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High-tensile strength welded steel tube for structural partsof automobiles and method of producing the same

A technology for welding steel pipes and automobile structures, applied in the direction of manufacturing tools, furnace types, furnaces, etc., can solve the problems of low ductility, unsuitability, poor formability, etc., and achieve excellent low temperature toughness, improved characteristics, and excellent formability.

Active Publication Date: 2009-07-15
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0007] However, the electric welded steel pipe manufactured by the technique described in Patent Document 1 has the problem that since the elongation E1 is 14% or less, it has low ductility and poor formability, and is not suitable for torsion steel pipes for press forming or hydroforming. Rods, axle beams and other automotive structural components

Method used

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  • High-tensile strength welded steel tube for structural partsof automobiles and method of producing the same
  • High-tensile strength welded steel tube for structural partsof automobiles and method of producing the same
  • High-tensile strength welded steel tube for structural partsof automobiles and method of producing the same

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0107] The molten steel with the composition shown in Table 1 was smelted and made into raw steel material (steel billet) by continuous casting. These steel raw materials are heated to about 1250°C, hot-rolled at a finishing temperature of about 860°C, and after hot rolling, slow-cooling at a temperature range of 750-650°C for 5 seconds, and then Coiling temperature: 590°C in the hot-rolling process to produce a hot-rolled steel strip (thickness: about 3mm).

[0108] Next, these hot-rolled steel strips are used as raw materials for steel pipes, pickled, and slit to a specified width, and then roll-formed continuously to form open pipes, and then performed by high-frequency resistance welding. This open pipe was subjected to an electric welding pipe manufacturing process of electric welding, thereby producing a welded steel pipe (outer diameter φ89.1 mm×wall thickness about 3 mm).

[0109] In addition, in the electric-welded pipe-making process, the width reduction rate define...

Embodiment 2

[0141] Steel raw materials (slabs) having the compositions of steel No.B and No.C in Table 1 were subjected to hot rolling under the conditions shown in Table 3 to form hot-rolled steel strips. Next, these hot-rolled steel strips are used as steel pipe raw materials, pickled, and slit into a predetermined width dimension, and then roll-formed continuously to form an open pipe, and then the open pipe is made by high-frequency resistance welding. The pipe is subjected to an electric welding pipe making process of electric welding, thereby producing a welded steel pipe (outer diameter 70 to 114.3mmφ x wall thickness t2.0 to 6.0mm). In addition, in the electric-welded pipe-making process, the width reduction rate defined by (1) formula was set to the value shown in Table 3.

[0142] From the obtained welded steel pipe, a test piece was taken in the same manner as in Example 1, and the same as in Example 1. The structure observation test, the precipitate observation test, the tensi...

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Abstract

A high-tension welded steel pipe for automotive structural members which has excellent formability and has excellent resistance to torsional fatigue after section forming and subsequent annealing for stress removal; and a process for producing the steel pipe. A raw steel material having a composition which contains C, Si, and Al in amounts in respective proper ranges and further contains 1.01-1.99% Mn, 0.041-0.150% Ti, and 0.017-0.150% Nb, provided that Ti+Nb is 0.08% or more, and in which the amounts of P, S, N, and O have been regulated so as to be not larger than given values is subjected to hot rolling in which the heating temperature and the finish-rolling completion temperature are in proper ranges. After completion of the hot rolling, the steel material is annealed in a temperature range of 750-650 DEG C for 2 seconds or longer. The steel is then wound at a winding temperature of 660-510 DEG C to obtain a hot-rolled steel strip comprising at least 60 vol.% ferrite phase having an average particle diameter of 2-8 [mu]m and a structure comprising an (Nb / Ti) composite carbide having an average particle diameter of 2-40 nm and precipitated in the ferrite phase. This steel strip is subjected to the step of pipe formation by electric-resistance welding at a width reduction of 10% or lower to thereby form a welded steel pipe. Thus, a high-tension welded steel pipe is obtained which has a high yield strength exceeding 660 MPa and is excellent in low-temperature toughness, formability, and resistance to torsional fatigue after annealing for stress removal.

Description

technical field [0001] The invention relates to a high-strength welded steel pipe with a yield strength exceeding 660 MPa, which is suitable for automotive structural components such as torsion bars, axle beams, trailing arms, and suspension arms. In particular, it relates to a high-strength welded steel pipe for a torsion bar, excellent in formability, excellent torsional fatigue resistance after cross-section forming and subsequent stress relief annealing, and a manufacturing method thereof. Background technique [0002] In recent years, from the viewpoint of protecting the global environment, it has been urgently required to increase the gasoline mileage of automobiles. Therefore, the goal is to completely reduce the weight of automobiles and other vehicles. Structural components such as automobiles are no exception. In order to achieve both weight reduction and safety, high-strength electric-welded steel pipes are used for some structural components. Conventionally, af...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C22C38/14C22C38/58B21C37/08C21D8/02C21D8/10
CPCC22C38/14C21D8/02C21D9/08C21D1/26C22C38/02C21D8/0226C22C38/12B21C37/08C22C38/04C21D2211/005C21D8/0263
Inventor 丰田俊介荒谷昌利河端良和桥本裕二铃木孝司坂田敬郡司牧男佐藤昭夫泽木哲郎
Owner JFE STEEL CORP
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