Recommendation? Z-finite Steel Failure

[Cypress Creek Knives]

Hey everybody, I recently finished up a dive knife in z-finit(LC200N) and I had a catastrophic failure while testing it. The knife has a compound grind with the hollow grind done on a 10" wheel.

I was batonning the blade on some soft deadwood and noticed a major edge deformation when I accidentally hit the spine with a glancing blow. I went to see if ai could straighten the bend, but ended up snapping out that portion of the blade. I went ahead and snapped the blade jn a couple places to look at the grain structure. The grain is tight, but it almost looks like the steel was only case hardened... the heat treat recipe I used is as follows


Preheat and equalize at 1200 for 10 minutes

Preheat and equalize at 1650 for 10 minutes

Austenitize at 1900 for 20 minutes


Plate quench


Liquid nitrogen soak 1hr


Temper at 350 twice for 2 hours

RC 59

Here are some quick photos, I can add more this evening.

 

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.I went to see if ai could straighten the bend

how did the bend get there?
Tried to straighten it how?

A year ago i had an experience with a z wear knife that was out being tested. There was a evidence of some crack at the spine. The user tapped the spine on his cutting Board and it broke in half

edit - I see the bend in the video

how did you confirm 59 rc?

 

[Cypress Creek Knives]

how did the bend get there?
Tried to straighten it how?

A year ago i had an experience with a z wear knife that was out being tested. There was a evidence of some crack at the spine. The user tapped the spine on his cutting Board and it broke in half

edit - I see the bend in the video

how did you confirm 59 rc?

The bend got there while batonning. Since I was in the field and did not have a vice, I laid it on a piece of flat steel and gave it a couple of very light taps with a hammer. The crack developed and spanned the whole length of the bend after the first tap

 

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Doesn’t seem like a catastrophic failure to me

seems like the hardened steel behaved as you would expect it for the repair you tried to do

 

[Cypress Creek Knives]

I agree with that statement, however the real failure is the steel bending to begin with. I wasn't testing it that hard and would not have expected to bend the way it did.

 

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I agree with that statement, however the real failure is the steel bending to begin with. I wasn't testing it that hard and would not have expected to bend the way it did.

So again, how did you confirm 59 rc?

when you austenitize 20 mins at 1900, what was your total time in the furnace? Door close to door open?

 

[Cypress Creek Knives]

With my Wilson hardness tester.
And yes, total austenitize time was 20 minutes at 1900. I left the blades in the furnace as it ramped from 1650 to 1900.

 

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I would say your soak time was insufficient In my opinion. If It was 20 minutes from the door close to the door open then I would say it was insufficient

 

[Cypress Creek Knives]

I would say your soak time was insufficient In my opinion. If It was 20 minutes from the door close to the door open then I would say it was insufficient

Interesting. What makes you think that? All of the data sheets that looked at said that a soak time of 20 to 40 minutes would be sufficient. My blade stock was .094" so I assumed the shorter soak time would be enough.

 

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What makes me say that is doing my own heat treat and my experience is that there’s no need to be cheap on soak times

I don’t know because you’ve confirmed your hardness with the tester so I don’t really have anything else to offer

And I haven’t heat treated that specific steel

I don’t test my work the same way that you have because I make different knives but I would expect the blade to chip out rather than bend

@DeadboxHero Might have some insight as he works with different steels and has experience with that sort of testing

 

[Cypress Creek Knives]

Thanks for the input! I'm going to grind a couple blades out tonight and heat treat them with a longer soak time. I'm thinking 35 minutes should do it.

 

[Robert Erickson]

It looks to me like more of a geometry issue. Assuming the grain looks good (it's a little hard to tell from the photos) I would put the issue with torque generated with the glancing blow. A hollow grind is not going to tolerate those types of forces as well as flat or convex grinds. The bend looks like it's isolated to the thin area of the hollow grind.

 

[Cypress Creek Knives]

It looks to me like more of a geometry issue. Assuming the grain looks good (it's a little hard to tell from the photos) I would put the issue with torque generated with the glancing blow. A hollow grind is not going to tolerate those types of forces as well as flat or convex grinds. The bend looks like it's isolated to the thin area of the hollow grind.

