Niobium-containing high-manganese ultralow-temperature steel as well as preparation method and application thereof

Abstract

The invention discloses niobium-containing high-manganese ultralow-temperature steel as well as a preparation method and application thereof. The ultralow-temperature steel comprises the following components in percentage by weight: 0.35%-0.55% of C, 0.11%-0.22% of Si, 22.5%-25.5% of Mn, less than or equal to 0.02% of P, less than or equal to 0.005% of S, 3%-4% of Cr, 0.03%-0.1% of Nb, 0.01%-0.1% of Alt, 0.0003%-0.005% of Ca and the balance of Fe and other inevitable impurities, the ultralow-temperature steel is prepared by adopting the procedures of continuous casting billet heating, descaling, rolling and cooling, and the components and the process are more economical. The ultralow-temperature-resistant and hydrogen-damage-resistant low-temperature-resistant cable material has excellent ultralow-temperature resistance and hydrogen damage resistance, is wide in application prospect, can be applied to storage and transportation of multiple ultralow-temperature media such as liquefied ethylene, liquefied natural gas, liquid hydrogen and liquid helium, and is suitable for multiple complex environments such as land, ocean and aviation.

Description

Technical Field

[0001] The invention relates to a niobium-containing high-manganese ultra-low temperature steel and a preparation method and application thereof, and in particular to an economical niobium-containing high-manganese ultra-low temperature steel and a preparation method and application thereof. Background Art

[0002] Nickel steels such as Invar steel (36% Ni), 316 stainless steel (12% Ni), and 9% Ni steel are often used as ultra-low temperature structural materials to manufacture storage and transportation containers for ultra-low temperature media such as liquefied ethylene, liquefied natural gas, liquid hydrogen, and liquid helium. Due to the limited reserves of nickel, the manufacturing cost is high and the economic efficiency is poor.

[0003] High manganese steel refers to alloy steel with a manganese content of more than 10%. It has high strength, good toughness, corrosion resistance and wear resistance, so it was originally used as wear-resistant steel. With the in-depth research on the composition design, organizational regulation, production process and application of high manganese steel, its application field has gradually expanded to non-magnetic steel, automotive steel, steel for corrosion and low-temperature environments, and even functional materials. In recent years, with the widespread application of clean energy, especially the substantial increase in demand for LNG, high manganese steel is gradually replacing nickel steel as a low-temperature material. However, the performance of conventionally designed high manganese steel can only meet the use in low-temperature environments as low as -196°C, and its application is still limited.

[0004] CN104894471 discloses a high manganese, high aluminum, vanadium-containing non-magnetic steel plate, whose chemical element composition is C: 0.14% to 0.20%, Mn: 21.50% to 25.00%, Al: 1.50% to 2.50%, V: 0.04% to 0.10%, N < 0.05%, and the balance is Fe and unavoidable impurities. The yield strength of the steel is only 280 to 300 MPa, and the tensile strength is 550 to 700 MPa, which is difficult to meet the high strength requirements of the steel plate.

[0005] CN102409227 discloses a hot-rolled steel strip with low relative magnetic permeability, the chemical element composition of which is C: 0.25% to 0.35%, Si: 0.5% to 0.6%, Mn: 25% to 26%, Al: 3.8% to 4.2%, V: 0.06% to 0.10%, P: 0.02% to 0.03%, S: 0.02% to 0.03%, and the rest is Fe and unavoidable impurities. The Al content in the steel is too high, which is very easy to form hot rolling cracks and reduce the yield rate.

[0006] CN108929993 discloses a microalloyed high-strength and high-plastic non-magnetic steel plate, the chemical element composition of which is C: 0.10% to 0.20%, 0<Si≤0.4%, Mn: 20% to 26%, A1: 2.0% to 3.0%, Ti: 0.01% to 0.02%, Nb: 0.04% to 0.09%, and the remainder is Fe and other inevitable impurities. The impact energy of the steel at -196°C is only ≥110J, which is difficult to meet the storage and transportation requirements of ultra-low temperature media such as liquid hydrogen and liquid helium. Summary of the invention

[0007] Purpose of the invention: The first purpose of the present invention is to provide an economical high manganese steel with high strength and excellent low temperature performance. The second purpose is to provide a preparation method of the high manganese steel. The third purpose is to provide an ultra-low temperature application of the high manganese steel.

