A bimetallic layered composite material and a method for preparing the same

Abstract

This invention relates to a bimetallic layered composite material and its preparation method, in order to solve the problem that existing low-temperature steel alloying cannot simultaneously achieve cost, strength, plasticity, and corrosion resistance. The main steps include: (1) billet pretreatment: cut 316 stainless steel and high manganese steel of the same size as raw materials, and after surface pickling, grinding, cleaning and drying, stack them alternately to form a billet to be composited; (2) hot rolling composite: heat the billet to 900-1200℃ in an inert atmosphere, hold for 0.5h and then perform two hot rolling passes, followed by air cooling to room temperature; (3) post-annealing treatment: heat the hot-rolled steel plate to 600-750℃ and hold for 1h, and then water cool to room temperature; This invention forms an ultrafine grain transition layer at the bimetallic interface, with high interface bonding strength. The prepared composite material exhibits high yield strength, high tensile strength, high elongation and high work hardening rate at both room temperature and ultra-low temperature environments, while also having excellent impact toughness, making it suitable for low-temperature structural parts.

Description

Technical Field

[0001] This invention belongs to the field of metal layered composite material preparation technology, specifically relating to a bimetallic layered composite material and its preparation method. Background Technology

[0002] With the rapid development of marine engineering, liquefied natural gas storage and transportation, and cryogenic pipelines, higher requirements are being placed on the strength, plasticity, and corrosion resistance of structural materials in low-temperature environments. While widely used Ni-based cryogenic steels possess excellent low-temperature toughness, they are expensive, and my country's nickel resources are scarce, necessitating imports. High-manganese austenitic steels have attracted attention due to their low cost and excellent work hardening properties, but their yield strength is relatively low, and their corrosion resistance is not as good as stainless steel.

[0003] 316 stainless steel possesses good corrosion resistance and a certain level of strength, but its toughness and work hardening ability at low temperatures are limited. If the high work hardening ability of high-manganese steel can be combined with the corrosion resistance of stainless steel to prepare a layered composite material, it is hoped that complementary and improved performance can be achieved while controlling costs.

[0004] However, in the existing technology, the preparation of bimetallic composite materials is mostly carried out by hot rolling, but the overall performance of the material is often poor due to problems such as insufficient interfacial bonding strength, coarse grains or insufficient recrystallization. In particular, it is difficult to balance strength and plasticity at low temperatures, and the work hardening ability often decreases during the composite process. Summary of the Invention

[0005] The purpose of this invention is to provide a bimetallic layered composite material and its preparation method. By optimizing the hot rolling process and post-annealing treatment, an ultrafine crystalline structure is formed at the interface, achieving comprehensive performance of high strength, high plasticity and excellent interfacial bonding.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a bimetallic layered composite material includes the following steps:

[0008] (1) Pre-treatment of billet: 316 stainless steel plate and high manganese steel plate are cut into the same size, and after surface pickling, grinding, ultrasonic cleaning and drying, they are stacked alternately to form multi-layer composite billet;

[0009] (2) Hot rolling composite: The composite billet is placed in an inert atmosphere and heated to 900℃~1200℃, and held for no less than 0.5h. Then it is hot rolled in two passes, with the first pass having a reduction rate of 60%~75% and the second pass having a reduction rate of 30%~40%. The final rolling temperature is 750℃~900℃, and then it is air-cooled to room temperature.

[0010] (3) Post-annealing treatment: Heat the hot-rolled composite plate obtained in step (2) to 600℃~750℃, keep it at that temperature for 1 hour, and then cool it to room temperature with water.

[0011] Preferably, the chemical composition of the 316 stainless steel in step (1) is as follows by mass percentage: C≤0.08%, Si≤1.0%, Mn≤2.0%, Cr:16%~18%, Ni:10%~14%, Mo:2%~3%, with the balance being Fe and unavoidable impurities.

[0012] Preferably, the chemical composition of the high manganese steel in step (1) is as follows by mass percentage: C: 0.2% to 0.6%, Si: 0.02% to 0.1%, Mn: 17% to 28%, Al: 0.5% to 3%, P≤0.005%, S≤0.002%, N: 0.004% to 0.010%, with the balance being Fe and unavoidable impurities.

[0013] Preferably, the heating temperature for hot rolling composite in step (2) is 1000℃~1100℃, and the holding time is 0.5h.

