A method for forming a 2.2gpa hot gas inflatable tubular member having excellent strength and a hot gas inflatable tubular member

Abstract

The present application relates to hot gas expansion pipe forming technology field, specifically to a kind of 2.2GPa excellent strength hot gas expansion pipe forming method and hot gas expansion pipe, comprising: welding metal plate to form pipe shape piece;Pipe shape piece is tempered heat treated;Pipe shape piece after tempering is heated to austenitizing state;Pipe shape piece in austenitizing state is placed in mould, closes mould to form sealed mould cavity, high-pressure gas is filled into pipe shape piece, forming and quenching are completed synchronously in mould, and forming piece is formed;Forming piece is baked, and the 2.2GPa hot gas expansion pipe of baking state tensile strength ≥1950MPa is obtained.The present application stably improves the final strength of product, and makes baking state tensile strength reach more than 1950MPa stably.

Description

Technical Field

[0001] This invention relates to the field of hot gas expansion tube forming technology, specifically to a method for forming a 2.2GPa hot gas expansion tube with excellent strength and a hot gas expansion tube. Background Technology

[0002] Hot gas expansion forming (HMGF) is an advanced manufacturing technology that integrates hot stamping and internal high-pressure forming. It uses high-temperature and high-pressure gas to form a tube blank by molding and then quickly quenching it, achieving integrated manufacturing of complex structures and ultra-high strength. It is widely used in safety structural components such as automotive A-pillars, B-pillars, door sill beams, and battery pack anti-collision beams.

[0003] However, existing hot gas expansion forming processes still face numerous technical bottlenecks in the pursuit of higher performance. The tensile strength of ultra-high strength 2200MPa hot-formed steel hot-expanded tubular parts after baking is only 1500-1900MPa, making it difficult to consistently reach the required 1950MPa or higher, which can severely impact the normal use of the material. Especially in the automotive industry, tensile strength is a crucial indicator of a material's crash performance and is closely related to vehicle safety; therefore, conducting relevant research is of great significance.

[0004] For example, Chinese patent application CN105921584A discloses a method for pneumatic bulging of ultra-high strength steel hollow components. The method involves heating the tube blank to 910℃-920℃ and holding it at that temperature for austenitization. After forming, liquid is introduced through a cooling device within the mold for rapid quenching. While this method improves component strength through an integrated forming and quenching process, it primarily focuses on obtaining a fully martensitic structure through rapid quenching. It does not address how to further optimize and stabilize the tensile strength after bake-hardening through process control.

[0005] Chinese patent application CN113528761A discloses a hot-formed part and its preparation method, which employs austenitization, hot forming quenching, and fractionation treatment at temperatures above the mold opening temperature to obtain a certain amount of retained austenite to improve plasticity. However, its focus is on improving plasticity (elongation) and resistance to hydrogen embrittlement, while its tensile strength is limited to around 1500 MPa.

[0006] Therefore, optimizing the hot gas expansion process, especially precisely controlling the heating process, to ensure that the material is fully austenitized and obtains a refined grain structure, so as to stably and reliably produce 2.2GPa-grade hot gas expansion tubular parts with a baked tensile strength ≥1950MPa, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-strength 2.2GPa hot-expanded tubular forming method that stably improves the final strength of the product, making the tensile strength in the baked state stably reach over 1950MPa.

[0008] To address the aforementioned technical problems, this invention provides a method for forming a 2.2 GPa hot-expanded tubular component with excellent strength, comprising: Metal sheets are welded together to form tubular components; The tubular parts are subjected to tempering heat treatment; Heat the tempered tubular parts to an austenitic state; The austenitized tubular part is placed in a mold, the mold is closed to form a sealed mold cavity, high-pressure gas is injected into the tubular part, and forming and quenching are completed simultaneously in the mold to form a shaped part. The formed part is baked to obtain a 2.2GPa hot gas expansion tubular part with a baked tensile strength ≥1950MPa.

[0009] In some embodiments, heating the tempered tubular part to an austenitic state includes: a heating temperature of 930~1050℃, a heating rate V of 0~50℃ / s, a holding time t of 0~30s, and satisfying the heat input Q=V×t≥500℃.

[0010] In some embodiments, resistance induction heating is used to heat the tempered tubular part to an austenitic state.

[0011] In some embodiments, high-pressure gas is injected into the tubular component to make the pressure of the sealed mold cavity 20~100MPa and the pressure holding time 4~10s.

[0012] In some embodiments, the pressure holding time is the period during which the internal gas pressure and mold closing force are maintained after the tubular part has expanded and adhered to the mold.

[0013] In some embodiments, the sheet metal is formed into the tubular component by ERW welding.

