WO2014139451A1

WO2014139451A1 - Super-high strength ferritic steel reinforced with nano-intermetallics and manufacturing method thereof

Info

Publication number: WO2014139451A1
Application number: PCT/CN2014/073398
Authority: WO
Inventors: 刘锦川; 焦增宝
Original assignee: 香港城市大学
Priority date: 2013-03-13
Filing date: 2014-03-13
Publication date: 2014-09-18
Also published as: JP2016514210A; JP6591290B2; CN104046891B; JP2019104990A; JP6794478B2; CN104046891A

Abstract

A super-high strength ferritic steel reinforced with nano-intermetallics and a manufacturing method thereof. The super-high-strength ferritic steel comprises the following components in percentage by weight: 0-0.2% of C, 2%-15% of Ni, 0-10% of Mn, 0.5-6% of Al, 0-4% of Cu, 0-12% of Cr, 0-3% of Mo, 0-3% of W, 0-0.5% of V, 0-0.5% of Ti, 0-0.5% of Nb, 0-1% of Si, 0.0005-0.05% of B, no more than 0.04% of P,no more than 0.04% of S, no more than 0.04% of N, no more than 0.05% of O, the balance being Fe and other inevitable impurities. These components are subjected to smelting, casting and forging rolling, and then treated with solid solution and aged to form a super-high strength ferritic steel which is mainly reinforced by nano-intermetallics incorporating composite reinforcements of nanoclusters and nano-carbides, obtaining excellent durability, solderability and corrosion resistance.

Description

Nano-intermetallic compound-reinforced ultra-high strength ferritic steel and manufacturing method thereof

Technical field

The present invention relates to an ultra high strength ferritic steel and a method for producing the same, and particularly to an ultrahigh strength ferritic steel in which a nano intermetallic compound is strengthened and a method for producing the same. Background technique

In recent years, with the rapid development of modern industry and national defense, the application of ultra-high-strength steel in aerospace, defense, power stations and other high-tech fields is becoming more and more important. Ultra-high-strength steel with tensile strength of 1400~2000 MPa is an important type of steel with a wide range of applications, especially in the field of rocket engine casing, aircraft landing gear, bulletproof steel plate and other special requirements. And its use is constantly expanding into construction, machinery, vehicles and other military and civilian equipment.

Traditional ultra-high-strength steel, such as low-temperature tempered martensite structure or lower bainite-structured low-alloy steel, high-temperature tempered alloy carbide precipitates, secondary hardened microstructure-enhanced ultra-high-strength steel, intermetallic compound precipitation strengthening horse Austenitic aging steels have reached the requirements of ultra-high strength to a certain extent, but high carbon, high alloys and heat treatment transitions require fast cooling and other characteristics, which still have poor weldability and poor plastic toughness, high cost, limited material size, etc. problem.

With the development of nanotechnology, the use of nano-precipitation phase strengthening mechanism has become an important way to develop new ultra-high-strength steel. The nano-precipitate particles interact with the sliding dislocation in the matrix to produce a strong precipitation strengthening effect. Controlling the grain size of the matrix and indirectly acting as a fine grain strengthening effect, thereby effectively increasing the strength of the steel. At present, the development of nano-precipitate-enhanced ultra-high-strength steel is relatively mature. The formation of nano-carbide MC by alloying produces precipitation strengthening and fine-grain strengthening to increase the strength of steel. For example, the patent CN1514887 discloses an ultra-high-strength, corrosion-resistant structural steel with enhanced nano-carbide deposition, and patent 101671771B discloses a method for preparing high-strength, high-plasticity ultrafine-crystalline ferrite and nano-carbide low-carbon steel. , and Huo Xiangdong et al. in the "CSP production of Ti microalloyed high-strength steel nano-carbide", Journal of University of Science and Technology Beijing, 2011 08 research on nano-carbide strengthening. However, modern industry has increasingly improved the comprehensive properties of ultra-high-strength steel such as weldability and toughness. Higher carbon content leads to poor weldability and low fracture toughness. Therefore, it is necessary to control the carbon content reasonably and utilize the new nano-precipitate phase. The alternative carbide strengthening strengthens the ultra-high-strength steel and effectively exerts the positive strengthening effect of the trace carbide without destroying the good comprehensive performance. In addition, ferritic steel has good toughness, which overcomes the limitation of material size for the rapid cooling of martensitic steel, especially It can be produced by continuous casting and rolling process, which can save energy and simplify the process. Therefore, compared with the conventional ultra-high-strength steel using martensite matrix, the development of new ultra-high-strength steel based on the ferrite structure using the new nano-precipitation phase strengthening mechanism has great process and cost advantages.

