CN117867246A - Toughening thermoforming method of ultrahigh-strength steel plate and high-strength and toughness thermoforming member - Google Patents
Toughening thermoforming method of ultrahigh-strength steel plate and high-strength and toughness thermoforming member Download PDFInfo
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- 229910000797 Ultra-high-strength steel Inorganic materials 0.000 title claims abstract description 106
- 238000000034 method Methods 0.000 title claims abstract description 59
- 238000003856 thermoforming Methods 0.000 title claims abstract description 18
- 238000010438 heat treatment Methods 0.000 claims abstract description 62
- 238000001816 cooling Methods 0.000 claims abstract description 23
- 238000010583 slow cooling Methods 0.000 claims abstract description 21
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 18
- 238000010791 quenching Methods 0.000 claims abstract description 18
- 230000000171 quenching effect Effects 0.000 claims abstract description 18
- 230000001502 supplementing effect Effects 0.000 claims abstract description 16
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- 239000011261 inert gas Substances 0.000 claims description 3
- 239000007788 liquid Substances 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 239000003921 oil Substances 0.000 claims description 3
- 229910001563 bainite Inorganic materials 0.000 abstract description 13
- 229910000831 Steel Inorganic materials 0.000 description 28
- 239000010959 steel Substances 0.000 description 28
- 229910000734 martensite Inorganic materials 0.000 description 11
- 239000003570 air Substances 0.000 description 9
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- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 2
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Abstract
The invention provides a toughening thermoforming method of an ultra-high strength steel plate and a high-strength thermoforming member, wherein the method comprises the following steps: firstly, carrying out rapid heating treatment and short-time heat preservation on an ultra-high strength steel plate for 0.5-5 min so as to ensure that the tissue structure of the ultra-high strength steel plate finishes austenite transformation and has uniform components; secondly, carrying out heat supplementing and slow cooling treatment on the ultra-high strength steel plate; thirdly, carrying out hot stamping warm die forming and pressure maintaining treatment on the ultra-high strength steel plate; and finally, carrying out quenching treatment on the ultra-high strength steel plate outside the die, and cooling to room temperature. thehigh-strengthandhigh-toughnesshotformingmemberpreparedbythemethodhasacomplexphasestructureofmartensite,bainite,nanocarbidesandasmallamountofresidualaustenite,whereinthemartensitelathbundlesaresmall,thebainiteismainlylowerbainitewithstrengthandtoughness,andgranularbainitewithsphericalM-Aislandsalsoexists,andthenanocarbidesaredispersed,precipitatedanduniformlydistributed,sothatthehigh-strengthandhigh-toughnesshotformingmemberhasgoodtoughnessinmechanicalproperty.
Description
Technical Field
The invention relates to the field of hot forming materials, in particular to a toughening hot forming method of an ultra-high strength steel plate and a high-strength hot forming member.
Background
The hot stamping of the ultrahigh-strength steel overcomes the limitations of poor room-temperature plasticity and large deformation resistance of materials by stamping and forming the hot plate, greatly improves the forming performance and forming precision of the high-strength and toughness hot-formed member, and becomes an important process for the lightweight forming and manufacturing of the high-strength and toughness hot-formed member of the automobile.
In the traditional hot stamping process, firstly, a steel plate is heated to 850-950 ℃ in a heating furnace, the heat preservation is carried out for a period of time, the complete austenitization of the tissue structure of the steel plate is ensured, and then, the steel plate is rapidly transferred into a quenching die for forming, pressure maintaining, quenching and cooling, thus forming a full martensitic structure. The strength of the formed high strength and toughness thermoformed component can reach 1500MPa, but the elongation is about 5%. For automobile collision safety parts such as an automobile middle upright post, an integral door ring, an anti-collision beam and the like, the lower extensibility is not beneficial to collision energy absorption, secondary collision injury is easy to cause, and the protection effect cannot be better exerted. Therefore, the cooperative regulation and control of the toughness of the existing ultra-high strength steel hot stamping component is a key technical problem to be solved urgently.
Disclosure of Invention
The invention aims to provide a toughening thermoforming method of an ultra-high strength steel plate and a high-strength and toughness thermoforming member, which can solve the technical problems that the conventional thermoforming member is difficult to coordinate in strength and toughness, long in regulation and control process period and the like.
