An ultra-high strength low density steel and a method of making the same

Abstract

This invention relates to the field of low-density high-strength steel technology, specifically to an ultra-high-strength low-density steel and its preparation method. The preparation materials include: 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron, by mass percentage. In this invention, an alloy raw material containing multiple specific elements is melted in a vacuum environment, and a precise programmed cooling rate is applied to suppress the formation of harmful impurities and segregation, obtaining a high-purity single austenitic structure. Subsequently, with the synergistic effect of an extremely low temperature environment and mechanical pressure, a high-density defect structure and complex phase transformation are induced inside the material, greatly enhancing its potential strength. The subsequent low-temperature aging treatment releases internal stress and further promotes the dispersion precipitation of nanoscale strengthening phases, achieving the coupling of multiple strengthening mechanisms. Finally, controlled forced air cooling locks in the composite ultrafine structure, resulting in a low-density steel with both excellent strength and stability.

Description

Technical Field

[0001] This invention relates to the field of low-density high-strength steel technology, and in particular to an ultra-high-strength low-density steel and its preparation method. Background Technology

[0002] The field of low-density high-strength steel technology mainly involves iron-based lightweight alloy systems and their composition design, metallurgical processes, heat treatment processes, and microstructure control technologies. Its core aspects include the introduction of low-density elements (such as Al, Mg, and Ti) into the steel, strengthening phase precipitation or solid solution strengthening mechanisms, microstructure refinement, and control of impurity elements, aiming to achieve high strength while maintaining low material density. In this technical field, traditional low-density high-strength steel refers to steel whose chemical composition includes aluminum or other lightweight alloying elements, and whose microstructure is controlled through smelting, casting, hot working, and heat treatment, thereby reducing density while maintaining strength.

[0003] In the preparation of aluminum-containing low-density steel, conventional smelting and casting processes are difficult to effectively suppress the oxidation and segregation of light elements, which easily leads to a decrease in the purity of the alloy melt and uneven composition. Subsequent hot working and heat treatment have insufficient precision in controlling the microstructure, and the synergistic effect of multiple strengthening mechanisms such as solid solution, precipitation and phase transformation strengthening is difficult to fully activate. The level of steel strength and toughness is limited, and conventional treatment is prone to accumulating internal residual stress, affecting the stability and uniformity of the final material in service. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose an ultra-high strength low density steel and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: an ultra-high strength low-density steel, wherein the materials for preparing the ultra-high strength low-density steel include:

[0006] It contains 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron by weight.

[0007] As a further aspect of the present invention, the aluminum is industrial pure aluminum powder with an average particle size of 50 micrometers to 100 micrometers.

[0008] As a further aspect of the present invention, the mass ratio of manganese to copper is 10:1 to 15:1.

[0009] As a further aspect of the present invention, the carbon is derived from graphene nanosheets, the graphene nanosheets having an average thickness of 1 nanometer to 5 nanometers.

[0010] A method for preparing ultra-high strength low-density steel, the method comprising the following steps:

[0011] S1: An alloy raw material containing 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron by mass percentage is loaded into a vacuum induction melting furnace and heated to 1600°C to 1650°C to obtain a molten metal. The molten metal is then cooled by a program-controlled cooling system at a cooling rate of 5K / min to 15K / min to obtain a solid austenitic steel billet.

[0012] S2: The solid austenitic steel billet is immersed in liquid nitrogen at a temperature of -196℃ for deep cryogenic treatment. When the overall temperature of the solid austenitic steel billet is the same as the temperature of the liquid nitrogen, unidirectional compression is applied to the solid austenitic steel billet by a mechanical pressurizing device until the solid austenitic steel billet produces 6% macroscopic plastic deformation to obtain a composite billet.

[0013] S3: Transfer the composite billet to a heating and tempering furnace, set the temperature of the heating and tempering furnace to 400°C, and hold the composite billet at the temperature of 400°C for 30 to 60 minutes to prepare a recovery billet;

[0014] S4: The recovered billet is taken out from the heating and tempering furnace, and forced air cooling is performed on the recovered billet by a blower at an air flow rate of 1m / s to 3m / s until the temperature of the recovered billet drops below 50°C.

[0015] As a further aspect of the present invention, step S1 specifically comprises:

[0016] S11: Using 5% to 9% by mass of the aluminum, 15% to 25% of the manganese, 1% to 3% of the copper, 0.1% to 0.5% of the carbon, and the balance of the iron as the alloy raw materials, the alloy is introduced into the vacuum induction melting furnace under an argon protective atmosphere. The vacuum system is then activated to extract the pressure inside the vacuum induction melting furnace to... Pa to Pa, to obtain pretreated raw materials;

[0017] S12: Start the induction heating system of the vacuum induction melting furnace, heat the pre-treated raw material to 1600°C to 1650°C at a heating rate of 20°C / min to 30°C / min, and hold it at this temperature for 20 minutes to 40 minutes to completely melt and uniformly mix the pre-treated raw material to obtain the metal melt.

[0018] S13: Activate the program-controlled cooling system, and control the cooling rate of the molten metal to 5K / min to 15K / min by adjusting the flow rate of the cooling medium. When the temperature of the molten metal drops below the solidus temperature of 1000℃ to 1100℃, the solid austenitic steel billet is obtained.

[0019] As a further aspect of the present invention, step S2 specifically comprises:

[0020] S21: The solid austenitic steel billet is completely immersed in a cryogenic treatment tank containing liquid nitrogen at -196°C. The core temperature of the solid austenitic steel billet is monitored in real time by multiple thermocouples set inside the solid austenitic steel billet. When the temperature difference between the core temperature and the liquid nitrogen is less than 1°C, the cryogenic treatment of the solid austenitic steel billet is confirmed to be completed, and a cryogenic billet is obtained.

