KR101657376B1 - Hot stamping product and method of manufacturing the same - Google Patents

Abstract

A hot stamping component and a method of manufacturing the same, which can improve elongation and impact performance while minimizing material deviation through control of alloy components and process conditions, are disclosed.
A method of manufacturing a hot stamped part according to the present invention comprises the steps of: (a) providing a steel sheet comprising 0.04 to 0.10% of C, 0.07% or less of Si, 1.0 to 1.6% of Mn, 0.02% or less of P, (Finishing Delivery Temperature): 860 to 900 占 폚. The slab plate is composed of 0.01 to 0.60% of Ti, 0.04 to 0.08% of Ti, 0.05 to 0.40% of Mo, and the balance of Fe and unavoidable impurities. ; (b) cooling the finished hot rolled plate by cooling to a CT (Coiling Temperature) of 580 to 620 캜; (c) uncoiling and pickling the rolled sheet material, followed by cold rolling; (d) annealing the cold-rolled sheet material at 720 to 850 ° C; And (e) hot stamping the annealed sheet material.

Description

TECHNICAL FIELD [0001] The present invention relates to a hot stamping component,

The present invention relates to a hot stamping component and a method of manufacturing the same, and more particularly, to a hot stamping component capable of improving an elongation and a collision performance while minimizing a material deviation by controlling an alloy component and controlling process conditions, .

In recent years, the automobile industry has been making efforts to improve fuel economy and safety by reducing the weight of components through application of ultra-high strength steels.

However, in the case of most automobile parts produced through the press work, as the strength is increased, the machinability of the workpiece is lowered. As a result, when an automobile part is manufactured using ultra-high strength steel, it is difficult to process it into a complicated shape, which makes it difficult to apply automobile parts.

However, in this case, the final microstructure is formed into a full-martensite structure, so that the ductility tends to be low and the collision absorption ability tends to be lowered. have.

A related prior art document is Korean Patent No. 10-0742818 (published on Jul. 30, 2007), which discloses a cold-rolled steel sheet having excellent workability and a manufacturing method thereof.

An object of the present invention is to provide a hot stamping component capable of improving elongation and impact performance while minimizing material variation through control of alloy components and process conditions, and a method for manufacturing the same.

Another object of the present invention is to provide a hot stamping part having a tensile strength (TS) of 700 to 850 MPa, a yield strength (YS) of 550 to 750 MPa and an elongation (EL) of 10 to 25% .

(A) 0.04 to 0.10% of C, 0.07 to 0.07% of Si, 1.0 to 1.6% of Mn, P: A slab plate composed of more than 0% to 0.02%, S: more than 0 to 0.003%, Al: 0.01 to 0.60%, Ti: 0.04 to 0.08%, Mo: 0.05 to 0.40% and balance iron (Fe) (Finishing Delivery Temperature): finishing hot rolling at a temperature of 860 to 900 占 폚; (b) cooling the finished hot rolled plate by cooling to a CT (Coiling Temperature) of 580 to 620 캜; (c) uncoiling and pickling the rolled sheet material, followed by cold rolling; (d) annealing the cold-rolled sheet material at 720 to 850 ° C; And (e) hot stamping the annealed sheet material.

In order to accomplish the above object, according to the present invention, there is provided a hot stamping component comprising 0.04 to 0.10% of C, 0.07 to 0.07% of Si, 1.0 to 1.6% of Mn, (Fe) and unavoidable impurities, and the final microstructure is composed of ferrite and martensite (hereinafter referred to as " ferrite and martensite "), Site, wherein the martensite structure has a cross-sectional area ratio of 40 to 60%.

The hot stamping component and the method of manufacturing the same according to the present invention include adding titanium (Ti) for grain refinement and aluminum (Al) for separating ferrite and austenite phase during transfer during a hot spamping process , The elongation and collision performance can be improved while minimizing the material deviation.

Therefore, the hot stamping parts manufactured by the method according to the present invention have a tensile strength (TS) of 700 to 850 MPa, a yield strength (YS) of 550 to 750 MPa and an elongation (EL) of 10 to 25% And is also suitable for use as an impact absorbing portion of the impact member.

1 is a process flow diagram illustrating a method of manufacturing a hot stamping component according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a hot stamping component according to a preferred embodiment of the present invention and a method of manufacturing the same will be described in detail with reference to the accompanying drawings.

Hot stamping parts

The hot stamping part according to the present invention aims to have a tensile strength (TS) of 700 to 850 MPa, a yield strength (YS) of 550 to 750 MPa and an elongation (EL) of 10 to 25%.