In order to solve the technical problems, the invention provides a toughening thermoforming method of an ultra-high strength steel plate, which comprises the following steps:
s10, after the ultra-high strength steel plate is rapidly heated to 800-1000 ℃, preserving heat for 0.5-5 min in a short time to ensure that the tissue structure of the ultra-high strength steel plate finishes austenite transformation and has uniform components, and the heating rate is 10-150 ℃/S;
s20, taking out the heated ultrahigh-strength steel plate, and carrying out heat supplementing and slow cooling treatment on the ultrahigh-strength steel plate, wherein the heat supplementing temperature is 600-800 ℃, and the slow cooling rate is 0.01-20 ℃/S;
s30, carrying out hot stamping warm die forming and pressure maintaining treatment on the ultra-high strength steel plate, wherein the die clamping rate is 0.1-10S -1 The pressure maintaining time is 1-60 s, and the pressure maintaining force is 5-60 KN;
s40, carrying out die quenching treatment on the ultra-high strength steel plate, and cooling to room temperature.
Preferably, before performing step S10, the method further includes:
and (3) blanking the ultra-high strength steel billet to obtain the ultra-high strength steel plate with proper appearance, wherein the thickness of the ultra-high strength steel plate is 0.5-10 mm.
Preferably, the step S10 specifically includes: transferring the ultrahigh-strength steel plate into a box-type heating furnace or a roller hearth-type heating furnace for rapid heating treatment, wherein the heating temperature rise rate is 50-150 ℃/s, the heating temperature is 900-950 ℃, and the short-time heat preservation time is 1-5 min.
Specifically, the rapid heating mode of the box-type heating furnace adopts an electric heating mode or an electric induction heating mode, and the roller hearth type heating furnace adopts an induction coil heating mode or a gas heating mode and the like. Preferably, in the S10 step, the ultra-high strength steel sheet is subjected to rapid heat treatment in an inert gas atmosphere.
Preferably, in the step S20, the ultra-high strength steel plate is subjected to heat supplementing and slow cooling treatment by a hot air heating mode or a radiation heating mode, and the temperature of the ultra-high strength steel plate is monitored and controlled in real time by a non-contact digital infrared thermometer.
Preferably, before performing step S30, the method further includes: and (3) preheating the hot stamping die, wherein the preheating temperature is 200-700 ℃.
Preferably, the preheating temperature is 300 to 500 ℃.
Preferably, in the step S30, the transfer time of the ultrahigh-strength steel plate to the hot stamping die is 3-8S; the strain rate of the hot stamping warm die forming and pressure maintaining treatment is 0.1-10.0/s.
Preferably, in the step S40, the cooling medium for the out-mold quenching treatment comprises at least one of cold air, water, oil and liquid nitrogen, and the cooling rate of the out-mold quenching treatment is more than or equal to 40 ℃/S.
Correspondingly, the invention also provides a high-strength and high-toughness hot forming component which is prepared by the strengthening and toughening hot forming method of the ultrahigh-strength steel plate.
The beneficial effects of the invention are as follows: different from the prior art, the invention provides a toughening thermoforming method of an ultra-high strength steel plate and a high-strength thermoforming member, which comprises the following steps: firstly, carrying out rapid heating treatment and short-time heat preservation on an ultra-high strength steel plate for 0.5-5 min so as to ensure that the tissue structure of the ultra-high strength steel plate finishes austenite transformation and has uniform components; secondly, carrying out heat supplementing and slow cooling treatment on the ultra-high strength steel plate; thirdly, carrying out hot stamping warm die forming and pressure maintaining treatment on the ultra-high strength steel plate; and finally, carrying out quenching treatment on the ultra-high strength steel plate outside the die, and cooling to room temperature. theinventionadoptsthetechnologicalprocessesofrapidheating,concurrentheatingslowcooling,hotstampingwarmdieformingandquenchingsoastoleadthepreparedhigh-strengthandhigh-toughnesshotformingcomponenttohavecomplexphasestructuresofmartensite,bainite,nanocarbideandasmallamountofresidualaustenite,whereinmartensitelathbundlesaretiny,bainiteismainlylowerbainitewithstrengthandtoughness,granularbainitewithsphericalM-Aislands(martensite/austeniteislands)alsoexists,nanocarbideisdispersed,precipitatedanduniformlydistributed,thusleadingthepreparedhigh-strengthandhigh-toughnesshotformingcomponenttohavegoodtoughnessinmechanicalproperty.
