High-strength and high-toughness cold-rolled dual-phase steel and preparation method therefor, and automobile part

Abstract

The present disclosure relates to the technical field of alloy production. Disclosed are a high-strength and high-toughness cold-rolled dual-phase steel and a preparation method therefor, and an automobile part. The high-strength and high-toughness cold-rolled dual-phase steel comprises the following chemical components in percentage by weight: 0.15-0.35% of C, 0.10-0.50% of Si, 0.50-4.00% of Mn, less than or equal to 0.5% of Mo+Nb+Ti+V, and the balance being Fe and impurity elements. The matrix structure of the dual-phase steel comprises elongated lath ferrite and martensite. The high-strength and high-toughness cold-rolled dual-phase steel having the described chemical components and the matrix structure has excellent toughness while having ultra-high strength, so that the hole expansion and cold bending properties of the dual-phase steel are effectively improved, and the high-strength and high-toughness cold-rolled dual-phase steel can be used as an excellent automobile part. The preparation method for the high-strength and high-toughness cold-rolled dual-phase steel comprises the following step: preparing raw materials on the basis of the preset chemical components of the high-strength and high-toughness cold-rolled dual-phase steel. The method is simple, easily implemented, and suitable for industrial production.

Description

A high-strength and high-toughness cold-rolled dual-phase steel and its preparation method for automotive parts

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411407131.1, filed on October 10, 2024, entitled "A High-Strength and Tough Cold-Rolled Duplex Steel and Its Preparation Method and Automotive Parts", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of alloy production technology, and more specifically, to a high-strength and high-toughness cold-rolled duplex steel, its preparation method, and automotive parts. Background Technology

[0004] Steel is widely used in the automotive industry. Previously, IF steel, low-carbon steel, and high-strength low-alloy steel were mainly used to manufacture automotive parts. However, to meet the demands of automotive safety, it is necessary to increase the thickness of the steel sheets. However, increasing the thickness of the steel sheets increases the overall weight of the vehicle, contradicting the goal of lightweighting. Based on this, some research has proposed the Ultra-Light Steel Body (ULSAB) research program. The biggest achievement of this program is the development and optimization of the use of new high-strength steels, forming a new series of automotive steels mainly composed of high-strength steel, ultra-high-strength steel, DP steel, and TRIP steel. In comparison, DP steel and TRIP steel possess both high strength and high elongation, allowing for weight reduction while meeting automotive safety requirements.

[0005] Dual-phase (DP) steel is an advanced high-strength steel composed of ferrite and martensite. Its unique microstructure endows it with excellent comprehensive mechanical properties: high work hardening rate, low yield point, high uniform elongation and total elongation, and high impact absorption energy. DP steel is widely used in automotive safety components, such as bumpers and side impact beams. Due to the ever-increasing demand for lightweight vehicles, the tensile strength of DP steel is gradually increasing. While this strength improvement is beneficial for the overall requirements of lightweight vehicles and energy conservation and emission reduction, it inevitably leads to a decrease in the damage resistance of DP steel, thus affecting its cold-forming performance and subsequent service performance. Fracture toughness is a crucial parameter characterizing a material's damage resistance, making the improvement of the fracture toughness of ultra-high-strength DP steel essential.

[0006] In view of this, this disclosure is hereby made.

[0007] Public content

[0008] The purpose of this disclosure is to provide a high-strength and high-toughness cold-rolled duplex steel, a method for preparing the same, and automotive parts, in order to solve or improve the aforementioned technical problems.

[0009] This disclosure can be implemented as follows:

[0010] In a first aspect, this disclosure provides a high-strength and high-toughness cold-rolled dual-phase steel, wherein the chemical composition of the high-strength and high-toughness cold-rolled dual-phase steel, by weight percentage, includes: 0.15% to 0.35% C, 0.10% to 0.50% Si, 0.50% to 4.00% Mn, ≤0.5% Mo+Nb+Ti+V, and the balance being Fe and impurity elements;

[0011] The matrix structure of high-strength and high-toughness cold-rolled dual-phase steel consists of long lath ferrite and martensite.

[0012] In an optional embodiment, the chemical composition of the high-strength and high-toughness cold-rolled dual-phase steel includes: 0.193% to 0.196% C, 0.262% to 0.265% Si, 3.229% to 3.234% Mn, 0.312% to 0.438% Mo+Nb+Ti+V, with the balance being Fe and impurity elements.

[0013] In an optional embodiment, the chemical composition of the high-strength and high-toughness cold-rolled dual-phase steel includes: 0.194% C, 0.264% Si, 3.234% Mn, 0.367% Mo+Nb+Ti+V, with the balance being Fe and impurity elements.

[0014] In an optional embodiment, the high-strength, high-toughness cold-rolled duplex steel also has at least one of the following characteristics:

[0015] Feature 1: The ferrite size of the medium and long strips in high-strength and high-toughness cold-rolled dual-phase steel is 5μm to 80μm;

[0016] Feature 2: In the matrix structure of high-strength and high-toughness cold-rolled dual-phase steel, the volume fraction of martensite is 60% to 90%;

[0017] Feature 3: The tensile strength of high-strength and high-toughness cold-rolled duplex steel is not less than 1200MPa;

[0018] Feature 4: The yield strength of high-strength and high-toughness cold-rolled duplex steel is not less than 410 MPa;

[0019] Feature 5: The uniform elongation of high-strength and high-toughness cold-rolled dual-phase steel is not less than 6.3%;

[0020] Feature 6: The elongation after fracture of high-strength and high-toughness cold-rolled duplex steel is not less than 7.2%;

[0021] Feature 7: The initial crack toughness of high-strength and high-toughness cold-rolled dual-phase steel is not less than 74.2 KJ·m. 0.5 ;

[0022] Feature 8: The crack propagation toughness of high-strength and high-toughness cold-rolled dual-phase steel at Δa = 3 mm is not less than 181.6 KJ·m. 0.5.

