A high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications and its preparation method

Abstract

This invention discloses a high-strength and high-toughness high-manganese steel plate for ultra-low temperatures and its preparation method. Its chemical composition and mass percentages are: C 0.04–0.10%, Mn 21.0–25.5%, Si 0.25–0.35%, P≤0.008%, S≤0.003%, O≤0.003%, Ti 0.02–0.05%, W 0.01–0.05%, with the balance being Fe and unavoidable impurities. The high-manganese steel plate has a stacking fault energy of 40–45 mJ / m at -196℃. 2 This steel plate achieves its design by controlling the stacking fault energy to 40–45 mJ / m. 2 This ensures that the steel undergoes a strong TWIP effect in the subsequent heavy impact pre-hardening step, forming a gradient nanocrystalline layer on the steel surface, which significantly improves the yield and tensile strength of the steel; it can improve the uniformity of the internal structure of the steel plate and significantly improve the low-temperature impact toughness of high manganese steel, with an impact toughness AKV≥200J at -196℃.

Description

Technical Field

[0001] This invention relates to the field of steel production technology, and in particular to a high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications and its preparation method. Background Technology

[0002] With the surge in energy consumption, over-reliance on fossil fuels such as oil and coal has caused severe air pollution and global warming. Vigorously developing clean energy sources such as natural gas has become an inevitable trend, which further increases the demand for LNG carriers, storage tank materials, and corresponding receiving terminals.

[0003] Currently, nickel-based cryogenic steels are still the most widely used in cryogenic engineering fields such as LNG storage and transportation facilities. However, since nickel is an expensive metallic element, developing low-nickel or nickel-free cryogenic steels is an important direction for the future development of cryogenic materials. Manganese and nickel are both austenite-forming elements and have similar properties in steel. Using manganese to replace nickel in cryogenic steel can ensure that its low-temperature performance is comparable to that of nickel-based cryogenic steels, while also achieving better weldability and low-temperature plasticity. Developing high-manganese steel for ultra-low temperatures can yield significant advantages in material construction costs.

[0004] Most of the reported high-manganese steel preparation technologies focus only on improving the tensile strength or impact toughness of high-manganese steel. There are no reports on low-cost preparation of high-manganese steel products that combine high strength and high low-temperature impact toughness.

[0005] Chinese patent application CN113637908A discloses a thick high-manganese steel plate for low-temperature environments and its production method. Its chemical composition is: C: 0.43–0.47%, Si: 0.30–0.35%, Mn: 22.5–25%, P≤0.010%, S≤0.004%, Cu: 0.40–0.50%, V: 0.02–0.05%, Cr: 3–4%, Nb: 0.010–0.015%, Al: 0.02–0.05%, with the balance being Fe and unavoidable impurities. The production method includes smelting, ingot casting, billet preparation, heating, rolling, and controlled cooling after rolling. The disadvantages of this high-manganese steel and its method lie in the addition of expensive Ni and Cu alloys. The controlled cooling after rolling employs a one-stage ultra-fast cooling process, which easily leads to the precipitation of a large amount of carbides between the austenite phase and the as-cast structure during solidification. This not only promotes the generation of internal stress and cracks but also deteriorates the steel's plasticity and toughness.

[0006] Chinese patent application CN108118255A discloses a high-manganese TWIP low-temperature resistant steel with high impact toughness and its manufacturing method. Its chemical composition is: C: 0.050–0.30%, Si: 0.30–1.5%, Mn: 25–35%, Al: 2.0–4.0%, with the balance being Fe and unavoidable impurities. This low-temperature resistant steel is designed to have a stacking fault energy of 25–40 mJ / m at -196℃. 2 The disadvantages of this low-temperature resistant steel and its method are that while adding a large amount of Al element to suppress intergranular cracking and promote the TWIP effect of the steel, this will lead to a significant decrease in the fluidity of the molten steel and coarsen the steel grains, thus deteriorating the casting performance and mechanical properties. Although the prepared low-temperature resistant steel achieves high impact toughness, it sacrifices the strength properties of the steel, with a yield strength of only 200-300 MPa and a tensile strength of only 600-700 MPa.

