JPH02192835A - Manufacture of high-strength structural member of steel sheet having close contact bent part - Google Patents

Abstract

PURPOSE:To easily manufacture a structural member having a high strength by giving required close contact bending to a steel sheet through roll forming and cold-rolling sites excepting a bent part and end parts at a specific draft. CONSTITUTION:In the manufacture of a high-strength structural member of steel sheet having a close contact bent part, after or when a close contact bending is performed by a roll forming machine to a cold rolled steel sheet stock, cold rolling is performed to 10 - 30% of the unbent part (oblique line part) excepting the ends of the steel sheet. By this method, a high-strength structural member having a close contact bent part can be manufactured easily.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a high-strength structural member made of a thin steel plate having a tightly bent portion.

Conventionally (2) Thin steel plates used for manufacturing high-strength structural members having tight bending portions are required to have both contradictory properties of excellent workability that can withstand tight bending and high strength.

Conventionally, such high-strength members are formed using relatively low-strength thin steel plates with good workability, and the strength of the finished product itself is supplemented by increasing the thickness of the plate.

For example, T-bars, which are steel members used to adjust the spacing and support formwork for pouring concrete when manufacturing erosion control dams, bridge piers, retaining walls, etc., are subjected to the pressure of concrete as finished products. 2000 to support formwork
kgf is required for safety, but currently, 50 to 60 kgf is required to withstand close bending.
A thin steel plate having a tensile strength of /mmz is used as the material. However, in order to satisfy the above-mentioned safety and strength, the material plate thickness needs to be about 1.6 mm, and thus,
There are problems such as increased weight, inconvenience in transportation, and problems with workability.

Recently, some attempts have been made to achieve thinner walls by using composite structure steel sheets with excellent workability and a tensile strength of 80 to 100 kgf/mm, which are used in automobile reinforcing members, etc. However, because composite steel plates have a structure in which a hard second phase structure such as martensite is dispersed in a soft funilite base to ensure strength, uniform deformation as represented by total elongation occurs. Although it has excellent performance, in the case of local deformation such as tight bending, voids easily occur and cracks occur due to the large difference in hardness at the interface between the ferrite phase and the second phase. In this way, the composite Mim steel plate is
Its fundamental properties itself preclude its application to structural members with tight bends.

Therefore, as an improvement to composite structure steel sheets, the ratio of the second phase is increased, and in order to adjust the strength, tempering treatment is performed at a relatively high temperature to reduce the difference in hardness between the ferritic base and the second phase. Various steel plates have been proposed that have improved local deformability, or steel plates that have been tempered to have a martensite or bainite single-phase structure. , has not been obtained yet.

In order to solve the above-mentioned conventional problems in the production of high-strength structural members made of thin steel sheets having closely bent parts, the present inventors aimed to improve the workability and strength of the thin steel sheet material itself. As a result of intensive research from a standpoint different from the method for achieving both, the above problem was solved by a processing method of cold rolling after or in the middle of the close bending process.

The present invention is directed to a manufacturing method for a high-strength structural member made of a thin steel plate having a close bending portion, in which the thin steel plate is subjected to a close bending process by roll forming or in the middle of the process. It is characterized by applying 10 to 30% cold rolling to the non-bending parts excluding the ends.

That is, according to the present invention, after a thin steel plate is roll-formed or at an intermediate stage, cold rolling is applied to the non-contact bending portion excluding the edge of the plate, and the strength of the product is improved by work hardening the material. This is to ensure that

The thin steel sheet material used in the present invention is not particularly limited as long as it has workability that can withstand close bending, but it is possible to increase the strength of the portion that is not subjected to cold rolling, which will be described later. Since thin-walled materials are advantageous for close bending, it is preferable that the strength be as high as possible.

According to the method of the present invention, after a thin steel sheet is subjected to the required close bending process by roll forming, or in the middle of the process, cold rolling is performed on the parts excluding the ends of the material and the bending process part.

Figure 1 shows the hardness distribution when a cold-rolled steel plate with a tensile strength of 55 f/mm” and a thickness of 1.2 mm is closely bent. Therefore, when further cold working is applied to the close bending part, cracks easily occur.On the other hand, in the middle stage of roll forming, that is, before the close bending, the bending part is cold worked. When additional machining is applied, it is similar to closely bending a material with high strength and poor workability, and cracks easily occur.

Next, when cold working is performed at the end, for example, as shown in Figure 2, the elongation in the rolling direction is large, while the unworked part restrains the deformation of the worked part, so This should be avoided as it will cause large warping later. Therefore, according to the present invention, as shown in FIG. 3, when applying cold working to parts other than the plate ends, both ends in the axial direction of the roll restrain the deformation, so that the elongation in the rolling direction is is relatively small, and deformation progresses in the axial direction of the rolling roll, so warping is less likely to occur.

The reduction ratio in cold rolling is in the range of 10 to 30%. This is because if the rolling reduction ratio is made larger than 30%, the elongation in the rolling direction becomes excessive, resulting in a shape of so-called medium elongation or breakage. However, when the rolling reduction ratio is less than 10%, as shown in FIG. 4, the increase in strength is small and the finished product cannot have sufficient strength.

As described above, according to the method of the present invention, after a thin steel plate is subjected to the required close bending process by roll forming, or in the middle of the process, the bending process part and the edge of the thin steel plate are By applying cold rolling to the parts other than the parts at a predetermined reduction rate,
It is possible to easily manufacture a structural member having high strength while having a tightly bent portion.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way.

Using a cold-rolled steel plate with a thickness of 11 m and a tensile strength of 50 kgf/mm2 as a material, a structural member having a shape as shown in FIG. 5 was manufactured using a 12-high roll forming machine. After this roll forming, the hatched areas in the drawing were cold rolled using small rolls, and then stretched in the longitudinal direction to obtain the strength shown in Table 1.

When the reduction rate is 5% (Comparative Example 2), when cold working is not performed (
Compared to Comparative Example 1), the breaking strength did not increase by 40 kgfL, and on the other hand, when the rolling reduction was 35% (Comparative Example 5)
, the medium elongation is significant and the shape is poor.

Table 1

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the distance from the bending center and Vickers hardness when a thin steel plate is bent, and Figure 2 is an example of cold rolling the edge of a plate obtained by bending. FIG. 3 is a diagram showing an example of cold rolling a portion of a member obtained by bending, excluding the non-bending portion and the plate end portion, and FIG. 4 is a diagram showing cold rolling according to the method of the present invention. FIG. 5, which is a graph showing the relationship between rolling reduction and tensile strength during processing, is a perspective view showing an example of a structural member manufactured by the method of the present invention. Patent applicant: Kobe Steel, Ltd. Patent attorney: Ittsu Makino Department Figure 1, 4t. 20'ftcI2. OJO song I! Nakaguma, Karoha Tokikara 8 A2 Figure 2 (C1) Figure 2 (b) Figure 3 CG) Figure 3 (b)

Claims (1)

[Claims] (1) In a method for manufacturing a high-strength structural member made of a thin steel plate having close bending parts, after or in the middle of applying close bending to a thin steel plate by roll forming, the non-bent parts excluding the ends of the thin steel plate are formed. A method for producing a high-strength structural member made of a thin steel sheet, the method comprising subjecting the steel sheet to cold rolling of 10 to 30%.