A high-strength, high-toughness, oxidation-resistant hot-formed steel and its mechanical metallurgical preparation method

Abstract

The present invention discloses a high-strength, high-toughness, oxidation-resistant hot-formed steel and its mechanical and metallurgical preparation method. The hot-formed steel comprises the following components: C: 0.20-0.30%, Mn: 1.00-1.80%, Cr: 2.00-2.50%, Si: 0.60-1.20%, Al: 0.60-1.20%, Nb: 0.05-0.20%, V: 0.05-0.20%, P ≤ 0.01%, S ≤ 0.005%, N ≤ 0.003%, and the remainder is Fe and unavoidable impurities. The preparation method comprises: smelting molten steel according to the chemical composition, then continuously casting the slab; and sequentially performing a heating pretreatment, a descaling treatment, and a hot-forming treatment on the slab to obtain the hot-formed steel. By combining the chemical composition with the preparation method, the present invention achieves a hot-formed steel with excellent oxidation resistance and strength and toughness.

Description

Technical Field

[0001] The present invention relates to the technical field of steel materials, and in particular to a high-strength, high-toughness, oxidation-resistant hot-formed steel and a mechanical metallurgical preparation method thereof. Background Art

[0002] In recent years, lightweighting of automobiles has become increasingly crucial, and hot-stamped steel is one of the strongest steel grades used in automotive body structures. Hot-stamped steel is formed in the austenitic region using a hot forming process, resulting in minimal springback and meeting assembly precision requirements. Through pressure-hold quenching, ultra-high-strength components with strengths of 1500 MPa and above can be produced. However, due to the high heating temperatures in the hot stamping process, the surface of high-strength steel sheets undergoes severe high-temperature oxidation, resulting in a large amount of scale. This hard scale can damage the mold surface and reduce its service life. Furthermore, because the loose scale impedes subsequent painting, shot peening equipment is required to remove the surface scale. However, shot peening can cause surface deformation, further increasing production costs. Another treatment option is to add an aluminum-silicon or zinc-based coating to prevent the formation of scale during the heating process, but this is more expensive and can easily lead to hydrogen embrittlement.

[0003] To address the problems of surface oxidation and decarburization during hot forming, reduce production steps, and lower production costs, patent publication number CN116200655A discloses an oxidation-resistant hot-forming steel and its production method. The synergistic effects of elements such as Mn, Cr, and Si enhance the steel's oxidation resistance, eliminating the need for subsequent shot peening. The hot-formed steel exhibits a yield strength ≥1000 MPa, a tensile strength ≥1500 MPa, and an elongation ≥6%. The addition of B improves the material's hardenability, resulting in a fully martensitic microstructure after hot forming, which limits its plasticity. Patent publication number CN116334489A proposes a hot-forming steel with ultra-high oxidation resistance. The rare earth elements RE and Cu are introduced to enhance the steel's oxidation resistance, while reducing the content of expensive alloying elements such as Cr and Mo to lower costs. The strength of the hot-formed steel reaches 1500 MPa or higher. However, the addition of rare earth elements still makes the hot-forming steel relatively expensive. Furthermore, existing hot-formed steel production processes are often complex, making them difficult to apply in actual production. Therefore, researchers in this field are currently focusing on how to improve the strength and ductility of hot-formed steel while maintaining oxidation resistance, while also reducing production costs, simplifying the production process, and improving production efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-strength, high-toughness, oxidation-resistant hot-formed steel and a mechanical metallurgical preparation method thereof, so as to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a high-strength, high-toughness, and oxidation-resistant hot-formed steel, wherein the chemical composition of the high-strength, high-toughness, and oxidation-resistant hot-formed steel is as follows, calculated by mass percentage: C: 0.20-0.30%, Mn: 1.00-1.80%, Cr: 2.00-2.50%, Si: 0.60-1.20%, Al: 0.60-1.20%, Nb: 0.05-0.20%, V: 0.05-0.20%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance is Fe and unavoidable impurities;

[0007] Calculated by volume percentage, the structure of the high-strength, high-toughness, oxidation-resistant hot-formed steel consists of 2-3.5% ferrite and 96.5-98% martensite.

[0008] The reasons for limiting the chemical composition of the high-strength, high-toughness, oxidation-resistant hot-formed steel of the present invention are as follows:

[0009] As a strengthening element in steel, C has a significant impact on the martensite content and tensile strength of the hot-formed steel plate. In order to ensure the martensite structure and sufficiently high tensile strength of the hot-formed steel, and to ensure good plasticity, toughness and weldability of the hot-formed steel, the C content is controlled to 0.20-0.30%.

