Table of Contents
- Steel Type (& Hardness) Edge Retention Test
- Carbides Hold Edges Better Than Hardness
- More Carbides Mean Less Toughness
- Edge Angle Matters Above All Else
- Other Factors That Affect Edge Retention
We wrote about how a knife’s edge angle (secondary bevel) determines edge retention. The type of steel your knife’s blade is forged from only plays a minor role.
Or does it?
With factors like angle and blade shape made equal, how does each type of knife steel compare when it comes to holding an edge?
Knife Steel Nerds conducted tests to find out. The steels are ranked from worst to best in the chart below.
They forged over 40 identical blades using the most popular alloys, ground them all to the same angle (30 degrees inclusive, or 15 degrees per side), recorded their Rockwell Hardness Ratings (“Rc,” or “C Ratings”) after quenching and tempering, and put them through a standardized, repeatable cutting test.
The test forced each blade to cut through stacks of cardstock, with the same force always applied. The cardstock was impregnated with 5% silica to dull each blade’s edge. Each blade was made to cut until it dulled to the point where it would no longer cut with the applied force. Below is a truncated version of their results.
Each orange bar represents the total amount of cardstock cut by each type of steel, in millimeters. Each blue bar represents that steel’s Rockwell Hardness Rating.
Steel Type (& Hardness) Edge Retention Test
Unsurprisingly, steels with the most carbides in their compositions performed the best.
Carbides Hold Edges Better Than Hardness
In testing, harder steels tended to retain an edge longer than softer steels. But the correlation is very weak, even negative with some steels tested at different C Ratings.
At 65.1 Rc, Hitachi Blue Super was one of the hardest steels tested. It cut 338mm of cardstock. That puts it in the bottom ten of tested steels for edge retention. Meanwhile, 10V steel was hardened to 59.5 Rc and cut 719mm of cardstock, placing it in the top ten for edge retention.
How is this possible?
The percentage of carbon and different available carbides in a steel — Chromium, Molybdenum, Tungsten, and especially Vanadium — contribute to edge retention substantially more than mere hardness. Higher carbon and carbide content also tends to increase a steel’s hardness.
This is correlation, not causation. Thus the misconception that harder steels hold edges longer.
Higher Hardness Can Lower Edge Retention
Thanks to the hard work of Larrin, the metallurgist at KSN, we know that increasing a steel’s hardness only provides negligible benefits for edge retention. In some cases, higher hardness can actually decrease edge retention. Some steels were tested at different C Ratings to prove this:
4V steel cut 526mm at 60.7 Rc and 538mm at 63 Rc, providing a tiny, 2% improvement in edge retention.
S30V steel cut 568mm at 59.8 Rc, 596mm at 61.9 Rc, and 634mm at 65.1 Rc. This is a modest 11.6% gain.
440C steel cut 350mm at 56 Rc and 300mm at 62.8 Rc. That’s a 14% reduction in edge retention with higher hardness.
D2 steel cut 499mm at 59.2 Rc and 486mm at 60.5 Rc. This yielded a 2.6% reduction in edge retention.
More Carbides Mean Less Toughness
It’s easy to get hung up on how well a steel holds an edge, which is why so many knife enthusiasts yearn for high-carbide “super steels.”
But we often forget that sharpening your knife is an easy, even enjoyable thing to do. The more carbides are present in a steel, the weaker its blade will be. As more carbon and other elements are added to a steel’s composition, it becomes noticeably easier to chip an edge, or crack a tip from a hard stab or strike.
Edge retention and toughness are competing opposites.
Blades with higher carbon and carbide contents are more difficult to sharpen. That means added work and sweat with a whetstone when those high-performing steels finally dull. Every knife owner who wants the best blade has to answer these questions:
Do you want a knife that’ll stay sharper, longer, but be weaker and harder to sharpen?
Or, do you want a stronger blade that requires more frequent, but easier sharpening?
Edge Angle Matters Above All Else
If we define “edge retention” as “how long a knife can cut effectively,” then edge angle matters above all else.
As we found in our guide to edge angles, a knife with a thin grind that provides high cutting ability does not dull noticeably faster than a knife with a wide grind.
Compared to wide grinds, thin grinds also retain more overall cutting ability when dulled. That means a soft, low-carbide blade (which might dull faster than a “super steel” blade) can still provide plenty of good performance for quite a long time, if it has a thin grind. When the time comes to re-sharpen — and yes, that time will come sooner compared to a “super steel” — it’ll be easier to get your knife honed and ready for more work.
Other Factors That Affect Edge Retention
Although bevel angle significantly contributes to edge retention, other factors help determine the overall performance of a knife, including toughness and sharpness. Learn more about them with our other guides: