Differential Heat Treatment and hard knife use

Fancier

Fancier

Joined
Jul 1, 2012
Messages
1,729
How hard would a knife need to be used in order to make differential heat treatment necessary to prevent breaking the knife?
Is there a hardness where a knife could be broken while being used as a knife (for cutting) without first suffering extensive edge chipping or other damage?
Is differential heat treating really only necessary for extremely hard use knives?
Most knives that I've seen have differential heat treatment primarily for aesthetic purposes.
Thank you for submitting your opinions.
 
The problems with differential heat treatment is that it leaves the edge hard, so the thinnest part of the blade is also the least ductile, and the rest of the blade is now softer, leaving the blade less resistant to plastic deformation, ie permanent bending. So the blade will still potentially chip at the edge, and now any hard use that involves lateral forces leaves the blade more prone to falling by bending.

What is usually left out of discussing differential treatment is that it both leaves the blade less prone to fracture, but much more prone to bending. It isn't that at the same level of force a softer blade will bend instead of break, it's that a softer blade will bend at a much lower force than a harder blade will break. If you can't pry with a hundred pounds of force because your blade will break, it isn't much of a fix to make your blade unable to pry because it bends at sixty pounds.
 
Differential HT only comlicates thing s. Better that you get a very good steel ,harden completely and start with a thick blade . Something like CPM 3V at 1/4".
 
Fancier said:
Is there a hardness where a knife could be broken while being used as a knife (for cutting) without first suffering extensive edge chipping or other damage?
Click to expand...

I doubt it... although if a very thin blade at 64Rc is used to chop hardwood, it could snap on the first blow, so I guess that might count as breaking before the edge chipped... but that would be silly. ;)

All the knife breakage I'm familiar with from personal experience, testing vids and hearsay alike can be traced to either poor design, engineering flaws, substandard materials/processes or outright flagrant abuse/willful destruction. (if not a combination of two or more of those)

The folks who promote differential tempering, and the ability to make a blade that can be bent while retaining a hard edge (American Bladesmith Society) do so as a means of demonstrating the smith's ability to control his processes. In their prescribed tests, a prescribed amount of cracking in the edge is permissible when the knife is bent. No one would want a bent knife with a cracked edge, and they don't claim that anyone would.

ABS testing guidelines
 
Last edited:
I know Swamp Rat used to do DHT and has since stopped because "We saw no gains other than added cost by doing DHT."
 
hardheart said:
What is usually left out of discussing differential treatment is that it both leaves the blade less prone to fracture, but much more prone to bending. It isn't that at the same level of force a softer blade will bend instead of break, it's that a softer blade will bend at a much lower force than a harder blade will break. If you can't pry with a hundred pounds of force because your blade will break, it isn't much of a fix to make your blade unable to pry because it bends at sixty pounds.
Click to expand...

That's the way I understand it too. The only advantage I can see is if your knife starts to bend you know to stop what you are doing and you still have a functioning knife. If it fractures then your knife is no longer useful.
 
You must log in or register to reply here.
Back
Top