CN118406971A

CN118406971A - A 1000MPa grade structural steel and its preparation method

Info

Publication number: CN118406971A
Application number: CN202410488544.0A
Authority: CN
Inventors: 杨永达; 韩承良; 王彦锋; 马长文; 狄国标; 黄乐庆; 马龙腾; 周德光; 路士平; 刘美艳; 徐海卫; 何元春; 王根矶; 马国金; 代锦; 王海宝; 王凯凯; 殷展鹏
Original assignee: Shougang Group Co Ltd
Current assignee: Shougang Group Co Ltd
Priority date: 2024-04-23
Filing date: 2024-04-23
Publication date: 2024-07-30

Abstract

The present invention provides a 1000MPa grade structural steel and a preparation method thereof, belonging to the field of steel preparation. The chemical composition of the structural steel includes: C, Si, Mn, P, S, Al, Ni, Cr, Mo, Nb, V, Ti and Fe; wherein, by mass fraction, the content of C is 0.04% to 0.15%, the content of Si is 0.20% to 0.50%, the content of Mn is ≤2.00%, the content of P is ≤0.008%, the content of S is ≤0.003%, the content of Al is 0.020% to 0.050%, the content of Ni is 7.00% to 12.00%, the content of Cr is ≤2.00%, the content of Mo is ≤2.00%, the content of Nb is ≤0.100%, the content of V is ≤0.200%, and the content of Ti is ≤0.030%. The hardenability of the steel plate is ensured by the composition design of low-carbon addition of Cr and Mo, and the structural steel is guaranteed to have a comprehensive match of high strength, high plasticity and high toughness by obtaining tempered martensite, reversed austenite and Nb, V and Ti precipitation phases. Specifically, the yield strength is greater than 1050MPa, the tensile strength is greater than 1180MPa, the elongation after fracture is ≥20.0%, and the impact energy at ‑85℃ is greater than 200J. Among the steel plates of the same strength level, the impact energy is significantly better than other steel plates.

Description

1000 MPa-level structural steel and preparation method thereof

Technical Field

The application relates to the technical field of steel preparation, in particular to 1000 MPa-level structural steel and a preparation method thereof.

Background

The 1000 MPa-level high-strength steel has wide application prospect in the fields of containers, engineering machinery, marine engineering and the like. The high-strength steel can effectively lighten the dead weight of engineering equipment, improve the manufacturing efficiency of the equipment and reduce the material cost, because 1000 MPa-level steel is often used for key parts, besides high strength, the steel plate is required to have higher impact performance and good plasticity, and particularly for the steel plate used for welding, in order to solve the problem of reduced impact toughness of a welded joint, the steel plate is often required to have higher impact toughness reserve.

The patent which gives consideration to the yield strength of more than or equal to 1000MPa and meets the low-temperature toughness of-84 ℃ and the like mainly comprises the following steps: the component system with the application number of CN114058790A, CN114058960A, CN114058790A adopts a technical thought of Cu precipitation strengthening, in order to achieve the strengthening effect, the addition amount of Cu is 1.5% -2.5%, cu is used as a noble alloy element, a large amount of Cu is added to obviously increase the manufacturing cost of the steel plate, and meanwhile, the Cu element easily causes cracks of casting blanks to influence the yield. The steel plate disclosed by the patent application number CN 114196879A has the yield strength reaching 1000MPa level and high toughness and plasticity, and the impact energy at the temperature of minus 85 ℃ reaches more than 100J, but the Ni content in the steel plate is between 10 and 15 percent, the Ni alloy price is higher, the higher Ni content can lead to higher cost of the steel plate alloy, and the manufacturing cost is increased.

Other steel with the yield strength reaching 1000MPa level has lower impact toughness, such as the patent application numbers CN106544590B, CN113444974A, CN 104561827A, CN109609848B, CN114134301A and CN 114277306A, and the steel plate has the yield strength reaching 1000MPa level, but has lower research temperature on the toughness of the steel plate, and the difference between the toughness guarantee temperature of-40 ℃ or-60 ℃ and the technical index of-85 ℃ is larger.

In view of the foregoing, there is a need for a steel sheet having a yield strength of 1000MPa and high plasticity and toughness at-85 ℃.