[0007] Patent application CN114717475A discloses a high-strength, high-ductility, Nb-containing high-manganese steel and its preparation method based on stacking fault energy design. The chemical composition is: C: 0.1–0.5%, Si: 1–4%, Mn: 18–22%, Cu: 0.5–2.5%, Nb: 0.1–0.3%, P < 0.010%, S < 0.005%, with the balance being Fe. This high-manganese steel and method improve yield strength by adding Nb to precipitate NbC, refining the grains and strengthening the steel through precipitation. Furthermore, the stacking fault energy is controlled to 18 mJ / m through composition design. 2 Nearby, the deformation mechanism of high-manganese steel is controlled by martensitic phase transformation and twinning, thereby achieving better plasticity. The drawbacks of this high-manganese steel and method are the addition of a large amount of expensive Nb and Cu alloys, significantly increasing the cost of the steel; and the stacking fault energy is controlled at 18 mJ / m. 2 Nearby, its deformation mechanism is mainly martensitic phase transformation, which can obtain high strength and plasticity, but will significantly deteriorate the low-temperature toughness of steel.

[0008] Chinese patent application CN113941430A discloses a wear-resistant high-manganese steel based on the TWIP effect and nanoprecipitation reinforcement, its preparation method, and its applications. Its chemical composition is: C: 1.2–1.6%, Si: 0.3–0.5%, Mn: 18–26%, Mo: 1.0–2.0%, Nb: 0.04–0.08%, V: 0.3–1.2%, P≤0.003%, S≤0.005%, with the balance being Fe and other unavoidable impurities. This high-manganese steel and its method control the stacking fault energy to 20–40 mJ / m. 2This method generates twins to induce the TWIP effect and enhances the wear resistance of high-manganese steel through the precipitation of carbide nanophases formed by Nb and Mo. However, the drawbacks of this high-manganese steel and its method include the addition of large amounts of expensive alloying elements such as Nb and Mo, resulting in high overall cost; furthermore, the controllable stacking fault energy is limited, leading to a weaker TWIP effect during steel plate use and generally lower mechanical properties in the prepared high-manganese steel products. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a low-cost high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications that combines high strength and high resistance to low-temperature impact toughness; the present invention also provides a method for preparing a low-cost high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications.

[0010] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: its chemical composition and mass percentage are: C 0.04~0.10%, Mn 21.0~25.5%, Si 0.25~0.35%, P≤0.008%, S≤0.003%, O≤0.003%, Ti 0.02~0.05%, W 0.01~0.05%, with the balance being Fe and unavoidable impurities; the high-manganese steel plate has a stacking fault energy of 40~45mJ / m at -196℃. 2 .

[0011] Furthermore, the high-manganese steel plate has a yield strength ≥520MPa, tensile strength ≥900MPa, elongation after fracture ≥50%, and low-temperature impact toughness AKV ≥200J at -196℃.

[0012] The method of this invention includes smelting, ingot casting, homogenization, rolling, cooling, and impact pre-hardening processes;

[0013] The cooling process is as follows: the steel plate is first cooled to 450-500°C at a cooling rate of 5-40°C / s, then air-cooled to 300-350°C, and finally cooled at a cooling rate of not less than 100°C / s.

[0014] The impact pre-hardening process involves using a metal impactor to deform the surface of the steel plate by impact. The impact energy is 30-80J, the impact frequency is 50-2000HZ, and the impact time for each hardening point is 8-30s.

[0015] Furthermore, the homogenization process involves heating the steel billet to 1170–1230°C and homogenizing it for 3–10 hours.

[0016] Furthermore, the rolling process involves rough rolling at a temperature range of 1030–1130°C, finish rolling at a temperature range of 800–1000°C, and final rolling at a temperature range of 780–880°C.

