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1. (WO2017018457) STEEL FOR SUSPENSION SPRING AND METHOD FOR MANUFACTURING SAME

Pub. No.:    WO/2017/018457    International Application No.:    PCT/JP2016/072051
Publication Date: Fri Feb 03 00:59:59 CET 2017 International Filing Date: Thu Jul 28 01:59:59 CEST 2016
IPC: C22C 38/00
C21D 8/06
C22C 38/18
C22C 38/54
Applicants: NIPPON STEEL & SUMITOMO METAL CORPORATION
新日鐵住金株式会社
NETUREN CO., LTD.
高周波熱錬株式会社
Inventors: SUZUKI, Takahisa
鈴木 崇久
CHIBA, Keisuke
千葉 圭介
MIYAMOTO, Hirotsugu
宮本 裕嗣
IWANAGA, Kengo
岩永 健吾
OKAMURA, Tsukasa
岡村 司
FUJIWARA, Fumiaki
藤原 文昭
EBANA, Yukio
江花 幸夫
Title: STEEL FOR SUSPENSION SPRING AND METHOD FOR MANUFACTURING SAME
Abstract:
Provided is a steel for a suspension spring that has a large tensile strength, excellent delayed fracture resistance and excellent cold workability while requiring little or no addition of expensive alloy elements. The steel for a suspension spring, said steel comprising, in terms of % by mass, 0.40-0.70% of C, 0.80-2.20% of Si, 0.05-1.50% of Mn, 0.05-1.00% of Cr, P in an amount limited to 0.020% or less, S in an amount limited to 0.020% or less and the remainder being Fe and inevitable impurities, is characterized in that: in a cross section parallel to a rolling direction, annealed martensite exists at a ratio by area of 90% or more relative to the metal structure; in a cross section parallel to the rolling direction, the ratio of the length in the major axis direction of prior austenite crystal grains and the length thereof in the direction orthogonal to the major axis direction is 1.5 or more, within a range of 10% of diameter or thickness from the surface; and the ratio [<011> texture ratio/<111> texture ratio] of a textured martensite structure viewed from the rolling direction is 3.0 or more.