[0021] S22: Immediately start the mechanical pressurization device to apply unidirectional compressive stress to the cryogenic billet, and at the same time monitor the macroscopic plastic deformation of the cryogenic billet through a strain sensor. When the macroscopic plastic deformation reaches 6%, immediately remove the unidirectional compressive stress to obtain the composite billet.

[0022] As a further aspect of the present invention, step S3 specifically comprises:

[0023] S31: Quickly transfer the composite billet to the heating and tempering furnace, set the furnace temperature of the heating and tempering furnace to 400℃, and adjust the heating power through the PID controller so that the heating rate of the composite billet is not less than 50℃ / min;

[0024] S32: When the overall temperature of the composite billet reaches 400℃, start timing and hold for 30 to 60 minutes. During the holding period, calculate the dynamic recovery factor based on the composition of the composite billet. , ;

[0025] in, Represents material constants. This represents the activation energy of the response. Represents the ideal gas constant. Represents the tempering temperature. Indicates the heat preservation time. Represents a time index;

[0026] S33: By monitoring the dynamic response factor in real time The value, when the When the preset recovery threshold of 0.6 to 0.8 is reached, heating is immediately stopped to obtain the recovered billet.

[0027] As a further aspect of the present invention, step S4 specifically comprises:

[0028] S41: Take the recovered billet out of the heating and tempering furnace and immediately place it in the forced cooling chamber. Start the blower array to blow cooling air with an air flow rate of 1 m / s to 3 m / s onto the entire surface of the recovered billet.

[0029] S42: The surface temperature of the recovery billet is monitored non-contactly by an infrared temperature sensor array, so that the cooling process of the recovery billet is uniform;

[0030] S43: When the average surface temperature of the recovered billet monitored by the infrared temperature sensor array drops below 50°C, the operation of the blower is stopped to complete the forced air cooling treatment and obtain the ultra-high strength low density steel finished product.

[0031] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0032] In this invention, by melting alloy raw materials containing multiple specific elements in a vacuum environment and applying a precise programmed cooling rate, the uniform solid solution of high-content lightweight elements can be ensured, the formation of harmful impurities and segregation can be suppressed, and a high-purity single austenitic structure can be obtained. Subsequently, with the synergistic effect of ultra-low temperature environment and mechanical pressure, a high-density defect structure and complex phase transformation are induced inside the material, which greatly enhances the potential strength. The subsequent low-temperature aging treatment releases internal stress and further promotes the dispersion precipitation of nanoscale strengthening phases, realizing the coupling of multiple strengthening mechanisms. Finally, the composite ultrafine structure is locked by controlled forced air cooling, resulting in low-density steel with both excellent strength and stability. Attached Figure Description

[0033] Figure 1 This is a system flowchart of the present invention;

[0034] Figure 2 This is a flowchart of the present invention;

[0035] Figure 3 This is a flowchart of the present invention;

[0036] Figure 4 This is a flowchart of the present invention;

[0037] Figure 5 This is a flowchart of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the software-based technical solution is described in detail below with reference to system architecture diagrams and embodiments. It should be understood that the specific embodiments described herein are only for explaining the technical solutions of this invention and do not constitute a limitation on the scope of protection.

[0039] In the description of this invention, the system architecture relationships or data processing flows indicated by terms such as "layer," "module," "interface," "data flow," "client," and "server" are all defined based on the architecture diagram or flowchart corresponding to the embodiments. This way of describing is only used to clearly illustrate the logical relationships between the elements in the technical solution, and not to limit the physical deployment form. The term "multiple" includes two or more technical units, including but not limited to multiple data nodes, processing threads, service instances, or functional components and other scalable elements. The specific number is determined according to the actual business scenario and needs to be specifically specified.

[0040] Example 1

[0041] In this embodiment, key process parameters such as alloy raw material ratio, melting temperature, cooling rate, holding time, tempering temperature, holding time, dynamic recovery factor threshold, and air flow rate are all set at their lower limits.

[0042] Please see Figure 1 This invention provides a technical solution: an ultra-high strength low-density steel, wherein the materials for preparing the ultra-high strength low-density steel include:

[0043] It contains 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron by weight.

[0044] Aluminum is industrial pure aluminum powder with an average particle size of 50 to 100 micrometers.

[0045] The mass ratio of manganese to copper is 10:1 to 15:1.

[0046] The carbon is derived from graphene nanosheets, which have an average thickness of 1 to 5 nanometers.

[0047] Please see Figure 1 and Figure 2 A method for preparing ultra-high strength low-density steel, wherein the method is performed based on the aforementioned ultra-high strength low-density steel, and includes the following steps:

[0048] S1: An alloy raw material containing 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron is loaded into a vacuum induction melting furnace and heated to 1600°C to 1650°C to obtain a molten metal. The molten metal is then cooled by a programmed cooling system at a cooling rate of 5K / min to 15K / min to obtain a solid austenitic steel billet.

[0049] The specific steps of S1 are as follows:

[0050] S11: Using 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron as alloying raw materials, the mixture is placed into a vacuum induction melting furnace under an argon protective atmosphere. The vacuum system is then activated to extract the pressure inside the vacuum induction melting furnace to... Pa to Pa, to obtain pretreated raw materials;

[0051] S12: Start the induction heating system of the vacuum induction melting furnace, heat the pre-treated raw material to 1600℃ to 1650℃ at a heating rate of 20℃ / min to 30℃ / min, and hold at this temperature for 20 minutes to 40 minutes to completely melt and uniformly mix the pre-treated raw material to obtain the metal melt.

