High-toughness cold-rolled dual-phase steel, preparation method thereof and automobile part

Abstract

The invention discloses high-toughness cold-rolled dual-phase steel, a preparation method thereof and an automobile part, and belongs to the technical field of alloy production. The 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 and V, and the balance of Fe and impurity elements, the matrix structure of the dual-phase steel is long lath ferrite and martensite. The high-toughness cold-rolled dual-phase steel with the chemical components and the matrix structure has excellent toughness while having ultrahigh strength, the reaming and cold bending properties of the dual-phase steel are effectively improved, and the high-toughness cold-rolled dual-phase steel can be applied as an excellent automobile part. The preparation method of the high-strength and high-toughness cold-rolled dual-phase steel comprises the following step of preparing raw materials according to preset chemical components of the high-strength and high-toughness cold-rolled dual-phase steel. The method is simple, easy to operate and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy production, and in particular to a high-strength and toughness cold-rolled dual-phase steel and a preparation method thereof and automobile parts. Background Art

[0002] Steel is widely used in the automotive industry. In the past, IF steel, low carbon steel and high strength low alloy steel were mainly used to manufacture automotive parts. However, in order to meet the requirements of automotive safety, it is necessary to increase the thickness of the steel plate. However, increasing the thickness of the steel plate will increase the overall weight of the car, which is inconsistent with the goal of lightweighting the car. Based on this, some studies have proposed an ultra-light steel body (ULSAB) research plan. The biggest achievement of this plan is the development and optimization of the use of new high-strength steel, forming a new automotive steel series mainly composed of high-strength steel, ultra-high-strength steel, DP steel and TRIP steel. In comparison, DP steel and TRIP steel have high strength and high elongation, which can reduce the weight of the car while meeting the safety requirements.

[0003] Dual-phase (DP) steel is an advanced high-strength steel composed of ferrite and martensite. Due to its special structure, it has good comprehensive mechanical properties: high work hardening rate, low yield point, high uniform elongation and total elongation, and high collision absorption energy. Dual-phase steel is widely used in automotive safety components, such as bumpers and side impact beams. Due to the need to always meet the lightweight demand of automobiles, the tensile strength level of DP steel is also gradually increasing. The increase in strength is beneficial to the overall demand for lightweight automobiles and energy conservation and emission reduction. However, the increase in strength will undoubtedly lead to a decrease in the damage resistance of DP steel, which in turn affects the cold forming performance and subsequent service performance of DP steel plates. Fracture toughness is an important parameter to characterize the damage resistance of materials. Improving the fracture toughness of ultra-high strength DP steel is crucial.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a high-strength and toughness cold-rolled dual-phase steel and a preparation method thereof and an automotive component to solve or improve the above-mentioned technical problems.

[0006] The present invention can be implemented like this:

[0007] In a first aspect, the present invention provides a high-strength and toughness cold-rolled dual-phase steel, wherein the chemical composition of the high-strength and toughness cold-rolled dual-phase steel comprises, by weight percentage: 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 is Fe and impurity elements;

[0008] The matrix structure of high strength and toughness cold rolled dual phase steel is long lath ferrite and martensite.

[0009] In an optional embodiment, the chemical composition of the high-strength and 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, and the remainder is Fe and impurity elements.

[0010] In an optional embodiment, the chemical composition of the high-strength and toughness cold-rolled dual-phase steel includes: 0.194% C, 0.264% Si, 3.234% Mn, 0.367% Mo+Nb+Ti+V, and the remainder is Fe and impurity elements.

[0011] In an optional embodiment, the high strength and toughness cold rolled dual phase steel further has at least one of the following characteristics:

[0012] Feature 1: The size of the ferrite in the long strip of high-strength and toughness cold-rolled dual-phase steel is 5μm to 80μm, preferably 10μm to 80μm;

[0013] Feature 2: In the matrix structure of the high-strength and toughness cold-rolled dual-phase steel, the volume fraction of martensite is 60% to 90%, preferably 70% to 90%;

[0014] Feature 3: The tensile strength of the high-strength and toughness cold-rolled dual-phase steel is not less than 1200 MPa, preferably 1200 MPa to 1443 MPa, and more preferably 1418 MPa to 1443 MPa;

[0015] Feature 4: The yield strength of high-strength and toughness cold-rolled dual-phase steel is not less than 410MPa, preferably 410MPa to 873MPa, more preferably 710MPa to 873MPa;

[0016] Feature 5: The uniform elongation of high-strength and toughness cold-rolled dual-phase steel is not less than 6.3%, preferably 6.3% to 7.0%;

[0017] Feature 6: The elongation after fracture of the high-strength and toughness cold-rolled dual-phase steel is not less than 7.2%, preferably 7.2% to 9.6%, more preferably 8.2% to 9.6%;

[0018] Feature 7: The crack initial toughness of high-strength cold-rolled dual-phase steel is not less than 74.2KJ·m 0.5 , preferably 74.2KJ·m 0.5 ~109.7KJ·m 0.5 ;

[0019] Feature 8: The crack extension toughness of high-strength and toughness cold-rolled dual-phase steel at Δa = 3mm is not less than 181.6KJ·m 0.5, preferably 181.6KJ·m 0.5 ~258.2KJ·m 0.5 .

