Low-nickel alloy steel for ultralow-temperature environment and preparation method of low-nickel alloy steel

Abstract

The invention discloses low-nickel alloy steel for an ultralow-temperature environment, which is prepared from the following components in percentage by mass: 5.00 to 6.00 percent of Ni, 0.03 to 0.08 percent of C, 4.00 to 5.00 percent of Mn, 0.1 to 0.20 percent of Mo, 0.01 to 0.06 percent of Nb, 0.02 to 0.05 percent of Al, 0.20 to 0.50 percent of Si, 0.02 to 0.10 percent of N, 0.01 to 0.04 percent of Ti and the balance of Fe and inevitable impurities, and the total mass of the low-nickel alloy steel is 100 percent. Compared with low-nickel alloy steel 9Ni steel commonly used in the field at present, the nickel content is reduced, meanwhile, the high strength and high toughness of the material are kept through the reasonable composition proportion and the fine machining technology, particularly, the content and stability of tempered austenite are optimized, and therefore the performance is further improved under the extremely low temperature condition.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy steels, and in particular relates to a low-nickel alloy steel for use in ultra-low temperature environments and a preparation method thereof. Background Art

[0002] As a clean and efficient energy source, the demand for liquefied natural gas (LNG) is growing rapidly worldwide. LNG is a liquid formed by cooling natural gas to -162°C under normal pressure, which greatly reduces the volume and is very convenient for storage and transportation. At present, the global demand for LNG is growing at a rate of about 8% per year, and Asia will grow faster in the next few years. my country has become one of the world's top five natural gas importers and consumers, with an average annual growth rate of more than 10% in domestic natural gas consumption. Since the storage and transportation temperature of liquefied natural gas is -162°C, this requires that the materials used to build LNG storage tanks must have good low-temperature impact toughness and excellent plasticity comprehensive properties. 9Ni steel is an important steel grade required for low-temperature storage and transportation equipment such as LNG. It is one of the most commonly used low-temperature alloy steels and is usually used in the construction of LNG storage tanks and transport ships. 9% nickel steel has excellent low-temperature toughness and brittle fracture resistance, and can maintain good mechanical properties at extremely low temperatures of -196°C. However, with the large-scale consumption of nickel resources, the proportion of nickel alloying cost in the cost of 9Ni steel is increasing, and saving nickel has become an important issue.

[0003] Both at home and abroad, research and exploration work on low-temperature steel with low Ni content has been carried out. In general, either the manganese content is too high or the subsequent treatment process is relatively complicated, resulting in high costs, and further research and discussion is still necessary. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and provide a low nickel alloy steel for ultra-low temperature environment. The nickel-saving steel can be used in low temperature environments above -196°C, has high toughness, high plasticity and high strength, and can reduce the cost of nickel alloying.

[0005] Another object of the present invention is to provide a method for preparing the low-nickel alloy steel for use in ultra-low temperature environments.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A low-nickel alloy steel for use in ultra-low temperature environments, which consists of the following components, based on the total mass of the low-nickel alloy steel being 100%, Ni: 5.00-6.00%, C: 0.03-0.08%, Mn: 4.00-5.00%, Mo: 0.1-0.20%, Nb: 0.01-0.06%, Al: 0.02-0.05%, Si: 0.20-0.50%, N: 0.02-0.10%, Ti: 0.01-0.04%, and the remainder being Fe and unavoidable inclusions.

[0008] The method for preparing the low-nickel alloy steel for ultra-low temperature environment comprises the following steps:

[0009] (1) Steelmaking:

[0010] Raw materials of iron ore, coke and limestone are placed in a blast furnace, heated to 1500°C for high-temperature smelting to obtain molten pig iron and slag, the molten pig iron is sent to a converter for steelmaking, and other trace element raw materials are added to make the content of each component meet the set mass percentage to obtain molten steel;

[0011] (2) Hot rolling:

[0012] During the hot rolling process, the billet is heated to 1100-1200°C and the deformation is controlled to be 30-60%. After the hot rolling is completed, it is ultra-rapidly cooled to room temperature to obtain rolled steel.

[0013] (3) Heat treatment:

[0014] The rolled steel is subjected to dual phase tempering to obtain a low nickel alloy steel for use in ultra-low temperature environments.

