Ferrium M54 steel small-specification bar and preparation method thereof

Abstract

The invention relates to the technical field of Ferric M54 steel production, and particularly discloses a Ferric M54 steel small-specification bar and a preparation method thereof.The preparation method comprises the steps that an intermediate blank bar is subjected to solution treatment at the first preset temperature; the bar obtained after solution treatment is continuously rolled, and a small-specification bar primary product is obtained; after online sizing blanking is conducted on the small-specification bar primary product, subcritical heat preservation treatment is conducted at the second preset temperature; quenching treatment is conducted on the small-specification bar primary product obtained after subcritical heat preservation treatment is completed, and the small-specification bar primary product is cooled to the room temperature; carrying out subzero treatment on the quenched primary small-specification bar product, and then carrying out air cooling to room temperature; and after secondary hardening and tempering treatment is conducted on the small-specification bar primary product obtained after subzero treatment, air cooling is conducted to the room temperature, and a small-specification bar finished product is obtained. According to the method, the Ferrium M54 steel small-specification bar is prepared and applied in an engineering mode through the technology of combining rolling deformation and quenching heat treatment, the process is simplified, and meanwhile grains are refined to improve the obdurability of the Ferrium M54 steel small-specification bar.

Description

Technical Field

[0001] The present invention relates to the technical field of Ferrium M54 steel production, and particularly relates to a small-sized bar of Ferrium M54 steel and a preparation method thereof. Background Art

[0002] In the fields of aerospace, military, and high-end manufacturing, extremely high requirements are placed on the strength and toughness of materials. High-cobalt nickel secondary hardening ultra-high strength steel has attracted much attention due to its excellent mechanical properties. Ferrium M54 is a new type of secondary hardening ultra-high strength steel containing W designed and developed by QuesTek Innovations LLC. Its strength and toughness are comparable to those of AerMet100 secondary hardening ultra-high strength steel, and its stress corrosion resistance is significantly superior. In addition, its Co content is greatly reduced compared to AerMet100 secondary hardening ultra-high strength steel, resulting in a decrease in production cost, so it has greater application prospects. The typical chemical composition of Ferrium M54 steel: 0.3% C, 7% Co, 1% Cr, 10% Ni, 2% Mo, 1.3% W, 0.1% V, Bal. Fe. Because it contains 1.3% W, it requires a higher quenching and solution temperature during heat treatment compared to AerMet100 steel. The optimal quenching and solution temperature of AerMet100 steel is 885°C, and the corresponding optimal quenching and solution temperature of Ferrium M54 steel is 1060°C.

[0003] A high solution temperature helps alloying elements dissolve more completely into the matrix to form a uniform solid solution, which is beneficial to improving the strength and toughness of the material. When the solution temperature is not high enough, the alloying elements will not dissolve sufficiently, affecting the material strength. However, if the solution temperature is too high, it may also cause grain growth, thereby reducing the strength and toughness of the material.

[0004] Research on the austenite grain growth behavior of high-cobalt nickel secondary hardening steel at different heating temperatures and holding times shows that as the heating temperature increases and the holding time prolongs, the austenite grain size increases. Especially when the heating temperature exceeds 1050°C, the grain growth rate increases significantly, and the grains will undergo severe coarsening. In practical engineering applications, the grain size grade requirement for AerMet100 steel is ≥7, while the grain size grade requirement for Ferrium M54 steel is ≥4.

[0005] The engineering preparation and application process of Ferrium M54 steel bars is mainly forging (rolling) bars + normalizing + high temperature annealing + rough machining + quenching + deep cooling + secondary hardening and tempering + finishing. However, in the engineering preparation and application of existing Ferrium M54 steel bars, due to the high quenching and solid solution temperature of 1060℃, the control of grain size has always been a difficult point, and the grain size of about level 6 is often difficult to achieve the optimal strength and toughness matching target requirements.

[0006] Based on this, the existing technology still needs to be improved. Summary of the invention

[0007] In order to solve the above technical problems, the embodiment of the present invention proposes a method for improving the strength and toughness of small-sized Ferrium M54 steel bars and a preparation method thereof, so as to solve the technical problem that the Ferrium M54 steel in the prior art cannot meet the application requirements.