The ultra-high-strength steel of the invention adopts a ferrite structure as a matrix, and by adding an appropriate amount of an intermetallic compound to form an element, a large amount of nano-intermetallic compound is precipitated on the ferrite matrix under a suitable heat treatment process, and the precipitation strengthening effect is exerted. Significantly increase the strength of the steel. In addition, the invention also adds nano-cluster forming elements, carbide forming elements and trace carbon elements to form a certain amount of nano-clusters and a small amount of nano-carbides, thereby strengthening nano-intermetallic compounds, combining nano-clusters and nano-carbonization. The composite strengthening, the three nano-precipitates work together to produce the maximum strengthening effect, and the ultra-high-strength ferritic steel strengthened by the nano-metal compound with low carbon and excellent comprehensive performance. Summary of the invention

An object of the present invention is to provide a nano-intermetallic compound-reinforced ultra-high-strength ferritic steel in which a large number of uniformly distributed and small-sized nano-metal intermetallic compounds are strengthened, and at the same time, nanoclusters and nano-carbides are combined. Composite strengthening, made of ultra-high strength ferritic steel with super high strength and toughness, excellent welding performance and corrosion resistance.

Another object of the present invention is to provide a process for producing the above-described nano intermetallic compound-reinforced ultrahigh strength ferritic steel.

In one aspect, the present invention provides a nano-intermetallic compound-reinforced ultra-high strength ferritic steel having a chemical composition as follows: C is 0 to 0.2%, Ni is 2 to 15%, and Mn is 0. ~10%, A1 is 0.5~6%, Cu is 0-4%, Cr is 0~12%, Mo is 0~3%, W is 0~3%, V is 0~0.5%, Ti is 0~ 0.5%, Nb is 0~0.5%, Si is 0~1%, B is 0.0005~0.05%, P is not higher than 0.04%, S is not higher than 0.04%, N is not higher than 0.04%, 0 is not higher than 0.05 %, the balance is Fe and inevitable impurities.

In one embodiment of the invention, the nano intermetallic compound is NiAl.

In another embodiment of the present invention, the nano-metallic compound has an average size of 3 nm, an average pitch of 2 to 20 nm, and no less than 10,000 nano-intermetallic compounds per cubic micrometer.

In another embodiment of the present invention, the nano-intermetallic compound-reinforced ultra-high-strength ferritic steel further comprises a nano-cluster, and the main constituent element of the nano-cluster is Cu.

In another embodiment of the present invention, the nano-intermetallic compound-reinforced ultra-high strength ferritic steel further comprises nano-carbide (Mo, W) ₂ C.

In another embodiment of the present invention, the nano-intermetallic compound-reinforced ultra-high-strength ferritic steel has a matrix structure of ferrite, and the ferrite has an average grain size of 1 to 20 μm. In another embodiment of the present invention, the nano-intermetallic compound-reinforced ultra-high-strength ferritic steel has a yield strength of 1200 to 1800 MPa, a tensile strength of 1400 to 2000 MPa, and a reduction ratio of 30 〜 60%, elongation is 5 to 20%.

In another aspect, the present invention also provides a method of producing the nano-intermetallic compound-reinforced ultra-high strength ferritic steel, the steps of which are as follows:

(1) a raw material composition composed of chemical components of the ultrahigh-strength ferritic steel reinforced with the nano-metal compound, followed by smelting, casting, and forging;

(2) performing solution treatment and then cooling to room temperature;

(3) Perform aging treatment and then cool to room temperature.

In one embodiment of the method of the present invention, the solution treatment is carried out at a temperature in the range of 800 to 1300 °C.

In another embodiment of the process of the invention, the solution treatment is carried out at 900 °C.