[0023] In an optional embodiment, the size of the ferrite in the long strips of the high-strength and high-toughness cold-rolled dual-phase steel is 10 μm to 80 μm.

[0024] In an optional embodiment, the volume fraction of martensite in the matrix of the high-strength and high-toughness cold-rolled dual-phase steel is 70% to 90%.

[0025] In an optional embodiment, the tensile strength of the high-strength and high-toughness cold-rolled duplex steel is 1200 MPa to 1443 MPa.

[0026] In an optional embodiment, the tensile strength of the high-strength and high-toughness cold-rolled duplex steel is 1418 MPa to 1443 MPa.

[0027] In an optional embodiment, the yield strength of the high-strength and high-toughness cold-rolled duplex steel is 410 MPa to 873 MPa.

[0028] In an optional embodiment, the yield strength of the high-strength and high-toughness cold-rolled duplex steel is 710 MPa to 873 MPa.

[0029] In an optional embodiment, the uniform elongation of the high-strength and high-toughness cold-rolled dual-phase steel is 6.3% to 7.0%.

[0030] In an optional embodiment, the elongation after fracture of the high-strength and high-toughness cold-rolled duplex steel is 7.2% to 9.6%.

[0031] In an optional embodiment, the elongation after fracture of the high-strength and high-toughness cold-rolled duplex steel is 8.2% to 9.6%.

[0032] In an optional embodiment, the initial crack toughness of the high-strength, high-toughness cold-rolled dual-phase steel is 74.2 kJ·m. 0.5 ~109.7 kJ·m 0.5 .

[0033] In an optional embodiment, the crack propagation toughness of the high-strength, high-toughness cold-rolled dual-phase steel at Δa = 3 mm is 181.6 KJ·m. 0.5 ~258.2 kJ·m 0.5 .

[0034] Secondly, this disclosure provides a method for preparing high-strength and high-toughness cold-rolled duplex steel as described in any of the foregoing embodiments, comprising the following steps: preparing raw materials according to a predetermined chemical composition for high-strength and high-toughness cold-rolled duplex steel.

[0035] In optional embodiments, the raw materials include iron ore, quicklime, ferromolybdenum, vanadium stone, niobium oxide powder, titanium powder, iron-silicon alloy, and iron-manganese alloy.

[0036] In an optional implementation, the raw materials are subjected to melting and smelting, refining, continuous casting, smelting, forging, hot rolling, pickling, cold rolling, quenching, and annealing.

[0037] In an optional embodiment, the raw materials are melted and smelted to obtain molten steel; the molten steel is refined to obtain refined molten steel; the refined molten steel is continuously cast to obtain a steel billet; the steel billet is heated to dissolve all C, Si, Mn, Mo, Nb, Ti, and V elements in the raw materials; the solution-dissolved steel billet is forged to obtain a forged billet; the forged billet is rolled to obtain a hot-rolled steel strip; the hot-rolled steel strip is pickled; the pickled hot-rolled steel strip is cold-rolled to obtain a cold-rolled sheet; the cold-rolled sheet is subjected to high-temperature austenitizing quenching treatment to obtain a quenched sheet; the quenched sheet is subjected to critical zone annealing treatment to obtain a high-strength and high-toughness cold-rolled duplex steel.

[0038] In an optional embodiment, the preparation process of high-strength and high-toughness cold-rolled dual-phase steel includes at least one of the following features:

[0039] Feature 9: Melting and smelting are carried out under an oxidizing atmosphere;

[0040] Feature 10: Refining is carried out under reducing atmosphere conditions;

[0041] Feature 11: The steel billet is heated at 1220℃~1280℃ and held for 1.5h~2.5h;

[0042] Feature 12: Forging temperature is 1150℃~1200℃;

[0043] Feature 13: The rolling process includes: using 1100℃~1200℃ as the initial rolling temperature, heating the forging billet to 1210℃~1270℃ and holding it for 2h~3h, and then using 850℃~950℃ as the final rolling temperature;

[0044] Feature 14: The temperature of the acid solution used for pickling is 75℃~85℃, and the pickling speed is 80m / min~100m / min;

[0045] Feature 15: The reduction rate of cold rolling is 40% to 60%, and the thickness of the cold-rolled sheet is 1.4 mm to 1.9 mm;

[0046] Feature 16: High-temperature austenitizing quenching includes the following conditions: quenching temperature is 920℃~1120℃, holding time is 8min~12min, and the final temperature after quenching and cooling is 20℃~50℃.

[0047] Feature 17: Critical zone annealing includes the following conditions: annealing temperature of 790℃~810℃, holding time of 8min~12min, and final temperature after annealing cooling of 20℃~50℃.

[0048] In an optional embodiment, the size of the original austenite grains in the quenched plate is 5μm to 100μm.

[0049] Thirdly, this disclosure provides an automotive component, the raw material for which the manufacturing process includes high-strength and high-toughness cold-rolled duplex steel according to any of the foregoing embodiments.

[0050] The beneficial effects of this disclosure include:

[0051] The chemical composition of the high-strength and high-toughness cold-rolled duplex steel disclosed herein includes: 0.15%–0.35% C, 0.10%–0.50% Si, 0.50%–4.00% Mn, ≤0.5% Mo+Nb+Ti+V, with the balance being Fe and impurity elements. C, as a solid solution strengthening element, is set within the above range to ensure high strength; Si and Mn provide solid solution strengthening and improve the hardenability of austenite; Mo and V simultaneously refine the grain size and provide precipitation strengthening; Nb, as a carbonitride precipitating element, refines the grain size and precipitates carbonitrides, thus improving material strength; Ti, as a carbonitride precipitating element, is used to improve material strength. The matrix structure of this duplex steel consists of lath ferrite and martensite.

