Work Hardening Knives
Work Hardening
Work hardening, also known as cold forging, is a process where metals are deformed without heating to increase their hardness. On an atomic level, this process increases the number of dislocations within a metal’s crystal structure, and on a larger scale, work hardening increases the hardness and also the brittleness of the material.
Because of this increase in brittleness, excessive work hardening has to be avoided for any part that needs to bend before it breaks - like the body of a knife blade. However, the edge is supported by the rest of the blade, so a hard brittle edge supported by a softer, more pliable body wears down much slower and creates the “ultimate” blade. That’s what this project set out to create and then measure.
In order to work harden my blades, I took several knife blades, dulled them on a cutting board or a sheet of metal, and then re-formed them into a triangular edge like this:
Measuring
In order to measure the blade life, I imitated ISO standard 8442 for measuring knife sharpness and repeatedly cut a stack of 200 sheets of paper with a fixed weight until the knife stopped moving.
Results
I only completed three trials each with a control and a hardened blade, and I had considerable variation in the hardened blade life - but hardening the blades always showed a significant increase in blade life. For the thre trials I did, the hardened blades had an average of 2.3 times the life of an unhardened blades.
Note the increased error bars for the hardened blades. Due to the fact that I was hardening these blade by hand, consistency is hard to achieve. However, the data does indicate that
- The unhardened blades have a relatively tight control group
- The hardened blades have a higher variation in life but it is significantly higher than an unhardened blade
More Pictures
