A low-cost, high-strength, high-low temperature toughness steel, its preparation method, and its products.

Abstract

This invention relates to a low-cost, high-strength, high- and low-temperature toughness steel, its preparation method, and products, belonging to the field of steel materials technology. It solves the problem in existing technologies where steel cannot simultaneously achieve both strength and low-temperature toughness. The high-strength, high- and low-temperature toughness steel comprises C: 0.15wt%–0.25wt%, Mn: 4.50wt%–5.50wt%, Al: 0.20wt%–2.90wt%, Cr: 0.010wt%–0.025wt%, P≤0.010wt%, S≤0.010wt%, with the balance being Fe. The steel contains relatively few alloying elements, resulting in a relatively simple composition and reduced production costs. Simultaneously, the obtained steel exhibits a tensile strength exceeding 1400MPa, a yield strength exceeding 865MPa, and an elongation after fracture exceeding 12%. At -40℃, the impact toughness Akv = 30–50J.

Description

Technical Field

[0001] This invention relates to the field of steel materials technology, and in particular to a low-cost, high-strength, high- and low-temperature toughness steel, its preparation method, and its products. Background Technology

[0002] Steel is one of the materials used to manufacture automotive and high-end equipment parts, and its performance directly affects the service life of these parts. Manganese steel is a commonly used type of steel. To achieve higher strength, a large number of alloying elements are often added to manganese steel. However, excessive addition of alloying elements increases costs and sacrifices some low-temperature safety. Therefore, low cost, high strength, and good low-temperature safety are key research directions for automotive steel, high-end equipment, and basic components, and are currently a research hotspot both domestically and internationally.

[0003] Currently, the manganese steel prepared in related studies can possess good low-temperature impact toughness, but its yield strength can only reach 500 MPa and its tensile strength is about 1000 MPa. Moreover, it contains a large number of alloys and types, making it unsuitable for the preparation of parts with higher requirements. Furthermore, it also suffers from problems such as high cost and metallurgical difficulty.

[0004] Therefore, a high-strength, high-low-temperature toughness steel is needed that combines high strength with low-temperature toughness and cost to meet the requirements of component manufacturing. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a low-cost, high-strength, high-low temperature toughness steel, its preparation method and products, which can obtain steel with high performance and low cost, while taking into account both high strength and high-low temperature toughness.

[0006] On the one hand, the present invention provides a low-cost, high-strength, high- and low-temperature toughness steel, which, by mass percentage, comprises C: 0.15wt% to 0.25wt%, Mn: 4.50wt% to 5.50wt%, Al: 0.20wt% to 2.90wt%, Cr: 0.010wt% to 0.025wt%, P≤0.010wt%, S≤0.010wt%, with the balance being Fe.

[0007] Furthermore, the low-cost, high-strength, high- and low-temperature toughness steel comprises, by mass percentage: C: 0.19wt%–0.22wt%, Mn: 4.90wt%–5.20wt%, Al: 0.45wt%–2.40wt%, Cr: 0.015wt%–0.021wt%, P≤0.010wt%, S≤0.010wt%, with the balance being Fe.

[0008] Furthermore, the microstructure of the low-cost, high-strength, high-temperature and high-temperature toughness steel is martensite and a small amount of carbides.

[0009] On the other hand, the present invention provides a method for preparing low-cost, high-strength, high- and low-temperature toughness steel, comprising the following steps:

[0010] S1: Smelting: According to the composition ratio, smelting is carried out in a vacuum induction furnace to obtain ingots;

[0011] S2: Forging: Heat the ingot to 1150-1220℃ and hold for 3-15 hours; cool it down to 1050-1150℃ and forge to obtain a forging.

[0012] S3: Rolling: The forging is heated to 1050-1150℃ and held for 1-3 hours. Then the heated forging is rolled to obtain a plate.

[0013] S4: Heat treatment: The plate is heated to 750℃-950℃ in a high-temperature heating furnace and held for 0.5-2 hours, and then oil-quenched or water-quenched to room temperature to obtain low-cost, high-strength, high-low temperature toughness steel.

[0014] Furthermore, the low-cost, high-strength, high-temperature and high-toughness steel has a tensile strength of over 1400 MPa and a yield strength of over 865 MPa.

