980MPa-grade low-yield-ratio hot-rolled dual-phase steel and manufacturing method thereof
By optimizing the chemical composition and process parameters of 980MPa grade low yield strength ratio hot-rolled dual-phase steel, the problem of efficient production of ferrite and martensite dual-phase structure during hot rolling was solved, achieving high strength, low yield strength ratio and good processing performance, meeting the needs of engineering machinery.
Patent Information
- Application Number
- CN202511013366.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-23
- Publication Date
- 2025-10-17
AI Technical Summary
Existing technologies make it difficult to efficiently obtain a dual-phase microstructure of ferrite and martensite during hot rolling, resulting in a high yield strength ratio, poor processing performance, and a long and inefficient production process.
By optimizing the chemical composition and process parameters of 980MPa grade low yield strength ratio hot-rolled dual-phase steel, including smelting, continuous casting, hot rolling, laminar cooling and leveling processes, the ferrite ratio is controlled to be 60-70%, and segmented cooling and segmented leveling are adopted to achieve high-efficiency production.
We produce 980MPa grade low yield strength ratio hot-rolled duplex steel with high strength, low yield strength ratio and easy processing, which meets the needs of the construction machinery industry. The process is short, low cost and high efficiency.
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Figure CN120796823A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of steel metallurgy, and particularly relates to a 980MPa-grade low yield ratio hot-rolled dual-phase steel and a manufacturing method thereof. BACKGROUND
[0002] Lightweight and high-strength steel are the development trends of the engineering machinery industry, but as the strength of steel continues to rise, higher requirements are put forward for processing equipment, and users need to modify or newly build the processing equipment, thereby increasing the use cost. Therefore, it is urgent to develop high-strength, low-yield ratio and easy-to-process materials.
[0003] By developing a ferrite + martensite dual-phase steel, the martensite structure is used to ensure a relatively high tensile strength of the material, and the ferrite is used to reduce the yield strength, so as to reduce the yield ratio of the material and improve the processing performance of the material. However, the current production process mainly uses a cold rolling process, which is long and low in efficiency. It is still a technical problem to efficiently obtain a ferrite + martensite dual-phase structure in a hot rolling process and ensure that the ferrite proportion is 60-70%. SUMMARY
[0004] To solve the above-mentioned technical problems in the prior art, the present application provides a 980MPa-grade low yield ratio hot-rolled dual-phase steel and a manufacturing method thereof.
[0005] In one aspect of the present application, the manufacturing method of the 980MPa-grade low yield ratio hot-rolled dual-phase steel comprises the following steps:
[0006] (1) Smelting and continuous casting
[0007] The chemical composition of the steel is optimized and controlled according to mass percentage by converter smelting and secondary refining: C: 0.10-0.18%, Si: 1.1-1.5%, Mn: 1.4-1.8%, P≤0.020%, S≤0.0250%, Ti: 0.010-0.040%, Cr: 0.1-0.2%, Al: 0.02-0.06%, and the rest is Fe and inevitable impurities. Then, the molten steel meeting the above composition requirements is continuously cast into a slab;
[0008] (2) Hot rolling
[0009] The slab is heated to 1250-1320℃, a single-stand reciprocating rough rolling mill is used to rough roll the slab into an intermediate billet, and then a multi-stand hot continuous rolling mill is used to finish rolling the intermediate billet into a steel plate with a target thickness, and the finish rolling temperature is controlled to be 860-900℃;
[0010] (3) Laminar cooling
[0011] The steel plate is cooled by laminar cooling, wherein the laminar cooling adopts a segmented cooling process, including three-stage cooling, wherein the front stage adopts laminar cooling water to cool the steel plate to 600-700 DEG C, the middle stage adopts air cooling, the air cooling stage length is controlled to be more than 50 meters, the air cooling time is controlled to be more than 6s, the rear stage adopts upper and lower water groups for intensive cooling, the water ratio of the upper and lower water groups is 10:12, the cooling speed is controlled to be greater than or equal to 80 DEG C / s, and the steel plate is cooled to below 150 DEG C and coiled into a steel coil;
[0012] (4) flattening
[0013] The steel coil is flattened by adopting a segmented flattening process, wherein the flattening pressure of the steel plate head and tail 60 meters is controlled to be 900-1000 tons, and the flattening pressure of other positions of the steel plate is controlled to be 600-800 tons.