[0017] The beneficial effects of adopting the above technical solution are as follows:

[0018] (1) When the stacking fault energy is less than 15 mJ / m 2 During plastic deformation, high-manganese steel forms ε-martensite, resulting in a transformation-induced plasticity (TRIP) effect; when the stacking fault energy is 18–45 mJ / m 2 At this time, the deformation mechanism of high manganese steel is mainly the twin-induced plasticity (TWIP) effect; when the stacking fault energy exceeds 45 mJ / m 2 At low temperatures, the deformation mechanism of high-manganese steel is mainly dislocation slip. High-manganese steel with excessively low stacking fault energy is prone to martensitic transformation under low-temperature impact load deformation conditions, which deteriorates its low-temperature impact toughness. Conversely, high-manganese steel with excessively high stacking fault energy exhibits a weakened TWIP effect under low-temperature impact deformation conditions, which is also detrimental to improving low-temperature impact toughness. This invention and its method control the stacking fault energy at 40–45 mJ / m 2 This ensures that the steel undergoes a strong twinning-induced plasticity (TWIP) effect during the subsequent impact pre-hardening step, forming a gradient nanocrystalline layer on the steel surface, significantly improving the yield and tensile strength of the steel. The steel plate of this invention has a yield strength ≥520MPa, a tensile strength ≥900MPa, and an elongation after fracture ≥50%.

[0019] (2) This invention and its method do not use expensive alloying elements such as Ni, Nb, and Mo to toughen the matrix. Instead, by adding a small amount of low-cost alloying elements Ti and W, some of these elements are dissolved in the high-manganese steel, refining the austenite grains, while others precipitate as carbides, hindering grain boundary movement. Simultaneously, the formed CW atomic bonds are stronger than C-Mn and C-Fe atomic bonds, increasing crack propagation resistance. Combined with a three-stage cooling process, this significantly reduces the austenite grain size, improves the uniformity of the internal structure of the steel plate, and significantly enhances the low-temperature impact toughness of the high-manganese steel, achieving an AKV ≥ 200J at -196℃. The method of this invention reduces the smelting cost per ton of steel by more than 15%. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to specific embodiments.

[0021] The chemical composition and mass percentage of this high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications are as follows: C 0.04–0.10%, Mn 21.0–25.5%, Si 0.25–0.35%, P ≤0.008%, S ≤0.003%, O ≤0.003%, Ti 0.02–0.05%, W 0.01–0.05%, with the balance being Fe and unavoidable impurities; the stacking fault energy of the high-manganese steel plate at -196℃ is 40–45 mJ / m. 2Yield strength ≥520MPa, tensile strength ≥900MPa, elongation after fracture ≥50%, low-temperature impact toughness AKV≥200J at -196℃, thickness 50~80mm.

[0022] The preparation method of this high-strength and high-toughness high-manganese steel plate for ultra-low temperatures includes smelting, ingot casting, homogenization, rolling, cooling, and impact pre-hardening processes; the processes for each step are described below:

[0023] (1) Smelting process: According to the mass ratio of the above alloys and the calculation of stacking fault energy, determine the amount of each alloy component to be fed, carry out converter or electric furnace smelting, and obtain molten steel that meets the composition and stacking fault energy range after multiple adjustments.

[0024] The stacking fault energy γ SFE The calculation formula is shown in equation (Ⅰ):

[0025] γ SFE =2ρΔG γ→ε +2σ γ→ε (I)

[0026] In the formula, ρ is the molar surface density of the {1,1,1} atoms in the close-packed plane of the γ phase; ΔG γ→ε The molar Gibbs free energy change for the transformation from the γ phase to the ε phase is calculated using equations (II)-(IV) below; σ γ→ε Let be the interfacial energy of the {1,1,1} phase interface between the γ phase and the ε phase;

[0027]

[0028] In the formula, x i and x j These represent the mole fractions of pure alloying elements i and j in the steel plate, respectively. This represents the change in molar Gibbs free energy of pure alloying element i between the γ and ε phases. Let i be the interaction energy between pure alloy elements i and j.

[0029] (2) Casting process: The molten steel prepared in the smelting process is cast into a steel billet by casting. The casting temperature is 1390~1430℃.

[0030] (3) Homogenization process: The steel billet obtained by die casting is heated to 1170-1230℃ and homogenized for 3-10 hours.

