Primary cooling method in continuously annealing steel strips

In a primary cooling method in continuously annealing steel strips which comprises a heating step (A), a soaking step (B), a primary cooling step (C) including at least a rapid cooling step in a second half thereof, an overaging step (D), and a final cooling step (E), inert atmosphere gas containing H2 gas is employed as cooling gas for use in the rapid cooling step and concentration of the H2 gas is switched between two ranges of low and high concentrations of H2 gas, depending on the required cooling rate of the rapid cooling step corresponding to the product grades of steel strips (26). Accordingly, the consumption of expensive H2 gas is reduced thus enhancing the economy of the cooling operation while assuring the safety and efficiency of the primary cooling operation.