Cracked blades

[Storm W]

I have done the first heat treatment in a couple of years. The first blades were thin stock AEB-L and S35VN and seemed to come out great. The other blades were 1/4" AEB-L and A2. All of the A2 blades cracked. The second HT was 1/4" A2 and 3V these seemed to have even more cracks. The HT was from Larrins book and on the lower end with a dry ice cryo. 400 degree temper. All I can think is that my oven might be messed up. The grain looks good but the cracks were old and not from grinding. Makes for a bad day.

I just remembered that I heard a couple of tinks before I put one of them in the cryo.

 

[Stacy E. Apelt - Bladesmith]

Give us some more info:
Any forging done?
What grit surface at HT?
HT temps and oven type?
Quench method?
Tempering schedule?
Why 1/4" thick blades???

 

[tito]

Maybe a dumb question, but were they still pretty warm when you put them in cryo?

 

[Storm W]

Stacy E. Apelt - Bladesmith
And evenheat with rampmaster control.
Plate quench. The second batch I used very little air even for the quench.
No Forging.
The A2 was 1750 for 20 minutes and the 3V was 2000 for 30.
Blades stayed in the bath until I took them for temper. They got 3 one hour plus cycles at 400 degrees.
The first ones were ground to 120 and the second batch were left full thickness.
The blades were rapped with foil.
Most of the blades were almost cool enough to handle when I cooled them in my water bucket and were room temperature when they went into the dry ice slurry.

I grabbed a S35VN blade last night and slammed it in the anvil with no problem as well as grinding a chefs knife out of one that turned out great and felt like it was perfect. It flexed and I did an couple of chopping sessions in the kitchen and it performed well. It didn't seem to be chippy or soft and felt like is was one of my better knives.

I used some acid and dye on the A2 blade from the second batch and it is full of cracks and they don't just start at the edge.

 

[Stacy E. Apelt - Bladesmith]

I don't see any red flags with yout HT regime.

Grind the surface down a bit on that A2 blade and check the cracks again. It could be some sort of alloy banding issue on the surface.

 

[Storm W]

I don't see any red flags with yout HT regime.

Grind the surface down a bit on that A2 blade and check the cracks again. It could be some sort of alloy banding issue on the surface.

The A2 blade was almost done and the same with one of the 3V blades. A sharp smack and they all broke. I thought maybe it was just a single crack on the A2 blade so I etched it and there are spiderweb cracks all through it.

 

[Stacy E. Apelt - Bladesmith]

Something is odd! Maybe the steel source?? Who did it come from?

BTW, You should change the TC in the oven if it is more than a year old. They can start reading inaccurately.

 

[HSC ///]

did you stress relieve the material first?
I suggest a 1200 F stress relieve cycle when you get the material.

 

[Storm W]

I have never heard that a stress relief was necessary for air hardened steel. I just used it as is. I just bent and impacted thinner 3V and dosed it with acid and it seemed fine. Same as the thinner blades from the last HT.

 

[Dominick Maone]

Not sure the exact recipe for A2, but Aaron Gough does one temper cycle before cryo. I think when one does cryo is sort of debated.

 

[Storm W]

Not sure the exact recipe for A2, but Aaron Gough does one temper cycle before cryo. I think when one does cryo is sort of debated.

This is the one out of Larrins book. I think it should be fine. If it was just A2 I might think there was something to chase down that road. The fact that it involves 3V leads me to believe something else is the problem. I also did some thinner 3V and it seems fine. I don't know if I would get anymore cracks if I water quenched them both.

 

[Willie71]

Not sure the exact recipe for A2, but Aaron Gough does one temper cycle before cryo. I think when one does cryo is sort of debated.

if you temper before cry, you stabilize the retained austenite, negating the benefit of the low temper protocol. Temper, then cryo can be used with high temper, as high temper converts retained austenite.

 

[Willie71]

Storm and I have been talking about this offline for the past couple of days. The process seemed fine from what he told me. I am leaning to a steel problem, but fir it to show up in two steels at the same time is odd.

Only other thing I can think of it the water dunk before cryo, but they were cool enough to handle. The cracks not starting at normal stress risers is leading me to say steel problem.