Drawings
FIG. 1 is a flow chart of a method for strengthening and toughening a hot forming of an ultra-high strength steel plate provided by the invention;
FIGS. 2a to 2e are schematic views of the process steps of the method for toughening and hot forming an ultra-high strength steel sheet according to example 1 of the present invention;
FIG. 3 is a schematic view of a scanning electron microscope of the microstructure of the high strength and toughness thermoformed article prepared in example 1 of the present invention.
FIG. 4 is a graph showing the mechanical properties of the high strength and toughness thermoformed part prepared in example 1 of the present invention and the thermoformed part prepared by the conventional hot stamping process.
Detailed Description
The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, are intended to fall within the scope of the present invention.
Aiming at the problems of difficult coordination of the toughness of the hot forming component, long regulation and control process period and the like in the existing hot stamping forming technology, the invention provides an ultra-high strength steel complex phase structure strengthening and toughening hot stamping process suitable for large-scale production through the process flow of the heat supplementing slow cooling, warm die forming and quenching, realizes the cooperative regulation and control of the toughness of the hot forming component, and can be used in the fields of vehicles, engineering machinery and the like.
The invention is realized by the following technical scheme: firstly, blanking the steel plate, then quickly heating and preserving heat by a box-type or roller-hearth heating furnace, then ensuring that the steel plate is slowly cooled to a proper temperature in a temperature regulation mode such as hot air, radiation and the like in the steel plate conveying process, transferring the steel plate into a stamping die which is heated to a set temperature for forming at a proper strain rate, and finally quickly quenching and cooling the formed high-strength and toughness hot forming member in a cooling medium to obtain the high-strength and toughness horse-shellfish complex phase structure. Therefore, the manufacture of the high-strength and high-toughness hot-formed component is realized on the premise of not adding any expensive alloy element and ensuring high production efficiency.
Referring to fig. 1, fig. 1 is a flowchart of a method for toughening and thermoforming an ultra-high strength steel sheet according to the present invention, wherein the method for toughening and thermoforming comprises the following steps:
s10, after the ultra-high strength steel plate is rapidly heated to 800-1000 ℃, the temperature is kept for 0.5-5 min in a short time to ensure that the tissue structure of the ultra-high strength steel plate is subjected to austenite transformation, and the heating rate is 10-150 ℃/S.
Specifically, before the step S10, the method further includes:
and (3) blanking the ultra-high strength steel billet to obtain the ultra-high strength steel plate with proper appearance, wherein the thickness of the ultra-high strength steel plate is 0.5-10 mm.
Specifically, the step S10 specifically includes:
transferring the ultrahigh-strength steel plate into a box type heating furnace or a roller hearth type heating furnace, wherein the heating temperature rising rate is 10-150 ℃/s, and rapidly heating to 800-1000 ℃, and preserving heat for 0.5-5 min in a short time, so that the austenitic transformation of a tissue structure is ensured, and the uniformity of the tissue is ensured.
Preferably, in the heating and heat-preserving process of the steps, the heating temperature rising rate is 50-150 ℃/s; the temperature rising rate is increased, austenite nucleation can be promoted, crystal grains are finer, and the concentration of elements such as C/Cr/Mn in original cementite or adjacent cementite areas of the austenite is higher.
Preferably, the heating temperature is 900-950 ℃, the short-time heat preservation time is 1-5 min, and the heating temperature and the heat preservation time can influence the hot stamping forming process and the performance of the formed part, so that the proper temperature and the proper heat preservation time are selected.
Further, for the heating temperature, the basis of the selection is as follows: firstly, the austenitizing temperature of the ultra-high strength steel plate is higher than the austenitizing temperature so as to obtain a complete austenitic structure, and a condition is provided for obtaining martensite for subsequent quenching; secondly, the heating temperature is not too high, otherwise, surface overburning and austenite grain coarsening are caused, and the toughness of the steel plate is reduced; thirdly, the heat loss in the subsequent steel plate transferring process needs to be considered. For the heat preservation time, when the heat preservation time is too short, the C enrichment degree in the austenite is insufficient, and the residual austenite phase is too small after the ultrahigh-strength steel plate is cooled to room temperature; therefore, in order to achieve the purpose of obtaining more martensite structures after stamping and quenching, the ultrahigh-strength steel plate is heated and then is subjected to heat preservation for a certain time to obtain uniform austenite structures; when the heat preservation time is too long, the grains can be grown, the enrichment of C in unconverted austenite is reduced, the residual austenite phase in the ultra-high strength steel plate is reduced, the performance of the high-strength and high-toughness hot forming component is further reduced, the production period is increased, and the production efficiency is reduced.
