"Rounded" hardening lines

M

Moonw

Joined
Nov 19, 2014
Messages
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What is the explanation for some old axes showing a "rounded" hardening line? My thinking is that dipping an axe in the quenching liquid would yield a somewhat straighter line, depending on how they were lowered. I'm thinking this effect you'd get if you were "spinning" axes slowly on a wheel holding several of them at critical temperature and would just lower them to be quenched.

Does it have anything to do with inserted bits, and the higher carbon simply reacting differently to heat treating? If it does, is there any connection usually between the exposed inserted bit's area and the depth at which manufacturers would harden behind the edge? In other words, is there usually a connection between the forge-weld line and the hardened area (extending up to this line)?

Hope this makes sense.
 
I believe in many of those cases it demonstrates a welded bit, as the lower carbon body steel is unable to harden like the edge steel. I may just not have seen this phenomena on modern axes, but in all cases of modern whole-steel axes I've observed a temper line on, it's been straight.
 
I think the curve of hamon line is caused by residual heat.
The blade near its toe & heel will quench faster than the portion whats backed up by the unquenched eye & cheeks.

Of course laminated blades will show a line following the highcarbon insert.
 
Lieblad said:
I think the curve of hamon line is caused by residual heat.
The blade near its toe & heel will quench faster than the portion whats backed up by the unquenched eye & cheeks.

Of course laminated blades will show a line following the highcarbon insert.
Click to expand...

Hmmm...you mean as a "self-tempering from the residual heat? I could see that, as well as the sheer mass of the steel exhibiting more "inertia" ("resistance" to quenching).

You know, that's a very interesting theory. Old axes exhibiting the "high centerline" may have even amplified the phenomena.
 
"Residual" perhaps not the best word for it, but I think you understand my point.
When quenching, getting the steel quickly below the transformation temperature is critical.
Steel, where its more adjacent to an unquenched mass wont quench as quickly as the flared out extremes of toe & heel.
 
It shouldn't be difficult to observe an overlaid or inserted bit if you can already see the hardening line. From the top of the axe there will be a pretty obvious V - with the bottom of the V pointing toward the bit if it's been overlaid. If you see that then you've got your answer. All overlaid bits I have seen have this "rounded" appearance you're describing.

This image shows an overlaid bit clearly.

NE_OLDYANK_forgeweld by city_ofthe_south, on Flickr
 
cityofthesouth said:
It shouldn't be difficult to observe an overlaid or inserted bit if you can already see the hardening line. From the top of the axe there will be a pretty obvious V - with the bottom of the V pointing toward the bit if it's been overlaid. If you see that then you've got your answer. All overlaid bits I have seen have this "rounded" appearance you're describing.

This image shows an overlaid bit clearly.

NE_OLDYANK_forgeweld by city_ofthe_south, on Flickr
Click to expand...

I mentally agreed with this at first, but then I thought about it. Techniques and brands may vary, but all of the Emerson & Stevens heads that I have are overcoat bits and the line of demarcation between hard and soft steel is as straight as an arrow.
 
jblyttle said:
I mentally agreed with this at first, but then I thought about it. Techniques and brands may vary, but all of the Emerson & Stevens heads that I have are overcoat bits and the line of demarcation between hard and soft steel is as straight as an arrow.
Click to expand...

Yeah you're right and of course you know that is what the axe in the pic probably is. In any case, the view from the top/bottom is the deciding factor if you can see it.
 
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