Will 1084 air harden???

D

Dan Zawacki

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Sep 23, 2006
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I am working with Aldo's 1084. The blade is almost ready to HT, but I like to drill my pin holes before I harden, so as not to end up with a hardened section of tang that I can't drill out.

On my last normalizing cycle before the pre-ht grinding, I killed the forge early, and used the residual heat in the forge to finish getting the blade up to temp, then I just left the blade on the floor of my forge, figuring it would cool nice and slow like that.

However, now, I am drilling the pin holes, and the steel doesn't want to drill out! It all started normally enough, with nice curly shavings coming off the bit, however, after going in like a millimeter or so, the drill bit started to scream, and wouldn't bite. It's like trying to drill freshly quenched steel!

I didn't think I'd have problems with a big carbide chunk with something this simple, but I didn't think it'd harden without quenching either. If I have to, I have no problem re-heating and annealing in wood ash, but I am intensely curious as to what the heck is going on!

Any thoughts?
 
It sounds like you are work-hardening the steel. You didn't mention cutting fluid, so I assume you are drilling dry.

The tip of your drill bit is spinning against the 1084, cutting initially, but building up heat as well. At the same time, you are putting pressure on the bit, and likely the harder it is to drill, the more pressure you're applying. So, more heat. You end up hardening the steel just in front of the bit.
 
Good ol' 10W40 for cutting

I tend to be careful with the pressure. Having shattered a drill bit whilst a teenager, I don't very much relish the idea of reliving the experience and not being lucky this time.

Although, all that being said, I suppose work hardening is a possibility that I hadn't considered. It just hasn't happened to me like this before. I can't say that I've been doing this for a long time, but a few years now, and I've drilled my fair share of 1/8" holes through some tangs. I've had things go slightly awry before, but never like this!
 
A little thing I picked up is to use a 5 gal bucket of speedy dry(aka Cat Litter) to let my knives cool in overnite after normalizing, they come out soft as can be. Grinding is a dream when I do them like this and its not as messy as ash.
 
Dan Zawacki said:
I am working with Aldo's 1084. The blade is almost ready to HT, but I like to drill my pin holes before I harden, so as not to end up with a hardened section of tang that I can't drill out.

On my last normalizing cycle before the pre-ht grinding, I killed the forge early, and used the residual heat in the forge to finish getting the blade up to temp, then I just left the blade on the floor of my forge, figuring it would cool nice and slow like that.

However, now, I am drilling the pin holes, and the steel doesn't want to drill out! It all started normally enough, with nice curly shavings coming off the bit, however, after going in like a millimeter or so, the drill bit started to scream, and wouldn't bite. It's like trying to drill freshly quenched steel!

I didn't think I'd have problems with a big carbide chunk with something this simple, but I didn't think it'd harden without quenching either. If I have to, I have no problem re-heating and annealing in wood ash, but I am intensely curious as to what the heck is going on!

Any thoughts?
Click to expand...

I have to be careful here so as not to accidentally blur the lines between eutectoid steel and hypereutectoid, and make things confusing. First, no it does not truly air harden, and strain hardening does not effect machining all that much (it decreases ductility but not cutting or abrasive actions) nor is the action of the drill quite enough to induce an appreciable amount of it. The key here is this "...then I just left the blade on the floor of my forge, figuring it would cool nice and slow like that." While it is a definite no no with carbon in excess of .85% it can still cause issues with eutectoid levels.

If there are areas of the steel where carbide can concentrate even a eutectoid steel will produce some problem hard spots. It will not be the huge carbide sheets that can form in 1095 but you could get areas of carbide concentration surrounded by more ferrite rich regions, while in 1095 you will get carbide surrounded by pearlite, basically pure carbon surrounded by a mixture of carbon. In 1084 you can still get these concentrations but the pearlite has to give it up to do it so things are a bit more contrasty.

What would cause the carbon distribution to deviate? Well artifacts left over from the ingot should always be considered, but something even more obvious... would this be some of Aldo's 1084 with a pinch of vanadium??:)

A carbide former of that magnitude would definitely take priority over the humble pearlite reaction in gathering carbon together in a drill eating bundle. This is much the same reason why folks have some of the same issues with even a well known hypo eutectoid steel- 5160. When hoping to always have a smooth machining after cooling, adding just a bit of chromium will make it so all bets are off. So it this case you can have nasty little drill eating carbides surrounded by almost pure iron.

Reheat your steel to redistribute the carbon and allow it to air cool and form very fine pearlite, then reheat it several times to a very dull red to stress relieve and ball up what is there and your drill should love you for it.
 
That's the bit I was really missing. I had actually completely forgotten that there was a pinch of vanadium in this batch. That makes perfect sense now. A big fat vanadium carbide. No wonder my bit screamed!

Thanks Kevin!
 
How much vanadium does Aldo put in it ? All you need for grain control is about .025 V.
 
mete said:
How much vanadium does Aldo put in it ? All you need for grain control is about .025 V.
Click to expand...

Just a pinch, I didn't meant to imply that it was a carbide rich steel, but that vanadium is one thing in the matrix with a greater affinity for carbon than iron.
 
Vanadium, Molybdenum, Tungsten have much stronger bonds with carbon than iron or chromium .Vanadium also tends to collect in the grain boundaries thus retarding grain boundary movement ,thus retarding grain growth.Columbium does the same thing.
 
Kevin does this mean that there is no point in annealing Aldo's 1084 after normalizing and before grinding? Just air cool and go to work?
 
I guess what it really means is that Kevin has a problem with the practice of stuffing the steel in the hot forge and allowing it to cool slowly, when there is more than .8% carbon or carbide formers present. But then I kind of quit messing with coarse pearlite altogether once I worked out how to really use spheroidizing techniques. Spheroidal carbides will always machine much better than lamellar structures, regardless of the carbon content. The old wood ash, forge, or vermiculite thing is great for very simple steels under .8% carbon where no machining will be used. Fine pearlite will reduce much of the need for soaking at hardening time, but really fine spheroids will get you there too.

It may just look like an extension of the normalizing process but finishing up with a few subcritical cycles to make lamellae into little spheres is the best annealing route if you have to machine the steel afterwards.
 
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