公开(公告)号：EP3222746A4

公开(公告)日：2018-05-23

申请号：EP16761816

申请日：2016-03-10

申请人： NIPPON STEEL & SUMITOMO METAL CORP

发明人： KUBOTA MANABU ,  BANNO KOICHI ,  CHIBA KEISUKE ,  SEKI RYUUICHI

IPC分类号： C22C38/00 ,  C21D8/06 ,  C21D9/52 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/18 ,  C22C38/20 ,  C22C38/22 ,  C22C38/24 ,  C22C38/26 ,  C22C38/28 ,  C22C38/40 ,  C22C38/58 ,  F16F1/02

CPC分类号： C21D8/06 ,  C21D9/52 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/18 ,  C22C38/20 ,  C22C38/22 ,  C22C38/24 ,  C22C38/26 ,  C22C38/28 ,  C22C38/40 ,  C22C38/58 ,  F16F1/02

摘要： Steel for a suspension spring including, as a chemical composition, by % by mass: C: more than 0.40% and 0.65% or less; Si: 1.00% to 3.50%; Mn: more than 2.00% and 3.00% or less; Cr: 0.01% to 2.00%; V: 0.02% to 0.50%; P: 0.020% or less; S: 0.020% or less: N: 0.0100% or less; and a remainder of Fe and impurities, in which Kf is 280 or more, in which a structure contains a tempered martensite of which an area ratio is 90% or more, in which a Fe-based carbide precipitated in the tempered martensite is a cementite, and in which an average of an area ratios of prior austenite grains which stretch in a longitudinal direction of the steel and of which an aspect ratio exceeds 3.0, is 80% or more in a case of depths of 0.1 mm, 0.2 mm, and 0.3 mm in a sheet thickness direction from a surface of the steel.