[0052] S13: Activate the program to control the cooling system. By adjusting the flow rate of the cooling medium, the cooling rate of the molten metal is controlled to be 5K / min to 15K / min. When the temperature of the molten metal drops below the solidus temperature of 1000℃ to 1100℃, a solid austenitic steel billet is obtained.

[0053] In S1, an alloy raw material containing 5% aluminum, 15% manganese, 1% copper, 0.1% carbon, and the balance 78.9% iron by mass is loaded into a vacuum induction melting furnace and heated to 1600°C to obtain a molten metal. The molten metal is then cooled by a program-controlled cooling system at a cooling rate of 5K / min to obtain a solid austenitic steel billet.

[0054] Weigh out 78.9 kg of DT4C electrical pure iron, 5.0 kg of 99.99% pure aluminum ingot, 15.0 kg of 99.9% electrolytic manganese flakes, 1.0 kg of 99.95% cathode copper, and 0.1 kg of high-purity graphite. Add these raw materials to the crucible of a ZG-500 vacuum induction melting furnace. After sealing the furnace, first start the mechanical pump and Roots pump unit to pump the furnace pressure to 1.0 Pa within 15 minutes. Then, start the three-stage diffusion pump unit while simultaneously baking and degassing the furnace body at 200°C. After 60 minutes, the vacuum level inside the furnace stabilizes at [value missing]. Pa. Then, argon gas with a purity of 99.999% is introduced into the furnace to 80 kPa and maintained for 10 minutes, after which the gas is evacuated. This charging / evacuation process is repeated three times to complete the purging of the furnace atmosphere. The final evacuation restores the furnace pressure to [normal value]. Pa, to obtain pretreated raw materials.

[0055] The 500kW medium-frequency induction heating system of the vacuum induction melting furnace was started, and the heating program was set. The PID controller adjusted the power output based on feedback from the type B thermocouple inside the furnace, allowing the furnace charge to begin heating at a rate of 20℃ / min. After approximately 79 minutes ((1600-25) / 20≈78.8), the furnace charge temperature reached 1600℃. The control system switched to the holding mode, precisely holding at this 1600℃ temperature for 20 minutes. At the 10th minute of holding, a sample was extracted from the melt using a quartz tube sampler inserted 200mm into the melt. After quenching, the sample was sent to an ARLiSpark8860 spark direct-reading spectrometer (OES) for compositional analysis, confirming that the contents of Al, Mn, Cu, and C were all within the target value ±0.05%, and that the elements were uniformly distributed.

[0056] After 20 minutes of heat preservation, the programmed cooling system is activated. This system controls the cooling rate of the molten metal by precisely adjusting the flow rate of cooling water in the furnace jacket and the thermal conductivity of the water-cooled copper base at the bottom of the furnace. The cooling program is set with a target cooling rate of 5 K / min. Type B thermocouples in the system monitor the core temperature of the melt in real time and feed it back to the PLC. The PLC adjusts the flow rate of the cooling medium through a proportional valve. The temperature begins to decrease from 1600℃. When the temperature drops to 1000℃ (the lower limit of the solidus temperature), the programmed cooling is stopped. The total cooling time is then (1600-1000) / 5 = 120 minutes. The furnace bottom mold is opened, and the solid steel billet is demolded, yielding a uniformly structured solid austenitic steel billet.

[0057] To determine the cooling rate of 5 K / min, the following verification experiment was conducted to investigate the effect of different cooling rates on the grain size of austenitic steel billets:

[0058] Table 1. Effect of Cooling Rate on Average Grain Size of Solid Austenitic Steel Billet

[0059]

[0060] As shown in Table 1, a minimum average grain size of 155 μm was obtained when the cooling rate was 5 K / min.

[0061] Please see Figure 1 and Figure 3S2: The solid austenitic steel billet is immersed in liquid nitrogen at a temperature of -196℃ for deep cryogenic treatment. When the overall temperature of the solid austenitic steel billet is the same as that of the liquid nitrogen, unidirectional compression is applied to the solid austenitic steel billet through a mechanical pressurization device until the solid austenitic steel billet produces 6% macroscopic plastic deformation to obtain composite billet.

[0062] The specific steps of S2 are as follows:

[0063] S21: The solid austenitic steel billet is completely immersed in a cryogenic treatment tank containing liquid nitrogen at -196℃. The core temperature of the solid austenitic steel billet is monitored in real time by multiple thermocouples set inside the solid austenitic steel billet. When the temperature difference between the core temperature and the liquid nitrogen is less than 1℃, the cryogenic treatment of the solid austenitic steel billet is confirmed to be completed, and the cryogenic billet is obtained.

[0064] S22: Immediately start the mechanical pressurization device to apply unidirectional compressive stress to the cryogenic billet, and at the same time monitor the macroscopic plastic deformation of the cryogenic billet through a strain sensor. When the macroscopic plastic deformation reaches 6%, immediately remove the unidirectional compressive stress to obtain a composite billet.

[0065] In S2, a solid austenitic steel billet is immersed in liquid nitrogen at a temperature of -196℃ for deep cryogenic treatment. When the overall temperature of the solid austenitic steel billet is the same as that of the liquid nitrogen, a mechanical pressure device is used to apply unidirectional compression to the solid austenitic steel billet until the solid austenitic steel billet produces a macroscopic plastic deformation of 6%, thus obtaining a composite billet.

