Preparation method of ultra-fine grain wear-resistant steel based on austenite inverse phase change regulation and control

Abstract

The invention discloses a preparation method of ultra-fine grain wear-resistant steel based on austenite inverse phase change regulation and control, and belongs to the technical field of ferrous metallurgy. According to the method, a large amount of metastable austenite or reversed austenite is reserved after low-temperature controlled rolling of the medium manganese steel, the ferrite-austenite inverse phase transformation behavior is induced in the subsequent reheating process, and the heating rate and the annealing temperature interval are accurately controlled, so that austenite high-density nucleation is promoted, grain growth is inhibited, and the yield of the medium manganese steel is improved. The average grain size of the ultrafine equiaxed austenite structure is less than or equal to 3 microns. And then quenching to obtain a fine grain martensite matrix, and carrying out low-temperature tempering treatment to finally obtain the wear-resistant steel with high strength, high hardness and excellent low-temperature toughness. The technical bottleneck that thick plate austenite grains are difficult to refine in a traditional heat treatment process is broken through, the grain ultra-refinement path taking back as the advance is achieved, and the method is suitable for industrial production of the medium-thick-specification wear-resisting steel plate and has the advantages of being simple in process, controllable in cost, stable in performance and the like.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a method for preparing ultrafine-grained wear-resistant steel based on austenite inverse phase transformation control, and particularly to a technique for achieving ultrafine austenite grains by controlling rolling to retain metastable austenite and combining it with precise inverse phase transformation annealing. Background Technology

[0002] With the development of heavy equipment, mining machinery, and engineering machinery towards larger scale and higher efficiency, higher requirements are being placed on the service life and safety of wear-resistant steel. Traditional low-alloy martensitic wear-resistant steels (such as NM400 and NM450), while possessing high hardness, are prone to early brittle fracture under impact and wear conditions due to their coarse grains and insufficient toughness. Current technologies improve hardenability by adding precious alloying elements such as Ni, Cr, and Mo, or refine the microstructure using TMCP (controlled rolling and cooling) processes. However, due to the recrystallization behavior of austenite, the grains in the central region of thick plates still tend to coarsen, making it difficult to achieve uniform control of the ultrafine grain structure across the entire thickness.

[0003] Existing patented technologies, such as CN113462957A, propose introducing retained austenite through critical zone annealing pretreatment to improve toughness. However, its annealing temperature is relatively high (620–650℃), leading to martensite recovery and softening, resulting in a decrease in hardness. CN114351053A uses normalizing and tempering processes to obtain ultrafine-grained martensite, but this relies on high Ti content for its formation. TiC Particle reinforcement is costly and has poor weldability; CN113388787A uses nanotwins to reinforce austenitic steel, which has high strength but complex plasticity matching; CN114686774A proposes nanoprecipitation-reinforced dual-phase steel, but it has high Co and Ni content, is expensive, and is not suitable for large-scale industrial applications.

[0004] The following problems exist in the existing wear-resistant steel preparation technology: 1. Traditional heat treatment processes are difficult to achieve ultra-fine austenite grains, especially in medium and thick plates, where the core structure is coarse, resulting in large martensite lath bundles and poor toughness; 2. Existing reverse phase transformation processes are mostly used to increase the content of residual austenite, without fully utilizing its potential in grain refinement; 3. High alloy design leads to increased costs and deteriorated welding performance, limiting engineering applications.

[0005] Therefore, there is an urgent need to develop a new method for preparing wear-resistant steel that does not require expensive alloys, has a simple process, and can achieve ultra-fine austenitic grains, in order to solve the technical problems of coarsening grains and mismatch between strength and toughness in thick plates. Summary of the Invention

