Titanium-containing high-manganese ultra-low-temperature steel, preparation method and application thereof

Abstract

This invention discloses a titanium-containing high-manganese cryogenic steel, its preparation method, and its applications. The chemical composition of this cryogenic steel is: C: 0.35%–0.55%, Si: 0.11%–0.22%, Mn: 22.5%–25.5%, P≤0.02%, S≤0.005%, Cr: 3%–4%, Ti: 0.03%–0.1%, Alt: 0.01%–0.1%, Ca: 0.0003%–0.005%, with the remainder being Fe and other unavoidable impurities. By combining chemical elements with the rolled steel, the low-temperature strength and corrosion resistance of the steel plate at -269℃ are significantly improved, while eliminating the need for precious metal elements such as Ni, Mo, and Cu, as well as post-processing steps. It exhibits excellent cryogenic performance and economic efficiency, and shows promising application prospects in the storage and transportation of cryogenic media such as liquefied ethylene, liquefied natural gas, liquid hydrogen, and liquid helium in complex environments such as land, sea, and air.

Description

Technical Field

[0001] This invention relates to a titanium-containing high-manganese ultra-low temperature steel, its preparation method and application, and more particularly to a titanium-containing high-manganese ultra-low temperature steel with high strength, its preparation method and application. Background Technology

[0002] With the deepening of the green development concept, clean energy is gradually replacing traditional energy. Among them, liquefied natural gas (LNG) has developed rapidly and has become an irreplaceable part of the energy supply, alleviating dependence on petroleum energy. Since LNG is typically stored at -163℃, the materials used in LNG storage and transportation facilities must possess high strength, high and low temperature toughness, and ease of welding. Currently, Invar alloys, austenitic stainless steel, and 9% Ni steel are commonly used to manufacture storage and transportation containers. However, the relatively rare nature of Ni makes Ni steel expensive, while austenitic stainless steel has low strength and a large coefficient of thermal expansion. In recent years, there has been a trend of high-manganese steel replacing Ni steel; however, existing high-manganese steel can only be used at a minimum temperature of -196℃, and its performance still cannot meet the requirements of ultra-low temperature environments.

[0003] CN104894471 discloses a high-manganese, high-alumina, vanadium-containing non-magnetic steel plate with the following chemical composition: C: 0.14–0.20%, Mn: 21.50–25.00%, Al: 1.50–2.50%, V: 0.04–0.10%, N < 0.05%, with the balance being Fe and unavoidable impurities. This austenitic steel plate has a yield strength of only 280–300 MPa and a tensile strength of 550–700 MPa, indicating limited strength.

[0004] CN102409227 discloses a hot-rolled strip steel with low relative magnetic permeability, whose chemical element composition is C: 0.25-0.35%, Si: 0.5-0.6%, Mn: 25-26%, Al: 3.8-4.2%, V: 0.06-0.10%, P: 0.02-0.03%, S: 0.02-0.03%, with the remainder being Fe and unavoidable impurities. Due to the excessively high Al content in this austenitic steel sheet, hot rolling easily leads to cracking, making process stability difficult to control.

[0005] CN108929993 discloses a microalloyed, high-strength, high-ductility, non-magnetic steel plate with the following chemical composition: C: 0.10–0.20%, 0 < Si ≤ 0.4%, Mn: 20–26%, Al: 2.0–3.0%, Ti: 0.01–0.02%, Nb: 0.04–0.09%, with the balance being Fe and other unavoidable impurities. This steel plate exhibits an impact energy of only ≥110 J at -196℃, which is insufficient to meet the storage and transportation requirements of cryogenic media such as liquid hydrogen and liquid helium. Summary of the Invention

[0006] Purpose of the invention: The first purpose of this invention is to provide an ultra-low temperature steel that saves precious metals and has high low-temperature strength; the second purpose is to provide a method for preparing the ultra-low temperature steel; and the third purpose is to provide an application of the ultra-low temperature steel.

[0007] Technical solution: The titanium-containing high-manganese ultra-low temperature steel of the present invention, by weight fraction, comprises C: 0.35%–0.55%, Si: 0.11%–0.22%, Mn: 22.5%–25.5%, P≤0.02%, S≤0.005%, Cr: 3%–4%, Ti: 0.03%–0.1%, Alt: 0.01%–0.1%, Ca: 0.0003%–0.005%, with the balance being Fe and other unavoidable impurities.

