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If you want to have fun anneal and rework old file to make chisels

when it comes down to it cheap steel is cheap steel. Nothing like tool steel for good tool . A2 and D2 are my favorites depending on cutting or banging

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

On the subject of rehardening steel that's already been hardened....

I think in this case - I have a significant advantage that the tools were already chisels and not lawnmower blades or BBQ tongs..... That means someone has already done all the legwork on alloy selection to nominally be suitable for chisels and their appropriate heat treatments.

Next - The steels are chosen with alloys and carbon contents that will cooperate with high volume industrial heat treatment methods. That means fancy super alloys and alloys that require hours and hours in the heat treatment process are (theoretically) out until you get to the lower volume higher price offerings.

It's kinda interesting - when you poke through the TTT curves for many different carbon alloy steels within the classes of stuff suitable for chisels - you realize that by and large - they mostly look about the same... They either have a nose around 10 seconds (oil hardening stuff like 5160 and O1) or a nose around 1 second (water quenching steels that fall between 1060 and 52100) the critical temperatures also fall within a fairly narrow band that varies with the carbon content. The major difference that I see is that carbon contents above 0.84 or so requires longer soak times prior to quench to diffuse the carbon properly.. That longer soak time a significant concern when working annealed or normalized stock that has not been properly hardened.. It may not matter that much on stuff that's already hardened assuming the prior heat treatment was well done - the carbon should already be well distributed.

And all that is a round about way of saying - this has a good chance of working right for some good reasons.

As David says this getting pretty funny with banana shaped chisels and edges crumbling into dust...

When Trevor put his first post up I thought right I'll just get that textbook out on hardening of steels because his notions seemed a bit simple compared to what I remembered from years ago. And I was right. The whole subject is enormously complicated! Just look at a few of those graphs they give about alloy composition, crystal size, proportions of different mixtures of carbon and iron - other alloys. What forms at what temperature, Gosh it would take years to understand. And that is what metallurgists do - spend years learning this stuff.

I think as practitioners the best we can do is simply to identify the best brands as we use them. And it is a shame that that rather wonderful tool maker in the States (Lie someone) seems to have ended up with a steel that is really hard to sharpen

Dave

Having been a machinist and done my share of tempering it is a fascination subject . You can use heat and cold to manipulate the molecules of steel.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

It's pretty amazing isn't it.

I really have to fight the urge to climb down a new rat hole - making my own chisels. But guitar building is enough of a hobby for now. So I will probably use these and then buy some "good" chisels. I keep eyeing those Lee Valley PM-V11 chisels.

I have to say though - these chisels just being a smidge harder makes a HUGE difference in terms of usefulness.

Yep. Whether it's "supposed" to work or not, it does, as John and I have found. My Marples set and the Irwins went basically from ornaments to useful tools.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I have since checked this process out with knife makers. Apparently - this is a well understood and very commonly practiced technique for finishing or resetting a heat treatment with high carbon steels. It's done all the time and has been done this way for (at least) hundreds of years.

It's typically not done this way to do the initial heat treatment.... But it works just fine if you temper something too soft and need a quick do-over.

An interesting update on this continuing saga.

Try sticking your chisels in the deep freezer for a little more hardness and no other gyrations. It sometimes works when they didnt quite get the heat treatment right on steel thats above 0.9% carbon. Its especially useful on many of the "bearing" steels like 52100, EN31 (Stanley), and Silver Steel 115CRV3 (Pfeil and Woodcraft). I would give this a higher probability of working with cheap chisels than with expensive name brand ones... As my assumption is that the name brand reputable manufacturers have the heat treatment sorted out... Where miscellaneous cheap Imports may simply be using the fancy pants alloy as a marketing scheme - not making sure they have the proper heat treatment sorted out.

And if it doesnt work - it doesnt hurt anything and it doesnt cost you anything.

So on to the longer story....

I had an interesting go round with Ace brand "pro" chisels. These look like Stanley Fat Max chisels except without the steel thru-tang. These act like they have a lot of potential but as with typical hardware store chisels seem a little soft. There was also a lot of variation in hardness within the pack. One was much harder than the others and one seemed much softer...

So I rehardened one that seemed softer than the rest and it got harder than it was - but not quite as hard as the hardest one in the pack. Hmmm.. Odd... Put it off to the side.

Well - I ended up sticking it in my deep freezer as an experiment... And that sucker came out hard hard hard. Hmmmm. Retained Austenite.

So.. I to gave the rest of the ones in the pack a go in the freezer and see if it evens things out without the flame. And early indications are yes - the hardness seems to be a little higher and more consistent. But we will see....