High-manganese steel plate for high-strength and high-toughness LNG storage tank and preparation method of high-manganese steel plate

Abstract

The invention discloses a high-manganese steel plate for a high-strength and high-toughness LNG storage tank and a preparation method of the high-manganese steel plate, and belongs to the technical field of steel and iron material preparation. According to the preparation method disclosed by the invention, the low-temperature toughness of the high-manganese steel is ensured by properly increasing the grain size of austenite, and meanwhile, the strength of the high-manganese steel is improved by combining multiple strengthening means such as dislocation strengthening and precipitation strengthening, so that the high-manganese steel plate for the LNG storage tank has excellent toughness. According to the high-manganese steel plate for the high-strength and high-toughness LNG storage tank, the room-temperature yield strength is 607.3-747.4 MPa, the tensile strength is 895.3-988.4 MPa, the ductility is 41.2%-50.6%, the impact absorbing energy at the temperature of 196 DEG C below zero is 108.4-113.4 J, and the high-manganese steel plate is obviously superior to existing recorded high-manganese steel in the high-strength and high-toughness level. The method for improving the high strength and toughness of the high-manganese steel plate for the LNG storage tank has small dependence on chemical components of the high-manganese steel, and can be suitable for the high-manganese steel with various components.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel material preparation, and particularly relates to a high-manganese steel plate for LNG storage tanks with high strength and toughness and a preparation method thereof. BACKGROUND

[0002] Liquefied natural gas (LNG) is an important way to ensure natural gas supply. At present, the demand for steel for LNG storage tanks is increasing rapidly, and new types of steel are urgently needed to reduce costs and improve the quality of storage tanks. In the development of new ultra-low temperature materials, high-manganese austenitic steel has attracted much attention due to its low price, low thermal expansion coefficient and good low-cycle fatigue performance. High-manganese austenitic steel uses manganese and carbon to stabilize the austenite phase, and a single-phase austenite structure is obtained at room temperature. Austenitic steel generally does not have a ductile-brittle transition phenomenon, so high-manganese austenitic steel has a congenital advantage for ultra-low temperature (-196℃) applications. However, due to the face-centered cubic crystal structure, the yield strength of high-manganese austenitic steel is relatively low (usually between 200-400 MPa), which limits its engineering application. It is urgent to solve the problem of low yield strength of high-manganese austenitic steel for LNG storage tanks.

[0003] For a long time, researchers have hoped to improve the yield strength of high-manganese austenitic steel through solid solution strengthening, precipitation strengthening and fine-grain strengthening. However, for high-manganese austenitic steel with a face-centered cubic crystal structure, the octahedral interstitial space is much larger than that of a body-centered cubic structure, which makes the solid solution strengthening effect of high-manganese austenitic steel weaker than that of a body-centered cubic structure steel. At the same time, it is also because of this reason that the precipitation of the second phase in austenitic steel is relatively difficult, resulting in weak precipitation strengthening effect.

[0004] In body-centered cubic steel, fine-grain strengthening is considered a method that can improve both strength and toughness, but this rule does not apply to single-phase austenitic steel. On the one hand, although fine-grain strengthening can effectively improve the yield strength of high-manganese steel, the yield strength of high-manganese austenitic steel can only be increased to about 400 MPa when the grain is refined to less than 5 μm, and the grain can only be refined to about 10 μm by conventional hot rolling. On the other hand, excessive grain refinement will inhibit the activation of twinning, which will actually reduce the impact toughness of high-manganese austenitic steel at -196℃. SUMMARY

[0005] The purpose of the present application is to provide a high-manganese steel plate for LNG storage tanks with high strength and toughness and a preparation method thereof, to solve the technical problem of the contradiction between strength and toughness control in the existing method of improving the strength and toughness of high-manganese steel plates for LNG storage tanks.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] The application discloses a preparation method of high-manganese steel plate for LNG storage tanks with high strength and toughness.