[0020] In a second aspect, the present invention provides a method for preparing high-strength and toughness cold-rolled dual-phase steel as described in any of the aforementioned embodiments, comprising the following steps: preparing raw materials according to a preset chemical composition of the high-strength and toughness cold-rolled dual-phase steel.

[0021] In an alternative embodiment, the raw materials include iron ore, quicklime, ferromolybdenum, vanadium ore, niobium oxide powder, titanium powder, iron silicon alloy and iron manganese alloy.

[0022] In an optional embodiment, the raw materials are melted, smelted, refined, continuously cast, smelted, forged, hot rolled, pickled, cold rolled, quenched, and annealed.

[0023] 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 the C, Si, Mn, Mo, Nb, Ti, and V elements in the raw materials; the solid-solution 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 plate; the cold-rolled plate is subjected to high-temperature austenitizing quenching treatment to obtain a quenched plate; the quenched plate is subjected to critical zone annealing treatment to obtain a high-strength and toughness cold-rolled dual-phase steel.

[0024] In an optional embodiment, the preparation process of high strength and toughness cold rolled dual phase steel includes at least one of the following features:

[0025] Feature 9: Melting and smelting are carried out under oxidizing atmosphere conditions;

[0026] Feature 10: Refining is carried out under reducing atmosphere conditions;

[0027] Feature 11: The heating of the steel billet is carried out at 1220℃~1280℃ for 1.5h~2.5h;

[0028] Feature 12: Forging temperature is 1150℃~1200℃;

[0029] Feature 13: The rolling process includes: starting the rolling process at 1100°C to 1200°C, heating the forged billet to 1210°C to 1270°C for 2h to 3h, and then finishing the rolling process at 850°C to 950°C;

[0030] Feature 14: The temperature of the acid solution used for pickling is 75°C to 85°C, and the pickling speed is 80m / min to 100m / min;

[0031] Feature 15: The cold rolling reduction rate is 40% to 60%, and the thickness of the cold-rolled sheet obtained by cold rolling is 1.4 mm to 1.9 mm;

[0032] Feature 16: High-temperature austenitizing quenching includes the following conditions: quenching temperature is 920°C to 1120°C, holding time is 8min to 12min, and the final temperature after quenching cooling is 20°C to 50°C; preferably, the size of the original austenite grains in the quenched plate is 5μm to 100μm;

[0033] Feature 17: The critical region annealing treatment includes the following conditions: the annealing temperature is 790°C to 810°C, the holding time is 8min to 12min, and the final temperature after annealing cooling is 20°C to 50°C.

[0034] In a third aspect, the present invention provides an automobile component, wherein the raw material for preparing the automobile component comprises the high-strength and toughness cold-rolled dual-phase steel of any one of the aforementioned embodiments.

[0035] The beneficial effects of the present invention include:

[0036] The chemical composition of the high-strength and toughness cold-rolled dual-phase steel provided by the present invention 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 is Fe and impurity elements. Among them, C is a solid solution strengthening element, and setting it in the above range can ensure that the material obtains high strength; Si and Mn can provide solid solution strengthening and improve the hardenability of austenite; Mo and V can simultaneously achieve the purpose of grain refinement and precipitation strengthening; Nb is a carbonitride precipitation element, which can refine grains and precipitate carbonitrides to improve material strength; Ti is a carbonitride precipitation element, which is used to improve material strength. The matrix structure of the dual-phase steel is long lath ferrite and martensite.

[0037] The dual-phase steel satisfying the above-mentioned chemical composition and matrix structure of the present invention has good comprehensive mechanical properties. Specifically, it has ultra-high strength and excellent toughness, which effectively improves the hole expansion and cold bending properties of the dual-phase steel and can be used as an excellent automotive component.

[0038] The high-strength and toughness cold-rolled dual-phase steel is simple to prepare and easy to operate, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0040] Figure 1 The engineering stress-strain curves of the dual-phase steels prepared in Examples 1 to 3 and Comparative Example 1 in the test examples;

[0041] Figure 2 It is a fracture toughness curve diagram of the dual-phase steel prepared in Examples 1 to 3 and Comparative Example 1 in the test example;

[0042] Figure 3 It is the SEM picture of the dual-phase steel prepared in Examples 1 to 3 and Comparative Example 1 in the test example. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0044] The high-strength and toughness cold-rolled dual-phase steel and its preparation method and automobile parts provided by the present invention are specifically described below.

