CN109762965B - Continuous online preparation method of Mn-B steel structural part with super high toughness - Google Patents
Continuous online preparation method of Mn-B steel structural part with super high toughness Download PDFInfo
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- 238000010791 quenching Methods 0.000 claims abstract description 88
- 238000001816 cooling Methods 0.000 claims abstract description 77
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- 238000000034 method Methods 0.000 claims abstract description 53
- 230000008569 process Effects 0.000 claims abstract description 44
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 36
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 26
- 230000005540 biological transmission Effects 0.000 claims abstract description 10
- 238000000265 homogenisation Methods 0.000 claims abstract description 9
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- 125000004122 cyclic group Chemical group 0.000 claims description 28
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
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Abstract
The invention belongs to the technical field of steel stamping forming, and discloses a continuous online preparation method of an ultra-high-toughness Mn-B steel structural member, which utilizes electrode roller continuous transmission to circularly heat and quench Mn-B steel strip, so that high-temperature austenite and quenched martensite crystal grains are ultra-refined; the electrode roller is heated at a high speed in a self-resistance heating mode in the continuous transmission process; and carrying out repeated heating-quenching for a plurality of times to realize the homogenization diffusion of the elements; the high-strength and high-toughness structural member is prepared by converting the ultra-fine grain austenite into ultra-fine grain martensite or ultra-fine grain martensite plus a small amount of bainite and other tissues through a high cooling speed in a die in the hot stamping, pressure maintaining and quenching process or a forced cooling method after stamping. The invention can effectively reduce oxidation, thereby being beneficial to popularization and use of the low-cost non-coated plate, realizing homogenization and diffusion of elements in a shorter time by repeated heating and quenching, and being beneficial to uniformity of performance of the component.
Description
Technical Field
The invention belongs to the technical field of steel stamping forming, and particularly relates to a continuous online preparation method of an Mn-B steel structural member with ultrahigh toughness.
Background
Currently, the current state of the art commonly used in the industry is as follows:
the double requirements of automobile light weight and safety promote the application proportion of high-strength and ultra-high-strength steel on a white automobile body to be larger and larger. The hot stamping forming is a forming process mode which is more and more popular in the automobile part manufacturing industry due to the characteristics of small forming force, high forming piece precision, high forming member strength and the like. The tensile strength level of the most commonly applied hot forming ultra-high strength steel is 1500MPa, and the strength level of partial products can even reach 1800MPa. According to incomplete statistics, the ultra-high strength steel plate produced by adopting a hot stamping forming technology is used as a main method for lightening automobiles and improving safety of the automobiles, wherein European and American automobiles are relatively more applied, for example, the proportion of hot forming steel used by an Audi A3 automobile body is 21.7%, and the consumption of the hot forming steel by individual automobile types under the Volvo brand is even more than 40% of the whole automobile body material.
At present, more than 100 hot stamping production lines are shared in China, but in the hot stamping process, a roller hearth furnace or a box furnace is adopted for heating blanks, and in order to ensure diffusion homogenization of carbon elements and the like after austenitizing, the heating time of the mode is longer, the heating time of the blanks is generally 3-5 minutes in the furnace, and the problem of oxidization of the blanks is directly caused, so that the surface quality of subsequent formed parts is affected. Therefore, the furnace type is usually provided with a protective atmosphere, and simultaneously, the blank with the Al-Si coating is required to be subjected to hot stamping production. Since the supply of the Al-Si coated plate is protected by foreign patents, only one foreign iron and steel enterprise can provide the product, so that the cost of hot stamping raw materials is high. This is also one of the main reasons that hot stamping is relatively costly compared to cold stamping. The hot stamping process flow under the traditional roller hearth furnace heating mode is long, the cost is high, a high-cost Al-Si coating plate is usually needed to avoid blank oxidation, and once the aluminum-silicon coating plate is adopted, the effective diffusion time of the coating and the iron matrix is ensured to form an anti-oxidation intermetallic compound, so that the problems of long heating process period, low efficiency, incapability of improving the heating speed of a part of temperature intervals and the like are caused. Under the traditional hot stamping forming process, the highest strength achieved by the most common steel 22MnB5 is about 1500MPa, the elongation is low (< 7%), and the impact toughness is poor (about 65J/cm < 2 >). Under the existing technology, to further improve the toughness comprehensive performance of the hot formed component, so as to further dig the potential of the component for lightening, the required purpose can be achieved only by changing the hot formed steel variety (adding microalloy elements such as Nb and the like on the basis of the 22MnB5 steel composition, or improving the carbon content and the like). This, in turn, undoubtedly increases the raw material cost and increases the carbon equivalent of the material, which is detrimental to the subsequent welding performance.