[0031] (4) Rolling process: The homogenized steel billet is rolled in multiple passes on a hot rolling mill. The temperature range is controlled at 1030-1130℃ for rough rolling, the temperature range is controlled at 800-1000℃ for finish rolling, and the final rolling temperature is controlled at 780-880℃.

[0032] (5) Three-stage cooling process: The rolled steel plate is cooled by a three-stage cooling process of "fast cooling + air cooling + ultra-fast cooling". The water temperature for the fast cooling is controlled at 780-830℃ and the cooling rate is controlled at 5-40℃ / s, cooling to 450-500℃; then air cooling is carried out to 300-350℃; finally, ultra-fast cooling equipment is used to cool to room temperature, with a cooling rate ≥100℃ / s.

[0033] (6) Impact pre-hardening process: The cooled steel plate is subjected to high-speed metal impact deformation on the surface. Through repeated impacts, a high-strength gradient nanocrystalline layer is formed on the surface of the steel plate. The impact energy is 30-80J, the impact frequency is 50-2000HZ, and the impact time for each hardening point is 8-30s; the final high-manganese steel plate product is obtained.

[0034] Example 1: The high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications and its preparation method are described in detail below.

[0035] (1) Smelting process: Prepare the amount of raw materials according to the above alloy composition, carry out converter smelting, and obtain molten steel that meets the composition and stacking fault energy range after multiple adjustments; the chemical composition and mass percentage of the molten steel are: C 0.045%, Mn 22.5%, Si 0.27%, P 0.006%, S 0.0025%, O 0.0026%, Ti 0.032%, W 0.025%, with the balance being Fe and unavoidable impurities.

[0036] (2) Molding process: The molten steel prepared in the above smelting steps is molded to obtain steel ingots at a molding temperature of 1395℃.

[0037] (3) Homogenization process: The steel billet obtained by die casting is heated to 1190℃ and homogenized for 5 hours.

[0038] (4) Rolling process: rough rolling at 1070℃, finish rolling at 860℃, and final rolling temperature controlled at 810℃; rolled into a high manganese steel plate with a thickness of 60mm.

[0039] (5) Three-stage cooling process: The inlet water temperature for rapid cooling is controlled at 810℃, the cooling rate is controlled at 10℃ / s, and when the temperature drops to 470℃, it is air-cooled to 320℃. Then, ultra-fast cooling equipment is used to cool it to room temperature at a cooling rate of 110℃ / s.

[0040] (6) Heavy impact pre-hardening process: The heavy impact energy is 40J, the heavy impact frequency is 100HZ, and the impact time for each hardening point is 30s. The final high manganese steel plate product is obtained.

[0041] The resulting high-manganese steel plate has a stacking fault energy of 41.52 mJ / m at -196℃. 2The yield strength is 524 MPa, the tensile strength is 946 MPa, the elongation after fracture is 52%, and the low-temperature impact toughness (AKV) at liquid nitrogen temperature (-196℃) is 207 J.

[0042] Example 2: The high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications and its preparation method are described in detail below.

[0043] (1) Smelting process: Prepare the amount of raw materials according to the above alloy composition, carry out converter smelting, and obtain molten steel that meets the composition and stacking fault energy range after multiple adjustments; the chemical composition and mass percentage of the molten steel are: C 0.051%, Mn 23.2%, Si 0.25%, P 0.007%, S 0.0028%, O 0.0021%, Ti 0.027%, W 0.035%, with the balance being Fe and unavoidable impurities.

[0044] (2) Casting process: The molten steel prepared in the above smelting steps is cast into steel ingots at a casting temperature of 1410℃.

[0045] (3) Homogenization process: The steel billet obtained by die casting is heated to 1180℃ and homogenized for 7 hours.

[0046] (4) Rolling process: rough rolling at 1090℃, fine rolling at 890℃, and final rolling temperature controlled at 820℃; rolled into a high manganese steel plate with a thickness of 70mm.

[0047] (5) Three-stage cooling process: The inlet water temperature for rapid cooling is controlled at 820℃, the cooling rate is controlled at 15℃ / s, and when the temperature drops to 480℃, it is air-cooled to 325℃. Then, ultra-fast cooling equipment is used to cool it to room temperature at a cooling rate of 130℃ / s.

