JP2000017338A - Production of electroseamed steel pipe for hydroform forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel pipe in which elongation suitable for hydroform forming is secured by forming an extra low C material having a specified C content into an electroseamed steel pipe and subjecting the electroseamed weld zone to heat treatment at a specified temp. SOLUTION: An extra low C material having <=0.01 wt.% C content is formed into an electroseamed steel pipe, and the electroseamed weld zone of this electroseamed steel pipe tube is subjected to heat treatment at 600 to 850 deg.C. By using the extra low C material, the elongation of the base material part can be secured to about 50%, and by subjecting the electroseamed weld zone to heat treatment at 600 to 850 deg.C, the elongation value in the base material part and the electroseamed weld zone can be made approximately equal. Moreover, the difference in the hardness by Vickers between the electroseamed weld zone and the base material part of about 30 to 80 which is the former value can be reduced to about 10 to 20. In this way, the electroseamed steel pipe excellent in hydroform formability and furthermore small in the risk of buckling, wrinkles and rupture can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electric resistance welded steel pipe for forming a hydroform.

[0002]

2. Description of the Related Art Generally, a metal tube is formed by a hydroforming method. As shown in FIG. 1, the molding method is as follows.
The liquid is introduced into the raw tube 1 from the inside, and the internal pressure is applied, and a compressive load is applied in the axial direction of the tube by the pressing cylinders 5 and 6 from both sides to be pressed in. In the example of FIG. Is what you do. That is, examples of molding include those in which the diameter of the base tube 1 is partially enlarged, those in which the diameter is enlarged to have various cross-sectional shapes, and the like, and the obtained molded article 7 is molded into a complicated shape. It is possible. Raw tube 1 used for hydroforming method
Is required to have a uniform wall thickness. As a steel pipe to be used as the raw pipe 1, an electric resistance welded steel pipe is advantageous for automobile parts and the like. This electric resistance welded steel pipe is generally manufactured by forming a steel strip manufactured by hot rolling into a tubular shape using a cage roll or the like, and butt welding.

[0003]

The product formed by the hydroforming method must have such strength and toughness that cracking, deformation and the like do not occur in the use environment in various applications such as automobile parts. On the other hand, from the viewpoint of workability, an electric resistance welded steel tube which is easy to form by a pushing force and an internal pressure is required. However, when manufacturing ERW steel pipes, in order to achieve stability before ERW welding, it is generally performed to give high strain that plastically deforms at the forming stage before welding. . The strength of the ERW pipe formed by applying such a high strain is increased, and it is difficult to form the ERW pipe as a raw pipe by the hydroforming method. . Generally, ERW pipes are
Since only the welded portion is heated and quenched at the time of welding, the hardness becomes higher in the range of 30 to 80 in Vickers than in the base material portion. Buckling occurs, and only the welded portion lacks elongation during hydroform molding, causing breakage and wrinkles.

[0004]

Means for Solving the Problems The gist of the present invention is that the weight%
C: 0.01% or less of a very low C material to make an ERW steel pipe, and then heat-treat the ERW weld at a temperature of 600 to 850 ° C. In the method of manufacturing a sewn steel pipe. That is, the present invention takes into account the workability of the ERW steel pipe itself after forming the ERW pipe when forming the ERW pipe for hydroforming, and the conventional knowledge shows that the ERW pipe has a certain strength. Although it was considered necessary to use ultra-low C, it was decided to use ultra-low C as the material for the steel pipe. Is performed so that the base material and the welded portion of the ERW steel pipe have workability.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Since conventional ERW pipes are formed by bending and welded, the material itself is not strictly required for workability.
ERW steel pipes were manufactured using medium carbon material (C: about 0.05%). However, in the hydroform forming method, after forming into ERW steel pipes, forming is performed. It is necessary to consider the workability, and the present invention requires that the C
By specifying the amount to 0.01% by weight or less and setting the C amount to the above-described specific range, the workability of the ERW pipe itself is imparted. Next, a tensile test was performed on the ERW steel pipe made of the extremely low C material, and the elongation of the ERW welded part and the base metal part was measured. The measurement results are shown in FIGS. 2 and 3. FIG. 2 shows a state before the heat treatment of the electric resistance welded portion, and FIG. 3 shows a state after the heat treatment. As is clear from FIGS. 2 and 3, the use of the ultra-low C material can ensure that the elongation of the base material portion is 50%. The elongation values of the ERW welds could be made almost equal. Further, the hardness of the electric resistance welded portion between the conventional Vickers and the base material portion of 30 to 80 can be reduced to 10 to 20 in the present invention. For this reason, while being excellent in hydroform moldability, the danger of buckling, wrinkling, and breakage is reduced, which is extremely advantageous.