[0052] Duplex steels that meet the above-mentioned chemical composition and matrix structure of this disclosure have good comprehensive mechanical properties. Specifically, they have both ultra-high strength and excellent toughness, which effectively improves the hole expansion and cold bending performance of duplex steels, making them suitable for use as excellent automotive parts.

[0053] The preparation of this high-strength and high-toughness cold-rolled dual-phase steel is simple and easy to operate, making it suitable for industrial production. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 shows the engineering stress-strain curves of the duplex steels prepared in Examples 1-3 and Comparative Example 1.

[0056] Figure 2 shows the fracture toughness curves of the dual-phase steels prepared in Examples 1-3 and Comparative Example 1.

[0057] Figure 3 shows the SEM images of the dual-phase steels prepared in Examples 1-3 and Comparative Example 1. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0059] The following provides a detailed description of the high-strength and high-toughness cold-rolled duplex steel, its preparation method, and its application in automotive parts.

[0060] This disclosure provides a high-strength and high-toughness cold-rolled dual-phase steel. The chemical composition of the high-strength and high-toughness cold-rolled dual-phase steel, by weight percentage, includes: 0.15% to 0.35% C, 0.10% to 0.50% Si, 0.50% to 4.00% Mn, ≤0.5% Mo+Nb+Ti+V, and the balance being Fe and impurity elements.

[0061] The matrix structure of dual-phase steel consists of lath ferrite and martensite.

[0062] In some optional embodiments, the carbon content in the chemical composition of high-strength and high-toughness cold-rolled dual-phase steel can be 0.15%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, or 0.35%, or any other value within the range of 0.15% to 0.35%. If the carbon content is too low, it is detrimental to improving yield strength and tensile strength; if the carbon content is too high, it easily reduces plasticity.

[0063] The Si content in the chemical composition of high-strength and high-toughness cold-rolled dual-phase steel can be 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, or 0.50%, or other values ​​within the range of 0.10% to 0.50%. If the Si content is too low, it is not conducive to the formation of a dual-phase structure; if the Si content is too high, it easily reduces plasticity, toughness, and corrosion resistance.

[0064] The Mn content in the chemical composition of high-strength and high-toughness cold-rolled duplex steel can be 0.50%, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, or 4.00%, or any other value within the range of 0.50% to 4.00%. If the Mn content is too low, it will reduce the hardenability of the material and affect the formation of martensite; if the Mn content is too high, it can easily lead to coarse grains in the steel after heat treatment, which may reduce the toughness and weldability of the steel.

[0065] The chemical composition of high-strength and high-toughness cold-rolled dual-phase steel can contain Mo+Nb+Ti+V at concentrations of 0.50%, 0.45%, 0.4%, 0.35%, 0.30%, 0.25%, 0.20%, or 0.18%, or other values ​​within the range of ≤0.5%. If the Mo+Nb+Ti+V content is greater than 0.5%, it will promote the precipitation of carbonitrides at grain boundaries, reducing plasticity.

[0066] In some preferred embodiments, the chemical composition of the high-strength, high-toughness cold-rolled dual-phase steel includes: 0.193%–0.196% C, 0.262%–0.265% Si, 3.229%–3.234% Mn, 0.312%–0.438% Mo+Nb+Ti+V, with the balance being Fe and impurity elements. In some more typical embodiments, the chemical composition of the high-strength, high-toughness cold-rolled dual-phase steel may include: 0.194% C, 0.264% Si, 3.234% Mn, 0.367% Mo+Nb+Ti+V, with the balance being Fe and impurity elements.

[0067] In the chemical composition of the high-strength and high-toughness cold-rolled dual-phase steel provided in this application, C is a solid solution strengthening element, ensuring the material achieves high strength; Si and Mn can provide solid solution strengthening and improve the hardenability of austenite; Mo and V can simultaneously refine grains and perform precipitation strengthening, with V having a more significant strengthening effect. However, a low V content will weaken the strengthening effect, while a high V content will increase the size of the precipitated phase and increase costs. Therefore, the V content in this disclosure is preferably controlled at 0.15% to 0.17%; Nb is a carbonitride precipitation element, which can refine grains and precipitate carbonitrides, improving the material strength; Ti is a carbonitride precipitation element used to improve the material strength.

[0068] In the matrix microstructure of the high-strength and high-toughness cold-rolled dual-phase steel provided in this disclosure, the volume fraction of martensite is approximately 60% to 90%, such as 60%, 65%, 70%, 75%, 80%, 85%, or 90%, or other values ​​within the range of 60% to 90%. In some preferred embodiments, the volume fraction of martensite can be 70% to 90%.

[0069] In some optional embodiments, the size of the long lath ferrite is 5 μm to 80 μm, such as 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, or 80 μm, or other values ​​within the range of 5 μm to 80 μm. In some more typical embodiments, the size of the long lath ferrite can be 10 μm to 80 μm.

[0070] In some alternative embodiments, the tensile strength of the high-strength and high-toughness cold-rolled dual-phase steel is not less than 1200 MPa, for example, it can be 1200 MPa to 1443 MPa. In some more typical embodiments, the tensile strength of the high-strength and high-toughness cold-rolled dual-phase steel is 1418 MPa to 1443 MPa.

[0071] In some alternative embodiments, the yield strength of the high-strength and high-toughness cold-rolled dual-phase steel is not less than 410 MPa, for example, it can be 410 MPa to 873 MPa. In some more typical embodiments, the yield strength of the high-strength and high-toughness cold-rolled dual-phase steel is 710 MPa to 873 MPa.

[0072] In some alternative implementations, the uniform elongation of the high-strength and high-toughness cold-rolled dual-phase steel is not less than 6.3%, for example, it can be 6.3% to 7.0%.

[0073] In some alternative embodiments, the elongation after fracture of the high-strength, high-toughness cold-rolled dual-phase steel is not less than 7.2%, for example, it can be 7.2% to 9.6%. In some more typical embodiments, the elongation after fracture of the high-strength, high-toughness cold-rolled dual-phase steel is 8.2% to 9.6%.

[0074] In some alternative implementations, the initial crack toughness of the high-strength, high-toughness cold-rolled dual-phase steel is not less than 74.2 kJ·m. 0.5 For example, it can be 74.2 kJ·m 0.5 ~109.7 kJ·m 0.5 .

[0075] In some alternative embodiments, the crack propagation toughness of the high-strength, high-toughness cold-rolled dual-phase steel at Δa = 3 mm is not less than 181.6 KJ·m. 0.5 For example, it could be 181.6 kJ·m 0.5 ~258.2 kJ·m 0.5 .

[0076] Continuing from the above, the dual-phase steel provided in this disclosure contains a sufficient amount of C (0.15%-0.35%) to ensure adequate yield and tensile strength; it contains a certain amount of Si (0.10%-0.50%) and Mn (0.50%-4.00%), which promotes the formation of the dual-phase structure and improves the hardenability of austenite; and it contains a certain amount of Mo+Nb+Ti+V (≤0.5%), which refines the grains and provides precipitation strengthening. Dual-phase steel meeting the above-mentioned chemical composition and matrix structure of this disclosure possesses excellent comprehensive mechanical properties. Specifically, it exhibits both ultra-high strength and excellent toughness, effectively improving the hole expansion and cold bending performance of the dual-phase steel.

[0077] Accordingly, this disclosure also provides a method for preparing the above-mentioned high-strength and high-toughness cold-rolled duplex steel, comprising the following steps: preparing raw materials according to the preset chemical composition of high-strength and high-toughness cold-rolled duplex steel.

[0078] In some alternative embodiments, the raw materials include iron ore, quicklime, ferromolybdenum, vanadium ore, niobium oxide powder, titanium powder, iron-silicon alloy, and iron-manganese alloy. In some other embodiments, other raw materials capable of providing the above-mentioned chemical elements may also be used. Any scheme that combines raw materials to obtain a chemical composition within the aforementioned range is within the scope of this disclosure.

[0079] In some alternative embodiments, the preparation of high-strength and high-toughness cold-rolled dual-phase steel includes: melting and smelting raw materials, refining, continuous casting, smelting, forging, hot rolling, pickling, cold rolling, quenching, and annealing.

[0080] For example, the process may involve melting and smelting raw materials to obtain molten steel; refining the molten steel to obtain refined molten steel; continuously casting the refined molten steel to obtain a steel billet; heating the steel billet to dissolve all C, Si, Mn, Mo, Nb, Ti, and V elements in the raw materials; forging the solution-dissolved steel billet to obtain a forged billet; rolling the forged billet to obtain a hot-rolled steel strip; pickling the hot-rolled steel strip; cold-rolling the pickled hot-rolled steel strip to obtain a cold-rolled sheet; subjecting the cold-rolled sheet to high-temperature austenitizing quenching treatment to obtain a quenched sheet; and subjecting the quenched sheet to critical zone annealing treatment to obtain a high-strength and high-toughness cold-rolled duplex steel.

[0081] Among them, melting and smelting can be carried out under oxidizing atmosphere conditions.

[0082] Refining can be carried out under reducing atmosphere conditions.

[0083] The steel billet can be heated at 1220℃~1280℃ (such as 1220℃, 1225℃, 1230℃, 1235℃, 1240℃, 1245℃, 1250℃, 1255℃, 1260℃, 1265℃, 1270℃, 1275℃ or 1280℃, etc.) and held for 1.5h~2.5h (such as 1.5h, 2h or 2.5h, etc.).

[0084] The forging temperature can be between 1150℃ and 1200℃, such as 1150℃, 1155℃, 1160℃, 1165℃, 1170℃, 1175℃, 1180℃, 1185℃, 1190℃, 1195℃ or 1200℃, or other values ​​within the range of 1150℃ to 1200℃.

[0085] Rolling may include: using 1100℃~1200℃ (e.g., 1100℃, 1150℃ or 1200℃, etc.) as the initial rolling temperature, heating the forging billet to 1210℃~1270℃ (e.g., 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, 1260℃ or 1270℃, etc.) and holding it at that temperature for 2h~3h (e.g., 2h, 2.5h or 3h, etc.), and then using 850℃~950℃ (e.g., 850℃, 880℃, 900℃, 920℃ or 950℃, etc.) as the final rolling temperature.

[0086] The temperature of the acid solution used for pickling can be 75℃~85℃ (such as 75℃, 80℃ or 85℃, etc.), and the pickling speed can be 80m / min~100m / min (such as 80m / min, 85m / min, 90m / min, 95m / min or 100m / min, etc.).

[0087] The reduction rate of cold rolling can be 40% to 60% (e.g., 40%, 45%, 50%, 55% or 60%), and the thickness of the cold-rolled sheet can be 1.4mm to 1.9mm (e.g., 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm or 1.9mm).