[0010] Mn plays a role in solid solution strengthening and improving toughness in steel. However, when the Mn content is too high, it is easy to cause segregation of the ingot and affect the uniformity of the structure. The Mn content is controlled to 1.00-1.80%.

[0011] The addition of Si can play a role in solid solution strengthening, improve the stability of austenite, and promote the subsequent martensite transformation. At the same time, Si can form a dense oxide film during the hot forming process, inhibiting the continued growth of the oxide film on the surface of the steel plate, thereby improving the high-temperature oxidation resistance of the steel. However, too high Si content will lead to deterioration of weldability and toughness of the weld heat-affected zone. The Si content is controlled to 0.60-1.20%;

[0012] Cr can improve the hardenability of steel and promote martensitic transformation. At the same time, Cr can improve the high-temperature oxidation resistance of steel. The Cr content is controlled at 2.00-2.5%.

[0013] The Al element can simultaneously improve the oxidation resistance and hydrogen embrittlement resistance of hot-formed steel and can also refine the grains. However, when the Al content is too high, non-metallic inclusions will be produced, causing adverse effects. Therefore, the Al content is controlled to 0.60-1.20%.

[0014] Nb and V are strong carbide-forming elements that precipitate to form composite carbides during the preparation process. The Nb and V composite carbides act as hydrogen traps, reducing the concentration of diffusible hydrogen, thereby reducing the hydrogen embrittlement sensitivity of hot-formed steel and improving the safety of automotive hot-stamped parts. Furthermore, the dispersion of the Nb and V composite carbides in ferrite can enhance the ferrite's strength and counteract the strength reduction caused by the presence of ferrite. Taking all factors into consideration, the mass percentage of Nb is 0.05-0.20%, and the mass percentage of V is 0.05-0.20%. The synergistic combination of these elements, combined with mechanical metallurgical preparation methods, yields a high-strength, high-toughness, and oxidation-resistant hot-formed steel composed of 2-3.5% ferrite and 96.5-98% martensite.

[0015] By introducing 2-3.5% fine ferrite and precipitating nano-phase carbides within it, the material's strength and toughness are simultaneously improved. During the ferrite precipitation process, excess carbon is expelled into the austenite, increasing the strength of the martensite produced during the forming process. However, excessive ferrite can reduce the strength of hot-formed steel and adversely affect safety, so the ferrite content is controlled to 2-3.5%.

[0016] Technical solution 2 of the present invention: The mechanical metallurgical preparation method of the above-mentioned high-strength, high-toughness, oxidation-resistant hot-formed steel comprises the following steps:

[0017] After molten steel is melted according to the chemical composition, slabs are prepared by continuous casting; the slabs are subjected to hot forming treatment to obtain the high-strength, high-toughness, and oxidation-resistant hot-formed steel;

[0018] The thermoforming treatment is performed in one of the following ways:

[0019] Method 1: hot rolling and cold rolling the slab in sequence to obtain a thin steel plate; the thin steel plate is kept at a two-phase temperature and then press-quenched to obtain the high-strength, high-toughness, and oxidation-resistant hot-formed steel;

[0020] Method 2: performing rough rolling and finish rolling on the slab in sequence to obtain a thin steel plate; then immediately performing press quenching on the thin steel plate to obtain the high-strength, high-toughness, and oxidation-resistant hot-formed steel;

[0021] The starting temperature of the finishing rolling is A c3 -10℃~A c3 , the final rolling temperature is A c1 ~A c3 .

[0022] In the first method, the thin steel plate obtained after hot rolling and cold rolling is kept at the two-phase temperature, which is conducive to the formation of fine proeutectoid ferrite in the structure;

[0023] In method 2, the starting rolling temperature is controlled to be A c3-10℃~A c3 , the final rolling temperature is A c1 ~A c3 Finish rolling is beneficial to the formation of fine proeutectoid ferrite in the structure, and the total deformation of finish rolling within the above temperature range is large, which is beneficial to the refinement of ferrite and the promotion of carbide precipitation.

[0024] Furthermore, the thickness of the slab is 150-200 mm, the casting speed during the continuous casting process is 1.4-1.5 m / min, and the superheat degree of the molten steel is 20-30°C.

[0025] Furthermore, the hot forming process also includes heating pretreatment and descaling steps for the slab.

[0026] Furthermore, the temperature of the heating pretreatment is 1210-1215° C., and the time is 4-5 hours.

[0027] Furthermore, the descaling treatment adopts a high-pressure water descaling method, the slab temperature before descaling is 1200-1210° C., and the descaling water pressure is 15-20 MPa.

