CN117867378A

CN117867378A - High-plasticity low-cost steel with tensile strength more than 2600MPa and preparation method thereof

Info

Publication number: CN117867378A
Application number: CN202311702483.5A
Authority: CN
Inventors: 吴桂林; 李国阳; 孙飞龙; 汪水泽; 赵海涛; 高军恒; 张朝磊; 吴宏辉; 毛新平
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2023-12-12
Filing date: 2023-12-12
Publication date: 2024-04-12

Abstract

The invention relates to the field of preparation of ultra-high strength steel, and provides high-plasticity low-cost steel with tensile strength more than 2600MPa and a preparation method thereof, wherein the preparation method comprises the following steps: s1, smelting alloy raw materials with a set proportion, and casting into a casting blank or a steel ingot; s2, heating a casting blank or a steel ingot to a set temperature, preserving heat, forging into a forging blank with a round or square cross section for multiple times in a rotating state, and cooling to room temperature; at least one furnace return heat preservation treatment is carried out between each two passes; s3, performing low-temperature tempering treatment on the forging stock. The hot forging and direct tempering process provided by the invention solves the problems that the traditional ultra-high strength low alloy steel is difficult to industrially produce and the production flow is long; meanwhile, the invention solves the problem that the strength and the plasticity of the ultra-high strength steel are difficult to be compatible, obtains the total elongation of more than 10 percent when the tensile strength is more than 2600MPa, and can be used in the special engineering field with extremely high requirements on strength and plasticity.

Description

High-plasticity low-cost steel with tensile strength more than 2600MPa and preparation method thereof

Technical Field

The invention relates to the technical field of preparation of ultrahigh-strength steel, in particular to high-plasticity low-cost steel with tensile strength more than 2600MPa and a preparation method thereof.

Background

The steel material has high strength and excellent plasticity, and is dominant in the aspect of metal structural materials. The ultra-high strength steel with the material strength of more than 2.0GPa has extremely important value in breaking through the application of materials, and is considered as an important material for breaking through the application in the fields of civil infrastructure, machinery, traffic, aerospace, ocean engineering and the like. With the increasing pressure of resources, energy and environment, development of ultra-high strength steel with excellent toughness is increasingly receiving attention, because the ultra-high strength steel can reduce the usage amount of materials to the greatest extent on the basis of meeting the same bearing capacity, thereby realizing the requirement of light weight. The method is not only beneficial to energy conservation and reduction of greenhouse gas emission and promotes sustainable development of the steel industry, but also can effectively solve the requirements of a series of key engineering construction in the national defense field on high-performance steel materials. In the automobile industry, ultra-high strength steel materials are becoming important materials used by many automobile manufacturers for producing components such as automobile chassis, frames, roofs, automobile bodies and the like, so that the safety performance and fuel efficiency of automobiles can be improved, meanwhile, the weight of the automobiles is reduced, and the carbon emission is reduced. In the field of aerospace, the ultra-high strength steel material can be used for manufacturing aero-engine parts, aerospace structural parts, satellite components and the like. In the field of energy, the ultra-high strength steel material can be used for manufacturing turbine components, nuclear reactor parts, oil gas pipelines and the like, can bear high-pressure, high-temperature and strong-corrosion environments, and has good toughness and weldability. In a word, the application range of the ultra-high strength steel material is wide, and the ultra-high strength steel material has wider application prospect in the future. However, the ultrahigh-strength steel has the problems of low plasticity, high preparation cost, difficult industrial application and the like, and greatly limits the application of the ultrahigh-strength steel.

The Chinese patent with publication number of CN 103898299A discloses a preparation method of 2400 MPa-grade low-cost nano Bayesian steel, which comprises the following alloy components in percentage by mass: c:0.5 to 1.0, si:2.0 to 3.0, mn:0.3 to 0.5, al:0.5 to 1.0, and the balance of Fe. The preparation method is that after forging, salt bath quenching and heat preservation are carried out. The steel adopts low-cost Al, si and other cheap elements as alloy elements, but the addition of Al can cause the problem of nozzle blockage in the molten steel pouring process. Meanwhile, the salt bath quenching causes the problem of environmental pollution. In addition, although the preferable composition and process strength of the steel can reach 2399MPa at the highest, at this time, the plasticity is greatly reduced, and the elongation is only 3.1%.