[0006] This invention addresses the technical problems existing in the prior art by providing a simple, industrially scalable method for preparing ultrafine-grained wear-resistant steel that eliminates the need for expensive alloys. This method achieves ultrafine austenite grains, resulting in high-strength, high-toughness, high-wear-resistance, and uniformly structured wear-resistant steel. The method provided by this invention, based on austenite reverse phase transformation control, is achieved through the following technical solution: A method for preparing ultrafine-grained wear-resistant steel based on austenite inverse phase transformation includes the following steps: (1) Smelting and casting: smelting and casting steel raw materials to obtain billets; (2) Controlled rolling treatment: The billet is heated to 1050-1200℃, held for 1-3 hours and then controlled rolling is performed. The initial rolling temperature is 950-1100℃, the final rolling temperature is 750-850℃, the total reduction rate is ≥60%, and the billet is air-cooled to room temperature after rolling to obtain a hot-rolled structure containing 5%-15% metastable austenite by volume. (3) First low-temperature tempering: The steel plate obtained in step (2) is subjected to low-temperature tempering treatment. The tempering temperature is 300-450℃, the holding time is 30-120 minutes, and it is air-cooled to stabilize the structure and regulate the reverse phase transformation driving force. (4) Reverse phase transformation annealing: The steel plate obtained in step (3) is heated to 650-800℃ at a heating rate of 5-50℃ / min and held for 10-60 minutes to carry out reverse phase transformation annealing treatment, so that ferrite undergoes reverse phase transformation to austenite and an ultrafine austenite structure with an average grain size ≤3μm is obtained. (5) Quenching treatment: The steel plate obtained in step (4) is quenched to room temperature at a cooling rate of ≥20℃ / s to obtain a fine-grained martensite structure. (6) Second low-temperature tempering: The steel plate obtained in step (5) is subjected to low-temperature tempering at a temperature of 200-350°C, held for 60-180 minutes, and then air-cooled to obtain the ultrafine-grained wear-resistant steel.

[0007] Further preferably, the chemical composition of the steel raw material, by mass percentage, is: C: 0.15-0.30%, Si: 0.20-0.80%, Mn: 4.0-7.0%, P≤0.015%, S≤0.008%, Al: 0.01-0.05%, with the balance being Fe and unavoidable impurities.

[0008] Further preferably, the steel raw material also includes one or more microalloying elements: Ti: 0.01-0.05%, Nb: 0.02-0.06%, V: 0.05-0.15%, Mo: 0.10-0.40%, Ni: 0.5-1.5%.

[0009] Further optimization is that the final rolling temperature in step (2) is controlled at 780 to 830°C so that the microstructure after rolling retains 5% to 15% metastable austenite or reverse austenite by volume.

[0010] Further preferred, the heating rate of the reverse phase transformation annealing treatment in step (4) is 10-30℃ / min, the holding temperature is 700-780℃, and the holding time is 20-40 minutes.

[0011] Further preferably, the heating rate in step (4) is 10–30 °C / min, the holding temperature is 700–780 °C, and the holding time is 20–40 minutes, so that the nucleation density of the reverse austenite transformation reaches 10. 8 ~10¹ 0 pcs / mm³.

[0012] Further preferred, the quenching in step (5) is carried out by water cooling or spray cooling, with a cooling rate ≥20℃ / s, to ensure complete martensitic phase transformation.

[0013] Further optimization, the microstructure of the wear-resistant steel obtained after low-temperature tempering in step (6) is lath martensite + retained austenite, wherein the average size of the martensite lath bundles is ≤3μm and the volume fraction of retained austenite is 3%~10%.

[0014] Further preferred, the microstructure of the wear-resistant steel is lath martensite + retained austenite, the average size of the martensite lath bundles is ≤3μm, and the volume fraction of retained austenite is 3% to 10%.

[0015] Further preferred, the ultrafine-grained wear-resistant steel has a yield strength of 1100-1300 MPa, a tensile strength of ≥1400 MPa, a surface hardness of 450-500 HBW, and a Charpy impact energy of ≥30 J at -20℃.

[0016] More specifically, a method for preparing ultrafine-grained wear-resistant steel based on austenite reverse phase transformation includes the following steps: (1) Smelting and casting The steel is prepared and smelted according to the following composition (wt.%): C: 0.15–0.30%, Si: 0.20–0.80%, Mn: 4.0–7.0%, P≤0.015%, S≤0.008%, Al: 0.01–0.05%, with optional addition of microalloying elements such as Ti, Nb, V, Mo, and Ni, and the balance being Fe and unavoidable impurities. The steel is smelted in an electric arc furnace or converter, refined by LF refining and RH vacuum degassing to obtain pure molten steel, which is then continuously cast or ingot cast into billets with a thickness of 30–200 mm, suitable for subsequent rolling.

