METHOD FOR BLOOMING HIGH PURITY FERRITIC STAINLESS STEEL

PROBLEM TO BE SOLVED: To provide a method for blooming a high purity ferritic stainless steel by which twisting and falling do not occur, and also wrinkles do not occur upon blooming the high purity ferritic stainless steel into a round cast billet.SOLUTION: In the method, a cast billet made of a high purity ferritic stainless steel containing, by mass, ≤0.01% C, ≤0.01% N, 17 to 20% Cr and ≤0.5% Ni and having a non-circular cross-sectional face is subjected to hot working by caliber rolling, and is bloomed into a round cast billet having a circular cross-sectional face. A ratio h/bof a height hto a width bin the cross-sectional face of the cast billet before rolling reduction is controlled to ≤2.0, and the heating temperature of the cast billet is controlled to 1,000 to 1,200°C. The blooming is performed at a draft [(the height hof the cast billet before the rolling reduction)-(the height hof the cast billet after the rolling reduction)/the height hof the bloom before the rolling reduction](%) satisfying following expression: the draft≤-10.619×(the ratio h/bof the height hto the width bin the cross-sectional face of the bloom before the rolling reduction)+23.298. According to this invention, a high purity ferritic stainless steel can be bloomed into a round cast billet without causing twisting and falling and also without causing wrinkles.