[0066] The solid austenitic steel billet obtained in S1 (air-cooled to room temperature of 25°C) was pre-drilled with holes at its center, 10mm below the surface, and 40mm below the surface, and T-type thermocouples (copper-constantan) were inserted into the holes. Then, using a specialized lifting device, the billet was slowly immersed in a YDS-100 liquid nitrogen tank, ensuring it was completely covered by liquid nitrogen at -196°C. A multi-channel temperature recorder (Agilent 34970A) was activated to monitor the readings of the three T-type thermocouples in real time. When the temperature reading of the thermocouple at the core location showed -195.2°C, the difference between it and the liquid nitrogen temperature of -196°C was 0.8°C, less than 1°C. At this point, the cryogenic treatment of the solid austenitic steel billet was confirmed to be complete, yielding a cryogenic billet. This process takes approximately 180 minutes, depending on the billet size.

[0067] Immediately remove the cryogenic billet from the liquid nitrogen tank and rapidly transfer it to the lower pressure head of a YA-32-500 four-column hydraulic press within one minute. This press is equipped with a die made of insulating material (e.g., PTFE) to slow the billet's rewarming. Activate the mechanical pressurization device to apply uniaxial compressive stress to the cryogenic billet. Simultaneously, monitor the billet's height change using two high-precision LVDT displacement sensors (MTSTemposonics R series) fixed to the side of the billet, and calculate the macroscopic plastic deformation. The initial reading of the strain sensors is... (e.g., 100.00 mm). When the strain sensor's real-time reading... satisfy Time (i.e.) The control system immediately triggers the pressure relief valve to release the unidirectional compressive stress. Compression is then completed, yielding the composite billet.

[0068] To determine the 6% macroscopic plastic deformation amount, the following verification experiment was conducted to investigate the effect of different deformation amounts on the mechanical properties of the material in the subsequent tempered state (after S3 treatment):

[0069] Table 2. Influence of Cryogenic Deformation on the Properties of Composite Billets After Tempering

[0070]

[0071] As shown in Table 2, when the deformation is 6%, the material maintains a good elongation of 14.2%, while the yield strength and tensile strength (1410MPa, 1650MPa) are significantly improved.

[0072] Please see Figure 1 and Figure 4 S3: Transfer the composite billet to a heating and tempering furnace, set the temperature of the heating and tempering furnace to 400℃, and hold the composite billet at 400℃ for 30 to 60 minutes to prepare the recovery billet;

[0073] The specific steps for S3 are as follows:

[0074] S31: Quickly transfer the composite billet to the heating and tempering furnace, set the furnace temperature to 400℃, and adjust the heating power through the PID controller to ensure that the heating rate of the composite billet is not less than 50℃ / min.

[0075] S32: When the overall temperature of the composite billet reaches 400℃, start timing and hold for 30 to 60 minutes. During the holding period, calculate the dynamic recovery factor based on the composition of the composite billet. , ;

[0076] in, Represents material constants. This represents the activation energy of the response. Represents the ideal gas constant. Represents the tempering temperature. Indicates the heat preservation time. Represents a time index;

[0077] S33: By monitoring dynamic response factors in real time The value, when When the preset recovery threshold of 0.6 to 0.8 is reached, heating is immediately stopped to obtain the recovered billet.

[0078] In S3, the composite billet is transferred to a heating and tempering furnace, the temperature of which is set to 400℃. The composite billet is held at 400℃ to prepare a recovery billet.

[0079] The composite billet obtained in S2 (at approximately -180℃) is quickly transferred to an SX2-10-12 box-type resistance furnace preheated to 400℃. The furnace door is closed, and the heating program is started. The heating power is controlled by precisely adjusting the conduction angle of the thyristor using an Omron E5CC PID controller. A K-type thermocouple embedded inside the billet provides real-time temperature feedback, and the PID controller ensures that the heating rate of the composite billet is not less than 50℃ / min.

[0080] The PLC control system starts timing when the core temperature of the composite billet reaches 400℃. During this process, the control system is based on a dynamic recovery factor. computational model Real-time computing Values. The explanations and values ​​of each parameter in the formula are as follows: It is a dynamic response factor that characterizes the extent of the response process. The material constant is determined by fitting the differential scanning calorimetry (DSC) and isothermal annealing experimental data of this alloy (Fe-15Mn-5Al-1Cu-0.1C), and its value is [value missing]. s -1 . To determine the activation energy, which characterizes the energy required for dislocation motion and rearrangement, the value was calculated using the Arrhenius plot method based on the experimental data described above. J / mol. Let be the ideal gas constant, and take the value of . J / (mol·K). The tempering temperature is expressed in Kelvin (K). In this embodiment, . The heat preservation time is measured in seconds (s) and is accumulated in real time by the PLC. The time exponent is obtained by fitting experimental data, and its value is... .

[0081] Real-time monitoring of dynamic response factors The value. The preset response threshold uses its lower limit of 0.6. The control system PLC in Starting from that time, continuously input the real-time heat preservation time. Perform the calculation: when When the calculated value reaches 0.5998 (approximately equal to 0.6), the PLC immediately issues a command to stop heating the tempering furnace. At this point, the total holding time is 30 minutes. The recovered billet is then obtained.

[0082] To determine With a threshold of 0.6, the following verification experiment was conducted to examine different... The impact of threshold values ​​(corresponding to different heat preservation times) on the final product performance:

[0083] Table 3 Dynamic Response Factors Table of the impact of threshold on product performance

[0084]

[0085] As shown in Table 3 When the threshold is 0.6 (corresponding to 30 minutes of heat preservation), the expected balance point between strength and plasticity is achieved.

[0086] Please see Figure 1 and Figure 5 S4: Remove the restored billet from the heating and tempering furnace, and use a blower to perform forced air cooling treatment on the restored billet at an air flow rate of 1m / s to 3m / s until the temperature of the restored billet drops below 50℃.

