Ultrafine Grained Steels
Recent progress in grain refinement of steels was overviewed. After energetic research works since middle 1990's including big national projects in Japan, ultrafine grained steels whose mean grain size is smaller than 1μm have been realized. There are principally two ways to obtain ultrafine grained structure in steels: the ultimate thermomechanical processing using various kinds of phase transformation in steels and the intense straining using a kind of recovery and recrystallization phenomena. Large amount of plastic strain is the key factor in both case. Microstructural characteristics and mechanical properties of the ultrafine grained steels were summarized. Future advance and prospect in the ultrafine grained steels was discussed.
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ISIJ International Vol.48(2008), No.8