Bainite non-quenched and tempered steel and preparation method and application thereof

Abstract

The invention relates to bainite non-quenched and tempered steel and a preparation method and application thereof, in particular to the field of steel, and the bainite non-quenched and tempered steel is prepared from, by mass, 0.22%-0.28% of C, 0.7%-0.9% of Si, 1.9%-2.1% of Mn, smaller than or equal to 0.015% of P, smaller than or equal to 0.015% of S, 0.2%-0.3% of Cr, 0.05%-0.15% of V, 0.014%-0.018% of N and the balance Fe and inevitable impurities. According to the bainite non-quenched and tempered steel provided by the invention, the design of steel components is optimized, and the synergistic strengthening effect among elements is utilized to ensure that the bainite non-quenched and tempered steel has good mechanical properties, the tensile strength is greater than or equal to 1023 MPa, and the yield strength is greater than or equal to 754 MPa.

Description

Technical Field

[0001] The present invention relates to the field of steel materials, and in particular to a bainite non-quenched and tempered steel and a preparation method and application thereof. Background Art

[0002] At present, automobile front axles are often made of non-tempered steel. For example, CN105803308A discloses a magnesium-calcium-containing 45MnVS free-cutting non-quenched and tempered steel and its manufacturing method. The main components of the steel are: C: 0.42-0.51%, Si: 0.15-0.6%, Mn: 0.90-1.50%, P: 0.010-0.035%, S: 0.040-0.080%, V: 0.06-0.13%, Mg: 0.0005-0.008%, Al: 0.01-0.04%, Ca: 0.0008-0.005%, and the balance is Fe and inevitable impurities; the present invention uses converter-controlled smelting, LF+VD magnesium-calcium composite treatment to modify the morphology of inclusions, M-EMS+F-EMS combined continuous casting, controlled rolling and controlled cooling, and adds trace amounts of magnesium and calcium to traditional 45MnVS to modify sulfur-containing inclusions, so that the material strength index is equivalent to that of 45 steel in the quenched and tempered state, while having better machinability and fatigue resistance than 45MnVS.

[0003] CN113201689A discloses a steel for a front axle of a medium-sized truck and a production method thereof. The chemical composition of the steel is as follows by weight: C: 0.39-0.43%, Si: 0.20-0.37%, Mn: 0.65-0.80%, Cr: 0.95-1.10%, Mo: 0.01-0.05%, Ni: 0.02-0.03%, Cu: 0.02-0.05%, P: ≤0.020%, S: 0.010-0.025%, Alt: 0.010-0.040%, so that the contents of Mo, Ni and Cu in the steel satisfy 0.013C+0.033Mn+0.034Cr≤Mo+Ni+Cu≤0.018C+0.026Mn+0.065Cr, and the remainder is Fe and other inevitable impurities.

[0004] However, the bainitic non-modulated steel currently widely used in automobile front axles can no longer meet the current high requirements as the requirements for use increase during use. Therefore, there is an urgent need for a high-performance bainitic non-modulated steel to meet the requirements. Summary of the Invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a bainitic non-quenched and tempered steel and its preparation method and use, so as to solve the defect that the current bainitic non-quenched and tempered steel has poor mechanical properties and cannot meet the requirements of use under high requirements.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a bainitic non-quenched and tempered steel, wherein the bainitic non-quenched and tempered steel comprises, by weight percentage:

[0008] C 0.22-0.28%, Si 0.7-0.9%, Mn 1.9-2.1%, P≤0.015%, S≤0.015%, Cr0.2-0.3%, V 0.05-0.15%, N 0.014-0.018%, and the balance is Fe and unavoidable impurities.

[0009] The bainitic non-quenched and tempered steel provided by the present invention ensures that the bainitic non-quenched and tempered steel has good mechanical properties by designing and reorganizing the steel components and utilizing the synergistic strengthening effect between elements, with a tensile strength of ≥1023MPa and a yield strength of ≥754MPa.

[0010] As a preferred technical solution of the present invention, the bainitic non-quenched and tempered steel comprises, by mass percentage:

[0011] C 0.24-0.26%, Si 0.8-0.9%, Mn 2-2.1%, P≤0.015%, S≤0.015%, Cr0.25-0.28%, V 0.08-0.12%, N 0.016-0.017%, and the balance is Fe and unavoidable impurities.

[0012] In a second aspect, the present invention provides a method for preparing the bainitic non-quenched and tempered steel as described in the first aspect, the preparation method comprising:

[0013] The process is carried out in sequence: molten iron pretreatment, converter smelting, ladle refining, vacuum refining, round billet continuous casting and rolling.

