A low-cost, low-yield ratio cold-rolled dual-phase steel and a method for manufacturing the same
By optimizing the C, Si, and Mn ratio and the medium-low temperature homogenization and slow cooling process, the problems of high yield strength ratio and high cost of cold-rolled duplex steel were solved, realizing the preparation of low-cost, low yield strength ratio cold-rolled duplex steel and improving the forming performance and safety performance of the material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HEBEI JINGYE WIDE BOARD TECH CO LTD
- Filing Date
- 2026-02-10
- Publication Date
- 2026-05-29
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention relates to the field of cold-rolled duplex steel technology, specifically to a low-cost, low-yield-strength-ratio cold-rolled duplex steel and its preparation method. Background Technology
[0002] Cold-rolled duplex steel CR340 / 590DP, as an advanced high-strength steel, effectively avoids local necking and improves the material's uniform deformation capability during the forming process due to its unique low yield strength ratio. Simultaneously, its high formability ensures high precision and a high yield rate in the stamping of complex automotive parts. These advantages make it one of the key materials for lightweighting and improving safety performance in automobiles, and it is widely used in the manufacture of core components such as structural and safety parts.
[0003] In traditional duplex steel production, limitations in equipment cooling and heating capabilities make it difficult to precisely control the phase transformation process and microstructure evolution when producing thicker strip steel. This results in a significant technical contradiction: while increasing material strength to meet application requirements, it is difficult to ensure a suitable low yield strength ratio. An excessively high yield strength ratio poses several risks to the application of cold-rolled duplex steel. On the one hand, a high yield strength ratio significantly reduces the material's uniform elongation and formability, making it prone to localized stress concentration during stamping, leading to localized necking or even cracking failure. This severely impacts the forming quality of complex-shaped automotive parts, resulting in a significant decrease in product qualification rate. On the other hand, materials with a high yield strength ratio have weak strain hardening capabilities and insufficient energy absorption under impact loads, failing to fully utilize their high strength advantages. This makes it difficult to meet the stringent requirements for impact toughness and deformation resistance in automotive safety components, posing a potential threat to overall vehicle safety.
[0004] In existing technologies, to reduce the yield strength ratio, the common practice is to add 0.2% to 0.3% Cr, or to use a combination of one or two elements from Cr, Mo, Ti, Nb, and V (where the total amount of Cr+Mo+Ti+Nb+V does not exceed 0.5%), in order to improve the nucleation rate of the microstructure during recovery, recrystallization, and austenitic phase transformation, thereby improving strength and stamping performance. However, the Mn content in the traditional C, Si, Mn system is usually higher than 1.70%, and the addition of excessively high alloying elements will lead to increased costs, making it difficult to meet the current industry's demand for cost reduction and efficiency improvement.
[0005] Therefore, it is very necessary to develop a low-cost, low-yield-strength-ratio cold-rolled dual-phase steel. Summary of the Invention
[0006] This invention proposes a low-cost, low yield strength ratio cold-rolled duplex steel and its preparation method, which solves the problems of high cost and high yield strength ratio of cold-rolled duplex steel in related technologies.
[0007] The technical solution of the present invention is as follows: The present invention proposes a low-cost, low yield strength ratio cold-rolled dual-phase steel, which is composed of the following components by weight percentage: C 0.06%~0.09%, Si 0.44%~0.57%, Mn 1.5%~1.65%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities, wherein Mn:(C+Si)=2.5~3.
[0008] As a further technical solution, the thickness of the low-cost, low-yield-strength-ratio cold-rolled duplex steel is 0.8~2mm.
[0009] This invention also proposes a method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel, comprising the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated before rolling, hot rolled, coiled, pickled, continuously annealed and finished to obtain the low-cost, low yield strength ratio cold-rolled dual-phase steel.
[0010] As a further technical solution, the temperature of the pre-rolling heating is 1200~1250℃.
[0011] As a further technical solution, the hot rolling includes roughing and finishing rolling, wherein the initial rolling temperature of the roughing rolling is 1100~1260℃, the initial rolling temperature of the finishing rolling is 840~920℃, and the final rolling temperature of the finishing rolling is 800~820℃.
[0012] As a further technical solution, the winding temperature is 620~640℃.
[0013] As a further technical solution, the continuous annealing includes the following steps: the pickled strip is preheated to 220~230℃, then heated to 780~790℃ at a heating rate of 2~5℃ / s, held at that temperature, then cooled to 620~640℃ in the first stage, then cooled to 260~270℃ in the second stage, and finally cooled to room temperature after aging. The cooling rates of the first stage cooling and the second stage cooling are different.