[0015] The specific steps are as follows:

[0016] Furthermore, in step (1), the steelmaking temperature is 1600-1700°C.

[0017] Furthermore, in step (2), the ultra-fast cooling rate is 100 to 500° C. / s.

[0018] Furthermore, in step (3), the dual-phase tempering method is as follows: in the first tempering, the steel billet is heated to 200-300°C and maintained for 1-2h; in the second tempering, the steel billet is further heated to 400-500°C, maintained for 2-3h, and naturally air-cooled to room temperature.

[0019] The design principle of the present invention is as follows:

[0020] a. From the perspective of components:

[0021] 1) Although the goal is to reduce the nickel content, a certain amount of nickel still needs to be retained to ensure toughness and impact resistance under ultra-low temperature conditions, while maintaining the low-temperature performance of the material while reducing costs;

[0022] 2) Manganese is a key austenite stabilizer. Manganese can replace part of nickel to ensure the stability and toughness of the austenite phase at low temperatures. Appropriate manganese content can also improve the strength and ductility of steel.

[0023] 3) Low carbon content helps maintain low temperature toughness and reduces carbides formed during welding, thereby reducing brittleness. In addition, lower carbon content can avoid the formation of excessive martensite phase, thereby improving the overall toughness of the material;

[0024] 4) Molybdenum can improve the strength and hardness of steel. In low temperature environment, molybdenum can also enhance the steel's resistance to brittle fracture;

[0025] 5) Aluminum acts as a deoxidizer and can promote the formation of fine and uniform tempered austenite, thereby improving low-temperature impact toughness;

[0026] 6) Silicon helps deoxidation, reduces the formation of inclusions, improves the toughness of steel in low temperature environments, reduces the formation of martensite, and thus improves low temperature performance;

[0027] 7) Niobium can refine grains by forming carbides or nitrides, and can also inhibit the growth of austenite grains, thereby further improving the low-temperature toughness of steel;

[0028] 8) Nitrogen is a strong austenite-forming element, which can replace the role of nickel to a certain extent and enhance the stability of austenite;

[0029] 9) Titanium can form stable carbonitrides with carbon and nitrogen, thereby preventing the precipitation of carbides at the grain boundaries, reducing grain boundary embrittlement, and helping to refine the grains, further improving the impact toughness at low temperatures.

[0030] In addition to the above-mentioned individual effects, there are also obvious synergistic effects:

[0031] 1) Synergistic effect of Mn and Ni: The content of manganese is used to replace part of the nickel to ensure the stability of austenite while reducing material costs;

[0032] 2) Auxiliary regulation of Mo, Al and Si: The addition of molybdenum enhances the strength and corrosion resistance, while aluminum and silicon further improve the low-temperature toughness of the material by promoting the refinement and stabilization of austenite;

[0033] 3) Comprehensive effect of trace elements: Trace elements such as niobium, nitrogen, and titanium further improve the comprehensive mechanical properties and low-temperature toughness of the material by refining the grains and forming stable carbonitrides;

[0034] 4) Combining low carbon content with appropriate amounts of Al or Si, this dual composition control method can effectively increase the content of tempered austenite and further improve the low temperature performance of steel.

[0035] b. From the perspective of heat treatment process:

[0036] 1) Precise hot rolling process control: A process for precisely controlling the deformation amount and deformation temperature during hot rolling is proposed. Compared with the traditional process, this can more effectively refine the grain structure and optimize the microstructure, thereby improving the low-temperature performance of the material; especially in the rapid cooling stage after deformation, it can better maintain the refined grain structure and improve the overall performance of the material;

[0037] 2) Combination of ultra-fast cooling and dual-phase tempering: In the traditional ultra-fast cooling process, dual-phase tempering treatment (i.e., primary tempering followed by secondary tempering) helps to maximize the formation of tempered austenite while maintaining the toughness and strength of the steel. This process combination can not only achieve grain refinement, but also reduce residual stress in the material through secondary tempering, thereby further improving low-temperature toughness.