[0008] Preferably, the titanium-containing high-manganese ultra-low temperature steel, by weight fraction, comprises C: 0.43%, Si: 0.17%, Mn: 24%, Cr: 3.6%, Ti: 0.08%, Alt: 0.06%, Ca: 0.002%, with the balance being Fe and unavoidable impurity elements;

[0009] Or its composition includes C: 0.35%, Si: 0.11%, Mn: 22.5%, Cr: 3%, Ti: 0.03%, Alt: 0.01%, Ca: 0.0003%, with the balance being Fe and unavoidable impurity elements;

[0010] Alternatively, its composition may include C: 0.55%, Si: 0.22%, Mn: 25.5%, Cr: 4.0%, Ti: 0.1%, Alt: 0.1%, Ca: 0.005%, with the balance being Fe and unavoidable impurity elements.

[0011] Preferably, the microstructure of the titanium-containing high-manganese ultra-low temperature steel is austenitic.

[0012] Further preferably, in the microstructure of the titanium-containing high-manganese ultra-low temperature steel, the volume ratio of austenite is not less than 95%.

[0013] Further preferred, in the titanium-containing high-manganese ultra-low temperature steel, the grain size of the austenite structure does not exceed 20 μm.

[0014] Preferably, the stacking fault energy of the titanium-containing high-manganese ultra-low temperature steel at -269°C is 18–21 mJ·m. -2 .

[0015] Preferably, the thickness of the titanium-containing high-manganese ultra-low temperature steel is 15-50 mm.

[0016] Preferably, the titanium-containing high-manganese cryogenic temperature test in the steel chamber has a yield strength R0.p0.2 ≥450MPa, tensile strength R m ≥800MPa, elongation after fracture ≥50%; yield strength R at -269℃ p0.2 ≥1000MPa, tensile strength R m ≥1400MPa, elongation after fracture ≥46%; impact energy Akv≥150J at -196℃, impact energy Akv≥60J at -269℃.

[0017] The compositional design mechanism of the high-manganese ultra-low temperature steel described in this invention is as follows:

[0018] This invention achieves a highly stable austenitic microstructure by adding 0.43% C, 24% Mn, and 3.6% Cr. Even after pre-exposing the microstructure to a true strain of 0.35 and then subjecting it to cryogenic treatment at -269℃, martensite remains absent. Simultaneously, the stacking fault energy of the austenite at -269℃ is controlled to be between 18 and 21 mJ·m⁻¹. -2 The combination of dislocation and twinning achieves a balance between strength and toughness, resulting in the ultra-low temperature steel of this invention having a Charpy impact absorption energy ≥60J at -269℃.

[0019] In particular, the economical high-manganese steel composition system of this invention emphasizes the addition of Ti element. The key role of Ti in steel is as follows:

[0020] (1) Refine grain size

[0021] Titanium combines with elements such as carbon and nitrogen in steel to form fine, dispersed particles such as carbides and nitrides. These particles can act as obstacles to austenite grain growth, thereby refining the grains of high-manganese steel. Grain refinement can significantly improve the strength and toughness of high-manganese steel.

[0022] (2) Improve strength and hardness

[0023] Titanium dissolved into the matrix of high-manganese steel easily causes lattice distortion, increasing the resistance to dislocation movement and thus improving the strength and hardness of high-manganese steel. An appropriate titanium content can significantly improve the yield strength and tensile strength of high-manganese steel while maintaining good toughness, better meeting the requirements of practical engineering applications.

[0024] (3) Enhanced wear resistance

[0025] The addition of titanium can promote the formation of hard phases in high manganese steel. These hard phases are uniformly distributed in the matrix and can effectively resist the cutting and ploughing action of abrasives during friction and wear, thereby significantly improving the wear resistance of high manganese steel.

[0026] (4) Improve corrosion resistance

[0027] Titanium can form a dense oxide film on the surface of high-manganese steel. This oxide film has good stability and can prevent external corrosive media from contacting the steel substrate, thereby improving the corrosion resistance of high-manganese steel. In humid, acidic, or alkaline corrosive environments, adding titanium can effectively reduce the corrosion rate and ensure the normal use and lifespan of components.

[0028] However, excessive titanium can form numerous inclusions with elements such as carbon and nitrogen in steel. These inclusions are large in size and unevenly distributed, disrupting the continuity of the high-manganese steel matrix, leading to stress concentration, and thus reducing the strength and toughness of the high-manganese steel. This makes it prone to failure modes such as cracking and fracture during use. Furthermore, titanium is a strong carbide-forming element; excessive titanium will consume a large amount of carbon in the steel, reducing the carbon content in austenite and consequently decreasing the stability of austenite. Excessive titanium also increases costs and deteriorates processing performance. Therefore, this invention controls the Ti content to 0.03–0.1%, preferably 0.08%.