[0015] Furthermore, the low-cost, high-strength, high-temperature and high-temperature toughness steel has a room temperature impact toughness Akv = 40~70J and an impact toughness Akv = 30~50J at -40℃.

[0016] Furthermore, the low-cost, high-strength, high- and low-temperature toughness steel after heat treatment is heated to 150-250℃ and held at that temperature for 1-3 hours.

[0017] Furthermore, the low-cost, high-strength, high-temperature and high-toughness steel has a tensile strength of over 1400 MPa and a yield strength of over 1000 MPa.

[0018] Furthermore, the low-cost, high-strength, high-temperature and high-temperature toughness steel has a room temperature impact toughness Akv = 60~85J and an impact toughness Akv = 45~65J at -40℃.

[0019] Thirdly, the present invention provides an article obtained by preparing the low-cost, high-strength, high- and low-temperature toughness steel described in the present invention, the article including parts for automobiles and high-end equipment.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. The high-strength, high-low temperature toughness steel provided by this invention has a relatively small content and variety of alloying elements, and its composition is relatively simple. Besides the necessary Mn and Al elements found in Fe-Mn-Al-C steels, it only contains very low amounts of Cr, greatly reducing production costs. Furthermore, performance testing shows that the obtained high-strength, high-low temperature toughness steel has a tensile strength exceeding 1400 MPa, a yield strength exceeding 865 MPa, and an elongation after fracture exceeding 12%. At room temperature, its impact toughness Akv = 40–70 J; at -40℃, its impact toughness Akv = 30–50 J, enabling the manufacture of parts with high performance requirements.

[0022] 2. The high-strength, high-low temperature toughness steel provided by this invention is obtained through smelting, forging, rolling and heat treatment. The preparation method is relatively simple and easy to control. When combined with simple components, the resulting high-strength, high-low temperature toughness steel can simultaneously take into account both strength and low-temperature toughness.

[0023] 3. In the heat treatment process, quenching is first used, followed by short-time tempering at low temperature. While the tensile strength remains unchanged, the yield strength can be increased to more than 1000MPa, and the low-temperature toughness is also improved. The room temperature impact toughness Akv = 60~85J, and the impact toughness at -40℃ Akv = 45~65J.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0026] Figure 1 Image (a) is a SEM image of the impact fracture surface in Example 1;

[0027] Figure 1 Image (b) is a SEM image of the tensile fracture surface in Example 1;

[0028] Figure 1 Image (c) is a TEM tissue diagram of Example 1;

[0029] Figure 1 Image (d) is a SEM image of the impact fracture surface in Example 2;

[0030] Figure 1Image (e) shows the SEM morphology of the tensile fracture surface in Example 2.

[0031] Figure 1 Image (f) is a TEM tissue diagram of Example 2;

[0032] Figure 1 Image (g) is a SEM image of the impact fracture surface in Example 3;

[0033] Figure 1 Image h is a SEM image of the tensile fracture surface in Example 3;

[0034] Figure 1 Image (i) is a TEM tissue diagram of Example 3;

[0035] Figure 2 Image (a) is a SEM image of the impact fracture surface in Example 4;

[0036] Figure 2 Image (b) is a SEM image of the tensile fracture surface in Example 4;

[0037] Figure 2 Image (c) is a TEM tissue diagram of Example 4;

[0038] Figure 2 Image (d) is a SEM image of the impact fracture surface in Example 5;

[0039] Figure 2 Image (e) is a SEM image of the tensile fracture surface in Example 5;

[0040] Figure 2 Image (f) is a TEM tissue diagram of Example 5;

[0041] Figure 2 Image (g) is a SEM image of the impact fracture surface in Example 6;

[0042] Figure 2 Image h is a SEM image of the tensile fracture surface in Example 6;

[0043] Figure 2 (i) is a TEM tissue diagram of Example 6. Detailed Implementation

[0044] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0045] In the manufacturing industry, on the one hand, there is a continuous pursuit of higher performance to meet the requirements of use in more demanding or harsher environments; on the other hand, there is a constant effort to control production costs and conserve resources. For example, in the production of high-strength, high- and low-temperature toughness steel, more alloys are added in order to obtain higher product performance, which leads to increased production costs. Moreover, the preparation process is not easy to control, or the performance cannot be balanced, often resulting in improved low-temperature toughness but reduced strength.

