70rc ??????

J.Wade

J.Wade

Joined
Sep 3, 2004
Messages
775
I was on another site an a fellows says he has a blade that has tested out at a 70 Rc at the edge and a softer spine, does this sound reasonable. I am going toask a few question about he knife but 70 rockwell seems really high to me,

I am no expert , but 70Rc that I would like to see



thanks
jimi
 
I was not aware that was possible or desirable. We talking C scale?


It is easy to test 70 when your penetrator is messed up..
 
Jim, as far as i know 65 is the highest you can go in the rockwell C scale with any real accuracy, like Nathan said anything higher is likelyfrom a badly calibrated machine or damaged penetrator or just bad practice. Theoretically 70RC is possible but in practice it is out of the range that the rockwell test is really intended to accurately measure.

TTYL
Eric
 
I just skimmed the Crucible book I have, there is one steel they list CPM REX 21 that will get to RC 71. It is a HSS for cutting tools, C 3.4%, W 10.0, Cr 4.0, Moly 5.0, V 9.5, Cobalt 9.0. Does not sound like a practical knife steel. I agree with the above posts, it is not good to have a blade edge in the high 60's or 70, too chippy. Also it may not be an accurate measurement.
 
My first thought when I read this post...... HYPE! Anyone who has experience using or making knives would know that any blade geometry that would provide decent cutting ability would be glass brittle at that hardness.
 
There was a post someone said above 70RC on this forum IIRC. The consensus was it was either a goofed reading by a damaged tester, or the measurement was made on the Rockwell D scale.
 
Some alloys will attain HRC70, But you would have to draw the temper back to a much lower point for normal use. Even ZDP is drawn back to RC67 for laminated blades, IIRC.Any blade with an edge harder than RC64 would be a waste of time unless it was for a specific purpose (microtome, etc.). Most using knives will be drawn to Rc57-62, depending on the use.
Stacy
 
From the technical side it would be very difficult to test a bevelled edge properly, that is, at a 90 degree angle. The tendancy would be for the tester to slide off. It is for this reason that my heat treater will not test any place other than the flats of the blade or handle.

Because the blade is thinner at the edge it is possible that it remained harder because it cooled faster??/

George
 
Diamond Blade Knives have a RC Hardness from 65-68 with a spine hardness from 42-45, so yes it can be done with excellent results. Maybe we are in a new generation of new found technology?
 
thanks guys,


it is just as I thought, I just want to ask the pros before I tell someone your 70Rc is wrong. Most likely it is a bad reading, he says the edge is 70 and softer at the spine, hard to test an edge.


thanks
jimi
 
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