JP6794479B2 - Copper-rich nanocluster reinforced ultra-high-strength ferritic steel and its manufacturing method - Google Patents

Description

The present invention relates to ultra-high strength ferritic steel and a method for producing the same, and more specifically, to copper-rich nanocluster reinforced ultra-high strength ferritic steel and a method for producing the same.

With increasing stress on resources and the environment, the steel industry is increasingly focusing on environmental protection and energy conservation. An important way for the steel industry to achieve sustainable development is to develop ultra-high strength steels that can save energy and resources and have excellent performance that meet structural and functional requirements in various technical fields. It is to be.

Conventional ultra-high strength steels such as low alloy steels reinforced with low temperature tempered martensite or bainite, high temperature tempered alloy carbide precipitates, secondary hardened ultra-high strength steels, or intermetal compound precipitation reinforced maraging steels Meets the requirements for ultra-high strength to some extent. However, due to the characteristics of high carbon and high alloy and the quenching conditions required for phase transition, conventional ultra-high strength steels have problems of poor weldability, poor plasticity and toughness, and high cost. The size is limited.

With the development of nanotechnology, improving the overall performance of ultra-high-strength steel by utilizing the nano-precipitation strengthening mechanism has become an important method for developing new ultra-high-strength steel. In particular, the development of new ultra-high strength steels based on ferritic structures using a nanoprecipitation strengthening mechanism, as compared to conventional martensite matrices, will bring significant technological benefits and cost savings. Recently, researchers have conducted preliminary research on Cu nanocluster precipitation hardening steels. Cu is an element with a face-centered cubic structure. Its solubility is very low in a ferrite matrix with a body-centered cubic structure. After an appropriate heat treatment, Cu is precipitated from the ferrite matrix to form Cu nanocluster precipitates, which can exert a precipitation strengthening effect to increase the strength of the steel. The study also showed that the precipitation strengthening effect was high when the size of the produced nanoclusters was small, the volume fraction was high, the interparticle voids were small, and the distribution was uniform. However, most of the Cu particles in existing Cu precipitation-strengthened steels exceed 50 nm in size. The amount of precipitation is small, the voids between the precipitates are large, and the particle distribution is not uniform. Therefore, the strengthening effect of Cu particles is limited. The strength of the obtained Cu precipitation reinforced steel is less than 1000 MPa. For example, patent number CN101238561A discloses nano Cu precipitation reinforced chrome ferrite stainless steel, wherein the size of the precipitated Cu particles is 50-200 nm. The yield strength of the reinforced ferritic steel produced from the Cu phase precipitation strengthening effect is 300 MPa or more, the tensile strength is 450 MPa or more, and the elongation is 25% or more.

The present invention rationally regulates the type and content of alloying elements and the heat treatment process to optimize nucleation and growth activity of Cu nanoclusters. In addition, the size, volume fraction, and distribution of nanoclusters are optimized to form copper-rich nanoclusters with high number density, uniform distribution, and fine size. Therefore, the strengthening effect of the copper-rich nanocluster is maximized. Copper-rich nanoclusters characterized by low carbon, low cost, and excellent overall performance by combining various strengthening methods such as grain refinement strengthening, solid solution strengthening, and dislocation strengthening together to achieve composite strengthening. Manufactures reinforced ultra-high strength ferritic steel.

An object of the present invention is to provide a copper-rich nanocluster-reinforced ultra-high-strength ferritic steel, which has a high number density, a uniformly distributed, and fine-sized copper-rich nanocluster reinforcement. Dominant. On the one hand, a new low price with high strength and toughness, excellent welding performance, and good corrosion resistance, combined with various strengthening methods such as granulation, solid solution strengthening, and dislocation strengthening. Manufactures ultra-high strength ferritic steel.

Another object of the present invention is to provide a method for producing the copper-rich nanocluster reinforced ultrahigh-strength ferritic steel.

In one embodiment, the invention is a copper-rich nanocluster reinforced ultra-high strength ferritic steel with the following weight percent chemical composition: 0-0.2% C, 0.5-5% Cu, 0. .01-4% Ni, 0.01-4% Mn, 0.001-2% Al, 0-12% Cr, 0-3% Mo, 0-3% W, 0.05 % Or more Mo + W, 0 to 0.5% V, 0 to 0.5% Ti, 0 to 0.5% Nb, 0.01% or more V + Ti + Nb, 0 to 1% Si, 0.0005 It contains ~ 0.05% B, 0.04% or less P, 0.04% or less S, 0.04% or less N, 0.05% or less O, and the balance is Fe and unavoidable impurities. Provided is a copper-rich nanocluster-reinforced ultra-high-strength ferritic steel.

In one embodiment of the invention, the constituent elements of the copper-rich nanoclusters are Cu, Ni, Mn, and Al.

In another embodiment of the present invention, the average diameter of copper-rich nanoclusters is 3 nm, the voids between average particles are 2 to 20 nm, and the number of copper-rich nanoclusters is 10,000 or more per cubic micron.

In another embodiment of the invention, the copper-rich nanocluster-reinforced ultrahigh-strength ferritic steel further comprises a composite nanocarbide (V, Ti, Nb) C having a size of 5-100 nm.

In another embodiment of the invention, the matrix of copper-rich nanocluster reinforced ultra-high strength ferritic steel is ferrite with an average particle size of 1-20 μm.

In another embodiment of the present invention, the copper-rich nanocluster reinforced ultrahigh-strength ferritic steel has a yield strength of 900 to 1200 MPa, a tensile strength of 1200 to 1500 MPa, an elongation of 10 to 20%, and a cross-section reduction rate of 50% to 80. %.

In another aspect, the invention further provides a method of producing copper-rich nanocluster reinforced ultrahigh strength ferritic steels comprising the following steps:
(1) A process of melting raw materials of chemical components of copper-rich nanocluster reinforced ultra-high-strength ferritic steel, casting, and forging / rolling ingots in order.
(2) A process of solution treatment and then cooling to room temperature.
(3) A step of performing aging treatment and then cooling to room temperature.

In one embodiment of the method of the invention, the solution treatment is carried out in the range of 800-1300 ° C.

In another embodiment of the method of the invention, the solution treatment is performed at 900 ° C.

In another embodiment of the method of the 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 400-600 ° 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 invention, the aging treatment is carried out for 0.1 to 20 hours.

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

The present invention rationally adjusts the type and content of alloying elements and the heat treatment process to obtain fine-sized copper-rich nanoclusters that are uniformly distributed at a high number density, and is effective in strengthening nanocluster precipitation. Demonstrate Composite reinforcement is also achieved by combining various reinforcement methods such as grain refinement enhancement, solid solution reinforcement, and dislocation reinforcement to achieve excellent strength and toughness. Copper-rich nanoclusters are the dominant strengthening phase, and their strengthening effect is the key strengthening. The carbon content in the steel is reduced and the steel has excellent weldability, excellent ductility and toughness. In addition, suitable amounts of Cr and Al can be added to form a stable protective film of chromium oxide and alumina. Cu can increase the corrosion resistance of steel to atmosphere and seawater, and can comprehensively enhance the antioxidant and corrosion resistance of steel. The present invention optimizes the types and contents of alloying elements for nanocluster strengthening, grain refinement strengthening, and solid solution strengthening. Therefore, the minimum amount of alloying elements and the optimum alloying elements are used. In addition, compared to existing ultra-high strength martensitic steels, the ultra-high strength ferritic steels of the present invention do not require a quenching process such as quenching after heat treatment. The production scale is large, steel is suitable for continuous casting and rolling production, and the production cost is low.

In summary, according to the copper-rich nanocluster-reinforced ultra-high-strength ferritic steels of the present invention, copper-rich nanoclusters dominate the reinforcement. Furthermore, various strengthening methods such as grain refinement strengthening due to the precipitation of nanocarbides, other solid solution strengthening with alloying elements, and dislocation strengthening are combined to achieve composite strengthening. Therefore, an excellent combination of high strength and high toughness can be obtained, excellent weldability and good corrosion resistance can be obtained, and the cost is relatively low. The steels of the present invention can be applied in fields such as automobiles, ships, bridges, pipelines, energy production, power plants, marine technology, construction, pressure vessels, industrial technology machinery, or containers, and defense equipment.

By reading in conjunction with the accompanying drawings, the above contents, other advantages and features of the present invention will become clearer to those skilled in the art from the following detailed description.
FIG. 1 is a high resolution transmission electron microscope (TEM) photograph of copper-rich nanoclusters in a matrix of ultra-high strength ferritic steel NSF104 produced according to Example 1 of the present invention. FIG. 2 is a high resolution TEM photograph of nanocarbide in a matrix of ultra-high strength ferritic steel NSF104 produced according to Example 1 of the present invention. FIG. 3 is a scanning electron micrograph (SEM) microstructure of ultra-high strength ferritic steel NSF104 manufactured according to Example 1 of the present invention. FIG. 4 is a tensile stress-strain curve of the ultra-high strength ferritic steel NSF108 and the reference steel T24 manufactured according to Example 1 of the present invention.

The technical solutions of the present invention will be further described below with reference to specific embodiments. The scope of the present invention is not limited to the following embodiments. These embodiments are given for illustrative purposes only and do not limit the invention in any way.

The present invention is a copper-rich nanocluster reinforced ultra-high strength ferritic steel with the following weight percentage chemical composition: 0-0.2% C, 0.5-5% Cu, 0.01-4% Ni, 0.01-4% Mn, 0.001-2% Al, 0-12% Cr, 0-3% Mo, 0-3% W, 0.05% or more Mo + W, 0-0.5% V, 0-0.5% Ti, 0-0.5% Nb, 0.01% or more V + Ti + Nb, 0-1% Si, 0.0005-0.05% B, 0.04% or less of P, 0.04% or less of S, 0.04% or less of N, 0.05% or less of O, and the balance is Fe and copper-rich nano, which is an unavoidable impurity. Provided are cluster reinforced ultra-high strength ferritic steels.

The range of the content of each chemical component in the copper-rich nanocluster-reinforced ultra-high-strength ferritic steel is defined for the following reasons.

C: C forms a stable nanocarbide with V, Ti, and Nb. Nanocarbide not only has a precipitation strengthening effect, but also refines ferrite particles to produce a crystal grain refinement strengthening effect, further increasing the strength of steel. In the present invention, a low carbon content is adopted to ensure that the steel has excellent welding performance and excellent toughness. Therefore, in the present invention, the content of C is limited to 0 to 0.2%.

Cu: Cu is the main constituent element of nanoclusters. Cu is also the most important element for strengthening the nanoclusters of the present invention. Low cost Cu is used to form nanoclusters, effectively strengthening ferritic steels, reducing carbide reinforcement and further reducing the carbon content in the steel. This improves the weldability and toughness of the steel. In addition, Cu can increase the atmosphere of steel and its corrosion resistance to seawater. However, when the Cu content is less than 0.5%, the strengthening effect is not clear. If the Cu content is too high, it becomes high temperature brittle, which is harmful to processing. Therefore, in the present invention, the Cu content is limited to 0.5-5%.

Ni: Ni is one of the constituent elements of nanoclusters and is involved in the strengthening of nanocluster precipitation. Ni can inhibit the growth of nanoclusters and promote the miniaturization of nanoclusters. Ni can also help improve the toughness of steel. However, Ni is an austenite-forming element. If the Ni content is too high, the steel will have retained austenite, which can lead to a non-uniform structural distribution and increase manufacturing costs. Therefore, in the present invention, the Ni content is limited to 0.01-4%.

