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1. (WO2017154494) PRODUCTION METHOD FOR HIGH-STRENGTH HOT-DIP GALVANIZED STEEL SHEET

Pub. No.:    WO/2017/154494    International Application No.:    PCT/JP2017/005603
Publication Date: Fri Sep 15 01:59:59 CEST 2017 International Filing Date: Fri Feb 17 00:59:59 CET 2017
IPC: C23C 2/02
C21D 9/46
C21D 9/56
C22C 18/04
C22C 38/00
C22C 38/60
C23C 2/06
C23C 2/28
C23C 2/40
Applicants: JFE STEEL CORPORATION
JFEスチール株式会社
Inventors: MAKIMIZU Yoichi
牧水 洋一
SUZUKI Yoshitsugu
鈴木 善継
TAKEDA Gentaro
武田 玄太郎
HASEGAWA Hiroshi
長谷川 寛
Title: PRODUCTION METHOD FOR HIGH-STRENGTH HOT-DIP GALVANIZED STEEL SHEET
Abstract:
[Problem] To provide a production method for a high-strength hot-dip galvanized steel sheet having excellent plating adhesion, workability, and resistance to fatigue. [Solution] In this invention, a steel sheet is subjected to oxidation processing comprising: in an early stage, heating at a temperature of 400 to 750°C in an atmosphere of O2 at a concentration of 1000 ppm by volume or more and H2O at a concentration of 1000 ppm by volume or more; and, in a later stage for oxidative treatment, heating at a temperature of 600 to 850°C in an atmosphere of O2 at a concentration of less than 1000 ppm by volume and H2O at a concentration of 1000 ppm by volume or more. Next, the steel sheet is subjected to reduction-annealing comprising: in a heating zone, heating at a temperature rising speed of 0.1°C/sec or faster to a temperature of 650 to 900°C in an atmosphere wherein the H2 concentration is 5 to 30% by volume, the H2O concentration is 10 to 1000 ppm by volume, and the remainder comprises N2 and unavoidable impurities; and then, in a soaking zone, maintaining a uniform heat within ±20°C temperature variation for 10 to 300 seconds, in an atmosphere wherein the H2 concentration is 5 to 30% by volume, the H2O concentration is 500 to 5000 ppm by volume, and the remainder comprises N2 and unavoidable impurities.