In another embodiment of the method of the present invention, the solution treatment is carried out for 0.1 to 3 hours.

In another embodiment of the method of the invention, the solution treatment is carried out for 0.5 hours.

In another embodiment of the method of the invention, the aging treatment is carried out in the range of from 400 to 600 °C.

In another embodiment of the method of the invention, the aging treatment is carried out at 550 °C.

In another embodiment of the method of the present invention, the aging treatment is carried out for 0.1 to 20 hours.

In another embodiment of the method of the invention, the aging treatment is carried out for 2 hours.

The invention can obtain a large number of nano-metal intermetallic compounds with uniform distribution and small size by rationally regulating the types and contents of alloying elements and the heat treatment process, effectively exerting the precipitation strengthening effect of the nano-metal intermetallic compounds, and combining with the nano-clusters and nano-carbides. The nano-precipitated phase realizes composite strengthening, and obtains excellent toughness, yield strength of 1200-1800 MPa, tensile strength of 1400-2000 MPa, reduction of area of 30-60%, and elongation of 5-20%. Among them, the nano-metal intermetallic compound is the main strengthening phase, and its precipitation strengthening is the most important strengthening method, which reduces the carbon content in the steel, and thus has excellent welding performance and plastic toughness, and also adds appropriate amounts of Cr and A1 elements. It can form a stable protective film of chromium oxide and aluminum oxide. Cu also plays a role in improving the corrosion resistance of steel in the atmosphere and seawater, thereby comprehensively improving the oxidation and corrosion resistance of steel. In addition, compared with the existing ultra-high-strength martensitic steel, the ultra-high-strength ferritic steel of the present invention can be subjected to a rapid cooling process without quenching after heat treatment, and has a large production size and is suitable for continuous casting and rolling production. Production costs are lower.

The nano-intermetallic compound-reinforced ultra-high-strength ferritic steel of the invention is mainly composed of a large number of uniformly distributed and small-sized nano-metal intermetallic compounds, and combined with a certain amount of nano-clusters and a small amount of nano-carbides to achieve composite strengthening. Extremely high strength and excellent toughness matching, excellent weldability and corrosion resistance, can be applied to cars, ships Ships, bridges, pipelines, energy, power stations, offshore engineering, building structures, pressure vessels, construction machinery, containers, especially for critical components in the field of defense equipment requiring ultra-high-strength rocket engines, aircraft landing gear, bullet-proof armored vehicles, etc. . DRAWINGS

The above and many other features and advantages of the present invention will be better understood by those skilled in the <RTIgt;

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a transmission electron microscope dark field image of a nano-metal intermetallic compound in a matrix of ultra high strength ferritic steel NIS103 manufactured according to Example 1 of the present invention;

2 is a transmission electron micrograph of nanocarbide in a matrix of ultra high strength ferritic steel NIS103 manufactured according to Example 1 of the present invention;

Figure 3 is a scanning electron micrograph of the microstructure of an ultra-high strength ferritic steel NIS102 manufactured according to Example 1 of the present invention;

4 is a room temperature tensile stress-strain curve of ultra high strength ferritic steel NIS103, NISI 07 and comparative steel CS1 manufactured according to Example 1 of the present invention. detailed description

The technical solution of the present invention will be further described below according to specific embodiments. The scope of the present invention is not limited to the following examples, which are merely for illustrative purposes and are not intended to limit the invention in any way.

The present invention provides a nano-intermetallic compound-reinforced ultra-high-strength ferritic steel having a chemical composition as follows: C is 0 to 0.2%, Ni is 2 to 15%, and Mn is 0 to 10%. , A1 is 0.5 to 6%, Cu is 0 to 4%, Cr is 0 to 12%, Mo is 0 to 3%, W is 0 to 3%, V is 0 to 0.5%, Ti is 0 to 0.5%, Nb is 0~0.5%, Si is 0-1%, B is 0.0005~0.05%, P is not higher than 0.04%, S is not higher than 0.04%, N is not higher than 0.04%, 0 is not higher than 0.05%, The amount is Fe and inevitable impurities.

