Ultrafine lamellar dual-phase high-strength and low-density steel and preparation method thereof

Abstract

The present invention belongs to the field of metal material design and preparation, and specifically relates to an ultrafine lamellar dual-phase high-strength and toughness low-density steel and a preparation method thereof. The ultrafine lamellar dual-phase high-strength and toughness low-density steel proposed in the present invention, compared with traditional low-density steel, has a greatly reduced C content in terms of composition, which can improve the weldability of the material; Mn can regulate the stability of austenite; the addition of a large amount of Al can not only greatly reduce the density of steel materials, but also improve corrosion resistance; the addition of Ni can promote the formation of NiAl-type B2 phase with certain plastic deformation ability, and can also greatly improve corrosion resistance. The present invention also proposes a method for preparing ultrafine lamellar dual-phase high-strength and toughness low-density steel, which can obtain an ultrafine lamellar layer structure in which B2 and austenite are distributed in layers through simple hot forging, hot rolling or annealing processes, effectively improving the strength and toughness of the material while greatly reducing the density.

Description

Technical Field

[0001] The invention belongs to the field of metal material design and preparation, and specifically relates to an ultra-fine lamellar dual-phase high-strength and toughness low-density steel and a preparation method thereof. Background Art

[0002] "The heavier the mass, the higher the power consumption and the greater the energy consumption" is one of the basic properties of a car. Lightweighting of automobiles is an important technical path to achieve energy conservation and emission reduction in automobiles, and it is also the only way for the sustainable development of the automobile industry. At present, the main structural materials used in automobiles are steel, magnesium, aluminum and fiber composite materials. Among them, magnesium, aluminum and fiber composite materials have a low density, which is conducive to the realization of lightweight, but the material strength is low and the price is expensive, which is greatly restricted in practical applications. At present, high-strength steel is still favored by domestic and foreign automobile companies for its high cost performance, familiar application technology, perfect industrial system and good application environment. However, the density and toughness of metal materials are inverted. How to obtain good toughness while reducing the density of the material is a key scientific and technological issue of concern in this field.

[0003] CN109628850A patent discloses a multi-purpose full austenitic low-density steel and its preparation method. Its density is 7.0-7.4g / cm 3 The structure type is full austenite + nano-scale VC and MoC precipitation phases. The yield strength of the steel plate can reach more than 1000MPa, the elongation can reach 30%, the area reduction can reach 50%, and the -40℃ V-notch low-temperature impact toughness can reach 40J / cm 2 However, this solution uses carbides as a precipitation strengthening method, resulting in a higher yield strength, but the low-temperature impact toughness is not high, and the density is not significantly reduced.

[0004] Patent CN114480988A discloses a multi-phase composite high-strength, high-toughness, low-density steel and its preparation method. The solution achieves a density of ≤6.6g / cm by adjusting the alloy composition and processing technology. 3 , yield strength of 585 910MPa, tensile strength of 8801100MPa, elongation of 42 68%, and V-notch impact energy at 40°C>50J. Although this scheme uses composite phases such as κ carbide, δ ferrite, NiAl phase and NbC precipitation phase for strengthening, the yield strength of the steel is low, all below 1000MPa, and the κ carbide or NbC precipitation phase in the low-density steel is easy to coarse, which deteriorates the low-temperature impact toughness of the steel.

[0005] This project proposes to obtain lightweight, high-strength and tough new materials for automobiles by designing the alloy composition of steel materials and optimizing the processing and heat treatment processes. This will provide a good material basis for the lightweight design of automobiles and help promote the low-carbon and sustainable development of the automotive industry. Summary of the invention

[0006] The present invention provides an ultrafine lamellar dual-phase high-strength and toughness low-density steel and a preparation method thereof, so as to solve the problem that the existing low-density steel materials often have too high or too low yield strength and low low-temperature impact toughness.

