High-strength and high-toughness automobile wheel steel added with rare earth elements and preparation method of high-strength and high-toughness automobile wheel steel

Abstract

The invention discloses high-strength and high-toughness automobile wheel steel added with rare earth elements and a preparation method thereof, belongs to the technical field of production and manufacturing of automobile wheel steel, and relates to a preparation method for improving the strength and the toughness of hot-press formed steel by adding the rare earth elements and combining the component synergistic change relation. The steel comprises the following chemical components: 0.15%-0.30% of C, 0.5%-1.5% of Si, 1.5%-2.5% of Mn, 0.3%-0.6% of Cr, 0.1%-0.3% of Mo, 0.02%-0.05% of Ti, 0.01%-0.20% of V, 0.01%-0.20% of Al, 0.05%-0.5% of RE, less than or equal to 0.005% of S, less than or equal to 0.010% of P and the balance of Fe and inevitable inclusions. RE is one or a combination of cerium and lanthanum. Material components are optimized on the basis of a collaborative change relation established in a cluster mode, production of a hot-pressing forming steel product with the strength grade of 1900 MPa improved is completed through process control, the yield strength of the product is larger than or equal to 1400 MPa, the tensile strength is larger than or equal to 1900 MPa, and the ductility is larger than or equal to 12%. The method provided by the invention is suitable for industrial production, the process is easy to control, and cost reduction and efficiency improvement of enterprises can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of production and manufacturing of automobile wheel steel, and relates to a preparation method for improving the strength and toughness of hot-pressed steel by adding rare earth elements (any one of cerium, lanthanum, etc. or a combination thereof) in combination with a synergistic change relationship of components, and specifically relates to a high-strength and high-toughness automobile wheel steel added with rare earth elements and a preparation method thereof. Background Art

[0002] With the rapid development of the automotive industry, lightweight and safety have become the main goals of automotive design and manufacturing. In order to meet the market's increasingly stringent requirements for vehicle performance, automakers are gradually turning to high-strength steel (HSS) and ultra-high-strength steel (UHSS) to achieve lighter and safer body structures. High-strength steel materials have played a key role in improving automobile collision safety, reducing fuel consumption and reducing environmental impact. However, current high-strength steel for wheels still has problems such as cracking and springback during the cold forming process, especially when the tensile strength of the steel plate reaches 980MPa or above, the challenges faced are more significant.

[0003] To solve these problems, the research and application of transformation induced plasticity (TRIP) steel and quenching and partitioning (QP) steel have received increasing attention. These materials use the phase transformation mechanism to achieve excellent strength-plasticity matching, which promotes lightweight vehicle bodies and energy conservation and emission reduction. However, despite the good mechanical properties of these steels, existing technologies still have shortcomings in strength level, composition design and production process. For example, in the production process of some hot-formed steels, the composition design is too complicated and the alloy element content is high, resulting in reduced welding performance, poor surface quality, and increased production costs.

[0004] At present, some research on high-strength hot-formed steels has focused on improving the chemical composition to increase its toughness and elongation. For example, the hot-formed steel mentioned in the patent application No. 202310068576.0, although its strength can reach 1500MPa, still fails to meet the strict standards of modern automobile design in terms of elongation and collision toughness. This makes it possible for automobile parts to suffer brittle failure in the event of a collision, reducing overall safety.

[0005] In view of this, the present invention introduces a cluster composition design method (hereinafter referred to as cluster method) that describes the chemical near-program structure, especially considering the synergistic effect of elements in the alloy to clarify the composition range of various elements in the alloy and the combination range of similar elements. This standard also has a demonstration effect, and its significance can be extended to any industrial alloy system.