Next, the reasons for limiting the steel components in the present invention will be described. C is a component that strongly affects the structure of steel, but if it exceeds 0.01% by weight, depending on the heat treatment conditions,
A second phase structure (pearlite, bainite) or the like is generated, and workability is deteriorated. Accordingly, since a clean ferrite phase and good workability steel are required, the content is set to 0.01% or less. In addition, after performing ERW after cold working, heat treatment of the ERW weld in a temperature range of 600 to 850 ° C. is because the change in the weld structure of the extremely low C material is 6%.
If the temperature is lower than 00 ° C., the state is maintained without any change, and if the temperature exceeds 850 ° C., the structure of the welded portion tends to be coarse and the workability tends to decrease.

[0007] In the cooling pattern after the heat treatment, if the annealing time is maintained for 5 seconds or more, a necessary hardness reduction can be obtained.
The cooling rate may be air cooling or water cooling of 5 ° C./sec or more. FIG. 4 shows an example of this heat treatment pattern.
Such a heat treatment, while moving the steel pipe after cold working in the pipe axis direction, approaching the induction heating coil, heating and holding,
Air-cooled or water-cooled.

[0008]

[Example] Roll forming was performed using a very low C material having a different C content, high frequency electric resistance welding was performed, and a hydro of 114.3 mm in outer diameter and 1.6 mm in wall thickness (t / D = 1.40%) was used. An electric resistance welded steel pipe for foam forming was manufactured. The electric resistance welded steel pipe is 20mm in width.
After cutting one end of the steel pipe, it was flattened with a press and chucked at both ends, and a tensile test was performed. At the same time, the hardness was measured, and the results are shown in Table 1.

[0009]

[Table 1]

[0010] As shown in Table 1, according to the ERW steel pipe for forming a hydroform of extremely low C of the present invention, the elongation of both the base material portion and the welded portion of the ERW steel pipe itself after forming into the ERW steel pipe. It is clear that an ERW steel pipe having excellent workability of 48% to 50% can be obtained.

[0011]

According to the present invention, it is possible to manufacture an electric resistance welded steel pipe which secures elongation suitable for hydroforming. In addition, ERW steel pipes that are excellent in workability by the hydroforming method can be easily bent and reduced in diameter during pre-forming before forming by the hydroforming method. A steel pipe can be advantageously obtained, and the effect is extremely large.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a hydroform molding method.

FIG. 2 is an explanatory diagram showing a relationship between an ERW steel pipe of a very low C material without seam heat treatment, elongation, and hardness.

FIG. 3 is an explanatory diagram showing the relationship between the ERW steel pipe of the present invention, elongation, and hardness.

FIG. 4 is an explanatory view showing a heat treatment pattern of an electric resistance welded portion in the present invention.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 raw pipe 2 split mold 3 split mold 4 liquid introduction hole 5 cylinder 6 cylinder 7

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/00 301 C22C 38/00 301Z (72) Inventor Ryuji Miyagi 5-3 Tokaicho, Tokai City, Aichi Prefecture New Nippon Steel Corporation Nagoya Works (72) Inventor Toshin Makoto 5-3 Tokaicho, Tokai City, Aichi Prefecture F-term in Nippon Steel Corporation Nagoya Works 4K042 AA06 AA24 BA05 BA13 DA03 DB01 DC02 DE02 DE05

Claims (1)

[Claims] 1. An extremely low C of 0.01% or less by weight% of C.
ERW steel pipe using the material, and then the ERW weld
A method for producing an electric resistance welded steel tube for hydroform molding, wherein the heat treatment is performed at a temperature of from about 850 ° C.