A multiphase synergistically toughened heterogeneous steel material and a method of making the same

Abstract

The application provides a preparation method of a multiphase synergistically toughened heterogeneous steel material, and comprises the following steps: inserting an ultralow-carbon steel rod into a low-carbon steel tube, and then carrying out drawing and annealing in sequence to obtain a composite steel rod; arranging the obtained composite steel rod in a cuboid low-carbon steel box in a regular manner, filling austenitic stainless steel beads and low-carbon steel powder in the gaps between the composite steel rods, carrying out high-temperature free forging after sealing the tank to obtain a steel billet; and carrying out hot rolling, cold rolling and vacuum heat treatment in sequence on the obtained steel billet to obtain a heterogeneous steel material. The preparation method provided by the application has a simple technological process, is composed of martensite, ferrite and austenite, has a reasonable distribution of soft and hard phases, and has good interface bonding of various materials.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation, specifically relating to a multiphase synergistic strengthening and toughening heterogeneous steel material and its preparation method. Background Technology

[0002] Steel is the most widely used and consumed metallic structural material in industry. Its applications are ubiquitous, spanning various fields of production and daily life. Developing high-strength and high-toughness steel materials is crucial for further expanding their industrial applications. Currently, steel materials are primarily strengthened through four methods: solid solution strengthening, dislocation strengthening, precipitation strengthening, and grain refinement strengthening. These methods mainly increase strength by increasing the number of interfaces and defects. However, while significantly improving strength, this often leads to a marked deterioration in plasticity. Therefore, developing new methods for preparing high-strength and high-toughness steel materials is essential.

[0003] In recent years, heterogeneous materials have attracted widespread attention from researchers. Heterogeneous materials refer to materials with non-uniform microstructures, exhibiting significant strength differences between different structural components. Numerous studies have shown that heterogeneous materials possess excellent mechanical properties, providing a pathway for the preparation of high-strength steel materials. For steel materials, two-phase or multi-phase structures are typical heterogeneous structures. Among them, the austenitic phase has a face-centered cubic structure, typically exhibiting low yield strength and excellent uniform elongation; ferrite, due to its low carbon content, also has relatively low strength but good elongation; martensite, due to its small internal size and high dislocation density, has high strength but low elongation. By organically combining these various phases, the strength and toughness of steel materials can be improved.

[0004] A search revealed that invention patent CN202111556232.1 discloses a ferritic martensitic dual-phase steel and its preparation method. The F / M dual-phase steel, developed in the 1960s and 70s, is a high-strength, high-toughness steel exhibiting excellent mechanical properties such as high strength, good formability, and a low yield strength ratio. Fine-grained ferritic martensitic dual-phase steel material is prepared through a simple heat treatment process. The dual-phase steel structure consists of ferrite and martensite, alternately distributed within the original austenite grains. This technology is simple to process and has high production efficiency, solving one or more problems in the production of dual-phase steel. However, this method has the following disadvantages: (1) poor strength and toughness, making it difficult to achieve a balance; (2) difficulty in flexibly adjusting the ratio of the two phases. Further research revealed that He et al. published a paper titled "Improving ductility by increasing fraction of interfacial zone in low Csteel / 304SS laminates" in Mater. Sci. Eng. A726 (2018) 288-297. This paper proposes a method to combine low-carbon steel and austenitic stainless steel into laminated sheets through hot rolling, followed by cold rolling and heat treatment to obtain a laminated structure composed of martensite and austenite, exhibiting good mechanical properties. The advantages of this technique are its relatively simple process and the high strength provided by martensite and the elongation provided by austenite in the resulting three-layer material. However, the disadvantages of this technique are: ensuring good interfacial bonding during hot rolling is difficult, which affects the final mechanical properties, and the fabrication of multilayer structures is relatively challenging. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a multiphase synergistic toughening heterogeneous steel material and its preparation method. The multiphase synergistic toughening heterogeneous steel material provided by this invention is composed of martensite, ferrite and austenite, with reasonable distribution of soft and hard phases and good interfacial bonding of various materials.