[0008] After one-time heating of the high-manganese austenite ingot, multi-pass hot continuous rolling is performed to obtain the steel material after hot continuous rolling;

[0009] After air cooling of the steel material after hot continuous rolling, rolling is continuously performed to obtain the steel material after rolling;

[0010] After heating and heat preservation of the steel material after rolling, cooling to room temperature is performed to obtain the high-manganese steel plate for LNG storage tanks with high strength and toughness.

[0011] Further, the process parameters of the one-time heating are that the high-manganese austenite ingot is heated to 1200 DEG C and heat preserved for 2h.

[0012] Further, the opening rolling temperature of the multi-pass hot continuous rolling is 1125-1165 DEG C, the final rolling temperature is 1020-1080 DEG C, and the total reduction is 60%-75%.

[0013] Further, the air cooling is air cooling of the steel material after hot continuous rolling to 700-750 DEG C.

[0014] Further, the rolling pass of the continuously performed rolling is 2-3 passes, and the total reduction is 35%-50%.

[0015] Further, the temperature of the heating and heat preservation is 700 DEG C, and the heat preservation time is 100-140s.

[0016] Further, the cooling mode is water cooling, and the cooling speed of the water cooling is 20-40 DEG C / s.

[0017] The application further discloses the high-manganese steel plate for LNG storage tanks with high strength and toughness prepared by the preparation method.

[0018] Further, in terms of mass percentage, the chemical components of the high-manganese steel plate for LNG storage tanks with high strength and toughness include C: 0.40%-0.61%, Mn: 18.0%-27.5%, Si: 0-0.48%, Al: 0-5.1%, Cr: 0-4.5%, Cu: 0-0.5%, V: 0-0.31%, and the rest is Fe and inevitable impurities.

[0019] Further, the microstructure of the high-manganese steel plate for LNG storage tanks with high strength and toughness is flattened austenite organization with a grain size of 25-40 mu m;

[0020] The room temperature yield strength, tensile strength and elongation of the high-manganese steel plate for LNG storage tanks with high strength and toughness are 607.3-747.4 MPa, 895.3-988.4 MPa and 41.2%-50.6% respectively.

[0021] The impact absorption energy of the high-toughness high manganese steel plate for LNG storage tank at -196 DEG C is 105.5-113.4 J.

[0022] Compared with the prior art, the application has the following beneficial effects:

[0023] The application discloses a preparation method of a high-toughness high manganese steel plate for LNG storage tank.

[0024] Further, the preparation method of the application has a simple process flow, and compared with conventional hot rolling, only by increasing short-time heat preservation, excellent toughness can be realized, and the method is suitable for production conditions of most steel plants.

[0025] Further, when the method is used to improve the high-toughness high manganese steel plate for LNG storage tank, the method has small dependence on chemical components of the high manganese steel, and can be applied to various high manganese steels. BRIEF DESCRIPTION OF DRAWINGS

[0026] Fig. 1 The figure is a hot rolling state metallographic structure of the high-toughness high manganese steel plate for LNG storage tank prepared in the application example 1.

[0027] Fig. 2 The figure is a hot rolling state metallographic structure of the high-toughness high manganese steel plate for LNG storage tank prepared in the application example 2.

[0028] Fig. 3 The figure is a hot rolling state metallographic structure of the high-toughness high manganese steel plate for LNG storage tank prepared in the application example 3.

[0029] Fig. 4 The figure is a hot rolling state metallographic structure of the high-toughness high manganese steel plate for LNG storage tank prepared in the application example 3. DETAILED DESCRIPTION

[0030] In order for those skilled in the art to understand the characteristics and effects of the application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used in the text are the usual meanings understood by those skilled in the art for the application, and in case of conflict, the definition in the specification shall prevail.

[0031] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0032] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0033] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0034] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0035] This invention provides a method for preparing high-manganese steel plates for LNG storage tanks to improve strength and toughness. The chemical composition, by weight percentage, is: C: 0.40%–0.61%, Mn: 18.0%–27.5%, Si: 0–0.48%, Al: 0–5.1%, Cr: 0–4.5%, Cu: 0–0.5%, V: 0–0.31%, with the remainder being Fe and unavoidable impurities. This is achieved through the following technical solution, with specific steps as follows:

[0036] Step 1, Casting:

[0037] High-manganese austenitic steel is smelted, and the molten steel is directly poured into a square mold to obtain a thin ingot.

