Corrosion and Edge Retention

[RustyIron]

Last year I tested edge degradation over time on a Maxamet blade and found zero difference using my homemade BESS tester. The results were posted in another thread that may or may not be found using the Forum's search function.

Of course the edge quality will be negatively affected from corrosion, but it all depends on the amount of corrosion. Because I live in SoCal where the humidity is typically low, my edges degrade more quickly from use than they do from rusting away in my pocket. The one exception was a REX45 blade on a Manix LW. I dyed the handle and chemically patinated the blade without taking the knife apart. Upon examination, the blade was covered with microscopic pockmarks. As you might imagine, I was less than pleased. Some of the pockmarks were at the apex, so it was no longer perfectly smooth. The pockmarks were pretty small, and I don't remember a noticeable degradation in performance. Over the next month or two, the pockmarks on the edge got polished out through regular sharpening.

[Bolster]

...I dyed the handle and chemically patinated the blade without taking the knife apart. Upon examination, the blade was covered with microscopic pockmarks. As you might imagine, I was less than pleased. Some of the pockmarks were at the apex, so it was no longer perfectly smooth. The pockmarks were pretty small, and I don't remember a noticeable degradation in performance. Over the next month or two, the pockmarks on the edge got polished out through regular sharpening.
[/color]

It's how you frame it. You say you got pockmarks. I say you very cleverly figured out how to make micro serrations.

[RustyIron]

It's how you frame it. You say you got pockmarks. I say you very cleverly figured out how to make micro serrations.

It's a little-known historical fact that the inventor of blades with scallops, Henry J. Serration, was an electrician by trade. His brilliant invention was the result of a serendipitous event while using his Spyderco Worker to strip a wire in a live circuit.

[Bolster]

It's how you frame it. You say you got pockmarks. I say you very cleverly figured out how to make micro serrations.

It's a little-known historical fact that the inventor of blades with scallops, Henry J. Serration, was an electrician by trade. His brilliant invention was the result of a serendipitous event while using his Spyderco Worker to strip a wire in a live circuit.

I didn't know that, but I find it very believable. Did the "J" stand for "Jagged"?

[sal]

Gerber's daggers were used in Viet Nam during the war. They were Chrome plated, which protected the blade, but the sharpened edges rusted like crazy.

sal

[N. Brian Huegel]

As I recall, Gerber Mark II daggers were L6 and hand ground or at least glazed lengthwise to the edge, sort of Scandi ground as thick cruciform daggers blade angles are not much more than 40°inclusive, so this was an "out of the box" solution to a grinding/finishing/sharpening problem. I have refinished/reground/sharpened several dozen Gerber Mark II (and Mark I Boot knives) over the years, but do not recall any that were plated. They did make some dive/frogman models with yellow or orange handles, some might have been plated, but I believe that most were 440C.

nb

[GarageBoy]

An "edge" is thin, and exposed on both sides, so it it the first part of a blade to respond to corrosion. This was the main problem in trying to find a Salt Water Steel. Even with blades that are coated or chrome plated, the edge is sharpened so it is not protected by the coating or plating.

sal

Speaking of chrome plating, back in 2018 I found the original guy that did the chrome plating for Gerber back in the late 70s early 80s

I had him flash chrome some samples for testing.

I envisioned the ultimate blade would have been CPM 4V which had an excellent balance of strength and toughness but with the chrome plating to make it invincible to rust on the blade. Initial testing was good however the problem was the chrome plating accelerated the rusting of the exposed edge compared to if there was no plating.

Than Dr Larrin comes along and does the impossible and makes a stainless CPM 4V.

So the chrome plating for me was completely abandoned.

Why did the plating process accelerate the corrosion? Chemicals used interact with the steel?

[Chumango]

It is due to the area effect of a large cathode (chrome plating) and a small anode (exposed edge, where metal dissolution occurs). Corrosion rate is a function of electrochemical potential and area. Reduce the area dissolved, and keep the same (or higher) galvanic current due to a relatively much larger cathode and a more noble metal and you get accelerated corrosion.

A similar thing happens when you paint the interior of a carbon steel tank holding a corrosive liquid if there are imperfections in the paint. The very large cathode/tiny anode (pin holes in paint) can lead to rapid failure due to perforations through the tank wall.

[chronovore]

Think about what an edge is. A fine edge is a shape defined by precision. Rust involves some loss of the material that was shaped there, and the rust itself takes on its own shape or structure in its place, effectively blurring the shape you created when you sharpened it.

While the effect is more dramatic with outright corrosion or the formation of rust, stainless changes too. Remember that it isn't stainless because it is totally resistant to change. It's stainless because it forms a protective layer from its available chromium. That is a chemical change and a slight deviation from the shape you carved with your stones. It's just a small and self-limiting change that we generally don't notice.