As with most things in life, almost all aspects of knife-making are a trade-off, and the hardness of the blade is possibly the most fundamental.
Rockwell Hardness Test
We use the Rockwell C (HRC) scale to describe knife hardness, concentrating on the range of 53 to 63. 53 is considered soft – in relative terms – whereas 63 would be considered very hard.
At the softer end of the spectrum, and many knives are around 56 HRC, it’s possible to establish a cutting edge very quickly, and that edge will be resistant to chipping and cracking if you’re hammering away at a beef carcass. On the other hand, the edge itself will be of poor quality (and so not very sharp) and will roll and deform relatively easy (thereby requiring a great deal of maintenance).
At the other end, you’ll have a blade that is a right pain to sharpen, but once you achieve it then it should be a splendid thing for extremely fine and precise cutting. Alas, it’ll also be delicate and brittle so will need to be used carefully and selectively or it will chip, and you’ll have your work cut out grinding the blade back to a new edge.
As a gross generalisation, most knives are towards the softer end of the spectrum, with the notable exception of the Japanese who have a predilection for 62+ HRC.
Of course, there’s always a third way, and that is to aim for 60 HRC. We would suggest this is the optimal hardness for a knife that can then be used in pretty much any fashion you’d care for. It is not hard to sharpen, but that edge will stay true and sharp for a good period. It’s not delicate or brittle and will respond very pleasingly to the gentle lick of a honing steel.
Understanding steel hardness
The obvious question is why are not all knives made like this, save the occasional specialist blade? The simple reason is that it’s neither cheap nor easy to achieve.
Commonly used knife steels simply won’t get much beyond 58 HRC whatever you do to them. In any event, for a large manufacturer to completely overhaul their manufacturing process in order to bump a few notches up the scale doesn’t really make much sense.
This doesn’t apply to most of the Japanese makers, as it would be relatively easy to soften their blades to 60 via tempering, but that’s not their style. Therefore, the marketing department have come out trumps and we have a whole generation of people in the west with overly brittle blades for their purposes and a slight dose of Stockholm Syndrome.
So, when you’re looking for a knife (and if you believe the details you’re being told) then we suggest you look for two things. Firstly, aim for as close to 60 HRC as you can get, and even one step down or up makes a big difference as the Rockwell scale is exponential, not linear.
And secondly, look for as tight a range as possible, or ideally just one value as the promised hardness. A knife that claims it is 55-58 HRC is like asking someone what the speed limit is, with the helpful reply being “somewhere between 10 and 70mph”.
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