Publication No. CN110055392A discloses a high-toughness bridge cable steel with tensile strength more than 2500MPa and a preparation method thereof, wherein the steel is prepared by drawing a wire rod with the length of 14mm to 6.9mm at a temperature, the strength can reach 2500MPa, the torsion times can reach more than 20 times, and the structure is carbon-free bainite. The drawing method is only suitable for the preparation of small-section-size wire samples, although the strength and toughness of the steel are excellent.

Chinese patent publication No. CN 113604753a discloses a high-ductility high-corrosion-resistance maraging stainless steel of 2700MPa grade and a method for preparing the same. The ultra-high strength steel alloy comprises the following components in percentage by mass: cr:11 to 17, ni:7 to 9, co:3 to 6, mo:5 to 7, ti:0.5 to 2. The steel is ultra-high strength steel with optimal comprehensive mechanical properties in the report of the current patent literature, and the steel is prepared from an R' phase rich in Mo, an alpha-Cr phase and Ni ₃ The synergistic strengthening of the (Ti, mo) nano phase realizes the strength improvement, the highest strength of the preferable components and the process can reach 2737MPa, the elongation is 10.3 percent, but the alloy content of the preferable components is as high as 33.8 percent, and the cost is extremely high. Meanwhile, the steel is prepared by cold rolling, and the cold rolling has extremely high requirements on equipment and is difficult to industrially produce.

The article "Li Junkui, yang Zhina, ma Hua, et al A medium-C martensite steel with 2.6GPa Tensile strength and large ductility[J ]. Scripta Materialia,2023,228,115327" reports a high-strength (tensile strength: 2590 MPa) high-plasticity (total elongation 14.5%) martensitic steel and a preparation method thereof, and the preparation of the alloy requires warm rolling treatment at 400-600 ℃, has large warm rolling deformation resistance, has extremely high requirements on rolling equipment and is difficult to be applied to industrial production.

The results retrieved from the prior art show that the existing ultra-high strength steel has the problems of poor plasticity, high alloy cost, severe preparation process, difficulty in realizing industrial production and the like, and is not suitable for large-scale popularization and application. Compared with the prior art, the alloy has simple components and low alloy content (less than 7 percent), and the mechanical properties superior to those reported in the above documents can be obtained only by adopting a hot forging and tempering process which is fully feasible in industrial production.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides high-plasticity low-cost steel with tensile strength more than 2600MPa and a preparation method thereof, adopts a hot forging and tempering process, does not need to carry out re-austenitizing treatment after hot forging such as 300M steel, greatly simplifies the preparation flow of the ultra-high strength steel, saves the preparation cost, and is completely and industrially feasible in the hot forging and tempering process, thereby being completely suitable for large-scale industrial production.

The invention adopts the following technical scheme:

in one aspect, the invention provides a method for preparing high-plasticity low-cost steel with tensile strength more than 2600MPa, comprising the following steps:

s1, smelting alloy raw materials with a set proportion, and casting into a casting blank or a steel ingot;

s2, heating the casting blank or the steel ingot to a set temperature, preserving heat, forging the casting blank or the steel ingot into a forging stock with a round or square cross section in a rotating state for multiple times, and cooling to room temperature; wherein, furnace return heat preservation treatment is carried out at least once among the multiple forging passes;

s3, carrying out low-temperature tempering treatment on the forging stock treated in the step S2 to obtain the high-plasticity low-cost steel with the tensile strength more than 2600 MPa.

In any one of the possible implementation manners described above, there is further provided an implementation manner, in step S1, the alloy raw materials include the following mass percentages: c:0.5 to 0.75 percent, si:0.2 to 2.5 percent, mn:0.2 to 2.0 percent, cr:0.2 to 2 percent, ni:0.3 to 3 percent, mo+V+Nb:0.4 to 3 percent and the balance of Fe and unavoidable impurity elements.