Mn: Mn is one of the constituent elements of nanoclusters and is involved in the strengthening of nanocluster precipitation. Mn is an austenite-forming element and has a function of delaying the conversion of austenite to ferrite. This can promote the refinement of ferrite grain size and increase the strength and toughness. However, if the Mn content is too high, the steel will have retained austenite, leading to a non-uniform structural distribution. Moreover, a high Mn content can result in segregation, toughness degradation and weldability reduction. Therefore, the Mn content of the present invention is limited to 0.01-4%.

Al: Al is one of the constituent elements of nanoclusters and is involved in the strengthening of nanocluster precipitation. Al is an oxygen scavenger in the steelmaking process of refining molten steel. However, if the Al content is too high, melting and casting will be difficult. Therefore, in the present invention, the Al content is limited to 0.001 to 2%.

Cr: Cr is an antioxidant and a corrosion resistant element. Cr can improve the antioxidant properties and corrosion resistance of steel. On the other hand, Cr is also a ferrite forming element, which can increase and stabilize the ferrite structure of steel. However, excess Cr reduces the toughness of the steel and increases the manufacturing cost. Therefore, in the present invention, the Cr content is limited to 0-12%.

Mo and W: Mo and W are ferrite forming elements that can stabilize the ferrite structure of steel and have a solid solution strengthening effect. However, excessive addition of Mo and W will precipitate the embrittled phases of Fe ₂ Mo and Fe ₂ W. Therefore, the toughness of steel is reduced. Therefore, in the present invention, the content of Mo and W is limited to 0 to 3%, and the total amount of Mo and W is 0.05% or more.

V, Ti, and Nb: V, Ti, and Nb are potent carbide-forming elements. V, Ti, Nb, and C together form an MC-type carbide (M: V, Ti, or Nb), which has a face-centered cubic structure, is small in size, and is thermally stable. It has a highly characteristic feature. Carbide can effectively inhibit crystal grain growth and exert grain refinement-enhancing and precipitation-enhancing effects. In the present invention, a low carbon content is adopted to ensure that the steel has excellent weldability and toughness. The carbon fixation effect can be saturated by adding 0.5% V, Ti, or Nb. Therefore, in the present invention, the content of V, Ti, and Nb is limited to 0 to 0.5%, and the total amount of V, Ti, and Nb is 0.01% or more.

Si: Si is used to increase carbon partitioning and prevent the formation of cementite. Further, Si can stabilize the ferrite structure of steel and have a solid solution strengthening effect. However, excessive amounts of Si result in a decrease in steel toughness. Therefore, in the present invention, the Si content is limited to 0 to 1%.

B: B can significantly purify grain boundaries and improve the strength and toughness of the steel. However, if the B content is too high, an excessive amount of boride may precipitate at the grain boundaries. Therefore, the toughness of steel can be reduced. Therefore, in the present invention, the content of B is limited to 0.0005 to 0.05%.

P and S: P and S are unavoidable impurity elements in steel. If the P and S contents are too high, they will form a brittle compound with Cu, which will adversely affect the toughness and weldability of the steel. Therefore, the contents of P and S are controlled to less than 0.04%.

N and O: N and O are unavoidable impurity elements in steel and have an adverse effect on the toughness and weldability of steel. Therefore, the N and O contents are controlled to less than 0.04% and less than 0.05%, respectively.

In addition to the listed components, the rest are Fe and other unavoidable impurities. Ingredients other than the above are not excluded as long as they do not affect the effect, purpose and scope of the present invention.

The present invention further provides a method for producing a copper-rich nanocluster-reinforced ultrahigh-strength ferritic steel comprising the following steps.
(1) A process of melting raw materials of chemical components of copper-rich nanocluster reinforced ultra-high-strength ferritic steel, casting, and forging / rolling ingots in order.
(2) A process of solution treatment and then cooling to room temperature.
(3) A step of performing aging treatment and then cooling to room temperature.