[0038] Step 2, Heating (single heating):

[0039] Heat the steel billet or thin ingot to 1200℃ and hold for 2 hours;

[0040] Step 3, Rolling:

[0041] The heated steel billet is subjected to multi-pass continuous rolling, with an initial rolling temperature of 1125-1165℃ and a final rolling temperature of 1020-1080℃; the total reduction rate is 60%-75%.

[0042] Step 4, wait for it to warm up:

[0043] The hot-rolled steel is placed on a roller table and air-cooled to 700-750°C.

[0044] Step 5, Rolling:

[0045] The air-cooled steel is then rolled in 2 to 3 passes, with a total reduction of 35% to 50%.

[0046] Step 6, Heating (Heating and Keeping Warm):

[0047] The rolled steel is placed in a furnace at 700℃ and held for 100-140 seconds.

[0048] Step 7, water cooling:

[0049] The heated steel is cooled to room temperature by water at a rate of 20–40°C / s.

[0050] The present invention prepares a flattened austenitic structure with a grain size of about 25-40 μm. The room temperature yield strength, tensile strength and elongation of the steel plate can reach 607.3-747.4 MPa, 895.3-988.4 MPa and 41.2%-50.6%, respectively, and the impact absorption energy at -196℃ is 105.5-113.4 J.

[0051] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0052] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0053] Example 1

[0054] A method for preparing high-manganese steel plates for high-strength and high-toughness LNG storage tanks includes the following steps:

[0055] The chemical composition of high-manganese austenitic steel by weight percentage is as follows: C: 0.57%, Si: 0.5%, Mn: 24.4%, Al: 1.92%, V: 0.31%, P: 0.004%, S: 0.006%, with the balance being Fe and unavoidable impurities;

[0056] Step 1, Casting:

[0057] High-manganese austenitic steel is smelted, and the molten steel is directly poured into a square mold to obtain a thin ingot.

[0058] Step 2: Heating:

[0059] A steel billet or thin ingot is heated to 1200℃ and held for 2 hours to obtain a heated steel billet.

[0060] Step 3, Rolling:

[0061] The heated steel billet is subjected to multi-pass continuous rolling with an initial rolling temperature of 1165℃ and a final rolling temperature of 1080℃; the total reduction rate is 70%, resulting in hot-rolled steel.

[0062] Step 4, wait for it to warm up:

[0063] The hot-rolled steel is placed on a roller table and air-cooled to 710°C.

[0064] Step 5, Rolling:

[0065] The air-cooled steel is then rolled in three passes with a total reduction of 45%, resulting in 12mm thick hot-rolled steel (the rolled steel).

[0066] Step 6, heating:

[0067] The rolled steel is placed in a furnace at 700℃ and held for 120 seconds.

[0068] Step 7, water cooling:

[0069] The heated steel was water-cooled to room temperature at a rate of 34°C / s, and the high-strength and high-toughness high-manganese steel plate for LNG storage tanks was obtained after water cooling.

[0070] Example 2

[0071] A method for preparing high-manganese steel plates for high-strength and high-toughness LNG storage tanks includes the following steps:

[0072] The chemical composition of high-manganese austenitic steel by weight percentage is: C: 0.61%, Si: 0.48%, Mn: 18.2%, Al: 5.1%, P: 0.003%, S: 0.002%, with the balance being Fe and unavoidable impurities;

[0073] Step 1, Casting:

[0074] High-manganese austenitic steel is smelted, and the molten steel is directly poured into a square mold to obtain a thin ingot.

[0075] Step 2: Heating:

[0076] A steel billet or thin ingot is heated to 1200℃ and held for 2 hours to obtain a heated steel billet.