[0008] In order to solve the above technical problems, on the one hand, some embodiments of the present invention disclose a method for preparing a small-size Ferrium M54 steel bar, comprising: Step 1: performing a solution treatment on the intermediate billet bar at a first predetermined temperature; Step 2: continuously rolling the solution treated bar to obtain a small-sized bar product; Step 3: After the small-size bar product is cut into fixed lengths online, a subcritical heat preservation treatment is performed at a second predetermined temperature; Step 4: After the subcritical heat preservation treatment, the small-sized bar product is quenched and cooled to room temperature; Step 5: After the quenched small-size bar is subjected to deep cooling within 8 hours, it is air-cooled to room temperature; Step 6: After the cryogenic treatment, the small-sized bar product is subjected to secondary hardening and tempering treatment, and then air-cooled to room temperature to obtain a small-sized bar product.

[0009] In some embodiments, in step 1, the cross-sectional area of ​​the intermediate billet bar is more than 3 times the cross-sectional area of ​​the finished small-sized bar.

[0010] In some embodiments, in step 1, the temperature of the solution treatment is 1060° C.-1100° C., and the holding time is 90-120 min.

[0011] In some embodiments, the cross-sectional area of ​​the intermediate billet bar is such that the total deformation amount of the continuous rolling process is greater than 80%.

[0012] In some embodiments, in step 2, the initial rolling temperature of the continuous rolling is ≥ 1000° C., and the final rolling temperature is ≥ 900° C., so as to balance the deformation of each rolling pass.

[0013] In some embodiments, in step three, the second predetermined temperature is 650 - 800 °C, and the holding time for the subcritical heat preservation treatment is 50 - 70 min.

[0014] In some embodiments, the greater the total deformation amount of continuous rolling, the lower the temperature and the shorter the time of the secondary hardening tempering treatment.

[0015] In some embodiments, when 70% ≤ total deformation amount of continuous rolling < 80%, tempering at 500 - 520 °C for 6 - 10 h is selected for the secondary hardening tempering treatment; when 80% ≤ total deformation amount of continuous rolling < 90%, tempering at 500 - 520 °C for 6 - 10 h is selected for the secondary hardening tempering treatment; when 90% ≤ total deformation amount of continuous rolling < 98%, tempering at 460 - 480 °C for 6 - 10 h is selected for the secondary hardening tempering treatment. In some embodiments, the diameter of the finished small - sized bar is 35 mm - 95 mm.

[0016] In some embodiments, in step six, the temperature of the secondary hardening tempering treatment is 430 - 530 °C, and the holding time is 6 - 12 h; Or, in step five, the temperature of the cryogenic treatment ≤ - 73 °C, and the time is 90 - 110 min.

[0017] On the other hand, the embodiments of the present invention also disclose a small - sized bar of Ferrium M54 steel, which is prepared by using the aforementioned preparation method of the small - sized bar of Ferrium M54 steel; and / or, the grain size is 10 - 11 grades, the tensile strength is 2153 - 2186 MPa, the yield strength is 1786 - 1806 MPa, the elongation is 14.5 - 15.5%, the reduction of area is 60 - 66%, and the fracture toughness is 132 - 146 MPa·m 1 / 2 .

[0018] Adopting the above - mentioned technical solution, the present invention has at least the following beneficial effects: A small - sized bar of Ferrium M54 steel and its preparation method provided by the present invention use a process that combines rolling deformation and quenching heat treatment to engineer the preparation and application of the small - sized bar of Ferrium M54 steel, simplifies the process and refines the grains to improve its strength and toughness. Description of the Drawings

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] Figure 1 It is a process flow diagram of a preparation method for small-sized bars of Ferrium M54 steel disclosed in some embodiments of the present invention. Specific embodiments

[0021] The following will further describe the embodiments of the present disclosure in detail in conjunction with the drawings and examples. The detailed description and drawings of the following examples are used to exemplarily illustrate the principles of the present disclosure, but cannot be used to limit the scope of the present disclosure. The present disclosure can be implemented in many different forms, not limited to the specific embodiments disclosed herein, but including all technical solutions falling within the scope of the claims.

