A super-high-strength steel component hot forming device and a maraging-bainite complex phase structure control method

Abstract

The application provides a kind of super high-strength steel component hot forming device and martensite-bainite complex structure control method, super high-strength steel component hot forming device includes the punch upper die and punch lower die of relative arrangement, the side surface of punch upper die and punch lower die close to each other is connected with layered working surface, layered working surface is used to cooperate with super high-strength steel component contact;Wherein, the surface between two layered working surfaces is provided with temperature induction component, the inside of layered working surface is also provided with electromagnetic induction heating component, the inside of the side of punch upper die or punch lower die close to layered working surface is provided with cooling component.The surface layer temperature of punch upper die or punch lower die is accurately controlled to finely regulate and control bainite structure morphology and quantity in the forming process of super high-strength steel component, and then the structure of super high-strength steel component is changed to form martensite-bainite complex structure, to further realize the hot stamping forming of high-strength and high-toughness super high-strength steel component.

Description

Technical Field

[0001] This invention relates to the field of high-end equipment manufacturing, and in particular to a hot forming device for ultra-high strength steel components and a method for controlling Marble-Bey multiphase microstructure. Background Technology

[0002] Hot forming is a novel material processing technology that integrates forming and heat treatment, and it represents a significant development direction for the high-performance, lightweight manufacturing of high-strength, lightweight materials such as ultra-high-strength steel, high-strength aluminum alloys, and titanium alloys. Components formed by hot stamping possess numerous advantages, including high strength, high rigidity, high precision, and lightweight properties, demonstrating significant technological advantages. Today, hot-formed steel products with tensile strengths of 1500 MPa or even higher are widely used in vehicle components such as A-pillars, B-pillars, bumpers, longitudinal beams, side beams, underbody frames, and door anti-collision beams. However, while hot-formed components achieve ultra-high strength single martensitic structures, their plasticity and toughness are significantly reduced, and their sensitivity to cold bending and delayed fracture is more pronounced, becoming a major problem restricting the application of ultra-high-strength steel hot-formed components.

[0003] Martensite-bainite multiphase microstructure exhibits superior strength and toughness compared to single-phase martensite microstructure. Furthermore, during the isothermal transformation of bainite, the preferentially formed bainite microstructure divides the original austenite grains into smaller regions, thereby reducing the growth space for martensite and resulting in finer martensite lath bundles. Ultimately, this leads to a reduction in the overall "effective grain size," thus improving the material's strength and toughness. However, the hot-formed microstructure of ultra-high-strength steel is extremely sensitive to process conditions. In actual industrial production, to produce a certain amount of bainite, the hot-forming pressure holding and shaping process typically requires precise control of the quenching cooling rate and cooling time. This is because precise control of the cooling rate during rapid quenching affects the morphology, distribution, and proportion of bainite by controlling carbon distribution and phase transformation processes, thereby significantly impacting the product's mechanical properties and other indicators.

[0004] Therefore, how to achieve dynamic and precise control of quenching temperature and cooling rate during the hot forming process has become a key technical problem that urgently needs to be solved in the intelligent, efficient and refined production of high-strength and tough hot stamping components. Summary of the Invention

[0005] The purpose of this invention is to provide a thermoforming device for ultra-high strength steel components and a method for controlling the Marble-Bey multiphase microstructure, which can improve the technical problems of difficulty in coordinating strength and toughness and long process cycle in thermoformed components prepared by existing thermoforming devices.

[0006] To solve the above-mentioned technical problems, the present invention first provides a thermoforming device for ultra-high strength steel components, including an upper stamping die and a lower stamping die arranged opposite to each other. The surfaces of the upper stamping die and the lower stamping die that are close to each other are connected with a layered working surface, which is used to make contact with the ultra-high strength steel component.

[0007] Temperature sensing components are installed on the surface between the two layered working surfaces, and electromagnetic induction heating components are installed inside the layered working surfaces. Cooling components are installed inside the upper or lower stamping die on the side closest to the layered working surfaces.

[0008] Preferably, a connecting guide rod is provided between the upper stamping die and the lower stamping die, and a draft spring is sleeved on the connecting guide rod. One end of the draft spring abuts against the upper stamping die, and the other end of the draft spring abuts against the lower stamping die.

[0009] Preferably, the upper and lower stamping dies are provided with sliding grooves on their surfaces closest to each other, and the layered working surfaces are located in the corresponding sliding grooves.

[0010] Preferably, the temperature sensing component includes a temperature probe, a data processing module, a data transmission module, and a battery pack electrically connected to the temperature probe, the data processing module, and the data transmission module, respectively.

[0011] The temperature sensing probe is used to monitor the surface temperature of the ultra-high strength steel components in real time, the data processing module is used to process the temperature data collected by the temperature sensing probe, and the data transmission module is used to transmit the temperature data to the electromagnetic induction heating component.

