Process for preparing heavy cold-rolled + superplastic medium-manganese steel without orientation difference

Abstract

The application relates to a heavy cold rolling + superplastic preparation process of anisotropy-free medium manganese steel, the chemical components of the medium manganese steel include, in percentage by weight, C: 0.1-0.4%, Mn: 2-12%, Al: 0.5-4%, Si: 0.5-4%, and the balance is Fe; the preparation method comprises the following steps: smelting molten steel according to the chemical components of the medium manganese steel, pouring the molten steel into ingots, forging the ingots into slabs, air cooling to room temperature, and cutting to obtain a plate; the plate blank is sequentially subjected to heavy cold rolling deformation, superplastic deformation and normal-temperature mechanical evaluation test, and finally anisotropy-free medium manganese steel plate containing a metastable austenite and ferrite dual phase and having a uniform orientation is prepared, and the subsequent mechanical test is excellent, which helps to develop the automobile superplastic forming and normal-temperature forming combined process.

Description

Technical Field

[0001] This invention relates to the field of medium manganese steel preparation technology, and in particular to a heavy-duty cold rolling + superplastic preparation process for non-oriented differential medium manganese steel. Background Technology

[0002] In recent years, medium-manganese steel materials have rapidly emerged in the research field, mainly due to their lower cost and superior mechanical properties of high strength and toughness. Medium-manganese steel plates have become one of the representatives of third-generation advanced automotive steels. However, the traditional manufacturing process of medium-manganese steel plates generally adopts the traditional rolling process. The traditional rolling process generally results in grain orientation differences in the plates, which leads to certain directional properties of the metal plates, i.e., anisotropy. This has a negative impact on the subsequent plate forming process and is one of the causes of wrinkling and cracking.

[0003] Medium manganese steel containing 2%-12% Mn generally exhibits a dual-phase structure of ferrite (BCC) and austenite (FCC) at room temperature. However, the proportion of the two phases and the grain size vary depending on the element ratio, heat treatment process, and processing technology. In this type of steel, the austenite has moderate stability at room temperature and can undergo the TRIP / TWIP effect during room temperature deformation, thereby effectively improving its comprehensive mechanical properties in cold deformation processes. This makes it a typical representative of advanced automotive steel.

[0004] Traditional rolling deformation processes involve high hot rolling temperatures, leading to oxidation of medium-manganese steel sheets. This not only results in higher material losses but also causes oxide and decarburized layers to form on the surface of the rolled sheet, causing differences in performance between the core and surface layers, ultimately leading to a loss of mechanical properties. Furthermore, the traditional hot-rolling-cold-rolling-critical annealing process introduces anisotropy into the sheet material. The presence of rolling texture results in variations in the mechanical properties of the metal sheet in different directions, which also limits its application and development to some extent. Summary of the Invention

[0005] The purpose of this invention is to provide a heavy-duty cold rolling + superplastic preparation process for non-oriented manganese steel. The heavy-duty cold rolling process gives the manganese steel sheet a large mechanical energy, while the superplastic stretching deformation process achieves secondary thinning of the manganese steel sheet during cold rolling. At the same time, it ensures the dynamic recrystallization of austenite and ferrite in the microstructure, the martensite reversal transformation and grain rotation occur simultaneously, and finally prepares a uniform fine-grained manganese steel sheet with no texture strength.

[0006] The technical solution adopted in this invention is as follows:

[0007] The present invention proposes a heavy-duty cold rolling + superplastic preparation process for non-oriented differential medium manganese steel, wherein the medium manganese steel comprises the following chemical composition by weight percentage: C: 0.1-0.4%, Mn: 2-12%, Al: 0.5-4%, Si: 0.5-4%, with the balance being Fe;

[0008] The preparation process includes the following steps:

[0009] S1. According to the above chemical composition of medium manganese steel, molten steel is smelted and cast into ingots. The ingots are then forged into slabs, air-cooled to room temperature, and cut into plates. The forging furnace temperature is 1150-1250℃. The forging is carried out on an air hammer using free forging. The initial forging temperature is controlled at 1100-1200℃, and the final forging temperature is ≥1100℃. The forging is carried out into square block billets, air-cooled to room temperature, and the slabs are cut into plates using medium wire cutting speed.

