Bainite non-quenched and tempered steel and preparation method thereof

Abstract

The invention provides bainite non-quenched and tempered steel and a preparation method thereof.The preparation method comprises the following steps that blast furnace molten iron is sequentially subjected to molten iron pretreatment, converter smelting, ladle refining, vacuum refining, vacuum degassing, continuous casting and rolling, and the bainite non-quenched and tempered steel is obtained; the content of P at the smelting end point of the converter is less than or equal to And the content of S in the molten steel subjected to vacuum refining is 0.038%-0.045%. The bainite non-quenched and tempered steel with excellent comprehensive performance is obtained through reasonable smelting, refining, continuous casting and rolling process design of blast furnace molten iron designed by adopting specific chemical components, the preparation process is simple, and the preparation cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of non-quenched and tempered steels, and particularly to a bainitic non-quenched and tempered steel and a preparation method thereof. Background Art

[0002] With the rapid development of modern industry, the requirements for the performance of steel are becoming increasingly stringent. In many industries such as automobiles and machinery manufacturing, not only is it required that the steel has high strength, high toughness and good wear resistance, but it is also hoped that the production cost can be reduced, the production process can be simplified and the impact on the environment can be reduced while ensuring the performance.

[0003] The production process of traditional quenched and tempered steels is complex and requires multiple heat treatment processes such as quenching and tempering. This not only consumes a large amount of energy, but also easily causes part deformation and cracking, increasing the production cost and the rejection rate. Non-quenched and tempered steels are developed to overcome the problems of complex production processes and high energy consumption of traditional quenched and tempered steels. Bainitic steels are a type of steel with bainite as the matrix metallographic structure in the as-used state, and have characteristics such as high strength and high toughness. Their tensile strength increases with the decrease of the bainite transformation temperature, and good mechanical properties can be obtained without quenching and tempering heat treatment, achieving the purpose of energy saving and cost reduction.

[0004] CN118996080A discloses a preparation method of a bainitic rail and the bainitic rail obtained by using this method. The method includes: heating the continuous casting billet and performing soaking heat treatment; performing multi-pass rolling on the soaked continuous casting billet, controlling the rolling temperature and the reduction ratio; performing controlled cooling on the rolled rail; and pre-bending the rail and placing it on a walking beam cooling bed to cool to room temperature. The bainitic rail obtained by this method has excellent mechanical properties and a long service life, meeting the high standards required for rails in modern railway transportation.

[0005] CN103866191A discloses a seamless pipe of bainitic matrix transformation-induced plasticity steel and a preparation method thereof. The method sequentially includes smelting, forging bars, turning, heating, piercing, cold drawing and heat treatment steps. The heat treatment steps are: first, heating the seamless cold-drawn steel pipe obtained after cold drawing to the austenitizing temperature range of 910-950°C at a rate of 35-50°C / s and performing annealing treatment for 60-90 s; then, cooling the annealed seamless cold-drawn steel pipe to the bainite region of 380-430°C at a rate of 40-80°C / s and performing isothermal treatment for 30-100 s; finally, cooling the isothermally treated seamless cold-drawn steel pipe to room temperature. Using the chemical composition of ordinary low-carbon steel to produce a seamless pipe of bainitic matrix transformation-induced plasticity steel with good comprehensive mechanical properties, the cost is relatively low, and the microstructure is composed of bainite and retained austenite, where the volume fraction of retained austenite ≥ 10.5%.

[0006] CN119433168A discloses a high-strength and high-toughness bainitic medium manganese steel, its preparation method and application. The method includes preparing a continuous casting billet of medium manganese steel, holding the continuous casting billet at 1150 - 1250 °C for 2 - 4 h, and then hot rolling it into a hot-rolled steel plate with a thickness of 10 - 12 mm; heating the hot-rolled steel plate to the austenite phase transformation temperature range to obtain a solution-treated steel plate; heating the solution-treated steel plate to the bainite phase transformation temperature range to obtain a bainitic steel plate; cooling the bainitic steel plate at room temperature to obtain a cold-rolled steel plate; and holding the cold-rolled steel plate at 280 - 350 °C for 10 - 20 min, and then water quenching it to room temperature to obtain the high-strength and high-toughness bainitic medium manganese steel.