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

[0007] This invention provides a method for preparing multiphase synergistically strengthened heterogeneous steel materials, comprising the following steps:

[0008] 1) Insert an ultra-low carbon steel bar into a low carbon steel pipe, and then draw and anneal it sequentially to obtain a composite steel bar; the composite steel bar is 50-95% of the diameter of the ultra-low carbon steel bar.

[0009] 2) Arrange the composite steel bars obtained in step 1) in a regular pattern in a cuboid low-carbon steel box, fill the gaps between the composite steel bars with austenitic stainless steel beads and low-carbon steel powder, seal the box and perform high-temperature free forging to obtain a steel billet; the free forging is performed 5-6 times.

[0010] 3) The steel billet obtained in step 2) is subjected to hot rolling, cold rolling and vacuum heat treatment in sequence to obtain heterogeneous steel material; the cumulative under-rolling amount of the hot rolling is 10% to 50%; the cumulative under-rolling amount of the cold rolling is 50% to 95%.

[0011] Preferably, in step 1), the ultra-low carbon steel rod is an interstitial atomless steel rod, and the carbon content of the interstitial atomless steel rod material is less than 0.01 wt%; the carbon content of the low carbon steel pipe material is 0.03 to 0.25 wt%.

[0012] Preferably, in step 1), the inner diameter of the low-carbon steel pipe is 1-10 mm, the outer diameter is 2-20 mm, and the length is 50-100 mm; the diameter of the ultra-low-carbon steel rod is equal to the inner diameter of the low-carbon steel pipe; and the length of the ultra-low-carbon steel rod is equal to the length of the low-carbon steel pipe.

[0013] Preferably, the annealing temperature in step 1) is 500–750°C, and the holding time is 10–30 min.

[0014] Preferably, in step 2), the low-carbon steel box is made of Q235 thin plate with a thickness of 1-3mm; the length and width of the inner side of the low-carbon steel box are independently 20-100mm, and the height is 50-100mm.

[0015] Preferably, the austenitic stainless steel beads in step 2) are made of 3-series austenitic stainless steel; the diameter of the austenitic stainless steel beads is 1-10 mm.

[0016] Preferably, in step 2), the forging temperature of the high-temperature free forging is 900-1200℃, and the low-carbon steel box is heated before each forging at a temperature of 1100-1200℃ for a time of 10-60 minutes.

[0017] Preferably, the hot rolling temperature in step 3) is 900-1000°C, and the amount of material rolled down in each hot rolling cycle is 5%-10%.

[0018] Preferably, the temperature of cold rolling in step 3) is 25-400°C, and the amount of cold rolling per pass is 1-5%.

[0019] The present invention also provides a method for preparing multiphase synergistically strengthened heterogeneous steel materials using the above-described preparation method.

[0020] Beneficial Technical Effects: This invention provides a method for preparing multiphase synergistically strengthened heterogeneous steel materials, comprising the following steps: inserting ultra-low carbon steel bars into low carbon steel tubes, sequentially drawing and annealing to obtain composite steel bars; arranging the obtained composite steel bars in a regular pattern in a cuboid low carbon steel box, filling the gaps between the composite steel bars with austenitic stainless steel beads and low carbon steel powder, sealing the box, and then performing high-temperature free forging to obtain steel billets; subjecting the obtained steel billets to hot rolling, cold rolling, and vacuum heat treatment sequentially to obtain heterogeneous steel materials. The preparation method provided by this invention has a simple process flow, is composed of martensite, ferrite, and austenite, has a reasonable distribution of soft and hard phases, and exhibits good interfacial bonding among various materials. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the preparation method of the present invention;

[0022] Figure 2 This is a diagram of the nested tube and rod of the present invention; where (a) represents nesting and (b) represents drawing.

[0023] Figure 3 This is a schematic diagram of the high-temperature free forging of the present invention;

[0024] Figure 4 A schematic diagram of the microstructure of the multiphase synergistic strengthening and toughening heterogeneous steel prepared in this invention;

[0025] Explanation of reference numerals in the attached figures:

[0026] 1-Low carbon steel pipe, 2-Ultra-low carbon steel bar, 3-Composite steel bar, 4-Pull-out sample, 5-Open low carbon steel box, 6-Austenitic stainless steel ball, 7-Low carbon steel powder, 8-Cube steel block, 9-Roll, 10-Heat treatment furnace, 11-Martensitic structure, 12-Ferrite structure, 13-Austenitic structure. Detailed Implementation

[0027] This invention provides a method for preparing multiphase synergistically strengthened heterogeneous steel materials, comprising the following steps:

[0028] 1) Insert an ultra-low carbon steel bar into a low carbon steel pipe, and then draw and anneal it sequentially to obtain a composite steel bar; the composite steel bar is 50-95% of the diameter of the ultra-low carbon steel bar.