[0012] Preferably, the electromagnetic induction heating component is built into a magnetic groove inside the layered working surface, and an energized coil is provided in the magnetic groove for connecting to an external power source.

[0013] The electromagnetic induction heating component includes a temperature sensing resistor and a signal receiver, which is communicatively connected to the data transmission module.

[0014] Preferably, the cooling assembly includes a cooling pipe, a cooling medium, and a cooling medium circulation pump. The cooling pipe is embedded and fixed in a preset groove inside the upper or lower stamping die. The cooling pipe is connected to a cooling medium circulation pump and is filled with cooling medium.

[0015] The preset groove is also equipped with multiple spaced heat-conducting inserts, which are in contact with the outer surface of the cooling pipe.

[0016] Accordingly, the present invention also provides a method for controlling the Marble-Bay multiphase microstructure of ultra-high-strength steel components by using the ultra-high-strength steel component hot forming apparatus as described in any of the above claims, the method comprising the following steps:

[0017] S10 involves rapidly heating the ultra-high strength steel component to a temperature of 800–1000℃ and then holding it at that temperature for 3–10 minutes to ensure that the microstructure of the ultra-high strength steel component completes the austenitic transformation and has a uniform composition. The heating rate is 5–50℃ / s.

[0018] S20, the heated ultra-high strength steel component is taken out and transferred to the ultra-high strength steel component hot forming device, and the transfer time is 2 to 4 seconds;

[0019] S30, the ultra-high strength steel component is subjected to the first mold closing hot stamping forming and pressure holding quenching treatment, so that the surface temperature of the ultra-high strength steel component drops to the bainite transformation zone temperature. At this time, the quenching cooling rate of the ultra-high strength steel component is greater than or equal to 40℃ / s.

[0020] S40, turn on the switch of the electromagnetic induction heating component to perform external quenching and heat preservation treatment on the ultra-high strength steel component, so that the microstructure of the ultra-high strength steel component is partially transformed into bainite. At this time, the quenching cooling rate of the ultra-high strength steel component is less than 5℃ / s.

[0021] S50, turn off the switch of the electromagnetic induction heating component, perform a second mold closing hot stamping forming and pressure holding quenching treatment on the ultra-high strength steel component, so that the microstructure of the ultra-high strength steel component is transformed into a martensite-bainite multiphase structure, and the quenching cooling rate of the ultra-high strength steel component is 60~80℃ / s.

[0022] Preferably, in step S30, the mold closing rate of the first hot stamping forming is 0.1 to 10 s. -1 The mold closing time is 1–10 s, the holding pressure time is 3–20 s, the holding pressure is 50–5000 kN, and the bainite transformation zone temperature is 400–600 °C; in step S50, the mold closing rate of the second mold closing hot stamping is 0.1–10 s. -1 The mold closing time is 2-4 seconds, the holding pressure time is 5-10 seconds, and the holding pressure is 50-5000 kN.

[0023] Preferably, the holding temperature at the end of step S30 is 400–500°C; in step S40, the heating temperature of the upper or lower stamping die heated by the electromagnetic induction heating component is 300–500°C, and the current density supplied to the electromagnetic induction heating component is 30–100 A / mm². 2 In step S50, the microstructure of ultra-high strength steel components transforms into a martensite-lower bainite complex structure.

[0024] Preferably, the holding temperature at the end of step S30 is 550–600°C; in step S40, the heating temperature of the upper or lower stamping die heated by the electromagnetic induction heating component is 550–600°C, and the current density supplied to the electromagnetic induction heating component is 101–200 A / mm².2 In step S50, the microstructure of ultra-high strength steel components transforms into a martensite-granular bainite complex structure.

[0025] The beneficial effects of this invention are as follows: Unlike the prior art, this invention provides a thermoforming device for ultra-high strength steel components and a method for controlling Marble-Bey multiphase microstructure. The thermoforming device for ultra-high strength steel components includes an upper stamping die and a lower stamping die arranged opposite to each other. The surfaces of the upper stamping die and the lower stamping die closest to each other are connected to a layered working surface, which is used to make contact with the ultra-high strength steel component. Temperature sensing components are provided on the surfaces between the two layered working surfaces, and electromagnetic induction heating components are also provided inside the layered working surfaces. Cooling components are provided inside the side of the upper stamping die or the lower stamping die closest to the layered working surface. This invention achieves close contact between the two sides of an ultra-high strength steel component through two layered working surfaces. Simultaneously, it uses electromagnetic induction heating and cooling components to precisely control the surface temperature of the upper or lower stamping die. This allows for fine control of the morphology and quantity of bainite in the forming process of the ultra-high strength steel component without affecting the hot stamping production cycle. This transforms the microstructure of the ultra-high strength steel component into a martensite-bainite multiphase structure, thereby realizing high-end intelligent manufacturing of high-strength and high-toughness ultra-high strength steel components through hot stamping. Attached Figure Description

[0026] Figure 1 A simplified structural diagram of the ultra-high strength steel component thermoforming device provided by the present invention;