[0014] As a preferred technical solution of the present invention, the endpoint sulfur content of the molten iron pretreatment is ≤0.04% by mass.

[0015] As a preferred technical solution of the present invention, the final carbon content of the converter smelting is 0.05-0.1% by mass.

[0016] Preferably, the endpoint phosphorus content in the converter smelting is ≤0.015% by mass.

[0017] As a preferred technical solution of the present invention, the slag used in the ladle refining comprises, by mass percentage, the following: CaO 55-60%, SiO2 4-9%, and Al2O3 32-36%.

[0018] Preferably, the maintenance time of the white slag in the ladle refining is ≥20 min.

[0019] As a preferred technical solution of the present invention, the vacuum time of the vacuum refining is ≥15 min.

[0020] Preferably, the soft blowing time of the vacuum refining is ≥20 min.

[0021] As a preferred technical solution of the present invention, the preheating and holding temperature of the cast billet before rolling is 1100-1150°C.

[0022] Preferably, the preheating and holding time of the cast billet before rolling is 300-350 minutes.

[0023] As a preferred technical solution of the present invention, the starting rolling temperature is 1000-1080°C.

[0024] Preferably, the final rolling temperature is 830-870°C.

[0025] In a third aspect, the present invention provides a use of the bainitic non-quenched and tempered steel as described in the first aspect, the use comprising: using the bainitic non-quenched and tempered steel to prepare an automobile front axle.

[0026] Compared with the existing technical solutions, the present invention has the following beneficial effects:

[0027] The bainitic non-quenched and tempered steel provided by the present invention is designed by adjusting the element composition and the preparation process, utilizing the coordination effect between the elements and a rolling process using controlled cooling and controlled rolling to form grains with good performance, thereby ensuring that the obtained bainitic non-quenched and tempered steel has good performance. The tensile strength of the obtained bainitic non-quenched and tempered steel is ≥1150MPa and the yield strength is ≥800MPa.

[0028] The present invention is further described in detail below. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0029] To better illustrate the present invention and facilitate understanding of the technical solutions of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0030] This embodiment provides a bainitic non-quenched and tempered steel, which comprises, by weight percentage:

[0031] C 0.22-0.28%, Si 0.7-0.9%, Mn 1.9-2.1%, P≤0.015%, S≤0.015%, Cr0.2-0.3%, V 0.05-0.15%, N 0.014-0.018%, and the balance is Fe and unavoidable impurities.

[0032] In the present invention, the C content in the bainitic non-quenched and tempered steel is 0.22-0.28% by mass, for example, 0.22%, 0.225%, 0.23%, 0.235%, 0.24%, 0.245%, 0.25%, 0.255%, 0.26%, 0.265%, 0.27%, 0.275% or 0.28%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0033] In the present invention, the Si content in the bainitic non-quenched and tempered steel is 0.7-0.9% by mass, for example, it can be 0.7%, 0.72%, 0.74%, 0.76%, 0.78%, 0.8%, 0.82%, 0.84%, 0.86%, 0.88% or 0.9%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0034] In the present invention, the Mn content in the bainitic non-quenched and tempered steel is 1.9-2.1% by mass, for example, 1.9%, 1.92%, 1.94%, 1.96%, 1.98%, 2%, 2.02%, 2.04%, 2.06%, 2.08% or 2.1%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0035] In the present invention, the P content in the bainitic non-quenched and tempered steel is ≤0.015% by mass, for example, it can be 0.015%, 0.014%, 0.013%, 0.012%, 0.011%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002% or 0.001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0036] In the present invention, the S content in the bainitic non-quenched and tempered steel is ≤0.015% by mass, and can be, for example, 0.015%, 0.014%, 0.013%, 0.012%, 0.011%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002% or 0.001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0037] In the present invention, the Cr content in the bainitic non-quenched and tempered steel is 0.2-0.3% by mass, for example, it can be 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29% or 0.3%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0038] In the present invention, the V content in the bainitic non-quenched and tempered steel is 0.05-0.15% by mass, for example, it can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14% or 0.15%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0039] In the present invention, the nitrogen content in the bainitic non-quenched and tempered steel is 0.014-0.018% by mass, for example, it can be 0.014%, 0.0142%, 0.0144%, 0.0146%, 0.0148%, 0.015%, 0.0152%, 0.0154%, 0.0156%, 0.0158%, 0.016%, 0.0162%, 0.0164%, 0.0166%, 0.0168%, 0.017%, 0.0172%, 0.0174%, 0.0176%, 0.0178% or 0.018%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0040] Wherein, the bainitic non-quenched and tempered steel includes, by mass percentage:

[0041] C 0.24-0.26%, Si 0.8-0.9%, Mn 2-2.1%, P≤0.015%, S≤0.015%, Cr0.25-0.28%, V 0.08-0.12%, N 0.016-0.017%, and the balance is Fe and unavoidable impurities.