For this, the hot stamping part according to the present invention preferably contains 0.04 to 0.10% of C, 0.07 to 0.07% of Si, 1.0 to 1.6% of Mn, more than 0 to 0.02% of P, % Of Al, 0.01 to 0.60% of Al, 0.04 to 0.08% of Ti, 0.05 to 0.40% of Mo, and the balance of iron (Fe) and unavoidable impurities.

At this time, the hot stamping part has a composite structure including ferrite and martensite as the final microstructure, and the martensite structure has 40 to 60% in cross-sectional area ratio.

Hereinafter, the role and content of each component included in the hot stamping component according to the present invention will be described.

Carbon (C)

Carbon (C) is added to ensure strength of the steel. In addition, the carbon serves to stabilize the austenite phase according to the amount that is concentrated in the austenite phase.

The carbon (C) is preferably added in a content ratio of 0.04 to 0.10 wt% of the total weight of the hot stamping component according to the present invention. When the content of carbon (C) is less than 0.04% by weight, it is difficult to secure sufficient strength. On the contrary, when the content of carbon (C) exceeds 0.10 wt%, the strength is increased but the toughness may be lowered.

Silicon (Si)

Silicon (Si) contributes to the improvement of the strength and elongation of the steel.

However, if the content of silicon (Si) is more than 0.07% by weight of the total weight of the hot stamping component according to the present invention, surface defects and plating characteristics may be deteriorated. Therefore, in the present invention, it is preferable that the content of silicon (Si) is added in a content ratio of 0 to 0.07% by weight or less of the total weight of the hot stamping parts.

Manganese (Mn)

Mn contributes to austenite stabilization and also contributes to strength improvement.

The manganese (Mn) is preferably added at a content ratio of 1.0 to 1.6 wt% of the total weight of the hot stamping component according to the present invention. When the content of manganese (Mn) is less than 1.0% by weight, the effect of addition is insufficient. On the contrary, when the content of manganese (Mn) exceeds 1.6% by weight, toughness is deteriorated due to occurrence of center segregation.

In (P)

Phosphorus (P) plays a role of improving the in-plane anisotropy and enhancing the strength of a substitutional alloy element having a large solid solution strengthening effect. As the content of phosphorus increases due to the competition with carbon, the hardening effect of carbon (C) . Further, since the grain size is reduced by the addition of phosphorus, it is expected that the hardening of the sintering property and the improvement of the anti-aging property as the grain size decreases.

However, when the content of phosphorus (P) exceeds 0.02% by weight of the total weight of the hot stamping component according to the present invention, there is a problem that generation of secondary processing brittleness and surface defects due to P segregation occur. Therefore, the phosphorus (P) is limited to a content ratio of not less than 0 to 0.02% by weight of the total weight of the hot stamping component according to the present invention.

Sulfur (S)

Sulfur (S) is a component that accelerates localized thickening and aggregation of manganese (Mn) in steelmaking, performance and reheating processes, and therefore, it is desirable to limit the content to a minimum. Therefore, it is preferable that the content of sulfur (S) is limited to 0.003% by weight of the total weight of the hot stamping component according to the present invention. When sulfur (S) is sufficiently controlled in the above content range, the concentration of manganese in the steelmaking and reheating process can be suppressed without being affected by the electromagnetism and the cooling rate of the casting.

Aluminum (Al)

Aluminum (Al) is used as a deacidification material, and plays a role of suppressing precipitation of cementite like silicon (Si) and stabilizing austenite, thereby enhancing strength.

The aluminum (Al) is preferably added at a content ratio of 0.01 to 0.60 wt% of the total weight of the hot stamping component according to the present invention. When the content of aluminum (Al) is less than 0.01% by weight, it is difficult to expect an austenite stabilizing effect. On the contrary, when the content of aluminum (Al) exceeds 0.60% by weight, there is a problem that the nozzle clogging problem may occur during the steel making, and hot brittleness occurs due to Al oxide or the like during casting, and cracking and ductility are deteriorated.

Titanium (Ti)

Titanium (Ti) contributes to the improvement of the elongation of steel by reducing the carbon content in steel by precipitating carbide in the hot stamping process.

The titanium (Ti) is preferably added at a content ratio of 0.04 to 0.08% by weight based on the total weight of the hot stamping component according to the present invention. When the content of titanium (Ti) is less than 0.04% by weight, the effect of the addition is insufficient. Conversely, if the content of titanium (Ti) exceeds 0.08% by weight, toughness may be deteriorated.

Molybdenum (Mo)

Molybdenum (Mo) is a substitutional element and improves the strength of steel by solid solution strengthening effect. In addition, molybdenum (Mo) serves to improve the hardenability of the steel.