[0014] Preferably, in step (2), the first pass reduction rate is 75%, the second pass reduction rate is 30%, and the final rolling temperature is 800℃.

[0015] Preferably, the heating temperature for the post-annealing treatment in step (3) is 600℃~650℃, and the holding time is 1h.

[0016] Preferably, the inert atmosphere in step (2) is argon.

[0017] Preferably, the number of alternating stacked layers in step (1) is an even number, and the number of 316 stainless steel layers and high manganese steel layers is equal, the thickness of a single layer is 0.5mm to 5mm, and the total thickness of the blank is 10mm to 30mm.

[0018] Another object of the present invention is to provide a bimetallic layered composite material prepared by the above process, wherein an ultrafine grain transition layer with a grain size of 200nm to 500nm is formed at the interface between the 316 stainless steel layer and the high manganese steel layer of the composite material.

[0019] Preferably, the mechanical properties of the composite material at 25°C satisfy: yield strength ≥ 550 MPa, tensile strength ≥ 940 MPa, elongation ≥ 30%, and work hardening rate ≥ 0.35; and the mechanical properties at −196°C satisfy: yield strength ≥ 1000 MPa, tensile strength ≥ 1650 MPa, elongation ≥ 45%, and work hardening rate ≥ 0.42; and the Charpy V-notch impact toughness at −196°C ≥ 100 J / cm².

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) Through alternating stacking design and optimized hot rolling composite process, a strong metallurgical bond between high manganese steel and stainless steel is achieved, forming an ultra-fine grain structure at the interface with high bonding strength;

[0022] (2) By utilizing the high work hardening capacity of high manganese steel and the corrosion resistance of stainless steel, the comprehensive mechanical properties of the material are significantly improved while controlling costs, especially the strength and plasticity at low temperatures.

[0023] (3) The interfacial structure was effectively optimized by medium-temperature annealing. Static recovery mainly occurs in this temperature range, which not only releases internal stress but also retains some dislocations and ultrafine grain structure, thereby synergistically improving the strength, plasticity and work hardening ability of the material;

[0024] (4) The process is simple and easy to industrialize, and it is suitable for mass production of low-temperature structural parts. Attached Figure Description

[0025] Figure 1 The image shows the electron backscatter diffraction pattern of the interface of the bimetallic composite material in Example 1 of the present invention, where a is the inverse pole figure of the microstructure; b is the phase distribution diagram; and c is the local orientation deviation diagram.

[0026] Figure 2 The image shows the electron backscatter diffraction pattern of the interface of the bimetallic composite material in Example 2 of the present invention, where a is the inverse pole figure of the microstructure; b is the phase distribution diagram; and c is the local orientation deviation diagram.

[0027] Figure 3 The image shows the electron backscatter diffraction pattern of the interface of the bimetallic composite material in Example 3 of the present invention, where a is the inverse pole figure of the microstructure; b is the phase distribution diagram; and c is the local orientation deviation diagram.

[0028] Figure 4 The image shows the electron backscatter diffraction pattern of the bimetallic composite interface in Example 4 of this invention, where a is the inverse pole figure of the microstructure; b is the phase distribution diagram; and c is the local orientation deviation diagram.

[0029] Figure 5 The image shows the electron backscatter diffraction pattern of the bimetallic composite interface in Example 5 of this invention, where a is the microstructure inverse pole figure; b is the phase distribution diagram; and c is the local orientation deviation diagram.

[0030] Figure 6 The image shows the electron backscatter diffraction pattern of the bimetallic composite interface in Example 6 of the present invention, where a is the inverse pole figure of the microstructure; b is the phase distribution diagram; and c is the local orientation deviation diagram.

[0031] Figure 7The image shows the electron backscatter diffraction pattern of the bimetallic composite interface in Comparative Example 1 of this invention, where a is the microstructure inverse pole figure; b is the phase distribution diagram; and c is the local orientation deviation diagram.

[0032] Figure 8 This is a scanning electron image of the interface of the bimetallic composite material in Comparative Example 2 of the present invention.

[0033] Figure 9 is The impact toughness comparison graph of the composite materials in Examples 1-2 and Comparative Example 1 of the present invention at -196℃ is shown, where the vertical axis represents the impact energy (J / cm²) and the horizontal axis represents each example and comparative example.

