A method for preparing low-density high-strength steel

Abstract

The present invention discloses a method for preparing low-density high-strength steel, and belongs to the technical field of metal materials. The present invention cross-stacks multiple pieces of pure aluminum or aluminum alloy foil (plate) and low-carbon steel foil (plate), welds the edges of the samples to form a blank, and then puts the blank into a press to first cold press and hold the pressure, takes it out after a certain period of cold pressing, preheats the cold pressed material and puts it into a hot rolling mill for rolling, cuts the plate after one rolling pass and stacks it again to continue rolling, obtains a solid-solid bonded low-density high-strength steel material after several hot rolling passes, and then performs annealing heat treatment on it. The present invention adopts hot pressing multi-layer composite to prepare low-density high-strength steel, realizes alloying between different elements under the joint action of temperature and pressure, has high production efficiency, low cost, high product quality, high material utilization rate, and obtains high-performance low-density high-strength steel plate.

Description

Technical Field

[0001] The invention relates to a method for preparing low-density high-strength steel, and belongs to the technical field of metal materials. Background Art

[0002] With the continuous and rapid development of the automobile industry, the number of cars has increased significantly, and the number of cars in the world has exceeded 1 billion. Automobiles have become the main source of energy consumption and pollutant emissions in the world. All developed countries have formulated strict regulations to limit automobile fuel consumption and greenhouse gas emissions. Studies have shown that automobile lightweighting is one of the most effective measures to reduce energy consumption and emissions. For example, for every 100kg reduction in a car, 0.3-0.5L / (100km) of fuel can be saved, and CO2 emissions can be reduced by 8-11g / (100km). Therefore, since the 1990s, many large-scale research programs have actively promoted the research of automobile lightweighting technology as a key technology to cope with the shortage of oil resources and environmental pollution. As the key to the lightweighting process of automobiles, low-density high-strength steel is a lightweight material with the characteristics of high strength, high plasticity, and low density. The application of low-density high-strength steel in the automobile industry can improve the strength of the body structure and improve safety on the basis of energy saving, emission reduction and environmental protection. At present, low-density high-strength steel has attracted the attention of the automobile industry, and my country has also achieved breakthroughs in the production of low-density steel. One way to achieve lightweight steel is to add lightweight alloying elements such as aluminum (Al). The density of iron (Fe) is 7.86 g / cm 3 The density of aluminum (Al) is 2.7 g / cm 3 There are two reasons why adding Al to steel can reduce density. One is that the metallurgical bonding between steel and aluminum changes the lattice parameters of the steel, which causes an increase in volume to reduce density. The other is that the atomic mass of aluminum itself is relatively low.

[0003] However, in the current production method, aluminum in steel is mostly added by smelting. In this production method, the melting temperature of steel is quite different from that of aluminum. When the temperature is high, the burning rate of aluminum will increase greatly, which is not conducive to reducing the consumption in the production process. Excessive smelting will also increase the ratio of molten oxides, nitrides, and carbides, leading to the generation of non-metallic inclusions. A large amount of aluminum will cause serious segregation when the molten steel solidifies, thereby reducing the performance of the product. Summary of the invention

[0004] The purpose of the present invention is to provide a novel method for preparing low-density high-strength steel in view of the problems of low material utilization, high production energy consumption, poor mechanical properties, and long production cycle in the existing low-density high-strength steel preparation method. The method uses the principle of high-pressure and high-temperature atomic diffusion chemical reaction to cross-stack and roll pure aluminum or aluminum alloy foil (plate) with low-carbon steel foil (plate) to prepare low-density high-strength steel with high material utilization, high production efficiency, and excellent mechanical properties. The method specifically comprises the following steps:

[0005] (1) First, the aluminum alloy plate and the steel plate are surface treated to remove surface pollutants such as surface oxide film and grease;

[0006] (2) Cross-stack the treated metal plates into a pressure mold and hold the pressure for a certain period of time before taking them out;

[0007] (3) preheating the plate in a furnace and then hot rolling it;

[0008] (4) cutting, stacking, heating and hot rolling the hot-rolled plates again;

[0009] (5) vacuum annealing heat treatment of the high-strength and low-density plate after hot rolling;

[0010] (6) The low-density high-strength steel plates after heat treatment are trimmed and surface treated.

[0011] The invention is characterized in that the low-density high-strength steel plate is produced by cold pressing and hot rolling. Pure aluminum or aluminum alloy foil (plate) and low-carbon steel foil (plate) are cross-stacked, cold pressed and rolled to effectively combine the steel and aluminum alloy tightly together and achieve a large amount of metallurgical bonding at the interface. This production method is low-cost and high-efficiency, and can reduce the loss of raw materials while ensuring that the composite plate meets the performance requirements.

