AEB-L warpage woes

[Natlek]

With all the shim-clamp-tempering and carbide hammer whacking, we shouldn't forget about good old fashing bending. It can fix a lot. I had 180 mm nakiri (2.5 mm 14c28n 61 hrc) come out like a steel colored banana a while back. The vast majority of that warp was fixed by sticking the blade in the vice, jaws slightly open, and then pulling on the tang multiple times. The warp was mostly in the tang/blade junction and the curve was long. With shorter curve warps towards the tip, I think the carbide hammer works best.

Why you don t try to HT strip of AEB-L ? I mean you will cut/grind shape knife after HT ? It works for me , I never shape tang / say for hidden tang style knife / because I notice same thing .............

 

[Hubert S.]

Welcome to the world of AEBL. We use to fight it and fight it. Sometimes clamping in the freezer would keep it straight and other times it wouldn’t. Clamping it straight for tempering does just about nothing. We do not have time to futz around with individual blades so we do our best to keep them straight from the get go. We have found out that aebl has to be treated very gently after coming out of the quench plates. It will bend by hand VERY EASY. Think of the blades as if made out of soft copper. So do not set them on any cold surface after you take them out of the foil. Be very gentle cutting the foil off. Also I will say this. Resist the urge to straighten the blades by hand at this point. It can easily be done as the steel is still very soft. But you create worse problems for your self after the cold treatment and tempering. For some reason if you straighten by hand it still bows back after the tempering and it’s worse and gets a kind of kink like bow to it.

honestly your best bet is to let the blade do what it want to and then straighten it after it’s been cold treated and double tempered. Straightening only takes us a few min as we surface peen The inside of the bow. We use a Starrett straight edge and work the blade in different areas to get the blade as flat as is practical.

The issue I have found with AEBL is how it’s manufactured which It’s cold rolled and coiled. So the radius of the section of the coil that your sheet came from affects the amount of warp your blade has. Now if you cut your blades across the grain the warping just about disappears. I’m not saying you should cut blades from Across the grain. But I have done a few tests and it’s clearly a HUGE difference.

Jarrod, thank you very much for sharing your tips and tricks so freely. I have learned a lot from your posts since I started making knives.

I did straighten a couple of blades between quench and cryo yesterday and like you said, they bowed back. I will quit doing that and also be more careful opening the pouches. Based on one of your previous posts, I quit grinding the surface before HT a while ago and had pretty good success until yesterday when only one blade came out straight.

 

[Scaniaman]

Why you don t try to HT strip of AEB-L ? I mean you will cut/grind shape knife after HT ? It works for me , I never shape tang / say for hidden tang style knife / because I notice same thing .............

Yes I have thought about it. Or at least wait with the pinhole closest to blade, until after heat treat.

 

[Scaniaman]

You'll take care of it in no time. Just don't over-whack. Start easy and see what/when works. I have over-corrected a time or two..

Thank you, this is very encouraging. It looks like about the same amount of warp I have, maybe 1mm give or take.

 

[Natlek]

Yes I have thought about it. Or at least wait with the pinhole closest to blade, until after heat treat.

That make sense to,with all that holes steel in handle cool much , much faster then rest of blade .

 

[Hubert S.]

I want to thank everybody for your help. I think I have a good idea how to get the lateral warp out. Maybe it got lost or was poorly explained, but nobody commented on the curvature some of my blades now have in the other direction. I tried to get a picture of it but it did not turn out so well, so I made the very exaggerated illustration below. Has anybody seen anything similar or am I the only one? This problem is also most severe at the tang/blade junction and it is almost like there is a kink and the tang is kicked up. I recall seeing this on one blade I made about a year ago, but back then I attributed it to a mistake in profiling the blade even though that did not seem very plausible.

 

[HSC ///]

I want to thank everybody for your help. I think I have a good idea how to get the lateral warp out. Maybe it got lost or was poorly explained, but nobody commented on the curvature some of my blades now have in the other direction. I tried to get a picture of it but it did not turn out so well, so I made the very exaggerated illustration below. Has anybody seen anything similar or am I the only one? This problem is also most severe at the tang/blade junction and it is almost like there is a kink and the tang is kicked up. I recall seeing this on one blade I made about a year ago, but back then I attributed it to a mistake in profiling the blade even though that did not seem very plausible.

I’ve never experienced this sort of bend or warp

 

[Joshua Fisher]

I heat treated eight AEB-L kitchen knife blanks yesterday and out of the eight, only one came out straight and the rest were warped to varying degrees. Four of them did not just warp side-to-side, but picked up a curve along the spine, like sori on a katana. I cannot think of anything I did differently compared to my last batch, where all the blades came out perfectly straight.

