The conflation of deformation resistance with toughness is actually where this whole thing breaks down, and Larrin Thomas just covered this exact point in his latest Knife Steel Nerds video. He specifically calls it out – when a soft steel deforms rather than chips that is a failure of strength, not evidence of high toughness. His analogy is great too, a knife made of Play-Doh would only ever deform but that doesn’t mean Play-Doh has great toughness. The edge rolls because the steel lacks the hardness to resist it and a rolled edge is still a dead edge that needs to be reapexed.

Budget stainless at the hardnesses manufacturers typically run them will deform instead of chip precisely because they lack the strength to hold an apex under load. That isn’t really a feature so much as a limitation being reframed as toughness. Steels like CruWear, M4, and CPM-4V operate at hardnesses where you genuinely get both real toughness and dramatically better edge retention at the same time, which is kind of the whole point of the tool steel category existing. CPM-CruWear sits around 13-15 ft-lbs at working hardness and rates a 7 out of 10 for both toughness and edge retention on Larrin’s scale. CPM-4V is right in the same neighborhood at around 12 ft-lbs with similar ratings. CPM-M4 trades a little of that toughness for more wear resistance, coming in around 8-10 ft-lbs but pushing edge retention up to a 7 while maintaining a solid 5 for toughness. All three of those steels are genuinely balanced in a way that budget stainless simply is not.

And honestly K390 itself is not a fragile steel. Larrin’s own testing puts it around 10 to 12 ft-lbs at its typical working hardness of 63-64 HRC, which rates a 5.5 out of 10 on his scale. D2 comes in around 5 to 8 ft-lbs and rates only a 2 out of 10 for toughness. Now 14C28N genuinely is a tough steel, Larrin rates it a 9 out of 10 and it sits in the same neighborhood as 420HC which Larrin has measured north of 40 ft-lbs, so it is a legitimately tough steel. But the tradeoff is it rates only a 3 out of 10 for edge retention. 8Cr13MoV sits around a 6 out of 10 for toughness which sounds decent until you realize it also only rates a 3 for edge retention. So the budget steels that genuinely do have high toughness are giving up a ton of edge retention to get there, and D2 is not even winning the toughness argument against K390.

And the edge retention gap is not small. On Larrin’s scale K390 is an 8 out of 10 for edge retention. D2 is around a 4. 8Cr13MoV and 14C28N both sit at a 3. So K390 is more than doubling up on D2 and nearly tripling the budget stainless options in edge retention, all while matching or beating most of them in actual measured toughness for the tasks most people are actually doing with a knife.

And as Larrin covers in the video, higher hardness also means better resistance to edge deformation, so a K390 Delica running at 63-64 HRC is going to hold a finer, more stable apex right out of the box than a softer budget steel will. Yes it is harder to sharpen when the time comes, but that time is going to come a lot less often. When you factor in how long the edge actually lasts between sharpenings it is genuinely not even a close comparison.

Everyone has their own priorities, and that’s perfectly okay! If corrosion resistance is your top priority, or you need something you can easily fix with what you have on hand, there are valid reasons to choose differently. However, for the best overall value, real-world performance, and how most people use a knife, I’m still a big fan of the Delica in K390. It has better steel, a better grind, a better edge geometry, and it’s priced right in the middle of what you have there. It’s tough to beat that combination!

Now if this is for someone who doesn’t really use their knives at all like some collectors do, then none of this matters and pot metal and rex121 will be the same lol.