Paper Title:
Nano-Grained Structure Induced by Mechanical Twinning during Multi-Directional Forging and the Mechanical Properties
  Abstract

A bulky SUS316 austenitic stainless steel (SUS316) was multi-directionally forged (MDFed) at 77 K and 300 K up to a cumulative strain of = 6 at maximum. With increasing cumulative strain, the grains were subdivided by mechanical twinning and martensitic transformation. Especially, mechanical twins accelerated grain fragmentation by subdivision of the initial grains and by intersection of the previously formed twins during MDF. The intersection of twins caused finally evolution of packet grains, which were composed of lamellar structured twins. The packet size and the lamellar twin spacing decreased down to 35 nm and 15 nm by MDF to  = 6 at 77 K. The average grain size achieved was estimated to be about 10 nm. Twinning appeared more frequently and uniformly at 77 K than at 300 K. Tensile test at 300 K revealed ultimate tensile strength of 2.1 GPa and fracture strain of about 0.2. The fracture strain, however, appeared to be constant over ∑Δε = 2.4 independent of cumulative strain. The observed excellent balance of strength and ductility of the nano-grained SUS316 is discussed in relation with the effects of twins on grain fragmentation and mechanical properties.

  Info
Periodical
Materials Science Forum (Volumes 633-634)
Edited by
Yonghao Zhao and Xiaozhou Liao
Pages
577-593
DOI
10.4028/www.scientific.net/MSF.633-634.577
Citation
H. Miura, Y. Nakao, "Nano-Grained Structure Induced by Mechanical Twinning during Multi-Directional Forging and the Mechanical Properties", Materials Science Forum, Vols. 633-634, pp. 577-593, 2010
Online since
November 2009
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