High strength spring steel wire with excellent coiling properties and hydrogen embrittlement resistance

Abstract

Disclosed herein is a high strength spring steel wire with excellent coiling properties and hydrogen embrittlement resistance. The steel wire comprises, by mass, 0.4 to 0.60% of C, 1.7 to 2.5% of Si, 0.1 to 0.4% of Mn, 0.5 to 2.0% of Cr, 0.015% or less of P (exceeding 0%), 0.015% or less of S (exceeding 0%), 0.006% or less of N (exceeding 0%), 0.001 to 0.07% of Al, and the remainder being Fe and unavoidable impurities. The steel wire has a structure wherein prior austenite has an average grain size of 12 μm or less, and retained austenite exists in an amount of 1.0 to 8.0 vol. % with respect to a whole structure of the steel wire. The retained austenite has an average grain size of 300 nm or less and a maximum grain size of 800 nm or less. The steel has a tensile strength of 1,900 MPa or more.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a high strength spring steel wire with excellent coiling properties and hydrogen embrittlement resistance, and more particularly, to a spring steel wire, which has enhanced coiling properties and hydrogen embrittlement resistance in a high strength range for a tensile strength of 1,900 MPa or more. [0003] 2. Description of the Related Art [0004] Requirement for weight reduction of an automotive vehicle is accompanied with reduction in size and thickness of vehicle components. In this regard, it is necessary for underbody components of the vehicle, such as a suspension spring and the like, to have high strength. However, since increase in strength of steel generally enhances atmospheric fatigue properties while reducing corrosion fatigue properties, it is difficult to improve both atmospheric fatigue properties and corrosion fatigue properties together with the strength of the steel. ...

AI Technical Summary

Benefits of technology

[0026] As apparent from the above description, according to the present invention, the high strength spring steel wire permits an effective coiling operation in a process of cold spring winding as well as a process of hot spring winding, and has...

Problems solved by technology

However, since increase in strength of steel generally enhances atmospheric fatigue properties while reducing corrosion fatigue properties, it is difficult to improve both atmospheric fatigue properties and corrosion fatigue properties together with the strength of the steel.

However, according to these methods, an increase in required level results in an increase of added amounts of alloy elements, thereby increasing material costs while deteriorating workability.

However, for the process of manufacturing the cold-wound coil spring, since the spring winding is performed after the quenching and tempering unlike the process of manufacturing the hot-wound coil spring in which the quenching and tempering are performed after the spring winding in order to adjust the strength, a steel wire with high strength and low workability is provided to the spring winding process, whereby the steel wire is likely to be broken during the spring winding process.

In addition, Patent Document 3 discloses a method which can ensure excellent ductility and high strength through refinement of the austenite structure with TiN by adjusting added amounts of Ti...

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