[0045] The present invention provides a high-strength and toughness cold-rolled dual-phase steel. The chemical composition of the high-strength and toughness cold-rolled dual-phase steel includes, by weight percentage: 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 is Fe and impurity elements;

[0046] The matrix structure of duplex steel is long lath ferrite and martensite.

[0047] In some optional embodiments, the C content in the chemical composition of the high-strength and 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%, etc., or any other value within the range of 0.15% to 0.35%. If the C content is too little, it is not conducive to the improvement of yield strength and tensile strength; if the C content is too much, it is easy to reduce plasticity.

[0048] The Si content in the chemical composition of high-strength and 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%, etc., or other values ​​within the range of 0.10% to 0.50%. If the Si content is too little, it is not conducive to the formation of the dual-phase structure; if the Si content is too much, it is easy to reduce the plasticity, toughness and corrosion resistance.

[0049] The Mn content in the chemical composition of high-strength and toughness cold-rolled dual-phase steel can be 0.50%, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50% or 4.00%, etc., or any other value within the range of 0.50% to 4.00%. If the Mn content is too little, the hardenability of the material will be reduced and the formation of martensite will be affected; if the Mn content is too much, it is easy to cause the steel to have coarse grains after heat treatment, which may reduce the toughness and welding performance of the steel.

[0050] The content of Mo+Nb+Ti+V in the chemical composition of high-strength and toughness cold-rolled dual-phase steel can be 0.50%, 0.45%, 0.4%, 0.35%, 0.30%, 0.25%, 0.20% or 0.18%, etc., or other values ​​within the range of ≤0.5%. If the content of Mo+Nb+Ti+V is greater than 0.5%, carbonitrides will be precipitated at the grain boundaries, reducing plasticity.

[0051] In some preferred embodiments, the chemical composition of high-strength and 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, and the balance is Fe and impurity elements. In some more typical embodiments, the chemical composition of high-strength and toughness cold-rolled dual-phase steel may include: 0.194% C, 0.264% Si, 3.234% Mn, 0.367% Mo+Nb+Ti+V, and the balance is Fe and impurity elements.

[0052] In the chemical composition of the high-strength and toughness cold-rolled dual-phase steel provided in the present application, C is a solid solution strengthening element, which ensures that the material obtains high strength; Si and Mn can provide solid solution strengthening and improve the hardenability of austenite; Mo and V can simultaneously achieve the purpose of grain refinement and precipitation strengthening, among which the strengthening purpose of V is more significant. At the same time, a low V content will lead to a weakened strengthening effect, and a high V content will lead to an increase in the size of the precipitated phase and increase the cost. Therefore, the V content in the present invention is preferably controlled at 0.15% to 0.17%; Nb is a carbonitride precipitation element, which can refine the grains and precipitate carbonitrides to improve the material strength; Ti is a carbonitride precipitation element, which is used to improve the material strength.

[0053] In the matrix structure of the high-strength and toughness cold-rolled dual-phase steel provided by the present invention, the volume fraction of martensite is about 60% to 90%. In some preferred embodiments, the volume fraction of martensite is 70 to 90%.

[0054] In some optional embodiments, the size of the long lath ferrite is 5 μm to 80 μm. In some more typical embodiments, the size of the long lath ferrite is 10 μm to 80 μm.

[0055] In some optional embodiments, the tensile strength of the high-strength and 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 toughness cold-rolled dual-phase steel is 1418 MPa to 1443 MPa.

[0056] In some optional embodiments, the yield strength of the high-strength and 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 toughness cold-rolled dual-phase steel is 710 MPa to 873 MPa.

[0057] In some optional embodiments, the uniform elongation of the high-strength and toughness cold-rolled dual-phase steel is not less than 6.3%, for example, it can be 6.3% to 7.0%.

[0058] In some optional embodiments, the elongation after fracture of the high-strength and 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 and toughness cold-rolled dual-phase steel is 8.2% to 9.6%.

[0059] In some optional embodiments, the crack initiation toughness of the high-strength and toughness cold-rolled dual-phase steel is not less than 74.2 kJ·m 0.5 , for example, it can be 74.2KJ·m 0.5 ~109.7KJ·m 0.5 .

[0060] In some optional embodiments, the crack extension toughness of the high-strength and toughness cold-rolled dual-phase steel at Δa=3 mm is not less than 181.6 KJ·m 0.5 , for example, it can be 181.6KJ·m 0.5 ~258.2KJ·m 0.5 .

