Hot-rolled round steel and preparation method and application thereof

Abstract

The invention relates to hot-rolled round steel as well as a preparation method and application thereof. The hot-rolled round steel comprises the following components: 0.39 to 0.41 weight percent of C, 0.20 to 0.24 weight percent of Si, 1.57 to 1.61 weight percent of Mn, 0.13 to 0.17 weight percent of Cr, 0.015 to 0.025 weight percent of Al, 0.008 to 0.016 weight percent of Ti, less than or equal to 0.10 weight percent of Ni, less than or equal to 0.06 weight percent of Cu, less than or equal to 0.03 weight percent of Mo, less than or equal to 0.020 weight percent of P, less than or equal to 0.010 weight percent of S, less than 0.0005 weight percent of B and the balance of Fe. The hardenability of the hot-rolled round steel is improved through the synergistic effect of all the components, the J1.5 reaches 54.1 HRC to 57.3 HRC, the J8 reaches 47.2 HRC to 51.2 HRC, the J14 reaches 34.8 HRC to 37.1 HRC, and the J35 reaches 24.5 HRC to 26.9 HRC, and the requirement for steel for a wheel body is met.

Description

Technical Field

[0001] This invention relates to the field of alloy smelting technology, and in particular to a hot-rolled round steel bar, its preparation method, and its application. Background Technology

[0002] Track rollers are crucial components of the chassis of tracked construction machinery. During operation, they bear the weight of the entire machine and require good wear resistance and deformation resistance. Given fixed parameters, the hardenability of the material significantly impacts the depth of the hardened layer in the roller body. Therefore, consistently ensuring the hardenability of the material is key to controlling the depth of the hardened layer in the roller body.

[0003] Currently, the hardenability of existing hot-rolled round steel still cannot meet the requirements of high load and high wear resistance for heavy-duty wheels. For example, CN116200653A discloses a narrow hardenability band 20CrMnTiH1 hot-rolled round steel and its preparation method. Its chemical composition percentages are as follows: C: 0.19~0.21%; Si: 0.25~0.35%; Mn: 0.95~1.00%; P: ≤0.025%; S: ≤0.025%; Cr: 1.00~1.05%; Ti: 0.04~0.07%; Al: 0.020~0.040%, with the remainder being Fe and impurity elements. Its hardenability J9 reaches a maximum of only 31.5HRC, and its hardenability J15 reaches a maximum of only 28.5HRC.

[0004] However, 40Mn2 alloy steel, due to its high hardness, wear resistance, good strength and toughness, and high fatigue resistance, can meet the stringent working conditions and excellent comprehensive mechanical properties required for the wheels of bulldozers, excavators, and other construction machinery. Furthermore, the main factors affecting hardenability are the alloying elements of the material, such as C, Si, Mn, Cr, Mo, and Ni. In actual production, the depth of the hardened layer in the wheel body is often unstable, necessitating strict control of the chemical composition of 40Mn2 material to ensure its hardenability. Therefore, the research and development of 40Mn2 steel for construction machinery wheels and the optimization of product structure are of great significance for the production of construction machinery and the processing of component parts.

[0005] Therefore, how to optimize the composition of the 40Mn2 steel and control the production and processing process to prepare high hardenability 40Mn2 steel that meets the requirements of high load and high wear resistance for engineering machinery steel is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a hot-rolled round steel bar, its preparation method, and its application. Considering the improvement of hardenability, strength, and toughness of the product by elements, the chemical composition of the original steel grade is optimized, and the production process is controlled. This improves and stabilizes the hardenability, strength, and toughness of the hot-rolled round steel bar, while also mitigating component segregation. This solves the problem that existing 40Mn2 steel still cannot meet the high load and high wear resistance requirements of steel used in engineering machinery.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a hot-rolled round steel bar comprising the following components: C: 0.39–0.41 wt%, Si: 0.20–0.24 wt%, Mn: 1.57–1.61 wt%, Cr: 0.13–0.17 wt%, Al: 0.015–0.025 wt%, Ti: 0.008–0.016 wt%, Ni ≤ 0.10 wt%, Cu ≤ 0.06 wt%, Mo ≤ 0.03 wt%, P ≤ 0.020 wt%, S ≤ 0.010 wt%, B < 0.0005 wt%, and the balance Fe.