According to the method of the present invention, melting can be carried out in an electric arc furnace, a converter, and an induction furnace. Next, a continuous casting process may be used to produce the slab, or a mold casting process may be used to produce the ingot. The slab or ingot has excellent cold workability or hot workability. Next, cold rolling, warm rolling, or hot forging / rolling in a temperature range of 800 to 1300 ° C. is performed. Then, the plate is proceeded to solution treatment within the range of 800 to 1300 ° C. The processing time is 0.1 to 3 hours. Next, cool the board. The cooling method may be air cooling, air cooling, oil quenching, or water quenching. The plate may be cooled directly to room temperature or to room temperature or the aging temperature for aging treatment. The aging treatment is performed in the range of 400 to 600 ° C. The processing time is 0.1 to 20 hours. Then cool the board again. Similarly, the cooling method may be air cooling, air cooling, oil quenching, or water quenching. Finally, the copper-rich nanocluster-reinforced ultrahigh-strength ferritic steel of the present invention is obtained.

The present invention refines particles through hot / cold deformation processes such as forging processes. In addition, a large number of defects such as dislocations and vacancies are introduced, resulting in good nucleation of high-density nanoclusters. Further, dislocation strengthening is also performed. In the present invention, heat treatment is followed. That is, the solution treatment and the aging treatment are performed at a specific temperature for a specific time. The supersaturated ferrite solid solution is then obtained from the solution treatment. By rationally controlling the aging temperature and aging time, the precipitation and growth of nanoclusters are rationally controlled. Regarding the solution treatment, the Cu element has a high solubility in austenite having a face-centered cubic structure. According to the solution treatment at 800 to 1300 ° C. in the present invention, the added Cu element can be surely completely dissolved in the matrix. If the temperature is too high, the particles will become very coarse and the strength and toughness of the steel will decrease. With respect to aging treatment, the solubility of the Cu element in ferrite is very low. In addition, the solubility decreases as the temperature decreases. If the aging temperature is too high, the nanoclusters will be coarse. If the aging temperature is too low, the precipitation of nanoclusters is inadequate. After the solution treatment and aging treatment at 400 to 600 ° C. of the present invention, a large amount of copper-rich nanoclusters having a high number density, a uniform distribution, and a fine size are precipitated in the ferrite matrix. Can be confirmed by TEM. According to the nanoprecipitation strengthening mechanism, dislocations interact with precipitates and the precipitation phase effectively inhibits dislocation motion to achieve a strengthening effect. Maximum reinforcement can be obtained under conditions of small size, uniformly distributed, high number density precipitates. Through rational control of the alloying elements and the heat treatment process, high number density, uniformly distributed, finely sized copper-rich nanoclusters are obtained in the present invention. The strengthening effect of copper-rich nanoclusters is maximized. In addition to the Cu element, other elements (Ni, Mn, and Al) are also important components of the nanoclusters in the present invention. Other elements not only affect the nucleation of nanoclusters, but also hinder the growth of nanoclusters and reduce the size of the nanoclusters.

Furthermore, the copper-rich nanocluster-reinforced ultra-high-strength ferritic steels of the present invention further contain carbide-forming elements (V, Ti, and Nb) and trace amounts of carbon (C). After the above heat treatment, a small amount of composite nanocarbide precipitate is precipitated as an interfacial precipitate of the ferrite matrix. These fine nanocarbides having high thermal stability bring about the effect of strengthening grain refinement without impairing weldability and toughness. On the other hand, the present invention actively produces a solid solution strengthening effect of alloying elements (such as Mo and W) by optimizing the types and contents of various alloying elements. Dislocation strengthening is achieved by rational thermal and cold deformation as well as heat treatment processes. As a result, composite strengthening is achieved, where copper-rich nanocluster strengthening is predominant, combined with grain refinement strengthening, solid solution strengthening, and dislocation strengthening.

Unless otherwise specified, the usual meanings of the terminology of the present invention will be generally understood by those skilled in the art.

The present invention will be described in detail through examples with the accompanying drawings.

