Low-cost ultrahigh-strength martensitic steel with tensile strength not lower than 2200MPa and preparation method thereof

Abstract

The invention provides low-cost ultra-high-strength martensitic steel with the tensile strength not lower than 2200 MPa and a preparation method, and relates to the technical field of design and preparation of ultra-high-strength steel. The ultrahigh-strength martensitic steel is a rod-shaped material with the cross section size phi ranging from 100 mm to 300 mm, and the ultrahigh-strength martensitic steel is prepared from, by mass, 0.4%-0.6% of C, 1.5%-2.5% of Mn, 2.0%-3.0% of Si, 1.5%-2.5% of Ni, 1.0%-2.0% of Cr, 0.4%-0.5% of Co, 0.3%-0.4% of Mo, 0.3%-0.6% of V, 0.02%-0.08% of Nb and the balance Fe and inevitable impurity elements. The preparation method comprises the steps of raw material weighing, smelting and casting, forging processing treatment, normalizing and annealing treatment, oil quenching treatment and tempering treatment. The preparation method is high in resource utilization rate, low in production cost, short in process, easy to operate, high in efficiency and beneficial to industrial large-scale production and popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of the design and preparation of ultra-high strength steel, in particular to a low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa and a preparation method thereof. Background Art

[0002] Ultra-high strength steel can be widely used in key components in industrial fields such as metallurgy, engineering machinery, and national defense; this is because the extremely high strength of ultra-high strength steel not only helps to improve the bearing capacity and wear resistance of components, but also contributes to the lightweight of components.

[0003] Currently, ultra-high strength steel mainly includes low-alloy martensitic steel, secondary hardening martensitic steel, and maraging steel. Among them: Maraging steel is currently recognized as an ultra-high strength steel grade, and its tensile strength can meet 2000 MPa - 2500 MPa. However, maraging steel needs to add Ni: 17% - 19%, Co: 8% - 12%, and Mo: 3% - 5%. Therefore, the content of high-cost alloying elements is high, such as 18Ni(300), 18Ni(350). And in the preparation process of maraging steel, in addition to the traditional preparation process, it also requires aging treatment for 3 - 10 h or even longer, which is contrary to the current concept of green metallurgy and green manufacturing.

[0004] For low-alloy martensitic steel or secondary hardening martensitic steel, through comprehensive means such as solid solution strengthening, phase transformation strengthening, precipitation strengthening, and dislocation strengthening, not only the alloy content of ultra-high strength steel is effectively reduced, but also the heat treatment time is effectively shortened, and the production cost of ultra-high strength steel is effectively reduced, such as 300M, AISI4340 steel, etc.

[0005] For example, Chinese Patent CN116926442A discloses a nano-phase co-precipitation strengthened ultra-high strength steel with a low yield ratio and a preparation method thereof. This method is obtained by normalizing, annealing, oil quenching + cryogenic treatment, and aging treatment of a forged steel ingot; obviously due to the cryogenic treatment, although the aging treatment temperature has decreased, it is still very high and the time is long; and although the cryogenic treatment improves the mechanical properties of the steel ingot, it will cause cracks in the steel ingot, resulting in increased brittleness and increased preparation cost.

[0006] Chinese Patent CN112375990A discloses a 1200MPa grade hot-rolled ultra-high strength steel plate and its preparation method. This method involves multi-pass forging of the designed composition of the billet under a rotating state, followed by tempering treatment. It is also required to perform a 2%-5% pre-deformation treatment at room temperature, and finally, tempering and partitioning treatment are carried out for preparation. However, the preparation process requires forging treatment under a rotating state, which is only available in a few special steel enterprises or research institutes. Two tempering treatments are needed, and the process requirements also limit the size range of the prepared ultra-high strength steel.

[0007] Chinese Patent CN116356216A discloses an ultra-high strength hydrogen embrittlement-resistant maraging steel and its preparation method. The nickel content in the composition of the steel is very high. This method is prepared by a short process of selective laser melting forming and a new type of low-temperature aging heat treatment by adding low-cost Al and Ti elements to replace the precious alloy element Co. Obviously, the preparation method is complex, the cost is high, the low-temperature aging treatment time is long, the yield ratio is higher than 0.85, and the toughness is poor.

[0008] Chinese Patent CN106906429A discloses an ultra-high strength martensitic stainless steel and its preparation method. This method prepares forgings through smelting, forging, quenching, and tempering steps. Although the preparation method is simple and the room-temperature impact toughness of the prepared steel plate is relatively good, the strength-ductility product of the prepared steel plate is relatively low, the tensile strength and yield strength are not high, and the strength-ductility product is relatively low.

