Rolled material for high strength spring, and wire for high strength spring using the same

Abstract

An object of the present invention is to provide a rolled material for high strength spring, which has excellent wire drawability even when suppressing the addition amount of an alloying element, and which can exhibit corrosion fatigue properties after quenching and tempering.

The present invention provides a rolled material for high strength spring, including C, Si, Mn, P, S, Al, Cu and Ni, wherein an amount of nondiffusible hydrogen is 0.40 ppm by mass or less, and an area ratio of ferrite expressed as a percentage satisfies an inequality expression (1) below, and a total area ratio of bainite and martensite is 2% or less:

Ferrite area ratio<{(0.77−[C])/0.77−[C]/3+0.08}×100  (1)

where [name of element] in the above inequality expression (1) means a content expressed in % by mass of each element.

Description

TECHNICAL FIELD[0001]The present invention relates to a rolled material for high strength spring, and a wire for high strength spring using the same. More particularly, the present invention relates to a rolled material and a wire, which are useful as raw materials of high strength springs that are used in a state of being subjected to heat treatment, namely, quenching and tempering, particularly a rolled material having excellent wire drawability, and a wire for high strength spring, which are excellent in corrosion fatigue properties even though a tensile strength is a high strength in a range of 1,900 MPa or more after wire drawing.BACKGROUND ART[0002]Coil springs used in automobiles, for example, a valve spring and a suspension spring used in the engine, suspension, and the like are required to reduce the weight and to increase the strength so as to achieve exhaust gas reduction and improvement in fuel efficiency. In the manufacture of a high strength wire, wire drawing is appli...

AI Technical Summary

Benefits of technology

[0019]According to the present invention, since the amount of nondiffusible hydrogen in a rolled material is suppressed and formation of supercooled structures such as bainite and martensite is suppressed, the rolled material exhibits excellent wire drawability without adding a large amount of an alloying element. In the rolled material of the present invention, an area ratio of ferrite is appropriately adjusted according to the concentration of C, specifically, the area ratio of ferrite decreases as the concentration of C increases, so that a wire obtained by wire-drawing this rolled material, follo

Problems solved by technology

The spring imparted with high strength is likely to cause hydrogen brittleness because of its poor toughness and ductility, leading to degradation of corrosion fatigue properties.

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