Example 1
Nine types of steels NSF101-109 of the present invention are made according to the composition range of copper-rich nanocluster reinforced ultra-high strength ferritic steels, and for comparison, steel T24 used in power plants is made. Based on the alloy compositions of the steels NSF 101-109 and T24 in Table 1, the components are melted and cast in an arc melting furnace. The produced ingot proceeds to rolling at a rolling rate of 5 to 10% each time, and a slab having a total deformation of about 70% is obtained. The rolled slab is solution-treated at 900 ° C. for 0.5 hours. The slab is then cooled to room temperature by argon quench cooling. It is then aged at 550 ° C. for 2 hours. Then similarly, it is cooled to room temperature by argon quench cooling. As a result, the steels NSF101 to 109 and the reference steel T24 of the present invention are obtained.

Example 2
Melting and casting are performed in an arc melting furnace according to the alloy composition of NSF104 in Table 1. The produced ingot is processed by rolling at a rolling rate of 5 to 10% each time to obtain a slab having a total deformation of about 70%. Next, the rolled slab is solution-treated at 850 ° C. for 0.5 hours, and then cooled to room temperature by water quenching. It was then aged at 550 ° C. for 2 hours. Then cool to room temperature by air cooling. In this way, the steel NSF104'of the present invention is obtained.

Example 3
Melting and casting are performed in an arc melting furnace according to the alloy composition of NSF104 in Table 1. The produced ingot is processed by rolling at a rolling rate of 5 to 10% each time to obtain a slab having a total deformation of about 70%. Next, the rolled slab is solution-treated at 1200 ° C. for 0.5 hours. After that, it was cooled to room temperature by water quenching. It is then aged at 550 ° C. for 2 hours and then cooled to room temperature by air cooling. In this way, the steel NSF104 "of the present invention can be obtained.

Experiment 1
The reference steel T24 and the steels NSF101-109 of the present invention produced after heat treatment are analyzed using TEM. It is understood from Table 1 that the composition of the reference steel T24 does not contain nanocluster forming elements. The TEM results show that the nanoclusters are absent in the reference steel T24, while the steels NSF101-109 of the present invention contain fine copper-rich nanoclusters of high number density and their distribution is uniform. .. FIG. 1 is a high-resolution TEM image of nanoclusters of the matrix of the steel NSF104 of the present invention, the average diameter of the nanoclusters being 3 nm, the distribution being uniform, the mean voids being 4 nm, and the nanoclusters. The amount of is 10,000 or more per cubic micron. TEM-EDS confirms that the nanoclusters mainly contain Cu, Ni, Mn, and Al. Therefore, uniformly distributed, finely sized, high number density copper-rich nanoclusters are formed in low-cost ultra-high-strength ferritic steel reinforced with the copper-rich nanoclusters of the present invention. Is confirmed. According to the nanoprecipitation strengthening mechanism, high number density, finely sized copper-rich nanoclusters can effectively inhibit dislocation motion and significantly increase the strength of ferritic steels.

In addition, TEM is used to detect a certain amount of nanocarbide. FIG. 2 is a high-resolution TEM photograph of the nanocarbide of the matrix of the steel NSF104 of the present invention. It is confirmed from TEM-EDS that the composite nanocarbide has an average diameter of 20 nm (V, Ti) C. Nanocarbide has the characteristics of being small in size, having high thermal stability, and capable of inhibiting crystal grain growth, thereby bringing about an effect of enhancing grain refinement. In addition, the composite carbide has a slower grain coarsening behavior and better thermal stability than the simple carbide. FIG. 3 is an SEM microstructure of the steel NSF104 of the present invention. As shown in the figure, the matrix structure is a fine ferrite containing uniform and fine particles. The average diameter of the particles is 1.5 μm. It can be seen that the nanoprecipitates precipitated from the matrix have the effect of grain refinement. According to the Hall-Petch relationship, the strength of the material can be increased through grain refinement. On the other hand, the smaller the particle size, the better the ductility and toughness.