[0007] However, the above preparation method of bainitic steel still has problems such as a relatively complex operation process and a relatively high preparation cost. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides a bainitic non-quenched and tempered steel and its preparation method. By adopting a specific chemical composition design and an accurate refining process, a bainitic non-quenched and tempered steel with excellent comprehensive properties can be directly obtained in the hot rolling state without subsequent quenching and tempering treatment, effectively solving many problems of traditional quenched and tempered steels.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a bainitic non-quenched and tempered steel, which, by mass percentage, includes: C: 0.25% - 0.27%, Si: 0.32% - 0.36%, Mn: 2.00% - 2.04%, Cr: 0.50% - 0.54%, Al: 0.005% - 0.015%, V: 0.11% - 0.13%, P ≤ 0.0205%, S: 0.038% - 0.045%, and the balance is Fe and inevitable impurities.

[0011] In the bainitic non-quenched and tempered steel of the present invention, through the reasonable combination of elements such as Mn, Si, Cr, and V, and controlling the contents of P and S within a specific range, the bainitic non-quenched and tempered steel has high strength while also having good toughness.

[0012] The carbon equivalent C of the bainitic non-quenched and tempered steel of the present invention eq is 0.79% - 0.81%, for example, it can be 0.79%, 0.795%, 0.8%, 0.802%, 0.805%, 0.807% or 0.81%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0013] In the bainitic non-quenched and tempered steel of the present invention, C is 0.25% - 0.27%, for example, it can be 0.25%, 0.253%, 0.255%, 0.26%, 0.265%, 0.267% or 0.27%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable;

[0014] Si is 0.32% - 0.36%, for example, it can be 0.32%, 0.325%, 0.33%, 0.34%, 0.35%, 0.355% or 0.36%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable;

[0015] Mn is 2.00% - 2.04%, for example, it can be 2.00%, 2.01%, 2.015%, 2.02%, 2.025%, 2.03% or 2.04%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable;

[0016] Cr is 0.50% - 0.54%, for example, it can be 0.50%, 0.51%, 0.52%, 0.525%, 0.53%, 0.535% or 0.54%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable;

[0017] Al is 0.005% - 0.015%, for example, it can be 0.005%, 0.008%, 0.01%, 0.012%, 0.014% or 0.015%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable;

[0018] V is 0.11% - 0.13%, for example, it can be 0.11%, 0.115%, 0.118%, 0.12%, 0.125%, 0.127% or 0.13%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable;

[0019] P ≤ 0.0205%, for example, it can be 0.0205%, 0.0202%, 0.020%, 0.018%, 0.015%, 0.013% or 0.01%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable;

[0020] S is 0.038% - 0.045%, for example, it can be 0.038%, 0.039%, 0.04%, 0.041%, 0.042%, 0.043% or 0.045%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0021] In a second aspect, the present invention also provides a method for preparing the bainitic non-quenched and tempered steel as described in the first aspect. The preparation method includes the following steps:

[0022] Subjecting the blast furnace hot metal to hot metal pretreatment, converter smelting, ladle refining, vacuum refining, vacuum degassing, continuous casting and rolling in sequence to obtain the bainitic non-quenched and tempered steel;

[0023] The P content at the end point of the converter smelting is ≤0.012%; the S content in the molten steel after vacuum refining is 0.038% - 0.045%.

[0024] The preparation method of the bainitic non-quenched and tempered steel of the present invention uses the blast furnace hot metal with a specific chemical composition design and undergoes reasonable smelting, refining, continuous casting and rolling process designs, enabling the bainitic non-quenched and tempered steel to have good comprehensive properties in the hot-rolled state, omitting subsequent complex and energy-consuming processes such as quenching and tempering, and reducing the energy consumption and time cost in the production process. The present invention conducts vacuum degassing after vacuum refining to effectively remove impurity elements such as O, N and H in the molten steel and improve the comprehensive properties of the bainitic non-quenched and tempered steel.