Further, in order to ensure that the surface oxidation and decarburization phenomenon of the ultra-high strength steel plate cannot occur in the austenitizing process, protective gas is introduced in the heating process, so that the ultra-high strength steel plate is heated in an inert gas environment, and contact with oxygen is avoided.
And S20, taking out the heated ultrahigh-strength steel plate, and carrying out heat supplementing and slow cooling treatment on the ultrahigh-strength steel plate, wherein the heat supplementing temperature is 600-800 ℃, and the slow cooling rate is 0.01-20 ℃/S.
Specifically, the step S20 specifically includes:
and taking out the heated steel plate, and carrying out heat supplementing and slow cooling on the ultrahigh-strength steel plate to 600-800 ℃ before hot stamping, wherein the slow cooling rate is 0.01-20 ℃/s.
Preferably, in step S20, in order to ensure uniform cooling in the slow cooling process of the steel plate, the ultra-high strength steel plate can be subjected to heat supplementing and slow cooling by adopting a heating mode such as hot air, radiation and the like through a prefabricated plate formed by a plurality of micropores, so that the ultra-high strength steel plate is slowly cooled to a preset temperature before stamping. Meanwhile, in order to monitor and control the temperature of the ultra-high strength steel plate in the transferring and heat supplementing slow cooling process, a non-contact digital infrared thermometer can be adopted to monitor and control the temperature in real time.
S30, carrying out hot stamping warm die forming and pressure maintaining treatment on the ultra-high strength steel plate, wherein the die clamping rate is 0.1-10S -1 The dwell time is 1-60 s, and the dwell pressure is 5-60 KN.
Specifically, the step S30 further includes:
transferring the super-high strength steel plate after slow cooling in the step S30 to a hot stamping die with a certain temperature for 3-8S, closing the die and taking 0.1-10S -1 And (3) carrying out speed stamping forming and pressure maintaining for 1-60 s, and keeping the pressure at 5-60 KN.
In the embodiment of the present invention, before performing step S30, the method further includes: and (3) preheating the hot stamping die, wherein the preheating temperature is 200-700 ℃.
Preferably, the heating temperature of the hot stamping die is 300-500 ℃, the ultrahigh-strength steel plate in the warm-die forming process is in contact with the hot stamping die, the temperature difference between the hot stamping die and the hot stamping die is small, the cooling rate is low, the transformation of bainite is realized, the toughness of the high-strength and high-toughness hot forming member is improved, the fluidity of the ultrahigh-strength steel plate is promoted, and the forming performance is improved.
Preferably, the strain rate of the S30 step is 0.1-10.0/S, the transformation of bainite is promoted by retarded stamping forming, and meanwhile, the martensite structure is thinned, so that the dispersion precipitation and uniform distribution of fine carbides are facilitated, and the toughness of the high-toughness thermoformed component is improved.
Preferably, in the step S30, the super-strength steel plate slowly cooled to a certain temperature is quickly transferred to the hot stamping die, and heat exchange is performed between the super-strength steel plate and air due to the fact that the steel plate is in contact with room temperature air in the process of being transferred to the hot stamping die, so that heat loss of the super-strength steel plate in the transferring process is reduced, and the transferring time is shortened as much as possible.
S40, carrying out die quenching treatment on the ultra-high strength steel plate, and cooling to room temperature.
Specifically, the step S40 further includes:
and (3) rapidly transferring the ultra-high strength steel plate subjected to pressure maintaining in the step (S30) to the outside of a hot stamping die for 3-8S, performing out-die quenching treatment in a cooling medium, and cooling to room temperature.
Preferably, the cooling medium in the step S40 comprises cold air, water, oil, liquid nitrogen and the like, and the cooling rate is more than or equal to 40 ℃/S; the cooling rate is too small to facilitate the transformation from supercooled austenite to martensite, and the high strength of the prepared high-strength and high-toughness thermoformed component cannot be ensured.