[0014] In some embodiments, the tempering temperature is 400~600℃ and the holding time is 1~5s.

[0015] In some embodiments, the molded part is baked for 20 minutes at a temperature of 170°C.

[0016] In some embodiments, the metal sheet has a tensile strength of 500–700 MPa and a thickness of 0.6–3.0 mm.

[0017] On the other hand, the present invention provides a hot-expanded tubular component, which is manufactured using the aforementioned high-strength 2.2GPa hot-expanded tubular component forming method.

[0018] The beneficial effects of this invention are as follows: 1. This invention ensures that tubular parts can achieve complete and uniform austenitization under rapid heating conditions by precisely controlling the heating rate and holding time during the austenitization stage, and by introducing a control parameter of heat input Q≥500℃. This allows for full solid solution of alloying elements and fine grain strengthening, thereby stably improving the final strength of the product and making the tensile strength in the baked state stably reach above 1950MPa.

[0019] 2. The tempering treatment after welding pipes in this invention effectively eliminates residual stress in the weld and avoids forming cracks.

[0020] 3. This invention uses resistance induction heating, which has a fast heating rate and high efficiency, and can achieve precise temperature control, which is beneficial for the formation of uniform initial austenite grains. Attached Figure Description

[0021] Figure 1 The results of the tensile test in Example 1; Figure 2 The results of the tensile test in Example 2; Figure 3 The results of the tensile test in Example 3; Figure 4 The tensile test results are for Comparative Example 1; Figure 5 The tensile test results are for Comparative Example 2; Figure 6 The tensile test results are for Comparative Example 3; Figure 7 The results are for the tensile test of Comparative Example 4. Detailed Implementation

[0022] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] This invention provides a method for forming a 2.2 GPa hot gas-expanded tubular component with excellent strength, comprising the following steps: S1. Metal sheets are welded into tubular components using ERW welding.

[0024] S2. Perform tempering heat treatment on the tubular parts. Tempering temperature: 400~600℃, holding time: 1~5s. Tempering heat treatment is used to reduce weld strength and prevent cracking during the forming process.

[0025] S3. The tempered tubular part is heated to the austenitic state by resistance induction heating. The heating temperature is 930~1050℃, the heating rate V is 0~50℃ / s, the holding time t is 0~30s, and the heat input Q=V×t≥500℃ is satisfied.

[0026] This invention employs resistance induction heating, which offers rapid heating, high thermal efficiency, precise temperature control, and good heating uniformity, thus promoting complete austenitization. By limiting the minimum heat input, complete austenitization and solid solution of alloying elements can be ensured, promoting fine-grain strengthening.

[0027] S4. Place the austenitized tubular part in the mold, close the mold to form a sealed mold cavity, and fill the tubular part with high-pressure gas so that the pressure in the sealed mold cavity is 20~100MPa. The pressure holding time is 4~10s. The pressure holding time is the period after the tubular part expands and fits into the mold, and the internal gas pressure and mold closing force are maintained. The forming and quenching are completed simultaneously in the mold to form the formed part.

[0028] S5. The formed part is baked for 20 minutes at a temperature of 170°C to obtain a 2.2 GPa hot gas expansion tubular part with a tensile strength ≥1950 MPa in the baked state.

[0029] The following detailed description utilizes examples and comparative examples: Example 1: This embodiment describes a method for forming a 2.2GPa hot-expanded tubular component with excellent strength properties. The metal sheet has a tensile strength of 585MPa and a material thickness of 2.4mm. The initial tube blank (i.e., the tubular part) is obtained by ERW welding. It is held at 500℃ for 2 seconds to eliminate residual stress and reduce weld strength. The tube blank is then placed in a resistance induction heating table and heated to 950℃ at a heating rate of 50℃ / s, and held for 20 seconds. At this point, the total heat input for hot gas expansion is Q = 50 × 20 = 1000℃ > 500℃. The heated tube blank is then placed in a hot gas expansion mold, and a high-pressure gas medium is introduced. A mold cavity pressure of 70MPa is applied simultaneously and held for 6 seconds. After forming, it is baked at 170℃ for 20 minutes.

[0030] Take a longitudinal specimen of 120×20mm and conduct a tensile test, such as Figure 1 As shown, the calculated tensile strength is 2014MPa ≥ 1950MPa, which is qualified.

[0031] Example 2: This embodiment describes a method for forming a 2.2GPa hot-expanded tubular component with excellent strength performance. The metal sheet has a tensile strength of 560MPa and a material thickness of 2.0mm.