[0007] To achieve the above object, the present invention proposes the following technical solutions:

[0008] An ultra-fine lamellar dual-phase high-strength and toughness low-density steel, wherein the chemical composition of the ultra-fine lamellar dual-phase high-strength and toughness low-density steel is calculated by mass percentage as follows:

[0009] C 0.4-1.2wt.%, Mn 14-35wt.%, Al 7-14wt.%, Ni 3-6wt.%, and the rest are Fe and inevitable impurities.

[0010] Preferably, the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel also includes:

[0011] V 0-3wt.%, Nb 0-3wt.%, Ti 0-3wt.%, Mo 0-3wt.%.

[0012] Preferably, in the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, the C content is 0.4-0.8wt.%, and the Mn content is 24-35%.

[0013] Preferably, in the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, the C content is 0.8-1.2wt.%, and the Mn content is 14-24%.

[0014] Preferably, the microstructure of the ultrafine lamellar dual-phase high-strength and toughness low-density steel consists of ultrafine lamellar B2 bands and austenite.

[0015] Preferably, the yield strength of the ultrafine lamellar dual-phase high-toughness low-density steel is 800-1500MPa, the tensile strength is 1100-1600MPa, the elongation is 15-50%, the strength-ductility product is 20-50GPa%, and the -40℃ V-notch low-temperature impact toughness is 30-70J / cm 2 , density is 6.1-7.0g / cm 3 .

[0016] A method for preparing ultrafine lamellar dual-phase high-strength and low-density steel comprises the following steps:

[0017] Step 1, material preparation: according to the chemical composition ratio of the ultra-fine lamellar dual-phase high-strength and tough low-density steel, Fe, Mn, C, Al, and Ni with a purity of ≥99.8% are weighed as alloy raw materials, and the alloy raw materials are placed in an electric arc furnace or an induction furnace for smelting to obtain molten steel;

[0018] Step 2, solidification casting: injecting the molten steel into a mold to solidify and cast into an ingot;

[0019] Step 3, forging; hot forging the ingot after blanking, and cooling to room temperature after forging; forging ratio ≥ 1.5;

[0020] Step 4, hot rolling: after forging, multiple hot rolling is performed to obtain a hot-rolled sample, and the hot-rolled sample is annealed and then cooled to room temperature to obtain a hot-rolled ultra-fine lamellar dual-phase high-strength and toughness low-density steel.

[0021] Preferably, in a specific embodiment, the holding temperature in step S3 is 1000-1250°C, the holding time is 1-6h, and the final thermal deformation temperature is ≥900°C.

[0022] Preferably, the hot rolling temperature in step 4 is 600-1200°C.

[0023] Preferably, the rolling reduction in step 4 is 80-99%;

[0024] The annealing temperature is 500-1000° C., and the holding time is 0.05-12 h.

[0025] The present invention is beneficial in that:

[0026] The present invention proposes an ultrafine lamellar dual-phase high-strength and toughness low-density steel. In terms of composition, compared with traditional low-density steel, the C content can be greatly reduced to improve the weldability of the material; the addition of Mn stabilizes austenite; the addition of a large amount of Al not only reduces the density of the steel, but also improves the corrosion resistance; the addition of Ni element can promote the formation of NiAl-type B2 phase with certain plastic deformation ability, and can also greatly improve the corrosion resistance.

[0027] The present invention also proposes a method for preparing ultrafine lamellar dual-phase high-strength and toughness low-density steel, which can obtain an ultrafine lamellar layer structure with layered distribution of B2 and austenite through simple hot forging, hot rolling or annealing processes, and can effectively improve the strength and toughness of the material while greatly reducing the density. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 A schematic diagram of a process for preparing an ultrafine lamellar dual-phase high-strength and tough low-density steel;

[0030] Figure 2 This is a SEM image of the hot-rolled ultra-fine lamellar dual-phase high-strength and toughness low-density steel of Example 1 of the present invention;

[0031] Figure 3 This is a SEM image of the hot-rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel of Example 2 of the present invention;

[0032] Figure 4 This is a SEM image of the hot-rolled ultra-fine lamellar dual-phase high-strength and toughness low-density steel of Example 3 of the present invention;

[0033] Figure 5 This is a SEM image of the hot-rolled ultra-fine lamellar dual-phase high-strength and toughness low-density steel of Example 4 of the present invention;

[0034] Figure 6 This is a SEM image of the annealed ultrafine lamellar dual-phase high-strength and toughness low-density steel of Example 5 of the present invention;

[0035] Figure 7 This is a SEM image of the annealed ultrafine lamellar dual-phase high-strength and toughness low-density steel of Example 6 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0037] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention.