[0014] In the preparation process of cold-rolled duplex steel of this invention, a specific combination of medium-low temperature homogenization heating (780~790℃) and medium-low temperature slow cooling (620~640℃) is adopted to achieve precise control over the quantity, composition and distribution morphology of austenite, and finally obtain an ideal microstructure, which makes the martensite fine and dispersed, inhibits the formation of bainite and banded structure, and effectively reduces the yield strength ratio of cold-rolled duplex steel.
[0015] In the preparation process of cold-rolled duplex steel of this invention, the pickled and rolled strip is heated and held at a certain temperature before being slowly cooled to 620~640℃. This temperature needs to be precisely controlled, as it is crucial for promoting the transformation of austenite into ferrite within the material; and this transformation is the fundamental reason for improving the material's plasticity. The cooling rate and final cooling temperature of the second stage are key to ensuring a certain amount of martensite.
[0016] As a further technical solution, the heating rate of the preheated strip is 8~10℃ / s.
[0017] As a further technical solution, the cooling rate of the first stage of cooling is 15~20℃ / s, and the cooling rate of the second stage of cooling is 30~35℃ / s.
[0018] In the preparation process of the cold-rolled duplex steel of this invention, the first stage involves medium-speed cooling to 620-640℃, providing sufficient time and suitable thermodynamic conditions for the complete transformation of austenite into ferrite, promoting the formation of a sufficiently large amount of fine and uniform ferrite matrix. This matrix can improve the material's plasticity through coordinated deformation. The second stage involves high-speed cooling to 260-270℃, which rapidly inhibits further ferrite transformation and promotes the rapid formation of fine and dispersed martensite second phase from untransformed austenite, avoiding coarse or aggregated martensite. By adjusting the cooling rate in both cooling processes, the yield strength ratio of the cold-rolled duplex steel is effectively reduced.
[0019] As a further technical solution, the heat preservation time is 200~220s.
[0020] The working principle and beneficial effects of this invention are as follows: In this invention, the Mn content in the cold-rolled dual-phase steel is reduced to 1.5%~1.65% compared to traditional techniques that require additional expensive alloying elements such as Cr, Mo, Ti, Nb, and V, without adding any expensive microalloying elements. Simultaneously, by optimizing the ratio of C, Si, and Mn, performance is synergistically improved, reducing the amount of high-cost alloying elements and simplifying the composition system. By limiting the content range of C, Si, and Mn and controlling the Mn:(C+Si) ratio to 2.5~3, the proportion and morphology of the ferrite and martensite dual-phase structure can be precisely controlled, effectively avoiding local necking during forming, improving the material's uniform deformation capability, reducing the cost of cold-rolled dual-phase steel, and lowering its yield strength ratio. Detailed Implementation
[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0022] Example 1 A low-cost, low-yield-strength-ratio cold-rolled dual-phase steel is composed of the following components by weight percentage: C 0.06%, Si 0.44%, Mn 1.5%, P 0.011%, S 0.003%, with the balance being Fe and unavoidable impurities; A method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel includes the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated to 1200℃ before rolling, rough rolling begins at 1100℃, finish rolling begins at 840℃, finish rolling ends at 800℃, and after coiling at 620℃, it is pickled. The pickled strip is preheated to 220℃ at a heating rate of 8℃ / s, then heated to 780℃ at a heating rate of 2℃ / s, held for 220s, cooled to 620℃ at a cooling rate of 15℃ / s, and then cooled to 260℃ at a cooling rate of 30℃ / s. After aging, it is finally cooled to room temperature for finishing, resulting in a low-cost, low-yield-strength-ratio cold-rolled duplex steel with a thickness of 1mm.
[0023] Example 2 A low-cost, low-yield-strength-ratio cold-rolled dual-phase steel is composed of the following components by weight percentage: C 0.08%, Si 0.50%, Mn 1.55%, P 0.009%, S 0.002%, with the balance being Fe and unavoidable impurities; A method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel includes the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated to 1225℃ before rolling, rough rolling begins at 1150℃, finish rolling begins at 900℃, finish rolling ends at 810℃, and after coiling at 630℃, it is pickled. The pickled strip is preheated to 225℃ at a heating rate of 9℃ / s, then heated to 785℃ at a heating rate of 3℃ / s, held for 210s, cooled to 630℃ at a cooling rate of 18℃ / s, and then cooled to 265℃ at a cooling rate of 32℃ / s. After aging, it is finally cooled to room temperature for finishing, resulting in a low-cost, low yield strength ratio cold-rolled duplex steel with a thickness of 1mm.