[0027] Figure 2 A flowchart of the hot forming method for ultra-high strength steel components provided by the present invention;

[0028] Figure 3 This is a process route diagram of the hot forming method for ultra-high strength steel components provided in Embodiment 1 of the present invention;

[0029] Figure 4 This is an optical microscope schematic diagram of the microstructure of the high-strength and tough thermoformed component prepared in Embodiment 1 of the present invention; in the figure, 100-thermoforming device for ultra-high-strength steel components; 101-upper stamping die; 102-lower stamping die; 1021-shock-absorbing buffer support; 103-layered working surface; 104-connecting guide rod; 105-reset spring; 106-sliding slot; 201-temperature sensing component; 301-electromagnetic induction heating component; 401-cooling component; 402-heat-conducting insert; 501-external medium-high frequency power supply; 601-ultra-high-strength steel component. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] To address the problems of difficulty in precisely controlling bainitic structure, high control costs, and long processes in existing hot stamping forming technologies, this invention provides a hot forming device for ultra-high strength steel components and a method for controlling martensitic-bainitic dual-phase structure. This device can precisely control the bainitic structure without changing the chemical composition of the material or the fast-paced hot stamping production, thereby achieving a balance between strength and toughness in the components. It can be used for safety components in vehicles and engineering machinery, etc.

[0032] This invention provides a hot forming device for ultra-high strength steel components and a method for controlling the martensite-lower bainite complex structure. The hot forming device for ultra-high strength steel components consists of an upper stamping die, a lower stamping die, a temperature sensing component, an electromagnetic induction heating component, and a cooling component. By precisely controlling the surface temperature of the die, it can finely regulate the morphology and quantity of bainite in the hot forming process of the steel component without affecting the hot stamping production cycle, thereby obtaining a martensite-lower bainite complex structure and realizing high-end intelligent manufacturing of high-strength and high-toughness ultra-high strength steel components through hot stamping.

[0033] To achieve the above objectives, the present invention provides the following technical solution:

[0034] Please see Figure 1 , Figure 1 The schematic diagram of the ultra-high strength steel component hot forming device 100 provided by the present invention is shown below; wherein, the ultra-high strength steel component hot forming device 100 includes a layered mechanical stamping die, a temperature sensing component 201, an electromagnetic induction heating component 301 and a cooling component 401.

[0035] In this embodiment of the invention, the layered mechanical stamping die includes an upper stamping die 101, a lower stamping die 102 and a layered working surface 103 arranged opposite to each other. The layered working surface 103 is connected to the side surface of the upper stamping die 101 and the lower stamping die 102 that is close to each other. The layered working surface 103 is used to make contact with the ultra-high strength steel component 601.

[0036] Specifically, connecting guide rods 104 are provided on both sides between the upper stamping die 101 and the lower stamping die 102. Draft springs are sleeved on the connecting guide rods 104, with one end of the draft spring abutting against the upper stamping die 101 and the other end abutting against the lower stamping die 102. Draft springs are typically used to assist in demolding. They are installed in the mold to provide a certain elastic force so that the molded parts can be smoothly pulled out of the mold after processes such as injection molding or die casting, preventing the parts from sticking to the mold.

[0037] Specifically, in this embodiment of the invention, the upper stamping die 101 and the lower stamping die 102 are positioned stably by connecting guide rods 104 on both sides of the layered mechanical stamping die, and the ultra-high strength steel component 601 is demolded by the draft spring sleeved on the connecting guide rods 104.

[0038] Furthermore, sliding grooves 106 are provided on the surfaces of the upper stamping die 101 and the lower stamping die 102 that are close to each other, and the layered working surface 103 is located in the corresponding sliding groove 106. The present invention avoids the deviation of the layered mechanical stamping die during stamping by setting the sliding grooves 106, thereby ensuring the stamping accuracy.

[0039] In this embodiment of the invention, the lower stamping die 102 is rotatably fixed to the stamping tool table, and a shock-absorbing buffer support 1021 is installed at the bottom of the lower stamping die 102. The shock-absorbing buffer support 1021 is slidably connected to the lower stamping die 102. A stamping hydraulic rod is provided on the upper part of the stamping tool table, and the slider at the lower end of the stamping hydraulic rod is connected to the upper stamping die 101.

[0040] In this embodiment of the invention, a temperature sensing component 201 is provided on the surface between the two layered working surfaces 103, and an electromagnetic induction heating component 301 is also provided inside the layered working surface 103. A cooling component 401 is provided inside the upper stamping die 101 or the lower stamping die 102 on the side close to the layered working surface 103.

[0041] Among them, the side surface of the layered working surface 103 away from the temperature sensing component 201 is fixedly connected to the first end of the return spring 105, and the second end of the return spring 105 is fixedly connected to the upper stamping die 101 or the lower stamping die 102; the return spring 105 is a mechanical element that is usually elastic, and its main function is to return a component or system to its initial position or a predetermined reference position after the component or system has moved.