[0088] High-temperature austenitizing quenching includes the following conditions: quenching temperature of 920℃~1120℃ (such as 920℃, 950℃, 980℃, 1000℃, 1050℃, 1100℃ or 1120℃, etc.), holding time of 8min~12min (such as 8min, 9min, 10min, 11min or 12min, etc.), and final temperature after quenching and cooling of 20℃~50℃ (such as 20℃, 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃, etc.).

[0089] In some preferred embodiments, the size of the original austenite grains in the quenched plate can be 5μm to 100μm, such as 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, or other values ​​in the range of 5μm to 100μm.

[0090] Critical zone annealing can include the following conditions: annealing temperature of 790℃~810℃ (e.g., 790℃, 795℃, 800℃, 805℃ or 810℃, etc.), holding time of 8min~12min (e.g., 8min, 9min, 10min, 11min or 12min, etc.), and final temperature after annealing cooling of 20℃~50℃ (e.g., 20℃, 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃, etc.).

[0091] Continuing from the above, in the production process of the aforementioned high-strength and high-toughness cold-rolled duplex steel, by using appropriate high-temperature austenitizing quenching and critical zone annealing process parameters, a duplex structure of long lath ferrite + martensite can be obtained. Specifically, high-temperature austenitizing quenching (920℃~1120℃) coarsens the original austenite grains, providing the microstructure basis for the formation of the duplex structure. Critical zone annealing (790℃~810℃) yields the final duplex structure with long lath ferrite + martensite. The duplex steel prepared using this process flow and parameters has long lath ferrite particles ranging from 5μm to 80μm in size. This long lath duplex structure can significantly improve the toughness of the duplex steel.

[0092] In addition, this disclosure also provides an automotive component, the raw materials for which the manufacturing process includes the aforementioned high-strength and high-toughness cold-rolled duplex steel.

[0093] For example, automotive parts may include bumpers and side impact beams, etc.

[0094] By using the aforementioned high-strength and high-toughness cold-rolled dual-phase steel as the raw material for manufacturing automotive parts, the overall mechanical properties of automotive parts can be improved while ensuring lightweight design.

[0095] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0096] Table 1 Chemical composition of each embodiment and comparative example

[0097] Example 1

[0098] This embodiment provides a high-strength, high-toughness cold-rolled dual-phase steel with a long lath ferrite microstructure, the preparation method of which includes the following steps:

[0099] S1: According to the chemical composition and proportion in Table 1 below, iron ore, quicklime, ferromolybdenum, vanadium stone, niobium oxide powder, titanium powder, iron-silicon alloy, and iron-manganese alloy are placed in an oxidizing atmosphere furnace for melting and smelting to obtain molten steel. Then, the molten steel is transferred to a reducing atmosphere furnace for refining to obtain refined molten steel. The molten steel is then continuously cast to obtain steel billets.

[0100] S2: The steel billet obtained in S1 is placed in a walking beam furnace and heated at 1250℃ for 2 hours to allow all C, Si, Mn, V, Mo and Al elements to be dissolved.

[0101] S3: The steel billet after S2 solution treatment is forged at a forging temperature of 1175℃ to obtain a forged billet;

[0102] S4: The forging billet obtained in S3 is heated to 1240℃ for 2.5 hours with 1150℃ as the initial rolling temperature, and then rolled at 900℃ to obtain hot-rolled steel strip.

[0103] S5: Pickling the hot-rolled steel strip obtained in S4 at an acid temperature of 80℃ and a pickling speed of 90m / min.

[0104] S6: The hot-rolled steel strip after S5 pickling is cold-rolled with a reduction rate of 50%. The thickness of the cold-rolled sheet after 50% cold rolling is 1.85mm.

[0105] S7: The cold-rolled sheet obtained in S6 is subjected to high-temperature austenitizing quenching treatment. The austenitizing temperature is set to 1120℃, held for 10 minutes, and then cooled to a final temperature of 35℃.

[0106] S8: The quenched plate obtained in S7 is subjected to critical zone annealing. The annealing temperature is set to 795℃, held for 10 minutes, and then cooled to a final temperature of 35℃ to obtain high-strength and high-toughness cold-rolled dual-phase steel.

[0107] Example 2

[0108] The only difference between this embodiment and Embodiment 1 is that the chemical composition is different in S1, as shown in Table 1; and the austenitizing temperature is 1020℃ in S7.

[0109] Example 3

[0110] The only difference between this embodiment and Embodiment 1 is that the chemical composition is different in S1, as shown in Table 1; and the austenitizing temperature is 920°C in S7.

[0111] Example 4

[0112] This embodiment provides a high-strength, high-toughness cold-rolled dual-phase steel with a long lath ferrite microstructure, the preparation method of which includes the following steps:

[0113] S1: According to the chemical composition and proportion in Table 1 below, iron ore, quicklime, ferromolybdenum, vanadium stone, niobium oxide powder, titanium powder, iron-silicon alloy, and iron-manganese alloy are placed in an oxidizing atmosphere furnace for melting and smelting to obtain molten steel. Then, the molten steel is transferred to a reducing atmosphere furnace for refining to obtain refined molten steel. The molten steel is then continuously cast to obtain steel billets.

[0114] S2: The steel billet obtained in S1 is placed in a walking beam furnace and heated at 1220℃ for 2.5h to allow all C, Si, Mn, V, Mo and Al elements to be dissolved.

[0115] S3: The steel billet after S2 solution treatment is forged at a forging temperature of 1150℃ to obtain a forged billet;

[0116] S4: The forging billet obtained in S3 is heated to 1210℃ for 3 hours with 1110℃ as the initial rolling temperature, and then the final rolling temperature is 850℃ to obtain hot-rolled steel strip.

