A high-strength and high-toughness corrosion-resistant high manganese steel with a dual-phase heterogeneous structure, and a preparation method and application thereof

Abstract

The application discloses a high-strength and high-toughness corrosion-resistant high manganese steel with a dual-phase heterogeneous structure and a preparation method and application thereof. The application belongs to the technical field of high manganese steel and its preparation. The application is aimed at solving the technical problem that the current existing high-strength and high-toughness high manganese steel cannot have high yield strength and corrosion resistance. The high manganese steel is composed of austenite and pearlite two heterogeneous structures, the pearlite is located at the austenite grain boundary, and the volume fraction of the pearlite is 15-35%. The method comprises the following steps: first, heat treating the hot-rolled high manganese steel above the Ac3 temperature, and then, aging heat treatment. The application adds Cu on the basis of the conventional high manganese steel component system, and simultaneously cooperates with the Ac3 complete austenite and isothermal aging heat treatment, thereby preparing the heterogeneous microstructure of the austenite and the pearlite with different volume fractions, obtaining the low-cost high manganese steel with high strength, high toughness and corrosion resistance, and expanding the application range of the high manganese steel. The high manganese steel can be applied as the offshore platform structural steel.

Description

Technical Field

[0001] This invention belongs to the field of high manganese steel and its preparation technology, specifically relating to a high-strength, high-toughness, and corrosion-resistant high manganese steel with a dual-phase heterogeneous structure, its preparation method, and its application. Background Technology

[0002] With the development of the offshore oil and gas industry, there are higher requirements for the economy, safety, and service life of structural components. Developing advanced high-strength steel with high strength, toughness, and corrosion resistance has become an urgent need for steel used in marine structural components. High-manganese TWIP steel, with its excellent comprehensive properties of high strength and high toughness, has attracted attention from the offshore platform industry, and research on improving its corrosion resistance is being conducted.

[0003] The hot-rolled microstructure of high-manganese steel is austenitic, exhibiting high plasticity and toughness, but relatively low yield and tensile strength. The pearlite produced after aging heat treatment is a lamellar mechanical mixture of ferrite and carbides, exhibiting low lattice slip number and high hardness during plastic deformation. Therefore, the yield strength of high-manganese steel increases after the formation of pearlite. After aging, a copper-rich phase precipitates dispersedly, forming CuO and CuFeO2 in the corrosion layer products. This reduces the destructive effect of Cl- on the matrix, improves the thermodynamic stability of the corrosion layer, and thus enhances the corrosion resistance of high-manganese steel. The manufacturing process of high-manganese steel involves complete austenitization in the hot-rolled state followed by aging heat treatment. Specifically, after austenitization, Cu dissolves in the austenite, and the copper-rich phase precipitates dispersedly during aging heat treatment. Simultaneously, pearlite is generated during isothermal aging heat treatment, resulting in a pearlite and austenitic microstructure in high-manganese steel.

[0004] Currently, research on improving the yield strength of high manganese steel mainly focuses on generating nanotwins through rolling deformation, which hinder dislocation movement during plastic deformation and thus improve yield strength. However, due to the generation of twins, the number of grain interfaces increases, and the twin boundaries become rapid corrosion channels, reducing the corrosion resistance of high manganese steel. Summary of the Invention

[0005] This invention addresses the technical problem that existing high-strength, high-toughness, and high-manganese steels cannot simultaneously possess high yield strength and corrosion resistance. Instead, it provides a high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure, its preparation method, and its applications.

[0006] The technical solution of the present invention is as follows:

[0007] One of the objectives of this invention is to provide a high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure. The high-manganese steel is composed of two heterogeneous structures: austenite and pearlite. The pearlite is located at the austenite grain boundaries, and the volume fraction of the pearlite is 15-35%.

[0008] Furthermore, the grain size of high-manganese steel is specified to be 20~40μm.

[0009] Further specifying, the chemical composition and its mass percentage of high manganese steel are as follows: C: 0.75~0.85%, Mn: 17~19%, Al: 1.7~1.9%, Cu: 1~3%, P≤0.005%, S≤0.007%, with the remainder being Fe.

[0010] Furthermore, the chemical composition and mass percentage of high manganese steel are as follows: C: 0.75~0.85%, Mn: 17~19%, Al: 1.7~1.9%, Cu: 1.95~2.05%, P≤0.005%, S≤0.007%, with the remainder being Fe.

[0011] Further specified, the yield strength of high-manganese steel is 480~500MPa, and the electrochemical impedance is 800~1100Ω·cm. 2 .