[0046] Therefore, the present invention provides a high-strength, high- and low-temperature toughness steel, comprising, by mass percentage: C: 0.15wt% to 0.25wt%, Mn: 4.50wt% to 5.50wt%, Al: 0.20wt% to 2.90wt%, Cr: 0.010wt% to 0.025wt%, P≤0.010wt%, S≤0.010wt%, with the balance being Fe.

[0047] Compared with existing technologies, the high-strength, high-low temperature toughness steel provided by this invention has fewer alloying elements and a simpler composition. Its preparation process is cost-effective. Besides the essential Mn and Al elements found in Fe-Mn-Al-C steels, it contains only a very low amount of Cr, resulting in relatively low cost. This invention uses fewer alloying elements, reducing production costs and saving resources. The combination of C, Mn, and Al achieves high hardenability and uniform quenched microstructure, ensuring high strength and high-low temperature toughness. Performance testing shows a tensile strength exceeding 1400 MPa, a yield strength exceeding 865 MPa, and an elongation after fracture of 12%. At room temperature, the impact toughness Akv = 40–70 J; at -40℃, the impact toughness Akv = 40–65 J, meeting the requirements for parts with high performance requirements.

[0048] In this invention, the alloying elements have the following functions:

[0049] Carbon (C): Carbon is the primary strengthening element in steel, responsible for interstitial solid solution strengthening, stabilizing and expanding the austenite region. When the C content is too low, the strength and low-temperature toughness do not achieve the expected strengthening effect; when the C content is too high, although the strength increases, the toughness decreases. To ensure that the resulting steel possesses both high strength and high toughness, this invention controls the C content between 0.15 wt% and 0.25 wt%.

[0050] Mn and Cr elements primarily improve the hardenability of steel and also have a solid solution strengthening effect, facilitating subsequent heat treatment. However, Mn and Cr elements expand the austenite region; excessively high Mn and Cr contents can form large carbide particles that segregate at grain and phase boundaries, leading to interfacial embrittlement and reducing the strength and toughness of the resulting steel. Therefore, this invention controls the Mn content between 4.5 wt% and 5.5 wt% and the Cr content between 0.01 wt% and 0.025 wt%.

[0051] Al element: Aluminum improves the hydrogen embrittlement resistance of steel; however, adding excessive Al can lead to a higher volume of ferrite or the formation of coarse ferrite and cementite at grain boundaries, thereby reducing the strength and plasticity of the steel. Therefore, this invention controls the Al content between 0.2 wt% and 2.9 wt%.

[0052] P element: The content of element P is controlled to ≤0.010wt% to avoid microsegregation of P element during the solidification of molten steel, reduce the delayed fracture sensitivity of steel, and thus ensure the strength and low temperature toughness of steel.

[0053] S element: The S content is controlled to ≤0.010wt% to avoid the formation of MnS inclusions by S and Mn elements, thereby reducing the impact of inclusions on the hot working properties of steel.

[0054] Furthermore, by mass percentage, it includes: C: 0.17wt% to 0.23wt%, Mn: 4.70wt% to 5.30wt%, Al: 0.35wt% to 2.70wt%, Cr: 0.013wt% to 0.023wt%, P≤0.010wt%, S≤0.010wt%, with the balance being Fe.

[0055] Furthermore, by mass percentage, it includes C: 0.19wt%–0.22wt%, Mn: 4.90wt%–5.20wt%, Al: 0.45wt%–2.40wt%, Cr: 0.015wt%–0.021wt%, P≤0.010wt%, S≤0.010wt%, with the balance being Fe.

[0056] This invention provides a method for preparing high-strength, high-low temperature toughness steel, comprising the following steps:

[0057] S1: Smelting: According to the composition ratio, smelting is carried out in a vacuum induction furnace to obtain ingots;

[0058] S2: Forging: Heat the ingot to 1150-1220℃ and hold for 3-15 hours; cool it down to 1050-1150℃ and forge to obtain a forging.

[0059] S3: Rolling: The forging is heated to 1050-1150℃ and held for 1-3 hours. Then the heated forging is rolled to obtain a plate.

