This is about steel and blades OK? Just to be clear upfront.
In my article Knifesharpenophobia I have mused a bit about how being all anal retentive about the hardness of a blade is not all that necessary. Now I wish to revisit that heme a bit, after my hardening attempt of a blade did not go as well as I would wish to.
If you remember when I was trying to harden the rondel dagger I was also hardening a kitchen knife blade and I was pretty sure that this particular blade is properly hardened. So I took it to work and measured the hardness on the tang (the knife is not finished yet), where it is hardened, but probably not as well as the blade. And the gage showed HRC 54. From technical standpoint, difference between 50 HRC and 54 HRC is not trivial (HRC is not a linear scale) and that knife is thus indeed properly hardened. What was the difference in the work process? For that knife then I have used the gas forge only for heat-soak, the final heating to 1050°C before quench was made with charcoal, which allows for more even heating. HRC 54 is still not full potential of this steel, but if the tang has it, the blade has probably more.
But this whole thing got me thinking again – is that even relevant? Do I really need to be afraid to give that knife to a fried as a gift because the hardness of the blade is “just” HRC 50? Am I being unnecessarily obsessive about an inconsequential detail (again)?
So I tried to look at what is the actual hardness of historical blades. I did not spend too much time with it, but the article Sword Blade Hardness: A look at the current research is an eye opener and a good read. To be clear, it is about swords, not kitchen knives, but it still clearly shows one thing – the crappiest knife that I have ever made is vastly superior to most knives that were used throughout history before the invention of blast furnace. Not because of my superior skill, but because I have access to superior steel. Furthermore, HRC 50 is not actually bad at all and someone who takes a good care of the knife would probably not even notice any downside when cutting. And it has an upside too – a blade in this hardness range needs to be sharpened more often, but stropping and sharpening should be reasonably easy and quick and the knife will not break easily when you drop it on the floor by accident.
It is not the best that could be, but it is good enough.