In any one of the possible implementation manners described above, there is further provided an implementation manner, in step S2, the casting blank or the steel ingot is heated to 950-1250 ℃, and is kept for 1-3 hours.

In any one of the possible implementations described above, there is further provided an implementation, in step S2, a heat preservation treatment of returning to the furnace is performed between each pass of the multi-pass forging, and a time for returning to the furnace is greater than 0.5h.

In any one of the possible implementation manners described above, there is further provided an implementation manner, in step S2, the forging ratio of forging the blank into a round or square section forging stock in a rotating state after the heat preservation in the furnace is greater than 8, and the alloy structure is a lamellar structure after the multi-pass forging.

In any one of the possible implementation manners as described above, there is further provided an implementation manner, in step S2, the cooling manner in which the forging stock with the round or square cross section obtained by forging is cooled to room temperature is air cooling or a cooling manner in which a cooling rate is greater than air cooling, and the volume fraction of martensite in the room temperature structure is not less than 90%.

In any of the possible implementations described above, there is further provided an implementation in which the cooling manner of the forging stock of the round or square cross section obtained by forging to room temperature is air cooling, water mist cooling, water cooling or liquid nitrogen cooling.

In any of the possible implementations described above, there is further provided an implementation, in step S2, the final forging temperature of the multi-pass forging is higher than Ar3 temperature and lower than the dynamic recrystallization temperature of the alloy.

In any one of the possible implementations as described above, there is further provided an implementation, in step S3, the tempering treatment is: and (3) preserving the temperature of the forging stock at 80-300 ℃ for 0.1-120 h, eliminating internal stress generated in the forging process and the quenching process, simultaneously separating out supersaturated carbon, mo, V and Nb to form high-density fine carbide, and cooling to room temperature to obtain the high-strength high-plasticity low-cost steel.

On the other hand, the invention also provides high-plasticity low-cost steel with tensile strength more than 2600MPa, which comprises the following components in percentage by weight: c C:0.5 to 0.75 percent, si:0.2 to 2.5 percent, mn:0.2 to 2.0 percent, cr:0.2 to 2 percent, ni:0.3 to 3 percent, mo+V+Nb:0.4 to 3 percent, and the balance of Fe and unavoidable impurity elements;

the high-plasticity low-cost steel is obtained by the preparation method; the residual austenite accounts for 2-10% of the volume of the high-strength high-plasticity low-cost steel.

In any of the possible implementations described above, there is further provided an implementation in which the high strength, high plasticity, low cost steel has an alloying element content of less than 7% and a total elongation of greater than 10%.

The principle of the invention is as follows:

the invention adopts low alloy component design, the total content of alloy elements is less than 7wt%, and the cost is low and economical. According to the invention, a microalloying component design scheme is adopted, and the precipitation of fine VC in the thermal deformation process is utilized to strengthen the martensitic matrix, reduce the carbon content in the matrix and inhibit the formation of twin martensite which is unfavorable for toughness. In the forging process, the forging is performed at a temperature above the austenitizing temperature and below the dynamic recrystallization temperature, so that the forging deformation resistance can be reduced, the recrystallization of austenite is inhibited, and the formation of coarse recrystallized original austenite and the damage to toughness are avoided. The invention is deformed below the recrystallization temperature to obtain a martensite topology structure with multiple martensite lath orientations, and the structure has proved to have good plasticizing and toughening effects in medium manganese steel. According to the invention, more than 90% of martensite structure is obtained by direct quenching after forging, the ultra-high strength is ensured to be obtained, meanwhile, certain residual austenite is reserved, the residual austenite is distributed between the film-shaped distribution and the lamellar martensite, the film-shaped residual austenite is more stable than massive martensite, and is gradually converted into martensite in the deformation process, so that a good work hardening effect is provided, and thus, good plasticity is obtained. Because the invention can obtain excellent plasticity on the premise of higher dislocation density and higher solid solution strengthening effect due to the excellent plasticity foundation provided by the residual austenite and martensite lamellar structure of the ultra-high strength steel, the invention widens the tempering temperature range from 150-300 ℃ of general martensitic steel to 80-300 ℃ of the ultra-high strength steel according to the invention in order to keep the minimum temperature of 80 ℃ based on carbon atom precipitation while retaining higher dislocation density and higher solid solution strengthening effect, and widens the tempering temperature lower limit of conventional tempering treatment of the martensitic steel, thereby successfully preparing the ultra-high strength steel with the strength of up to 2800MPa and the total elongation of more than 10%.