[0032] The initial tube blank was obtained using ERW welding and held at 500℃ for 2 seconds to eliminate residual stress and reduce weld strength. The tube blank was then placed in a resistance induction heating stage and heated to 950℃ at a rate of 50℃ / s, held for 10 seconds. At this point, the total heat input for hot gas expansion was Q = 50 × 10 = 500℃, satisfying the requirement of ≥500℃. The heated tube blank was then placed in a hot gas expansion mold, and a high-pressure gas medium was introduced, simultaneously applying a mold cavity pressure of 70MPa and holding for 6 seconds. After forming, it was baked at 170℃ for 20 minutes.

[0033] Take a longitudinal specimen of 120×20mm and conduct a tensile test, such as Figure 2 As shown, the calculated tensile strength is 1986MPa ≥ 1950MPa, which is qualified.

[0034] Example 3: This embodiment describes a method for forming a 2.2GPa hot-expanded tubular part with excellent strength performance. The metal sheet has a tensile strength of 590MPa and a material thickness of 1.4mm.

[0035] The initial tube blank was obtained using ERW welding and held at 500℃ for 2 seconds to eliminate residual stress and reduce weld strength. The tube blank was then placed in a resistance induction heating stage and heated to 960℃ at a rate of 35℃ / s, held for 15 seconds. At this point, the total heat input for hot gas expansion, Q = 35 × 15 = 525℃, meets the requirement of ≥500℃. The heated tube blank was then placed in a hot gas expansion mold, and a high-pressure gas medium was introduced, simultaneously applying a mold cavity pressure of 70MPa and holding for 6 seconds. After forming, it was baked at 170℃ for 20 minutes.

[0036] Take a longitudinal specimen of 120×20mm and conduct a tensile test, such as Figure 3 As shown, the calculated tensile strength is 2015MPa ≥ 1950MPa, which is qualified.

[0037] Comparative Example 1: This embodiment describes a method for forming a 2.2 GPa hot-expanded tubular component with excellent strength performance. The metal sheet has a tensile strength of 585 MPa and a material thickness of 2.4 mm. The initial tube blank was obtained using ERW welding and held at 500℃ for 2 seconds to eliminate residual stress and reduce weld strength. The tube blank was then placed in a resistance induction heating stage and heated to 980℃ at a rate of 25℃ / s, held for 10 seconds. At this point, the total heat input for hot gas expansion, Q = 25 × 10 = 250℃ < 500℃, was placed in a hot gas expansion mold. A high-pressure gas medium was introduced, and a mold cavity pressure of 70 MPa was applied simultaneously and held for 6 seconds. After forming, the tube blank was baked at 170℃ for 20 minutes.

[0038] Take a longitudinal specimen of 120×20mm and conduct a tensile test, such as Figure 4As shown, the calculated tensile strength is 1829MPa < 1950MPa, which is unqualified. The austenitization is insufficient, the microstructure is uneven, and both the strength and toughness are poor.

[0039] Comparative Example 2: This embodiment describes a method for forming a 2.2GPa hot-expanded tubular component with excellent strength performance. The metal sheet has a tensile strength of 560MPa and a material thickness of 2.0mm.

[0040] The initial tube blank was obtained using ERW welding and held at 500℃ for 2 seconds to eliminate residual stress and reduce weld strength. The tube blank was then placed in a resistance induction heating stage and heated to 950℃ at a rate of 25℃ / s, held for 15 seconds. At this point, the total heat input for hot gas expansion, Q = 25 × 15 = 375℃ < 500℃, was placed in a hot gas expansion mold. A high-pressure gas medium was introduced, and a mold cavity pressure of 70 MPa was applied simultaneously and held for 6 seconds. After forming, the tube blank was baked at 170℃ for 20 minutes.

[0041] Take a longitudinal specimen of 120×20mm and conduct a tensile test, such as Figure 5 As shown, the calculated tensile strength is 1783 MPa < 1950 MPa, which is unacceptable. The austenite transformation is incomplete, and there are local soft areas, resulting in the overall strength being too low. Comparative Example 3: Example 1: A method for forming a 2.2 GPa hot gas expansion tube with excellent strength performance, wherein the metal sheet has a tensile strength of 590 MPa and a material thickness of 1.4 mm.

[0042] The initial tube blank was obtained using ERW welding and held at 500℃ for 2 seconds to eliminate residual stress and reduce weld strength. The tube blank was then placed in a resistance induction heating stage and heated to 930℃ at a rate of 25℃ / s, held for 18 seconds. At this point, the total heat input for hot gas expansion, Q = 25 × 18 = 450℃ < 500℃, was placed in a hot gas expansion mold. A high-pressure gas medium was introduced, and a mold cavity pressure of 70 MPa was applied simultaneously and held for 6 seconds. After forming, the tube blank was baked at 170℃ for 20 minutes.

