1:

[0134] Warm-up phase:

[0135] The SLM-molded gun steel product was placed in a preheating furnace, heated to 300°C at a heating rate of 50°C / h, and kept warm for 1 hour;

[0136] During the preheating process, 99.9% pure nitrogen is introduced as an inert gas to reduce oxidation and decarburization; the gas flow rate is set at 20 liters per minute, and the pressure in the furnace is maintained at 0.02MPa;

[0137] Quenching stage:

[0138] The first stage: the preheated steel product is quickly placed in cold water at room temperature, and the quenching time is set to 1 minute;

[0139] Second stage: The gun steel product is then transferred to a polyacrylamide solution at 60°C and quenched for 4 minutes.

[0140] Tempering stage:

[0141] The quenched artillery steel product is placed in a tempering furnace, heated to 250°C at a heating rate of 60°C / h, and taken out after keeping warm for 1.5 hours.

[0142] Cooling phase:

[0143] After tempering, the steel product is cooled naturally to room temperature.

[0144] Chemical plating stage:

[0145] First, use ethanol to clean the surface to remove oil and impurities. Then use dilute sulfuric acid to activate the surface of the cannon steel product; pre-plate a layer of nickel on the surface of the cannon steel product to increase the uniformity of the coating;

[0146] A nickel-phosphorus plating solution was used for chemical plating, the plating solution temperature was controlled at 85° C., the pH value was set to 5.0, and the plating solution deposition time was set to 1.5 hours.

[0147] Results and Analysis:

[0148] Thermal stress test: Using a stress measuring instrument before and after preheat treatment, the untreated sample showed a maximum stress of 150MPa, which dropped to 30MPa after treatment;

[0149] Metallographic analysis: Structural uniformity was observed under a microscope, and the treated samples showed a more uniform grain distribution.

[0150] Embodiment 2:

[0151] Warm-up phase:

[0152] The SLM-molded gun steel product was heated to 450°C at a rate of 75°C / h in a preheating furnace and kept at this temperature for 2 hours;

[0153] Argon gas with a purity of 99.9% was introduced as the preheating atmosphere, the gas flow rate was set to 30 liters per minute, and the pressure in the furnace was 0.03 MPa.

[0154] Quenching stage:

[0155] The first stage: the product is placed in cold water and the quenching time is 2 minutes.

[0156] The second stage: the product is transferred to 80℃ oil for quenching, and the quenching time is 5 minutes.

[0157] Tempering stage:

[0158] After quenching, the product was heated to 350°C at a rate of 80°C / h and kept at this temperature for 2 hours.

[0159] Cooling phase:

[0160] Cool directly to room temperature after removal from the tempering furnace.

[0161] Chemical plating stage:

[0162] Surface pretreatment includes cleaning with acetone and treating with dilute hydrochloric acid, followed by pre-plating a layer of copper on the surface of the gun steel;

[0163] A nickel-boron plating solution was selected, the temperature was set to 88° C., the pH value was 4.8, and the chemical plating deposition time was 2 hours.

[0164] Results and Analysis:

[0165] Hardness test: The hardness before quenching is 250HB, after quenching it reaches 650HB, and after tempering it is adjusted to 500HB;

[0166] Tensile test:

[0167] Before quenching: tensile strength is 800MPa;

[0168] After quenching: tensile strength increased to 1400MPa;

[0169] After tempering: tensile strength is 1200MPa and ductility is significantly improved.

[0170] Embodiment 3:

[0171] Warm-up phase:

[0172] The SLM-molded gun steel product was heated to 500°C at a rate of 100°C / h and kept warm for 1 hour.

[0173] Nitrogen gas with a purity of 99.9% was used as the atmosphere, the gas flow rate was 50 liters per minute, and the pressure in the furnace was 0.05 MPa.

[0174] Quenching stage:

[0175] Stage 1: The product is quenched in cold water for 1 minute;

[0176] Second stage: the product is quenched in a polyethylene glycol solution at 90°C for 3 minutes.

[0177] Tempering stage:

[0178] Heat to 400°C at a rate of 100°C / h and keep warm for 1 hour.

[0179] Cooling phase:

[0180] Warm directly to room temperature.