[0087] The specific steps for S4 are as follows:

[0088] S41: Remove the restored billet from the heating and tempering furnace and immediately place it in the forced cooling chamber. Start the blower array to blow cooling air with an air flow rate of 1 m / s to 3 m / s onto the entire surface of the restored billet.

[0089] S42: The surface temperature of the recovery billet is monitored non-contactly through an infrared temperature sensor array, ensuring a uniform cooling process for the recovery billet;

[0090] S43: When the average surface temperature of the recovered billet monitored by the infrared temperature sensor array drops below 50°C, the blower stops running, and the forced air cooling process is completed to obtain the ultra-high strength low density steel finished product.

[0091] In step S4, the restored billet is removed from the heating and tempering furnace and subjected to forced air cooling treatment by a blower at an air flow rate of 1 m / s until the temperature of the restored billet drops below 50°C.

[0092] The recovered billet (400℃) obtained in S3 is removed from the heating and tempering furnace and immediately placed in the QL-20 type forced cooling chamber via roller conveyor. The blower array (a total of 10 DF-5 type axial flow fans) is started. The fan speed is adjusted by frequency converter, and multiple measurements are taken at a distance of 100mm from the billet surface using a Testo410i impeller anemometer to confirm that the average flow velocity of the cooling air on the entire surface of the billet is 1m / s.

[0093] The cooling chamber is equipped with a Raytek MI3 series infrared temperature sensor array to perform non-contact scanning and monitoring of the surface temperature of the billet. The data from the sensor array is collected by the PLC to calculate the highest, lowest, and average temperatures of the billet surface. By adjusting the fan speeds at different locations, the temperature difference on the billet surface is maintained within 10°C.

[0094] When the average surface temperature of the recovered billet, monitored by the infrared temperature sensor array, drops to 50°C, the PLC stops the operation of the blower array. Forced air cooling is then completed, yielding the ultra-high strength, low-density steel finished product.

[0095] Table 4 Comparison of Product Performance in Example 1

[0096]

[0097] Example 2

[0098] Please see Figure 1 This invention provides a technical solution: an ultra-high strength low-density steel, wherein the materials for preparing the ultra-high strength low-density steel include:

[0099] It contains 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron by weight.

[0100] Aluminum is industrial pure aluminum powder with an average particle size of 50 to 100 micrometers.

[0101] The mass ratio of manganese to copper is 10:1 to 15:1.

[0102] The carbon is derived from graphene nanosheets, which have an average thickness of 1 to 5 nanometers.

[0103] Please see Figure 1 and Figure 2 A method for preparing ultra-high strength low-density steel, wherein the method is performed based on the aforementioned ultra-high strength low-density steel, and includes the following steps:

[0104] S1: An alloy raw material containing 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron is loaded into a vacuum induction melting furnace and heated to 1600°C to 1650°C to obtain a molten metal. The molten metal is then cooled by a programmed cooling system at a cooling rate of 5K / min to 15K / min to obtain a solid austenitic steel billet.

[0105] The specific steps of S1 are as follows:

[0106] S11: Using 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron as alloying raw materials, the mixture is placed into a vacuum induction melting furnace under an argon protective atmosphere. The vacuum system is then activated to extract the pressure inside the vacuum induction melting furnace to... Pa to Pa, to obtain pretreated raw materials;

[0107] S12: Start the induction heating system of the vacuum induction melting furnace, heat the pre-treated raw material to 1600℃ to 1650℃ at a heating rate of 20℃ / min to 30℃ / min, and hold at this temperature for 20 minutes to 40 minutes to completely melt and uniformly mix the pre-treated raw material to obtain the metal melt.

[0108] S13: Activate the program to control the cooling system. By adjusting the flow rate of the cooling medium, the cooling rate of the molten metal is controlled to be 5K / min to 15K / min. When the temperature of the molten metal drops below the solidus temperature of 1000℃ to 1100℃, a solid austenitic steel billet is obtained.

[0109] In this embodiment, key process parameters such as alloy raw material ratio, melting temperature, cooling rate, holding time, tempering temperature, holding time, dynamic recovery factor threshold, and air flow rate all adopt their upper limits.

[0110] S1: The alloy raw material containing 9% aluminum, 25% manganese, 3% copper, 0.5% carbon and the balance 62.5% iron by mass is loaded into a vacuum induction melting furnace and heated to 1650℃ to obtain a molten metal. The molten metal is then cooled by a program-controlled cooling system at a cooling rate of 15K / min to obtain a solid austenitic steel billet.

[0111] Weigh out 62.5 kg of DT4C electrical pure iron, 9.0 kg of 99.99% pure aluminum ingot, 25.0 kg of 99.9% electrolytic manganese flakes, 3.0 kg of 99.95% cathode copper, and 0.5 kg of high-purity graphite. Add these raw materials to the crucible of a ZG-500 vacuum induction melting furnace. After sealing the furnace, start the mechanical pump and Roots pump unit to pump the furnace pressure to 1.0 Pa within 10 minutes. Then, start the three-stage diffusion pump unit while simultaneously baking and degassing the furnace at 250°C. After 90 minutes, the vacuum level inside the furnace stabilizes at [value missing]. Pa. Then, argon gas with a purity of 99.999% is introduced into the furnace to 80 kPa and maintained for 10 minutes, after which the gas is evacuated. This charging / evacuation process is repeated three times. The final evacuation restores the furnace pressure to [normal value]. Pa, to obtain pretreated raw materials.

