A low-cost copper-containing twip steel with high yield strength and a preparation process thereof
By using low-cost composition design and warm/cold rolling processes to prepare high-yield-strength TWIP steel, the problems of insufficient yield strength and high production cost of TWIP steel are solved, achieving a combination of high strength and plasticity, and simplifying the process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- FUZHOU UNIV
- Filing Date
- 2024-01-17
- Publication Date
- 2026-07-07
AI Technical Summary
The yield strength of existing TWIP steel is not ideal, and traditional methods to improve yield strength increase production costs and complexity. Too many alloying elements make smelting difficult, and copper-containing TWIP steel is prone to cracking.
By employing a low-cost composition design, including elements such as C, Mn, Cu, Nb, Ti, or Al, and combining warm rolling and cold rolling processes, controlling the heat treatment temperature and time, and suppressing the precipitation of Cu-rich phases, high yield strength TWIP steel can be prepared.
It achieves a combination of high yield strength and plasticity, reduces production costs and smelting difficulty, avoids steel surface cracking, improves scrap steel utilization, and simplifies the preparation process.
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Figure CN117867401B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of steel material preparation, and relates to a low-cost copper-containing TWIP steel with high yield strength and its preparation process. Background Technology
[0002] TWIP steel is considered the most promising advanced high-strength steel for automotive applications due to its excellent mechanical properties, formability, and impact energy absorption capacity. Although high-manganese austenitic steel has good comprehensive properties, its yield strength is often not ideal. Based on this problem, many scholars are looking for methods to improve the yield strength of high-manganese steel while ensuring its good plastic deformation capacity.
[0003] Modern research on Cu-containing steels shows that the precipitation of Cu phases in steel leads to precipitation strengthening, significantly improving steel strength. For high-manganese steel, Cu, as an austenite stabilizing element, has high solid solubility in austenite and is a common strengthening element in alloy steels. Furthermore, Cu can increase the stacking fault energy of alloys, promote twinning mechanisms, and expand the austenite region, theoretically benefiting the microstructure stability, mechanical properties, and corrosion resistance of TWIP steel. Meanwhile, the Cu content in the central and southern iron ore regions of my country is relatively high (0.2%–1.0%), making research on the influence of Cu on the microstructure and properties of TWIP steel important for its composition design and industrial production. However, the solubility of Cu in austenite, the easy penetration of the copper-rich liquid phase at grain boundaries, and the low melting point of the copper-rich phase all increase the tendency for cracking. Therefore, Cu is generally considered a harmful element in steel and is controlled. The most direct way to solve the surface cracking problem in Cu-containing steel is to add the alloying element Ni, making the atomic ratio of Ni to Cu in the steel 1:2. Ni can promote the formation of high-melting-point Cu-rich phases and seal them within the oxide scale, thus preventing the low-melting-point Cu-rich phases from existing at the body / oxide scale interface, effectively preventing cracking. However, adding Ni significantly increases the production cost of steel and affects its production and application.
[0004] Although the Fe–Mn–C series copper-containing TWIP steel invented by Joong-Ki Hwang et al. (Materials Science & Engineering A, 2018, 737) has few element types, its yield strength is 297–311 MPa and its tensile strength is 861–916 MPa, indicating low mechanical properties. Currently, methods to improve the performance of copper-containing TWIP steel mainly fall into two categories: increasing the carbon content and adding trace amounts of various alloying elements such as Cr and Ni. Patent CN101956134A discloses a high-strength, high-ductility copper-containing high-carbon TWIP steel with a yield strength of 580 MPa, a tensile strength of 1212 MPa, and an elongation of 77%. Patent CN101429590A discloses a method for preparing a high-carbon twin-induced plasticity steel material with a yield strength of 575 MPa, a tensile strength of 1150 MPa, and an elongation of 56%. However, the high carbon content makes TWIP steel have poor weldability. In particular, the preparation process of patent CN101429590A is relatively complex and the production cost is high, which greatly limits the production and application of TWIP steel. Patents CN116121662A, CN115976303A, CN115537677A, CN115491614A, CN113637908A, CN114717484A, CN112281074A, CN112955577A, and CN112912529A disclose some steels with yield strengths ranging from 250 to 1300 MPa. However, these steels contain a large amount of Cr and microalloying elements such as Nb, Ti, and V. This excessive variety of alloying elements increases the difficulty of the steel smelting process, especially in the smelting of large ingots. The elements are difficult to mix evenly, and compositional segregation is likely to occur, which has a significant impact on the performance of the smelted steel. Excessive use of alloying elements, especially high levels of Ni and Cr, significantly increases steel production costs, raises prices, and affects applications. Furthermore, on October 27, 2017, the International Agency for Research on Cancer (IARC) of the World Health Organization published a preliminary list of carcinogens, which placed nickel metal and nickel alloys in Group 2B and chromium metal in Group 3, posing potential health risks.
