Cracked blade from peening - 14C28N?

FredyCro

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Jan 11, 2019
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I was just figuring out how to grind with the new jig when I noticed this nasty crack. Seems to be in line with the marks from peening. What do you think? The blade is 2.5mm at 63 HRC.
zWvvOTV.jpg

PTpnvDC.jpg

WKUWR0Y.jpg


In the future, I will try to

1.peen straight after grinding some
2.temper again after peening
3.not bash the blade as hard
4.peen further away from spine

First nasty crack in my short knifemaking adventure, I guess I know how all those mini nakiris came to life now :)
 

Joshua Fisher

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I think the shape of the chisel could also have an effect, I know in Japan the chisel is normally sharp/blunt edge and what I am using is round and domed, in my mind the round divets seem like they would create less of a stress point than the sharp chisel, and Ive Damascus blades warp significantly and require quite a bit of peening to straighten out and never had one crack.
 

FredyCro

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I think the shape of the chisel could also have an effect, I know in Japan the chisel is normally sharp/blunt edge and what I am using is round and domed, in my mind the round divets seem like they would create less of a stress point than the sharp chisel, and Ive Damascus blades warp significantly and require quite a bit of peening to straighten out and never had one crack.

Yeah, that's a good point. I was wondering about that, since M Carter shows a straight edge hammer (contrary of rounded edges that most use here).

Still a big old crack like that was not expected. You can see that I ground most of the main bevel before it decided to crack like that.

I am interested if anyone has a theory that's not related to peening (highly unlike able).
 
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I changed from more pointy chisel to a rounded point in a hammer. It gives more control, less deep marks to grind out. Works great. And I imagine it stresses the steel less too.
 
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I was just figuring out how to grind with the new jig when I noticed this nasty crack. Seems to be in line with the marks from peening. What do you think? The blade is 2.5mm at 63 HRC.
zWvvOTV.jpg

PTpnvDC.jpg

WKUWR0Y.jpg


In the future, I will try to
Next one leave on 64 Hrc....so you can save some time ... it will break when it sees the hammer before the first blow .Seriously , what s wrong with 60 HRC ? It is Yugo not Ferrari ! If you want Ferrari buy better steel !
So many problems with this steel, it's unbelievable that you're still using it.............
 
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14C28N performs very well. And extremely well when also considering its silly low price. I have a hard time motivating buying another stainless because of this, but do use some RWL-34 as well.
14C28N is really good at 61 Hrc.
 

FredyCro

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I consider myself a beginner, so I tend to try out things that others have reported to work well.

Also cheap steel makes cheap mistakes. Expensive steel makes expensive mistakes.

420hc and 14c28n are readily available in good dimensions and thicknesses for kitchen knives. It was my first time HT them myself and I still haven't tested them yet.

420hc didn't get any warps and grinds easy at 60 hrc (it's max hardness after tempering fo this steel). 14c28n warped and grinds easy but it does take longer at 63 HRC. I will try to temper it down to 61-62 next time, I guess that not much performance will be lost in edge retention, but grinding and straigtening might be easier.
I might try stress relieving the next batch to avoid warps.
 
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I am not aiming this at you personally FredyCro, but I do think there is some exaggeration in this community in chasing highest possible hardness, and thinnest possible geometry. A lot if the time, it may just not be very useful/practical.
 
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I consider myself a beginner, so I tend to try out things that others have reported to work well.
Don t believe everything you read on net .... Some grind them almost to sharp edge and then sharpen them on 12 DPS .....................my a** !
You will read something like this to here ..............I worn 3 belts to grind ONE blade from M2 steel ???????? I can t grind single blade with Klingspor belts ............???
In the meantime I can grind ten M2 blades with half length Klingspor belt ??????
 

FredyCro

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It's not that I take everything that I read here for granted. I am stubborn as well and have done a lot against the advice that was given here. Sometimes successful, sometimes not. I do a lot of research on everything beforehand and based on that I give it a try with the equipment I have. Again, sometimes it works sometimes it doesn't.

I learnt sharpening by hand long before I was in knifemaking so that's how I do it.

And as always, thanks for your opinion and input.

N Natlek I really liked the jig and felt comfortable at max speed (29 m/s) and a 40 grit belt. Progress was fast! I feel the cheap no name belt isn't a great performer, so I am looking forward to try out those purple Boras.
 

JTknives

Blade Heat Treating www.jarodtodd.com
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A couple things.
First off those peens look really deep, especially for a 63rc blade. Also the peens look to be in the wrong direction to fix bowing. 63rc can be quite brittle especially when whacking it with a hammer. Aebl which is quite tough will snap from surface peening if it’s in the 63-64 range.

I don’t personally get the obsession with pushing the hardness to the max. I can see chasing performance but it’s not all about hardness. The rounded surfacc peening hammers are gentler on steel then a sharp line. Also how did you test the hardness and where?
 

FredyCro

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i think you should snap it at the crack. if its black inside and not silver, the crack was probably there before or during heat treat.
Thats a good idea. I will cut if off first and then snap it.
A couple things.
First off those peens look really deep, especially for a 63rc blade. Also the peens look to be in the wrong direction to fix bowing. 63rc can be quite brittle especially when whacking it with a hammer. Aebl which is quite tough will snap from surface peening if it’s in the 63-64 range.

