High-plasticity 3GPa-grade medium-low alloy steel and preparation method thereof

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to high-plasticity 3GPa-grade medium-low alloy steel and a preparation method thereof. The preparation method comprises the following steps: austenitizing the medium-low alloy steel, performing high-temperature thermal deformation treatment, cooling to a first preset temperature at a first cooling speed, performing continuous temperature deformation between the first preset temperature and a second preset temperature, cooling to room temperature, and performing low-temperature tempering treatment to prepare the high-plasticity 3GPa-grade medium-low alloy steel. The high-plasticity 3GPa-grade medium-low alloy steel has excellent work hardening capacity, the problem that existing ultrahigh-strength steel is low in plasticity is solved, the material has excellent plasticity under the condition of ultrahigh strength, meanwhile, the total amount of expensive metal elements such as Mo and Ni is remarkably reduced, material composition segregation of the material is reduced, and the service life of the material is prolonged. And the service stability of a part prepared from the material is improved.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical technology, and more specifically relates to a high-plasticity 3 GPa-grade medium and low alloy steel and a preparation method thereof. Background Art

[0002] Ultra-high strength steel is not only the most important application material for key load-bearing components of high-end equipment in fields such as aviation, energy, transportation, and weapons, such as aircraft landing gears and protective armors, but also a key structural material necessary for major projects such as "deep earth, deep sea, and deep space" and key high-end equipment such as future interstellar exploration and comprehensive utilization of resources.

[0003] The inverted relationship between the strength and plasticity of traditional materials results in very low plasticity of ultra-high strength steel. Currently, for ultra-high strength steel at the 3 GPa level, only maraging steel or pearlitic steel wire treated by cold drawing can reach it. However, the plasticity of both of these two types of materials is very low, <5%, and the plasticity of cold-drawn steel wire is even <2%, with brittle fracture.

[0004] In addition, for maraging steel, it contains a large amount of expensive metal elements such as Co, Mo, and Ni, and the total alloy content is usually above 40%. This not only greatly increases the cost of steel materials, but also due to the addition of a large amount of alloying elements, the fluidity of the molten steel is poor, the material composition segregation is serious, and it is very easy to cause instability in the service performance of key components.

[0005] Therefore, developing medium or low alloy steel preparation technology to achieve an ultra-high strength of 3 GPa level is the forefront of current research in the field of steel materials and also a challenge in the field of high-end steel materials. Summary of the Invention

[0006] The purpose of the present invention is to provide a high-plasticity 3 GPa-grade medium and low alloy steel and a preparation method thereof to solve the problems existing in the above-mentioned prior art and achieve the preparation of high-plasticity 3 GPa-grade medium and low alloy steel.

[0007] To achieve the above purpose, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention: Provide a preparation method of a high-plasticity 3 GPa-grade medium and low alloy steel, and the steps include:

[0009] After subjecting the medium and low alloy steel to austenitization treatment, perform hot deformation treatment at high temperature, cool to a first preset temperature at a first cooling rate, perform continuous warm deformation between the first preset temperature and the second preset temperature and then cool, and then perform low-temperature tempering treatment to obtain the high-plasticity 3 GPa-grade medium and low alloy steel.

[0010] In the present invention, medium and low alloy steels are austenitized by conventional heating methods or rapid heating methods such as induction heating, so that the medium and low alloy steels form austenite structures. Then, through hot deformation treatment at high temperatures, the austenite grains are effectively refined. Subsequently, by controlling the first cooling rate, during which no ferrite or pearlite phase transformation occurs in the supercooled austenite during cooling, and through continuous warm deformation treatment, the supercooled austenite undergoes warm deformation and precipitates nano second phases. After tempering treatment after cooling, the quenching stress is effectively eliminated.

[0011] Furthermore, the temperature of the hot deformation treatment at high temperatures is 850 - 1250 °C, and the deformation amount > 30%.

[0012] Furthermore, the first cooling rate is 1 - 100 °C / s.

[0013] Furthermore, the first preset temperature is 500 - 700 °C.

[0014] Furthermore, the second preset temperature is 100 - 500 °C.

[0015] Furthermore, the number of passes of the continuous warm deformation ≥ 2, and the total deformation amount ≥ 50%.

[0016] Furthermore, the cooling rate during cooling after continuous warm deformation > 2 °C / s.

[0017] Furthermore, the temperature of the low-temperature tempering treatment is 100 - 300 °C, and the time is 0.1 - 5 h.

[0018] Furthermore, by mass percentage, the composition of the medium and low alloy steels includes: C 0.40 - 0.65%, Mn + Cr 1.0 - 3.5%, Al + Si 1.0 - 2.0%, Mo + Ni < 2.0%, V + Nb + Ti 0 - 0.3%, P < 0.02, S < 0.02, O < 0.0015%, N < 0.008%, and H < 0.0001%, with the balance being Fe and inevitable impurities.