[0038] The invention provides an ultrafine lamellar dual-phase high-strength and toughness low-density steel. The chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel is calculated by mass percentage as follows: C 0.4-1.2wt.%, Mn 14-35wt.%, Al 7-14wt.%, Ni 3-6wt.%, on this basis, V 0-3wt.%, Nb 0-3wt.%, Ti 0-3wt.%, Mo 0-3wt.%, and the rest is Fe and unavoidable impurities.

[0039] In a specific embodiment, the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel can also be: C0.4-0.8wt.%, Mn 24-35wt.%, Al 7-14wt.%, Ni 3-6wt.%, on this basis, V 0-3wt.%, Nb0-3wt.%, Ti 0-3wt.%, Mo 0-3wt.%, and the rest are Fe and unavoidable impurities.

[0040] In a specific embodiment, the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel can also be: C0.8-1.2wt.%, Mn 14-24wt.%, Al 7-14wt.%, Ni 3-6wt.%, on this basis, V 0-3wt.%, Nb0-3wt.%, Ti 0-3wt.%, Mo 0-3wt.%, and the rest are Fe and unavoidable impurities.

[0041] In a specific embodiment, the structure of the ultrafine lamellar dual-phase high-strength and toughness low-density steel consists of ultrafine lamellar B2 bands and austenite.

[0042] In a specific embodiment, the ultrafine lamellar dual-phase high-strength and toughness low-density steel is characterized in that the ultrafine lamellar dual-phase high-strength and toughness low-density steel has a yield strength of 800-1500MPa, a tensile strength of 1100-1600MPa, an elongation of 15-50%, a strength-ductility product of 20-50GPa%, and a -40°C V-notch low-temperature impact toughness of 30-70J / cm 2 , density is 6.1-7.0g / cm 3 .

[0043] See also Figure 1 As shown, the present invention also provides a method for preparing ultra-fine lamellar dual-phase high-strength and low-density steel, including common die casting and continuous casting. The following preparation method takes die casting as an example, and specifically includes the following steps:

[0044] Step 1, material preparation: Fe, Mn, C, Al, and Ni with a purity of ≥99.8% are weighed as alloy raw materials according to the chemical composition ratio of the ultra-fine lamellar dual-phase high-strength and toughness low-density steel, and V, Nb, Ti, and Mo can also be added on this basis, and the alloy raw materials are placed in an electric arc furnace or an induction furnace for smelting;

[0045] Step 2, solidification casting: injecting the molten steel obtained in step 1 into a mold for solidification and casting into an ingot;

[0046] Step 3, forging: hot forging is performed after the casting or ingot obtained in step 2 is opened, and the forging ratio must be ensured to be ≥1.5, and the casting is cooled to room temperature after forging;

[0047] Step 4, hot rolling: after forging, multiple hot rollings are performed, and then the hot rolled sample is cooled to room temperature by water quenching, oil quenching or air cooling to obtain hot rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel;

[0048] Furthermore, the sample that has been hot-rolled in the above step 4 is annealed, and then rapidly quenched in water or oil and cooled to room temperature to obtain an annealed ultrafine lamellar dual-phase high-strength and toughness low-density steel.

[0049] In a specific embodiment, the holding temperature in step S3 is 1000-1250°C, the holding time is 1-6h, and the final thermal deformation temperature is ≥900°C.

[0050] In a specific embodiment, the hot rolling temperature in step S4 is 600-1200°C.

[0051] In a specific embodiment, the rolling reduction in step S4 is 80-99%.

[0052] In a specific embodiment, the annealing temperature is 500-1000° C., and the holding time is 0.05-12 h.

