TITLE:
Sensitisation Study of Normalized 316L Stainless Steel
AUTHORS:
P. Atanda, A. Fatudimu, O. Oluwole
KEYWORDS:
Sensitisation; Normalization treatment; 316L Stainless steel
JOURNAL NAME:
Journal of Minerals and Materials Characterization and Engineering,
Vol.9 No.1,
January
20,
2010
ABSTRACT: Austenitic stainless steels with excellent corrosion resistance and good weldability have wide
applications in industry. These iron-based alloys contain a high level of chromium which form
protective oxide film on the surface hence resisting corrosion. The oxide film regenerates when
damaged, making the steel 'stainless'. However, carbide precipitation due to a welding process
or heat treatment can cause the occurrence of chromium-depleted zones at the boundaries,
leading to a phenomenon known as sensitisation, in which the depleted zones become the focus
of the intense corrosion.
The present work was concerned with the study of the sensitization and desensitisation of 316L
steel at the normalizing temperatures of 750- 950℃ and soaking times of 0.5, 1, 2 and 8 hrs.
316L stainless steel was observed to be sensitized when heated to 750- 850℃ and held for short
soaking times of 0.5 – 2hrs before normalizing. Increasing soaking times at these temperatures
to 8 hrs triggered the desensitization process which was fully accomplished at 750℃ but
ongoing at 800 and 850℃. At 900℃, sensitization did not occur at 30 mins soaking time but
observed at soaking times of 1 and 2hrs. At a longer soaking time of 8 hrs, there was full
desensitization. At 950℃, sensitization was already observed at 30 mins. Soaking time and
desensitization was observed to be in progress at 1 and 2 hrs soaking time. By 8 hrs there was
full desensitization. Thus it was observed that at 950℃, diffusion of Cr was thermally aided
making desensitization fast. The hardness of normalized 316L stainless steel was also observed
to decrease with soaking time and normalization temperature.