[0028] Furthermore, the starting rolling temperature of the hot rolling is 1200° C., the finishing rolling temperature is 950-960° C., and the total reduction ratio is 70-98%; the total reduction ratio of the cold rolling is 50-60%.

[0029] Furthermore, the two-phase region temperature is A c3 -30℃~A c3 The time for keeping warm at the two-phase temperature is 1 to 5 minutes.

[0030] Furthermore, the starting rolling temperature of the rough rolling is 1200° C., the finishing rolling temperature is 920-930° C., and the total reduction ratio is 70-90%; the total reduction ratio of the finish rolling is 70-90%.

[0031] Furthermore, after the hot rolling and before the cold rolling, a coiling operation is also included.

[0032] Furthermore, the press quenching forming parameters include: a pressure of 500t and a holding time of 10s.

[0033] Furthermore, the coiling temperature is 640°C.

[0034] The present invention discloses the following technical effects:

[0035] The present invention provides a high-strength, high-toughness, oxidation-resistant hot-formed steel and a mechanical metallurgical preparation method thereof. By combining the chemical composition and the mechanical metallurgical preparation method, a hot-formed steel product with excellent oxidation resistance and excellent strength and toughness is obtained.

[0036] The chemical components used in the high-strength, high-toughness, oxidation-resistant hot-formed steel of the present invention are cheap and readily available, and the production cost is low.

[0037] The mechanical metallurgical preparation method of the present invention has simple production process and high production efficiency.

[0038] The thermoforming temperature in the present invention is relatively low, which can save energy, reduce carbon dioxide emissions, and reduce costs. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0041] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0042] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0043] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0044] As a first aspect of the present invention, the present invention provides a high-strength, high-toughness, oxidation-resistant hot-formed steel. The chemical composition of the high-strength, high-toughness, oxidation-resistant hot-formed steel is as follows, calculated by mass percentage: C: 0.20-0.30%, Mn: 1.00-1.80%, Cr: 2.00-2.50%, Si: 0.60-1.20%, Al: 0.60-1.20%, Nb: 0.05-0.20%, V: 0.05-0.20%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance is Fe and unavoidable impurities.

[0045] Calculated by volume percentage, the structure of the high-strength, high-toughness, oxidation-resistant hot-formed steel consists of 2-3.5% ferrite and 96.5-98% martensite.

[0046] As a second aspect of the present invention, the present invention provides a mechanical metallurgical preparation method of the above-mentioned high-strength, high-toughness, oxidation-resistant hot-formed steel, comprising the following steps:

[0047] After molten steel is melted according to the chemical composition, slabs are prepared by continuous casting; the slabs are subjected to hot forming treatment to obtain the high-strength, high-toughness, and oxidation-resistant hot-formed steel;

[0048] The thermoforming treatment is performed in one of the following ways:

[0049] Method 1: hot rolling and cold rolling the slab in sequence to obtain a thin steel plate; the thin steel plate is kept at a two-phase temperature and then press-quenched to obtain the high-strength, high-toughness, and oxidation-resistant hot-formed steel;

[0050] Method 2: performing rough rolling and finish rolling on the slab in sequence to obtain a thin steel plate; then immediately performing press quenching on the thin steel plate to obtain the high-strength, high-toughness, and oxidation-resistant hot-formed steel;

[0051] The starting temperature of the finishing rolling is A c3 -10℃~A c3 , the final rolling temperature is A c1 ~A c3 .

[0052] As a preferred embodiment of the present invention, the thickness of the slab is 150-200 mm, the casting speed during the continuous casting process is 1.4-1.5 m / min, and the superheat degree of the molten steel is 20-30°C.

[0053] As a preferred embodiment of the present invention, the hot forming process further includes heating pretreatment and descaling steps of the slab.

[0054] As a preferred embodiment of the present invention, the temperature of the heating pretreatment is 1210-1215° C., and the time is 4-5 hours.

[0055] As a preferred embodiment of the present invention, the descaling treatment adopts a high-pressure water descaling method, the slab temperature before descaling is 1200-1210° C., and the descaling water pressure is 15-20 MPa.

[0056] As a preferred embodiment of the present invention, the hot rolling start temperature is 1200°C, the final rolling temperature is 950-960°C, and the total reduction ratio is 70-98%; the cold rolling total reduction ratio is 50-60%.

[0057] As a preferred embodiment of the present invention, the two-phase region temperature is A c3 -30℃~A c3 The time for keeping warm at the two-phase temperature is 1 to 5 minutes.

[0058] As a preferred embodiment of the present invention, the starting rolling temperature of the rough rolling is 1200°C, the finishing rolling temperature is 920-930°C, and the total reduction ratio is 70-90%; the total reduction ratio of the finish rolling is 70-90%.

