From the Lehman's website:

After being hand forged, each blade is plunged into boiling lead, then quenched in water and sharpened. Blades stay sharp longer and will last a lifetime. Made in France.
I think TI claims "lead hardening", and I haven't seen any other maker that does.

Now, "boiling lead" tells me that somebody doesn't know anything about metallurgy. "Melted lead" I could believe.

Charles