[0010] S2. Perform heavy-duty cold rolling on wire-cut sheet metal;

[0011] S3. Perform superplastic deformation on the final heavy-duty cold-rolled manganese sheet: Perform superplastic tensile deformation on the heavy-duty cold-rolled sheet;

[0012] S4. Perform subsequent mechanical evaluation tests and microscopic characterization on the sheet material after superplastic deformation.

[0013] Furthermore, the medium manganese steel also includes one or more of the following chemical components by weight percentage: Ni: 0.1-3.0%; Nb: 0-0.3%; Cu: 0.5-2.0%.

[0014] Furthermore, in step S1, during the forging process of the ingot, the ingot is first heated to 1100-1200℃ and held at that temperature for 1.5-2.5 hours.

[0015] Furthermore, in step S2, the cold rolling deformation is 75% to 90%, the cold rolling deformation passes are 4, the cold rolling deformation per pass is 20%, a heat preservation process is used between two adjacent rolling passes, the annealing temperature range is 300℃ to 400℃, the heat preservation time is 3-6 min, the maximum annealing temperature is 1000℃, the heating furnace heating section is 30℃ / min, the heating time range is 10-15 min, and then it is taken out with metal clamps and quickly placed in water for cooling by water quenching.

[0016] Furthermore, in step S3, the temperature-controlled heating rate is 25℃ / min, the target temperature is reached and held for 5 minutes before superplastic tensile deformation, the superplastic deformation temperature range is 700℃~800℃, and the superplastic strain rate range is 10. -2 s -1 ~10- 1 s -1 The superplastic deformation ranges from 200% to 400%.

[0017] Furthermore, in step S4, the subsequent mechanical evaluation test adopts a room temperature tensile test of the sheet metal with a tensile rate of 10. -3 s -1 Quasi-static tensile rate until fracture.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The medium-manganese steel provided by this invention uses a special ratio of elemental components. Generally, the addition of C and Mn elements can stabilize the austenite phase and achieve the effect of preserving the austenite phase at room temperature. Therefore, the C content ranges from 0.1% to 0.4%, and the Mn content ranges from 2% to 12%. At the same time, the addition of Al element can effectively broaden the two-phase temperature range of medium-manganese steel. The superplastic deformation temperature range is generally half the melting point of the alloy material. By reasonably controlling the Al element content, the two-phase temperature range of medium-manganese steel can be highly overlapped with the recrystallization temperature range and the superplastic deformation temperature range. This is a key step in achieving improved superplastic deformation of heavily cold-rolled medium-manganese steel plates. Therefore, the control of Al element content is very important. Through experimental control, the mass percentage of Al element ranges from 0.5% to 4%.

[0020] 2. The dual-phase structure designed in this invention, namely the austenite-ferrite dual-phase structure, is due to the solute exchange between the austenite and ferrite dual-phase components during superplastic deformation. That is, C and Mn elements are enriched towards austenite, while Al and Si are enriched towards ferrite. The solute drag effect caused by this dual-phase structure is also the key to achieving superplasticity of manganese steel in this invention.

[0021] 3. To ensure the preparation of uniform and anisotropic medium-manganese steel plates, a combination of heavy cold rolling and superplastic deformation processes is used. The heavy cold rolling process employs large deformation, with a cold rolling deformation of 75% to 90%. Heavy cold rolling ensures the storage of a large amount of deformation energy during the deformation process, while also enabling the near-complete breaking of all grains of different grades in the original forged plate. This ensures that the grain size remains consistent during dynamic recrystallization in the superplastic deformation of the plate. At the same time, the large deformation ensures the triggering of dynamic recrystallization during superplastic deformation.