[0038] Beneficial effects of the present invention:

[0039] 1) While reducing the nickel content, the high strength and toughness of the material are maintained through reasonable composition ratio and sophisticated processing technology, especially optimizing the content and stability of tempered austenite, thereby achieving further improvement in performance under extremely low temperature conditions;

[0040] 2) Comprehensive consideration of cost and performance: The design takes into account both economy and performance. By reducing the use of nickel and introducing relatively cheap and effective alloying elements (such as manganese, silicon, molybdenum, etc.), the cost is controlled while ensuring the excellent performance of the material at low temperatures. This balance has obvious innovative advantages over the existing low-nickel high-manganese steel;

[0041] 3) Auxiliary regulation of Mo, Al and Si: The addition of molybdenum enhances the strength and corrosion resistance, while aluminum and silicon further improve the low-temperature toughness of the material by promoting the refinement and stabilization of austenite;

[0042] 4) Comprehensive effect of trace elements: Trace elements such as niobium, nitrogen, and titanium further improve the comprehensive mechanical properties and low-temperature toughness of the material by refining the grains and forming stable carbonitrides;

[0043] 5) Combined with dual-phase tempering treatment (i.e., primary tempering followed by secondary tempering), it helps to maximize the formation of tempered austenite while maintaining the toughness and strength of the steel. This process combination can not only achieve grain refinement, but also reduce residual stress in the material through secondary tempering, thereby further improving low-temperature toughness. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is clearly and completely described below in conjunction with specific embodiments.

[0045] Example 1

[0046] A low-nickel alloy steel for use in ultra-low temperature environments, which consists of the following components, based on the total mass of the low-nickel alloy steel being 100%, Ni: 5.10%, C: 0.08%, Mn: 5.00%, Mo: 0.12%, Nb: 0.01%, Al: 0.03%, Si: 0.20%, N: 0.03%, Ti: 0.01%, and the balance being Fe and unavoidable inclusions.

[0047] The method for preparing the low-nickel alloy steel for ultra-low temperature environment comprises the following steps:

[0048] (1) Steelmaking:

[0049] The raw materials of iron ore, coke and limestone are put into a blast furnace in a mass ratio of 13:5:2, and the temperature is raised to 1500°C for 10 hours of high-temperature smelting to obtain molten pig iron and slag. The molten pig iron is sent to a converter at 1600-1700°C for steelmaking for 30 minutes, and other trace element raw materials are added to make the content of each component meet the mass percentage set above, and finally molten steel is obtained;

[0050] (2) Hot rolling:

[0051] During the hot rolling process, the billet is heated to 1100°C and the deformation is controlled to be 30%. After the hot rolling, it is ultra-fast cooled to room temperature at a cooling rate of 200°C / s to obtain rolled steel.

[0052] (3) Heat treatment:

[0053] The rolled steel is subjected to dual phase tempering to obtain a low nickel alloy steel for use in ultra-low temperature environments.

[0054] The dual-phase tempering method is as follows: in the first tempering, the steel billet is heated to 200° C. and maintained for 1 hour; in the second tempering, the steel billet is further heated to 500° C. and maintained for 2 hours, and then naturally air-cooled to room temperature.

[0055] According to Part 3: Low Temperature Test Method of GB / T 228-2019 "Tensile Test of Metallic Materials", the low nickel alloy steel prepared in Example 1 was tested, and the yield strength of the low nickel alloy steel was measured to be 635 MPa, the tensile strength was 723 MPa, and the low temperature (-196°C) impact energy was 169 J.

[0056] Example 2

[0057] A low-nickel alloy steel for use in ultra-low temperature environments, comprising the following components, based on the total mass of the low-nickel alloy steel being 100%, Ni: 5.20%, C: 0.05%, Mn: 4.80%, Mo: 0.14%, Nb: 0.01%, Al: 0.04%, Si: 0.44%, N: 0.08%, Ti: 0.01%, and the remainder being Fe and unavoidable inclusions.

[0058] The method for preparing the low-nickel alloy steel for ultra-low temperature environment comprises the following steps:

[0059] (1) Steelmaking:

[0060] The raw materials of iron ore, coke and limestone are put into a blast furnace in a mass ratio of 13:5:2, and the temperature is raised to 1500°C for 10 hours of high-temperature smelting to obtain molten pig iron and slag. The molten pig iron is sent to a converter at 1600-1700°C for steelmaking for 30 minutes, and other trace element raw materials are added to make the content of each component meet the mass percentage set above, and finally molten steel is obtained;

[0061] (2) Hot rolling:

[0062] During the hot rolling process, the billet is heated to 1150°C and the deformation is controlled to be 50%. After the hot rolling, the billet is ultra-fast cooled to room temperature at a cooling rate of 100°C / s to obtain rolled steel.

