JPH06534A - Ultra high-tension electric resistance-welded tube excellent in bending characteristic - Google Patents

Abstract

PURPOSE:To provide an ultra high-tension electric resistance welded tube excellent in tensile strength and bending characteristic which is used as reinforcing material for an automobile door. CONSTITUTION:When, in a square shape steel tube, the thickness (t) is given, the height does not exceed 20t, the width H does not exceed 11t and the corner radius R is set to (1.5-5.0)t, when, in a trapezoidal shape steel tube, the thickness (t) is given, the height V does not exceed 20t, the width HU of the upside does not exceed 11t, the width HL of the base does not exceed 15t and the corner radius R is set to (1.5-5.0)t, and when, in a triangular shape steel tube, the thickness (t) is given, the height V does not exceed 20t, the width H of the base does not exceed 18t and the corner radius R is set to (1.5-5.0)t. In this way, the shape tubes can be improved in bending characteristic and saved in weight as compared with a circular tube. Further, since generation of buckling can be prevented, distortion generated at the time of bending can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-high-strength electric resistance welded steel pipe used for structural members of automobiles, etc., in particular, an ultra-high-strength electric resistance welded pipe having a tensile strength of 150 kgf / mm ² or more for door reinforcement and having excellent bending characteristics. Regarding steel pipes.

[0002]

2. Description of the Related Art Regarding structural members such as automobiles, thorough weight reduction is being considered to improve fuel efficiency and environmental measures, and 150 kgf / mm for some members is one of the measures to achieve compatibility with safety. More than ² ultra high strength steel pipes are being adopted.

As a steel pipe material for reinforcing automobile doors, a method of tempering after electric resistance welding, that is, quenching or quenching and tempering, as described in JP-A-3-122219, etc. Although a method of normalizing a predetermined low alloy steel such as Japanese Patent Laid-Open No. 3-140441 is generally used, the cross-sectional shape of each is a round steel pipe.

[0004]

FIG. 4 is a diagram showing the results of an examination of the displacement and load characteristics of the punch during three-point bending of a conventional round steel pipe having an outer diameter of 31.8 mm and a wall thickness of 2.6 mm by the method of FIG. 2 shows. As described above, in the conventional round steel pipe, under bending conditions where the span L is short, buckling (local depression) of the steel pipe occurs immediately below the punch as shown in FIG. 3, and the load decreases. Therefore, the bending energy E represented by the shaded area is smaller than that in the case where the buckling does not occur, which is disadvantageous. Moreover, since the buckling causes local deformation, the maximum strain generated is large. Ultra high-strength steel pipes of 150 kgf / mm ² or more generally have low elongation and deformability of drawing, so cracking during bending,
Breakage easily occurs.

The present invention provides an ultra-high-strength electric resistance welded steel pipe having a modified cross section of 150 kgf / mm ² or more, which is more resistant to buckling than a round steel pipe, has a large bending energy E, and has a small cross-sectional area so as to be lightweight. The purpose is to do.

[0006]

The subject matter of the present invention is as follows. (1) In a rectangular steel pipe, when the wall thickness is t, the height V is 20 t or less, the width H is 11 t or less, and the corner radius R is (1.5 to 5.0) t. Super high tensile ERW steel pipe with excellent characteristics. (2) In the trapezoidal steel pipe, when the wall thickness is t, the height V
Is 20t or less, the upper side width H _U is 11t or less, the bottom side width H _U
L is 15t or less, corner radius R is (1.5 to 5.0)
An ultra-high-strength electric resistance welded steel pipe with excellent bending characteristics, characterized in that it is t. (3) In the triangular steel pipe, when the wall thickness is t, the height V is 20t or less, the width H of the base is 18t or less, and the corner radius R is (1.5 to 5.0) t. Super high tensile ERW steel pipe with excellent bending properties.

The present invention will be described in detail below. First, the reason for limitation described in claim 1 of the present invention will be described. As with a round steel pipe, the punch load when buckling does not occur is substantially proportional to the second moment of area. Assuming that the wall thickness of the square steel pipe in FIG. 1 is t, the height V and the width H at which buckling does not occur in the bending test of FIG. 4 are investigated, and the function of the wall thickness t is shown in FIGS. 5 and 6, respectively. Become. Therefore, the height V is 20
The width H was 11t or less. Corner radius R
The smaller the radius is, the more difficult it is to buckle, but if the radius R is 1.5 t or less, cracks are likely to occur during cold working of a square tube. Therefore, the corner radius R is (1.5
.About.5.0) t.

Next, the reason for limiting the trapezoidal steel pipe according to claim 2 of the present invention will be described. As with a round steel pipe, the punch load when buckling does not occur is substantially proportional to the second moment of area. In the trapezoidal steel pipe of FIG. 1, when the bending test of FIG. 4 is performed with the upper side being the punch side, the relationship between the buckling height V of the trapezoidal steel pipe and the upper side width H _U and the wall thickness t is shown in FIGS. 5 and 6. It is almost the same as the square steel pipe shown. In addition, the non-buckling range of the bottom side _HL is 18 as shown in FIG.
It is less than or equal to t. The corner radius R is the same limiting reason as the square tube. Therefore, the height V is 20 t or less, the upper side width H _U is 11 t or less, the lower side width H _L is 18 t or less, and the corner radius R is (1.5 to 5.0) t.