[0017] (2) Controlled rolling treatment The billet is heated to 1050–1200℃ and held for 1–3 hours to ensure complete solution dissolution of the alloying elements. The initial rolling temperature is controlled at 950–1100℃, and the final rolling temperature is 750–850℃, with a total reduction of ≥60%. After rolling, it is air-cooled to room temperature. This process aims to obtain a fine ferrite / bainite structure while retaining 5%–15% metastable austenite or reverse-transformed austenite, providing a high-density nucleation core for subsequent reverse transformation.

[0018] (3) First low-temperature tempering The hot-rolled plate is tempered at 300–450℃ for 30–120 minutes and then air-cooled. This step can eliminate some residual stress, stabilize metastable austenite, regulate carbon distribution, and provide a uniform microstructure for the reverse phase transformation.

[0019] (4) Reverse phase transformation annealing The tempered steel plate is heated to 650–800°C at a heating rate of 5–50°C / min, held for 10–60 minutes, and then air-cooled. Rapid heating (e.g., 10–30°C / min) can suppress the early nucleation of coarse austenite in the low-temperature region, allowing the system to accumulate greater phase transformation driving force at higher temperatures. 650–800°C is the thermodynamically favorable range for the transformation of ferrite to austenite, and at this temperature, the retained austenite is not completely dissolved, serving as an efficient nucleation site. A large amount of retained austenite exists per unit area, with low interfacial energy with ferrite, making it a preferred site for austenite nucleation, with a nucleation density reaching 10-1. 8 ~10 10 pcs / mm 3 Due to the dense nucleation sites, the newly formed austenite grains meet rapidly during growth, hindering grain boundary migration and ultimately forming ultrafine equiaxed austenite with an average size ≤3μm. The optimal grain refinement effect is achieved under the following conditions: heating rate 10–30℃ / min, annealing temperature 700–780℃, and holding time 20–40 min.

[0020] (5) Quenching treatment The steel sheet after reverse phase transformation annealing is quenched to room temperature at a cooling rate of ≥20℃ / s (such as water cooling or spray cooling) to obtain a fine-grained martensite structure. Due to the ultra-fine austenite grains, the resulting martensite lath bundles are also significantly refined.

[0021] (6) Second low-temperature tempering Temper at 200–350℃ for 60–180 minutes, then air cool. This eliminates quenching stress, precipitates fine carbides, and yields a stable tempered martensite + retained austenite microstructure.

[0022] The alloy composition in this invention has the following characteristics: (1) C: 0.15~0.30% As the main solid solution strengthening element, the carbon content needs to be sufficient to ensure a hardness ≥450 HBW after quenching, but it should not be too high to avoid the formation of coarse carbides or welding cracks. 0.20–0.25% is preferred.

[0023] (2) Mn: 4.0~7.0% Manganese is a strong austenite stabilizer, which can significantly lower the Ac3 temperature, expand the reverse transformation temperature window (650–800℃), and improve hardenability, ensuring that the core of thick plates can also be fully quenched. At the same time, Mn helps promote austenite nucleation during the reverse transformation process. The preferred concentration is 5.0–6.5%.

[0024] (3) Si: 0.20~0.80% Silicon inhibits carbide precipitation, promotes carbon enrichment in austenite, enhances its stability, and facilitates the TRIP effect. Simultaneously, Si can improve tempering resistance. However, excessive levels can lead to surface decarburization; therefore, the upper limit is controlled at 0.8%.

[0025] (4) Al: 0.01~0.05% Aluminum is a strong deoxidizer that can refine cast grains and combine with nitrogen to form AlN, which pins grain boundaries and inhibits austenite grain growth during high-temperature heating.

[0026] (5) Microalloying elements (optional): Nb, V: 0.02~0.15%: form carbonitrides, precipitation strengthens the structure, and at the same time refines the austenite grains; Mo: 0.10~0.40%: Improves hardenability and inhibits bainite transformation; Ni: 0.5~1.5%: Improves low-temperature toughness and lowers the ductile-brittle transition temperature, but it is expensive and can be added in appropriate amounts.

