Re: Practical Significance of Findings

Posted by Wing-yan Ng on August 05, 1996 at 02:00:31:

In Reply to: Practical Significance of Findings posted by Dr. R.D. Kane on July 28, 1996 at 10:21:47:

: Normally, we think that coldworking will increase susceptibility
: to localized corrosion in stainless steels. Your paper
: suggests that it may be more complicated than that.

: Please elaborate on the mechanism by which the presence
: of the coldworked surface layer could provide an increase
: in protection from corrosion.

: Is it of any practical significance?

Coldworking will increase susceptibility to corrosion in stainless steel. This phenomenon has been well documented in the literature. Our investigations have added further information on the susceptibility of corrosion for coldworking below room temperatures. Corrosion susceptibility shows a rapid dive with a‘-martensite contents of less than 6% but decreases rapidly in the range of 6 - 22% a‘-martensite contents to over 75% of the original value. However, corrosion susceptibility increases again with a‘-martensite contents > 22%.
We believe that the transformation process plays an important role in the formation of defects leading to the deterioration of the protective film formed on stainless steel. Localized distribution of Cr resulting from transformation controls resistance to corrosion. We are in the process expanding our investigations to support our observations.
One of the immediate applications in our investigations is on the monitoring of metal characteristics at low temperatures and under strain. We have also observed that coldworking at low temperaures contributes to stress corrosion cracking.

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Comments:
         : : Normally, we think that coldworking will increase susceptibility
: : to localized corrosion in stainless steels. Your paper
: : suggests that it may be more complicated than that.

: : Please elaborate on the mechanism by which the presence
: : of the coldworked surface layer could provide an increase
: : in protection from corrosion.

: : Is it of any practical significance?

: 
: 	Coldworking will increase susceptibility to corrosion in stainless steel.  This phenomenon has been well documented in the literature.  Our investigations have added further information on the susceptibility of corrosion for coldworking below room temperatures.  Corrosion susceptibility shows a rapid dive with a‘-martensite contents of less than 6% but decreases rapidly in the range of 6 - 22% a‘-martensite contents to over 75% of the original value.  However, corrosion susceptibility increases again with a‘-martensite contents > 22%.  
: 	We believe that the transformation process plays an important role in the formation of defects leading to the deterioration of the protective film formed on stainless steel.  Localized distribution of Cr resulting from transformation controls resistance to corrosion.  We are in the process expanding our investigations to support our observations.
: 	One of the immediate applications in our investigations is on the monitoring of metal characteristics at low temperatures and under strain.  We have also observed that coldworking at low temperaures contributes to stress corrosion cracking.