[0022] These embodiments of the present disclosure are provided to make the present disclosure thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, the components of materials, numerical expressions and values described in these embodiments should be construed as merely exemplary, rather than as limitations.

[0023] It should be noted that in the description of the present disclosure, unless otherwise specified, "a plurality" means greater than or equal to two; the orientation or positional relationships indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", etc. are only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present disclosure. When the absolute position of the described object changes, the relative position relationship may also change accordingly.

[0024] In addition, the "first", "second" and similar terms used in the present disclosure do not denote any order, quantity or importance, but are only used to distinguish different parts. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range. Terms such as "comprising" or "including" mean that the elements before the term cover the elements listed after the term, and do not exclude the possibility of also covering other elements.

[0025] It should also be noted that in the description of the present disclosure, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances. When it is described that a specific device is located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0026] All terms used in the present disclosure have the same meanings as those understood by those of ordinary skill in the art to which the present disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in, for example, a general dictionary should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such here.

[0027] Technologies, methods, and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but where appropriate, the technologies, methods, and devices should be regarded as part of the specification.

[0028] As Figure 1 shown, some embodiments of the present invention disclose a preparation method for Ferrium M54 steel bars with a specification of 35 mm ≤ φ ≤ 95 mm. By using a process that combines rolling deformation and quenching heat treatment, the engineering preparation and application of small-sized Ferrium M54 steel bars are realized, simplifying the process while refining the grains and improving their strength and toughness.

[0029] To achieve the above object, the present invention can be implemented by the following technical solutions: 1) Preparation of intermediate billets: The cross-sectional area of the intermediate billet is more than 3 times that of the finished bar; as a preferred embodiment, the recommended cross-sectional area of the intermediate billet is more than 6 times that of the finished bar, ensuring that the total rolling deformation is more than 80%, so as to ensure that the bar obtains the best microstructure and properties after rolling.

[0030] 2) Solution treatment: Heat the bar to the temperature range of 1060 °C - 1100 °C and hold for 90 - 120 min for solution treatment; as a preferred embodiment, heat the bar to the optimal solution temperature of 1060 °C and hold for 90 min for solution treatment to ensure that alloying elements are fully dissolved while the grains do not grow excessively.

[0031] 3) Continuous rolling: Immediately perform continuous rolling on the bar that has undergone solution treatment in step 2) to obtain the required small-sized bar; generally, the initial rolling temperature ≥ 1000 °C and the final rolling temperature ≥ 900 °C, and balance the deformation amount of each rolling pass.

[0032] 4) Subcritical insulation: After the bars are cut to length online after the rolling in step 3), they are immediately sent to a 650-800℃ heating furnace for insulation for 1 hour for subcritical insulation treatment; generally, different subcritical insulation temperatures correspond to different total deformation amounts of continuous rolling. The larger the total deformation amount of continuous rolling, the higher the subcritical insulation temperature can be.

[0033] 5) Quenching treatment: The bar from step 4) is immediately placed in a water tank for quenching treatment and cooled to room temperature; the water tank flow can be circulated and the water temperature can be controlled below 30°C to ensure sufficient quenching cooling speed.

[0034] 6) Cryogenic treatment: The bar material in step 5) is cryogenically treated within 8 hours at ≤-73°C for 100 minutes, and then air-cooled to room temperature; 7) Secondary hardening and tempering treatment: The bar in step 6) is kept at a temperature range of 430-530℃ for 6-12h for secondary hardening and tempering treatment, and then air-cooled to room temperature. Different optimal secondary hardening and tempering temperatures and times correspond to different total deformation amounts. The greater the total deformation amount of continuous rolling, the lower the secondary hardening and tempering temperature can be and the shorter the time can be.

[0035] The "immediately" in this embodiment means that the previous and next processes are carried out uninterruptedly, which generally depends on the position of the previous process and the next process. The time required for bar transportation is the time interval between their processes, which is generally between 1-3 minutes. Because the bar is at high temperature, if the time interval is too long, the temperature of the bar will drop too much, which will cause adverse effects.