[0043] Take a longitudinal specimen of 120×20mm and conduct a tensile test, such as Figure 6 As shown, the calculated tensile strength is 1899MPa < 1950MPa, which is unqualified. This is because the heating temperature is too low, the heat input is insufficient, the austenite uniformity is poor, and the overall performance stability is insufficient.

[0044] Comparative Example 4: Example 1: A method for forming a 2.2 GPa hot gas expansion tube with excellent strength performance, wherein the metal sheet has a tensile strength of 565 MPa and a material thickness of 1.4 mm.

[0045] The initial tube blank was obtained using ERW welding and held at 500℃ for 2 seconds to eliminate residual stress and reduce weld strength. The tube blank was then placed in a resistance induction heating stage and heated to 1000℃ at a rate of 20℃ / s, held for 20 seconds. At this point, the total heat input for hot gas expansion, Q = 20 × 20 = 400℃ < 500℃, was placed in a hot gas expansion mold. A high-pressure gas medium was introduced, and a mold cavity pressure of 70MPa was applied simultaneously and held for 6 seconds. After forming, the tube blank was baked at 170℃ for 20 minutes.

[0046] Take a longitudinal specimen of 120×20mm and conduct a tensile test, such as Figure 7 As shown, the calculated tensile strength is 1872MPa < 1950MPa, which is unqualified. The heating rate is too slow, which leads to coarsening of austenite grains. After quenching, the martensite structure is coarse, the brittleness is increased, and it is easy to crack when bent.

[0047] Examples 1 to 3 collectively demonstrate that as long as the heat input Q is strictly controlled to be ≥500℃ and other process conditions are combined, a product with a baked tensile strength ≥1950MPa can be stably obtained. The test results of Comparative Examples 1 to 4 are between 1829-1899MPa, all of which are lower than the qualified standard of 1950MPa. They all indicate that when the heating rate is too slow and the holding time is too short, resulting in a heat input Q <500℃, the target strength cannot be obtained, whether due to insufficient or incomplete austenitization or poor microstructure uniformity.

[0048] In summary, the metal sheet obtained by the 2.2GPa hot gas expansion tube forming method provided by the present invention has good tensile properties and is also beneficial to improving the impact performance of the material.

[0049] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for forming a high-strength, 2.2 GPa hot-expanded tubular component, characterized in that, include: Metal sheets are welded together to form tubular components; The tubular parts are subjected to tempering heat treatment; Heat the tempered tubular parts to an austenitic state; The austenitic tubular part is placed in a mold, the mold is closed to form a sealed mold cavity, high-pressure gas is injected into the tubular part, and forming and quenching are completed simultaneously in the mold to form a shaped part; The formed part is baked to obtain a 2.2GPa hot gas expansion tubular part with a baked tensile strength ≥1950MPa.

2. The method for forming a high-strength 2.2 GPa hot-expanded tubular component according to claim 1, characterized in that, Heating the tempered tubular parts to the austenitic state includes: heating temperature of 930~1050℃, heating rate V of 0~50℃ / s, holding time t of 0~30s, and satisfying the heat input Q=V×t≥500℃.

3. The method for forming a high-strength 2.2 GPa hot-expanded tubular component according to claim 2, characterized in that, The tempered tubular parts are heated to the austenitic state by resistance induction heating.

4. The method for forming a 2.2 GPa hot-expanded tubular part with excellent strength according to any one of claims 1 to 3, characterized in that, High-pressure gas is injected into the tubular component to make the pressure of the sealed mold cavity 20~100MPa, and the pressure holding time is 4~10s.

5. The method for forming a high-strength 2.2 GPa hot-expanded tubular component according to claim 4, characterized in that, The pressure holding time is the period during which the internal gas pressure and mold closing force are maintained after the tubular part has expanded and adhered to the mold.

6. The method for forming a 2.2 GPa hot-expanded tubular part with excellent strength according to any one of claims 1 to 3, characterized in that, The metal sheet is welded into the tubular component using ERW welding.

7. The method for forming a 2.2 GPa hot-expanded tubular part with excellent strength according to any one of claims 1 to 3, characterized in that, Tempering temperature 400~600℃, holding time 1~5s.

8. The method for forming a 2.2 GPa hot-expanded tubular part with excellent strength according to any one of claims 1 to 3, characterized in that, The molded part is baked for 20 minutes at a temperature of 170℃.

9. The method for forming a 2.2 GPa hot-expanded tubular part with excellent strength according to any one of claims 1 to 3, characterized in that, The metal sheet has a tensile strength of 500-700 MPa and a thickness of 0.6-3.0 mm.

10. A hot-air-expandable tubular component, characterized in that, It is manufactured using the hot gas expansion tube forming method with excellent strength as described in any one of claims 1 to 9.

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