[0008] Technical solution: The niobium-containing high-manganese ultra-low temperature steel of the present invention comprises, by weight percentage, C: 0.35%-0.55%, Si: 0.11%-0.22%, Mn: 22.5%-25.5%, P≤0.020%, S≤0.005%, Cr: 3%-4%, Nb: 0.03%-0.1%, Alt: 0.01%-0.1%, Ca: 0.0003%-0.005%, and the balance is Fe and unavoidable impurities.

[0009] Preferably, the niobium-containing high-manganese ultra-low temperature steel comprises, by weight percentage, C: 0.43%, Si: 0.17%, Mn: 24%, Cr: 3.6%, Nb: 0.08%, Alt: 0.06%, Ca: 0.002%, and the remainder is Fe and unavoidable impurities.

[0010] Preferably, the niobium-containing high-manganese ultra-low temperature steel comprises, by weight percentage, C: 0.35%, Si: 0.11%, Mn: 22.5%, Cr: 3%, Nb: 0.03%, Alt: 0.01%, Ca: 0.0003%, and the remainder is Fe and unavoidable impurities.

[0011] Preferably, the niobium-containing high-manganese ultra-low temperature steel comprises, by weight percentage, C: 0.55%, Si: 0.22%, Mn: 25.5%, Cr: 4%, Nb: 0.1%, Alt: 0.1%, Ca: 0.005%, and the remainder is Fe and unavoidable impurities.

[0012] The composition design mechanism of the above-mentioned high manganese ultra-low temperature steel is as follows:

[0013] The present invention obtains a highly stable austenite structure by adding 0.43% C, 24% Mn and 3.6% Cr. After pre-straining 0.35 true strain and then performing -269°C deep cryogenic treatment, martensite structure still does not appear. At the same time, the stacking fault energy of austenite at -269°C is controlled to 18-21mJ·m -2 The matching of strength and toughness is achieved by the composite mechanism of dislocation + twinning, so that the Charpy impact absorption energy of the ultra-low temperature steel of the present invention at -269°C is ≥60J.

[0014] In particular, the Nb element is mainly added to the composition system of the economical high manganese steel of the present invention, and the key functions of Nb in the steel are as follows:

[0015] (1) Grain refinement

[0016] Nb combines with carbon, nitrogen and other elements in steel to form fine carbides, nitrides and other particles, which can hinder the growth of austenite grains, thereby effectively refining the grains of high manganese steel. The refined grains improve the strength and toughness of high manganese steel, while improving its processing performance and wear resistance, and reducing crack initiation and expansion.

[0017] (2) Improve welding performance

[0018] Nb can reduce the overheating sensitivity of high manganese steel, prevent the occurrence of overheated structure during welding, and reduce the occurrence of welding cracks.

[0019] In the present invention, the Nb content is preferably controlled within a range of 0.03% to 0.1%, and more preferably 0.08%.

[0020] Austenite structure has excellent strength, plasticity, toughness matching and lower operating temperature. Although adding high content of Ni can obtain austenite structure, such as 316 austenite stainless steel with 12% Ni content, the alloy cost is high. Mn can inhibit the transformation of austenite to martensite, so it can be used as a substitute element for Ni to obtain austenite structure. Since the effect of Mn on the stability of austenite is about half that of Ni, the content of Mn in the ultra-low temperature steel of the present invention is 22.5% to 25.5%, more preferably 24%.

[0021] C has a strong austenite stabilizing effect and is also an effective element for improving austenite stability. Moreover, C can hinder dislocation movement and improve strength. From the perspective of austenite stabilization, the addition of C can increase the stacking fault energy of austenite, so that austenite produces twins instead of martensitic transformation when strained. The strain-induced twinning mechanism of austenite can significantly improve plasticity. Therefore, the C content in the ultra-low temperature steel of the present invention is 0.35% to 0.55%, and more preferably 0.43%.

[0022] Although Cr is a ferrite-forming element, it can reduce the martensite transformation temperature, thereby improving the stability of austenite. Too high a Cr content leads to aggravated carbide precipitation and reduced toughness. Therefore, the Cr content in the ultra-low temperature steel of the present invention is 3% to 4%, and more preferably 3.6%.