[0053] Embodiment 1:

[0054] Disclosed is an ultrafine lamellar dual-phase high-strength and toughness low-density steel, wherein the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel is as follows by mass percentage: C 0.5wt.%, Mn 26wt.%, Al 11wt.%, Ni 5wt.%, V 0.03wt.%, Nb 0.05wt.%, Ti 0.1wt.%, and the remainder is Fe and unavoidable impurities.

[0055] The method for preparing the ultrafine lamellar dual-phase high-strength and toughness low-density steel comprises the following steps:

[0056] Step 1, material preparation: Fe, Mn, C, Al, Ni, V, Nb, Ti, and Mo with a purity of ≥99.8% are weighed as alloy raw materials according to the chemical composition ratio of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, and the alloy raw materials are placed in an arc melting furnace and melted under argon protection;

[0057] Step 2, solidification casting: injecting the molten steel obtained in step 1 into a mold for solidification and casting into an ingot;

[0058] Step 3, forging: hot forging the billet or ingot obtained in step 2 after blanking, with a forging holding temperature of 1100° C. for 2 hours, ensuring that the forging ratio is ≥1.5, and cooling to room temperature after forging;

[0059] Step 4, hot rolling: keep the temperature at 700°C for 1 hour, perform multiple hot rolling, then cool the hot rolled sample to room temperature by water quenching, and the total rolling reduction is 98% to obtain hot rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel.

[0060] like Figure 2 As shown, the microstructure of the hot-rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel is composed of ultrafine lamellar B2 bands and austenite.

[0061] The tensile properties of the ultra-fine lamellar dual-phase high-strength and tough low-density steel prepared in this embodiment are tested, and the tensile properties are shown in Table 1. The high-strength and lightweight steel prepared in Example 1 has a yield strength of 1510 MPa, a tensile strength of 1591 MPa, a total elongation of 22%, a strength-ductility product of 35 GPa%, and a -40°C V-notch low-temperature impact toughness of 32 J / cm 2 , density is 6.7g / cm 3 .

[0062] Embodiment 2:

[0063] The invention discloses an ultrafine lamellar dual-phase high-strength and toughness low-density steel, wherein the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel is as follows by mass percentage: C 0.6wt.%, Mn 35wt.%, Al 12wt.%, Ni 6wt.%, V 0.05wt.%, Nb 0.05wt.%, and the rest is Fe and unavoidable impurities.

[0064] The method for preparing the ultrafine lamellar dual-phase high-strength and toughness low-density steel comprises the following steps:

[0065] Step 1, weighing Fe, Mn, C, Al, Ni, V, and Nb with a purity of ≥99.8% as alloy raw materials according to the chemical composition ratio of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, placing the alloy raw materials in an arc melting furnace, and melting them under argon protection;

[0066] Step 2, solidification casting: injecting the molten steel obtained in step 1 into a mold for solidification and casting into an ingot;

[0067] Step 3, forging: hot forging the billet or ingot obtained in step 2 after blanking, with a forging holding temperature of 1200° C. for 4 hours, ensuring that the forging ratio is ≥1.5, and cooling to room temperature after forging;

[0068] Step 4, hot rolling: keep the temperature at 800°C for 1 hour, perform multiple hot rolling, then cool the hot rolled sample to room temperature by water quenching, and the total rolling reduction is 95% to obtain hot rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel.

[0069] like Figure 3As shown, the microstructure of the hot-rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel is composed of ultrafine lamellar B2 bands and austenite.

[0070] The tensile properties of the ultra-fine lamellar dual-phase high-strength and tough low-density steel prepared in this embodiment are tested, and the tensile properties are shown in Table 1. The high-strength and lightweight steel prepared in Example 2 has a yield strength of 1373 MPa, a tensile strength of 1443 MPa, a total elongation of 23%, a strength-ductility product of 33.2 GPa%, and a -40°C V-notch low-temperature impact toughness of 38 J / cm 2 , density is 6.6g / cm 3 .