The molybdenum (Mo) is preferably added at a content ratio of 0.05 to 0.40% by weight based on the total weight of the hot stamping component according to the present invention. If the content of molybdenum (Mo) is less than 0.05% by weight, the above effects can not be exhibited properly. On the contrary, when the content of molybdenum (Mo) exceeds 0.40% by weight, there is a problem that the manufacturing cost is increased without any further effect.

Niobium (Nb)

Niobium (Nb) forms precipitates to refine grains and improve fracture toughness, and precipitates carbides to reduce the solid carbon content in the steel, thereby contributing to an improvement in elongation.

The niobium (Nb) is preferably added in an amount of 0.01 to 0.10% by weight based on the total weight of the hot stamping component according to the present invention. When the content of niobium (Nb) is less than 0.01% by weight, the effect of the addition is insufficient. On the contrary, when the content of niobium (Nb) is more than 0.10 wt% and added in a large amount, the yield strength is excessively increased and the toughness is lowered.

How to make hot stamping parts

1 is a process flow diagram illustrating a method of manufacturing a hot stamping component according to an embodiment of the present invention.

Referring to FIG. 1, a hot stamping component manufacturing method according to an embodiment of the present invention includes a hot rolling step S110, a cooling / winding step S120, a cold rolling step S130, a annealing heat treatment step S140, And a hot stamping step (S150). Although not shown in the drawing, it may further include a slab reheating step (not shown) carried out before the hot rolling step S110. Such slab reheating step is not necessarily performed, but it is more preferable to carry out the step of re-heating the precipitate.

In the hot stamping component manufacturing method according to the present invention, the slab plate of the semi-finished product to be subjected to the hot rolling process contains 0.04 to 0.10% of C, 0.07 to 0.07% of Si, 1.0 to 1.6% of Mn, More than 0 to 0.02%, S: more than 0 to 0.003%, Al: 0.01 to 0.60%, Ti: 0.04 to 0.08%, Mo: 0.05 to 0.40% and the balance of iron (Fe) and unavoidable impurities.

At this time, in the slab reheating step, the slab plate obtained through the continuous casting process is reheated to SRT (Slab Reheating Temperature): 1150 to 1250 ° C., so that the segregated components can be reused.

When the slab reheating temperature (SRT) is less than 1150 ° C, there is a problem that the segregated components are not sufficiently reused during casting. On the contrary, when the SRT exceeds 1250 DEG C, the austenite grain size increases and the strength is hardly ensured. In addition, the hardening ability and endurance are also reduced. Also, Can only rise.

Hot rolling

In the hot rolling step (S110), the reheated plate is subjected to finishing hot rolling under the conditions of FDT (Finishing Delivery Temperature): 860 to 900 ° C.

At this time, if the finishing rolling temperature (FDT) is too low to be less than 860 占 폚, there is a problem that blended structure due to an abnormal reverse rolling occurs, and a problem of ductility during hot rolling occurs due to a rapid phase change. On the other hand, when the finish rolling temperature (FDT) exceeds 900 占 폚, the austenite grains are coarsened and the hardening ability and the anti-aging property are decreased.

Cooling / Winding

In the cooling / winding step (S120), the finished hot rolled plate is cooled to a CT (Coiling Temperature) of 580 to 620 ° C at a rate of 50 to 80 ° C / sec and wound.

If the coiling temperature is less than 580 DEG C, it is advantageous in securing strength but the ductility is drastically lowered. On the other hand, when the coiling temperature exceeds 620 占 폚, there is a problem that extraneous crystal grain growth and excessive crystal grain growth cause moldability and strength deterioration.

When the cooling rate is less than 50 DEG C / sec, it is difficult to secure sufficient strength and toughness. Conversely, when the cooling rate exceeds 80 DEG C / sec, cooling control is difficult, and excessive cooling may adversely affect the shape of the steel sheet.

Cold rolling

In the cold rolling step (S130), the rolled sheet is subjected to pickling treatment by uncoiling, followed by cold rolling. At this time, the pickling is carried out for the purpose of removing the scale of the rolled plate, that is, the hot-rolled coil produced through the hot rolling process.

In this case, it is preferable that the cold rolled sheet is subjected to cold rolling at a cold rolling reduction rate of 60 to 80%. When the cold rolling reduction is less than 60%, the deformation effect of the hot-rolled steel is small. On the other hand, when the cold rolling reduction ratio exceeds 80%, not only the cost required for cold rolling increases, but also drawability is hindered and cracks are generated at the edges of the steel sheet, which may cause the steel sheet to break.