[0012] The second objective of this invention is to provide a method for preparing high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure, the method comprising the following steps:

[0013] Hot-rolled high-manganese steel is first held at a temperature above Ac3, and then subjected to aging heat treatment.

[0014] Further specifying the preparation of hot-rolled high-manganese steel: melting according to the composition ratio, followed by casting, forging and hot rolling in sequence.

[0015] Furthermore, the hot rolling process is defined as follows: heating the forged billet to 1100~1300℃, holding it at that temperature for 1~3 hours, and then performing multiple hot rolling passes with a cumulative reduction rate of 90~91%.

[0016] To further specify, the temperature above Ac3 is specifically 800~900℃.

[0017] Further specified, the aging heat treatment temperature is 450~550℃, and the holding time is 1~4 days.

[0018] The third objective of this invention is to provide an application of high-strength, high-toughness, corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure, which is used as structural steel for offshore platforms.

[0019] The advantages of this invention compared to the prior art are:

[0020] This invention utilizes austenitic and pearlitic microstructures instead of the traditional all-austenitic design to prepare materials with a yield strength of 480-500 MPa and an electrochemical impedance of approximately 800-1100 Ω·cm. 2 High-strength, corrosion-resistant high-manganese steel, compared to ordinary high-manganese steel (yield strength 440MPa, electrochemical impedance 654Ω·cm). 2The mechanical properties and electrochemical corrosion resistance are significantly improved. This method is simple, highly operable, and conducive to promoting the practical application of high-manganese steel. Specific advantages are as follows:

[0021] (1) Based on the conventional high manganese steel composition system, this invention adds 1~3wt% Cu, and at the same time combines Ac3 complete austenite and isothermal aging heat treatment to prepare heterogeneous microstructures of austenite and pearlite with different volume fractions, thereby obtaining high strength, toughness and corrosion resistance low cost high manganese steel. This method avoids the problems of low yield strength and poor electrochemical corrosion resistance of high manganese steel, and can better meet the strength requirements of structural materials, thus expanding the application range of high manganese steel.

[0022] (2) This invention uses an aging process to form pearlite instead of austenite in the material, creating a heterogeneous structure between pearlite and austenite. The nanoindentation hardness of pearlite is greater than that of austenite, and this dual-phase heterogeneous structure increases the microhardness of high-manganese steel, leading to increased yield strength during plastic deformation. After aging, a copper-rich phase is dispersed between austenite and pearlite, and during immersion corrosion or electrochemical corrosion, the corrosion layer products form CuO and CuFeO2, reducing Cl... - The damage to the substrate increases the thermodynamic stability of the corrosion layer, thereby enhancing the corrosion resistance of high-manganese steel. Attached Figure Description

[0023] Figure 1 The images show the microstructure of high-manganese steel after step 3 in Example 1; (a) and (b) represent different magnifications.

[0024] Figure 2 The microstructure of the high-manganese steel after step 3 in Example 2 is shown in (a) and (b) respectively, representing different magnifications.

[0025] Figure 3 The images show the hardness characterization of the high-manganese steel obtained in Examples 1 and 2; (a) represents austenite and pearlite nanoindentation, and (b) represents microhardness.

[0026] Figure 4 The following are engineering stress-strain curves of the high-manganese steel obtained in Comparative Example 1 and Examples 1-2;

[0027] Figure 5 Electrochemical impedance spectra of high-manganese steel obtained in Comparative Example 1 and Examples 1-2; (a) represents the impedance value, and (b) represents the relationship between frequency, impedance magnitude, and phase angle.

[0028] Figure 6 The image shows the microstructure of the high-manganese steel obtained in Comparative Example 1; (a) and (b) represent different magnifications. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0031] The microscopic characterization technique used in the following examples and comparative examples was performed using a Zeiss Sigma 500 scanning electron microscope mounted on an electron backscatter diffraction analysis system (EBSD).

[0032] The nanoindentation hardness of the following embodiments was tested at room temperature using a Bruker Ti980 instrument.

[0033] The room temperature microhardness test equipment used in the following examples and comparative examples was the MHVS-1000AT automatic turret microhardness tester.

[0034] The room temperature tensile tests in the following examples and comparative examples were performed on a WDW-50C hydraulic servo tensile testing machine.

[0035] The room temperature electrochemical corrosion performance tests conducted in the following examples and comparative examples were performed using the Wantong Autolab-PGSTAT302N electrochemical workstation.