[0036] However, after water quenching, cryogenic treatment is carried out. Because after water quenching, the bar material is at room temperature, and sometimes due to various negligence, cryogenic treatment may not be carried out in time between this time and the next process of cryogenic treatment. However, in the principle of heat treatment, cryogenic treatment is required in time, especially not overnight (that is, cryogenic treatment after 24 hours). The process regulations of this application are to carry out cryogenic treatment within 8 hours after quenching.

[0037] As a preferred implementation, when the total deformation of continuous rolling is 70%≤80%, the secondary hardening and tempering treatment is performed by tempering at 500-520°C for 6-10h.

[0038] As a preferred implementation, when the total deformation of continuous rolling is 80%≤90%, the secondary hardening and tempering treatment is performed by tempering at 500-520°C for 6-10h.

[0039] As a preferred embodiment, when 90% ≤ total continuous rolling deformation < 98%, tempering at 460 - 480°C for 6 - 10 h is selected for secondary hardening tempering treatment. The above-mentioned embodiments of the present invention combine the engineering preparation process (heating to above the solution temperature + rolling + bar + normalizing + high-temperature annealing) and application process (rough machining + quenching + cryogenic treatment + secondary hardening tempering + finish machining) of Ferrium M54 steel bars with a diameter of 35 mm ≤ φ ≤ 95 mm. The combined rolling forming and quenching in the application process simplifies the engineering preparation and application process to: heating to the solution temperature + rolling + subcritical holding + cryogenic treatment + secondary hardening tempering + rough machining + finish machining. Simplifying the engineering preparation and application of small-sized Ferrium M54 steel bars in this way can refine the grains and improve their applied strength and toughness at the same time.

[0040] For the conventional engineering preparation and application process of Ferrium M54 steel, because quenching + cryogenic treatment + secondary hardening tempering treatment are required after rough machining during application, its high quenching solution temperature of 1060°C results in the grain size generally being controlled at about grade 6, and it is difficult to achieve the best matching goal of strength and toughness. The present invention combines the bar rolling forming and application quenching tightly together, and the simplified engineering preparation and application process can be summarized as: heating to the solution temperature + rolling + subcritical holding + quenching + cryogenic treatment + secondary hardening tempering + rough machining + finish machining. The main advantages of the preparation and application of small-sized bars in the technical solution of the present invention are as follows: During the process of heating to the solution temperature + rolling + subcritical holding + quenching + cryogenic treatment + secondary hardening tempering, it causes the formation of an ultrafine-grained martensite structure in the steel, which has a high density of dislocations, nano-scale M2C precipitation hardening, and nano-scale reverse transformation austenite thin films. This structure provides excellent strength and toughness, enabling the steel to have good ductility while maintaining high strength.

[0041] During the process of heating to the solution temperature + rolling + subcritical holding + quenching + cryogenic treatment + secondary hardening tempering, the subcritical holding after rolling can eliminate part of the internal stress formed during the rolling process and avoid crack generation during the subsequent quenching process.

[0042] Rolling accelerates the precipitation process of M2C carbides by increasing the dislocation density and providing more precipitation phase nucleation sites, changing the kinetics of M2C precipitation and reverse transformation austenite precipitation. This allows the use of a lower tempering temperature or a shorter tempering time. After secondary hardening by tempering, although the dislocation density decreases, the precipitation hardening compensates for the strength loss due to dislocation recovery, and the precipitation of reverse transformation austenite further increases the toughness.

[0043] After rough machining, there is no need for quenching + cryogenic treatment + secondary hardening tempering treatment, no need to go through the high quenching solution temperature of 1060°C, and there is no need to worry about the grain growth tendency during high-temperature solution. The grain size can be controlled at grade 10 or above, which can lead to higher strength and better toughness.

[0044] The present invention will be described in detail below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0045] A preparation method for Ferrium M54 steel bars with a specification of 35mm ≤ φ ≤ 95mm uses a process that combines rolling deformation and quenching heat treatment to engineer the preparation and application of small-sized Ferrium M54 steel bars, simplifying the process while refining the grains and improving their strength and toughness. The specific steps of its preparation method: intermediate billet preparation + solution treatment + continuous rolling + quenching treatment + cryogenic treatment + secondary hardening tempering treatment.