It looks to me like more of a geometry issue. Assuming the grain looks good (it's a little hard to tell from the photos) I would put the issue with torque generated with the glancing blow. A hollow grind is not going to tolerate those types of forces as well as flat or convex grinds. The bend looks like it's isolated to the thin area of the hollow grind.

I have considered that too. And I'm thinking that may be the culprit, but it isn't a very thin hollow grind. That is why I'm a little surprised at the outcome. I'll post a better photo of the grain and the cross section of the grind later this afternoon.

If the geometry is the reason for the bend, then I'm not too concerned. This knife isn't meant to be batoned, but I was hoping it could hold up to a little more stress than I put it through.

 

[JTknives]

It’s surprising how long a blade takes to come up to temp when inserted into an oven. We added a viewing window to our oven so we can keep an eye on the blades and start the soak time when the blade is at temp. But generally it is not recommended to have blades in the oven as you ramp to temp. Normal practice is to insert the blade after the oven reaches temp and had a good amount of time to soak and even out. If you wanted to send me a chunk I can double check the hardness on my hardness tester.

 

[FredyCro]

I would love for someone with more experience to explain that bend. Is it possible that it didn't break because it was thicker toward the edge (from the hollow towards the edge) so the edge portion kept it together? Also I guess the lower hardness/higher toughness plays a roll? Would it have probably chipped out if the hardness was higher? Also how would have the longer soak helped if the hardness is confirmed (can stainless really case harden or is that very immprobable at this thickness and soak time)?

 

[JTknives]

That hallow grind is quite thin. What’s the thickness behind the edge, spine thickness and the size wheel you used

 

[Cypress Creek Knives]

It’s surprising how long a blade takes to come up to temp when inserted into an oven. We added a viewing window to our oven so we can keep an eye on the blades and start the soak time when the blade is at temp. But generally it is not recommended to have blades in the oven as you ramp to temp. Normal practice is to insert the blade after the oven reaches temp and had a good amount of time to soak and even out. If you wanted to send me a chunk I can double check the hardness on my hardness tester.

I'm a little confused by not letting the blade be in the furnace as it ramps up to temp. According to the AKS heat treat recipe, you preheat the furnace to 1200 and insert the blade to let it preheat, then increase the temp to 1650 and equalize/preheat again. And finally ramp up to temp and austenitize. Am I misunderstanding those instructions? Does the blade need to preheat, or am I just supposed to out it in the furnace at he austenitization temp and let it soak?

I would send you a piece to test, but I dont have a large or flat enough piece to send.

That hallow grind is quite thin. What’s the thickness behind the edge, spine thickness and the size wheel you used

The spine thickness is .092" and the blade is .015" bte. I used a 10"contact whew for tge grind.

 

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I'm a little confused by not letting the blade be in the furnace as it ramps up to temp. According to the AKS heat treat recipe, you preheat the furnace to 1200 and insert the blade to let it preheat, then increase the temp to 1650 and equalize/preheat again. And finally ramp up to temp and austenitize. Am I misunderstanding those instructions? Does the blade need to preheat, or am I just supposed to out it in the furnace at he austenitization temp and let it soak?

I would send you a piece to test, but I dont have a large or flat enough piece to send.



The spine thickness is .092" and the blade is .015" bte. I used a 10"contact whew for tge grind.

I really don’t think you need any of that preheat stuff for a thin knife blade... that is for several inch thick Dies and Tools

after the furnace is soaked at whatever temp u choose, I would stick it in the furnace, close the door and set a timer for 40 mins. Open the door and quench when the timer goes off.

 

[Cypress Creek Knives]

I really don’t think you need any of that preheat stuff for a thin knife blade... that is for several inch thick Dies and Tools

after the furnace is soaked at whatever temp u choose, I would stick it in the furnace, close the door and set a timer for 40 mins. Open the door and quench when the timer goes off.

I'm gonna give that a go this evening. Thanks!

 

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I'm gonna give that a go this evening. Thanks!

However I would pay attention to the foil wrap notes which I’m sure you’ve seen