A duplex steel material, a preparation method thereof, and applications as a high-temperature pressure sensing material and a structural material

Abstract

The present invention discloses a duplex steel material, a preparation method thereof, and applications as a high-temperature pressure sensing material and a structural material. The chemical composition in weight percentage is as follows: C: 0.1 - 0.35%, Si: 0.15 - 0.45%, Mn: 0.5 - 1.05%, Cr: 1.5 - 3.8%, Ni: 3.5 - 6.5%, Al: 1.0 - 3.0%, Mo: 0.1 - 1.5%, V: 0.1 - 0.2%, Nb: 0.01 - 0.06%, Ca: 0.001 - 0.01%, P ≤ 0.015%, S ≤ 0.005%, and the balance is Fe. Its room-temperature structure consists of two phases, martensite and austenite, wherein the mass percentage content of austenite is 5 - 15%. The preparation method of the present invention: vacuum smelting → vacuum electroslag remelting smelting → machining into a high-temperature pressure sensing component or a structural component. The duplex steel material of the present invention can sensitively sense the changes in stress-strain at high temperatures. By sensing the sudden changes in its stress and strain, the temperature and pressure of the medium in a high-temperature and high-pressure container can be effectively controlled, thereby achieving the purposes of early warning, explosion prevention, and control in the case of exceeding the rated temperature and rated pressure.

Description

Technical Field

[0001] The present invention relates to a metal material, a preparation method and an application thereof, and particularly to a steel material for a high-temperature pressure sensing structure, a preparation method and an application thereof. Background Art

[0002] During the normal operation of high-temperature and high-pressure vessels and pipelines, how to sense the change of the pressure condition of the working medium, so as to timely discover and locate the potential safety hazards that may exist in each structure and component inside the pressure vessel, is of great significance for ensuring equipment safety and improving the pertinence of maintenance. Especially in equipment related to coal gasification, atmosphere heat treatment, hot isostatic pressing, etc., as well as pipelines such as aircraft air ducts serving as high-temperature and high-pressure gas transmission channels, the working temperature of the medium inside these high-temperature and high-pressure vessels can reach up to 2000 °C at most, and the pressure can reach 200 MPa. Therefore, it is very important and particularly urgent for the early warning, explosion protection and control of their vessels and related pipelines under conditions exceeding the rated temperature and rated pressure.

[0003] Currently, the materials for pressure sensors used under high-temperature and high-pressure conditions are mainly inorganic materials, such as semiconductor silicon wafer-based piezoresistive materials, capacitive ceramic pressure-sensitive materials, etc. Alumina particles are sintered to obtain a ceramic sheet, and then a capacitive high-temperature piezoresistive material composed of two diaphragm sheets is prepared through microelectronic technology. Its principle is to use the change in capacitance between two electrode plates to reflect the change in pressure received by the sensor, and convert the change in capacitance into an electrical signal proportional to voltage through a post-processing circuit as the signal output. For the sensor based on this working principle, not only is the post-processing circuit complex, but it is also very inconvenient to use. For example, the patent document with the application number 201710120242.8 discloses a pressure-sensitive material for a high-temperature and high-pressure sensor and a preparation method thereof. By adding non-conductive silica, the pressure sensitivity of the pressure-sensitive material can be adjusted, so that the pressure-sensitive material can maintain good piezoresistive performance under high-temperature (within 200 °C) and high-pressure (within 2.5 MPa) conditions, including good piezoresistive stability and good pressure responsiveness. Preparing a grating type pressure sensor through encapsulation is also a commonly used high-temperature pressure detection solution. For example, the patent document with the application number 201420487807.8 discloses an optical fiber grating pressure sensor for a high-temperature and high-pressure environment, which can work at a high temperature of 400 °C for a long time and can reach a high-pressure environment of dozens of MPa.

[0004] Obviously, the working temperature range of current high-temperature pressure sensor materials is below 500 °C and the working pressure is below 100 MPa. With the development of contemporary advanced technologies such as aviation and aerospace technologies, the safety performance of equipment is constantly breaking through and improving, and the importance of steel's perception of mechanical properties under high-temperature conditions has become increasingly prominent. The known high-temperature pressure sensor materials can no longer meet the needs of the current rapid development of science and technology.

