TY - JOUR
T1 - Pitting at the δ/γ boundary of Type 304 stainless steel in NaCl solution
T2 - The role of oxide inclusions and segregation
AU - Otake, Asako
AU - Muto, Izumi
AU - Chiba, Aya
AU - Sugawara, Yu
AU - Hara, Nobuyoshi
N1 - Funding Information:
This work was supported by JSPS KAKENHI grant Numbers JP25630319 and JP17H01331. This research was also supported by the Japan Society and Technology Agency (JST) under Collaborative Research Based on Industrial Demand “Heterogeneous Structure Control: Towards Innovation Development of Metallic Structural Materials.”
Publisher Copyright:
© The Author(s) 2017. All rights reserved.
PY - 2017
Y1 - 2017
N2 - The role of inclusion compositions and the pit initiation mechanism at the δ/γ boundary of cast Type 304 stainless steel was investigated in 1 M NaCl. Three types of inclusions were detected: large CaO-SiO2-MgO-Al2O3 slag inclusions (Type I) and small SiO2-Al2O3-MnO-Cr2O3-TiO2 complex oxide inclusions that were located at the δ/γ boundaries (Type II) or found in the γ phases (Type III). In Types II and III, a small amount of Ca was occasionally detected. In micro-scale polarization, the size of the electrode area was changed from 0.01 to 10 mm2, and the number densities for the stable and meta-stable pit initiation sites were estimated to be 0.1 and 1 site mm-2, respectively. Type II inclusions acted as the pit initiation sites at the δ/γ boundary. At the δ/γ boundary without an inclusion, a meta-stable pit was initiated. The segregation of P and S was detected at the boundary where the pit was initiated, but no accumulation of Si was observed. At a randomly selected boundary of δ/γ on the steel, no clear segregation of P and S was observed, but the Si concentration was two to three times higher than the average Si concentration in the steel.
AB - The role of inclusion compositions and the pit initiation mechanism at the δ/γ boundary of cast Type 304 stainless steel was investigated in 1 M NaCl. Three types of inclusions were detected: large CaO-SiO2-MgO-Al2O3 slag inclusions (Type I) and small SiO2-Al2O3-MnO-Cr2O3-TiO2 complex oxide inclusions that were located at the δ/γ boundaries (Type II) or found in the γ phases (Type III). In Types II and III, a small amount of Ca was occasionally detected. In micro-scale polarization, the size of the electrode area was changed from 0.01 to 10 mm2, and the number densities for the stable and meta-stable pit initiation sites were estimated to be 0.1 and 1 site mm-2, respectively. Type II inclusions acted as the pit initiation sites at the δ/γ boundary. At the δ/γ boundary without an inclusion, a meta-stable pit was initiated. The segregation of P and S was detected at the boundary where the pit was initiated, but no accumulation of Si was observed. At a randomly selected boundary of δ/γ on the steel, no clear segregation of P and S was observed, but the Si concentration was two to three times higher than the average Si concentration in the steel.
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U2 - 10.1149/2.0561714jes
DO - 10.1149/2.0561714jes
M3 - Article
AN - SCOPUS:85040766511
SN - 0013-4651
VL - 164
SP - C991-C1002
JO - Journal of the Electrochemical Society
JF - Journal of the Electrochemical Society
IS - 14
ER -