[0005] Meanwhile, in all the above patents, the rolling process is hot rolling, with a temperature above 1000℃. Excessive temperature increases the risk of smelting and also increases the cost of smelting. Summary of the Invention
[0006] The purpose of this invention is to provide a low-cost copper-containing TWIP steel with high yield strength and its preparation process. This preparation process is simple to operate and low in cost. By adding Cu as an alloying element to the steel and combining it with a specific heat treatment process, a TWIP steel with high yield strength and plasticity is obtained, further strengthening the connection between theoretical research and practical applications of TWIP steel.
[0007] A low-cost copper-containing TWIP steel material with high yield strength has the following composition by mass percentage (wt.%): C: 0.1~0.6%, Mn: 19~24%, Cu: 0.5~5.2%, Nb: 0.02-0.15%, Ti: 0.02-0.15%, Al: 0.7~1.2%, with the balance being Fe and unavoidable impurities, wherein Al, Ti, and Nb are selectively added. The preparation includes the following steps:
[0008] 1) Smelting: Add C: 0.1~0.6%, Mn: 19~24%, Cu: 0.5~5.2%, Nb: 0.02-0.15%, Ti: 0.02-0.15%, Al: 0.7~1.2%, which can be added selectively according to the mechanical property requirements (Al, Ti, and Nb are optional, only one of them is added), with the balance being Fe, in a proportional manner to vacuum melt in an electromagnetic induction furnace, protected by argon gas, and then cast into shape;
[0009] 2) Solution treatment: The alloy obtained in step 1) is heated to 600~650℃ for solution treatment and held at that temperature for 1~3 hours;
[0010] 3) Warm rolling: The sample obtained in step 2) is quickly placed in the rolling mill for rolling. The initial rolling temperature is 600~650℃, and the final rolling temperature is maintained at 500~630℃. The total rolling deformation is 50%~70%. The above deformation is completed through 5 rolling passes. After each rolling pass, the temperature is heated to 600℃ and held for 10 minutes.
[0011] 4) Cold rolling: The sample treated in step 3) is subjected to controlled rolling in a two-roll mill in multiple passes. The deformation amount of each rolling pass is controlled at 10~20%, the thickness after rolling is 1.0~1.2mm, and the total rolling deformation is 70~90%.
[0012] 5) Heat treatment: Anneal the cold-rolled alloy at 600~1000℃, hold for 10~20min, and then quickly quench it in water.
[0013] The alloy prepared by the above steps has a yield strength of 650~760MPa, a tensile strength of 970~1100MPa, and an elongation of 50~70%.
[0014] The present invention has the following advantages:
[0015] (1) Excellent performance. This invention utilizes traditional rolling and heat treatment techniques to produce steels with excellent mechanical properties, especially yield strength, which far exceeds that of other traditional TWIP steels.
[0016] (2) Rational utilization of Cu element. Traditional steel materials control Cu as a harmful element, but Cu in scrap steel is unavoidable. This invention suppresses the precipitation and enrichment of Cu-rich phases by controlling the temperature and time of heat treatment and rolling, which can effectively avoid the problem of surface cracking of copper-containing steel and rationally utilize the copper element in scrap steel, thereby improving the utilization rate of scrap steel. This saves resources and protects the environment while developing new materials.
[0017] (3) The preparation process is simple. The rolling process of warm rolling plus cold rolling is adopted to ensure strength while maximizing its plasticity. Moreover, the rolling temperature is relatively low, which significantly reduces the cost and difficulty of industrial production.
[0018] (4) Low cost. The steel material of the present invention has fewer types of elements, with no more than 5 types of each component element, which significantly reduces the cost of the material and the difficulty of smelting. Attached Figure Description
[0019] Figure 1 These are the engineering stress-strain curves of alloys in Examples 1-4. Detailed Implementation
[0020] The present invention will now be described in detail with reference to the accompanying drawings.
[0021] The present invention and its embodiments are described below. This description is not restrictive, and the actual embodiments are not limited thereto.
[0022] This is the limitation. In conclusion, if anyone skilled in the art, inspired by this invention, designs a similar structure and embodiment without departing from the spirit of the invention, and without creative effort, such design should fall within the scope of protection of this invention.