[0025] The preparation method of the present invention controls the P content during the converter smelting process and controls the S content during the vacuum refining process. After subsequent vacuum degassing, continuous casting and rolling, the finally prepared bainitic non-quenched and tempered steel has P ≤0.0205% and has excellent comprehensive properties.

[0026] The P content at the end point of the converter smelting in the present invention is ≤0.012%, for example, it can be 0.012%, 0.011%, 0.01%, 0.009%, 0.006%, 0.005% or 0.002%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable;

[0027] The S content in the molten steel after vacuum refining is 0.038% - 0.045%, for example, it can be 0.038%, 0.039%, 0.04%, 0.041%, 0.042%, 0.043% or 0.045%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] Preferably, the hot metal pretreatment includes stirring desulfurization treatment.

[0029] Preferably, the C content at the end point of the converter smelting is 0.08% - 0.13%, for example, it can be 0.08%, 0.085%, 0.09%, 0.095%, 0.1%, 0.12% or 0.13%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] Preferably, the ladle refining time ≥ 48 min, for example, it can be 48 min, 48.5 min, 49 min, 49.5 min, 50 min, 53 min, 55 min, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] In the present invention, hot metal with specific element contents is successively subjected to hot metal pretreatment and converter smelting to become molten steel with specific element contents, and by combining with a specific ladle refining time, the mass fractions of various elements in the molten steel are precisely controlled to improve the purity and compositional uniformity of the molten steel.

[0032] The white slag time ≥ 15 min, for example, it can be 15 min, 17 min, 20 min, 23 min, 25 min, 27 min, 30 min, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0033] Preferably, the vacuum degree of the vacuum degassing ≤ 67 Pa, for example, it can be 67 Pa, 65 Pa, 63 Pa, 61 Pa, 60 Pa, 58 Pa, 50 Pa, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0034] Preferably, the static stirring time of the vacuum degassing ≥ 12 min, for example, it can be 12 min, 13 min, 15 min, 18 min, 20 min, 25 min, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable;

[0035] The argon flow rate is 10 - 20 NL / min, for example, it can be 10 NL / min, 12 NL / min, 13 NL / min, 15 NL / min, 17 NL / min, 19 NL / min, 20 NL / min, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] Preferably, the vacuum degassing time ≥ 12 min, for example, it can be 12 min, 13 min, 15 min, 18 min, 20 min, 25 min, 30 min, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] Preferably, the soft blowing time of the vacuum degassing ≥ 15 min, for example, it can be 15 min, 18 min, 20 min, 23 min, 25 min, 28 min, 30 min, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable; ensure that the H content in the molten steel ≤ 2.0×10 -6, for example, it can be 2.0×10 -6 , 1.8×10 -6 , 1.5×10 -6 , 1×10 -6 , 5×10 -7 or 3×10 -7 etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0038] In the present invention, by strictly controlling the vacuum degree and time of vacuum degassing, it is ensured that the H content in the molten steel ≤ 2.0×10 -6 . At the same time, the static stirring time and argon flow rate are controlled to promote the full floating of inclusions and further improve the purity of the molten steel. The H content in the molten steel refers to the content of hydrogen gas in the molten steel.

[0039] Preferably, the specific water consumption during the continuous casting process is 0.8 - 0.9 L / kg, for example, it can be 0.8 L / kg, 0.82 L / kg, 0.85 L / kg, 0.87 L / kg, 0.88 L / kg, 0.89 L / kg or 0.9 L / kg etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable; the superheat of the tundish is 20℃ - 30℃, for example, it can be 20℃, 22℃, 24℃, 25℃, 26℃, 28℃ or 30℃ etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable; the casting speed is 0.3 - 0.48 m / min, for example, it can be 0.3 min, 0.32 min, 0.35 min, 0.38 min, 0.4 min, 0.45 min or 0.48 min etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0040] During the continuous casting process of the present invention, open-pouring with drainage sand and retaining molten steel in the ladle are adopted to ensure the cleanliness of the molten steel. At the same time, argon sealing full protection is adopted to prevent secondary oxidation of the molten steel. The best matching among the casting speed, secondary cooling intensity, and superheat is achieved through mold electromagnetic stirring and final light pressure technology to ensure the quality of the cast slab.

