Visualizing the Tradeoff of Higher Hardness

[20yard]

Would it make sense to have a steel that had that extreme toughness & edge retention but non stainless. And make up for the corrosion aspect by coating it in a very high quality DLC coating? Or something similar to that.

I see that as essentially being M4.

 

[dan35]

I see that as essentially being M4.

Some DLC coated 4V from Spyderco. In a way it’s almost perfect. Cruwear has a great balance as well.

 

[Synov]

Added CPM-1V, Vanadis 8 and K390 to the chart.

 

[Synov]

New data from Larrin for 3V shows much better toughness/hardness, perhaps because the old data were based on a slower plate quench. So I have relabeled the old data and added the new data.

 

[SharpBits]

There might be value in leaving the old 3v values since most 3v will not have used the new lower tempering temperature. Just mark it as such.

 

[Synov]

There might be value in leaving the old 3v values since most 3v will not have used the new lower tempering temperature. Just mark it as such.

I would agree but I think it's now fairly common knowledge in the knife world that 3V does better at lower temperatures than the datasheet recommends.

Nathan the Machinist what do you think of austenitizing temperature of 2000°F, plate quench, cryo, and temper at 400°F?

 

[Synov]

I was trying to think of a way to visualize the effect of blade thickness and edge angle on toughness and edge retention at the same time.

A convenient mathematical relationship is that toughness is proportional to the cube of blade thickness, while edge retention is related both to the contact force at the blade tip and the thickness of the edge bevel: the larger the edge angle is, the thicker the edge bevel is, and the less contact pressure there is on the material being cut at the actual edge. As the edge wears away, contact pressure is reduced further until the blade ceases to cut.

Empirical data on edge angle and edge retention gives the relationship:

Edge Retention ∝ (sin(Edge Angle/2))^(-9/4)

If we reduce the blade thickness while keeping the bevel height the same, the bevel thickness decreases proportionally with blade thickness and we can get a simple relationship between toughness, edge retention and thickness.

Bevel Thickness ∝ sin(Edge Angle/2)
Edge Retention ∝ (Bevel Thickness)^(-9/4)
Edge Retention ∝ (Thickness)^(-9/4)

Since Toughness ∝ (Thickness)^3, we can use the results above to get the relationship:

Edge Retention ∝ (Toughness)^(-3/4)

And this can be visualized as such:



The dashed lines show the effect of reducing the blade/bevel thickness (and edge angle), confirming that edge angle can be even more important than the steel type.