[0061] As mentioned above, the chemical composition of the dual-phase steel provided by the present invention contains a sufficient amount of C (0.15%-0.35%), which can ensure sufficient yield and tensile strength; contains a certain amount of Si (0.10%-0.50%) and Mn (0.50%-4.00%), which can promote the formation of dual-phase structure and improve the hardenability of austenite; contains a certain amount of Mo+Nb+Ti+V (≤0.5%), which can play a role in grain refinement and precipitation strengthening. The dual-phase steel that meets the above chemical composition and matrix structure of the present invention has good comprehensive mechanical properties. Specifically, it has excellent toughness while having ultra-high strength, which effectively improves the hole expansion and cold bending performance of the dual-phase steel.

[0062] Correspondingly, the present invention also provides a method for preparing the above-mentioned high-strength and toughness cold-rolled dual-phase steel, comprising the following steps: preparing raw materials according to the preset chemical composition of the high-strength and toughness cold-rolled dual-phase steel.

[0063] In some optional embodiments, the raw materials include iron ore, quicklime, ferromolybdenum, vanadium stone, niobium oxide powder, titanium powder, iron silicon alloy and iron manganese alloy. In some other embodiments, other raw materials that can provide the above chemical elements can also be used. The schemes that meet the above chemical composition range by combining the raw materials are all within the protection scope of the present invention.

[0064] In some optional embodiments, the preparation of high-strength and 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.

[0065] More specifically, the raw materials may be 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 the C, Si, Mn, Mo, Nb, Ti, and V elements in the raw materials; the solid-solution 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 plate; the cold-rolled plate is subjected to high-temperature austenitizing quenching treatment to obtain a quenched plate; the quenched plate is subjected to critical zone annealing treatment to obtain a high-strength and toughness cold-rolled dual-phase steel.

[0066] Among them, melting and smelting are carried out under oxidizing atmosphere conditions.

[0067] Refining is carried out under reducing atmosphere conditions.

[0068] The steel billet can be heated at 1220°C to 1280°C (such as 1220°C, 1225°C, 1230°C, 1235°C, 1240°C, 1245°C, 1250°C, 1255°C, 1260°C, 1265°C, 1270°C, 1275°C or 1280°C, etc.) and kept warm for 1.5h to 2.5h (such as 1.5h, 2h or 2.5h, etc.).

[0069] The forging temperature may be 1150°C to 1200°C, such as 1150°C, 1155°C, 1160°C, 1165°C, 1170°C, 1175°C, 1180°C, 1185°C, 1190°C, 1195°C or 1200°C, or other values ​​within the range of 1150°C to 1200°C.

[0070] The rolling may include: using 1100°C to 1200°C (such as 1100°C, 1150°C or 1200°C, etc.) as the start rolling temperature, heating the forging billet to 1210°C to 1270°C (such as 1210°C, 1220°C, 1230°C, 1240°C, 1250°C, 1260°C or 1270°C, etc.) and keeping it for 2h to 3h (such as 2h, 2.5h or 3h, etc.), and then using 850°C to 950°C (such as 850°C, 880°C, 900°C, 920°C or 950°C, etc.) as the final rolling temperature.

[0071] The temperature of the acid solution used for pickling can be 75°C to 85°C (such as 75°C, 80°C or 85°C, etc.), and the pickling speed can be 80m / min to 100m / min (such as 80m / min, 85m / min, 90m / min, 95m / min or 100m / min, etc.).

[0072] The cold rolling reduction rate can be 40% to 60% (such as 40%, 45%, 50%, 55% or 60%, etc.), and the thickness of the cold-rolled sheet obtained by cold rolling can be 1.4mm to 1.9mm (such as 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm or 1.9mm, etc.).

[0073] High temperature austenitizing quenching includes the following conditions: quenching temperature is 920℃~1120℃ (such as 920℃, 950℃, 980℃, 1000℃, 1050℃, 1100℃ or 1120℃, etc.), holding time is 8min~12min (such as 8min, 9min, 10min, 11min or 12min, etc.), and the final temperature after quenching cooling is 20℃~50℃ (such as 20℃, 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃, etc.).

[0074] In some preferred embodiments, the size of the original austenite grains in the quenched plate is 5 μm to 100 μm.

[0075] The critical region annealing treatment includes the following conditions: the annealing temperature is 790°C to 810°C (such as 790°C, 795°C, 800°C, 805°C or 810°C, etc.), the holding time is 8min to 12min (such as 8min, 9min, 10min, 11min or 12min, etc.), and the final temperature after annealing cooling is 20°C to 50°C (such as 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, etc.).