[0041] Preferably, after continuous casting, the cast slab is heated, the temperature is 1120 - 1210℃, for example, it can be 1120℃, 1150℃, 1180℃, 1200℃, 1205℃ or 1210℃ etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable; the time is 280 - 480 min, for example, it can be 280 min, 290 min, 300 min, 320 min, 350 min, 400 min, 450 min or 480 min etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0042] The continuous casting billet of the present invention is heated at a high temperature, so that alloying elements and the like are all dissolved in the austenite matrix, laying a foundation for subsequent microstructure transformation and property control.

[0043] Preferably, the rolling starting temperature is 1060 - 1110 °C, for example, it can be 1060 °C, 1070 °C, 1080 °C, 1090 °C, 1100 °C or 1110 °C, etc., but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] After the bainitic non - quenched and tempered steel prepared by the present invention is produced, it is put into a pit for slow cooling to avoid the generation of abnormal microstructure.

[0045] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0046] The blast furnace hot metal is successively subjected to hot metal pretreatment, converter smelting, ladle refining, vacuum refining, vacuum degassing, continuous casting and rolling to obtain the bainitic non - quenched and tempered steel;

[0047] The hot metal pretreatment includes stirring desulfurization treatment;

[0048] The carbon C content at the end of converter smelting is 0.08% - 0.13%; the phosphorus P content at the end of converter smelting ≤ 0.012%;

[0049] The time of ladle refining ≥ 48 min, and the white slag time ≥ 15 min;

[0050] The sulfur S content in the molten steel after vacuum refining is 0.038% - 0.045%;

[0051] The vacuum degree of the vacuum degassing ≤ 67 Pa; the static stirring time of the vacuum degassing ≥ 12 min, and the argon flow rate is 10 - 20 NL / min; the time of the vacuum degassing ≥ 12 min; the soft blowing time of the vacuum degassing ≥ 15 min to ensure that the hydrogen H content in the molten steel ≤ 2.0×10 -6 ;

[0052] The specific water consumption during continuous casting is 0.8 - 0.9 L / kg, the superheat of the tundish is 20 °C - 30 °C, and the casting speed is 0.3 - 0.48 m / min; after continuous casting, the billet is heated, the temperature is 1120 - 1210 °C, and the time is 280 - 480 min;

[0053] The rolling starting temperature is 1060 - 1110 °C.

[0054] Compared with the prior art, the present invention has at least the following beneficial effects:

[0055] The preparation method of the bainitic non-quenched and tempered steel provided by the present invention has a simple operation process and low preparation cost. Through reasonable chemical composition design and reasonable smelting, refining, continuous casting, and rolling process design, the bainitic non-quenched and tempered steel can have good comprehensive properties in the hot-rolled state, and has broad prospects for large-scale popularization and application. Specific Embodiments

[0056] To facilitate the understanding of the present invention, the following are examples of the present invention. Those skilled in the art should understand that the said examples are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0057] The present invention will be further described in detail below. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0058] The following are typical but non-limiting embodiments of the present invention:

[0059] Example 1

[0060] This example provides a bainitic non-quenched and tempered steel, which, by mass percentage, includes: C: 0.26%, Si: 0.34%, Mn: 2.02%, Cr: 0.53%, Al: 0.01%, V: 0.12%, P: 0.02%, S: 0.04%, and the balance is Fe and unavoidable impurities.

[0061] This example also provides a preparation method for the above bainitic non-quenched and tempered steel, and the preparation method includes the following steps:

[0062] The blast furnace hot metal is successively subjected to hot metal pretreatment, converter smelting, ladle refining, vacuum refining, vacuum degassing, continuous casting, and rolling to obtain the bainitic non-quenched and tempered steel;

[0063] The hot metal pretreatment includes stirring desulfurization treatment;

[0064] The carbon C content at the end point of the converter smelting is 0.09%; the phosphorus P content at the end point of the converter smelting is 0.012%;

[0065] The time of the ladle refining is 50 min, and the white slag time is 22 min;