[0006] In addition, for high-strength and high-toughness steel, current research is limited to discussing the influence of a single element on alloy properties. Therefore, the current technical standards are limited to specifying the composition range of a single element, lacking the interaction between elements. In fact, even if the widely accepted composition standards in the industry are followed, the alloy properties vary greatly, and the comprehensive performance cannot be accurately guaranteed. In actual industrial production, each company usually manufactures alloys according to empirical compositions, and the complexity of the preparation process often makes it impossible to obtain alloys with excellent performance. In fact, this is also a common problem faced by all industrial alloys, that is, the types of elements and composition ranges are derived from engineering practice, and their theoretical basis is missing. Mechanistically speaking, the above engineering problems originate from people's understanding of solid solution structure. As we all know, industrial alloys are based on solid solutions, and solid solutions are characterized by chemical near-processes, with both order and disorder. The alloy composition must be implicit in this near-process structure, and the academic community lacks a structural model for the chemical near-process of solid solutions.

[0007] In view of this, the present invention introduces a cluster composition design method (hereinafter referred to as cluster method) that describes the chemical near-program structure, especially considering the synergistic effect of elements in the alloy to clarify the composition range of various elements in the alloy and the combination range of similar elements. This standard also has a demonstration effect, and its significance can be extended to any industrial alloy system. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention aims to provide a high-strength and high-toughness automotive steel with added rare earth elements and a preparation method thereof, so as to solve the balance problem between strength and toughness of existing automotive steel and meet the needs of modern automobiles for lightweighting and safety improvement.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A high-strength and high-toughness automobile wheel steel with added rare earth elements. The chemical composition of the high-strength and high-toughness automobile wheel steel, measured by weight percentage, includes: C: 0.15-0.30%, Si: 0.5-1.5%, Mn: 1.5-2.5%, Cr: 0.3-0.6%, Mo: 0.1-0.3%, Ti: 0.02-0.05%, V: 0.01-0.20%, Al: 0.01-0.20%, RE (any one of cerium or lanthanum or a combination thereof): 0.05-0.5%, S≤0.005%, P≤0.010%, and the balance is Fe and inevitable inclusions.

[0011] Further, the present invention determines the synergistic variation relationship of each element based on the cluster method, and the above alloying elements include matrix elements, Ni-like elements (stable austenite elements) entering the cluster formula, Cr-like elements (stable ferrite elements), trace elements that do not enter the cluster formula, and rare earth elements, wherein the matrix element is Fe, the Ni-like elements that enter the cluster formula are Mn, the Cr-like elements include Cr, Si, Mo, Al, Ti, and V, and the trace elements that do not enter the cluster formula include C, S, P, and RE (any one or a combination of cerium or lanthanum). The synergistic variation relationship (mass percentage) of each element satisfies: 1.50≤Mn≤2.50; 1.32≤Cr+1.83Si+0.54Mo+1.92Al+1.09Ti+1.02V≤4.15; 94.67≤Fe≤96.58. The above-mentioned synergistic variation relationship is based on the cluster model. According to this model, the component carrier of any alloy is a local structural unit, covering the first-neighbor cluster plus several second-neighbor connecting atoms, which is expressed as a cluster type: [cluster center-cluster first-neighbor shell] (next-neighbor connecting atoms). Therefore, the elements in the alloy are divided into only three categories: located in the center, shell, and connected, plus interstitial and trace elements that do not enter the cluster type. Therefore, only four element classifications are required, which can simplify the complex alloying of high-strength and high-toughness steels.

[0012] Furthermore, the yield strength of the high-strength and high-toughness automobile wheel steel is ≥1400MPa, the tensile strength is ≥1900MPa, and the elongation is ≥12%.

[0013] A method for preparing high-strength and high-toughness automobile wheel steel with rare earth elements added thereto, wherein the preparation method is a method for producing products of the strength level of the steel grade by controlling the composition through process control, and comprises the following process flow: smelting, hot rolling, cold rolling, heat treatment, and surface treatment (microball peening). The specific steps are as follows:

[0014] The first step is to prepare slab products by smelting method, specifically:

[0015] Step 1.1, after smelting in an electric arc furnace through various stages of smelting process operations such as melting, decarburization, dephosphorization, degassing, inclusion removal, temperature control, composition adjustment (alloying), etc., the temperature is controlled between 1500°C and 1600°C to obtain molten steel with chemical composition meeting the requirements.