[0023] In addition to the above chemical composition, the present invention has optimized the types and contents of other elements added. Among them, Si can produce a certain degree of solid solution strengthening, but Si segregation at the grain boundary will weaken the grain boundary and increase the intergranular brittleness. In addition, Si will also reduce plasticity, so the present invention preferably controls the content of Si to 0.11% to 0.22%. Al, as a deoxidizing element in the manufacturing process, can also improve the performance of the welded joint, but excessive addition is easy to form a coarse precipitate phase and damage toughness, so the present invention preferably controls the content of Al to 0.01% to 0.1%. Ca can react with oxygen and sulfur in steel to form stable compounds, such as CaO, CaS, etc. These compounds can float to the surface of the molten steel and be removed, thereby reducing the content of oxygen and sulfur in the steel and improving the purity of the steel. At the same time, a small amount of Ca can change the morphology and distribution of inclusions in the steel, reduce the adverse effects of inclusions on steel performance, and improve the toughness and plasticity of the steel. Therefore, the present invention preferably controls the content of Ca to 0.0003% to 0.005%, more preferably 0.002%.

[0024] It should be noted that the actual content of alloying elements in the material manufacturing process fluctuates within a certain small range near the design range, which is an inevitable fluctuation in normal industrial production. Although the present invention clearly stipulates the content range of each element, it will not have a significant impact on the effect of the present invention within a reasonable deviation range.

[0025] Preferably, the microstructure of the niobium-containing high-manganese ultra-low temperature steel is an austenite structure.

[0026] Further preferably, in the microstructure of the niobium-containing high-manganese ultra-low temperature steel, the volume proportion of austenite structure is not less than 95%.

[0027] Preferably, the niobium-containing high-manganese ultra-low temperature steel has a yield strength R p0.2 ≥450MPa, tensile strength R m ≥800MPa, elongation after fracture ≥50%; at -269℃, yield strength R p0.2 ≥1000MPa, tensile strength R m ≥1400MPa, elongation at break ≥46%.

[0028] Preferably, the impact energy Akv of the niobium-containing high-manganese ultra-low temperature steel at -196°C is ≥150J; and the impact energy Akv at -269°C is ≥60J.

[0029] Preferably, the thickness of the niobium-containing high-manganese ultra-low temperature steel is 15 to 50 mm.

[0030] The method for preparing niobium-containing high-manganese ultra-low temperature steel of the present invention comprises the following steps:

[0031] (1) Heating: Heating temperature 1180-1230°C, total furnace time 1.5-1.7 min / mm × billet thickness;

[0032] (2) Descaling;

[0033] (3) Rolling: the starting rolling temperature is 1080-1120°C, and the final rolling temperature is 920-950°C;

[0034] (4) Cooling: The rolled steel plate is cooled at an accelerated rate, with the water inlet temperature at 900-930°C, the water outlet temperature at 130-240°C, and the cooling rate at 17-48°C / s.

[0035] In step (2), high-pressure water with a pressure of 22 to 24 MPa is used to remove the iron oxide scale of the heated billet, in step (3), a walking beam heating furnace is used to heat the billet, and in step (4), an ACC cooling method is used to accelerate the cooling of the rolled steel plate, and the thickness specification of the rolled steel plate is 15 to 50 mm.

[0036] The rolling process mechanism of the high manganese ultra-low temperature steel of the present invention is as follows:

[0037] In order to obtain sufficient grain refinement and strain accumulation through thermomechanical rolling and obtain sufficient finished steel plate strength, a sufficient compression ratio is required in the selection of slab thickness, that is, the ratio (H / h) of slab thickness (H) to finished steel plate thickness (h). The present invention controls the compression ratio to 6 to 12.

[0038] Because the thermal conductivity of the ultra-low temperature steel of the present invention is only about one-third of that of ordinary low alloy steel, it is necessary to ensure that the slabs of different thicknesses have sufficient heating time in the furnace to ensure complete austenitization. The present invention controls the furnace time to (1.5-1.7min / mm)×H, where H is the thickness of the billet. For example, when the billet thickness is 220mm, the furnace time is 330-374min.

[0039] The slab is heated in a walking beam heating furnace and then taken out of the furnace. It passes through a descaling box to remove the oxidized iron scale. The high-pressure water pressure is 22 to 24 MPa to ensure the descaling effect.