[0009] In summary, although the ultra-high strength steels obtained in the above-mentioned prior arts can achieve a tensile strength of 2000MPa or higher, the ultra-high strength steels described are still mainly maraging steels with ultra-high alloy contents, or special preparation processes are added, such as rotary forging treatment, pressing after crushing the ingot into powder, double tempering treatment, or room-temperature deformation treatment, etc., which increase the manufacturing cost and control difficulty. Summary of the Invention

[0010] In order to solve the technical problems existing in the preparation of ultra-high strength martensitic steels with a tensile strength of not less than 2200MPa in the prior art, such as cryogenic treatment increasing brittleness, rotary forging limiting the size range, replacing precious alloy element Co with low-cost Al and Ti elements, the strength and plasticity and impact toughness of the prepared martensitic steel cannot be improved synergistically at low cost, and the yield ratio and the probability of crack occurrence cannot be reduced synergistically, etc.; therefore, the embodiments of the present invention provide a low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200MPa that can synergistically improve strength and plasticity and impact toughness and reduce the yield ratio, and its preparation method. The technical solutions are as follows:

[0011] Ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa and low cost. The ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is a rod-shaped material with a cross-sectional size of φ100 mm - φ300 mm. The chemical composition by mass percentage is as follows: C 0.4 - 0.6%, Mn 1.5 - 2.5%, Si 2.0 - 3.0%, Ni 1.5 - 2.5%, Cr 1.0 - 2.0%, Co 0.4 - 0.5%, Mo 0.3 - 0.4%, V 0.3 - 0.6%, Nb 0.02 - 0.08%, and the balance is Fe and inevitable impurity elements.

[0012] Optionally, the structure of the ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is tempered martensite, with a retained austenite content of 10 - 20 vol.%, and contains nano-precipitates with a size not greater than 100 nm.

[0013] Optionally, the density of the ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is 7.04 - 7.44 g / cm 3 , the hardness is 50 HRC - 57 HRC, the tensile strength is greater than 2200 MPa, the yield strength is greater than 1700 MPa, the yield ratio is 0.68 - 0.86, the elongation after fracture is greater than 8%, the product of strength and plasticity is not less than 17 GPa·%, and the impact toughness at room temperature is not less than 25 J / cm 2 .

[0014] Based on the above preparation method of ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa, the preparation method of the ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is as follows:

[0015] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition to obtain raw materials;

[0016] S2. Smelting and casting: Smelting the raw materials in S1 by induction melting + consumable electrode remelting or electroslag remelting and continuously casting to obtain a clean ingot;

[0017] S3. Forging and processing: Performing forging and processing of upsetting and drawing on the clean ingot in S2 to obtain a rod-shaped ingot;

[0018] S4. Normalizing and annealing treatment: Performing normalizing and annealing heat treatment on the rod-shaped ingot in S3 to obtain a heat-treated ingot;

[0019] S5. Oil quenching treatment: Performing oil quenching treatment on the heat-treated ingot in S4 to obtain a quenched ingot;

[0020] S6. Tempering treatment: The quenched steel ingot of S5 is subjected to tempering treatment to obtain a low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa.

[0021] Optionally, the size of the clean steel ingot in S2 is φ300 - φ500 mm.

[0022] Optionally, the forging ratio in S3 is not less than 5; the starting forging temperature is 1100 - 1200 °C, and the final forging temperature is not lower than 850 °C; the size of the bar-shaped steel ingot is φ100 - φ300 mm.

[0023] Optionally, the normalizing heating temperature in S4 is 1000 - 1050 °C, and the normalizing heating time is 1 - 3 h; the annealing temperature is 600 - 650 °C, and the annealing time is 8 - 10 h; the microstructure of the heat-treated steel ingot is tempered sorbite.

[0024] Optionally, the quenching temperature of the oil quenching treatment in S5 is 850 - 950 °C, the holding time is 1 - 3 h, and it is oil quenched to room temperature. The microstructure of the quenched steel ingot is quenched martensite.

[0025] Optionally, the tempering temperature of the tempering treatment in S6 is 200 - 350 °C, and the tempering time is 1 - 3 h.

[0026] The above technical solution has at least the following beneficial effects compared with the prior art:

[0027] In the above solution, the present invention provides a low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa and a preparation method, which can solve the technical problems existing in the preparation of ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa in the prior art, such as cryogenic treatment increasing brittleness, rotary forging restricting the size range, replacing precious alloy element Co with low-cost Al and Ti elements, the strength, plasticity and impact toughness of the prepared martensitic steel cannot be synergistically improved at low cost, and the yield ratio and the probability of crack appearance cannot be synergistically reduced.

[0028] By increasing C and decreasing Co, substituting Ni with Mn, and combining the idea of Nb and V microalloying, the present invention designs the chemical composition of ultra-high-strength martensitic steel, and the alloy content is significantly lower than that of traditional maraging steel.

[0029] The present invention synergistically regulates the martensite lath size and the precipitate phase content through short-process normalizing + annealing treatment and quenching + tempering process, realizes comprehensive strengthening means such as solid solution strengthening, phase transformation strengthening, precipitation strengthening, and dislocation strengthening, and provides a new idea for the composition design and preparation process of 2200 MPa low-cost ultra-high-strength martensitic steel.

[0030] The density of the low-cost ultra-high-strength martensitic steel prepared by the present invention with a tensile strength of not less than 2200 MPa is 7.04 - 7.44 g / cm3 with a hardness of 50HRC - 57HRC, a tensile strength greater than 2200MPa, a yield strength greater than 1700MPa, a yield ratio of 0.68 - 0.86, an elongation after fracture greater than 8%, a product of strength and plasticity not less than 17GPa·%, and a room temperature impact toughness not less than 25J / cm 2 .

