KR20150049724A - method of determining formablity of high strength steel - Google Patents

method of determining formablity of high strength steel Download PDF

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Publication number
KR20150049724A
KR20150049724A KR1020130130620A KR20130130620A KR20150049724A KR 20150049724 A KR20150049724 A KR 20150049724A KR 1020130130620 A KR1020130130620 A KR 1020130130620A KR 20130130620 A KR20130130620 A KR 20130130620A KR 20150049724 A KR20150049724 A KR 20150049724A
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KR
South Korea
Prior art keywords
steel sheet
sheet material
press
formability
thickness reduction
Prior art date
Application number
KR1020130130620A
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Korean (ko)
Inventor
김병주
Original Assignee
현대모비스 주식회사
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Priority to KR1020130130620A priority Critical patent/KR20150049724A/en
Publication of KR20150049724A publication Critical patent/KR20150049724A/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
    • G01B21/32—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring the deformation in a solid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0014—Type of force applied
    • G01N2203/0016—Tensile or compressive
    • G01N2203/0017—Tensile

Abstract

In the method for determining the formability of a high-strength steel material according to an embodiment, first, a steel sheet material as a target specimen is prepared. The steel sheet material is broken by applying a tensile force to each of the steel sheet materials, and the thickness reduction ratio of the steel sheet material to the breaking is measured. The steel sheet material is press-formed according to the press angle of the metal mold, and the thickness reduction rate of the steel sheet material reaching the forming threshold value is measured. The correlation between the thickness reduction rate at the time of the tensile test and the thickness reduction rate at the time of the press molding is data and the formability at the press process is judged based on the formability at the time of the tensile test.

Description

[0001] The present invention relates to a method of determining the formability of high strength steels,

The present invention relates to a method of determining the formability of a high-strength steel material, and more particularly, to a method of determining the formability of a high-strength steel material subjected to a pressing process.

The high-strength steel material, specifically, the high-strength steel sheet, can be molded and formed into various parts including automobile parts by a press method. However, when the press method is carried out, the high-strength steel material may cause problems such as tearing or wrinkling of the material due to lack of moldability of the material. Fig. 1 is a view schematically showing defects occurring in a high-strength steel sheet when a conventional press method is carried out. Referring to FIG. 1, it can be seen that a burst 101 or wrinkle 102 occurs in the high-strength steel sheet due to a kind of burr-like problem.

In order to prevent such a problem, conventionally, the tensile / work hardening index (n-value) and the plastic strain (r-value) of the high strength steel are obtained and the moldability analyzing mechanism is simulated using this, Respectively. However, with such an analysis prediction, it is difficult to effectively prevent the phenomenon of material break 101 or wrinkle 102 occurring in an actual pressing process. Therefore, there is a demand for a new method that can previously evaluate the molding stability of the press-formed portion in place of the conventional analysis mechanism.

An object of the present invention is to provide a method of predicting the formability of a high-strength steel material when proceeding with a press method.

In the method for determining the formability of a high-strength steel material according to an aspect of the present invention, first, a steel sheet material as a target specimen is prepared. The steel sheet material is fractured by applying a tensile force, and the thickness reduction rate of the steel sheet material that reaches the fracture is measured. The steel sheet material is press-formed according to the press angle of the metal mold, and the thickness reduction rate of the steel sheet material reaching the forming threshold value is measured. The correlation between the thickness reduction rate at the time of the tensile test and the thickness reduction rate at the time of the press molding is data and the formability at the press process is judged based on the formability at the time of the tensile test.

In one embodiment, the step of breaking the steel sheet material by applying a tensile force may include breaking the steel sheet material having different rolling directions with respect to the crystal grain direction using the tensile force.

In another embodiment, the rolling direction may be 45 [deg.], 90 [deg.] And 180 [deg.] With respect to the orientation of the crystal grains.

In another embodiment, the mold angle of the mold may be 45 °, 90 °, and 180 ° with one side of the mold.

In yet another embodiment, the step of determining the formability of the press process on the basis of the formability at the time of the tensile test includes a step of data of the tensile test result of the steel material by the thickness and the thickness reduction rate ; Data of press molding test results of the steel sheet material by thickness, rolling direction, and thickness reduction rate by press angle; And matching the results of the tensile test and the results of the press molding test to each other at the same thickness and the same thickness reduction rate for the steel sheet material in the same rolling direction.

In yet another embodiment, the step of determining the formability at the pressing step based on the formability at the time of the tensile test may include using the thickness reduction rate results of steps (b) and (c) And predicting a critical press angle in a press process of the steel sheet material.

