Found an AEB-L Knife...but you have to have a decoder ring

Re: Found an AEB-L Knife...but you have to have a decoder ring

Is the dry ice for initial quench?

Re: Found an AEB-L Knife...but you have to have a decoder ring

No - crack city. Basically, it's always, do quench process, check blade for straight quickly, put in something cold to convert more austenite to martensite. Some steels have trouble retaining a lot of austenite, and converting more of it to something hard and stable is a matter if getting the tail end of the quench faster. A faster quench even for steels that don't need a super fast quench will help a little. if there's any significant retained amount, colder is better, too. A little cold (like a freezer) means get there fast. Freezer and salted ice water get about the same result, but having a big tub of ice water on hand to heat treat a few things is a bit inconvenient. A lot cold and there's a lot more time for some reason (e.g., if you screw around for an hour or two and then put a tool in liquid nitrogen later, it'll still do something to convert retained austenite). 

My steps after heating in a forge are one air quench, and then a reheat to a higher temperature and the following:

1) first half in quench oil

2) slap said knife between two aluminum plates that are kept in the freezer

3) dunk entire knife in cold water so heat in the tang doesn't creep up to the blade

4) throw in the freezer immediately

The lower the terminal temperature, the longer you can screw around a little.

heat treatment is kind of an interesting thing to play with because there are often "always do" rules given by folks (always temper right away before the steel cools is one, for example - it's at odds with cryo treatment, or any cold treatment - both hold the steel at a lower temperature to attain higher hardness. Minor carbide changes may also occur, but not to the extent that's often touted). the plates in this case set straightness pretty well so there's no real concern of warp in the freezer. Experience (at least in forge heat treatment) helps avoid warp, too. anything that isn't evenly heated will warp, but you can usually see uneven heating very well, just by minor color variation. 

The other virtue of cryo treatment is you can accidentally venture into overtemp situations during heat treat that would result in excess retained austenite (underhardness being the result to the level of defect) and liquid nitrogen, for example, will clean up the back end, drastically widening the range of temperatures OK in soak, or the range of error allowed on the upper side). 

if there was an easy way to keep a dewar of liquid nitrogen (really needs to be used constantly to make it make economic sense), I would dip every single thing I heat treat. 

cryo treatment and cold treatments in general

Aside from the maybe less than intuitive comment above about them helping to allow either higher soak temps or sloppy temp control (one of those could be on purpose), cryo treatments increase hardness by converting more of the steel to the final state that we like (untempered martensite). 

the hardness comes at a cost of "toughness", but listings constantly talk about how tough steel is made by cryogenic treatment. It's not - shrinking grain is done at temps around quench temp and a little below going back and forth at the limit, reestablishing new grain boundaries without reaching temperatures that will make grain large. It can also be done by forging, but even forging is improved by subsequent thermal cycles. 

Cryo treatment improves hardness/strength, which we like in woodworking. toughness is harder to gauge - I think too much is actually detrimental, and too little is easy to see (chipping, easy breaking with any prying). 

But in any boutique tools, it would seem useful for any steel that is improved by trading gummy toughness for hardness. AEB-L is one of those. 3V would be another. And if it costs a dollar for cryo treatment (probably doesn't cost that much at an industrial level), then add A2 and V11. 

Understanding getting tools really cold fast is a big boon for a garage woodworker. I figured freezer was the only way, but Philip (near wmsbg, can't remember last names) tipped me off to read further when he mentioned a bladesmith finishing a quench tail in ice water. 

In complicated steels there are cryo treatments between tempers, but I don't think they're doing anything magical - tempering can convert more austenite and I think the idea of tempering between is to convert as much as possible to improve hardness. 

I realize most people have no interest in this. I obviously have an interest in it trying to meet a challenge like Bill saying "I would like a surgically shaped boning knife that will last an entire deer" as it rubs bone in use. And doing that without resorting to sending stuff off (blech - too many stories of inconvenience and long waiting, and I will have something tempered before the end of the day - it's freeing). 

but I'm also wildly interested in why there's such a gap between what's attainable breaking rules even by a dummy in a garage vs. what's done commercially. I see from Larrin that breaking knives and stainless knives that take any stain at all result in returns. thus, we get steels like the 17% chromium stainless types that don't have great hardness properties, but it doesn't matter because it's what the customer wants. 

it's like finding an Easter egg to find out that AEB-L *is* being used in a commercial knife, albeit not one widespread.

Mules and Bananas

AEB-L and XHP / V11 are two steels that are kind of steel for knives for woodworkers who are toolmakers. 

meaning you can buy the stock and learn what it likes and it doesn't take some 1400 pound three phase powered oven and a separate tempering oven. 

these mules are just the infancy of knife making - the bar is low enough that when i miss a little (Wiley's knife is a touch soft because I misunderstood some of the reasoning for so much overshot on stainless steels and overestimated how "unsafe" it is to heat treat them in the open atmosphere. 

this knife is ground thin, it's tempered only at 300F (AEB-L) and is chisel hard. I think practical knives are not ground quite as thin, or you would really want a pair for foods that suction to knives (cabbage heads, fruits with conviction in their hardness, etc.). But I can make a "slicer and a chopper" as separate knives and maybe as the kids get older, eventually get them into knife blocks upstairs. 

It is nice to make these at the same time as chisels - i can't describe why that would be, it just is. 

(the drop here is only about 14-16 inches)

https://i.imgur.com/C4Lteur.mp4

XHP has mostly disappeared from the knife scene. I don't know that it makes a better knife in any way than AEB-L, and it costs a lot more, but it's still interesting - it's a big carbide version, and AEB-L is the small carbide version. 

I left this knife on the sander for only finish sanding (already thin bevel an edge installed as part of freehand grinding - the bevel itself becomes the visual indicator of how even things are), and then plugged in the sander, which shot the knife off the end and into a steel tool cabinet at a moderate speed. the tip of the knife drew up something similar to a rasp tooth in the side of the cabinet and saved the knife by allowing it to fall handle first on the concrete floor. No deflection or damage noted on the tip of the knife.