[0181] Chemical plating stage:

[0182] The surface is first cleaned with toluene and then treated with plasma to improve the adhesion of the coating. After that, copper is pre-plated on the surface of the product;

[0183] Nickel phosphorus chemical plating was performed at a temperature of 90° C., a pH value of 4.5, and a deposition time of 1 hour.

[0184] Results and Analysis:

[0185] Salt spray test (used to evaluate corrosion resistance): The uncoated sample began to rust after 48 hours in the salt spray test, while the coated sample showed no obvious corrosion after 192 hours under the same conditions;

[0186] Friction coefficient test: Comparing the friction coefficient before and after coating, it dropped from 0.5 to 0.3, indicating that the coating significantly reduced the friction characteristics of the material and is suitable for high wear environments.

[0187] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A heat treatment method for SLM-formed gun steel products, characterized in that: The following steps are involved: S1. Preheating: Place the SLM-molded steel product into a preheating furnace, heat it to 300-500℃ at a heating rate of 50-100℃ / h, and keep it warm for 1-2h; S2. Quenching: The preheated steel product is quickly placed in a quenching medium, which is water, oil or polymer solution. The quenching time is 1-5 minutes depending on the size and shape of the steel product. S3, tempering: put the quenched gun steel product into the tempering furnace, heat it to 200-400℃ at a heating rate of 50-100℃ / h, and keep it warm for 1-2h; S4, cooling: take out the tempered steel product and cool it to room temperature; S5. Chemical plating: depositing a layer of metal or alloy on the surface of the steel product to increase its corrosion resistance and wear resistance.

2. A heat treatment method for a SLM-formed gun steel product according to claim 1, characterized in that: Preheating steps: Gradient heating: The preheating process is divided into multiple stages, each stage uses a different heating rate, in the initial stage, the heating is carried out at a slower heating rate of 50℃ / h, and then the heating rate is gradually increased to 80℃ / h-100℃ / h to reduce thermal stress; Preheating atmosphere control: During the preheating process, specific inert gas is introduced to reduce the occurrence of oxidation and decarburization.

3. A heat treatment method for a SLM-formed gun steel product according to claim 2, characterized in that: Inert gas selection: including nitrogen or argon with an atmosphere purity of more than 99.9%; Gas flow rate: range is 10-50 liters per minute; Furnace pressure: range is 0.01-0.05MPa.

4. A heat treatment method for a SLM-formed gun steel product according to claim 3, characterized in that: Using multi-stage quenching: The quenching process is divided into multiple stages, each stage using different quenching media or quenching conditions; a fast-cooling quenching medium is used in the first stage to quickly reduce the temperature of the gun steel product; a slower-cooling quenching medium is used in the second stage to reduce thermal stress and deformation.

5. A heat treatment method for a SLM-formed gun steel product according to claim 4, characterized in that: Phase 1: Quenching medium: cold water; Temperature: room temperature; Time: 1-3 minutes, depending on the size and shape of the steel product; Phase 2: Quenching medium: oil or polymer solution; Temperature: 60-100℃; Time: 3-5 minutes, depending on the size and shape of the steel product.

6. A heat treatment method for a SLM-formed gun steel product according to claim 5, characterized in that: The polymer includes any one of polyvinyl alcohol, polyacrylamide or polyethylene glycol.

7. A heat treatment method for a SLM-formed gun steel product according to claim 6, characterized in that: Specific steps of chemical plating: Surface preparation: Use organic solvents or alkaline solutions to clean the surface of steel products to remove oil stains and impurities; Use acidic solution or plasma to treat the surface of gun steel products to activate the surface and increase the adhesion of the coating; Pre-plating a thin metal layer, such as nickel or copper, on the surface of the gun steel product to increase the uniformity and adhesion of the coating; Chemical plating: Select the plating solution according to your needs; According to the composition of the plating solution and the material characteristics of the blasting steel product, the plating solution temperature is between 80-90°C; According to the composition of the plating solution and the material properties of the blasting steel products, the pH value of the plating solution is between 4.5 and 5.5; Select an appropriate deposition time between 1 and 2 hours according to needs.

8. A heat treatment method for a SLM-formed gun steel product according to claim 7, characterized in that: The plating solution is a nickel-phosphorus plating solution or a nickel-boron plating solution.