[0014] Further, in the above-mentioned 980MPa grade low yield ratio hot-rolled dual-phase steel manufacturing method, in the smelting and continuous casting step, the roller electromagnetic stirring is put into the continuous casting process.
[0015] Further, in the above-mentioned 980MPa grade low yield ratio hot-rolled dual-phase steel manufacturing method, in the hot-rolling step, the intermediate billet thickness is controlled to be less than or equal to 40mm.
[0016] Further, in the above-mentioned 980MPa grade low yield ratio hot-rolled dual-phase steel manufacturing method, the thickness of the obtained hot-rolled dual-phase steel plate material is 3-8mm.
[0017] In another aspect of the present application, the chemical composition of the provided 980MPa grade low yield ratio hot-rolled dual-phase steel is as follows in terms of mass percentage: C: 0.10-0.18%, Si: 1.1-1.5%, Mn: 1.4-1.8%, P≤0.020%, S≤0.0250%, Ti: 0.010-0.040%, Cr: 0.1-0.2%, Al: 0.02-0.06%, and the rest is Fe and inevitable impurities.
[0018] Preferably, the chemical composition of the above-mentioned 980MPa grade low yield ratio hot-rolled dual-phase steel is as follows in terms of mass percentage: C: 0.13-0.16%, Si: 1.1-1.3%, Mn: 1.5-1.8%, P≤0.020%, S≤0.0250%, Ti: 0.010-0.025%, Cr: 0.15-0.2%, Al: 0.02-0.04%, and the rest is Fe and inevitable impurities.
[0019] Further, the microstructure of the above-mentioned 980MPa grade low yield ratio hot-rolled dual-phase steel is mainly ferrite and martensite dual-phase structure, wherein the ferrite proportion is 60-70%.
[0020] Further, the 980MPa grade low yield ratio hot-rolled dual-phase steel has a yield strength of 600-700MPa, a tensile strength of ≥980MPa, an elongation of ≥12%, a yield ratio of ≤0.7, and a flatness of ≤7mm / m.
[0021] The 980MPa grade low yield ratio hot-rolled dual-phase steel and the manufacturing method thereof have the following advantages and beneficial effects:
[0022] The 980MPa grade low yield ratio hot-rolled dual-phase steel is produced by optimizing the chemical composition and controlling the process parameters of slab heating, hot rolling, laminar cooling and leveling in the production process. The metallographic structure of the 980MPa grade low yield ratio hot-rolled dual-phase steel is mainly ferrite and martensite dual-phase structure, in which the proportion of ferrite is 60-70%. The steel has high strength, low yield ratio, excellent plate shape, easy forming, yield strength ReL of 600-700MPa, tensile strength Rm of ≥980MPa, elongation A50 of ≥12%, yield ratio of ≤0.7, cold bending (D=5a, 90°) qualification, and flatness of ≤7mm / m. The steel meets the demand of the engineering machinery industry for high-strength and easy-to-form materials, and has the advantages of short process flow, low manufacturing cost and high processing efficiency. BRIEF DESCRIPTION OF DRAWINGS
[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only used to further understand the embodiments of the present application and form a part of the present application. For those skilled in the art, other drawings can also be obtained without creative labor based on these drawings. In the drawings:
[0024] Figure 1 The figure is the metallographic structure of the 980MPa grade low yield ratio hot-rolled dual-phase steel of the embodiment 1 of the present application. DETAILED DESCRIPTION
[0025] In order to make the purpose, technical solutions and advantages of the present application more clear, the following will combine the specific embodiments of the present application and the corresponding drawings to clearly and completely describe the technical solutions of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.