Disclosure of Invention

The application provides 1000 MPa-level structural steel and a preparation method thereof, which are used for solving the technical problem that the existing high-strength structural steel plate cannot realize high toughness and plasticity.

In a first aspect, the present application provides a 1000 MPa-grade structural steel, the structural steel comprising the chemical components of: C. si, mn, P, S, al, ni, cr, mo, nb, V, ti and Fe; wherein, the mass fraction of the material is calculated,

The alloy comprises 0.04% -0.15% of C, 0.20% -0.50% of Si, less than or equal to 2.00% of Mn, less than or equal to 0.008% of P, less than or equal to 0.003% of S, 0.020% -0.050% of Al, 7.00% -12.00% of Ni, less than or equal to 2.00% of Cr, less than or equal to 2.00% of Mo, less than or equal to 0.100% of Nb, less than or equal to 0.200% of V and less than or equal to 0.030% of Ti.

Optionally, the metallographic structure of the structural steel comprises tempered martensite and reverse transformation austenite, wherein the volume fraction of the tempered martensite is 80-98%, and the volume fraction of the reverse transformation austenite is 2-20%; wherein the tempered martensite has a lath average width of < 0.3 μm.

Optionally, nb, V and Ti precipitated phases are dispersed in the matrix of the structural steel, and the size of the precipitated phases is less than 100nm.

Optionally, the structural steel satisfies at least one of the following properties: the yield strength is 1050 MPa-1200 MPa, the tensile strength is 1190 MPa-1300 MPa, the elongation is more than or equal to 22%, and the impact energy at minus 85 ℃ is more than 200J.

Optionally, the thickness of the structural steel is 10 mm-50 mm.

In a second aspect, the present application provides a method for preparing structural steel according to any one of the embodiments of the first aspect, the method comprising:

Obtaining a steel billet with the chemical composition;

heating the billet before rolling, generally hot rolling and air cooling after rolling in sequence to obtain a hot rolled steel plate;

and carrying out heat treatment on the hot rolled steel plate to obtain the structural steel.

Optionally, the temperature of heating before rolling is 1120-1180 ℃, and the heat preservation time of heating before rolling is 240-360 min.

Optionally, the general hot rolling is a recrystallization zone rolling, the initial rolling temperature of the recrystallization zone rolling is 1000 ℃ to 1100 ℃, and the final rolling temperature of the recrystallization zone rolling is 900 ℃ to 1000 ℃.

Optionally, the heat treatment includes: primary quenching, secondary quenching and tempering;

The primary quenching includes: heating the hot rolled steel plate to 850-900 ℃, preserving heat for 3d min, and then quenching in water for the first time, wherein d is the thickness of the structural steel;

The secondary quenching includes: heating the hot rolled steel plate after primary quenching to 650-750 ℃, preserving heat for 3d min, and then performing secondary water quenching, wherein d is the thickness of the structural steel;

The tempering includes: and heating the hot rolled steel plate after secondary quenching to 500-600 ℃, preserving heat for 3d min, and then cooling to room temperature, wherein d is the thickness of the structural steel.

Optionally, the thickness of the steel billet is 120-240 mm.

Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:

The application reasonably designs the components of the alloy, ensures the hardenability of the steel plate through the component design of adding Cr and Mo into low carbon, and ensures the structural steel to have high strength, high plasticity and high toughness through obtaining tempered martensite, reverse transformation austenite and Nb, V and Ti precipitated phases. The concrete steps are as follows: the yield strength is more than 1050MPa, the tensile strength is more than 1180MPa, the elongation after fracture is more than or equal to 20.0 percent, the impact energy at the temperature of minus 85 ℃ is more than 200J, and the impact energy is obviously better than other steel plates in the steel plates with the same strength level.

In addition, the application can greatly reduce the addition of Ni alloy through proper component design and process design, thereby being beneficial to reducing the manufacturing cost and reducing the consumption of alloy resources.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and together with the description, serve to explain the principles of the application.

In order to more clearly illustrate the embodiments of the application or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, and it will be obvious to a person skilled in the art that other drawings can be obtained from these drawings without inventive effort.