[0029] 2) Arrange the composite steel bars obtained in step 1) in a regular pattern in a cuboid low-carbon steel box, fill the gaps between the composite steel bars with austenitic stainless steel beads and low-carbon steel powder, seal the box and perform high-temperature free forging to obtain a steel billet; the free forging is performed 5-6 times.

[0030] 3) The steel billet obtained in step 2) is subjected to hot rolling, cold rolling and vacuum heat treatment in sequence to obtain heterogeneous steel material; the cumulative under-rolling amount of the hot rolling is 10% to 50%; the cumulative under-rolling amount of the cold rolling is 50% to 95%.

[0031] This invention involves inserting an ultra-low carbon steel rod into a low-carbon steel pipe, followed by sequential drawing and annealing to obtain a composite steel rod; the composite steel rod is 50-95% of the diameter of the ultra-low carbon steel rod.

[0032] In this invention, the ultra-low carbon steel bars and low-carbon steel pipes are preferably subjected to surface pretreatment before use. The surface pretreatment preferably involves sequentially grinding and pickling the surface of the ultra-low carbon steel bars or low-carbon steel pipes. In this invention, the grinding is preferably done with sandpaper. This invention does not specifically limit the specific methods of grinding and pickling; any method sufficient to remove oil and impurities from the surface of the ultra-low carbon steel bars or low-carbon steel pipes is acceptable.

[0033] In this invention, the ultra-low carbon steel rod is a gapless atomic steel rod, and the carbon content of the gapless atomic steel rod material is preferably less than 0.01 wt%; the diameter of the ultra-low carbon steel rod is preferably equal to the inner diameter of the low carbon steel pipe, and the length of the ultra-low carbon steel rod is preferably equal to the length of the low carbon steel pipe.

[0034] In this invention, the carbon content of the low-carbon steel pipe material is preferably 0.03-0.25 wt%, the inner diameter of the low-carbon steel pipe is preferably 1-10 mm, more preferably 2-8 mm, and most preferably 3-5 mm; the outer diameter of the low-carbon steel pipe is preferably 2-20 mm, more preferably 4-16 mm, and most preferably 6-10 mm; the length of the carbon steel pipe is preferably 50-100 mm, more preferably 60-90 mm, and most preferably 70-80 mm.

[0035] In this invention, the drawing is preferably performed in multiple stages, and the number of drawing stages is preferably such that the diameter of the composite steel bar reaches 50-95% of the diameter of the ultra-low carbon steel bar.

[0036] This invention involves inserting an ultra-low carbon steel bar into a low-carbon steel pipe and then drawing it under external tension using a drawing die fixed to the equipment. This causes a certain degree of plastic deformation, resulting in a composite steel bar with good interfacial bonding. This invention controls the deformation amount by changing the diameter of the feed and discharge ports of the extrusion die, and obtains the composite steel bar through multiple drawing passes.

[0037] In this invention, the composite steel bar is annealed after each drawing process.

[0038] In this invention, the annealing temperature is preferably 500-750°C, more preferably 550-700°C, and most preferably 600-650°C. The holding time is preferably 10-30 min, more preferably 15-25 min, and most preferably 20 min.

[0039] After obtaining the composite steel bars, the present invention arranges the composite steel bars in a regular pattern in a cuboid low-carbon steel box, fills the gaps between the composite steel bars with austenitic stainless steel beads and low-carbon steel powder, seals the box and performs high-temperature free forging to obtain steel billets.

[0040] In this invention, the number of free forgings is preferably 5-6 times, and the total deformation of the free forging is preferably 45-55%.