[0076] As mentioned above, in the production process of the above-mentioned high-strength and toughness cold-rolled dual-phase steel, with appropriate high-temperature austenitizing quenching and intercritical annealing process parameters, a dual-phase structure of long-slat ferrite + martensite can be obtained. Among them, high-temperature austenitizing quenching (920℃~1120℃) can coarsen the original austenite grains and provide a tissue basis for the formation of the dual-phase structure. Intercritical annealing (790℃~810℃) can obtain the final dual-phase structure of long-slat ferrite + martensite. The dual-phase steel prepared by this process flow and process parameters has a long-slat ferrite size of 5μm~80μm. This long-slat dual-phase structure can greatly improve the toughness of the dual-phase steel.

[0077] In addition, the present invention also provides an automobile component, the raw materials for preparing the automobile component include the above-mentioned high-strength and toughness cold-rolled dual-phase steel.

[0078] For example, automobile parts may include bumpers and side impact beams, etc.

[0079] By using the above-mentioned high-strength and toughness cold-rolled dual-phase steel as the raw material for preparing automotive parts, the comprehensive mechanical properties of automotive parts can be improved while ensuring lightweight.

[0080] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0081] Table 1 Chemical composition of each embodiment and comparative example

[0082] Steel Type C Si Mn Mo+Nb+Ti+V,V Fe Example 1, Comparative Examples 7 to 10 0.194 0.264 3.234 0.367，0.17 margin Example 2 0.196 0.262 3.229 0.312，0.16 margin Example 3 0.193 0.265 3.231 0.438，0.15 margin Example 4 0.151 0.113 0.586 0.216，0.11 margin Example 5 0.348 0.481 3.832 0.474，0.18 margin Example 6 0.194 0.264 3.234 0.367，0.1 margin Example 7 0.194 0.264 3.234 0.367，0.2 margin Comparative Example 1 0.191 0.266 3.233 0.346，0.13 margin Comparative Example 2 0.395 0.264 3.234 0.367，0.17 margin Comparative Example 3 0.194 0.616 3.234 0.367，0.12 margin Comparative Example 4 0.194 0.264 4.520 0.367，0.09 margin Comparative Example 5 0.194 0.264 3.234 0.673，0.16 margin Comparative Example 6 0.194 0.264 3.234 0.401，0 margin

[0083] Example 1

[0084] This embodiment provides a high-strength and toughness cold-rolled dual-phase steel with a long-strip ferrite structure, and a preparation method thereof comprises the following steps:

[0085] 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, which is then transferred to a reducing atmosphere furnace for refining to obtain refined molten steel, and the molten steel is continuously cast to obtain a steel billet;

[0086] S2: The steel billet obtained in S1 is placed in a walking beam heating furnace and heated at 1250°C for 2 hours to dissolve all the elements C, Si, Mn, V, Mo and Al;

[0087] S3: forging the steel billet after solid solution treatment of S2 at a forging temperature of 1175°C to obtain a forged billet;

[0088] S4: The forging billet obtained in S3 is heated to 1240°C at a starting rolling temperature of 1150°C and kept at that temperature for 2.5 hours, and then the final rolling temperature is 900°C to obtain a hot-rolled steel strip;

[0089] S5: pickling the hot-rolled steel strip obtained in S4, with the acid solution temperature being 80° C. and the pickling speed being 90 m / min;

[0090] S6: cold rolling the hot-rolled steel strip after pickling in S5, with a reduction rate of 50%, and the thickness of the cold-rolled sheet after 50% cold rolling is 1.85 mm;

[0091] S7: subjecting the cold-rolled sheet obtained in S6 to a high-temperature austenitizing quenching treatment, setting the austenitizing temperature to 1120°C, keeping the temperature for 10 minutes, and then cooling, with the final temperature being 35°C;

[0092] S8: The quenched plate obtained in S7 is subjected to intercritical zone annealing, the annealing temperature is set to 795°C, the temperature is kept for 10 minutes, and then cooled to a final temperature of 35°C to obtain a high-strength and toughness cold-rolled dual-phase steel.

[0093] Example 2

[0094] The difference between this embodiment and embodiment 1 is that: in S1, the chemical composition is different, as shown in Table 1; in S7, the austenitizing temperature is 1020°C.

[0095] Example 3

[0096] The difference between this embodiment and embodiment 1 is that: in S1, the chemical composition is different, as shown in Table 1; in S7, the austenitizing temperature is 920°C.

