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Old 02-28-2011, 02:27 PM
Ed Caffrey's Avatar
Ed Caffrey Ed Caffrey is offline
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I have done it both ways, and I choose to differentially harden. The reason that I choose this method is that differential tempering is difficult to correctly accomplish. To explain: Everything to do with steel is about time AND temp.....a specific temp, or a specific period of time. Most often than not, when people try to accomplish differential tempering or "soft back draw", they wind up with a tempered "skin" of about .005 to .010", with the remainder of the blade staying "as tempered". With 52100 you also have to realize that the steel does exhibit some air hardening characteristics, and even when an edge quench is conducted, there is a small degree of hardening that takes place in the spine.

The key...and the ease of creating a blade using differential hardening is that you have the ability to dictate how limber or stiff the blade will be, simply adjusting the depth of the quench. This gives me much more control and predictability than trying to soft back draw a blade.

When I really started to notice this was during testing folks for their JS.....those who chose to differentially harden generally had no problems getting through the tests. Those who fully hardened their blade(s), and then tried to soft back draw, often failed. After questioning those individual who had failed, the common theme was that they would heat the spine of the fully hardened blade "until it was blue", and when their blades broke, the tempered "skin" that I mentioned previously was evident.
IF a person can conduct the differential tempering is such a manner that they can achieve full tempering of the spine, it will work....but that requires at least an hour of soak time, and generally more, at the desired tempering temp.


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