My process is as follows: 1,950°F for 15 minutes, aluminum quench plates for about 90 seconds, then dry ice/alcohol slurry. Prior to that, I used @DevinT's prequench followed by a subcritical anneal. These last two steps were done on separate days for four of the blanks each time. I tempered the blades at 325°F for a couple hours last night and left it at that.

Does anybody have any ideas what I might be doing wrong that would create the sori? I have another batch of knives I want to heat treat next week and would really like to avoid this problem.

The knives are all hidden tang and I can take a lot of the curvature out of the tang and nobody will ever know, so I am not too worried about that. But I have to figure out how to get rid of the side-to-side warp first. There has been some discussion recently about chisels and hammers with carbide inserts for straightening in this thread about straightening high-speed steels. How well do these tools work on AEB-L and how much of a warp can one expect to correct with them? Some of the blades I did yesterday have pretty minor warps, but a couple of the 0.06" thick blades have about a 1mm gap when I put them on the surface plate and they are only short little petty knives. Can a warp that bad be corrected with a carbide tipped hammer or a chisel? I've straightened minor warps with a sandblaster in the past, but I am pretty certain it will not work to correct some of the blades I did yesterday.

Are there any other methods for straightening AEB-L? I have tried straightening during tempering by overcorrecting the curvature in a jig a couple of times without success, so I don't think I'm going to bother trying that again. This method seems to only work on carbon steel knives for me. Any suggestions would be greatly appreciated.

I’ve been using one of Jarods straightening hammers for quite a few blades now, i don’t work with Abel but I do work with a lot of thin stock that likes to warp/move, I find it faster than trying to mess with shim tempers. If your making a hammer yourself make 100% sure that you have impact grade carbide. I recently was at another smiths shop to help teach a class and we were talking about Alabama Damascus warping and he had 2 blades only 6” in total length from tip to butt that had about 3/8” of a warp in the middle that he couldn’t figure out how to straighten, I happened to have my straightening hammer with me in my tool box so 5 minutes later I had both blades down to under 1/16” warp that he was easily able to finish flattening on the grinder. So needless to say you can get a lot of warp out if needed.

 

[Hubert S.]

If your making a hammer yourself make 100% sure that you have impact grade carbide.

I don't know if the piece I have is impact grade or not, I think it was labelled as C2 tungsten carbide. I can check tomorrow. Honestly, I did not know there was such a thing as impact grade carbide until very recently. Assuming I have non-impact grade carbide, will it immediately shatter?

 

[Joshua Fisher]

I don't know if the piece I have is impact grade or not, I think it was labelled as C2 tungsten carbide. I can check tomorrow. Honestly, I did not know there was such a thing as impact grade carbide until very recently. Assuming I have non-impact grade carbide, will it immediately shatter?

It very well could, some grades of carbide are very brittle. I’d just be careful and make sure you have safety glasses on, I was teaching a class recently and had a student drilling a hole through a socket on a spear head and had the drill bit snap and glance off my cheek about 1/2” below my eye, jokingly told the class “There goes all of my luck for the week” was a good reminder that things happen when you least expect.

 

[Hubert S.]

It very well could, some grades of carbide are very brittle. I’d just be careful and make sure you have safety glasses on, I was teaching a class recently and had a student drilling a hole through a socket on a spear head and had the drill bit snap and glance off my cheek about 1/2” below my eye, jokingly told the class “There goes all of my luck for the week” was a good reminder that things happen when you least expect.

I'm glad the drill bit missed your eye. I used to be a lot more casual about safety equipment, but I have become pretty good about wearing safety glasses in the shop, as well as a respirator and hearing protection. I'll make sure to be careful with it.

 

[PEU]

I heat 14C28N to 900C for 10 minutes and then to 650C and leave it to cool in the oven, greatly reduces warpage, then harden and cool in my hardening press, most of the blades come out flat, unfortunately, some don't and are hammer straightened or re hardened.

I found that a masonry hammer with the tips slightly flattened work better than my carbide tipped slot hammer.
As long the hammer is hardened it works. Yup, my first two hammers I bought locally were soft... ¿? weird but true.

Pablo

 

[Hubert S.]

I heat 14C28N to 900C for 10 minutes and then to 650C and leave it to cool in the oven, greatly reduces warpage, then harden and cool in my hardening press, most of the blades come out flat, unfortunately, some don't and are hammer straightened or re hardened.

I found that a masonry hammer with the tips slightly flattened work better than my carbide tipped slot hammer.
As long the hammer is hardened it works. Yup, my first two hammers I bought locally were soft... ¿? weird but true.