[0022] 4. In the superplastic preparation process of the sheet material of this invention, the superplastic deformation temperature is 650℃-750℃, and the strain rate is 10. -2 -10 -3The deformation range is 250%–400% per second, and the temperature range is selected to ensure dynamic recrystallization. Both superplastic deformation triggering and martensitic reverse transformation occur simultaneously within this range. The range of deformation rate and amount for superplastic sheet metal is selected to ensure the triggering of the superplastic deformation mechanism. Specifically, within this strain rate and strain range, grain rotation and grain boundary slip can be achieved, ensuring the disappearance of cold-rolled texture, thus eliminating the anisotropy of medium-manganese steel sheet metal, while simultaneously preventing the formation of voids due to superplastic deformation.

[0023] 5. Compared with the traditional hot rolling + cold rolling + critical annealing process, the traditional process is cumbersome, and hot rolling causes severe oxidation of medium manganese steel sheets. In contrast, this invention uses a heavy-duty cold rolling process and a superplastic deformation process to prepare non-textured isotropic medium manganese steel sheets, eliminating the need for hot rolling and critical annealing, thus optimizing the process. Attached Figure Description

[0024] Figure 1 This is a heat treatment process route diagram for the heavy-duty cold rolling + superplastic deformation process in this invention;

[0025] Figure 2 This is the dimensional drawing of the subsequent mechanical tensile drawing of this invention;

[0026] Figure 3 This is a graph showing the subsequent mechanical properties of the product after heavy cold rolling and superplastic deformation in the experimental examples of this invention.

[0027] Figure 4 These are ODF diagrams of austenitic structures under different superplastic deformation amounts in the experimental examples of this invention;

[0028] Figure 5 This is a heat treatment process route diagram for the traditional hot rolling + cold rolling + critical annealing process in Comparative Example 1.

[0029] Figure 6 This is the ODF diagram of the medium-manganese steel sheet under the traditional process route in Comparative Example 1;

[0030] Figure 7 This is a SEM image of Comparative Example 2 with a superplastic deformation of 450%;

[0031] Figure 8 This is the engineering stress-strain curve diagram of the superplastic deformation in Comparative Example 3;

[0032] Figure 9 This is a stress-strain curve diagram of the subsequent mechanical property test project under low cold rolling deformation in Comparative Example 4.

[0033] Figure 10 This invention uses Thermo-calc thermodynamic calculation software to simulate phase diagrams. Detailed Implementation

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] The present invention proposes a heavy-duty cold-rolling + superplastic preparation process for non-oriented differential manganese steel, such as... Figures 1 to 10 As shown, the specific implementation process is as follows:

[0036] The present invention proposes a heavy-duty cold rolling + superplastic preparation process for non-oriented differential medium manganese steel, wherein the medium manganese steel comprises the following chemical composition by weight percentage: C: 0.1-0.4%, Mn: 2-12%, Al: 0.5-4%, Si: 0.5-4%, with the balance being Fe;

[0037] The preparation process includes the following steps:

[0038] S1. According to the weight percentage, take the above-mentioned chemical composition of medium manganese steel to smelt molten steel, cast it into ingots, and then forge the ingots into slabs. The forging temperature is 1150-1250℃. The slabs are forged using free forging on a 750kg air hammer. The initial forging temperature is controlled at 1100-1200℃ and the final forging temperature is ≥1100℃. The slabs are forged into square block billets of 200mm×100mm×35mm. The billets are air-cooled to room temperature and then cut into plates using a medium wire cutting speed.

[0039] S2. The wire-cut sheet metal is subjected to heavy cold rolling; the cold rolling deformation is 75% to 90%, and the cold rolling deformation is carried out in 4 passes, each with 20% deformation annealing and heat preservation, that is, 4 passes of cyclic rolling, with a single pass cold rolling deformation of 20%, and a heat preservation process is used between two similar rolling processes. The annealing temperature range is 300℃ to 400℃, and the heat preservation time is 3-6min; the maximum annealing temperature is 1000℃, and the heating part of the heating furnace is 30℃ / min, with a heating time range of 10-15min. Then, it is taken out with metal clamps and quickly placed in water for cooling by water quenching.