In addition, the existing Mn-B series hot forming steel structural member has the adverse characteristics of ultrahigh strength, but generally has poor toughness, especially low-temperature toughness, and the defects in the aspect are more remarkable when the strength is higher, so that the hidden danger of brittle fracture exists in the use process of the corresponding structural member all the time, and further popularization and application of the structural member are limited to a great extent.
In summary, the problems of the prior art are:
the hot stamping process flow under the traditional roller hearth furnace heating mode is long, the cost is high, a high-cost Al-Si coating plate is usually needed to avoid blank oxidation, and once the aluminum-silicon coating plate is adopted, the effective diffusion time of the coating and the iron matrix is ensured to form an anti-oxidation intermetallic compound, so that the problems of long heating process period, low efficiency, incapability of improving the heating speed of a part of temperature intervals and the like are caused;
under the traditional hot stamping forming process, the highest strength which can be realized by the most common steel 22MnB5 is about 1500MPa, and the elongation is low<7%) and poor impact toughness (about 65J/cm 2 ). Under the existing technology, to further improve the toughness comprehensive performance of the hot formed component, so as to further dig the potential of the component for lightening, the required purpose can be achieved only by changing the hot formed steel variety (adding microalloy elements such as Nb and the like on the basis of the 22MnB5 steel composition, or improving the carbon content and the like). This, in turn, undoubtedly increases the raw material cost and increases the carbon equivalent of the material, which is detrimental to the subsequent welding performance.
Under the traditional hot stamping forming process, the blank needs to be subjected to laser blanking or cold blanking in advance before heating, and especially if the cost of laser blanking is high, the price and popularization and application of a hot formed part are not facilitated to be reduced.
Difficulty and meaning for solving the technical problems:
the problems are solved by comprehensively considering the key problems of the cost of the compression heating section, oxidation protection in the blank heating process, and the ultra-fine and uniform structure of the hot forming part.
The novel hot stamping process flow is adopted, the key problems can be effectively solved simultaneously by adopting a heating mode of circulating rapid heating-quenching and short-time soaking, and after hot blanking and hot stamping forming are effectively integrated in the later period, the cold blanking or laser blanking process under the traditional process flow is hopefully further canceled, so that the hot stamping process flow is a prospective hot stamping process flow with very development prospect. Because the method can simultaneously bring a plurality of advantages of improving the comprehensive performance of the hot forming part, reducing the oxidation of the component, reducing the cost of the hot forming component, improving the production efficiency of hot stamping forming and the like.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a continuous online preparation method of an Mn-B steel structural member with super high toughness.
The invention is realized in such a way that the continuous online preparation method of the super-high-toughness Mn-B steel structural part comprises the following steps:
carrying out Mn-B steel strip cyclic heating-quenching by utilizing continuous transmission of an electrode roller, so that high-temperature austenite and quenched martensite crystal grains are ultra-refined;
meanwhile, the high speed of the self-resistance heating mode is higher than 100 ℃/s heating in the continuous transmission process of the electrode roller;
and carrying out repeated heating-quenching for a plurality of times to realize the homogenization diffusion of the elements;
the ultra-fine grain austenite is converted into ultra-fine grain martensite or ultra-fine grain martensite plus a small amount of bainite structure by a high cooling speed in a die in the hot stamping, pressure maintaining and quenching process or a forced cooling method after stamping, so that the preparation of the high-strength and high-toughness structural member is realized.
Further, the steel strip is a steel grade which realizes the required structural transformation in the hot stamping forming pressure-maintaining quenching or the cooling process after forming;
in the ultra-fine of high-temperature austenite and quenched martensite crystal grains, continuous repeated circulation self-resistance heating and cooling processes and devices are applied on line, and the blank before hot stamping forming is subjected to ultra-fine treatment of high-temperature austenite crystal grains and component homogenization.
Furthermore, the method of heating the electrode roller with the last pair of resistivity and the subsequent rapid temperature equalizing furnace are combined, so that the prefabrication of the high-temperature blank with the ultra-fine austenitic structure before hot stamping is realized.