[0117] S5: Pickling the hot-rolled steel strip obtained in S4 at a temperature of 75°C and a pickling speed of 80m / min.

[0118] S6: The hot-rolled steel strip after S5 pickling is cold-rolled with a reduction rate of 40%. The thickness of the cold-rolled sheet after 40% cold rolling is 1.9mm.

[0119] S7: The cold-rolled sheet obtained in S6 is subjected to high-temperature austenitizing quenching treatment. The austenitizing temperature is set to 920℃, held for 12 minutes, and then cooled to a final temperature of 20℃.

[0120] S8: The quenched plate obtained in S7 is subjected to critical zone annealing. The annealing temperature is set to 790℃, held for 12 minutes, and then cooled to a final temperature of 20℃ to obtain high-strength and high-toughness cold-rolled dual-phase steel.

[0121] Example 5

[0122] This embodiment provides a high-strength, high-toughness cold-rolled dual-phase steel with a long lath ferrite microstructure, the preparation method of which includes the following steps:

[0123] S1: According to the chemical composition and proportion in Table 1 below, iron ore, quicklime, ferromolybdenum, vanadium stone, niobium oxide powder, titanium powder, iron-silicon alloy, and iron-manganese alloy are placed in an oxidizing atmosphere furnace for melting and smelting to obtain molten steel. Then, the molten steel is transferred to a reducing atmosphere furnace for refining to obtain refined molten steel. The molten steel is then continuously cast to obtain steel billets.

[0124] S2: The steel billet obtained in S1 is placed in a walking beam furnace and heated at 1280℃ for 1.5h to allow all C, Si, Mn, V, Mo and Al elements to be dissolved.

[0125] S3: The steel billet after S2 solution treatment is forged at a forging temperature of 1200℃ to obtain a forged billet;

[0126] S4: The forging billet obtained in S3 is heated to 1270℃ for 2 hours with 1200℃ as the initial rolling temperature, and then the final rolling temperature is 950℃ to obtain hot-rolled steel strip.

[0127] S5: Pickling the hot-rolled steel strip obtained in S4 at an acid temperature of 85℃ and a pickling speed of 100m / min.

[0128] S6: The hot-rolled steel strip after S5 pickling is cold-rolled with a reduction rate of 60%. The thickness of the cold-rolled sheet after 60% cold rolling is 1.4mm.

[0129] S7: The cold-rolled sheet obtained in S6 is subjected to high-temperature austenitizing quenching treatment. The austenitizing temperature is set to 1120℃, held for 8 minutes, and then cooled to a final temperature of 50℃.

[0130] S8: The quenched plate obtained in S7 is subjected to critical zone annealing. The annealing temperature is set to 810℃, held for 8 minutes, and then cooled to a final temperature of 50℃ to obtain high-strength and high-toughness cold-rolled dual-phase steel.

[0131] Example 6

[0132] This embodiment provides a duplex steel, which differs from Embodiment 1 in that the V content in its chemical composition is 0.1%.

[0133] Example 7

[0134] This embodiment provides a duplex steel, which differs from Embodiment 1 in that the V content in its chemical composition is 0.2%.

[0135] Comparative Example 1

[0136] This comparative example provides a cold-rolled dual-phase steel with an equiaxed ferrite structure, which differs from Example 1 only in that: in S1, the chemical composition is different, as shown in Table 1; and in S7, the austenitizing temperature is 820°C.

[0137] Comparative Example 2

[0138] This comparative example provides a dual-phase steel that differs from Example 1 in that the C content in its chemical composition is 0.395%.

[0139] Comparative Example 3

[0140] This comparative example provides a dual-phase steel that differs from Example 1 in that the Si content in its chemical composition is 0.616%.

[0141] Comparative Example 4

[0142] This comparative example provides a dual-phase steel that differs from Example 1 in that the Mn content in its chemical composition is 4.520%.

[0143] Comparative Example 5

[0144] This comparative example provides a dual-phase steel that differs from Example 1 in that the chemical composition contains 0.673% Mo+Nb+Ti+V.

[0145] Comparative Example 6

[0146] This comparative example provides a dual-phase steel that differs from Example 1 in that it does not contain V in its chemical composition.

[0147] Comparative Example 7

[0148] This comparative example provides a duplex steel, which differs from Example 1 in that its high-temperature austenitizing temperature is 900°C.

[0149] Comparative Example 8

[0150] This comparative example provides a duplex steel, which differs from Example 1 in that its high-temperature austenitizing temperature is 1150°C.

[0151] Comparative Example 9

[0152] This comparative example provides a dual-phase steel, which differs from Example 1 in that its critical annealing temperature is 760°C.

[0153] Comparative Example 10

[0154] This comparative example provides a dual-phase steel, which differs from Example 1 in that its critical annealing temperature is 840°C.

[0155] Test case

[0156] The tensile properties and fracture toughness of the duplex steels prepared in the above embodiments and comparative examples were tested and their microstructures were characterized. The results are shown in Table 2.

[0157] The yield strength, tensile strength, uniform elongation, elongation after fracture, and crack initiation toughness were all tested according to GB / T 228.1-2010. The crack propagation toughness was tested according to GB / T 21143-2012. The longest ferrite half-strip dimension was measured from the SEM image.

[0158] Taking Examples 1-3 and Comparative Example 1 as examples, the engineering stress-strain curves of these dual-phase steels are shown in Figure 1, the fracture toughness curves are shown in Figure 2, and the SEM images are shown in Figure 3. In Figure 3, (a) to (d) correspond to Examples 1-3 and Comparative Example 1, respectively.

