Cracked blades

[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

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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.

I don’t think so... I’ve done it the same way in the past as you described

 

[JamesBro]

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.

I use about a brick sized chunk or a little less, enough alcohol to make a slush in a narrow small ice chest. Deep enough to submerge entire blade. The blades groan when inserted but never ping.
I have done a lot of A2 and never had a crack or done a stress relief. Most of my A2 was in Marshall steel wrappers from different suppliers. My hardness was high with 2 hr tempers at 400, Since getting a tester, I am tempering between 450 and 475 depending on the Rockwell number after the cold treatment. I shoot for 60rc.
James

 

[Storm W]

I use about a brick sized chunk or a little less, enough alcohol to make a slush in a narrow small ice chest. Deep enough to submerge entire blade. The blades groan when inserted but never ping.
I have done a lot of A2 and never had a crack or done a stress relief. Most of my A2 was in Marshall steel wrappers from different suppliers. My hardness was high with 2 hr tempers at 400, Since getting a tester, I am tempering between 450 and 475 depending on the Rockwell number after the cold treatment. I shoot for 60rc.
James

It didn't ping when I put it in. If I remember correctly it was after I took it out of the wrap and then a second time after I cooled it down right before I put it in. It was also only the one piece of 3V that I thought I heard that. Since it was not at any of the normal times for it to happen I thought I was being paranoid. All of the thinner blades still seem to be spot on. Do you ever get 0.300 thickness and use it with that setup?

How far off would I have to be to get something like this to happen if it's my oven? I was using 321 foil and it looks fine. I forgot and used it for some M2 before and it looked hammered. I would think that if I was running say 200 degrees off it would have affected my S35VN blade instead of giving me a the best HT I did so far. It wasn't at either end of the spectrum so 50 degrees wouldn't have been that bad. I am able to deflect the thinner blades of 3V out of the same batch till it took a slight set. I don't want to go further.

 

[Matthew Gregory]

It was your water quench. I’ve had similar things happen to me, in the past. My guess is that there’s a section which was hotter than you thought it was after plate quenching (when you thougt it was ‘almost cool enough to hand hold’) and the temperature delta was sufficient to produce stress in an already really stressed blade to crack.

Buying a replacement thermocouple for your furnace because it’s a year old is absurd. Determining if there‘s an issue with your thermocouple by using a second means of reading is the way to determine a problem with a thermocouple. They don’t go bad due to age, they go bad from lots of use, and for most of us, that means YEARS. Being able to confirm your reading from it with a second tool is a good idea, anyway.

Pointing a finger at the steel when TWO different steels failed in a similar fashion is a serious stretch. That fact alone points to something in the process.

 

[Savaga]

I wrap the blade with cloth and tape before placing it in liquid nitrogen. (a sock is a great idea!)) this saves from curvature

 

[DevinT]

I’ve seen this happen on some steels that have excess decarb on the surface. Take off ~.005-.006 per side and see if that helps. A stress relief cycle is a good idea too, as others have said.

Hoss

 

[JamesBro]

It didn't ping when I put it in. If I remember correctly it was after I took it out of the wrap and then a second time after I cooled it down right before I put it in. It was also only the one piece of 3V that I thought I heard that. Since it was not at any of the normal times for it to happen I thought I was being paranoid. All of the thinner blades still seem to be spot on. Do you ever get 0.300 thickness and use it with that setup?

How far off would I have to be to get something like this to happen if it's my oven? I was using 321 foil and it looks fine. I forgot and used it for some M2 before and it looked hammered. I would think that if I was running say 200 degrees off it would have affected my S35VN blade instead of giving me a the best HT I did so far. It wasn't at either end of the spectrum so 50 degrees wouldn't have been that bad. I am able to deflect the thinner blades of 3V out of the same batch till it took a slight set. I don't want to go further.