[0097] Example 4

[0098] This embodiment provides a high-strength and toughness cold-rolled dual-phase steel with a long-strip ferrite structure, and a preparation method thereof comprises 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, which is then transferred to a reducing atmosphere furnace for refining to obtain refined molten steel, and the molten steel is continuously cast to obtain a steel billet;

[0100] S2: The steel billet obtained in S1 is placed in a walking beam heating furnace and heated at 1220°C for 2.5 hours to dissolve all the elements C, Si, Mn, V, Mo and Al;

[0101] S3: forging the steel billet after solid solution treatment of S2 at a forging temperature of 1150°C to obtain a forged billet;

[0102] S4: The forging billet obtained in S3 is heated to 1210°C at a starting rolling temperature of 1110°C and kept at that temperature for 3 hours, and then the final rolling temperature is 850°C to obtain a hot-rolled steel strip;

[0103] S5: pickling the hot-rolled steel strip obtained in S4, with the acid solution temperature being 75° C. and the pickling speed being 80 m / min;

[0104] S6: cold rolling the hot-rolled steel strip after pickling in S5, with a reduction rate of 40%, and the thickness of the cold-rolled sheet after 40% cold rolling is 1.9 mm;

[0105] S7: subjecting the cold-rolled sheet obtained in S6 to a high-temperature austenitizing quenching treatment, setting the austenitizing temperature to 920°C, keeping the temperature for 12 minutes, and then cooling, with the final temperature being 20°C;

[0106] S8: The quenched plate obtained in S7 is subjected to intercritical zone annealing, the annealing temperature is set to 790°C, the temperature is kept for 12 minutes, and then cooled to a final temperature of 20°C to obtain a high-strength and toughness cold-rolled dual-phase steel.

[0107] Example 5

[0108] This embodiment provides a high-strength and toughness cold-rolled dual-phase steel with a long-strip ferrite structure, and a preparation method thereof comprises the following steps:

[0109] 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, which is then transferred to a reducing atmosphere furnace for refining to obtain refined molten steel, and the molten steel is continuously cast to obtain a steel billet;

[0110] S2: The steel billet obtained in S1 is placed in a walking beam heating furnace and heated at 1280°C for 1.5 hours to dissolve all the elements C, Si, Mn, V, Mo and Al;

[0111] S3: forging the steel billet after solid solution treatment of S2 at a forging temperature of 1200°C to obtain a forged billet;

[0112] S4: The forging billet obtained in S3 is heated to 1270°C at a starting rolling temperature of 1200°C and kept at that temperature for 2 hours, and then the final rolling temperature is 950°C to obtain a hot-rolled steel strip;

[0113] S5: pickling the hot-rolled steel strip obtained in S4, with the acid solution temperature being 85° C. and the pickling speed being 100 m / min;

[0114] S6: cold rolling the hot-rolled steel strip after pickling in S5, with a reduction rate of 60%, and the thickness of the cold-rolled sheet after 60% cold rolling is 1.4 mm;

[0115] S7: subjecting the cold-rolled sheet obtained in S6 to a high-temperature austenitizing quenching treatment, setting the austenitizing temperature to 1120°C, keeping the temperature for 8 minutes, and then cooling, with the final temperature being 50°C;

[0116] S8: The quenched plate obtained in S7 is subjected to intercritical zone annealing, the annealing temperature is set to 810°C, the temperature is kept for 8 minutes, and then cooled to a final temperature of 50°C to obtain a high-strength and toughness cold-rolled dual-phase steel.

[0117] Example 6

[0118] This embodiment provides a dual-phase steel, which is different from the embodiment 1 in that the content of V in the chemical composition is 0.1%.

[0119] Example 7

[0120] This embodiment provides a dual-phase steel, which is different from the embodiment 1 in that the content of V in the chemical composition is 0.2%.

[0121] Comparative Example 1

[0122] 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; in S7, the austenitizing temperature is 820°C.

[0123] Comparative Example 2

[0124] This comparative example provides a dual-phase steel, which is different from Example 1 in that the content of C in the chemical composition is 0.395%.

[0125] Comparative Example 3

[0126] This comparative example provides a dual-phase steel, which is different from Example 1 in that the content of Si in the chemical composition is 0.616%.

[0127] Comparative Example 4

[0128] This comparative example provides a dual-phase steel, which is different from Example 1 in that the content of Mn in the chemical composition is 4.520%.

[0129] Comparative Example 5

[0130] This comparative example provides a dual-phase steel, which is different from Example 1 in that the chemical composition of Mo+Nb+Ti+V is 0.673%.

[0131] Comparative Example 6

[0132] This comparative example provides a dual-phase steel, which is different from Example 1 in that V is not contained in the chemical composition.

[0133] Comparative Example 7

[0134] This comparative example provides a dual-phase steel, which differs from Example 1 in that the high-temperature austenitizing temperature is 900°C.

