2相ステンレス鋼におけるα相から析出するγ相の形態と結晶学的特徴
1986 年 50 巻 1 号 p. 10-19
詳細
1986 年 50 巻 1 号 p. 10-19
The morphology and crystallographic feature of austenite (γ) precipitated from ferrite (α) grain during aging in the (α+γ) two phase region have been investigated using Fe-25%Cr-7%Ni-3%Mo and Fe-25%Cr-6%Ni (α+γ) two phase stainless steels.
The starting structure of the steels before aging was fully ferritic. The precipitation process of γ from α was found as follows: (1) precipitation of fine γ allotriomorphs at α grain boundary, (2) formation of filmed γ along α grain boundary by coalescence of the γ allotriomorphs, (3) growth of spiked γ from the filmed γ into α grain, and (4) intragranular precipitation of γ particles in α grain.
The intragranular precipitated γ shows rod-like shape with the growth direction of ⟨111⟩α. Among rod-like γ, twinned γ pairs were frequently observed. Each γ of the pair was found to hold not only Kurdjumov-Sachs (K-S) orientation relationship against α matrix but also twin relation to the other γ of the pair at the same time. There is only one K-S variant allowed for the formation of twinned γ pairs to satisfy the above two conditions. The twinned γ pairs also frequently change to be pipe-shaped in a later growth stage, because of loccal dilution of Ni atoms in α near a concave surface of the γ pairs.