The method of the toughening and hot forming of the ultra-high strength steel sheet will be described in detail with reference to specific examples.
Example 1:
referring to fig. 2a to 2e, fig. 2a to 2e are schematic process diagrams of the toughening hot forming method of the ultra-high strength steel plate according to embodiment 1 of the present invention; specifically, the strengthening and toughening thermoforming method comprises the following steps:
step (1): firstly, selecting a B1500HS steel plate with the thickness of 1.6mm, wherein the B1500HS steel plate comprises the following components in percentage by mass: c:0.23%, mn:1.35%, si:0.25%, cr:0.19%, ti:0.03%, B:0.0032%, S:0.006%, P:0.015% of Fe and the balance of unavoidable impurities.
At this time, the microstructure of the B1500HS steel sheet was uniform ferrite and fine pearlite, the ferrite ratio was about 75%, and the pearlite ratio was about 25%; wherein, the average grain size of ferrite is less than or equal to 10 mu m, the yield strength is about 370MPa, and the tensile strength is about 650MPa.
And blanking the B1500HS steel plate, and cutting the B1500HS steel plate into an ultra-high strength steel plate with the shape suitable for hot stamping forming by a plate shearing machine.
Step (2): the super-strength steel plate is heated by adopting a box type heating furnace through resistance wires, as shown in fig. 2 b; in order to avoid decarburization and oxide scale generation on the surface of the ultra-high strength steel plate in the heating process, N is introduced 2 And (3) protecting gas, heating at a rate of 30-50 ℃/s, and when the furnace temperature of the box-type heating furnace is raised to 920-950 ℃, placing the ultra-high strength steel plate into the box-type heating furnace for heating and preserving heat for 100s, so that the austenitic transformation of all the structures is ensured and the components are uniform.
Step (3): and heating the hot stamping die while heating and preserving the heat of the ultra-high strength steel plate, and heating the hot stamping die to 500 ℃. The temperature difference between the ultra-high strength steel plate and the hot stamping die is shortened, the cooling rate is reduced, the transformation of bainite is realized during forming, and the toughness of the high-strength and high-toughness hot-formed component prepared later is improved.
Step (4): the ultra-high strength steel sheet after uniform austenitizing was taken out by a mechanical gripper, and during the transfer, heat-compensating and slow-cooling was performed by radiation heating at a cooling rate of 5 deg.c/s and slow-cooling to 690 deg.c, as shown in fig. 2 c.
Step (5): rapidly transferring the slowly cooled ultrahigh-strength steel plate to a hot stamping die through a mechanical gripper, wherein the transfer time is 3s, the die closing and pressure maintaining forming are performed for 6s, and the pressure maintaining force is 8-20 KN, as shown in fig. 2 d; the hot stamping die consists of an upper die and a lower die; meanwhile, in order to ensure the real-time accuracy of temperature monitoring and control, before the steel plate is placed into a box-type furnace for heating in the step (2), a K-type thermocouple is welded in the center of the steel plate, and the other end of the K-type thermocouple is connected to a temperature acquisition and display system, as shown in fig. 2 a.
Specifically, in the warm die forming process, the proper strain rate forming is beneficial to the transformation of austenite to lower bainite/granular bainite, meanwhile, the refinement of martensite laths and the dispersion distribution of carbide are promoted, and the strength and toughness of the high-strength and high-toughness hot forming member are improved.
Step (6): the formed super-high strength steel plate is rapidly transferred to the outside of the hot stamping die through the mechanical gripper for 4s, and is quenched and cooled to room temperature in ice water, wherein the cooling rate is about 70-100 ℃/s, and the martensitic transformation of the high-strength and high-toughness hot-formed component is ensured, as shown in figure 2 e.
Referring to FIG. 3, FIG. 3 is a schematic view of a scanning electron microscope of the microstructure of the high strength and toughness thermoformed article according to example 1 of the present invention; in particular, as can be seen from the structural morphology analysis of the high strength and toughness thermoformed article, the martensite lath bundles are significantly refined and the microstructure is more uniform, with relatively high strength and hardness, and a small amount of lath ferrite and island austenite distributed therein form uniformly distributed granular bainite (10%); the occupied area and the distribution position of the granular or island-shaped carbide are related to the toughness of granular bainite, and the higher the area ratio is, the more uniform the distribution is, and the better the toughness is improved. Fine carbide (5-20 nm) is dispersed in ferrite to form lower bainite (5%), the transformation temperature is generally below 350 ℃, the temperature is lower, carbon atoms are difficult to diffuse, the dispersion degree of the carbide is high, the strength is generally similar to that of martensite, but the toughness is greatly improved. The mixed bainite structure exhibits a high impact toughness.