The beneficial effects of the invention are as follows:

(1) The invention has simple components and low alloy content, and compared with high alloy high-strength steel such as maraging steel, the steel has extremely low cost. Compared with other low-cost alloy high-strength steel, the invention has remarkable comprehensive mechanical property advantage. The strength of the optimized components and the process of the invention can reach 2814MPa, and meanwhile, the excellent plasticity of 11.6 percent is maintained, so that the invention is the only ultra-high strength steel with the strength reaching 2800MPa and the elongation exceeding 10 percent in the literature reported at present.

(2) Compared with cold rolling, warm rolling and the like which are difficult to realize industrial mass production and high plastic deformation at medium temperature, the invention has simple process, and obtains the comprehensive mechanical properties of the high-strength steel with high plastic deformation, which are better than those of cold rolling, warm rolling and the like, by adopting the simple process of hot forging and low-temperature tempering which are fully feasible industrially. In addition, the tempering treatment is directly carried out after hot forging, so that the re-austenitizing quenching process of the general low-alloy high-strength steel is omitted, and the preparation flow of the traditional low-alloy high-strength steel is greatly simplified.

(3) The steel has excellent hardenability, flexible cooling process selection, and can be quenched into martensite by adopting air cooling, water mist cooling, water cooling, liquid nitrogen cooling and the like, and the volume fraction of the martensite is more than 90%, thereby ensuring the strength of the ultra-high strength steel exceeding 2600 MPa.

(4) Compared with the conventional martensitic steel, the ultra-high strength steel can obtain certain plasticity by tempering at the temperature of more than 150 ℃, and the ultra-high strength steel has excellent performances of strength of more than 2600MPa and total elongation of more than 10% under the condition of retaining higher dislocation density because the martensite layered topological structure and the film-shaped residual austenite provide good plastic foundation.

Drawings

FIG. 1 is a timing diagram of the preparation process in the example.

FIG. 2 is a schematic flow chart of a method for preparing high-plasticity low-cost steel with tensile strength more than 2600MPa according to the embodiment of the invention.

Fig. 3 shows the engineering stress-strain curve of example 2.

FIG. 4 shows an X-ray diffraction pattern of example 2.

FIG. 5 is a diagram showing the retained austenite distribution of the thin film austenite of example 2.

FIG. 6 is a layered structure diagram of example 2.

Fig. 7 is a transmission electron microscope image of example 2.

Figure 8 shows a large isometric view of comparative example 2.

Detailed Description

Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be regarded as being isolated, and they may be combined with each other to achieve a better technical effect.

As shown in fig. 1, the preparation method of the high-plasticity low-cost steel with tensile strength more than 2600MPa according to the embodiment of the invention comprises the following steps:

The specific process sequence is shown in fig. 2.

In a specific embodiment, in step S1, the alloy raw materials include the following mass percentages: c:0.5 to 0.75 percent, si:0.2 to 2.5 percent, mn:0.2 to 2.0 percent, cr:0.2 to 2 percent, ni:0.3 to 3 percent, mo+V+Nb:0.4 to 3 percent and the balance of Fe and unavoidable impurity elements.

In a specific embodiment, in the step S2, the casting blank or the steel ingot is heated to 950-1250 ℃ and is kept for 1-3 hours.

In a specific embodiment, in step S2, a furnace-returning heat-preserving treatment is performed between each pass of the multi-pass forging, and the time of furnace-returning heat preservation is greater than 0.5h.