The reasons for limiting the range of chemical components in the nano-intermetallic compound-reinforced ultra-high-strength ferritic steel are described below:

C: Forming stable nano-carbides with Mo and W, which can not only produce precipitation strengthening, but also effectively refine ferrite grains and produce fine-grain strengthening, thereby increasing the strength of steel. In the present invention, in order to ensure excellent weldability and toughness of steel, only a low carbon content is used. Therefore, the present invention limits the content of C to 0 to 0.2%.

Ni and A1: an intermetallic compound forms an element, and Ni forms a nano-intermetallic compound NiAl with A1 to cause precipitation. The strengthening effect is the main strengthening phase of the invention. When the content of Ni and A1 reaches the solid solubility of NiAl in the ferrite matrix, the intermetallic compound NiAl can be precipitated from the matrix. The intermetallic compound NiAl has high strength and hardness, and can effectively pin dislocations, thereby significantly improving The strength of the steel. In addition, Ni also contributes to the improvement of the toughness of steel. However, Ni is an austenite forming element. When the content is too high, austenite remains in the steel, resulting in uneven structure and increased production cost. A1 is also one of the constituent elements of nano-metal intermetallic compounds. It participates in the precipitation strengthening of nano-metal intermetallic compounds. A1 is also a deoxidizer in the steelmaking process. It has the function of purifying molten steel. However, when the A1 content is too high, it will bring smelting and casting. difficult. Therefore, the present invention limits the Ni content to 2 to 15% and the A1 content to 0.5 to 6%.

Cu: The main constituent element of the nano-cluster, the nano-cluster precipitated phase is formed by using Cu with lower cost, and the precipitated phase of the inter-mica metal compound is assisted to play a precipitation strengthening effect to further strengthen the ferritic steel. In addition, Cu also has the effect of improving the corrosion resistance of steel in the atmosphere and seawater, but when the Cu content is too high, hot brittleness is generated, which is detrimental to the processing property. Therefore, the present invention limits the Cu content to 0 to 4%.

M enters the intermetallic compound in the form of a substituted atom, participates in the precipitation strengthening of the intermetallic compound, Mn is an austenite forming element, and has the effect of delaying the transformation of austenite to ferrite, which is beneficial to refining ferrite grains. , improve strength and toughness. However, when the Mn content is too high, austenite remains in the steel, resulting in uneven structure, and a high Mn content causes segregation of the billet, deterioration of toughness, and deterioration of weldability. Therefore, the present invention limits the Mn content to 0 to 10%.

Cr: Anti-oxidation and anti-corrosion elements, which can improve the oxidation and corrosion resistance of steel. At the same time, it is also a ferrite forming element, which can increase and stabilize the ferrite structure of steel. However, too high Cr content will reduce the toughness of steel. Moreover, the production cost is increased, so the present invention limits the Cr content to 0 to 12%.

Mo and W: a nano-carbide forming element, and a carbide having a face-centered cubic structure with C, which has the characteristics of small size and high thermal stability, can effectively hinder grain growth, and exerts a role of fine grain strengthening and precipitation strengthening. In addition, it can stabilize the ferrite structure of steel and also provide solid solution strengthening. However, in the present invention, in order to ensure excellent weldability and toughness of steel, only a low carbon content is used, a small amount of Mo and W may be added to saturate the carbon fixation effect, and Mo and W are excessively added, and the matrix precipitates Fe ₂ Mo. The brittleness phase of Fe ₂ W reduces the toughness of the steel, so the content of Mo and W in the present invention is limited to 0 to 3%.

V, Ti, and Nb: Carbide forming elements, which form a face-centered cubic carbide with C, can effectively inhibit grain growth and play the role of fine grain strengthening and precipitation strengthening. Since only a low carbon content is used in order to ensure excellent weldability and toughness of steel, the present invention limits the contents of V, Ti and Nb to 0 to 0.5%.

Si: Improves carbon partitioning, prevents the formation of cementite, and stabilizes the ferrite structure of steel to provide solid solution strengthening. However, when Si is added too much, the toughness of steel is lowered. Therefore, the present invention limits Si content to 0~1%.

B: It can significantly purify the grain boundary and improve the strength and toughness of the steel. However, when the B content is too high, the grain boundary will precipitate too much boron. The compound reduces the toughness of the steel, so the present invention limits the B content to 0.0005 to 0.05%.

