Rockstead question?

joeyza

joeyza

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Feb 27, 2013
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I was looking at the Rockstead website and a few vids on their knives an they look super impressive. The main thing I noticed was how they say their blades are heat treated up to hrc 67 but are still tough and not at all brittle. Can anyone explain to me how this is possible? I thought there was a limit to what hrc you can heat treat metal before it HAS to become brittle which is why most blades are around 57-62hrc or something around that..
thanks
sorry if this is in wrong section but i think its falls under general knife discussion...
 
Toughness decreases when hardness increases but some steels are far tougher than others.

So, CPM-3V at 62hrc is ~2x tougher than D2 at 60hrc. Hardness is only one part of a complex equation.
 
Their steel is ZDP-189 which in general is run that hard.

I don't know much about rockstead but most ZDP-189 is laminated to increase toughness.
 
It depends on which steel and whether the edge is convexed or not. Rockstead uses YXR7 and ZDP-189 clad in softer ATS-34. YXR7 is not treated to as high a hardness as the ZDP-189. YXR7 retains a lot of toughness and flexibility at higher hardness. ZDP-189 has been known to be a bit brittle and chippy at the edge at high hardness, but when a convex edge is applied, this chipping becomes less of a problem. By cladding this thinner harder steel with a thicker softer steel the whole blade becomes tougher and offers more flexible than solid ZDP-189.

Edit: It is not marketing BS. I've watched the cutting demonstrations by the Rockstead associates with my very own eyes. These blades can take some punishment.
 
ZDP-189 is usually ran in the 64-67 HRC range so what they run it at is in the normal range for the steel.

It's edge geometry and edge finish that make the difference really.
 
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