[0026] The 980MPa-grade low yield ratio hot-rolled dual-phase steel provided by the application takes C, Si, Mn, Ti and Cr as main elements, adds ferrite forming element Si to facilitate the generation of ferrite structure, adds C, Cr and Mn elements with good hardenability to obtain martensite structure, and on this basis, plays the solid solution strengthening of Si and Mn elements and the fine grain strengthening of Ti element to further improve the strength of the material to reach 980MPa grade. Specifically, the chemical composition of the 980MPa-grade low yield ratio hot-rolled dual-phase steel according to the application is controlled as follows in terms of mass percentage: C: 0.10-0.18%, Si: 1.1-1.5%, Mn: 1.4-1.8%, P≤0.020%, S≤0.0250%, Ti: 0.010-0.040%, Cr: 0.1-0.2%, Al: 0.02-0.06%, and the rest is Fe and inevitable impurities.
[0027] The reasons for the chemical composition design in the 980MPa-grade low yield ratio hot-rolled dual-phase steel according to the application are as follows:
[0028] Carbon C is the most economical strengthening element in steel and is also a strong hardenability element. The content of C element has a significant impact on the strength of martensite structure. Too low C content will result in insufficient strength, but too high C content will result in poor cold bending performance of the material. Therefore, the C content is controlled to be 0.10-0.18% in the application, preferably 0.13-0.16%.
[0029] Silicon Si is an element that expands the dual-phase zone, improves the stability of austenite during cooling after hot rolling, accelerates the precipitation of ferrite, promotes the enrichment of carbon in austenite, and improves the hardness of martensite. Too low Si content cannot achieve the above effects, and too high Si content will deteriorate the surface quality of the steel. Therefore, the Si content is controlled to be 1.1-1.5% in the application, preferably 1.1-1.3%.
[0030] Manganese Mn is an economical solid solution strengthening element commonly used to improve the yield strength and tensile strength of steel. However, too high Mn content will reduce the plasticity of the steel and increase the carbon equivalent, resulting in poor welding performance. Therefore, the Mn content is controlled to be 1.4-1.8% in the application, preferably 1.5-1.8%.
[0031] Chromium Cr is a hardenability element that helps to generate martensite and thus improve the strength of the material. Too low Cr content cannot achieve the effect of improving hardenability, and too high Cr content is not conducive to cost control. Therefore, the Cr content is controlled to be 0.1-0.2% in the application, preferably 0.15-0.2%.
[0032] Niobium Ti is mainly used to play the role of fine grain strengthening and precipitation strengthening to improve the strength of the material. Therefore, the Ti content is controlled to be 0.010-0.040% in the application, preferably 0.010-0.025%.
[0033] Al mainly plays a role in removing oxygen from molten steel, and the Al content is controlled to be 0.02-0.06% in the present application. When the Al content is greater than the maximum value of the present application, the flowability of the molten steel is reduced. When the Al content is less than the minimum value of the present application, the deoxidation of the steel is insufficient, and subcutaneous bubbles are easily formed in the casting blank. Preferably, the Al content is 0.02-0.04%.
[0034] P and S are harmful elements in steel, and the lower the content, the better. Therefore, the P content is controlled to be ≤0.020% and the S content is controlled to be ≤0.025% in the present application.
[0035] The manufacturing method of the 980MPa-grade low yield ratio hot-rolled dual-phase steel provided by the present application relies on a hot continuous rolling mill group, adopts a smelting and continuous casting→hot rolling→laminar cooling→leveling process route, and produces the 980MPa-grade low yield ratio hot-rolled dual-phase steel through a short-process hot rolling process, and specifically includes the following steps:
[0036] (1) Smelting and continuous casting
[0037] The chemical composition of the steel is optimized and controlled according to mass percentage through converter smelting and secondary refining (LF+RH) to be C: 0.10-0.18%, Si: 1.1-1.5%, Mn: 1.4-1.8%, P≤0.020%, S≤0.0250%, Ti: 0.010-0.040%, Cr: 0.1-0.2%, Al: 0.02-0.06%, and the rest is Fe and inevitable impurities, and then the molten steel prepared according to the above composition requirements is continuously cast into a slab. Roll-type electromagnetic stirring is used in the continuous casting process to eliminate center deviation.
[0038] (2) Hot rolling
[0039] The slab is heated to 1250-1320℃, a single-stand reciprocating rough rolling mill group is used to rough roll the slab into an intermediate blank with a thickness of less than 40mm, and then a multi-stand hot continuous rolling mill group is used to finish rolling the intermediate blank into a steel plate with a target thickness, and the finish rolling temperature is controlled to be 860-900℃.