[0040] S3. Superplastic deformation of the final heavy-duty cold-rolled manganese sheet: The heavy-duty cold-rolled sheet is subjected to superplastic tensile deformation. The heating rate is controlled at 25℃ / min. The sheet is held at the target temperature for 5 minutes before superplastic tensile deformation. The temperature range for superplastic deformation is 700℃~800℃, and the superplastic strain rate range is 10. -2 s -1 ~10 -1 s -1The range of superplastic deformation is 200-400%;

[0041] S4. Subsequent mechanical evaluation tests and microscopic characterization were performed on the sheet metal after superplastic deformation. The subsequent mechanical testing equipment used was an INSTRON 8801 hydraulic servo fatigue testing machine, which was used to perform uniaxial quasi-static tensile deformation at a tensile deformation rate of 10. -3 s -1 The sheet metal tensile test specimens were subjected to direct clamping tensile testing, with strain rate control mode. The measurement method used an extensometer, and a laser extensometer was used for positioning and distance measurement.

[0042] The chemical composition of the medium manganese steel may also include one or more of the following chemical components in weight percentage: Ni: 0.1-3.0%; Nb: 0-0.3%; Cu: 0.5-2.0%.

[0043] The principle of the preparation method of this invention is as follows: First, the cast steel ingot is forged. The high-temperature forging process first breaks down the cast grains, achieving grain refinement within the ingot, which facilitates processing by heavy cold rolling. The subsequent heavy cold rolling process utilizes large deformation to ensure a large accumulation of deformation energy and dislocation density in the sheet, while simultaneously ensuring that all austenite in the forged sheet is transformed into martensite. Stress-relieving annealing at 300-400℃ is used in the intermediate stage to reduce deformation resistance during rolling and to ensure good surface flatness of the sheet. In the case of heavy-duty cold-rolled medium-manganese steel plates, superplastic deformation is applied to uniformly elongate the plate, achieving a secondary thinning of the plate thickness from 1-1.5 mm. Simultaneously, during the superplastic deformation process, the inverse transformation of martensite into austenite occurs simultaneously through deformation temperature control. Due to the preceding heavy-duty cold rolling process, the manganese steel plate stores a large amount of dislocation and distortion energy before superplastic deformation. The dynamic recrystallization process of austenite and ferrite phases occurs simultaneously in the initial stage of superplastic deformation, thereby achieving equiaxed grains and grain refinement during the superplastic deformation process. In the subsequent superplastic deformation process, the cold-rolled texture gradually decreases due to the superplastic deformation mechanism (i.e., the effect of grain boundary slip and grain rotation). Finally, through strain rate control and deformation amount control, the secondary thinning and texture weakening of the medium-manganese steel plate are achieved, realizing the homogeneity of each phase in the medium-manganese steel plate and eliminating phase anisotropy.

[0044] The invention will be further illustrated below through specific experimental examples and comparative examples:

[0045] Test case

[0046] A heavy-duty cold-rolling and superplasticizing process for preparing non-oriented differential manganese steel includes the following steps:

[0047] S1. The mass percentages of each component in the molten steel are: C: 0.3%, Mn: 11%, Al: 3%, Si: 2%, with the balance being Fe and unavoidable impurities. The molten steel with the above chemical composition of medium manganese steel is smelted and cast into ingots. The ingots are then forged into slabs. The forging temperature is 1200℃, and the holding time is 1.5h. The slabs are forged using free forging on a 750kg air hammer. The initial forging temperature is controlled at 1100-1200℃, and the final forging temperature is ≥1100℃. The slabs are forged into square blocks of 200mm×100mm×35mm. They are then air-cooled to room temperature and cut into plates using a medium wire cutting speed. The cut plates are 200mm*35mm*15mm steel plates.

[0048] S2. The wire-cut sheet metal is subjected to heavy cold rolling; the cold rolling deformation is 80%, the cold rolling deformation is 4 passes, and each pass is 20% deformation annealing and heat preservation. The annealing temperature range is 350℃, the heat preservation time is 3-6 minutes, and the cooling method is water quenching.