[0060] S4: Heat treatment: The plate is heated to 750℃-950℃ in a high-temperature heating furnace and held for 0.5-2 hours, and then oil-quenched or water-quenched to room temperature to obtain low-cost, high-strength, high-low temperature toughness steel.

[0061] Compared with existing technologies, this invention prepares high-strength, high-low temperature toughness steel through smelting, forging, rolling and heat treatment. With the combination of elements such as C, Mn and Al, it not only achieves high hardenability and uniformity of quenched structure, but also inhibits the precipitation of carbides at grain boundaries during quenching. The resulting high-strength, high-low temperature toughness steel takes into account both strength and low-temperature toughness, and its tensile strength can reach more than 1400 MPa, its yield strength can reach more than 865 MPa, its room temperature impact toughness Akv = 40~70 J, and its impact toughness at -40℃ Akv = 30~50 J.

[0062] The smelting process employs vacuum induction melting, which strictly controls the S and P content to prevent the corrosion of S and P elements from reducing the low-temperature toughness of the steel. It is impossible to simultaneously achieve both the strength and low-temperature toughness of the steel.

[0063] Specifically, the ingot is heated to 1150-1220℃ and held at that temperature for 3-15 hours for homogenization.

[0064] During the forging process, the ingot is heated and kept at a constant temperature to carry out homogenization treatment. After forging, the uniform distribution of elements such as C, Mn, and Al and the microstructure are achieved, avoiding the problem of element segregation. This facilitates subsequent processes and ensures the performance of the steel, while taking into account both the strength and low-temperature toughness of the steel.

[0065] Specifically, the ingot is forged at a temperature of 1050-1150℃.

[0066] In this invention, the ingot can be prepared into a bar with a diameter of 20mm or 60mm, or a plate with a thickness of 20mm and a width of 150mm.

[0067] Specifically, the forging is heated to 1050-1150℃ and then rolled.

[0068] Preferably, the rolling temperature can be 1080-1150℃ or 1100-1150℃.

[0069] During the rolling process, the 20mm thick plate after forging is rolled to 12mm. Rolling can further refine the microstructure, allowing each grain to bond tightly, increasing the density of the steel, thereby improving the strength and low-temperature toughness of the steel.

[0070] During the heat treatment process, the rolled plate is heated and held at 750℃-950℃ for 0.5-2 hours, and then quenched, oil-quenched or water-quenched to room temperature. The resulting high-strength, high-low-temperature toughness steel is composed of martensite and a small amount of M3C type carbides, and it has both high strength and low-temperature toughness.

[0071] Specifically, the high-strength, high-low temperature toughness steel after heat treatment is heated to 150-250℃ and held at that temperature for 1-3 hours.

[0072] In this invention, high-strength, high-low temperature toughness steel is subjected to a short-time low-temperature treatment after heat treatment. This reduces the stress in the high-strength, high-low temperature toughness steel, increasing the yield strength while maintaining tensile strength. The tensile strength is above 1400 MPa, and the yield strength is above 1000 MPa. Furthermore, the toughness of the high-strength, high-low temperature toughness steel is also improved after the short-time low-temperature treatment. The room temperature impact toughness Akv of the high-strength, high-low temperature toughness steel is 60–85 J, and the impact toughness Akv at -40℃ is 45–65 J.

[0073] Preferably, the high-strength, high-low temperature toughness steel after heat treatment is heated to 150-200℃ and held at that temperature for 1-2 hours.

[0074] This invention provides an article of manufacture prepared from the high-strength, high-low temperature toughness steel obtained by this invention. The article includes parts for automobiles and high-end equipment, including but not limited to automobile A / B pillars, bolts and fasteners, etc., wherein the high-end equipment includes aerospace and marine transportation, etc.

[0075] To more clearly describe the present invention, Example 1 is further illustrated by the following embodiments and comparative examples.

[0076] A method for preparing high-strength, high- and low-temperature toughness steel includes the following steps:

[0077] S1: Smelting: According to the composition ratio, smelting is carried out in a 50kg vacuum induction furnace, and the casting is poured and cooled to room temperature to obtain an ingot with a diameter of 120mm.