[0031] In summary, compared with other traditional methods, the method of the present invention creatively improves the strength, plasticity, impact toughness, lightweight degree and surface hardness of the prepared martensitic steel through the selection of alloying elements and the adjustment of their contents, combined with the short - process normalizing + annealing treatment and quenching + tempering process. At the same time, the yield ratio and the probability of crack occurrence are synergistically reduced; moreover, it has high resource utilization rate, low production cost, short process, easy operation, high efficiency, and is conducive to large - scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following - described drawings 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.

[0033] Figure 1 is the process flow chart of the preparation method of the low - cost ultra - high - strength martensitic steel with a tensile strength not less than 2200MPa of the present invention;

[0034] Figure 2 is the engineering stress - strain curve of the low - cost ultra - high - strength martensitic steel with a tensile strength not less than 2200MPa in Example 1 of the present invention;

[0035] Figure 3 is the tissue scanning diagram of the low - cost ultra - high - strength martensitic steel with a tensile strength not less than 2200MPa in Example 1 of the present invention;

[0036] Figure 4 is the engineering stress - strain curve of the low - cost ultra - high - strength martensitic steel with a tensile strength not less than 2200MPa in Example 2 of the present invention;

[0037] Figure 5 is the tissue scanning diagram of the low - cost ultra - high - strength martensitic steel with a tensile strength not less than 2200MPa in Example 2 of the present invention;

[0038] Figure 6 is the engineering stress - strain curve of the low - cost ultra - high - strength martensitic steel with a tensile strength not less than 2200MPa in Example 3 of the present invention;

[0039] Figure 7It is the microstructure scanning diagram of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa in Embodiment 3 of the present invention. Detailed implementation manners

[0040] The technical solutions in the present invention will be described below with reference to the accompanying drawings.

[0041] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to represent examples, illustrations or explanations. Any embodiment or design solution described as an "example" in the present invention should not be construed as being more preferred or more advantageous than other embodiments or design solutions. Rather, the use of the word "example" is intended to present concepts in a specific manner. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one of the two can be selected.

[0042] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference is not emphasized, the meanings they express are the same. "Of", "corresponding" and "corresponding to" can sometimes be used interchangeably. It should be noted that when the difference is not emphasized, the meanings they express are the same.

[0043] In the embodiments of the present invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meanings they express are the same.

[0044] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0045] A low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa. The low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is a rod-shaped material with a cross-sectional size of φ100 mm - φ300 mm. The chemical composition is calculated by mass percentage as follows: C 0.4 - 0.6%, Mn 1.5 - 2.5%, Si 2.0 - 3.0%, Ni 1.5 - 2.5%, Cr 1.0 - 2.0%, Co 0.4 - 0.5%, Mo 0.3 - 0.4%, V 0.3 - 0.6%, Nb 0.02 - 0.08%, and the balance is Fe and inevitable impurity elements.

[0046] Particularly, the microstructure of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is tempered martensite, in which the retained austenite content is 10 - 20 vol.%, and contains nano-precipitates with a size not greater than 100 nm.

[0047] Particularly, the density of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is 7.04 - 7.44 g / cm 3, with a hardness of 50HRC - 57HRC, a tensile strength greater than 2200MPa, a yield strength greater than 1700MPa, a yield ratio of 0.68 - 0.86, an elongation after fracture greater than 8%, a product of strength and plasticity not less than 17GPa·%, and a room temperature impact toughness not less than 25J / cm 2 . Based on the preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength not less than 2200MPa, the preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength not less than 2200MPa combines Figure 1 the following steps:

[0048] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition to obtain raw materials;

[0049] S2. Smelting and casting: Smelting the raw materials in S1 by induction melting + consumable electrode remelting or electroslag remelting and continuously casting to obtain a pure ingot;

[0050] S3. Forging and processing: Conducting forging and processing of upsetting and drawing on the pure ingot in S2 to obtain a bar-shaped ingot;

[0051] S4. Normalizing and annealing treatment: Conducting normalizing and annealing heat treatment on the bar-shaped ingot in S3 to obtain a heat-treated ingot;

[0052] S5. Oil quenching treatment: Conducting oil quenching treatment on the heat-treated ingot in S4 to obtain a quenched ingot;

[0053] S6. Tempering treatment: Conducting tempering treatment on the quenched ingot in S5 to obtain a low-cost ultra-high strength martensitic steel with a tensile strength not less than 2200MPa.

[0054] Particularly, the size of the pure ingot in S2 is φ300 - φ500mm.

[0055] Particularly, the forging ratio in S3 is not less than 5; the starting forging temperature is 1100 - 1200°C, and the final forging temperature is not lower than 850°C; the size of the bar-shaped ingot is φ100 - φ300mm.