Pablo

How long do you keep it at 650°C? I assume you do this step without foil in the blade rack you showed a picture of a while back?

I would be interested to know what the purpose of the two different temperatures is. @DevinT recommends a pre-quench from 20 minutes at 1,725°F for grain refinement before hardening. In a separate thread, he recommended a sub-critical anneal at 1,350°F for a couple of hours if the hardening occurs a significant amount of time after the pre-quench. Your temperatures are relatively close, do they serve the same purpose?

I've been looking at your oven build thread recently, that turned out really nice. I am starting to plan for a bigger furnace.

 

[PEU]

It was trial and error, my idea was to do a poor HT at 850-900C and then soften the steel at 650C. What you saw with the rack was an ongoing test following some ideas from Larrin, so far so good.
650C I leave it for at least two hours and then let the batch cool inside the oven overnight.

Regarding the oven, it's still my current oven, purchased the same PID again to make a second one, probably this year. If you need help just post in that thread and I'll do my best to help you out!


Pablo

 

[Hubert S.]

I used an old 12oz ball peen hammer and drilled a 1/4" hole with a carbide drill bit. The hole turned out a bit smaller than the carbide insert, but I was able to press it in there and it seems very solid. I tried it on a few of the blades and it is just amazing. It worked even for a 3mm thick honesuki blade that had a pretty decent warp.

The carbide I used was indeed C2 carbide rod from McMaster. I could not find much online in a quick search about impact resistance. The piece started out 2" long, I scored it in the middle with a diamond disc, wrapped it in a rag and hit it to break it in half. It took a couple of good blows without breaking before I hit it for real and it fractured into two pieces. I think it will be fine but I will be careful with it and report here if it breaks.

Thanks again everybody for your help.

 

[LCoop]

I found that a masonry hammer with the tips slightly flattened work better than my carbide tipped slot hammer.
As long the hammer is hardened it works. Yup, my first two hammers I bought locally were soft... ¿? weird but true.

I'm really curious. Most masonry hammers I have seen have like a chisel end. Do you grind them to a single point?

 

[Hubert S.]

It was trial and error, my idea was to do a poor HT at 850-900C and then soften the steel at 650C. What you saw with the rack was an ongoing test following some ideas from Larrin, so far so good.
650C I leave it for at least two hours and then let the batch cool inside the oven overnight.

Regarding the oven, it's still my current oven, purchased the same PID again to make a second one, probably this year. If you need help just post in that thread and I'll do my best to help you out!


Pablo

Your heat treat sounds convenient, saves the first plate quench compared to what I have been doing. With my small HT oven, I try to build up a bunch of blades to do the final HT on in a single day. So I'll pre-quench and then anneal a couple of blades when I can until I have enough together and a free weekend day.

It will be a while before I start building a new oven. I'm interested in what you will do differently for your next oven and hope you'll do another WIP thread. I like the idea of putting the coils up top like JT's and Drew Riley's ovens, it seems a lot easier to service. I dread the day the coil burns out in my current oven and I will have to replace it.

 

[PEU]

It will be a while before I start building a new oven. I'm interested in what you will do differently for your next oven and hope you'll do another WIP thread. I like the idea of putting the coils up top like JT's and Drew Riley's ovens, it seems a lot easier to service. I dread the day the coil burns out in my current oven and I will have to replace it.

I had to service mine a couple of times and found no problems it was rather easy. I'm sure I'll improve on the thermocouple location, not that current is wrong, but I hit it from time to time, so I think next one will come from the top instead of the side. Besides that I'm happy with the oven.

I'm really curious. Most masonry hammers I have seen have like a chisel end. Do you grind them to a single point?

My hammer is not a single ballpoint but a slot, 2mm by 15mm (0.08" by 0.6") so a slightly modified masonry hammer works great. Its holiday tomorrow, on wed I'll take a photo and post it.

Pablo

 

[Lee Hester]

How are you guys grinding the points on your carbide rod? Will ceramic belts on a grinder cut them?

 

[Hubert S.]

How are you guys grinding the points on your carbide rod? Will ceramic belts on a grinder cut them?

I used a diamond coated wheel in a Dremel tool. The wheels are pretty cheap at Harbor Freight. I had the carbide spinning in the drill press and just shaped it with the wheel. It is very quick to do. I then spun it in a hand held drill against a cork belt loaded with compound to polish it a bit. Maybe that did something, the surface came out pretty smooth.

I have scratched my carbide file guide using ceramic belts, but I don't think they would grind carbide very efficiently. I am curious now, I'll try to test it tomorrow if I remember.