Finally, the high-strength and high-toughness hot-formed component prepared in the embodiment 1 of the invention has the tensile strength of about 1600MPa, the elongation of about 10 percent and the impact toughness of up to 700 to 810 kJ.m -2 。
In order to embody the process application range of the toughening thermoforming method of the ultra-high strength steel plate provided by the embodiment of the invention, a hot stamping process test, specifically an embodiment 2, is performed on the D1800HFD steel plate.
Example 2:
step (1): firstly, selecting a D1800HFD ultra-high strength steel plate with the thickness of 3mm, wherein the ultra-high strength steel plate comprises the following components in percentage by mass: c:0.195%, mn:1.158%, si:0.219%, cr:0.194%, ti:0.049%, nb:0.046%, mo:0.181%, al:0.161, cr:0.194%, P:0.014%, fe:98.589%;
and then, cutting and blanking the ultra-high strength steel plate to obtain the ultra-high strength steel plate with the appearance suitable for hot stamping.
Step (2): the roller hearth type heating furnace is adopted to heat the ultrahigh-strength steel plate, the ultrahigh-strength steel plate is placed into the roller hearth type heating furnace and is rapidly heated to 970 ℃ and is kept at the temperature for 300 seconds, and the whole structure of the roller hearth type heating furnace is ensured to finish austenite transformation.
Step (3): and heating the hot stamping die to 500 ℃ while heating and preserving heat by a roller hearth type heating furnace.
Step (4): taking out the heated ultrahigh-strength steel plate through a mechanical gripper, cooling at a cooling rate of 8-12 ℃/s in air, and carrying out heat supplementing and slow cooling on the ultrahigh-strength steel plate through a hot air blower prefabricated with uniform ventilation holes, wherein the cooling rate is 2 ℃/s, and cooling to 750 ℃.
Step (5): the ultra-high strength steel plate is rapidly transferred to a hot stamping die through a mechanical gripper, the transfer time is 4s, the die assembly and the pressure maintaining forming are carried out, the pressure maintaining time is 10s, and the pressure maintaining force is 10-30 KN.
Step (6): and rapidly transferring the formed steel plate to the outside of a hot stamping die for 4s, quenching in water and cooling to room temperature at a cooling rate of about 90-150 ℃/s, and ensuring the martensitic transformation of the high-strength and high-toughness hot-formed component.
Finally, the high-strength and high-toughness hot-formed component prepared in the embodiment 2 has high strength and good plasticity in mechanical properties, and the mixed bainite with a small proportion has high impact toughness, and the tensile strength can reach 1800MPa.
Referring to fig. 4, fig. 4 is a schematic diagram showing the mechanical properties of the high strength and toughness hot formed member prepared in example 1 according to the present invention and the hot formed member prepared by the conventional hot stamping process. Compared with the hot formed member prepared by the conventional hot stamping process, the high strength and toughness hot formed member prepared in example 1 of the present invention is known to have peak tensile strength (MPa), elongation after break (%), product of strength and elongation (GPa%) and impact toughness (KJ m) -2 ) Any one of the mechanical properties has better mechanical data.
Compared with the prior art, the invention has the beneficial effects that:
(1) The invention makes the ultra-high strength steel plate have a high strength and toughness structure of horse-Bei Fuxiang through the process flow of heat supplementing slow cooling, warm die forming and quenching. Firstly, heating rapidly to avoid austenite grain growth; then,carryingoutheatsupplementingslowcoolingandwarmdieformingtoensureisothermalornearisothermaltransformationofpartialausteniteinthemicrostructureoftheultra-highstrengthsteelplatetobainite,andincreasingthecarboncontentandenhancingthestabilityofresidualausteniteinM-Aislandsdistributedinadispersingwaythroughcarbonatomdiffusionanddistribution; andthenrapidlyquenchingandcoolingatahighcoolingrate,andfinallyobtainingacomplexphasestructurewithmartensite,bainite,nanocarbideandasmallamountofresidualaustenite,whereinthemartensitelathbundlesaresmall,thebainiteismainlylowerbainitewithstrengthandtoughness,granularbainitewithsphericalM-Aislandsalsoexists,thenanocarbideisdispersedandprecipitatedanduniformlydistributed,andthecomplexphasestructurehasgoodtoughnessinmechanicalproperty.