[0042] Specifically, the temperature sensing component 201 includes a temperature sensing probe, a data processing module, a data transmission module, and a battery pack that is electrically connected to the temperature sensing probe, the data processing module, and the data transmission module, respectively.

[0043] Among them, the temperature sensing probe is used to monitor the surface temperature of the ultra-high strength steel component 601 in real time, the data processing module is used to process the temperature data collected by the temperature sensing probe, and the data transmission module is used to transmit the temperature data to the electromagnetic induction heating component 301.

[0044] Furthermore, the temperature sensing component 201 is placed in the layered working surface 103 close to the outer surface of the ultra-high strength steel component 601 to detect the surface temperature of the layered mechanical stamping die in a timely and accurate manner; the temperature sensing component 201 is connected to the electromagnetic induction heating component 301 through a wire.

[0045] Specifically, the electromagnetic induction heating component 301 is built into the magnetic groove in the core of the layered working surface 103. An energized coil is installed in the magnetic groove. An external medium-high frequency power supply 501 is connected to the energized coil in the magnetic groove to obtain medium-high frequency current to generate an alternating magnetic field, so as to realize rapid heating of the surface of the layered mechanical stamping die.

[0046] The electromagnetic induction heating component 301 includes a temperature sensing resistor and a signal receiver, which is communicatively connected to the data transmission module.

[0047] Specifically, the cooling component 401 includes a cooling pipe, a cooling medium, and a cooling medium circulation pump. The cooling pipe is embedded and fixed in a preset groove provided inside the upper stamping die 101 or the lower stamping die 102, in which a parallel inner mold forming contour is coiled. The cooling pipe is connected to a cooling medium circulation pump, and the cooling pipe is filled with a cooling medium to achieve rapid cooling of the surface of the layered mechanical stamping die.

[0048] The preset groove is also equipped with multiple spaced heat-conducting inserts 402, which are in contact with the outer surface of the cooling pipe. The heat-conducting inserts 402 are made of high thermal conductivity material, which can ensure the rapid reduction of temperature of the layered mechanical stamping die.

[0049] Preferably, while ensuring the strength of the mold, the thickness of the layered working surface 103 needs to be reduced as much as possible to enable rapid heating of the layered working surface 103 and rapid cooling after contact with the upper stamping die 101 or the lower stamping die 102.

[0050] Preferably, the pipe material of the cooling pipe should have excellent thermal conductivity and corrosion resistance to ensure that the layered mechanical stamping die can quickly cool the ultra-high strength steel component 601, while preventing the cooling pipe from being corroded by the cooling medium.

[0051] Furthermore, while ensuring the structural strength of the mold, the spacing between cooling pipes should be minimized, the number of cooling pipes increased, and the diameter of the cooling pipes appropriately increased. This design helps to improve the cooling rate of the ultra-high strength steel component 601, and the cooling rate of the ultra-high strength steel component 601 can be controlled by controlling the flow rate of the cooling medium.

[0052] Preferably, except for the area above the magnetic groove, the material of the layered working surface 103 is made of magnetic ceramic material, so as to concentrate heat towards the side of the layered working surface 103 closer to the ultra-high strength steel component 601.

[0053] Preferably, the energized coil inside the magnetic groove is made of a conductor material, preferably copper with high conductivity and high temperature resistance, to facilitate rapid heat transfer. By adjusting the current input in the electromagnetic induction heating component 301, the surface of the layered mechanical stamping die is precisely controlled, thereby achieving dynamic control of quenching temperature and cooling rate during industrial production.

[0054] Accordingly, the present invention also provides a method for hot forming an ultra-high strength steel component 601 using an ultra-high strength steel component hot forming apparatus 100 as described above.

[0055] Please see Figure 1 as well as Figure 2 , Figure 2 A flowchart of the hot forming method for the ultra-high strength steel component 601 provided by the present invention; wherein the hot forming method includes the following steps:

[0056] S10, the ultra-high strength steel component 601 is rapidly heated to a temperature of 800-1000℃ and then held at that temperature for 3-10 minutes to ensure that the microstructure of the ultra-high strength steel component 601 completes the austenitic transformation and has a uniform composition. The heating rate is 5-50℃ / s.

[0057] Specifically, step S10 also includes:

[0058] The billet is heated to full austenitization using a box-type or roller hearth furnace. The heating rate is 5–50℃ / s, the austenitization temperature is 800–1000℃, and the holding time is 3–10 min to ensure that the steel plate completes the austenitic transformation and that the structure is uniform. The thickness of the ultra-high strength steel plate is 0.5–10 mm.

[0059] S20, the heated ultra-high strength steel component 601 is taken out and transferred to the ultra-high strength steel component hot forming device 100, and the transfer time is 2 to 4 seconds.

[0060] Specifically, step S20 also includes:

[0061] The uniformly heated ultra-high strength steel component 601 is taken out and transported by conveyor belt to the ultra-high strength steel component thermoforming device 100 provided by the present invention. It is then quickly transferred into the ultra-high strength steel component thermoforming device 100 by a robotic arm, with a transfer time of 2 to 4 seconds.

[0062] Preferably, in step S20, the fully austenitized heated ultra-high strength steel component 601 should be quickly transferred to the ultra-high strength steel component hot forming device 100. Since the ultra-high strength steel component 601 comes into contact with room temperature air during the transfer process, heat exchange will occur between the ultra-high strength steel component 601 and the air. In order to reduce the heat loss of the ultra-high strength steel component 601 during the transfer process, the transfer time should be shortened as much as possible.

[0063] S30, the ultra-high strength steel component 601 is subjected to the first mold closing hot stamping forming and pressure holding quenching treatment, so that the surface temperature of the ultra-high strength steel component 601 drops to the bainite transformation zone temperature. At this time, the quenching cooling rate of the ultra-high strength steel component 601 is greater than or equal to 40℃ / s.

[0064] Specifically, step S30 also includes:

[0065] The ultra-high strength steel component 601 is placed between the two layered working surfaces 103, and then the upper stamping die 101 and the stamping die are moved together at a speed of 0.1 to 10 seconds. -1 Rapid stamping forming; under pressure, the layered working surfaces 103 are tightly bonded to the die surfaces of the upper stamping die 101 and the lower stamping die 102, which have cooling functions, respectively. While achieving high-temperature short-time pressure holding, the ultra-high-strength steel component 601 is rapidly quenched. The tight bonding time is 1-10s, the pressure holding time is 3-20s, the pressure holding pressure is 50-5000kN, the cooling rate of the ultra-high-strength steel component 601 is ≥40℃ / s, and the bainite transformation zone temperature is 400-600℃.

[0066] Furthermore, in order to transform the microstructure of the ultra-high strength steel component 601 into lower bainite as much as possible, the ultra-high strength steel component 601 is subjected to a first mold-closing hot stamping forming and pressure holding quenching treatment, so that the surface temperature of the ultra-high strength steel component 601 is reduced to the lower bainite transformation zone temperature, which is 400-500℃.

[0067] Furthermore, the cooling medium in the cooling components 401 provided in the upper stamping die 101 and the lower stamping die 102 includes liquid ammonia, liquid carbon dioxide, liquid nitrogen, etc., with a cooling rate ≥40℃ / s. A cooling rate that is too low is detrimental to the transformation of the ultra-high strength steel component 601 from supercooled austenite to martensite during assembly, failing to guarantee the high strength of the ultra-high strength steel component 601 and shortening the processing time.

[0068] S40, turn on the switch of the electromagnetic induction heating component 301 to perform external quenching and heat preservation treatment on the ultra-high strength steel component 601, so that the microstructure of the ultra-high strength steel component 601 is partially transformed into bainite. At this time, the quenching cooling rate of the ultra-high strength steel component 601 is less than 5℃ / s.

[0069] Specifically, step S40 also includes:

[0070] When the surface temperature of the ultra-high strength steel component 601 drops to the bainite transformation zone temperature, the press releases the holding pressure, moves slightly upward, and ends the short-term holding pressure (400-600℃). At this time, it is necessary to slow down the quenching and cooling rate of the ultra-high strength steel component 601 so that the microstructure of the ultra-high strength steel component 601 can transform into bainite as much as possible.

[0071] Therefore, when the electromagnetic induction heating component 301 is turned on, the layered working surface 103 of the layered mechanical stamping die is rapidly heated by the intermittent switching of the electromagnetic induction energized coil. At this time, the layered working surface 103 of the lower stamping die 102 separates outward under the elastic force of the return spring 105 and fits tightly against the lower surface of the ultra-high strength steel component 601. The layered working surface 103 of the upper stamping die 101 fits tightly against the upper surface of the ultra-high strength steel component 601 due to its own gravity, thereby achieving external quenching and heat preservation treatment of the ultra-high strength steel component 601, ultimately making the quenching and cooling rate of the ultra-high strength steel component 601 less than 5℃ / s.

[0072] The current density supplied to the electromagnetic induction heating component 301 is 30–200 A / mm². 2 The electromagnetic induction heating component 301 heats the upper stamping die 101 or the lower stamping die 102 at a temperature of 420-450°C. The external quenching and heat preservation treatment time is 10-30 seconds. The upward displacement of the lower stamping die 102 is set according to the reset displacement of the layered working surface 103.

[0073] Furthermore, to ensure that the microstructure transformation of the ultra-high strength steel component 601 forms a certain amount of bainite, for ultra-high strength steel components 601 with high strength and toughness requirements, the formation of upper bainite should be prevented, and lower bainite with a certain content of high strength and good toughness should dominate; the holding temperature at the end of step S30 should be controlled at 400-500℃; in step S40, the heating temperature of the electromagnetic induction heating component 301 for heating the upper stamping die 101 or the lower stamping die 102 should be controlled at 300-500℃, and the current density of the electromagnetic induction heating component 301 should be controlled at 30-100 A / mm. 2 .