[0041] In this invention, the low-carbon steel box is made of Q235 sheet metal with a thickness of 1-3 mm. The length and width of the inner side of the low-carbon steel box are preferably 20-100 mm, more preferably 60-90 mm, and most preferably 70-80 mm; even more preferably 10-80 mm, and most preferably 40-60 mm. The height of the inner side of the low-carbon steel box is preferably 50-100 mm, more preferably 60-90 mm, and most preferably 70-80 mm. When the length of the composite steel rod exceeds the height of the low-carbon steel box, the excess portion is cut off to make it consistent with the length of the steel box.

[0042] In this invention, the austenitic stainless steel beads are preferably made of 3-series austenitic stainless steel; the diameter of the austenitic stainless steel beads is preferably 1-10 mm, more preferably 2-8 mm, and most preferably 5 mm. The austenitic stainless steel beads of this invention preferably undergo surface pretreatment before use. In this invention, the surface pretreatment preferably involves sequentially grinding and pickling the surface of the austenitic stainless steel beads. In this invention, the grinding is preferably sandpaper grinding. This invention does not specifically limit the specific methods of grinding and pickling; any method sufficient to remove oil and impurities from the surface of the ultra-low carbon steel bar or low carbon steel pipe is acceptable.

[0043] In this invention, the forging temperature of the high-temperature free forging is preferably 900-1200℃, more preferably 1000-1100℃; the low-carbon steel box is heated before each forging, and the heating temperature is preferably 1100-1200℃, more preferably 1150-1180℃; the heating time is preferably 10-60 min, more preferably 20-40 min, and most preferably 30-35 min.

[0044] Specifically, the present invention arranges multiple composite steel bars in a certain arrangement in an open low-carbon steel box, fills the gaps between the steel bars with austenitic stainless steel beads and low-carbon steel powder, and makes the stainless steel beads evenly distributed. Then the open steel box is welded and sealed, and then the steel box is subjected to high-temperature free forging treatment to fully combine the steel bars, steel beads and steel powder inside.

[0045] After obtaining the steel billet, the present invention sequentially performs hot rolling, cold rolling and vacuum heat treatment on the steel billet to obtain heterogeneous steel material; the cumulative under-rolling amount of the hot rolling is 10% to 50%; the cumulative under-rolling amount of the cold rolling is 50% to 95%.

[0046] In this invention, the hot rolling temperature is preferably 900–1000°C, more preferably 950–980°C; the hot rolling is preferably multi-stage hot rolling; the rolling amount per hot rolling is preferably 5–10%, more preferably 8%; the cumulative rolling amount is preferably 10–50%, more preferably 20–40%, and most preferably 25–30%. This invention further improves the interfacial bonding between various steel grades through hot rolling.

[0047] In this invention, the cold rolling temperature is preferably 25–400°C, more preferably 50–200°C, and most preferably 100–150°C; the cold rolling is preferably multiple cold rolling processes; the amount of material rolled down in each cold rolling process is preferably 1–5%, more preferably 3%; the cumulative amount of material rolled down in the cold rolling process is preferably 50%–95%, more preferably 60%–80%. This invention refines the microstructure through cold rolling and induces stress-induced martensitic transformation in the austenite region.

[0048] In this invention, it is preferable to place the sample in a muffle furnace and heat it for 5 to 30 minutes before each hot rolling and cold rolling, with the preferred holding temperature being 400°C.

[0049] In this invention, the vacuum heat treatment temperature is preferably 700–950°C, more preferably 750–900°C, and most preferably 800–850°C; the vacuum heat treatment time is preferably 1–60 min, more preferably 20–40 min, and most preferably 25–35 min. The vacuum heat treatment of this invention further includes quenching the resulting steel plate. This invention does not impose any special limitations on the quenching method; any quenching method well-known to those skilled in the art can be used.

[0050] In this invention, the microalloyed low-carbon steel pipe and low-carbon steel powder regions are transformed into a martensitic structure or a ferrite-martensitic dual-phase structure with dispersed carbides. The austenitic stainless steel bead region undergoes a reverse martensitic transformation to form fine equiaxed austenitic grains. Meanwhile, the interstitial atomless steel rod and austenitic stainless steel bead regions respectively form soft phase regions with ultrafine ferrite and austenitic grains. The interstitial atomless steel rod is recrystallized into a fine ferrite structure. Among them, the martensitic region has high strength, and the ferrite and austenitic regions have good plasticity, forming a multiphase synergistic strengthening and toughening heterogeneous steel material with both strength and plasticity and good interfacial bonding.

