I got off on this tangent when researching Bohler s390, which is the blade steel on a Kunwu Gringo I received the other day. Per Bohler's data sheet (if I'm reading it correctly), the recommended tempering temp for s390 is around 1000°F. That surprised me, as I thought blade steels were generally tempered in the 300-400°F range.
It occurred to me that this is significant for consumers--as opposed to knife makers--for a couple reasons. One, many blade coatings are applied at temperatures significantly higher than 400°. That means that coated blades often have sub-optimal heat treats, because as noted above, optimal heat treatment often means tempering at 300-400°. I believe this is why WE advertises hrc ranges for coated 20cv blades that are one point lower than their ranges for otherwise identical, but uncoated blades.
If optimal heat treat entails a temperature in the 1000°F range, however, there should be no hrc penalty, or at least a trivial one, for choosing a coated blade versus uncoated. Already I'm feeling better about having opted for the DLC Gringo.
The other consumer-facing issue with tempering is that it can be altered, in a bad way, by high-speed sharpening on a belt sander or bench grinder. Evidence I've seen indicates that factory edges are usually affected by this. It's not something that ruins a knife, but it can take two or three (or more) sharpenings to reach "good" steel that wasn't de-tempered during the sharpening process. This isn't just an issue with factory edges, but it's a *potential* problem with any high-speed sharpening.
I believe burned edges should not be an issue with steels tempered in the 1000°F range. While I'm sure it's possible to heat an edge to that extreme, you'd have to be something of a mad man to actually pull it off.
Having gone down this rabbit hole, I had a look at Larrin's recommended tempering temps in, "Knife Engineering." The not-uncommon knife steels for which he recommends 1000° tempering are M4 and Rex 45.
Not a metallurgist or a knife maker, so please set me straight if this is all nonsense!
On a side note, in my early testing, Kunwu's s390 is looking IMPRESSIVE.
It occurred to me that this is significant for consumers--as opposed to knife makers--for a couple reasons. One, many blade coatings are applied at temperatures significantly higher than 400°. That means that coated blades often have sub-optimal heat treats, because as noted above, optimal heat treatment often means tempering at 300-400°. I believe this is why WE advertises hrc ranges for coated 20cv blades that are one point lower than their ranges for otherwise identical, but uncoated blades.
If optimal heat treat entails a temperature in the 1000°F range, however, there should be no hrc penalty, or at least a trivial one, for choosing a coated blade versus uncoated. Already I'm feeling better about having opted for the DLC Gringo.
The other consumer-facing issue with tempering is that it can be altered, in a bad way, by high-speed sharpening on a belt sander or bench grinder. Evidence I've seen indicates that factory edges are usually affected by this. It's not something that ruins a knife, but it can take two or three (or more) sharpenings to reach "good" steel that wasn't de-tempered during the sharpening process. This isn't just an issue with factory edges, but it's a *potential* problem with any high-speed sharpening.
I believe burned edges should not be an issue with steels tempered in the 1000°F range. While I'm sure it's possible to heat an edge to that extreme, you'd have to be something of a mad man to actually pull it off.
Having gone down this rabbit hole, I had a look at Larrin's recommended tempering temps in, "Knife Engineering." The not-uncommon knife steels for which he recommends 1000° tempering are M4 and Rex 45.
Not a metallurgist or a knife maker, so please set me straight if this is all nonsense!
On a side note, in my early testing, Kunwu's s390 is looking IMPRESSIVE.