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Title:
METHOD FOR MANUFACTURING HIGH-STRENGTH HOT-DIP GALVANIZED STEEL SHEET
Document Type and Number:
WIPO Patent Application WO/2015/087549
Kind Code:
A1
Abstract:
　Provided is a method for manufacturing a high-strength hot-dip galvanized steel sheet having excellent workability and fatigue resistance. In the present invention, a steel sheet containing 0.1-2.5% Si is subjected to oxidation treatment and reduction annealing, followed by a hot-dip plating treatment and an alloying treatment. In the oxidation treatment, the steel sheet is heated at a temperature of 400-750°C in an atmosphere having an O2 concentration of at least 1000 ppm by volume and an H2O concentration of at least 1000 ppm by volume in a first stage, and is heated at a temperature of 600-850°C in an atmosphere having an O2 concentration of less than 1000 ppm by volume and an H2O concentration of at least 1000 ppm by volume in a later stage. In the reduction annealing, the steel sheet is heated at a temperature of 650-900°C in an atmosphere comprising H2 at a concentration of 5-30 vol% and H2O at a concentration of 500-5000 ppm by volume, the remainder being N2 and unavoidable impurities. In the alloying treatment, the steel sheet is treated for 10-60 seconds at a temperature (T (°C)) satisfying the expression -50 log ([H2O]) + 650 ≤ T ≤ -40 log ([H2O]) + 680 ( where [H2O] is the concentration (ppm by volume) of H2O during reduction annealing).

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Inventors:
MAKIMIZU YOICHI (JP)
SUZUKI YOSHITSUGU (JP)
AOYAMA MAI (JP)
HASEGAWA HIROSHI (JP)
TAKEDA GENTARO (JP)
Application Number:
PCT/JP2014/006177
Publication Date:
June 18, 2015
Filing Date:
December 11, 2014
Export Citation:
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Assignee:
JFE STEEL CORP (JP)
International Classes:
C21D9/46; C23C2/28; C22C18/04; C22C38/00; C22C38/04; C22C38/58; C23C2/02; C23C2/06; C23C2/40
Foreign References:
JP2012251192A2012-12-20
JP2012126983A2012-07-05
JP2012177147A2012-09-13
JPS55122865A1980-09-20
JPH04202630A1992-07-23
JPH04202631A1992-07-23
JPH04202632A1992-07-23
JPH04202633A1992-07-23
JPH04254531A1992-09-09
JPH04254532A1992-09-09
JPH0734210A1995-02-03
JP2004211157A2004-07-29
JP2005060742A2005-03-10
JP2007291498A2007-11-08
Other References:
See also references of EP 3081665A4
Attorney, Agent or Firm:
KUMASAKA, Akira et al. (JP)
Akira Kumasaka (JP)
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