[0074] Furthermore, for ultra-high strength steel components 601 with lower strength requirements but higher toughness requirements, the holding temperature at the end of step S30 can be controlled at 550–600℃; in step S40, the heating temperature of the upper stamping die 101 or the lower stamping die 102 heated by the electromagnetic induction heating component 301 should be controlled at 550℃–600℃ (granular bainite transformation zone), and the current density introduced into the electromagnetic induction heating component 301 should be controlled at 101–200 A / mm. 2 Ultimately, this transforms the microstructure of the 601 ultra-high strength steel component into a structure with a certain content of granular bainite with relatively low strength but good toughness, as well as a spherically distributed Marshall-Oisle microstructure.

[0075] In step S40 of the present invention, the surface temperature of the layered mechanical stamping die is precisely controlled by adjusting the current density of the electromagnetic induction heating component 301, so that the microstructure of the ultra-high strength steel component 601 undergoes a non-isothermal slow continuous transformation process of bainite, thereby achieving fine control over the bainite morphology, distribution and proportion of the microstructure of the ultra-high strength steel component 601.

[0076] S50, turn off the switch of the electromagnetic induction heating component 301, and perform a second mold closing hot stamping forming and pressure holding quenching treatment on the ultra-high strength steel component 601, so that the microstructure of the ultra-high strength steel component 601 is transformed into a martensite-lower bainite multiphase structure. The quenching cooling rate of the ultra-high strength steel component 601 is 60~80℃ / s.

[0077] Specifically, step S50 also includes:

[0078] When the electromagnetic induction heating component 301 is turned off, the layered working surface 103 stops heating. The upper stamping die 101 and the lower stamping die 102 close again and perform pressure holding and straightening. At this time, the upper stamping die 101 or the lower stamping die 102 with cooling function contacts the corresponding layered working surface 103 for heat exchange, so as to achieve a gradual decrease in the quenching cooling rate of the ultra-high strength steel component 601, ultimately making the quenching cooling rate of the ultra-high strength steel component 601 60-80℃ / s, so that the microstructure of the ultra-high strength steel component 601 obtains sufficient martensite structure, and at the same time, the ultra-high strength steel component 601 is subjected to in-mold rapid quenching and straightening.

[0079] Furthermore, in step S50, the mold closing rate of the second hot stamping forming is 0.1–10 s. -1 The mold closing time is 2-4 seconds, the holding pressure time is 5-10 seconds, and the holding pressure is 50-5000 kN.

[0080] The hot forming method of the above-mentioned ultra-high strength steel component 601 is described in detail below through specific embodiments.

[0081] Example 1:

[0082] Please see Figures 1 to 3 , Figure 3 This is a process route diagram of the hot forming method for the ultra-high strength steel component 601 provided in Embodiment 1 of the present invention; wherein, Figure 3 M in s M is the starting point of the martensitic phase transformation. f M is the martensitic transformation end point, B is the martensitic transformation region, F is the ferrite transformation region, and P is the pearlite transformation region.

[0083] Example 1 of this invention illustrates a hot stamping process for strengthening and toughening B1500HS steel sheet used in mass production. The hot forming method includes the following steps:

[0084] Step (1): First, select a 1.6mm thick B1500HS steel plate. The composition of the steel plate by mass fraction is as follows: C: 0.23%, Mn: 1.35%, Si: 0.25%, Cr: 0.19%, Ti: 0.03%, B: 0.0032%, S: 0.006%, P: 0.015%, with the remainder being Fe and unavoidable impurities. The microstructure of the B1500HS steel plate is uniform ferrite and fine pearlite, with ferrite accounting for approximately 75% and pearlite accounting for approximately 25%. The average grain size of the ferrite is ≤10μm, the yield strength is approximately 370MPa, and the tensile strength is approximately 650MPa. Then, the B1500HS steel plate is blanked and cut into steel plates of suitable shape using a shearing machine.

[0085] Step (2): Use a box-type heating furnace to rapidly heat the steel plate at a heating rate of 10℃ / s. When the furnace temperature reaches 950℃, put the steel plate into the heating furnace for heating and hold for 5 minutes to ensure that all its microstructures complete the austenitic transformation and have a uniform composition.

[0086] Step (3): While the steel plate is heated and kept at a constant temperature, the layered mechanical stamping die in the ultra-high strength steel component hot forming device 100 provided by this invention is pre-cooled. Liquid ammonia is selected as the cooling medium. After the surface temperature of the layered mechanical stamping die drops below room temperature (25°C), the cooling pipe is closed. Increasing the temperature difference between the steel plate and the layered mechanical stamping die when they come into contact improves the cooling rate, which helps to shorten the process time, promotes the transformation of bainite during forming, and avoids the formation of pearlite.