[0036] Example 1: The preparation method of the high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure in this example is carried out according to the following steps:

[0037] (1) The chemical composition and mass percentage of high manganese steel are as follows: C: 0.81%, Mn: 17.85%, Al: 1.79%, Si: 0.47%, Cu: 1.97%, P < 0.005%, S: 0.007%, with the remainder being Fe. The mixture is smelted, then cast, and then forged into 60mm*80mm billets. The forged billets are then... Hot rolling is performed in a twin-roll high-rigidity rolling mill. The temperature is first heated to 1200℃ and held for 2 hours before rolling. The initial rolling temperature is 1150℃ and the final rolling temperature is 900℃. After 6 passes of hot rolling, the cumulative reduction rate is 90.6%. After hot rolling, laminar flow cooling is performed to simulate the coiling temperature to 600℃, followed by air cooling to room temperature to obtain a hot-rolled plate with a thickness of 7.2mm. Then, pickling is performed.

[0038] (2) Heat the hot-rolled high-manganese steel to 850℃ and hold for 10 minutes, then quench it in water to room temperature;

[0039] (3) The sample after step 2 was heated to 500℃ and held for 1 day for aging heat treatment, then air-cooled to room temperature to obtain high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure. Its microstructure is as follows: Figure 1 As shown in (ab), the microstructure of the prepared Cu-containing high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure consists of austenite and pearlite, with pearlite precipitating at the austenite grain boundaries. The volume fraction of austenite in the sample aged for 1 day was 83%, and the volume fraction of pearlite was 17%.

[0040] Example 2: The preparation method of the high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure in this example is carried out according to the following steps:

[0041] (1) The chemical composition and mass percentage of high manganese steel are as follows: C: 0.81%, Mn: 17.85%, Al: 1.79%, Si: 0.47%, Cu: 1.97%, P < 0.005%, S: 0.007%, with the remainder being Fe. The mixture is smelted, then cast, and then forged into 60mm*80mm billets. The forged billets are then... Hot rolling is performed in a twin-roll high-rigidity rolling mill. The temperature is first heated to 1200℃ and held for 2 hours before rolling. The initial rolling temperature is 1150℃ and the final rolling temperature is 900℃. After 6 passes of hot rolling, the cumulative reduction rate is 90.6%. After hot rolling, laminar flow cooling is performed to simulate the coiling temperature to 600℃, followed by air cooling to room temperature to obtain a hot-rolled plate with a thickness of 7.2mm. Then, pickling is performed.

[0042] (2) Heat the hot-rolled high-manganese steel to 850℃ and hold for 10 minutes, then quench it in water to room temperature;

[0043] (3) The sample after step 2 was heated to 500℃ and held for 3 days for aging heat treatment, then air-cooled to room temperature to obtain high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure. Its microstructure is as follows: Figure 2 As shown in (ab), it can be seen that the volume fraction of austenite in the sample aged for 3 days is 68%, and the volume fraction of pearlite is 32%. The volume fraction of pearlite increases with the extension of aging time.

[0044] The test results of nanoindentation hardness of austenite and pearlite in Examples 1 and 2 are as follows: Figure 3 As shown in Figure a. In Example 1, the nanohardness of pearlite was 7.8 GPa, and the nanohardness of austenite was 2.95 GPa; in Example 2, the nanohardness of pearlite was 7.5 GPa, and the nanohardness of austenite was 2.53 GPa. Microhardness is as follows... Figure 3As shown in b and Table 1, the microhardness of Example 1 is 236 HV, and the microhardness of Example 2 is 259 HV. The longer the aging time, the greater the microhardness of the high manganese steel. The microhardness of Example 2 is greater than that of Example 1.

[0045] The mechanical properties of the high-manganese steels prepared in Examples 1 and 2 were tested at 5 × 10⁻⁶ mm. -4 Quasi-static tensile testing was conducted at room temperature at a tensile rate of / s, and the mechanical properties are shown in Table 1. The engineering stress-strain curves are shown in... Figure 4 As shown, the yield strength of Example 1 is 479 MPa, and the yield strength of Example 2 is 497 MPa.

[0046] Electrochemical performance tests were conducted on the Cu-containing high-strength, high-toughness, and corrosion-resistant high-manganese steels with biphase isomer structures prepared in Examples 1 and 2. The AC impedance spectroscopy was performed using an Ag / AgCl electrode as a reference electrode, after stabilizing the open-circuit potential, at a frequency of 10 Hz. 5 ~10 -2 The Hz frequency and the amplitude of the sinusoidal signal are 10mV. The impedance test results for Examples 1 and 2 are shown in Table 1 and Table 2. Figure 5 As shown, the impedance value of Example 1 is 1079 Ω·cm. 2 The impedance value of Example 2 is 787 Ω·cm 2 .