FIG. 1 is a schematic flow chart of a method for preparing 1000 MPa-level structural steel according to an embodiment of the application;

FIG. 2 is a microstructure of the structural steel provided in example 1 of the present application;

FIG. 3 is a drawing showing a tempered martensite transmission electron microscope analysis of the structural steel provided in example 1 of the present application;

FIG. 4 is a morphology diagram of Nb, V and Ti nano precipitated phases of the structural steel provided in the embodiment 1 of the application;

Fig. 5 is an energy spectrum analysis chart of Nb, V, ti nano precipitated phases of the structural steel provided in example 1 of the present application.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

Various embodiments of the application may exist in a range of forms; it should be understood that the description in a range format is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the application; it is therefore to be understood that the range description has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that a description of a range from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1,2,3,4,5, and 6, wherever applicable. In addition, whenever a numerical range is referred to herein, it is meant to include any reference number (fractional or integer) within the indicated range.

In addition, in the description of the present specification, the terms "include", "comprising" and the like mean "including but not limited to". Relational terms such as "first" and "second", and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Herein, "and/or" describing an association relationship of an association object means that there may be three relationships, for example, a and/or B, may mean: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. Herein, "at least one" means one or more, and "a plurality" means two or more. "at least one", "at least one" or the like refer to any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.

Unless otherwise specifically indicated, the various raw materials, reagents, instruments, equipment and the like used in the present application are commercially available or may be prepared by existing methods.

The technical scheme provided by the application aims to solve the technical problems, and the general idea is as follows:

At present, few enterprises develop steel with the yield strength reaching 1000MPa level, but the low-temperature toughness storage is insufficient, and when welding is performed, the impact toughness of a welding joint is greatly reduced, and the risk of poor impact toughness of the welding joint exists. In addition, a strengthening route of Cu alloy precipitation adopted by scientific research institutions is adopted, 1000 MPa-grade high-toughness plastic steel is successfully manufactured in trial, but the addition amount of Cu element is more, so that the manufacturing cost is higher. Few enterprises develop 1000 MPa-grade high-toughness structural steel by adopting a quenching and tempering process, but Ni alloy elements with higher content are added, so that the manufacturing cost is higher.

Based on the above, the application provides a high-toughness plastic structural steel plate with 1000 MPa-grade yield strength and a low-cost manufacturing method, wherein the hardenability of the steel plate is ensured through the component design of low-carbon Cr and Mo addition, and the high strength, high plasticity and high toughness of the structural steel are ensured through obtaining tempered martensite, reverse transformation austenite and Nb, V and Ti precipitated phases. And heating to complete austenitization at the primary quenching temperature in the process, and quenching to obtain a primary quenched martensitic structure with uniform size and components. The secondary quenching temperature is controlled at the temperature of a martensite and austenite two-phase region, the heating process before secondary quenching causes enrichment of Ni, mn and other elements in the austenite, meanwhile, the Ni and Mn content in the martensite which does not undergo phase transformation is reduced, then the austenite enriched with the Ni and Mn elements is transformed into secondary quenching martensite enriched with the Mn and Ni elements during quenching, and the lath size in the martensite is finer than that of the lath of the primary quenching martensite. The secondary quenching martensite enriched with Ni and Mn elements is partially transformed into a reverse transformation austenite structure during subsequent tempering, the rest part and the primary quenching martensite form a tempered martensite structure together, and meanwhile, tempering heat treatment promotes precipitation of second phases of Nb, V and Ti. The target structure is obtained through the general hot rolling and heat treatment process, the high-toughness plastic structural steel plate with the yield strength of 1000MPa is obtained, the tempered martensite and reverse transformation austenite structure is obtained through the two quenching and tempering processes, meanwhile, a large amount of second phases separated from Nb, V and Ti are contained, the reverse transformation austenite is beneficial to improving the plasticity and toughness of the steel plate, and the tempered martensite structure and a large amount of second phases separated from Nb, V and Ti are beneficial to improving the strength.