[0087] Step (4): The uniformly austenitized steel plate is transferred to a layered mechanical stamping die using a robotic gripper. The transfer time is 3 seconds. The die is then closed and pressure is maintained for 2 seconds, with a holding pressure of 6 seconds and a holding pressure of 1000 kN. Short-time pressure holding quenching rapidly lowers the steel plate temperature to the bainite transformation zone B. Figure 2(In the dashed area B), the cooling rate is 50℃ / s, and the surface temperature of the steel plate is cooled to 550℃.

[0088] Step (5): After the surface temperature of the steel plate drops to 550℃, turn on the electromagnetic induction heating switch and adjust the current density supplied to the electromagnetic induction heating component 301 to 50A / mm². 2 The surface temperature of the layered working surface 103 is rapidly increased. When the temperature sensing component 201 detects that the surface temperature of the layered working surface 103 is 450℃, it performs a short-term heat preservation for 20 seconds to realize the slow and continuous phase transformation process of bainite at medium temperature and non-isothermal temperature, forming a certain content of lower bainite with high strength and good toughness.

[0089] Depend on Figure 3 It is known that in order to prevent the temperature-time curve of the steel plate from falling directly into the martensitic transformation region M, it is necessary to slow down the cooling rate of the steel plate. That is, in order to make the temperature-time curve of the steel plate shift towards the bainitic transformation region B, it is necessary to turn on the electromagnetic induction heating switch to quickly increase the surface temperature of the layered working surface 103, thereby realizing the slow and continuous phase transformation process of bainite at medium temperature and non-isothermal temperature, forming a certain content of lower bainite with high strength and good toughness.

[0090] Step (6): After the short-term heat preservation, turn off the electromagnetic heating power supply, close the mold again for pressure holding and straightening, so that the two layered working surfaces 103 are in close contact with the upper stamping die 101 and the lower stamping die 102 respectively, so as to achieve a slow-to-rapid quenching and cooling temperature of the steel plate. The mold closing time is 2s, the pressure holding time is 20s, and the pressure holding pressure is 800KN. Finally, the cooling rate of the steel plate is about 75℃ / s, ensuring that the microstructure of the formed steel plate transforms into martensite. At the same time, rapid cooling promotes the refinement of the martensite laths and the dispersion distribution of carbides in the microstructure of the steel plate, thereby improving the strength and toughness of the hot stamping formed component.

[0091] Please see Figure 4 , Figure 4 This is an optical microscope schematic diagram of the microstructure of the high-strength and tough hot-formed component prepared in Example 1 of the present invention; wherein, the microstructure of the hot-stamped formed component finally prepared from the above-mentioned B1500HS steel sheet is shown. Figure 4 Morphological analysis revealed that the martensite (77%) lath bundles were significantly refined, with closely adjacent lath martensite sections running parallel to each other. Different martensite regions intersected at certain angles, and a small amount of carbides were distributed throughout, resulting in a more uniform microstructure. Nanoscale carbides (5–20 nm) were dispersed within the fine ferrite, forming lower bainite (23%), which possesses high strength and toughness. The mixed microstructure of the hot-stamped component exhibited high strength and elongation after fracture. The final hot-stamped component had a tensile strength of approximately 1650 MPa and an elongation after fracture as high as 10%–12%.

[0092] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0093] (1) The present invention aims to solve the technical problems existing in the prior art. By dynamically and precisely controlling the quenching temperature and cooling rate of the components during the hot forming production process, the morphology, distribution and proportion of bainite in the microstructure of ultra-high strength steel can be finely controlled.

[0094] (2) Compared with traditional heating furnace heat preservation methods, the present invention cleverly combines rapid mold heating and cooling technology, and realizes the mass production of high-strength and high-toughness multiphase components of martensitic-bainitic structure in hot stamping industry without adding extra processes.

[0095] (3) Compared with traditional hot stamping, the hot forming process of the present invention significantly improves the toughness of the hot-formed component while slightly increasing its strength, and has a high degree of technological advancement.