[0024] Example 3 A low-cost, low-yield-strength-ratio cold-rolled dual-phase steel is composed of the following components by weight percentage: C 0.09%, Si 0.57%, Mn 1.65%, P 0.005%, S 0.003%, with the balance being Fe and unavoidable impurities; A method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel includes the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated to 1250℃ before rolling, rough rolling begins at 1260℃, finish rolling begins at 920℃, finish rolling ends at 820℃, and after coiling at 640℃, it is pickled. The pickled strip is preheated to 230℃ at a heating rate of 10℃ / s, then heated to 790℃ at a heating rate of 5℃ / s, held for 200s, and then cooled to 640℃ at a cooling rate of 20℃ / s, and then cooled to 270℃ at a cooling rate of 35℃ / s. After aging, it is finally cooled to room temperature for finishing, resulting in a low-cost, low-yield-strength-ratio cold-rolled duplex steel with a thickness of 1mm.
[0025] Example 4 Compared with Example 2, Example 4 differs in that it includes a method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel, comprising the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated to 1225℃ before rolling, rough rolling begins at 1150℃, finish rolling begins at 900℃, finish rolling ends at 810℃, and after coiling at 630℃, it is pickled. The pickled strip is preheated to 225℃ at a heating rate of 9℃ / s, then heated to 750℃ at a heating rate of 3℃ / s, held for 210s, cooled to 600℃ at a cooling rate of 18℃ / s, and then cooled to 265℃ at a cooling rate of 32℃ / s. After aging, it is finally cooled to room temperature for finishing, resulting in a low-cost, low yield strength ratio cold-rolled duplex steel with a thickness of 1mm.
[0026] Example 5 Compared with Example 2, Example 5 differs in that it includes a method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel, comprising the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated to 1225℃ before rolling, rough rolling begins at 1150℃, finish rolling begins at 900℃, finish rolling ends at 810℃, and after coiling at 630℃, it is pickled. The pickled strip is preheated to 225℃ at a heating rate of 9℃ / s, then heated to 820℃ at a heating rate of 3℃ / s, held for 210s, cooled to 680℃ at a cooling rate of 18℃ / s, and then cooled to 265℃ at a cooling rate of 32℃ / s. After aging, it is finally cooled to room temperature for finishing, resulting in a low-cost, low yield strength ratio cold-rolled duplex steel with a thickness of 1mm.
[0027] Example 6 Compared with Example 2, Example 6 differs in that the method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel includes the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated to 1225℃ before rolling, rough rolling begins at 1150℃, finish rolling begins at 900℃, finish rolling ends at 810℃, and after coiling at 630℃, it is pickled. The pickled strip is preheated to 225℃ at a heating rate of 9℃ / s, then heated to 785℃ at a heating rate of 3℃ / s, held for 210s, and then cooled to 265℃ at a cooling rate of 18℃ / s. After aging, it is finally cooled to room temperature for finishing, resulting in a low-cost, low yield strength ratio cold-rolled duplex steel with a thickness of 1mm.
[0028] Example 7 Compared with Example 2, Example 7 differs in that the method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel includes the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated to 1225℃ before rolling, rough rolling begins at 1150℃, finish rolling begins at 900℃, finish rolling ends at 810℃, and after coiling at 630℃, it is pickled. The pickled strip is preheated to 225℃ at a heating rate of 9℃ / s, then heated to 785℃ at a heating rate of 3℃ / s, held for 210s, and then cooled to 265℃ at a cooling rate of 32℃ / s. After aging, it is finally cooled to room temperature for finishing, resulting in a low-cost, low yield strength ratio cold-rolled duplex steel with a thickness of 1mm.
[0029] Example 8 Compared with Example 2, Example 8 differs in that it includes a method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel, comprising the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated to 1225℃ before rolling, rough rolling begins at 1150℃, finish rolling begins at 900℃, finish rolling ends at 810℃, and after coiling at 630℃, it is pickled. The pickled strip is preheated to 225℃ at a heating rate of 9℃ / s, then heated to 785℃ at a heating rate of 3℃ / s, held for 210s, cooled to 630℃ at a cooling rate of 10℃ / s, and then cooled to 265℃ at a cooling rate of 32℃ / s. After aging, it is finally cooled to room temperature for finishing, resulting in a low-cost, low yield strength ratio cold-rolled duplex steel with a thickness of 1mm.
[0030] Example 9 Compared with Example 2, Example 9 differs in that the method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel includes the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated to 1225℃ before rolling, rough rolling begins at 1150℃, finish rolling begins at 900℃, finish rolling ends at 810℃, and after coiling at 630℃, it is pickled. The pickled strip is preheated to 225℃ at a heating rate of 9℃ / s, then heated to 785℃ at a heating rate of 3℃ / s, held for 210s, cooled to 630℃ at a cooling rate of 18℃ / s, and then cooled to 265℃ at a cooling rate of 40℃ / s. After aging, it is finally cooled to room temperature for finishing, resulting in a low-cost, low yield strength ratio cold-rolled duplex steel with a thickness of 1mm.