The application provides 1000 MPa-level structural steel, which comprises the following chemical components: C. si, mn, P, S, al, ni, cr, mo, nb, V, ti and Fe; wherein, the mass fraction of the material is calculated,

In some embodiments, controlling the content of C to be 0.04-0.15% has the positive effect: the element C is an element for expanding an austenite phase region and has strong solid solution strengthening effect, and can form a precipitated second phase with Nb and Ti elements, so that the strength of the steel plate is improved through precipitation strengthening effect, but the content of C is too high, and the toughness and welding performance of the product are poor. In combination, the steel grade requires excellent toughness.

The positive effect of controlling the content of Si to be 0.20-0.50 percent: si does not form carbide with C, exists in steel in a solid solution form, and by interacting with stress fields of movable dislocations, dislocation movement is hindered, and strength of the steel sheet is improved. However, if the Si content is high, the weldability of the steel is adversely affected.

The positive effect of controlling the Mn content to be less than or equal to 2.00 percent is that: mn is an austenite forming element, and enlarges the austenite phase region. During cooling, mn dissipates free energy through solute drag, inhibiting diffusion-type phase transitions. By adding a proper amount of Mn, the microstructure of the steel plate can be controlled under proper process conditions, and when the Mn content in the austenite is increased, the stability of the austenite is greatly improved, thereby creating conditions for obtaining the reverse transformed austenite.

The positive effect of controlling the content of P to be less than or equal to 0.008 percent is that: the phosphorus has strong solid solution strengthening effect in steel, and can be added into low alloy structural steel as an alloy element to improve the strength and the atmospheric corrosion resistance of the steel, but the biggest harm of the phosphorus is that the segregation is serious, the plasticity and the toughness of the steel are obviously reduced, and the steel is easy to be cracked during cold working, namely the phenomenon of cold embrittlement. Phosphorus also has an adverse effect on the weldability, and phosphorus as a harmful element should be tightly controlled.

The positive effect of controlling the S content to be less than or equal to 0.003 percent is that: sulfur segregates severely in steel, deteriorating the quality of steel, and at high temperatures, reducing the plasticity of steel, it exists in the form of FeS with a lower melting point. The melting point of FeS alone is only 1190 ℃, whereas the eutectic temperature to form a eutectic with iron in steel is lower, only 988 ℃, and iron sulfide aggregates at the primary grain boundaries when the steel solidifies. When the steel is rolled at 1100-1200 ℃, feS on grain boundary will melt, so that the binding force between grains is greatly weakened, and the hot embrittlement phenomenon of the steel is caused, so that sulfur is tightly controlled.

The positive effect of controlling the content of Al to be 0.020-0.050 percent: al increases the phase change driving force, and Al interacts with N in the steel to form fine and dispersed AlN precipitation, so that the growth of crystal grains can be inhibited, the crystal grains are refined, and the toughness of the steel at low temperature is improved.

The positive effect of controlling the Cr content to be less than or equal to 2.00 percent is that: cr can prevent graphitization tendency of Mo-added steel, belongs to stable austenite elements, can greatly improve hardenability of steel and strength of steel, but too high Cr can reduce welding performance of steel.

The positive effect of controlling the Ni content to be 7.00-12.00 percent: ni plays a role in strengthening ferrite by forming a simple substitutional solid solution, so that the strength of steel can be improved, meanwhile, ni is an austenite stabilizing element, and the low-temperature impact toughness of the steel can be remarkably improved.

The positive effect of controlling the Mo content to be less than or equal to 2.00 percent is that: mo element is the most effective element for improving the high-temperature strength of a steel sheet, and generally the higher the content thereof, the higher the effect on tensile strength is on yield strength.

The positive effects of controlling the Nb content to be less than or equal to 0.100 percent and the Ti content to be less than or equal to 0.030 percent are that: the Nb and Ti microalloying elements play a role in strengthening fine grains of the steel plate, and the grain refinement is beneficial to improving the low-temperature toughness of the steel plate.

The positive effect of controlling the content of V to be less than or equal to 0.200 percent is that: v is an element for refining grains, and meanwhile, the strength of the steel can be obviously improved through V (C, N) dispersion precipitation. However, if the amount is too high, toughness and weldability of the material are deteriorated.

The purity of the molten steel is strictly controlled, and adverse effects of impurity elements P, S on the low-temperature toughness of the steel plate are avoided.

Intentional addition of Cu element and B element to steel is strictly prohibited.