[0049] S3. Superplastic deformation of the final heavy-duty cold-rolled manganese sheet: Superplastic tensile deformation of the heavy-duty cold-rolled sheet was carried out. The temperature control heating rate was 25℃ / min. The sample was held at the target temperature for 5 minutes before superplastic tensile deformation. The temperature range of superplastic deformation was 700℃. The superplastic strain rate range was 10-3s-1. The superplastic tensile deformation amount was 150%, 250%, and 350% strain. After the superplastic deformation was completed, the sample was removed with heat-resistant gloves and quickly placed in water to cool to room temperature.

[0050] S4. Subsequent mechanical evaluation tests and microscopic characterization were performed on the superplastic deformation plate. The subsequent mechanical testing equipment was an INSTRON 8801 hydraulic servo fatigue testing machine. Uniaxial quasi-static tensile deformation was performed with a tensile deformation rate of 10⁻³ s⁻¹. The plate tensile specimens were subjected to direct clamping tensile testing with strain rate control mode. The measurement method was an extensometer, and a laser extensometer was used for positioning and distance measurement until the tensile specimen broke.

[0051] The results of subsequent mechanical tests are shown in Table 1:

[0052] Table 1. Results of mechanical property tests after deformation process.

[0053]

[0054] The microstructure of superplastic deformed plates under different deformation amounts was determined, and the microstructure was as follows: Figure 4 As shown, it can be observed that with the introduction of superplasticity and the increase in deformation, the rolling strength of the medium-manganese steel gradually decreases, while the uniformity of each phase gradually increases.

[0055] Figure 10 To simulate the phase diagram using Thermo-calc thermodynamic calculation software, it can be seen from the phase diagram that the Ac3 (temperature at which all ferrite transforms into austenite) of the experimental steel is about 800℃. This indicates that above 800℃, ferrite will completely transform into austenite, that is, at 800℃, the ferrite structure can undergo a sufficient phase transformation reaction to produce austenite.

[0056] Comparative Example 1 (Comparison with Traditional Rolling Process)

[0057] This comparative example provides a traditional method for preparing medium-manganese steel plates, and its hot deformation process route diagram is as follows: Figure 5 As shown, the preparation method includes:

[0058] 1. The mass percentage of each component in the molten steel is: C: 0.3%, Mn: 11%, Al: 3%, Si: 2%, with the balance being Fe and unavoidable impurities. The molten steel with the above chemical composition of medium manganese steel is smelted and cast into ingots. The ingots are then forged into slabs. The forging temperature is 1200℃, and the holding time is 1.5h. The slabs are forged using free forging on a 750kg air hammer. The initial forging temperature is controlled at 1100-1200℃, and the final forging temperature is ≥1100℃. The slabs are forged into square blocks of 200mm×100mm×35mm. They are then air-cooled to room temperature and cut into plates using a medium wire cutting speed. The cut plates are 200mm*35mm*15mm steel plates.

[0059] 2. The cut sheet metal is hot-rolled and deformed. The hot rolling process is as follows: First, the muffle furnace is heated to 1100℃ to heat the metal sheet metal as described above. The heat treatment time is 1.5h. Then, the sheet metal is taken out of the furnace and hot-rolled. The hot rolling process is carried out in a single pass. The total deformation of hot rolling is 50%. After hot rolling deformation, water cooling is used. Since the hot rolling produces oxide scale, the oxide scale is pickled with 15% hydrochloric acid aqueous solution to remove the oxide scale from the hot-rolled sheet metal.

[0060] 3. Perform conventional cold rolling process on wire-cut sheet metal; cold rolling deformation is 50%, cold rolling deformation is single-pass, there is no intermediate annealing and heat preservation process, no water cooling method, and critical annealing is performed on the final cold-rolled sheet metal. Critical annealing is performed by heating in a muffle furnace at a temperature of 700℃ for 30 minutes.

[0061] 4. Subsequent mechanical evaluation tests and microscopic characterization were performed on the superplastic deformation sheet. The subsequent mechanical testing equipment was an INSTRON 8801 hydraulic servo fatigue testing machine. Uniaxial quasi-static tensile deformation was performed at a tensile deformation rate of 10⁻³ s⁻¹. The sheet tensile specimens were subjected to direct clamping tensile testing with strain rate control mode. The measurement method used an extensometer, and a laser extensometer was used for positioning and distance measurement until the tensile specimen broke.