[0159] Table 2. Microstructure and mechanical properties of duplex steel prepared in each embodiment and comparative example.

[0160] As can be seen from Table 2, the method of this disclosure can produce high-strength and high-toughness cold-rolled dual-phase steel sheets. These high-strength and high-toughness cold-rolled dual-phase steel sheets have excellent mechanical properties and suitable microstructure. In contrast, although Comparative Example 1 can also achieve this strength level, and even better plasticity, its fracture toughness is much lower than that of the examples, and it does not have the dual-phase structure of long strips.

[0161] Furthermore, as can be seen from Example 1 and Comparative Examples 2-10 in Table 2, improper chemical composition or inadequate preparation conditions will result in the prepared duplex steel failing to possess both good strength and toughness.

[0162] As shown in Figure 1, with the change in high-temperature austenitizing quenching temperature (920℃~1120℃), the tensile strength and elongation after fracture of the duplex steels prepared in Examples 1-3 remained basically unchanged, with the tensile strength maintained at 1418MPa~1443MPa and the elongation after fracture maintained at 8.2%~9.6%. In contrast, Comparative Example 1 achieved an elongation after fracture of 12.7% at the same tensile strength level, which is a result of microstructure refinement.

[0163] As shown in Figure 2, the fracture toughness values ​​of the dual-phase steels prepared in Examples 1-3 all remained at a high level, with an initial crack toughness of 74.2 kJ·m. 0.5 ~109.7 kJ·m 0.5 The crack propagation toughness (Δa=3mm) is 181.6KJ·m. 0.5 ~258.2 kJ·m 0.5 In contrast, Comparative Example 1 exhibits very low fracture toughness, with an initial crack toughness of 6.6 kJ·m. 0.5 The crack propagation toughness (Δa=3mm) is 15.5KJ·m. 0.5 Overall, the fracture toughness of the dual-phase steels prepared in Examples 1-3 is much higher than that in Comparative Example 1.

[0164] As shown in Figure 3, the dual-phase steels prepared in Examples 1-3 all exhibit a dual-phase microstructure with long lath ferrite. The maximum ferrite lath size in Example 1 is 80 μm, in Example 2 it is 30 μm, and in Example 3 it is 10 μm. In contrast, Comparative Example 1 exhibits an equiaxed dual-phase microstructure, and the morphology of long lath ferrite cannot be observed.

[0165] In summary, the high-strength and high-toughness cold-rolled duplex steel sheet produced by this disclosure has a duplex steel microstructure consisting of long strip ferrite and martensite, exhibiting high strength and good toughness. The duplex steel produced using the method of this disclosure enables the manufacture and engineering application of ultra-high strength and high-toughness duplex steel.

[0166] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure. Industrial applicability

[0167] The high-strength and high-toughness cold-rolled duplex steel disclosed herein possesses both ultra-high strength and excellent toughness, effectively improving the hole expansion and cold bending properties of duplex steel, making it suitable for use as an excellent automotive component. The preparation method of this high-strength and high-toughness cold-rolled duplex steel is simple, easy to operate, and suitable for industrial production.

Claims

1. A high-strength, high-toughness cold-rolled dual-phase steel, characterized in that, The chemical composition of the high-strength and high-toughness cold-rolled dual-phase steel, by weight percentage, includes: 0.15% to 0.35% C, 0.10% to 0.50% Si, 0.50% to 4.00% Mn, ≤0.5% Mo+Nb+Ti+V, with the balance being Fe and impurity elements. The matrix structure of the high-strength and high-toughness cold-rolled dual-phase steel is long lath ferrite and martensite.

2. The high-strength, high-toughness cold-rolled dual-phase steel according to claim 1, characterized in that, The chemical composition of the high-strength and high-toughness cold-rolled dual-phase steel includes: 0.193% to 0.196% C, 0.262% to 0.265% Si, 3.229% to 3.234% Mn, 0.312% to 0.438% Mo+Nb+Ti+V, with the balance being Fe and impurity elements.

3. The high-strength, high-toughness cold-rolled dual-phase steel according to claim 2, characterized in that, The content of vitamin V is 0.15% to 0.17%.

4. The high-strength, high-toughness cold-rolled dual-phase steel according to any one of claims 1 to 3, characterized in that, The chemical composition of the high-strength and high-toughness cold-rolled dual-phase steel includes: 0.194% C, 0.264% Si, 3.234% Mn, 0.367% Mo+Nb+Ti+V, with the balance being Fe and impurity elements.

5. The high-strength, high-toughness cold-rolled dual-phase steel according to any one of claims 1 to 4, characterized in that, The high-strength and high-toughness cold-rolled duplex steel also has at least one of the following characteristics: Feature 1: The size of the long strip ferrite in the high-strength and high-toughness cold-rolled dual-phase steel is 5μm to 80μm; Feature 2: In the matrix structure of the high-strength and high-toughness cold-rolled dual-phase steel, the volume fraction of martensite is 60% to 90%; Feature 3: The tensile strength of the high-strength and high-toughness cold-rolled duplex steel is not less than 1200 MPa; Feature 4: The yield strength of the high-strength and high-toughness cold-rolled duplex steel is not less than 410 MPa; Feature 5: The uniform elongation of the high-strength and high-toughness cold-rolled duplex steel is not less than 6.3%; Feature 6: The elongation after fracture of the high-strength and high-toughness cold-rolled dual-phase steel is not less than 7.2%; Feature 7: The high ductility cold rolled dual phase steel has a crack initiation toughness no less than 74.2 KJ.m 0.5 ; Feature 8: The crack propagation toughness of the high-strength and high-toughness cold-rolled dual-phase steel at Δa = 3 mm is not less than 181.6 KJ·m. 0.5 .

