The effect of multiple deformations on the formation of ultrafine grained steels
Beladi, Hossein, Kelly, Georgina and Hodgson, Peter 2007, The effect of multiple deformations on the formation of ultrafine grained steels, Metallurgical and materials transactions A - physical metallurgy and materials science, vol. 38, no. 3, pp. 450-463.
Title
The effect of multiple deformations on the formation of ultrafine grained steels
Metallurgical and materials transactions A - physical metallurgy and materials science
Volume number
38
Issue number
3
Start page
450
End page
463
Publisher
Minerals, Metals & Materials Society
Place of publication
Warrendale, PA.
Publication date
2007-04-12
ISSN
1543-1940 1073-5623
Summary
A C-Mn-Nb-Ti steel was deformed by hot torsion to study ultrafine ferrite formation through dynamic strain-induced transformation (DSIT) in conjunction with air cooling. A systematic study was carried out first to evaluate the effect of deformation temperature and prior austenite grain size on the critical strain for ultrafine ferrite formation (ε C,UFF) through single-pass deformation. Then, multiple deformations in the nonrecrystallization region were used to study the effect of thermomechanical parameters (i.e., strain, deformation temperature, etc.) on ε C,UFF. The multiple deformations in the nonrecrystallization region significantly reduced ε C,UFF, although the total equivalent strain for a given thermomechanical condition was higher than that required in single-pass deformation. The current study on a Ni-30Fe austenitic model alloy revealed that laminar microband structures were the key intragranular defects in the austenite for nucleation of ferrite during the hot torsion test. The microbands were refined and overall misorientation angle distribution increased with a decrease in the deformation temperature for a given thermomechanical processing condition. For nonisothermal multipass deformation, there was some contribution to the formation of high-angle microband boundaries from strains at higher temperature, although the strains were not completely additive.