If I'm understanding correctly, to get a very hard rating, a material has to resist a large amount of force spread over a small area. As the depth of the penetration increases, the area over which the force is spread increases dramatically. In this sense, the rating is not linear with respect to pressure (force per unit area). It would seem that a 55-56 difference is much smaller than a 61-62 difference. I'm sure it's more complex than that but this reduction seems pretty intuitive.What I wanted to find out is what is the difference between two HRC values, for example 55 and 58? If I remember correctly it is not linear, I remember people posting it was either exponential increase or log increase, I am not sure if this was even correct. I was not able to find info on that online.
Thanks
Ok so not a linear behavior, I guess that is what I have seen in posts before but not explained in terms of tensile strength to HRC relation.
I am looking at Larrin's plot and the data suggest that the tensile strength change is not linear with HRC increase.No, it is linear. You just need to draw a best fit line.
-AJ
No, it is linear. You just need to draw a best fit line.
-AJ
^^ x2. It's parabolic (or maybe even a higher order). But in the 55-60 range, you could interpret linearly and be pretty close.
true my interest was for HRC above 60 actually, and in relation to razors. Usually German Carbons are tempered ~61 HRC, Japanese straights are harder some going up to 65-66. I wanted to find out how the tensile strength changes with hardness.^^ x2. It's parabolic (or maybe even a higher order). But in the 55-60 range, you could interpret linearly and be pretty close.
Wouldn't a best fit line (if you are actually saying it is a line not a curve) make any function "look" linear?
Yeah, it looks parabolic to me.
But that equation isn't for Rockwell hardness. Rockwell testing isn't perfect, especially in its upper and lower range.That graph is based on averages and conversions. Hardness has a linear relationship with strength. H = 3x Yield Strength.
.
-AJ
yes but as tk mentioned earlier as the cone gets deeper in the metal the cross section of the area on which the force is applied does not increase linearly it increases as r^2, so to get same pressure fro larger diameter one has to apply larger force.OK, but in hardness testing the load applied is constant, not variable.
-AJ
Thanks for this. Could you say more about this, namely the relationship between hardness and edge retention?
I ask because I've been stalking this board for a few months as I contemplate my own knife upgrades, and I see a pattern of ppl recommending knives with high HRC grades, as if this automatically translated into better edge retention. Some studies I've seen confound this equation.
So how is resistance against abrasion achieved with a knife? By the heat treatment? And if so, you just have to know the reputation of the maker?
Sorry if these questions seem dumb. Still a little new to all this.
yes but as tk mentioned earlier as the cone gets deeper in the metal the cross section of the area on which the force is applied does not increase linearly it increases as r^2, so to get same pressure fro larger diameter one has to apply larger force.
Edge retention is a function of several factors mostly relating to the size and quantity of carbides in the steel. Higher hardness mainly prevents the edge from deforming (rolling, etc) so it would be a factor in allowing you to cut in steeper bevels (sharper edge). To much hardness leads to brittleness. In the end you want a nice balance. Japanese knives lean toward higher hardness.
Enter your email address to join: