KR101377487B1 - Method for manufacturing steel product using warm press forming - Google Patents

Abstract

Disclosed is a method for manufacturing a steel product using warm press molding, which can prevent a decrease in press die life and can produce a steel product excellent in strength, toughness and corrosion resistance.
Method for producing a steel product using warm press molding according to the present invention comprises the steps of (a) heating the steel to a molding temperature range of recrystallization temperature to Ac3 temperature; (b) forming the heated steel at the molding temperature to form a molded body; And (c) cooling the formed body.

Description

Method for manufacturing steel products using warm press molding {METHOD FOR MANUFACTURING STEEL PRODUCT USING WARM PRESS FORMING}

TECHNICAL FIELD The present invention relates to a steel product manufacturing technology, and more particularly, to a method that can produce a steel product excellent in strength, toughness and corrosion resistance using warm press molding.

In the era of high oil prices, much efforts have been made to reduce the weight of components such as the body in the automobile industry. As a part of this effort, recently, a component having an ultra-high strength of 980 MPa or more in tensile strength has been developed.

Ultra-high strength automotive parts having a tensile strength of 980 MPa or more are mainly used at room temperature press molding or hot stamping.

The room temperature press molding method is a technique for press molding steel materials having a tensile strength of 980 MPa or more at room temperature.

In the press molding method of the normal temperature, the mold may be prematurely worn or damaged due to the high yield strength of the steel, and there are problems of low forming rate and severe spring back after molding.

On the other hand, the hot stamping method is to heat the steel having a tensile strength of about 980MPa to 900 ~ 950 ℃ corresponding to the Ac3 temperature or more to create austenite phase, and then quenched at the same time to form martensite phase to make ultra high strength steel It is a technology that can manufacture a product.

Such a hot stamping method can solve the problems of the above-mentioned press molding method of normal temperature, but there is a problem in that energy consumption is large when heating is required because high temperature heating is required at about 900 to 950 ° C.

In addition, in the case of hot stamping, the elongation at break in the tensile test is low at a level of 6 to 10% due to brittleness of the martensite phase formed by quenching.

In addition, in the case of the hot stamping method, since the steel sheet must be heated to a high temperature of about 900 ~ 950 ℃, it is difficult to apply a galvanized steel or galvanized steel which has a vaporization problem at the temperature, Al-Si-based plating steel is mainly applied It is becoming.

A background art related to the present invention is Korean Patent Laid-Open Publication No. 10-2010-0037854 (Apr. 12, 2010). The above document discloses a method for manufacturing a steel forming body and a steel forming body manufactured using the same.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a steel product which can solve a mold life problem, a low mold rate and springback phenomenon, and a low elongation at break and a plated layer vaporization problem, which are a problem when applying a conventional room temperature press molding. To provide.

Through this, an object of the present invention is to provide a method for producing a steel product excellent in strength, toughness and corrosion resistance.

Steel product manufacturing method using a warm press molding according to an embodiment of the present invention for achieving the above object comprises the steps of (a) heating the steel to a molding temperature range of recrystallization temperature to Ac3 temperature; (b) forming the heated steel at the molding temperature to form a molded body; And (c) cooling the formed body.

In this case, the steel material may be one containing a microstructure of martensite, residual austenite and bainite. In this case, the steel may be used having a tensile strength of 980 MPa or more. In addition, the steel material may be one that is formed with a plated layer containing zinc on the surface.

In addition, the step (a) is preferably heating the steel to 450 ~ 700 ℃. In addition, the step (a) is maintained after the steel heating, the molding temperature, the heating and maintenance of the steel is preferably carried out for 10 to 150 seconds.

In addition, the steps (b) and (c) may be performed inside the press mold including the cooling means.

In addition, the step (c) is preferably carried out at an average cooling rate of 10 ~ 200 ℃ / sec. In this case, in the step (c), the molded body may be locally cooled so that the tensile strength of a part of the steel product to be manufactured is 980 MPa or more. In addition, in the step (c), the entire molded body may be cooled such that the tensile strength of all the steel products to be manufactured may be 980 MPa or more.