[0056] Particularly, the normalizing heating temperature in S4 is 1000 - 1050°C, and the normalizing heating time is 1 - 3h; the annealing temperature is 600 - 650°C, and the annealing time is 8 - 10h; the microstructure of the heat-treated ingot is tempered sorbite.

[0057] Optionally, the quenching temperature of the oil quenching treatment in S5 is 850 - 950°C, the holding time is 1 - 3h, quenching to room temperature, and the microstructure of the quenched ingot is quenched martensite.

[0058] Specifically, the tempering temperature in S6 is 200 - 350°C, and the tempering time is 1 - 3h.

[0059] Example 1

[0060] A low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa. The low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is a rod-shaped material with a cross-sectional size of φ100 mm. The chemical composition by mass percentage is: C 0.45%, Mn 2.10%, Si 2.36%, Ni 1.81%, Cr 1.45%, Co 0.50%, Mo 0.38%, V 0.36%, Nb 0.036%, and the balance is Fe and unavoidable impurity elements.

[0061] Based on the above preparation method of a low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa, the preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is as follows:

[0062] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition to obtain raw materials;

[0063] S2. Smelting and casting: Smelting the raw materials in S1 by induction melting + consumable electrode remelting or electroslag remelting and continuously casting to obtain a pure steel ingot; the size of the pure steel ingot is φ300 mm;

[0064] S3. Forging and processing: Conducting forging and processing of upsetting and drawing on the pure steel ingot in S2, with a forging ratio of 5, an initial forging temperature of 1150°C, and a final forging temperature of 950°C to obtain a rod-shaped steel ingot; the size of the rod-shaped steel ingot is φ100 mm;

[0065] S4. Normalizing and annealing treatment: Conducting normalizing and annealing heat treatments on the rod-shaped steel ingot in S3. The heating temperature for normalizing is 1000°C, and the heating time for normalizing is 1h; the annealing temperature is 600°C, and the annealing time is 8h to obtain a heat-treated steel ingot; the microstructure of the heat-treated steel ingot is tempered sorbite;

[0066] S5. Oil quenching treatment: Conducting oil quenching treatment on the heat-treated steel ingot in S4. The quenching temperature for oil quenching is 850°C, and the holding time is 1h. Quench to room temperature to obtain a quenched steel ingot; the microstructure of the quenched steel ingot is quenched martensite;

[0067] S6. Tempering treatment: Conducting tempering treatment on the quenched steel ingot in S5. The tempering temperature for tempering treatment is 200°C, and the tempering time is 1h to obtain a low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa.

[0068] AsFigure 3 As shown, the structure of the low-cost ultra-high strength martensitic steel prepared in this example with a tensile strength of not less than 2200 MPa is tempered martensite, and the retained austenite content is 17 vol.%.

[0069] The density of the low-cost ultra-high strength martensitic steel prepared in this example with a tensile strength of not less than 2200 MPa is 7.36 g / cm 3 , the hardness is 52.0 HRC, as Figure 2 shown, the tensile strength is 2426 MPa, the yield strength is 1710 MPa, the yield ratio is 0.71, the elongation after fracture is 9.3%, the product of strength and plasticity is 22.56 GPa·%, and the impact toughness at room temperature is 28.7 J / cm 2 .

[0070] Example 2

[0071] A low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa, the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is a rod-shaped material with a cross-sectional size of φ150 mm, and the chemical composition is by mass percentage: C 0.46%, Mn 2.08%, Si 2.39%, Ni 1.81%, Cr 1.46%, Co 0.45%, Mo 0.35%, V 0.44%, Nb 0.039%, and the balance is Fe and unavoidable impurity elements.

[0072] Based on the above preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa, the preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is as follows:

[0073] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition to obtain raw materials;

[0074] S2. Smelting and casting: Smelting the raw materials in S1 by induction melting + consumable electroslag remelting or electroslag remelting and continuously casting to obtain a pure ingot; the size of the pure ingot is φ500 mm;

[0075] S3. Forging and processing: Performing forging and processing of upsetting and drawing on the pure ingot in S2, with a forging ratio of 6, an initial forging temperature of 1200 °C, and a final forging temperature of 980 °C to obtain a rod-shaped ingot; the size of the rod-shaped ingot is φ150 mm;

[0076] S4, Normalizing and Annealing Treatment: The S3 bar-shaped ingot is subjected to normalizing and annealing heat treatments. The normalizing heating temperature is 1050 °C, and the normalizing heating time is 1 h; the annealing temperature is 620 °C, and the annealing time is 8 h to obtain a heat-treated ingot; the microstructure of the heat-treated ingot is tempered sorbite;

[0077] S5, Oil Quenching Treatment: The S4 heat-treated ingot is subjected to oil quenching treatment. The quenching temperature for the oil quenching treatment is 860 °C, and the holding time is 1 h. It is quenched to room temperature to obtain a quenched ingot; the microstructure of the quenched ingot is quenched martensite;

[0078] S6, Tempering Treatment: The S5 quenched ingot is subjected to tempering treatment. The tempering temperature for the tempering treatment is 250 °C, and the tempering time is 1 h to obtain a low-cost ultra-high-strength martensitic steel with a tensile strength not less than 2200 MPa.