[0034] Figure 10 This is a comparison chart of the peel strength (rolling direction) of the composite materials in Examples 1-2 and Comparative Example 1 of the present invention at 25°C, where the vertical axis represents the peel strength in the rolling direction and the horizontal axis represents the peel strength of each example and the comparative example. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0036] Example 1

[0037] (1) Pre-treatment of billet: 316 stainless steel and high manganese steel plates are cut into 200mm×100mm×1mm plates, pickled, polished, cleaned and dried, and then stacked alternately to form a billet with a total thickness of 20mm; the chemical composition of 316 stainless steel is: C: 0.06%, Si: 0.8%, Mn: 2.0%, Cr: 18%, Ni: 12%, Mo: 2%, with the balance being Fe; the chemical composition of high manganese steel is: C: 0.45%, Si: 0.05%, Mn: 24%, Al: 2%, P: 0.002%, S: 0.002%, N: 0.005%, with the balance being Fe.

[0038] (2) Hot rolling composite: Under argon protection, the billet is heated to 1000℃ and held for 1 hour. The first hot rolling is carried out with a reduction rate of 65%. Then the second hot rolling is carried out with a reduction rate of 35%. The final rolling temperature is 800℃. The billet is then air-cooled to room temperature.

[0039] (3) Post-annealing treatment: Heat the hot-rolled plate to 650℃ and hold for 1 hour, then cool it to room temperature with water.

[0040] The composite sample #1 was examined under an electron backscatter diffraction probe (Oxford, Symmetry S3) on a scanning electron microscope (TESCAN, MIRA3).

[0041] Example 2

[0042] (1) Billet pretreatment: Same as in Example 1;

[0043] (2) Hot rolling composite: Heat to 1100℃ and hold for 0.5h, first pass reduction rate 70%, second pass reduction rate 30%, final rolling temperature 850℃, air cooling;

[0044] (3) Post-annealing treatment: heat to 600℃ and hold for 1 hour, then cool with water.

[0045] The composite sample #2 was examined under the electron backscatter diffraction probe of a scanning electron microscope.

[0046] Example 3

[0047] (1) Billet pretreatment: Same as in Example 1;

[0048] (2) Hot-rolled composite: Same as Example 1;

[0049] (3) Post-annealing treatment: heat to 700℃ and hold for 1 hour, then cool with water.

[0050] The composite sample #3 was examined under the electron backscatter diffraction probe of a scanning electron microscope.

[0051] Example 4

[0052] (1) Billet pretreatment: Same as in Example 1;

[0053] (2) Hot-rolled composite: Same as Example 1;

[0054] (3) Post-annealing treatment: heat to 750℃ and hold for 1 hour, then cool with water.

[0055] The composite sample #4 was examined under the electron backscatter diffraction probe of a scanning electron microscope.

[0056] Example 5

[0057] (1) Pretreatment of billet: The steps are the same as in Example 1; wherein, the chemical composition of 316 stainless steel is: C: 0.06%, Si: 0.8%, Mn: 2.0%, Cr: 18%, Ni: 12%, Mo: 2%, with the balance being Fe; the chemical composition of high manganese steel is: C: 0.6%, Si: 0.1%, Mn: 18%, Al: 3%, P: 0.003%, S: 0.002%, N: 0.005%, with the balance being Fe.

[0058] (2) Hot-rolled composite: Same as Example 1;

[0059] (3) Post-annealing treatment: Same as in Example 1.

[0060] The composite sample #5 was examined under the electron backscatter diffraction probe of a scanning electron microscope.

[0061] Example 6

[0062] (1) Billet pretreatment: The steps are the same as in Example 1; wherein, the chemical composition of 316 stainless steel is: C: 0.06%, Si: 0.8%, Mn: 2.0%, Cr: 18%, Ni: 12%, Mo: 2%, with the balance being Fe; the chemical composition of high manganese steel is: C: 0.3%, Si: 0.05%, Mn: 24%, Al: 2%, P: 0.002%, S: 0.002%, N: 0.005%, with the balance being Fe;

[0063] (2) Hot-rolled composite: Same as Example 1;

[0064] (3) Post-annealing treatment: Same as in Example 1.

[0065] The composite sample #6 was examined under the electron backscatter diffraction probe of a scanning electron microscope.