P and S: Inevitable impurity elements in steel. When the content is high, brittle compounds are formed with Cu, which impairs the toughness and weldability of steel. Therefore, the contents of P and S are both controlled below 0.04%.

N and B O: Inevitable impurity elements in steel, which impair the toughness and weldability of steel, so the contents of N and 0 are controlled below 0.04% and 0.05%, respectively.

The components other than the above are Fe and other unavoidable impurities, and the components other than the above are not excluded insofar as the effects of the present invention are not impaired.

The present invention also provides a method of producing the nano-intermetallic compound-reinforced ultra-high strength ferritic steel, the steps of which are as follows:

(2) performing solution treatment and then cooling to room temperature;

(3) Perform aging treatment and then cool to room temperature.

According to the method of the present invention, smelting can be carried out in an electric arc furnace, a converter, an induction furnace, and then the slab can be produced by continuous casting or the ingot can be produced by die casting, and the slab or ingot has good cold and heat. The processing property can be followed by cold rolling, warm rolling or forging or hot rolling in the range of 800~1300 °C. After rolling or forging, the sheet is solution treated at 800~1300 °C for treatment time. 0.1~3 hours, followed by cooling. The cooling method can be air cooling, air cooling, oil quenching or water quenching. It can be cooled to room temperature or directly cooled to aging temperature for aging treatment. The aging treatment is carried out in the range of 400~600 °C. The time is from 0.1 to 20 hours, followed by cooling, and the cooling method can also be air-cooled, air-cooled, oil-quenched or water-quenched, and finally the nano-intermetallic compound-reinforced ultra-high-strength ferritic steel of the present invention is obtained.

The invention can refine the crystal grains by cold and hot deformation processes such as forging and rolling, and can also introduce a large number of defects such as dislocations and vacancies, and provide favorable conditions for high concentration of nano metal intermetallic compounds and a certain amount of nanoclusters and nano carbide nucleation. It also enables dislocation enhancement. Then, according to the invention, the heat treatment is carried out, that is, the solution treatment and the aging treatment are carried out for a certain period of time at a specific temperature, and the ferrite supersaturated solid solution is obtained by solution treatment, and the main strengthening phase nanometer is effectively controlled by reasonable control of the aging temperature and the aging time. Precipitation and growth of intermetallic compounds and auxiliary strengthening phase nanoclusters and nanocarbides. In terms of solution treatment, the elements Ni and A1 formed between the nanometals have a large solid solubility in the austenite of the face-centered cubic structure, and the solution treatment at 800 to 1300 ° C according to the present invention ensures the addition. The inter-metal intermetallic elements can be completely dissolved in the matrix, while the too high temperature grains will be severely coarsened, and the strength and toughness of the steel will decrease. In terms of aging treatment, the solid solubility of the nano-metallic compound NiAl in ferrite is very low, and the solid solubility decreases with the decrease of temperature. If the aging temperature is too high, the nano-metal intermetallic compound will be coarse. If too low an aging temperature is used, The intermetallic compounds are insufficiently precipitated. According to the present invention, after the above solution treatment and aging treatment at 400 to 600 ° C, it was confirmed by transmission electron micrograph that a large number of nano-intermetallic compounds having a uniform distribution and a small size were precipitated in the ferrite matrix. According to the nano-precipitation phase strengthening mechanism, the dislocations interact with the precipitation phase, and the precipitation phase effectively hinders the movement of dislocations, thereby achieving reinforcement, and the maximum strengthening effect can be obtained in the case of a large number of precipitated phases, small size, and uniform distribution. The invention obtains the nano-metal intermetallic compound with high concentration, uniform distribution and small size by rationally adjusting the alloying elements and the heat treatment process, and maximizes the strengthening effect of the nano-metal intermetallic compound. In addition, it was confirmed by transmission electron microscopy that a certain amount of nanoclusters and a small amount of nano-carbides were formed in the ferrite matrix by adding appropriate nano-clusters and nano-carbide forming elements, which assisted the main strengthening of nano-intermetallic compounds. To the composite strengthening effect.

Unless otherwise defined, the terms used in the present invention are intended to be understood by those skilled in the art.

The present invention will be further described in detail below with reference to the accompanying drawings.