[0040] The slab is rolled after being descaled by the descaling box. The starting rolling temperature is 1080-1120℃, and the final rolling temperature is controlled to be relatively low, i.e. 920-950℃. Thermomechanical rolling refines the austenite grains, accumulates sufficient strain, and improves the strength of the finished steel plate. The slab has sufficient thickness, which is conducive to improving the thermomechanical rolling effect.

[0041] After rolling, the steel plate enters the ultra-fast cooling equipment for high-pressure water cooling, with the water inlet temperature of 900-930°C and the cooling rate of 17-48°C / s to the water outlet temperature of 130-240°C. The role of accelerated cooling is, on the one hand, to retain the accumulation of thermomechanical rolling strain and improve the strength of the steel plate, and on the other hand, to inhibit the precipitation of carbides and improve the plasticity of the steel plate.

[0042] The niobium-containing high-manganese ultra-low temperature steel of the present invention is used in storage and transportation containers or transportation pipelines for preparing liquefied ethylene, liquefied natural gas, liquid hydrogen or liquid helium.

[0043] Preferably, the method is used in storage and transportation containers or transportation pipelines for preparing ultra-low temperature media in land, ocean or aviation environments.

[0044] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0045] The ultra-low temperature steel designed by the present invention has no precious metal elements such as Ni / Mo / Cu added through composition and process optimization, and has excellent ultra-low temperature resistance and hydrogen damage resistance. The rolling process eliminates the need for post-processing procedures, and the manufacturing cost is more economical. It has a wide range of application prospects and can be used for the storage and transportation of various ultra-low temperature media such as liquefied ethylene, liquefied natural gas, liquid hydrogen, and liquid helium, and is suitable for various complex environments such as land, sea, and aviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is the microstructure diagram of the steel plate prepared in Example 1. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below in conjunction with embodiments.

[0048] The tests of yield strength, tensile strength, elongation after fracture and impact energy shall refer to "GB / T 228.1-2021 Tensile test of metal materials Part 1: Room temperature test method", "GB / T 228.3-2019 Tensile test of metal materials Part 3: Low temperature test method", "GB / T 228.4-2019 Tensile test of metal materials Part 4: Liquid helium test method" and "GB / T 229-2020 Charpy pendulum impact test method for metal materials".

[0049] Example 1

[0050] An economical niobium-containing high-manganese ultra-low temperature steel with a tensile strength of 800MPa and a preparation method thereof, wherein the chemical composition mass percentage is C: 0.43%, Si: 0.17%, Mn: 24.0%, Cr: 3.6%, Nb: 0.08%, Alt: 0.06%, Ca: 0.002%, and the remainder is Fe and unavoidable impurity elements. The slab thickness is 220mm, and the rolled steel plate thickness is 25mm. The billet is heated using a walking beam heating furnace, with a target temperature of 1200°C and a total furnace time of 1.6H. A descaling box is used to remove the iron oxide scale of the billet after heating and leaving the furnace, and the high-pressure water pressure is 23MPa. The starting rolling temperature is 1106°C, and the final rolling temperature is 935°C. Ultra-fast cooling equipment is used to accelerate the cooling of the rolled steel plate, with a water inlet temperature of 916°C, a water outlet temperature of 181°C, and a cooling rate of 33°C / s. The steel plate structure is austenite, with a room temperature yield strength of 465MPa, a room temperature tensile strength of 842MPa, a room temperature elongation of 56%, a -269℃ yield strength of 1052MPa, a -269℃ tensile strength of 1453MPa, a -269℃ elongation of 48.5%, an -196℃ impact energy of 168J, and a -269℃ impact energy of 77J.

[0051] Example 2

[0052] An economical niobium-containing high-manganese ultra-low temperature steel with a tensile strength of 800MPa and a preparation method thereof, wherein the chemical composition mass percentage is C: 0.35%, Si: 0.11%, Mn: 22.5%, Cr: 3.0%, Nb: 0.03%, Alt: 0.01%, Ca: 0.0003%, and the remainder is Fe and unavoidable impurity elements. The slab thickness is 180mm, and the rolled steel plate thickness is 15mm. The billet is heated using a walking beam heating furnace, with a target temperature of 1230°C and a total furnace time of 1.7H. A descaling box is used to remove the iron oxide scale of the billet after heating and taking it out of the furnace, and the high-pressure water pressure is 24MPa. The starting rolling temperature is 1084°C, and the final rolling temperature is 922°C. Ultra-fast cooling equipment is used to accelerate the cooling of the rolled steel plate, with a water inlet temperature of 903°C, a water outlet temperature of 135°C, and a cooling rate of 48°C / s. The steel plate structure is austenite, with a room temperature yield strength of 469MPa, a room temperature tensile strength of 851MPa, a room temperature elongation of 55%, a -269℃ yield strength of 1047MPa, a -269℃ tensile strength of 1429MPa, a -269℃ elongation of 47.5%, an -196℃ impact energy of 173J, and a -269℃ impact energy of 75J.