[0112] The 500kW medium-frequency induction heating system of the vacuum induction melting furnace was started, and the heating program was set. The PID controller adjusted the power output based on feedback from the type B thermocouple inside the furnace, allowing the furnace charge to begin heating at a rate of 30℃ / min. After approximately 54 minutes ((1650-25) / 30≈54.2), the furnace charge temperature reached 1650℃. The control system switched to the holding mode, precisely holding at this 1650℃ temperature for 40 minutes. At the 10th and 30th minutes of holding, samples were extracted from the melt at a depth of 200mm using a quartz tube sampler. After quenching, the samples were sent to an ARLiSpark8860 spark direct-reading spectrometer (OES) for compositional analysis. It was confirmed that the contents of Al, Mn, Cu, and C were all within the target value ±0.05%, and the compositions of the two samples were consistent.

[0113] After 40 minutes of heat preservation, the programmed cooling system is activated. This system controls the cooling rate of the molten metal by precisely adjusting the flow rate of cooling water in the furnace jacket and the thermal conductivity of the water-cooled copper base at the bottom of the furnace. The cooling program is set with a target cooling rate of 15 K / min. Type B thermocouples in the system monitor the core temperature of the melt in real time and feed it back to the PLC. The PLC adjusts the flow rate of the cooling medium through a proportional valve. The temperature begins to decrease from 1650℃. When the temperature drops to 1100℃ (the upper limit of the solidus temperature), the programmed cooling is stopped. The total cooling time is (1650-1100) / 15 = 36.7 minutes. The furnace bottom mold is opened, and the solid steel billet is demolded, yielding a solid austenitic steel billet with a uniform microstructure.

[0114] To determine the optimal cooling rate of 15 K / min, the following verification experiment was conducted to investigate the effect of different cooling rates on the grain size of austenitic steel billets (see Table 1 for data). Using a rate of 15 K / min, the average grain size obtained was 210 μm.

[0115] Please see Figure 1 and Figure 3 S2: The solid austenitic steel billet is immersed in liquid nitrogen at a temperature of -196℃ for deep cryogenic treatment. When the overall temperature of the solid austenitic steel billet is the same as that of the liquid nitrogen, unidirectional compression is applied to the solid austenitic steel billet through a mechanical pressurization device until the solid austenitic steel billet produces 6% macroscopic plastic deformation to obtain composite billet.

[0116] The specific steps of S2 are as follows:

[0117] S21: The solid austenitic steel billet is completely immersed in a cryogenic treatment tank containing liquid nitrogen at -196℃. The core temperature of the solid austenitic steel billet is monitored in real time by multiple thermocouples set inside the solid austenitic steel billet. When the temperature difference between the core temperature and the liquid nitrogen is less than 1℃, the cryogenic treatment of the solid austenitic steel billet is confirmed to be completed, and the cryogenic billet is obtained.

[0118] S22: Immediately start the mechanical pressurization device to apply unidirectional compressive stress to the cryogenic billet, and at the same time monitor the macroscopic plastic deformation of the cryogenic billet through a strain sensor. When the macroscopic plastic deformation reaches 6%, immediately remove the unidirectional compressive stress to obtain a composite billet.

[0119] In S2, a solid austenitic steel billet is immersed in liquid nitrogen at a temperature of -196℃ for deep cryogenic treatment. When the overall temperature of the solid austenitic steel billet is the same as that of the liquid nitrogen, a mechanical pressure device is used to apply unidirectional compression to the solid austenitic steel billet until the solid austenitic steel billet produces a macroscopic plastic deformation of 6%, thus obtaining a composite billet.

[0120] The solid austenitic steel billet obtained in S1 (air-cooled to room temperature of 25°C) was pre-drilled with holes at its center, 10mm below the surface, and 40mm below the surface, and T-type thermocouples (copper-constantan) were inserted into the holes. Then, using a specialized lifting device, the billet was slowly immersed in a YDS-100 liquid nitrogen tank, ensuring it was completely covered by liquid nitrogen at -196°C. A multi-channel temperature recorder (Agilent 34970A) was activated to monitor the readings of the three T-type thermocouples in real time. When the temperature reading of the thermocouple at the core location showed -195.1°C, the difference between it and the liquid nitrogen temperature of -196°C was 0.9°C, less than 1°C. At this point, the cryogenic treatment of the solid austenitic steel billet was confirmed to be complete, yielding a cryogenic billet. This process takes approximately 185 minutes, depending on the billet size.

[0121] Immediately remove the cryogenic billet from the liquid nitrogen tank and rapidly transfer it to the lower pressure head of a YA-32-500 four-column hydraulic press within one minute. This press is equipped with a PTFE-insulated die. Activate the mechanical pressurization device to apply unidirectional compressive stress to the cryogenic billet. Simultaneously, monitor the height change of the billet using two high-precision LVDT displacement sensors (MTSTemposonics R series) fixed to the side of the billet, and calculate the macroscopic plastic deformation. The initial reading of the strain sensor is... (e.g., 100.00 mm). When the strain sensor's real-time reading... satisfy Time (i.e.) The control system immediately triggers the pressure relief valve to release the unidirectional compressive stress. Compression is then completed, yielding the composite billet.

[0122] To determine the 6% macroscopic plastic deformation amount, verification experiments were conducted as shown in Table 2. A 6% deformation amount was used to balance strength and plasticity.

[0123] Please see Figure 1 and Figure 4 S3: Transfer the composite billet to a heating and tempering furnace, set the temperature of the heating and tempering furnace to 400℃, and hold the composite billet at 400℃ for 30 to 60 minutes to prepare the recovery billet;

[0124] The specific steps for S3 are as follows:

[0125] S31: Quickly transfer the composite billet to the heating and tempering furnace, set the furnace temperature to 400℃, and adjust the heating power through the PID controller to ensure that the heating rate of the composite billet is not less than 50℃ / min.