[0059] A c1 is the starting temperature of pearlite to austenite transformation during heating, A c3 It is the final temperature at which all the proeutectoid ferrite is transformed into austenite during heating, which can be obtained by testing with a dynamic phase change thermal expansion instrument.

[0060] As a preferred embodiment of the present invention, a coiling operation is further included after the hot rolling and before the cold rolling.

[0061] As a preferred embodiment of the present invention, the press-quenching forming parameters include: a pressure of 500t and a holding time of 10s.

[0062] As a preferred embodiment of the present invention, the coiling temperature is 640°C.

[0063] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0064] In the specific embodiments of the present invention, there is no limit on the number of hot rolling, cold rolling, rough rolling, and finish rolling passes, and multiple passes can be performed. For hot rolling, rough rolling, and finish rolling, as long as the required total reduction ratio is achieved within the required start and finish temperature ranges, the specific number of rolling passes has no effect on the properties of the hot-formed steel. For cold rolling, as long as the required total reduction ratio is achieved, the specific number of rolling passes has no effect on the properties of the hot-formed steel.

[0065] Example 1

[0066] A high-strength, high-toughness, oxidation-resistant hot-formed steel, whose chemical composition, calculated by mass percentage, is: C: 0.20%, Mn: 1.00%, Cr: 2.00%, Si: 1.20%, Al: 0.60%, Nb: 0.20%, V: 0.20%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance is Fe and unavoidable impurities.

[0067] The mechanical metallurgical preparation method is as follows: molten steel is melted according to the set chemical composition, and the molten steel is passed through a continuous casting device to prepare a slab. The slab thickness is 200mm, the casting speed is 1.5m / min, and the superheat of the molten steel during the continuous casting process is 30℃; the slab is heated in a heating furnace at a temperature of 1210℃ and a holding time of 4 hours; after the slab is taken out of the heating furnace, it is quickly descaled using a high-pressure water descaling technology. The slab temperature before descaling is 1200℃. The descaling water pressure is 20 MPa; the descaling slab is hot rolled with a starting rolling temperature of 1200°C, a finishing rolling temperature of 950°C, and a total reduction ratio of 97.5% to obtain a 5 mm thick steel plate; the steel plate is then cooled in a 640°C furnace to a coiling temperature (640°C), and the steel plate is coiled to obtain a hot-rolled thin strip; the hot-rolled thin strip is cold rolled with a total reduction ratio of 60% to obtain a 2 mm thick thin steel plate; the thin steel plate is placed in a 840°C furnace (tested by A c3 The steel was then placed in a heating furnace at 848°C for 5 minutes, then immediately subjected to press quenching. Specifically, the hot steel was placed in a press and held at 500t for 10 seconds. The steel was then removed and naturally cooled to room temperature to produce high-strength, high-toughness, and oxidation-resistant hot-formed steel sheet parts. The formed steel was subjected to room-temperature tensile and hardness testing in accordance with GB / T 228.1-2021 and GB T4340.1-2009 to obtain mechanical property data. The oxide layer thickness of the formed steel was measured in accordance with GB / T 13303-1991 to obtain oxidation resistance data. Microstructure observation was also performed to determine the ferrite content and carbide distribution. The results are shown in Table 1.

[0068] Table 1

[0069]

[0070] Example 2

[0071] A high-strength, high-toughness, oxidation-resistant hot-formed steel, whose chemical composition, calculated by mass percentage, is: C: 0.30%, Mn: 1.00%, Cr: 2.50%, Si: 0.60%, Al: 1.20%, Nb: 0.05%, V: 0.05%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance is Fe and unavoidable impurities.

[0072] The mechanical metallurgical preparation method is as follows: molten steel is melted according to the set chemical composition, and the molten steel is passed through a continuous casting device to prepare a slab. The slab thickness is 200mm, the casting speed is 1.5m / min, and the superheat of the molten steel during the continuous casting process is 30℃; the slab is heated in a heating furnace at a temperature of 1210℃ and a holding time of 4 hours; after the slab is taken out of the heating furnace, it is quickly descaled using a high-pressure water descaling technology. The slab temperature before descaling is 1200℃. The descaling water pressure is 20 MPa; the descaling slab is hot rolled with a starting rolling temperature of 1200°C, a finishing rolling temperature of 950°C, and a total reduction ratio of 97.5% to obtain a 5 mm thick steel plate; the steel plate is then cooled in a 640°C furnace to a coiling temperature (640°C), and the steel plate is coiled to obtain a hot-rolled thin strip; the hot-rolled thin strip is cold rolled with a total reduction ratio of 60% to obtain a 2 mm thick thin steel plate; the thin steel plate is placed in a 820°C (test A c3 The steel was then placed in a heating furnace at 825°C for 5 minutes, then immediately subjected to press quenching. Specifically, the hot steel was placed in a press and held at 500 tons for 10 seconds. The steel was then removed and naturally cooled to room temperature to produce high-strength, high-toughness, and oxidation-resistant hot-formed steel sheet parts. The formed steel was subjected to tensile and hardness testing in accordance with GB / T 228.1-2021 and GB T4340.1-2009 to obtain mechanical property data. The thickness of the oxide layer of the formed steel was measured in accordance with GB / T 13303-1991 to obtain oxidation resistance data. Microstructure observation was also performed to determine the ferrite content and carbide distribution. The results are shown in Table 2.