[0005] As is well known, metal materials will undergo high-temperature creep under the simultaneous action of high temperature and stress. Even if the stress remains unchanged, the inelastic deformation of the material will continuously and slowly increase over time. In the case of stress changes, its inelastic strain shows a continuous change trend and does not undergo sudden changes. Therefore, if a new material can be designed to keenly sense the stress-strain changes at high temperatures, and through the perception of the stress and strain mutations, the temperature and pressure of the medium in a high-temperature and high-pressure container can be effectively controlled, so as to achieve the purpose of early warning, explosion prevention, and control in the case of exceeding the rated temperature and rated pressure, which has important significance and value. Summary of the Invention

[0006] In order to solve the problems of the existing technology, the purpose of the present invention is to overcome the deficiencies of the existing technology and provide a dual-phase steel material and its preparation method. The dual-phase steel material of the present invention can keenly sense the stress-strain changes at high temperatures, and through the perception of the stress and strain mutations, the temperature and pressure of the medium in a high-temperature and high-pressure container can be effectively controlled, so as to achieve the purpose of early warning, explosion prevention, and control in the case of exceeding the rated temperature and rated pressure.

[0007] To achieve the above object, the present invention adopts the following inventive concept:

[0008] The duplex steel material of the present invention utilizes the different deformation responses of different regions of the material at high temperatures to stress, thereby achieving the control of temperature and pressure. Specifically, through appropriate chemical composition design, during the solidification process of the high-temperature melt of the material, through the fractional crystallization of alloy components, the high-temperature ferrite with a low alloy component content is first precipitated, so that the alloy content of the melt gradually increases; during the subsequent cooling process, when the steel material reaches its austenite temperature range, the melt and the previously precipitated ferrite undergo a peritectic reaction to form austenite, causing the previously precipitated ferrite to disappear; finally, the melt rich in solute elements between dendrites forms austenite with a high alloy element content. After the material is cooled to room temperature, the austenite with a low alloy element content transforms into martensite, while the austenite with a high alloy element content remains, thereby forming a duplex steel material of martensite and austenite at room temperature. Since in the high-temperature austenite range, both two-phase regions are austenite, but due to the different alloy element contents, there are certain differences in their deformation abilities. Therefore, when the deformation switches between the two-phase regions, the responses of stress and strain will undergo sudden changes, and the perception of such sudden changes is the core point of the present invention.

[0009] To achieve the above object, first, it is necessary to overcome the problem of alloy element homogenization caused by the diffusion of alloy elements in the high-temperature austenite range. Because once homogenization occurs, the material becomes austenite with a uniform composition, and under the condition of stress change, its inelastic strain shows a continuous change trend and will not undergo sudden changes, thus making it impossible to achieve perception control.

[0010] According to the above inventive concept, the present invention adopts the following technical solutions:

[0011] A duplex steel material, the chemical composition of which is in weight percentages: C: 0.1 - 0.35%, Si: 0.15 - 0.45%, Mn: 0.5 - 1.05%, Cr: 1.5 - 3.8%, Ni: 3.5 - 6.5%, Al: 1.0 - 3.0%, Mo: 0.1 - 1.5%, V: 0.1 - 0.2%, Nb: 0.01 - 0.06%, Ca: 0.001 - 0.01%, P ≤ 0.015%, S ≤ 0.005%, with the balance being Fe; the room-temperature structure of the duplex steel material consists of two phases, martensite and austenite, wherein the mass percentage content of austenite is 5 - 15%.

[0012] Preferably, for the duplex steel material of the present invention, the metallographic structure at room temperature consists of acicular martensite and austenite between dendrites.

[0013] Preferably, for the duplex steel material of the present invention, the metallographic structure at room temperature further includes a NiAl phase with a body-centered cubic structure and a Ni3Al phase with a face-centered cubic structure.

[0014] Preferably, for the duplex steel material of the present invention, in the high-temperature region, the duplex steel material is used as a material for preparing high-temperature pressure-sensing steel with a critical service temperature of 1000 - 1275 °C and a critical load pressure of 50 - 120 MPa; in the high-temperature region, the room-temperature martensite structure of the duplex steel material transforms into an austenite structure, forming a single-phase homogeneous austenite metallographic structure mainly composed of austenite.

[0015] More preferably, for the duplex steel material of the present invention, between the high-temperature region and the room-temperature region, the metallographic structure of the duplex steel material reversibly transforms between a duplex structure of martensite and austenite and a single-phase homogeneous austenite metallographic structure.

[0016] The functions and ratios of the various elements in the steel of the present invention are as follows:

[0017] Carbon (C): It is an austenite-forming element, which can effectively improve the strength of the steel and is one of the key elements for adjusting the sensing strength level. With the increase of carbon content, the strength of the steel increases, but the plasticity and toughness decrease significantly. The carbon content of the steel of the present invention is preferably controlled at 0.1% - 0.35%.

[0018] Silicon (Si): It dissolves in ferrite to improve the yield strength of the steel, but at the same time, the plasticity and toughness are lost. The silicon content is preferably 0.15 - 0.45%.

[0019] Manganese (Mn): It is an austenite-forming element and forms a solid solution with iron to play a strengthening role. However, when the content is too high, segregation is serious. The Mn content is preferably 0.5 - 1.05%.

