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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.45  No.7 (2004)  >  pp.2252-2258

MATERIALS TRANSACTIONS
<<Previous article Vol.45  No.7 (2004)   pp.2252 - 2258 Next article>>

Effect of Nano-Sized Oxides on Annealing Behaviour of Ultrafine Grained Steels

Andrey Belyakov1), Yoshikazu Sakai1), Toru Hara1), Yuuji Kimura1) and Kaneaki Tsuzaki1)
1) Steel Research Center, National Institute for Materials Science

The annealing behaviour of ultrafine grained steels containing nano-scale dispersed oxides was studied in a temperature range of 600—900°C by means of microstructural observations and hardness measurement. The starting materials with submicrocrystalline structures were developed by mechanical milling of Fe-Fe3O4 powders followed by consolidating bar rolling at 700°C. Depending on the initial oxygen content and the mechanical milling time, the fraction of dispersed oxides varied from 0.3 to 3.0 vol%. During the heating up to 800°C (i.e. within the ferrite region), the initial ultrafine grained microstructures were essentially stable against any discontinuous grain growth. The grain coarsening and the softening can be roughly expressed by power-law functions of annealing time. The main mechanism of microstructure evolution that operated during annealing is considered as a normal grain growth accompanied by recovery. The grain coarsening is characterized by a rather high value of the grain-growth exponent of about 20. The grain growth kinetics correlates with the oxide coarsening. The effect of dispersed oxides on the annealing behaviour of submicrocrystalline oxide bearing steels is discussed in some detail.


Keyword:
ultrafine grained steels, dispersed oxides, mechanical milling, powder consolidation, grain coarsening

Received: January 16, 2004
Accepted: February 26, 2004 , Published online: June 24, 2005
Copyright (c) 2005 The Japan Institute of Metals

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