[0063] (3) Heat treatment:

[0064] The rolled steel is subjected to dual phase tempering to obtain a low nickel alloy steel for use in ultra-low temperature environments.

[0065] The dual-phase tempering method is as follows: in the first tempering, the steel billet is heated to 220° C. and maintained for 1.3 h; in the second tempering, the steel billet is further heated to 480° C. and maintained for 2.4 h, and then naturally air-cooled to room temperature.

[0066] The yield strength of the low nickel alloy steel prepared in Example 2 was measured to be 640 MPa, the tensile strength was 720 MPa, and the low temperature (-196°C) impact energy was 170 J.

[0067] Example 3

[0068] A low-nickel alloy steel for use in ultra-low temperature environments, comprising the following components, based on the total mass of the low-nickel alloy steel being 100%, Ni: 5.50%, C: 0.04%, Mn: 4.60%, Mo: 0.16%, Nb: 0.02%, Al: 0.02%, Si: 0.36%, N: 0.1%, Ti: 0.02%, and the remainder being Fe and unavoidable inclusions.

[0069] The method for preparing the low-nickel alloy steel for ultra-low temperature environment comprises the following steps:

[0070] (1) Steelmaking:

[0071] The raw materials of iron ore, coke and limestone are put into a blast furnace in a mass ratio of 13:5:2, and the temperature is raised to 1500°C for 10 hours of high-temperature smelting to obtain molten pig iron and slag. The molten pig iron is sent to a converter at 1600-1700°C for steelmaking for 30 minutes, and other trace element raw materials are added to make the content of each component meet the mass percentage set above, and finally molten steel is obtained;

[0072] (2) Hot rolling:

[0073] During the hot rolling process, the billet is heated to 1130°C and the deformation is controlled to be 40%. After the hot rolling, it is ultra-fast cooled to room temperature at a cooling rate of 300°C / s to obtain rolled steel.

[0074] (3) Heat treatment:

[0075] The rolled steel is subjected to dual phase tempering to obtain a low nickel alloy steel for use in ultra-low temperature environments.

[0076] The dual-phase tempering method is as follows: in the first tempering, the steel billet is heated to 300° C. and maintained for 1.5 hours; in the second tempering, the steel billet is further heated to 460° C. and maintained for 2.5 hours, and then naturally air-cooled to room temperature.

[0077] The yield strength of the low nickel alloy steel prepared in Example 3 was measured to be 638 MPa, the tensile strength was 725 MPa, and the impact energy was 173 J at a low temperature of -196°C.

[0078] Example 4

[0079] A low-nickel alloy steel for use in ultra-low temperature environments, comprising the following components, based on 100% of the total mass of the low-nickel alloy steel: Ni: 5.40%, C: 0.05%, Mn: 4.20%, Mo: 0.18%, Nb: 0.04%, Al: 0.04%, Si: 0.28%, N: 0.04%, Ti: 0.04%, and the balance being Fe and unavoidable inclusions.

[0080] The method for preparing the low-nickel alloy steel for ultra-low temperature environment comprises the following steps:

[0081] (1) Steelmaking:

[0082] The raw materials of iron ore, coke and limestone are put into a blast furnace in a mass ratio of 13:5:2, and the temperature is raised to 1500°C for 10 hours of high-temperature smelting to obtain molten pig iron and slag. The molten pig iron is sent to a converter at 1600-1700°C for steelmaking for 30 minutes, and other trace element raw materials are added to make the content of each component meet the mass percentage set above, and finally molten steel is obtained;

[0083] (2) Hot rolling:

[0084] During the hot rolling process, the billet is heated to 1180°C and the deformation is controlled to be 30%. After the hot rolling, the billet is ultra-fast cooled to room temperature at a cooling rate of 400°C / s to obtain rolled steel.

[0085] (3) Heat treatment:

[0086] The rolled steel is subjected to dual phase tempering to obtain a low nickel alloy steel for use in ultra-low temperature environments.