[0066] Comparative Example 1

[0067] (1) Billet pretreatment: Same as in Example 1;

[0068] (2) Hot rolling composite: Heat to 1100℃ and hold for 0.5h, first pass reduction rate 70%, second pass reduction rate 30%, final rolling temperature 850℃, air cooling;

[0069] (3) Post-annealing treatment: heat to 800℃ and hold for 1 hour, then cool with water.

[0070] The composite sample #7 was examined under the electron backscatter diffraction probe of a scanning electron microscope.

[0071] Comparative Example 2

[0072] (1) Billet pretreatment: Same as in Example 1;

[0073] (2) Hot rolling composite: The billet is heated to 1000℃ and held for 1 hour. The first pass has a reduction rate of 40%, followed by a second pass of hot rolling with a reduction rate of 60%. The final rolling temperature is 800℃, and the billet is air-cooled to room temperature.

[0074] (3) Post-annealing treatment: heat to 650℃ and hold for 1 hour, then cool with water.

[0075] The morphology of the composite sample #8 was examined under a scanning electron microscope.

[0076] Comparative Example 3

[0077] (1) Billet pretreatment: Same as in Example 1;

[0078] (2) Hot-rolled composite: Same as Example 1;

[0079] The mechanical properties of the composite sample #9 were tested.

[0080] Comparative Example 4

[0081] (1) Hot rolling: The initial 316 stainless steel billet of 20mm is heated to 1000℃ and held for 1h under argon protection. The first hot rolling is carried out with a reduction rate of 65%. Then the second hot rolling is carried out with a reduction rate of 35%. The final rolling temperature is 800℃ and air-cooled to room temperature.

[0082] (2) Post-annealing treatment: Heat the hot-rolled plate to 650℃ and hold for 1 hour, then cool it to room temperature with water.

[0083] Mechanical properties of sample #10, which underwent hot rolling and annealing, were tested.

[0084] The morphology, constituent phases, and local orientation differences of the layered composite samples 1-7# from Examples 1-6 and Comparative Example 1 were observed using electron backscattering diffraction. Specific results are shown in [link to results]. Figure 1-7 In the diagram, a is the inverse pole figure; b is the phase distribution diagram; and c is the local orientation deviation diagram, with the stainless steel layer on the left and the high-manganese steel layer on the right. Samples 1#-6# showed no cracks or pores at the interface, indicating good bonding and significant grain refinement at the interface, forming an ultrafine-grained transition layer of 200-500 nm. The ultrafine-grained layer of sample 5# was martensite, while the other samples were austenite. Sample 7# showed acceptable bonding at the interface, but no obvious ultrafine-grained transition layer appeared, and the grain size was relatively coarse. The layered composite sample 8# from Comparative Example 2 was observed using a scanning electron microscope, with the stainless steel layer on the left and the high-manganese steel layer on the right. Sample 8# showed numerous gaps at the interface, indicating poor bonding.

[0085] Table 1. Comparison of tensile properties of composite materials in Examples 1-2 and Comparative Example 1 at 25°C and -196°C.

[0086]

[0087] Uniaxial tensile tests were conducted on the layered composite samples 1-10# of Examples 1-6 and Comparative Examples 1-4 at 25°C and -196°C. The tensile tests were performed according to ASTM standard (E 8M-04), with the tensile direction along the rolling direction, on a Zwick / Roell Z100 universal testing machine. The results are shown in Table 1. Samples 1#-6# using the process of this invention exhibited excellent combination of strength, plasticity, and work hardening rate at both room temperature and -196°C, significantly better than Comparative Examples 1-4. Comparative Example 2 fractured directly due to poor interfacial bonding, so its yield strength could not be measured. Compared to Comparative Example 4 (single 316 stainless steel), the layered composite plate exhibited higher yield strength, tensile strength, and comparable elongation under the same rolling conditions. In particular, at -196°C, the sample of this invention still maintained a high elongation of over 50% and a high work hardening rate of over 0.45, demonstrating excellent low-temperature toughness and deformation capacity.