[0071] Embodiment 3:

[0072] The invention discloses an ultrafine lamellar dual-phase high-strength and toughness low-density steel, wherein the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel is as follows by mass percentage: C 0.9wt.%, Mn 20wt.%, Al 10wt.%, Ni 4wt.%, and the rest is Fe and unavoidable impurities.

[0073] The method for preparing the ultrafine lamellar dual-phase high-strength and toughness low-density steel comprises the following steps:

[0074] Step 1, weighing Fe, Mn, C, Al, and Ni with a purity of ≥99.8% as alloy raw materials according to the chemical composition ratio of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, placing the alloy raw materials in an arc melting furnace, and melting them under argon protection;

[0075] Step 2, solidification casting: injecting the molten steel obtained in step 1 into a mold for solidification and casting into an ingot;

[0076] Step 3, forging: hot forging the billet or ingot obtained in step 2 after blanking, with a forging holding temperature of 1050° C. for 3 hours, ensuring that the forging ratio is ≥1.5, and cooling to room temperature after forging;

[0077] Step 4, hot rolling: keep the temperature at 1100°C for 10 minutes, perform multiple hot rolling, then cool the hot rolled sample to room temperature by water quenching, and the total rolling reduction is 90%, so as to obtain hot rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel.

[0078] like Figure 4 As shown, the microstructure of the hot-rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel is composed of ultrafine lamellar B2 bands and austenite.

[0079] The tensile properties of the ultra-fine lamellar dual-phase high-strength and tough low-density steel prepared in this embodiment were tested, and the tensile properties are shown in Table 1. The high-strength and lightweight steel prepared in Example 3 has a yield strength of 1395 MPa, a tensile strength of 1444 MPa, a total elongation of 28%, a strength-ductility product of 40.4 GPa%, and a -40°C V-notch low-temperature impact toughness of 40 J / cm 2 , density is 6.8g / cm 3 .

[0080] Embodiment 4:

[0081] The invention discloses an ultrafine lamellar dual-phase high-strength and toughness low-density steel, wherein the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel is as follows by mass percentage: C 0.6wt.%, Mn 30wt.%, Al 12wt.%, Ni 5wt.%, V 0.15wt.%, Nb 0.05wt.%, Ti 1wt.%, Mo 1wt.%, and the rest is Fe and unavoidable impurities.

[0082] The method for preparing the ultrafine lamellar dual-phase high-strength and toughness low-density steel comprises the following steps:

[0083] Step 1, weighing Fe, Mn, C, Al, Ni, V, Nb, Ti, and Mo with a purity of ≥99.8% as alloy raw materials according to the chemical composition ratio of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, placing the alloy raw materials in an arc melting furnace, and melting them under argon protection;

[0084] Step 2, solidification casting: injecting the molten steel obtained in step 1 into a mold for solidification and casting into an ingot;

[0085] Step 3, forging: hot forging the billet or ingot obtained in step 2 after blanking, with a forging holding temperature of 1050° C. for 4 hours, ensuring that the forging ratio is ≥1.5, and cooling to room temperature after forging;

[0086] Step 4, hot rolling: keep the temperature at 800°C for 1 hour, perform multiple hot rolling, then cool the hot rolled sample to room temperature by water quenching, and the total rolling reduction is 90% to obtain hot rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel.

[0087] like Figure 5 As shown, the microstructure of the hot-rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel is composed of ultrafine lamellar B2 bands and austenite.

[0088] The tensile properties of the ultra-fine lamellar dual-phase high-strength and tough low-density steel prepared in this embodiment were tested, and the tensile properties are shown in Table 1. The high-strength and lightweight steel prepared in Example 4 has a yield strength of 1456 MPa, a tensile strength of 1500 MPa, a total elongation of 15.4%, a strength-ductility product of 23.1 GPa%, and a -40°C V-notch low-temperature impact toughness of 30 J / cm 2 , density is 6.4g / cm 3 .

[0089] Embodiment 5:

[0090] The invention discloses an ultrafine lamellar dual-phase high-strength and toughness low-density steel, wherein the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel is as follows by mass percentage: C 1.0wt.%, Mn 18wt.%, Al 10wt.%, Ni 5wt.%, Nb 0.03wt.%, and the rest is Fe and unavoidable impurities.