In the method of manufacturing steel products using the warm press molding according to the present invention, the steel is heated to a temperature above the recrystallization temperature or higher than the Ac3 temperature, and then maintained for a certain time to maintain mechanical properties such as low yield strength, high elongation and work hardening index. Can be satisfied.

Therefore, the steel product manufacturing method using the warm press molding according to the present invention can solve the problems of using the conventional room temperature press molding, the problems of using the hot stamping method, and accordingly the steel products excellent in strength and toughness It can manufacture.

In addition, in the method of manufacturing steel products using warm press molding according to the present invention, the molding temperature is lower than the vaporization temperature of the zinc plated layer or the zinc alloyed layer. Therefore, even when the plating material containing zinc, such as a temperature zinc plating layer, is formed in steel materials, vaporization of a plating layer at the time of heating and shaping | molding can be prevented, and corrosion resistance can be maintained as it is after shaping | molding.

1 is a flow chart schematically showing a method for manufacturing steel products using warm press molding according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments and drawings described in detail below.

However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.

Hereinafter, a steel product manufacturing method using warm press molding according to the present invention will be described in detail.

1 is a flow chart schematically showing a method for manufacturing steel products using warm press molding according to an embodiment of the present invention.

Referring to FIG. 1, the illustrated steel product manufacturing method includes a steel heating step S110, a warm press forming step S120, and a cooling step S130.

In the steel heating step (S110), the steel to be formed is heated to a predetermined molding temperature. The heating may be a variety of methods such as induction heating method or heating method.

The heating temperature, that is, the molding temperature is preferably in the range of recrystallization temperature to Ac3 temperature, more preferably 450 to 700 ° C. When the molding temperature is less than the recrystallization temperature, the yield strength reduction, the elongation increase, and the like required for molding are not sufficient. On the contrary, when the molding temperature exceeds the Ac3 temperature, energy consumption for heating the steel is high, and there is a problem in that the toughness of the steel product to be manufactured is lowered.

On the other hand, it is preferable to use what contains hard microstructures, such as martensite, residual austenite, and bainite, as steel materials to be formed. Furthermore, it is more preferable to use what has the tensile strength of 980 Mpa or more including the said hard microstructure as a steel material to be shape | molded.

In the case of hot stamping, the austenitic phase is formed by heating to approximately 900 to 950 ° C., and then martensite phase is formed by quenching at the same time of forming, thereby easily securing tensile strength of 980 MPa or more even if the tensile strength of the steel before heating is rather low. can do.

However, in the case of warm press molding according to the present invention, the heating temperature is relatively low compared to hot stamping. Therefore, it is difficult for the tensile strength to rise rapidly even after cooling after molding. Therefore, it is preferable to use what consists of hard structures, such as martensite, as a steel material to be shape | molded previously, and it is more preferable to use what has a tensile strength of 980 Mpa or more before heating.

In addition, any steel material to be formed may be applied to any of hot rolled steel sheet, hot rolled steel sheet, cold rolled steel sheet, cold rolled steel sheet.

Further, the steel to be formed can be used to improve the corrosion resistance, a plated layer containing zinc, that is, a galvanized layer or zinc alloyed layer formed on the surface. This is because the heating temperature is lower than approximately 903 ° C. which is the vaporization temperature of the galvanized layer or the like, so that the galvanized layer or the like can be maintained even after molding.

For this reason, even if steel products are manufactured by the method according to the present invention, there is an effect that can maintain the corrosion resistance as it is.

Next, in the warm press forming step (S120), the heated steel is molded to form a molded body.

In the present invention, the molding temperature is in the range of recrystallization temperature to Ac3 temperature as described above.

In the case of hot stamping, molding is performed at a high temperature of about 900 to 950 ° C., with a sufficient austenite phase generated by heating. However, in the present invention, since the molding is performed at a relatively low temperature, it is preferable to sufficiently induce recrystallization when heating the steel.

To this end, after the steel heating in the above-described steel heating step (S110), it is preferable to induce a sufficient recrystallization of the steel by maintaining a predetermined time at the heated temperature, that is, the molding temperature, and then perform a warm press molding.