Further, the continuous online preparation method of the super high-strength and toughness Mn-B steel structural part comprises the following steps:
(1) Selecting a hot-rolled or cold-rolled non-coated plate, selecting an initial rectangular blank size with a reasonable size according to the number of parts in a lower forming die with a stroke frequency, wherein the maximum length of a single Zhang Piliao plate is not lower than the roller spacing between two pairs of self-resistance heating rollers;
(2) The blank is subjected to continuous on-line cyclic heating and quenching process by a longitudinal self-resistance heating quenching device, is rapidly heated by low-voltage high current loaded between two adjacent pairs of electrode rollers, and is subjected to quenching cooling when passing through a water-cooled electrode roller; continuously passing through a plurality of pairs of electrode rollers to realize repeated cyclic heating-quenching cooling treatment on the blank plate;
(3) The final pair of electrode rolls are made of high-resistivity materials and matched with a short-time temperature equalizing furnace to obtain homogenized high-temperature blanks with ultrafine-grained austenite before hot stamping forming;
(4) After the blank is quickly taken out from the temperature equalizing furnace, the blank is placed on a hot stamping forming press, and the blank is clamped and quenched under pressure, so that the forming property of the part is realized while the transformation from austenite to martensite is completed;
(5) And taking out the part after the die is opened, and performing natural cooling or adopting subsequent forced cooling measures to obtain the required structural part with higher strength and toughness.
Further, the continuous online preparation method of the Mn-B steel structural part with the super high toughness comprises the following steps:
(1) Selecting a hot-rolled or cold-rolled non-coated plate, and selecting an initial rectangular blank size with a reasonable size according to the number of parts in a lower forming die with a stroke frequency;
(2) The blank is subjected to continuous online cyclic heating and quenching process by heating equipment of a transverse self-resistance heating quenching device, wherein the rapid heating process realizes rapid temperature rise along the width direction of the plate by means of low-voltage high current generated between each pair of roller electrodes, and rapid cooling quenching is subsequently implemented; continuously passing through a plurality of pairs of electrode rollers to realize repeated cyclic heating-quenching cooling treatment on the blank plate;
(3) The blank plate can be heated by the last counter roller electrode, then enters a short-time temperature equalizing furnace without cooling, and a homogenized high-temperature blank with ultrafine-grained austenite before hot stamping forming is obtained;
(4) After the blank is quickly taken out from the temperature equalizing furnace, the blank is placed on a hot stamping forming press, and the blank is clamped and quenched under pressure, so that the forming property of the part is realized while the transformation from austenite to martensite is completed;
(5) And taking out the part after the die is opened, and performing natural cooling or adopting subsequent forced cooling measures to finally obtain the structural part with higher toughness.
The invention also aims to provide the super-high-toughness Mn-B steel structural member prepared by the continuous online preparation method of the super-high-toughness Mn-B steel structural member.
Another object of the present invention is to provide a continuous on-line manufacturing apparatus for an ultra-high toughness Mn-B steel structural member, which implements the continuous on-line manufacturing method for an ultra-high toughness Mn-B steel structural member, the continuous on-line manufacturing apparatus for an ultra-high toughness Mn-B steel structural member being provided with:
a self-resistance heating quenching device;
the self-resistance heating quenching device is communicated with a blank short-time temperature equalizing furnace through a conveyor belt, and the blank short-time temperature equalizing furnace is communicated with a forming press;
the self-resistance heating quenching device is a longitudinal self-resistance heating quenching device or a transverse self-resistance heating quenching device;
the bottom of the blank short-time temperature equalizing furnace is fixed with a plurality of heating electrode rollers through bolts.
Further, the vertical self-resistance heating quenching device is provided with upper and lower groups of water-cooling copper electrode rollers in parallel, annular distributed inner roller water-cooling channels are formed in the water-cooling copper electrode rollers, two adjacent groups of water-cooling copper electrode rollers are communicated through a low-voltage high-current circuit, a power supply is communicated with the low-voltage high-current circuit, a high-resistivity electrode roller is fixed on the right side of the water-cooling copper electrode roller through a shaft, and the high-resistivity electrode roller is communicated with the adjacent water-cooling copper electrode rollers through the low-voltage high-current circuit.
Further, the transverse self-resistance heating quenching device is provided with two rows of vertical parallel vertical roller electrodes, and a quenching device is arranged between the adjacent vertical roller electrodes.
In summary, the invention has the advantages and positive effects that:
(1) The length of the heating furnace section can be obviously shortened from 30-40 meters of the length of a single roller hearth furnace to not more than 10 meters.
(2) The construction investment cost and the maintenance cost of the heating furnace can be obviously reduced, the construction investment cost can be reduced by at least more than 30 percent, and the ceramic roller with higher manufacturing cost and the high-purity nitrogen use amount are reduced, so that the heating furnace has obvious advantages in the aspect of maintenance cost.