According to the present invention, a tensile test and a press forming test are respectively performed on a high-strength steel material, and the results are compared with each other, and the correlation between the tensile test result and the press forming test can be data. Thereafter, even if the press forming test is not directly conducted, the formability of the target high strength steel can be predicted effectively in advance.

Fig. 1 is a view schematically showing defects occurring in a high-strength steel sheet when a conventional press method is carried out.
2 is a flowchart schematically showing a method of determining the formability of a high-strength steel material according to an embodiment of the present invention.
3 is a view showing a high-strength steel sheet material according to an embodiment of the present invention.
4 is a schematic representation of a tensile test according to an embodiment of the present invention.
5 is a view schematically showing a press forming test according to an embodiment of the present invention.

One embodiment of a method for determining the formability of a high strength steel material according to the present invention will now be described. The following terms are defined in consideration of the functions of the present invention, which may vary depending on the intentions or customs of the user, the operator. Therefore, definitions of these terms should be made based on the contents throughout this specification.

2 is a flowchart schematically showing a method of determining the formability of a high-strength steel material according to an embodiment of the present invention. 3 is a view showing a high-strength steel sheet material according to an embodiment of the present invention. 4 is a schematic representation of a tensile test according to an embodiment of the present invention. 5 is a view schematically showing a press forming test according to an embodiment of the present invention.

Referring to FIG. 2, in step 210, a steel sheet material is prepared as a target specimen. Specifically, as shown in FIG. 3, a plurality of steel sheet materials 310, 320, and 330 rolled at various angles with respect to the array direction of the crystal grains 310a, 320a, and 330a in the steel sheet material are prepared. As shown in the figure, the steel sheet material is composed of a first steel sheet 310 having a direction perpendicular to the long axis of the crystal grain 310a and a rolling direction of 45 °, a direction perpendicular to the long axis of the crystal grain 320a, A second steel sheet material 320 having a rolling direction of 90 ° and a third steel sheet material 330 having a direction perpendicular to the longitudinal axis of the crystal grain 330a and a rolling direction of 180 ° (or 0 °). Although the steel sheet materials having angles of 45 °, 90 °, and 180 ° are illustrated in the drawings, the present invention is not limited thereto, and various numbers of steel sheet materials having various angles may be applied.

The steel sheet material may be prepared as a plurality of steel sheet materials having various thicknesses. For example, the steel sheet material may be prepared as a steel sheet having a thickness of 2 mm, 3 mm, or 4 mm, but the present invention is not limited thereto. A plurality of steel sheets having different thicknesses may be prepared.

In step 220, the steel sheet material is fractured by applying a tensile force, and the thickness reduction rate of the steel sheet material to the fracture is measured. Specifically, as shown in FIG. 4, tensile testing is performed on the steel sheet materials having various thicknesses and various rolling directions shown in FIG. 3, and the thickness reduction rate of the steel sheet material until the fracture is measured. The thickness reduction rate can be calculated from the thickness reduction (Rt) of the steel sheet material in the direction perpendicular to the direction of applying the tensile force (Ft) to the steel sheet material.

As an example, the thickness reduction ratio can be calculated as a ratio of the difference between the initial thickness and the final thickness divided by the initial thickness before and after the tensile test.

In step 230, the steel sheet material is press-formed according to the press angle of the metal mold, and the thickness reduction rate of the steel sheet material reaching the forming threshold value is measured. Specifically, as shown in FIG. 5, the steel sheet material 520 is disposed between the upper and lower parts of the metal mold 510. The press angle of the mold 510 is set at various angles. For example, the first mold 510a, the second mold 510b, and the third mold 510c can be set to 90 °, 120 °, and 180 °, respectively. That is, the press angle of the mold may be defined as an angle formed by one side surface and one side surface of the molds 510a, 510b, and 510c.

In this step, the press forming may proceed to reach a forming threshold at which the steel sheet material is broken. At this time, the thickness reduction rate when the forming threshold is reached is measured. The thickness reduction rate can be calculated, for example, as a ratio of (initial thickness - final thickness) / initial thickness before and after the press forming test.

In step 240, the correlation between the thickness reduction rate in step 220 and the thickness reduction rate in step 230 is calculated. Then, the formability at the time of the pressing step is judged based on the formability at the time of the tensile test.