Example 1

According to the composition range of the ultra-high-strength ferritic steel strengthened by the nano-metal compound of the present invention, the invention steel is smelted

NIS101~108, while smelting comparative steel CS1 and CS2 as comparisons. According to the composition of the invention steels NIS101 to 108 and the comparative steels CS1 and CS2 shown in Table 1, the smelting and casting were carried out in an arc melting furnace, and the obtained ingot was rolled at a reduction of 5 to 10% each time. The treatment was carried out to obtain a sheet having a total deformation of about 70%. The rolled sheet was solution treated at 900 ° C for 0.5 hours, then cooled to room temperature by argon quenching, then incubated at 550 ° C for 2 hours, and then cooled by argon quenching. To room temperature, inventive steels NIS101~108 and comparative steels CS1, CS2 were obtained.

Table 1. Alloy composition of inventive steel NIS101~108 and comparative steel CS1, CS2

Component (wt%)

Numbering

Fe and not

C Ni Al Mn Cu Cr Mo W V Ti Nb Si B

Avoid impurities

NIS 101 0.05 3 1 5 - - 1.5 1.5 - - 0.07 - 0.03 balance

NIS I 02 0.05 5 1 1.5 2.5 - 1.5 1.5 - - 0.07 - 0.03 balance

NIS 103 0.05 5 2 3 - - 1.5 1.5 - - 0.07 - 0.03 balance

NIS I 04 0.05 5 1 - 1.5 2.25 1.5 1.5 - - 0.07 - 0.03 balance

NIS 105 0.08 5 2 3 - 9 1.5 1.5 0.25 0.07 - 0.3 0.01 balance

NIS 106 0.05 5 2 5 - - 1.5 1.5 - - 0.07 - 0.03 balance

NIS 107 0.05 8 2 3 - - 1.5 1.5 - - 0.07 - 0.03 balance

NIS 108 0.05 8 4 8 - - 1.5 1.5 - - 0.07 - 0.03 balance

CS 1 0.05 5 - 1.5 - - - - - - 0.07 - 0.03 balance

CS2 0.05 0.75 1 1.5 - - 1.5 1.5 - - 0.07 - 0.03 balance Example 2

According to the alloy composition of NIS103 in Table 1, smelting and casting are carried out in an arc melting furnace, and the obtained ingot is subjected to rolling treatment at a reduction of 5 to 10% each time to obtain a total deformation of about 70%. Plate. The rolled sheet was solution treated at 1200 ° C for 0.2 hours, then cooled to room temperature by water quenching, then aged at 550 ° C for 2 hours, and then cooled to room temperature by air cooling. Thus, the inventive steel NIS103' was obtained.

Test example 1

The above-mentioned heat-treated comparative steels CS1, CS2 and inventive steels NIS101 to 108 were analyzed by transmission electron microscopy. It can be seen from Table 1 that there is no intermetallic compound forming element Al in the comparative steel CS1, and the intermetallic compound forming elements M and A1 in the comparative steel CS2 are less. The transmission electron microscopy results show that no intermetallic metal is formed in the comparative steels CS1 and CS2. Compounds, and a large number of well-distributed, small-sized nano-intermetallic compounds were found in the inventive steels NIS101-108. Figure 1 is a transmission electron micrograph of a nano-metallic compound in the NIS103 matrix of the inventive steel. The average size of the nano-metallic compound is about 3 nm, and the distribution is uniform. The average spacing is 2~20 nm. The number of nano-intermetallic particles per cubic micron is shown. Not less than 10,000, determined by transmission electron microscopy, the nano-metallic compounds mainly include Ni and A1 elements. It can be seen that the nano-intermetallic compound-reinforced ultra-high-strength ferritic steel of the present invention forms a nano-intermetallic compound having a high concentration, a uniform distribution, and a small size. According to the nano-precipitation phase strengthening mechanism, these concentrations are high and the size is small. The nano-intermetallic compound effectively hinders the dislocation motion and significantly enhances the strength of the ferritic steel.