[0062] 5. The microstructure of medium-manganese steel plates after conventional rolling deformation was measured, and the texture strength was determined and characterized. The plates were polished with 400#, 800#, 1500#, 2000#, and 2500# grit sandpaper, followed by polishing with an automatic polishing machine at a speed of 30 r / min, a disc pressure of 10 N, and a polishing time of 2 hours. Microscopic detection was performed using a Sigma 500 / VP field emission scanning electron microscope with an electron backscatter diffraction (EBSD) module. The texture was tested as follows: Figure 6 As shown.

[0063] In comparison, the medium-manganese steel plates produced by deep rolling and superplastic deformation processes in the experimental examples showed a significant reduction in texture strength, especially under 350% superplastic deformation, where the extreme density strength was below 2. In contrast, the medium-manganese steel plates produced by conventional rolling processes still exhibited an extreme density texture strength above 10, indicating that conventional rolling processes cannot eliminate the texture of medium-manganese steel plates.

[0064] Comparative Example 2 (Comparison of Superplastic Deformation)

[0065] This comparative example provides a method for preparing medium-manganese steel plates, including:

[0066] 1. The mass percentage of each component in the molten steel is: C: 0.3%, Mn: 11%, Al: 3%, Si: 2%, with the balance being Fe and unavoidable impurities. The molten steel with the above chemical composition of medium manganese steel is smelted and cast into ingots. The ingots are then forged into slabs. The forging temperature is 1200℃, and the holding time is 1.5h. The slabs are forged using free forging on a 750kg air hammer. The initial forging temperature is controlled at 1100-1200℃, and the final forging temperature is ≥1100℃. The slabs are forged into square blocks of 200mm×100mm×35mm. They are then air-cooled to room temperature and cut into plates using a medium wire cutting speed. The cut plates are 200mm*35mm*15mm steel plates.

[0067] 2. The wire-cut sheet metal is subjected to heavy cold rolling; the cold rolling deformation is 80%, the cold rolling deformation is 4 passes, and each pass is 20% deformation annealing and heat preservation. The annealing temperature range is 350℃, the heat preservation time is 3-6 minutes, and the cooling method is water quenching.

[0068] 3. Superplastic deformation of the final heavy-duty cold-rolled manganese sheet: The heavy-duty cold-rolled sheet was subjected to superplastic tensile deformation with a temperature-controlled heating rate of 25℃ / min. The sample was held at the target temperature for 5 minutes before superplastic tensile deformation. The temperature range of superplastic deformation was 700℃, the superplastic strain rate range was 10-3s-1, and the superplastic tensile deformation amount was 500% strain. After the superplastic deformation was completed, the sample was removed with heat-resistant gloves and quickly placed in water to cool to room temperature.

[0069] 4. Subsequent mechanical evaluation tests and microscopic characterization were performed on the superplastic deformation sheet. The subsequent mechanical testing equipment was an INSTRON 8801 hydraulic servo fatigue testing machine. Uniaxial quasi-static tensile deformation was performed at a tensile deformation rate of 10⁻³ s⁻¹. The sheet tensile specimens were subjected to direct clamping tensile testing with strain rate control mode. The measurement method used an extensometer, and a laser extensometer was used for positioning and distance measurement until the tensile specimen broke.

[0070] 5. The microstructure of medium-manganese steel plates after traditional rolling deformation was measured, and the texture strength was determined and characterized. The plates were polished with 400#, 800#, 1500#, 2000#, and 2500# grit sandpaper, followed by polishing with an automatic polishing machine at a speed of 30 r / min, a disc pressure of 10 N, and a polishing time of 0.5 h. Microscopic analysis was performed using a Sigma 500 / VP field emission scanning electron microscope with an electron backscatter diffraction (EBSD) module. The scanned microstructure is shown in the figure. Figure 6 As shown, Figure 7 As shown.