[0023] Example 1
[0024] The composition of low-cost copper-containing TWIP steel with high yield strength is as follows: by mass fraction (wt.%), its chemical composition is: C: 0.4%, Mn: 22%, Cu: 3%, Nb: 0.06%, with the balance being Fe and unavoidable impurities.
[0025] Melting: Vacuum melting is carried out in an electromagnetic induction furnace with argon protection, and then cast into slabs.
[0026] Solution treatment: Heat the sample to 600℃ and keep it at that temperature for 2 hours for uniform treatment.
[0027] Warm rolling: The solution-treated sample is warm rolled on a two-roll mill to obtain a hot-rolled sheet with a thickness of about 5.6 mm and a total deformation of 61%. The initial rolling temperature and the final rolling temperature are 600℃ and 550℃, respectively. After each rolling pass, the sample is put back into the furnace and heated to 600℃ for 10 minutes. After the last holding pass, it is water quenched. A total of 5 rolling passes are performed.
[0028] Cold rolling: The warm-rolled sample is subjected to controlled rolling in multiple passes on a two-roll mill. The deformation amount of each rolling pass is controlled at about 15%, and the thickness after rolling is about 1.2 mm. The total deformation amount of rolling is 79%.
[0029] Recrystallization recovery: The cold-rolled alloy was held at 750℃ for 20 minutes and then water-quenched.
[0030] The room temperature mechanical properties of this alloy are: yield strength of 650 MPa, tensile strength of 1063 MPa, and elongation of 64%.
[0031] Example 2
[0032] The composition of low-cost copper-containing TWIP steel with high yield strength is as follows: by mass fraction (wt.%), its chemical composition is: C: 0.4%, Mn: 22%, Cu: 3%, Ti: 0.06%, with the balance being Fe and unavoidable impurities.
[0033] Melting: Vacuum melting is carried out in an electromagnetic induction furnace with argon protection, and then cast into slabs.
[0034] Solution treatment: Heat the sample to 600℃ and keep it at that temperature for 2 hours for uniform treatment.
[0035] Warm rolling: The solution-treated sample is warm rolled on a two-roll mill to obtain a hot-rolled sheet with a thickness of about 5.6 mm and a total deformation of 61%. The initial rolling temperature and the final rolling temperature are 600℃ and 550℃, respectively. After each rolling pass, the sample is put back into the furnace and heated to 600℃ for 10 minutes. After the last holding pass, it is water quenched. A total of 5 rolling passes are performed.
[0036] Cold rolling: The warm-rolled sample is subjected to controlled rolling in multiple passes on a two-roll mill. The deformation amount of each rolling pass is controlled at about 15%, and the thickness after rolling is about 1.2 mm. The total deformation amount of rolling is 79%.
[0037] Recrystallization recovery: The cold-rolled alloy was held at 750℃ for 20 minutes and then water-quenched.
[0038] The room temperature mechanical properties of this alloy are: yield strength of 657 MPa, tensile strength of 1071 MPa, and elongation of 64%.
[0039] Example 3
[0040] Composition of low-cost copper-containing TWIP steel with high yield strength: Its chemical composition by mass fraction (wt.%) is: C: 0.4%, Mn: 22%, Cu: 1.5%, Al: 1%, with the balance being Fe and unavoidable impurities.
[0041] Melting: Vacuum melting is carried out in an electromagnetic induction furnace with argon protection, and then cast into slabs.
[0042] Solution treatment: Heat the sample to 600℃ and keep it at that temperature for 2 hours for uniform treatment.
[0043] Warm rolling: The solution-treated sample is warm rolled on a two-roll mill to obtain a hot-rolled sheet with a thickness of about 5.6 mm and a total deformation of 61%. The initial rolling temperature and the final rolling temperature are 600℃ and 550℃, respectively. After each rolling pass, the sample is put back into the furnace and heated to 600℃ for 10 minutes. After the last holding pass, it is water quenched. A total of 5 rolling passes are performed.
[0044] Cold rolling: The warm-rolled sample is subjected to controlled rolling in multiple passes on a two-roll mill. The deformation amount of each rolling pass is controlled at about 15%, and the thickness after rolling is about 1.2 mm. The total deformation amount of rolling is 79%.
[0045] Recrystallization recovery: The cold-rolled alloy was held at 600℃ for 20 minutes and then water-quenched.
[0046] The room temperature mechanical properties of this alloy are: a yield strength of 700 MPa, a tensile strength of 977 MPa, and an elongation of 54%.
