The edge would chip or roll on cutting open plastic packaging, no matter how often I resharpened it. UCI testing then revealed overheated steel in the lower blade area from the factory grinding - as with so many knives. Usually it is not that bad with Spyderco though that a few sharpenings could not fix it. (Reason I like Spyderco so much.) In addition, there was a ton of burr formation during sharpening. So what to do - re heat treat!
Also, somebody asked under the youtube video above:
"What does tripple tempering and cryo do to the steel?"
I thought that this is an excellent question and maybe you guys also are interested to know, so below you will find my answer:
I am glad you ask! But be warned, your question leads to a huuuuuge rabbit hole. If you want to know the details, follow the link at the end of this comment. What follows is a (very!!) brief summary partially based on the link below.
Here we go:
Cryo drastically reduces and in some cases completely eliminates retained austenite which will remain especially in stainless steels after quench to various degrees. Retained austenite is unwanted for several reasons - mainly because it lowers edge retention and leads to excessive burr formation during sharpening. Therefore, a first cryo after quench is done because it reduces the retained austenite (the article linked below explains the mechanisms behind this process in detail) and it is by far the most important cryo.
Now, why several temperings and also another cryo inbetween each of those several temperings? Super short answer: Because the retained austenite transformation is more complete that way.
More detailed answer:
One must first understand why we temper: Basically, after quench, we (hopefully!) have a lot of martensite. This martensite is brittle however. Without going into details on how it works, the tempering removes this brittleness.
However, despite the initial cryo after quench, in addition to the martensite we also must expect to be some retained austenite still present in the steel. This retained austenite will, if tempering temperatures are high enough (their height depends on the steel, but generally true for the so called "secondary hardening range" for high alloyed steels) transform this retained austenite into martensite. This martensite - again, just like after quench- is brittle, so this is why we should add at least one other temper after the first temper in order to "take out the brittleness" of this newly "born" martensite. And studies give hints for a third temper being beneficial. (Therefore I do it.) However, during tempering, and especially low tempering like it was done on this CTS-XHP steel blade, the carbon in the steel can "wander" (diffuse) back into this retained austenite we actually want to eliminate and stabilize it instead - "stabilizing" meaning in this context that cooling to room temperature in order to get rid of it like it is often done after the first tempering will not transform it to martensite. This is where and why the additional cryos come into play: By going to - 196°Celsius, we can eliminate or at least reduce even that stabilized austenite.
Allright, I hope I could give some insights and maybe answer your questions - here is the afformentioned link:
https://knifesteelnerds.com/2018/12/10/ ... el-part-2/