[0020] Chromium (Cr): It is a strong carbide-forming element. When tempered, carbides precipitate to improve the strength of the steel and are beneficial to improving the high-temperature oxidation resistance. However, when the content is too high, coarse M 23 C6 carbides precipitate, losing its beneficial effect. The content is preferably 1.5 - 3.8%.

[0021] Nickel (Ni): It is one of the "anchoring" elements of the present invention. It can improve the strength of the steel without significantly reducing its toughness and is beneficial to improving the high-temperature oxidation resistance. Ni is an austenite-forming element and together with the contents of Mn, C, etc. determines the content of austenite at room temperature. In the steel of the present invention, the nickel content is controlled at 3.5 - 6.5%.

[0022] Aluminum (Al): It is one of the "anchoring" elements of the present invention, a traditional deoxidizing and nitrogen-fixing element, and a ferrite-forming element, which is beneficial to improving the high-temperature oxidation resistance. It can combine with nickel to precipitate dispersed NiAl / Ni3Al intermetallic compounds, respectively achieving the "anchoring" of chemical composition in the martensite phase region and the austenite phase region. The content is preferably controlled at 1 - 3%.

[0023] Molybdenum (Mo): A strong carbide-forming element that can effectively improve the tempering stability of steel. During tempering, carbides precipitate to increase the strength of the steel and enhance its high-temperature creep resistance. It is also a key element for regulating the perceived strength level of the material. Due to the high price of molybdenum, the molybdenum content is controlled within 0.1 - 1.5%.

[0024] Vanadium (V): It dissolves in iron to play a strengthening role. Vanadium carbonitrides can precipitate finely and dispersedly in ferrite, and further achieve the effect of precipitation strengthening during the tempering process, which is beneficial to maintaining the stability of high-temperature service performance. At the same time, the price of vanadium is high, so the vanadium content should be controlled within 0.1 - 0.2%.

[0025] Niobium (Nb): A strong carbonitride-forming element. During the reheating process, it can hinder the growth of austenite grains and delay the occurrence of austenite recrystallization under high-temperature working conditions, improving the high-temperature creep resistance and helping to maintain the stability of high-temperature service performance. The content is preferably controlled within 0.01 - 0.06%.

[0026] Calcium (Ca): It can purify the molten steel, reduce the oxygen content in the molten steel, promote the spheroidization of MnS, and improve the mechanical properties of the material. However, when the content is too high, it is easy to form coarse non-metallic inclusions. The content is preferably 0.005 - 0.01%.

[0027] The present invention also provides a method for preparing a duplex steel material, which includes the following steps:

[0028] (1) Vacuum smelting:

[0029] Weigh the raw materials according to the component ratio of the target duplex steel material by weight percentage for batching. Place the raw materials in a crucible and melt them in a vacuum induction melting furnace. Inductively heat to 1600 ± 50 °C to fully melt the raw materials, and then cast them into a master alloy ingot in the vacuum chamber;

[0030] (2) Vacuum electroslag remelting:

[0031] Under vacuum conditions, perform electroslag remelting on the master alloy ingot to eliminate the macroscopic segregation existing in the master alloy ingot and obtain an ingot with relatively uniform composition;

[0032] (3) Processing and manufacturing:

[0033] Process the ingot to obtain the required metal material components.

[0034] A high-temperature pressure sensing material provided by the present invention is prepared according to the following technological steps: Vacuum smelting → Vacuum electroslag remelting → Processing into a high-temperature pressure sensing component. According to the service conditions, process it into a high-temperature pressure sensing component suitable for different temperature and pressure response controls.

[0035] The present invention also provides an application of a duplex steel material as a high-temperature pressure sensing material, and uses the duplex steel material to prepare a high-temperature pressure sensing material element.

[0036] Preferably, a measurement end sensitive element that responds to sudden changes in stress and strain of the material is prepared using the duplex steel material, and is signal-connected to a temperature and pressure regulation device through a control device to form a temperature and pressure sensing sensor; by using the different responses of the measurement end sensitive element to the deformation of different regions of the material under test to stress at high temperature or high pressure, the temperature and pressure of the material under test are controlled.

[0037] The present invention also provides an application of a duplex steel material as a self-adaptive regulation structural material, and uses the duplex steel material to prepare a structural material component with high-temperature pressure sensing and material self-adaptive regulation.

[0038] Preferably, using the duplex steel material, a high-temperature pressure vessel shell, the inner wall of a high-temperature and high-pressure pipe fitting, and a high-temperature pressure pipeline connector are prepared.