6. The high strength-to-toughness cold rolled dual phase steel according to claim 5, characterized by, The ferrite size of the long strips in high-strength and high-toughness cold-rolled dual-phase steel is 10μm to 80μm.

7. The high-strength, high-toughness cold-rolled dual-phase steel according to claim 5 or 6, characterized in that, In the matrix structure of high-strength and high-toughness cold-rolled dual-phase steel, the volume fraction of martensite is 70% to 90%.

8. The high-strength, high-toughness cold-rolled dual-phase steel according to any one of claims 5 to 7, characterized in that, The tensile strength of high-strength and high-toughness cold-rolled dual-phase steel is 1200MPa~1443MPa.

9. The high-strength, high-toughness cold-rolled dual-phase steel according to claim 8, characterized in that, The tensile strength of high-strength and high-toughness cold-rolled dual-phase steel is 1418MPa~1443MPa.

10. The high-strength, high-toughness cold-rolled dual-phase steel according to any one of claims 5 to 9, characterized in that, The yield strength of high-strength and high-toughness cold-rolled dual-phase steel is 410 MPa to 873 MPa.

11. The high-strength, high-toughness cold-rolled dual-phase steel according to claim 10, characterized in that, The yield strength of high-strength and high-toughness cold-rolled dual-phase steel is 710MPa to 873MPa.

12. The high ductility cold rolled dual phase steel according to any one of claims 5 to 11, characterized in that, The uniform elongation of high-strength and high-toughness cold-rolled dual-phase steel is 6.3% to 7.0%.

13. The high ductility cold rolled dual phase steel according to any one of claims 5 to 12, characterized in that, The elongation after fracture of high-strength and high-toughness cold-rolled dual-phase steel is 7.2% to 9.6%.

14. The high strength-to-toughness cold rolled dual phase steel according to claim 13, characterized in that, The elongation after fracture of high-strength and high-toughness cold-rolled dual-phase steel is 8.2% to 9.6%.

15. The high-strength, high-toughness cold-rolled dual-phase steel according to any one of claims 5 to 14, characterized in that, The crack initiation toughness of high-strength and high-toughness cold-rolled dual-phase steel is 74.2 kJ·m. 0.5 ~109.7 kJ·m 0.5 .

16. The high ductility cold rolled dual phase steel according to any one of claims 5 to 15, characterized in that, The crack propagation toughness of high-strength and high-toughness cold-rolled dual-phase steel at Δa = 3 mm is 181.6 KJ·m. 0.5 ~258.2 kJ·m 0.5 .

17. A method for preparing high-strength, high-toughness cold-rolled dual-phase steel as described in any one of claims 1 to 16, characterized in that, Includes the following steps: The raw materials are prepared according to the preset chemical composition of high-strength and high-toughness cold-rolled duplex steel.

18. The preparation method according to claim 17, characterized in that, The raw materials include iron ore, quicklime, ferromolybdenum, vanadium stone, niobium oxide powder, titanium powder, iron-silicon alloy, and iron-manganese alloy.

19. The preparation method according to claim 17 or 18, characterized in that, The raw materials are subjected to melting, refining, continuous casting, smelting, forging, hot rolling, pickling, cold rolling, quenching, and annealing.

20. The method of claim 19, wherein, The raw materials are melted and smelted to obtain molten steel; the molten steel is refined to obtain refined molten steel; the refined molten steel is continuously cast to obtain a steel billet; the steel billet is heated to dissolve all C, Si, Mn, Mo, Nb, Ti, and V elements in the raw materials; the solution-dissolved steel billet is forged to obtain a forged billet; the forged billet is rolled to obtain a hot-rolled steel strip; the hot-rolled steel strip is pickled; the pickled hot-rolled steel strip is cold-rolled to obtain a cold-rolled sheet; the cold-rolled sheet is subjected to high-temperature austenitizing quenching treatment to obtain a quenched sheet; the quenched sheet is subjected to critical zone annealing treatment to obtain the high-strength and high-toughness cold-rolled duplex steel.

21. The preparation method according to claim 20, characterized in that, The preparation process of the high-strength and high-toughness cold-rolled dual-phase steel includes at least one of the following features: Feature 9: Melting and smelting are carried out under an oxidizing atmosphere; feature 10: Refining is carried out under reducing atmosphere conditions; Feature 11: The steel billet is heated at 1220℃~1280℃ and held for 1.5h~2.5h; Feature 12: Forging temperature is 1150℃~1200℃; Feature 13: The rolling process includes: heating the forging billet to 1210℃~1270℃ for 2h~3h with 1100℃~1200℃ as the initial rolling temperature, and then using 850℃~950℃ as the final rolling temperature. Feature 14: The temperature of the acid solution used for pickling is 75℃~85℃, and the pickling speed is 80m / min~100m / min; Feature 15: The reduction rate of cold rolling is 40% to 60%, and the thickness of the cold-rolled sheet is 1.4 mm to 1.9 mm; Feature 16: High-temperature austenitizing quenching includes the following conditions: quenching temperature is 920℃~1120℃, holding time is 8min~12min, and the final temperature after quenching and cooling is 20℃~50℃. Feature 17: Critical zone annealing includes the following conditions: annealing temperature of 790℃~810℃, holding time of 8min~12min, and final temperature after annealing cooling of 20℃~50℃.

22. The method of claim 21, wherein, The size of the original austenite grains in the quenched plate is 5μm to 100μm.

23. An automotive part, characterized by The raw materials for manufacturing the automotive parts include the high-strength, high-toughness cold-rolled duplex steel as described in any one of claims 1 to 16.

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