In some embodiments, the metallurgical structure of the structural steel comprises tempered martensite having a volume fraction of 80-98% and reverse transformed austenite having a volume fraction of 2-20%; wherein the tempered martensite has a lath average width of < 0.3 μm.

In some embodiments, nb, V and Ti precipitated phases are dispersed in the matrix of the structural steel, and the size of the precipitated phases is less than 100nm.

In some embodiments, hardenability is ensured through component design of low carbon addition of Cr and Mo, conditions are created for obtaining reverse transformation austenite through addition of proper Mn and Ni elements, primary quenching martensitic structure with uniform size and component is obtained through primary quenching, secondary quenching temperature is controlled at the temperature of martensite and austenite two-phase region, heating process before secondary quenching causes enrichment of Ni and Mn and other elements in austenite, meanwhile Ni and Mn content in martensite without transformation is reduced, austenite enriched with Ni and Mn elements is transformed into secondary quenching martensite enriched with Mn and Ni elements during quenching, and martensite laths are finer than primary quenching martensite laths. The secondary quenching martensite enriched with Ni and Mn elements is partially transformed into a reverse transformation austenite structure during subsequent tempering, the rest part and the primary quenching martensite form a tempered martensite structure together, and meanwhile, tempering heat treatment promotes precipitation of second phases of Nb, V and Ti. The general hot rolling, air cooling and heat treatment processes are adopted to obtain the target tempered martensite and reverse transformation austenite structure and Nb, V and Ti precipitated phases, so that the yield strength of the steel plate reaches 1000MPa, and the steel plate has high plasticity and high toughness.

In some embodiments, the structural steel satisfies at least one of the following properties: the yield strength is 1050 MPa-1200 MPa, the tensile strength is 1190 MPa-1300 MPa, the elongation is more than or equal to 22%, and the impact energy at minus 85 ℃ is more than 200J.

The structural steel provided by the application has comprehensive matching of high strength, high plasticity and high toughness.

In some embodiments, the structural steel has a thickness of 10mm to 50mm.

Fig. 1 is a schematic flow chart of a preparation method of 1000 MPa-level structural steel according to an embodiment of the present application.

Referring to fig. 1, the present application provides a method for preparing structural steel, which includes:

s1, obtaining a steel billet with the chemical components;

in some embodiments, the step S1 above is preceded by a pretreatment of molten iron, smelting, and forging.

In some embodiments, the smelting is performed using a 500Kg vacuum smelter steelmaking.

In some embodiments, the thickness of the steel blank is 120mm to 240mm.

S2, heating the steel billet before rolling, generally hot rolling and air cooling after rolling in sequence to obtain a hot rolled steel plate;

In some embodiments, the temperature of the heating before rolling is 1120-1180 ℃, and the heat preservation time of the heating before rolling is 240-360 min.

In some embodiments, the general hot rolling is a recrystallization zone rolling having an initial rolling temperature of 1000 ℃ to 1100 ℃ and a final rolling temperature of 900 ℃ to 1000 ℃.

The application obtains the target tempered martensite and reverse transformation austenite structure and Nb, V and Ti precipitated phases by adopting the general hot rolling, air cooling and heat treatment process, ensures that the yield strength of the steel plate reaches 1000MPa, and has high plasticity and high toughness.

And S3, performing heat treatment on the hot rolled steel plate to obtain the structural steel.

In some embodiments, the heat treatment comprises: primary quenching, secondary quenching and tempering;

According to the application, a primary quenched martensitic structure with uniform size and components is obtained through primary quenching, the secondary quenching temperature is controlled at the temperature of a martensite and austenite two-phase region, the heating process before secondary quenching causes enrichment of Ni, mn and other elements in austenite, meanwhile, the Ni and Mn content in martensite which does not undergo phase transformation is reduced, then the austenite enriched with Ni and Mn elements is transformed into secondary quenched martensite enriched with Mn and Ni elements during quenching, and the size of martensite laths is finer than that of the primary quenched martensite laths. The secondary quenching martensite enriched with Ni and Mn elements is partially transformed into a reverse transformation austenite structure during subsequent tempering, the rest part and the primary quenching martensite form a tempered martensite structure together, and meanwhile, tempering heat treatment promotes precipitation of second phases of Nb, V and Ti.