I don’t personally get the obsession with pushing the hardness to the max. I can see chasing performance but it’s not all about hardness. The rounded surfacc peening hammers are gentler on steel then a sharp line. Also how did you test the hardness and where?

I tested the other blade from the batch that took less curve on couple of places where I could grind to reasonable parallel surfaces. I used a new 120 belt, and tested at least 15 times. The hardness tester I posted in my other thread was consistent on the 64+-1 hrc block. Also other steels (420hc and becut) that I tested were consistent with targeted hardness and spec sheets. 14c28n tested 62/63. I agree that the marks are deep and the orientation is off, I guess thats what you get when you use a drill bit. I will use dremel diamond bits to shape the drill head somewhat and temper down to 61/62 in the future, especially if this warping problems continue..
 
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Well I have also peened a few knives in AEB-L which is quite similar at 62-63 rockwell and not had issues yet so it won't happen every time at least.
 
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Whacking any steel at that hardness with a hammer is asking for trouble. If you're trying to remove a warp, do it while straight out of the quench or after tempering while it's still too hot to touch. Wear heavy gloves or use a jig, obviously.

If you're peening for something other than removing a warp, e.g. aesthetics, do it before heat treating.
 

JTknives

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Whacking any steel at that hardness with a hammer is asking for trouble. If you're trying to remove a warp, do it while straight out of the quench or after tempering while it's still too hot to touch. Wear heavy gloves or use a jig, obviously.

If you're peening for something other than removing a warp, e.g. aesthetics, do it before heat treating.
not sure what experience you have with blade straightening but surface peening is quite common. Its super common in the sawmill industry as that's how the keep their blades straight and I also believe that how the Japanese straighten their blades.
As for straightening by hand is just about impossible with the steels we are talking about as thy are air hardening steels that are wrapped in foil. Thy get clamped between aluminum or steel quench plates while still in the foil, this quenches and keeps the blades straight. But even if you pulled the blades out of the plates while still "to hot to to touch" which is 400deg by the way your asking for a world of hurt. The blades need some time to form martensite from the austenite. This conversion process is what seams to cause most o the warping so if you pull it from the plates at 400deg that warping is going to get bad real quick. Also with the thousands of blades I have heat treated I will be the first to tell you to deal with warps after all the sub zero and tempering processes are done. If you hand straighten the blade after the quench "which is possible with the slow conversion process of these air hardening steels" the warp will come back even worse in the sub zero and temper. Even clamping straight or counter bent for the subzero and tempering cycles will not solve the bows. Clamping can reduce a really bad bow and we do it of really thin aebl that's less then .060.

Now low temp carbon steels are a completely different beast all to gather. If you clamp them between straight steel plates right after the quench (blade at 350deg-400deg) thy will come out just about if not perfectly straight.
 

HSC ///

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if the blade thickness is 2.5 mm in the area of the crack, I'm pretty surprised. I've cracked AEBL during straightening with a carbide chisel but it was in an area that was thinly ground.

The divots look fine to me., although a little deep for that hardness as already mentioned.

The term whacking has been used twice in this thread, Did you whack it hard? was the backing an anvil?
I found the best results are with taps on the blade with the backing of an anvil.

The variables of amount of bend, hardness of steel, thickness of steel all matter in this type of straightening.
If the blade cracked from your peening, I would suggest you are hitting it too hard.

Harbeer
 
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I also use an anvil, and get better results now compared to when I used a piece of mild steel ,that was a bit off in the surface too. You can get a new 20 kg Kanca anvil on amazon.de for good money. It's what I have.

I use a fairly rounded carbide tip, stuck in a hammer. I never hammer hard, just tap, and the divots are shallow and sand out easily. This is 2 mm 14c28n at 61 hrc on its way to a flat grind. You can see the divots in 2nd pic.

dSOMOGr.jpg

3VKRhVP.jpg
 

FredyCro

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Jan 11, 2019
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901
if the blade thickness is 2.5 mm in the area of the crack, I'm pretty surprised. I've cracked AEBL during straightening with a carbide chisel but it was in an area that was thinly ground.

The divots look fine to me., although a little deep for that hardness as already mentioned.

The term whacking has been used twice in this thread, Did you whack it hard? was the backing an anvil?
I found the best results are with taps on the blade with the backing of an anvil.

The variables of amount of bend, hardness of steel, thickness of steel all matter in this type of straightening.
If the blade cracked from your peening, I would suggest you are hitting it too hard.

Harbeer
I straightened at full thickness. First I tapped lightly with a soft backing. Then I switched to metal backing and stronger taps and thing started to straighten out. I am quite sure that the crack was not there before grinding. Or at least it was not that big and it expanded after the internal stresses were released through grinding.

So, I think,

1. Wrong "chisel“ (sharpish large masonry drill bit)
2. Too much force
3. Too near to the edges
4. Wrong orientation
5. too hard (arguable?) blade

I ordered a 175g tile hammer with carbide tip that I will blunt down and will temper other too blades down in hope that they don't decide to crack as well.
 
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