How can one tell if a blade is heat treated properly?

B

Bob Litt

Joined
Feb 7, 1999
Messages
94
Hello all,

I have a custom ATS-34 folder that doesn't want to hold an edge. Every time I get it razor sharp with my Spydie 203, it gets dull within a few days from light cutting and opening mail. I have factory ATS-34 blade that holds an edge much longer than my handmade custom. Is there a way for the maker to determine if the blade has been heat treated properly?

Thanks in advance for and comments
 
A Rockwell hardness test is a good indicator, the blade should be at least Rc 57 for ATS. Unfortunately the test will not determine if the blade was cryo treated as well as heat treated.

Cryo treating will increase edge holding significantly. Can cryo be done after final assembly....I don't think so, at least I have never heard of it being done after assembly.
 
NO, the quality of the heat-treatment can not be seen or even measured without actually using the blade. Rockwell hardness is only a rough approximation of heat-treatment.

There are many ways in which the steel structure can be modified by heat (cold) treatment techniques to ideally balance the conflicting physical properties of the steel necessary to make a high performance blade (edge holding, flexibility, ease of sharpening, toughness, strength, etc). The 'ideal' heat-treatment may vary greatly depending on the steel, the size and shape of the blade, its intended function, and the edge geometry. This is why blade making is an Art, not exactly a science.

And YES, you can get some idea ahead of time about how well a particular knife has been heat-treated, but only by ordering a custom knife from someone who knows what they are doing with heat-treatment, or a maker who sends their blades to a professional heat-treater like Paul Bos.

Makers Must do destructive testing of blades in order to determine how well their heat-treatment process works. Ask custom makers how they do it and you will quickly start to understand who really cares about making a great knife, and who is just grinding steel. Folks like the makers in the ABS are required to be constantly striving to perfect their blade making techniques.

BUT, if you are talking about production knives, there is no way to tell how good the heat-treatment is except by the reputation of the maker and direct experience with a particular knife. If the company is serious about making good using knives, they should be willing to discuss their heat-treating methods with customers.

SO, there is no good way to measure the quality of any blades heat-treatment beyond Rockwell hardness testing except for the old tried and true empirical method, use it. :)

Paracelsus
 
Cryo does make a difference, but if edgeholding sucked before, it still won't be well HT-ed ATS-34. Cryo has an increase in 10-15 %edgeholding ... and 10-15 5 of not much to begin with is still not that much.

You can test if a blade was HT-ed correctly if you do the brass rod test. Pretty simple really..get something round and smooth made of brass that won't bend too easy (thick rod, edge of a plate..), secure it horizontally. Then pull the edge over, about a 30 degrees angle, away from the edge.. about the opposite of sharpening stuff with a spydie 204. Look at the edge in the light. If steel is too hard, it'll chip, if steel is too soft it will bend. If It's HT-ed correctly there will be no damage at all to the edge. If there is damage (bent or chipped edge) you know the problem.. bad HT.

Now don't get all upset, sometimes this happens. I had a piece of 5160, and after HT is was still dead soft, even in the core. Then I quenched it in water and it went ping.. Still haven't figured out what went wrong. All the other 5160 I did came out hard, out of excactly the some quenchtank, excactly the same salt bath.

Greetz and take care, bart.
 
Have you checked for a wire edge on the custom? A wire edge can develop on thinly ground customs with little effort.
Concerning the brass rod test, refer to Cliff Stamps thread on the subject in the reviews and testing forum. This can be a very informative test, but only if you know what to look for.
 
Easy one... try to find a Paul BOS stamp on the blade - then it's propoerly heat treated ;)
 
If it really dulls that fast, I would wonder if it is really ATS 34? If you have a custom knife, it isn't that far-fetched to think the maker accidentally got the wrong material into it. If ATS 34 was heat treated anywhere even close to properly, it should hold a similar edge under cutting of papers, envelopes, etc. If you are pushing it against something hard (think anvil), that's another matter, but in high alloy steels like ATS 34, D2, 440C, CPM grades, etc., if the hardness is close, the microstructure (carbides in the steel) should still provide some reasonable wear life. I think the hardness test (Rockwell C) is a good place to start, because it won't damage the knife (except to leave a tiny dimple), and it will tell you if the heat treatment was done or maybe accidentally messed up. If it's Rockwell C 40, take it up with the knifemaker. If it's close to the right hardness, I agree with frank k - take it up with the knifemaker anyway, to confirm the grade. If it's an expensive knife, there are some non-destructive ways to confirm the right grade, at a sophisticated test lab - but sophisticated test labs charge $$$. If it's an inexpensive knife, buy a bunch of cheap stones or rods & stash them around your desk, house, car, and get good at sharpening!
 
Paracelsus :

Rockwell hardness is only a rough approximation of heat-treatment.
Click to expand...

To clarify, a given heat treatment should produce a set hardness as one of its material properties, thus a RC test exactly quantifies one of the performance attributes. Thus if you do a RC test and it is outside the expected range you know something went wrong as one and possible more of the attributes are not where you want them. However you RC test and the value is as expected then all you know is that one thing is right. And while you can reject the blade if it has one fatal flaw, you can't simply accept it with confidence if it doesn't have that particular problem.

So in short, RC testing can be used to catch some flaws, but not all of them. Etching can also be used to check heat treatment. Regarding the brass rod test, yes it is far from trivial to interpret as, any blade will pass or fail (which ever way you want, ebdn or fracture) depending on many factors such as the diameter of the rod, the force used, the angle of the blade etc. . Without all these factors controlled it is simply saying a blade passed a "flex test" without saying how much you bent it, or how much force you applied. It is meaningless.


-Cliff
 
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