[0051] This invention can flexibly control the distribution and ratio of soft and hard phases. By changing the diameter of the steel rod, steel pipe and steel ball, the ratio of each component can be adjusted. By changing the arrangement of the composite steel rod and steel ball, the distribution of soft and hard phases can be changed, thereby flexibly adjusting the comprehensive mechanical properties of the steel.

[0052] The present invention also provides a method for preparing multiphase synergistically strengthened heterogeneous steel materials using the above-described preparation method.

[0053] The heterogeneous steel material of the present invention has a repeating layered structure, wherein the repeating unit sequentially includes a first martensite layer, a ferrite layer, a second martensite layer and an austenite-martensite mixed layer.

[0054] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0055] Example 1

[0056] The composition of low-carbon steel pipe material is: Fe-0.12C-1.5Mn-0.25Si-0.05V-0.03Nb;

[0057] The composition of the interstitial atom-free steel rod is: Fe-0.003C-0.005Si-0.15Mn-0.054Al-0.042Ti;

[0058] The low-carbon steel pipe has an inner diameter of 3mm, an outer diameter of 8mm, and a length of 100mm. The interstitial steel bar has a diameter of 3mm and a length of 100mm. The austenitic stainless steel beads used are 316L stainless steel with a diameter of 3mm.

[0059] (1) Surface pretreatment: Use sandpaper to grind the surface of steel pipes, steel bars and steel balls and pickle them to remove surface oil and impurities.

[0060] (2) Pipe-bar nesting drawing: A gapless atomic steel bar is inserted into a low carbon steel pipe to obtain a composite steel bar. The composite steel bar is drawn by a machine. Under the action of external tension, the composite steel bar passes through the drawing die fixed on the equipment and produces a certain plastic deformation. The diameter decreases by 1 mm after each drawing. After drawing, the composite steel bar is annealed at a temperature of 600℃ and a holding time of 20 min. Through multiple drawing passes, the diameter of the composite steel bar is reduced to 4 mm.

[0061] (3) Sealing and free forging: Weld an open rectangular low-carbon steel box using a 1mm thick Q235 low-carbon steel sheet. The inner height of the open rectangular low-carbon steel box is 60mm, and the length and width are 20mm. Use wire EDM to cut the drawn composite steel bar into short bars with a length of 60mm. Take 25 composite steel bars and arrange them in close proximity in the open steel box. Fill the gaps between the steel bars with austenitic stainless steel beads and low-carbon steel powder and make the steel beads evenly distributed. Then weld the open steel box to seal it. Subsequently, the steel box is subjected to high-temperature free forging treatment to fully combine the steel bars, steel beads and steel powder inside. Before each forging, the steel box is heated to 1200℃ for 20min. The forging temperature range of high-temperature free forging is 900~1200℃.

[0062] (4) Rolling process: Rolling is divided into two steps: hot rolling and cold rolling. First, the forged block material is hot rolled at 900℃. Before hot rolling, the sample is placed in a muffle furnace and heated and held for 15 minutes. The rolling amount is 3mm per pass, and the cumulative rolling amount is 15mm. The thickness of the plate after hot rolling is 10mm. Then, the hot-rolled plate is rolled at room temperature. The rolling amount is 0.5mm per pass, and the cumulative rolling amount is 80%. The thickness of the plate after rolling is 2mm.

[0063] (5) Vacuum heat treatment: The steel plate rolled at room temperature was heat-treated at 850℃ for 5 minutes, followed by quenching to obtain a multiphase synergistic strengthening and toughening heterogeneous steel material composed of martensite, ferrite and austenite. Its microstructure diagram is shown in the figure. Figure 4 As shown.