(2) The invention forms the steel plate member with high strength and high toughness by a simple and efficient production process with lower production cost. Compared with the traditional hot stamping component, the high-toughness hot forming component formed by the process has obviously improved toughness on the premise that the tensile strength is not reduced or even improved.
(3) Compared with the traditional hot forming process, the method has equivalent production efficiency and is suitable for large-scale hot stamping forming production of the ultra-high strength steel.
It should be noted that, the foregoing embodiments all belong to the same inventive concept, and the descriptions of the embodiments have emphasis, and where the descriptions of the individual embodiments are not exhaustive, reference may be made to the descriptions of the other embodiments. The foregoing examples merely illustrate embodiments of the invention and are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (10)
1. A toughening thermoforming method of an ultra-high strength steel plate is characterized by comprising the following steps:
s10, rapidly heating the ultra-high strength steel plate to 800-1000 ℃, and then preserving heat for 0.5-5 min in a short time to ensure that the tissue structure of the ultra-high strength steel plate finishes austenite transformation and has uniform components, wherein the heating rate is 10-150 ℃/S;
s20, taking out the heated ultrahigh-strength steel plate, and carrying out heat supplementing and slow cooling treatment on the ultrahigh-strength steel plate, wherein the heat supplementing temperature is 600-800 ℃, and the slow cooling rate is 0.01-20 ℃/S;
s30, carrying out hot stamping, warm die forming and pressure maintaining treatment on the ultra-high strength steel plate, wherein the die clamping rate is 0.1-10S -1 The pressure maintaining time is 1-60 s, and the pressure maintaining force is 5-60 KN;
and S40, carrying out die quenching treatment on the ultra-high strength steel plate, and cooling to room temperature.
2. The method of toughening a hot forming of an ultra-high strength steel sheet according to claim 1, further comprising, before performing the step S10:
and blanking the ultra-high strength steel billet to obtain the ultra-high strength steel plate with proper appearance, wherein the thickness of the ultra-high strength steel plate is 0.5-10 mm.
3. The method of forming an ultra-high strength steel sheet according to claim 1, wherein the step S10 comprises:
transferring the ultra-high strength steel plate into a box type heating furnace or a roller hearth type heating furnace for rapid heating treatment, wherein the heating temperature rise rate is 50-150 ℃/s, the heating temperature is 900-950 ℃, and the short-time heat preservation time is 1-5 min.
4. The method of toughening a hot forming of an ultra-high strength steel sheet according to claim 3, wherein in the step S10, the ultra-high strength steel sheet is subjected to rapid heat treatment in an inert gas atmosphere.
5. The method for toughening and thermoforming an ultra-high strength steel plate according to claim 1, wherein in the step S20, the ultra-high strength steel plate is subjected to heat supplementing and slow cooling treatment by a hot air heating mode or a radiation heating mode, and the temperature of the ultra-high strength steel plate is monitored and controlled in real time by a non-contact digital infrared thermometer.
6. The method of toughening a hot forming of an ultra-high strength steel sheet according to claim 1, further comprising, before performing the step S30: and (3) preheating the hot stamping die, wherein the preheating temperature is 200-700 ℃.
7. The method of toughening a hot forming ultra-high strength steel sheet according to claim 6, wherein the preheating temperature is 300 to 500 ℃.
8. The method of toughening a heat-formable ultra-high strength steel sheet according to claim 6, wherein in the step S30, the transfer time of the ultra-high strength steel sheet to the hot stamping die is 3 to 8S; the strain rate of the hot stamping warm die forming and pressure maintaining treatment is 0.1-10.0/s.
9. The method for toughening and hot forming an ultra-high strength steel sheet according to claim 1, wherein in the step S40, the cooling medium for the out-mold quenching treatment comprises at least one of cold gas, water, oil and liquid nitrogen, and the cooling rate of the out-mold quenching treatment is not less than 40 ℃/S.
10. A high strength and toughness hot formed member, characterized by being produced by the method for strengthening and toughening hot forming an ultra-high strength steel sheet according to any one of claims 1 to 9.
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