[0039] Compared with the prior art, the present invention has the following obvious outstanding substantive features and remarkable advantages:

[0040] 1. Since the NiAl phase with a body-centered cubic structure has a lattice constant close to that of ferrite, and the Ni3Al phase with a face-centered cubic structure has a lattice constant close to that of austenite, therefore, by reasonably designing the chemical composition of the material, the present invention realizes the "anchoring" of the chemical composition in the martensite phase region and the austenite phase region through the NiAl metal bond with a body-centered cubic structure and the Ni3Al metal bond with a face-centered cubic structure formed during the alloy solidification process. Thus, even during long-term service in the high-temperature austenite range, the chemical composition of the alloy will not undergo a diffusion process to achieve homogenization, and thus the purpose of effective sensing and control can be achieved by using the sudden changes in stress and strain responses in different composition ranges.

[0041] 2. The present invention utilizes the strengthening mechanism of alloying elements, enabling the steel material of the present invention to have different strengths at different temperatures, thereby realizing the sensing and control of a pressure vessel at different pressures and different temperatures.

[0042] 3. The present invention is a steel material with a low price. More importantly, the present invention breaks through the limitation of the narrow service temperature and service pressure ranges of existing high-temperature and high-pressure sensor materials, and can prepare high-temperature pressure sensing steel with a service temperature of 1000 - 1275 °C and a pressure of 50 - 120 MPa, having great application potential under extreme working conditions such as high temperature and high pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of a high-temperature sensing specimen of the duplex steel material of the present invention.

[0044] Figure 2 This is the X-ray diffraction result and phase composition diagram of the duplex steel material in Example 1 of the present invention at room temperature.

[0045] Figure 3 This is the metallographic photo of the microstructure of the duplex steel material in Example 1 of the present invention at room temperature.

[0046] Figure 4 This is the stress-strain response curve of the duplex steel material in Example 1 of the present invention at the service temperature of 1150°C.

[0047] Figure 5 This is the stress-strain response curve of the duplex steel material in Example 4 of the present invention at the service temperature of 1250°C.

[0048] Figure 6 This is the stress-strain response curve of the steel material in Comparative Example 1 at the service temperature of 1200°C. Detailed implementation manners

[0049] For a better understanding of the present invention, the following examples are further explanations of the present invention, but the content of the present invention is not limited to the following examples.

[0050] The above scheme is further described below in conjunction with specific implementation examples. The preferred implementation examples of the present invention are described in detail as follows:

[0051] Example 1

[0052] In this example, a duplex steel material has the following chemical composition by weight percentage (%): C: 0.35, Si: 0.25, Mn: 0.5, Cr: 1.5, Ni: 3.5, Al: 3.0, Mo: 1.3, V: 0.1, Nb: 0.01, Ca: 0.005, P ≤ 0.015, S ≤ 0.005, and the balance is Fe.

[0053] A preparation method of a duplex steel material includes the following steps:

[0054] (1) Vacuum smelting:

[0055] Weigh the raw materials according to the composition ratio of the duplex steel material prepared according to the target of this example by weight percentage for batching. Place the raw materials in a crucible and melt them in a vacuum induction melting furnace. Inductively heat to 1600°C to fully melt the raw materials, and cast them into a master alloy ingot in the vacuum chamber;

[0056] (2) Vacuum electroslag remelting:

[0057] Under vacuum conditions, perform electroslag remelting on the master alloy ingot to eliminate the macrosegregation existing in the master alloy ingot and obtain an ingot with relatively uniform composition;

[0058] (3) Machining and manufacturing:

[0059] The ingot is processed to obtain the required metal material components. That is, the prepared high-temperature sensing specimen is shown in the appendix Figure 1 .

[0060] Test and analysis

[0061] The metal material prepared in this embodiment is microscopically observed and tested. The phase composition of the material at room temperature is shown in Figure 2 , which is composed of two phases, martensite and austenite. Among them, the mass percentage of austenite is 15%. The metallographic structure at room temperature consists of acicular martensite and white austenite between dendrites, as shown in Figure 3 . Simulate the high-temperature and high-pressure environment of 1100 °C. When the high-temperature sensing specimen is stretched at a nominal strain rate of 2 / s, its stress-strain response changes suddenly at 120 MPa. This sensing component can control the critical temperature of 1100 °C and the critical pressure of 120 MPa. See Figure 4 . The metallographic structure at room temperature also includes the NiAl phase with a body-centered cubic structure and the Ni3Al phase with a face-centered cubic structure. Since the NiAl phase with a body-centered cubic structure is close to the ferrite lattice constant, and the Ni3Al phase with a face-centered cubic structure is close to the austenite lattice constant, therefore, in the present invention, by reasonably designing the chemical composition of the material, the NiAl metal bond with a body-centered cubic structure and the Ni3Al metal bond with a face-centered cubic structure formed during the alloy solidification process are used to respectively "anchor" the chemical composition in the martensite phase region and the austenite phase region. Thus, even when serving in the high-temperature austenite range for a long time, the chemical composition of the alloy will not undergo a diffusion process to achieve homogenization, so that the purpose of effective sensing and control can be achieved by using the sudden change of stress and strain responses in different composition ranges.