[0064] Example 2

[0065] The composition of low-carbon steel pipe material is: Fe-0.12C-1.5Mn-0.25Si-0.05V-0.03Nb;

[0066] The composition of interstitial atom-free steel is: Fe-0.003C-0.005Si-0.15Mn-0.054Al-0.042Ti;

[0067] The low-carbon steel pipe has an inner diameter of 5mm, an outer diameter of 8mm, and a length of 100mm. The interstitial steel bar has a diameter of 5mm and a length of 100mm. The austenitic stainless steel beads used are 316L stainless steel with a diameter of 4mm.

[0068] (1) Surface pretreatment: Use sandpaper to grind the surface of steel pipes, steel bars and steel balls and pickle them to remove surface oil and impurities.

[0069] (2) Pipe-bar nesting drawing: A gapless atomic steel bar is inserted into a low carbon steel pipe to obtain a composite steel bar. The composite steel bar is drawn by a machine. Under the action of external tension, the composite steel bar passes through the drawing die fixed on the equipment and produces a certain plastic deformation. The diameter decreases by 1 mm after each drawing. After drawing, the composite steel bar is annealed at a temperature of 500℃ and a holding time of 20 min. Through multiple drawing passes, the diameter of the composite steel bar is reduced to 3.2 mm.

[0070] (3) Sealing and free forging: Weld an open rectangular low-carbon steel box using a 1mm thick Q235 low-carbon steel sheet. The inner height of the open rectangular low-carbon steel box is 65mm, and the length and width are 20mm. Use wire EDM to cut the drawn composite steel bar into short bars with a length of 65mm. Take 25 composite steel bars and arrange them adjacent to each other in the open steel box with a gap of 8-10mm as shown in the figure. Fill the gaps between the steel bars with austenitic stainless steel beads and low-carbon steel powder and make the steel beads evenly distributed. Then weld the open steel box to seal it. Then the steel box is subjected to high-temperature free forging treatment to fully combine the steel bars, steel beads and steel powder inside. Before each forging, the steel box is heated to 1000℃ for 20min. The forging temperature range of high-temperature free forging is 900-1200℃.

[0071] (4) Rolling process: Rolling is divided into two steps: hot rolling and cold rolling. First, the forged block material is hot rolled at 900℃. Before hot rolling, the sample is placed in a muffle furnace and heated and held for 15 minutes. The rolling amount is 3mm per pass, and the cumulative rolling amount is 15mm. The thickness of the plate after hot rolling is 10mm. Then, the hot-rolled plate is rolled at room temperature. The rolling amount is 0.5mm per pass, and the cumulative rolling amount is 80%. The thickness of the plate after rolling is 2mm.

[0072] (5) Vacuum heat treatment: The steel plate rolled at room temperature is heat treated at 900℃ for 5 minutes, and then the steel plate is quenched to obtain a multiphase synergistic toughening heterogeneous steel material composed of martensite, ferrite and austenite.

[0073] Example 3

[0074] The composition of low-carbon steel pipe material is: Fe-0.12C-1.5Mn-0.25Si-0.05V-0.03Nb;

[0075] The composition of interstitial atomless steel material is: Fe-0.003C-0.005Si-0.15Mn-0.054Al-0.042Ti;

[0076] The low-carbon steel pipe has an inner diameter of 3mm, an outer diameter of 8mm, and a length of 100mm. The gapless atomized steel has a diameter of 3mm and a length of 100mm. The austenitic stainless steel beads used are 316L stainless steel with a diameter of 3mm.

[0077] (1) Surface pretreatment: Use sandpaper to grind the surface of steel pipes, steel bars and steel balls and pickle them to remove surface oil and impurities.

[0078] (2) Pipe-bar nesting drawing: A gapless atomic steel bar is inserted into a low carbon steel pipe to obtain a composite steel bar. The composite steel bar is drawn by a machine. Under the action of external tension, the composite steel bar passes through the drawing die fixed on the equipment and produces a certain plastic deformation. The diameter decreases by 1 mm after each drawing. After drawing, the composite steel bar is annealed at a temperature of 600℃ and a holding time of 20 min. Through multiple drawing passes, the diameter of the composite steel bar is reduced by 4 mm.