[0047] Comparative Example 1: The preparation method of a high-strength, high-toughness, and corrosion-resistant high-manganese steel with a fully austenitic structure according to this comparative example is carried out according to the following steps:

[0048] The chemical composition and mass percentage of high-manganese steel are as follows: C: 0.81%, Mn: 17.85%, Al: 1.79%, Si: 0.47%, P < 0.005%, S: 0.007%, with the remainder being Fe. The mixture is then smelted, cast, and forged into 60mm × 80mm billets. The forged billets are then... Hot rolling was performed in a twin-roll high-rigidity rolling mill. The temperature was first raised to 1200℃ and held for 2 hours before rolling. The initial rolling temperature was 1150℃, and the final rolling temperature was 900℃. After 6 passes of hot rolling, the cumulative reduction was 90.6%. Laminar flow cooling was then performed after hot rolling, simulating a coiling temperature of 600℃, followed by air cooling to room temperature, resulting in a 7.2mm thick hot-rolled sheet. This sheet was then pickled. Its microstructure is as follows: Figure 6 As shown in (ab), it can be seen that the microstructure of high manganese steel is a fully austenitic structure.

[0049] Microhardness tests were performed on the comparative example, and the results are shown in Table 1. The hardness of the comparative example was 209 HV.

[0050] The mechanical properties of the high-manganese steel prepared in this comparative example were tested at 5×10⁻⁶.-4 Quasi-static tensile testing was conducted at room temperature at a tensile rate of / s, and the mechanical properties are shown in Table 1. The engineering stress-strain curves are shown in... Figure 4 As shown, the yield strength of the comparative example is 440 MPa.

[0051] Electrochemical performance tests were performed on the high-manganese steel of Comparative Example 1. The AC impedance test used an Ag / AgCl electrode as a reference electrode. The test was conducted after stabilizing the open-circuit potential at a frequency of 10 Hz. 5 ~10 -2 The Hz frequency and the amplitude of the sinusoidal signal are 10mV. The impedance test results of Comparative Example 1 are shown in Table 1 and... Figure 5 The impedance value of Comparative Example 1 shown is 654 Ω·cm. 2 .

[0052] Table 1 Mechanical properties of high-manganese steel from Examples 1-2 and Comparative Example 1

[0053]

[0054] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-strength, high-toughness, corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure, characterized in that, Hot-rolled high-manganese steel is first held at a temperature above Ac3, and then subjected to aging heat treatment. The high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterostructure is composed of two heterostructures: austenite and pearlite. The pearlite is located at the austenite grain boundaries, and the volume fraction of pearlite is 15-35%. After aging, a copper-rich phase is dispersedly precipitated from the austenite and pearlite. The chemical composition of the high-manganese steel and its mass percentage are as follows: C: 0.75-0.85%, Mn: 17-19%, Al: 1.7-1.9%, Cu: 1-3%, P≤0.005%, S≤0.007%, and the remainder is Fe.

2. The high-manganese steel according to claim 1, characterized in that, The grain size of high manganese steel is 20~40μm.

3. The high-manganese steel according to claim 1, characterized in that, The chemical composition and mass percentage of high manganese steel are as follows: C: 0.75~0.85%, Mn: 17~19%, Al: 1.7~1.9%, Cu: 1.95~2.05%, P≤0.005%, S≤0.007%, and the remainder is Fe.

4. The high-manganese steel according to claim 1, characterized in that, High-manganese steel has a yield strength of 480~500MPa and an electrochemical impedance of 800~1100Ω·cm. 2 .

5. The method for preparing high-strength, high-toughness, and corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure according to any one of claims 1-4, characterized in that, Hot-rolled high-manganese steel is first held at a temperature above Ac3, and then subjected to aging heat treatment.

6. The method according to claim 5, characterized in that, Preparation of hot-rolled high-manganese steel: smelting according to the composition ratio, followed by casting, forging and hot rolling in sequence.

7. The method according to claim 6, characterized in that, The hot rolling process consists of heating the forged billet to 1100~1300℃, holding it at that temperature for 1~3 hours, and then performing multiple hot rolling passes with a cumulative reduction rate of 90~91%.

8. The method according to claim 5, characterized in that, The specific temperature range above Ac3 is 800~900℃, the aging heat treatment temperature is 450~550℃, and the holding time is 1~4 days.

9. The high-strength, high-toughness, corrosion-resistant high-manganese steel with a dual-phase heterogeneous structure as described in any one of claims 1-4 is used as structural steel for offshore platforms.

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