Annealing heat treatment

In the annealing heat treatment step (S140), the cold-rolled sheet material is annealed at 720 to 850 ° C.

At this time, the annealing heat treatment is performed in a continuous annealing line including an SS (Soaking Section) section for performing annealing, a RQS (Roll Quenching Section) section for performing cooling, and an OAS (Over Aging Section) .

That is, the cold-rolled sheet is heated to 720 to 850 ° C at 10 to 20 ° C / sec in the SS section of the continuous annealing line, annealed for 100 to 110 seconds, and then annealed in the RQS section, / sec to 480 ~ 540 ℃, and the plate cooled in the OAS section is subjected to overheat treatment at a temperature of 460 ~ 540 ℃ for 100 ~ 200 seconds.

At this time, if the annealing heat treatment temperature is less than 700 占 폚 or the continuous annealing time is less than 100 seconds, there is a problem that the ductility is lowered. Conversely, if the annealing heat treatment temperature exceeds 820 占 폚 or the continuous annealing time exceeds 110 seconds, the physical properties of the steel sheet may be deteriorated due to an increase in the austenite grain size.

At this time, if the annealing heat treatment temperature is less than 720 占 폚 or the continuous annealing time is less than 100 seconds, the ferrite recrystallization is not smoothly performed, and the ductility after hot stamping is deteriorated. On the contrary, when the annealing heat treatment temperature exceeds 850 占 폚 or the continuous annealing time exceeds 110 seconds, there is a problem that the strength is lowered after hot stamping due to an increase in the grain size in the annealing heat treatment process.

If the cooling termination temperature in the RQS section is less than 480 DEG C, the problem of material unevenness may occur. Conversely, if the cooling termination temperature in the RQS section exceeds 540 占 폚, the austenite may transform into ferrite and bainite during the cooling process.

On the other hand, in the OAS section, it is preferable to maintain the temperature at 460 to 540 DEG C for 100 to 200 seconds. In the over aging section, when the temperature is maintained at a temperature lower than 460 DEG C, or when the temperature is maintained at less than 100 seconds, there is a problem that the yield ratio increases. On the other hand, if the temperature exceeds 540 占 폚 in the overfeed condition, or if it exceeds 200 seconds, the elongation rate is rapidly lowered.

Hot stamping

In the hot stamping step (S150), the hot-stamped plate material is hot stamped to produce hot stamping parts.

At this time, the hot stamping step (S150) includes a step of cutting the annealed heat-treated plate to form a blank, heating the blank at 930 占 폚 to 20 占 폚 for 200 to 300 seconds, cooling the heated blank by air, And a step of hot-stamping the blank transferred into the press mold and cooling the press mold in a closed state.

The blank can be cut to fit the mold shape. At this time, the blank can be manufactured by laser welding the same type of blank in a butt manner, or by laser welding the blanks of dissimilar materials having different thicknesses and different thicknesses in a butt manner.

Particularly, when the blanks of different materials are laser welded by the butt-welding method, the steel material proposed in the present invention is used as the impact absorbing portion, and the impact supporting portion is formed by hot stamping, and the final microstructure is 1200 to 1500 MPa It is preferable to use a steel material having a tensile strength.

At this time, if the blank heat treatment temperature is less than 910 占 폚 or the blank heat treatment time is less than 200 seconds, it may be difficult to secure the target strength after hot stamping. On the other hand, when the blank heat treatment temperature exceeds 950 占 폚 or the blank heat treatment time exceeds 300 seconds, the austenite crystal grains grow excessively and the strength after hot stamping is lowered.

Further, since the interior of the mold maintains a high temperature immediately after the hot stamping molding, when the hot stamping molding is performed and then the component is cooled immediately after the hot stamping molding, problems such as material property and shape may be deformed. Therefore, it is preferable to pressurize the mold while the press mold is closed and cool it in the mold.

In particular, it is preferable that the heated blank is air-cooled for 8 to 10 seconds and then transferred to a press mold, which leads to smooth separation of ferrite and austenite phase during transfer, thereby minimizing occurrence of material deviation . Although not shown in the drawings, the press mold may be provided with a cooling channel through which the refrigerant circulates. It is possible to quickly quench the heated blank by circulation by the refrigerant supplied through the provided cooling channel.

At this time, in order to prevent the spring back phenomenon of the blank and maintain a desired shape, it is preferable to perform quenching while pressurizing while pressing the press mold.

In particular, it is preferable that the cooling in the closed press mold is performed at a cooling rate of 40 to 60 DEG C / sec and cooled to 200 DEG C or less. If the cooling rate exceeds 60 ° C / sec, it is advantageous in terms of securing strength but it may be difficult to secure the desired elongation. Conversely, if the cooling rate is less than 40 DEG C / sec, it may be difficult to ensure high strength.

