Axe heads with hard spots

[slloyd]

I have a couple of heads that have certain areas where a file bites very little (similar to the hardened bit if not harder). These areas were discovered while cleaning up a mushroomed poll or removing sharp edges from inside the eye. Adjacent areas would file as expected like soft steel. Are these typical of and/or unique to older cast steel heads or simply signs of a poor quality steel with impurities? One head is an unmarked Jersey pattern and the other is a Collins Legitimus broad axe (labeled with Cast Steel). I am wondering if the Jersey is cast steel as well and quite old. Approximately, when was cast steel discontinued in favor of more modern steel for the production of axes?

And by the way, I just joined today and am looking forward to contributing where possible. I have gained much knowledge over the last year following this forum.

 

[jake pogg]

Slloyd,hi,and welcome,and the question(-s) that you ask are not simple.(At least as formulated).
For an example:

cast steel heads

Chances are(and as we all know there's NO 100% certainty with old heads Or metallurgy(especially the latter),the heads you mention are Cast Steel on their edge only,the term does not refer to the eye,or the poll(unless it's also hardened,and then probably only the welded-on face of it).

So the body of the axe that you're testing is probably some sort of lower-Carbon steel.And yes,it can very well be not consistent hardness-wise,either because of it's composition,or it's Heat-treatment(far from same things).
Back long ago when they built composite tool heads(someone here may tell you about when,the dates and such),using cast steel for edging those,they often used a non-homogeneous material for the softer body of the axe.That material could have been "piled",or layered,from a variety of different hardness alloys.It could be so-called "puddled" material,where the extra carbon was burned away in special ovens,some cheap,carelessly processed iron where the high-ish C content remained and incidentally hardened during heat-treatment process.
Possibilities are many and varied...

But testing steel with a file is in itself not a simple proposition.
Many folks seem to forget that the file tooth,as it comes to it's sharp point, contains very little material,and no matter how hard it may be,distorts,breaks,gets all kinds of damaged when it comes in contact with something approaching it's own hardness.
So if you test some material that is very hard,every stroke more damage is done to the cutting tips of that spot on the file,and the information you seek to obtain changes therefore,the file dulls and bites in less.

Theoretically,to obtain consistent idea of hardness one doesn't try to use a file as a File is used normally.It's better to use the sharp corner of a sq. or rectangular file(a new, virgin corner for most critical testing).
And in a manner where you try to "stick" that corner in,and then scoot it along as a graver,or a scratcher.

 

[300Six]

'Rust hardening' is a common frustration that folks experience in trying to file-sharpen old and/or neglected blades (and polls in your case). Once you break through the oxidized surface layer the material will often behave as it should. And as Jake mentions this initial effort can wreak havoc with the teeth of a sharp file.
I file-sharpened many dozens of Ontario Dept of Lands & Forests axes one summer many years ago and quickly grew to appreciate ones that were freshly dulled compared to 'surface-blackened' ones that hadn't been tangled with for quite some time. Ultimately I received permission to claim one axe as my own and kept it under the bunk at night because of the aggravation of beginning every day with another dull axe.