In a specific embodiment, in step S2, after the heat preservation in the furnace is performed, the forging ratio of forging the forging stock with the round or square cross section in the rotating state is greater than 8, and after the multi-pass forging, the alloy structure is a lamellar structure.

In a specific embodiment, in step S2, the cooling mode of cooling the forging blank with the round or square cross section obtained by forging to room temperature is an air cooling mode or a cooling mode with a cooling rate greater than that of air cooling, and the volume fraction of martensite in the room temperature structure is not less than 90%.

In a specific embodiment, the cooling mode of cooling the forged blank with the round or square section obtained by forging to room temperature is air cooling, water mist cooling, water cooling or liquid nitrogen cooling.

In a specific embodiment, in step S2, the final forging temperature of the multi-pass forging is higher than Ar3 temperature and lower than the dynamic recrystallization temperature of the alloy.

In one embodiment, in step S3, the tempering treatment is: and (3) preserving the temperature of the forging stock at 80-300 ℃ for 0.1-120 h, eliminating internal stress generated in the forging process and the quenching process, simultaneously separating out supersaturated carbon, mo, V and Nb to form high-density fine carbide, and cooling to room temperature to obtain the high-strength high-plasticity low-cost steel.

The embodiment of the invention relates to high-plasticity low-cost steel with tensile strength more than 2600MPa, which comprises the following components in percentage by weight: c:0.5 to 0.75 percent, si:0.2 to 2.5 percent, mn:0.2 to 2.0 percent, cr:0.2 to 2 percent, ni:0.3 to 3 percent, mo+V+Nb:0.4 to 3 percent, and the balance of Fe and unavoidable impurity elements;

The alloy element of the high-strength high-plasticity low-cost steel accounts for less than 7 percent, and the total elongation is more than 10 percent.

The invention is further illustrated by the following specific examples.

The chemical compositions of each example and comparative example are shown in Table 1, and the preparation processes and mechanical properties of each example and comparative example are shown in Table 2.

Table 1 chemical composition (wt.%) of inventive and comparative examples

Numbering device	C	Mn	Si	Cr	Ni	Mo	V	Nb
									Example 1	0.48	0.4	0.8	0.8	0.8	1.2	0.7	0.1
Example 2	0.59	0.8	1.4	0.8	1.8	0.5	0.3	0
									Example 3	0.59	0.8	1.4	0.8	1.8	0.5	0.3	0
Example 4	0.59	0.8	1.4	0.8	1.8	0.5	0.3	0
									Example 5	0.59	0.8	1.4	0.8	1.8	0.5	0.3	0
Example 6	0.59	0.8	1.4	0.8	1.8	0.5	0.3	0
									Example 7	0.65	2	0.2	1.8	0.3	0.3	0.1	0.5
Example 8	0.68	0.4	2.4	0.2	3	0.3	0.2	0
									Comparative example 1	0.59	0.8	1.4	0.8	1.8	0.5	0.3	0
Comparative example 2	0.59	0.8	1.4	0.8	1.8	0.5	0.3	0

TABLE 2 preparation process and mechanical Properties of examples and comparative examples of the present invention

As apparent from the mechanical properties in Table 2, the strength of the examples of the present invention is higher than 2600MPa, the elongation is higher than 10%, and the most preferred components and processes in the examples can obtain 2814MPa strength while obtaining 11.6% high elongation, as shown in FIG. 3. The excellent overall mechanical properties of example 2 are related to a certain amount of thin film-like retained austenite and layered martensite topology, as shown in fig. 4,5 and 6, while the presence of fine carbides of high density in the martensite matrix provides excellent precipitation strengthening effect, as shown in fig. 7. In comparative example 1, at too low a tempering temperature, carbon atoms cannot be separated out from supersaturated martensite, quenching stress cannot be released, and brittle fracture occurs during the sample stretching process. Comparative example 2, in which dynamic recrystallization occurred at a temperature higher than the dynamic recrystallization temperature, the grain size was large, and coarse recrystallized grains promoted brittle martensite twin formation, and strength of 2600MPa or more could be obtained at this time, but the plastic loss was serious, less than 10%, as shown in fig. 8 and table 2.