(3) The oxidation of the plate during the heating process is significantly reduced. The novel heating mode has high heating speed, and quenching and purging of high-pressure low-temperature gas are performed immediately after heating, so that oxidation is greatly weakened, even oxidation is avoided, the application proportion of the non-coated plate in the hot stamping production process is increased, and the cost is reduced.
(4) The circulating rapid heating-quenching process can refine austenite grains to the greatest extent and ensure the uniformity of chemical components, so that the toughness of a structural member prepared by hot stamping quenching of the existing hot forming steel can be further improved.
(5) By the preparation method, the hot stamping cutting blanking and the hot stamping pressure maintaining quenching of the plate can be effectively integrated into one process, the laser blanking process with high cost before heating is canceled, the cost of the hot stamping ultrahigh-strength structural member can be further compressed, and the method is beneficial to further popularization and application.
The invention also has the advantages that:
according to the invention, mn-B steel strip is circularly heated and quenched in the continuous transmission process by utilizing a self-resistance heating quenching device, so that high-temperature austenite and quenched martensite crystal grains are ultra-refined, and the low-temperature toughness of an ultra-high-strength steel structural member is improved; meanwhile, the oxidation can be effectively reduced by means of high heating speed of a self-resistance heating mode in the continuous transmission process, so that popularization and use of the low-cost non-coated plate are facilitated, and uniform diffusion of elements can be realized in a short time by repeated heating and quenching for multiple times, so that the uniformity of the performance of the component is facilitated.
The longitudinal self-resistance heating quenching device provided by the invention realizes rapid heating of a plate through low-voltage high current loaded between two adjacent pairs of electrode rollers, realizes quenching cooling through water injection into a water cooling channel in the roller, continuously realizes repeated cyclic heating-quenching cooling treatment on the blank plate through a plurality of pairs of electrode rollers, and the high-resistivity electrode rollers are made of high-resistivity materials so as to ensure that the blank plate can not be cooled after being continuously conveyed and rapidly heated to a high-temperature austenite region when being matched with the previous copper electrode rollers for heating.
The transverse self-resistance heating quenching device provided by the invention realizes rapid temperature rise along the width direction of the plate by low-voltage high current generated between each pair of electrode rolls, and immediately carries out rapid cooling quenching subsequently, so that the blank plate is continuously passed through a plurality of pairs of electrode rolls to realize repeated cyclic heating-quenching cooling treatment.
According to the invention, the blank plate is subjected to rapid and repeated cyclic heating-quenching treatment before hot stamping forming, an initial high-temperature blank with ultrafine austenite grains is provided for subsequent hot stamping by matching with a temperature equalizing furnace, and the ultrafine of microstructure martensite of a final structural member is realized through the pressure maintaining quenching process of subsequent hot stamping forming, so that the purpose of reinforcing and toughening the 22MnB5 hot-formed structural member with low cost is achieved. In addition, the heating mode adopted by the process method is rapid heating, and can effectively avoid the oxidation of the steel plate, so the process method is suitable for producing low-cost non-coated plates (domesticated) and replaces expensive Al-Si coated plates. And the repeated heating-quenching for multiple times can realize the homogenization and diffusion of elements in a shorter time, thereby being beneficial to the uniformity of the performance of the component. Meanwhile, if the design of the future hot stamping die can realize the blanking and stamping integrated function, the technology can also obviously shorten the hot stamping process flow, and the raw materials can directly utilize cold rolling or hot rolling coils of a steel mill, so that the technology has great advantages in the aspect of production cost control.
Drawings
FIG. 1 is a flowchart of a continuous on-line preparation method of an ultra-high-toughness Mn-B steel structural member provided in the embodiment 1 of the invention.
Fig. 2 is a flowchart of a continuous online preparation method of an ultra-high strength and toughness Mn-B steel structural member provided in example 2 of the present invention.
FIG. 3 is a schematic diagram of a continuous multi-cycle self-resistance heating and cooling device according to an embodiment of the present invention;
fig. 4 is a schematic structural view of a longitudinal self-resistance heating quenching device provided by an embodiment of the invention;
FIG. 5 is a schematic structural view of a transverse self-resistance heating quenching device provided by an embodiment of the invention;
in the figure: 1. a self-resistance heating quenching device; 2. a blank short-time temperature equalizing furnace; 3. a forming press; 4. heating the electrode roller; 5. a water-cooled copper electrode roll; 6. a high resistivity electrode roll; 7. a low-voltage high-current line; 8. a water cooling channel in the roller; 9. a vertical roller electrode.
