Smelting preparation method of Fe-Mn-Al-C series low-density steel

Abstract

The invention discloses a smelting preparation method of Fe-Mn-Al-C series low-density steel, and belongs to the technical field of ferrous metallurgy. The vacuum induction furnace is adopted for test preparation, the density of the low-density steel is low, and the structural weight can be effectively reduced while the basic performance of the steel is kept. The method is of great significance in the fields of automobile manufacturing, aerospace and the like, and the self weight of transportation tools such as automobiles and aircrafts can be reduced, so that the transportation efficiency is improved, and the energy consumption and the operation cost are reduced. And due to reasonable matching of alloy elements, a more compact oxidation film can be formed, and the corrosion resistance of the steel is improved. Therefore, the service life of the steel in a severe environment is prolonged, and the maintenance and replacement cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and particularly relates to a method for smelting and preparing Fe-Mn-Al-C series low-density steel. Background Technology

[0002] With the rapid development of the automotive industry, automobile production and ownership have increased rapidly. While bringing convenience to people's travel, this also presents three major challenges: fuel consumption, safety, and environmental protection. Lightweighting of automobiles can be achieved through lightweight materials, advanced processes, and structural optimization, with the use of lightweight materials being the current mainstream approach. For every 1 wt% increase in Al in steel, the weight of the steel decreases by 1.3%, and low-density steel possesses high strength and ductility, thus showing promising application prospects. Therefore, the development of low-density steel with high aluminum content has become a problem urgently needing to be solved by those skilled in the art.

[0003] Chinese Patent Application No. 202310984145.9 discloses a low-density steel plate with ultra-high strength and ductility and its preparation method. Its composition, by weight percentage, is: C: 0.26–0.40%, Si: 0.25–0.75%, Mn: 5.60–11.50%, P: ≤0.010%, S: ≤0.002%, Al: 3.7–7.5%, Cr: 0.2–0.5%, Ni: 0.20–0.35%, Mo: 0.20–0.30%, Nb: 0.02–0.04%, with the remainder being Fe and unavoidable impurities. The preparation method includes: smelting and casting into billets → hot rolling → solution treatment → warm rolling → annealing + deep cooling + tempering; the steel plate produced by this invention has a thickness of 2.1-2.4 mm, a density of 6.50-6.80, a yield strength of 1039-1334 MPa, a tensile strength of 1590-1740 MPa, an elongation of ≥30.2%, and a strength-ductility product of ≥52.4 GPa%. It has both high strength and high ductility, and can be used for cold-formed parts, providing the automotive industry with impact-resistant lightweight materials.

[0004] Chinese patent application number 201911291126.8 discloses a low-density high-strength steel for automobiles and its preparation method. The composition is: C: 0.3–0.5%, Si: 0.2–0.5%, Mn: 1.0–2.0%, P: ≤0.01%, S: ≤0.01%, Al: 3.5–4.8%, Ce: 0.02–0.04%, N: ≤0.004%. The remainder is Fe and unavoidable impurities. Its density is approximately 5% lower than that of traditional steel, thus solving the problem that existing steel sheets cannot simultaneously meet the requirements of lightness, ductility, and weight reduction. When applied to automobiles, it will substantially reduce the weight of the vehicle.

[0005] Chinese patent application number 201611262438.2 discloses a method for preparing TRIP steel containing δ-ferrite, with the following composition: C: 0.24–0.28%, Si: 0.5–1.0%, Mn: 1.8–2.5%, P: ≤0.01%, S+N: ≤0.008%, Al: 2.9–3.7%. The remainder is Fe and unavoidable impurities. The preparation method includes hot rolling, induction heating, ultra-rapid cooling, and heat treatment. The composition design increases the Al content, achieving high tensile strength while reducing the steel's density, effectively achieving lightweighting. The finished steel microstructure consists of α-ferrite, δ-ferrite, bainite, and thin-film retained austenite (or Mao islands), with a retained austenite volume percentage of 11.31–13.39%. The steel has a yield strength of 468-516 MPa, a tensile strength of 729-799 MPa, an elongation of 28.2-29.8%, and a strength-ductility product of 20.6-23.8 GPa·s. Summary of the Invention

[0006] The purpose of this invention is to provide a method for smelting and preparing Fe-Mn-Al-C series low-density steel, using a vacuum induction furnace to prepare low-density automotive steel. This provides a conceptual approach for achieving lightweighting in automobiles.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for smelting and preparing Fe-Mn-Al-C system low-density steel, comprising the following steps:

[0009] 1) Select DP780 duplex steel for automobiles as the research target, and design the composition of low-density steel based on the composition of DP780 duplex steel.

[0010] 2) Conduct material sampling tests based on the design results of the low-density steel composition;

[0011] 3) Use steel similar to the target steel grade as raw material to break it into long strips for smelting;

[0012] 4) Vacuum induction furnace was used to smelt the test steel.

[0013] 5) Calculate the amount of aluminum to be added based on the target composition of low-density steel;

[0014] 6) Add all raw materials to the crucible for smelting, and ensure that the process is carried out under vacuum.

[0015] 7) Add the calculated alloy 0.5-2 minutes after the raw materials have melted;

[0016] 8) Ensure the alloy is completely melted before casting under vacuum;

[0017] 9) Inspect the chemical composition of the smelted steel to ensure it is the same as the target composition;

[0018] 10) Dual-phase steel is obtained by rolling and heat treatment of smelted ingots.

[0019] Furthermore, the long strip furnace charge is a strip 25-35cm long and 2-4cm wide.

[0020] Furthermore, the long strip of furnace charge is a strip 30cm long and 3cm wide.

