title: Inverse temperature dependence of toughness in an ultrafine grain-structure steel.
abstract: Materials are typically ductile at higher temperatures and become brittle at lower temperatures. In contrast to the typical ductile-to-brittle transition behavior of body-centered cubic (bcc) steels, we observed an inverse temperature dependence of toughness in an ultrahigh-strength bcc steel with an ultrafine elongated ferrite grain structure that was processed by a thermomechanical treatment without the addition of a large amount of an alloying element. The enhanced toughness is attributed to a delamination that was a result of crack branching on the aligned {100} cleavage planes in the bundles of the ultrafine elongated ferrite grains strengthened by nanometer-sized carbides. In the temperature range from 60 degrees to -60 degrees C, the yield strength was greater, leading to the enhancement of the toughness.
authors.affiliation: National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan. kimura.yuuji@nims.go.jp
authors.forename: Yuuji
authors.initials: Y
authors.lastname: Kimura
authors.forename: Tadanobu
authors.initials: T
authors.lastname: Inoue
authors.forename: Fuxing
authors.initials: F
authors.lastname: Yin
authors.forename: Kaneaki
authors.initials: K
authors.lastname: Tsuzaki