Recommendation? Z-finite Steel Failure

[Robert Erickson]

I agree with Harbeer, I don't do any preheat treatments except AEB-L.
@Larrin has talked about not needing a preheat because knife steel is thinner than industry steel parts in general.
Here is his latest post which talks about this.
https://knifesteelnerds.com/2021/03/01/how-to-use-a-steel-datasheet-to-develop-a-heat-treatment/

 

[Cliff Carter 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.

I’m leaning towards this. .094” at spine is thin stock to baton with in general, and with a hollow ground blade I’m not shocked that you took that edge bend. I’ll leave the HT advice to the pros, I tend to stick to high carbon steels in my oven as I’m not set up for cryo.

I’d take JT up on his offer, that would at least let you know your HT recipe is close and giving you the rc you’re looking for.

 

[JTknives]

Generally most of the heat treat data you see is from industry and usually for large parts. The hole it to heat it evenly so the part does not crack in corners or have other issues with a hot outside and cold center. You will also see things like soak 30-45min plus 1/2hr per inch of thickness. This is to make sure the part is evenly soaked through. But a blade is so thin considering that it’s usually up to temp In 5min.

 

[Cypress Creek Knives]

I’m leaning towards this. .094” at spine is thin stock to baton with in general, and with a hollow ground blade I’m not shocked that you took that edge bend. I’ll leave the HT advice to the pros, I tend to stick to high carbon steels in my oven as I’m not set up for cryo.

I’d take JT up on his offer, that would at least let you know your HT recipe is close and giving you the rc you’re looking for.

I agree, it is thin stock, however I have had no problems with my convex ground blades. I'm not surprised that the hollow grind bent easier and sooner than the convex ground blades, but I am still surprised at how little force it took to bend it. This knife is definitely not designed to be batoned, but I would like to know that it can if necessary. I wonder if it would make a differene if I do a shorter height hollow grind. I would think that there would be less room for "flex"

Generally most of the heat treat data you see is from industry and usually for large parts. The hole it to heat it evenly so the part does not crack in corners or have other issues with a hot outside and cold center. You will also see things like soak 30-45min plus 1/2hr per inch of thickness. This is to make sure the part is evenly soaked through. But a blade is so thin considering that it’s usually up to temp In 5min.

Thanks JT! I may end up sending you one of the new blades I heat treat to check the hardness. I do have a wilson tester and it is calibrated, but a second test definitely couldn't hurt. I currently have a new blade in the furnace and I put it in at 1900. I'm letting it soak for 40 minutes then I will quench, cryo and temper it tomorrow. I'll report back with an update. Hopefully I'll have the blade ground by the weekend and I'm going to test it in the same way to see what happens.

 

[Daniel Carraher]

That’s a deep hollow for that thickness blade. That’s about the height hollow I use with a 10” wheel on 3/16” folder blades of similar size that I’d never baton with. The area where the bend is located is all very thin, convex grind would be at least twice as thick in that area.

 

[Cypress Creek Knives]

That’s a deep hollow for that thickness blade. That’s about the height hollow I use with a 10” wheel on 3/16” folder blades of similar size that I’d never baton with. The area where the bend is located is all very thin, convex grind would be at least twice as thick in that area.

Thanks for the input! I didn't realize that was a thin hollow grind. If I wanted it thicker behind the edge, I would go with a larger diameter wheel?

edit: I think I misread your post. If I wanted a stronger hollow grind that is thicker behind the edge I should do a shorter height on the grind?

 

[Daniel Carraher]

Thanks for the input! I didn't realize that was a thin hollow grind. If I wanted it thicker behind the edge, I would go with a larger diameter wheel?

edit: I think I misread your post. If I wanted a stronger hollow grind that is thicker behind the edge I should do a shorter height on the grind?

Can have a shorter height or same height on a bigger wheel. Or use thicker stock.

 

[Cypress Creek Knives]

Can have a shorter height or same height on a bigger wheel. Or use thicker stock.

That makes a lot of sense. I will try a shorter height grind because I really like this thin stock.

 

[Cypress Creek Knives]

I ground a few more knives and tested them out. It looks like the hollow grind in combination with the thin steel is the issue. I ground 4 blades in total. 3 in Zfinit and one in .100" S35VN.
Of the 3 Zfinit knives, two were hollow ground and one was flat ground. One hollow grind was ground to ~5thou bte and the other was about ~15thou. I batoned all of the knives into pressure treated pine as well as a hickory axe handle. All three knives made it through the pine with no edge deflection. They also did well on the axe handle until I started hitting them from "off" angles, think glancing blows.
The thin hollow ground blade deformed and snapped in the axe handle when I hit it with a sideways blow. The thicker hollow ground knife showed only minor deflection when hit in the same manner. Only dimpling was noticeable. The flat ground blade showed no signs of damage after seeing more abuse than the hollow ground knives.

I should mention that these knives were hardened to 60-61 RC instead of 59 on the last blade.

The S35VN blade has not been tested yet, but will be tested shortly. I expect to see good results. I do not think I will see any deflection in the edge of the blade after heavy testing.

I am very pleased with these results. Again, this knife is not meant to be batoned. But if someone were to use it to split kindling , I believe it would fare well.

