Heat Treating

Heat treating is probably the second most important step to making a knife, the first being the steel is actually in the shape of a knife! During heat treat the steel undergoes a change in structure making it much harder than its soft annealed state. This hardness is what gives a knife its ability to hold an edge a long time and also to take a good sharp edge.

The first part of the heat treat is the hardening (or austenitizing) phase; the blades are brought up to a very high critical temperature and then cooled very rapidly to room temperature between aluminium plates. After this step the blades are very hard and also very brittle.

The second step is the tempering phase which slightly reduces the hardness but brings down the brittleness a lot making the blade much tougher; The blades are brought to a lower temperature (typically a few hundred degrees Fahrenheit) and held there for 2 hours. The blades a re cooled and an identical second tempering step is preformed.

Every type of steel has a slightly different heat treat "recipe". Depending on its chemical composition the temperatures used will vary. The steel we use (CPM S35VN by crucible industries) is in a group of high alloy steels that require extremely high temperatures to properly harden. The knives are hardened at 2000 Fahrenheit and tempered at 600.

The extreme temperature of the hardening phase will badly damaged the steel through oxidation and decarburization if it isn't protected. To prevent damage each blades is wrapped in a pouch of thin stainless steel foil with double folded seams.

We do all of our heat treat in house using an evenheat electric kiln.

[punishr]

Great video! I have a questions about your heat treat furnace. What is the max temp and what is the highest you have had it too? Thanks

[killerkane]

All fine and good. I have a shop with all the equipment anyone could dream of. But my thing is hammers and tools. Getting ready to make some knives. You quench on aluminum blocks. What type of steel? What about oil quench? What is a good procedure for getting the blade out of the foil and into the quench with minimal loss of time/temperature??

[killerkane]

One more thing: I have ready access to many gallons of liquid nitrogen. I’ve treated hammers and it seems to add toughness. Your opinion on knives please.

[sonicify]

I like your chef's knife ;-) ..but a Santoku shall be lighter, shorter und more "broader" up front .

And an cutting-angle of +-20* is best for the style of use for such a Japanese knife.


thx

[akashsinghal]

hey nice video
we require a machine for hardening our industrial tools
can this machine do that also ??

[matthiasgr]

Nice video! I just started using the cpm s35vn. Do you use deep freezing? If not, at 600f what hardness do you get? Crucible steel is not very clear about it.
Thanks for the help

[sonicify]

So great making process ! :D ...please make a Santoku kitchen knife in a 10 min Video. If u have something like this to offer i would buy it. But please try to give it a tanto like top for a more modern look ;)

[g-codeonedesign]

I bleed out every time.... I love heat treating...lol. Usually add some paper in there