To provide a high-strength galvanized steel plate having tensile strength of ≥ 400 MPa, and also having excellent secondary work-embrittlement resistance, deep drawability and plating characteristic.
Extremely low carbon steel containing 0.01-1.50 mass % Si is obtained by using a base stock in which B, Ti, P and N out of the composition are adjusted in a range to satisfy an inequality (3): 100 × ([%B] + 5.7[%Ti] - 19.6[%N])/([%P]/[%B]) ≥ 0.040. The base stock is heated and soaked at 950-1,300°C, is hot-rolled at 1,000°C, and is wound at 500-850°C after the hot rolling. After pickling, the rolled steel is cold-rolled at a draft of 50-95%, and is subjected to a re-crystallization annealing at the temperature of 700-950°C by a continuous annealing. Then, the steel is pickled, then is annealed in the condition that the stay time in the temperature range of 690-710°C is < 30s, and is galvanized in the temperature range of 550-900°C.
MATSUOKA SAIJI
SHIMIZU TETSUO
SAKATA TAKASHI
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