Duce
My home town had a Nicholson file factory, long since closed. One problem they had when they torn it down was lead contamination. Seems that they used molten lead in vats, used in the tempering process. Anyone have an idea how?
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jmccustomknives
Yes, they used molten lead heated to the austinization temp of the steel they were using, about 1350F.  They would take the file blanks and place them in a jig that would dip them end down into the molten lead.  The jig was there because the steel would float up on the lead.  (the irony of steel floating, lol).  They would do 6 at a time and by the time the last one went in the first one was ready to come out.  The files were then grasped in another jig to keep them strait and quenched in brine.  Since the alloy at the time was around 1.3% carbon it made them very hard (those files test out around 70RCH).  After the government got involved because of the toxic nature of lead they went to molten bizmouth. 

In the early '80's Nicholson retooled completely and went to an induction heater.  The later files aren't near as good nor as hard.  The steel is different also.

There's a gentleman who comes to our blacksmith meetings, I guess he must travel around.  He worked for Nicholson and when they retooled he bought all the old stock.  He's been selling those files for the last 35 years or so.  I got the info from him just because I wanted to know.

Rule #10;  "I can make that" translates to; "I'm to cheap to buy it new."

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Duce
Wonder if you could use a bullet casting furnace and lead to draw back/temper with?
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jmccustomknives
Duce wrote:
Wonder if you could use a bullet casting furnace and lead to draw back/temper with?


I guess the first thing is to distinguish between tempering and hardening.  Hardening is when you take the steel to it austinization temp and quench forming martinsite (hardened steel). 
Tempering is when you degrade the maratinsite softening the steel.  Temperature and time are critical in this process.  So, yes some steels might could be tempered in molten lead (625F).  Depending on the alloy one could get a spring temper to a using temper (high alloy tool steel like HSS).

Nicholson heated the lead to 1375, this brought the steel up to temperature very fast because the lead is so dense.  Of course it is very toxic also. 

Rule #10;  "I can make that" translates to; "I'm to cheap to buy it new."

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