[0091] The method for preparing the ultrafine lamellar dual-phase high-strength and toughness low-density steel comprises the following steps:

[0092] Step 1, weighing Fe, Mn, C, Al, Ni, and Nb with a purity of ≥99.8% as alloy raw materials according to the chemical composition ratio of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, placing the alloy raw materials in an arc melting furnace, and melting them under argon protection;

[0093] Step 2, solidification casting: injecting the molten steel obtained in step 1 into a mold for solidification and casting into an ingot;

[0094] Step 3, forging: hot forging the billet or ingot obtained in step 2 after blanking, with a forging holding temperature of 1050° C. for 1 hour, ensuring that the forging ratio is ≥1.5, and cooling to room temperature after forging;

[0095] Step 4, hot rolling: keep the temperature at 700°C for 1 hour, perform multiple hot rolling, then cool the hot rolled sample to room temperature by water quenching, and the total rolling reduction is 95% to obtain hot rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel.

[0096] Furthermore, the sample after hot rolling in the above step 4 is annealed at a temperature of 800° C. for 30 min, and then rapidly quenched in water and cooled to room temperature to obtain an annealed ultrafine lamellar dual-phase high-strength and toughness low-density steel.

[0097] like Figure 6 As shown, the microstructure of the hot-rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel is composed of ultrafine lamellar B2 bands and austenite.

[0098] The tensile properties of the ultra-fine lamellar dual-phase high-strength and tough low-density steel prepared in this embodiment are tested, and the tensile properties are shown in Table 1. The high-strength and lightweight steel prepared in Example 1 has a yield strength of 1088 MPa, a tensile strength of 1296 MPa, a total elongation of 42.4%, a strength-ductility product of 55 GPa%, and a -40°C V-notch low-temperature impact toughness of 60 J / cm 2 , density is 6.7g / cm 3 .

[0099] Embodiment 6:

[0100] The invention discloses an ultrafine lamellar dual-phase high-strength and toughness low-density steel, wherein the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel is as follows by mass percentage: C 0.5wt.%, Mn 26wt.%, Al 11wt.%, Ni 5wt.%, and the rest is Fe and unavoidable impurities.

[0101] The method for preparing the ultrafine lamellar dual-phase high-strength and toughness low-density steel comprises the following steps:

[0102] Step 1, weighing Fe, Mn, C, Al, and Ni with a purity of ≥99.8% as alloy raw materials according to the chemical composition ratio of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, placing the alloy raw materials in an arc melting furnace, and melting them under argon protection;

[0103] Step 2, solidification casting: injecting the molten steel obtained in step 1 into a mold for solidification and casting into an ingot;

[0104] Step 3, forging: hot forging the billet or ingot obtained in step 2 after blanking, with a forging holding temperature of 1100° C. for 1 hour, ensuring that the forging ratio is ≥1.5, and cooling to room temperature after forging;

[0105] Step 4, hot rolling: keep the temperature at 700°C for 1 hour, perform multiple hot rolling, then cool the hot rolled sample to room temperature by water quenching, and the total rolling reduction is 98%, so as to obtain hot rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel.

[0106] Furthermore, the sample after hot rolling in the above step 4 is annealed at a temperature of 800° C. for 15 min, and then rapidly quenched in water and cooled to room temperature to obtain an annealed ultrafine lamellar dual-phase high-strength and toughness low-density steel.

[0107] like Figure 7 As shown, the microstructure of the hot-rolled ultrafine lamellar dual-phase high-strength and toughness low-density steel is composed of ultrafine lamellar B2 bands and austenite.

[0108] The tensile properties of the ultra-fine lamellar dual-phase high-strength and tough low-density steel prepared in this embodiment were tested, and the tensile properties are shown in Table 1. The high-strength and lightweight steel prepared in Example 6 has a yield strength of 1058 MPa, a tensile strength of 1286 MPa, a total elongation of 43%, a strength-ductility product of 55 GPa%, and a -40°C V-notch low-temperature impact toughness of 63 J / cm 2 , density is 6.8g / cm 3 .