[0126] S32: When the overall temperature of the composite billet reaches 400℃, start timing and hold for 30 to 60 minutes. During the holding period, calculate the dynamic recovery factor based on the composition of the composite billet. , ;

[0127] in, Represents material constants. This represents the activation energy of the response. Represents the ideal gas constant. Represents the tempering temperature. Indicates the heat preservation time. Represents a time index;

[0128] S33: By monitoring dynamic response factors in real time The value, when When the preset recovery threshold of 0.6 to 0.8 is reached, heating is immediately stopped to obtain the recovered billet.

[0129] In S3, the composite billet is transferred to a heating and tempering furnace, the temperature of which is set to 400℃. The composite billet is held at 400℃ to prepare a recovery billet.

[0130] The composite billet obtained in S2 (at approximately -180°C) is quickly transferred to an SX2-10-12 box-type resistance furnace preheated to 400°C. The furnace door is closed, and the heating program is started. The heating power is controlled by precisely adjusting the conduction angle of the thyristor using an Omron E5CC PID controller. A K-type thermocouple embedded inside the billet provides real-time temperature feedback, and the PID controller ensures that the heating rate of the composite billet is not less than 50°C / min (controlled at 55°C / min in this embodiment).

[0131] The PLC control system starts timing when the core temperature of the composite billet reaches 400℃. During this process, the control system is based on a dynamic recovery factor. computational model Real-time computing Values. The explanations and values ​​of each parameter in the formula are as follows: It is a dynamic response factor. The material constant is determined by fitting the DSC and isothermal annealing experimental data of this alloy (Fe-25Mn-9Al-3Cu-0.5C), and its value is [value missing]. s -1 . To restore the activation energy, it was calculated using the Arrhenius plot method based on the above experimental data, and its value is... J / mol. Let be the ideal gas constant, and take the value of . J / (mol·K). The tempering temperature is expressed in Kelvin (K). In this embodiment, . The heat preservation time is measured in seconds (s) and is accumulated in real time by the PLC. The time exponent is obtained by fitting experimental data, and its value is... (Note: Due to the alloy composition reaching its upper limit, the values ​​of A and Qs have changed compared to Example 1.)

[0132] Real-time monitoring of dynamic response factors The value. The preset response threshold uses its upper limit of 0.8. The control system PLC in Starting from that time, continuously input the real-time heat preservation time. Perform the calculation:

[0133] when The calculated value needs to reach 0.8: when (i.e., 234.1 minutes) The calculated value reaches 0.8. (The calculated result of 234.1 minutes here exceeds the range of [30, 60] minutes in S3. In actual implementation, the process constraint is based on 60 minutes in S3.) The control system starts timing, and when the holding time... When the maximum time (60 minutes, 3600 seconds) is reached, the PLC immediately issues a command to stop heating the tempering furnace. At this time, the calculation... value: The recovered billet was obtained. (Note: This result indicates that for Example 2 with high alloy content, holding at 400°C for 60 minutes results in a high degree of recovery.) The value only reached 0.405, which did not meet the threshold of 0.8. (Process execution is based on the maximum time limit.)

[0134] Please see Figure 1 and Figure 5 S4: Remove the restored billet from the heating and tempering furnace, and use a blower to perform forced air cooling treatment on the restored billet at an air flow rate of 1m / s to 3m / s until the temperature of the restored billet drops below 50℃.

[0135] The specific steps for S4 are as follows:

[0136] S41: Remove the restored billet from the heating and tempering furnace and immediately place it in the forced cooling chamber. Start the blower array to blow cooling air with an air flow rate of 1 m / s to 3 m / s onto the entire surface of the restored billet.

[0137] S42: The surface temperature of the recovery billet is monitored non-contactly through an infrared temperature sensor array, ensuring a uniform cooling process for the recovery billet;

[0138] S43: When the average surface temperature of the recovered billet monitored by the infrared temperature sensor array drops below 50°C, the blower stops running, and the forced air cooling process is completed to obtain the ultra-high strength low density steel finished product.

[0139] In step S4, the restored billet is removed from the heating and tempering furnace and subjected to forced air cooling treatment by a blower at an air flow rate of 3 m / s until the temperature of the restored billet drops below 50°C.

[0140] The recovered billet (400℃) obtained in S3 is removed from the heating and tempering furnace and immediately placed in the QL-20 type forced cooling chamber via roller conveyor. The blower array (a total of 10 DF-5 type axial flow fans) is started. The fan speed is adjusted to maximum power using a frequency converter. Using a Testo410i impeller anemometer, multiple measurements are taken at a distance of 100mm from the billet surface to confirm that the average flow velocity of the cooling air across the entire surface of the billet is 3m / s.

[0141] The cooling chamber is equipped with a Raytek MI3 series infrared temperature sensor array to perform non-contact scanning and monitoring of the surface temperature of the billet. The data from the sensor array is collected by the PLC to calculate the highest, lowest, and average temperatures of the billet surface. By adjusting the fan speeds at different locations, the temperature difference on the billet surface is maintained within 10°C.

[0142] When the average surface temperature of the recovered billet, monitored by the infrared temperature sensor array, drops to 50°C (this process takes approximately 35 minutes), the PLC stops the operation of the blower array. Forced air cooling is then complete, yielding the ultra-high strength, low-density steel finished product.