[0066] The S content in the molten steel after vacuum refining is 0.04%;

[0067] The vacuum degree of the vacuum degassing is 67 Pa; the static stirring time of the vacuum degassing is 12 min, and the argon flow rate is 15 NL / min; the time of the vacuum degassing is 15 min; the soft blowing time of the vacuum degassing is 18 min to ensure that the H content in the molten steel is 1.0×10 -6 ;

[0068] The specific water consumption during continuous casting is 0.83 L / kg, the superheat of tundish is 25 °C, and the casting speed is 0.35 m / min; after continuous casting, the billet is heated at a temperature of 1180 °C for 300 min;

[0069] The rolling starting temperature is 1080 °C.

[0070] Example 2

[0071] This example provides a bainitic non-quenched and tempered steel, which, by mass percentage, includes: C: 0.25%, Si: 0.32%, Mn: 2.04%, Cr: 0.54%, Al: 0.005%, V: 0.13%, P: 0.0205%, S: 0.038%, and the balance is Fe and unavoidable impurities.

[0072] This example also provides a preparation method of the above bainitic non-quenched and tempered steel, and the preparation method includes the following steps:

[0073] The blast furnace hot metal is successively subjected to hot metal pretreatment, converter smelting, ladle refining, vacuum refining, vacuum degassing, continuous casting and rolling to obtain the bainitic non-quenched and tempered steel;

[0074] The hot metal pretreatment includes stirring desulfurization treatment;

[0075] The carbon C content at the end of converter smelting is 0.13%; the phosphorus P content at the end of converter smelting is 0.012%;

[0076] The time of ladle refining is 48 min, and the white slag time is 30 min;

[0077] The S content in the molten steel after vacuum refining is 0.038%;

[0078] The vacuum degree of vacuum degassing is 65 Pa; the static stirring time of vacuum degassing is 18 min, and the argon flow rate is 13 NL / min; the time of vacuum degassing is 12 min; the soft blowing time of vacuum degassing is 17 min to ensure that the H content in the molten steel is 2.0×10 -6 ;

[0079] The specific water consumption during continuous casting is 0.9 L / kg, the superheat of tundish is 30 °C, and the casting speed is 0.48 m / min; after continuous casting, the billet is heated at a temperature of 1210 °C for 280 min;

[0080] The rolling starting temperature is 1060 °C.

[0081] Example 3

[0082] This embodiment provides a bainitic non-quenched and tempered steel, which, by mass percentage, comprises: C: 0.27%, Si: 0.36%, Mn: 2.00%, Cr: 0.50%, Al: 0.015%, V: 0.11%, P: 0.01%, S: 0.045%, and the balance is Fe and inevitable impurities.

[0083] This embodiment also provides a preparation method of the above bainitic non-quenched and tempered steel, and the preparation method comprises the following steps:

[0084] Subjecting the blast furnace hot metal to hot metal pretreatment, converter smelting, ladle refining, vacuum refining, vacuum degassing, continuous casting and rolling in sequence to obtain the bainitic non-quenched and tempered steel;

[0085] The hot metal pretreatment includes stirring desulfurization treatment;

[0086] The carbon C content at the end point of the converter smelting is 0.08%; the phosphorus P content at the end point of the converter smelting is 0.005%;

[0087] The time of the ladle refining is 55 min, and the white slag time is 24 min;

[0088] The S content in the molten steel after the vacuum refining is 0.045%;

[0089] The vacuum degree of the vacuum degassing is 60 Pa; the static stirring time of the vacuum degassing is 20 min, and the argon flow rate is 20 NL / min; the time of the vacuum degassing is 15 min; the soft blowing time of the vacuum degassing is 22 min to ensure that the H content in the molten steel is 5×10 -7 ;

[0090] The specific water consumption during the continuous casting process is 0.8 L / kg, the superheat of the tundish is 20 °C, and the casting speed is 0.3 m / min; after the continuous casting, the slab is heated, and the temperature is 1120 °C and the time is 480 min;

[0091] The rolling starting temperature is 1110 °C.

[0092] Example 4

[0093] This embodiment provides a bainitic non-quenched and tempered steel, which, by mass percentage, comprises: C: 0.255%, Si: 0.32% - 0.36%, Mn: 2.022%, Cr: 0.513%, Al: 0.0074%, V: 0.115%, P: 0.01%, S: 0.0388%, and the balance is Fe and inevitable impurities.

[0094] This embodiment also provides a preparation method of the above bainitic non-quenched and tempered steel, and the preparation method comprises the following steps:

[0095] The blast furnace hot metal is successively subjected to hot metal pretreatment, converter smelting, ladle refining, vacuum refining, vacuum degassing, continuous casting and rolling to obtain the bainitic non-quenched and tempered steel;

[0096] The hot metal pretreatment includes stirring desulfurization treatment;

[0097] The carbon C content at the end point of the converter smelting is 0.088%; the phosphorus P content at the end point of the converter smelting is 0.002%;

[0098] The time of the ladle refining is 55 min, and the white slag time is 17 min;

[0099] The S content in the molten steel after vacuum refining is 0.0388%;

[0100] The vacuum degree of the vacuum degassing is 58 Pa; the static stirring time of the vacuum degassing is 13.5 min, and the argon flow rate is 10 NL / min; the time of the vacuum degassing is 15 min; the soft blowing time of the vacuum degassing is 16.5 min, ensuring that the H content in the molten steel is 2.0×10 -6 ;

[0101] The specific water ratio in the continuous casting process is 0.83 L / kg, the superheat degree of the tundish is 21.5 °C, and the casting speed is 0.366 m / min; after continuous casting, the billet is heated, the temperature is 1123 °C, and the time is 288 min;

[0102] The starting rolling temperature of the rolling is 1065 °C.

[0103] From the comprehensive implementation of Examples 1 to 4, it can be seen that the preparation method of the bainitic non-quenched and tempered steel provided by the present invention uses blast furnace hot metal with specific chemical compositions and contents, and through hot metal pretreatment, converter smelting, ladle refining, vacuum refining, vacuum degassing, continuous casting and rolling processes, a bainitic non-quenched and tempered steel with high strength and high toughness is obtained, wherein the tensile strength is 880 - 900 MPa, the yield strength is 665 - 680 MPa, and the Brinell hardness is 260 - 300 HBW.

[0104] Example 5

[0105] This example provides a bainitic non-quenched and tempered steel, and the composition of the bainitic non-quenched and tempered steel is the same as that in Example 1.

[0106] This example also provides the preparation method of the above bainitic non-quenched and tempered steel. Except that the time of the ladle refining is 40 min, the rest are the same as those in Example 1.

[0107] In this example, due to the shorter time of the ladle refining, the uniformity of the molten steel composition is poor, which in turn leads to a decrease in the strength and toughness of the finally prepared bainitic non-quenched and tempered steel.

[0108] Example 6

[0109] This example provides a bainitic non - quenched and tempered steel, and the composition of the bainitic non - quenched and tempered steel is the same as that in Example 1.

[0110] This example also provides a preparation method of the above - mentioned bainitic non - quenched and tempered steel. Except that the heating temperature of the continuous - casting billet after continuous casting is 1100 °C, the rest are the same as those in Example 1.

[0111] Example 7

[0112] This example provides a bainitic non - quenched and tempered steel, and the composition of the bainitic non - quenched and tempered steel is the same as that in Example 1.

[0113] This example also provides a preparation method of the above - mentioned bainitic non - quenched and tempered steel. Except that the heating temperature of the continuous - casting billet after continuous casting is 1250 °C, the rest are the same as those in Example 1.

[0114] From a comprehensive view of Example 1 and Examples 6 - 7, it can be seen that in Example 6, the relatively low heating temperature of the continuous - casting billet after continuous casting will cause alloying elements not to be completely dissolved in the austenite matrix, resulting in a decrease in the strength and toughness of the finally prepared bainitic non - quenched and tempered steel; in Example 7, the relatively high heating temperature of the continuous - casting billet after continuous casting will not only cause a relatively high preparation cost, but also lead to grain growth, thereby affecting the toughness of the finally prepared bainitic non - quenched and tempered steel.