The following Tables 1 and 2 are the results of the tensile test and the press forming test proceeding from Step 210 to Step 230 according to an embodiment of the present invention. Specifically, Table 1 shows the results of the tensile test according to Step 220, and Table 2 shows the results of the press forming test according to Step 230. [

Material thickness (mm) Rolling direction (°) Thickness reduction ratio (%) 2.0t

45 15 90 10 180 20 3.0t

45 10 90 20 180 20 4.0t

45 10 90 20 180 25

Material thickness (mm) Rolling direction (°) Press angle (°) Thickness reduction ratio (%) 2.0t

180





160 5 120 15 90 30 3.0t

160 10 120 20 90 35 4.0t

160 15 120 25 90 40

Referring to Table 1, the tensile test results of the steel sheet material are converted into data by the thickness reduction ratio and the thickness reduction ratio by the rolling direction. Referring to Table 2, the press molding test results of the steel sheet material are dataized by thickness, rolling direction, and thickness reduction rate by press angle.

In step 240, the tensile test result and the press-formed test result may be matched to each other with the same thickness reduction ratio for the steel sheet material of the same thickness and the same rolling direction. As an example, in Table 1, the steel sheet material showing a 25% thickness reduction rate until the fracture at the time of the tensile test when the material thickness is 4.0t and the rolling direction is 180 ° is shown in Table 2 as a result of the press molding test, Can be matched to the result when the press forming is carried out in the mold having the mold.

In other words, a 25% thickness reduction rate condition at the time of tensile test of the steel sheet material corresponds to a processing condition of a press angle of 120 deg. When the steel sheet material is press-formed. Further, referring to Table 2, in the case of 160 ° which exceeds the pressing angle of 120 °, the reduction rate of the thickness until fracture is only 15%, and before the thickness reduction by 25% Can be expected to break. That is, it can be judged that the steel sheet material having a 25% thickness reduction rate in the tensile test should be subjected to a molding process in a die having a pressing angle of 120 ° or less.

As described above, the threshold pressure angle at the time of press processing of the steel sheet material can be easily predicted by using the result of the thickness reduction rate at the time of tensile test on the steel sheet material and the result of the thickness reduction rate at the press molding test.

As described above, in the embodiment of the present invention, the tensile test and the press forming test are respectively conducted on the high-strength steel sheet material, and the result of the thickness reduction rate can be obtained. Thereafter, even if the press forming test is not directly conducted, the formability of the target high strength steel can be predicted effectively in advance.

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 . In addition, the above-described rolling apparatus is only one embodiment, and the technical idea of the present invention can be applied to other rolling apparatuses. Accordingly, the true scope of the present invention should be determined by the following claims.

101: Breaking of steel 102: Crease of steel
310, 320, 330: Steel sheet material 510, 510a, 510b, 510c:

Claims (6)

(a) preparing a steel sheet material as a target specimen;
(b) breaking the steel sheet by applying a tensile force, and measuring a thickness reduction ratio of the steel sheet to the breaking;
(c) press molding the steel sheet material according to the press angle of the metal mold, and measuring a thickness reduction rate of the steel sheet material to a forming threshold value; And
(d) calculating the correlation between the thickness reduction rate in the step (b) and the thickness reduction rate in the step (c), and determining the formability in the press process based on the formability at the time of the tensile test
Determination of formability of high strength steels.
The method according to claim 1,
(b)
And breaking the steel sheet material having different rolling directions with respect to the crystal grain direction using the tensile force
Determination of formability of high strength steels.
3. The method of claim 2,
Wherein the rolling direction is 45 DEG, 90 DEG and 180 DEG with respect to the direction of the crystal grains
Determination of formability of high strength steels.
The method according to claim 1,
In the step (c)
The press angle of the mold is such that angles formed by one side surface and one side surface of the mold are 45 deg., 90 deg., And 180 deg.
Determination of formability of high strength steels.
The method according to claim 1,
(d)
(d1) data of the tensile test results of the steel sheet material in the step (b) in terms of the thickness and the rolling direction in the rolling direction;
(d2) data of the press forming test results of the steel sheet material in the step (c) in terms of thickness, rolling direction, and thickness reduction rate by press angle; And
(d3) matching the results of the tensile test and the results of the press-molding test to each other at the same thickness and the same thickness reduction rate for the steel sheet material in the same rolling direction
Determination of formability of high strength steels.
The method according to claim 1,
(d)
And predicting a critical press angle in a press process of the steel sheet material by using the results of the thickness reduction rates of steps (b) and (c) for the steel sheet material
Determination of formability of high strength steels.


KR1020130130620A 2013-10-30 2013-10-30 method of determining formablity of high strength steel KR20150049724A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108279165A (en) * 2018-04-03 2018-07-13 苏州拓博机械设备有限公司 A kind of multi-angle tensile testing machine

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108279165A (en) * 2018-04-03 2018-07-13 苏州拓博机械设备有限公司 A kind of multi-angle tensile testing machine
CN108279165B (en) * 2018-04-03 2023-11-24 拓博试验设备技术(苏州)有限公司 Multi-angle tensile testing machine

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