The Effect of Hydrostatic Extrusion on the Corrosion Stability of Austenitic Stainless Steels
|Marcin Pisarek 1,2, Piotr Kędzierzawski 2, Maria Janik-Czachor 2, Krzysztof J. Kurzydlowski 1|
1. Warsaw University of Technology, Faculty of Materials Science and Engineering (InMat), Wołoska 141, Warszawa 02-507, Poland
The stability of passive film formed on austenitic 303 and 316 stainless steels in the as-received state and after a heavy deformation by hydrostatic extrusion (HE) was investigated in an aggressive environment containing Cl- ions.
TEM and stereological image analysis were used to examine structural changes introduced by HE treatment. The effects of surface oxide film on pit nucleation in stainless steel was investigated by anodic polarization in borate buffer + 0.1 M NaCl. Surface analytical techniques such as light microscopy, SEM, AES and SAM were employed to characterize morphology, grain size, and chemistry of the surface, including local characterization of nonmetallic inclusions and their surface before and after HE modification. The results confirm a drastic reduction of grain size, due to HE process and a distinct reduction of the size of sulphide inclusions occurring in the 303 matrix. Moreover a discontinuity of the surface oxide film on MnS inclusions was found using a local SAM analysis. These factors apparently result in a lowering of resistance of 303 HE to pit nucleation as compared to the as-received material. On the contrary, 316 stainless steel, where only scarce nonmetallic inclusions occurred, has shown a higher resistance against passivity breakdown after HE process. A tentative role of the above differences in stability of the passive oxide film on these materials is discussed.
This work was financially supported by the Polish Ministry of Education and Science through grant 3T08C 013 29. Surface characterizations were performed using a Microlab 350 located at the Physical Chemistry of Materials Center of the Institute of Physical Chemistry, PAS and of the Faculty of Materials Science and Engineering, WUT.
Presentation: Oral at E-MRS Fall Meeting 2007, Symposium D, by Marcin Pisarek
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-14 13:17 Revised: 2009-06-07 00:44