[0115] Comparative Example 1

[0116] This comparative example provides a bainitic non - quenched and tempered steel. Except that the P content is 0.05%, the rest are the same as those in Example 1.

[0117] This comparative example also provides a preparation method of the above - mentioned bainitic non - quenched and tempered steel. Except that the end - point P content is not controlled during converter smelting, the rest are the same as those in Example 1.

[0118] In this comparative example, due to the relatively high P content, although the strength of the steel can be improved, the toughness of the bainitic non - quenched and tempered steel will be sharply reduced.

[0119] Comparative Example 2

[0120] This comparative example provides a bainitic non - quenched and tempered steel. Except that the S content is 0.02%, the rest are the same as those in Example 1.

[0121] This comparative example also provides a preparation method of the above - mentioned bainitic non - quenched and tempered steel. Except that the S content in the molten steel after vacuum refining is 0.02%, the rest are the same as those in Example 1.

[0122] Comparative Example 3

[0123] This comparative example provides a bainitic non-quenched and tempered steel. Except that the S content is 0.05%, the rest are the same as those in Example 1.

[0124] This comparative example also provides a preparation method of the above bainitic non-quenched and tempered steel. Except that the S content in the molten steel after vacuum refining is 0.05%, the rest are the same as those in Example 1.

[0125] From a comprehensive comparison of Example 1 and Comparative Examples 2 to 3, it can be seen that in Comparative Example 2, the low S content will lead to an increase in the cutting resistance of the bainitic non-quenched and tempered steel; in Comparative Example 3, the high S content will cause a significant reduction in the toughness of the bainitic non-quenched and tempered steel.

[0126] The applicant declares that the above are only specific embodiments of the present invention, but the protection scope 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 within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A bainitic non-quenched and tempered steel, characterized in that, The bainitic non-quenched and tempered steel comprises, by mass percentage: C: 0.25% to 0.27%, Si: 0.32% to 0.36%, Mn: 2.00% to 2.04%, Cr: 0.50% to 0.54%, Al: 0.005% to 0.015%, V: 0.11% to 0.13%, P≤0.0205%, S: 0.038% to 0.045%, and the balance is Fe and unavoidable impurities.

2. A preparation method of the bainitic non-quenched and tempered steel as described in claim 1, characterized in that, The preparation method comprises the following steps: The blast furnace hot metal is successively subjected to hot metal pretreatment, converter smelting, ladle refining, vacuum refining, vacuum degassing, continuous casting and rolling to obtain the bainitic non-quenched and tempered steel; The P content at the end of converter smelting is ≤0.012%; the S content in the molten steel after vacuum refining is 0.038% to 0.045%.

3. The preparation method according to claim 2, wherein The hot metal pretreatment includes stirring desulfurization treatment.

4. The preparation method according to claim 2 or 3, characterized in that, The carbon C content at the end of converter smelting is 0.08% to 0.13%.

5. The preparation method according to any one of claims 2 to 4, characterized in that, The time of ladle refining is ≥48 min, and the white slag time is ≥15 min.

6. The preparation method according to any one of claims 2 to 5, characterized in that, The vacuum degree of the vacuum degassing is ≤67 Pa; Preferably, the static stirring time of the vacuum degassing is ≥12 min, and the argon flow rate is 10 to 20 NL / min.

7. The preparation method according to any one of claims 2 to 6, characterized in that, The time of the vacuum degassing is ≥12 min; Preferably, the soft blowing time for vacuum degassing ≥ 15 min to ensure that the H content in the molten steel ≤ 2.0×10 -6 .

8. The preparation method according to any one of claims 2 to 7, characterized in that The specific water volume during continuous casting is 0.8 to 0.9 L / kg, the superheat degree of the tundish is 20°C to 30°C, and the casting speed is 0.3 to 0.48 m / min.

9. The preparation method according to any one of claims 2 to 8, characterized in that, After continuous casting, the slab is heated, the temperature is 1120 to 1210°C, and the time is 280 to 480 min.

10. The preparation method according to any one of claims 2 to 9, characterized in that, The starting rolling temperature of the rolling is 1060 to 1110°C.