Metallurgical Trivia

Not really knife related, but I heard something recently about 300 series stainless truck mufflers rusting at the seams. Could this be caused by a lack of passivation of the welds or is it more likely that the company just used non-stainless wire when welding?

-d
 
A gal I met in the office a little while ago turned out to be a metallurgist by training (and former occupation).

After some discussion I mused aloud wondering how Howard Clark manages to heat treat his L6 katana blades so they have a bainite body and a martensitic edge.

She thought for a moment and gave me a lengthy explanation that I followed quite well: her reply boiled down to the process for case hardening.

Now I know why she isn't a metallurgist anymore!
 
Deker , recently ? About 30 years ago they started to use a stainless steel for mufflers ,I can't remember which. The funny thing is that we found , not the people who made it , that it wasn't stainless anymore if you welded or brazed it !!! You think they would have tested that !
But mufflers have two problems - the rusting from condensation inside , and the rusting from road salt etc. My F-150 is rusted from the salt, of course it would be a lot worse with plain steel.
These days they are using things like the 200 series for many things and if you buy from China or India you get some weird "200" series alloys.
 
Fun fact that is good to know, and fun to share:

Room temperature is a bit on the toasty side for aluminum, which is measurably stronger a bit colder.
 
(at least it used to be) You saw mufflers, etc that were said to be "aluminized steel for corrosion resistance." I always wondered if this was a fancy way of saying aluminum plated? :eek:
 
Why is it you can mix two metals together and have a lower melting or higher melting point than either pure metal?
 
Probably fairly common knowledge, but I went "huh" when I heard it: Aluminum is actually an extremely reactive metal, but a thin automatically formed oxide layer keeps it in check. However, throw some mercury in the mix, and things change. Exposure to mercury almalgamates the aluminum and will allow aluminum to "rust" VERY quickly, basically turning it into a useless pile in a matter of minutes (depending on the quantity of aluminum and mercury).

--nathan
 
McAhorn, I think alloying generally lowers the melting point of the metal being alloyed, (although there may be some exceptions), which can be a very useful thing to know,... for example, gold and silver solders come to mind. In general, it also makes the pure metal harder and more brittle.

... Why?,... I couldn't tell you. :)
 
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silver_pilate said:
Probably fairly common knowledge, but I went "huh" when I heard it: Aluminum is actually an extremely reactive metal, but a thin automatically formed oxide layer keeps it in check. However, throw some mercury in the mix, and things change. Exposure to mercury almalgamates the aluminum and will allow aluminum to "rust" VERY quickly, basically turning it into a useless pile in a matter of minutes (depending on the quantity of aluminum and mercury).

--nathan
Click to expand...

I heard of this from a buddy that was in the navy. He was on some aluminum hulled hydrofoil boat doing drug interdiction. They had their belongings searched to insure that nobody had a thermometer or any other item that contained mercury. A big no-no on that boat.
 
Cyclic austempering (10 degrees per minute) can speed up transformation to bainite by 80% ralative to isothermal austrmpering. And kevin Cashen still doesn't care. Insert martensite smiley face here.
 
Most stainless for exhaust applications is 409 stainless. Barely stainless. When steels containing chromium and carbon are exposed to temperatures between roughly 800-just over 1000F you will get chromium carbide precipitation. The metallurgical term is sensitization. On welding stainless the heat up is very rapid but the cool down is slow enough for the chromium to precipitate in the weld area knocking down the corrosion resistance of the weld and heat affected zone. 300 series stainless steels avoid this by having very low carbon contents. Search sensitization of stainless steel on the web for a lot more detail on this.
 
Not exactly metallurgical, but:
Yesterday a customer was in the store talking about how hot it was out at Laker Tahoe when she visited. Another nearby young lady commented ,"That's because Tahoe is, like, 5000 feet elevation". The first lady looked confused, and the younger claimed in a very scientific tone, " Yes, it is hotter because at that elevation you are, like, a lot closer to the sun. " Then she said the thing that made everyone in the store laugh out loud..... "You know, the sun is several thousand miles from earth, but at 5000feet, you are, like, 10% closer!" ..........I don't think the girl had a clue what everyone was laughing about.


The sun is primarily made of hydrogen and helium. The elements up to iron are produced in the fiery furnace of the core. The other elements, and especially the heavy metals,are produced in the slow burn of the star as it dies. So, in about 4-5 billion years, our sun will die....and seed the universe with more gold,lead, and knife making alloy metals for the next go round!
There ,that makes this a metallurgical trivia post.

Stacy
 
Making a platinum flute (solid platinum-not plated) can destroy the maker's tools which are typically tough enough to work on gold and silver. Not realizing this fact one maker ruined his tools and swore he would never make another platinum flute. To this day they are rare, also having something to do with cost:D.

Also due to the density of platinum the flutes must have gold or silver keys (there is one exception that I know of) so that the flute is not too heavy to use. The density also gives the flute a very dark, almost dead sound which is not very versiitile IMO.
 
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