[0046] Comparative Example 1: Prepare a 200mm × 200mm square billet, heat it in a heating furnace to 1100°C and hold for 120 min, continuously roll it to a φ90mm specification, air cool it to room temperature, normalize it at 1075°C × 60 min and air cool it to room temperature, anneal it at 650°C × 8 h and air cool it to room temperature. Rough machining, solution quench at 1060°C × 90 min, cryogenic treatment at -73°C × 100 min, secondary hardening tempering at 516°C × 10 h, and finish machining for application.

[0047] Comparative Example 2: Prepare a 150mm × 150mm square billet, heat it in a heating furnace to 1070°C and hold for 120 min, continuously roll it to a φ60mm specification, air cool it to room temperature, normalize it at 1075°C × 60 min and air cool it to room temperature, anneal it at 650°C × 8 h and air cool it to room temperature. Rough machining, solution quench at 1060°C × 90 min, cryogenic treatment at -73°C × 100 min, secondary hardening tempering at 516°C × 10 h, and finish machining for application.

[0048] Comparative Example 3: Prepare a 150mm × 150mm square billet, heat it in a heating furnace to 1060°C and hold for 120 min, continuously roll it to a φ35mm specification, air cool it to room temperature, normalize it at 1075°C × 60 min and air cool it to room temperature, anneal it at 650°C × 8 h and air cool it to room temperature. Rough machining, solution quench at 1060°C × 90 min, cryogenic treatment at -73°C × 100 min, secondary hardening tempering at 516°C × 10 h, and finish machining for application.

[0049] Example 1: Prepare a 200mm×200mm square billet, heat it in a heating furnace to 1060°C and hold for 90 min, continuously roll it to a φ90mm specification, cut it to a fixed length online, hold it at 700°C for subcritical treatment for 1 h, quench it in a water tank to room temperature, perform cryogenic treatment at -73°C for 100 min within 1 hour and then air cool back to room temperature, and perform secondary hardening tempering treatment at 490°C×8 h. For rough machining and finish machining applications.

[0050] Example 2: Prepare a 150mm×150mm square billet, heat it in a heating furnace to 1060°C and hold for 90 min, continuously roll it to a φ60mm specification, cut it to a fixed length online, hold it at 700°C for subcritical treatment for 1 h, quench it in a water tank to room temperature, perform cryogenic treatment at -73°C for 100 min within 0.5 hour and then air cool back to room temperature, and perform secondary hardening tempering treatment at 490°C×8 h. For rough machining and finish machining applications.

[0051] Example 3: Prepare a 150mm×150mm square billet, heat it in a heating furnace to 1060°C and hold for 90 min, continuously roll it to a φ35mm specification, cut it to a fixed length online, hold it at 750°C for subcritical treatment for 1 h, quench it in a water tank to room temperature, perform cryogenic treatment at -73°C for 100 min within 2 hours and then air cool back to room temperature, and perform secondary hardening tempering treatment at 470°C×8 h. For rough machining and finish machining applications.

[0052] Table 1 Grain size, strength and toughness of Ferrium M54 steel bars in examples and comparative examples during application

[0053] As can be seen from Table 1, in Comparative Examples 1-3, the grain sizes corresponding to the φ35, φ60, and φ90mm bars are 6, 6.5, and 7.5 levels, and the corresponding tensile strengths are 2002-2010 MPa, yield strengths are 1737-1750 MPa, elongation rates are 11.5-12%, reduction of area rates are 55-59%, and fracture toughnesses are 112-120 MPa·m1 / 2. In Examples 1-3, the grain sizes corresponding to the φ35, φ60, and φ90mm bars are 10, 10.5, and 11 levels, and the corresponding tensile strengths are 2153-2186 MPa, yield strengths are 1786-1806 MPa, elongation rates are 14.5-15.5%, reduction of area rates are 60-66%, and fracture toughnesses are 132-146 MPa·m 1 / 2。Comparing the comparative examples and the control examples, it can be seen that by adopting the preparation scheme of small-sized bars with the compact combination of rolling forming and quenching, the grain size of Ferrium M54 steel can be increased from grade 6-7.5 to grade 10 and above, and at the same time, the strength and toughness (tensile properties and fracture toughness) can be relatively increased by more than 10%. The technical scheme of using the compact combination of rolling forming and quenching described in the present invention is particularly suitable for the production of small-sized bars of high-cobalt-nickel secondary hardening ultra-high-strength steel with a high solid solution temperature.