I have never used A2 for a thin kitchen knife but I checked a hollow ground A2 knife and it’s under .003 for the last .4 inches approaching the edge. I have never started with .3 stock..maybe .2, always very clean out of the foil.
I have never dipped a hot blade in water, I cut them out of the foil with no gloves after about 3 to 4 minutes of frozen plate quench. If I want to cool the blade further it’s under running water that’s starts out a little warm and I turn to cool. J

 

[Stacy E. Apelt - Bladesmith]

Matthew is right. I did not consider the thickness. 1/4" stock could well be over 400F inside when you dunked it in the water. That could easily lead to cracking due to rapid cooling stress.

My comment on the TC was because he said he wasn't sure it was reading right. A new TC will solve that concern. The manufacturers recommend every 2-3 years replacement if the oven gets regular use.

 

[Storm W]

I’ve seen this happen on some steels that have excess decarb on the surface. Take off ~.005-.006 per side and see if that helps. A stress relief cycle is a good idea too, as others have said.

Hoss

Can you see this wavy lines in there? I thought those were a bunch of cracks but I'm not sure. Both steels are very over thickness with factory decarb. The 3V knife seemed like it was really thick. I'm wondering if those lines might be my imagination and if they are if I just didn't grind the plasma cut edge back far enough. It was rougher on the A2 blade. I can only see the one spot where the end cracked of of the A2 blade and all of my problems with it have been cracks coming in from the edge. The knife will take hard raps on steel and can take the blade being flexed hard from side to side. The last batch of A2 blades were all edge cracks and warps were easy to fix. I don't want to sell a blade that is full of hidden cracks but having 2 separate cracking mechanisms would actually make this a lot simpler. The 3V does have that really heavy CPM rind on it.

 

[Storm W]

It was your water quench. I’ve had similar things happen to me, in the past. My guess is that there’s a section which was hotter than you thought it was after plate quenching (when you thougt it was ‘almost cool enough to hand hold’) and the temperature delta was sufficient to produce stress in an already really stressed blade to crack.

Buying a replacement thermocouple for your furnace because it’s a year old is absurd. Determining if there‘s an issue with your thermocouple by using a second means of reading is the way to determine a problem with a thermocouple. They don’t go bad due to age, they go bad from lots of use, and for most of us, that means YEARS. Being able to confirm your reading from it with a second tool is a good idea, anyway.

Pointing a finger at the steel when TWO different steels failed in a similar fashion is a serious stretch. That fact alone points to something in the process.

Unless there were a difference In how the two pieces cracked like I replied to Devin Thomas it's the only thing that makes sense.

 

[Matthew Gregory]

If they were plasma cut, the cracks could also be from HAZ not being completely ground away. That was the determined mode of failure for a friend of mine that had a few laser cut blades crack during HT.

 

[Storm W]

If they were plasma cut, the cracks could also be from HAZ not being completely ground away. That was the determined mode of failure for a friend of mine that had a few laser cut blades crack during HT.

That's what I'm leaning towards right now for the A2. The 3V is filled with cracks. The previous A2 blades were profiled and partially ground the cracks all came in from the plaz cut side. I ground in on this one but possibly not enough. I can only see the one spot that was a crack for sure. The marks on the surface might just be from how the acid beads up on it. I don't have a way to dunk it.

If I remember correctly it I heard the tink from the 3V before I ever out it in water. That's why I didn't think there was a problem. That one had been in plates for a few minutes and didn't go into water right away. I just swished it in there to make sure it was as cool as possible before I put in in cryo.

Is there anything I can do to make sure that the A2 blade doesn't have fine cracking that will be a problem? Right now hard wacks and bending isn't causing any more cracks to show. There is just some patterns in the acid wash of the blade.

 

[Storm W]

I just went and took a look at the pieces I had wiped down with acid. It looks like what I thought was a crack pattern on the blade is banding from the mill and is consistent and attractive. I'm not seeing sharp or black lines and no rust bleeds.

I had ground off the surface of about 4" of scrap 3V and it looks very much like I am seeing a crack in there. When I can get to it later I'm going to try etching it better. It could be wishful thinking on my part but it might fit. I don't know where my dye pen kit is or even if I still have one.