[0040] In the above hot rolling step, the slab is heated at a relatively high heating temperature, so that the micro-alloying elements are fully solid-solved, and at the same time, the rolling load is reduced. The thickness of the intermediate blank is controlled to be less than 40mm, so that the finish rolling load is reduced and the rolling stability is ensured. The finish rolling temperature is reasonably controlled to be 860-900℃, so that the rolling load is not large due to the low finish rolling temperature, which is not conducive to the plate shape quality, and the grain is not coarse due to the high finish rolling temperature, which is not conducive to the strength improvement.
[0041] (3) Laminar cooling
[0042] The steel plate is cooled by laminar cooling, wherein the laminar cooling adopts a segmented cooling process, including three-stage cooling, wherein the front stage adopts laminar cooling water to water cool the steel plate to 600-700 DEG C, to reach the thermodynamic and kinetic conditions for easy formation of ferrite; the middle stage adopts air cooling, the air cooling stage length is controlled to be more than 50 meters, and the air cooling time is controlled to be more than 6s, to ensure sufficient ferrite formation; the rear stage adopts upper and lower water groups for strong cooling, the water ratio of the upper and lower water groups is 10:12, the cooling speed is controlled to be greater than or equal to 80 DEG C / s, the steel plate is cooled to below 150 DEG C and coiled into a steel coil, so that the remaining austenite organization is transformed into martensite organization.
[0043] (4) flattening
[0044] The steel coil is flattened by adopting a segmented flattening process, wherein the head and tail 60 meters of the steel plate are not uniformly cooled due to no tension constraint in the laminar cooling process, and the original plate shape is poor, so large flattening pressure is adopted to improve the plate shape, that is, the flattening pressure of the head and tail 60 meters of the steel plate is controlled to be 900-1000 tons; the original plate shape of other positions of the steel plate is good, and normal flattening pressure is adopted, that is, the flattening pressure of other positions of the steel plate is controlled to be 600-800 tons, so that the plate shape of the steel plate after flattening is stable and controllable by reasonably adjusting the flattening pressure.
[0045] As a specific embodiment, in the manufacturing method of the 980MPa-grade low yield ratio hot-rolled dual-phase steel of the present application, the thickness of the hot-rolled dual-phase steel plate prepared is 3-8mm.
[0046] Through actual production detection, the 980MPa-grade low yield ratio hot-rolled dual-phase steel of the present application has a structure mainly in ferrite and martensite dual-phase structure, wherein the ferrite proportion is 60-70%, the yield strength ReL is 600-700MPa, the tensile strength Rm is greater than or equal to 980MPa, the elongation A50 is greater than or equal to 12%, the yield ratio is less than or equal to 0.7, the cold bending (D=5a, 90 DEG) is qualified, and the unevenness of the steel plate is less than or equal to 7mm / m.
[0047] The 980MPa-grade low yield ratio hot-rolled dual-phase steel and the manufacturing method thereof of the present application are further described below in combination with specific embodiments.
[0048] Embodiment 1
[0049] The 980MPa-grade low yield ratio hot-rolled dual-phase steel plate and the manufacturing method thereof of the present application are further described below in combination with specific embodiments.
[0050] The manufacturing method of the 980MPa grade low yield ratio hot-rolled dual-phase steel of the embodiment 1 specifically comprises the following steps:
[0051] (1) Smelting and continuous casting
[0052] The chemical composition of the steel is optimized and controlled according to mass percentage through converter smelting and secondary refining (LF+RH) as follows: C: 0.14%, Si: 1.30%, Mn: 1.65%, P: 0.012%, S: 0.011%, Ti: 0.018%, Cr: 0.17%, Al: 0.030%, and the rest is Fe and inevitable impurities, and then the molten steel meeting the above composition requirements is continuously cast into a slab with a thickness of 230mm.
[0053] (2) Hot rolling
[0054] The slab is heated to 1280℃, and the single-stand reciprocating rough rolling mill is used to rough roll the slab into an intermediate slab with a thickness of 35mm, and then the multi-stand hot continuous rolling mill is used to finish rolling the intermediate slab into a steel plate with a target thickness of 4mm, and the finish rolling temperature is controlled to be 880℃.