In the hot stamping part manufactured in the above steps S110 to S150, titanium (Ti) is added for grain refinement. Aluminum (Al) is added for the ferrite and austenite phase separation during the feeding time during the hot- The elongation and collision performance can be improved while minimizing the material deviation.

Therefore, the hot stamping parts manufactured by the method according to the present invention have a tensile strength (TS) of 700 to 850 MPa, a yield strength (YS) of 550 to 750 MPa and an elongation (EL) of 10 to 25% And is also suitable for use as an impact absorbing portion of the impact member.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Preparation of specimens

Specimens according to Examples 1 to 4 and Comparative Examples 1 and 2 were prepared with the composition shown in Table 1 and the process conditions shown in Table 2.

[Table 1] (unit:% by weight)

[Table 2]

2. Evaluation of mechanical properties

Table 3 shows evaluation results of mechanical properties of the specimens prepared according to Examples 1 to 4 and Comparative Examples 1 and 2 and the results thereof.

[Table 3]

Tensile strength (TS): 700 to 850 MPa, yield strength (YS): 550 to 750 MPa and elongation (EL) corresponding to the target values in the case of the specimens according to Examples 1 to 4 are shown in Tables 1 to 3, And 10 to 25%, respectively.

Particularly, in the case of the specimens according to Examples 1 to 4, the deviation of the tensile strength (TS) at the 1 / 2t point corresponding to the thickness center portion and the tensile strength (TS) value at the 1 / 4t point corresponding to the surface portion is 50 MPa or less As shown in Fig.

On the other hand, in the case of the specimens according to Comparative Examples 1 and 2, the elongation (EL) was less than the target value while the tensile strength (TS) was increased as compared with Examples 1 to 4. In the case of the specimens according to Comparative Examples 1 and 2, the deviation of the tensile strength (TS) at 1 / 2t corresponding to the center of thickness and the tensile strength (TS) at 1 / 4t corresponding to the surface portion was 50 MPa It is confirmed that the material deviation is excessive.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

S110: Hot rolling step
S120: cooling / winding step
S130: Cold rolling step
S140: annealing heat treatment step
S150: Hot stamping step

Claims (7)

(a) 0.04 to 0.10% of C, more than 0.07% of Si, not more than 0.07% of Mn, 1.0 to 1.6% of Mn, more than 0 to 0.02% of P, (Finishing Delivery Temperature): 860 to 900 占 폚; a hot rolled slab plate consisting of 0.04 to 0.08% of Ti, 0.05 to 0.40% of Mo and 0.05 to 0.40% of Mo and the balance of Fe and unavoidable impurities;
(b) cooling the finished hot rolled plate by cooling to a CT (Coiling Temperature) of 580 to 620 캜;
(c) uncoiling and pickling the rolled sheet material, followed by cold rolling;
(d) annealing the cold-rolled sheet material at 720 to 850 ° C; And
(e) hot stamping the annealed sheet material. < RTI ID = 0.0 > 11. < / RTI >
The method according to claim 1,
The step (e)
(e-1) cutting the annealed heat-treated plate material to form a blank;
(e-2) heating the blank at 930 占 폚 to 200 占 폚 to 300 seconds;
(e-3) air-cooling the heated blank and transferring the blank to a press mold,
(e-4) hot-stamping the blank transferred into the press die, and cooling the press die in a closed state.
3. The method of claim 2,
In the step (e-3)
The air-
Wherein the heat treatment is performed for 8 to 12 seconds.
3. The method of claim 2,
In the step (e-4)
The cooling
At a speed of 40 to 60 DEG C / sec.
P: more than 0 and not more than 0.02%, S: more than 0 and not more than 0.003%, Al: 0.01 to 0.60%, Ti: not more than 0.07% : 0.04 to 0.08%, Mo: 0.05 to 0.40%, and the balance of iron (Fe) and unavoidable impurities,
Wherein the final microstructure has a composite structure including ferrite and martensite, wherein the martensite structure has a cross-sectional area ratio of 40 to 60%.
6. The method of claim 5,
The hot stamping component
A tensile strength (TS) of 700 to 850 MPa, a yield strength (YS) of 550 to 750 MPa and an elongation (EL) of 10 to 25%.
6. The method of claim 5,
The hot stamping component
Wherein the deviation of the tensile strength (TS) at the 1 / 2t point and the tensile strength (TS) at the 1 / 4t point indicates 50 MPa or less.

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