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A Totally casual question,(just in case Jarrod is bored:)),especially since i think it's come up before...and maybe more than once.

 

Lead bath pops up in HT sequence of tooling,files in particular for some reason.

 

I can't quite figger this one out:The melting point of Pb is around 625F,not enough for quench,and seems kinda high for tempering anything(particularly files).

 

What was at the bottom of the industry's attraction to Pb bath,historically?

God is in his heaven,and Czar is far away...

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Lead boils at just above 3,000 degrees F, so it acts like a molten salt bath in that you can keep it as a liquid over a wide range of temperatures.  That's really why industry used it, and molten salts have replaced it.  It is kind of high for tempering files, but perfect for swords and springs made from straight carbon steels. Plus it doesn't stick to the parts unless you flux them, so they come out dry. 

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Polished steel parts that I have dipped in molten lead also come with a very nice blue temper color too.

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1 hour ago, Gazz said:

Polished steel parts that I have dipped in molten lead also come with a very nice blue temper color too.

 

I forgot about that!  But yes, that's why old gunlock and clock springs are that beautiful uniform bright blue.

 

 

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On thing to keep in mind when using molten lead is the fumes.  When I was working for a clinic that did heavy metal testing on people we had at least a couple of welders who refused to wear respirators come in with high lead levels and had to be laid off from their jobs.

 

Doug

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HELP...I'm a twenty year old trapped in the body of an old man!!!

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Alan beat me to it, but I do have more to add.  The specific heat capacity of lead is 0.129 J/gC, whereas salt (NaCl) is 0.88 (other salt blends will be different, but you can see the general magnitude of the difference).  

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