Detailed Description
For a further understanding of the invention, its features and advantages, reference is now made to the following examples, which are illustrated in the accompanying drawings.
The hot stamping process flow under the traditional roller hearth furnace heating mode is long, the cost is high, a high-cost Al-Si coating plate is usually needed to avoid blank oxidation, and once the aluminum-silicon coating plate is adopted, the effective diffusion time of the coating and the iron matrix is ensured to form an anti-oxidation intermetallic compound, so that the problems of long heating process period, low efficiency, incapability of improving the heating speed of a part of temperature intervals and the like are caused;
under the traditional hot stamping forming process, the most common steel 22MnB5 can be applied at the present stageHigh strength of about 1500MPa and low elongation<7%) and poor impact toughness (about 65J/cm 2 ). Under the existing technology, to further improve the toughness comprehensive performance of the hot formed component, so as to further dig the potential of the component for lightening, the required purpose can be achieved only by changing the hot formed steel variety (adding microalloy elements such as Nb and the like on the basis of the 22MnB5 steel composition, or improving the carbon content and the like). This, in turn, undoubtedly increases the raw material cost and increases the carbon equivalent of the material, which is detrimental to the subsequent welding performance.
In order to solve the above technical problems, the application principle of the present invention will be described in detail with reference to the technical scheme.
The continuous online preparation method of the Mn-B steel structural part with the super high toughness provided by the embodiment of the invention comprises the following steps:
and (3) carrying out circulating heating-quenching on the Mn-B steel strip by using continuous transmission of an electrode roller, so that high-temperature austenite and quenched martensite grains are ultra-refined.
Meanwhile, the electrode roller is heated at a high speed in a self-resistance heating mode in the continuous transmission process.
And the element is uniformly diffused by repeatedly heating and quenching for a plurality of times.
The ultra-fine grain austenite is converted into ultra-fine grain martensite or ultra-fine grain martensite plus a small amount of bainite structure by a high cooling speed in a die in the hot stamping, pressure maintaining and quenching process or a forced cooling method after stamping, so that the preparation of the high-strength and high-toughness structural member is realized.
In an embodiment of the invention, the steel strip is either a steel grade that achieves the desired structural transformation during hot stamping press-forming dwell quenching or post-forming cooling.
In the ultra-fine of high-temperature austenite and quenched martensite crystal grains, continuous repeated circulation self-resistance heating and cooling processes and devices are applied on line, and the blank before hot stamping forming is subjected to ultra-fine treatment of high-temperature austenite crystal grains and component homogenization.
In the embodiment of the invention, the preparation of the high-temperature blank with the ultra-fine austenitic structure before hot stamping is realized by combining the heating method of the last pair of electrode rolls with resistivity and the subsequent rapid temperature equalizing furnace.
The invention is further described below in connection with a multiple cycle self-resistance heating and cooling device.
As shown in fig. 1 to 3, the continuous multi-cycle self-resistance heating and cooling device provided by the embodiment of the invention includes: the self-resistance heating quenching device 1, a blank short-time soaking furnace 2, a forming press 3, a heating electrode roller 4, a water-cooled copper electrode roller 5, a high-resistivity electrode roller 6, a low-voltage high-current circuit 7, a water-cooling channel 8 in the roller and a vertical roller electrode 9.
The self-resistance heating quenching device 1 is communicated with a blank short-time temperature equalizing furnace 2 through a conveyor belt, and the blank short-time temperature equalizing furnace 2 is communicated with a forming press 3; the self-resistance heating quenching device 1 is a longitudinal self-resistance heating quenching device or a transverse self-resistance heating quenching device; a plurality of heating electrode rollers 4 are fixed at the bottom of the blank short-time soaking furnace 2 through bolts.
The vertical self-resistance heating quenching device is provided with an upper water-cooling copper electrode roller 5 and a lower water-cooling copper electrode roller 5 in parallel, an annular-distributed roller inner water-cooling channel 8 is formed in the water-cooling copper electrode roller 5, two adjacent water-cooling copper electrode rollers 5 are communicated through a low-voltage high-current line 7, the low-voltage high-current line 7 is communicated with a power supply, a high-resistivity electrode roller 6 is fixed on the right side of the water-cooling copper electrode roller 5 through a shaft, and the high-resistivity electrode roller 6 is communicated with the adjacent water-cooling copper electrode roller 5 through the low-voltage high-current line 7.