[0062] Example 2

[0063] This embodiment is basically the same as Example 1, with the special feature being:

[0064] In this embodiment, a duplex steel material has the following chemical composition in weight percentage (%): C: 0.25, Si: 0.15, Mn: 0.8, Cr: 2.5, Ni: 5.3, Al: 2.0, Mo: 0.5, V: 0.12, Nb: 0.04, Ca: 0.001, P ≤ 0.015, S ≤ 0.005, and the balance is Fe.

[0065] A preparation method of a duplex steel material includes the following steps:

[0066] (1) Vacuum smelting:

[0067] Weigh the raw materials according to the composition ratio of the duplex steel material prepared according to the target of this embodiment by weight percentage, place the raw materials in a crucible, and melt them in a vacuum induction melting furnace. Inductively heat to 1650 °C to fully melt the raw materials, and cast them into a master alloy ingot in a vacuum chamber;

[0068] (2) Vacuum electroslag remelting and smelting:

[0069] Under vacuum conditions, perform electroslag remelting on the master alloy ingot to eliminate the macroscopic segregation existing in the master alloy ingot and obtain an ingot with relatively uniform composition;

[0070] (3) Processing and manufacturing:

[0071] Process the ingot to obtain the required metal material components. That is, the prepared high-temperature sensing specimen is shown in the appendix Figure 1 .

[0072] Experimental test and analysis

[0073] Microscopically observe and test the metal material prepared in this embodiment. At room temperature, the material's phase consists of two phases, martensite and austenite, where the mass percentage of austenite is 10%. The metallographic structure at room temperature consists of acicular martensite and white austenite between dendrites. Simulate the high-temperature and high-pressure environment of 1150 °C, and perform tensile testing on the high-temperature sensing specimen at a nominal strain rate of 2 / s. Its stress-strain response undergoes a sudden change at 100 MPa. This sensing component can control the critical temperature of 1150 °C and the critical pressure of 100 MPa. The metallographic structure at room temperature also includes the NiAl phase with a body-centered cubic structure and the Ni3Al phase with a face-centered cubic structure. Since the lattice constants of the NiAl phase with a body-centered cubic structure are close to those of ferrite, and the lattice constants of the Ni3Al phase with a face-centered cubic structure are close to those of austenite, therefore, in the present invention, by reasonably designing the chemical composition of the material, the "anchoring" of the chemical composition in the martensite phase region and the austenite phase region is realized respectively through the NiAl metal bond with a body-centered cubic structure and the Ni3Al metal bond with a face-centered cubic structure formed during the alloy solidification process. Thus, even during long-term service in the high-temperature austenite range, the chemical composition of the alloy will not undergo a diffusion process to achieve homogenization, and thus the purpose of effective sensing and control can be achieved by utilizing the sudden changes in stress and strain responses in different composition ranges.

[0074] Example 3

[0075] This example is basically the same as the above example, with the special feature being:

[0076] In this embodiment, a duplex steel material has the following chemical composition in weight percentage (%): C: 0.1, Si: 0.45, Mn: 1.05, Cr: 3.8, Ni: 6.5, Al: 1.0, Mo: 0.1, V: 0.15, Nb: 0.06, Ca: 0.003, P ≤ 0.015, S ≤ 0.005, with the balance being Fe.

[0077] A method for preparing a duplex steel material includes the following steps:

[0078] (1) Vacuum smelting:

[0079] Weigh the raw materials according to the weight percentage ratio of the composition of the duplex steel material to be prepared in this embodiment for batching. Place the raw materials in a crucible and melt them in a vacuum induction melting furnace. Inductively heat to 1550 °C to fully melt the raw materials, and cast them into a master alloy ingot in the vacuum chamber;

[0080] (2) Vacuum electroslag remelting:

[0081] Under vacuum conditions, perform electroslag remelting on the master alloy ingot to eliminate the macrosegregation existing in the master alloy ingot and obtain an ingot with relatively uniform composition;

[0082] (3) Processing and manufacturing:

[0083] Process the ingot to obtain the required metal material component. That is, the prepared high-temperature sensing specimen is shown in the appendix Figure 1 .

