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

The invention suppresses the amount of nondiffusible hydrogen in a rolled material, which reduces the formation of supercooled structures such as bainite and martensite. This improves the wire drawability and corrosion fatigue properties of the material, even when using a high strength steel. The rolled material has a suitable ferrite area ratio that decreases with increasing carbon concentration, resulting in a wire with excellent properties. This allows for the production of a high strength spring that is cost-effective and less likely to cause corrosion fatigue fracture.

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.

However, such a method is not necessarily desirable from a viewpoint of an increase in manufacturing costs and resource saving because of use of a large amount of an alloying element.

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