[0009] Wherein, C: 0.39–0.41 wt%, for example, 0.39 wt%, 0.395 wt%, 0.40 wt%, 0.405 wt%, or 0.41 wt%, etc.; Si: 0.20–0.24 wt%, for example, 0.20 wt%, 0.21 wt%, 0.22 wt%, 0.23 wt%, or 0.24 wt%, etc.; Mn: 1.57–1.61 wt%, for example, 1.57 wt%, 1.58 wt%, 1.59 wt%, 1.60 wt%, or 1.6 wt%. 1 wt%, etc.; Cr: 0.13–0.17 wt%, for example, 0.13 wt%, 0.14 wt%, 0.15 wt%, 0.16 wt%, or 0.17 wt%, etc.; Al: 0.015–0.025 wt%, for example, 0.015 wt%, 0.018 wt%, 0.020 wt%, 0.022 wt%, or 0.025 wt%, etc.; Ti: 0.008–0.016 wt%, for example, 0.008 wt%, 0.010 wt%, 0.012 wt%, etc. 0.014 wt% or 0.016 wt%, etc.; Ni ≤ 0.10 wt%, for example, 0.10 wt%, 0.09 wt%, 0.08 wt%, 0.07 wt%, 0.06 wt%, or 0.05 wt%, etc.; Cu ≤ 0.06 wt%, for example, 0.06 wt%, 0.05 wt%, 0.04 wt%, or 0.03 wt%, etc.; Mo ≤ 0.03 wt%, for example, 0.03 wt%, 0.02 wt%, or 0.01 wt%, etc.; P ≤ 0.020 wt%. %, for example, can be 0.020wt%, 0.018wt%, 0.015wt%, 0.012wt%, or 0.010wt%, etc.; S≤0.010wt%, for example, can be 0.010wt%, 0.009wt%, 0.008wt%, 0.007wt%, 0.006wt%, or 0.005wt%, etc.; B<0.0005wt%, for example, can be 0.00048wt%, 0.00045wt%, 0.00042wt%, and 0.0004wt%, etc.

[0010] This invention optimizes the chemical composition of 40Mn2 steel, mainly by optimizing Cr and Mn elements, and by adding specific amounts of Ti and Al elements for compounding. The synergistic effect of the components improves the hardenability of the resulting hot-rolled round steel and stabilizes the hardenability, thereby improving and stabilizing the strength and toughness of the wheel body steel. This solves the problem of unstable hardened layer depth in wheel body during actual production and meets the high strength and high toughness requirements of wheel body steel.

[0011] Preferably, the Cr content in the hot-rolled round steel is 0.14 to 0.16 wt%.

[0012] Preferably, the Ti content in the hot-rolled round steel is 0.010 to 0.014 wt%.

[0013] Preferably, the Al content in the hot-rolled round steel is 0.019 to 0.021 wt%.

[0014] Preferably, the mass ratio of Cr to Ti in the hot-rolled round steel is (11-15):1, for example, it can be 11:1, 11.5:1, 12:1, 12.5:1, 13:1, 13.5:1, 14:1, 14.5:1 or 15:1, etc.

[0015] Preferably, the mass ratio of Cr to Mn in the hot-rolled round steel is 1:(10-11), for example, it can be 1:10, 1:10.2, 1:10.4, 1:10.6, 1:10.8 or 1:11, etc.

[0016] Preferably, the diameter of the hot-rolled round steel is 100-150mm, for example, it can be 100mm, 110mm, 120mm, 130mm, 140mm or 150mm.

[0017] In a second aspect, the present invention provides a method for preparing the hot-rolled round steel described in the first aspect, the method comprising the following steps:

[0018] The hot-rolled round steel is obtained by sequentially casting, rolling and cooling molten steel.

[0019] This invention uses molten steel to obtain hot-rolled round steel by sequentially casting, rolling and cooling. By controlling the elemental composition of the molten steel and the process parameters of continuous casting and rolling, hot-rolled round steel with high hardenability can be prepared. The preparation method is controllable, simple, low-cost and easy to mass-produce.