 

[Cliff Carter Knives]

If you’re going to stick with that stock thickness, I’d run with flat or convex grinds. Looks like that’s backed up in your testing as well.

Additionally, just as an FYI, lc200n doesn’t get much harder than 59 or 59.5, regardless of recipe. That’s where it tends to top out as per Peter’s, JT, etc.

Love the design and the grinds man!

 

[Joshua Fisher]

Realistically I don’t see someone using a knife that size to baton with even small kindling or atleast they shouldn’t, a larger knife or axe is much better suited for that task, I’d do another test doing appropriate cutting tasks and see what conclusion you come to for both sets of data and go from there. Liam Hoffman did a test video a while back with one of his knife designs comparing flat ground to hollow grind blade styles doing more realistic cutting tests and if I remember correctly his opinion was the hollow ground blade performed better on most tests while still being tough enough for the intended use. I’m in the camp of a knife is made to cut and should do so well and I find that hollow grinds do make a noticeable difference in cutting performance, if I need to split something I grab an axe or hatchet. Just my opinion.

 

[Cypress Creek Knives]

If you’re going to stick with that stock thickness, I’d run with flat or convex grinds. Looks like that’s backed up in your testing as well.

Additionally, just as an FYI, lc200n doesn’t get much harder than 59 or 59.5, regardless of recipe. That’s where it tends to top out as per Peter’s, JT, etc.


Love the design and the grinds man!

I don't really plan on doing flat or convex on this knife. The grinds just don't look right to me. Definitely was not a fan of the look ok flat ground blade in my testing.
I have seen cases where makers have squeaked 60-61 out of lc200n and I followed such recipes. After multiple hardness tests on the blades, I am confident that my 60-61 readings are correct.

Thanks! I'm hoping the design process to be a solid edc design as I'm really liking the design.

Realistically I don’t see someone using a knife that size to baton with even small kindling or atleast they shouldn’t, a larger knife or axe is much better suited for that task, I’d do another test doing appropriate cutting tasks and see what conclusion you come to for both sets of data and go from there. Liam Hoffman did a test video a while back with one of his knife designs comparing flat ground to hollow grind blade styles doing more realistic cutting tests and if I remember correctly his opinion was the hollow ground blade performed better on most tests while still being tough enough for the intended use. I’m in the camp of a knife is made to cut and should do so well and I find that hollow grinds do make a noticeable difference in cutting performance, if I need to split something I grab an axe or hatchet. Just my opinion.

i dont think I've seen that video of Liam Hofmann's. I'm going to try to track it down. I am agreement with you, I to think knives are meant to cut and other tools should be used to split wood. I love thr hollow ground blade on my Sebenza and it cuts noticeably better than my flat ground fixed blades. I guess I have to decide if the improved cutting ability outweighs the loss of strength in a fixed knife.

 

[JTknives]

I don't really plan on doing flat or convex on this knife. The grinds just don't look right to me. Definitely was not a fan of the look ok flat ground blade in my testing.
I have seen cases where makers have squeaked 60-61 out of lc200n and I followed such recipes. After multiple hardness tests on the blades, I am confident that my 60-61 readings are correct.

Thanks! I'm hoping the design process to be a solid edc design as I'm really liking the design.




i dont think I've seen that video of Liam Hofmann's. I'm going to try to track it down. I am agreement with you, I to think knives are meant to cut and other tools should be used to split wood. I love thr hollow ground blade on my Sebenza and it cuts noticeably better than my flat ground fixed blades. I guess I have to decide if the improved cutting ability outweighs the loss of strength in a fixed knife.

According to the data you would have to be in the upper temper range of 850-900° to get a possibility of 60-61rc. But from my experience and what the paper says that’s the wrong temper if your wanting toughness. Some alloys will specifically say DO NOT temper in that range because the steel will have some brittleness issues.

 

[Cypress Creek Knives]

According to the data you would have to be in the upper temper range of 850-900° to get a possibility of 60-61rc. But from my experience and what the paper says that’s the wrong temper if your wanting toughness. Some alloys will specifically say DO NOT temper in that range because the steel will have some brittleness issues.

Interesting.. I'll have to go back and test those blades again, there is a chance I'm recalling the S35VN hardness, I'll report back later.

 

[grundl3r]

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?

[ Just learned about LC200N - that's how I found this thread and this question is probably the only part I can add anything too (better late than never...) ]

The fact that the edge was *thinner* is why it didn't break right at the edge. Think of the edge like a double edged razor blade that is flexible. The thinner the steel, the more flex it can tolerate for a given hardness.

So in other words, the thicker part of the steel was too hard for how much it was being bent. Temper the thicker part more and leave the thinnest part of the edge hard (59Hrc).

Ben Abbott (yes, that one) explained to me (in person @ Vista Forge in 2017 CBA Spring Conf) why he quenched only a 1/2 inch of the edge of a "test knife" made of 5160 (Handle was duct tape ). He didn't temper the blade at all. The goal was to make a blade that could bend 90 degrees and maintain an edge. We ran through the American Bladesmith "Journeyman" blade test sequence 3 times with this knife that evening. We just kept bending it back straight again and continued to chop through 2x4s + cut hanging 1-inch manila rope. I don't recall if or how the blade eventually failed or if we just got tired of doing the same thing over and over again.

cheers,
grant