HIGH-STRENGTH COLD-ROLLED STEEL SHEET AND MANUFACTURING METHOD THEREFOR

WIPO Patent Application WO/2019/021695

A1

Provided is a high-strength cold-rolled steel sheet to which Cu is added to improve delayed fracture resistance characteristics, which has good chemical conversion treatability during low-temperature chemical conversion treatment and for which excellent post-painting corrosion resistance and delayed fracture resistance characteristics can be attained. The high-strength cold-rolled steel sheet contains at least one of Si, Mn, and Al and 0.05-0.25 mass% of Cu, wherein: the steel structure is a recrystallized structure; no oxide layer containing at least one of Al, Si, and Mn is present on the surface of the steel sheet; and cross-sectional coverage by a deposited metal Cu on the steel sheet surface is 30% or less. A film of a pickling liquid on the surface of the steel sheet reacts with the steel sheet between a period after pickling until washing with water causing Cu to be eluted from the steel plate and deposited on the surface of the steel plate. This deposited metal Cu lowers the chemical conversion treatability, and so, by keeping the cross-sectional coverage by this deposited metal Cu to a low level, chemical conversion treatability can be improved.

MASUOKA HIROYUKI (JP)
FURUYA SHINICHI (JP)
TAKEYAMA HAYATO (JP)
MATSUZAKI AKIRA (JP)

PCT/JP2018/023302

January 31, 2019

June 19, 2018

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JFE STEEL CORP (JP)

C23G1/08; C22C38/00; C22C38/16

WO2016147549A1

2016-09-22

JP2016050354A	2016-04-11
JP2009221586A	2009-10-01
JP2011246764A	2011-12-08

KUMASAKA Akira et al. (JP)

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