Mini electric kiln project

[Mark Reich]

Mr. Mark and Mr. Scott, I would like to ask you about some practical aspects of knife steel heat treatment.

a)      At what temp do you insert the blade in the kiln? for low alloy high carbon steel, 1475F/800C

a) I always preheat the kiln to the desired temp and let it soak for at least 15 minutes before inserting blades.

b)      Do you use the heat treating foil? no

b) Doesn't apply to carbon steel nearly as much as it does to stainless with long, high temp hold times, but I'd much rather use shielding gas in my kiln instead. That would take practically nothing in your kiln, and greatly simplify your process. Foil makes quenching very problematic. There are anti-scale compounds that work better than foil, but I wouldn't use anything except gas if the situation dictates ongoing anti scale procedure.  

c)      How many preheat stages do you use and at what temps? How long do you hold the steel at that preheat stages? none, this is dependent on the steel you use and the source.  I mostly use O1/1.2510 precision ground flat stock that is ready to be hardened without pre-heat

c) Doesn't apply to carbon steel. If your stainless requires soaking at lower temps, it's for specific temps and time. Probably specific ramps too.


d)Can cooking oil be used for quenching?  yes, I use canola/rapeseed oil heated to 120F/50C

d) You've invested so much time and energy into your kiln, and secured excellent steel. Real quench oil of the correct speed is a very logical, wise investment. It will last forever, and it's one less variable to ever consider. 

e) Is there some time delay between quenching and tempering?  you want to keep the delay as short as possible.  I quench to room temperature then into ice water, scrub then into tempering oven.  

e) Park 50 at 100° is a 5 second quench, which is almost as severe as brine. I maintain constant cooling to -290° F with liquid nitrogen, hold, thaw, then temper. Tempering before the most thorough cooling you're capable of defeats the purpose, but it's a common practice for fear of broken blades. If you totally remove stress risers you will never break a blade.