Method for controlling equiaxed crystals in slab of the ferritic stainless steel

摘要

PURPOSE: A method is provided which accurately controls the equiaxed ratio of steel billets to a wanted content using the relationship between the equiaxed ratio and degree of overheating of steel billets. CONSTITUTION: The method for controlling the equiaxed ratio of steel billets of ferritic stainless steel comprises the steps of predetermining a target equiaxed ratio of steel billets comprising 0.08 wt.% or less of C, 0.8 wt.% or less of Si, 1 wt.% or less of Mn, 0.035 wt.% or less of P, 0.02 wt.% or less of S, 12 to 20 wt.% of Cr, 0.5 wt.% or less of Mo, 0.05 wt.% or less of N, 1 wt.% or less of Cu, 1 wt.% or less of Ni, 0.2 wt.% or less of Ti, 0.3 wt.% or less of Nb, 0.05 wt.% or less of Al and a balance of Fe and inevitably contained impurities; obtaining a casting temperature by substituting the target equiaxed ratio into the following related formula 1: £Related Formula 1| Target equiaxed ratio (%)="c"+b(T)+a(T)¬2 where T(degree of overheating, deg.C)="casting temperature-theoretic solidifying temperature", c is 103-106, b is -2.186, and a is 0.0113; and obtaining steel billets having a target equiaxed ratio by controlling an average cooling rate of the steel billets within the range of 30 to 50 deg.C/min as casting the steel billets to the obtained casting temperature in the actual operation.