[0042] Furthermore, this embodiment provides a method for preparing the aforementioned bainitic non-quenched and tempered steel, comprising:

[0043] The process is carried out in sequence: molten iron pretreatment, converter smelting, ladle refining, vacuum refining, round billet continuous casting and rolling.

[0044] The endpoint sulfur content of the molten iron pretreatment is ≤0.04% by mass, for example, it can be 0.04%, 0.035%, 0.03%, 0.025%, 0.02%, 0.015%, 0.01%, 0.005% or 0.001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0045] Among them, the endpoint carbon content of the converter smelting is 0.05-0.1% by mass, for example, it can be 0.05%, 0.055%, 0.06%, 0.065%, 0.07%, 0.075%, 0.08%, 0.085%, 0.09%, 0.095% or 0.1%, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0046] Among them, preferably, the endpoint phosphorus content of the converter smelting is ≤0.015% by mass, for example, it can be 0.015%, 0.014%, 0.013%, 0.012%, 0.011%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002% or 0.001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0047] The slag used in the ladle refining comprises, by mass percentage, 55-60% CaO, 4-9% SiO2, and 32-36% Al2O3, which total 100%. The CaO content may be, for example, 55%, 55.5%, 56%, 56.5%, 57%, 57.5%, 58%, 58.5%, 59%, 59.5%, or 60%, the SiO2 content may be, for example, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, or 9%, and the Al2O3 content may be, for example, 32%, 32.5%, 33%, 33.5%, 34%, 34.5%, 35%, 35.5%, or 36%, but is not limited to the values ​​listed above. Other values ​​within this range that are not listed also meet the requirements.

[0048] The maintenance time of the white slag in the ladle refining is ≥20 min, for example, it can be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0049] The vacuum time of the vacuum refining is ≥15 min, for example, it can be 15 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min or 30 min, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0050] The soft blowing time of the vacuum refining is ≥20 min, for example, it can be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0051] In the present invention, during vacuum refining, N is controlled to be 0.014-0.018%, and V is controlled to be 0.05-0.15%, calculated in percentage by mass.

[0052] Among them, the preheating and holding temperature of the ingot before rolling is 1100-1150℃, for example, it can be 1100℃, 1105℃, 1110℃, 1115℃, 1120℃, 1125℃, 1130℃, 1135℃, 1140℃, 1145℃ or 1150℃, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0053] Among them, the preheating and holding time of the ingot before rolling is 300-350min, for example, it can be 300min, 305min, 310min, 315min, 320min, 325min, 330min, 335min, 340min, 345min or 350min, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0054] Wherein, the starting rolling temperature is 1000-1080℃, for example, it can be 1000℃, 1005℃, 1010℃, 1015℃, 1020℃, 1025℃, 1030℃, 1035℃, 1040℃, 1045℃, 1050℃, 1055℃, 1060℃, 1065℃, 1070℃, 1075℃ or 1080℃, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0055] The final rolling temperature is 830-870°C, for example, it can be 830°C, 835°C, 840°C, 845°C, 850°C, 855°C, 860°C, 865°C or 870°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0056] Furthermore, this embodiment provides a use of the aforementioned bainitic non-quenched and tempered steel, which includes: using the bainitic non-quenched and tempered steel to prepare an automobile front axle.

[0057] Furthermore, in order to illustrate the excellent performance that can be achieved by the bainitic non-quenched and tempered steel provided by the present invention, the following actual examples are used for illustration, as follows:

[0058] Example 1

[0059] This embodiment provides a bainitic non-quenched and tempered steel, which comprises, by weight percentage:

[0060] C 0.24%, Si 0.8%, Mn 2.05%, P 0.005%, S 0.005%, Cr 0.26%, V 0.1%, N 0.017%, and the balance is Fe and inevitable impurities.

[0061] The preparation process is as follows:

[0062] The process includes hot metal pretreatment, converter smelting, ladle refining, vacuum refining, round billet continuous casting and rolling;

[0063] The endpoint sulfur content of the molten iron pretreatment is 0.005% by mass;

[0064] The end point carbon content of the converter smelting is 0.08% by mass, and the end point phosphorus content is 0.005% by mass;

[0065] The slag used in the ladle refining comprises, by mass percentage, 56% CaO, 8% SiO2, and 36% Al2O3; the white slag is maintained for 20 minutes;

[0066] The vacuum time of the vacuum refining is 20 minutes, and the soft blowing time is 30 minutes;

[0067] The preheating and holding temperature of the cast slab before rolling is 1120° C., and the preheating and holding time is 320 min;

[0068] The starting rolling temperature is 1020°C and the finishing rolling temperature is 840°C.

[0069] Example 2

[0070] This embodiment provides a bainitic non-quenched and tempered steel, which comprises, by weight percentage:

[0071] C 0.26%, Si 0.85%, Mn 2%, P 0.008%, S 0.005%, Cr 0.27%, V 0.09%, N 0.016%, and the balance is Fe and inevitable impurities.

[0072] The preparation process is as follows:

[0073] The process includes hot metal pretreatment, converter smelting, ladle refining, vacuum refining, round billet continuous casting and rolling;

[0074] The endpoint sulfur content of the molten iron pretreatment is 0.005% by mass;

[0075] The endpoint carbon content of the converter smelting is 0.06% by mass, and the endpoint phosphorus content is 0.008% by mass;

[0076] The slag used in the ladle refining comprises, by mass percentage, 58% CaO, 6% SiO2, and 36% Al2O3; the white slag is maintained for 30 minutes;

[0077] The vacuum time of the vacuum refining is 25 minutes, and the soft blowing time is 25 minutes;

[0078] The preheating and holding temperature of the cast slab before rolling is 1130° C., and the preheating and holding time is 330 min;

[0079] The starting rolling temperature is 1050°C and the finishing rolling temperature is 850°C.

[0080] Example 3

[0081] This embodiment provides a bainitic non-quenched and tempered steel, which comprises, by weight percentage:

[0082] C 0.28%, Si 0.7%, Mn 2.1%, P 0.015%, S 0.015%, Cr 0.3%, V 0.05%, N 0.018%, and the balance is Fe and inevitable impurities.

[0083] The preparation process is as follows:

[0084] The process includes hot metal pretreatment, converter smelting, ladle refining, vacuum refining, round billet continuous casting and rolling;

[0085] The endpoint sulfur content of the molten iron pretreatment is 0.015% by mass;

[0086] The end point carbon content of the converter smelting is 0.1% by mass, and the end point phosphorus content is 0.015% by mass;

[0087] The slag used in the ladle refining comprises, by mass percentage, 60% CaO, 8% SiO2, and 32% Al2O3; the white slag is maintained for 20 minutes;

[0088] The vacuum time of the vacuum refining is 18 minutes, and the soft blowing time is 22 minutes;

[0089] The preheating and holding temperature of the cast slab before rolling is 1150° C., and the preheating and holding time is 300 min;

[0090] The starting rolling temperature is 1080°C and the finishing rolling temperature is 870°C.

[0091] Example 4

[0092] This embodiment provides a bainitic non-quenched and tempered steel, which comprises, by weight percentage:

[0093] C 0.22%, Si 0.9%, Mn 2.1%, P 0.015%, S 0.015%, Cr 0.2%, V 0.15%, N 0.014%, and the balance is Fe and inevitable impurities.

[0094] The preparation process is as follows:

[0095] The process includes hot metal pretreatment, converter smelting, ladle refining, vacuum refining, round billet continuous casting and rolling;

[0096] The endpoint sulfur content of the molten iron pretreatment is 0.015% by mass;

[0097] The endpoint carbon content of the converter smelting is 0.05% by mass, and the endpoint phosphorus content is 0.015% by mass;

[0098] The ladle refining comprises, by mass percentage, 60% CaO, 5% SiO2, and 35% Al2O3; the white slag is maintained for 22 minutes;

[0099] The vacuum time of the vacuum refining is 18 minutes, and the soft blowing time is 20 minutes;

[0100] The preheating and holding temperature of the cast slab before rolling is 1100° C., and the preheating and holding time is 350 min;

[0101] The starting rolling temperature of the rolling is 1000°C, and the finishing rolling temperature is 830°C.

[0102] Comparative Example 1

[0103] The only difference from Example 1 is that the Si content in the bainitic non-quenched and tempered steel is 0.4% by mass.