[0031] Comparative Example 1 Compared with Example 2, Comparative Example 1 differs in that the low-cost, low-yield-strength-ratio cold-rolled dual-phase steel in this comparative example is composed of the following components by weight percentage: C 0.08%, Si 0.57%, Mn 1.50%, P 0.009%, S 0.002%, with the balance being Fe and unavoidable impurities.
[0032] Comparative Example 2 Compared with Example 2, Comparative Example 2 differs in that the low-cost, low-yield-strength-ratio cold-rolled dual-phase steel in this comparative example is composed of the following components by weight percentage: C 0.08%, Si 0.44%, Mn 1.65%, P 0.009%, S 0.002%, with the balance being Fe and unavoidable impurities.
[0033] Experimental Example 1 The yield strength and tensile strength of the cold-rolled duplex steels prepared in Examples 1-9 and Comparative Examples 1-2 were tested according to the test methods specified in GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test method at room temperature", and the yield strength ratio was calculated.
[0034] The test results are shown in Table 1: Table 1 Performance test results of Examples 1-9 and Comparative Examples 1-2
[0035] Table 1 shows that when the composition of cold-rolled duplex steel is within the specified range and Mn:(C+Si)=2.5~3, the yield strength ratio of the cold-rolled duplex steel can be reduced. When the strip after pickling and rolling undergoes a process of medium-low temperature homogenization at 780~790℃ and slow cooling at 620~640℃ during the preparation of cold-rolled duplex steel, the yield strength ratio can be further reduced. When a continuous annealing process employs a two-stage cooling method, with the first stage cooling rate at 15~20℃ / s and the second stage cooling rate at 30~35℃ / s, the yield strength ratio of the obtained cold-rolled duplex steel is even lower.
[0036] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A low-cost, low-yield-strength-ratio cold-rolled dual-phase steel, characterized in that, It consists of the following components by weight percentage: C 0.06%~0.09%, Si 0.44%~0.57%, Mn 1.5%~1.65%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities, wherein Mn:(C+Si)=2.5~3.
2. The low-cost, low-yield-strength-ratio cold-rolled duplex steel according to claim 1, characterized in that, The thickness of the low-cost, low-yield-strength-ratio cold-rolled duplex steel is 0.8~2mm.
3. A method for preparing low-cost, low-yield-strength-ratio cold-rolled dual-phase steel, used to prepare the low-cost, low-yield-strength-ratio cold-rolled dual-phase steel according to any one of claims 1-2, characterized in that, Includes the following steps: S1. After mixing according to the target composition, the mixture is melted, deoxidized, refined, and continuously cast to obtain a billet. S2. The billet is heated before rolling, hot rolled, coiled, pickled, continuously annealed and finished to obtain the low-cost, low yield strength ratio cold-rolled dual-phase steel.
4. The method for preparing low-cost, low-yield-strength-ratio cold-rolled duplex steel according to claim 3, characterized in that, The temperature of the pre-rolling heating is 1200~1250℃.
5. The method for preparing low-cost, low-yield-strength-ratio cold-rolled duplex steel according to claim 3, characterized in that, The hot rolling includes roughing and finishing rolling. The initial rolling temperature of the roughing rolling is 1100~1260℃, the initial rolling temperature of the finishing rolling is 840~920℃, and the final rolling temperature of the finishing rolling is 800~820℃.
6. The method for preparing low-cost, low-yield-strength-ratio cold-rolled duplex steel according to claim 3, characterized in that, The winding temperature is 620~640℃.
7. The method for preparing low-cost, low-yield-strength-ratio cold-rolled duplex steel according to claim 3, characterized in that, The continuous annealing includes the following steps: the pickled strip is preheated to 220~230℃, then heated to 780~790℃ at a heating rate of 2~5℃ / s, held at that temperature, cooled to 620~640℃ in the first stage, then cooled to 260~270℃ in the second stage, and finally cooled to room temperature after aging. The cooling rates of the first stage cooling and the second stage cooling are different.
8. The method for preparing low-cost, low-yield-strength-ratio cold-rolled duplex steel according to claim 7, characterized in that, The heating rate of the strip preheating is 8~10℃ / s.
9. The method for preparing low-cost, low-yield-strength-ratio cold-rolled duplex steel according to claim 7, characterized in that, The cooling rate of the first stage of cooling is 15~20℃ / s, and the cooling rate of the second stage of cooling is 30~35℃ / s.
10. The method for preparing a low-cost, low-yield-strength-ratio cold-rolled duplex steel according to claim 7, characterized in that, The heat preservation time is 200~220s.