[0088] The layered composite samples 1-3# of Examples 1-2 and Comparative Example 1 were subjected to Charpy V-notch impact tests at -196°C on a 300 J impact testing machine. The results are as follows. Figure 9 As shown, the impact toughness values ​​of samples 1# and 2# are 125 J / cm² and 115 J / cm², respectively, which are much higher than the 75 J / cm² of Comparative Example 1, and significantly exceed the standard requirements commonly used for low-temperature structural materials (such as ≥42 J / cm²), indicating that the material prepared by this invention has excellent low-temperature toughness.

[0089] The layered composite samples 1-3# of Examples 1-2 and Comparative Example 1 were subjected to room temperature peel strength tests on a DNS200 electronic universal testing machine. The results are as follows: Figure 10 As shown, the peel strength (rolling direction) values ​​of samples 1# and 2# are 28.5 N / mm and 30.6 N / mm, respectively, which are much higher than the 19.2 N / mm of Comparative Example 1, indicating that the material prepared by the present invention has good bonding strength.

[0090] In summary, through reasonable material design and process control, this invention has successfully prepared a bimetallic layered composite material with an ultrafine-grained transition layer (200-500 nm) at the bimetallic interface, which is suitable for engineering structural components in low-temperature environments and has broad industrial application prospects.

Claims

1. A method for preparing a bimetallic layered composite material, comprising the following steps: (1) Pre-treatment of billet: 316 stainless steel plate and high manganese steel plate are cut into the same size, and after surface pickling, grinding, ultrasonic cleaning and drying, they are stacked alternately to form multi-layer composite billet; (2) Hot rolling composite: The composite billet is placed in an inert atmosphere and heated to 900℃~1200℃, and held for no less than 0.5h. Then it is hot rolled in two passes, with the first pass having a reduction rate of 60%~75% and the second pass having a reduction rate of 30%~40%. The final rolling temperature is 750℃~900℃, and then it is air-cooled to room temperature. (3) Post-annealing treatment: Heat the hot-rolled composite plate obtained in step (2) to 600℃~750℃, keep it at that temperature for 1 hour, and then cool it to room temperature with water.

2. The preparation method according to claim 1, characterized in that, The chemical composition of the 316 stainless steel mentioned in step (1) by mass percentage is: C≤0.08%, Si≤1.0%, Mn≤2.0%, Cr:16%~18%, Ni:10%~14%, Mo:2%~3%, with the balance being Fe and unavoidable impurities.

3. The preparation method according to claim 1, characterized in that, The chemical composition of the high manganese steel mentioned in step (1) by mass percentage is as follows: C: 0.2%~0.6%, Si: 0.02%~0.1%, Mn: 17%~28%, Al: 0.5%~3%, P≤0.005%, S≤0.002%, N: 0.004%~0.010%, with the balance being Fe and unavoidable impurities.

4. The preparation method according to claim 1, characterized in that, In step (2), the heating temperature for hot rolling composite is 1000℃~1100℃, and the holding time is 0.5h.

5. The preparation method according to claim 1 or 4, characterized in that, In step (2), the first pass reduction rate is 75%, the second pass reduction rate is 30%, and the final rolling temperature is 800℃.

6. The preparation method according to claim 1, characterized in that, In step (3), the heating temperature for post-annealing is 600℃~650℃, and the holding time is 1h.

7. The preparation method according to claim 1, characterized in that, The inert atmosphere mentioned in step (2) is argon.

8. The preparation method according to claim 1, characterized in that, In step (1), the number of alternating stacked layers is an even number, and the number of 316 stainless steel layers and high manganese steel layers is equal. The thickness of a single layer is 0.5mm to 5mm, and the total thickness of the blank is 10mm to 30mm.

9. A bimetallic layered composite material, prepared by the preparation method according to any one of claims 1 to 8, characterized in that, At the interface between the 316 stainless steel layer and the high manganese steel layer of the composite material, an ultrafine grain transition layer with a grain size of 200nm to 500nm is formed.

10. The bimetallic layered composite material according to claim 9, characterized in that, The composite material has the following mechanical properties at 25℃: yield strength ≥ 550 MPa, tensile strength ≥ 940 MPa, elongation ≥ 30%, and work hardening rate ≥ 0.35; and at −196℃: yield strength ≥ 1000 MPa, tensile strength ≥ 1650 MPa, elongation ≥ 45%, and work hardening rate ≥ 0.42; and at −196℃, Charpy V-notch impact toughness ≥ 100 J / cm².

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