Formation of a nanocrystalline structure during direct and reverse martensitic transformations

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• 作者：Sagaradze ; V.V. ; Kabanova ; I.G.
• 关键词：Martensite ; Austenitic steels ; Misorientation angles ; Nanocrystalline microstructure
• 刊名：Materials Science and Engineering ; A
• 出版年：1999
• 期刊代码：61_09215093
• 类别：ms
• 出版时间：December 15, 1999
• 卷：273-275
• 期：Complete
• 页码：457-461
• 文件大小：397 K

摘要

We studied different methods employing direct and reverse γ→α¹→γ transformations for producing a fine fcc structure in austenitic steels alloyed with Ni, Cr or Ti. Finest nanodimensional austenitic crystals were obtained not by fast heating during the α¹→γ transformation (or subsequent recrystallization) but by slow heating at a rate of 0.2–0.4 K min⁻¹, when multiplication of γ-crystallite orientations occurred. The electron microscopy showed that 24²=576 orientations of the γ-phase appeared in each initial austenitic grain during a single cycle of γ→α¹→γ transformations. Crystallographic calculations of all possible misorientations of any adjacent γ-crystals having the Kurdyumov–Sachs relationship suggested that a limited number (approximately 10.5, 49.5, 60°, etc.) of unlike misorientation angles was formed. The nanocrystalline state and predominance of large-angle boundaries between fine γ-crystals account for a very strong strengthening of the steels. This may be used in practical applications.