[0016] Step 1.2, the rare earth elements are gradually added to the molten steel in small doses by pressing or spraying. During this process, electromagnetic stirring technology is used to ensure that the rare earth alloy is evenly dispersed and fully dissolved in the molten steel; the stirring time should be controlled within 10-15 minutes to ensure that the rare earth elements are completely mixed and evenly distributed and fully in contact with the molten steel. In order to improve the purity of the molten steel, argon protection is used during the smelting process to prevent oxidation and reduce the impurity content. The addition of the rare earth elements can significantly improve the grain refinement and organizational uniformity of the steel, and remove impurities in the steel, such as low-melting-point metal elements, oxides, sulfides, hydrogen, etc. The smelting process adopts vacuum smelting technology to reduce the impurity content and improve the purity of the steel.

[0017] Step 1.3, pouring the molten steel into a mold, and obtaining a cast billet after cooling.

[0018] Furthermore, in step 1.2, the rare earth element is added during the smelting process after the molten steel is melted, the temperature is controlled between 1400-1500°C, and the time is controlled within 10-15 minutes. A bell jar can be used to press the rare earth into the bottom of the molten steel, or an inert gas can be sprayed in to ensure that the rare earth element is fully dissolved and reacts with the molten steel.

[0019] In the second step, the ingot obtained in the first step is processed by hot rolling process, specifically, a combined rolling process of a roughing mill and a finishing mill is adopted, including rolling the ingot by the roughing mill and rolling the plate by the finishing mill, as follows:

[0020] Step 2.1, heating the smelted ingot in a walking beam heating furnace at 1220-1260° C. for 2-2.5 hours, so that the alloy elements and rare earth elements are basically dissolved in the steel matrix;

[0021] Step 2.2, rough rolling mill rolling treatment: after the ingot is descaled by high-pressure water after being taken out of the furnace, it enters the rough rolling mill for rolling and opening, and the opening rolling temperature is 1100-1180℃; the temperature of the intermediate ingot after rough rolling is ≥960℃.

[0022] Step 2.3, rolling treatment in the finishing mill: the intermediate billet then enters the finishing mill group for 7 passes of rolling, with the final rolling temperature being 860-900°C; it is coiled after laminar cooling, with the coiling temperature being 680-720°C, and finally a hot-rolled steel plate with a thickness of 2.5-3.2 mm is obtained.

[0023] The third step is to use a cold rolling process to treat the hot-rolled steel plate obtained in the second step, and cold-roll the steel plate to obtain a cold-rolled steel plate. Specifically, it includes pickling of the hot-rolled steel plate and cold-rolling of the steel plate, as follows:

[0024] Step 3.1, pickling of hot-rolled steel plate: The hot-rolled steel plate obtained in the second step is subjected to a high-temperature and low-speed pickling process, with the acid solution temperature being 85-90°C and the pickling speed being 100-120m / min, to remove surface oxide scale, slag and other contaminants, and finally obtain a steel plate with a smooth surface.

[0025] Step 3.2, cold rolling of the steel plate: the cold rolling reduction ratio of the cold rolling process is ≥50%, and the steel plate is cold rolled to the required specification size.

[0026] The fourth step is to heat treat the cold-rolled steel sheet obtained in the third step, specifically:

[0027] The steel plate is heated to 850-950℃, kept at this temperature for 5-10 minutes, and then rapidly cooled to room temperature at 60-80℃ / s to form a martensite structure. To increase the toughness of the steel, it is then tempered at 180-220℃, kept at this temperature for 20-30 minutes, and then cooled to room temperature at 40-60℃ / s.

[0028] The fifth step is to perform surface treatment (micro-ball shot peening) on ​​the heat-treated plate obtained in the fourth step, specifically:

[0029] The surface of the heat-treated steel plate is shot blasted with 0.2mm diameter tungsten-gold micro-balls to refine the coarse grains on the surface and remove the oxide scale generated during the heat treatment process. This improves the surface hardness while effectively removing the surface residual stress, thereby improving the fatigue resistance and surface finish of the steel.