[0143] Table 5 Comparison of Product Performance in Example 2

[0144]

[0145] The above embodiments illustrate preferred embodiments of the present invention. Any equivalent adjustments to the technical solution based on software engineering methods are within the scope of protection, including but not limited to: implementing algorithm logic using different programming languages, refactoring functional modules into services, adjusting data interaction protocols, and optimizing resource scheduling strategies. Any implementation scheme derived from reasonable modifications to the data processing flow, service call chain, or system architecture layer without departing from the core technology of the present invention should be considered within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing ultra-high strength low-density steel, characterized in that, The materials used to prepare the ultra-high strength low density steel include: The composition comprises 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron by weight. The method for preparing ultra-high strength low-density steel includes the following steps: S1: An alloy raw material containing 5% to 9% aluminum, 15% to 25% manganese, 1% to 3% copper, 0.1% to 0.5% carbon, and the balance iron by mass percentage is loaded into a vacuum induction melting furnace and heated to 1600°C to 1650°C to obtain a molten metal. The molten metal is then cooled by a program-controlled cooling system at a cooling rate of 5K / min to 15K / min to obtain a solid austenitic steel billet. S2: The solid austenitic steel billet is immersed in liquid nitrogen at a temperature of -196℃ for deep cryogenic treatment. When the overall temperature of the solid austenitic steel billet is the same as the temperature of the liquid nitrogen, unidirectional compression is applied to the solid austenitic steel billet by a mechanical pressurizing device until the solid austenitic steel billet produces 6% macroscopic plastic deformation to obtain a composite billet. S3: Transfer the composite billet to a heating and tempering furnace, set the temperature of the heating and tempering furnace to 400°C, and hold the composite billet at the temperature of 400°C for 30 to 60 minutes to prepare a recovery billet; S4: The recovered billet is taken out from the heating and tempering furnace, and forced air cooling is performed on the recovered billet by a blower at an air flow rate of 1m / s to 3m / s until the temperature of the recovered billet drops below 50°C.

2. The method for preparing ultra-high strength low-density steel according to claim 1, characterized in that, The aluminum is industrial pure aluminum powder with an average particle size of 50 to 100 micrometers.

3. The method for preparing ultra-high strength low-density steel according to claim 1, characterized in that, The mass ratio of manganese to copper is 10:1 to 15:

1.

4. The method for preparing ultra-high strength low-density steel according to claim 1, characterized in that, The carbon is derived from graphene nanosheets, which have an average thickness of 1 nanometer to 5 nanometers.

5. The method for preparing ultra-high strength low-density steel according to claim 1, characterized in that, The specific steps of S1 are as follows: S11: Using 5% to 9% by mass of the aluminum, 15% to 25% of the manganese, 1% to 3% of the copper, 0.1% to 0.5% of the carbon, and the balance of the iron as the alloy raw materials, the alloy is introduced into the vacuum induction melting furnace under an argon protective atmosphere. The vacuum system is then activated to extract the pressure inside the vacuum induction melting furnace to... Pa to Pa, to obtain pretreated raw materials; S12: Start the induction heating system of the vacuum induction melting furnace, heat the pre-treated raw material to 1600°C to 1650°C at a heating rate of 20°C / min to 30°C / min, and hold it at this temperature for 20 minutes to 40 minutes to completely melt and uniformly mix the pre-treated raw material to obtain the metal melt. S13: Activate the program-controlled cooling system, and control the cooling rate of the molten metal to 5K / min to 15K / min by adjusting the flow rate of the cooling medium. When the temperature of the molten metal drops below the solidus temperature of 1000℃ to 1100℃, the solid austenitic steel billet is obtained.

6. The method for preparing ultra-high strength low-density steel according to claim 5, characterized in that, The specific steps of S2 are as follows: S21: The solid austenitic steel billet is completely immersed in a cryogenic treatment tank containing liquid nitrogen at -196°C. The core temperature of the solid austenitic steel billet is monitored in real time by multiple thermocouples set inside the solid austenitic steel billet. When the temperature difference between the core temperature and the liquid nitrogen is less than 1°C, the cryogenic treatment of the solid austenitic steel billet is confirmed to be completed, and a cryogenic billet is obtained. S22: Immediately start the mechanical pressurization device to apply unidirectional compressive stress to the cryogenic billet, and at the same time monitor the macroscopic plastic deformation of the cryogenic billet through a strain sensor. When the macroscopic plastic deformation reaches 6%, immediately remove the unidirectional compressive stress to obtain the composite billet.

7. The method for preparing ultra-high strength low-density steel according to claim 6, characterized in that, The specific steps of S3 are as follows: S31: Quickly transfer the composite billet to the heating and tempering furnace, set the furnace temperature of the heating and tempering furnace to 400℃, and adjust the heating power through the PID controller so that the heating rate of the composite billet is not less than 50℃ / min; S32: When the overall temperature of the composite billet reaches 400℃, start timing and hold for 30 to 60 minutes. During the holding period, calculate the dynamic recovery factor based on the composition of the composite billet. , ; in, Represents material constants. This represents the activation energy of the response. Represents the ideal gas constant. Represents the tempering temperature. Indicates the heat preservation time. Represents a time index; S33: By monitoring the dynamic response factor in real time The value, when the When the preset recovery threshold of 0.6 to 0.8 is reached, heating is immediately stopped to obtain the recovered billet.

8. The method for preparing ultra-high strength low-density steel according to claim 7, characterized in that, The specific steps of S4 are as follows: S41: Take the recovered billet out of the heating and tempering furnace and immediately place it in the forced cooling chamber. Start the blower array to blow cooling air with an air flow rate of 1 m / s to 3 m / s onto the entire surface of the recovered billet. S42: The surface temperature of the recovery billet is monitored non-contactly by an infrared temperature sensor array, so that the cooling process of the recovery billet is uniform; S43: When the average surface temperature of the recovered billet monitored by the infrared temperature sensor array drops below 50°C, the operation of the blower is stopped to complete the forced air cooling treatment and obtain the ultra-high strength low density steel finished product.

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