[0029] The roles of C, Mn, and Cr in the economical titanium-containing high-manganese steel of this invention are as follows:

[0030] Austenitic microstructures possess excellent strength, plasticity, and toughness characteristics, along with lower service temperatures. While adding high Ni content can achieve an austenitic microstructure, such as 316 austenitic stainless steel with 12% Ni content, the alloy cost is high. Mn can inhibit the transformation of austenite to martensite and can therefore be used as a substitute for Ni to obtain an austenitic microstructure. Since the effect of Mn on austenite stability is approximately half that of Ni, the Mn content in the ultra-low temperature steel of this invention is controlled at 22.5%–25.5%, with 24% being the most preferred.

[0031] Carbon (C) has a strong austenite stabilizing effect and is an effective element for improving austenite stability. Furthermore, C can hinder dislocation movement, thus increasing strength. From the perspective of austenite stabilization, the addition of C can increase the stacking fault energy of austenite, causing austenite to twinnize under strain instead of undergoing a martensitic transformation. The strain-induced twinning mechanism of austenite can significantly improve plasticity. Therefore, the C content in the ultra-low temperature steel of this invention is controlled at 0.35% to 0.55%, with a most preferably 0.43%.

[0032] Although Cr is a ferrite-forming element, it can lower the martensite transformation temperature, thereby improving the stability of austenite. Excessive Cr content leads to intensified carbide precipitation and reduced toughness. Therefore, the Cr content in the ultra-low temperature steel of this invention is controlled at 3% to 4%, with 3.6% being the most preferred.

[0033] In addition to the aforementioned chemical components, this invention has optimized the types and contents of other added elements. Si can provide a certain degree of solid solution strengthening, but Si segregation at grain boundaries weakens grain boundaries and increases intergranular brittleness. Furthermore, Si reduces plasticity. Therefore, this invention preferably controls the Si content to 0.11%–0.22%. Al, as a deoxidizing element in the manufacturing process, can also improve the performance of welded joints. However, excessive addition can easily form coarse precipitates and impair toughness. Therefore, this invention preferably controls the Al content to 0.01%–0.1%. Ca can react with oxygen and sulfur in steel to form stable compounds such as CaO and CaS. These compounds can float to the surface of the molten steel and be removed, thereby reducing the oxygen and sulfur content in the steel and improving its purity. Simultaneously, a small amount of Ca can alter the morphology and distribution of inclusions in the steel, reducing the adverse effects of inclusions on steel properties and improving the steel's toughness and plasticity. Therefore, this invention preferably controls the Ca content to 0.0003%–0.005%, most preferably 0.002%.

[0034] It should be noted that the actual content of alloying elements during material manufacturing fluctuates within a small range near the design range, which is an unavoidable fluctuation in normal industrial production. Although this invention clearly specifies the content range of each element, within a reasonable deviation range, it will not significantly affect the effectiveness of this invention.

[0035] The preparation method of titanium-containing high-manganese ultra-low temperature steel according to the present invention includes the following steps:

[0036] (1) Heating: The billet heating temperature is 1180~1230℃, and the total furnace time is 1.5~1.7min / mm×bill thickness;

[0037] (2) Phosphorus removal;

[0038] (3) Rolling: The initial rolling temperature of the billet is 1080~1120℃, and the final rolling temperature is 920~950℃;

[0039] (4) Cooling: The water temperature of the rolled steel plate is 900-930℃, the water temperature is 130-240℃, and the cooling rate is 17-48℃ / s.

[0040] The titanium-containing high-manganese cryogenic steel described in this invention is used in storage and transportation containers or pipelines for the preparation of liquefied ethylene, liquefied natural gas, liquid hydrogen, or liquid helium.

[0041] The heating process uses a walking beam furnace, the descaling process uses high-pressure water at a pressure of 22-24 MPa, and the cooling process uses ACC cooling to accelerate the cooling of the rolled steel plate. The thickness of the rolled steel plate is 15-50 mm.

[0042] The rolling mechanism of ultra-low temperature steel described in this invention is as follows:

[0043] To achieve sufficient grain refinement and strain accumulation through thermomechanical rolling, and thus sufficient strength in the finished steel plate, a sufficient compression ratio is required in the selection of slab thickness, i.e., the ratio of slab thickness (H) to finished steel plate thickness (h) (H / h). This invention controls the compression ratio between 6 and 12.

[0044] Because the thermal conductivity of the ultra-low temperature steel of this invention is only about one-third that of ordinary low-alloy steel, it is necessary to ensure that slabs of different thicknesses have sufficient furnace heating time to ensure complete austenitization. This invention controls the furnace time at (1.5–1.7 min / mm) × H, where H is the slab thickness. For example, when the slab thickness is 220 mm, the furnace time is 330–374 min.

