METHOD FOR PRODUCING HIGH-STRENGTH HOT DIPPED GALVANIZED STEEL SHEET

WIPO Patent Application WO/2023/182524

A1

Provided is a method for producing a high-strength hot dipped galvanized steel sheet, wherein satisfactory appearance quality of the steel sheet and excellent LME cracking resistance are achieved, and the deterioration of delayed fracture resistance caused by hydrogen embrittlement is suppressed.　In the method for producing a hot dipped galvanized steel sheet according to the present invention, a steel sheet containing a predetermined amount of Si is subjected to oxidation followed by reduction annealing, and then hot dipped galvanizing. The oxidation treatment is performed at a temperature of 500-800°C in an atmosphere containing N2 and 500 volume ppm or more of O2. The reduction annealing comprises: a first reduction annealing at the front stage in which the steel sheet is held at a predetermined temperature for a predetermined time in an atmosphere containing a dew point of -45°C to +20°C, a hydrogen content of 5.0-25 vol%, and N2 as the balance; and a second reduction annealing at the rear stage in which the steel sheet is held at a predetermined temperature for a predetermined time in an atmosphere containing a dew point of -10°C to +20°C, a hydrogen content of 2.0-8.0 vol%, and N2 as the balance. In addition, the hydrogen concentration is adjusted such that the hydrogen concentration in the first reduction annealing at the front stage is higher than the hydrogen concentration in the second reduction annealing at the rear stage.

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YAMAMOTO SHUNSUKE (JP)
KANAZAWA TOMOMI (JP)
TAMAKI SHOGO (JP)
HOSHINO KATSUYA (JP)
TAKASHIMA KATSUTOSHI (JP)
SAWANISHI CHIKAUMI (JP)

PCT/JP2023/012037

September 28, 2023

March 24, 2023

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JFE STEEL CORP (JP)

C21D9/46; C21D9/56; C23C2/02; C23C2/06; C23C2/28; C22C38/00; C22C38/06; C22C38/60

WO2021166350A1	2021-08-26
WO2014073520A1	2014-05-15

JP2012149307A	2012-08-09
JP2014525986A	2014-10-02

KUMASAKA Akira et al. (JP)

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