[0019] Furthermore, the high-plasticity 3 GPa grade medium and low alloy steels include martensite and retained austenite, wherein the content of retained austenite < 20%.

[0020] Optionally, the high-plasticity 3 GPa grade medium and low alloy steels further include bainite and / or nano second phases.

[0021] The second technical solution of the present invention: Provide a high-plasticity 3 GPa grade medium and low alloy steel, which is obtained by the above preparation method.

[0022] The third technical solution of the present invention: Provide an application of the above-mentioned high-plasticity 3GPa-grade medium and low-alloy steel in the preparation of load-bearing components.

[0023] The fourth technical solution of the present invention: Provide a method for improving the strength and plasticity of medium and low-alloy steel, the steps include:

[0024] After austenitizing the medium and low-alloy steel, perform hot deformation treatment at high temperature, then cool to the first preset temperature at the first cooling rate, and then perform continuous warm deformation between the first preset temperature and the second preset temperature. After cooling to room temperature, perform low-temperature tempering treatment to obtain high-plasticity 3GPa-grade medium and low-alloy steel.

[0025] Further, the temperature of the hot deformation treatment at high temperature is 850-1250°C, and the deformation amount > 30%.

[0026] Further, the first cooling rate is 1-100°C / s.

[0027] Further, the first preset temperature is 500-700°C.

[0028] Further, the second preset temperature is 100-500°C.

[0029] Further, the number of deformation passes of the continuous warm deformation ≥ 2, and the total deformation amount ≥ 50%.

[0030] Further, the cooling rate for cooling to room temperature > 2°C / s.

[0031] Further, the temperature of the low-temperature tempering treatment is 100-300°C, and the time is 0.1-5h.

[0032] Further, by mass percentage, the composition of the medium and low-alloy steel includes: C 0.40-0.65%, Mn+Cr 1.0-3.5%, Al+Si 1.0-2.0%, Mo+Ni < 2.0%, V+Nb+Ti 0-0.3%, P < 0.02, S < 0.02, O < 0.0015%, N < 0.008% and H < 0.0001%, and the balance is Fe and unavoidable impurities.

[0033] Further, the high-plasticity 3GPa-grade medium and low-alloy steel includes martensite and retained austenite, wherein the content of retained austenite < 20%.

[0034] Optionally, the high-plasticity 3GPa-grade medium and low-alloy steel further includes bainite and / or nano-second phase.

[0035] The present invention discloses the following technical effects:

[0036] Through the control of the mechanical metallurgy process, the present invention prepares an ultra-high strength steel with a tensile strength ≥ 3 GPa and an elongation ≥ 5% from medium and low alloy steel. It has excellent work hardening ability, solves the problem of low plasticity of existing ultra-high strength steels, enables the material to have excellent plasticity while having ultra-high strength, and at the same time significantly reduces the total amount of expensive metal elements such as Mo and Ni, reduces the material composition segregation of the material, and improves the service stability of the components prepared therefrom. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0038] Figure 1 TEM image of the high-plasticity 3 GPa grade medium and low alloy steel prepared in Example 1.

[0039] Figure 2 TEM image of the high-plasticity 3 GPa grade medium and low alloy steel prepared in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation to the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0041] It should be understood that the terms used in the present invention are only for describing particular embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0042] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0043] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the specification of the present invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0044] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0045] It should be noted that the aspects not described in detail in the present invention are all conventional operating means in the art and are not the focus of the present invention.

[0046] Unless otherwise specified, the room temperature and normal temperature referred to in the specific embodiments of the present invention both refer to 20 - 30 °C.

[0047] Example 1

[0048] The preparation steps of the high - plasticity 3GPa - grade medium - low alloy steel include:

[0049] Raw material preparation: By mass percentage, the components of the medium - low alloy steel include: C 0.47%, Al + Si 1.35%, Mn + Cr 3.0%, Mo + Ni 0.70%, V + Nb + Ti 0.17%, O 0.0011%, H 0.00005%, N 0.005%, P 0.01% and S 0.01%, and the balance is iron and unavoidable impurities.

[0050] Austenitize the above - mentioned medium - low alloy steel, heat it at 1150 °C, hold for 5 minutes to make it austenitized, conduct hot deformation at high temperature (1150 °C), the deformation amount is 60%, then cool it to 650 °C at a cooling rate of 10 °C / s, then continuously deform it for 5 passes, the deformation amount of each pass is 15%, 12%, 11%, 12%, 15% respectively, the temperature after deformation is 380 °C, then cool it to room temperature at a cooling rate of 5 °C / s, and finally conduct tempering treatment at 170 °C, hold for 2 h to obtain the high - plasticity 3GPa - grade medium - low alloy steel.