[0084] Experimental test and analysis

[0085] The metal material prepared in this embodiment was microscopically observed and tested. At room temperature, the material's phase consists of two phases, martensite and austenite, where the mass percentage of austenite is 5%. The metallographic structure at room temperature consists of acicular martensite and white austenite between dendrites. Simulating a high-temperature and high-pressure environment of 1250 °C, when the high-temperature sensing specimen was stretched at a nominal strain rate of 2 / s, its stress-strain response mutated at 65 MPa. This sensing component can control a critical temperature of 1250 °C and a critical pressure of 65 MPa. The metallographic structure at room temperature also includes a NiAl phase with a body-centered cubic structure and a Ni3Al phase with a face-centered cubic structure. Since the lattice constants of the NiAl phase with a body-centered cubic structure are close to those of ferrite, and the lattice constants of the Ni3Al phase with a face-centered cubic structure are close to those of austenite, therefore, in the present invention, by reasonably designing the chemical composition of the material, the "anchoring" of the chemical composition in the martensite phase region and the austenite phase region is realized respectively through the formation of NiAl metal bonds with a body-centered cubic structure and Ni3Al metal bonds with a face-centered cubic structure during the alloy solidification process. Thus, even when serving in the high-temperature austenite range for a long time, the chemical composition of the alloy will not undergo a diffusion process to achieve homogenization, and thus the purpose of effective sensing and control can be achieved by utilizing the mutations of stress and strain responses in different composition ranges.

[0086] Example 4

[0087] This embodiment is basically the same as the above embodiment, with the special feature that:

[0088] In this embodiment, a duplex steel material has the following chemical composition in weight percentage (%): C: 0.2, Si: 0.25, Mn: 0.8, Cr: 3.0, Ni: 4.5, Al: 1.5, Mo: 1.5, V: 0.12, Nb: 0.01, Ca: 0.001, P ≤ 0.015, S ≤ 0.005, and the balance is Fe.

[0089] A method for preparing a duplex steel material includes the following steps:

[0090] (1) Vacuum smelting:

[0091] Weigh the raw materials according to the composition ratio of the duplex steel material prepared according to the target of this embodiment by weight percentage for batching. Place the raw materials in a crucible and melt them in a vacuum induction melting furnace. Inductively heat to 1600 °C to fully melt the raw materials, and cast them into a master alloy ingot in a vacuum chamber;

[0092] (2) Vacuum electroslag remelting:

[0093] Under vacuum conditions, perform electroslag remelting on the master alloy ingot to eliminate the macroscopic segregation existing in the master alloy ingot and obtain an ingot with relatively uniform composition;

[0094] (3) Processing and manufacturing:

[0095] The ingot is processed to obtain the required metal material components. That is, the prepared high-temperature sensing specimen is shown in the appendix Figure 1 .

[0096] Test and analysis

[0097] The metal material prepared in this embodiment is microscopically observed and tested. At room temperature, the phase composition of the material consists of two phases, martensite and austenite, where the austenite content is 11%. The metallographic structure at room temperature consists of acicular martensite and white austenite between dendrites. Simulating a high-temperature and high-pressure environment of 1275 °C, the high-temperature sensing specimen is stretched at a nominal strain rate of 2 / s, and its stress-strain response undergoes a sudden change at 50 MPa. This sensing component can control the critical temperature of 1275 °C and the critical pressure of 50 MPa. See Figure 5 . The metallographic structure at room temperature also includes the NiAl phase with a body-centered cubic structure and the Ni3Al phase with a face-centered cubic structure. Since the lattice constants of the NiAl phase with a body-centered cubic structure are close to those of ferrite, and the lattice constants of the Ni3Al phase with a face-centered cubic structure are close to those of austenite, therefore, in the present invention, by reasonably designing the chemical composition of the material, the "anchoring" of the chemical composition in the martensite phase region and the austenite phase region is respectively achieved through the NiAl metal bond with a body-centered cubic structure and the Ni3Al metal bond with a face-centered cubic structure formed during the alloy solidification process. Thus, even when serving in the high-temperature austenite range for a long time, the chemical composition of the alloy will not undergo a diffusion process to achieve homogenization, and thus the purpose of effective sensing and control can be achieved by utilizing the sudden changes in stress and strain responses in different composition ranges.

[0098] Comparative example

[0099] A steel material, with the chemical composition in weight percentage (%) as follows: C: 0.32, Si: 0.25, Mn: 0.5, Cr: 1.5, Ni: 6.5, Al: 0.5, Mo: 1.3, V: 0.1, Nb: 0.01, Ca: 0.005, P ≤ 0.015, S ≤ 0.005, and the balance is Fe.

[0100] A preparation method of a steel material includes the following steps:

[0101] (1) Vacuum smelting:

[0102] Weigh the raw materials according to the component ratio of the steel material prepared according to the target of this comparative example and perform batching. Place the raw materials in a crucible and melt them in a vacuum induction melting furnace. Inductively heat to 1600 °C to fully melt the raw materials, and cast them into a master alloy ingot in a vacuum chamber;

[0103] (2) Vacuum electroslag remelting and smelting:

[0104] Under vacuum conditions, the master alloy ingot is subjected to electroslag remelting to eliminate the macroscopic segregation existing in the master alloy ingot and obtain an ingot with relatively uniform composition;

[0105] (3) Processing and manufacturing:

[0106] The ingot is processed to obtain the required metal material components. See Figure 1 .