[0079] (3) Sealing and free forging: Weld an open rectangular low-carbon steel box using a 1mm thick Q235 low-carbon steel sheet. The height of the open rectangular low-carbon steel box is 65mm, and the length and width are 20mm. Use wire EDM to cut the drawn composite steel bar into short bars with a length of 65mm. Take 25 composite steel bars and arrange them in close proximity in the open steel box. Fill the gaps between the steel bars with austenitic stainless steel beads and low-carbon steel powder and make the steel beads evenly distributed. Then weld the open steel box to seal it. Then the steel box is subjected to high-temperature free forging treatment to fully combine the steel bars, steel beads and steel powder inside. Before each forging, the steel box is heated to 1200℃ for 20min. The forging temperature range of high-temperature free forging is 900-1200℃.

[0080] (4) Rolling process: Rolling is divided into two steps: hot rolling and cold rolling. First, the forged block material is hot rolled at 850℃. Before hot rolling, the sample is placed in a muffle furnace and heated and held for 15 minutes. The rolling amount is 4mm per pass, and the cumulative rolling amount is 16mm. The thickness of the plate after hot rolling is 12mm. Then, the hot-rolled plate is rolled at room temperature. The rolling amount is 0.5mm per pass, and the cumulative rolling amount is 60%. The thickness of the plate after rolling is 2mm.

[0081] (5) Vacuum heat treatment: The steel plate rolled at room temperature is heat treated at 900℃ for 10 minutes, and then the steel plate is quenched to obtain a multiphase synergistic toughening heterogeneous steel material composed of martensite, ferrite and austenite.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a multiphase synergistically strengthened and toughened heterogeneous steel material, characterized in that, Includes the following steps: 1) Insert an ultra-low carbon steel bar into a low-carbon steel pipe, and then draw and anneal it sequentially to obtain a composite steel bar; the diameter of the composite steel bar is 50-95% of the diameter of the ultra-low carbon steel bar; 2) Arrange the composite steel bars obtained in step 1) in a regular pattern in a cuboid low-carbon steel box, fill the gaps between the composite steel bars with austenitic stainless steel beads and low-carbon steel powder, seal the box and perform high-temperature free forging to obtain a steel billet; the free forging is performed 5-6 times. 3) The steel billet obtained in step 2) is subjected to hot rolling, cold rolling and vacuum heat treatment in sequence to obtain heterogeneous steel material; the cumulative rolling amount of hot rolling is 10~50%; the cumulative rolling amount of cold rolling is 50%~95%.

2. The method according to claim 1, characterized in that, In step 1), the ultra-low carbon steel bar is an interstitial atomless steel bar with a carbon content of less than 0.01 wt%; the carbon content of the low carbon steel pipe is 0.03~0.25 wt%.

3. The method according to claim 1, characterized in that, In step 1), the inner diameter of the low-carbon steel pipe is 1~10mm, the outer diameter is 2~20mm, and the length is 50~100mm; the diameter of the ultra-low carbon steel rod is equal to the inner diameter of the low-carbon steel pipe; and the length of the ultra-low carbon steel rod is equal to the length of the low-carbon steel pipe.

4. The method according to any one of claims 1 to 3, characterized in that, In step 1), the annealing temperature is 500~750℃ and the holding time is 10~30min.

5. The method according to claim 1, characterized in that, In step 2), the low-carbon steel box is made of Q235 thin plate with a thickness of 1-3mm; the inner length of the low-carbon steel box is 20-100mm, the width is 20-100mm, and the height is 50-100mm.

6. The method according to claim 1, characterized in that, In step 2), the austenitic stainless steel beads are made of 3-series austenitic stainless steel; the diameter of the austenitic stainless steel beads is 1~10mm.

7. The method according to claim 1, 5, or 6, characterized in that, In step 2), the forging temperature of high-temperature free forging is 900~1200℃. Before each forging, the low-carbon steel box is heated to 1100~1200℃ for 10~60 minutes.

8. The method according to claim 1, characterized in that, In step 3), the hot rolling temperature is 900~1000℃, and the amount of material rolled down each time is 5%~10%.

9. The method according to claim 1, characterized in that, In step 3), the cold rolling temperature is 25~400℃, and the amount of cold rolling per cycle is 1~5%.

10. A multiphase synergistic strengthening and toughening heterogeneous steel material, which is prepared by the preparation method described in any one of claims 1 to 9.

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