Differences in edge retention as a function of the harshness of the material cut


Introduction

In general the edge retention of a knife, or how fast it dulls is caused by a mix of :

As the extent of these effects is dependent on different properties of the steel it is possible to have vastly different edge retention in different materials. In order to explore this difference a selection of materials was cut with two steels which in several respects are in the extreme end of material properties for steels.

Method

The two knives used :

In terms of general material properties :

In terms of general method :

Three different materials were used :

Results

On the cardboard, the comparison was over a wide variety of steels which showed a few general trends :

Focusing on 10V and 15N20 in the two knives being compared specifically the results favor 10V and are statistically significant with an approximate ratio of :

The material was harsh enough to cause blunting by a mix of :

On the ropes, a more focused comparison was done on just the two knives being specifically compared. The results changed significantly depending on which rope was cut. The advantage in both cases was to 10V however the magnitude changed significantly from used polypropylene to the new hemp :

On the used rope the blunting was quite severe and happened mainly by :

In this comparison there was no significant difference in the edge retention of either steel. However on the new hemp there was very little deformation and fracture and blunting took place mainly by slow abrasive wear.

Note the images to the right of the 10V blade after one of the used polypropylene rope and see :

When blunting is taking place by fracture to this extent then the higher hardness of 10V and the higher wear resistance is having very little effect because blunting is taking place by a completely different mechanism. As 15N20 has a higher fracture toughness then it can greatly compensate and almost equal 10V in edge retention slicing the rope.

Discussion

Over the range of materials used the edge retention advantage of 10V over 15n20 changed significantly. As the materials got more harsh as they were used/dirty then the edge retention advantage was minimized. In general, because edge retention depends on many material properties, the nature of the material cut is critical to the edge retention performance of a steel.

Recap

More extended commentary can be seen in the forum thread :

References


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Written: 30/07/2015 Updated: Copyright (c) 2015 : Cliff Stamp