[0107] Test and analysis

[0108] The metal material prepared in this comparative example is microscopically observed and tested. At room temperature, the phase composition of the material consists of two phases, martensite and austenite, where the mass percentage content of austenite is 12%. The metallographic structure at room temperature consists of acicular martensite and white austenite between dendrites. Simulating a high-temperature and high-pressure environment of 1100 °C, the high-temperature sensing specimen is stretched at a nominal strain rate of 2 / s. Its stress-strain response curve is smooth and stable. Due to the action of very few NiAl metal bonds and Ni3Al metal bonds, no mutation occurs, and the sensing and control of temperature and pressure cannot be achieved. See Figure 6 .

[0109] Example 5

[0110] In this example, a high-temperature sensing specimen is prepared using the duplex steel material in Examples 1-4. In the high-temperature region, the duplex steel material is used as the material for preparing a high-temperature pressure-sensing steel with a critical service temperature of 1000-1275 °C and a critical load pressure of 50-120 MPa; in the high-temperature region, the room-temperature martensite structure of the duplex steel material transforms into an austenite structure, forming a single-phase uniform austenite metallographic structure mainly composed of austenite.

[0111] Between the high-temperature region and the room-temperature region, the metallographic structure of the duplex steel material reversibly transforms between a two-phase structure of martensite and austenite and a single-phase uniform austenite metallographic structure.

[0112] In this example, the application of a duplex steel material as a high-temperature pressure-sensing material is used to prepare a high-temperature pressure-sensing structural material element using the duplex steel material. In this example, a measuring-end sensitive element that responds to the mutation of stress and strain of the material is prepared using the duplex steel material. Through a control device, it is signal-connected to a temperature and pressure regulation device to form a temperature and pressure sensing sensor; by using the different responses of the measuring-end sensitive element to the deformation of different regions of the measured material under high temperature or high pressure, the control of the temperature and pressure of the measured material is achieved.

[0113] The application of the embodiments of the present invention breaks through the limitations of the narrow service temperature and service pressure ranges of existing high-temperature and high-pressure sensor materials. High-temperature and high-pressure sensing steel materials with a service critical temperature of 1000 - 1275°C and a critical pressure of 50 - 120 MPa can be prepared, and they have great application potential under extreme working conditions such as high temperature and high pressure.

[0114] Example 6

[0115] In this embodiment, using the duplex steel materials in Examples 1 - 4, a structural material component with high-temperature pressure sensing and material self-adaptive regulation is prepared and used as a self-adaptive regulation structural material.

[0116] In this embodiment, using the said duplex steel material, a high-temperature pressure vessel shell, the inner wall of high-temperature and high-pressure pipe fittings, and high-temperature pressure pipeline connectors are prepared.

[0117] Utilizing the strengthening mechanism of alloying elements of the duplex steel materials in the above embodiments of the present invention, the steel materials of the present invention can have different strengths at different temperatures, so as to realize the sensing control of pressure vessels at different pressures and different temperatures. When the service critical temperature reaches 1000 - 1275°C and the critical pressure reaches 50 - 120 MPa, the metallographic structure of the duplex steel material at room temperature changes from a dual-phase structure of martensite and austenite to a single-phase uniform austenite metallographic structure, increasing the toughness of the structure. Within a certain strength range, it can effectively resist the risk of brittle material failure caused by the increase in temperature and pressure.

[0118] In summary, in the above Examples 1 - 4, through appropriate chemical composition design, during the solidification process of the high-temperature melt of the material, through the fractional crystallization of alloy components, high-temperature ferrite with a low alloy component content is first precipitated, thus gradually increasing the alloy content of the melt; during the subsequent cooling process, when the steel material reaches its austenite temperature range, the melt and the previously precipitated ferrite undergo a peritectic reaction to form austenite, causing the previously precipitated ferrite to disappear; finally, the melt rich in solute elements between the dendrites forms austenite with a high alloy element content. After the material is cooled to room temperature, the austenite with a low alloy element content transforms into martensite, while the austenite with a high alloy element content remains, thus forming a duplex steel material of martensite and austenite at room temperature. Since in the high-temperature austenite range, both phases are austenite, but due to the different alloy element contents, there are also certain differences in their deformation abilities. Therefore, when the deformation switches between the two-phase regions, the responses of stress and strain will undergo mutations. The duplex steel materials in the above Examples 1 - 6 of the present invention can keenly sense the changes in stress-strain at high temperatures. By sensing the mutations of stress and strain, the temperature and pressure of the medium in the high-temperature and high-pressure vessel can be effectively controlled, thereby achieving the purpose of early warning, explosion prevention, and control under conditions exceeding the rated temperature and rated pressure.