 

[Storm W]

Something is odd! Maybe the steel source?? Who did it come from?

BTW, You should change the TC in the oven if it is more than a year old. They can start reading inaccurately.

I got it from NJSB about 4 or so years ago.

I'm not really in a position at the moment to spend on equipment. I don't think I have more than a dozen cycle on it. I was busy with work and them moved and this is the first time in about 3 years that I fired it up. The S35VN blade that I just finished was fantastic. If my thermocouple is off I need to find out what I did because it was spot on.

I was thinking that maybe they could have been to hot when I dunked them but they were probably in the plates for 5 minutes. My plates are 1.5" X8"X14" I think. The plates and the blades were the same temperature and should have been ok to dunk. One got in there a bit hot and I was careful on the next two.

 

[Stacy E. Apelt - Bladesmith]

I just remembered you are in Canada. You need to check under the benches and in the corners to look for Gremlins, Coblynau, or Fuggies. They regularly cause unexplainable things to happen.

 

[samuraistuart]

Just a side note, that second photo showing the grain structure.....EXCELLENT JOB on the photo. Not only does the grain structure look fantastic, the photo is fantastic as well. But as for the issue, it is odd. Stacy might just be on to something with those Gremlins. Here in Texas we have to worry about Chupacabras and Lechuzas messing up our work.

 

[Storm W]

I just remembered you are in Canada. You need to check under the benches and in the corners to look for Gremlins, Coblynau, or Fuggies. They regularly cause unexplainable things to happen.

Lol. Well I have lived close enough to Canada to feel like some could rub off but I'm in Syracuse NY. I was bummed when I moved here and learned that I couldn't just go down to Crucible and get chunks of steel all hot and fresh. Willie is Canadian but he still doesn't mind talking with me sometimes and doesn't even make me convert everything to metric.

 

[Storm W]

Just a side note, that second photo showing the grain structure.....EXCELLENT JOB on the photo. Not only does the grain structure look fantastic, the photo is fantastic as well. But as for the issue, it is odd. Stacy might just be on to something with those Gremlins. Here in Texas we have to worry about Chupacabras and Lechuzas messing up our work.

My phone has one of those flowers settings were you have to be within 2 inches. It's nice for this stuff.

 

[HSC ///]

I have never heard that a stress relief was necessary for air hardened steel. I just used it as is. I just bent and impacted thinner 3V and dosed it with acid and it seemed fine. Same as the thinner blades from the last HT.

Well one of my mentors taught me to stress relieve material before heat treating so i generally do

From knifesteelnerds.com

“
Stress Relieving

Another type of heat treatment that can be performed prior to the final austenitize is a “stress relief” treatment. This one is commonly done because of stresses induced in the steel during grinding the annealed steel. If the steel is significantly heated in different portions from grinding this can lead to increased chances of warping or cracking during austenitizing and quenching. A stress relief is typically done from 1200°F/650°C for 2 hours.”

While he speaks about the grinding, I’m stress relieving the material when I get it.

 

[Storm W]

Well one of my mentors taught me to stress relieve material before heat treating so i generally do

From knifesteelnerds.com

“
Stress Relieving

Another type of heat treatment that can be performed prior to the final austenitize is a “stress relief” treatment. This one is commonly done because of stresses induced in the steel during grinding the annealed steel. If the steel is significantly heated in different portions from grinding this can lead to increased chances of warping or cracking during austenitizing and quenching. A stress relief is typically done from 1200°F/650°C for 2 hours.”

While he speaks about the grinding, I’m stress relieving the material when I get it.

I get that. If we were talking heavy warping and perhaps a random crack it would be something to look into but these were just profiled and from what I understand are not known for cracks and I think something else is wrong.

How much solvent and dry ice do people use normally? I used about a half gallon if solvent in a large cooler and it was about 3/4-1" deep. I had probably about 8lbs or so of dry ice left by the time I added it to the solvent and chopped it up the best I could. The gave me a 10lb solid cube and I wasn't thinking and didn't chop it up before adding it so I just chopped it the best I could and stirred it up. These were both close to 3/8" thick. Would being in a shallow bath with floating chunks of dry ice lead to uneven cooling and be enough to form cracks? If that were the case it would make sense that the thinner stock would be fine.