[0135] Comparative Example 8

[0136] This comparative example provides a dual-phase steel, which differs from Example 1 in that the high-temperature austenitizing temperature is 1150°C.

[0137] Comparative Example 9

[0138] This comparative example provides a dual-phase steel, which is different from Example 1 in that the intercritical region annealing temperature is 760°C.

[0139] Comparative Example 10

[0140] This comparative example provides a dual-phase steel, which is different from Example 1 in that the intercritical region annealing temperature is 840°C.

[0141] Test example

[0142] The tensile properties and fracture toughness tests and microstructure characterization of the dual-phase steels prepared in the above-mentioned embodiments and comparative examples were respectively carried out, and the results are shown in Table 2.

[0143] Among them, the yield strength is tested with reference to GB / T 228.1-2010, the tensile strength is tested with reference to GB / T228.1-2010, the uniform elongation is tested with reference to GB / T 228.1-2010, the elongation after fracture is tested with reference to GB / T 228.1-2010, the initial crack toughness is tested with reference to GB / T 21143-2012, the crack propagation toughness is tested with reference to GB / T 21143-2012, and the longest ferrite half-bar size is measured from the SEM image.

[0144] Taking Examples 1 to 3 and Comparative Example 1 as examples, the engineering stress-strain curves of these dual-phase steels are as follows: Figure 1 As shown, the fracture toughness curve is as follows Figure 2 As shown in the SEM images Figure 3 As shown, Figure 3 (a) to (d) correspond to Examples 1 to 3 and Comparative Example 1 respectively.

[0145] Table 2 Microstructure and mechanical properties of dual-phase steels prepared in various embodiments and comparative examples

[0146]

[0147] As can be seen from Table 2, the method of the present invention can be used to prepare high-strength and toughness cold-rolled dual-phase steel plates, which have excellent mechanical properties and suitable microstructures. In contrast, although Comparative Example 1 can also achieve the strength level and even better plasticity, its fracture toughness is much lower than that of the embodiment, and it does not have a long strip dual-phase structure.

[0148] In addition, it can be seen from Example 1 and Comparative Examples 2 to 10 in Table 2 that when the chemical composition is improperly set or the preparation conditions are improperly set, the prepared dual-phase steel will not have both good strength and toughness.

[0149] Depend on Figure 1 It can be seen that as the high-temperature austenitizing quenching temperature changes (920°C to 1120°C), the tensile strength and elongation after fracture of the dual-phase steels prepared in Examples 1 to 3 remain essentially unchanged, with the tensile strength maintained at 1418MPa to 1443MPa and the elongation after fracture maintained at 8.2% to 9.6%. In contrast, at the same tensile strength level, the elongation after fracture of Comparative Example 1 reaches 12.7%, which is the result of microstructure refinement.

[0150] Depend on Figure 2 It can be seen that the fracture toughness values ​​of the dual-phase steels prepared in Examples 1 to 3 are all maintained at a relatively high level, and the initial crack toughness is 74.2 kJ·m 0.5 ~109.7KJ·m 0.5 , crack extension toughness (Δa = 3mm) is 181.6KJ·m 0.5 ~258.2KJ·m 0.5 In contrast, the fracture toughness of comparative example 1 is very low, and its crack initial toughness is 6.6 KJ·m 0.5 , crack extension toughness (Δa = 3mm) is 15.5KJ·m 0.5 In general, the fracture toughness of the dual-phase steels prepared in Examples 1 to 3 is much higher than that in Comparative Example 1.

[0151] Depend on Figure 3 It can be seen that the dual-phase steels prepared in Examples 1 to 3 all exhibit a dual-phase structure with long lath ferrite, the maximum ferrite lath size of Example 1 is 80 μm, the maximum ferrite lath size of Example 2 is 30 μm, and the maximum ferrite lath size of Example 3 is 10 μm. In contrast, Comparative Example 1 exhibits an equiaxed dual-phase structure, and no long lath ferrite morphology can be observed.

[0152] In summary, the high-strength and toughness cold-rolled dual-phase steel plate produced by the present invention has a dual-phase steel structure of long-strip ferrite and martensite, high strength and good toughness. The dual-phase steel produced by the method of the present invention realizes the manufacturing and engineering application of ultra-high strength and high toughness dual-phase steel.

[0153] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-strength and toughness cold-rolled dual-phase steel, characterized in that: The chemical composition of the high-strength and toughness cold-rolled dual-phase steel includes, by weight percentage: 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 is Fe and impurity elements; The matrix structure of the high-strength and toughness cold-rolled dual-phase steel is long-strip ferrite and martensite.

2. The high-strength and toughness cold-rolled dual-phase steel according to claim 1, characterized in that: The chemical composition of the high-strength and 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, and the balance is Fe and impurity elements; Preferably, the content of V is 0.15% to 0.17%.