[0053] Example 3

[0054] An economical niobium-containing high-manganese ultra-low temperature steel with a tensile strength of 800MPa and a preparation method thereof, wherein the chemical composition mass percentage is C: 0.55%, Si: 0.22%, Mn: 25.5%, Cr: 4.0%, Nb: 0.10%, Alt: 0.10%, Ca: 0.005%, and the remainder is Fe and unavoidable impurity elements. The slab thickness is 320mm, and the rolled steel plate thickness is 50mm. The billet is heated using a walking beam heating furnace, with a target temperature of 1180°C and a total furnace time of 1.5H. A descaling box is used to remove the iron oxide scale of the billet after heating out of the furnace, and the high-pressure water pressure is 22MPa. The starting rolling temperature is 1120°C, and the final rolling temperature is 950°C. Ultra-fast cooling equipment is used to accelerate the cooling of the rolled steel plate, with a water inlet temperature of 930°C, a water outlet temperature of 237°C, and a cooling rate of 17°C / s. The steel plate structure is austenite, with a room temperature yield strength of 456MPa, a room temperature tensile strength of 831MPa, a room temperature elongation of 56%, a -269℃ yield strength of 1026MPa, a -269℃ tensile strength of 1431MPa, a -269℃ elongation of 46.5%, a -196℃ impact energy of 169J, and a -269℃ impact energy of 76J.

Claims

1. A niobium-containing high-manganese ultra-low temperature steel, characterized in that: In terms of weight fraction, its composition includes C: 0.35% ~ 0.55%, Si: 0.11% ~ 0.22%, Mn: 22.5% ~ 25.5%, P ≤ 0.020%, S ≤ 0.005%, Cr: 3% ~ 4%, Nb: 0.03% ~ 0.1%, Alt: 0.01% ~ 0.1%, Ca: 0.0003% ~ 0.005%, and the balance is Fe and unavoidable impurities.

2. The niobium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that: In terms of weight percentage, its composition includes C: 0.43%, Si: 0.17%, Mn: 24%, Cr: 3.6%, Nb: 0.08%, Alt: 0.06%, Ca: 0.002%, and the balance is Fe and inevitable impurities.

3. The niobium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that: In terms of weight percentage, its composition includes C: 0.35%, Si: 0.11%, Mn: 22.5%, Cr: 3.0%, Nb: 0.03%, Alt: 0.01%, Ca: 0.0003%, and the balance is Fe and inevitable impurities.

4. The niobium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that: In terms of weight percentage, its composition includes C: 0.55%, Si: 0.22%, Mn: 25.5%, Cr: 4%, Nb: 0.1%, Alt: 0.1%, Ca: 0.005%, and the balance is Fe and inevitable impurities.

5. The niobium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that: Its microstructure is austenite.

6. The niobium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that: At -269℃, the yield strength R p0.2 ≥1000MPa, tensile strength R m ≥1400MPa, elongation at break ≥46%.

7. The niobium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that: Its impact energy Akv at -269°C is ≥60J.

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

9. A method for preparing niobium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that: The following steps are involved: (1) Heating: The billet heating temperature is 1180-1230°C, and the total furnace time is 1.5-1.7 min / mm × billet thickness; (2) Descaling; (3) Rolling: The billet starting rolling temperature is 1080-1120°C, and the final rolling temperature is 920-950°C; (4) Cooling: The rolled steel plate is cooled at an accelerated rate, with the water inlet temperature at 900-930°C, the water outlet temperature at 130-240°C, and the cooling rate at 17-48°C / s.

10. Use of the niobium-containing high-manganese ultra-low temperature steel according to claim 1 in the preparation of storage and transportation containers or transportation pipelines for liquefied ethylene, liquefied natural gas, liquid hydrogen or liquid helium.

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