Heat treatment.. this is bizzare

Jan 16, 2001
ok... i work at a knife retailer and had an argument with another worker about blade heat treatment. He states that EVERY decent knife (buck, spyderco, benchmade, any quality production piece) they only heat treat along where the edge is on the knife and that the spine is softer steel. So basically he says that they stick the ground portion of the blade into the heating machine of some sort thus only heating along where the edge is and not on the spine. This sounds ridiculous and even more time consuming than just heating the whole thing. Please, someone put this to rest?
That would be induction heat treating as is done on some saw blades, etc. THe edge is heated very rapidly using electricity. I've never heard of any knife company doing that and a s far I know, it's not suited to the steels used in knife blades. There's no way to heat only the edge portion of a knife blade without also heating the spine. Try it with a torch.

Some knife makers do selective heat treating / tempering of their blades, 2 who come to mind are Ed Fowler and Mad Dog McClung. This is a one blade at a time hand process that no factory can afford.

Sounds like your co-worker is mis-informed.

hes probably mixing up the methods used to heat treat japanese swords, which are fine quality pieces, with decent knives. I dont think they heat treat just the edge.

Take a file to the spine of one of these knives and you will see that it is hardened as well.

Most production knife manufacturers produce what are called 'all-hard' blades. That means the blade is the same hardness throughout. This is a much easier way to make a knife blade. Almost all stainless steel blades are heat-treated in this manner. Carbon steel blades are more frequently made with differential heat-treatment by some smiths.

The American Bladesmith Society requires candidate members (journeyman and mastersmith levels) to test knives in such a way (slicing, chopping, and finally bending) that differential heat treatments are required to pass the test. This is the proper term for a blade which has a hard edge and a soft spine. Often blades that have been heat-treated in such a manner are etched lightly to show the temper line, or the line which distinguishes the hard part of the blade from the softer. There are different ways of creating and showing this demarcation. In a older Japanese sword, this line is called the hamon, and it character is very important to the overall aesthetic properties of the blade.

Differential heat-treatment is more time consuming that making an 'all-hard' blade. It's benefits in the real world of knives are debatable. Many ABS Mastersmiths make their damascus blades all-hard (a single hardness) because doing a differential treatment will not add functionality to the blade (particularly in the sub five inch range), the temper line can not be displayed in a pattern-welded blade without distoring the pattern, and it will cause unnecessary time and expense.

None of the manufacturers your friend names are making differentially heat-treated blades. If you want to know more about heat-treatment, look at this thread: Heat-treatment, what is it?, and look at the web sites of ABS masters like Ed Caffrey and Don Fogg. The testing criteria for the American Bladesmith Society can be found here: ABS site

Hope that helps!


[This message has been edited by Paracelsus (edited 04-14-2001).]
Your coworker is mistaken.

Production folder blades are not differentially heat treated.

As I understand it, large production companies like BM throw all the blades into a big oven. This is one of the problems with knives like that, because depending on where the blade is in the oven the quality of the heat treat may vary.

Someone please correct me if I'm wrong about the last statement.
RKnight, you are right about that. In a large oven, it is very difficult or impossible to get each and every part of the oven the same temperature. So some blades will be a little different than others. Nevertheless, if the manufacturer is paying close attention to quality control, they should be able to produce blades that are very similar in temper.

I think one of the biggest problems recently is that many manufacturers like to talk about their high RC values (60+) but forget that higher RC will not necessarily make a better knife. Some of the reports you hear about brittle ATS34 steel are probably in knives that have been left Too hard for real world use. For every different steel alloy there is sort of an optimal heat treatment that balances conflicting properties of the steel (hardness, brittleness, edge holding, flexibility, etc). Finding that optimal state is more art than science.

RKnight and Para,
I'm not sure about all large knife companies, but that is not how its done @ CAMILLUS. Our heat treat equipment[for stainless] works more like a 'pizza oven' with the blade traveling through various sections of the oven on a 'conveyor belt'. Very controlled and timed[ you program in the temps and times based on the types of steel and the SIZE of each blade type ]. It long, and takes quite awhile, with the blade going through different temps in different sections. This ensures all blades pass through the same heat zones for the same amount of time. We get very controlled and consistant heat treatment of our blades this way.

Other companies may have the same type ovens, .....I dunno, but don't think that ALL production companies produce inconsistantly heat treated blades. It would be tough to stay in business for 125 years if we did that

Stay Sharp!
Will Fennell
Camillus Cutlery
I appreciate you guys giving so much information. Its great to be able to learn so much on here because then i can pass the information on to my customers... thanks so much