[0048] (6) Heavy impact pre-hardening process: The heavy impact energy is 60J, the heavy impact frequency is 200HZ, and the impact time for each hardening point is 15s. The final high manganese steel plate product is obtained.

[0049] The resulting high-manganese steel plate has a stacking fault energy of 43.57 mJ / m at -196℃. 2 The yield strength is 531 MPa, the tensile strength is 955 MPa, the elongation after fracture is 54%, and the low-temperature impact toughness (AKV) at liquid nitrogen temperature (-196℃) is 225 J.

[0050] Example 3: The high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications and its preparation method are described in detail below.

[0051] (1) Smelting process: Prepare the amount of raw materials according to the above alloy composition, carry out converter smelting, and obtain molten steel that meets the composition and stacking fault energy range after multiple adjustments; the chemical composition and mass percentage of the molten steel are: C 0.048%, Mn 24.2%, Si 0.31%, P 0.005%, S 0.0020%, O 0.0021%, Ti 0.028%, W 0.035%, with the balance being Fe and unavoidable impurities.

[0052] (2) Molding process: The molten steel prepared in the above smelting steps is molded to obtain steel ingots at a molding temperature of 1395℃.

[0053] (3) Homogenization process: The steel billet obtained by casting is heated to 1210℃ and homogenized for 8 hours.

[0054] (4) Rolling process: rough rolling at 1100℃, fine rolling at 920℃, and final rolling temperature controlled at 830℃; rolled into a high manganese steel plate with a thickness of 75mm.

[0055] (5) Three-stage cooling process: The inlet water temperature for rapid cooling is controlled at 820℃, the cooling rate is controlled at 20℃ / s, and when the temperature drops to 480℃, it is air-cooled to 340℃. Then, ultra-fast cooling equipment is used to cool it to room temperature at a cooling rate of 150℃ / s.

[0056] (6) Heavy impact pre-hardening process: The heavy impact energy is 60J, the heavy impact frequency is 500HZ, and the impact time for each hardening point is 10s. The final high manganese steel plate product is obtained.

[0057] The resulting high-manganese steel plate has a stacking fault energy of 44.72 mJ / m at -196℃. 2 The yield strength is 530 MPa, the tensile strength is 955 MPa, the elongation after fracture is 53%, and the low-temperature impact toughness (AKV) at liquid nitrogen temperature (-196℃) is 236 J.

[0058] Example 4: The high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications and its preparation method are described in detail below.

[0059] (1) Smelting process: Prepare the amount of raw materials according to the above alloy composition, carry out converter smelting, and obtain molten steel that meets the composition and stacking fault energy range after multiple adjustments; the chemical composition and mass percentage of the molten steel are: C 0.082%, Mn 21.4%, Si 0.28%, P 0.006%, S 0.0023%, O 0.0024%, Ti 0.020%, W 0.050%, with the balance being Fe and unavoidable impurities.

[0060] (2) Casting process: The molten steel prepared in the above smelting steps is cast into steel ingots at a casting temperature of 1430℃.

[0061] (3) Homogenization process: The steel billet obtained by die casting is heated to 1230℃ and homogenized for 3 hours.

[0062] (4) Rolling process: rough rolling at 1130℃, finish rolling at 1000℃, and final rolling temperature controlled at 880℃; rolled into a high manganese steel plate with a thickness of 50mm.

[0063] (5) Three-stage cooling process: The inlet water temperature for rapid cooling is controlled at 880℃, the cooling rate is controlled at 40℃ / s, and when the temperature drops to 500℃, it is air-cooled to 350℃. Then, ultra-fast cooling equipment is used to cool it to room temperature at a cooling rate of 120℃ / s.

[0064] (6) Heavy impact pre-hardening process: The heavy impact energy is 30J, the heavy impact frequency is 2000HZ, and the impact time for each hardening point is 8s. The final high manganese steel plate product is obtained.