[0030] Beneficial effects of the present invention:

[0031] (1) The present invention achieves grain refinement and effectively removes oxides, sulfides, hydrogen, non-metallic inclusions, etc. by adding rare earth elements, thereby significantly improving the strength and toughness of automobile steel, so that the final product can meet high strength requirements while maintaining good elongation and impact toughness.

[0032] (2) The present invention further refines the surface grains of steel, removes oxide scale and surface residual stress through micron-level tungsten-gold micro-ball shot blasting surface treatment, and improves the strength, fatigue resistance and corrosion resistance of steel.

[0033] (3) In addition, the production method of the present invention is simple and easy to implement, does not require special equipment, and can be implemented on a traditional steel production line. By reasonably controlling various process parameters, the performance indicators of the high-strength and high-toughness automotive steel finally obtained can reach the advanced level at home and abroad, thereby providing a more efficient and economical material solution for automobile manufacturing.

[0034] In summary, the innovative method provided by the present invention not only helps to promote the development of the automotive industry, but also provides new ideas and methods for technological progress in related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the hot rolling process curve diagram of Example 1;

[0036] Figure 2 This is a SEM morphology image of the steel of Example 1 obtained by rapid cooling at 60°C / s after solid solution at 850°C;

[0037] Figure 3 It is the hot rolling process curve diagram of Example 2;

[0038] Figure 4 This is a SEM morphology image of the steel material of Example 2 obtained after solution treatment at 950°C and cooling at 80°C / s. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with specific implementation cases.

[0040] The chemical composition of the selected steel in Example 1 is as follows: C: 0.22%, Si: 1.0%, Mn: 1.9%, Cr: 0.45%, Mo: 0.16%, Ti: 0.035%, V: 0.01%, Al: 0.12%, RE (any one of cerium, lanthanum, etc. or a combination thereof): 0.11%, S: 0.005%, P: 0.010%, and the remainder is Fe and unavoidable inclusions.

[0041] Table 1 Chemical composition of Example 1 (wt%)

[0042]

[0043] The preparation method is as follows:

[0044] Molten steel with the above alloy composition is smelted in an electric arc furnace at a temperature of 1510°C. After the molten steel is melted, rare earth elements are gradually added for 3 hours, and electromagnetic stirring is used to ensure uniform dispersion and full dissolution, and the stirring time is 10 minutes. Argon protection is used to reduce the impurity content and ensure the purity of the molten steel. Subsequently, the molten metal is cast into a preheated mold and cooled to room temperature to obtain a cast billet.

[0045] The ingot is heated to 1240℃ and kept at this temperature for 2.5 hours to achieve uniform solid solution of alloy elements. Then hot rolling is carried out with the start rolling temperature at 1140℃; the intermediate billet temperature after rough rolling is 1000℃, and then it enters the finishing mill for 7 passes with the final rolling temperature at 865℃; it is coiled after laminar cooling with the coiling temperature at 685℃, and finally rolled to a hot rolled plate with a thickness of 3mm.

[0046] Table 2 Example 1 Hot rolling heating system and temperature control range

[0047]

[0048] The hot-rolled plate is cold rolled, and the reduction rate is controlled at 62% to improve the strength and toughness of the plate. The pickling process is adopted: the pickling temperature is 70℃, the acid liquid temperature is 90℃, and the pickling speed is 120m / min.

[0049] Table 3 Example 1 Pickling Process Table

[0050]

[0051] The cold rolled sheet was fully austenitized by heating to 900°C for 5 minutes and then rapidly cooled to room temperature at 60°C / s to form a martensite structure. To increase the toughness of the steel, it was subsequently tempered at 200°C for 25 minutes to release internal stress and improve plasticity.

[0052] Table 4 Mechanical properties of Example 1 without tempering

[0053]

[0054] Table 5 Mechanical properties of Example 1 after tempering (200°C, 25min)

[0055]

[0056] The tensile strength test results of the high-strength and high-toughness automotive steel prepared without tempering and after tempering were both 1935MPa and 1950MPa, and the elongation test results were 12.3% and 12.8%, which meet the requirements of the automotive industry for ultra-high strength steel.

