Please learn from my mistakes.

[Bensbites]

I am copying the text of a post I made to a few knifemaking Facebook groups
“
Sometimes you have to walk before you can run... I just tried sprinting.

For my first heat treatment I tried differental hardening 26c3 bunkas. I am running this in my basement so I am trying an interrupted quench water 3 sec, followed by canola oil. Since I am in my basement, I am not interested in oil quenching.

The blanks were cut out, ground and sharp edges were radiused with 120 grit belt.

Clayed blanks were heated in my paragon oven 1440 F for 10 min. Then water (3 sec), then air (3 sec), then canola oil until cool. If you advice is to tel me to use parks 50, please don’t comment.

One blank cracked in the canola oil, one 10 min after it was cool while I was quenching another blade, and the third one cracked in the temper.

I could try 1425 vs 1440... any other suggestions?

Edit: people keep asking why I want to avoid oil, I am
Working in my basement. A bunch of burnt oil fumes would not be fair to the other people in my house. I am well aware of the higher fail rate, but I am having fun and learning.”

here’s a summary of what I learned today.
1) hotter water or hot brine
2) thinner clay
3) don’t let the blade cool to ambient temp, get it on the oven at about the tempering temps.

I thought some people here might have tips, other might enjoy watching.

 

[TB_London]

You could try a polymer quench as straight water is much more likely to lead to cracks. It’s more gentle but has the benefits of no fires/fumes.

https://www.gfsknifesupplies.com/Products/Heat-Treatment/accessories1/poly-quench-xl400-f1

Are you getting success without coating the spine? Going straight to interrupted quench and clay, gives a lot of variables to work through, maybe simplify with some test pieces and work up.

 

[Bensbites]

You could try a polymer quench as straight water is much more likely to lead to cracks. It’s more gentle but has the benefits of no fires/fumes.

https://www.gfsknifesupplies.com/Products/Heat-Treatment/accessories1/poly-quench-xl400-f1

Are you getting success without coating the spine? Going straight to interrupted quench and clay, gives a lot of variables to work through, maybe simplify with some test pieces and work up.

Thanks. I will look into the polymer quench.

 

[inferno]

i use 50/50 compressor oil and old motor oil from a diesel engine. its the best most healthy quench media. especially indoors.

what i would try is:
first test if you can quench the blades unclayed in water/brine/oil without them cracking. i would probably start with the least aggressive quench first. then move up using the same blade. oil-brine-water, even though brine is technically faster. water is probably more likely to crack the blades.

are these unground? maybe test grinding them to 80% done and then HT.

brine might help during the quench since you dont get gas bubbles that creates large temp gradients on the blade. but it wont help if stuff is cracking afterwards. but then again the blades might have already cracked in the quench without you knowing it.

i've seen japanese swordsmiths coat the whole blade, but its simply thicker at the spine.

in some tool steels datasheets they recommend you temper immediately after the blade has reached 80C, but those are tool steels with complex machining and such.

btw did you heat the oil?? iirc oil should be between 60-80C. i quench all my blades in 80-85C oil.

other things i can think of that might crack blades: no stress relieving after grinding, no normalizing, no ramps/holds in the HT cycle to equalize the temps in the blade.

 

[Bensbites]

i use 50/50 compressor oil and old motor oil from a diesel engine. its the best most healthy quench media. especially indoors.

what i would try is:
first test if you can quench the blades unclayed in water/brine/oil without them cracking. i would probably start with the least aggressive quench first. then move up using the same blade. oil-brine-water, even though brine is technically faster. water is probably more likely to crack the blades.

are these unground? maybe test grinding them to 80% done and then HT.

brine might help during the quench since you dont get gas bubbles that creates large temp gradients on the blade. but it wont help if stuff is cracking afterwards. but then again the blades might have already cracked in the quench without you knowing it.

i've seen japanese swordsmiths coat the whole blade, but its simply thicker at the spine.

in some tool steels datasheets they recommend you temper immediately after the blade has reached 80C, but those are tool steels with complex machining and such.

btw did you heat the oil?? iirc oil should be between 60-80C. i quench all my blades in 80-85C oil.

other things i can think of that might crack blades: no stress relieving after grinding, no normalizing, no ramps/holds in the HT cycle to equalize the temps in the blade.

Thank you.
1) I may go oil, but I want to flush out the water further.
2) I did try a rough coupon of the steel, the size of the area under the tang. No prep, no smoothing of edges, no stress relieve. I heated this and dunked it in water my grinder swarf bucket. A file skated. I snapped it and check the grain it looked great.
3) this was 1/8th (3.1 mm) thick unground steel. I cut the profile on my bandsaw, then rounded all the edges with 120 grit.

 

[inferno]

try coating the whole blade in thin clay and see how that works.
also with all these interrupted quenches you introduce a lot of variables that might not be reproducible.

if i was making honakis i would find a way/steel that i could simply dunk in brine or oil. then when cool put it in the tempering oven.
and it might not be easy. i have a feeling a lot of steels will crack in water no matter what.

 

[Bensbites]

try coating the whole blade in thin clay and see how that works.
also with all these interrupted quenches you introduce a lot of variables that might not be reproducible.

if i was making honakis i would find a way/steel that i could simply dunk in brine or oil. then when cool put it in the tempering oven.
and it might not be easy. i have a feeling a lot of steels will crack in water no matter what.

Thank you again

 

[Staystrapped]

Alpha knife supply says:
Austenitize: Heat to 1,475°F. Soak for ten minutes. The mill recommends quenching in water. We used Parks 50 with excellent results. The as quenched hardness was a little under HRC 68.

 

[Bensbites]

Alpha knife supply says:
Austenitize: Heat to 1,475°F. Soak for ten minutes. The mill recommends quenching in water. We used Parks 50 with excellent results. The as quenched hardness was a little under HRC 68.

Thank you. I did that with an off cut first. This time I was trying differentally hardening.

 

[Staystrapped]

It sounds like a nice steel but they don’t sell it on Amazon lol