Further, a small amount of nano-carbide was also observed in the nano-intermetallic compound-reinforced ultrahigh-strength ferritic steel of the present invention by transmission electron microscopy. 2 is a transmission electron micrograph of nano-carbide in the inventive NIS103 matrix. The nano-carbide is (Mo, W) ₂ C with an average size of 20 nm as determined by transmission electron microscopy. The nano-carbide acts as a nano-precipitating phase, and also exhibits a precipitation strengthening effect. In addition, since the size is small and the thermal stability is high, the nano-carbide is also effective in inhibiting grain growth and fine-grain strengthening. Figure 3 is a scanning electron micrograph of the microstructure of the inventive steel NIS103. The matrix structure is fine-grained ferrite, the grain size is uniform and fine, and the average grain size is 2 μηι, which can be seen in the matrix. The above-mentioned nanoprecipitate phase effectively functions to refine the crystal grains. According to the Hall-Petch relationship, the grain strength can be improved by refining the grain size, and the smaller the grain size, the better the plasticity and the higher the toughness index. Test example 2

Comparative steels CS1, CS2 and inventive steels NIS101~108 were processed into tensile specimens by wire cutting, and tensile tensile tests were carried out on MTS testing machines. The results of yield strength, tensile strength, section shrinkage and elongation are listed in Table 2. . 4 is a tensile stress-strain curve of inventive steels NIS103, NISI 07 and comparative steel CS1 made in accordance with the present invention. By Table 2 As can be seen from Fig. 4, after the same smelting and heat treatment processes, the comparative steels CS1 and CS2 have yield strengths of 534 MPa and 466 MPa, respectively, and tensile strengths of 651 MPa and 663 MPA, respectively, consistent with published literature, and according to the present document. The invention steel NIS101~108 has a yield strength of 1200~1800 MPa and a tensile strength of 1400~2000 MPa. Compared with the comparative steels CS1 and CS2, the yield strength and tensile strength are significantly improved, and the area shrinkage rate is maintained. At 30-60%, the elongation is maintained at 5 to 20%, and the toughness is excellent. It can be seen that the present invention greatly improves the strength of the steel by adjusting the nano-metal intermetallic compound, the nano-cluster and the nano-carbide strengthening element, and adopting an appropriate heat treatment process.

Table 2. Tensile Mechanical Properties of Inventive Steel NIS101~108 and Comparative Steel CS1, CS2 at Room Temperature

Test Example 3

The inventive steel NIS103' obtained in Example 2 was processed into a tensile specimen by wire cutting, and subjected to a room temperature tensile test on an MTS tester, and the yield strength was measured to be 1,403 MPa, and the tensile strength was 1,722 MPa. It is 42% and the elongation is 9.1%.

As described in Example 2, the alloy composition of the inventive steel NIS103' and NIS103 and the heat treatment process were the same, except that the inventive steel NIS103' was solution treated at 1200 °C. By increasing the solution treatment temperature, the alloying elements are fully dissolved. After cooling, the alloying elements will have a greater degree of supersaturation in the ferrite matrix, thereby increasing the nucleation rate of the nanoprecipitates, which in turn can be produced during aging treatment. More nano-reinforced phases. Therefore, from the mechanical properties measured by the above room temperature tensile test, it is known that the nano-intermetallic compound-reinforced ultra-high-strength ferritic steel obtained by solution treatment at the above temperature also has ultra-high strength and good plasticity. toughness.

In summary, the present invention optimizes the design of the alloy composition from the viewpoint of thermodynamics, and rationally adjusts the intermetallic combination. The ratio of the element forming element, the nano-cluster forming element, the nano-carbide forming element and the C element, maximally increases the volume fraction of the nano-precipitated phase, and simultaneously controls the precipitation temperature and the precipitation time, thereby creating a large number of nucleation sites, making solid The molten alloy elements are uniformly precipitated to the maximum extent, and the growth of the nano-precipitated phase is controlled during in-situ precipitation, and nano-intermetallic compounds with high concentration, uniform distribution and small size are obtained, which realizes the ultra-high strength of the new ultra-high-strength steel. To the most critical role, in addition, combined with a certain amount of nano-cluster precipitation phase and a small amount of nano-carbide precipitation phase to achieve composite strengthening, together with precipitation strengthening and fine-grain strengthening. Therefore, the nano-intermetallic compound-reinforced ultra-high-strength ferritic steel of the present invention is an ultra-high-strength steel mainly composed of nano-metal compound strengthening, combined with nano-cluster and nano-carbide composite, and has ultra-high strength and excellent Excellent welding performance, plastic toughness, corrosion resistance, comprehensive performance, can be applied to automobiles, ships, bridges, pipelines, energy, power stations, offshore engineering, building structures, pressure vessels, construction machinery, containers, especially It requires key components in the field of defense equipment such as ultra-high-strength rocket engines, aircraft landing gear, and bullet-proof armored vehicles.