[0045] After being heated in a walking beam furnace, the slabs are removed from the furnace and then pass through a descaling box to remove iron oxide scale. High-pressure water at a pressure of 22-24 MPa is used to ensure the descaling effect.

[0046] The slab is descaled in a descaling box before rolling. The initial rolling temperature is 1080–1120℃, and the final rolling temperature is controlled at a relatively low level, i.e., 920–950℃. Thermomechanical rolling refines the austenite grains, accumulates sufficient strain, and improves the strength of the finished steel plate. Sufficient slab thickness is beneficial for improving the thermomechanical rolling effect.

[0047] After rolling, the steel plate enters an ultra-fast cooling system for high-pressure water cooling. The inlet water temperature is 900–930℃, and the cooling rate is 17–48℃ / s to the outlet water temperature of 130–240℃. The accelerated cooling serves two purposes: firstly, it preserves the accumulated thermomechanical rolling strain and improves the strength of the steel plate; secondly, it inhibits carbide precipitation and improves the plasticity of the steel plate.

[0048] The cryogenic steel described in this invention is used for the storage and transportation of liquefied ethylene, liquefied natural gas, liquid hydrogen, or liquid helium, and is specifically manufactured into storage and transportation containers or pipelines for use in land, marine, or aviation environments.

[0049] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0050] The ultra-low temperature steel designed in this invention combines chemical elements with optimized steel rolling to focus on improving the low-temperature strength and corrosion resistance of the steel plate at -269℃, while eliminating the need for precious metal elements such as Ni, Mo, and Cu, as well as post-processing steps. It has excellent ultra-low temperature resistance and economy, and has application prospects in storing and transporting ultra-low temperature media such as liquefied ethylene, liquefied natural gas, liquid hydrogen, and liquid helium in complex environments such as land, sea, and aviation. Attached Figure Description

[0051] Figure 1 The image shows the microstructure of the steel plate prepared in Example 1. Detailed Implementation

[0052] The technical solution of the present invention will be further described below with reference to the embodiments.

[0053] Example 1

[0054] An economical niobium-containing high-manganese ultra-low temperature steel with a tensile strength of 800 MPa and its preparation method are disclosed. The chemical composition (mass percentage) is: C: 0.43%, Si: 0.17%, Mn: 24.0%, Cr: 3.6%, Ti: 0.08%, Alt: 0.06%, Ca: 0.002%, with the balance being Fe and unavoidable impurities. The slab thickness is 220 mm, and the rolled steel plate thickness is 25 mm. The slab is heated in a walking beam furnace to a target temperature of 1200℃ for a total furnace time of 1.6 hours. A descaling box is used to remove the iron oxide scale from the heated slab after exiting the furnace, with a high-pressure water pressure of 23 MPa. The initial rolling temperature is 1102℃, and the final rolling temperature is 937℃. The rolled steel plate is accelerated cooled using an ultra-fast cooling system, with an inlet water temperature of 917℃, an outlet water temperature of 182℃, and a cooling rate of 29℃ / s. The steel plate has an austenitic microstructure. Its room temperature yield strength is 468 MPa, room temperature tensile strength is 843 MPa, room temperature elongation after fracture is 55%, -269℃ yield strength is 1032 MPa, -269℃ tensile strength is 1413 MPa, -269℃ elongation after fracture is 49%, -196℃ impact energy is 165 J, and -269℃ impact energy is 76 J.

[0055] Example 2

[0056] An economical niobium-containing high-manganese ultra-low temperature steel with a tensile strength of 800 MPa and its preparation method are disclosed. The chemical composition (mass percentage) is: C: 0.35%, Si: 0.11%, Mn: 22.5%, Cr: 3.0%, Ti: 0.03%, Alt: 0.01%, Ca: 0.0003%, with the balance being Fe and unavoidable impurities. The slab thickness is 180 mm, and the rolled steel plate thickness is 15 mm. The slab is heated in a walking beam furnace to a target temperature of 1230 °C for a total furnace time of 1.7 hours. A descaling box is used to remove the iron oxide scale from the heated slab after exiting the furnace, with a high-pressure water pressure of 24 MPa. The initial rolling temperature is 1083 °C, and the final rolling temperature is 922 °C. The rolled steel plate is accelerated cooled using an ultra-fast cooling system, with an inlet water temperature of 903 °C, an outlet water temperature of 134 °C, and a cooling rate of 48 °C / s. The steel plate has an austenitic microstructure. Its room temperature yield strength is 462 MPa, room temperature tensile strength is 844 MPa, room temperature elongation after fracture is 53%, -269℃ yield strength is 1026 MPa, -269℃ tensile strength is 1421 MPa, -269℃ elongation after fracture is 47.5%, -196℃ impact energy is 175 J, and -269℃ impact energy is 73 J.