[0020] The method for preparing molten steel includes: selecting steel ingot raw materials according to the composition of hot-rolled round steel as described in the first aspect, and sequentially subjecting the steel ingot raw materials to converter smelting, ladle refining and vacuum refining to obtain the molten steel.

[0021] Preferably, the continuous casting is carried out in a continuous casting machine.

[0022] Preferably, the casting speed is 0.45 to 0.50 m / min, for example, it can be 0.45 m / min, 0.46 m / min, 0.47 m / min, 0.48 m / min, 0.49 m / min or 0.50 m / min, etc.

[0023] Preferably, the superheat of the continuous casting is 15 to 35°C, for example, it can be 15°C, 20°C, 25°C, 30°C or 35°C.

[0024] Preferably, the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 240-260A, for example, it can be 240A, 245A, 250A, 255A or 260A.

[0025] Preferably, the frequency of the electromagnetic stirring of the crystallizer is 2.2 to 2.6 Hz, for example, it can be 2.2 Hz, 2.3 Hz, 2.4 Hz, 2.5 Hz or 2.6 Hz.

[0026] Preferably, the current of the end electromagnetic stirrer in the continuous casting machine is 430-460A, for example, it can be 430A, 435A, 440A, 445A, 450A, 455A or 460A, etc.

[0027] Preferably, the frequency of the end electromagnetic stirring is 5.8 to 6.3 Hz, for example, it can be 5.8 Hz, 5.9 Hz, 6.0 Hz, 6.1 Hz, 6.2 Hz or 6.3 Hz.

[0028] Preferably, the starting rolling temperature of the continuous rolling is 1030 to 1100°C, for example, it can be 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C or 1100°C.

[0029] Preferably, the continuous rolling includes a first rolling and a second rolling.

[0030] The first rolling process is rough rolling, and the second rolling process is finish rolling.

[0031] Preferably, the first rolling speed is lower than the second rolling speed.

[0032] Preferably, the first rolling speed is 0.50 to 0.55 m / s, for example, it can be 0.50 m / s, 0.51 m / s, 0.52 m / s, 0.53 m / s, 0.54 m / s or 0.55 m / s, etc.

[0033] Preferably, the second rolling speed is 2.0 to 2.2 m / s, for example, it can be 2.0 m / s, 2.03 m / s, 2.05 m / s, 2.08 m / s, 2.1 m / s, 2.13 m / s, 2.15 m / s, 2.18 m / s or 2.2 m / s, etc.

[0034] Preferably, the single-pass reduction of the continuous rolling mill is 28-102 mm, for example, it can be 28 mm, 32 mm, 38 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, 95 mm or 102 mm.

[0035] Preferably, the total reduction of the continuous rolling mill is 250-275 mm, for example, it can be 250 mm, 265 mm, 268 mm, 270 mm, 272 mm or 275 mm.

[0036] It is worth noting that when using a φ400mm round billet to roll a φ130mm round bar, the total reduction is 270mm. If rolling a 150mm round bar, the total reduction is 250mm.

[0037] Preferably, the final rolling temperature of the continuous rolling is 762-890℃, for example, it can be 762℃, 780℃, 800℃, 820℃, 850℃, 870℃ or 890℃.

[0038] Preferably, the cooling method includes slow cooling in a pit or slow cooling in a box.

[0039] Preferably, the starting temperature for cooling is ≥450°C, for example, it can be 450°C, 455°C, 460°C, 465°C or 470°C, etc.

[0040] Preferably, the cooling process also includes heat preservation.

[0041] Preferably, the heat preservation time is 20 to 25 hours, for example, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, or 25 hours.

[0042] Preferably, the final temperature of the cooling is ≤250℃, for example, it can be 250℃, 240℃, 230℃, 220℃, 210℃ or 200℃, etc.

