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

Abstract

The invention discloses titanium-containing high-manganese ultralow-temperature steel as well as a preparation method and application thereof. The ultralow-temperature steel comprises the following chemical 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 Ti, 0.01%-0.1% of Alt, 0.0003%-0.005% of Ca and the balance of Fe and other inevitable impurities. Chemical elements are combined with rolled steel, the low-temperature strength and corrosion resistance of the steel plate at the temperature of-269 DEG C are emphatically improved, precious metal elements such as Ni, Mo and Cu and post-treatment procedures are omitted, and the steel plate has excellent ultralow temperature resistance and economical efficiency; the device has application prospects in storage and transportation of liquefied ethylene, liquefied natural gas, liquid hydrogen, liquid helium and other ultralow-temperature media in land, ocean, aviation and other complex environments.

Description

Technical Field

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

[0002] With the deepening of the concept of green development, clean energy is gradually replacing traditional energy. Among them, natural liquefied gas (LNG) has become an irreplaceable part of energy supply after rapid development, alleviating dependence on petroleum energy. Since LNG is usually stored at low temperatures of -163°C, the materials available for LNG storage and transportation facilities must have high strength, high and low temperature toughness, and high performance that is easy to weld. At present, Invar alloy, austenitic stainless steel and 9% Ni steel are conventionally used to manufacture storage and transportation containers, but the cost of Ni steel remains high due to the relative rarity of the Ni element, and austenitic stainless steel has low strength and a large expansion coefficient. In recent years, there has been a trend of high manganese steel replacing Ni steel, but the existing high manganese steel can only be used at a minimum of -196°C, and its performance still cannot meet the requirements of ultra-low temperature environments.

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

[0004] CN102409227 discloses a hot-rolled steel strip with low relative magnetic permeability, wherein the 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%, and the rest is Fe and inevitable impurities. Since the Al content in the austenitic steel plate is too high, hot rolling is prone to cracks, and process stability is difficult to control.

[0005] CN108929993 discloses a microalloyed high-strength and high-plastic non-magnetic steel plate, the chemical element composition of which is C: 0.10-0.20%, 0<Si≤0.4%, Mn: 20-26%, A1: 2.0-3.0%, Ti: 0.01-0.02%, Nb: 0.04-0.09%, and the balance is Fe and other inevitable impurities. The impact energy of the steel plate 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

[0006] Purpose of the invention: The first purpose of the present 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. 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 described in the present invention comprises, by weight percentage, 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%, and the balance is Fe and other inevitable impurities.

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

[0009] or its composition comprises C: 0.35%, Si: 0.11%, Mn: 22.5%, Cr: 3%, Ti: 0.03%, Alt: 0.01%, Ca: 0.0003%, and the balance is Fe and inevitable impurity elements;

[0010] Alternatively, its composition includes C: 0.55%, Si: 0.22%, Mn: 25.5%, Cr: 4.0%, Ti: 0.1%, Alt: 0.1%, Ca: 0.005%, and the balance is Fe and inevitable impurity elements.

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

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

[0013] Further preferably, 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 to 21 mJ·m -2 .

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

[0016] Preferably, the titanium-containing high-manganese ultra-low temperature steel chamber has a yield strength Rp0.2 ≥450MPa, tensile strength R m ≥800MPa, elongation after fracture ≥50%; at -269℃, yield strength R p0.2 ≥1000MPa, tensile strength R m ≥1400MPa, elongation after break ≥46%; -196℃ impact energy Akv ≥150J, -269℃ impact energy Akv ≥60J.

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

[0018] 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.

[0019] In particular, the Ti element is mainly added to the composition system of the economical high manganese steel of the present invention, and the key functions of Ti in the steel are as follows:

[0020] (1) Grain refinement

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

[0022] (2) Improve strength and hardness

[0023] The titanium element is dissolved in the matrix of high manganese steel, which can easily cause lattice distortion and increase the resistance to dislocation movement, thereby improving the strength and hardness of high manganese steel. The appropriate amount of titanium content can significantly improve the yield strength and tensile strength of high manganese steel while maintaining good toughness, better meeting the actual use requirements of engineering.

[0024] (3) Enhance wear resistance

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

[0026] (4) Improved 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 the contact between external corrosive media and the steel matrix, thereby improving the corrosion resistance of high manganese steel. In humid, acidic and alkaline corrosive environments, adding titanium can effectively reduce the corrosion rate and ensure the normal use and life of the components.

[0028] However, excessive titanium will form a large number of inclusions with elements such as carbon and nitrogen in steel, and these inclusions are large in size and unevenly distributed, which will destroy the continuity of the high manganese steel matrix, leading to stress concentration, thereby reducing the strength and toughness of high manganese steel, making it prone to failure forms such as cracks and fractures during use. At the same time, titanium is a strong carbide-forming element, and excessive titanium will consume a large amount of carbon in steel, reduce the carbon content in austenite, and further reduce the stability of austenite. Excessive titanium will also increase costs and deteriorate processing performance. Therefore, the present invention controls the content of Ti to 0.03-0.1%, preferably 0.08%.

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

[0030] 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 into 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 controlled at 22.5% to 25.5%, and most preferably 24%.

[0031] 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 phase 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 controlled at 0.35% to 0.55%, and most preferably 0.43%.

[0032] 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 controlled at 3% to 4%, and most preferably 3.6%.

[0033] 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 oxygen and sulfur content 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%, and the most preferred is 0.002%.

[0034] 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.

