Steel for high strength spring, and high strength spring and method for manufacture thereof

Abstract

A steel for a high strength spring which has a chemical composition, in mass %, that C: 0.36 to 0.48 %, Si: 1.80 to 2.80 %, Mn: 0.20 to 1.40 %, P: 0.015 % or less, S: 0.010 % or less, Cu: 0.10 to 0.50 %, Ni: 0.10 to 2.00 %, Cr: 0.05 to 1.20 %, s-Al: 0.005 to 0.040 %, N: 0.002 to 0.012 %, O: 0.002 % or less, and the balance: Fe and inevitable impurities, satisfies the following formulae (1), (2) and (3): 1.2 % = C(%) + Mn(%) + Cr(%) = 2.0 % (1) 1.4 % = Si(%) / 3 + Cr(%) / 2 + Mn(%) = 2.4 % (2) 0.4 % = Cu(%) + Ni(%) (3), and contains inclusions having a diameter of 10 [mu]m or more in an amount of 10 pieces or less per 100 mm2 of a visual field; and a method for manufacturing a high strength spring, characterized in that the above steel for a high strength spring having been refined to have a hardness of HRC52 or more is hot- or cold-formed into a shape of a spring and then the resultant spring is subjected to warm shotpeening, to manufacture a high strength spring exhibiting a maximum shearing stress of 1176 Ma or more. A high strength spring manufactured by the above method exhibits improved resistance to setting due to its hardness of HRC52 or more, and also good durability, and further can be manufactured practically.

Description

[0001] related application [0002] This application claims priority to PCT Patent Application No. PCT / JP2004 / 012277 filed on August 26, 2004, which is hereby incorporated by reference herein. technical field [0003] The invention relates to a high-strength spring steel, a high-strength spring and a preparation method thereof. Background technique [0004] In recent years, reduction of carbon dioxide gas emission has been recognized as a problem to be solved from the viewpoint of suppression of global warming. Therefore, in the field of automobiles, it is considered important to reduce the weight of vehicles to improve fuel efficiency, so that weight reduction of various springs, such as suspension coil springs, has been sought. In order to achieve the purpose of reducing the weight of the spring while maintaining the necessary spring performance, a spring with high strength is required, and its maximum design stress τ max It is 1176MPa or higher, and the hardness is HRC5...

AI Technical Summary

Problems solved by technology

In addition, there are other problems that the shot peening (SP) material becomes prone to cracking, thus resulting in higher cost, and the falling particles penetrate into the spring, thus reducing the durability of the spring

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