[0043] As a further preferred technical solution of the present invention, the preparation method includes the following steps:

[0044] Molten steel is continuously cast in a continuous casting machine at a casting speed of 0.45–0.50 m / min and a superheat of 15–35 °C. The electromagnetic stirring current in the crystallizer of the continuous casting machine is 240–260 A with a frequency of 2.2–2.6 Hz, and the electromagnetic stirring current at the end of the continuous casting machine is 430–460 A with a frequency of 5.8–6.3 Hz, resulting in hot-rolled round steel. Then, it is rolled at an initial rolling temperature of 1030–1100 °C and a first rolling speed... The hot-rolled round steel is continuously rolled at a rolling speed of 0.50–0.55 m / s for the first pass and 2.0–2.2 m / s for the second pass, with a total reduction of 250–275 mm and a single-pass reduction of 28–102 mm. The final rolling temperature is 762–890 °C. Finally, the steel is cooled by slow cooling in a pit and / or slow cooling in a box, with an initial cooling temperature ≥450 °C, a holding time of 20–25 h, and an end temperature ≤250 °C, to obtain the hot-rolled round steel.

[0045] Thirdly, the present invention provides an application of the hot-rolled round steel described in the first aspect, wherein the hot-rolled round steel is used to prepare the support wheel body.

[0046] The hot-rolled round steel provided by this invention is widely used as steel for engineering machinery, especially for manufacturing support roller bodies. Due to its high hardenability, the hot-rolled round steel can obtain a deep hardened layer after quenching, which improves its strength and toughness. When manufacturing mechanical parts that bear high loads (such as gears, shafts, and support roller bodies), the parts have better wear resistance and fatigue resistance, which can extend their service life and has great application potential.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] (1) The hot-rolled round steel provided by the present invention optimizes the chemical composition of the original 40Mn2 steel, mainly including the optimization of the content of Cr and Mn elements, and adds a specific amount of Ti and Al elements for compounding. The elements work together to improve and stabilize the hardenability of the obtained hot-rolled round steel. The hardenability test shows that the hardness value at J1.5 is preferably 54.1-57.3HRC, the hardness value at J8 is 47.2-51.2HRC, the hardness value at J14 is below 34.8-37.1HRC, and the hardness value at J35 is 24.5-26.9HRC. This solves the problem of unstable hardened layer depth of the wheel body in actual production and meets the high strength and high toughness requirements of the steel for the wheel body.

[0049] (2) The hot-rolled round steel preparation method provided by the present invention uses molten steel to be continuously cast, continuously rolled and cooled in sequence to obtain the hot-rolled round steel. By adjusting the elemental composition of the molten steel and the process parameters of the continuous casting process and the continuous rolling process, a hot-rolled round steel with high hardenability is prepared. The preparation method has controllable conditions, simple process, low cost and is easy to mass-produce.

[0050] (3) Application of hot-rolled round steel provided by the present invention: The hot-rolled round steel, with its high hardenability, solves the problem of unstable hardened layer depth of wheel body in actual production process, meets the high strength and high toughness requirements of wheel body steel, and is widely used as steel for engineering machinery, especially for preparing support wheel bodies. Detailed Implementation

[0051] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0052] I. Implementation Examples

[0053] Example 1

[0054] This embodiment provides a hot-rolled round steel bar and its preparation method, wherein the hot-rolled round steel bar comprises the following components:

[0055] C: 0.40wt%, Si: 0.22wt%, Mn: 1.59wt%, Cr: 0.15wt%, Al: 0.020wt%, Ti: 0.012wt%, Ni :0.08wt%, Cu: 0.04wt%, Mo: 0.02wt%, P: 0.018wt%, S: 0.009wt%, B: 0.0004wt% and balance Fe.

[0056] The preparation method includes the following steps: molten steel is continuously cast in a continuous casting machine at a casting speed of 0.48 m / min and a superheat of 25°C. The electromagnetic stirring current in the crystallizer of the continuous casting machine is 250 A with a frequency of 2.5 Hz, and the electromagnetic stirring current at the end of the continuous casting machine is 450 A with a frequency of 6.0 Hz to obtain hot-rolled round steel. Then, continuous rolling is performed at an initial rolling temperature of 1060°C, a first finishing rolling speed of 0.52 m / s, and a second finishing rolling speed of 2.03 m / s. The total reduction in continuous rolling is 270 mm, the single-pass reduction is 50 mm, and the final rolling temperature is 810°C. Finally, slow cooling in a pit is used for cooling. The initial cooling temperature is 450°C, the holding temperature is 24 h, and the final temperature is 220°C to obtain the hot-rolled round steel.

