Influence of P, S and O impurities on Corrosion of High-Purity 316L 1

[kenvlach]

FYI, an article in ISIJ Int., Vol. 46, pp.567-572 (2006):
Influence of Phosphorus, Sulpher, and Oxygen on 65% Nitric Acid Corrosion Resistance of Super High-clean 316L Stainless Steel [abstract only w/o subscription] by Kazuyuki Sakuraya et al.

"By decreasing phosphorus content in these steels from 0.026 to 0.0002 mass%, the corrosion rate in 65% nitric acid solutions decreased remarkably.
...
there were linear relations between corrosion rate and the very small amount of sulfur and oxygen contents in the super-low phosphorus stainless steels containing under 0.0002 mass% phosphorus.
...
the corrosion of super-low phosphorus content 316L type stainless steels even at 0.0002 mass% was not uniform corrosion but intergranular corrosion."

http://www.jstage.jst.go.jp/article/isijinternational/46/4/46_567/_article

 

[EdStainless]

Impressive chemistries, but nothing new.
Considering that if I buy AOD/ESR stainless today I still get 0.025% P this doesn't mean much.
I do need to hunt through my sample box. I ran some 316LN that was 0.010% P, I wonder how it would do?

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[mcguire]

Ken
It's very difficult to remove P from Cr containing alloys. Why do you think that its influence can't be negated by gettering it with something like Ti? This really sounds like something worth pursuing.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[mcguire]

After thinking about it, I realize that the solubility product must be such that ultra low P in solution can't be attained with Ti.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[kenvlach]

mcguire,
There is always enrichment of surface-active elements in the grain boundaries, to levels above solubility limits for the bulk phases. Perhaps you've done a few high-resolution line scans?

 

[EdStainless]

You could look at some 321 samples an see where the P is.

Low S is easy. S<0.0003 is common in remelted alloys. O tends to be a bit higher, esp in high N alloys, maybe 0.002.
But what about Ca and B?
It is almost impossible to hot roll stainless without a bit of B 0.0005

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