[0078] The composition ratio is C: 0.19wt%, Mn: 5.01wt%, Al: 0.56wt%, Cr: 0.017wt%, P: 0.003wt%, S: 0.006wt%, with the balance being Fe;

[0079] S2: Forging: The ingot is heated to 1200℃ and held for 10 hours; then cooled to 1150℃ for forging to obtain a forging, which is a plate with a thickness of 20mm and a width of 150mm.

[0080] S3: Rolling: The forging is heated to 1150℃ and held for 2 hours. Then the heated forging is rolled to obtain a plate with a thickness of 12mm.

[0081] S4: Heat treatment: The plate is heated to 825°C in a high-temperature furnace and held for 1.8 hours, and then oil-quenched to room temperature to obtain high-strength, high-low temperature toughness steel.

[0082] Example 2

[0083] The preparation process of Example 2 is largely the same as that of Example 1, except that the chemical composition of Example 2 includes C: 0.20wt%, Mn: 5.07wt%, Al: 1.26wt%, Cr: 0.016wt%, P: 0.002wt%, S: 0.006wt%, with the balance being Fe;

[0084] Example 3

[0085] The preparation process of Example 3 is largely the same as that of Example 1, except that the chemical composition of Example 3 includes C: 0.21wt%, Mn: 5.20wt%, Al: 2.30wt%, Cr: 0.018wt%, P: 0.003wt%, S: 0.007wt%, with the balance being Fe;

[0086] Example 4

[0087] The preparation process of Example 4 is largely the same as that of Example 1, except that in Example 4, the heat-treated high-strength high-low temperature toughness steel is heated to 200°C and held at that temperature for 2 hours.

[0088] Example 5

[0089] The preparation process of Example 5 is largely the same as that of Example 2, except that in Example 5, the heat-treated high-strength high- and low-temperature tough steel is heated to 200°C and held at that temperature for 2 hours.

[0090] Example 6

[0091] The preparation process of Example 6 is largely the same as that of Example 3, except that in Example 6, the heat-treated high-strength high-low temperature toughness steel is heated to 200°C and held at that temperature for 2 hours.

[0092] Comparative Example 1

[0093] The preparation process of Comparative Example 1 is largely the same as that of Example 3. The difference is that in Comparative Example 1, after Example 3, the temperature was kept at 750°C for 1 hour and then circulated with water twice.

[0094] Comparative Example 2

[0095] The preparation process of Comparative Example 2 is largely the same as that of Example 1, except that the content of Mn element in Comparative Example 2 is 3.0 wt% and the content of Al element is 3.0 wt%.

[0096] Comparative Example 3

[0097] The preparation process of Comparative Example 3 is largely the same as that of Example 1, except that the content of Mn element in Comparative Example 3 is 5.0 wt% and the content of Al element is 4.0 wt%.

[0098] Performance testing

[0099] The steels obtained in Examples 1-6 and Comparative Examples 1-3 were tested, including tensile strength, yield strength, room temperature impact, low temperature (-40°C) impact, and elongation after fracture.

[0100] The tests were conducted according to GB / T 228 Metallic Materials - Tensile Testing at Room Temperature and GB / T 229 Metallic Materials - Charpy Impact Test. The results are shown in Table 1. The SEM morphology of the impact fracture surface and the tensile fracture surface are shown in the table below. Figure 1 As shown in (a)-(i) and (a)-(i) of 2.

[0101] Table 1 Test Results

[0102]

[0103]

[0104] As can be seen from Examples 1-3 and Table 1, the present invention uses fewer alloying elements, which can reduce production costs. In addition, the combination of elements such as C, Mn and Al achieves high hardenability and uniformity of quenched structure, ensuring high strength and high and low temperature toughness of the steel. Performance testing shows that the tensile strength can reach more than 1400 MPa, the yield strength can reach more than 875 MPa, the room temperature impact toughness Akv = 40~70 J, and the impact toughness Akv at -40℃ = 30~50 J.

[0105] As can be seen from Examples 1-6 and Table 1, under the combination of elements such as C, Mn and Al, the steel obtained after smelting, forging, rolling, heat treatment and low-temperature short-time tempering can further improve the yield strength and toughness. The test results show that the yield strength of the obtained steel reaches more than 1000 MPa, its room temperature impact toughness Akv = 60~85 J, and its impact toughness at -40℃ Akv = 45~65 J.

[0106] To more clearly illustrate the technical solutions of the embodiments of this application, the following figures show microstructure photographs of embodiments 1-6 of this application. Figure 1 The scanning electron microscope and transmission electron microscope images from Examples 1-3 clearly show that the impact and tensile fracture morphology of the obtained steel is mainly a ductile fracture with typical dimple morphology. The bright field image of the transmission electron microscope shows that it is composed of ultrafine martensitic lath structure and thin film-like retained austenite structure at the lath boundary, which provides strong evidence for its high impact fracture and elongation after fracture. Figure 2 As shown in the scanning electron microscope and transmission electron microscope images in Figures 4-6, it can be clearly seen that although it has undergone low-temperature short-time tempering, its impact and tensile fracture surfaces still have a dimple structure. The transmission electron microscope bright-field image shows that the martensitic lath structure has not been significantly coarsened, and no large-sized carbides that affect its mechanical properties have been generated, indicating that the matrix structure remains highly stable after low-temperature short-time tempering.

[0107] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing low-cost, high-strength, high- and low-temperature toughness steel, characterized in that, Includes the following steps: S1: Smelting: According to the composition ratio, smelting is carried out in a vacuum induction furnace to obtain ingots; S2: Forging: The ingot is heated to 1150-1220℃ and held for 3-15 hours; then cooled to 1050-1150℃ for forging to obtain a forging. S3: Rolling: The forging is heated to 1050-1150℃ and held for 1-3 hours. Then the heated forging is rolled to obtain a plate. S4: Heat treatment: The plate is heated to 750℃-950℃ in a high-temperature heating furnace and held for 0.5-2 hours, then oil-quenched or water-quenched to room temperature to obtain low-cost, high-strength, high-low-temperature toughness steel; then the low-cost, high-strength, high-low-temperature toughness steel is heated to 150-250℃ and held for 1-3 hours. The composition of the low-cost, high-strength, high- and low-temperature toughness steel, by mass percentage, includes C: 0.15wt%~0.25wt%, Mn: 4.50wt%~5.50wt%, Al: 0.20wt%~2.90wt%, Cr: 0.010wt%~0.025wt%, P≤0.010wt%, S≤0.010wt%, with the balance being Fe; the microstructure is martensite and a small amount of carbides; the tensile strength is above 1400 MPa, the yield strength is above 1000 MPa, the room temperature impact toughness Akv = 60~85J, and the impact toughness Akv at -40℃ = 45~65J.

2. The method for preparing low-cost, high-strength, high- and low-temperature toughness steel according to claim 1, characterized in that, It includes C: 0.19wt%~0.22wt%, Mn: 4.90wt%~5.20wt%, Al: 0.45wt%~2.40wt%, Cr: 0.015wt%~0.021wt%, P≤0.010wt%, S≤0.010wt%, with the balance being Fe.

3. The method for preparing low-cost, high-strength, high- and low-temperature toughness steel according to claim 1, characterized in that, It includes C: 0.17wt%~0.23wt%, Mn: 4.70wt%~5.30wt%, Al: 0.35wt%~2.70wt%, Cr: 0.013wt%~0.023wt%, P≤0.010wt%, S≤0.010wt%, with the balance being Fe.

4. The method for preparing low-cost, high-strength, high- and low-temperature toughness steel according to claim 1, characterized in that, In step S3, the rolling temperature is 1080-1150℃.

5. The method for preparing low-cost, high-strength, high- and low-temperature toughness steel according to claim 1, characterized in that, Low-cost, high-strength, high-low temperature toughness steel that has been oil-quenched or water-quenched to room temperature is heated to 150-200℃ and held at that temperature for 1-3 hours.

6. A low-cost, high-strength, high- and low-temperature toughness steel, characterized in that, Obtained by the preparation method according to any one of claims 1-5.

7. An article characterized in that, The product is prepared by the low-cost, high-strength, high-low temperature toughness steel obtained by the preparation method according to any one of claims 1-5, and the product includes parts for automobiles and high-end equipment.

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