[0096] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not exhaustive, please refer to the descriptions in other embodiments. The above embodiments only illustrate the implementation of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method of controlling a martensite-bainite dual phase structure for processing a member of ultra-high strength steel, characterized by, The method comprises the following steps: S10, the ultra-high strength steel member is rapidly heated to a temperature of 800-1000℃, and then short-time holding is performed for 3-10 min, so as to ensure that the microstructure of the ultra-high strength steel member is completely transformed into austenite and the composition is uniform, and the heating rate is 5-50℃ / s; S20, the heated ultra-high strength steel member is taken out and transferred to an ultra-high strength steel member hot forming device, and the transfer time is 2-4 s; the ultra-high strength steel member hot forming device comprises a stamping upper die and a stamping lower die arranged oppositely, and the side surfaces of the stamping upper die and the stamping lower die close to each other are connected with layered working surfaces, which are used for cooperating with the ultra-high strength steel member; wherein, temperature sensing assemblies are arranged on the surfaces between the two layered working surfaces, and electromagnetic induction heating assemblies are further arranged in the layered working surfaces; a cooling assembly is arranged in the side of the stamping upper die or the stamping lower die close to the layered working surface; S30, the ultra-high strength steel member is subjected to first die closing hot stamping forming and pressure holding quenching treatment, so that the surface temperature of the ultra-high strength steel member is reduced to the temperature of the bainite transformation region, and at this time, the quenching cooling rate of the ultra-high strength steel member is greater than or equal to 40℃ / s; S40, the switch of the electromagnetic induction heating assembly is turned on, the ultra-high strength steel member is subjected to off-die quenching holding treatment, so that the microstructure of the ultra-high strength steel member is partially transformed into bainite, and at this time, the quenching cooling rate of the ultra-high strength steel member is less than 5℃ / s; S50, the switch of the electromagnetic induction heating assembly is turned off, the ultra-high strength steel member is subjected to second die closing hot stamping forming and pressure holding quenching treatment, so that the microstructure of the ultra-high strength steel member is transformed into a martensite-bainite complex phase structure, and the quenching cooling rate of the ultra-high strength steel member is 60-80℃ / s.

2. The martensite-bainite dual phase microstructure control method according to claim 1, characterized by The die closing rate of the first die closing hot stamping forming in the S30 step is 0.1-10 s -1 , the die closing time is 1-10 s, the holding time is 3-20 s, the holding pressure is 50-5000 kN, and the bainite transformation zone temperature is 400-600 ℃; the die closing rate of the second die closing hot stamping forming in the S50 step is 0.1-10 s -1 , the die closing time is 2-4 s, the holding time is 5-10 s, and the holding pressure is 50-5000 kN.

3. The martensite-bainite dual phase microstructure control method according to claim 2, characterized by The pressure maintaining end temperature in the S30 step is 400-500 DEG C; in the S40 step, the heating temperature of the electromagnetic induction heating assembly for heating the punch upper die or the punch lower die is 300-500 DEG C, and the current density input into the electromagnetic induction heating assembly is 30-100 A / mm 2 ; in the S50 step, the microstructure of the ultra-high strength steel member is transformed to form a martensite-low bainite complex phase structure.

4. The martensite-bainite dual phase microstructure control method according to claim 2, characterized by The pressure maintaining end temperature in the S30 step is 550-600 DEG C; in the S40 step, the heating temperature of the electromagnetic induction heating assembly for heating the punch upper die or the punch lower die is 550-600 DEG C, and the current density input into the electromagnetic induction heating assembly is 101-200 A / mm 2 ; in the S50 step, the microstructure of the ultra-high strength steel member is transformed to form a martensite-granular bainite complex phase structure.

5. The martensite-bainite dual phase microstructure control method according to claim 1, wherein In the S20 step, a connecting guide rod is arranged between the stamping upper die and the stamping lower die, a draw spring is sleeved on the connecting guide rod, one end of the draw spring abuts against the stamping upper die, and the other end of the draw spring abuts against the stamping lower die.

6. The martensite-bainite dual phase microstructure control method according to claim 1, characterized by In the S20 step, sliding clamping grooves are formed in the side surfaces of the stamping upper die and the stamping lower die close to each other, and the layered working surfaces are located in the corresponding sliding clamping grooves.

7. The martensite-bainite complex microstructure control method according to claim 1, characterized by In the S20 step, a temperature sensing probe, a data processing module, a data transmission module, and a battery pack electrically connected with the temperature sensing probe, the data processing module, and the data transmission module are arranged in the temperature sensing assembly; The temperature sensing probe is used for monitoring the surface temperature of the ultra-high strength steel member in real time, the data processing module is used for processing the temperature data collected by the temperature sensing probe, and the data transmission module is used for transmitting the temperature data to the electromagnetic induction heating assembly.

8. The martensite-bainite complex microstructure control method according to claim 7, characterized by The electromagnetic induction heating assembly is arranged in a magnetic conductive groove arranged in the layered working surface, an energized coil is arranged in the magnetic conductive groove, and the energized coil is used for external connection with an external power supply. The electromagnetic induction heating assembly comprises a temperature-sensitive resistor and a signal receiver, and the signal receiver is in communication connection with the data delivery module.

9. The martensite-bainite dual phase microstructure control method according to claim 1, wherein In the step S20, the cooling assembly comprises a cooling pipeline, a cooling medium and a cooling medium circulating pump. The cooling pipeline is fixedly embedded in a preset groove arranged inside the upper punch or the lower punch. The cooling pipeline is connected with the cooling medium circulating pump. The cooling pipeline is filled with the cooling medium. A plurality of heat-conducting inserts are arranged in the preset groove in a spaced manner. The plurality of heat-conducting inserts are in contact with the outer surface of the cooling pipeline.

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