In the embodiment of the invention, the transverse self-resistance heating quenching device is provided with two vertical parallel rows of vertical roller electrodes 9, and a quenching device is arranged between the adjacent vertical roller electrodes 9.
In the embodiment of the present invention, when the self-resistance heating and quenching device 1 is a longitudinal self-resistance heating and quenching device:
(1) The hot-rolled or cold-rolled non-coated plate with proper thickness level required by weight reduction is selected, the initial rectangular blank size with reasonable size is selected according to the number of parts in a forming die under one stroke, but the maximum length of a single blank plate is ensured not to be lower than the roller spacing between two pairs of self-resistance heating rollers, otherwise, the online heating cannot be completed.
(2) The blank is subjected to a continuous on-line cyclic heating and quenching process by a heating device, wherein the rapid heating process is realized by means of low-voltage high-current loaded between two adjacent pairs of electrode rollers, and quenching cooling is then performed when passing through the water-cooled electrode rollers. The blank plate is continuously passed through a plurality of pairs of electrode rollers to realize repeated cyclic heating-quenching cooling treatment, the number of the cyclic treatment is generally 3-4, and the number of the pairs of electrode rollers can be appropriately increased or decreased according to the requirement so as to change the number of the cyclic treatment.
(3) The last pair of electrode rolls are made of high-resistivity materials, so that when the electrode rolls are matched and heated with the front copper electrode rolls, the blank plate can be continuously conveyed and rapidly heated to a high-temperature austenite region and then is not cooled, and the blank plate is matched with a middle-short-time temperature equalizing furnace, so that a homogenized high-temperature blank with ultrafine-grained austenite before hot stamping forming is obtained.
(4) And after the blank is quickly taken out of the temperature equalizing furnace, the blank is placed in a hot stamping press, and is subjected to die assembly, pressure maintaining and quenching (blanking of rim charge is completed before die assembly), so that the formation of the part is realized while the transformation from austenite to martensite is completed.
(5) And taking out the part after die opening, and performing natural cooling or adopting subsequent forced cooling measures to finally obtain the structural part with higher toughness under the required 22MnB5 component.
In the embodiment of the present invention, when the self-resistance heating and quenching device 1 is a lateral self-resistance heating and quenching device:
(1) And selecting a hot-rolled or cold-rolled non-coated plate with a proper thickness level required by weight reduction, and selecting an initial rectangular blank size with a reasonable size according to the number of parts in a punch lower forming die.
(2) The blank is subjected to continuous on-line cyclic heating and quenching processes by heating equipment, wherein the rapid heating process realizes rapid temperature rise along the width direction of the plate by means of low-voltage high current generated between each pair of roller electrodes, and rapid cooling quenching is then carried out subsequently. The blank plate is continuously passed through a plurality of pairs of electrode rollers to realize repeated cyclic heating-quenching cooling treatment, the number of the cyclic treatment is generally 3-4, and the number of the pairs of electrode rollers can be appropriately increased or decreased according to the requirement so as to change the number of the cyclic treatment.
(3) The blank plate can be heated by the last counter roller electrode, then enters the blank short-time temperature equalizing furnace 2 without cooling, so as to ensure that the blank is not cooled after being in a high-temperature austenite region, and a homogenized high-temperature blank with ultrafine-grained austenite before hot stamping forming is obtained.
(4) And after the blank is quickly taken out of the temperature equalizing furnace, placing the blank on a hot stamping press, closing the die, maintaining the pressure, quenching (blanking the rim charge is completed before closing the die), and completing the transformation from austenite to martensite and simultaneously realizing the forming property of the part.
(5) And taking out the part after die opening, and performing natural cooling or adopting subsequent forced cooling measures to finally obtain the structural part with higher toughness under the required 22MnB5 component.
The principle of application of the present invention is further described below with reference to examples.
Example 1:
as shown in fig. 1; the continuous online preparation method of the Mn-B steel structural part with the ultrahigh strength and toughness provided by the invention comprises the following steps:
(1) The hot-rolled or cold-rolled non-coated plate with proper thickness level required by weight reduction is selected, the initial rectangular blank size with reasonable size is selected according to the number of parts in a forming die under one stroke, but the maximum length of a single blank plate is ensured not to be lower than the roller distance between two pairs of self-resistance heating rollers in the figure 1 (a), otherwise, the online heating cannot be finished.