[0079] As Figure 5 shown, the microstructure of the low-cost ultra-high-strength martensitic steel with a tensile strength not less than 2200 MPa prepared in this example is tempered martensite, and the retained austenite content is 19 vol.%.

[0080] The density of the low-cost ultra-high-strength martensitic steel with a tensile strength not less than 2200 MPa prepared in this example is 7.35 g / cm 3 , the hardness is 53.1 HRC. As Figure 4 shown, the tensile strength is 2278 MPa, the yield strength is 1787 MPa, the yield ratio is 0.784, the elongation after fracture is 9.1%, the product of strength and plasticity is 20.7 GPa·%, and the room temperature impact toughness is 39.7 J / cm 2 .

[0081] Example 3

[0082] A low-cost ultra-high-strength martensitic steel with a tensile strength not less than 2200 MPa, the low-cost ultra-high-strength martensitic steel with a tensile strength not less than 2200 MPa is a bar-shaped material with a cross-sectional size of φ120 mm, and the chemical composition is by mass percentage: C 0.52%, Mn 2.10%, Si 2.36%, Ni 1.81%, Cr 1.45%, Co 0.50%, Mo 0.38%, V 0.40%, Nb 0.036%, and the balance is Fe and inevitable impurity elements.

[0083] Based on the above preparation method of a low-cost ultra-high-strength martensitic steel with a tensile strength not less than 2200 MPa, the preparation method of the low-cost ultra-high-strength martensitic steel with a tensile strength not less than 2200 MPa is as follows:

[0084] S1. Raw material weighing: Use pure metals with a purity of 99.99% and intermediate alloys as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0085] S2. Smelting and casting: Smelt the raw materials in S1 by induction melting + consumable electrode remelting or electroslag remelting and continuously cast to obtain pure ingots; The size of the pure ingot is φ300mm;

[0086] S3. Forging processing: Conduct forging processing of upsetting and drawing on the pure ingot in S2, with a forging ratio of 5, an initial forging temperature of 1200°C, and a final forging temperature of 960°C to obtain a bar-shaped ingot; The size of the bar-shaped ingot is φ120mm;

[0087] S4. Normalizing and annealing treatment: Conduct normalizing and annealing heat treatment on the bar-shaped ingot in S3. The heating temperature for normalizing is 1050°C, and the heating time for normalizing is 1h; The annealing temperature is 650°C, and the annealing time is 8h to obtain a heat-treated ingot; The microstructure of the heat-treated ingot is tempered sorbite;

[0088] S5. Oil quenching treatment: Conduct oil quenching treatment on the heat-treated ingot in S4. The quenching temperature for oil quenching is 900°C, and the holding time is 1h. Quench to room temperature to obtain a quenched ingot; The microstructure of the quenched ingot is quenched martensite structure;

[0089] S6. Tempering treatment: Conduct tempering treatment on the quenched ingot in S5. The tempering temperature for tempering treatment is 200°C, and the tempering time is 1h to obtain a low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200MPa.

[0090] As Figure 7 shown, the microstructure of the low-cost ultra-high-strength martensitic steel prepared in this example with a tensile strength of not less than 2200MPa is tempered martensite, and the residual austenite content is 16vol.%.

[0091] The density of the low-cost ultra-high-strength martensitic steel prepared in this example with a tensile strength of not less than 2200MPa is 7.35g / cm 3 , the hardness is 51.5HRC. As Figure 6 shown, the tensile strength is 2265MPa, the yield strength is 1854MPa, the yield ratio is 0.82, the elongation after fracture is 9.3%, the strength-ductility product is 21.1GPa·%, and the room temperature impact toughness is 36.9J / cm 2 .

[0092] Example 4

[0093] A low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa. The low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is a rod-shaped material with a cross-sectional size of φ100 mm. The chemical composition is by mass percentage: C 0.51%, Mn 2.13%, Si 2.33%, Ni 2.00%, Cr 1.56%, Co 0.48%, Mo 0.38%, V 0.39%, Nb 0.06%, and the balance is Fe and unavoidable impurity elements.

[0094] Based on the above preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa, the preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is as follows:

[0095] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition to obtain raw materials;

[0096] S2. Smelting and casting: The raw materials in S1 are smelted by induction melting + consumable electrode remelting or electroslag remelting and continuously cast to obtain a pure ingot; the size of the pure ingot is φ300 mm;

[0097] S3. Forging and processing: Conduct forging and processing of upsetting and drawing on the pure ingot in S2, with a forging ratio of 6, an initial forging temperature of 1150 °C, and a final forging temperature of 980 °C to obtain a rod-shaped ingot; the size of the rod-shaped ingot is φ100 mm;

[0098] S4. Normalizing and annealing treatment: The rod-shaped ingot in S3 is subjected to normalizing and annealing heat treatment. The heating temperature for normalizing is 1000 °C, and the heating time for normalizing is 1.5 h; the annealing temperature is 600 °C, and the annealing time is 8 h to obtain a heat-treated ingot; the microstructure of the heat-treated ingot is tempered sorbite;

[0099] S5. Oil quenching treatment: The heat-treated ingot in S4 is subjected to oil quenching treatment. The quenching temperature for oil quenching is 870 °C, the holding time is 2 h, and it is quenched to room temperature to obtain a quenched ingot; the microstructure of the quenched ingot is quenched martensite structure;

[0100] S6. Tempering treatment: The quenched ingot in S5 is subjected to tempering treatment. The tempering temperature for tempering is 200 °C, and the tempering time is 1 h to obtain a low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa.