[0071] In comparison with the experimental example, the superplastic deformation process involves a larger tensile deformation, which leads to the formation of void nuclei, i.e., crack initiation, in the medium manganese steel sheet at the microscopic level. This is very detrimental to the forming of the medium manganese steel sheet, indicating that the deformation amount needs to be precisely controlled in superplastic deformation.

[0072] Comparative Example 3 (Ingredient Comparison)

[0073] This comparative example provides a method for preparing medium-manganese steel, including:

[0074] 1. Smelt steel according to the set composition, and then cast it into 20kg ingots. The mass percentage of each component in the molten steel is: C: 0.09%, Mn: 10.34%, Mo: 0.35%, Si: 0.33%, V: 0.09%, Cr: 0.14%, with the balance being Fe and unavoidable impurities. Smelt steel with the above-mentioned chemical composition of medium manganese steel, cast it into ingots, and then forge the ingots into slabs. The forging furnace temperature is 1200℃, the holding time is 1.5h, and the forging is carried out using free forging on a 750kg air hammer. During forging, the initial forging temperature is controlled at 1100-1200℃, and the final forging temperature is ≥1100℃. The forged slabs are square blocks of 200mm×100mm×35mm, air-cooled to room temperature, and then cut into plates using a medium-speed wire EDM to obtain 200mm*35mm*15mm steel plates.

[0075] 2. The wire-cut sheet metal is subjected to heavy cold rolling; the cold rolling deformation is 80%, the cold rolling deformation is 4 passes, and each pass is 20% deformation annealing and heat preservation. The annealing temperature range is 350℃, the heat preservation time is 3-6 minutes, and the cooling method is water quenching.

[0076] 3. Superplastic deformation of the final heavy-duty cold-rolled manganese sheet: The heavy-duty cold-rolled sheet is subjected to superplastic tensile deformation with a temperature-controlled heating rate of 25℃ / min. Before superplastic tensile deformation, the sample is held at the target temperature for 5 minutes. The temperature range of superplastic deformation is 700℃, and the superplastic strain rate range is 10-3s-1. The sample is directly broken. After the superplastic deformation is completed, the sample is removed with heat-resistant gloves and quickly placed in water to cool to room temperature.

[0077] The experimental results showed that its superplastic mechanical curve was as follows: Figure 8 As shown, this experimental steel cannot achieve the superplastic deformation process for preparing manganese steel plates.

[0078] Comparative Example 4 (Comparison of Cold Rolling Deformation)

[0079] This comparative example provides a method for preparing medium-manganese steel, including:

[0080] 1. The mass percentage of each component in the molten steel is: C: 0.3%, Mn: 11%, Al: 3%, Si: 2%, with the balance being Fe and unavoidable impurities. The molten steel with the above chemical composition of medium manganese steel is smelted and cast into ingots. The ingots are then forged into slabs. The forging temperature is 1200℃, and the holding time is 1.5h. The slabs are forged using free forging on a 750kg air hammer. The initial forging temperature is controlled at 1100-1200℃, and the final forging temperature is ≥1100℃. The slabs are forged into square blocks of 200mm×100mm×35mm. They are then air-cooled to room temperature and cut into plates using a medium wire cutting speed. The cut plates are 200mm*35mm*15mm steel plates.

[0081] 2. Cold rolling of wire-cut sheet metal; cold rolling deformation amount is 40%, cold rolling deformation passes are 2 passes, each with 20% deformation annealing and heat preservation, annealing temperature range is 350℃, heat preservation time is 3-6min, cooling method is water quenching.

[0082] 3. Superplastic deformation of the final heavy-duty cold-rolled manganese sheet: The heavy-duty cold-rolled sheet was subjected to superplastic tensile deformation. The temperature control heating rate was 25℃ / min. The sample was held at the target temperature for 5 minutes before superplastic tensile deformation. The temperature range of superplastic deformation was 700℃, the superplastic strain rate range was 10-3s-1, and the superplastic tensile deformation amount was 150%, 250%, and 350% strain. After the superplastic deformation was completed, the sample was removed with heat-resistant gloves and quickly placed in water to cool to room temperature.