[0057] The diameter of the hot-rolled round steel in this embodiment is 130mm.

[0058] Example 2

[0059] This embodiment provides a hot-rolled round steel bar and its preparation method, wherein the hot-rolled round steel bar comprises the following components:

[0060] C: 0.39wt%, Si: 0.20wt%, Mn: 1.57wt%, Cr: 0.14wt%, Al: 0.019wt%, Ti: 0.010wt%, Ni :0.06wt%, Cu: 0.02wt%, Mo: 0.01wt%, P: 0.015wt%, S: 0.008wt%, B: 0.0003wt% and balance Fe.

[0061] The preparation method includes the following steps: molten steel is continuously cast in a continuous casting machine at a casting speed of 0.40 m / min and a superheat of 20°C. The electromagnetic stirring current in the crystallizer of the continuous casting machine is 240 A with a frequency of 2.2 Hz, and the electromagnetic stirring current at the end of the continuous casting machine is 430 A with a frequency of 5.8 Hz to obtain hot-rolled round steel. Then, continuous rolling is performed at an initial rolling temperature of 1030°C, a first finishing rolling speed of 0.50 m / s, and a second finishing rolling speed of 2.0 m / s. The total reduction in continuous rolling is 265 mm, the single-pass reduction is 28 mm, and the final rolling temperature is 762°C. Finally, slow cooling in a pit is used for cooling. The initial cooling temperature is 480°C, the holding temperature is 20 h, and the final temperature is 200°C to obtain the hot-rolled round steel.

[0062] The diameter of the hot-rolled round steel in this embodiment is 100mm.

[0063] Example 3

[0064] This embodiment provides a hot-rolled round steel bar and its preparation method, wherein the hot-rolled round steel bar comprises the following components:

[0065] C: 0.41wt%, Si: 0.24wt%, Mn: 1.61wt%, Cr: 0.16wt%, Al: 0.021wt%, Ti: 0.014wt%, Ni : 0.10wt%, Cu: 0.06wt%, Mo: 0.03wt%, P: 0.020wt%, S: 0.010wt%, B: 0.0004wt% and balance Fe.

[0066] The preparation method includes the following steps: molten steel is continuously cast in a continuous casting machine at a casting speed of 0.50 m / min and a superheat of 35°C. The electromagnetic stirring current in the crystallizer of the continuous casting machine is 260 A with a frequency of 2.6 Hz, and the electromagnetic stirring current at the end of the continuous casting machine is 460 A with a frequency of 6.3 Hz, to obtain hot-rolled round steel. Then, continuous rolling is performed at an initial rolling temperature of 1100°C, with a first finishing rolling speed of 0.55 m / s and a second finishing rolling speed of 2.2 m / s. The total reduction in continuous rolling is 250 mm, the single-pass reduction is 100 mm, and the final rolling temperature is 890°C. Finally, slow cooling in a pit is used for cooling. The initial cooling temperature is 500°C, the holding temperature is 25 h, and the final temperature is 250°C, to obtain the hot-rolled round steel.

[0067] The diameter of the hot-rolled round steel in this embodiment is 150mm.

[0068] Example 4

[0069] This embodiment provides a hot-rolled round steel bar and its preparation method. The preparation method of the hot-rolled round steel bar is the same as that in Embodiment 1, except that the continuous casting speed is 0.40 m / min.

[0070] Example 5

[0071] This embodiment provides a hot-rolled round steel bar and its preparation method. The preparation method of the hot-rolled round steel bar is the same as that in Embodiment 1, except that the continuous casting speed is 0.55m / min.

[0072] Examples 6 to 11

[0073] Examples 6 to 11 are based on Example 1, with adjustments made to the elemental composition and content ratio. The rest are the same as in Example 1. The elemental composition and content ratio are shown in Table 1 for Examples 6 to 11. The content of the unadjusted components is the same as in Example 1. The content of the adjusted components is adjusted accordingly by adjusting the Fe content.