(2) The blank is subjected to a continuous in-line cyclic heating and quenching process by a heating apparatus as shown in fig. 1 (a), wherein the rapid heating process is carried out by means of a low-voltage high-current applied between two adjacent pairs of electrode rolls, and then quenching cooling is carried out while passing through the water-cooled electrode rolls. The blank plate is continuously passed through a plurality of pairs of electrode rollers to realize repeated cyclic heating-quenching cooling treatment, the number of the cyclic treatment is generally 3-4, and the number of the pairs of electrode rollers can be appropriately increased or decreased according to the requirement so as to change the number of the cyclic treatment.
(3) The last pair of electrode rolls are made of high-resistivity materials, so that when the electrode rolls are matched and heated with the front copper electrode rolls, the blank plate can be continuously conveyed and rapidly heated to a high-temperature austenite region and then is not cooled, and the blank plate is matched with a short-time temperature homogenizing furnace in the step (b) of fig. 1, so that a homogenized high-temperature blank with ultrafine-grained austenite before hot stamping forming is obtained.
(4) After the blank is quickly taken out from the temperature equalizing furnace, the blank is placed on a hot stamping press for forming as shown in fig. 1 (c), and the blank is subjected to die assembly, pressure maintaining and quenching (blanking of rim charge is completed before die assembly), so that the austenite-martensite transformation is completed, and meanwhile, the part forming property is realized.
(5) And (3) taking out the part after die opening, and performing natural cooling or adopting subsequent forced cooling measures to finally obtain the structural member with higher toughness under the required 22MnB5 composition.
Example 2:
as shown in FIG. 2, the continuous online preparation method of the ultra-high-toughness Mn-B steel structural member provided by the invention comprises the following steps:
(1) And selecting a hot-rolled or cold-rolled non-coated plate with a proper thickness level required by weight reduction, and selecting an initial rectangular blank size with a reasonable size according to the number of parts in a punch lower forming die.
(2) The blank is subjected to continuous on-line cyclic heating and quenching by the heating device shown in fig. 2 (a), wherein the rapid heating process realizes rapid temperature rise along the width direction of the plate by means of low-voltage high current generated between each pair of roller electrodes, and rapid cooling quenching is then carried out subsequently. The blank plate is continuously passed through a plurality of pairs of electrode rollers to realize repeated cyclic heating-quenching cooling treatment, the number of the cyclic treatment is generally 3-4, and the number of the pairs of electrode rollers can be appropriately increased or decreased according to the requirement so as to change the number of the cyclic treatment.
(3) The blank sheet can be heated by the last counter roller electrode without cooling and then enters the short-time temperature equalizing furnace in the figure 2 (b) so as to ensure that the blank is not cooled after being in a high-temperature austenite region, and a homogenized high-temperature blank with ultrafine-grained austenite before hot stamping forming is obtained.
(4) After the blank is quickly taken out from the temperature equalizing furnace, the blank is placed on a hot stamping press for forming as shown in fig. 2 (c), and the blank is subjected to die assembly, pressure maintaining and quenching (blanking of rim charge is completed before die assembly), so that the austenite-martensite transformation is completed, and meanwhile, the part forming property is realized.
(5) And (3) taking out the part after die opening, and performing natural cooling or adopting subsequent forced cooling measures to finally obtain the structural member with higher toughness under the required 22MnB5 composition.
The principle of application of the invention is further described in connection with effects.
The invention aims at blank plates for hot forming (the steel grade is not limited to Mn-B steel, and can be changed into steel grade which can realize required structure transformation in the hot stamping forming pressure-maintaining quenching or post-forming cooling process), and continuous and repeated circulation self-resistance heating and cooling processes and devices are applied on line, so that high-temperature austenite grain ultra-refining treatment and component homogenization are carried out on blanks before hot stamping forming.
The invention combines the scheme design of heating the electrode roller with the last pair of resistivity and the subsequent rapid temperature equalizing furnace to realize the prefabrication of the high-temperature blank with the ultra-fine austenitic structure before hot stamping.
According to the invention, through the high cooling speed in the die in the hot stamping, pressure maintaining and quenching process or the forced cooling measure after stamping, the ultra-fine austenite can be ensured to be effectively converted into ultra-fine martensite or ultra-fine martensite plus a small amount of bainite structure, and the preparation of the high-strength and high-toughness structural member is realized.
The process method is particularly suitable for hot stamping forming of the low-cost non-coated hot-formed steel plate, and can reduce the oxidization problem in the heating process of the non-coated plate, thereby reducing the cost of the produced structural member.
The process of the invention eliminates the technological process of pre-blanking and reheating in the traditional hot stamping process, integrates blanking (high-temperature blanking) and hot stamping forming into a whole, not only can greatly shorten the technological process and improve the production efficiency of hot stamping forming, but also greatly reduces the production cost.