Experiment 2
Tensile test samples of the steels NSF101-109 and the reference steel T24 of the present invention are prepared by wire cutting. A room temperature tensile test is performed on an MTS tester. The results of yield strength, tensile strength, cross-sectional reduction rate, and elongation are shown in Table 2. FIG. 4 is a tensile stress-strain curve of the steel NSF108 and the reference steel T24 manufactured according to the present invention. After a similar melting and heat treatment process, it is understood from Table 2 and FIG. 4 that the reference steel T24 has a yield strength of 347 MPa and a tensile strength of 586 MPa. The results are consistent with published literature. The steels NSF 101 to 109 of the present invention have a yield strength of 900 to 1200 MPa and a tensile strength of 1200 to 1500 MPa. Compared to the reference steel T24, both the yield strength and the tensile strength of the steel of the present invention are significantly increased. The cross-sectional reduction rate is maintained at 50% -80% and the elongation is maintained at 10-20%, which is a good combination of high strength and high ductility. It is understood that the present invention substantially increases the strength of steels by adjusting the strengthening elements of nanocluster strengthening, grain refinement strengthening, and solid solution strengthening, and by adopting appropriate heat treatment processes.

Experiment 3
A tensile test sample of the steel NSF104'of the present invention produced according to Example 2 is prepared by wire cutting. A room temperature tensile test is performed on an MTS tester. The measured yield strength is 1082 MPa, the tensile strength is 1240 MPa, the cross-sectional reduction rate is 67%, and the elongation is 12.4%.

As described in Example 2, the alloy composition and heat treatment process of the steels NSF104'and NSF104 of the present invention are the same. The difference is that the steel NSF104'of the present invention undergoes solution treatment at 850 ° C. By lowering the temperature of the solution treatment, rapid growth of particles can be prevented and a fine structure of fine particles can be obtained.

Therefore, from the measured mechanical properties obtained from the room temperature tensile test, the copper-rich nanocluster reinforced ultra-high-strength ferritic steel manufactured at the temperature mentioned under the solution treatment has ultra-high strength and good ductility. Is understood.

Experiment 4
A tensile sample of the steel NSF104 of the present invention produced according to Example 3 is prepared by wire cutting. A room temperature tensile test is performed on an MTS tester. The measured yield strength is 944 MPa, the tensile strength is 1207 MPa, and the cross section is reduced. The rate is 62% and the growth is 12.7%.

As described in Example 3, the alloy composition and heat treatment process of the steel NSF104 "and NSF104 of the present invention are the same. The difference is that the steel NSF104" of the present invention undergoes solution treatment at 1200 ° C. By raising the temperature of the solution treatment so that the alloying elements can be sufficiently solidified, the cooled alloying elements in the ferrite matrix will be significantly oversaturated and the rate of nucleation of nanoprecipitates will increase. Is done. Therefore, more nanoprecipitation strengthened phases can be produced during the aging treatment. Therefore, from the measured mechanical properties obtained from the room temperature tensile test, the copper-rich nanocluster-reinforced ultra-high-strength ferritic steel manufactured at the temperature mentioned under the solution treatment has ultra-high strength and good ductility. Is understood.

In summary, the present invention optimizes the alloy composition from a thermodynamic aspect to reasonably adjust the proportions of face-centered cubic elements, carbon, and other elements. The volume fraction of nanoprecipitates is raised to the maximum limit. On the other hand, the precipitation temperature and the precipitation time are controlled to create a large number of nucleation sites, and all the alloy element solutes can be uniformly deposited. The growth of nanoprecipitates is controlled during in-situ precipitation to give finely sized copper-rich nanoclusters that are uniformly distributed at high number densities. This has a dominant effect on the ultra-high strength of the new ultra-high strength steel. In addition, nanocarbides can effectively micronize particles. The optimized alloying elements exert a solid solution effect. Hot deformation and cold deformation exert the effect of grain refinement and dislocation strengthening. Therefore, the copper-rich nanocluster reinforced ultra-high-strength ferritic steel of the present invention is a new composite reinforced ultra-high-strength steel in which nanocluster reinforcement is dominant. Various reinforcement methods such as grain refinement reinforcement, solid solution reinforcement, and dislocation reinforcement are combined to produce such new composite reinforced steels. The new composite reinforced steel is a low carbon, low cost ultra high strength steel with ultra high strength and excellent weldability, excellent ductility and toughness, and good corrosion resistance, and exhibits excellent overall performance. The steels of the present invention can be applied in fields such as automobiles, ships, bridges, pipelines, energy production, power plants, marine technology, construction, pressure vessels, industrial technology machinery, or containers, and defense equipment.