[0073] Table 2

[0074]

[0075] Example 3

[0076] A high-strength, high-toughness, oxidation-resistant hot-formed steel, whose chemical composition, calculated by mass percentage, is: C: 0.20%, Mn: 1.00%, Cr: 2.00%, Si: 1.20%, Al: 0.60%, Nb: 0.20%, V: 0.20%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance is Fe and unavoidable impurities.

[0077] The mechanical metallurgical preparation method is as follows: molten steel is melted according to the set chemical composition, and the molten steel is prepared into a slab through a continuous casting device, wherein the slab thickness is 200 mm, the casting speed is 1.5 m / min, and the superheat of the molten steel during the continuous casting process is 30°C; the slab is pre-heated in a heating furnace at a heating temperature of 1210°C and a holding time of 4 hours; the slab is quickly descaled by a high-pressure water descaling technology after being taken out of the heating furnace, the slab temperature before descaling is 1200°C, and the descaling water pressure is 20 MPa; the slab after dephosphorization is rough rolled and finished rolled, the starting rolling temperature of the rough rolling is 1200°C, the final rolling temperature is 920°C, and the total reduction ratio is 90%; the starting rolling temperature of the finishing rolling is 840°C, and the final rolling temperature is 820°C (after testing A c3 848℃, A c1 The steel sheet was quenched immediately after finishing rolling, specifically by placing the hot steel sheet into a press at 500t for 10 seconds. The sheet was then removed and naturally cooled to room temperature to produce a high-strength, high-toughness, and oxidation-resistant hot-formed steel sheet. The formed sheet was subjected to tensile and hardness testing in accordance with GB / T 228.1-2021 and GB T4340.1-2009 to obtain mechanical properties. The thickness of the oxide layer of the formed sheet was measured in accordance with GB / T 13303-1991 to obtain antioxidant data. Microstructure observation was also performed to determine the ferrite content and carbide distribution. The results are shown in Table 3.

[0078] Table 3

[0079]

[0080] Example 4

[0081] A high-strength, high-toughness, oxidation-resistant hot-formed steel, whose chemical composition, calculated by mass percentage, is: C: 0.30%, Mn: 1.00%, Cr: 2.50%, Si: 0.60%, Al: 1.20%, Nb: 0.05%, V: 0.05%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance is Fe and unavoidable impurities.

[0082] The mechanical metallurgical preparation method is as follows: molten steel is melted according to the set chemical composition, and the molten steel is prepared into a slab through a continuous casting device, the slab thickness is 200 mm, the casting speed is 1.5 m / min, and the superheat of the molten steel during the continuous casting process is 30°C; the slab is heated in a heating furnace for pretreatment, the heating temperature is 1210°C, and the holding time is 4 hours; after the slab is taken out of the heating furnace, it is quickly descaled by a high-pressure water descaling technology, the slab temperature before descaling is 1200°C, and the descaling water pressure is 20 MPa; the slab after dephosphorization is rough rolled and finished rolled, the starting rolling temperature of the rough rolling is 1200°C, the final rolling temperature is 920°C, and the total reduction rate is 90%; the starting rolling temperature of the finishing rolling is 820°C, and the final rolling temperature is 810°C (after testing A c3 At 825℃, A c1 The steel sheet was subjected to press quenching immediately after finishing rolling, specifically by placing the hot steel sheet into a press at 500t for 10 seconds. The sheet was then removed and naturally cooled to room temperature to produce a high-strength, high-toughness, and oxidation-resistant hot-formed steel sheet. The formed sheet was subjected to tensile and hardness testing in accordance with GB / T 228.1-2021 and GB T4340.1-2009 to obtain mechanical property data. The oxide layer thickness of the formed sheet was measured in accordance with GB / T 13303-1991 to obtain antioxidant data. Microstructure observation was also performed to determine the ferrite content and carbide distribution. The results are shown in Table 4.