[0065] The resulting high-manganese steel plate has a stacking fault energy of 40.1 mJ / m at -196℃. 2 The yield strength is 522 MPa, the tensile strength is 905 MPa, the elongation after fracture is 55%, and the low-temperature impact toughness (AKV) at liquid nitrogen temperature (-196℃) is 247 J.

[0066] Example 5: The high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications and its preparation method are described in detail below.

[0067] (1) Smelting process: Prepare the amount of raw materials according to the above alloy composition, carry out converter smelting, and obtain molten steel that meets the composition and stacking fault energy range after multiple adjustments; the chemical composition and mass percentage of the molten steel are: C 0.067%, Mn 23.7%, Si 0.35%, P 0.008%, S 0.0027%, O 0.0028%, Ti 0.050%, W 0.010%, with the balance being Fe and unavoidable impurities.

[0068] (2) Molding process: The molten steel prepared in the above smelting steps is molded to obtain steel ingots at a molding temperature of 1390℃.

[0069] (3) Homogenization process: The steel billet obtained by die casting is heated to 1170℃ and homogenized for 10 hours.

[0070] (4) Rolling process: rough rolling at 1030℃, fine rolling at 800℃, and final rolling temperature controlled at 780℃; rolled into a high manganese steel plate with a thickness of 80mm.

[0071] (5) Three-stage cooling process: The inlet water temperature for rapid cooling is controlled at 780℃, the cooling rate is controlled at 5℃ / s, and when the temperature drops to 450℃, it is air-cooled to 300℃. Then, ultra-fast cooling equipment is used to cool it to room temperature at a cooling rate of 100℃ / s.

[0072] (6) Heavy impact pre-hardening process: The heavy impact energy is 80J, the heavy impact frequency is 50HZ, and the impact time for each hardening point is 20s. The final high manganese steel plate product is obtained.

[0073] The resulting high-manganese steel plate has a stacking fault energy of 44.8 mJ / m at -196℃. 2 The yield strength is 538 MPa, the tensile strength is 926 MPa, the elongation after fracture is 50%, and the low-temperature impact toughness (AKV) at liquid nitrogen temperature (-196℃) is 202 J.

Claims

1. A method for preparing high-strength and high-toughness high-manganese steel plate for ultra-low temperature applications, characterized in that: The chemical composition and mass percentage of the high-manganese steel plate are as follows: C 0.04~0.10%, Mn 21.0~25.5%, Si 0.25~0.35%, P≤0.008%, S≤0.003%, O≤0.003%, Ti 0.02~0.05%, W 0.01~0.05%, with the balance being Fe and unavoidable impurities; the stacking fault energy of the high-manganese steel plate at -196℃ is 40~45mJ / m. 2 It includes smelting, ingot casting, homogenization, rolling, cooling, and impact pre-hardening processes; The cooling process is as follows: the steel plate is first cooled to 450-500°C at a cooling rate of 5-40°C / s, then air-cooled to 300-350°C, and finally cooled at a cooling rate of not less than 100°C / s. The impact pre-hardening process involves using a metal impactor to deform the surface of the steel plate by impact. The impact energy is 30-80J, the impact frequency is 50-2000HZ, and the impact time for each hardening point is 8-30s.

2. The method for preparing a high-strength, high-toughness high-manganese steel plate for ultra-low temperatures according to claim 1, characterized in that, The homogenization process involves heating the steel billet to 1170–1230°C and homogenizing it for 3–10 hours.

3. A method for preparing a high-strength, high-toughness high-manganese steel plate for ultra-low temperatures according to claim 1 or 2, characterized in that, The rolling process is as follows: rough rolling is carried out at a temperature range of 1030 to 1130°C, finish rolling is carried out at a temperature range of 800 to 1000°C, and the final rolling temperature is controlled at 780 to 880°C.

4. The method for preparing a high-strength, high-toughness high-manganese steel plate for ultra-low temperature applications according to claim 3, characterized in that, The high-manganese steel plate has a yield strength ≥520MPa, tensile strength ≥900MPa, elongation after fracture ≥50%, and low-temperature impact toughness AKV ≥200J at -196℃.

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