The contstruction of Randall Knives

[Carol]

Mr. Bo Randall and company shows how a slab of carbon steel gets transferred in to a Randall Made Knife (http://www.randallknives.com/construction.php).

[arnisador]

Interesting! I know many people who do this and so many others who would like to do it.

What's tempering oil? I couldn't find much on a search.

[Carol]

Tempering oil is the hot-oil bath given to the newly forged steel. The cherry-red temperature that Randall mentions is about 900° C. From there, the blade is precisely cooled to a specific temperature.

Air cannot be used, as that would not first bring the blade down to a specific temperature. Water risks rusting the iron molecules, plus water turns gaseous at 100° C. So, tempering oil is used instead.

Tempering oil...which is a viscous oil that can withstand the high heats of the forge...would be heated to 490° C. The cherry red steel would then be totally immersed in the oil bath until it was cooled all the way through to a temperature of 490° C. It is this precise cooling that encourages additional crystalization of the steel molecules...hence making for a harder metal.

[arnisador]

Ah, OK! So it isn't so much a unique type of oil as how it's used, then?