[0057] The steel surface is subsequently treated with 0.2mm diameter tungsten-gold micro-ball shot blasting to refine the coarse grains on the surface and remove the oxide scale produced during the process, thereby increasing the hardness by 2-3HRC. At the same time, the surface residual stress is effectively removed, and the fatigue resistance and surface finish of the steel are improved.

[0058] The chemical composition of the materials selected in Example 2 is as follows: C: 0.28%, Si: 1.3%, Mn: 1.9%, Cr: 0.55%, Mo: 0.12%, Ti: 0.028%, V: 0.015%, Al: 0.15%, RE (any one of cerium, lanthanum, neodymium, etc. or a combination thereof): 0.38%, S: 0.003%, P: 0.010%, and the remainder is Fe and unavoidable inclusions.

[0059] Table 6 Chemical composition of Example 2 (wt%)

[0060]

[0061] The preparation method is as follows:

[0062] Prepare the raw materials according to the above chemical components, use an electric arc furnace for smelting, set the smelting temperature to 1550℃, and keep it for 2.5 hours to ensure that the alloy elements are fully mixed and dissolved. The rare earth element lanthanum is added in small doses after the steel liquid is melted, and electromagnetic stirring is used to ensure uniform dispersion. The stirring time is controlled within 15 minutes. Subsequently, the molten metal is cast into a preheated mold and cooled to room temperature to obtain a cast billet.

[0063] The ingot is heated to 1200℃ and kept at this temperature for 1.5 hours to achieve uniform solid solution of alloy elements. Then hot rolling is carried out with the starting rolling temperature at 1100℃ and the final rolling temperature at 860℃. After laminar cooling, coiling is carried out with the coiling temperature at 680℃, and finally rolled into a hot-rolled plate with a thickness of 2.5mm.

[0064] Table 7 Example 2 Hot rolling heating system and temperature control range

[0065]

[0066] The hot-rolled steel plate was cold rolled with a reduction rate of 65%, and a high-temperature and low-speed pickling process was adopted: the pickling temperature was 70-80°C, the acid solution temperature was 90°C, and the pickling speed was 120m / min.

[0067] Table 8 Example 2 Pickling Process Table

[0068]

[0069] The cold-rolled steel is heated to 950°C and maintained for 5 minutes to promote the solid solution of alloy elements. It is rapidly cooled to room temperature at 80°C / s to form an austenite structure. It is then tempered at 180°C for 30 minutes to improve the toughness of the steel.

[0070] Table 9 Mechanical properties of Example 2 without tempering treatment

[0071]

[0072] Table 10 Mechanical properties of Example 2 after tempering (180°C, 30min)

[0073]

[0074] The tensile strength test results of the high-strength and high-toughness automotive steel finally prepared were 1923MPa and 1908MPa, and the elongation test results were 12% and 12.5%, meeting the requirements of the automotive industry for ultra-high-strength steel.

[0075] By subsequently subjecting the steel surface to 0.2mm diameter tungsten-gold micro-ball shot blasting treatment, the coarse surface grains are refined, the oxide scale produced during the process is removed, and the hardness is increased by 2-3HRC. At the same time, the surface residual stress is effectively removed, and the fatigue resistance and surface finish of the steel are improved.

[0076] The chemical composition of the materials selected in Example 3 is as follows: C: 0.26%, Si: 1.23%, Mn: 2.05%, Cr: 0.58%, Mo: 0.15%, Ti: 0.026%, V: 0.015%, Al: 0.15%, RE (any one of cerium, lanthanum, neodymium, etc. or a combination thereof): 0.45%, S: 0.004%, P: 0.010%, and the remainder is Fe and unavoidable inclusions.

[0077] Table 11 Chemical composition of Example 3 (wt%)

[0078]

[0079] The preparation method is as follows:

[0080] Prepare the raw materials according to the above chemical components, use an electric arc furnace for smelting, set the smelting temperature to 1580℃, and keep it for 3 hours to ensure that the alloy elements are fully mixed and dissolved. The rare earth element lanthanum is added in small doses after the steel liquid is melted, and electromagnetic stirring is used to ensure uniform dispersion. The stirring time is controlled within 15 minutes. Subsequently, the molten metal is cast into a preheated mold and cooled to room temperature to obtain a cast billet.