[0027] P≤0.015%, S≤0.008%: Strictly control impurity content to avoid segregation and thermal brittleness.

[0028] Compared with the prior art, the present invention has the following significant advantages: Innovative Grain Refinement Mechanism: Those skilled in the art generally believe that reverse transformation is primarily used to increase the residual austenite content to improve toughness, rather than for grain refinement, because austenite grains tend to coarsen during the reverse transformation process. This paper proposes and applies a "reverse transformation-induced ultrafine austenite" strategy, breaking through the traditional recrystallization refinement limit and achieving austenite grains ≤3μm, providing a microstructure basis for high-strength, high-toughness, and wear-resistant steel. By precisely controlling the heating rate and holding temperature, the metastable austenite remaining after hot rolling is used as a high-density nucleation site to induce a "ferrite → austenite" reverse transformation. Rapid heating suppresses early coarse austenite nucleation, while the mid-temperature range (700–780℃) provides sufficient driving force to promote the nucleation of a large number of fine austenite grains. This process can achieve ultrafine austenite grains with an average size ≤3μm.

[0029] Excellent comprehensive performance: The prepared wear-resistant steel has a yield strength ≥1100MPa, tensile strength ≥1400MPa, hardness 450~500HBW, and impact energy ≥30J at -20℃. Its strength and toughness are better than those of traditional NM450 steel.

[0030] Cost advantage: It does not require expensive alloys such as Ni, Co, and Mo, and mainly relies on Mn, C, and microalloying elements, resulting in low cost and suitability for large-scale production.

[0031] High process compatibility: It is suitable for existing medium and heavy plate production lines, requiring only the addition of a precise temperature-controlled annealing process, making it easy to promote industrialization.

[0032] Good uniformity of structure: The reverse phase transformation process is carried out synchronously throughout the entire cross section, avoiding the problem of grain coarsening in the core of thick plates and achieving uniform performance across the entire thickness. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the process flow for the preparation method of ultrafine-grained wear-resistant steel based on austenite reverse phase transformation control involved in this invention. Figure 2 This is a microscopic tissue SEM image (288x) of Example 5 of the present invention. Figure 3 This is a microscopic tissue SEM image (704x) of Example 5 of the present invention. Figure 4 This is a microscopic tissue SEM image (1010x) of Example 5 of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, in the following description, specific details such as particular system structures and techniques are set forth for illustrative purposes rather than for limiting purposes, in order to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the art should understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary details.

[0036] This invention provides a method for preparing ultrafine-grained wear-resistant steel based on austenite inverse phase transformation. The following examples further illustrate this invention, but the invention is not limited to these examples.

[0037] This invention relates to a method for preparing ultrafine-grained wear-resistant steel based on austenite reverse phase transformation and the prepared ultrafine-grained wear-resistant steel. By rationally designing the medium-manganese steel composition, combining controlled rolling process to retain metastable austenite, and performing reverse phase transformation annealing in a low-temperature range to induce the phase transformation of ferrite to austenite, significant refinement of austenite grains (average size ≤3μm) is achieved. Subsequently, quenching and low-temperature tempering treatments are performed to obtain a composite microstructure with fine-grained martensite as the matrix and containing an appropriate amount of stable retained austenite, fully utilizing the TRIP effect to significantly improve the strength, toughness, and wear resistance of the material.

[0038] In this embodiment of the invention, a continuously cast slab is used, which is heated, controlled rolled, and air-cooled before undergoing reverse phase transformation annealing and tempering. The billet heating temperature is 1120–1200℃, and the furnace time is controlled at 1.5–2.0 min / mm; the initial rolling temperature is 1000–1100℃, the final rolling temperature is 780–850℃, and the billet is air-cooled to room temperature after rolling.

[0039] The reverse phase transformation annealing process is the core technology of this invention: the heating temperature is controlled at 680-780℃, the heating rate is 10-40℃ / min, the holding time is 20-60min, and then air-cooled or rapidly cooled to room temperature; the tempering temperature is 260-340℃, the holding time is 1.2-2.0min / mm, and then air-cooled.