The foregoing description is only of the preferred embodiments of the present invention, and is not intended to limit the invention in any way, but any simple modification, equivalent variation and modification of the above embodiments according to the technical principles of the present invention are within the scope of the technical solutions of the present invention.
Claims (1)
1. The continuous online preparation method of the ultra-high-toughness Mn-B steel structural part is characterized in that a continuous online preparation device is adopted in the continuous online preparation method of the ultra-high-toughness Mn-B steel structural part, and the continuous online preparation device is provided with:
a self-resistance heating quenching device;
the self-resistance heating quenching device is communicated with a blank short-time temperature equalizing furnace through a conveyor belt, and the blank short-time temperature equalizing furnace is communicated with a forming press;
the self-resistance heating quenching device is a longitudinal self-resistance heating quenching device;
the bottom of the blank short-time temperature equalizing furnace is fixed with a plurality of heating electrode rollers through bolts;
the longitudinal self-resistance heating quenching device is provided with an upper water-cooling copper electrode roller and a lower water-cooling copper electrode roller which are arranged in parallel, wherein the inside of the water-cooling copper electrode roller is provided with an annular-distributed water-cooling channel in the roller, two adjacent water-cooling copper electrode rollers are communicated through a low-voltage high-current circuit, the low-voltage high-current circuit is communicated with a power supply, the right side of the water-cooling copper electrode roller is fixedly provided with a high-resistivity electrode roller through a shaft, and the high-resistivity electrode roller is communicated with the adjacent water-cooling copper electrode roller through the low-voltage high-current circuit;
the continuous online preparation method of the Mn-B steel structural part with the super high toughness comprises the following steps:
carrying out Mn-B steel strip cyclic heating-quenching by utilizing continuous transmission of an electrode roller, and carrying out superfine treatment on high-temperature austenite and quenched martensite grains; heating in the continuous transmission process of the electrode roller is self-resistance heating, and the heating speed is more than 100 ℃/s; the Mn-B steel strip elements can be uniformly diffused by repeated heating and quenching for many times;
in the ultra-fine treatment of high-temperature austenite and quenched martensite grains, continuous repeated circulation self-resistance heating and cooling processes and devices are applied on line, and the blank before hot stamping forming is subjected to the ultra-fine treatment of high-temperature austenite grains and component homogenization;
the method for heating the electrode roller with the last pair of high resistivity and the subsequent rapid temperature equalizing furnace are combined, and the high-temperature blank with the ultra-fine austenitic structure is prepared in advance before hot stamping;
the ultra-fine grain austenite is converted into ultra-fine grain martensite or ultra-fine grain martensite plus a small amount of bainite structure through high cooling speed in a die in the hot stamping forming pressure-maintaining quenching process, so that a high-strength and high-toughness structural member is obtained;
the continuous online preparation method of the Mn-B steel structural part with the super high toughness specifically comprises the following steps:
(1) Selecting a hot-rolled or cold-rolled non-coated plate, selecting an initial rectangular blank size according to the number of parts in a lower forming die of a punching time, wherein the maximum length of a single Zhang Piliao plate is not lower than the roller distance between two pairs of self-resistance heating rollers;
(2) The blank is subjected to continuous on-line cyclic heating and quenching process by a longitudinal self-resistance heating quenching device, is rapidly heated by low-voltage high current loaded between two adjacent pairs of electrode rollers, and is quenched and cooled by injecting water into a water cooling channel in the rollers; continuously carrying out repeated cyclic heating-quenching cooling treatment on the blank plate through a plurality of pairs of electrode rollers, wherein the cyclic treatment times are 3-4 times;
(3) The final pair of electrode rolls are made of high-resistivity materials and matched with a short-time temperature equalizing furnace to obtain homogenized high-temperature blanks with ultrafine-grained austenite before hot stamping forming;
(4) After the blank is quickly taken out from the temperature equalizing furnace, the blank is placed on a hot stamping forming press, and the blank is clamped and quenched under pressure, so that the formability of the part is realized while the transformation from austenite to martensite is completed;
(5) Taking out the part after die opening, and carrying out natural cooling or adopting subsequent forced cooling measures to obtain a structural member with higher strength and toughness;
the Mn-B steel is 22MnB5.
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| CN113941599A (en) * | 2021-09-14 | 2022-01-18 | 中国第一汽车股份有限公司 | Preparation method of high-toughness hot forming part for automobile |
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