[0083] Table 4

[0084]

[0085] Comparative Example 1

[0086] Disclosed is an oxidation-resistant hot-formed steel, which has the following chemical composition, measured by mass percentage: C: 0.20%, Mn: 1.00%, Cr: 2.00%, Si: 1.20%, Al: 0.60%, Nb: 0.20%, V: 0.20%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance Fe and unavoidable impurities.

[0087] The mechanical metallurgical preparation method is as follows: molten steel is melted according to the set chemical composition, and the molten steel is used to prepare slabs through continuous casting equipment. The slab thickness is 200mm, the casting speed is 1.5m / min, and the superheat of the molten steel during the continuous casting process is 30℃; the slab is heated in a heating furnace for pretreatment at a heating temperature of 1210℃ and a holding time of 4 hours; the slab is quickly descaled by high-pressure water descaling technology after being taken out of the heating furnace, the slab temperature before descaling is 1200℃, and the descaling water pressure is 20MPa; the descaled slab is hot rolled, and the rolling start temperature is 120 0℃, the final rolling temperature is 950℃, the total reduction rate is 97.5%, and a 5mm thick steel plate is obtained. The steel plate is then cooled in a 640℃ furnace to the coiling temperature (640℃) to obtain a hot-rolled thin strip; the hot-rolled thin strip is cold rolled with a total reduction rate of 60% to obtain a 2mm thick thin steel plate; the thin steel plate is placed in a heating furnace at 930℃ and kept warm for 5 minutes, and then press quenched immediately, specifically, placed in a press while hot and kept under a pressure of 500t for 10s, and then the steel plate is taken out and naturally cooled to room temperature to obtain an oxidation-resistant hot-formed steel plate formed part. The tensile properties and hardness of the formed plates were tested in accordance with GB / T 228.1-2021 and GBT4340.1-2009 to obtain their mechanical properties data. The oxide layer thickness of the formed plates was tested in accordance with GB / T 13303-1991 to obtain their antioxidant performance data. The microstructure was observed and the ferrite content and carbide distribution were statistically analyzed. The results are shown in Table 5.

[0088] Table 5

[0089]

[0090] Comparative Example 2

[0091] Disclosed is an oxidation-resistant hot-formed steel, which has the following chemical composition, measured by mass percentage: C: 0.21%, Mn: 0.84%, Cr: 2.62%, Si: 0.42%, Al: 0.60%, Nb: 0.50%, V: 0.10%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance Fe and unavoidable impurities.

[0092] The mechanical metallurgical preparation method is as follows: molten steel is melted according to the set chemical composition, and the molten steel is used to prepare slabs through continuous casting equipment. The slab thickness is 200mm, the casting speed is 1.5m / min, and the superheat of the molten steel during the continuous casting process is 30℃; the slab is heated in a heating furnace at a temperature of 1210℃ and a holding time of 4 hours; the slab is taken out of the heating furnace and quickly descaled by high-pressure water descaling technology. The slab temperature before descaling is 12 00℃, descaling water pressure is 20MPa; the descaling slab is hot rolled with the starting rolling temperature of 1200℃, the finishing rolling temperature of 950℃, and the total reduction ratio of 97.5% to obtain a 5mm thick steel plate, and then the steel plate is cooled in a 640℃ furnace to the coiling temperature (640℃) to obtain a hot-rolled thin strip; the hot-rolled thin strip is cold rolled with a total reduction ratio of 60% to obtain a 2mm thick thin steel plate; the thin steel plate is placed in a 930℃ (tested by A c3 The steel was then placed in a heating furnace at 838°C for 5 minutes, then immediately subjected to press quenching. Specifically, the steel was placed in a press while still hot and held at 500 tons for 10 seconds. The steel was then removed and naturally cooled to room temperature to produce oxidation-resistant hot-formed steel sheet parts. The formed sheets were subjected to tensile and hardness testing in accordance with GB / T 228.1-2021 and GB T4340.1-2009 to obtain mechanical property data. The oxide layer thickness of the formed sheets was measured in accordance with GB / T 13303-1991 to obtain oxidation resistance data. Microstructure observation was also performed to determine the ferrite content and carbide distribution. The results are shown in Table 6.

[0093] Table 6

[0094]

[0095] Comparative Example 3

[0096] Disclosed is an oxidation-resistant hot-formed steel, which has the following chemical composition, measured by mass percentage: C: 0.30%, Mn: 1.00%, Cr: 2.50%, Si: 0.60%, Al: 1.20%, Nb: 0.05%, V: 0.05%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance Fe and unavoidable impurities.