[0101] The low-cost ultra-high strength martensitic steel prepared in this example has a structure of tempered martensite, and the retained austenite content is 18 vol.%.

[0102] The density of the low-cost ultra-high-strength martensitic steel prepared in this example with a tensile strength of not less than 2200 MPa is 7.36 g / cm 3 , the hardness is 53.0 HRC, the tensile strength is 2338 MPa, the yield strength is 1724 MPa, the yield ratio is 0.74, the elongation after fracture is 11.6%, the product of strength and plasticity is 27.1 GPa·%, and the impact toughness at room temperature is 25.4 J / cm 2 .

[0103] Example 5

[0104] A low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa. The low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa is a rod-shaped material with a cross-sectional size of φ150 mm. The chemical composition is calculated by mass percentage as follows: C 0.49%, Mn 2.42%, Si 2.92%, Ni 1.97%, Cr 1.87%, Co 0.45%, Mo 0.38%, V 0.58%, Nb 0.07%, and the balance is Fe and inevitable impurity elements.

[0105] Based on the above preparation method of a low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa, the preparation method of the low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa is as follows:

[0106] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and mixing according to the chemical composition ratio to obtain raw materials;

[0107] S2. Smelting and casting: Smelting the raw materials in S1 by induction melting + consumable electrode remelting or electroslag remelting and continuously casting to obtain a pure ingot; the size of the pure ingot is φ250 mm;

[0108] S3. Forging and processing: Performing forging and processing of upsetting and drawing on the pure ingot in S2, with a forging ratio of 5, an initial forging temperature of 1100 °C, and a final forging temperature of 900 °C to obtain a rod-shaped ingot; the size of the rod-shaped ingot is φ150 mm;

[0109] S4. Normalizing and annealing treatment: Performing normalizing and annealing heat treatment on the rod-shaped ingot in S3. The heating temperature for normalizing is 1020 °C, and the heating time for normalizing is 2.5 h; the annealing temperature is 620 °C, and the annealing time is 10 h to obtain a heat-treated ingot; the microstructure of the heat-treated ingot is tempered sorbite;

[0110] S5. Oil quenching treatment: Performing oil quenching treatment on the heat-treated ingot in S4. The quenching temperature for oil quenching is 860 °C, the holding time is 1.5 h, and it is quenched to room temperature to obtain a quenched ingot; the microstructure of the quenched ingot is quenched martensite structure;

[0111] S6. Tempering treatment: The quenched steel ingot of S5 is subjected to tempering treatment. The tempering temperature is 250 °C and the tempering time is 2 h, obtaining a low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa.

[0112] The microstructure of the low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa prepared in this example is tempered martensite, and the retained austenite content is 18.5 vol.%.

[0113] The density of the low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa prepared in this example is 7.23 g / cm 3 , the hardness is 57.8 HRC, the tensile strength is 2263 MPa, the yield strength is 1816 MPa, the yield ratio is 0.80, the elongation after fracture is 9.4%, the product of strength and plasticity is 21.3 GPa·%, and the impact toughness at room temperature is 36.3 J / cm 2 .

[0114] Comparative Example 1

[0115] As a comparison, a kind of martensitic steel, which is a rod-shaped material with a cross-sectional size of φ100 mm, and its chemical composition by mass percentage is: C 0.45%, Mn 1.20%, Si 1.33%, Ni 1.45%, Cr 1.27%, Co 0.30%, Mo 0.21%, V 0.16%, Nb 0%, and the balance is Fe and inevitable impurity elements.

[0116] The preparation method of the martensitic steel is as follows:

[0117] S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and mixing according to the chemical composition ratio to obtain raw materials;

[0118] S2. Smelting and casting: The raw materials of S1 are smelted by induction melting + consumable electroslag remelting or electroslag remelting and continuously cast to obtain a pure steel ingot; the size of the pure steel ingot is φ300 mm;

[0119] S3. Forging and processing treatment: The pure steel ingot of S2 is subjected to forging and processing treatment of upsetting and drawing, the forging ratio is 6, the starting forging temperature is 1100 °C, and the final forging temperature is 850 °C to obtain a rod-shaped steel ingot; the size of the rod-shaped steel ingot is φ100 mm;

[0120] S4, Normalizing and Annealing Treatment: The S3 bar-shaped ingot is subjected to normalizing and annealing heat treatments. The normalizing heating temperature is 1050 °C, and the normalizing heating time is 1 h; the annealing temperature is 500 °C, and the annealing time is 8 h to obtain a heat-treated ingot; the microstructure of the heat-treated ingot is tempered sorbite;

[0121] S5, Oil Quenching Treatment: The S4 heat-treated ingot is subjected to oil quenching treatment. The quenching temperature for the oil quenching treatment is 860 °C, the holding time is 1 h, and it is quenched to room temperature to obtain a quenched ingot; the microstructure of the quenched ingot is quenched martensite structure;

[0122] S6, Tempering Treatment: The S5 quenched ingot is subjected to tempering treatment. The tempering temperature for the tempering treatment is 200 °C, and the tempering time is 1 h to obtain martensitic steel.