[0057] Example 3

[0058] An economical niobium-containing high-manganese ultra-low temperature steel with a tensile strength of 800 MPa and its preparation method are disclosed. The chemical composition (mass percentage) is: C: 0.55%, Si: 0.22%, Mn: 25.5%, Cr: 4.0%, Ti: 0.10%, Alt: 0.10%, Ca: 0.005%, with the balance being Fe and unavoidable impurities. The slab thickness is 320 mm, and the rolled steel plate thickness is 50 mm. The slab is heated in a walking beam furnace to a target temperature of 1180℃ for a total furnace time of 1.5 hours. A descaling box is used to remove the iron oxide scale from the heated slab after exiting the furnace, with a high-pressure water pressure of 22 MPa. The initial rolling temperature is 1123℃, and the final rolling temperature is 954℃. The rolled steel plate is accelerated cooled using an ultra-fast cooling system, with an inlet water temperature of 931℃, an outlet water temperature of 235℃, and a cooling rate of 17℃ / s. The steel plate has an austenitic microstructure. Its room temperature yield strength is 454 MPa, room temperature tensile strength is 835 MPa, room temperature elongation after fracture is 56.5%, -269℃ yield strength is 1029 MPa, -269℃ tensile strength is 1434 MPa, -269℃ elongation after fracture is 48.5%, -196℃ impact energy is 171 J, and -269℃ impact energy is 78 J.

Claims

1. A titanium-containing high-manganese ultra-low temperature steel, characterized in that, By weight fraction, its composition includes C: 0.35%~0.55%, Si: 0.11%~0.22%, Mn: 22.5%~25.5%, P≤0.02%, S≤0.005%, Cr: 3%~4%, Ti: 0.03%~0.1%, Alt: 0.01%~0.1%, Ca: 0.0003%~0.005%, with the balance being Fe and other unavoidable impurities; Its microstructure is austenitic, and the grain size of its austenitic structure is less than 20 μm; The preparation method of the titanium-containing high-manganese ultra-low temperature steel includes the following steps: (1) Heating: The billet heating temperature is 1180~1230℃, and the total furnace time is 1.5~1.7min / mm×bill thickness; (2) Remove scales; (3) Rolling: The initial rolling temperature of the billet is 1080~1120℃, and the final rolling temperature is 920~937℃; (4) Cooling: The water temperature of the rolled steel plate is 900~930℃, the water temperature is 130~240℃, and the cooling rate is 17~48℃ / s.

2. The titanium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that, By weight fraction, its composition includes C: 0.43%, Si: 0.17%, Mn: 24%, Cr: 3.6%, Ti: 0.08%, Alt: 0.06%, Ca: 0.002%, with the balance being Fe and unavoidable impurity elements; Or its composition may include C: 0.35%, Si: 0.11%, Mn: 22.5%, Cr: 3%, Ti: 0.03%, Alt: 0.01%, Ca: 0.0003%, with the balance being Fe and unavoidable impurity elements; Alternatively, its composition may include C: 0.55%, Si: 0.22%, Mn: 25.5%, Cr: 4.0%, Ti: 0.1%, Alt: 0.1%, Ca: 0.005%, with the balance being Fe and unavoidable impurity elements.

3. The titanium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that, In its microstructure, the volume of austenite accounts for no less than 95%.

4. The titanium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that, Its stacking fault energy at -269℃ is 18~21 mJ·m -2 .

5. The titanium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that, Its thickness is 15~50mm.

6. The titanium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that, Its yield strength R at -269℃ p0.2 ≥1000MPa, tensile strength R m ≥1400MPa, elongation after fracture ≥46%, impact energy Akv≥60J.

7. A method for preparing the titanium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that, Includes the following steps: (1) Heating: The billet heating temperature is 1180~1230℃, and the total furnace time is 1.5~1.7min / mm×bill thickness; (2) Remove scales; (3) Rolling: The initial rolling temperature of the billet is 1080~1120℃, and the final rolling temperature is 920~937℃; (4) Cooling: The water temperature of the rolled steel plate is 900~930℃, the water temperature is 130~240℃, and the cooling rate is 17~48℃ / s.

8. The application of the titanium-containing high-manganese cryogenic steel of claim 1 in the preparation of storage and transportation containers or pipelines for liquefied ethylene, liquefied natural gas, liquid hydrogen or liquid helium.

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