[0040] This invention includes 10 embodiments and 4 comparative examples to verify the rationality of the components and processes and the superiority of the technical effects.

[0041] (I) Chemical composition of steel in the example Table 1 Chemical composition (wt%) of steel in the embodiments of the present invention, balance being Fe and unavoidable impurities. (II) Main hot rolling process parameters of the steel in the example Table 2 Main hot rolling process parameters of the steel in the examples (III) Heat treatment process parameters of the steel in the example Table 3 Heat treatment process parameters for the steel in the examples (iv) Chemical composition of the comparative steel Table 4 Chemical composition (wt%) of comparative steels, balance being Fe and unavoidable impurities. (v) Production process of comparative steel Table 5 Production process of comparative steel (vi) Mechanical properties and microstructure of the steels in the examples and comparative examples Table 6 Mechanical properties and microstructure of the steels in the examples and comparative examples Table 6 shows that the steels in the 10 examples are significantly superior to the steels in the 4 comparative examples in terms of both mechanical properties and microstructure. In terms of mechanical properties, the yield strength of the examples (1160-1310 MPa) and tensile strength (1430-1570 MPa) are approximately 9.4%-16.8% and 3.4%-8.3% higher than the comparative examples (1060-1130 MPa and 1380-1450 MPa), respectively, and the elongation after fracture is 13.0%-15.8%. The impact energy at -20℃ was 31-44 J, significantly better than the comparative examples' 11.0%-12.2% and 15-21 J. In terms of microstructure, the average martensite lath bundle width of the examples was only 1.5-2.5 μm (compared to 11.5-13.0 μm in the comparative examples), the retained austenite content was 6.0%-8.5% (compared to 2.5%-3.2% in the comparative examples), and the hardness uniformity exceeded 98.9% (compared to 96.5%-96.8% in the comparative examples). This difference stems from the fact that the examples obtained a fine-grained martensite + retained austenite composite microstructure through a reverse phase transformation control process. The small martensite lath bundles improved strength (martensite lath size is a key control unit for tensile strength), and the retained austenite absorbed deformation energy through the TRIP effect, improving toughness. In contrast, the comparative examples, lacking key processes, resulted in a coarse microstructure and unbalanced performance.

[0042] (vii) Test results of wear resistance of the steel in the examples and comparative examples Table 7. Test results of wear resistance of the steels in the examples and comparative examples. Results Analysis: As shown in Table 7, the wear mass loss of all the steels in the examples was significantly lower than that of the comparative steels. Example 10 showed the smallest wear mass loss, at only 0.0379 g, while the comparative steel showed a wear mass loss as high as 0.0778 g. Regarding relative wear resistance, the steels in the examples exhibited 1.94-2.08 times the relative wear resistance of the comparative steels, indicating that the ultrafine-grained wear-resistant steel prepared in this invention has a significant advantage in wear resistance. This advantage is attributed to the refinement of austenite grains through rational composition design and a unique controlled rolling and reverse phase transformation annealing process, resulting in a fine-grained martensite + retained austenite composite structure with excellent strength and toughness. This fully utilizes the TRIP effect, effectively enhancing the material's resistance to wear.

[0043] In summary, this invention, through a synergistic design of "low-temperature controlled rolling → low-temperature tempering → reverse phase transformation annealing," rationally designs the composition of medium-manganese steel and combines controlled rolling and reverse phase transformation annealing processes, using reverse phase transformation as an active grain refinement tool to prepare ultrafine-grained wear-resistant steel with an average grain size ≤3μm. The tensile strength of the steels in the examples all exceed 1430MPa, the impact energy at -20℃ reaches 31-44J, the relative wear resistance is 1.94-2.08 times that of the comparative examples, and the hardness difference between the core and surface is less than 1.1%, exhibiting excellent microstructure uniformity. Furthermore, the process employed in this invention has good stability, enabling the stable production of high-performance wear-resistant steel plates with a thickness of 15-30mm, demonstrating high application value and broad market prospects in actual industrial production. This method is simple, low-cost, and industrially scalable, solving the industry problem of grain coarsening and strength-toughness mismatch in thick plates, and possesses significant economic benefits and application prospects.