[0035] The method for preparing titanium-containing high-manganese ultra-low temperature steel of the present invention comprises the following steps:

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

[0037] (2) Phosphorus removal;

[0038] (3) Rolling: The starting rolling temperature of the billet is 1080-1120°C, and the final rolling temperature is 920-950°C;

[0039] (4) Cooling: After rolling, the water inlet temperature of the steel plate is 900-930°C, the water outlet temperature is 130-240°C, and the cooling rate is 17-48°C / s.

[0040] The titanium-containing high-manganese ultra-low temperature steel of the present invention is used in storage and transportation containers or pipelines for preparing liquefied ethylene, liquefied natural gas, liquid hydrogen or liquid helium.

[0041] Among them, a walking beam heating furnace is used for heating, the high-pressure water pressure used for dephosphorization is 22 to 24 MPa, and the ACC cooling method is used for cooling to accelerate the cooling of the rolled steel plate. The thickness specification of the rolled steel plate is 15 to 50 mm.

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

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The ultra-low temperature steel of the present invention is used for the storage and transportation of liquefied ethylene, liquefied natural gas, liquid hydrogen or liquid helium, and is specifically made into storage and transportation containers or transmission pipelines for use in land, sea 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 by the present invention combines chemical elements with steel rolling optimization, focuses on improving the low-temperature strength and corrosion resistance of the steel plate at -269°C, and omits precious metal elements such as Ni, Mo, Cu and post-processing procedures. It has excellent ultra-low temperature resistance and economy, and has application prospects in the storage and transportation of ultra-low temperature media such as liquefied ethylene, liquefied natural gas, liquid hydrogen, and liquid helium in complex environments such as land, ocean, and aviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is the microstructure diagram of the steel plate prepared in Example 1. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is further described below in conjunction with embodiments.

[0053] Example 1

[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: 0.43%, Si: 0.17%, Mn: 24.0%, Cr: 3.6%, Ti: 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 furnace discharge, and the high-pressure water pressure is 23MPa. The starting rolling temperature is 1102°C, and the final rolling temperature is 937°C. Ultra-fast cooling equipment is used to accelerate the cooling of the rolled steel plate, with a water inlet temperature of 917°C, a water outlet temperature of 182°C, and a cooling rate of 29°C / s. The steel plate structure is austenite, with a room temperature yield strength of 468MPa, a room temperature tensile strength of 843MPa, a room temperature elongation of 55%, a -269℃ yield strength of 1032MPa, a -269℃ tensile strength of 1413MPa, a -269℃ elongation of 49%, an -196℃ impact energy of 165J, and a -269℃ impact energy of 76J.

[0055] Example 2

[0056] An economical ultra-low temperature steel containing high manganese and niobium with a tensile strength of 800 MPa and a preparation method thereof, wherein 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%, and the remainder is Fe and unavoidable impurity elements. The slab thickness is 180 mm, and the rolled steel plate thickness is 15 mm. The billet is heated using a walking beam heating furnace, with a target temperature of 1230°C and a total furnace time of 1.7 hours. 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 24 MPa. The starting rolling temperature is 1083°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 134°C, and a cooling rate of 48°C / s. The steel plate structure is austenite, with a room temperature yield strength of 462MPa, a room temperature tensile strength of 844MPa, a room temperature elongation of 53%, a -269℃ yield strength of 1026MPa, a -269℃ tensile strength of 1421MPa, a -269℃ elongation of 47.5%, an -196℃ impact energy of 175J, and a -269℃ impact energy of 73J.

[0057] Example 3

[0058] An economical ultra-low temperature steel containing niobium and high manganese 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%, Ti: 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 1123°C, and the final rolling temperature is 954°C. Ultra-fast cooling equipment is used to accelerate the cooling of the rolled steel plate, with a water inlet temperature of 931°C, a water outlet temperature of 235°C, and a cooling rate of 17°C / s. The steel plate structure is austenite, with a room temperature yield strength of 454MPa, a room temperature tensile strength of 835MPa, a room temperature elongation of 56.5%, a -269℃ yield strength of 1029MPa, a -269℃ tensile strength of 1434MPa, a -269℃ elongation of 48.5%, an -196℃ impact energy of 171J, and a -269℃ impact energy of 78J.

Claims

1. A titanium-containing high-manganese ultra-low temperature steel, characterized in that: Calculated by weight, 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%, and the balance is Fe and other inevitable impurities.

2. The titanium-containing high-manganese ultra-low temperature steel according to claim 1, characterized in that: In terms of 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%, and the balance is Fe and unavoidable impurity elements; or its composition comprises C: 0.35%, Si: 0.11%, Mn: 22.5%, Cr: 3%, Ti: 0.03%, Alt: 0.01%, Ca: 0.0003%, and the balance is Fe and inevitable impurity elements; Alternatively, its composition includes C: 0.55%, Si: 0.22%, Mn: 25.5%, Cr: 4.0%, Ti: 0.1%, Alt: 0.1%, Ca: 0.005%, and the balance is Fe and inevitable impurity elements.

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

4. The titanium-containing high-manganese ultra-low temperature steel according to claim 3, characterized in that: In its microstructure, the volume proportion of austenite structure is not less than 95%.

5. The titanium-containing high-manganese ultra-low temperature steel according to claim 3, characterized in that: The grain size of its austenite structure does not exceed 20μm.

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

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

8. The titanium-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 after fracture ≥46%, impact energy Akv ≥60J.

9. A method for preparing the titanium-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) Phosphorus removal; (3) Rolling: The starting rolling temperature of the billet is 1080-1120°C, and the final rolling temperature is 920-950°C; (4) Cooling: After rolling, the water inlet temperature of the steel plate is 900-930°C, the water outlet temperature is 130-240°C, and the cooling rate is 17-48°C / s.

10. Use of the titanium-containing high-manganese ultra-low temperature steel according to 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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