[0077] Step 3, Rolling:

[0078] The heated steel billet is subjected to multi-pass continuous rolling with an initial rolling temperature of 1125℃ and a final rolling temperature of 1020℃; the total reduction rate is 72%, resulting in hot-rolled steel.

[0079] Step 4, wait for it to warm up:

[0080] The hot-rolled steel is placed on a roller table and air-cooled to 705°C.

[0081] Step 5, Rolling:

[0082] The air-cooled steel is then rolled in 3 passes with a total reduction of 41%, resulting in 12mm thick hot-rolled steel (the rolled steel).

[0083] Step 6, heating:

[0084] The rolled steel is placed in a furnace at 700℃ and held for 120 seconds.

[0085] Step 7, water cooling:

[0086] The heated steel was water-cooled to room temperature at a rate of 35°C / s, and the high-strength and high-toughness high-manganese steel plate for LNG storage tanks was obtained after water cooling.

[0087] Example 3

[0088] A method for preparing high-manganese steel plates for high-strength and high-toughness LNG storage tanks includes the following steps:

[0089] The chemical composition of high-manganese austenitic steel by weight percentage is: C: 0.40%, Mn: 27.5%, Si: 0.3%, Cr: 4.5%, Cu: 0.5%, P: 0.003%, S: 0.004%, with the balance being Fe and unavoidable impurities;

[0090] Step 1, Casting:

[0091] High-manganese austenitic steel is smelted, and the molten steel is directly poured into a square mold to obtain a thin ingot.

[0092] Step 2: Heating:

[0093] A steel billet or thin ingot is heated to 1200℃ and held for 2 hours to obtain a heated steel billet.

[0094] Step 3, Rolling:

[0095] The heated steel billet is subjected to multi-pass continuous rolling with an initial rolling temperature of 1150℃ and a final rolling temperature of 1060℃; the total reduction rate is 65%, resulting in hot-rolled steel.

[0096] Step 4, wait for it to warm up:

[0097] The hot-rolled steel is placed on a roller table and air-cooled to 720°C.

[0098] Step 5, Rolling:

[0099] The air-cooled steel is then rolled in three passes with a total reduction of 35%, resulting in 12mm thick hot-rolled steel (the rolled steel).

[0100] Step 6, heating:

[0101] The rolled steel is placed in a furnace at 700℃ and held for 140 seconds.

[0102] Step 7, water cooling:

[0103] The heated steel was water-cooled to room temperature at a rate of 31°C / s, and the high-strength and high-toughness high-manganese steel plate for LNG storage tanks was obtained after water cooling.

[0104] Comparative Example 1

[0105] The chemical composition of high-manganese austenitic steel by weight percentage is: C: 0.57%, Si: 0.5%, Mn: 24.4%, Al: 1.92%, V: 0.31%, P: 0.004%, S: 0.006%, with the balance being Fe and unavoidable impurities.

[0106] A method for preparing high-manganese steel plates for LNG storage tanks, which improves strength and toughness, is achieved through the following technical solution, with specific steps as follows:

[0107] Step 1, Forging:

[0108] High-manganese austenitic steel is smelted, and the molten steel is directly poured into a square mold to obtain a thin ingot.

[0109] Step 2, heating:

[0110] Heat the steel billet or ingot to 1200℃ and hold for 2 hours;

[0111] Step 3, Rolling:

[0112] The heated steel billet was subjected to multi-pass continuous rolling with an initial rolling temperature of 1150℃ and a final rolling temperature of 810℃; the total reduction rate was 84%, resulting in 12mm thick hot-rolled steel.

[0113] Step 4, Cooling:

[0114] After rolling, the hot-rolled steel was cooled to room temperature using ultra-fast cooling to obtain the high-manganese steel plate for LNG storage tanks, which is sample 4.

