High Strength Thick-Gauge Electric-Resistance Welded Steel Pipe Excellent in Hardenability, Hot Workability and Fatigue Strength and Method of Production of the Same

Abstract

The present invention provides high strength thick-gauge electric-resistance welded steel pipe excellent in hardenability, hot workability, and fatigue strength and a method of production of the same, that is, thick-gauge electric-resistance welded steel pipe containing, by mass %, C: 0.25 to 0.4%, Si: 0.01 to 0.50%, Mn: 0.8 to 1.5%, P: 0.05% or less, S: 0.05% or less, Al: 0.05% or less, Ti: 0.005 to 0.05%, B: 0.0005 to 0.01%, N: 0.001 to 0.05%, and a balance of Fe and unavoidable impurities, having a critical cooling rate Vc expressed by equation <1> of less than 30° C. / s, and having a ratio of thickness t and outside diameter D, t / D, of over 0.15 to 0.30 in range:log Vc=2.94−0.75β  <1>where, β=2.7C+0.4Si+Mn

Description

TECHNICAL FIELD[0001]The present invention relates to high strength thick-gauge electric-resistance welded steel pipe excellent in hardenability, hot workability, and fatigue strength suitable for a hollow stabilizer for securing running stability of an automobile and method of production of the same.BACKGROUND ART[0002]As one measure for improvement of the fuel economy of automobiles, the chasses of automobiles are being reduced in weight. The stabilizer easing the rolling of the chassis at the time of cornering of the automobile and securing stability of the chassis at the time of high speed running may be mentioned as being part of this. In the past, stabilizers have been produced by working a steel bar or other solid material into the required shape, but to lighten the weight, they are increasingly being produced using seamless steel pipe, electric-resistance welded steel pipe, or other hollow members.[0003]As electric-resistance welded steel pipe for a stabilizer, WO2002 / 070767...

AI Technical Summary

Benefits of technology

The present invention provides a high strength thick-gauge electric-resistance welded steel pipe with sufficient hardenability, hot workability, and fatigue strength. The steel pipe has a specific composition and a critical cooling rate to achieve hardenability. The heating temperature and cross-section reduction rate are set to specific ranges for stretch reducing rolling of the steel pipe. The thick-gauge electric-resistance welded steel pipe is excellent in hardenability, hot workability, and fatigue strength and can be used for automobile structural members. The method of production involves heating the steel pipe to a specific temperature and then stretch reducing it to a specific size. The resulting steel pipe has excellent hardenability, hot workability, fatigue strength, and durability against repeated load.

Problems solved by technology

Further, they cannot be said to be sufficient in terms of fatigue characteristics either.

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