Patent ID: 8491734
Filing Date: 2013-07-23
Classification: C21D,C22C,C23C

Abstract:
1. A process of production of a high strength galvannealed steel sheet, comprising pickling a hot-rolled steel sheet having a content of Si of 0.4 to 2.0 wt %, then, cold-rolling the steel sheet, then, continuously hot-dip galvanizing the steel sheet in an all radiant tube type annealing furnace with a reducing atmosphere and without an oxidizing zone, wherein the all radiant tube type annealing furnace comprises a heating zone ( in the all radiant tube type annealing furnace, a reducing gas ( the atmosphere is made not to cause iron to oxidize, during the continuously hot-dip galvanizing: introducing the combustion gas ( making the atmosphere of the annealing furnace an atmosphere containing H controlling, in the atmosphere, (i) the log(PCO (ii) the log(PH (iii) the log(P performing annealing in the reducing atmosphere in a ferrite-austenite two-phase temperature region at 720° C. to 880° C., then cooling by a plating bath and performing molten zinc plating so as to form a hot-dip galvanizing layer on the surface of the steel sheet, and then heating for alloying the steel sheet on which the hot-dip galvanizing layer is formed at 460 to 550° C., so as to produce a high strength galvannealed steel sheet.