It should be noted by those skilled in the art that the described embodiments of the present invention are merely exemplary and other substitutions, modifications, and improvements may be made within the scope of the present invention. Therefore, the present invention is not limited to the above embodiment, but is defined only by the claims.

Claims (12)

Copper-rich nanocluster reinforced ultra-high-strength ferritic steel with the following weight percentage chemical composition: 0-0.2% C, 0.5-5% Cu, 0.01-4% Ni, 0 .01-4% Mn, 0.001-2% Al, 0-12% Cr, 0-3% Mo, 0-3% W, 0.05% or more Mo + W, 0-0. 5% V, 0-0.5% Ti, 0-0.5% Nb, 0.01% or more V + Ti + Nb, 0-1% Si, 0.0005-0.05% B, 0 It contains .04% or less of P, 0.04% or less of S, 0.04% or less of N, and 0.05% or less of O, and the balance is Fe and unavoidable impurities.
The matrix of the copper-rich nanocluster-reinforced ultra-high-strength ferritic steel is ferrite, and the amount of the copper-rich nanoclusters precipitated in the matrix is 10,000 or more per cubic micron .
The steel is characterized in that the yield strength is 900 to 1200 MPa, the ultimate tensile strength is 1200 to 1500 MPa, the elongation is 10 to 20%, and the cross-sectional reduction rate is 50% to 80%. Copper-rich nanocluster reinforced ultra-high strength ferritic steel. The copper-rich nanocluster-reinforced ultra-high-strength ferritic steel according to claim 1, wherein the constituent elements of the copper-rich nanoclusters are Cu, Ni, Mn, and Al. The average size of the copper-rich nanoclusters 3 nm, gaps between the average particle is 2 to 20 nm, the copper-rich nanoclusters reinforced ultra high strength ferritic steel according to claim 1. The copper-rich nanocluster-reinforced ultrahigh-strength ferritic steel according to claim 1, further comprising a composite nanocarbide (V, Ti, Nb) C having a size of 5 to 100 nm. The copper-rich nanocluster-reinforced ultrahigh-strength ferritic steel according to claim 1, wherein the copper-rich nanocluster-reinforced ultrahigh-strength ferritic steel has an average particle size of 1 to 20 μm. The method for producing the copper-rich nanocluster-reinforced ultrahigh-strength ferritic steel according to any one of claims 1 to 5 .
(1) A step of sequentially melting, casting, and forging / rolling the ingot of the raw material of the chemical component of the copper-rich nanocluster reinforced ultra-high-strength ferritic steel.
(2) A step of performing solution treatment in the range of 800 to 1300 ° C. and then cooling to room temperature.
(3) A method including a step of aging treatment in the range of 400 to 600 ° C. and then cooling to room temperature. The method according to claim 6 , wherein the solution treatment is performed at 900 ° C. The method according to claim 6 or 7 , wherein the solution treatment is carried out for 0.1 to 3 hours. The method according to claim 8 , wherein the solution treatment is carried out for 0.5 hours. The method according to claim 6 , wherein the aging treatment is performed at 550 ° C. The method according to claim 6 or 10 , wherein the aging treatment is carried out for 0.1 to 20 hours. 11. The method of claim 11 , wherein the aging process is performed for 2 hours.