[0074] II. Comparative Example

[0075] Comparative Examples 1 to 4

[0076] Comparative Examples 1 to 4 are based on Example 1, with adjustments made to the elemental composition and content ratio. The rest are the same as Example 1. The elemental composition and content ratio are shown in Table 1 for Comparative Examples 1 to 4. The content of the unadjusted components is the same as in Example 1. The content of the adjusted components is adjusted accordingly by adjusting the Fe content.

[0077] Table 1

[0078] project Mn / wt% Cr / wt% Al / wt% Ti / wt% Example 1 1.59 0.15 0.020 0.012 Example 6 1.59 0.13 0.020 0.012 Example 7 1.59 0.17 0.020 0.012 Example 8 1.59 1.59 0.015 0.012 Example 9 1.59 1.59 0.025 0.012 Example 10 1.59 0.15 0.020 0.008 Example 11 1.59 0.15 0.020 0.016 Comparative Example 1 1.50 0.15 0.020 0.012 Comparative Example 2 1.70 0.15 0.020 0.012 Comparative Example 3 1.59 0.15 0 0.012 Comparative Example 4 1.59 0.15 0.020 0

[0079] III. Tests and Results

[0080] The hot-rolled round steel obtained in the above embodiments or comparative examples was subjected to a hardenability test. The sampling location and standard were in accordance with the end-quenching test method for hardenability of steel in GB / T225-2006. The sample blank was first normalized and then subjected to the end-quenchability test. The heat treatment process was as follows: the normalizing process of the sample was (870±10)℃, held for 60min, and the end-quenching process was (845±5)℃, held for 60min. The hardenability results are shown in Table 2.

[0081] Table 2

[0082]

[0083]

[0084] According to the data in Table 2:

[0085] (1) As can be seen from Examples 1 to 3, the hot-rolled round steel and its preparation method provided by the present invention, by controlling the content of elements such as Cr and Mn in the original 40Mn2 steel and adding a specific amount of Ti and Al elements for compounding, the elements work together to improve the hardenability of the hot-rolled round steel. The hardness value at J1.5 reaches 54.1-57.3 HRC, the hardness value at J8 reaches 47.2-51.2 HRC, the hardness value at J14 reaches 34.8-37.1 HRC, and the hardness value at J35 reaches 24.5-26.9 HRC or above, which meets the hardenability requirements of steel for engineering machinery such as support wheel bodies.

[0086] (2) It can be seen from the combined examples 1, 4 and 5 that whether the casting speed of the continuous casting is too high or too low, the hardenability of the hot-rolled round steel decreases. This indicates that the present invention further prefers the casting speed of the continuous casting to be 0.45 to 0.50 m / min, which further improves the hardenability of the obtained hot-rolled round steel, thereby improving its high load wear resistance and flexibility.

[0087] (3) As can be seen from the combined examples 1 and 6 to 11, the present invention further improves the hardenability of the obtained hot-rolled round steel by synergistically using elements of other specific contents, by further optimizing the Cr content in the hot-rolled round steel to be 0.14 to 0.16 wt%; or further optimizing the Al content in the hot-rolled round steel to be 0.019 to 0.021 wt%; or further optimizing the Ti content in the hot-rolled round steel to be 0.010 to 0.014 wt%.

[0088] (4) It can be seen from the comprehensive comparison of Example 1 and Comparative Examples 1 to 4 that: the low Mn content in Comparative Example 1 resulted in a significant decrease in the hardenability of the obtained hot-rolled round steel; the high Mn content in Comparative Example 2 did not significantly improve the hardenability, but instead increased the cost; the absence of Al in Comparative Example 3 or the absence of Ti in Comparative Example 4 also resulted in a decrease in the hardenability of the obtained hot-rolled round steel; thus, it is shown that the continuous casting round steel and its preparation method of the present invention, by selecting the Mn content in the range of 1.57 to 1.61 wt%, and by adding Al and Ti to the original 40Mn2 steel grade, and combining them with other elements, improves the hardenability of the obtained hot-rolled round steel, thus meeting the hardenability requirements of steel used in engineering machinery such as support wheel bodies.