It should be understood by those skilled in the art that the presently described embodiments of the present invention are merely exemplary and that various alternatives, modifications and improvements are possible within the scope of the invention. Therefore, the invention is not limited to the embodiments described above, but only by the claims.

Claims

Rights request

1. A nano-intermetallic compound-reinforced ultra-high-strength ferritic steel having a chemical composition as follows:

C is 0-0.2%, Ni is 2 to 15%, Mn is 0 to 10%, A1 is 0.5-6%, Cu is 0-4%, Cr is 0 to 12%, Mo is 0 to 3%, W 0 to 3%, V is 0 to 0.5%, Ti is 0 to 0.5%, Nb is 0 to 0.5%, Si is 0 to 1%, B 3⁄4 is 0.0005-0.05%, P is not higher than 0.04%, S is not Above 0.04%, N is not higher than 0.04%, 0 is not higher than 0.05%, and the balance is Fe and unavoidable impurities.

The nano-metal compound-reinforced ultrahigh-strength ferritic steel according to claim 1, wherein the nano-intermetallic compound is MA1.

3. The nano-intermetallic compound-reinforced ultrahigh-strength ferritic steel according to claim 2, wherein the nano-intermetallic compound has an average size of 3 nm, an average spacing of 2 to 20 nm, and a number of intermetallic compounds per cubic micrometer. Not less than 10,000.

The nano-metal compound-reinforced ultrahigh-strength ferritic steel according to claim 1, further comprising a nanocluster whose main constituent element is Cu.

5. The nano-intermetallic compound-reinforced ultra-high strength ferritic steel according to claim 1, which further comprises nano-carbide (Mo, W) ₂ C.

The nano-intermetallic compound-reinforced ultrahigh-strength ferritic steel according to claim 1, wherein the matrix structure is ferrite, and the ferrite has an average grain size of 1 to 20 μη.

The nano-intermetallic compound-reinforced ultrahigh-strength ferritic steel according to any one of claims 1 to 6, which has a yield strength of 1200 to 1800 MPa.

The nano-intermetallic compound-reinforced ultrahigh-strength ferritic steel according to any one of claims 1 to 6, which has a tensile strength of 1400 to 2000 MPa.

The nano-intermetallic compound-reinforced ultrahigh-strength ferritic steel according to any one of claims 1 to 6, which has a reduction in area of from 30 to 60%.

The nano-intermetallic compound-reinforced ultrahigh-strength ferritic steel according to any one of claims 1 to 6, which has an elongation of 5 to 20%.

A method of producing a nano-intermetallic compound-reinforced ultra-high-strength ferritic steel according to any of the preceding claims, wherein the steps are as follows:

(1) smelting, casting, and forging a raw material composition composed of chemical components of the ultrahigh-strength ferritic steel strengthened by the nano-metal compound; (2) performing solution treatment and then cooling to room temperature;

(3) Perform aging treatment and then cool to room temperature.

The method according to claim 11, wherein the solution treatment is carried out in the range of 800 to 1300 °C.

13. The method according to claim 12, wherein the solution treatment is carried out at 900 °C.

The method according to claim 12 or 13, wherein the solution treatment is carried out for 0.1 to 3 hours.

15. The method according to claim 14, wherein the solution treatment is carried out for 0.5 hours.

16. The method according to claim 11, wherein the aging treatment is carried out in the range of 400 to 600 °C.

17. The method according to claim 16, wherein said aging treatment is performed at 550 °C.

18. The method according to claim 16 or 17, wherein said aging treatment is carried out for 0.1 to 20 hours.

19. The method according to claim 18, wherein said aging treatment is carried out for 2 hours.