[0081] The ingot was heated to 1220°C and kept at this temperature for 1.5 hours to achieve uniform solid solution of alloy elements. It was then hot rolled with a starting rolling temperature of 1110°C and a final rolling temperature of 900°C. It was coiled after laminar cooling at a coiling temperature of 690°C and finally rolled to a hot rolled plate with a thickness of 2.5 mm.

[0082] Table 12 Example 3 Hot rolling heating system and temperature control range

[0083]

[0084] The hot-rolled steel plate was cold rolled with a reduction rate of 65%, and a high-temperature and low-speed pickling process was adopted: the pickling temperature was 70-80°C, the acid solution temperature was 90°C, and the pickling speed was 120m / min.

[0085] Table 13 Example 3 Pickling Process Table

[0086]

[0087] The cold-rolled steel is heated to 950°C and maintained for 5 minutes to promote the solid solution of alloy elements. It is rapidly cooled to room temperature at 80°C / s to form an austenite structure. It is then tempered at 180°C for 30 minutes to improve the toughness of the steel.

[0088] Table 14 Mechanical properties of Example 3 without tempering treatment

[0089]

[0090] Table 15 Mechanical properties of Example 3 after tempering (180°C, 30min)

[0091]

[0092] The tensile strength test results of the high-strength and high-toughness automotive steel finally prepared were 1934MPa and 1916MPa, and the elongation test results were 12.3% and 12.5%, meeting the requirements of the automotive industry for ultra-high-strength steel.

[0093] The steel surface is subsequently treated with 0.2mm diameter tungsten-gold micro-ball shot blasting to refine the coarse grains on the surface and remove the oxide scale produced during the process, thereby increasing the hardness by 2-3HRC. At the same time, the surface residual stress is effectively removed, and the fatigue resistance and surface finish of the steel are improved.

[0094] In this embodiment, by adding rare earth elements and precisely controlling each process link, the preparation of high-strength and high-toughness automotive steel is achieved, which has excellent mechanical properties and processing properties and meets industry standards and market demands.

[0095] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high-strength and high-toughness automobile wheel steel added with rare earth elements, characterized in that: The chemical composition of the high-strength and high-toughness automobile wheel steel includes, by weight percentage, C: 0.15-0.30%, Si: 0.5-1.5%, Mn: 1.5-2.5%, Cr: 0.3-0.6%, Mo: 0.1-0.3%, Ti: 0.02-0.05%, V: 0.01-0.20%, Al: 0.01-0.20%, RE: 0.05-0.5%, S≤0.005%, P≤0.010%, and the remainder is Fe and inevitable inclusions; the RE is one of cerium and lanthanum or a combination thereof; and the synergistic change relationship of each element is determined based on the cluster method.

2. The high-strength and high-toughness automobile wheel steel with rare earth elements added thereto according to claim 1, characterized in that: Calculated by mass percentage, the synergistic variation relationship of the elements in the high-strength and high-toughness automobile wheel steel satisfies: 1.50≤Mn≤2.50; 1.32≤Cr+1.83Si+0.54Mo+1.92Al+1.09Ti+1.02V≤4.15; 94.67≤Fe≤96.

58.

3. The high-strength and high-toughness automobile wheel steel with rare earth elements added thereto according to claim 1, characterized in that: The chemical composition includes matrix elements, Ni-like elements that enter cluster form, Cr-like elements, trace elements that do not enter cluster form, and rare earth elements, wherein the matrix element is Fe, the Ni-like element that enters cluster form is Mn, the Cr-like elements include Cr, Si, Mo, Al, Ti, and V, and the trace elements that do not enter cluster form include C, S, P, and RE.

4. The high-strength and high-toughness automobile wheel steel with rare earth elements added thereto according to claim 1, characterized in that: The high-strength and high-toughness automobile wheel steel has a yield strength of ≥1400MPa, a tensile strength of ≥1900MPa, and an elongation of ≥12%.