[0012] Beneficial effects of the present invention:

[0013] (1) The present invention adopts the cold pressing-rolling method to prepare low-density high-strength steel. Compared with traditional alloy smelting, it greatly reduces the energy consumption in the production process. It also effectively reduces the process loss of aluminum alloy raw materials by directly deforming and combining solid steel and aluminum raw materials, and avoids the generation of inclusions, thereby improving the physical properties of the product. On the other hand, due to the extrusion effect during the forming process, the structure is dense, without shrinkage defects, and has high mechanical properties. In addition, the material prepared by the invention increases the contact area between the aluminum alloy and the steel and refines the grains after lateral extension and longitudinal thinning. The material performance is further improved. Cold pressing the material in the initial stage can help squeeze out the gas between the plates and avoid a large amount of surface oxidation during the subsequent heating process. At the same time, the interface is fitted to allow the metal atoms to begin to diffuse and the material to undergo initial deformation. Controlling the preheating temperature of the plate and adjusting the appropriate reduction rate during the hot rolling stage can effectively avoid cracking during the deformation of the steel plate, which is a key factor in ensuring the performance of the material. At the same time, due to the thinning and extension of the plate during deformation, a large number of fresh metal interfaces are bonded, and the diffusion between steel and aluminum can be better carried out on such interfaces, ultimately achieving the excellent effect of a large number of metallurgical bonds between the plates. Multiple rolling passes allow complete alloying between steel and aluminum.

[0014] (2) Since the present invention adopts a solid-solid combination method for production, the content of aluminum in the material can be easily adjusted. By controlling the amount of aluminum added and the change in temperature, the content of different intermetallic compounds such as Fe3Al, FeAl3, FeAl, etc. can be adjusted as needed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a process flow chart of the present invention;

[0016] Figure 2 This is a SEM image of the interface joint during the initial rolling process of low-density high-strength steel;

[0017] Figure 3 It is a schematic diagram of the microstructural changes during the processing. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0019] Implementation Case 1

[0020] The surface treated Q345B steel plate and 6061 aluminum were cut to a thickness of 0.3 mm for the aluminum plate and 0.5 mm for the steel plate. The aluminum plate and the steel plate were stacked crosswise in sequence and placed in a cold pressing mold with 9 layers. The mold pre-pressing pressure was 15 tons, the holding time was 10 minutes, and then it was taken out for hot rolling, the preheating temperature was 400°C, and the reduction rate was 50%. The total number of rolling passes was 5. The annealing temperature was 400°C.

[0021] The test performance of the low-density high-strength steel plate prepared in this embodiment is as follows: the tensile strength is 482.6MPa, the yield strength is 395.1MPa, the elongation is 21.3%, and the material density is less than 7.0g / cm 3 Its performance indicators such as tensile strength and elongation meet the requirements for automobile frame steel, while achieving the goal of lightweighting.

[0022] Implementation Case 2

[0023] The surface treated Q345B steel plate and 6061 aluminum were cut to a thickness of 0.3 mm for the aluminum plate and 0.5 mm for the steel plate. The aluminum plate and the steel plate were stacked crosswise in sequence and placed in a cold pressing mold with 9 layers. The mold pre-pressing pressure was 15t, the holding time was 10min, and then it was taken out for hot rolling, the preheating temperature was 450℃, and the reduction rate was 50%. The total number of rolling passes was 5. The annealing temperature was 400℃.

[0024] The test performance of the low-density high-strength steel plate prepared in this embodiment is as follows: the tensile strength is 476.4MPa, the yield strength is 392.9MPa, the elongation is 20.7%, and the material density is less than 7.0g / cm 3 Its performance indicators such as tensile strength and elongation meet the requirements for automobile frame steel, while achieving the goal of lightweighting.

[0025] Implementation Case 3

[0026] The surface treated Q345B steel plate and 6061 aluminum were cut to a thickness of 0.3 mm for the aluminum plate and 0.5 mm for the steel plate. The aluminum plate and the steel plate were stacked crosswise in sequence and placed in a cold pressing mold with 9 layers. The mold pre-pressing pressure was 15t, the holding time was 10min, and then it was taken out for hot rolling, the preheating temperature was 500℃, and the reduction rate was 50%. The total rolling passes were 5 passes. The annealing temperature was 400℃.

[0027] The test performance of the low-density high-strength steel plate prepared in this embodiment is as follows: the tensile strength is 453.5MPa, the yield strength is 384.8MPa, the elongation is 22.5%, and the material density is less than 7.0g / cm 3Its performance indicators such as tensile strength and elongation meet the requirements for automobile frame steel, while achieving the goal of lightweighting.

[0028] Implementation Case 4

[0029] The surface treated Q345B steel plate and 6061 aluminum were cut to a thickness of 0.3 mm for the aluminum plate and 0.5 mm for the steel plate. The aluminum plate and the steel plate were stacked crosswise in sequence and placed in a cold pressing mold with 9 layers. The mold pre-pressing pressure was 15t, the holding time was 10min, and then it was taken out for hot rolling, the preheating temperature was 400℃, and the reduction rate was 50%. The total number of rolling passes was 3. The annealing temperature was 400℃.