[0097] The mechanical metallurgical preparation method is as follows: molten steel is melted according to the set chemical composition, and the molten steel is prepared into slabs through continuous casting equipment. The slab thickness is 200mm, the casting speed is 1.5m / min, and the superheat of the molten steel during the continuous casting process is 30℃; the slab is heated in a heating furnace for pretreatment at a heating temperature of 1210℃ and a holding time of 4 hours; the slab is quickly descaled by high-pressure water descaling technology after being taken out of the heating furnace, the slab temperature before descaling is 1200℃, and the descaling water pressure is 20MPa; the descaled slab is hot rolled at a starting rolling temperature of 1200℃, and the final The rolling temperature is 950°C, the total reduction rate is 97.5%, and a 5mm thick steel plate is obtained; the steel plate is then cooled in a 640°C furnace to the coiling temperature (640°C), and the steel plate is coiled to obtain a hot-rolled thin strip; the hot-rolled thin strip is cold rolled with a total reduction rate of 60% to obtain a 2mm thick thin steel plate; the thin steel plate is placed in a 930°C heating furnace and kept warm for 5 minutes, and then immediately press quenched, specifically, placed in a press while hot and kept at a pressure of 500t for 10 seconds, and then the steel plate is taken out and naturally cooled to room temperature to obtain an oxidation-resistant hot-formed steel plate formed part. The tensile properties and hardness tests of the formed plates were carried out in accordance with GB / T228.1-2021 and GB T4340.1-2009 to obtain their mechanical properties data. The thickness of the oxide layer of the formed plates was statistically analyzed in accordance with GB / T 13303-1991 to obtain their antioxidant performance data. The microstructure was observed and the ferrite content and carbide distribution were statistically analyzed. The results are shown in Table 7.

[0098] Table 7

[0099]

[0100] Comparative Example 4

[0101] Disclosed is an oxidation-resistant hot-formed steel, which has the following chemical composition, measured by mass percentage: C: 0.20%, Mn: 1.00%, Cr: 2.00%, Si: 1.20%, Al: 0.60%, Nb: 0.20%, V: 0.20%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance Fe and unavoidable impurities.

[0102] The mechanical metallurgical preparation method is as follows: molten steel is melted according to the set chemical composition, and the molten steel is used to prepare a slab through a continuous casting device. The slab thickness is 200 mm, the casting speed is 1.5 m / min, and the superheat of the molten steel during the continuous casting process is 30°C; the slab is heated in a heating furnace for pretreatment at a heating temperature of 1210°C and a holding time of 4 hours; the slab is quickly descaled by a high-pressure water descaling technology after being taken out of the heating furnace, the slab temperature before descaling is 1200°C, and the descaling water pressure is 20 MPa; the slab after dephosphorization is rough rolled and finished rolled, the starting rolling temperature of the rough rolling is 1200°C, the final rolling temperature is 950°C, and the total reduction ratio is 90%; the starting rolling temperature of the finishing rolling is 920°C, and the final rolling temperature is 860°C (after testing A c3 848℃, A c1 The steel sheet was prepared at a temperature of 771°C (771°C) with a total reduction ratio of 90%, resulting in a 2mm thick sheet. After finishing rolling, the steel sheet was immediately press-quenched. Specifically, the sheet was placed in a press while hot and held at 500t for 10 seconds. The sheet was then removed and naturally cooled to room temperature to obtain an oxidation-resistant hot-formed steel sheet. The formed sheet was subjected to tensile and hardness testing in accordance with GB / T 228.1-2021 and GB T4340.1-2009 to obtain mechanical properties. The thickness of the oxide layer of the formed sheet was measured in accordance with GB / T 13303-1991 to obtain antioxidant data. Microstructure observation was also performed to determine the ferrite content and carbide distribution. The results are shown in Table 8.

[0103] Table 8

[0104]

[0105] Comparative Example 5

[0106] Disclosed is an oxidation-resistant hot-formed steel, which has the following chemical composition, measured by mass percentage: C: 0.30%, Mn: 1.00%, Cr: 2.50%, Si: 0.60%, Al: 1.20%, Nb: 0.05%, V: 0.05%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance Fe and unavoidable impurities.