Next, the reasons for limiting the triangular steel pipe according to claim 3 of the present invention will be described. As with a round steel pipe, the punch load when buckling does not occur is substantially proportional to the second moment of area. In the triangular steel pipe of FIG. 1, when the bending test of FIG. 4 is performed with the upper part on the punch side and the bottom side on the die side, the relationship between the non-buckling height V and the wall thickness t is the same as that of the rectangular steel pipe shown in FIG. is there. Further, the relationship between the width H of the bottom that does not buckle and the wall thickness t is almost the same as the case where the width H _L of the base and the wall thickness t of the trapezoidal steel pipe shown in FIG. The reason for limiting the corner radius R is the same as for the trapezoidal steel pipe. Therefore, the height V is 20t
Hereinafter, the width H of the bottom side is set to 18 t or less, and the corner radius R is set to (1.5 to 5.0) t.

[0010]

EXAMPLE The composition of the components is C by weight; 0.24%, Si;
0.25%, Mn; 2.4%, Cr; 0.5%, Mo;
0.7%, Ti: 0.03%, B: 20 ppm, balance F
It manufactured with the manufacturing process of FIG. 8 using e and the hot-rolled steel strip which is an unavoidable element.

The manufacturing dimension was an outer diameter of φ38.1 mm, and the heat treatment of the blank was air-cooled at 700 ° C. in order to soften the work-hardened part by molding and the quench-hardened part during welding almost uniformly. The cold drawing was performed by cold drawing using a die. Table 1 shows the shape, the second moment of area, and the sectional area of the examples of the present invention. Further, as a comparative material, a round steel pipe having the same height and the same second moment of area was manufactured in the same manufacturing process. In the finish heat treatment, normalization was performed at 850 ° C. in order to make the microstructure of the welded portion and the base metal portion uniform. Result of tensile test after finishing heat treatment, TS = 170kgf / mm
² , El = 10%.

FIG. 9 shows the results of punch displacement and load characteristics in the bending test of FIG. 4 for each shape. In all of the present invention, buckling does not occur and the load does not decrease, and it is superior to the round pipe in almost all displacements. as a result,
The present invention was able to make the bending energy 20 to 30% larger than that of the round tube. Further, since the deformed pipe of the present invention does not buckle, as shown in FIG. 10, the maximum equivalent plastic strain of the lower surface of the pipe immediately below the punch can be reduced to about half that of the round pipe, and necessary materials such as elongation and drawing can be obtained. This is very advantageous because the characteristics can be reduced.

An ultra-high-strength steel pipe of 150 kgf / mm ² or more cannot be made sufficiently large with an elongation of about 10% and a drawing of about 20 to 30%, but since buckling does not occur according to the present invention, cracking and breakage occur during bending. do not do. Although cold-rolled pipes were used in this example, similar deformed pipe shapes can be obtained by drawing by roll forming.

[0014]

[Table 1]

[0015]

According to the present invention, the bending characteristics can be improved and the weight can be reduced as compared with the round tube. Moreover, since buckling can be prevented, the strain generated during bending can be reduced.
Therefore, the manufacturing is easy, and the contribution to the industry such as the use of the ultra-high tensile ERW steel pipe of 150 kgf / mm ² or more can be greatly contributed to the industry.

[Brief description of drawings]

FIG. 1 is a sectional view of a rectangular, trapezoidal, or triangular steel pipe of the present invention.

[Fig. 2] Punch displacement in bending test of a conventional round tube-
The figure which shows a punch load characteristic.

FIG. 3 is a view showing a shape of a steel pipe immediately below a punch after buckling.

FIG. 4 is a front view showing a bending test method.

FIG. 5 is a diagram showing a limiting condition in which buckling of a quadrangular height V of the present invention does not occur.

FIG. 6 is a diagram showing a limiting condition for preventing buckling of a quadrangle width H of the present invention.

FIG. 7 is a diagram showing a limiting condition for preventing buckling of a width H _L of a lower side of a trapezoid of the present invention.

FIG. 8 is a diagram showing a manufacturing process of the deformed pipe of the present invention.

FIG. 9 is a diagram showing punch displacement-load characteristics in a bending test of the deformed pipe of the present invention.

FIG. 10 is a diagram comparing the maximum equivalent plastic strain of the lower part of the pipe generated during the bending test of the deformed pipe of the present invention.

Claims (3)

[Claims] 1. A rectangular steel pipe, wherein when the wall thickness is t, the height V is 20 t or less, the width H is 11 t or less, and the corner radius R is (1.5 to 5.0) t. Super high tensile ERW steel pipe with excellent bending properties. 2. In a trapezoidal steel pipe, when the wall thickness is t, the height V is 20 t or less, the width H _U of the upper side is 11 t or less,
The width H _L of the base is 15t or less, and the corner radius R is (1.5
~ 5.0) t, an ultra-high-strength electric resistance welded steel pipe with excellent bending properties. 3. In a triangular steel pipe, when the wall thickness is t, the height V is 20 t or less, the width H of the base is 18 t or less, and the corner radius R is (1.5 to 5.0) t. Ultra high tensile ERW steel pipe with excellent bending characteristics.