[0054] So far, the embodiments of the present disclosure have been described in detail. To avoid obscuring the concept of the present disclosure, some details well known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein based on the above description.

[0055] Although some specific embodiments of the present disclosure have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Those skilled in the art should understand that the above embodiments can be modified or partial technical features can be equivalently replaced without departing from the scope and spirit of the present disclosure. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way.

Claims

1. A method for preparing small-size bars of Ferrium M54 steel, characterized in that: include: Step 1: performing a solution treatment on the intermediate billet bar at a first predetermined temperature; Step 2: continuously rolling the solution treated bar to obtain a small-sized bar product; Step 3: After the small-size bar product is cut into fixed lengths online, a subcritical heat preservation treatment is performed at a second predetermined temperature; Step 4: After the subcritical heat preservation treatment, the small-sized bar product is quenched within 8 hours and cooled to room temperature; Step 5: subjecting the quenched small-size bar to cryogenic treatment and then air cooling to room temperature; Step 6: After the cryogenic treatment, the small-sized bar product is subjected to secondary hardening and tempering treatment, and then air-cooled to room temperature to obtain a small-sized bar product.

2. The method for preparing small-size Ferrium M54 steel bars according to claim 1, characterized in that: In step 1, the cross-sectional area of ​​the intermediate billet bar is more than 3 times the cross-sectional area of ​​the finished small-size bar.

3. The method for preparing small-size bars of Ferrium M54 steel according to claim 1, characterized in that: In step 1, the temperature of the solution treatment is 1060°C-1100°C, and the holding time is 90-120 minutes.

4. The method for preparing small-size bars of Ferrium M54 steel according to claim 1, characterized in that: The cross-sectional area of ​​the intermediate billet bar is such that the total deformation amount of the continuous rolling process is above 80%.

5. The method for preparing small-size bars of Ferrium M54 steel according to claim 1, characterized in that: In step 2, the initial rolling temperature of continuous rolling is ≥1000°C and the final rolling temperature is ≥900°C, and the deformation of each rolling pass is balanced.

6. The method for preparing small-size bars of Ferrium M54 steel according to claim 1, characterized in that: In step three, the second predetermined temperature is 650-800° C., and the insulation time of the subcritical insulation treatment is 50-70 minutes.

7. The method for preparing small-size bars of Ferrium M54 steel according to claim 1, characterized in that: The greater the total deformation of continuous rolling, the lower the temperature and the shorter the time of secondary hardening and tempering treatment.

8. The method for preparing small-size bars of Ferrium M54 steel according to claim 1, characterized in that: When the total deformation of continuous rolling is less than 70% and the total deformation is less than 80%, the secondary hardening and tempering treatment is carried out at 500-520℃ for 6-10h; When the total deformation of continuous rolling is less than 80% and the total deformation is less than 90%, the secondary hardening and tempering treatment is carried out at 500-520℃ for 6-10h; When the total deformation of continuous rolling is 90%≤98%, select 460-480℃ tempering for 6-10h for secondary hardening and tempering treatment.

9. The method for preparing small-size Ferrium M54 steel bars according to claim 1, characterized in that: The diameter of the finished small-size bar product is 35mm-95mm; And / or, in step 6, the temperature of the secondary hardening and tempering treatment is 430-530°C, and the holding time is 6-12h; And / or, in step 5, the temperature of the cryogenic treatment is ≤-73°C and the time is 90-110 min.

10. A Ferrium M54 steel small size bar, characterized in that: The method for preparing small-size bars of Ferrium M54 steel is adopted according to any one of claims 1 to 9; and / or, the grain size is 10-11, the tensile strength is 2153-2186 MPa, the yield strength is 1786-1806 MPa, the elongation is 14.5-15.5%, the cross-sectional reduction is 60-66%, and the fracture toughness is 132-146 MPa·m 1 / 2 .

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