The hot forging and direct tempering process provided by the invention solves the problems that the traditional ultra-high strength low alloy steel is difficult to industrially produce (the traditional ultra-high strength low alloy steel is prepared by adopting cold rolling, warm rolling and other processes), and the production flow is long (the traditional ultra-high strength low alloy steel is required to be subjected to re-austenitizing quenching treatment in the middle of hot rolling/hot forging and tempering). Meanwhile, the invention solves the problem that the strength and the plasticity of the ultra-high strength steel are difficult to be compatible, obtains the total elongation of more than 10 percent when the tensile strength is more than 2600MPa, and can be used in the special engineering field with extremely high requirements on strength and plasticity.

Although a few embodiments of the present invention have been described herein, those skilled in the art will appreciate that changes can be made to the embodiments herein without departing from the spirit of the invention. The above-described embodiments are exemplary only, and should not be taken as limiting the scope of the claims herein.

Claims

1. A method for preparing high-plasticity low-cost steel with tensile strength more than 2600MPa, which is characterized by comprising the following steps:

2. The method for producing high-plasticity low-cost steel having a tensile strength of > 2600MPa as claimed in claim 1, wherein in step S1, the alloy raw materials are in mass percent: c:0.5 to 0.75 percent, si:0.2 to 2.5 percent, mn:0.2 to 2.0 percent, cr:0.2 to 2 percent, ni:0.3 to 3 percent, mo+V+Nb:0.4 to 3 percent and the balance of Fe and unavoidable impurity elements.

3. The method for producing high-plasticity low-cost steel with tensile strength > 2600MPa according to claim 1, wherein in step S2, the cast blank or ingot is heated to 950 ℃ to 1250 ℃ and kept for 1 to 3 hours.

4. The method for producing high-plasticity low-cost steel having a tensile strength of > 2600MPa according to claim 1, wherein in step S2, a heat-preserving treatment is performed between each of the multiple forging passes, and the heat-preserving time is longer than 0.5h.

5. The method for producing high-plasticity low-cost steel having a tensile strength of > 2600MPa according to claim 1, wherein in step S2, the forging ratio of the forging stock having a round or square cross section in a rotary state after heat preservation by the tempering is more than 8, and the alloy structure after multi-pass forging is a layered structure.

6. The method for producing high-plasticity low-cost steel having a tensile strength of > 2600MPa according to claim 1, wherein in step S2, the cooling means for cooling the round or square-section forged blank obtained by forging to room temperature is air cooling or a cooling means having a cooling rate greater than air cooling.

7. The method for producing high plasticity low cost steel having a tensile strength > 2600MPa according to claim 1, wherein in step S2, the final forging temperature of the multi-pass forging is higher than Ar3 temperature and lower than the dynamic recrystallization temperature of the alloy.

8. The method for producing high-plasticity low-cost steel having a tensile strength of > 2600MPa according to claim 1, wherein in step S3, the tempering treatment is: and (3) preserving the temperature of the forging stock at 80-300 ℃ for 0.1-120 h, eliminating internal stress generated in the forging process and the quenching process, simultaneously separating out supersaturated carbon, mo, V and Nb to form high-density fine carbide, and cooling to room temperature to obtain the high-strength high-plasticity low-cost steel.

9. A high-plasticity, low-cost steel having a tensile strength > 2600MPa, characterized in that it is obtained by the preparation method according to any one of claims 1-8; the high-plasticity low-cost steel comprises the following components in percentage by weight: c:0.5 to 0.75 percent, si:0.2 to 2.5 percent, mn:0.2 to 2.0 percent, cr:0.2 to 2 percent, ni:0.3 to 3 percent, mo+V+Nb:0.4 to 3 percent, and the balance of Fe and unavoidable impurity elements;

the residual austenite accounts for 2-10% of the volume of the high-strength high-plasticity low-cost steel.

10. A high plasticity low cost steel having a tensile strength > 2600MPa as claimed in claim 9, wherein the high strength high plasticity low cost steel has an alloying element content of less than 7% and a total elongation of greater than 10%.