At this time, the total heating time including the holding time is preferably 10 to 150 seconds. Of course, in the case of heating the steel up to the molding temperature, the holding process is omitted, and in this case, the total heating time is preferably 10 to 150 seconds. If the total heating time is less than 10 seconds, it may be difficult to induce sufficient recrystallization of the steel. Conversely, if the total heating time exceeds 150 seconds, it may be difficult to produce steel products with a tensile strength of 980 MPa or more after cooling due to excessive ferrite transformation.

However, in the case where the plated layer including zinc is formed in the steel, when the rapid heating to the molding temperature is excessively, melting of the plated layer (melting) may be a problem. Therefore, in this case, it is necessary to adjust the temperature increase time so that the melting of the plating layer does not occur, and it can be suggested that the temperature is raised to a molding temperature of about 5 seconds or more.

Next, in the cooling step (S130), the molded body is cooled from the molding temperature at a predetermined cooling rate.

At this time, the cooling is preferably carried out at an average cooling rate of 10 ~ 200 ℃ / sec.

If the average cooling rate is less than 10 ° C / sec, it is difficult to secure the tensile strength of 980 MPa or more of the steel product to be manufactured. Conversely, when the average cooling rate exceeds 200 ° C / sec, there is a problem that the toughness of the steel product to be produced is lowered.

On the other hand, in the cooling step (S130), the molded body can be locally cooled so that the tensile strength of a part of the steel product to be manufactured is 980 MPa or more. The locally cooled portion may be a high strength portion, and the other portion may be a high toughness portion. Therefore, when such a local cooling method is applied, it is possible to produce a steel product having a heterogeneous strength using the same steel.

Of course, in the cooling step (S130), the entire molded body can be cooled so that the tensile strength of all the steel products to be manufactured is 980 MPa or more.

On the other hand, the warm press forming step (S120) and the cooling step (S130) may be carried out inside the press mold including the cooling means. Warm press molding and cooling can be performed together inside the press die to solve problems such as spring back.

In addition, it is possible to easily secure the desired microstructure and mechanical properties by adjusting the cooling rate in the press die.

Steel products may be manufactured through the processes S110 to S130, and a post-treatment process such as trimming and piercing using laser processing may be further performed as necessary.

As described above, the steel product manufacturing method using the warm press molding according to the present invention can solve the problem when the conventional room temperature press molding or hot stamping method is applied to the steel by using the warm press molding, according to the strength and Steel products with excellent toughness can be produced.

In addition, in the steel product manufacturing method using the warm press molding according to the present invention, heating is performed to a temperature lower than the vaporization temperature of the galvanized layer, and press molding is performed at a temperature lower than the vaporization temperature of the galvanized layer. Therefore, even when the temperature zinc plating layer etc. are formed in steel materials, vaporization of the plating layer at the time of heating and shaping | molding can be prevented, and corrosion resistance can be maintained as it is after shaping | molding.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. I will understand.

Accordingly, the true scope of protection of the present invention should be defined by the following claims.

S110: Steel Heating Steps
S120: Warm Press Forming Step
S130: cooling step

Claims (10)

delete delete (a) A steel having a tensile strength of at least 980 MPa comprising at least one microstructure of martensite, residual austenite and bainite is heated to 450-700 ° C. and maintained at 450-700 ° C., inducing sufficient recrystallization of the steel. Performing heating and maintenance of the steel for 10 to 150 seconds while preventing excessive ferrite transformation;
(b) forming a molded body by molding the heated steel at 450 to 700 ° C. in a press mold including cooling means; And
(c) cooling the molded body in the press mold at an average cooling rate of 10 to 200 ° C./sec, and locally cooling the molded body so that the tensile strength of a part of the steel product to be manufactured is 980 MPa or more, or all of the manufactured steel products Cooling the entire molded body so that the tensile strength of 980MPa or more; steel product manufacturing method using a warm press molding comprising a.
The method of claim 3,
The steel
A method for manufacturing steel products using warm press molding, wherein a plated layer containing zinc is formed on a surface thereof. delete delete delete delete delete delete

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