[0055] (3) Laminar cooling
[0056] The steel plate is cooled through laminar cooling, wherein the laminar cooling adopts a segmented cooling process, including three-stage cooling, wherein the front stage adopts laminar cooling water to cool the steel plate to 630℃, the middle stage adopts air cooling, the air cooling length is 55 meters, the air cooling time is 8-10s, the rear stage adopts upper and lower water groups for intensive cooling, the water ratio of the upper and lower water groups is 10:12, and the cooling speed is ≥80℃ / s, and the steel plate is cooled to below 150℃ and coiled.
[0057] (4) Leveling
[0058] The steel coil is leveled by adopting a segmented leveling process, wherein the leveling pressure of the steel plate head and tail 60 meters is 950 tons, and the leveling pressure of other positions of the steel plate is 700 tons.
[0059] The metallographic structure of the 980MPa grade low yield ratio hot-rolled dual-phase steel of the embodiment 1 of the application is mainly ferrite and martensite dual-phase structure, wherein the ferrite proportion is 60-70%, and the microstructure diagram is shown in Figure 1 , and through actual production detection, the yield strength ReL of the 980MPa grade low yield ratio hot-rolled dual-phase steel of the embodiment 1 of the application is 635MPa, the tensile strength Rm is 1076MPa, the elongation A50 is 15%, the cold bending (D=5a, 90°) is qualified, the yield ratio is 0.59, and the maximum unevenness of the steel plate is 5mm / m.
[0060] Other embodiments
[0061] The chemical composition (mass percentage, %) of the 980MPa grade low yield ratio hot-rolled dual-phase steel of other embodiments is shown in Table 1.
[0062] Table 1 Chemical composition (unit: %) of the 980MPa grade low yield ratio hot-rolled dual-phase steel of other embodiments
[0063] Examples C Si Mn P S Ti Cr Al Example 2 0.13 1.26 1.65 0.009 0.012 0.021 0.18 0.04 Example 3 0.14 1.15 1.67 0.008 0.010 0.016 0.17 0.04 Example 4 0.15 1.18 1.58 0.007 0.013 0.018 0.17 0.03 Example 5 0.15 1.25 1.65 0.009 0.012 0.020 0.19 0.03 Example 6 0.15 1.20 1.73 0.010 0.010 0.023 0.18 0.04
[0064] The process parameters of the manufacturing method of the 980MPa grade low yield ratio hot-rolled dual-phase steel of other embodiments are shown in Table 2.
[0065] Table 2 Process parameters of the manufacturing method of the 980MPa grade low yield ratio hot-rolled dual-phase steel of other embodiments
[0066]
[0067] The performance test results of the 980MPa grade low yield ratio hot-rolled dual-phase steel of other embodiments are shown in Table 3.
[0068] Table 3 Performance of the 980MPa grade low yield ratio hot-rolled dual-phase steel of other embodiments
[0069]
[0070] In summary, the 980MPa grade low yield ratio hot-rolled dual-phase steel and the manufacturing method thereof of the present application are optimized by chemical composition, and combined with the process parameter control of slab heating, hot rolling, laminar cooling and leveling in the production process. The 980MPa grade low yield ratio hot-rolled dual-phase steel produced has a microstructure mainly of ferrite and martensite dual-phase, with a ferrite proportion of 60-70%, high strength, low yield ratio, excellent plate shape, easy forming, yield strength ReL of 600-700MPa, tensile strength Rm≥980MPa, elongation A50≥12%, yield ratio ≤0.7, cold bending (D=5a, 90°) qualified, steel plate unevenness ≤7mm / m, meeting the demand of the engineering machinery industry for high-strength, easy-to-form materials, and having the advantages of short process flow, low manufacturing cost, high processing efficiency, etc.
[0071] It should be noted that the terms and phrases herein have the meanings commonly understood by those skilled in the art, unless otherwise indicated. Also, when a range of values is disclosed, the disclosure is to be construed to include both the minimum and maximum values, as well as every value between the minimum and maximum values. Further, when a range of integers is disclosed, every integer within the range is included. In addition, when multiple ranges are provided, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be construed as including any and all sub-ranges falling within the range.
[0072] It is also to be noted that, as used herein, the terms "comprise" or "comprising" or any other variation thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.