[0047] Example 4
[0048] Composition of low-cost copper-containing TWIP steel with high yield strength: Its chemical composition by mass fraction (wt.%) is: C: 0.4%, Mn: 22%, Cu: 0.5%, Al: 1%, with the balance being Fe and unavoidable impurities.
[0049] Melting: Vacuum melting is carried out in an electromagnetic induction furnace with argon protection, and then cast into slabs.
[0050] Solution treatment: Heat the sample to 600℃ and keep it at that temperature for 2 hours for uniform treatment.
[0051] Warm rolling: The solution-treated sample is warm rolled on a two-roll mill to obtain a hot-rolled sheet with a thickness of about 5.6 mm and a total deformation of 61%. The initial rolling temperature and the final rolling temperature are 600℃ and 550℃, respectively. After each rolling pass, the sample is put back into the furnace and heated to 600℃ for 10 minutes. After the last holding pass, it is water quenched. A total of 5 rolling passes are performed.
[0052] Cold rolling: The warm-rolled sample is subjected to controlled rolling in multiple passes on a two-roll mill. The deformation amount of each rolling pass is controlled at about 15%, and the thickness after rolling is about 1.2 mm. The total deformation amount of rolling is 79%.
[0053] Recrystallization recovery: The cold-rolled alloy was held at 600℃ for 20 minutes and then water-quenched.
[0054] The room-temperature mechanical properties of this alloy are: a yield strength of 760 MPa, a tensile strength of 1026 MPa, and an elongation of 50%.
[0055] Figure 1 These are the engineering stress-strain curves of alloys in Examples 1-4. The sawtooth pattern on the curves reflects the onset of twinning deformation. As another mechanism of plastic deformation, twinning often nucleates at high stress concentration points, and the stress required for twin nucleation is much greater than the stress required for twin growth (dislocation sliding). Therefore, when twinning occurs, the stress-strain curve shows a sudden drop; the sawtooth undulations on the curve are caused by twin formation. This indicates that during deformation, a large number of fine deformation twins are formed, resulting in a twinning-induced plasticity effect. First, twinning is induced at the location of maximum tensile deformation. The twin boundaries prevent slip in this region, leading to dislocation pile-up and hindering further local deformation. This causes deformation to shift to a lower strain region, delaying necking and increasing the overall elongation of the material. Second, a large number of deformation twins penetrate and divide the austenite grains, subsequently forming even finer secondary deformation twins that are interwoven within the austenite grains, hindering dislocation slip and improving the material's work hardening ability. TWIP steel thus achieves very high tensile strength. Finally, the twins and austenite have a coherent relationship, effectively hindering crack propagation. Macroscopically, this delays fracture and increases uniform elongation. Thus, the alloy maintains high plasticity while possessing high strength. Meanwhile, trace microalloying elements Al, Ti, and Nb are strong carbide-forming elements, which can play a role in grain refinement and precipitation strengthening of manganese steel.
[0056] Table 1. Performance comparison of various embodiments of the present invention with other copper-containing TWIP steels.
[0057]
[0058] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.
Claims
1. A process for preparing high-yield-strength, low-cost copper-containing TWIP steel, characterized in that: The chemical composition of the TWIP steel, by mass percentage, is: C: 0.1-0.6%, Mn: 19-24%, Cu: 0.5-5.2%, Nb: 0.02-0.15%, Ti: 0.02-0.15%, Al: 0.7-1.2%, with the balance being Fe and unavoidable impurities; wherein Al, Ti, and Nb are selectively added; the preparation process includes the following steps: 1) Melting: C, Mn, Cu, Nb or Ti or Al, Fe are added to an electromagnetic induction furnace in proportion for vacuum melting, protected by argon gas, and then cast into shape; 2) Solution treatment: The alloy obtained in step 1) is heated to 600~650℃ for solution treatment and held at that temperature for 1~3 hours; 3) Warm rolling: The sample obtained in step 2) is quickly placed on a two-roll mill for rolling. The initial rolling temperature is 600~650℃, and the final rolling temperature is maintained at 500~630℃. The total rolling deformation is 50%~70%. The above deformation is completed through 5 passes of rolling. After each pass, the temperature is heated to 600℃ and held for 10 minutes. 4) Cold rolling: The sample treated in step 3) is subjected to controlled rolling in multiple passes on a two-roll mill. The deformation amount of each rolling pass is controlled at 10~20%, the thickness after rolling is 1.0-1.2mm, and the total rolling deformation is 70~90%. 5) Heat treatment: Anneal the cold-rolled alloy at 600~1000℃, hold for 10~20min, and then quickly quench it in water.