[0087] The dual-phase tempering method is as follows: in the first tempering, the steel billet is heated to 260° C. and maintained for 1.7 hours; in the second tempering, the steel billet is further heated to 440° C. and maintained for 2.6 hours, and then naturally air-cooled to room temperature.

[0088] The yield strength of the low nickel alloy steel prepared in Example 4 was measured to be 641 MPa, the tensile strength was 721 MPa, and the impact energy was 168 J at a low temperature of -196°C.

[0089] Example 5

[0090] A low-nickel alloy steel for use in ultra-low temperature environments, which consists of the following components, based on the total mass of the low-nickel alloy steel being 100%, Ni: 5.90%, C: 0.07%, Mn: 4.30%, Mo: 0.2%, Nb: 0.05%, Al: 0.05%, Si: 0.3%, N: 0.02%, Ti: 0.02%, and the balance being Fe and unavoidable inclusions.

[0091] The method for preparing the low-nickel alloy steel for ultra-low temperature environment comprises the following steps:

[0092] (1) Steelmaking:

[0093] The raw materials of iron ore, coke and limestone are put into a blast furnace in a mass ratio of 13:5:2, and the temperature is raised to 1500°C for 10 hours of high-temperature smelting to obtain molten pig iron and slag. The molten pig iron is sent to a converter at 1600-1700°C for steelmaking for 30 minutes, and other trace element raw materials are added to make the content of each component meet the mass percentage set above, and finally molten steel is obtained;

[0094] (2) Hot rolling:

[0095] During the hot rolling process, the billet is heated to 1160°C and the deformation is controlled to be 60%. After the hot rolling, the billet is ultra-fast cooled to room temperature at a cooling rate of 200°C / s to obtain rolled steel.

[0096] (3) Heat treatment:

[0097] The rolled steel is subjected to dual phase tempering to obtain a low nickel alloy steel for use in ultra-low temperature environments.

[0098] The dual-phase tempering method is as follows: in the first tempering, the steel billet is heated to 240° C. and maintained for 1.6 hours; in the second tempering, the steel billet is further heated to 410° C. and maintained for 2.3 hours, and then naturally air-cooled to room temperature.

[0099] The yield strength of the low nickel alloy steel prepared in Example 5 was measured to be 638 MPa, the tensile strength was 722 MPa, and the impact energy was 170 J at a low temperature of -196°C.

[0100] Example 6

[0101] A low-nickel alloy steel for use in ultra-low temperature environments, which consists of the following components, based on the total mass of the low-nickel alloy steel being 100%, Ni: 6.00%, C: 0.03%, Mn: 4.00%, Mo: 0.14%, Nb: 0.06%, Al: 0.03%, Si: 0.4%, N: 0.05%, Ti: 0.03%, and the balance being Fe and unavoidable inclusions.

[0102] The method for preparing the low-nickel alloy steel for ultra-low temperature environment comprises the following steps:

[0103] (1) Steelmaking:

[0104] The raw materials of iron ore, coke and limestone are put into a blast furnace in a mass ratio of 13:5:2, and the temperature is raised to 1500°C for 10 hours of high-temperature smelting to obtain molten pig iron and slag. The molten pig iron is sent to a converter at 1600-1700°C for steelmaking for 30 minutes, and other trace element raw materials are added to make the content of each component meet the mass percentage set above, and finally molten steel is obtained;

[0105] (2) Hot rolling:

[0106] During the hot rolling process, the billet is heated to 1200°C and the deformation is controlled to be 40%. After the hot rolling, it is ultra-fast cooled to room temperature at a cooling rate of 500°C / s to obtain rolled steel.

[0107] (3) Heat treatment:

[0108] The rolled steel is subjected to dual phase tempering to obtain a low nickel alloy steel for use in ultra-low temperature environments.

[0109] The dual-phase tempering method is as follows: in the first tempering, the steel billet is heated to 280° C. and maintained for 2 hours; in the second tempering, the steel billet is further heated to 400° C. and maintained for 3 hours, and then naturally air-cooled to room temperature.

[0110] The yield strength of the low nickel alloy steel prepared in Example 6 was measured to be 635 MPa, the tensile strength was 719 MPa, and the impact energy was 171 J at a low temperature of -196°C.