[0073] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the present application.
Claims
1. A method for manufacturing 980MPa grade low yield ratio hot-rolled dual-phase steel, characterized in that: The steps include: (1) Smelting and continuous casting The chemical composition of the steel is optimized and controlled by mass percentage through converter smelting and external refining to be: C: 0.10-0.18%, Si: 1.1-1.5%, Mn: 1.4-1.8%, P≤0.020%, S≤0.0250%, Ti: 0.010-0.040%, Cr: 0.1-0.2%, Al: 0.02-0.06%, with the remainder being Fe and unavoidable impurities. The molten steel obtained by smelting and meeting the above composition requirements is then continuously cast into slabs. (2) Hot rolling The slab is heated to 1250-1320℃, and is rough-rolled into an intermediate billet using a single-stand reciprocating roughing mill. The intermediate billet is then finish-rolled into a steel plate of target thickness using a multi-stand hot rolling mill. The final rolling temperature is controlled at 860-900℃. (3) Laminar cooling The steel plate is cooled by laminar cooling, wherein the laminar cooling adopts a segmented cooling process, including three cooling stages. In the front stage, laminar cooling water is used to cool the steel plate to 600-700°C, the middle stage is air-cooled, and the length of the air-cooling stage is controlled to be more than 50 meters, and the air-cooling time is controlled to be more than 6 seconds. The rear stage uses upper and lower water groups for strong cooling, and the water ratio of the upper and lower water groups is 10:
12. The cooling rate is controlled to be ≥80°C / s. The steel plate is cooled to below 150°C and coiled into a steel coil; (4) Leveling The steel coil is leveled using a segmented leveling process, in which the leveling pressure at the head and tail 60 meters of the steel plate is controlled at 900 to 1,000 tons, and the leveling pressure at other positions of the steel plate is controlled at 600 to 800 tons.
2. The method for manufacturing 980 MPa grade low yield ratio hot-rolled dual-phase steel according to claim 1, characterized in that: During the smelting and continuous casting steps, roller electromagnetic stirring is used in the continuous casting process.
3. The method for manufacturing 980 MPa grade low yield ratio hot-rolled dual-phase steel according to claim 1, characterized in that: During the hot rolling step, the intermediate bar thickness is controlled to be less than 40 mm.
4. The method for manufacturing 980 MPa grade low yield ratio hot-rolled dual-phase steel according to claim 1, characterized in that: The thickness of the prepared hot-rolled dual-phase steel plate is 3 to 8 mm.
5. A 980MPa grade low yield ratio hot-rolled dual-phase steel, characterized in that: The chemical composition of the 980 MPa grade low yield ratio hot-rolled dual-phase steel is as follows by mass percentage: C: 0.10-0.18%, Si: 1.1-1.5%, Mn: 1.4-1.8%, P≤0.020%, S≤0.0250%, Ti: 0.010-0.040%, Cr: 0.1-0.2%, Al: 0.02-0.06%, and the rest is Fe and unavoidable impurities.
6. The 980 MPa grade low yield ratio hot-rolled dual-phase steel according to claim 5, characterized in that: The chemical composition of the 980 MPa grade low yield ratio hot-rolled dual-phase steel is as follows by mass percentage: C: 0.13-0.16%, Si: 1.1-1.3%, Mn: 1.5-1.8%, P≤0.020%, S≤0.0250%, Ti: 0.010-0.025%, Cr: 0.15-0.2%, Al: 0.02-0.04%, and the rest is Fe and unavoidable impurities.
7. The 980 MPa grade low yield ratio hot rolled dual phase steel according to claim 5, characterized in that: The microstructure of the 980MPa grade low yield ratio hot-rolled dual-phase steel is mainly composed of a ferrite and martensite dual-phase microstructure, wherein the proportion of ferrite is 60-70%.
8. The 980 MPa grade low yield ratio hot-rolled dual-phase steel according to claim 5, characterized in that: The 980MPa grade low yield ratio hot rolled dual phase steel has a yield strength of 600-700MPa, a tensile strength of ≥980MPa, an elongation of ≥12%, a yield ratio of ≤0.7, and a steel plate unevenness of ≤7mm / m.