The ability for steels to retain a sharp cutting edge is obviously of importance for knives. It is of interest to note that the properties of steels which provide superior performance are very dependent on the type of material being cut. In soft and not overly abrasive materials such as hemp then very high hardness and wear resistance is of benefit 1 . As materials get harder and more abrasive then toughness and durability become very important as otherwise the apex can dull by significant fracture 2, 3 .
In the following piece of work an extremely demanding media is cut, sods. In that class of work the blunting is so severe that edge retention is essentially a moot point as the edge is effectively dull in a short period of work. What becomes of interest then is the ease of sharpening when is dependent on the inherent ease of grinding of the steel plus its ability to resist significant material loss due to an effective combination of strength, toughness and wear resistance.
The following knives were used to remove a two foot by two foot section of sod :
They were then reground to form an apex using, in two different trials, the coarse and fine side of a basic oil stone. The grind details of the various knives :
The results are as shown in the graph on the right. Basic description of the edge behavior :
This experiment unfortunately had a few too many sources of error, the most significant being that the edge width, the amount of steel being sharpened varied significant from one knife to another and the edge angle varied significantly as well. It therefore isn't that trivial to draw conclusions on the steels, however the very hard and high alloy steels which can do well in cutting softer and less abrasive materials do not tend to do well. They tend to blunt as do all of the knives but the low grindability makes them very inefficient to sharpen.
An interesting point of comparison is the S30V Surefite Delta. It has the fastest response time to sharpening but isn't the lowest alloy steel and has an edge width and edge angle in the medium range. At first glance it seems that this may be the sweet spot for abrasion resistance and toughness. However there is a lot of high variability in such work and it would need to be repeated with larger samples to draw even a weak conclusion and ideally have much more consistent edge grinds.
Again though, the obvious conclusion can be noted that it doesn't seem apparent for heavier work that the same steel properties which make a knife excel in holding a sharp edge on materials such as hemp or cardboard would be what is needed/desired for much more demanding cutting. This isn't that surprising considering the types of steels used for grinding ore and digging in general.
More details and discussion can be found on the forum thread :
and the YT video.
1 : Edge Retention : Hemp
2 : Edge Retention : slicing cardboard
3 : Edge Retention : Carpet
|Written: 17/01/2015||Updated: 03/02/2015||Copyright (c) 2015 : Cliff Stamp|