[0111] Comparative Example 1

[0112] Taking the currently widely used 9Ni steel as a comparative example, the composition of the low nickel alloy steel is: Ni: 9.01%, C: 0.031%, Mn: 0.67%, S: 0.002%, P: 0.01%, Si: 0.28%, and the remainder is Fe and inevitable inclusions.

[0113] The method for preparing the low nickel alloy steel comprises the following steps:

[0114] (1) Steelmaking:

[0115] The raw materials of iron ore, coke and limestone are put into a blast furnace in a mass ratio of 13:5:2, and the temperature is raised to 1500°C for 10 hours of high-temperature smelting to obtain molten pig iron and slag. The molten pig iron is sent to a converter at 1600-1700°C for steelmaking for 30 minutes, and other trace element raw materials are added to make the content of each component meet the mass percentage set above, and finally molten steel is obtained;

[0116] (2) Hot rolling:

[0117] The starting rolling temperature is controlled at 1090℃, the ending temperature of rough rolling is 1050℃, the finishing rolling is carried out in the non-complete recrystallization zone of austenite, the starting rolling temperature is controlled at 780℃, and the final rolling temperature is controlled at 730℃; a total of seven rolling passes are performed, of which the first two passes are rough rolling and the last five passes are finishing rolling.

[0118] (3) Heat treatment:

[0119] The rolled steel was air-cooled to 670°C, placed in a heating furnace at 670°C, kept warm for 10 minutes and then quenched, kept warm at 580°C for 1 hour, tempered and water-cooled to obtain low-nickel alloy steel.

[0120] The yield strength of the low nickel alloy steel of Comparative Example 1 was measured to be 708 MPa, the tensile strength was 722 MPa, and the low temperature (-196°C) impact energy was 152 J.

[0121] By comparing the yield strength and tensile strength of the low nickel alloy steel of Examples 1-6 and Comparative Example 1, which is 719 MPa, and the impact energy test results at a low temperature of -196°C, it can be seen that the present invention, while reducing the nickel content, still maintains the high strength and high toughness of the material through a reasonable composition ratio and sophisticated processing technology.

Claims

1. A low nickel alloy steel for ultra-low temperature environment, characterized in that: Taking the total mass of the low nickel alloy steel as 100%, the low nickel alloy steel comprises the following components: Composition: Ni: 5.00-6.00%, C: 0.03-0.08%, Mn: 4.00-5.00%, Mo: 0.1-0.20%, Nb: 0.01-0.06%, Al: 0.02-0.05%, Si: 0.20-0.50%, N: 0.02-0.10%, Ti: 0.01-0.04%, the balance is Fe and inevitable inclusions.

2. The method for preparing low-nickel alloy steel for ultra-low temperature environment according to claim 1, characterized in that: The steps include: (1) Steelmaking: The raw materials of iron ore, coke and limestone are placed in a blast furnace, heated to 1500° C. for high-temperature smelting to obtain molten pig iron and slag, the molten pig iron is sent to a converter for steelmaking, and other trace element raw materials are added so that the content of each component meets the mass percentage set in claim 1 to obtain molten steel; (2) Hot rolling: During the hot rolling process, the billet is heated to 1100-1200°C and the deformation is controlled to be 30-60%. After the hot rolling is completed, it is ultra-rapidly cooled to room temperature to obtain rolled steel. (3) Heat treatment: The rolled steel is subjected to dual phase tempering to obtain a low nickel alloy steel for use in ultra-low temperature environments.

3. The method for preparing low nickel alloy steel for ultra-low temperature environment as claimed in claim 2, characterized in that: In step (1), the steelmaking temperature is 1600-1700°C.

4. The method for preparing low nickel alloy steel for ultra-low temperature environment as claimed in claim 2, characterized in that: In step (2), the ultra-fast cooling rate is 100 to 500° C. / s.

5. The method for preparing low nickel alloy steel for ultra-low temperature environment as claimed in claim 2, 3 or 4, characterized in that: In step (3), the dual-phase tempering method is as follows: in the first tempering, the steel billet is heated to 200-300°C and maintained for 1-2h; in the second tempering, the steel billet is further heated to 400-500°C, maintained for 2-3h, and naturally air-cooled to room temperature.