[0109] Table 1 Mechanical properties data of ultra-fine lamellar dual-phase high-strength and low-density steel obtained in each embodiment

[0110]

[0111] In the above scheme, compared with the high-strength low-density steel in the prior art:

[0112] In terms of composition, compared with traditional low-density steel, the C content can be greatly reduced to improve the weldability of the material; the addition of Mn stabilizes austenite; the addition of a large amount of Al not only reduces the density of the steel, but also improves corrosion resistance; the addition of Ni can promote the formation of NiAl-type B2 phase with certain plastic deformation ability, and can also greatly improve corrosion resistance. In terms of hot processing technology, an ultra-fine crystalline layer structure with layered distribution of B2 and austenite can be prepared through simple hot forging, hot rolling or annealing processes, which can effectively improve the strength and toughness of the material while greatly reducing the density.

[0113] The ultrafine lamellar dual-phase high-toughness low-density steel of the present invention has a yield strength of 800-1500MPa, a tensile strength of 1100-1600MPa, an elongation of 15-50%, a strength-ductility product of 20-50GPa%, and a -40°C V-notch low-temperature impact toughness of 30-70J / cm 2 , density is 6.1-7.0g / cm 3 , meeting the demand for lightweight, high-strength and tough new materials for automobiles.

[0114] The preparation process of the finished steel of the present invention is simple and economical, and can realize large-scale industrial production. The research and development of the ultra-fine lamellar dual-phase high-strength and low-density steel provides a good material basis for the lightweight design of automobiles, is conducive to promoting the low-carbon and sustainable development of the automobile industry, and plays an important supporting role in the development of my country's key parts industry for smart cars and the advanced layout of related technologies.

[0115] In the above scheme, compared with the high-strength low-density steel in the prior art: from the aspect of composition, the finished steel in the present invention has a significantly reduced C content compared with the traditional low-density steel, which can improve the weldability of the material; Mn can stabilize austenite; the addition of a large amount of Al can not only significantly reduce the density of the steel material, but also improve the corrosion resistance; the addition of Ni can promote the formation of NiAl-type B2 phase with a certain plastic deformation ability, and can also significantly improve the corrosion resistance. From the aspect of hot processing technology, an ultra-fine lamellar layer structure with layered distribution of B2 and austenite can be obtained through simple hot forging, hot rolling or annealing processes, which can effectively improve the strength and toughness of the material while significantly reducing the density.

[0116] The ultrafine lamellar dual-phase high-toughness low-density steel of the present invention has a yield strength of 800-1500MPa, a tensile strength of 1100-1600MPa, an elongation of 15-50%, a strength-ductility product of 20-50GPa%, and a -40°C V-notch low-temperature impact toughness of 30-70J / cm 2 , density is 6.1-7.0g / cm 3 , meeting the demand for lightweight, high-strength and tough new materials for automobiles.

[0117] The preparation process of the finished steel of the present invention is simple and economical, and can realize large-scale industrial production. The research and development of the ultra-fine lamellar dual-phase high-strength and low-density steel provides a good material basis for the lightweight design of automobiles, is conducive to promoting the low-carbon and sustainable development of the automobile industry, and plays an important supporting role in the development of my country's key parts industry for smart cars and the advanced layout of related technologies.

[0118] In the above scheme, compared with the high-strength low-density steel in the prior art: in terms of composition, compared with traditional low-density steel, the C content can be greatly reduced to improve the weldability of the material; the addition of Mn stabilizes austenite; the addition of a large amount of Al not only reduces the density of the steel, but also improves corrosion resistance; the addition of Ni elements can promote the formation of NiAl-type B2 phase with certain plastic deformation ability, and can also greatly improve corrosion resistance. In terms of hot processing technology, an ultra-fine wafer layer structure with layered distribution of B2 and austenite can be obtained through simple hot forging, hot rolling or annealing processes, which can effectively improve the strength and toughness of the material while greatly reducing the density.