[0030] The test performance of the low-density high-strength steel plate prepared in this embodiment is as follows: the tensile strength is 462.0MPa, the yield strength is 381.2MPa, the elongation is 24.1%, and the material density is less than 7.0g / cm 3 Its performance indicators such as tensile strength and elongation meet the requirements for automobile frame steel, while achieving the goal of lightweighting.

[0031] Implementation Case 5

[0032] The surface treated Q345B steel plate and 6061 aluminum were cut to a thickness of 0.3 mm for the aluminum plate and 0.5 mm for the steel plate. The aluminum plate and the steel plate were stacked crosswise in sequence and placed in a cold pressing mold with 9 layers. The mold pre-pressing pressure was 15 tons, the holding time was 10 minutes, and then it was taken out for hot rolling, the preheating temperature was 400°C, and the reduction rate was 50%. The total number of rolling passes was 3. The annealing temperature was 450°C.

[0033] The test performance of the low-density high-strength steel plate prepared in this embodiment is as follows: the tensile strength is 451.0MPa, the yield strength is 382.2MPa, the elongation is 20.6%, and the material density is less than 7.0g / cm 3 Its performance indicators such as tensile strength and elongation meet the requirements for automobile frame steel, while achieving the goal of lightweighting.

[0034] Implementation Case 6

[0035] The surface treated Q345B steel plate and 6061 aluminum were cut to a thickness of 0.3 mm for the aluminum plate and 0.5 mm for the steel plate. The aluminum plate and the steel plate were stacked crosswise in sequence and placed in a cold pressing mold with 9 layers. The mold pre-pressing pressure was 15t, the holding time was 10min, and then it was taken out for hot rolling, the preheating temperature was 400℃, and the reduction rate was 50%. The total rolling passes were 3 passes. The annealing temperature was 500℃.

[0036] The test performance of the low-density high-strength steel plate prepared in this embodiment is as follows: the tensile strength is 473.8MPa, the yield strength is 391.5MPa, the elongation is 21.2%, and the material density is less than 7.0g / cm 3 Its performance indicators such as tensile strength and elongation meet the requirements for automobile frame steel, while achieving the goal of lightweighting.

[0037] The present invention cross-stacks multiple pieces of pure aluminum or aluminum alloy foil (plate) and low-carbon steel foil (plate), then puts them into a press for cold pressing and pressure holding, takes them out after a certain period of cold pressing, preheats the cold pressed material and puts them into a hot rolling mill for rolling, cuts the plate after one rolling pass and stacks them again for further rolling, obtains a solid-solid bonded low-density high-strength steel material after several hot rolling passes, and then performs annealing heat treatment on it. The present invention prepares low-density high-strength steel by hot pressing multi-layer composite, realizes alloying between different elements under the joint action of temperature and pressure, has high production efficiency, low cost, high product quality, high material utilization rate, and obtains high-performance low-density high-strength steel plate. The obtained plate has the characteristics of higher strength, lower density, better corrosion resistance and uniform surface structure.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a low-density high-strength steel plate, characterized in that: The following steps are involved: (1) First, the aluminum alloy plate and steel plate are surface treated to remove the surface oxide film and grease; (2) Cross-stacking the treated aluminum alloy plates and steel plates into a pressure mold for cold pressing, and then taking them out after holding the pressure for a certain period of time; the cross-stacking method is to stack the single layers crosswise and the outermost layer is aluminum alloy or steel, the holding pressure is 40-160 MPa, and the holding time is 5-10 minutes; (3) preheating the plate obtained in step 2 in a furnace and then hot rolling it; the preheating temperature is 300°C-500°C, the heating rate does not exceed 20°C / min, the rolling roller temperature is 400°C-500°C, and the reduction rate is 40%-60%; (4) Cutting and stacking the hot-rolled plates for preheating and hot-rolling again; (5) vacuum annealing heat treatment of the low-density high-strength steel plate after hot rolling; (6) Trimming and surface treatment of the low-density high-strength steel plate after heat treatment.

2. The method for preparing a low-density high-strength steel plate according to claim 1, characterized in that: In the step (1), the surface treatment of the aluminum alloy plate and the steel plate includes alkaline washing to remove grease, acid washing to remove surface oxide film, and mechanical grinding with a wire brush.

3. The method for preparing the low-density high-strength steel plate according to claim 1, characterized in that: The thickness of the aluminum alloy plate is 0.1-2 mm, and the thickness of the steel plate is 0.1-1 mm.

4. The method for preparing a low-density high-strength steel plate according to claim 1, characterized in that: The preheating and hot rolling conditions in step (4) are the same as those in step (3), and step (4) can be repeated multiple times until the desired diffusion bonding effect is achieved.

5. The method for preparing the low-density high-strength steel plate according to claim 1, characterized in that: The annealing temperature in step (5) is 400°C-600°C.

6. A low-density high-strength steel plate, prepared based on the preparation method of claim 1, characterized in that: The density of the low-density high-strength steel plate is lower than 7.0 g / cm 3 And the elongation is not less than 20%.

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