3. The high-strength and toughness cold-rolled dual-phase steel according to claim 2, characterized in that: The chemical composition of the high-strength and toughness cold-rolled dual-phase steel includes: 0.194% C, 0.264% Si, 3.234% Mn, 0.367% Mo+Nb+Ti+V, and the remainder is Fe and impurity elements.

4. The high-strength and toughness cold-rolled dual-phase steel according to any one of claims 1 to 3, characterized in that: The high-strength and toughness cold-rolled dual-phase steel also has at least one of the following characteristics: Feature 1: The size of the long strip ferrite in the high-strength and toughness cold-rolled dual-phase steel is 5 μm to 80 μm, preferably 10 μm to 80 μm; Feature 2: In the matrix structure of the high-strength and toughness cold-rolled dual-phase steel, the volume fraction of martensite is 60% to 90%, preferably 70% to 90%; Feature 3: The tensile strength of the high-strength and toughness cold-rolled dual-phase steel is not less than 1200 MPa, preferably 1200 MPa to 1443 MPa, and more preferably 1418 MPa to 1443 MPa; Feature 4: The yield strength of the high-strength and toughness cold-rolled dual-phase steel is not less than 410 MPa, preferably 410 MPa to 873 MPa, and more preferably 710 MPa to 873 MPa; Feature 5: The uniform elongation of the high-strength and toughness cold-rolled dual-phase steel is not less than 6.3%, preferably 6.3% to 7.0%; Feature 6: The elongation after fracture of the high-strength and toughness cold-rolled dual-phase steel is not less than 7.2%, preferably 7.2% to 9.6%, and more preferably 8.2% to 9.6%; Feature 7: The crack initial toughness of the high-strength and toughness cold-rolled dual-phase steel is not less than 74.2 KJ·m 0.5 , preferably 74.2KJ·m 0.5 ~109.7KJ·m 0.5 ; Feature 8: The crack extension toughness of the high-strength and toughness cold-rolled dual-phase steel at Δa = 3 mm is not less than 181.6 KJ·m 0.5 , preferably 181.6KJ·m 0.5 ~258.2KJ·m 0.5 .

5. A method for preparing high-strength and toughness cold-rolled dual-phase steel according to any one of claims 1 to 4, characterized in that: The following steps are involved: The raw materials are prepared according to the preset chemical composition of high-strength and toughness cold-rolled dual-phase steel.

6. The preparation method according to claim 5, 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.

7. The preparation method according to claim 5 or 6, characterized in that: The raw materials are melted, smelted, refined, continuously cast, smelted, forged, hot rolled, pickled, cold rolled, quenched and annealed.

8. The preparation method according to claim 7, characterized in that: 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 the C, Si, Mn, Mo, Nb, Ti, and V elements in the raw materials; the solid-solution 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 plate; the cold-rolled plate is subjected to high-temperature austenitizing quenching treatment to obtain a quenched plate; the quenched plate is subjected to intercritical zone annealing treatment to obtain the high-strength and toughness cold-rolled dual-phase steel.

9. The preparation method according to claim 8, characterized in that: The preparation process of the high-strength and toughness cold-rolled dual-phase steel includes at least one of the following features: Feature 9: Melting and smelting are carried out under oxidizing atmosphere conditions; feature 10: Refining is carried out under reducing atmosphere; Feature 11: The steel billet is heated at 1220°C to 1280°C for 1.5h to 2.5h; Feature 12: Forging temperature is 1150℃~1200℃; Feature 13: The rolling process includes: using 1100°C to 1200°C as the start rolling temperature, heating the forging billet to 1210°C to 1270°C for 2h to 3h, and then using 850°C to 950°C as the final rolling temperature; Feature 14: The temperature of the acid solution used for pickling is 75°C to 85°C, and the pickling speed is 80m / min to 100m / min; Feature 15: The cold rolling reduction rate is 40% to 60%, and the thickness of the cold-rolled sheet obtained by cold rolling is 1.4 mm to 1.9 mm; Feature 16: High-temperature austenitizing quenching includes the following conditions: quenching temperature is 920°C to 1120°C, holding time is 8min to 12min, and the final temperature after quenching cooling is 20°C to 50°C; preferably, the size of the original austenite grains in the quenched plate is 5μm to 100μm; feature 17: The critical region annealing treatment includes the following conditions: the annealing temperature is 790°C to 810°C, the holding time is 8min to 12min, and the final temperature after annealing cooling is 20°C to 50°C.

10. An automobile component, characterized in that: The raw materials for preparing the automobile parts include the high-strength and toughness cold-rolled dual-phase steel according to any one of claims 1 to 4.

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