[0044] In this patent application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, the phrase "comprising an element defined as..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for preparing ultrafine-grained wear-resistant steel based on austenite reverse phase transformation regulation, characterized in that, Includes the following steps: (1) Smelting and casting: smelting and casting steel raw materials to obtain billets; (2) Controlled rolling treatment: The billet is heated to 1050-1200℃, held for 1-3 hours and then controlled rolling is performed. The initial rolling temperature is 950-1100℃, the final rolling temperature is 750-850℃, the total reduction rate is ≥60%, and the billet is air-cooled to room temperature after rolling to obtain a hot-rolled structure containing 5%-15% metastable austenite by volume. (3) First low-temperature tempering: The steel plate obtained in step (2) is subjected to low-temperature tempering treatment. The tempering temperature is 300-450℃, the holding time is 30-120 minutes, and it is air-cooled to stabilize the structure and regulate the reverse phase transformation driving force. (4) Reverse phase transformation annealing: The steel plate obtained in step (3) is heated to 650-800℃ at a heating rate of 5-50℃ / min and held for 10-60 minutes to carry out reverse phase transformation annealing treatment, so that ferrite undergoes reverse phase transformation to austenite and an ultrafine austenite structure with an average grain size ≤3μm is obtained. (5) Quenching treatment: The steel plate obtained in step (4) is quenched to room temperature at a cooling rate of ≥20℃ / s to obtain a fine-grained martensite structure. (6) Second low-temperature tempering: The steel plate obtained in step (5) is subjected to low-temperature tempering at a temperature of 200-350°C, held for 60-180 minutes, and then air-cooled to obtain the ultrafine-grained wear-resistant steel.

2. The preparation method according to claim 1, characterized in that, The chemical composition of the steel raw material, by mass percentage, is as follows: C: 0.15-0.30%, Si: 0.20-0.80%, Mn: 4.0-7.0%, P≤0.015%, S≤0.008%, Al: 0.01-0.05%, with the balance being Fe and unavoidable impurities.

3. The preparation method according to claim 2, characterized in that, The steel raw material also includes one or more microalloying elements: Ti: 0.01-0.05%, Nb: 0.02-0.06%, V: 0.05-0.15%, Mo: 0.10-0.40%, Ni: 0.5-1.5%.

4. The preparation method according to claim 1, characterized in that, In step (2), the final rolling temperature is controlled at 780-830℃ so that the microstructure after rolling retains 5%-15% metastable austenite or reverse-transformed austenite by volume.

5. The preparation method according to claim 1, characterized in that, The heating rate of the reverse phase transformation annealing process in step (4) is 10-30℃ / min, the holding temperature is 700-780℃, and the holding time is 20-40 minutes.

6. The preparation method according to claim 5, characterized in that, The heating rate in step (4) is 10–30 °C / min, the holding temperature is 700–780 °C, and the holding time is 20–40 minutes, so that the nucleation density of austenite in reverse phase transformation reaches 10. 8 ~10 10 pcs / mm 3 .

7. The preparation method according to claim 1, characterized in that, The quenching in step (5) is carried out by water cooling or spray cooling, with a cooling rate of ≥20℃ / s, to ensure complete martensitic phase transformation.

8. The preparation method according to claim 1, characterized in that, The microstructure of the wear-resistant steel obtained after low-temperature tempering in step (6) is lath martensite + retained austenite, wherein the average size of the martensite lath bundles is ≤3μm and the volume fraction of retained austenite is 3%~10%.

9. An ultrafine-grained wear-resistant steel prepared by the method according to any one of claims 1 to 8, characterized in that, The microstructure of the wear-resistant steel is lath martensite + retained austenite, with an average size of martensite lath bundles ≤3μm and a volume fraction of retained austenite of 3% to 10%.

10. The ultrafine-grained wear-resistant steel according to claim 9, characterized in that, The ultrafine-grained wear-resistant steel has a yield strength of 1100-1300 MPa, a tensile strength of ≥1400 MPa, a surface hardness of 450-500 HBW, and a Charpy impact energy of ≥30 J at -20℃.

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