 

[Willie71]

That's what I'm leaning towards right now for the A2. The 3V is filled with cracks. The previous A2 blades were profiled and partially ground the cracks all came in from the plaz cut side. I ground in on this one but possibly not enough. I can only see the one spot that was a crack for sure. The marks on the surface might just be from how the acid beads up on it. I don't have a way to dunk it.

If I remember correctly it I heard the tink from the 3V before I ever out it in water. That's why I didn't think there was a problem. That one had been in plates for a few minutes and didn't go into water right away. I just swished it in there to make sure it was as cool as possible before I put in in cryo.

Is there anything I can do to make sure that the A2 blade doesn't have fine cracking that will be a problem? Right now hard wacks and bending isn't causing any more cracks to show. There is just some patterns in the acid wash of the blade.

I looked through my texts, and you said the tink was before cryo.

 

[Storm W]

I looked through my texts, and you said the tink was before cryo.

The way I remember is that the first one was still way hotter than I remembered so I was very careful on the second (both were 3V) I remember picking up the second with my bare hands and heard a tink. I thought it must be my imagination and then put it in my bucket to cool it as much as possible but that wasn't cold by any means. Room temperature at the coolest. Then as I was getting ready to drop it in the the slurry I heard a second tink. Before it was in. Granted it was late and I may not remember everything right but I definitely heard them both before cryo and I was being careful that it was cool before it went in the water.

I think my panic with the A2 was off. I think it was a single edge crack from the plasma edge. What I thought were cracks seems to be alloy banding and is everywhere after the acid set overnight. It actually looks really good.

The 3V is full of cracks and they run both directions. D DevinT you said heavy decarb will do that. Could you explain more? These were huge knives for a huge guy and I would like to keep as much thickness possible if he wants me to repeat the order but I very much don't want to shatter another bar. I have 4 or so inches with NJSB markings on it. Is it worth asking them about it or is there a lesson for me in hear?

 

[Storm W]

I have never used A2 for a thin kitchen knife but I checked a hollow ground A2 knife and it’s under .003 for the last .4 inches approaching the edge. I have never started with .3 stock..maybe .2, always very clean out of the foil.
I have never dipped a hot blade in water, I cut them out of the foil with no gloves after about 3 to 4 minutes of frozen plate quench. If I want to cool the blade further it’s under running water that’s starts out a little warm and I turn to cool. J

I'm not sure if I understand. These are massive thick blades. I never had a problem with thin blades. Both 3V blades are equally as bad and the second I cut out and could handle it with bare hands. It wasn't cold water. I had used it to cool my quench blocks first and it was warm. If I remember correctly the second blade had 3 to 5 minutes in the blocks and then sat on the deck while I filled my bucket and dunked the blocks and then I forgot about it for a bit so it probably had 15 minutes to cool in all. That's the one I heard tink twice before cryo

 

[DevinT]

I’ve never seen it cause multiple cracks. The decarb surface doesn’t move or grow during the quench but the core does resulting in lots of stress. Removing the decarb results less stress. Spider cracks usually are caused by too fast/severe of a quench, like water too soon after the quench.

Hoss

 

[Storm W]

I’ve never seen it cause multiple cracks. The decarb surface doesn’t move or grow during the quench but the core does resulting in lots of stress. Removing the decarb results less stress. Spider cracks usually are caused by too fast/severe of a quench, like water too soon after the quench.

Hoss

I think I over reacted. The A2 blade seems to be fine and what I thought were spider cracks seemed to be alloy banding that I could just start to see when I first put acid on it. It had a single edge crack coming in from the edge. It was a rough plasma cut. The blade seems perfectly fine. The 3V has cracks and some might be coming from the edge as well and the one that had multiple cracks might be the first one that went in while it was far hotter than I thought. I will have to have a good look tomorrow and see what parts go to each blade. Right now the thing that seems to make the most sense is that the first one was to hot when it hit the water and that the HAZ from plasma cutting goes far deeper on the thicker steel than I thought and there is probably more strain in the quench. Probably the heavy decarb adds to it. The pieces are to big to dunk in acid and only big cracks are easy to see.