Here's a page that talks about the test:
http://www.gordonengland.co.uk/hardness/rockwell.htm
It leaves a pinprick in the knife blade , which bothers me not at all.
Two comments about this that the metallurgists in my group tell me.
The Rocwell test is only good to ±1 point.
So it's hard to know exactly what you've produced to any level tighter than that. So a range of 56-58 is about as tight as you can ever achieve.
It's hard to get an exact heat treat hardness every time,
Especially when you are doing large numbers of blades in one batch or if you have a continuous heat treat line like Buck does. Not only do you have problems ensuring that every blade sees exactly the same temp profile but there are variations in steel composition in the same alloy. That's why the steel companies, when they are being exact on the composition of their steels, give compositions as ranges, not exact numbers. The composition varies from lot to lot. Look at this composition for 440C from Carpenter Technologies, one of the premier steel makers:
Single Figures are Maximums
0.95/1.20 C, 1.00 Mn, 1.00 Si, 16.00/18.00 Cr, 0.75 Mo, Bal. Fe
That "single figures" notation is theirs, not mine. So there will be variations in the steel composition from lot to lot as well as variations in the heat treat from knife to knife as well as a somewhat imprecise hardness test. 56-58 is about as tight as you're going to get.
I'm not a metallurgist, but I don't get excited by a 1 point difference in a hardness range. I do take notice when there is a 3 point difference. Case in point. Columbia River Knife and Tool treats their AUS 8 to 57-58. Benchmade treats some of theirs to a 58-60. That's enough of a difference for me to be interested. But I also see that KaBar treats their Doziers AUS 8 to a hardness of 56-58. Not enough difference between the KaBar range and the CRKT range for me to get excited.
As usual, more than anyone except me is interested in.