[0119] The ultrafine lamellar dual-phase high-toughness low-density steel of the present invention has a yield strength of 800-1500MPa, a tensile strength of 1100-1600MPa, an elongation of 15-50%, a strength-ductility product of 20-50GPa%, and a -40°C V-notch low-temperature impact toughness of 30-70J / cm 2 , density is 6.1-7.0g / cm 3 , meeting the demand for lightweight, high-strength and tough new materials for automobiles.

[0120] The preparation process of the finished steel of the present invention is simple and economical, and can realize large-scale industrial production. The research and development of the ultra-fine lamellar dual-phase high-strength and low-density steel provides a good material basis for the lightweight design of automobiles, is conducive to promoting the low-carbon and sustainable development of the automobile industry, and plays an important supporting role in the development of my country's key parts industry for smart cars and the advanced layout of related technologies.

[0121] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

[0122] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0123] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0124] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0125] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An ultra-fine lamellar dual-phase high-strength and low-density steel, characterized in that: The chemical composition of the ultra-fine lamellar dual-phase high-strength and toughness low-density steel is calculated by mass percentage: C 0.4-1.2wt.%, Mn 14-35wt.%, Al 7-14wt.%, Ni 3-6wt.%, the rest is Fe and unavoidable impurities; In the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, when the C content is 0.4-0.8wt.%, the Mn content is 24-35%; In the chemical composition of the ultrafine lamellar dual-phase high-strength and toughness low-density steel, when the C content is 0.8-1.2wt.%, the Mn content is 14-24%; The microstructure of the ultrafine lamellar dual-phase high-strength and toughness low-density steel is composed of ultrafine lamellar B2 bands and austenite; The ultra-fine lamellar dual-phase high-strength and toughness low-density steel is formed by hot rolling; The ultra-fine lamellar dual-phase high-strength and tough low-density steel has a yield strength of 800-1500MPa, a tensile strength of 1100-1600MPa, an elongation of 15-50%, a strength-ductility product of 20-50GPa%, and a -40°C V-notch low-temperature impact toughness of 30-70J / cm 2 , density is 6.1-7.0g / cm 3 .

2. The ultra-fine lamellar dual-phase high-strength and toughness low-density steel according to claim 1, characterized in that: The chemical composition of the ultra-fine lamellar dual-phase high-strength and toughness low-density steel also includes: V 0-3wt.%, Nb 0-3wt.%, Ti 0-3wt.%, Mo 0-3wt.%.

3. A method for preparing ultrafine lamellar dual-phase high-strength and toughness low-density steel according to claim 1 or 2, characterized in that: The steps include: Step 1, material preparation: Fe, Mn, C, Al, and Ni with a purity of ≥99.8% are weighed as alloy raw materials according to the chemical composition ratio of the ultra-fine lamellar dual-phase high-strength and toughness low-density steel, and the alloy raw materials are placed in an electric arc furnace or an induction furnace for smelting to obtain molten steel; Step 2, solidification casting: injecting the molten steel into a mold to solidify and cast into an ingot; Step 3, forging; hot forging the ingot after blanking, and cooling to room temperature after forging; forging ratio ≥ 1.5; Step 4, hot rolling: after forging, multiple hot rolling is performed to obtain a hot-rolled sample, and the hot-rolled sample is annealed and then cooled to room temperature to obtain a hot-rolled ultra-fine lamellar dual-phase high-strength and toughness low-density steel.

4. The method for preparing ultrafine lamellar dual-phase high-strength and toughness low-density steel according to claim 3, characterized in that: The forging holding temperature in step S3 is 1000-1250°C, the holding time is 1-6h, and the final thermal deformation temperature is ≥900°C.

5. The method for preparing ultrafine lamellar dual-phase high-strength and toughness low-density steel according to claim 3, characterized in that: The hot rolling temperature in step 4 is 600-1200°C.

6. The method for preparing ultrafine lamellar dual-phase high-strength and toughness low-density steel according to claim 3, characterized in that: The rolling reduction in step 4 is 80-99%; The annealing temperature is 500-1000° C., and the holding time is 0.05-12 h.

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