Abstract
Mechanical properties and microstructural changes of 18wt%Cr-8wt%Ni stainless steel deformed at 4.2°K. were investigated.
The elastic limit and tensile strength of 18wt%Cr-8wt%Ni stainless steel annealed at 1, 050°C for 1hr were 45kg/mm2 and 155kg/mm2, respectively. Serrated stress-strain curve was observed and several stages in work hardening were experimentally distinguishable. The first stage is characterized by the pseudo-easy glide of γ phase, the second stage shows a rapid increase in work hardening by the martensite transformation. These two stages are linear hardening, but the third stage is parabolic hardening. α′ phase is formed in ε phase at least in the first stage and the process of γ phase to α′ phase transformation is appeared by γ→ε→α′. The relation between grain diameter and elastic limit was given by the “Petch” formula.
Lattice constants of α′ and ε phase formed at 4.2°K are a=2.87Å for α′ phase, and a=2.55Å and c=4.01Å for ε phase.