[0051] After being processed by the process of Example 1, the retained austenite content in the obtained high - plasticity 3GPa - grade medium - low alloy steel is 12.5%, the yield strength of the steel is 1950 MPa, the tensile strength is 3025 MPa, the uniform elongation is 5.8%, and the total elongation is 7.2%.

[0052] Figure 1 It is the TEM image of the high - plasticity 3GPa - grade medium - low alloy steel prepared for Example 1.

[0053] Example 2

[0054] The preparation steps of a high-plasticity medium-low alloy steel with a strength level of 3 GPa include:

[0055] Raw material preparation: By mass percentage, the composition of the medium-low alloy steel includes: C 0.57%, Al + Si 1.80%, Mn + Cr 2.5%, Mo + Ni 0.52%, V + Nb + Ti 0.28%, O 0.0010%, H 0.00007%, N 0.004%, P: 0.01% and S: 0.01%, with the balance being iron and unavoidable impurities.

[0056] Austenitize the above medium-low alloy steel at a heating temperature of 1000 °C for 5 minutes, perform hot deformation at high temperature (1000 °C) with a deformation amount of 45%, then cool it to 550 °C at a cooling rate of 30 °C / s. Subsequently, continuously deform it in 3 passes with deformation amounts of 20%, 15%, and 28% respectively for each pass. After the deformation is completed, the temperature is 350 °C, and then cool it to room temperature at 8 °C / s. Finally, perform tempering treatment at 220 °C for a holding time of 0.5 h to obtain a high-plasticity medium-low alloy steel with a strength level of 3 GPa.

[0057] After being processed by the process of Example 2, the retained austenite content in the obtained high-plasticity medium-low alloy steel with a strength level of 3 GPa is 11.0%, the yield strength of the steel is 1760 MPa, the tensile strength is 3083 MPa, the uniform elongation is 6.4%, and the total elongation is 6.8%.

[0058] Figure 2 TEM image of the high-plasticity medium-low alloy steel with a strength level of 3 GPa prepared in Example 2.

[0059] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other.

[0060] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing high plasticity 3GPa grade low-medium alloy steel, characterized in that the steps include: After austenitizing the medium and low alloy steel, a high-temperature heat deformation treatment is performed, and the steel is cooled to a first preset temperature at a first cooling rate, and then continuously warm-deformed and cooled between the first preset temperature and the second preset temperature, and then a low-temperature tempering treatment is performed to obtain the high-plasticity 3GPa grade medium and low alloy steel.

2. The preparation method according to claim 1, characterized in that Measured by mass percentage, the composition of the medium and low alloy steel includes: C 0.40-0.65%, Mn+Cr 1.0-3.5%, Al+Si 1.0-2.0%, Mo+Ni<2.0%, V+Nb+Ti 0-0.3%, P<0.02, S<0.02, O<0.0015%, N<0.008% and H<0.0001%, and the balance is Fe and unavoidable impurities.

3. The preparation method according to claim 1, characterized in that: The temperature of the high temperature thermal deformation treatment is 850-1250° C., and the deformation amount is >30%.

4. The preparation method according to claim 3, characterized in that: The first cooling rate is 1-100° C. / s.

5. The preparation method according to claim 1, characterized in that The first preset temperature is 500-700°C.

6. The preparation method according to claim 1, characterized in that: The second preset temperature is 100-500° C.; and / or the number of deformation passes of the continuous warm deformation is ≥2, and the total deformation amount is ≥50%.

7. The preparation method according to claim 1, characterized in that: The cooling rate of the cooling after the continuous warm deformation is >2°C / s; and / or the temperature of the low-temperature tempering treatment is 100-300°C and the time is 0.1-5h.

8. A high plasticity 3GPa grade low-medium alloy steel, characterized in that: The high-plasticity 3GPa-grade low-alloy steel is prepared by the preparation method described in any one of claims 1-7.

9. Use of the high-plasticity 3GPa-grade low-medium alloy steel according to claim 8 in the preparation of load-bearing components.

10. A method for improving the strength and plasticity of medium and low alloy steel, characterized in that the steps include: After austenitizing the medium and low alloy steel, a high-temperature heat deformation treatment is performed, and then the steel is cooled to a first preset temperature at a first cooling rate, and then continuous warm deformation is performed between the first preset temperature and a second preset temperature. After cooling to room temperature, the steel is subjected to low-temperature tempering to obtain a high-plasticity 3GPa grade medium and low alloy steel.

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