[0115] Table 1 shows a comparison of the mechanical properties of the samples obtained in Comparative Example 1 and Examples 1-3. As can be seen from the table, the high-manganese steel plate for LNG storage tanks prepared by the method of the present invention has a room temperature yield strength, tensile strength, and elongation of 607.3-747.4 MPa, 895.3-988.4 MPa, and 41.2%-50.6%, respectively. The impact absorption energy at -196℃ is 108.4-113.4 J. The yield strength is significantly better than that of Comparative Example 1, and the impact absorption energy and elongation at -196℃ are also higher than those of Comparative Example 1. At the same time, the comprehensive mechanical properties are also significantly better than the strength and toughness levels of high-manganese steel recorded in the literature.

[0116] Table 1 Mechanical properties of high manganese steel plates

[0117]

[0118] Figs. 1-4 The figures show the microstructure morphology of the samples obtained in Examples 1-3 and Comparative Example 1. As can be seen from the figures, the present invention prepares a flattened austenite structure with a grain size of approximately 25-40 μm. The present invention ensures the low-temperature toughness of high-manganese steel by moderately increasing the grain size of austenite, while simultaneously improving the strength of high-manganese steel by combining multiple strengthening methods such as dislocation strengthening and precipitation strengthening.

[0119] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing high-manganese steel plates for high-strength and high-toughness LNG storage tanks, characterized in that, Includes the following steps: After heating the high-manganese austenitic ingot once, it is subjected to multiple hot rolling passes to obtain hot-rolled steel. After hot-rolled steel is air-cooled, it is rolled again to obtain rolled steel. After the rolled steel is heated and kept at a constant temperature, it is cooled to room temperature to obtain high-strength and high-toughness high-manganese steel plates for LNG storage tanks.

2. The method for preparing high-manganese steel plate for high-strength and high-toughness LNG storage tanks according to claim 1, characterized in that, The process parameters for the first heating are: heating the high-manganese austenitic ingot to 1200℃ and holding it at that temperature for 2 hours.

3. The method for preparing high-manganese steel plate for high-strength and high-toughness LNG storage tanks according to claim 1, characterized in that, The multi-pass hot continuous rolling has an initial rolling temperature of 1125–1165°C, a final rolling temperature of 1020–1080°C, and a total reduction rate of 60%–75%.

4. The method for preparing high-manganese steel plate for high-strength and high-toughness LNG storage tanks according to claim 1, characterized in that, The air cooling refers to air cooling the hot-rolled steel to 700-750°C.

5. The method for preparing high-manganese steel plate for high-strength and high-toughness LNG storage tanks according to claim 1, characterized in that, The rolling process continues with 2 to 3 rolling passes, and the total reduction rate is 35% to 50%.

6. The method for preparing high-manganese steel plate for high-strength and high-toughness LNG storage tanks according to claim 1, characterized in that, The heating and heat preservation temperature is 700℃, and the heat preservation time is 100-140s.

7. The method for preparing high-manganese steel plate for high-strength and high-toughness LNG storage tanks according to claim 1, characterized in that, The cooling method is water cooling; the cooling rate of the water cooling is 20-40℃ / s.

8. A high-manganese steel plate for high-strength and high-toughness LNG storage tanks, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 7.

9. The high-strength and high-toughness high-manganese steel plate for LNG storage tanks according to claim 8, characterized in that, The chemical composition of the high-manganese steel plate for the high-strength and high-toughness LNG storage tank, by mass percentage, includes: C: 0.40%–0.61%, Mn: 18.0%–27.5%, Si: 0–0.48%, Al: 0–5.1%, Cr: 0–4.5%, Cu: 0–0.5%, V: 0–0.31%, with the remainder being Fe and unavoidable impurities.

10. A high-strength and high-toughness high-manganese steel plate for LNG storage tanks according to claim 8, characterized in that, The microstructure of the high-manganese steel plate used in the high-strength and high-toughness LNG storage tank is a flattened austenitic structure with a grain size of 25-40 μm. The high-manganese steel plate used in the high-strength and high-toughness LNG storage tank has a room temperature yield strength, tensile strength, and elongation of 607.3–747.4 MPa, 895.3–988.4 MPa, and 41.2%–50.6%, respectively. The high-manganese steel plate used in the high-strength and high-toughness LNG storage tank has an impact absorption energy of 108.4 to 113.4 J at -196℃.

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