[0083] 4. Subsequent mechanical evaluation tests and microscopic characterization were performed on the sheet metal after superplastic deformation. The subsequent mechanical testing equipment used was an INSTRON 8801 hydraulic servo fatigue testing machine, which was used to perform uniaxial quasi-static tensile deformation at a tensile deformation rate of 10. -3 s -1 The sheet metal tensile test specimens were subjected to direct clamping tensile testing, with strain rate control mode. The measurement method used an extensometer, and a laser extensometer was used for positioning and distance measurement until the tensile test specimen broke.

[0084] Mechanical property tests were conducted on the superplastic deformable sheet metal. The test results are as follows: Figure 9 As shown.

[0085] The comparison revealed that the reduction in deformation during the heavy cold rolling process led to a deterioration in the subsequent mechanical properties of the superplastic deformation, thus failing to produce medium-manganese steel plates with high mechanical properties. This indicates that the deformation in the heavy cold rolling process needs to be strictly controlled.

[0086] All matters not covered in this invention are common knowledge.

[0087] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A process for the production of heavy cold rolled + superplastic of non-oriented electrical steel of medium manganese characterized by: The medium manganese steel comprises the following chemical components in percentage by weight: C: 0.1-0.4%, Mn: 2-12%, Al: 0.5-4%, Si: 0.5-4%, and the balance being Fe; The preparation process comprises the following steps: S1, taking the chemical components of the medium manganese steel in percentage by weight to smelt molten steel, cast into ingots, and then forge the ingots into slabs, and cut the slabs into plates after air cooling to room temperature; the forging out of the furnace temperature is 1150-1250 DEG C, and the free forging method is used on the air hammer to forge the slabs, the initial forging temperature is controlled to be 1100-1200 DEG C, the final forging temperature is greater than or equal to 1100 DEG C, the slabs are forged into square block blanks, and the slabs are cut into plates by adopting the medium wire speed rate line cutting; S2, the line-cutting plate is subjected to severe cold rolling; S3, the final severe cold-rolled manganese plate is subjected to plate superplastic deformation: the severe cold-rolled plate is subjected to superplastic tensile deformation; S4, the plate after superplastic deformation is subjected to subsequent mechanical evaluation test and microscopic characterization; In the step S2, the cold rolling deformation is 75%-90%, the cold rolling deformation pass is 4 passes, the single pass cold rolling deformation is 20%, the heat preservation process is used between the similar two passes, the annealing temperature is in the range of 300-400 DEG C, the heat preservation time is 3-6 min, the highest annealing temperature is 1000 DEG C, the heating furnace heating part is 30 DEG C / min, the heating time is in the range of 10-15 min, then the metal clamp is used to take out and quickly placed in water, and the cooling method is water quenching; The temperature control heating rate in the step S3 is 25℃ / min, and the target temperature is reached and kept for 5min before the superplastic tensile deformation, the superplastic deformation temperature range is 700℃-800℃, the superplastic strain rate range is 10 -2 s -1 ~10 -1 s -1 , and the superplastic deformation range is 200-400%.

2. A process for the production of heavy cold rolled + superplastic of non-oriented electrical steel of medium manganese steel as claimed in claim 1, wherein said process comprises the steps of: The medium manganese steel further comprises one or more of the following chemical components in percentage by weight: Ni: 0.1-3.0%; Nb: 0-0.3%; Cu: 0.5-2.0%.

3. A process for the production of heavy cold rolled + superplastic of non-oriented electrical steel of medium manganese steel as claimed in claim 1, wherein said process comprises the steps of: In the step S1, during the forging of the ingot, the ingot is heated to 1100-1200 DEG C and preserved for 1.5-2.5 h.

4. A process for the production of heavy cold rolled + superplastic of non-oriented electrical steel of medium manganese steel as claimed in claim 1, wherein said process comprises of the steps of: In the step S4, the subsequent mechanical evaluation test adopts the plate normal temperature tensile test, the tensile rate is 10 -3 s -1 Quasi-static tensile rate, until fracture.

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