[0104] Comparative Example 2

[0105] The only difference from Example 1 is that the Si content in the bainitic non-quenched and tempered steel is 1% by mass.

[0106] Comparative Example 3

[0107] The only difference from Example 1 is that the mass percentage of Mn in the bainitic non-quenched and tempered steel is 1.82%.

[0108] Comparative Example 4

[0109] The only difference from Example 1 is that the Cr content in the bainitic non-quenched and tempered steel is 0.13% by mass.

[0110] Comparative Example 5

[0111] The only difference from Example 1 is that the N content in the bainitic non-quenched and tempered steel is 0.012% by mass.

[0112] Example 5

[0113] The only difference from Example 1 is that the preheating and holding temperature of the slab before rolling is 1000°C.

[0114] Example 6

[0115] The only difference from Example 1 is that the preheating and holding temperature of the cast slab before rolling is 1180°C.

[0116] Example 7

[0117] The only difference from Example 1 is that the starting rolling temperature is controlled at 950°C.

[0118] Example 8

[0119] The only difference from Example 1 is that the starting rolling temperature is controlled at 1100°C.

[0120] Example 9

[0121] The only difference from Example 1 is that the final rolling temperature is controlled at 800°C.

[0122] Example 10

[0123] The only difference from Example 1 is that the final rolling temperature is controlled at 900°C.

[0124] The steels obtained in the above examples and comparative examples were subjected to mechanical property tests according to GB / T 228.1 "Tensile tests on metallic materials - Part 1: Room temperature test methods". The results are detailed in Table 1 below.

[0125] Table 1

[0126]

[0127]

[0128] As can be seen from Table 1, in the solution provided by the present invention, the bainitic non-quenched and tempered steel provided by the present invention has good mechanical properties by designing and reorganizing the steel composition and utilizing the synergistic strengthening effect between elements, with a tensile strength of ≥1023 MPa and a yield strength of ≥754 MPa. In the preferred solution, the tensile strength is ≥1150 MPa and the yield strength is ≥800 MPa.

[0129] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0130] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0131] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A bainitic non-quenched and tempered steel, characterized in that: The bainite non-quenched and tempered steel comprises, by weight percentage: C 0.22-0.28%, Si 0.7-0.9%, Mn 1.9-2.1%, P≤0.015%, S≤0.015%, Cr0.2-0.3%, V 0.05-0.15%, N 0.014-0.018%, and the balance is Fe and unavoidable impurities.

2. The bainitic non-quenched and tempered steel according to claim 1, characterized in that: The bainite non-quenched and tempered steel comprises, by weight percentage: C 0.24-0.26%, Si 0.8-0.9%, Mn 2-2.1%, P≤0.015%, S≤0.015%, Cr0.25-0.28%, V 0.08-0.12%, N 0.016-0.017%, and the balance is Fe and unavoidable impurities.

3. A method for preparing bainitic non-quenched and tempered steel according to claim 1 or 2, characterized in that: The preparation method comprises: The process is carried out in sequence: molten iron pretreatment, converter smelting, ladle refining, vacuum refining, round billet continuous casting and rolling.

4. The preparation method according to claim 3, wherein The endpoint sulfur content of the molten iron pretreatment is ≤0.04% by mass.

5. The preparation method according to claim 3 or 4, characterized in that The final carbon content of the converter smelting is 0.05-0.1% by mass; Preferably, the endpoint phosphorus content in the converter smelting is ≤0.015% by mass.

6. The preparation method according to any one of claims 3 to 5, characterized in that The slag used in the ladle refining comprises, by mass percentage, 55-60% CaO, 4-9% SiO2, and 32-36% Al2O3; Preferably, the maintenance time of the white slag in the ladle refining is ≥20 min.

7. The preparation method according to any one of claims 3 to 6, wherein The vacuum time of the vacuum refining is ≥15min; Preferably, the soft blowing time of the vacuum refining is ≥20 min.

8. The preparation method according to any one of claims 3 to 7, wherein The preheating and holding temperature of the cast slab before rolling is 1100-1150°C; Preferably, the preheating and holding time of the cast billet before rolling is 300-350 minutes.

9. The preparation method according to any one of claims 3 to 8, wherein The rolling start temperature is 1000-1080°C; Preferably, the final rolling temperature is 830-870°C.

10. Use of the bainitic non-quenched and tempered steel according to claim 1 or 2, characterized in that: The application includes: using the bainite non-quenched and tempered steel to prepare an automobile front axle.

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