[0119] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments and can also be subject to various changes based on the purpose of the inventive concept of the present invention. Any changes, modifications, substitutions, combinations or simplifications made in accordance with the spirit and principle of the technical solution of the present invention shall be equivalent replacement methods. As long as they meet the inventive purpose of the present invention and do not deviate from the technical principle and inventive concept of the present invention, they all fall within the protection scope of the present invention.

Claims

1. A duplex steel material, characterized in that: The weight percentages of its chemical components are as follows: C: 0.2 - 0.35%, Si: 0.15 - 0.45%, Mn: 0.5 - 1.05%, Cr: 1.5 - 3.8%, Ni: 3.5 - 6.5%, Al: 2.0 - 3.0%, Mo: 0.5 - 1.5%, V: 0.1 - 0.2%, Nb: 0.01 - 0.06%, Ca: 0.001 - 0.01%, P ≤ 0.015%, S ≤ 0.005%, and the balance is Fe; among them, elements C and Mo are the key elements for adjusting the material perception strength level; the room-temperature structure of the duplex steel material consists of two phases, martensite and austenite, where the mass percentage content of austenite is 5 - 15%; in the high-temperature region, the room-temperature martensite structure of the duplex steel material transforms into an austenite structure, forming a single-phase uniform austenite metallographic structure mainly composed of austenite, making both two-phase regions austenite. When the deformation switches in the two-phase region, the response of stress and strain will undergo a mutation. By sensing the change of stress-strain of the duplex steel material at high temperature, a high-temperature pressure sensing material element or a structural material component with high-temperature pressure sensing and material self-adaptive regulation is prepared; the duplex steel material is used as the material for preparing high-temperature pressure sensing steel with a critical service temperature of 1000 - 1275°C and a load critical pressure of 50 - 120 MPa.

2. The duplex steel material according to claim 1, characterized in that: The metallographic structure consists of acicular martensite and inter-dendritic austenite at room temperature.

3. The duplex steel material according to claim 1, characterized in that: The metallographic structure at room temperature also includes NiAl phase with a body-centered cubic structure and Ni3Al phase with a face-centered cubic structure.

4. The duplex steel material according to claim 1, characterized in that: In the high-temperature region, the duplex steel material is used as the material for preparing high-temperature pressure sensing steel with a critical service temperature of 1000 - 1250°C and a load critical pressure of 65 - 120 MPa.

5. The duplex steel material according to claim 4, characterized in that: Between the high-temperature region and the room-temperature region, the metallographic structure of the duplex steel material reversibly transforms between the duplex structure of martensite and austenite and the single-phase uniform austenite metallographic structure.

6. A method for preparing the duplex steel material according to claim 1, characterized in that, It includes the following steps: (1) Vacuum melting: Weigh the raw materials according to the weight percentage ratio of the composition of the target-prepared duplex steel material for batching. Place the raw materials in a crucible and melt them in a vacuum induction melting furnace. Induction heat to 1600 ± 50°C to fully melt the raw materials, and cast them into a master alloy ingot in the vacuum chamber. (2) Vacuum electroslag remelting: Under vacuum conditions, perform electroslag remelting on the master alloy ingot to eliminate the macroscopic segregation existing in the master alloy ingot and obtain an ingot with relatively uniform composition. (3) Processing and manufacturing: Process the ingot to obtain the required metal material component.

7. Use of the duplex steel material according to claim 1 as a high-temperature pressure sensing material, characterized in that: Use the duplex steel material to prepare a high-temperature pressure sensing material element.

8. Use of the duplex steel material according to claim 7 as a high-temperature pressure sensing material, characterized in that: Use the duplex steel material to prepare a measuring end sensitive element that responds to the mutation of stress and strain of the material. Through a control device, it is signal-connected to the temperature and pressure regulation device to form a temperature and pressure sensing sensor; by using the different responses of the measuring end sensitive element to the deformation of different regions of the measured material under high temperature or high pressure, the control of the temperature and pressure of the measured material is realized.

9. Use of the duplex steel material according to claim 1 as a self-adaptive regulation structural material, characterized in that: Prepare a structural material component with high-temperature pressure sensing and material self-adaptive regulation by using the duplex steel material.

10. Use of the duplex steel material according to claim 9 as a self-adaptive regulation structural material, characterized in that: Prepare the outer shell of a high-temperature pressure vessel, the inner wall of a high-temperature and high-pressure pipe fitting, and the connecting piece of a high-temperature pressure pipeline by using the duplex steel material.

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