The preparation method of the structural steel is realized based on the chemical components of the structural steel, and the chemical components of the structural steel can be specifically referred to the above embodiments.

The application will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. The experimental procedures, which are not specified in the following examples, are generally determined according to national standards. If the corresponding national standard does not exist, the method is carried out according to the general international standard, the conventional condition or the condition recommended by the manufacturer.

Molten steels of examples 1 to 5 were prepared and cast into billets having chemical compositions shown in table 1.

TABLE 1 chemical composition mass percent (wt%) of the billets of each example and comparative example, and the balance of Fe and unavoidable impurities

Group of	C	Si	Mn	P	S	Al	Ni	Cr	Mo	Nb	V	Ti
													Example 1	0.10	0.35	1.60	0.007	0.003	0.031	7.2	0.55	0.70	0.045	0.060	0.013
Example 2	0.11	0.31	0.65	0.006	0.003	0.035	7.5	0.55	0.70	0.055	0.060	0.015
													Example 3	0.10	0.28	1.77	0.006	0.002	0.030	8	0.60	0.80	0.070	0.070	0.015
Example 4	0.10	0.30	1.75	0.005	0.001	0.027	9.5	0.80	1.00	0.072	0.095	0.017
													Example 5	0.12	0.33	1.80	0.005	0.001	0.029	11.6	0.80	1.00	0.080	0.085	0.016

Based on the chemical components of the structural steel, the embodiment of the application provides a preparation method of the structural steel, which comprises the following steps:

S11, obtaining a steel billet with the chemical components;

s21, heating the steel billet before rolling, generally hot rolling and air cooling after rolling in sequence to obtain a hot rolled steel plate;

S31, carrying out primary quenching, secondary quenching and tempering on the hot rolled steel plate to obtain structural steel, wherein the rolling process parameters are shown in table 2, and the heat treatment process parameters are shown in table 3.

Table 2 process parameters of rolling

Group of	Thickness of billet, mm	Heating temperature, DEG C	Heating time, min	The initial rolling temperature, DEG C	Finishing temperature, DEG C
						Example 1	120	1160	240	1085	970
Example 2	120	1160	240	1085	950
						Example 3	180	1170	270	1080	940
Example 4	200	1170	300	1060	925
						Example 5	240	1175	360	1050	910

TABLE 3 heat treatment process parameters

The mechanical properties of the structural steels obtained in examples 1 to 5 were measured, and the results are shown in Table 4. The mechanical property testing method comprises the following steps: the tensile properties of the steel plate were measured according to GB/T228 method for tensile test of metallic Material at room temperature, and the impact properties at 1/4 of the thickness of the steel plate were measured according to GB/T229-2007 method for impact test of Charpy pendulum of metallic Material.

Table 4 mechanical properties index of structural steel sheet

Group of	Yield strength, MPa	Tensile strength, MPa	Elongation percentage,%	Impact energy at-85 ℃, J
					Example 1	1165	1285	23.5	268
Example 2	1190	1296	22.0	249
					Example 3	1122	1250	25.0	256
Example 4	1075	1192	25.5	230
					Example 5	1055	1199	26.0	231

As is clear from tables 1to 4, in the embodiments 1to 5 of the present invention, hardenability is ensured by the composition design of low carbon addition of Cr and Mo, conditions are created for obtaining reverse transformation austenite by adding appropriate Mn and Ni elements, primary quenched martensite structure with uniform size and composition is obtained by primary quenching, secondary quenching temperature is controlled at the temperature of two-phase regions of martensite and austenite, heating process before secondary quenching causes enrichment of Ni and Mn and other elements in austenite, ni and Mn content in martensite without phase transformation is reduced, austenite enriched with Ni and Mn elements is transformed into secondary quenched martensite enriched with Mn and Ni elements during subsequent quenching, and martensite laths are finer in size than primary quenched martensite laths. The secondary quenching martensite enriched with Ni and Mn elements is partially transformed into a reverse transformation austenite structure during subsequent tempering, the rest part and the primary quenching martensite form a tempered martensite structure together, and meanwhile, tempering heat treatment promotes precipitation of second phases of Nb, V and Ti. The general hot rolling, air cooling and heat treatment processes are adopted to obtain the target tempered martensite and reverse transformation austenite structure and Nb, V and Ti precipitated phases, so that the yield strength of the steel plate reaches 1000MPa, and the steel plate has high plasticity and high toughness.

