David Pawley wrote:
>Somewhere recently, I read in a trade magazine, that a stainless
>steel outdoor work of art, had to undergo a factory process to stop
>rust setting in. I will try to find it again.
Hopefully the information includes what type of stainless steel was
used. Some of the "cheaper" (low nickel-chromium) stainless steel
alloys (many of which are magnetic) are not exactly "stainless", and
will rust more readily than the better grades (higher nickel-chromium)
stainless alloys, such as Type 316L (part of the "18-8" family, a low
carbon alloy.) Generally, the higher the chromium content (and the
nickel helps, too -- carbon should be very low), the better with
respect to resistance to rusting and corrosion.
Of course, going to a very low iron or iron-free nickel-chromium alloy
will eliminate the red rust problem entirely (which is due to the
iron) but brings in other considerations, such as cost and
machineability as I have noted in prior messages. And corrosion of
other types (such as "white rust") is not eliminated, especially that
due to chloride attack, which one would see in marine environments.
Btw, I did a quick web search on rusting, corrosion and stainless
steel and came across the following web sites, which should be of
interest to those who are interested in this topic. There are
thousands more pages, but I found these quickly and at first glance
they cover a lot of the important issues for dialists when considering
using stainless steel and other alloys in sundials:
http://www.finishing.com/107/57.html
http://www.hitchiner.com/HIMCO/HIMCO_Library/2D4_Rusting_of_Stainless.pdf
http://www.burnsstainless.com/TechArticles/Stainless_article/stainless_article.html
http://www.mcnallyinstitute.com/04-html/4-1.html
>From looking at the above, and corrosion charts in my Handbook of
Chemical Engineering, Hastelloy C looks very promising from a
corrosion viewpoint: Hastelloy C has 16% Mo, 16% Cr, 5% Fe, 4% W
(tungsten), traces of MN and Si, and the balance nickel (~59%). It
seems to resist most everything under the sun. I'm sure it is very
expensive, but maybe worth exploring. I'm also intrigued with
titanium as well... Anyone here built a sundial using a titanium
alloy? Titanium is being used more and more for architectural and
art.
Jon Noring
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