[0021] Furthermore, the test steel was smelted using a 25kg vacuum induction furnace.

[0022] Furthermore, the calculated alloy is added 1 minute after the raw materials have melted.

[0023] Furthermore, smelting is carried out under vacuum conditions, with a vacuum level of 90 Pa.

[0024] Furthermore, it can form a denser oxide film, improving the corrosion resistance of the steel.

[0025] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0026] This invention utilizes a vacuum induction furnace for experimental preparation. The low-density steel, with its lower density, effectively reduces structural weight while maintaining the basic properties of steel. This is significant for fields such as automotive manufacturing and aerospace, enabling the reduction of the weight of transportation vehicles such as automobiles and aircraft, thereby improving transportation efficiency and reducing energy consumption and operating costs. Due to the rational combination of alloying elements, a denser oxide film can be formed, improving the steel's corrosion resistance. This helps extend the service life of the steel in harsh environments, reducing maintenance and replacement costs. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings.

[0028] Figure 1 This is a metallographic image of the sample. Detailed Implementation

[0029] Case 1:

[0030] 1. Raw Material Preparation: Using DP780 as the research target, samples of cast billets produced on-site were processed into 30cm long and 3cm wide strips as furnace charge for the next smelting step. Six heats of low-density steel with different aluminum contents were designed. The Al content of the target steel grade was 0.05%, 0.5%, 1.0%, 1.5%, 2.0%, and 4.0%, respectively, for experimental research. The corresponding aluminum block addition amounts were 0g, 127.5g, 225g, 382.5g, 510g, and 1020g. The addition amounts of other elements were consistent: C: 5g, Si: 150g, Mn: 225g, Cr: 164g, Nb: 13g, Ti: 6g. The specific chemical composition is shown in the table below. The furnace charge was then shot-blasted to remove iron oxide and rust impurities generated during the processing.

[0031]

[0032] 2. Melting: The test steel was melted in a 25kg vacuum induction furnace, ensuring smelting under vacuum conditions at a vacuum level of 90 Pa. The prepared charge was placed into the furnace, and aluminum blocks, ferrochrome alloy, ferroniobium alloy, and ferrotitanium alloy were added to the charging hopper above the furnace. The power was turned on and the vacuum pump was activated for melting. The melting process was continuously observed throughout the process. After approximately 20 minutes, the steel was completely melted. One minute after the raw materials had melted, the aluminum blocks, ferrochrome alloy, ferroniobium alloy, and ferrotitanium alloy were added. After heating for 2 minutes to ensure complete melting of the alloys, the mixture was cast under vacuum. The ingot was cooled in the furnace before proceeding to the next rolling process.

[0033] 3. Composition analysis: Steel scrap from 6 heats of samples were taken and the required elements for the target steel grade were analyzed according to the requirements of chemical analysis. The chemical composition of each heat of steel sample is shown in the table below.

[0034]

[0035] 4. Metallographic Analysis: Metallographic samples from 6 heats of steel were processed into 2*2*2cm samples. Coarse grinding, fine grinding, and polishing were performed. The samples were then etched with 4% nitric acid alcohol for 15 seconds, rinsed with water, and dried with filter paper. The microstructure was observed under a microscope. Metallographic observation revealed that the microstructure consisted of ferrite and cementite. The proportion of ferrite increased with increasing Al content. When the Al content was above 1.6%, the grain size of both ferrite and cementite significantly increased. When the Al content was 4.0%, the crystal structure exhibited an irregular structure, with black precipitates along the grain boundaries. The metallographic analysis indicates that an Al content below 1.1% is suitable for this composition design, with an optimal Al content below 1.0%.

[0036] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for smelting and preparing Fe-Mn-Al-C series low-density steel, characterized in that: Includes the following steps: 1) Select DP780 duplex steel for automobiles as the research target. Based on the composition of DP780 duplex steel, design the composition of low-density steel, and control the Al content to below 1.1%. 2) Conduct material sampling tests based on the design results of the low-density steel composition; 3) Use steel similar to the target steel grade as raw material to break it into long strips for smelting; 4) Vacuum induction furnace was used to smelt the test steel. 5) Calculate the amount of aluminum to be added based on the target composition of low-density steel; 6) Add all raw materials to the crucible for smelting, and ensure that the process is carried out under vacuum. 7) Add the calculated alloy 0.5-2 minutes after the raw materials have melted; 8) Ensure the alloy is completely melted before casting under vacuum; 9) Inspect the chemical composition of the smelted steel to ensure it is the same as the target composition; 10) Dual-phase steel is obtained by rolling and heat treatment of smelted ingots.

2. The smelting and preparation method of Fe-Mn-Al-C system low-density steel according to claim 1, characterized in that: The long strip furnace charge is a strip 25-35cm long and 2-4cm wide.

3. The smelting and preparation method of Fe-Mn-Al-C system low-density steel according to claim 2, characterized in that: The long strip of furnace charge is a strip 30cm long and 3cm wide.

4. The smelting and preparation method of Fe-Mn-Al-C system low-density steel according to claim 1, characterized in that: The test steel was smelted using a 25kg vacuum induction furnace.

5. The smelting and preparation method of Fe-Mn-Al-C system low-density steel according to claim 1, characterized in that: One minute after the raw materials have melted, the calculated alloy is added.

6. The smelting and preparation method of Fe-Mn-Al-C system low-density steel according to claim 1, characterized in that: The smelting is carried out under vacuum conditions, with a vacuum level of 90 Pa.

7. The smelting and preparation method of Fe-Mn-Al-C system low-density steel according to claim 1, characterized in that: It can form a denser oxide film, improving the corrosion resistance of steel.

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