Under the component design and process conditions of the invention, the structural steel of the examples 1-5 has excellent mechanical properties, the yield strength is more than or equal to 1055MPa, the tensile strength is more than or equal to 1192MPa, the elongation after fracture is more than or equal to 22%, the impact energy at minus 85 ℃ is more than 200J, and all the mechanical indexes of the developed structural steel are good.

Detailed description of the drawings 2-5:

fig. 2 is a microstructure of the structural steel provided in example 1 of the present application.

As can be seen from fig. 2, the structural steel provided in example 1 has a metallographic structure in which the volume fraction of tempered martensite is 87.2% and the volume fraction of reverse transformed austenite is 12.8%.

Fig. 3 is a drawing showing a tempered martensite transmission electron microscope analysis of the structural steel provided in example 1 of the present application.

As can be seen from FIG. 3, the average lath width of tempered martensite of the structural steel of example 1 was 0.18. Mu.m.

Fig. 4 is a morphology diagram of Nb, V, ti nano-precipitates of the structural steel provided in example 1 of the present application.

As is clear from fig. 4, the size of Nb, V, ti nano-precipitates in the structural steel obtained in example 1 was less than 100nm.

As can be seen from fig. 5, the structural steel of example 1 contains nano precipitated phases of Nb, V, and Ti.

In addition, one or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:

In the embodiment of the invention, the structural steel realizes comprehensive matching of high strength, high plasticity and high toughness, and the higher toughness provides performance reserve for subsequent welding; compared with precipitation strengthening steel added with Cu, the method of the invention eliminates the addition of Cu element, and compared with some high-toughness steel added with higher Ni element, the method of the invention ensures the high strength and high toughness plasticity of the steel plate by refining martensite lath through secondary quenching and combining with precipitation strengthening means of Nb, V and Ti, and has more advantages in cost.

The foregoing is only a specific embodiment of the application to enable those skilled in the art to understand or practice the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A 1000 MPa-grade structural steel, characterized in that the chemical composition of the structural steel comprises: C. si, mn, P, S, al, ni, cr, mo, nb, V, ti and Fe; wherein, the mass fraction of the material is calculated,

2. The structural steel of claim 1, wherein the metallurgical structure of the structural steel comprises tempered martensite having a volume fraction of 80-98% and reverse transformed austenite having a volume fraction of 2-20%; wherein the tempered martensite has a lath average width of < 0.3 μm.

3. Structural steel according to claim 1, characterized in that the matrix of the structural steel is diffusely distributed with Nb, V, ti precipitated phases, the size of which is < 100nm.

4. The structural steel of claim 1, wherein the structural steel meets at least one of the following properties: the yield strength is 1050 MPa-1200 MPa, the tensile strength is 1190 MPa-1300 MPa, the elongation is more than or equal to 22%, and the impact energy at minus 85 ℃ is more than 200J.

5. The structural steel of claim 1, wherein the structural steel has a thickness of 10mm to 50mm.

6. A method of producing a structural steel according to any one of claims 1 to 5, characterized in that the method comprises:

Obtaining a steel billet with the chemical composition;

7. The method according to claim 6, wherein the temperature of the heating before rolling is 1120-1180 ℃, and the heat preservation time of the heating before rolling is 240-360 min.

8. The method according to claim 6, wherein the general hot rolling is a recrystallization zone rolling having an initial rolling temperature of 1000 ℃ to 1100 ℃ and a final rolling temperature of 900 ℃ to 1000 ℃.

9. The method of claim 6, wherein the heat treating comprises: primary quenching, secondary quenching and tempering;

The secondary quenching includes: heating the hot rolled steel plate after primary quenching to 650-750 ℃, preserving heat for 3dmin, and then performing secondary water quenching, wherein d is the thickness of the structural steel;

10. The method of claim 6, wherein the thickness of the steel blank is 120mm to 240mm.