[0107] The mechanical metallurgical preparation method is as follows: molten steel is melted according to the set chemical composition, and the molten steel is used to prepare a slab through a continuous casting device. The slab thickness is 200 mm, the casting speed is 1.5 m / min, and the superheat of the molten steel during the continuous casting process is 30°C; the slab is heated in a heating furnace for pretreatment at a heating temperature of 1210°C and a holding time of 4 hours; the slab is quickly descaled by a high-pressure water descaling technology after being taken out of the heating furnace, the slab temperature before descaling is 1200°C, and the descaling water pressure is 20 MPa; the slab after dephosphorization is rough rolled and finished rolled, the starting rolling temperature of the rough rolling is 1200°C, the final rolling temperature is 950°C, and the total reduction ratio is 90%; the starting rolling temperature of the finishing rolling is 920°C, and the final rolling temperature is 860°C (after testing A c3 At 825℃, A c1 The steel sheet was subjected to press quenching immediately after finishing rolling, specifically by placing the hot steel sheet into a press at 500t for 10 seconds. The sheet was then removed and naturally cooled to room temperature to obtain the oxidation-resistant hot-formed steel sheet. The formed sheet was subjected to tensile and hardness testing in accordance with GB / T 228.1-2021 and GB T4340.1-2009 to obtain mechanical property data. The oxide layer thickness of the formed sheet was measured in accordance with GB / T 13303-1991 to obtain oxidation resistance data. Microstructure observation was also performed to determine the ferrite content and carbide distribution. The results are shown in Table 9.

[0108] Table 9

[0109]

[0110] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A high-strength, high-toughness, oxidation-resistant hot-formed steel, characterized in that: The chemical composition of the high-strength, high-toughness, oxidation-resistant hot-formed steel is as follows, by mass percentage: C: 0.20-0.30%, Mn: 1.00-1.80%, Cr: 2.00-2.50%, Si: 0.60-1.20%, Al: 0.60-1.20%, Nb: 0.05-0.20%, V: 0.05-0.20%, P≤0.01%, S≤0.005%, N≤0.003%, and the balance is Fe and unavoidable impurities; The microstructure of the high-strength, high-toughness, oxidation-resistant hot-formed steel consists of 2-3.5% ferrite and 96.5-98% martensite in terms of volume percentage; The mechanical metallurgical preparation steps of the high-strength, high-toughness, oxidation-resistant hot-formed steel include: After molten steel is melted according to the chemical composition, slabs are prepared by continuous casting; the slabs are subjected to hot forming treatment to obtain the high-strength, high-toughness, and oxidation-resistant hot-formed steel; The thermoforming treatment is performed in one of the following ways: Method 1: hot rolling and cold rolling the slab in sequence to obtain a thin steel plate; the thin steel plate is kept at a two-phase temperature and then press-quenched to obtain the high-strength, high-toughness, and oxidation-resistant hot-formed steel; Method 2: performing rough rolling and finish rolling on the slab in sequence to obtain a thin steel plate; then immediately performing press quenching on the thin steel plate to obtain the high-strength, high-toughness, and oxidation-resistant hot-formed steel; The starting temperature of the finishing rolling is A c3 -10℃~A c3 , the final rolling temperature is A c1 ~A c3 ; The two-phase region temperature is A c3 -30℃~A c3 The time for keeping warm at the two-phase temperature is 1 to 5 minutes.

2. The high-strength, high-toughness, oxidation-resistant hot-formed steel according to claim 1, characterized in that: The thickness of the slab is 150-200 mm, the casting speed during the continuous casting process is 1.4-1.5 m / min, and the superheat degree of the molten steel is 20-30° C.

3. The high-strength, high-toughness, oxidation-resistant hot-formed steel according to claim 1, characterized in that: The hot forming process also includes heating pretreatment and descaling steps for the slab.

4. The high-strength, high-toughness, oxidation-resistant hot-formed steel according to claim 3, characterized in that: The temperature of the heating pretreatment is 1210-1215° C., and the time is 4-5 hours; the descaling treatment adopts a high-pressure water descaling method, the slab temperature before descaling is 1200-1210° C., and the descaling water pressure is 15-20 MPa.

5. The high-strength, high-toughness, oxidation-resistant hot-formed steel according to claim 1, characterized in that: The starting rolling temperature of the hot rolling is 1200° C., the finishing rolling temperature is 950-960° C., and the total reduction ratio is 70-98%. The total reduction ratio of the cold rolling is 50-60%.

6. The high-strength, high-toughness, oxidation-resistant hot-formed steel according to claim 1, characterized in that: The starting rolling temperature of the rough rolling is 1200° C., the finishing rolling temperature is 920-930° C., and the total reduction ratio is 70-90%. The total reduction ratio of the finish rolling is 70-90%.

7. The high-strength, high-toughness, oxidation-resistant hot-formed steel according to claim 1, characterized in that: After the hot rolling and before the cold rolling, the process also includes a coiling operation.

8. The high-strength, high-toughness, oxidation-resistant hot-formed steel according to claim 1, characterized in that: The press quenching forming parameters include: a pressure of 500t and a holding time of 10s.

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