[0123] The metallographic composition of the high-strength martensitic steel prepared in this example is tempered martensite.

[0124] The density of the low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa prepared in this example is 7.54 g / cm 3 , the hardness is 57.3 HRC, the tensile strength is 2225 MPa, the yield strength is 1546 MPa, the yield ratio is 0.70, the elongation after fracture is 9.4%, the product of strength and plasticity is 28.5 GPa·%, and the room-temperature impact toughness is 12.8 J / cm 2 .

[0125] Comparative Example 2

[0126] As a comparison, a kind of martensitic steel, a bar-shaped material with a cross-sectional size of φ150 mm, and its chemical composition by mass percentage is: C 0.38%, Mn 1.12%, Si 1.38%, Ni 1.40%, Cr 1.01%, Co 0.30%, Mo 0.28%, V 0.12%, Nb 0.003%, and the balance is Fe and unavoidable impurity elements.

[0127] The preparation method of the martensitic steel is as follows:

[0128] S1, Raw Material Weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and mixing according to the chemical composition ratio to obtain raw materials;

[0129] S2, Smelting and Casting: The S1 raw materials are smelted by induction melting + consumable electrode remelting or electroslag remelting and continuously cast to obtain a pure ingot; the size of the pure ingot is φ300 mm;

[0130] S3. Forging processing: Perform upsetting and drawing out forging processing on the S2 pure steel ingot, with a forging ratio of 6, an initial forging temperature of 1150 °C, and a final forging temperature of 950 °C to obtain a bar-shaped steel ingot; the size of the bar-shaped steel ingot is φ150 mm;

[0131] S4. Normalizing and annealing treatment: Perform normalizing and annealing heat treatment on the S3 bar-shaped steel ingot. The heating temperature for normalizing is 1000 °C, and the heating time for normalizing is 3 h; the annealing temperature is 650 °C, and the annealing time is 9 h to obtain a heat-treated steel ingot; the microstructure of the heat-treated steel ingot is tempered sorbite;

[0132] S5. Oil quenching treatment: Perform oil quenching treatment on the S4 heat-treated steel ingot. The quenching temperature for oil quenching is 900 °C, and the holding time is 1 h. Quench to room temperature to obtain a quenched steel ingot; the microstructure of the quenched steel ingot is quenched martensite structure;

[0133] S6. Tempering treatment: Perform tempering treatment on the S5 quenched steel ingot. The tempering temperature for tempering treatment is 400 °C, and the tempering time is 1 h to obtain a kind of martensitic steel.

[0134] The high-strength martensitic steel prepared in this example has a structure of tempered martensite.

[0135] The density of the high-strength martensitic steel prepared in this example is 7.42 g / cm 3 , the hardness is 55.7 HRC, the tensile strength is 2084 MPa, the yield strength is 1691 MPa, the yield ratio is 0.81, the elongation after fracture is 8.2%, the product of strength and plasticity is 17.1 GPa·%, and the impact toughness at room temperature is 21.0 J / cm 2 .

[0136] In summary, after comparing the examples with the comparative examples, it can be found that the 5 kinds of ultra-high-strength martensitic steels prepared according to the patent specification can meet the ultra-high-strength performance with a tensile strength of not less than 2200 MPa, and the density is 7.04 - 7.44 g / cm 3 , the hardness is 50 - 57 HRC, the tensile strength is greater than 2200 MPa, the yield strength is greater than 1700 MPa, the yield ratio is 0.68 - 0.86, the elongation after fracture is greater than 8%, the product of strength and plasticity is not less than 17 GPa·%, and the impact toughness at room temperature is not less than 25 J / cm 2 .

[0137] For the above solution, the present invention provides a low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa and a preparation method, which can solve the technical problems existing in the preparation of ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa in the prior art, such as cryogenic treatment increasing brittleness, rotary forging restricting the size range, replacing precious alloy element Co with low-cost Al and Ti elements, the strength, plasticity and impact toughness of the prepared martensitic steel cannot be synergistically improved at low cost, and the yield ratio and the probability of crack appearance cannot be synergistically decreased, etc.

[0138] By increasing C and decreasing Co, substituting Ni with Mn, and combining the idea of microalloying with Nb and V, the present invention designs the chemical composition of the ultra-high strength martensitic steel, and the alloy content is significantly lower than that of the traditional maraging steel.

[0139] Through the short-process normalizing + annealing treatment and quenching + tempering process, the present invention synergistically regulates the martensite lath size and the precipitation phase content, realizes comprehensive strengthening means such as solid solution strengthening, phase transformation strengthening, precipitation strengthening, and dislocation strengthening, and provides a new idea for the composition design and preparation process of 2200 MPa low-cost ultra-high strength martensitic steel.

[0140] The density of the low-cost ultra-high strength martensitic steel prepared by the present invention with a tensile strength of not less than 2200 MPa is 7.04 - 7.44 g / cm 3 , the hardness is 50 HRC - 57 HRC, the tensile strength is greater than 2200 MPa, the yield strength is greater than 1700 MPa, the yield ratio is 0.68 - 0.86, the elongation after fracture is greater than 8%, the strength-plasticity product is not less than 17 GPa·%, and the room temperature impact toughness is not less than 25 J / cm 2 .

[0141] In summary, compared with other traditional methods, the method of the present invention creatively combines the selection of alloy elements and the adjustment of their contents, and combines the short-process normalizing + annealing treatment and quenching + tempering process to synergistically improve the strength, plasticity, impact toughness, lightweight degree and surface hardness of the prepared martensitic steel. At the same time, the yield ratio and the probability of crack appearance are synergistically decreased; and it has high resource utilization rate, low production cost, short process, easy operation, high efficiency, and is conducive to large-scale industrial production and promotion.

[0142] It should be understood that the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Among them, A and B can be singular or plural. In addition, the character " / " in this article generally represents an "or" relationship between the front and rear associated objects, but it may also represent an "and / or" relationship, which can be specifically understood with reference to the context.

[0143] In the present invention, "at least one" means one or more, and "a plurality of" means two or more. "At least one of the following" or a similar expression means any combination of these items, including any combination of single item(s) or plural item(s). For example, at least one of a, b, or c may represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, and c may be single or plural.

[0144] It should be understood that in various embodiments of the present invention, the magnitudes of the sequence numbers of the above - mentioned processes do not imply the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0145] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A low-cost ultra-high-strength martensitic steel with a tensile strength of not less than 2200 MPa, characterized in that, The low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is a rod-shaped material with a cross-sectional size of φ100mm - φ300mm. The chemical composition by mass percentage is as follows: C 0.4 - 0.6%, Mn 1.5 - 2.5%, Si 2.0 - 3.0%, Ni 1.5 - 2.5%, Cr 1.0 - 2.0%, Co 0.4 - 0.5%, Mo 0.3 - 0.4%, V 0.3 - 0.6%, Nb 0.02 - 0.08%, and the balance is Fe and inevitable impurity elements.

2. The low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa according to claim 1, characterized in that, The structure of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is tempered martensite, in which the retained austenite content is 10 - 20 vol.%, and it contains nano-precipitates with a size of not more than 100 nm.

3. The low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa according to claim 2, characterized in that, The density of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is 7.04 - 7.44 g / cm 3 , the hardness is 50HRC - 57HRC, the tensile strength is greater than 2200 MPa, the yield strength is greater than 1700 MPa, the yield ratio is 0.68 - 0.86, the elongation after fracture is greater than 8%, the product of strength and plasticity is not less than 17 GPa·%, and the impact toughness at room temperature is not less than 25 J / cm 2 .

4. The preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa according to claim 1, characterized in that, The preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa is as follows: S1. Raw material weighing: Using pure metals with a purity of 99.99% and master alloys as raw materials, accurately weighing and proportioning according to the chemical composition to obtain raw materials; S2. Smelting and casting: Smelting the raw materials in S1 by induction melting + consumable electroslag remelting or electroslag remelting and continuously casting to obtain a pure ingot; S3. Forging and processing: Conducting forging and processing of upsetting and drawing on the pure ingot in S2 to obtain a rod-shaped ingot; S4. Normalizing and annealing treatment: Conducting normalizing and annealing heat treatment on the rod-shaped ingot in S3 to obtain a heat-treated ingot; S5. Oil quenching treatment: Conducting oil quenching treatment on the heat-treated ingot in S4 to obtain a quenched ingot; S6. Tempering treatment: Conducting tempering treatment on the quenched ingot in S5 to obtain the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa.

5. The preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa according to claim 4, characterized in that, The size of the pure ingot in S2 is φ300 - φ500mm.

6. The preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa according to claim 4, characterized in that, The forging ratio in S3 is not less than 5; the starting forging temperature is 1100 - 1200 °C, and the final forging temperature is not lower than 850 °C; the size of the rod-shaped ingot is φ100 - φ300mm.

7. The preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa according to claim 4, characterized in that, In S4, the heating temperature for normalizing is 1000 - 1050 °C, and the heating time for normalizing is 1 - 3 h; the annealing temperature is 600 - 650 °C, and the annealing time is 8 - 10 h.

8. The preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa according to claim 4, characterized in that, In S5, the quenching temperature for oil quenching treatment is 850 - 950 °C, the holding time is 1 - 3 h, and it is oil quenched to room temperature.

9. The preparation method of the low-cost ultra-high strength martensitic steel with a tensile strength of not less than 2200 MPa according to claim 4, characterized in that, In S6, the tempering temperature for tempering treatment is 200 - 350 °C, and the tempering time is 1 - 3 h.

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