5. A method for preparing the high-strength and high-toughness automobile wheel steel with rare earth elements added thereto according to any one of claims 1 to 4, characterized in that: The preparation method includes smelting, hot rolling, cold rolling, heat treatment, and surface treatment. The following steps are involved: The first step is to prepare slab products by smelting method, specifically: Step 1.1, smelting in an electric arc furnace to obtain molten steel with chemical composition meeting the requirements; Step 1.2, gradually adding rare earth elements to the molten steel, stirring during the addition process and using argon protection; Step 1.3, pouring the molten steel into a mold, and obtaining a casting after cooling; The second step is to use hot rolling process to process the ingot obtained in the first step, including rolling the ingot by the rough rolling mill and rolling the plate by the finishing rolling mill. Specifically: Step 2.1, heating the ingot obtained in the first step in a walking beam heating furnace at 1220-1260° C. for 2-2.5 hours, so that the alloy elements and rare earth elements are basically dissolved in the steel matrix; Step 2.2, rough rolling mill rolling treatment: after the cast billet is descaled by high-pressure water after being taken out of the furnace, it enters the rough rolling mill for rolling and opening the billet, and the opening rolling temperature is 1100-1180℃; the temperature of the intermediate billet after rough rolling is ≥960℃; Step 2.3, finishing mill rolling treatment: the intermediate billet then enters the finishing mill group for multiple rolling passes, with the final rolling temperature being 860-900°C; laminar cooling is adopted and then coiling is performed, with the coiling temperature being 680-720°C, to obtain a hot-rolled steel plate; The third step is to use a cold rolling process to process the hot-rolled steel sheet obtained in the second step to obtain a cold-rolled steel sheet; specifically: Step 3.1, pickling the hot-rolled steel plate: the hot-rolled steel plate obtained in the second step is pickled by a high-temperature and low-speed pickling process to obtain a steel plate with a smooth surface; Step 3.2, cold-rolled steel plate: obtain the required specifications and dimensions; The fourth step is to heat treat the cold-rolled steel sheet obtained in the third step; The fifth step is to perform surface treatment on the heat-treated plate obtained in the fourth step to obtain high-strength and high-toughness steel for automobile wheels.

6. The method for preparing a high-strength and high-toughness automobile wheel steel with rare earth elements added thereto according to claim 5, characterized in that: The first step is specifically: In the step 1.1, the smelting temperature is controlled between 1500°C and 1600°C; In the step 1.2, the rare earth element is gradually added into the molten steel by pressing or spraying; In the step 1.2, the rare earth element is added after the molten steel is melted, the temperature is controlled between 1400-1500° C., and the time is controlled within 10-15 minutes.

7. The method for preparing a high-strength and high-toughness automobile wheel steel with rare earth elements added thereto according to claim 5, characterized in that: In the second step 2.3, the finishing mill performs rolling treatment through seven passes.

8. The method for preparing a high-strength and high-toughness automobile wheel steel with rare earth elements added thereto according to claim 5, characterized in that: The third step is specifically as follows: In the step 3.1, the acid solution temperature of the high temperature and low speed pickling process is 85-90°C, and the pickling speed is 100-120m / min; In the step 3.2, the cold rolling reduction ratio of the cold rolling is ≥50%.

9. The method for preparing a high-strength and high-toughness automobile wheel steel with rare earth elements added thereto according to claim 5, characterized in that: The heat treatment in the fourth step is specifically as follows: heating the cold-rolled steel plate obtained in the third step to 850-950°C, keeping it at this temperature for 5-10 minutes, and then rapidly cooling it to room temperature at a rate of 60-80°C / s to form a martensitic structure; and then subjecting it to tempering treatment at a temperature of 180-220°C, keeping it at this temperature for 20-30 minutes, and then cooling it to room temperature at a rate of 40-60°C / s.

10. The method for preparing a high-strength and high-toughness automobile wheel steel with rare earth elements added thereto according to claim 5, characterized in that: The surface treatment in the fifth step is micro-ball shot peening, specifically, the surface of the steel plate after the heat treatment in the fourth step is subjected to 0.2 mm diameter tungsten gold micro-ball shot peening.

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