[0089] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A hot-rolled round steel bar, characterized in that, The hot-rolled round steel comprises the following components: C: 0.39–0.41 wt%, Si: 0.20–0.24 wt%, Mn: 1.57–1.61 wt%, Cr: 0.13–0.17 wt%, Al: 0.015–0.025 wt%, Ti: 0.008–0.016 wt%, Ni ≤ 0.10 wt%, Cu ≤ 0.06 wt%, Mo ≤ 0.03 wt%, P ≤ 0.020 wt%, S ≤ 0.010 wt%, B < 0.0005 wt%, and the balance Fe.

2. The hot-rolled round steel according to claim 1, characterized in that, The Cr content in the hot-rolled round steel is 0.14–0.16 wt%. Preferably, the Ti content in the hot-rolled round steel is 0.010–0.014 wt%. Preferably, the Al content in the hot-rolled round steel is 0.019 to 0.021 wt%.

3. The hot-rolled round steel according to claim 1 or 2, characterized in that, The mass ratio of Cr to Ti in the hot-rolled round steel is (11-15):1; Preferably, the mass ratio of Cr to Mn in the hot-rolled round steel is 1:(10-11).

4. The hot-rolled round steel according to any one of claims 1 to 3, characterized in that, The diameter of the hot-rolled round steel is 100-150 mm.

5. A method for preparing hot-rolled round steel according to any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: The hot-rolled round steel is obtained by sequentially casting, rolling and cooling molten steel.

6. The preparation method according to claim 5, characterized in that, The continuous casting is carried out in a continuous casting machine; Preferably, the casting speed is 0.45–0.50 m / min; Preferably, the superheat of the continuous casting is 15–35°C; Preferably, the current of the electromagnetic stirring in the crystallizer of the continuous casting machine is 240-260A; Preferably, the frequency of the electromagnetic stirring in the crystallizer is 2.2 to 2.6 Hz; Preferably, the current of the end electromagnetic stirrer in the continuous casting machine is 430-460A; Preferably, the frequency of the end electromagnetic stirring is 5.8 to 6.3 Hz.

7. The preparation method according to claim 5 or 6, characterized in that, The starting rolling temperature of the continuous rolling mill is 1030–1100℃; Preferably, the continuous rolling includes a first rolling process and a second rolling process; Preferably, the first rolling speed is lower than the second rolling speed; Preferably, the first rolling speed is 0.50 to 0.55 m / s; Preferably, the second rolling speed is 2.0 to 2.2 m / s; Preferably, the single-pass reduction in the continuous rolling mill is 28–102 mm; Preferably, the total reduction in the continuous rolling mill is 250–275 mm; Preferably, the final rolling temperature of the continuous rolling is 762–890°C.

8. The preparation method according to any one of claims 5 to 7, characterized in that, The cooling methods include slow cooling in a pit or slow cooling in a box; Preferably, the initial cooling temperature is ≥450°C; Preferably, the cooling process also includes heat preservation; Preferably, the heat preservation time is 20-25 hours; Preferably, the final temperature of the cooling is ≤250°C.

9. The preparation method according to any one of claims 5 to 8, characterized in that, The preparation method includes the following steps: Molten steel is continuously cast in a continuous casting machine at a casting speed of 0.45–0.50 m / min and a superheat of 15–35 °C. The electromagnetic stirring current in the crystallizer of the continuous casting machine is 240–260 A with a frequency of 2.2–2.6 Hz, and the electromagnetic stirring current at the end of the continuous casting machine is 430–460 A with a frequency of 5.8–6.3 Hz, resulting in hot-rolled round steel. Then, it is rolled at an initial rolling temperature of 1030–1100 °C, using the first rolling process... The hot-rolled round steel is continuously rolled at a speed of 0.50–0.55 m / s for the first rolling pass and 2.0–2.2 m / s for the second rolling pass. The total reduction in the continuous rolling is 250–275 mm, the reduction per pass is 28–102 mm, and the final rolling temperature is 762–890 °C. Finally, the steel is cooled by slow cooling in a pit or box. The initial cooling temperature is ≥450 °C, and the cooling is maintained for 20–25 hours. The final cooling temperature is ≤250 °C, thus obtaining the hot-rolled round steel.

10. An application of the hot-rolled round steel according to any one of claims 1 to 4, characterized in that, The hot-rolled round steel is used to manufacture the support wheel body.

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